Department Process Engineering

Publications Process Engineering

Peer Reviewed Publications

Hu, Y., Morgenroth, E., & Jacquin, C. (2025). Online monitoring of greywater reuse system using excitation-emission matrix (EEM) and K-PARAFACs. Water Research, 268, 122604 (13 pp.). doi:10.1016/j.watres.2024.122604, Institutional Repository

A currently increasing interest in water reuse is met with the concern about water quality. Excitation-emission matrix (EEM) measurements, which are widely implemented in laboratory analysis, emerge as a promising tool for characterizing both microbial and chemical water qualities in the online monitoring of water reuse systems. However, the robustness of EEM measurements has been rarely validated in actual online monitoring campaigns where predictions are made for new samples independent of those used to establish EEM analysis models, including the popular parallel factor analysis (PARAFAC). In this study, two strategies of conducting PARAFAC were examined for the online monitoring of a greywater reuse system using two EEM datasets from two monitoring periods for model establishment and model testing respectively. With the first strategy that is commonly used in laboratory analyses, an entire EEM datasets from one period was used to establish one PARAFAC model, and the maximum fluorescence intensity (Fmax) of a PARAFAC component was used to predict total cell count (TCC) in another period. However, under the disturbance of dissolved organic matter (DOM) fluorescence in the background, Fmax gave unreliable predictions in model testing. To address this problem, a second and novel strategy was proposed using an EEM clustering and PARAFAC component shift mining technique. This unsupervised algorithm, named K-PARAFACs, automatically groups EEMs into K clusters and on each cluster establishes a cluster-specific PARAFAC model with distinct component shapes. With this method, multiple PARAFAC models were established on one EEM dataset, with each model representing samples with certain TCC ranges and DOM compositions. In model testing, these cluster-specific PARAFAC models served as EEM classifiers. A new sample was not characterized by Fmax but by the cluster-specific model that best fitted the EEM signal of the sample with the least numerical error. The proposed strategy demonstrates its robustness by successfully predicting the TCC trend in test datasets. Our findings suggest that K-PARAFACs is a promising tool that enables robust qualitative monitoring of water reuse systems with background DOM variability.
Rothwell, K. A., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2025). Low molecular weight organic acids stabilise siderite against oxidation and influence the composition of iron (oxyhydr)oxide oxidation products. Environmental Science: Processes and Impacts (13 pp.). doi:10.1039/d4em00363b, Institutional Repository

Siderite (FeCO3) is an important reservoir of mineral-bound ferrous iron in non-sulfidic, reducing soils and sediments. It is redox sensitive, and its oxidation may facilitate the reduction of a range of pollutants, produce reactive oxygen species, or induce the formation of oxidation products with large surface areas for contaminant sorption. However, there is currently a limited understanding of the stability of siderite in complex environments such as soils and sediments. Here, we use a series of batch experiments complemented with thorough characterisation of mineral oxidation products to investigate the oxidation of siderite in the presence and absence of the low molecular weight organic acids (LMWOAs) citrate, tiron, salicylate, and EDTA as analogues for naturally occurring compounds or functional groups of natural organic matter that ubiquitously coexist with siderite. Our results show that siderite alone at pH 7.5 was completely oxidised to form ferrihydrite, nanocrystalline lepidocrocite, and nanocrystalline goethite in less than 6 hours. However, in the presence of LMWOAs, up to 48% of the siderite was preserved for more than 500 hours and the formation of goethite was inhibited in favour of ferrihydrite and lepidocrocite. Using experimental data from electron microscopy and chemical speciation modelling, we hypothesise that the siderite may be preserved through the formation of an Fe(iii)-passivation layer at the siderite surface.
Akert, F., Aebischer, P., Udert, K. M., & Reidy, B. (2024). Aurin, ein Dünger aus menschlichem Urin im Praxistest auf Sportrasen. Rasen: Turf: Gazon: European Journal of Turfgrass Science, 55(1), 16-21. , Institutional Repository

Um Nährstoffkreisläufe möglichst zu schließen und Nährstoffe effizient zu nutzen, wurde ein aus menschlichem Urin produzierter Dünger (Aurin) auf einem für Fußball genutzten Sportrasen getestet. Dabei wurde die Rasenfläche in drei Teilflächen unterteilt und von April bis Oktober mit herkömmlichem Handelsdünger (HD), Aurin (A) und Aurin mit Ergänzungsdüngung von Kalium, Phosphor und Magnesium (A+) gedüngt. Die Teilflächen wurden zwischen April und November regelmäßig bonitiert und mittels Multispektralbildanalyse untersucht. Im April, September und Oktober wurden Bodenproben entnommen, um den Nmin Gehalt im Boden zu bestimmen. Aus den Ergebnissen der Untersuchungen zeigten sich nur bei der Rasenfarbe und beim Nmin Gehalt des Bodens geringe Unterschiede. Dabei schien die Nährstoffergänzung von Aurin einen positiven Effekt auf die Stickstoffaufnahme in die Pflanze zu haben. Dies wirkte sich vor allem während Trockenperioden positiv auf die Rasenfarbe aus. Praktische Beobachtungen durch die Pflegeverantwortlichen zeigten, dass ein höheres Ausbringungsintervall mit geringeren Aurin-Mengen sinnvoll war. So konnten die Vernässung der Fläche und die kurzzeitige Verätzung des Rasens verhindert werden. Auch das Stoßwachstum in den Tagen nach der Düngung konnte so gebremst werden. Dieser Praxistest zeigt auf, dass Dünger aus menschlichem Urin eine interessante Option für eine kreislauffähige Bewirtschaftung von Sportrasen oder andere Kulturen mit hohem Stickstoffbedarf darstellen kann. Dies ist allerdings mit einem höheren Arbeitsaufwand in der Bewirtschaftung verbunden.
Bosshard, J., Eugster, F., Gulde, R., & Singer, H. (2024). Abwasser aus der Formulierung von Arzneimitteln. Wirkstoffeinträge in Schweizer Gewässer. Aqua & Gas, 104(3), 50-57. , Institutional Repository

Wirkstoffeinträge von formulierenden Pharmabetrieben führen häufig zu Spitzenkonzentrationen in kommunalen Abwasserreinigungsanlagen. Schweizweite Untersuchungen in Zusammenarbeit mit neun Betrieben zeigen das Ausmass der Einträge für unterschiedliche Abwasservorbehandlungen. Die Studie schliesst wichtige Kenntnislücken bezüglich der Abwasserbelastung von formulierenden Pharmabetrieben und zeigt Handlungsoptionen für die Unternehmen auf.
Bou-Sarkis, A., Paul, E., Bessiere, Y., Derlon, N., & Girbal-Neuhauser, E. (2024). Impact of biochemical properties on the gelation of EPS extracted from aerobic granules. Journal of Environmental Chemical Engineering, 12(5), 113648 (10 pp.). doi:10.1016/j.jece.2024.113648, Institutional Repository

Extracellular Polymeric Substances (EPS) extracted from aerobic granular sludge are a promising source of gel-forming biopolymers. Gaining insights on the charge distribution of these polymers was performed through a fractionation using anionic chromatography. A gelling factor (GF) based on the apparent gel volume and the reactivity of polymers to calcium was attributed to each eluted fraction. The GF values of the eluted anionic EPS correlated with their negative charge. A GF of 0.04 ± 0.03 is measured for molecules eluted at NaCl 0.25 M and a GF of 0.32 ± 0.02 for the molecules eluted at NaCl 0.75 M. However, upon reaching a very high negative charge (elution at NaCl 1 M), the gelation capacity decreases. The size distribution of gelling molecules was analyzed by Size Exclusion Chromatography. High Molecular Weight (MW) molecules are predominantly involved in gelation (between 65 % and 100 % of the high molecular weight fraction from each sample) while low MW molecules participation is relatively limited (lower than 40 % of the low molecular weight fraction from each sample). Moreover, infra-red spectroscopy analysis of the molecules before and after calcium addition showed that mostly proteins and polysaccharides contribute to the hydrogel formation. Colorimetric methods showed that around 60 % of the uronic acids present in the samples could form hydrogels whereas proteins’ participation varied between 0 % and 100 % depending on the fraction. Thus, modulating EPS extraction and purification methods to ensure the preservation of their molecular weight and the selection of appropriate negative charge could be a strategy for EPS valorization.
Brander, A., Wunderlin, P., Gulde, R., & Böhler, M. (2024). MV-Stufen Stabil Betreiben. Hilfreiche Betriebsparameter. Aqua & Gas, 104(1), 54-61. , Institutional Repository

Der Reinigungseffekt für Mikroverunreinigungen wird von ARA über periodische Messungen der Leitsubstanzen bestimmt. Für den täglichen Betrieb lassen sich zusätzlich anhand von UV-Messungen sowie anhand der dosierten Mengen an Ozon oder Aktivkohle zeitnahe Aussagen zur Reinigungsleistung machen.
Endres, L. S., Jacquin, C., González-Lemos, S., Rodríguez-Rodríguez, L., Sliwinski, J., Kaushal, N., … Stoll, H. M. (2024). Climatic and cave settings influence on drip water fluorescent organic matter with implications for fluorescent laminations in stalagmites. Quaternary Research, 118, 41-61. doi:10.1017/qua.2023.41, Institutional Repository

Speleothem fluorescence can provide insights into past vegetation dynamics and stalagmite chronology. However, its origin and especially the formation of fluorescent laminations in stalagmites are poorly understood. We conducted a year-long monthly monitoring of drip water fluorescence in La Vallina Cave (northern Iberian Peninsula) and compared the results to drip water chemistry and active speleothems from the same sites. Drip waters were analyzed using fluorescence spectroscopy and parallel factor analysis (PARAFAC). The resulting five-component model indicates contributions from vegetation, microbial activity, and bedrock. Intra-site fluorescence variability is mainly influenced by changes in overlying vegetation, water reservoir time, and respiration rates. Contrary to prevailing views, we find no systematic increase in drip water fluorescence during rainy conditions across drip sites and seasonal variations in drip water fluorescence are absent at a location where present-day speleothem layers form. Our findings challenge the notion of a higher abundance of humic-like fluorescence during the rainy season as the primary cause for layer formation and suggest additional controls on drip water fluorescence, such as bedrock interaction and microbial reprocessing. We also propose that growth rate may control the dilation of the fluorescence signal in stalagmites, indicating other potential mechanisms for fluorescent layer formation.
Fau, Z., Damien, T., Azais, A., Derlon, N., Chazarenc, F., & Gillot, S. (2024). Towards a standardised analysis of experimental Threshold Of Flocculation (TOF) curves. Water Science and Technology, 90(7), 2103-2113. doi:10.2166/wst.2024.308, Institutional Repository

Characterising bioflocculation and settling in activated sludge processes is mandatory to better understand and optimise organic matter removal and capture. Among the few indicators available, Threshold Of Flocculation (TOF) reflects the ability of activated sludge to settle following Stokesian settling mechanisms. In this work, the original method to determine TOF has been improved to gain accuracy and reproducibility. An R-script was proposed for systematic analysis of the experimental curves representing the total suspended solids supernatant concentration as a function of the initial concentration of the total suspended solids. The strength of this new method is to base curve analysis on the settling mechanisms that occur in the experimental setup. Two thresholds are mathematically identified, corresponding to (i) the solid concentration required to induce discrete flocculent settling and (ii) the minimum concentration to form large flocs that interact with each other (TOF). The novel method was successfully applied to different types of sludge (HRAS, CAS, and densified sludge).
Faust, V., Markus, P., Schielke-Jenni, S., Timmer, M. J., De Paepe, J., Ganigué, R., … Udert, K. M. (2024). Conditions for successful nitrogen removal from source-separated urine by partial nitritation/anammox. PLoS Water, 3(5), e0000235 (23 pp.). doi:10.1371/journal.pwat.0000235, Institutional Repository

Partial nitritation/anammox (PN/A) of source-separated urine is less energy-intensive and potentially cheaper and more environmentally friendly than conventional nitrogen removal from mixed sewage. However, PN/A of undiluted source-separated urine has not yet been established. In this study, the feasibility of PN/A for source-separated urine (total nitrogen 2 to 3 g-N L-1). To evaluate the influence of different factors, one- and two-stage configurations were operated using different influents, i.e. source-separated urine, synthetic urine, and urine with additional divalent cations. While partial nitritation was successfully achieved in both configurations with digester supernatant and urine, anammox activity was lost shortly after switching from digester supernatant to the urine influents. Toxic organic compounds or pharmaceuticals and the high monovalent to divalent cation ratio were suspected as causes of anammox failure, but were ruled out due to the different reactor configurations and influent compositions tested. Other suspected factors such as COD/N ratio, phosphate and sulfate inhibition, nitrogen compound inhibition, metal inhibition, pH and dissolved oxygen were also systematically excluded. Instead, the high salt concentration in urine compared to the digester supernatant most likely caused the reactor to fail due to the disintegration of large flocs, and the resulting challenge of biomass retention. The shortcomings of the floccular sludge system were overcome by using biofilm carriers, resulting in successful PN/A. This hybrid system ran for 140 days with nitrogen removal rates of up to 1000 mg-N L-1 d-1 with an average of 410 ± 220 mg-N L-1 d-1, and a nitrogen removal efficiency of 93 ± 3% at 30C.
Faust, V., Vlaeminck, S. E., Ganigué, R., & Udert, K. M. (2024). Influence of pH on urine nitrification: community shifts of ammonia-oxidizing bacteria and inhibition of nitrite-oxidizing bacteria. ACS ES&T Engineering, 4(2), 342-353. doi:10.1021/acsestengg.3c00320, Institutional Repository

Urine nitrification is pH-sensitive due to limited alkalinity and high residual ammonium concentrations. This study aimed to investigate how the pH affects nitrogen conversion and the microbial community of urine nitrification with a pH-based feeding strategy. First, kinetic parameters for NH3, HNO2, and NO2- limitation and inhibition were determined for nitrifiers from a urine nitrification reactor. The turning point for ammonia-oxidizing bacteria (AOB), i.e., the substrate concentration at which a further increase would lead to a decrease in activity due to inhibitory effects, was at an NH3 concentration of 12 mg-N L-1, which was reached only at pH values above 7. The total nitrite turning point for nitrite-oxidizing bacteria (NOB) was pH-dependent, e.g., 18 mg-N L-1 at pH 6.3. Second, four years of data from two 120 L reactors were analyzed, showing that stable nitrification with low nitrite was most likely between pH 5.8 and 6.7. And third, six 12 L urine nitrification reactors were operated at total nitrogen concentrations of 1300 and 3600 mg-N L-1 and pH values between 2.5 and 8.5. At pH 6, the AOB Nitrosomonas europaea was found, and the NOB belonged to the genus Nitrobacter. At pH 7, nitrite accumulated, and Nitrosomonas halophila was the dominant AOB. NOB were inhibited by HNO2 accumulation. At pH 8.5, the AOB Nitrosomonas stercoris became dominant, and NH3 inhibited NOB. Without influent, the pH dropped to 2.5 due to the growth of the acid-tolerant AOB “Candidatus Nitrosacidococcus urinae”. In conclusion, pH is a decisive process control parameter for urine nitrification by influencing the selection and kinetics of nitrifiers.
Frossard, E., Crain, G., Giménez de Azcárate Bordóns, I., Hirschvogel, C., Oberson, A., Paille, C., … Udert, K. M. (2024). Recycling nutrients from organic waste for growing higher plants in the Micro Ecological Life Support System Alternative (MELiSSA) loop during long-term space missions. Life Sciences in Space Research, 40, 176-185. doi:10.1016/j.lssr.2023.08.005, Institutional Repository

Space agencies are developing Bioregenerative Life Support Systems (BLSS) in view of upcoming long-term crewed space missions. Most of these BLSS plan to include various crops to produce different types of foods, clean water, and O2 while capturing CO2 from the atmosphere. However, growing these plants will require the appropriate addition of nutrients in forms that are available. As shipping fertilizers from Earth would be too costly, it will be necessary to use waste-derived nutrients. Using the example of the MELiSSA (Micro-Ecological Life Support System Alternative) loop of the European Space Agency, this paper reviews what should be considered so that nutrients recycled from waste streams could be used by plants grown in a hydroponic system. Whereas substantial research has been conducted on nitrogen and phosphorus recovery from human urine, much work remains to be done on recovering nutrients from other liquid and solid organic waste. It is essential to continue to study ways to efficiently remove sodium and chloride from urine and other organic waste to prevent the spread of these elements to the rest of the MELiSSA loop. A full nitrogen balance at habitat level will have to be achieved; on one hand, sufficient N2 will be needed to maintain atmospheric pressure at a proper level and on the other, enough mineral nitrogen will have to be provided to the plants to ensure biomass production. From a plant nutrition point of view, we will need to evaluate whether the flux of nutrients reaching the hydroponic system will enable the production of nutrient solutions able to sustain a wide variety of crops. We will also have to assess the nutrient use efficiency of these crops and how that efficiency might be increased. Techniques and sensors will have to be developed to grow the plants, considering low levels or the total absence of gravity, the limited volume available to plant growth systems, variations in plant needs, the recycling of nutrient solutions, and eventually the ultimate disposal of waste that can no longer be used.
Fumasoli, A., Probst, M., Wett, B., Derlon, N., Wenger, R., & Rérolle, M. (2024). Indense - Verfahren für Granulierten Schlamm. Erfahrungen und Erkenntnisse aus einem ein jährigen Pilotenversuch auf der ARA Gossau-Grüningen. Aqua & Gas, 104(1), 32-39. , Institutional Repository

Das inDENSE®-Verfahren wurde auf der ARA Gossau-Grüningen getestet. Nach einem Jahr wurde ein Anteil an granuliertem Schlamm von rund 50% und ein Schlammvolumenindex zwischen 40 und 70 ml/g beobachtet. DNA-Analysen zeigten, dass die bakterielle Gesamtpopulation saisonal konstanter blieb und Nitrit-oxidierende Bakterien im granulierten Schlamm akkumulierten. Durch die verbesserten Absetzeigenschaften können die Kapazität der ARA und die Stickstoffelimination signifikant gesteigert werden.
Galgani, F., Lusher, A. L., Strand, J., Haarr, M. L., Vinci, M., Molina Jack, E., … van Bavel, B. (2024). Revisiting the strategy for marine litter monitoring within the european marine strategy framework directive (MSFD). Ocean and Coastal Management, 255, 107254 (11 pp.). doi:10.1016/j.ocecoaman.2024.107254, Institutional Repository

Marine litter and non-degradable plastic pollution is of global concern. Regular monitoring programs are being established to assess and understand the scale of this pollution. In Europe, the goal of the European Marine Strategy Framework Directive (MSFD) is to assess trends in Good Environmental Status and support large-scale actions at the regional level. Marine litter monitoring requires tailored sampling strategies, protocols and indicators, that align with specific objectives and are tailored for local or regional needs. In addition, the uneven spatial and temporal distributions of marine litter present a challenge when designing a statistically powerful monitoring program. In this paper, we critically review the existing marine litter monitoring programs in Europe. We discuss the main constraints, including environmental, logistical, scientific, and ethical factors. Additionally, we outline the critical gaps and shortcomings in monitoring MSFD beaches/shorelines, floating litter, seafloor litter, microplastics, and harm. Several priorities must be established to shape the future of monitoring within the MSFD. Recent developments in analytical approaches, including optimizing protocols and sampling strategies, gaining a better understanding of the spatiotemporal heterogeneity of litter and its implications for survey design and replication, and the inclusion of newly validated methodologies that have achieved sufficient technical readiness, must be considered. Although there are well-established methods for assessing beaches, floating and seafloor litter, it will be necessary to implement monitoring schemes for microplastics in sediments and invertebrates as robust analytical methods become available for targeting smaller particle size classes. Furthermore, the inclusion of indicators for entanglement and injury to marine organisms will have to be considered in the near future. Moreover, the following actions will enhance the effectiveness of monitoring efforts: (1) creating an inventory of accumulation areas and sources of specific types of litter (e.g., fishing gear), (2) monitoring riverine inputs of litter, (3) monitoring atmospheric inputs including microplastics, (4) accidental inputs during extreme weather events, and (5) studying how species at risk may be transported by litter. We provide recommendations to support long-term, effective, and well-coordinated marine litter monitoring within the MSFD to achieve a comprehensive and accurate understanding of marine litter in EU waters. This will allow the development of measures to mitigate the impacts of marine pollution and eventually to evaluate the success of the respective measures.
Ganesanandamoorthy, P., Joss, A., Gruber, W., Bührer, T., & Thomann, M. (2024). Online-Nitritmessung. Vergleich von Online-Nitritsensoren für die Abwassereinigung. Aqua & Gas, 104(1), 26-31. , Institutional Repository

Nitrit ist eine ökotoxikologisch problematische Substanz und führt auf Kläranlagen ausserdem zur Bildung von klimaschädlichem Lachgas. In der hier vorgestellten Studie werden verschiedene Online-Sensoren verglichen und deren Messunsicherheit in Ablauf und Belebtschlamm erfasst.
Grigg, A. R. C., Notini, L., Kaegi, R., ThomasArrigo, L. K., & Kretzschmar, R. (2024). Aluminium substitution affects jarosite transformation to iron oxyhydroxides in the presence of aqueous Fe(II). Geochimica et Cosmochimica Acta, 374, 72-84. doi:10.1016/j.gca.2024.04.008, Institutional Repository

Jarosite is an abundant mineral in acidic environments, often found in acid sulfate soil (ASS) and acid-mine drainage (AMD). As a store of Fe, K, S and acidity, and a scavenger for major and trace elements, jarosite plays an important role in the biogeochemistry of acid sulfate environments. When ASS and AMD become anoxic, reducing conditions can set in, producing conditions that are outside the thermodynamic stability field of jarosite. In this study, we investigated the transformation of synthetic and natural jarosite with various degrees of Al-for-Fe substitution under circumneutral anoxic conditions in the presence of Fe(II), to understand the rates and pathways of jarosite and Al-jarosite transformation, the role of competing transformation pathways, the fate of Al during transformation and the different reactivity of natural and synthetic Al-jarosite. Synthetic jarosite (containing 0 %–7 % Al-for-Fe substitution) and a natural Al-substituted jarosite sample from an ASS in Thailand were suspended in solutions of 57Fe(II) at pH 7 for 24 h under anoxic conditions. The chosen experimental conditions mimic the Fe(II) concentrations and pH found in flooded ASS under reducing conditions. Changes in mineral composition of the suspensions were determined by Rietveld analysis of X-ray diffraction patterns at six time points. The fate of Al was determined by XRD, Raman spectroscopy and energy dispersive X-ray spectroscopy analysis of the jarosite and product minerals. Different transformation pathways that occurred simultaneously were traced by using 57Fe Mössbauer spectroscopy and aqueous Fe isotope composition. The analysis showed that 7 % Al-for-Fe substitution in jarosite more than halved the mineral transformation rate compared to unsubstituted jarosite, regardless of the Fe(II) concentrations. Indeed, 7 % Al-for-Fe substitution had a greater effect on the transformation rate than an order-of-magnitude decrease in the Fe(II) concentrations in all Al-for-Fe substitution treatments. The transformation products in all samples were goethite, lepidocrocite and ferrihydrite, with minor amounts of magnetite forming from jarosite with no or low Al-for-Fe substitution reacted with high Fe(II) concentrations. Lepidocrocite was the dominant product in reactors without aluminium, but lepidocrocite was not strongly enriched in 57Fe, suggesting that it may not have formed exclusively from Fe in solution during the Fe(II)-catalysed transformation of other minerals. In high-Al systems, lepidocrocite appeared to be a sink for Al, although its formation in Al-rich samples was suppressed. Natural jarosite reacted more than an order of magnitude more slowly than the synthetic jarosite and Al-jarosite, indicating that the properties of the synthetic jarosite do not completely account for the stability of natural jarosite under anoxic circumneutral conditions. The results provide an important baseline for understanding the drivers of jarosite transformation or stability in ASS and AMD.
Grigg, A. R. C., Notini, L., Kaegi, R., ThomasArrigo, L. K., & Kretzschmar, R. (2024). Structural effects of aluminum and iron occupancy in minerals of the jarosite-alunite solid solution. ACS Earth and Space Chemistry, 8(2), 194-206. doi:10.1021/acsearthspacechem.3c00174, Institutional Repository

The alunite supergroup of minerals contains several hydroxysulfate mineral phases that commonly occur in acidic natural and engineered environments. The main division of the mineral supergroup defines two minerals, jarosite and alunite, based on the relative structural occupancy by Al or Fe, respectively. However, intermediate members of the jarosite-alunite solid solution have not been extensively characterized, especially in the environment. Here, we link the mineral unit cell sizes measured by X-ray diffraction, peak shifts in Raman spectra, fitting parameters in Mössbauer spectroscopy, and elemental quantification by EDX spectroscopy to known amounts of Al substitution in two synthetic series of Al-substituted jarosite (up to Al-for-Fe substitution of 9.5%) and unknown Al substitution in a natural jarosite isolated from an acid sulfate soil. Strong correlations were observed between the Al substitution of the jarosite samples and unit cell size, position of several vibrational peaks in Raman spectroscopy, and the temperature of magnetic ordering. In addition, elemental mapping provided a robust way to characterize the Al content of jarosite. As the techniques were effective in quantifying the Al or Fe content of jarosite-alunite supergroup mineral samples, without the need for sample dissolution, the findings support the application of these spectroscopy techniques to characterize natural jarosite-alunite samples. Using these techniques, we demonstrate at least 5% Al-for-Fe substitution in a jarosite sample from an acid sulfate soil. Application to environmental samples is especially useful in cases where it is otherwise difficult to directly measure the Al content of a mineral sample or when Al-for-Fe substitution influences the spectral responses to substitution at other sites in the crystal structure.
Harder, R., Metson, G. S., Macura, B., Johannesdottir, S., Wielemaker, R., Seddon, D., … McConville, J. R. (2024). Egestabase - an online evidence platform to discover and explore options to recover plant nutrients from human excreta and domestic wastewater for reuse in agriculture. MethodsX, 12, 102774 (10 pp.). doi:10.1016/j.mex.2024.102774, Institutional Repository

Restoring nutrient circularity across scales is important for ecosystem integrity as well as nutrient and food security. As such, research and development of technologies to recover plant nutrients from various organic residues has intensified. Yet, this emerging field is diverse and difficult to navigate, especially for newcomers. As an increasing number of actors search for circular solutions to nutrient management, there is a need to simplify access to the latest knowledge. Since the majority of nutrients entering urban areas end up in human excreta, we have chosen to focus on human excreta and domestic wastewater. Through systematic mapping with stakeholder engagement, we compiled and consolidated available evidence from research and practice. In this paper, we present ‘Egestabase’ – a carefully curated open-access online evidence platform that presents this evidence base in a systematic and accessible manner. We hope that this online evidence platform helps a variety of actors to navigate evidence on circular nutrient solutions for human excreta and domestic wastewater with ease and keep track of new findings.
Heusser, A., Dax, A., McArdell, C. S., & Udert, K. M. (2024). Comparing the adsorption of micropollutants on activated carbon from anaerobically stored, organics-depleted, and nitrified urine. Water Research, 257, 121615 (12 pp.). doi:10.1016/j.watres.2024.121615, Institutional Repository

Separate collection and treatment of urine optimizes nutrient recovery and enhances micropollutant removal from municipal wastewater. One typical urine treatment train includes nutrient recovery in three biological processes: anaerobic storage, followed by aerobic organics degradation concurrently with nitrification. These are usually followed by activated carbon adsorption to remove micropollutants. However, removing micropollutants prior to nitrification would protect nitrifiers from potential inhibition by pharmaceuticals. In addition, combining simplified biological treatment with activated carbon adsorption could offer a cheap and robust process for removing micropollutants where nutrient recovery is not the first priority, as a partial loss of ammonia occurs without nitrification. In this study, we investigated whether activated carbon adsorption could also take place between the three biological treatment steps. We tested the effectiveness of micropollutant removal with activated carbon after each biological treatment step by conducting experiments with anaerobically stored urine, organics-depleted urine, and nitrified urine. The urine solutions were spiked with 19 pharmaceuticals: amisulpride, atenolol, atenolol acid, candesartan, carbamazepine, citalopram, clarithromycin, darunavir, diclofenac, emtricitabine, fexofenadine, hydrochlorothiazide, irbesartan, lidocaine, metoprolol, N4-acetylsulfamethoxazole, sulfamethoxazole, trimethoprim, venlafaxine, and two artificial sweeteners, acesulfame and sucralose. Batch experiments were conducted with powdered activated carbon (PAC) to determine how much activated carbon achieve which degree of micropollutant removal and how organics, pH, and speciation change from ammonium to nitrate influence adsorption. Micropollutant removal was also tested in granular activated carbon (GAC) columns, which is the preferred technology for micropollutant removal from urine. The carbon usage rates (CUR) per person were lower for all urine solutions than for municipal wastewater. The results showed that organics depletion would be needed when micropollutant removal was the sole aim of urine treatment, as the degradation of easily biodegradable organics prevented clogging of GAC columns. However, CUR did hardly improve with organics-depleted urine compared to stored urine. The lowest CUR was achieved with nitrified urine. This resulted from the additional organics removal during nitrification and not the lower pH or the partial conversion of ammonium to nitrate. In addition, we showed that the relative pharmaceutical removal in all solutions was independent of the initial pharmaceutical concentration unless the background organics matrix changed considerably. We conclude that removal of micropollutants in GAC columns from organics-depleted urine can be performed without clogging, but with the drawback of a higher carbon usage compared to removal from nitrified urine.
Heusser, A., Wackernagel, I., Reinmann, M., & Udert, K. M. (2024). Increasing urine nitrification performance with sequential membrane aerated biofilm reactors. Water Research, 261, 122019 (10 pp.). doi:10.1016/j.watres.2024.122019, Institutional Repository

This study aimed to investigate whether separating organics depletion from nitrification increases the overall performance of urine nitrification. Separate organics depletion was facilitated with membrane aerated biofilm reactors (MABRs). The high pH and ammonia concentration in stored urine inhibited nitrification in the first stage and therewith allowed the separation of organics depletion from nitrification. An organics removal of 70 % was achieved at organic loading rates in the influent of 3.7 gCOD d−1 m−2. Organics depletion in a continuous flow stirred tank reactor (CSTR) for organics depletion led to ammonia stripping through diffused aeration of up to 13 %. Using an MABR, diffusion into the lumen amounted for 4 % ammonia loss only. In the MABR, headspace volume and therefore ammonia loss through the headspace was negligible. By aerating the downstream MABR for nitrification with the off-gas of the MABR for organics depletion, 96 % of the ammonia stripped in the first stage could be recovered in the second stage, so that the overall ammonia loss was negligibly low. Nitrification of the organics-depleted urine was studied in MABRs, CSTRs, and sequencing batch reactors in fed batch mode (FBRs), the latter two operated with suspended biomass. The experiments demonstrated that upstream organics depletion can double the nitrification rate. In a laboratory-scale MABR, nitrification rates were recorded of up to 830 mgN L−1 d−1 (3.1 gN m−2 d−1) with ambient air and over 1500 mgN L−1 d−1 (6.7 gN m−2 d−1) with oxygen-enriched air. Experiments with a laboratory-scale MABR showed that increasing operational parameters such as pH, recirculation flow, scouring frequency, and oxygen content increased the nitrification rate. The nitrification in the MABR was robust even at high pH setpoints of 6.9 and was robust against process failures arising from operational mistakes. The hydraulic retention time (HRT) required for nitrification was only 1 to 2 days. With the preceding organics depletion, the HRT for our system requires 2 to 3 days in total, whereas a combined activated sludge system requires 4 to 8 days. The N2O concentration in the off-gas increases with increasing nitrification rates; however, the N2O emission factor was 2.8 % on average and independent of nitrification rates. These results indicate that the MABR technology has a high potential for efficient and robust production of ammonium nitrate from source-separated urine.
Kaiser, S., Kaegi, R., & Rhein, F. (2024). Influence of aging, morphology and particle size on the behavior of microplastics during magnetic seeded filtration. Science of the Total Environment, 957, 177353 (12 pp.). doi:10.1016/j.scitotenv.2024.177353, Institutional Repository

Magnetic seeded filtration (MSF) is a solid-liquid separation process based on the formation of hetero-agglomerates between target (non-magnetic) particles and added magnetic particles, followed by magnetic separation. Previous experimental studies reported high separation efficiencies for hydrophobic microplastic particles (MP) and focused mainly on the polymer type. This study investigates the influence of the particle size, morphology and aging on the separation efficiency of different polymer types. Surface morphology and particle size only marginally affect the separation of particles larger than 30μm. However, the agglomeration of particles in the lower micron range is increasingly dominated by repulsive electrostatic interactions. After oxidative treatment with Fenton's reagent, separation efficiencies for most MP remain between 55% and 96%. Exposure to UV light results in a significant decrease in separation efficiency, particularly for polystyrene, where the separation efficiency decreases from 86% to 9%. Mechanical aging, simulated by mixing MP in a sand matrix on a horizontal shaker, reduces the separation to below 50% for all polymer types. Exposure to UV light causes surface oxidation, as evidenced by the formation of carbonyl peaks in the Fourier transformed infrared spectra. Mechanical treatment results in the deposition of small silica particles on the MP surface, as revealed by electron microscopy. Both mechanisms render the polymer surface more hydrophilic and reduce the tendency to form hetero-agglomerates with (hydrophobic) magnetic seed particles. MSF is a promising technique for MP separation but also offers the possibility to probe surface properties of (environmentally aged) MPs. This study demonstrates that environmental aging can significantly affect the behavior of MP and highlights the importance of environmental aging in MP fate studies.
Kirchgeorg, S., Aucone, E., Wenk, F., & Mintchev, S. (2024). Design, modeling, and control of AVOCADO: a multimodal aerial-tethered robot for tree canopy exploration. IEEE Transactions on Robotics, 40, 592-605. doi:10.1109/TRO.2023.3334630, Institutional Repository

Forests provide vital resources and services for humanity, but preserving and restoring them is challenging due to the difficulty of obtaining actionable data, especially in inaccessible areas, such as forest canopies. To address this, we follow the lead of arboreal animals that exploit multiple modes of locomotion. We combine aerial and tethered movements to enable AVOCADO to navigate within a tree canopy. Starting from the top of a tree, it can descend with the tether and maneuver around obstacles with thrusters. We extend our previous work with a new mechanical design with a protective shell, increased computational power and cameras for state estimation. We introduce a dynamic model and simulation, and perform a quasistatic and dynamic validation. For autonomy, we derive a control framework in simulation to regulate tether length, tilt, and heading, before transfer to the robot. We evaluate the controllers for trajectory tracking through experiments. AVOCADO can follow trajectories around obstacles and reject disturbances on the tether. Exploiting multimodal mobility will advance the exploration of tree canopies to actively monitor the true value of our forests.
Kuehr, S., Kaegi, R., Raths, J., Sinnet, B., Kipf, M., Rehkämper, M., … Georgantzopoulou, A. (2024). Reduced bioavailability of Au and isotopically enriched 109Ag nanoparticles transformed through a pilot wastewater treatment plant in Hyalella azteca under environmentally relevant exposure scenarios. Science of the Total Environment, 949, 174768 (13 pp.). doi:10.1016/j.scitotenv.2024.174768, Institutional Repository

Wastewater Treatment Plants (WWTP) are a major repository and entrance path of nanoparticles (NP) in the environment and hence play a major role in the final NP fate and toxicity. Studies on silver nanoparticles (AgNP) transport via the WWTP system and uptake by aquatic organisms have so far been carried out using unrealistically high AgNP concentrations, unlikely to be encountered in the aquatic environment. The use of high AgNP concentrations is necessitated by both the low sensitivity of the detection methods used and the need to distinguish background Ag from spiked AgNP.
In this study, isotopically enriched 109AgNP were synthesized to overcome these shortcomings and characterized by a broad range of methods including transmission electron microscopy, dynamic and electrophoretic light scattering. 109AgNP and gold NP (AuNP) were spiked to a pilot wastewater treatment plant fed with municipal wastewater for up to 21 days. AuNP were used as chemically less reactive tracer. The uptake of the pristine and transformed NP present in the effluent was assessed using the benthic amphipod Hyalella azteca in fresh- and brackish water exposures at environmentally relevant concentrations of 30 to 500 ng Au/L and 39 to 260 ng Ag/L. The unique isotopic signature of the 109AgNP allowed to detect the material at environmentally relevant concentrations in the presence of a much higher natural Ag background. The results show that the transformations reduce the NP uptake at environmentally relevant exposure concentrations. For 109Ag, lower accumulation factors (AF) were obtained after exposure to transformed NP (250–350) compared to the AF values obtained for pristine 109AgNP (750–840). The reduced AF values observed for H. azteca exposed to effluent from the AuNP-spiked WWTP indicate that biological transformation processes (e.g. eco-corona formation) seem to be involved in addition to chemical transformation.
Käser, D., Kägi, R., Hattendorf, B., & Günther, D. (2024). Fundamental studies of laser ablation ICPMS using a nitrogen plasma source and helium, argon and nitrogen as carrier gas. Journal of Analytical Atomic Spectrometry, 39(12), 3069-3081. doi:10.1039/d4ja00327f, Institutional Repository

Laser-generated aerosols in helium, argon and nitrogen were directly compared using a nitrogen microwave inductively coupled plasma in combination with a mass spectrometer. An increased surface darkening of the sample was observed during ablation in nitrogen, suggesting a more pronounced particle deposition in comparison to helium, but only 30% lower sensitivities were obtained for nitrogen. Crater depth measurements proved that these variations were not the consequence of a difference in ablation rate (271 ± 17 nm per pulse for He vs. 267 ± 12 nm per pulse for N2). Particle size measurements and electron microscopy images indicated that the aerosol generated in nitrogen or argon tends to form smaller agglomerates in comparison to helium. This dependence in agglomeration however appeared to be dependent on the ablation cell used. Furthermore, the fluence of the 193 nm laser system used for the experiments significantly influenced the temporal stability of the signals (e.g.238U+/232Th+). Finally, the quantification capabilities of nitrogen as an ablation environment and carrier gas were studied and compared to helium generated aerosols transported in nitrogen. A selection of samples (NIST SRM 612, USGS BCR-2G, USGS GSD-1G and GSE-1G) were quantified using NIST SRM 610 as an external standard. The potential of nitrogen as an alternative carrier gas was highlighted with deviations from the reference values calculated between −13% and +16% in comparison to the deviations between −15% and +17% obtained with helium in a cylindrical ablation cell for most elements in the different reference materials analyzed.
Meynet, P., Joss, A., Davenport, R. J., & Fenner, K. (2024). Impact of long-term temperature shifts on activated sludge microbiome dynamics and micropollutant removal. Water Research, 258, 121790 (10 pp.). doi:10.1016/j.watres.2024.121790, Institutional Repository

Micropollutants removal efficiency strongly vary across different aerobic wastewater treatment plants, resulting in their frequent detection in surface and ground waters. Seasonal temperature variation is a major factor influencing plant performance, but it is still unclear how prolonged periods of temperature change impact microbiome and micropollutant biotransformation. This work investigates the effect of long-term temperature variation on the microbial dynamics in an activated sludge system, and the impact on micropollutant biotransformation. Sequencing batch reactors were used as model system and 4–40 °C temperature range was studied. 16S rRNA amplicon sequencing showed that temperature drives microbial structure (gDNA) and activity (RNA), rather than time, and this was stronger below 15 °C and above 25 °C. The microbial community was richest and more diverse at 20 °C, while rarer and more specific taxa became predominant over time, at more extreme temperatures. This suggested that less abundant taxa might be responsible for maintaining the biotransformation capability in the activated sludge at extreme temperatures. Micropollutant biotransformation rates mostly deviated from the classic Arrhenius model below 15 °C and above 25 °C, indicating that prolonged exposure to temperature changes leads to temperature-induced taxonomic shifts, resulting in the emerging of different sets of biotransformation pathways over different temperature ranges.
Nopp-Mayr, U., Layendecker, S., Sittenthaler, M., Philipp, M., Kägi, R., & Weinberger, I. (2024). Microplastic loads in Eurasian otter (Lutra lutra) feces - targeting a standardized protocol and first results from an alpine stream, the River Inn. Environmental Monitoring and Assessment, 196(8), 707 (14 pp.). doi:10.1007/s10661-024-12791-z, Institutional Repository

Microplastics (MP) are omnipresent in a wide range of environments, constituting a potential threat for aquatic and terrestrial wildlife. Effects in consumers range from physical injuries to pathological reactions. Due to potential bioaccumulation of MP, predators are of particular concern for MP induced health effects. The Eurasian otter is an apex predator in (semi-)aquatic habitats feeding primarily on fish. Furthermore, the species is classified as “near threatened” on the IUCN Red List. Thus, the Eurasian otter is of conservation concern and may serve as a bioindicator for MP pollution. Feces can be used to detect pollutants, including MP. Initial studies confirmed the presence of MP in otter feces (= spraints). However, as specific, validated protocols targeting at an efficient and standardized extraction of MP from otter spraints are missing, experimental results reported from different groups are challenging to compare. Therefore, we (i) present steps towards a standardized protocol for the extraction of MP from otter feces, (ii) give recommendations for field sample collection of otter spraints, and (iii) provide a user-friendly step-by-step workflow for MP extraction and analysis. Applying this framework to field samples from five study sites along the River Inn (n = 50), we detected MP of different sizes and shapes (ranging from microfibers to road abrasion and tire wear) in all otter spraint samples.
Pechaud, Y., Derlon, N., Queinnec, I., Bessiere, Y., & Paul, E. (2024). Modelling biofilm development: the importance of considering the link between EPS distribution, detachment mechanisms and physical properties. Water Research, 250, 120985 (16 pp.). doi:10.1016/j.watres.2023.120985, Institutional Repository

In industry, treatments against biofilms need to be optimized and, in the wastewater treatment field, biofilm composition needs to be controlled. Therefore, describing the biochemical and physical structures of biofilms is now required to better understand the influence of operating parameters and treatment on biofilms. The present study aims to investigate how growth conditions influence EPS composition, biofilm physical properties and volume detachment using a 1D biofilm model. Two types of EPS are considered in the present model, proteins and polysaccharides. The main hypotheses are that: (i) the production of polysaccharides occurs mainly under strong nutrient limitation(s) while the production of proteins is coupled to both the substrate uptake rate and the lysis process; (ii) the local biofilm porosity depends on the local biofilm composition. Both volume and surface detachment occur in biofilms and volume detachment extent depends on the biofilm local cohesion and thus on the local composition of biofilms for a given shear stress.
The model is based on experimental trends and aims to represent these observations on the basis of biochemical and physical processes. Four case studies covering a wide range of contrasting growth conditions such as different COD/N ratios, applied SOLR and shear stresses are investigated. The model predicts how the biochemical and physical biofilm structures change as a result of contrasting growth conditions. More precisely simulation results are in good agreement with the main experimental observations reported in the literature, such as: (i) a strong nitrogen limitation of growth induces an important accumulation of polysaccharides leading to a more porous and homogenous biofilm, (ii) a high applied surface organic loading load allows to obtain a high biofilm thickness, (iii) a strong shear stress applied during the biofilm growth leads to a reduction of the biofilm thickness and to a consolidation of the biofilm structure. Overall, this model represents a relevant decision tool for the selection of appropriate enzymatic treatments in the context of negative biofilm control. From our results, it appears that protease based treatments should be more appropriate for biofilms developed under low COD/N ratios (about 20 gCOD/gN) whereas both glucosidases and proteases based treatments should be more appropriate for biofilms developed under high COD/N ratio (about 70 gCOD/gN). In addition, the model could be useful for other applications such as resource recovery in biofilms or granules, and help to better understand biological membrane fouling.
Reynaert, E., Nagappa, D., Sigrist, J. A., & Morgenroth, E. (2024). Ensuring microbial water quality for on-site water reuse: importance of online sensors for reliable operation. Water Research X, 22, 100215 (8 pp.). doi:10.1016/j.wroa.2024.100215, Institutional Repository

A growing number of cities and regions are promoting or mandating on-site treatment and reuse of wastewater, which has resulted in the implementation of several thousand on-site water reuse systems on a global scale. However, there is only limited information on the (microbial) water quality from implemented systems. The focus of this study was on two best-in-class on-site water reuse systems in Bengaluru, India, which typically met the local water quality requirements during monthly compliance testing. This study aimed to (i) assess the microbial quality of the reclaimed water at a high temporal resolution (daily or every 15 min), and (ii) explore whether measurements from commercially available sensors can be used to improve the operation of such systems. The monitoring campaign revealed high variations in microbial water quality, even in these best-in-class systems, rendering the water inadequate for the intended reuse applications (toilet flushing and landscape irrigation). These variations were attributed to two key factors: (1) the low frequency of chlorination, and (2) fluctuations of the chlorine demand of the water, in particular of ammonium concentrations. Such fluctuations are likely inherent to on-site systems, which rely on a low level of process control. The monitoring campaign showed that the microbial water quality was most closely related to oxidation–reduction potential (ORP) and free chlorine sensors. Due to its relatively low cost and low need for maintenance, the ORP emerges as a compelling candidate for automating the chlorination to effectively manage variations in chlorine demand and ensure safe water reuse. Overall, this study underscores the necessity of integrating treatment trains, operation, and monitoring for safe on-site water reuse.
Reynaert, E., Sylvestre, É., Morgenroth, E., & Julian, T. R. (2024). Greywater recycling for diverse collection scales and appliances: enteric pathogen log-removal targets and treatment trains. Water Research, 264, 122216 (13 pp.). doi:10.1016/j.watres.2024.122216, Institutional Repository

In light of increasingly diverse greywater reuse applications, this study proposes risk-based log-removal targets (LRTs) to aid the selection of treatment trains for greywater recycling at different collection scales, including appliance-scale reuse of individual greywater streams. An epidemiology-based model was used to simulate the concentrations of prevalent and treatment-resistant reference pathogens (protozoa: Giardia and Cryptosporidium spp., bacteria: Salmonella and Campylobacter spp., viruses: rotavirus, norovirus, adenovirus, and Coxsackievirus B5) in the greywater streams for collection scales of 5-, 100-, and a 1000-people. Using quantitative microbial risk assessment (QMRA), we calculated LRTs to meet a health benchmark of 10–4 infections per person per year over 10′000 Monte Carlo iterations. LRTs were highest for norovirus at the 5-people scale and for adenovirus at the 100- and 1000-people scales. Example treatment trains were designed to meet the 95 % quantiles of LRTs. Treatment trains consisted of an aerated membrane bioreactor, chlorination, and, if required, UV disinfection. In most cases, rotavirus, norovirus, adenovirus and Cryptosporidium spp. determined the overall treatment train requirements. Norovirus was most often critical to dimension the chlorination (concentration × time values) and adenovirus determined the required UV dose. Smaller collection scales did not generally allow for simpler treatment trains due to the high LRTs associated with viruses, with the exception of recirculating washing machines and handwashing stations. Similarly, treating greywater sources individually resulted in lower LRTs, but the lower required LRTs nevertheless did not generally allow for simpler treatment trains. For instance, LRTs for a recirculating washing machine were around 3-log units lower compared to LRTs for indoor reuse of combined greywater (1000-people scale), but both scenarios necessitated treatment with a membrane bioreactor, chlorination and UV disinfection. However, simpler treatment trains may be feasible for small-scale and application-scale reuse if: (i) less conservative health benchmarks are used for household-based systems, considering the reduced relative importance of treated greywater in pathogen transmission in households, and (ii) higher log-removal values (LRVs) can be validated for unit processes, enabling simpler treatment trains for a larger number of appliance-scale reuse systems.
Schwarzfischer, M., Ruoss, T. S., Niechcial, A., Lee, S. S., Wawrzyniak, M., Laimbacher, A., … Spalinger, M. R. (2024). Impact of nanoplastic particles on macrophage inflammation and intestinal health in a mouse model of inflammatory bowel disease. Nanomaterials, 14(16), 1350 (15 pp.). doi:10.3390/nano14161350, Institutional Repository

Background: The increasing presence of plastics in the human diet is raising public concern about the potential risks posed by nanoplastic (NP) particles, which can emerge from the degradation of plastic debris. NP ingestion poses particular risks to individuals with inflammatory bowel disease (IBD), as compromised epithelial barriers may facilitate NP translocation. Methods: In vitro, bone-marrow-derived macrophages (BMDMs) were exposed to 25 nm polymethacrylate (PMMA) or 50 nm polystyrene (PS) particles to assess morphological changes and alterations in pro- and anti-inflammatory gene expression. In vivo, mice received PMMA NP particles for 6 months before acute dextran sodium sulfate (DSS) colitis was induced to investigate NP impacts on intestinal health and inflammation. Results: PMMA and PS NP exposure in BMDMs induced morphological changes indicative of a proinflammatory phenotype characterized by enlarged amoeboid cell shapes. It also triggered an inflammatory response, indicated by increased expression of proinflammatory cytokines such as Tnfa and Il6. Unexpectedly, long-term PMMA NP administration did not affect the intestinal epithelial barrier or exacerbate acute DSS-induced colitis in mice. Colonoscopy and histological analysis revealed no NP-related changes, suggesting adverse effects on intestinal health or inflammation. Conclusion: Our findings from animal models offer some reassurance to IBD patients regarding the effects of NP ingestion. However, variations in lifestyle and dietary habits may lead to significantly higher plastic intake in certain individuals, raising concerns about potential long-term gastrointestinal effects of lifelong plastic consumption.
Seller-Brison, C., Brison, A., Yu, Y., Robinson, S. L., & Fenner, K. (2024). Adaptation towards catabolic biodegradation of trace organic contaminants in activated sludge. Water Research, 266, 122431 (14 pp.). doi:10.1016/j.watres.2024.122431, Institutional Repository

Trace organic contaminants (TrOCs) are omnipresent in wastewater treatment plants (WWTPs), yet, their removal during wastewater treatment is oftentimes incomplete and underlying biotransformation mechanisms are not fully understood. In this study, we elucidate how different factors, including pre-exposure levels and duration, influence microbial adaptation towards catabolic TrOC biodegradation and its potential role in biological wastewater treatment. Four sequencing batch reactors (SBRs) were operated in parallel in three succeeding phases, adding and removing a selection of 26 TrOCs at different concentration levels. After each phase of SBR operation, a series of batch experiments was conducted to monitor biotransformation kinetics of those same TrOCs across various spike concentrations. For half of our test TrOCs, we detected increased biotransformation in sludge pre-exposed to TrOC concentrations ≥5 µg L−1 over a 30-day period, with most significant differences observed for the insect repellent DEET and the artificial sweetener saccharin. Accordingly, 16S rRNA amplicon sequencing revealed enrichment of taxa that have previously been linked to catabolic biodegradation of several test TrOCs, e.g., Bosea sp. and Shinella sp. for acesulfame degradation, and Pseudomonas sp. for caffeine, cyclamate, DEET, metformin, paracetamol, and isoproturon degradation. We further conducted shotgun metagenomics to query for gene products previously reported to be involved in the TrOCs’ biodegradation pathways. In the future, directed microbial adaptation may be a solution to improve bioremediation of TrOCs in contaminated environments or in WWTPs.
Stetten, L., Kaegi, R., Hofmann, T., & von der Kammer, F. (2024). Depth-dependent transformation of ZnO and Ag nanoparticles in sulfate-reducing sediments tracked using scanning transmission electron microscopy. Environmental Science: Nano, 11(1), 136-148. doi:10.1039/d3en00550j, Institutional Repository

Studies on the transformation of engineered nanomaterials (ENMs) based on relevant environmental exposure scenarios are scarce. In this context, we investigated the use of Transmission Electron Microscopy (TEM) grids to expose minute amounts of ZnO and Ag nanoparticles (NPs) to artificial and natural aqueous media and follow their transformation using scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy. Short-term experiments conducted with inorganic sulfides confirmed the potential of using TEM grids to monitor the transformation of ENMs at the single particle level. After 30 min, Ag NPs transformed into Ag-sulfides, with Ag : S ratios ≈ 2 : 1, while ZnO NPs showed little evidence of Zn-sulfides precipitation after 6 hours. Ag NPs and ZnO NPs were also exposed to depth-dependent pore water concentration gradients in freshwater sediment columns. After three days and four weeks, all the Ag NPs observed were transformed into Ag-sulfides with various morphologies and Ag : S ratios (1 ≤ Ag/S ≤ 2), depending on the depth and duration of the exposure. Furthermore, a depth-dependent transformation was observed for ZnO NPs. At low sulfide concentration, in the first millimeters below the water-sediment interface, ZnO NPs were completely transformed into ZnS harboring empty shell structures, together with smaller particles in their vicinity. By contrast, ZnO cores persisted in the deeper layers, indicating that ZnO NPs dissolution was inhibited at high sulfide concentrations. Our results demonstrate the advantage of experimental and analytical strategies adapted to study the transformation of ENMs under environmentally relevant conditions, to unravel transformation rates and products not yet considered in risk assessment studies.
Sylvestre, É., Jahne, M. A., Reynaert, E., Morgenroth, E., & Julian, T. R. (2024). A critical evaluation of parametric models for predicting faecal indicator bacteria concentrations in greywater. Microbial Risk Analysis, 26, 100297 (8 pp.). doi:10.1016/j.mran.2024.100297, Institutional Repository

Greywater reuse is a strategy to address water scarcity, necessitating the selection of treatment processes that balance cost-efficiency and human health risks. A key aspect in evaluating these risks is understanding pathogen contamination levels in greywater, a complex task due to intermittent pathogen occurrences. To address this, faecal indicator organisms like E. coli are often monitored as proxies to evaluate faecal contamination levels and infer pathogen concentrations. However, the wide variability in faecal indicator concentrations poses challenges in their modelling for quantitative microbial risk assessment (QMRA). Our study critically assesses the adequacy of parametric models in predicting the variability in E. coli concentrations in greywater. We found that models that build on summary statistics, like medians and standard deviations, can substantially underestimate the variability in E. coli concentrations. More appropriate models may provide more accurate estimations of, and uncertainty around, peak E. coli concentrations. To demonstrate this, a Poisson lognormal distribution model is fit to a data set of E. coli concentrations measured in shower and laundry greywater sources. This model estimated arithmetic mean E. coli concentrations in laundry waters at approximately 1.0E + 06 MPN 100 mL−1. These results are around 2.0 log10 units higher than estimations from a previously used hierarchical lognormal model based on aggregated summary data from multiple studies. Such differences are considerable when assessing human health risks and setting pathogen reduction targets for greywater reuse. This research highlights the importance of making raw monitoring data available for more accurate statistical evaluations than those based on summary statistics. It also emphasizes the crucial role of model comparison, selection, and validation to inform policy-relevant outcomes.
Timmer, M. J., De Paepe, J., Van Winckel, T., Spiller, M., Spacova, I., De Paepe, K., … Vlaeminck, S. E. (2024). Resource-efficient nitrogen removal from source-separated urine with partial nitritation/anammox in a membrane-aerated biofilm reactor. ACS ES&T Engineering, 4(7), 1609-1621. doi:10.1021/acsestengg.4c00058, Institutional Repository

Source separation and decentralized urine treatment can cut costs in centralized wastewater treatment by diverting 80% of the nitrogen load in sewage. One promising approach for nitrogen removal from source-separated urine is partial nitritation/anammox (PN/A), reducing the aeration demand by 67% and organic dosage by 100% compared to nitrification/denitrification. While previous studies with suspended biomass have encountered stability issues during PN/A treatment of urine, a PN/A biofilm was hypothesized to be more resilient. Its use for urine treatment has been pioneered here for maximum rates and efficiencies in an energy-efficient membrane-aerated biofilm reactor (MABR). Nitrogen removal rates of 1.0 g N L-1 d-1 and removal efficiencies of 80-95% were achieved during a 335-day operational period at 28 °C on stabilized (pH > 11.5), diluted urine (10%). A balance between N2 and NO3- formation was observed while optimizing the supply of O2 through intermittent aeration and was rate limiting for the conversion toward N2. A short-term operation on less- and undiluted urine yielded N removal rates of 0.6-0.8 g N L-1 d-1 and removal efficiencies of 93% on 66% urine and 85% on undiluted urine. Metataxonomic analysis and fluorescence in situ hybridization confirmed the presence in the biofilm of nitrifiers (Nitrosomonas, Nitrospira) at the membrane side and anammox bacteria ("Candidatus Brocadia") at the anoxic bulk side. The findings suggest that a biofilm approach to PN/A treatment of urine overcomes stability issues and that a PN/A-MABR has significant potential for resource-efficient decentralized urine treatment. In human long-duration deep-space missions, this gravity-independent technology could produce N2 to compensate artificial atmosphere losses while facilitating water recovery from urine.
la Cecilia, D., Philipp, M., Kaegi, R., Schirmer, M., & Moeck, C. (2024). Microplastics attenuation from surface water to drinking water: impact of treatment and managed aquifer recharge – and identification uncertainties. Science of the Total Environment, 908, 168378 (12 pp.). doi:10.1016/j.scitotenv.2023.168378, Institutional Repository

River water can be used to recharge aquifers exploited for drinking water production. Several recent studies reported microplastics (MPs) in river water, and therefore, the potential contamination of groundwater by MPs is a growing concern among stakeholders and citizens. In this research, we investigate the fate of MPs (> 20 μm) along six different stages of a major Managed Aquifer Recharge (MAR)-water supply system in Switzerland. About 20 l of water were filtered using steel meshes at each location in triplicates. In the laboratory, MPs deposited on the anodisc filters were identified using Focal Plane Array (FPA) micro-Fourier-Transform-InfraRed (μFTIR) spectroscopy. The obtained hyperspectral data were processed using the imaging software Microplastics Finder for MPs identification and classification. Our results revealed a 20-fold decrease in MPs concentration from the Rhine River bed water (112 ± 27.4 MPs/l) to after the coagulation, flocculation and sedimentation (5.5 ± 2.2 MPs/l), a further 3-fold decrease to after the sand-filtration system (1.8 ± 0.9 MPs/l), corresponding to an overall removal efficiency of 98.4 %. The MPs concentrations remained low following MAR (2.7 ± 0.7 MPs/l) through a Quaternary gravel aquifer. Activated carbon filters did not substantially further reduce MPs concentrations. The percentage of fragments (≈95 %) prevailed over fibers (≈5 %) at all locations, with fibers being longer and more abundant in the river water. Overall, this study demonstrates the effectiveness of the treatment systems to remove MPs larger than 20 μm. Finally, we calculated an uncertainty in MPs concentrations of one order of magnitude depending on the user-defined parameters inside the MPs identification and classification model. The Quality Assurance/Quality Control approach followed during laboratory analysis highlighted an accumulation of surrogate particles at the edges of the disc, which would have an impact for MPs number upscaling.
Ballikaya, P., Brunner, I., Cocozza, C., Grolimund, D., Kaegi, R., Murazzi, M. E., … Cherubini, P. (2023). First evidence of nanoparticle uptake through leaves and roots in beech (Fagus sylvatica L.) and pine (Pinus sylvestris L.). Tree Physiology, 43(2), 262-276. doi:10.1093/treephys/tpac117, Institutional Repository

Trees have been used for phytoremediation and as biomonitors of air pollution. However, the mechanisms by which trees mitigate nanoparticle pollution in the environment are still unclear. We investigated whether two important tree species, European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.), are able to take up and transport differently charged gold nanoparticles (Au-NPs) into their stem by comparing leaf-to-root and root-to-leaf pathways. Au-NPs were taken up by roots and leaves, and a small fraction was transported to the stem in both species. Au-NPs were transported from leaves to roots but not vice versa. Leaf Au uptake was higher in beech than in pine, probably because of the higher stomatal density and wood characteristics of beech. Confocal (3D) analysis confirmed the presence of Au-NPs in trichomes and leaf blade, about 20–30 μm below the leaf surface in beech. Most Au-NPs likely penetrated into the stomatal openings through diffusion of Au-NPs as suggested by the 3D XRF scanning analysis. However, trichomes were probably involved in the uptake and internal immobilization of NPs, besides their ability to retain them on the leaf surface. The surface charge of Au-NPs may have played a role in their adhesion and uptake, but not in their transport to different tree compartments. Stomatal conductance did not influence the uptake of Au-NPs. This is the first study that shows nanoparticle uptake and transport in beech and pine, contributing to a better understanding of the interactions of NPs with different tree species.
Bou-Sarkis, A., Paul, E., Girbal-Neuhauser, E., Derlon, N., & Bessiere, Y. (2023). Detection of gel-forming polymers via calcium crosslinking, applied to the screening of extracellular polymeric substances extracted from biological aggregates. Gels, 9(2), 157 (14 pp.). doi:10.3390/gels9020157, Institutional Repository

The valorization of biological aggregates through the extraction of hydrogel-forming polymers can enhance the economics and sustainability of various processes in which bacteria are involved in organic waste transformation, such as wastewater treatment. Achieving these goals requires the development of a method capable of detecting the presence of gel-forming polymers in complex mixtures containing biopolymers that are most often unknown and uncharacterized. A miniaturized screening method capable of detecting gelation via ionic crosslinking using only 1 to 3 mg of the tested samples (commercial molecules or extracellular polymeric substances, EPSs) is proposed. The method consists of calculating a percentage of reactivity (%R) through UV-vis spectra and determining the percentage of gel volume (%Vg) formed after the addition of calcium. Both factors were combined to give a gelling factor (GF), and the test was applied to pure commercial molecules (BSA, DNA, alginate (ALV), and a mixture of them), allowing the classification of the following solutions according to their gel-forming capacity: GF(ALV) > GF(ALV+DNA) > GF(BSA+ALV+DNA) > GF(BSA+ALV) > GF(DNA) > GF(BSA+DNA) > GF(BSA). As a relevant tool for screening hydrogel-forming solutions, the method was applied to the EPS extracted from aerobic granular sludge. The EPS (0.5% w/v) had a GF of 0.16 ± 0.03, equivalent to approximately half of the GF of ALV (0.38 ± 0.02 at 0.5% w/v). The developed test pushes the limits of the existing gel-detection techniques because it allows for quicker, less consuming, and more informative gelation detection through the use of simple methods that do not require sophisticated equipment.
Brison, A., Rossi, P., & Derlon, N. (2023). Single CSTR can be as effective as an SBR in selecting PHA-storing biomass from municipal wastewater-derived feedstock. Water Research X, 18, 100165 (13 pp.). doi:10.1016/j.wroa.2023.100165, Institutional Repository

A key step for the production of polyhydroxyalkanoates (PHAs) from organic waste streams is the selection of a biomass with a high PHA-storage capacity (selection-step), which is usually performed in sequencing batch reactors (SBR). A major advancement would be to perform such selection in continuous reactors to facilitate the full-scale implementation of PHA production from municipal wastewater (MWW)-derived feedstock. The present study therefore investigates to what extent a simple continuous-flow stirred-tank reactor (CSTR) represents a relevant alternative to anSBR. To this end, we operated two selection reactors (CSTR vs. SBR) on filtered primary sludge fermentate while performing a detailed analysis of the microbial communities, and monitoring PHA-storage over long-term (∼150 days) and during accumulation batches. Our study demonstrates that a simple CSTR is as effective as an SBR in selecting biomass with high PHA-storage capacity (up to 0.65 gPHA gVSS−1) while being 50% more efficient in terms of substrate to biomass conversion yields. We also show that such selection can occur on VFA-rich feedstock containing nitrogen (N) and phosphorus (P) in excess, whereas previously, selection of PHA-storing organisms in a single CSTR has only been studied under P limitation. We further found that microbial competition was mostly affected by nutrient availability (N and P) rather than by the reactor operation mode (CSTR vs. SBR). Similar microbial communities therefore developed in both selection reactors, while microbial communities were very different depending on N availability. Rhodobacteraceae gen. were most abundant when growth conditions were stable and N-limited, whereas dynamic N- (and P-) excess conditions favoured the selection of the known PHA-storer Comamonas, and led to the highest observed PHA-storage capacity. Overall, we demonstrate that biomass with high storage capacity can be selected in a simple CSTR on a wider range of feedstock than just P-limited ones.
Daigger, G. T., Kuo, J., Derlon, N., Houweling, D., Jimenez, J. A., Johnson, B. R., … Boltz, J. P. (2023). Biological and physical selectors for mobile biofilms, aerobic granules, and densified-biological flocs in continuously flowing wastewater treatment processes: a state-of-the-art review. Water Research, 242, 120245 (13 pp.). doi:10.1016/j.watres.2023.120245, Institutional Repository

There have been significant advances in the use of biological and physical selectors for the intensification of continuously flowing biological wastewater treatment (WWT) processes. Biological selection allows for the development of large biological aggregates (e.g., mobile biofilm, aerobic granules, and densified biological flocs). Physical selection controls the solids residence times of large biological aggregates and ordinary biological flocs, and is usually accomplished using screens or hydrocyclones. Large biological aggregates can facilitate different biological transformations in a single reactor and enhance liquid and solids separation. Continuous-flow WWT processes incorporating biological and physical selectors offer benefits that can include reduced footprint, lower costs, and improved WWT process performance. Thus, it is expected that both interest in and application of these processes will increase significantly in the future. This review provides a comprehensive summary of biological and physical selectors and their design and operation.
Faust, V., Boon, N., Ganigué, R., Vlaeminck, S. E., & Udert, K. M. (2023). Optimizing control strategies for urine nitrification: narrow pH control band enhances process stability and reduces nitrous oxide emissions. Frontiers in Environmental Science, 11, 1275152 (14 pp.). doi:10.3389/fenvs.2023.1275152, Institutional Repository

Nitrification is well-suited for urine stabilization. No base dosage is required if the pH is controlled within an appropriate operating range by urine feeding, producing an ammonium-nitrate fertilizer. However, the process is highly dependent on the selected pH set-points and is susceptible to process failures such as nitrite accumulation or the growth of acid-tolerant ammonia-oxidizing bacteria. To address the need for a robust and reliable process in decentralized applications, two different strategies were tested: operating a two-position pH controller (inflow on/off) with a narrow pH control band at 6.20/6.25 (∆pH = 0.05, narrow-pH) vs. a wider pH control band at 6.00/6.50 (∆pH = 0.50, wide-pH). These variations in pH also cause variations in the chemical speciation of ammonia and nitrite and, as shown, the microbial production of nitrite. It was hypothesized that the higher fluctuations would result in greater microbial diversity and, thus, a more robust process. The diversity of nitrifiers was higher in the wide-pH reactor, while the diversity of the entire microbiome was similar in both systems. However, the wide-pH reactor was more susceptible to tested process disturbances caused by increasing pH or temperature, decreasing dissolved oxygen, or an influent stop. In addition, with an emission factor of 0.47%, the nitrous oxide (N2O) emissions from the wide-pH reactor were twice as high as the N2O emissions from the narrow-pH reactor, most likely due to the nitrite fluctuations. Based on these results, a narrow control band is recommended for pH control in urine nitrification.
Gottschalk, F., Debray, B., Klaessig, F., Park, B., Lacome, J. M., Vignes, A., … Kaegi, R. (2023). Predicting accidental release of engineered nanomaterials to the environment. Nature Nanotechnology, 18, 412-418. doi:10.1038/s41565-022-01290-2, Institutional Repository

Challenges in distinguishing between natural and engineered nanomaterials (ENMs) and the lack of historical records on ENM accidents have hampered attempts to estimate the accidental release and associated environmental impacts of ENMs. Building on knowledge from the nuclear power industry, we provide an assessment of the likelihood of accidental release rates of ENMs within the next 10 and 30 years. We evaluate risk predictive methodology and compare the results with empirical evidence, which enables us to propose modelling approaches to estimate accidental release risk probabilities. Results from two independent modelling approaches based on either assigning 0.5% of reported accidents to ENM-releasing accidents (M1) or based on an evaluation of expert opinions (M2) correlate well and predict severe accidental release of 7% (M1) in the next 10 years and of 10% and 20% for M2 and M1, respectively, in the next 30 years. We discuss the relevance of these results in a regulatory context.
Herold, G., Rodino, F., Golparvar, A., Reynaert, E., & Carrara, S. (2023). Enhancing water safety in decentralized water reuse systems with low-cost prussian blue amperometric sensors for free chlorine monitoring. IEEE Sensors Letters, 7(9), 6005704 (4 pp.). doi:10.1109/LSENS.2023.3307084, Institutional Repository

The challenge of providing sustainable and safe water services in regions lacking centralized water infrastructure can be addressed through the utilization of on-site treatment and reuse of wastewater. However, the widespread implementation of decentralized water reuse systems is currently hindered by the considerable expenses associated with remote water quality monitoring. Specifically, when using chlorination for treatment, the fabrication and maintenance costs of free chlorine sensors pose significant drawbacks to their implementation. In this study, we present an alternative solution by mitigating the sensor cost through the utilization of electrochemical sensing coupled with a cleanroom-free sensor fabrication process. We meticulously optimized the electrodeposition process to enhance sensor stability and ensure reproducibility, achieved through precise control of reactant concentrations. Our findings demonstrate the feasibility of obtaining consistent measurements in treated greywater by employing controlled Prussian Blue electrodeposition on readily available screen-printed electrodes, resulting in variation as low as 7.44% (n = 6). Furthermore, cyclic voltammetry experiments reveal a distinct peak at -0.11 V, indicating the presence of free chlorine in treated greywater samples. This characteristic is leveraged in chronoamperometric sensing, enabling robust chemical detection with a wide dynamic linearity range (R2 = 0.9933) spanning from 0.06 to 6.28 ppm of free chlorine in treated greywater samples and a competitive sensitivity reaching 7.6 μA/cm2 per ppm.
Heusser, A., Dax, A., McArdell, C. S., & Udert, K. M. (2023). High content of low molecular weight organics does not always affect pharmaceutical adsorption on activated carbon: the case of acetate, propionate and ethanol in source-separated urine. Water Research X, 21, 100199 (10 pp.). doi:10.1016/j.wroa.2023.100199, Institutional Repository

Adsorption on activated carbon is a common process to remove pharmaceuticals in wastewater treatment. Activated carbon adsorption is usually applied to wastewater with a low content of biological degradable organics, i.e. after biological treatment. Especially low molecular weight (LMW) compounds are known to compete with pharmaceuticals for adsorption sites. The goal of this study was to test the hypothesis that biological treatment is necessary for efficient pharmaceutical removal. Source-separated urine after anaerobic storage (anaerobically stored urine) and after aerobic biological removal of organics without nitrification (organics-depleted urine) were used in this study. In anaerobically stored urine 60% of the organic compounds were LMW organics, of which about 40% were acetate and propionate. 74% of the DOC and 100% of acetate and propionate were removed during aerobic biological treatment. To investigate the effect of the organic compounds on pharmaceutical removal, sorption experiments with 19 spiked pharmaceuticals and one artificial sweetener were conducted with powdered activated carbon. Ethanol, another LMW organic, was included in the study, as it is regularly used for pharmaceutical spiking thereby strongly increasing the DOC content. The experiments showed that the adsorption of the pharmaceuticals and the sweetener were hardly affected by the easily biodegradable LMW organics or ethanol. Therefore, it was concluded that biological pre-treatment is not necessary for efficient pharmaceutical adsorption. Since acetate, propionate and ethanol contribute substantially to the DOC content but do not absorb UV light, the latter is recommended as indicator for pharmaceutical removal in solutions with high contents of biodegradable LMW organics.
Huang, K., Eschenbach, W., Wei, J., Hausherr, D., Frey, C., Kupferschmid, A., … Mohn, J. (2023). Simultaneous 15N online analysis in NH4+, NO2-, NO3-, and N2O to trace N2O production pathways in nitrogen-polluted aqueous environments. ACS ES&T Water, 3(11), 3485-3495. doi:10.1021/acsestwater.3c00216, Institutional Repository

Engineered nitrogen (N) removal processes in water treatment plants and N-transformation reactions in polluted environments represent prominent sources of the potent greenhouse gas, nitrous oxide (N2O). The relevance of microbial and abiotic formation pathways can be assessed by using 15N tracer techniques. While 15N-N2O analysis with optical analyzers is straightforward, the quantification of atom % 15N of inorganic N compounds, such as ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-), requires discrete sample analyses that are time-consuming and labor-intensive. In this study, we developed an automated sample preparation unit, coupled to a membrane inlet quadrupole mass spectrometer, for the online, quasi-simultaneous analysis of atom % 15N in NH4+, NO2-, and NO3-. This technique was designed and validated for 15N-spiking applications at moderate (100-200 μmol L-1, 1 atom % 15N) to high (2-3 mmol L-1, 33 atom % 15N) dissolved inorganic N concentrations typically encountered in sewer systems or contaminated watersheds. The high potential of the developed system, in combination with 15N-N2O analysis by Fourier-transform infrared spectroscopy, to constrain N transformations and sources of N2O was demonstrated in a feasibility study, where nitrifier denitrification was identified as the primary N2O formation pathway during the partial NH4+ oxidation to NO2- in a lab-scale sequencing batch reactor.
Joëlle Kubeneck, L., ThomasArrigo, L. K., Rothwell, K. A., Kaegi, R., & Kretzschmar, R. (2023). Competitive incorporation of Mn and Mg in vivianite at varying salinity and effects on crystal structure and morphology. Geochimica et Cosmochimica Acta, 346, 231-244. doi:10.1016/j.gca.2023.01.029, Institutional Repository

Vivianite, a ferrous phosphate mineral, can be an important phosphorus (P) sink in non-sulfidic, reducing coastal sediments. The Fe in the crystal structure of vivianite can be substituted by other divalent metal cations such as Mn2+ or Mg2+. Since Mg is much more abundant in coastal porewaters than Mn, the more frequent reports of Mn substitution in vivianites of coastal sediments has been suggested to indicate a preferential incorporation of Mn over Mg into the crystal structure of vivianite. However, although both Mn and Mg substitution in vivianite are environmentally relevant, it is yet unknown whether Mn or Mg is preferentially incorporated and how these isomorphic substitutions alter the crystal structure and morphology of vivianite, parameters which may influence vivianite reactivity. Here, we studied the incorporation of Mn and/or Mg in vivianites formed by co-precipitation at pH 7 in the presence of varying dissolved Mn and/or Mg concentrations and solution salinities resembling an estuarine gradient from 0 to 9 psu. In total, 19 different vivianites were synthesized, with up to 50% of Fe substituted by Mn and Mg. Thermodynamic equilibrium calculations showed that aqueous Mg speciation was altered with increasing salinity, while Mn speciation was less affected, likely explaining the preferential incorporation of Mn in the vivianite structure at higher salinities. 57Fe-Mössbauer spectroscopy revealed that both Mn and Mg were preferentially incorporated in the double-octahedral Fe position, at which intervalence charge transfer is possible during the oxidation of vivianite. In contrast to Mg, which is redox inactive, incorporated Mn can participate in heteronuclear intervalence charge transfer with Fe. Thus, incorporation of either cation may impact the reactivity of vivianite under oxidizing conditions in element specific ways. Results of complementary analyses including X-ray diffraction, electron microscopy and Fe K-edge X-ray absorption spectroscopy further showed that incorporation of Mn and/or Mg led to smaller particle size, increased crystal roughness and thinner crystals, as well as systematic changes in unit cell parameters. These observed changes in crystal morphology might impact the reactivity of vivianite in natural environments and thus the effect of cation incorporation in vivianite should be considered when studying Fe and P cycling in coastal sediments.
Kizgin, A., Schmidt, D., Joss, A., Hollender, J., Morgenroth, E., Kienle, C., & Langer, M. (2023). Application of biological early warning systems in wastewater treatment plants: Introducing a promising approach to monitor changing wastewater composition. Journal of Environmental Management, 347, 119001 (12 pp.). doi:10.1016/j.jenvman.2023.119001, Institutional Repository

Wastewater treatment plants (WWTPs) are a major source of micropollutants to surface waters. Currently, their chemical or biological monitoring is realized by using grab or composite samples, which provides only snapshots of the current wastewater composition. Especially in WWTPs with industrial input, the wastewater composition can be highly variable and a continuous assessment would be advantageous, but very labor and cost intensive. A promising concept are automated real-time biological early warning systems (BEWS), where living organisms are constantly exposed to the water and an alarm is triggered if the organism's responses exceed a harmful threshold of acute toxicity. Currently, BEWS are established for drinking water and surface water but are seldom applied to monitor wastewater. This study demonstrates that a battery of BEWS using algae (Chlorella vulgaris in the Algae Toximeter, bbe Moldaenke), water flea (Daphnia magna in the DaphTox II, bbe Moldaenke) and gammarids (Gammarus pulex in the Sensaguard, REMONDIS Aqua) can be adapted for wastewater surveillance. For continuous low-maintenance operation, a back-washable membrane filtration system is indispensable for adequate preparation of treated wastewater. Only minor deviations in the reaction of the organisms towards treated and filtered wastewater compared to surface waters were detected. After spiking treated wastewater with two concentrations of the model compounds diuron, chlorpyrifos methyl, and sertraline, the organisms in the different BEWS showed clear responses depending on the respective compound, concentration and mode of action. Immediate effects on photosynthetic activity of algae were detected for diuron exposure, and strong behavioral changes in water flea and gammarids after exposure to chlorpyrifos methyl or sertraline were observed, which triggered automated alarms. Different types of data analysis were applied to extract more information out of the specific behavioral traits, than only provided by the vendors algorithms. To investigate, whether behavioral movement changes can be linked to impact other endpoints, the effects on feeding activity of G. pulex were evaluated and results indicated significant differences between the exposures. Overall, these findings provide an important basis indicating that BEWS have the potential to act as alarm systems for pollution events in the wastewater sector.
Kollmann, J., Nath, S., Singh, S., Balasubramanian, S., Reynaert, E., Morgenroth, E., & Contzen, N. (2023). Acceptance of on-site wastewater treatment and reuse in Bengaluru, India: the role of perceived costs, risks, and benefits. Science of the Total Environment, 895, 165042 (11 pp.). doi:10.1016/j.scitotenv.2023.165042, Institutional Repository

In dealing with water pollution and freshwater scarcity, on-site treatment and reuse of domestic wastewater has shown to be a promising solution. To increase on-site wastewater treatment and reuse, some cities, among them Bengaluru in India, have mandated the installation and use of the necessary technology in certain building types. However, even with a mandate, a successful and sustainable implementation of the technology, including reliable operation, monitoring, and maintenance, depends on the acceptance (i.e. positive valuation) of the technology and its use by the (prospective) users. Literature on technology acceptance indicates perceived costs, risks, and benefits of the respective technology as key predictors of acceptance. Therefore, the present online study assessed this relationship for on-site systems in Bengaluru. The relation was analysed separately for mandated users of on-site systems (N = 103) and current non-users (i.e. potential prospective users, should the mandate be expanded; N = 232), as the perceptions might differ between the two groups, due to the personal experience with the technology among users. The results show that for mandated users and non-users, acceptance of on-site systems is explained by perceived benefits only, namely a positive image of users, environmental benefits, and, only for non-users, also financial benefits for the city. The findings suggest that interventions aimed at promoting on-site systems should include emphasis on the benefits of on-site systems. Whenever possible, interventions should be tailored to the target group's individual cost, risk, and benefit perception.
Larivé, O., Torii, S., Derlon, N., & Kohn, T. (2023). Selective elimination of enterovirus genotypes by activated sludge and chlorination. Environmental Science: Water Research and Technology, 9(6), 1620-1633. doi:10.1039/d3ew00050h, Institutional Repository

Enteroviruses, which are commonly circulating viruses shed in the stool, are released into the sewage system and only partially removed or inactivated, resulting in the discharge of infectious enteroviruses into the environment. Activated sludge and chlorination remove or inactivate enterovirus genotypes to different extents, and thus have the potential to shape the population that will be discharged. The goal of this study was to evaluate how activated sludge and chlorination treatment shape an enterovirus population at the genotype level, using a population of eight genotypes commonly found in sewage: CVA9, CVB1, CVB2, CVB3, CVB4, CVB5, E25, E30. Our results show that the extent of inactivation varied among genotypes, but also across sludge samples. We find that the effluent of activated sludge systems will be depleted in CVA9, CVB1 and CVB2 while E25 together with CVB3, CVB4 and CVB5 will be prevalent. Furthermore, we found that microbial inactivation was the main mechanism of infectivity loss in the activated sludge, while adsorption to the sludge flocs was not significant. During effluent chlorination, we also observed that CVB5, CVB3 and to a lesser extent E25 were less susceptible to chlorination while E30 was readily inactivated, and activated sludge-derived EPS provided further protection against chlorination. This study contributes to a better understanding of the variability of sewage treatment efficacy against different enteroviruses.
Maghsoodi, M., Jacquin, C., Teychené, B., Lesage, G., & Snow, S. D. (2023). Delineating the effects of molecular and colloidal interactions of dissolved organic matter on titania photocatalysis. Langmuir, 39(10), 3752-3761. doi:10.1021/acs.langmuir.2c03487, Institutional Repository

In the face of significant challenges to practical applications of photocatalysis for water treatment, recent reports revealed a potential route to overcome a problem posed by dissolved organic matter (DOM). These studies showed that inhibition of photocatalytic processes by DOM is driven largely by competition for active surface sites on TiO2 or other catalysts, and controlling the type of DOM present in solution could significantly mitigate DOM fouling. Whether or not control of solution parameters could achieve the same preventative action is not known. Here, a series of DOM isolates, including humic acid (HA) and transphilic (TPI), hydrophobic (HPO), or colloidal fractions of organic matter from a membrane bioreactor mixed liquor supernatant, were tested for inhibitory activity under a range of pH values (3, 5, 7, and 9) and ionic compositions (NaCl, CaCl2, and Al2(SO4)3 with ionic strengths (IS) ranging from 0 to 3 M). The resulting TiO2-DOM agglomerates were monitored for size and ζ-potential. Inhibitory profiles were generated using para-chlorobenzoic acid (pCBA) as probe with varying concentrations of inhibitory DOM for each solution condition to discern the extent of surface-phase quenching of radicals. Manipulation of pH clearly impacted inhibition, and the effect varied by DOM type; for example, interference occurred at all pHs for HA, at neutral or basic pHs for TPI, and only at pH 7 for HPO. Particle sizes did not correlate with inhibitory action of DOM. Increases in ionic strength induced growth of TiO2 and TiO2-DOM agglomerates, but again, particle sizes did not correlate to inhibition by DOM. The changes to IS, regardless of ion type, were not affected by the presence of TPI or HPO. Since particle stability did not correlate directly with photocatalytic activity, we suggest that surface-based quenching reactions arise from site-specific adsorption rather than generalized particle destabilization and aggregation.
Nenonen, V. V., Kaegi, R., Hug, S. J., Göttlicher, J., Mangold, S., Winkel, L. H. E., & Voegelin, A. (2023). Formation and transformation of Fe(III)- and Ca-precipitates in aqueous solutions and effects on phosphate retention over time. Geochimica et Cosmochimica Acta, 360, 207-230. doi:10.1016/j.gca.2023.09.004, Institutional Repository

Exfiltration of anoxic phosphate-rich groundwater into surface water leads to the oxidation of dissolved Fe(II) and the formation of Fe(III)-precipitates that can retain phosphate (PO4) and thereby attenuate eutrophication. Fresh Fe(III)-precipitates transform into more stable phases over time, and retained PO4 may be released again. In parallel, CO2 outgassing can promote the formation of Ca-phosphates or -carbonates that also sequester PO4. In laboratory experiments, we studied the effects of Mg, Ca, silicate (SiO4) and PO4 on these processes. Fresh Fe(III)-precipitates were formed in bicarbonate-buffered aqueous solutions at pH ∼ 7.0 via the oxidation of 0.5 mM Fe(II) in the presence of 0.15 or 0.025 mM PO4, at Mg or Ca concentrations of 0, 0.4, 1.2 or 4 mM and in the absence or presence of 0.5 mM SiO4. After CO2 outgassing, the suspensions were allowed to age for 100 d at pH ∼ 8. Changes in the composition and structure of Fe(III)- and Ca-precipitates over time were probed with spectroscopic and microscopic techniques and were linked to variations in the retention of PO4. The oxidation of Fe(II) led to effective PO4 removal via the formation of Fe(III)-precipitates that consisted of amorphous (Ca-)Fe(III)-phosphate ((Ca)FeP), ferrihydrite (Fh) and, in SiO4-free treatments, lepidocrocite (Lp). During aging, FeP and Fh that had formed in the absence of Mg, Ca and SiO4 rapidly and nearly completely transformed into Lp. Via effects on molecular- and nanoscale precipitate structure, Mg slowed down FeP transformation into Fh, stabilized Fh, and decreased the crystallinity of Lp (in SiO4-free suspensions), Ca stabilized CaFeP against transformation into Fh, and SiO4 stabilized Fh and (Ca)FeP. Core/shell CaFeP/Fh particles formed in electrolytes that contained Ca and SiO4 hardly transformed within 100 d. Calcite only formed at low dissolved PO4 concentrations and, by incorporation of PO4, contributed to PO4 retention. Higher levels of dissolved PO4 inhibited calcite formation but could induce Ca-phosphate precipitation. Differences in precipitate formation and transformation pathways and kinetics were reflected in the extents of PO4 release over the 100-d aging period, ranging from rapid release of 77% of the total PO4 in the treatment without Mg, Ca and SiO4 at 0.15 mM total PO4 to slow release of only 0.1% of the total PO4 at initial concentrations of 4 mM Ca, 0.5 mM SiO4, and 0.025 mM PO4. In summary, this study reveals the conditions and the extents and timescales over which Fe(III)- and Ca-precipitates form and transform and how these processes affect PO4 immobilization in near-neutral natural waters. The detailed new insights into the coupling between Fe(III)- and Ca-precipitate formation and into the interdependent effects of Mg, Ca, SiO4 and PO4 are not only relevant with respect to PO4 but also with respect to the cycling of trace elements in natural and engineered systems.
Reynaert, E., Steiner, P., Yu, Q., D'Olif, L., Joller, N., Schneider, M. Y., & Morgenroth, E. (2023). Predicting microbial water quality in on-site water reuse systems with online sensors. Water Research, 240, 120075 (13 pp.). doi:10.1016/j.watres.2023.120075, Institutional Repository

Widespread implementation of on-site water reuse is hindered by the limited availability of monitoring approaches that ensure microbial quality during operation. In this study, we developed a methodology for monitoring microbial water quality in on-site water reuse systems using inexpensive and commercially available online sensors. An extensive dataset containing sensor and microbial water quality data for six of the most critical types of disruptions in membrane bioreactors with chlorination was collected. We then tested the ability of three typological machine learning algorithms - logistic regression, support-vector machine, and random forest - to predict the microbial water quality as "safe" or "unsafe" for reuse. The main criteria for model optimization was to ensure a low false positive rate (FPR) - the percentage of safe predictions when the actual condition is unsafe - which is essential to protect users health. This resulted in enforcing a fixed FPR ≤ 2%. Maximizing the true positive rate (TPR) - the percentage of safe predictions when the actual condition is safe - was given second priority. Our results show that logistic-regression-based models using only two out of the six sensors (free chlorine and oxidation-reduction potential) achieved the highest TPR. Including sensor slopes as engineered features allowed to reach similar TPRs using only one sensor instead of two. Analysis of the occurrence of false predictions showed that these were mostly early alarms, a characteristic that could be regarded as an asset in alarm management. In conclusion, the simplest algorithm in combination with only one or two sensors performed best at predicting the microbial water quality. This result provides useful insights for water quality modeling or for applications where small datasets are a common challenge and a general advantage might be gained by using simpler models that reduce the risk of overfitting, allow better interpretability, and require less computational power.
Reynaert, E., Gretener, F., Julian, T. R., & Morgenroth, E. (2023). Sensor setpoints that ensure compliance with microbial water quality targets for membrane bioreactor and chlorination treatment in on-site water reuse systems. Water Research X, 18, 100164 (13 pp.). doi:10.1016/j.wroa.2022.100164, Institutional Repository

Widespread implementation of on-site water reuse systems is hindered by the limited ability to ensure the level of treatment and protection of human health during operation. In this study, we tested the ability of five commercially available online sensors (free chlorine (FC), oxidation-reduction potential (ORP), pH, turbidity, UV absorbance at 254 nm) to predict the microbial water quality in membrane bioreactors followed by chlorination using logistic regression-based and mechanism-based models. The microbial water quality was assessed in terms of removal of enteric bacteria from the wastewater, removal of enteric viruses, and regrowth of bacteria in the treated water. We found that FC and ORP alone could predict the microbial water quality well, with ORP-based models generally performing better. We further observed that prediction accuracy did not increase when data from multiple sensors were integrated. We propose a methodology to link online sensor measurements to risk-based water quality targets, providing operation setpoints protective of human health for specific combinations of wastewaters and reuse applications. For instance, we recommend a minimum ORP of 705 mV to ensure a virus log-removal of 5, and an ORP of 765 mV for a log-removal of 6. These setpoints were selected to ensure that the percentage of events where the water is predicted to meet the quality target but it does not remains below 5%. Such a systematic approach to set sensor setpoints could be used in the development of water reuse guidelines and regulations that aim to cover a range of reuse applications with differential risks to human health.
Sam, S. B., Morgenroth, E., & Strande, L. (2023). Changes in organic fractions, cations, and stabilization from feces to fecal sludge: implications for dewatering performance and management solutions. Journal of Water Sanitation and Hygiene for Development, 13(9), 699-710. doi:10.2166/washdev.2023.086, Institutional Repository

Reliable dewatering performance remains a key challenge in fecal sludge management, and the controlling factors or mechanisms are not well understood. There remain limited studies on constituents in feces and fecal sludge and how they affect the dewaterability of fecal sludge. This study aimed at evaluating a range of constituents in feces, and to gain empirical knowledge toward a mechanistic understanding of how they influence dewaterability. In this study, cellulose reduced capillary suction time, decreased supernatant turbidity, and increased cake solids. While hemicellulose decreased supernatant turbidity, lignin increased supernatant turbidity, capillary suction time, and cake solids. Extracellular polymeric substances (EPS) increased both capillary suction time and supernatant turbidity and decreased cake solids, whereas lipids increased turbidity. Cations had no significant effect on dewatering properties. Overall, fecal sludge stored in containments had better dewatering performance than ‘fresh’ fecal sludge, which was attributed to stabilization. Field fecal sludge had a higher relative abundance of Pseudomonas, which is associated with better aggregation, and fewer small particles (<10 μm) that clog filters to reduce dewatering performance. Further understanding of stabilization and developing an agreed-upon metrics of stabilization are essential for predicting fecal sludge dewatering performance, and developing smaller footprint dewatering treatment technologies.
Sodnikar, K., Kaegi, R., Christl, I., Schroth, M. H., & Sander, M. (2023). Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries. Environmental Science: Processes and Impacts, 25(12), 2067-2080. doi:10.1039/d3em00294b, Institutional Repository

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.
Stoffel, D., Derlon, N., Traber, J., Staaks, C., Heijnen, M., Morgenroth, E., & Jacquin, C. (2023). Gravity-driven membrane filtration with compact second-life modules daily backwashed: an alternative to conventional ultrafiltration for centralized facilities. Water Research X, 18, 100178 (12 pp.). doi:10.1016/j.wroa.2023.100178, Institutional Repository

Gravity-driven membrane (GDM) filtration is a strategic alternative to conventional ultrafiltration (UF) for the resilient production of drinking water via ultrafiltration when resources become scarce, given the low dependency on energy and chemicals, and longer membrane lifetime. Implementation at large scale requires the use of compact and low-cost membrane modules with high biopolymer removal capacity. We therefore evaluated (1) to what extent stable flux can be obtained with compact membrane modules, i.e., inside-out hollow fiber membranes, and frequent gravity-driven backwash, (2) whether we can reduce membrane expenses by effectively utilizing second-life UF modules, i.e., modules that have been discarded by treatment plant operators because they are no longer under warranty, (3) if biopolymer removal could be maintained when applying a frequent backwash and with second-life modules and (4) which GDM filtration scenarios are economically viable compared to conventional UF, when considering the influence of new or second-life modules, membrane lifetime, stable flux value and energy pricing. Our findings showed that it was possible to maintain stable fluxes around 10 L/m2/h with both new and second-life modules for 142 days, but a daily gravity-driven backwash was necessary and sufficient to compensate the continuous flux drop observed with compact modules. In addition, the backwash did not affect the biopolymer removal. Costs calculations revealed two significant findings: (1) using second-life modules made GDM filtration membrane investment less expensive than conventional UF, despite the higher module requirements for GDM filtration and (2) overall costs of GDM filtration with a gravity-driven backwash were unaffected by energy prices rise, while conventional UF costs rose significantly. The later increased the number of economically viable GDM filtration scenarios, including scenarios with new modules. In summary, we proposed an approach that could make GDM filtration in centralized facilities feasible and increase the range of UF operating conditions to better adapt to increasing environmental and societal constraints.
Sylvestre, É., Reynaert, E., & Julian, T. R. (2023). Defining risk-based monitoring frequencies to verify the performance of water treatment barriers. Environmental Science and Technology Letters, 10(4), 374-384. doi:10.1021/acs.estlett.3c00154, Institutional Repository

Preventing failures of water treatment barriers can play an important role in meeting the increasing demand for microbiologically safe water. The development and integration of failure prevention strategies into quantitative microbial risk assessment (QMRA) offer opportunities to support the design and operation of treatment trains. This study presents existing failure models and extends them to guide the development of risk-based operational monitoring strategies. For barriers with rapid performance loss, results show that a failure of 15 s should be reliably detected to verify a log reduction value (LRV) of 6.0; thus, detecting and remediating these failures may be beyond current technology. For chemical disinfection with a residual, failure durations in order of minutes should be reliably detected to verify a LRV of 6.0. Short-term failures are buffered because the disinfectant residual concentration sustains a partial reduction performance. Therefore, increasing the contact time and hydraulic mixing reduces the impact of failures. These findings demonstrate the importance of defining precise frequencies to monitor barrier performances during operation. Overall, this study highlights the utility of process-specific models for developing failure prevention strategies for water safety management.
Tamayo-Belda, M., Pérez-Olivares, A. V., Pulido-Reyes, G., Martin-Betancor, K., González-Pleiter, M., Leganés, F., … Fernández-Piñas, F. (2023). Tracking nanoplastics in freshwater microcosms and their impacts to aquatic organisms. Journal of Hazardous Materials, 445, 130625 (12 pp.). doi:10.1016/j.jhazmat.2022.130625, Institutional Repository

In this work, we used palladium-doped polystyrene NPLs (PS-NPLs with a primary size of 286 ± 4 nm) with an irregular surface morphology which allowed for particle tracking and evaluation of their toxicity on two primary producers (cyanobacterium, Anabaena sp. PCC7120 and green algae, Chlamydomonas reinhardtii) and one primary consumer (crustacean, Daphnia magna). the concentration range for Anabaena and C. reinhardtii was from 0.01 to 1000 mg/L and for D. magna, the range was from 7.5 to 120 mg/L.EC50 s ranged from 49 mg NPLs/L for D. magna (48hEC50 s) to 248 mg NPLs/L (72hEC50 s for C. reinhardtii). PS-NPLs induced dose-dependent reactive oxygen species overproduction, membrane damage and metabolic alterations. To shed light on the environmental fate of PS-NPLs, the short-term distribution of PS-NPLs under static (using lake water and sediments) and stirring (using river water and sediments) conditions was studied at laboratory scale. The results showed that most NPLs remained in the water column over the course of 48 h. The maximum percentage of settled particles (∼ 30 %) was found under stirring conditions in comparison with the ∼ 10 % observed under static ones. Natural organic matter increased the stability of the NPLs under colloidal state while organisms favored their settlement. This study expands the current knowledge of the biological effects and fate of NPLs in freshwater environments.
Ward, B. J., Nguyen, M. T., Sam, S. B., Korir, N., Niwagaba, C. B., Morgenroth, E., & Strande, L. (2023). Particle size as a driver of dewatering performance and its relationship to stabilization in fecal sludge. Journal of Environmental Management, 326, 116801 (12 pp.). doi:10.1016/j.jenvman.2022.116801, Institutional Repository

Poor and unpredictable dewatering performance of fecal sludge is a major barrier to sanitation provision in urban areas not served by sewers. Fecal sludge comprises everything that accumulates in onsite containments, and its characteristics are distinct from wastewater sludges and from feces. There is little fundamental understanding of what causes poor dewatering in fecal sludge. For the first time, we demonstrate that particle size distribution is a driver of dewatering performance in fecal sludge, and is associated with level of stabilization. Higher concentrations of small particles (<10 μm) and smaller median aggregate size (D50) corresponded to poor dewatering performance (measured by capillary suction time (CST) and supernatant turbidity) in field samples from Kenya and Uganda and in controlled laboratory anaerobic storage experiments. More stabilized fecal sludge (higher C/N, lower VSS/TSS) had better dewatering performance, corresponding to lower concentrations of small particles. Samples with the largest aggregates (D50 > 90 μm) had higher abundance of Gammaproteobacteria Pseudomonas, and samples with the smallest aggregates (D50 ≤ 50 μm) were characterized by higher abundance of Bacteroidetes Vadin HA17 and Rikenellaceae. Contrary to common perceptions, stabilization, particle size distribution, and dewatering performance were not dependent on time intervals between emptying of onsite containments or on time in controlled anaerobic storage experiments. Our results suggest that the stabilization process in onsite containments, and hence the dewaterability of sludge arriving at treatment facilities, is not dependent on time in containment but is more likely associated with specific microbial populations and the in-situ environmental conditions which promote or discourage their growth.
Wiprächtiger, M., Haupt, M., Froemelt, A., Klotz, M., Beretta, C., Osterwalder, D., … Hellweg, S. (2023). Combining industrial ecology tools to assess potential greenhouse gas reductions of a circular economy. Method development and application to Switzerland. Journal of Industrial Ecology, 27(1), 254-271. doi:10.1111/jiec.13364, Institutional Repository

Industrial ecology (IE) methodologies, such as input/output or material flow analysis and life cycle assessment (LCA), are often used for the environmental evaluation of circular economy strategies. Up to now, an approach that utilizes these methods in a systematic, integrated framework for a holistic assessment of a geographic region's sustainable circular economy potential has been lacking. The approach developed in this study (IE4CE approach) combines IE methodologies to determine the environmental impact mitigation potential of circular economy strategies for a defined geographic region. The approach foresees five steps. First, input/output analysis helps identify sectors with high environmental impacts. Second, a refined analysis is conducted using material flow and LCA. In step 3, circular strategies are used for scenario design and evaluated in step 4. In step 5, the assessment results are compiled and compared across sectors. The approach was applied to a case study of Switzerland, analyzing 8 sectors and more than 30 scenarios in depth. Carbon capture and storage (CCS) from waste incineration, biogas and cement production, food waste prevention in households, hospitality and production, and the increased recycling of plastics had the highest mitigation potential. Most of the scenarios do not influence each other. One exception is the CCS scenarios: waste avoidance scenarios decrease the reduction potential of CCS. A combination of scenarios from different sectors, including their impact on the CCS scenario potential, led to an environmental impact mitigation potential of 11.9 Mt CO2-eq for 2050, which equals 14% of Switzerland's current consumption-based impacts.
Xu, J., Chen, C., Hu, X., Chen, D., Bland, G., Wielinski, J., … Lowry, G. V. (2023). Particle-scale understanding of arsenic interactions with sulfidized nanoscale zerovalent iron and their impacts on dehalogenation reactivity. Environmental Science and Technology, 57(51), 21917-21926. doi:10.1021/acs.est.3c08635, Institutional Repository

Co-occurrence of organic contaminants and arsenic oxoanions occurs often at polluted groundwater sites, but the effect of arsenite on the reactivity of sulfidized nanoscale zerovalent iron (SNZVI) used to remediate groundwater has not been evaluated. Here, we study the interaction of arsenite [As(III)] with SNZVI at the individual-particle scale to better understand the impacts on the SNZVI properties and reactivity. Surface and intraparticle accumulation of As was observed on hydrophilic FeS-Fe0 and hydrophobic FeS2-Fe0 particles, respectively. X-ray absorption spectroscopy indicated the presence of realgar-like As-S and elemental As0 species at low and high As/Fe concentration ratios, respectively. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis identified As-containing particles both with and without Fe. The probability of finding As-containing particles without Fe increased with the S-induced hydrophobicity of SNZVI. The interactions of SNZVI materials with coexisting arsenite inhibited their reactivity with water (∼5.8-230.7-fold), trichloroethylene (∼3.6-67.5-fold), and florfenicol (∼1.1-5.9-fold). However, the overall selectivity toward trichloroethylene and florfenicol relative to water was improved (up to 9.0-fold) because the surface-associated As increased the SNZVI hydrophobicity. These results indicate that reactions of SNZVI with arsenite can remove As from groundwater and improve the properties of SNZVI for dehalogenation selectivity.
Bou-Sarkis, A., Pagliaccia, B., Ric, A., Derlon, N., Paul, E., Bessiere, Y., & Girbal-Neuhauser, E. (2022). Effects of alkaline solvents and heating temperatures on the solubilization and degradation of gel-forming Extracellular Polymeric Substances (EPS) extracted from aerobic granular sludge. Biochemical Engineering Journal, 185, 108500 (9 pp.). doi:10.1016/j.bej.2022.108500, Institutional Repository

The effects of solvents and heating temperatures on the recovery and degradation of gel-forming EPS (Extracellular Polymeric Substances) extracted from aerobic granular sludge were investigated. Sodium hydroxide has allowed a better EPS solubilization compared to sodium carbonate (711.3 ± 38 and 408.4 ± 4 mg VS /g VS respectively) but the capacity to precipitate gel-forming EPS at acidic pH was higher in sodium carbonate (22% compared to 6% in sodium hydroxide at 80 °C). Increasing the temperature from 20 °C to 80 °C during EPS solubilization has multiplied the amount of solubilized matter by 4 in sodium carbonate and 2.2 in sodium hydroxide. Similar biochemical composition but different molecular weight profiles were observed for the two solubilized EPS extracts, evidencing partial degradation of the polymers in sodium hydroxide. Furthermore, coupling molecular weight analysis and precipitation yield measurement revealed that the lower precipitation of sodium hydroxide solubilized EPS is related to the size reduction due to degradation. Altogether these results help to guide towards a unified protocol for the extraction of gel-forming EPS.
Brison, A., Rossi, P., & Derlon, N. (2022). Influent carbon to phosphorus ratio drives the selection of PHA-storing organisms in a single CSTR. Water Research X, 16, 100150 (11 pp.). doi:10.1016/j.wroa.2022.100150, Institutional Repository

Enriching a biomass with a high fraction of polyhydroxyalkanoate-storing organisms (PHA-storers) represents an essential step in the production of PHAs (bioplastics) from municipal wastewater using mixed microbial cultures. A major challenge is however to create selective growth conditions that are favourable to PHA-storers. Our study thus investigates to what extent the influent COD to phosphorus (COD:P) ratio can be used as a tool for the robust selection of PHA-storers in a single continuous-flow stirred-tank reactor (CSTR). Therefore, we operated five CSTRs in parallel, fed with synthetic wastewater (50% acetate - 50% propionate) with different COD:P ratios (200−1000 gCOD gP−1), and performed a detailed analysis of the microbial communities over long-term (30−70 solid retention times). Our study demonstrates that efficient and robust selection of PHA-storers can be achieved in a single CSTR at high influent COD:P ratios. The selective advantage for PHA-storers increases with the influent COD:P ratio, but only if growth conditions remain limited by both C-substrate and P. In contrast, selection performance deteriorates when COD:P ratios are too high and growth conditions are limited by P only. At an optimal COD:P ratio of 800 gCOD gP−1, a stable microbial community consisting of >90% PHA-storers and dominated by Pannonibacter sp. was selected in the long-term. Finally, our results suggest that high COD:P ratios provide a selective advantage to microorganisms with low cellular P requirements, explaining why different PHA-storers (i.e., Xanthobacter sp. vs. Pannonibacter sp.) were selected depending on the influent COD:P ratio (i.e., 200 vs. 800 gCOD gP−1). Overall, our results provide relevant insights for the development of a new approach for selecting PHA-storers, based on the use of a single CSTR and control of the influent COD:P ratio.
Brison, A., Rossi, P., Gelb, A., & Derlon, N. (2022). The capture technology matters: composition of municipal wastewater solids drives complexity of microbial community structure and volatile fatty acid profile during anaerobic fermentation. Science of the Total Environment, 815, 152762 (13 pp.). doi:10.1016/j.scitotenv.2021.152762, Institutional Repository

The production of volatile fatty acids (VFAs) represents a relevant option to valorize municipal wastewater (MWW). In this context, different capture technologies can be used to recover organic carbon from wastewater in form of solids, while pre-treatment of those solids has the potential to increase VFA production during subsequent fermentation. Our study investigates how VFA composition produced by fermentation is influenced (i) by the choice of the capture technology, as well as (ii) by the use of thermal alkaline pre-treatment (TAP). Therefore, the fermentation of solids originating from a primary settler, a micro-sieve, and a high-rate activated sludge (HRAS) system was investigated in continuous lab-scale fermenters, with and without TAP. Our study demonstrates that the capture technology strongly influences the composition of the produced solids, which in turn drives the complexity of the fermenter's microbial community and ultimately, of the VFA composition. Solids captured with the primary settler or micro-sieve consisted primarily of polysaccharides, and led to the establishment of a microbial community specialized in the degradation of complex carbohydrates. The produced VFA composition was relatively simple, with acetate and propionate accounting for >90% of the VFAs. In contrast, the HRAS system produced biomass-rich solids associated with higher protein contents. The microbial community which then developed in the fermenter was therefore more diversified and capable of converting a wider range of substrates (polysaccharides, proteins, amino acids). Ultimately, the produced VFA composition was more complex, with equal fractions of isoacids and propionate (both ~20%), while acetate remained the dominant acid (~50%). Finally, TAP did not significantly modify the VFA composition while increasing VFA yields on HRAS and sieved material by 35% and 20%, respectively. Overall, we demonstrated that the selection of the technology used to capture organic substrates from MWW governs the composition of the VFA cocktail, ultimately with implications for their further utilization.
Cariti, F., Tuñas Corzon, A., Fernandez-Cassi, X., Ganesanandamoorthy, P., Ort, C., Julian, T. R., & Kohn, T. (2022). Wastewater reveals the spatiotemporal spread of SARS-CoV-2 in the Canton of Ticino (Switzerland) during the onset of the COVID-19 pandemic. ACS ES&T Water, 2(11), 2194-2200. doi:10.1021/acsestwater.2c00082, Institutional Repository

Wastewater-based epidemiology (WBE) has emerged as an effective tool for monitoring SARS-CoV-2 dynamics during the COVID-19 pandemic. Here, we add a spatial component to WBE and use it to investigate SARS-CoV-2 spread in the canton of Ticino during the onset of the pandemic in Switzerland (end of February 2020 to beginning of March 2020). Ticino is located at the border to Northern Italy, where a large COVID-19 outbreak occurred in February 2020. Not surprisingly, Ticino was the site of the first clinically confirmed COVID-19 case in Switzerland. We retrospectively analyzed daily influent samples from nine wastewater treatment plants in Ticino that jointly cover an area of 20 km × 60 km and 351,000 people (>99% of the population). Our result is a fine-grained view of the spatiotemporal evolution of the COVID-19 pandemic in this canton. The wastewater analysis revealed that by February 29, 2020, SARS-CoV-2 had already spread to all catchments. At the same time, only four individual cases had been clinically confirmed across the region served by the treatment plants investigated. Our results demonstrate that WBE could serve as a versatile tool to monitor the introduction and spread of an infectious agent on a regional scale. To fully exploit its utility, WBE should be implemented in real time and become an integral part of future disease surveillance efforts.
Carles, L., Wullschleger, S., Joss, A., Eggen, R. I. L., Schirmer, K., Schuwirth, N., … Tlili, A. (2022). Wastewater microorganisms impact microbial diversity and important ecological functions of stream periphyton. Water Research, 225, 119119 (13 pp.). doi:10.1016/j.watres.2022.119119, Institutional Repository

Effluents of wastewater treatment plants can impact microbial communities in the receiving streams. However, little is known about the role of microorganisms in wastewater as opposed to other wastewater constituents, such as nutrients and micropollutants. We aimed therefore at determining the impact of wastewater microorganisms on the microbial diversity and function of periphyton, key microbial communities in streams. We used a flow-through channel system to grow periphyton upon exposure to a mixture of stream water and unfiltered or ultra-filtered wastewater. Impacts were assessed on periphyton biomass, activities and tolerance to micropollutants, as well as on microbial diversity. Our results showed that wastewater microorganisms colonized periphyton and modified its community composition, resulting for instance in an increased abundance of Chloroflexi and a decreased abundance of diatoms and green algae. This led to shifts towards heterotrophy, as suggested by the changes in nutrient stoichiometry and the increased mineralization potential of carbon substrates. An increased tolerance towards micropollutants was only found for periphyton exposed to unfiltered wastewater but not to ultra-filtered wastewater, suggesting that wastewater microorganisms were responsible for this increased tolerance. Overall, our results highlight the need to consider the role of wastewater microorganisms when studying potential impacts of wastewater on the receiving water body.
Derlon, N., Desmond, P., Rühs, P. A., & Morgenroth, E. (2022). Cross flow frequency determines the physical structure and cohesion of membrane biofilms developed during gravity-driven membrane ultrafiltration of river water: implication for hydraulic resistance. Journal of Membrane Science, 643, 120079 (10 pp.). doi:10.1016/j.memsci.2021.120079, Institutional Repository

We evaluated how intermittent shear influences the physical structure, material properties and hydraulic resistance of membrane biofilms developed during gravity-driven ultrafiltration of river water, with the ultimate goal of increasing the filtration performances. Our results indicate intermittent shear helps slowing-down the flux decline but does not help to increase the level of stabilisation of the permeate flux. After several weeks, the biofilms exposed to different shear regimes were indeed characterised by similar hydraulic resistance. But the characteristic time to achieve a stable flux increased from 7 d to 25d when increasing the shear frequency. Also, most of the hydraulic resistance (up to 95%) was governed by the base layer that remained attached after erosion tests. With increasing exposure to shear conditions, the biofilms became more cohesive and more elastic, thus resisting better to cross flow conditions. Overall, our results demonstrate that engineering membrane biofilms with a desired permeability is not feasible using intermittent shear due to significant adaptability of the biofilms to their hydraulic environment.
Derlon, N., Garcia Villodres, M., Kovács, R., Brison, A., Layer, M., Takács, I., & Morgenroth, E. (2022). Modelling of aerobic granular sludge reactors: the importance of hydrodynamic regimes, selective sludge removal and gradients. Water Science and Technology, 86(3), 410-431. doi:10.2166/wst.2022.220, Institutional Repository

Hydraulic selection is a key feature of aerobic granular sludge (AGS) systems but existing aerobic granular sludge (AGS) models neglect those mechanisms: gradients over reactor height (Hreactor), selective removal of slow settling sludge, etc. This study aimed at evaluating to what extent integration of those additional processes into AGS models is needed, i.e., at demonstrating that model predictions (biomass inventory, microbial activities and effluent quality) are affected by such additional model complexity. We therefore developed a new AGS model that includes key features of full-scale AGS systems: fill-draw operation, selective sludge removal, distinct settling models for flocs/granules. We then compared predictions of our model to those of a fully mixed AGS model. Our results demonstrate that hydraulic selection can be predicted with an assembly of four continuous stirred tank reactors in series together with a correction code for plug-flow. Concentration gradients over the reactor height during settling/plug-flow feeding strongly impact the predictions of aerobic granular sludge models in terms of microbial selection, microbial activities and ultimately effluent quality. Hydraulic selection is a key to predict selection of storing microorganisms (phosphorus-accumulating organisms (PAO) and glycogen-accumulating organisms (GAO)) and in turn effluent quality in terms of total phosphorus, and for predicting effluent solid concentration and dynamic during plug-flow feeding.
Desiante, W. L., Carles, L., Wullschleger, S., Joss, A., Stamm, C., & Fenner, K. (2022). Wastewater microorganisms impact the micropollutant biotransformation potential of natural stream biofilms. Water Research, 217, 118413 (13 pp.). doi:10.1016/j.watres.2022.118413, Institutional Repository

Biotransformation is the most important process removing manmade chemicals from the environment, yet mechanisms governing this essential ecosystem function are underexplored. To understand these mechanisms, we conducted experiments in flow-through systems, by colonizing stream biofilms under different conditions of mixing river water with treated (and ultrafiltered) wastewater. We performed biotransformation experiments with those biofilms, using a set of 75 micropollutants, and could disentangle potential mechanisms determining the biotransformation potential of stream biofilms. We showed that the increased biotransformation potential downstream of wastewater treatment plants that we observed for specific micropollutants contained in household wastewaters (downstream effect) is caused by microorganisms released with the treated effluent, rather than by the in-stream exposure to those micropollutants. Complementary data from 16S rRNA amplicon-sequencing revealed 146 amplicon sequence variants (ASVs) that followed the observed biotransformation patterns. Our results align with findings for community tolerance, and provide clear experimental evidence that microorganisms released with treated wastewater integrate into downstream biofilms and impact crucial ecosystem functions.
Desmond, P., Huisman, K. T., Sanawar, H., Farhat, N. M., Traber, J., Fridjonsson, E. O., … Vrouwenvelder, J. S. (2022). Controlling the hydraulic resistance of membrane biofilms by engineering biofilm physical structure. Water Research, 210, 118031 (14 pp.). doi:10.1016/j.watres.2021.118031, Institutional Repository

The application of membrane technology for water treatment and reuse is hampered by the development of a microbial biofilm. Biofilm growth in micro-and ultrafiltration (MF/UF) membrane modules, on both the membrane surface and feed spacer, can form a secondary membrane and exert resistance to permeation and crossflow, increasing energy demand and decreasing permeate quantity and quality. In recent years, exhaustive efforts were made to understand the chemical, structural and hydraulic characteristics of membrane biofilms. In this review, we critically assess which specific structural features of membrane biofilms exert resistance to forced water passage in MF/UF membranes systems applied to water and wastewater treatment, and how biofilm physical structure can be engineered by process operation to impose less hydraulic resistance (“below-the-pain threshold”). Counter-intuitively, biofilms with greater thickness do not always cause a higher hydraulic resistance than thinner biofilms. Dense biofilms, however, had consistently higher hydraulic resistances compared to less dense biofilms. The mechanism by which density exerts hydraulic resistance is reported in the literature to be dependant on the biofilms’ internal packing structure and EPS chemical composition (e.g., porosity, polymer concentration). Current reports of internal porosity in membrane biofilms are not supported by adequate experimental evidence or by a reliable methodology, limiting a unified understanding of biofilm internal structure. Identifying the dependency of hydraulic resistance on biofilm density invites efforts to control the hydraulic resistance of membrane biofilms by engineering internal biofilm structure. Regulation of biofilm internal structure is possible by alteration of key determinants such as feed water nutrient composition/concentration, hydraulic shear stress and resistance and can engineer biofilm structural development to decrease density and therein hydraulic resistance. Future efforts should seek to determine the extent to which the concept of “biofilm engineering” can be extended to other biofilm parameters such as mechanical stability and the implication for biofilm control/removal in engineered water systems (e.g., pipelines and/or, cooling towers) susceptible to biofouling.
Donati, F., Dente, S. M. R., Li, C., Vilaysouk, X., Froemelt, A., Nishant, R., … Hashimoto, S. (2022). The future of artificial intelligence in the context of industrial ecology. Journal of Industrial Ecology, 26(4), 1175-1181. doi:10.1111/jiec.13313, Institutional Repository

Artificial intelligence (AI) applications and digital technologies (DTs) are increasingly present in the daily lives of citizens, in cities and in industries. These developments generate large amounts of data and enhance analytical capabilities that could benefit the industrial ecology (IE) community and sustainability research in general. With this communication, we would like to address some of the opportunities, challenges, and next steps that could be undertaken by the industrial ecology community in this realm. This article is an adapted summary of the discussion held by experts in industrial ecology, AI, and sustainability during the 2021 Industrial Ecology Day conference session titled "The Future of Artificial Intelligence in the Context of Industrial Ecology." In brief, building on previous studies and communications, we advise the industrial ecology community to: (1) create internal committees and working groups to monitor and coordinate AI applications within and outside the community; (2) promote and ensure transdisciplinary efforts; (3) determine optimal infrastructure and governance of AI for IE to minimize undesired effects; and (4) act on effective representation and on reduction of digital divides.
Faust, V., van Alen, T. A., Op den Camp, H. J. M., Vlaeminck, S. E., Ganigué, R., Boon, N., & Udert, K. M. (2022). Ammonia oxidation by novel "Candidatus Nitrosacidococcus urinae" is sensitive to process disturbances at low pH and to iron limitation at neutral pH. Water Research X, 17, 100157 (11 pp.). doi:10.1016/j.wroa.2022.100157, Institutional Repository

Acid-tolerant ammonia-oxidizing bacteria (AOB) can open the door to new applications, such as partial nitritation at low pH. However, they can also be problematic because chemical nitrite oxidation occurs at low pH, leading to the release of harmful nitrogen oxide gases. In this publication, the role of acid-tolerant AOB in urine treatment was explored. On the one hand, the technical feasibility of ammonia oxidation under acidic conditions for source-separated urine with total nitrogen concentrations up to 3.5 g-N L-1 was investigated. On the other hand, the abundance and growth of acid-tolerant AOB at more neutral pH was explored. Under acidic conditions (pH of 5), ammonia oxidation rates of 500 mg-N L-1 d-1 and 10 g-N g-VSS-1 d-1 were observed, despite high concentrations of 15 mg-N L-1 of the AOB-inhibiting compound nitrous acid and low concentration of 0.04 mg-N L-1 of the substrate ammonia. However, ammonia oxidation under acidic conditions was very sensitive to process disturbances. Even short periods of less than 12 h without oxygen or without influent resulted in a complete cessation of ammonia oxidation with a recovery time of up to two months, which is a problem for low maintenance applications such as decentralized treatment. Furthermore, undesirable nitrogen losses of about 10% were observed. Under acidic conditions, a novel AOB strain was enriched with a relative abundance of up to 80%, for which the name “Candidatus (Ca.) Nitrosacidococcus urinae” is proposed. While Nitrosacidococcus members were present only to a small extent (0.004%) in urine nitrification reactors operated at pH values between 5.8 and 7, acid-tolerant AOB were always enriched during long periods without influent, resulting in an uncontrolled drop in pH to as low as 2.5. Long-term experiments at different pH values showed that the activity of “Ca. Nitrosacidococcus urinae” decreased strongly at a pH of 7, where they were also outcompeted by the acid-sensitive AOB Nitrosomonas halophila. The experiment results showed that the decreased activity of “Ca. Nitrosacidococcus urinae” correlated with the limited availability of dissolved iron at neutral pH.
Faust, V., Gruber, W., Ganigué, R., Vlaeminck, S. E., & Udert, K. M. (2022). Nitrous oxide emissions and carbon footprint of decentralized urine fertilizer production by nitrification and distillation. ACS ES&T Engineering, 2(9), 1745-1755. doi:10.1021/acsestengg.2c00082, Institutional Repository

Combining partial nitrification, granular activated carbon (GAC) filtration, and distillation is a well-studied approach to convert urine into a fertilizer. To evaluate the environmental sustainability of a technology, the operational carbon footprint and therefore nitrous oxide (N2O) emissions should be known, but N2O emissions from urine nitrification have not been assessed yet. Therefore, N2O emissions of a decentralized urine nitrification reactor were monitored for 1 month. During nitrification, 0.4-1.2% of the total nitrogen load was emitted as N2O-N with an average N2O emission factor (EFN2O) of 0.7%. Additional N2O was produced during anoxic storage between nitrification and GAC filtration with an estimated EFN2O of 0.8%, resulting in an EFN2O of 1.5% for the treatment chain. N2O emissions during nitrification can be mitigated by 60% by avoiding low dissolved oxygen or anoxic conditions and nitrite concentrations above 5 mg-N L-1. Minimizing the hydraulic retention time between nitrification and GAC filtration can reduce N2O formation during intermediate storage by 100%. Overall, the N2O emissions accounted for 45% of the operational carbon footprint of 14 kg-CO2,equiv kg-N-1 for urine fertilizer production. Using electricity from renewable sources and applying the proposed N2O mitigation strategies could potentially lower the carbon footprint by 85%.
Grigg, A. R. C., ThomasArrigo, L. K., Schulz, K., Rothwell, K. A., Kaegi, R., & Kretzschmar, R. (2022). Ferrihydrite transformations in flooded paddy soils: rates, pathways, and product spatial distributions. Environmental Science: Processes and Impacts, 24(10), 1867-1882. doi:10.1039/d2em00290f, Institutional Repository

Complex interactions between redox-driven element cycles in soils influence iron mineral transformation processes. The rates and pathways of iron mineral transformation processes have been studied intensely in model systems such as mixed suspensions, but transformation in complex heterogeneous porous media is not well understood. Here, mesh bags containing 0.5 g of ferrihydrite were incubated in five water-saturated paddy soils with contrasting microbial iron-reduction potential for up to twelve weeks. Using X-ray diffraction analysis, we show near-complete transformation of the ferrihydrite to lepidocrocite and goethite within six weeks in the soil with the highest iron(II) release, and slower transformation with higher ratios of goethite to lepidocrocite in soils with lower iron(II) release. In the least reduced soil, no mineral transformations were observed. In soils where ferrihydrite transformation occurred, the transformation rate was one to three orders of magnitude slower than transformation in comparable mixed-suspension studies. To interpret the spatial distribution of ferrihydrite and its transformation products, we developed a novel application of confocal micro-Raman spectroscopy in which we identified and mapped minerals on selected cross sections of mesh bag contents. After two weeks of flooded incubation, ferrihydrite was still abundant in the core of some mesh bags, and as a rim at the mineral–soil interface. The reacted outer core contained unevenly mixed ferrihydrite, goethite and lepidocrocite on the micrometre scale. The slower rate of transformation and uneven distribution of product minerals highlight the influence of biogeochemically complex matrices and diffusion processes on the transformation of minerals, and the importance of studying iron mineral transformation in environmental media.
Gruber, W., Magyar, P. M., Mitrovic, I., Zeyer, K., Vogel, M., von Känel, L., … Mohn, J. (2022). Tracing N2O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings. Water Research X, 15, 100130 (11 pp.). doi:10.1016/j.wroa.2022.100130, Institutional Repository

Nitrous oxide (N2O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N2O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N2O mitigation strategies require an improved understanding of nitrogen transformation pathways and their modulating controls. Analyses of the nitrogen (N) and oxygen (O) isotopic composition of N2O and its substrates at natural abundance have been shown to provide valuable information on formation and reduction pathways in laboratory settings, but have rarely been applied to full-scale WWTPs.
Here we show that N-species isotope ratio measurements at natural abundance level, combined with long-term N2O monitoring, allow identification of the N2O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). Heterotrophic denitrification appears as the main N2O production pathway under all tested process conditions (0-2 mgO2/l, high and low loading conditions), while nitrifier denitrification was less important, and more variable. N2O production by hydroxylamine oxidation was not observed. Fractional N2O elimination by reduction to dinitrogen (N2) during anoxic conditions was clearly indicated by a concomitant increase in site preference, δ18O(N2O) and δ15N(N2O). N2O reduction increased with decreasing availability of dissolved inorganic N and organic substrates, which represents the link between diurnal N2O emission dynamics and organic substrate fluctuations. Consequently, dosing ammonium-rich reject water under low-organic-substrate conditions is unfavorable, as it is very likely to cause high net N2O emissions.
Our results demonstrate that monitoring of the N2O isotopic composition holds a high potential to disentangle N2O formation mechanisms in engineered systems, such as full-scale WWTP. Our study serves as a starting point for advanced campaigns in the future combining isotopic technologies in WWTP with complementary approaches, such as mathematical modeling of N2O formation or microbial assays to develop efficient N2O mitigation strategies.
Hadengue, B., Morgenroth, E., & Larsen, T. A. (2022). How to get your feet wet: Integrating urban water and building engineering for low-energy domestic hot water systems. Energy and Buildings, 271, 112318 (6 pp.). doi:10.1016/j.enbuild.2022.112318, Institutional Repository

Thanks to intense research efforts, modern low-energy buildings consume only a fraction of the space heating loads of their older counterparts. However, reducing their energy footprint further requires optimization of domestic hot water systems. This is a difficult task, because the relationship between water and energy in domestic systems is intricate and complex. In general, the intrinsic uncertainty and variability of water demand makes the planning and assessment of new technologies challenging, but also risks related for instance to water pathogens like Legionella pneumophila impose trade-offs that diminish the performance of energy-saving measures. In this short communication, we argue that truly sustainable solutions will only be found if a multi-scale, multi-disciplinary mindset is adopted by the community. We show how the collaboration and knowledge integration between experts of various fields, notably urban water specialists and building engineers, is a prerequisite to resolve some of the most pressing issues on the way to optimizing domestic hot water systems. Through concrete examples, we describe how a new, common modeling framework has already triggered the required knowledge integration, and how it could be expanded further to integrate additional disciplines.
Hadengue, B., Morgenroth, E., Larsen, T. A., & Baldini, L. (2022). Performance and dynamics of active greywater heat recovery in buildings. Applied Energy, 305, 117677 (13 pp.). doi:10.1016/j.apenergy.2021.117677, Institutional Repository

In the effort to de-carbonize the building stock, heat pumps are increasingly utilized in Switzerland, with 70% of the fast-growing heat pump market using ambient air as heat source. Inexpensive and easy to implement, these heat pumps are, however, less efficient than their ground- or water-source counterparts. In this modeling study, we aim at increasing the efficiency of air-source heat pumps using domestic greywater-contained heat. We assess the performance improvement relative to standard heat pump configurations across various climates, seasons, building envelopes, and domestic hot water consumption patterns. The results show that the annually-averaged coefficient of performance improves by 4.1% on average - ranging from 0.6% to 7.5%. This efficiency gain translates on average to 1.8 kWh/week of compressor electricity savings. Although attractive due to its simplicity, the proposed open-loop configuration - preheating of an external heat source - only leads to moderate performance improvement of air-source heat pumps. Based on these results, we extensively discuss and compare alternative system configurations and identify several fundamental differences in the heat recovery dynamics of each configuration. We show that closed-loop systems - using greywater as direct heat source - show the largest performance improvement potential, although being more expensive and complex to implement.
Hadengue, B., Morgenroth, E., & Larsen, T. A. (2022). Screening innovative technologies for energy-efficient domestic hot water systems. Journal of Environmental Management, 320, 115713 (9 pp.). doi:10.1016/j.jenvman.2022.115713, Institutional Repository

Domestic hot water systems are large energy consumers. With the aim of reducing the energy footprint of these systems, we selected and simulated five technologies across a wide range of technology readiness levels: established technologies - pipe insulation and low-flow faucets -, relatively new technologies - shower drain heat exchangers and an innovative pipe system - and a novel experimental technology - a heat exchanger connected to membrane bioreactor for on-site greywater treatment. Using the WaterHub modeling framework, we simulated the technologies alone and in combination and compared the energetic performance of fifteen scenarios with a validated reference domestic hot water system. Low-flow appliances as standalone technologies performed best with 30% less energy required for the boiler tank, but combining low-flow appliances with a membrane bioreactor heat exchanger performed best overall (50% reduction). Deep insights into the temperature dynamics at all locations in the system led to the identification of technological competition patterns to prevent and synergies to exploit. Through our results, we are able to discuss and recommend further investigations regarding critical aspects like hygiene and economic performance.
Hausherr, D., Niederdorfer, R., Bürgmann, H., Lehmann, M. F., Magyar, P., Mohn, J., … Joss, A. (2022). Successful mainstream nitritation through NOB inactivation. Science of the Total Environment, 822, 153546 (11 pp.). doi:10.1016/j.scitotenv.2022.153546, Institutional Repository

The development of new wastewater treatment processes can assist in reducing the impact of wastewater treatment on the environment. The recently developed partial nitritation anammox (PNA) process, for example, consumes less energy for aeration and reduces nitrate in the effluent without requiring additional organic carbon. However, achieving stable nitritation (ammonium oxidation; NH4+ → NO2−) at mainstream conditions (T = 10–25 °C, C:N > 10, influent ammonium < 50 mgNH4-N/L and effluent < 1 mgNH4-N/L) remains challenging. This study explores the potential and mechanism of nitrite-oxidizing bacteria (NOB) suppression in a bottom-fed sequencing batch reactor (SBR). Two bench-scale (11 L) reactors and a pilot-scale reactor (8 m3) were operated for over a year and were fed with organic substrate depleted municipal wastewater. Initially, nitratation (nitrite oxidation; NO2− → NO3−) occurred occasionally until an anaerobic phase was integrated into the operating cycle. The introduction of the anaerobic phase effectively suppressed the regrowth of NOB while nitritation was stable over 300 days, down to 8 °C and at ammonium influent concentrations < 25 mgNH4-N/L. Batch experiments and process data revealed that parameters typically affecting NOB growth (e.g., dissolved oxygen, alkalinity, trace elements, lag-phase after anoxia, free nitrous acid (FNA), free ammonia (FA), pH, sulfide, or solids retention time (SRT)) could not fully explain the suppression of nitratation. Experiments in which fresh nitrifying microbial biomass was added to the nitritation system indicated that NOB inactivation explained NOB suppression better than NOB washout at high SRT. This study concludes that bottom-fed SBRs with anaerobic phases allow for stable nitritation over a broad range of operational parameters. Coupling this type of SBR to an anammox reactor can enable efficient mainstream anammox-based wastewater treatment.
Hausherr, D., Niederdorfer, R., Bürgmann, H., Lehmann, M. F., Magyar, P., Mohn, J., … Joss, A. (2022). Successful year-round mainstream partial nitritation anammox: assessment of effluent quality, performance and N2O emissions. Water Research X, 16, 100145 (11 pp.). doi:10.1016/j.wroa.2022.100145, Institutional Repository

For two decades now, partial nitritation anammox (PNA) systems were suggested to more efficiently remove nitrogen (N) from mainstream municipal wastewater. Yet to date, only a few pilot-scale systems and even fewer full-scale implementations of this technology have been described. Process instability continues to restrict the broad application of PNA. Especially problematic are insufficient anammox biomass retention, the growth of undesired aerobic nitrite-oxidizers, and nitrous oxide (N2O) emissions. In this study, a two-stage mainstream pilot-scale PNA system, consisting of three reactors (carbon pre-treatment, nitritation, anammox - 8 m3 each), was operated over a year, treating municipal wastewater. The aim was to test whether both, robust autotrophic N removal and high effluent quality, can be achieved throughout the year. A second aim was to better understand rate limiting processes, potentially affecting the overall performance of PNA systems. In this pilot study, excellent effluent quality, in terms of inorganic nitrogen, was accomplished (average effluent concentrations: 0.4 mgNH4-N/L, 0.1 mgNO2-N/L, 0.9 mgNO3-N/L) even at wastewater temperatures previously considered problematic (as low as 8 °C). N removal was limited by nitritation rates (84 ± 43 mgNH4-N/L/d), while surplus anammox activity was observed at all times (178 ± 43 mgN/L/d). Throughout the study, nitrite-oxidation was maintained at a low level (<2.5% of ammonium consumption rate). Unfortunately, high N2O emissions from the nitritation stage (1.2% of total nitrogen in the influent) were observed, and, based on natural isotope abundance measurements, could be attributed to heterotrophic denitrification. In situ batch experiments were conducted to identify the role of dissolved oxygen (DO) and organic substrate availability in N2O emission-mitigation. The addition of organic substrate, to promote complete denitrification, was not successful in decreasing N2O emission, but increasing the DO from 0.3 to 2.9 mgO2/L decreased N2O emissions by a factor of 3.4.
Huisman, J. S., Scire, J., Caduff, L., Fernandez-Cassi, X., Ganesanandamoorthy, P., Kull, A., … Julian, T. R. (2022). Wastewater-based estimation of the effective reproductive number of SARS-CoV-2. Environmental Health Perspectives, 130(5), 057011 (12 pp.). doi:10.1289/EHP10050, Institutional Repository

BACKGROUND: The effective reproductive number, Re, is a critical indicator to monitor disease dynamics, inform regional and national policies, and estimate the effectiveness of interventions. It describes the average number of new infections caused by a single infectious person through time. To date, Re estimates are based on clinical data such as observed cases, hospitalizations, and/or deaths. These estimates are temporarily biased when clinical testing or reporting strategies change.
OBJECTIVES: We show that the dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in wastewater can be used to estimate Re in near real time, independent of clinical data and without the associated biases.
METHODS: We collected longitudinal measurements of SARS-CoV-2 RNA in wastewater in Zurich, Switzerland, and San Jose, California, USA. We combined this data with information on the temporal dynamics of shedding (the shedding load distribution) to estimate a time series proportional to the daily COVID-19 infection incidence. We estimated a wastewater-based Re from this incidence.
RESULTS: The method to estimate Re from wastewater worked robustly on data from two different countries and two wastewater matrices. The resulting estimates were as similar to the Re estimates from case report data as Re estimates based on observed cases, hospitalizations, and deaths are among each other. We further provide details on the effect of sampling frequency and the shedding load distribution on the ability to infer Re.
DISCUSSION: To our knowledge, this is the first time Re has been estimated from wastewater. This method provides a low-cost, rapid, and independent way to inform SARS-CoV-2 monitoring during the ongoing pandemic and is applicable to future wastewater-based epidemiology targeting other pathogens.
Jahn, K., Dreifuss, D., Topolsky, I., Kull, A., Ganesanandamoorthy, P., Fernandez-Cassi, X., … Beerenwinkel, N. (2022). Early detection and surveillance of SARS-CoV-2 genomic variants in wastewater using COJAC. Nature Microbiology, 7, 1151-1160. doi:10.1038/s41564-022-01185-x, Institutional Repository

The continuing emergence of SARS-CoV-2 variants of concern and variants of interest emphasizes the need for early detection and epidemiological surveillance of novel variants. We used genomic sequencing of 122 wastewater samples from three locations in Switzerland to monitor the local spread of B.1.1.7 (Alpha), B.1.351 (Beta) and P.1 (Gamma) variants of SARS-CoV-2 at a population level. We devised a bioinformatics method named COJAC (Co-Occurrence adJusted Analysis and Calling) that uses read pairs carrying multiple variant-specific signature mutations as a robust indicator of low-frequency variants. Application of COJAC revealed that a local outbreak of the Alpha variant in two Swiss cities was observable in wastewater up to 13 d before being first reported in clinical samples. We further confirmed the ability of COJAC to detect emerging variants early for the Delta variant by analysing an additional 1,339 wastewater samples. While sequencing data of single wastewater samples provide limited precision for the quantification of relative prevalence of a variant, we show that replicate and close-meshed longitudinal sequencing allow for robust estimation not only of the local prevalence but also of the transmission fitness advantage of any variant. We conclude that genomic sequencing and our computational analysis can provide population-level estimates of prevalence and fitness of emerging variants from wastewater samples earlier and on the basis of substantially fewer samples than from clinical samples. Our framework is being routinely used in large national projects in Switzerland and the UK.
Kim, A., Mutel, C. L., Froemelt, A., & Hellweg, S. (2022). Global sensitivity analysis of background life cycle inventories. Environmental Science and Technology, 56(9), 5874-5885. doi:10.1021/acs.est.1c07438, Institutional Repository

In recent years many Life Cycle Assessment (LCA) studies have been conducted to quantify the environmental performance of products and services. Some of these studies propagated numerical uncertainties in underlying data to LCA results, and several applied Global Sensitivity Analysis (GSA) to some parts of the LCA model to determine its main uncertainty drivers. However, only a few studies have tackled the GSA of complete LCA models due to the high computational cost of such analysis and the lack of appropriate methods for very high-dimensional models. This study proposes a new GSA protocol suitable for large LCA problems that, unlike existing approaches, does not make assumptions on model linearity and complexity and includes extensive validation of GSA results. We illustrate the benefits of our protocol by comparing it with an existing method in terms of filtering of noninfluential and ranking of influential uncertainty drivers and include an application example of Swiss household food consumption. We note that our protocol obtains more accurate GSA results, which leads to better understanding of LCA models, and less data collection efforts to achieve more robust estimation of environmental impacts. Implementations supporting this work are available as free and open source Python packages.
Kocic, J., Dirin, D. N., Kägi, R., Kovalenko, M. V., Günther, D., & Hattendorf, B. (2022). Direct analysis of nanoparticles in organic solvents by ICPMS with microdroplet injection. Journal of Analytical Atomic Spectrometry, 37(8), 1738-1750. doi:10.1039/d1ja00358e, Institutional Repository

In recent years, the capabilities for characterizing inorganic nanoparticles (NPs) in aqueous solvents with respect to their elemental composition, mass and particle number concentration have been expanded using single particle inductively coupled plasma mass spectrometry (sp-ICPMS). However, NPs with high monodispersity, size, shape and surface chemistry control are frequently synthesized using hot-injection methods, utilizing hydrophobic organic ligands which are only soluble in non-polar organic solvents. Due to several instrumental limitations, suspensions in organic solvents are not commonly analysed by sp-ICPMS. In this study, we investigated the direct introduction of toluene and mesitylene into an ICPMS using a microdroplet generator. With this configuration the solvent load in the ICP is substantially reduced and soot formation, causing instrumental drift, was minimized while maintaining a transport efficiency (TE) of 100%. Furthermore, the effect of different vacuum interface configurations and the addition of oxygen or nitrogen on the detection efficiency (DE) and instrumental background signals was investigated for Al, Si, Ti, Fe Cu, Ag, Cd, and Pb. The highest DE was obtained for a “Jet” interface with the addition of nitrogen at a flow rate of 10 mL min−1, resulting in an increase by a factor of 2-8 depending on the element. The lowest detectable mass, based on counting statistics, was 1.4 ag for Pb, which corresponds to a diameter of 6.1 nm of a spherical, metallic NP. The approach can not only be used for NP characterization, but also holds promise for the sensitive determination of trace elements in organic solvents.
Lamprecht, O., Wagner, B., Derlon, N., & Tlili, A. (2022). Synthetic periphyton as a model system to understand species dynamics in complex microbial freshwater communities. npj Biofilms and Microbiomes, 8, 61 (14 pp.). doi:10.1038/s41522-022-00322-y, Institutional Repository

Phototrophic biofilms, also known as periphyton, are microbial freshwater communities that drive crucial ecological processes in streams and lakes. Gaining a deep mechanistic understanding of the biological processes occurring in natural periphyton remains challenging due to the high complexity and variability of such communities. To address this challenge, we rationally developed a workflow to construct a synthetic community by co-culturing 26 phototrophic species (i.e., diatoms, green algae, and cyanobacteria) that were inoculated in a successional sequence to create a periphytic biofilm on glass slides. We show that this community is diverse, stable, and highly reproducible in terms of microbial composition, function, and 3D spatial structure of the biofilm. We also demonstrate the ability to monitor microbial dynamics at the single species level during periphyton development and how their abundances are impacted by stressors such as increased temperature and a herbicide, singly and in combination. Overall, such a synthetic periphyton, grown under controlled conditions, can be used as a model system for theory testing through targeted manipulation.
Layer, M., Brison, A., Garcia Villodres, M., Stähle, M., Házi, F., Takács, I., … Derlon, N. (2022). Microbial conversion pathways of particulate organic substrate conversion of aerobic granular sludge systems: limited anaerobic conversion and the essential role of flocs. Environmental Science: Water Research and Technology, 8(6), 1236-1251. doi:10.1039/D1EW00841B, Institutional Repository

Particulate organic substrate (XB) represents the major fraction of organic substrate in low-strength municipal wastewater (MWW) but its hydrolysis, conversion and utilisation in aerobic granular sludge (AGS) are not well understood. We systematically analysed through modelling the microbial conversion pathways of XB in AGS systems operated as sequencing batch reactors and treating municipal wastewater. Based on our current understanding of AGS systems, we developed an AGS model in Sumo® to better understand (1) during which phases of the SBR cycle (anaerobic plug-flow feeding or aerobic fully-mixed conditions), (2) by what biomass fraction (granules or flocs) and (3) via which microbial processes XB is converted into soluble organic substrate (SB) and volatile fatty acids (SVFA) and further utilised. The validity of all our results was evaluated by assessing the sensitivity of findings on the biomass distribution (floc fraction) (SCENARIO #1), SBR cycle (SCENARIO #2), and biofilm properties (SCENARIO #3). Our results indicate that only 20% of influent XB was hydrolysed and 11% of influent XB was then used for internal carbon-storage during 90 min anaerobic plug-flow feeding. The major fraction of influent XB (80%) leaked into the aerobic SBR phase, where XB was then hydrolysed and oxidised aerobically by ordinary heterotrophic organisms (OHOs). Under aerobic fully-mixed conditions, the flocs successfully competed for XB with the granules. Aerobic XB hydrolysis and its further utilisation by OHOs occurred mainly in flocs despite their minor biomass fraction (13% of total suspended solids), preventing excessive OHO growth on granules and demonstrating that flocs are beneficial for AGS systems treating MWW. Also, the model allowed us to better understand that the SBR sequence can be optimised to make better use of XB under anaerobic conditions and to reduce the leakage of XB to aerobic conditions. The introduction of a 60 min anaerobic idle phase after a 60 min plug-flow feeding phase almost doubled the anaerobic XB hydrolysis and internal carbon-storage by phosphorus and glycogen accumulating organisms (PAOs and GAOs), respectively, compared to 90 min plug-flow feeding. Nonetheless, most influent XB was still utilised by OHOs during the aerobic SBR phase.
Murazzi, M. E., Cherubini, P., Brunner, I., Kägi, R., Saurer, M., Ballikaya, P., … Gessler, A. (2022). Can forest trees take up and transport nanoplastics?. iForest, 15(2), 128-132. doi:10.3832/ifor4021-015, Institutional Repository

Plastic contamination of ecosystems has increased dramatically over the last decades, raising concerns about the negative impacts of plastic particles on aquatic and terrestrial systems. In recent years, the focus of most research has shifted from large fragments (macroplastic) to micro- (<5 mm) and more recently to nano-plastic (<1000 nm) particles as more evidence has come to light about their ubiquity in water, soils, and living systems, and their effects on ecosystem and human health. In this study, we investigate nanoplastic uptake in the roots of seedlings (1-2 years old) of three different tree species and assess their transport to different tissues. Parts of the main roots of silver birch (Betula pendula Roth), sessile oak (Quercus petraea Matt. [Liebl.]), and Norway spruce (Picea abies [L.] Karst.) were immersed for one or four days in a suspension containing 13C-labelled nano-sized polystyrene particles (13C-nPS; 99% 13C, d = 28 ± 8 (1 σ) nm). Carbon stable isotope analysis showed significant 13C enrichment (P < 0.05) in the immersed part of the root after one day of treatment in all three species, and after four days in Q. petraea alone. Signals of significant 13C enrichment were also found in the aboveground tissues of the trees. The stem of B. pendula in particular showed a significant 13C enrichment after one day of treatment (P < 0.01). This indicates that nanoplastic particles can be taken up through tree roots into the tree’s central cylinder, where they are subsequently conveyed through the tree by acropetal transport via the xylem.
Notini, L., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2022). Coexisting goethite promotes Fe(II)-catalyzed transformation of ferrihydrite to goethite. Environmental Science and Technology, 56(17), 12723-12733. doi:10.1021/acs.est.2c03925, Institutional Repository

In redox-affected soil environments, electron transfer between aqueous Fe(II) and solid-phase Fe(III) catalyzes mineral transformation and recrystallization processes. While these processes have been studied extensively as independent systems, the coexistence of iron minerals is common in nature. Yet it remains unclear how coexisting goethite influences ferrihydrite transformation. Here, we reacted ferrihydrite and goethite mixtures with Fe(II) for 24 h. Our results demonstrate that with more goethite initially present in the mixture more ferrihydrite turned into goethite. We further used stable Fe isotopes to label different Fe pools and probed ferrihydrite transformation in the presence of goethite using 57Fe Mössbauer spectroscopy and changes in the isotopic composition of solid and aqueous phases. When ferrihydrite alone underwent Fe(II)-catalyzed transformation, Fe atoms initially in the aqueous phase mostly formed lepidocrocite, while those from ferrihydrite mostly formed goethite. When goethite was initially present, more goethite was formed from atoms initially in the aqueous phase, and nanogoethite formed from atoms initially in ferrihydrite. Our results suggest that coexisting goethite promotes formation of more goethite via Fe(II)-goethite electron transfer and template-directed nucleation and growth. We further hypothesize that electron transfer onto goethite followed by electron hopping onto ferrihydrite is another possible pathway to goethite formation. Our findings demonstrate that mineral transformation is strongly influenced by the composition of soil solid phases.
Philipp, M., Bucheli, T. D., & Kaegi, R. (2022). The use of surrogate standards as a QA/QC tool for routine analysis of microplastics in sewage sludge. Science of the Total Environment, 835, 155485 (9 pp.). doi:10.1016/j.scitotenv.2022.155485, Institutional Repository

The efficient retention of microplastic particles (MP) during wastewater treatment results in their accumulation in the sewage sludge. Thus, sewage sludge represents a key matrix for understanding MP flows between engineered and natural systems. Building on previous reports, we present a sample preparation protocol optimized for digested sewage sludge. The key steps include acid digestion supported by Fenton reagents, enzymatic digestion, and density separation using sodium polytungstate (density of 1.9 gcm−3). We use colored polyethylene (PE) spheres as surrogate standards to assess sample specific recoveries in terms of number and size, based on visible light (vis) microscopy and focal plane array - micro-Fourier transform - infrared (FPA-μ-FT-IR) imaging. The FT-IR spectra of common MP were identical before and after the digestion procedures and morphological changes were observed for polylactide fibers only. Average recovery rates for PE spheres, polypropylene fibers and polyethylene terephthalate fragments extracted from spiked digested sewage sludge and determined using (automated) vis microscopy ranged from 80% to 100%. Similar recovery rates of around 80% were also obtained for PE spheres based on FPA-μ-FT-IR measurements. The median diameters of red and blue PE spheres in dry state and recovered from spiked deionized water and from extracts of spiked digested sewage sludge determined using vis microscopy ranged between 46 μm and 67 μm. These diameters were similar to 54 μm and 61 μm obtained from the FPA-μ-FT-IR measurements of the corresponding deionized water samples and digested sludge extracts and in line with data from the producer (53 μm–63 μm). Using our digestion protocol in combination with surrogate standards, we measured MP number concentrations of around 10,000 #/g in dried, digested sewage sludge, in agreement with recent results from other studies.
Pulido-Reyes, G., Magherini, L., Bianco, C., Sethi, R., von Gunten, U., Kaegi, R., & Mitrano, D. M. (2022). Nanoplastics removal during drinking water treatment: laboratory- and pilot-scale experiments and modeling. Journal of Hazardous Materials, 436, 129011 (13 pp.). doi:10.1016/j.jhazmat.2022.129011, Institutional Repository

Microplastics detected in potable water sources and tap water have led to concerns about the efficacy of current drinking water treatment processes to remove these contaminants. It is hypothesized that drinking water resources contain nanoplastics (NPs), but the detection of NPs is challenging. We, therefore, used palladium (Pd)-labeled NPs to investigate the behavior and removal of NPs during conventional drinking water treatment processes including ozonation, sand and activated carbon filtration. Ozone doses typically applied in drinking water treatment plants (DWTPs) hardly affect the NPs transport in the subsequent filtration systems. Amongst the different filtration media, NPs particles were most efficiently retained when aged (i.e. biofilm coated) sand was used with good agreements between laboratory and pilot scale systems. The removal of NPs through multiple filtration steps in a municipal full-scale DWTP was simulated using the MNMs software code. Removal efficiencies exceeding 3-log units were modeled for a combination of three consecutive filtration steps (rapid sand filtration, activated carbon filtration and slow sand filtration with 0.4-, 0.2- and 3.0-log-removal, respectively). According to the results from the model, the removal of NPs during slow sand filtration dominated the overall NPs removal which is also supported by the laboratory-scale and pilot-scale data. The results from this study can be used to estimate the NPs removal efficiency of typical DWTPs with similar water treatment chains.
Randall, D. G., Brison, A., & Udert, K. M. (2022). High temperatures and CO2 dissolution can cause nitrogen losses from urine stabilized with base. Frontiers in Environmental Science, 10, 998743 (13 pp.). doi:10.3389/fenvs.2022.998743, Institutional Repository

Human urine is rich in valuable nitrogen which can easily be lost due to biological urea hydrolysis and subsequent ammonia volatilization. While this enzymatic reaction can be prevented by alkalizing the urine, recent studies suggest that chemical urea hydrolysis can result in substantial nitrogen losses when drying alkalinized urine at high temperatures. Furthermore, it was previously suggested that CO2 dissolution from the air used to evaporate water from alkalinized urine could result in a pH decrease to values which allows for biological urea hydrolysis and subsequent ammonia losses. This study aimed to determine the kinetics of chemical urea hydrolysis in alkalinized human urine and confirm the effect of CO2 dissolution with controlled laboratory experiments. We measured the change in urea concentration at different temperatures and pH values for real human urine and determined the corresponding rate constants for chemical urea hydrolysis. We showed that the rate constant increases as a function of temperature and that pH has a negligible effect on the rate of chemical urea hydrolysis in the high pH range of alkalized urine (>11). The rate constants for chemical urea hydrolysis in a saturated calcium hydroxide solution were found to be 0.00147 d-1, 0.00595 d-1, 0.0204 d-1 and 0.0848 d-1 for temperatures of 25°C, 40°C, 55°C and 70°C, respectively. The effect of CO2 dissolution on urea hydrolysis was determined by aerating human urine alkalinized with calcium hydroxide (Ca(OH)2). In order to represent biological urea hydrolysis, urease was added to the solution. The computer simulations of the experimental results showed that CO2 dissolution and the subsequent dissociation of carbonic acid to carbonate ions, bicarbonate ions and protons is the main cause of the pH decrease, but CaCO3 precipitation, and NH3 volatilization foster the pH decrease. However, biological urea hydrolysis prevents the pH from decreasing below 9. Residual undissolved Ca(OH)2 was shown to substantially delay the pH decrease. Overall, this work provides valuable insights into the mechanisms of urea hydrolysis in alkalinized urine during dehydration, which can be used to design more efficient decentralized sanitation systems and minimize nitrogen losses.
Rhein, F., Nirschl, H., & Kaegi, R. (2022). Separation of microplastic particles from sewage sludge extracts using magnetic seeded filtration. Water Research X, 17, 100155 (11 pp.). doi:10.1016/j.wroa.2022.100155, Institutional Repository

Microplastic particles (MP) are efficiently retained in wastewater treatment plants and enriched in sewage sludge. For monitoring MP contents in wastewater systems, sewage sludge is thus well suited, but also requires an isolation of MP from the sludge matrix, as other sewage sludge components may interfere with the MP identification and quantification. Although organic matter in sludge samples can be removed through acid and enzymatic digestion procedures, cellulose - mainly from toilet paper - remains in the digests, due to its high chemical resistivity and similar density to MP. We apply the separation concept of magnetic seeded filtration to isolate MP through selective hetero-agglomeration with magnetic seed particles. MP and cellulose differ in their hydrophobic properties and we investigate to what extent these differences can be exploited to selectively form MP-magnetite hetero-agglomerates in the presence of cellulose. These hetero-agglomerates are subsequently separated using a magnet. Five MP types (Polyethylene terephthalate (PET), polypropylene (PP), low density polyethylene (LDPE), polyvinyl chloride (PVC) and polystyrene (PS)) and cellulose particles were mixed in different combinations with both hydrophilic and hydrophobic (silanized) magnetite particles. PET, PP, LDPE and PS only poorly agglomerated with pristine (hydrophilic) magnetite, but efficiently formed hetero-agglomerates with hydrophobic magnetite and were successfully removed from suspensions (80 - 100 %). PVC agglomerated more efficiently with pristine than with hydrophobic magnetite and cellulose only agglomerated to a limited extent with either hydrophilic or hydrophobic magnetite, resulting in a high process selectivity. Results from experiments conducted at different ionic strengths and with hydrophilic and hydrophobic magnetite suggests that the agglomeration process was dominated by hydrophobic interactions. Enzymatic and oxidative treatment of the MP only marginally affected the separation efficiencies and (treated) MP spiked to sewage sludge extracts were successfully recovered using magnetic seeded filtration.
Sam, S. B., Ward, B. J., Niederdorfer, R., Morgenroth, E., & Strande, L. (2022). Elucidating the role of extracellular polymeric substances (EPS) in dewaterability of fecal sludge from onsite sanitation systems, and changes during anaerobic storage. Water Research, 222, 118915 (12 pp.). doi:10.1016/j.watres.2022.118915, Institutional Repository

As the importance of fecal sludge management (FSM) is increasingly being realized, the need for adequately designed and functioning fecal sludge (FS) treatment plants is also increasing. Research to fill this gap is only emerging and dewatering is a key challenge for developing sustainable treatment solutions. This study evaluated the effect of extracellular polymeric substances (EPS) on dewaterability of FS, and how EPS and dewaterability change during anaerobic storage (as a proxy for time in onsite containment). EPS was extracted from FS and activated sludge using Na2CO3 and sonication and added to sludge samples to determine the effect on dewaterability. The results confirmed that an increase in EPS had a direct impact of decreasing FS dewaterability (as capillary suction time). In this context, we evaluated FS degradation during anaerobic storage, the effect of anaerobic storage time on EPS, EPS fractions and particle size distribution, and the effect of variations in these factors on FS dewaterability. Variations in EPS, EPS fraction and particle size distribution during anaerobic storage were less than expected and average VS reduction of 20% was recorded over 7 weeks. Although anaerobic digestion was verified (biogas production), the results indicate that kinetics of degradation of FS is different from wastewater sludges. Comparatively, EPS fractions in FS were 70 – 75% lower and with higher fractions of humic-like substances than wastewater sludges. Although EPS significantly affects FS dewaterability, anaerobic storage time is not a predictor of dewaterability.
Schneider, M. Y., Quaghebeur, W., Borzooei, S., Froemelt, A., Li, F., Saagi, R., … Torfs, E. (2022). Hybrid modelling of water resource recovery facilities: status and opportunities. Water Science and Technology, 85(9), 2503-2524. doi:10.2166/wst.2022.115, Institutional Repository

Mathematical modelling is an indispensable tool to support water resource recovery facility (WRRF) operators and engineers with the ambition of creating a truly circular economy and assuring a sustainable future. Despite the successful application of mechanistic models in the water sector, they show some important limitations and do not fully profit from the increasing digitalisation of systems and processes. Recent advances in data-driven methods have provided options for harnessing the power of Industry 4.0, but they are often limited by the lack of interpretability and extrapolation capabilities. Hybrid modelling (HM) combines these two modelling paradigms and aims to leverage both the rapidly increasing volumes of data collected, as well as the continued pursuit of greater process understanding. Despite the potential of HM in a sector that is undergoing a significant digital and cultural transformation, the application of hybrid models remains vague. This article presents an overview of HM methodologies applied to WRRFs and aims to stimulate the wider adoption and development of HM. We also highlight challenges and research needs for HM design and architecture, good modelling practice, data assurance, and software compatibility. HM is a paradigm for WRRF modelling to transition towards a more resource-efficient, resilient, and sustainable future.
Schulz, K., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2022). Stabilization of ferrihydrite and lepidocrocite by silicate during Fe(II)-catalyzed mineral transformation: impact on particle morphology and silicate distribution. Environmental Science and Technology, 56(9), 5929-5938. doi:10.1021/acs.est.1c08789, Institutional Repository

Interactions between aqueous ferrous iron (Fe(II)) and secondary Fe oxyhydroxides catalyze mineral recrystallization and/or transformation processes in anoxic soils and sediments, where oxyanions, such as silicate, are abundant. However, the effect and the fate of silicate during Fe mineral recrystallization and transformation are not entirely understood and especially remain unclear for lepidocrocite. In this study, we reacted (Si-)ferrihydrite (Si/Fe = 0, 0.05, and 0.18) and (Si-)lepidocrocite (Si/Fe = 0 and 0.08) with isotopically labeled 57Fe(II) (Fe(II)/Fe(III) = 0.02 and 0.2) at pH 7 for up to 4 weeks. We followed Fe mineral transformations with X-ray diffraction and tracked Fe atom exchange by measuring aqueous and solid phase Fe isotope fractions. Our results show that the extent of ferrihydrite transformation in the presence of Fe(II) was strongly influenced by the solid phase Si/Fe ratio, while increasing the Fe(II)/Fe(III) ratio (from 0.02 to 0.2) had only a minor effect. The presence of silicate increased the thickness of newly formed lepidocrocite crystallites, and elemental distribution maps of Fe(II)-reacted Si-ferrihydrites revealed that much more Si was associated with the remaining ferrihydrite than with the newly formed lepidocrocite. Pure lepidocrocite underwent recrystallization in the low Fe(II) treatment and transformed to magnetite at the high Fe(II)/Fe(III) ratio. Adsorbed silicate inactivated the lepidocrocite surfaces, which strongly reduced Fe atom exchange and inhibited mineral transformation. Collectively, the results of this study demonstrate that Fe(II)-catalyzed Si-ferrihydrite transformation leads to the redistribution of silicate in the solid phase and the formation of thicker lepidocrocite platelets, while lepidocrocite transformation can be completely inhibited by adsorbed silicate. Therefore, silicate is an important factor to include when considering Fe mineral dynamics in soils under reducing conditions.
Schwarzfischer, M., Niechcial, A., Lee, S. S., Sinnet, B., Wawrzyniak, M., Laimbacher, A., … Spalinger, M. R. (2022). Ingested nano- and microsized polystyrene particles surpass the intestinal barrier and accumulate in the body. NanoImpact, 25, 100374 (9 pp.). doi:10.1016/j.impact.2021.100374, Institutional Repository

Plastic pollution is a major global challenge of our times, baring a potential threat for the environment and the human health. The increasing abundance of nanoplastic (NP) and microplastic (MP) particles in the human diet might negatively affect human health since they - particularly in patients suffering from inflammatory bowel disease (IBD) – might surpass the intestinal barrier. To investigate whether ingested plastic particles cross the intestinal epithelium and promote bowel inflammation, mice were supplemented with NP or MP polystyrene (PS) particles for 24 or 12 weeks before inducing acute or chronic dextran sodium sulfate (DSS) colitis with continuous plastic administration. Although ingested PS particles accumulated in the small intestine and organs distant from the gastrointestinal tract, PS ingestion did not affect intestinal health nor did it promote colitis severity. Although the lack of colitis-promoting effects of small PS particles might be a relief for IBD patients, potential accumulative effects of ingested plastic particles on the gastrointestinal health cannot be excluded.
Stamm, C., Binder, C. R., Frossard, E., Haygarth, P. M., Oberson, A., Richardson, A. E., … Udert, K. M. (2022). Towards circular phosphorus: the need of inter- and transdisciplinary research to close the broken cycle. Ambio, 51, 611-622. doi:10.1007/s13280-021-01562-6, Institutional Repository

Phosphorus (P) is an essential element to all living beings but also a finite resource. P-related problems center around broken P cycles from local to global scales. This paper presents outcomes from the 9th International Phosphorus Workshop (IPW9) held 2019 on how to move towards a sustainable P management. It is based on two sequential discussion rounds with all participants. Important progress was reported regarding the awareness of P as finite mineable resource, technologies to recycle P, and legislation towards a circular P economy. Yet, critical deficits were identified such as how to handle legacy P, how climate change may affect ecosystem P cycling, or working business models to up-scale existing recycling models. Workshop participants argued for more transdisciplinary networks to narrow a perceived science-practice/policy gap. While this gap may be smaller in reality as illustrated with a Swiss example, we formulate recommendations how to bridge this gap more effectively.
Stetten, L., Hofmann, T., Proux, O., Landrot, G., Kaegi, R., & von der Kammer, F. (2022). Transformation of zinc oxide nanoparticles in freshwater sediments under oxic and anoxic conditions. Environmental Science: Nano, 9(11), 4255-4267. doi:10.1039/d2en00709f, Institutional Repository

The transformation of zinc oxide nanoparticles (ZnO NPs) has been largely investigated in wastewater treatment plants, recognized as important intermediates before the discharge of NPs into the environment. However, considering direct releases of the pristine ZnO NP forms, additional studies on ZnO NP fate in different environmental compartments are encouraged. In this work, we investigated ZnO NP transformation in lacustrine sediments under defined redox conditions. Using X-ray absorption spectroscopy and wet chemical analyses, we followed ZnO NP and Zn2+ fate over a three-month period in sediments incubated under oxic or anoxic sulfide-rich conditions. Under oxic conditions, ZnO NPs were dissolved within a few hours. By contrast, ZnO NP dissolution under anoxic conditions was much slower, with ∼19% of ZnO NPs remaining at the end of the incubation, together with ∼41% of ZnS, ∼15% of Zn adsorbed onto phyllosilicates and ∼27% of Zn-phyllosilicate-like species. The transient formation of Zn–organic complexes under oxic conditions supports that ZnO NP dissolution is driven by organic compounds, followed by Zn adsorption onto phyllosilicates and the subsequent formation of Zn-layered minerals. Under anoxic conditions, ZnO NP dissolution is inhibited by the precipitation of amorphous ZnS and controlled by the progressive growth of ZnS NPs. These results improve the understanding of ZnO NP transformation in slightly alkaline freshwater sediments and highlight the need to assess NP fate under environmentally relevant conditions.
Stoffel, D., Rigo, E., Derlon, N., Staaks, C., Heijnen, M., Morgenroth, E., & Jacquin, C. (2022). Low maintenance gravity-driven membrane filtration using hollow fibers: effect of reducing space for biofilm growth and control strategies on permeate flux. Science of the Total Environment, 811, 152307 (13 pp.). doi:10.1016/j.scitotenv.2021.152307, Institutional Repository

The implementation of centralized drinking water treatment systems necessitates lower operational costs and improved biopolymer removal during ultrafiltration (UF), which can be afforded by gravity-driven membrane (GDM) filtration. However, prior to implementing GDM filtration in centralized systems, biofilm growth in compacted membrane configurations, such as inside-out hollow fiber (HF), and its impact on permeate flux need to be investigated. To this end, we operated modules with distinct limits on available space for biofilm growth: (1) outside-in 1.5 mm 7-capillary HF (non-limited), (2) inside-out 1.5 mm 7-capillary HF (limited), and (3) inside-out 0.9 mm 7-capillary HF (very limited). Here, we observed that the lower the space available for biofilm growth, the lower the permeate flux. To improve GDM performance with inside-out HF, we applied daily shear stress to the biofilm surface with forward flush (FF) or combined relaxation and forward flush (R+FF). We showed that applying shear stress to the biofilm surface was insufficient for controlling flux loss due to low available space for biofilm growth. At the experimental endpoint, we backwashed with a stepwise transmembrane pressure (TMP) increase or a single TMP on all inside-out HF modules, which removed the biofilm from its base. Afterwards, higher fluxes were yielded. We also showed that all modules exhibited a gradual increase in biopolymer removal followed by stabilization between 70 and 90%. Additionally, control of biofilm growth with surface shear stress did not affect biopolymer removal. In summary, the implementation of inside-out HF with GDM filtration is challenged by low available space for biofilm growth, but may be remedied with a regular backwash to remove biofilm from its base. We showed that a wider range of GDM applications are available; making GDM potentially compatible with implementation in centralized systems, if space limitation is taken into consideration for operation optimization.
Szakas, S. E., Lancaster, R., Kaegi, R., & Gundlach-Graham, A. (2022). Quantification and classification of engineered, incidental, and natural cerium-containing particles by spICP-TOFMS. Environmental Science: Nano, 9, 1627-1638. doi:10.1039/d1en01039e, Institutional Repository

Cerium containing nanoparticles (Ce-NPs) from geogenic and anthropogenic sources are frequently found in the environment, and the ability to determine the origins of Ce-NPs relies on the presence of other rare earth elements (REEs), such as La. In this study, we develop a scheme to classify individual natural, incidental, and engineered Ce-containing particles using spICP-TOFMS. Well-characterized CeO2 engineered particles (Ce-ENPs), incidental particles (Ce-INPs) from ferrocerium mischmetal, and natural particles (Ce-NNPs) from ground minerals (bastnaesite and parisite) are used as a model particle system. Based on mixtures of these three Ce-NP types, we demonstrate that the measured signals of Ce, La, and Nd in Ce-NNPs follow Poisson statistics and have conserved element ratios. The Ce-INPs we measure have similar Ce : La mass ratios to those of the Ce-NNPs, and Ce : Nd mass ratios can be used to distinguish these two Ce-NP types. Based on this, we develop particle-type-specific detection limits (LD,sp) for the measurement of La and Nd in Ce-NNPs. Our approach establishes LD,sp values with defined confidence intervals to control false-positive particle-type assignments, and allows us to accurately classify engineered, incidental, and natural Ce-NPs down to effective spherical diameters of 32, 35, and 45 nm, respectively. In pure Ce-NNP suspensions, this approach accurately classifies 68% of all detected Ce-NPs with <4% false assignments. For ternary mixtures of Ce-ENPs, INPs, and NNPs, we classify 56% to 76% of all detected Ce-NPs. We demonstrate a linear response with increasing concentrations of Ce-INPs and Ce-ENPs across approximately three orders of magnitude and can classify particles down to ratios of ∼1:50 for anthropogenic : natural Ce-NPs.
Walpen, N., Joss, A., & von Gunten, U. (2022). Application of UV absorbance and electron-donating capacity as surrogates for micropollutant abatement during full-scale ozonation of secondary-treated wastewater. Water Research, 209, 117858 (11 pp.). doi:10.1016/j.watres.2021.117858, Institutional Repository

Ozonation of secondary-treated wastewater for the abatement of micropollutants requires a reliable control of ozone doses. Changes in the UV absorbance of dissolved organic matter (DOM) during ozonation allow to estimate micropollutant abatement on-line and were therefore identified as feed-back control parameter. In this study, the suitability of the electron-donating capacity (EDC) as an additional surrogate parameter which is independent of optical DOM properties was evaluated during full-scale ozonation. For this purpose, a recently developed EDC analyzer was enhanced to enable continuous on-line EDC and UV absorbance measurements. During a multi-week monitoring campaign at the wastewater treatment plant of Zurich, Switzerland, specific ozone doses were varied from 0.13 to 0.91 mgO3⋅mgDOC-1 and selected micropollutants with different ozone reactivities were analyzed by LC-MS in conjunction with bromate analysis by IC-MS. In agreement with previous laboratory studies, the relative residual UV absorbance and EDC both decreased exponentially as a function of the specific ozone dose and, in comparison to the residual UV absorbance, residual EDC values showed a more pronounced decrease at low specific ozone doses ≤0.34 mgO3⋅mgDOC-1. Logistic regression models allowed to estimate relative residual micropollutant concentrations in the ozonation effluent using either the residual UV absorbance or EDC as explanatory variable. Averaging those models along the explanatory variables allowed to estimate target values in relative residual UV absorbances and EDC for specific micropollutant abatement targets. In addition, both parameters allowed to identify conditions with elevated conversions of bromide to bromate. Taken together, these findings show that the integration of relative residual EDC values as a second control parameter can improve existing absorbance-based ozonation control systems to meet micropollutant abatement targets, particularly for treatment systems where low ozone doses are applied.
Cai, Y., Mitrano, D. M., Hufenus, R., & Nowack, B. (2021). Formation of fiber fragments during abrasion of polyester textiles. Environmental Science and Technology, 55(12), 8001-8009. doi:10.1021/acs.est.1c00650, Institutional Repository

Fiber fragments are one of the dominant types of microplastics in environmental samples, suggesting that synthetic textiles are a potential source of microplastics to the environment. Whereas the release of microplastics during washing of textiles is already well studied, much less is known about the release during abrasion processes. The abrasion of textiles may induce fibrillation of fibers and therefore result in the formation of much finer fiber fragments. The aim of this study was to investigate the influence of abrasion of synthetic textiles on the formation of microplastic fibers and fibrils. Fleece and interlock textile swatches made of polyester were abraded using abrasion tests with a Martindale tester. The microplastic fibers and fibrils formed during abrasion were extracted from the textiles and characterized in terms of number, length, and diameter. The microplastic fibers demonstrated the same diameter than the fibers found in the textiles (fleece: 12.3 μm; interlock: 12.7 μm), while fibrils with a much smaller diameter (fleece: 2.4 μm; interlock: 4.9 μm) were also found. The number of fibrils formed during abrasion in both textiles was higher than the number of microplastic fibers. The majority of the extracted microplastic fibers had a length between 200 and 800 μm, while most fibrils were between 30 and 150 μm, forming two distinct fiber fragment morphologies. The number of microplastic fibers formed during abrasion was 5 to 30 times higher than the number of microplastic fibers that could be extracted from non-abraded samples. The number of fibrils increased after abrasion by more than a factor of 200 for both fabric types. The fibrils formed during abrasion have diameters that fall within the inhalable size for airborne particles. The potential release of fibrils into air during wear of textiles thus raises questions about the human exposure to these materials. Since the Martindale tester can simulate a daily application scenario of textiles over a prolonged period only in a limited way, future studies are needed to establish the correlation between the test results with a real-world scenario.
Carles, L., Wullschleger, S., Joss, A., Eggen, R. I. L., Schirmer, K., Schuwirth, N., … Tlili, A. (2021). Impact of wastewater on the microbial diversity of periphyton and its tolerance to micropollutants in an engineered flow-through channel system. Water Research, 203, 117486 (14 pp.). doi:10.1016/j.watres.2021.117486, Institutional Repository

Wastewater treatment plants (WWTPs) play an important role in retaining organic matter and nutrients but to a lesser extent micropollutants. Therefore, treated wastewater is recognized as a major source of multiple stressors, including complex mixtures of micropollutants. These can potentially affect microbial communities in the receiving water bodies and the ecological functions they provide. In this study, we evaluated in flow-through channels the consequences of an exposure to a mixture of stream water and different percentages of urban WWTP effluent, ranging from 0% to 80%, on the microbial diversity and function of periphyton communities. Assuming that micropollutants exert a selective pressure for tolerant microorganisms within communities, we further examined the periphyton sensitivity to a micropollutant mixture extracted from passive samplers that were immersed in the wastewater effluent. As well, micropollutants in water and in periphyton were comprehensively quantified. Our results show that micropollutants detected in periphyton differed from those found in water, both in term of concentration and composition. Especially photosystem II inhibitors accumulated in periphyton more than other pesticides. Although effects of other substances cannot be excluded, this accumulation may have contributed to the observed higher tolerance of phototrophic communities to micropollutants upon exposure to 30% and 80% of wastewater. On the contrary, no difference in tolerance was observed for heterotrophic communities. Exposure to the gradient of wastewater led to structural differences in both prokaryotic and eukaryotic communities. For instance, the relative abundance of cyanobacteria was higher with increasing percentage of wastewater effluent, whereas the opposite was observed for diatoms. Such results could indicate that differences in community structure do not necessarily lead to higher tolerance. This highlights the need to consider other wastewater constituents such as nutrients and wastewater-derived microorganisms that can modulate community structure and tolerance. By using engineered flow-through channels that mimic to some extent the required field conditions for the development of tolerance in periphyton, our study constitutes a base to investigate the mechanisms underlying the increased tolerance, such as the potential role of microorganisms originating from wastewater effluents, and different treatment options to reduce the micropollutant load in effluents.
Courtney, C., Brison, A., & Randall, D. G. (2021). Calcium removal from stabilized human urine by air and CO2 bubbling. Water Research, 202, 117467 (10 pp.). doi:10.1016/j.watres.2021.117467, Institutional Repository

Stabilization of urine with calcium hydroxide prevents enzymatic urea hydrolysis, thus allowing for maximum nitrogen recovery. The process also produces a calcium phosphate bi-product which has value as a fertilizer. However, the treated solution is saturated with calcium that could ultimately result in calcium carbonate scaling of reverse osmosis membranes during urine concentration. This would result in a decrease in maximum water removal and an increase in operational costs.
This study therefore investigated if bubbling air and carbon dioxide through stabilized urine could remove calcium ions as calcium carbonate. The process was modelled to better understand the mechanisms controlling the reactions in the process. The model was then used to determine the most cost and time efficient operating conditions. Calcium removal of between 85–98% was achieved at air flow rates of 1.5 to 9 L min−1. Increasing the CO2 concentration from 0.04% (air) to 1% decreased the reaction time from 20.5 h to 2.5 h but the cost of CO2 outweighed the shorter operating time. Air bubbling was the more cost-efficient option. It was estimated that 95% of the calcium could be removed in 7.6 h at an air flow rate of 4 L min−1 L−1 of urine and at a cost of $0.65 m−3. It was also determined that even if the pH decreased to below 11, the urine remained stabilized and no enzymatic urea hydrolysis occurred.
Domagała, K., Bell, J., Yüzbasi, N. S., Sinnet, B., Kata, D., & Graule, T. (2021). Virus removal from drinking water using modified activated carbon fibers. RSC Advances, 11(50), 31547-31556. doi:10.1039/d1ra06373a, Institutional Repository

Activated carbon (AC) exhibits superior sorption properties compared to other porous materials, due to well-developed porous structures and high surface areas. Therefore, it is widely applied in its various forms in water purification to remove a diverse range of contaminating species. The presence of viruses in fresh water bodies poses a serious issue for human health. However, AC has not yet been commonly applied to waterborne virus removal. In this study, we present oxidation and copper impregnation treatment procedures of activated carbon fibers (ACFs) that resulted in porous structure and surface chemistry modifications. The effect of these modifications on virus removal was investigated by experimental flow studies and revealed up to 2.8 log10 reduction value (LRV) and 3.6 LRV of MS2 bacterio-phages for non-modified and oxidized ACFs, respectively, emphasizing the advantages of ACF surface functionalization. Copper modified fibers demonstrated a high sensitivity to media composition, resulting in a release of metal and therefore limited virucidal capacity.
Etique, M., Bouchet, S., Byrne, J. M., Thomasarrigo, L. K., Kaegi, R., & Kretzschmar, R. (2021). Mercury reduction by nanoparticulate vivianite. Environmental Science and Technology, 55(5), 3399-3407. doi:10.1021/acs.est.0c05203, Institutional Repository

Mercury (Hg) is a toxic trace element of global environmental concern which has been increasingly dispersed into the environment since the industrial revolution. In aquatic and terrestrial systems, Hg can be reduced to elemental Hg (Hg0) and escape to the atmosphere or converted to methylmercury (MeHg), a potent neurotoxin that accumulates in food webs. FeII-bearing minerals such as magnetite, green rusts, siderite, and mackinawite are recognized HgII reducers. Another potentially Hg-reducing mineral, which commonly occurs in Fe- and organic/P-rich sediments and soils, is the ferrous iron phosphate mineral vivianite (FeII3(PO4)2·8H2O), but its reaction with HgII has not been studied to date. Here, nanoparticulate vivianite (particle size ∼ 50 nm; FeII content > 98%) was chemically synthesized and characterized by a combination of chemical, spectroscopic, and microscopic analyses. Its ability to reduce HgII was investigated at circumneutral pH under anoxic conditions over a range of FeII/HgII ratios (0.1–1000). For FeII/HgII ratios ≥1, which are representative of natural environments, HgII was very quickly and efficiently reduced to Hg0. The ability of vivianite to reduce HgII was found to be similar to those of carbonate green rust and siderite, two of the most effective Hg-reducing minerals. Our results suggest that vivianite may be involved in abiotic HgII reduction in Fe and organic/P-rich soils and sediments, potentially contributing to Hg evasion while also limiting MeHg formation in these ecosystems.
González-Pleiter, M., Edo, C., Aguilera, Á., Viúdez-Moreiras, D., Pulido-Reyes, G., González-Toril, E., … Rosal, R. (2021). Occurrence and transport of microplastics sampled within and above the planetary boundary layer. Science of the Total Environment, 761, 143213 (11 pp.). doi:10.1016/j.scitotenv.2020.143213, Institutional Repository

Nowadays, there is no direct evidence about the presence of microplastics (MPs) in the atmosphere above ground level. Here, we investigated the occurrence, chemical composition, shape, and size of MPs in aircraft sampling campaigns flying within and above the planetary boundary layer (PBL). The results showed that MPs were present with concentrations ranging from 1.5 MPs m−3 above rural areas to 13.9 MPs m−3 above urban areas. MPs represented up to almost one third of the total amount of microparticles collected. Fourier Transform Infrared Spectroscopy allowed identifying seven types of MPs with the highest diversity corresponding to urban areas. Atmospheric transport and deposition simulations were performed using the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Air mass trajectory analyses showed that MPs could be transported more than 1000 km before being deposited. This pioneer study is the first evidence of the microplastic presence above PBL and their potential long-range transport from their point of release even crossing distant borders.
Gruber, W., von Känel, L., Vogt, L., Luck, M., Biolley, L., Feller, K., … Joss, A. (2021). Estimation of countrywide N2O emissions from wastewater treatment in Switzerland using long-term monitoring data. Water Research X, 13, 100122 (12 pp.). doi:10.1016/j.wroa.2021.100122, Institutional Repository

Nitrous oxides (N2O) emissions contribute to climate change and stratospheric ozone depletion. Wastewater treatment is an important, yet likely underestimated, source of N2O emissions, as recent, long-term monitoring campaigns have demonstrated. However, the available data are insufficient to representatively estimate countrywide emission due to the brevity of most monitoring campaigns. This study showed that the emission estimates can be significantly improved using an advanced approach based on multiple continuous, long-term monitoring campaigns. In monitoring studies on 14 full-scale wastewater treatment plants (WWTPs), we found a strong variability in the yearly emission factors (EFs) (0.1 to 8% of the incoming nitrogen load) which exhibited a good correlation with effluent nitrite. But countrywide data on nitrite effluent concentrations is very limited and unavailable for emission estimation in many countries. Hence, we propose a countrywide emission factor calculated from the weighted EFs of three WWTP categories (carbon removal, EF: 0.1-8%, nitrification only: 1.8%, and full nitrogen removal: 0.9%). However, EF of carbon removal WWTPs are still highly uncertain given the expected variability in performance.
The newly developed approach allows representative, country-specific estimations of the N2O emissions from WWTP. Applied to Switzerland, the estimations result in an average EF of 0.9 to 3.6% and total emissions of 410 to 1690 tN2O-N/year, which corresponds to 0.3-1.4% of the total greenhouse gas emissions in Switzerland. Our results demonstrate that better data availability and an improved understanding of long-term monitoring campaigns is crucial to improve current emission estimations. Finally, our results confirm several measures to mitigate N2O emissions from wastewater treatment; year-round denitrification, limiting nitrite accumulation, and stringent control of sludge age in carbon removal plants.
Gruber, W., Niederdorfer, R., Ringwald, J., Morgenroth, E., Bürgmann, H., & Joss, A. (2021). Linking seasonal N2O emissions and nitrification failures to microbial dynamics in a SBR wastewater treatment plant. Water Research X, 11, 100098 (13 pp.). doi:10.1016/j.wroa.2021.100098, Institutional Repository

Nitrous oxide (N2O) is a strong greenhouse gas and causal for stratospheric ozone depletion. During biological nitrogen removal in wastewater treatment plants (WWTP), high N2O fluxes to the atmosphere can occur, typically exhibiting a seasonal emission pattern. Attempts to explain the peak emission phases in winter and spring using physico-chemical process data from WWTP were so far unsuccessful and new approaches are required. The complex and diverse microbial community of activated sludge used in biological treatment systems also exhibit substantial seasonal patterns. However, a potentially causal link between the seasonal patterns of microbial diversity and N2O emissions has not yet been investigated. Here we show that in a full-scale WWTP nitrification failure and N2O peak emissions, bad settleability of the activated sludge and a turbid effluent strongly correlate with a significant reduction in the microbial community diversity and shifts in community composition. During episodes of impaired performance, we observed a significant reduction in abundance for filamentous and nitrite oxidizing bacteria in all affected reactors. In some reactors that did not exhibit nitrification and settling failures, we observed a stable microbial community and no drastic loss of species. Standard engineering approaches to stabilize nitrification, such as increasing the aerobic sludge age and oxygen availability failed to improve the plant performance on this particular WWTP and replacing the activated sludge was the only measure applied by the operators to recover treatment performance in affected reactors. Our results demonstrate that disturbances of the sludge microbiome affect key structural and functional microbial groups, which lead to seasonal N2O emission patterns. To reduce N2O emissions from WWTP, it is therefore crucial to understand the drivers that lead to the microbial population dynamics in the activated sludge.
Hausherr, D., Niederdorfer, R., Morgenroth, E., & Joss, A. (2021). Robustness of mainstream anammox activity at bench and pilot scale. Science of the Total Environment, 796, 148920 (11 pp.). doi:10.1016/j.scitotenv.2021.148920, Institutional Repository

New technologies and processes, such as mainstream anammox, aim to reduce energy requirements of wastewater treatment and improve effluent quality. However, in municipal wastewater (MWW) anammox system are often unstable due to process control disturbance, influent variability, or unwanted nitrite oxidizing bacteria (NOB). This study examines the anammox system by focusing on anammox activity and its robustness in a mainstream environment. An 8 m3 pilot-scale sequencing batch reactor (SBR) receiving pretreated MWW (with external nitrite addition) was seeded with pre-colonized carriers. Within six months at 12–20 °C an anammox activity of 200 gN·m−3·d−1 was achieved. After the startup an anammox activity of 260 ± 83 gN·m−3·d−1 was maintained over 450 days. The robustness of the anammox activity was analyzed through three disturbance experiments. Anammox biofilm on carriers were exposed to dissolved oxygen (DO = 1.6 mg·L−1, intermittent aeration), organic loading rate (OLR, C/N increased from 2:1 to 5:1) and temperature disturbances (20 °C to 12 °C) in triplicate 12 L bench scale reactors. The anammox activity and microbial community was monitored during these disturbances. The DO and OLR disturbance experiments were replicated at pilot scale to investigate upscaling effects. Bench and pilot scale anammox activity were unaffected by the DO disturbance. Similarly, an increase in OLR did not deteriorate the bench and pilot scale anammox activity, if nitrate was available. When, at bench scale, the reactor temperature was reduced from 20 °C to 12 °C overnight, anammox activity decreased significantly, this was not the case for the slow seasonal temperature changes (12–25 °C) at pilot scale where no strong temperature dependency was detected in winter. Metagenomic analysis revealed a broad range of Brocadiaceae species with no single dominant anammox species. Anammox thrive under mainstream conditions and can withstand typical process disruptions.
Hess, A., & Morgenroth, E. (2021). Biological activated carbon filter for greywater post-treatment: Long-term TOC removal with adsorption and biodegradation. Water Research X, 13, 100113 (9 pp.). doi:10.1016/j.wroa.2021.100113, Institutional Repository

Biological activated carbon (BAC) filters can be used to remove residual total organic carbon (TOC) from greywater after a membrane bioreactor. The two main TOC removal processes are adsorption to the granular activated carbon (GAC) and biological degradation. Biodegradation leads to the growth of microorganisms in the filter bed, which can lead to increased pressure loss over the filter bed. However, the roles of sorption and biodegradation in long-term TOC removal and how they complement each other are unclear. We monitored TOC removal from greywater in a BAC filter installed following a membrane bioreactor over more than 900 days. Removal performance depended on the operational time of the BAC filter, the influent TOC concentration, and in the upper part of the filter on the empty bed contact time (EBCT). Across the overall filter, the EBCT did not significantly influence TOC removal, showing that the filter was sufficiently large for the range of flow rates observed. Analysis of the long-term data revealed the equal importance of sorption and biodegradation over the whole operation period and the whole filter bed. Most of the TOC was removed in the upper part of the filter, where biodegradation was the dominant mechanism. In the lower part of the filter, sorption capacity remained and allowed high influent TOC concentrations to be buffered. The generous filter design with low average filtration rates ensured long-term TOC removal. The only maintenance needed was backwashing, which was required only after more than 800 days of operation. Backwashing effectively reduced the pressure loss but had no significant influence on the effluent water quality. Our study shows that BAC filters are a suitable post-treatment step for the treatment of greywater with highly variable flow and TOC concentrations.
Hess, A., Baum, C., Schiessl, K., Besmer, M. D., Hammes, F., & Morgenroth, E. (2021). Stagnation leads to short-term fluctuations in the effluent water quality of biofilters: a problem for greywater reuse?. Water Research X, 13, 100120 (9 pp.). doi:10.1016/j.wroa.2021.100120, Institutional Repository

A key characteristic of decentralized greywater treatment and reuse is high variability in both nutrient concentrations and flow. This variability in flow leads to stagnant water in the system and causes short-term fluctuations in the effluent water quality. Automated monitoring tools provide data to understand the mechanisms underlying the dynamics and to adapt control strategies accordingly. We investigated the fluctuations in a building-scale greywater treatment system comprising a membrane bioreactor followed by a biological activated carbon filter. Short-term dynamics in the effluent of the biological activated carbon filter were monitored with automated flow cytometry and turbidity, and the impact of these fluctuations on various hygiene-relevant parameters in the reuse water was evaluated. Continuous biofilm detachment into the stagnant water in the biological activated carbon filter led to temporarily increased turbidity and cell concentrations in the effluent after periods of stagnation. The fluctuations in cell concentrations were consistent with a model assuming higher detachment rates during flow than during times with stagnant water. For this system, total cell concentration and turbidity were strongly correlated. We also showed that the observed increase in cell concentration was not related to either an increase of organic carbon concentration or the concentration of two opportunistic pathogens, P. aeruginosa and L. pneumophila. Our findings demonstrate that turbidity measurements are sensitive to changes in the effluent water quality and can be used to monitor the fluctuations caused by intermittent flow. Intermittent flow did not lead to an increase in opportunistic pathogens, and this study provides no indications that stagnant water in biological activated carbon filters need be prevented.
Kaegi, R., Gogos, A., Voegelin, A., Hug, S. J., Winkel, L. H. E., Buser, A. M., & Berg, M. (2021). Quantification of individual Rare Earth Elements from industrial sources in sewage sludge. Water Research X, 11, 100092 (11 pp.). doi:10.1016/j.wroa.2021.100092, Institutional Repository

Rare Earth Elements (REEs) are used in increasing amounts in technical applications and consumer products. However, to date, the contribution of industrial sources to the loads of individual REEs in wastewater streams have not been quantified. Here, we determine the REE contents in sludge collected from 63 wastewater treatment plants (WWTPs) across Switzerland. To quantify the industrial fraction of individual REEs in the sewage sludge, we develop two complementary approaches, based on REE ratios and REE pattern fitting. Unspecific (background) inputs, with REE patterns similar to the averaged REE pattern of soils collected across Switzerland, dominate the REE budget of most WWTPs. A few WWTPs receive significant REE inputs from specific industrial sources. Based on population equivalents of Switzerland, we estimate a total annual load of 4200 kg Cerium (Ce, 0.5 g Ce year-1 capita-1), with an industrial contribution of 2000 kg year-1. The latter agrees with estimates of probabilistic mass flow models for engineered nanoscale CeO2 particles discharged to the sewer network. About 7 kg year-1 of Samarium (Sm,total for Switzerland: 184 kg year-1 or 0.02 g Sm year-1 capita-1) and 3 kg year-1 of Europium (Eu,total for Switzerland: 44 kg year-1 or 0.005 g Eu year-1 capita-1) are assigned to industrial inputs from single WWTPs. Gadolinium (Gd) is used in the form of a stable complex as contrast agent in magnetic resonance imaging. Assuming 10% removal of Gd during wastewater treatment, we calculate an annual discharge of 90 kg of Gd from one individual WWTP to surface waters. WWTPs with exceptionally high industrial inputs of specific REEs warrant detailed investigations to identify the respective sources and to assess whether REE concentrations in effluents are elevated to the same degree.
Kaegi, R., Fierz, M., & Hattendorf, B. (2021). Quantification of nanoparticles in dispersions using transmission electron microscopy. Microscopy and Microanalysis, 27(3), 557-565. doi:10.1017/S1431927621000398, Institutional Repository

The quantification of the particle size and the number concentration (PNC) of nanoparticles (NPs) is key for the characterization of nanomaterials. Transmission electron microscopy (TEM) is often considered as the gold standard for assessing the size of NPs; however, the TEM sample preparation suitable for estimating the PNC based on deposited NPs is challenging. Here, we use an ultrasonic nebulizer (USN) to transfer NPs from aqueous suspensions into dried aerosols which are deposited on TEM grids in an electrostatic precipitator of an aerosol monitor. The deposition efficiency of the electrostatic precipitator was ≈2%, and the transport efficiency of the USN was ≈7%. Experiments using SiO2NPs (50-200 nm) confirmed an even deposition of the nebulized particles in the center of the TEM grids. PNCs of the SiO2NPs derived from TEM images underestimated the expected PNCs of the suspensions by a factor of up to three, most likely resulting from droplet coagulation and NP aggregation in the USN. Nevertheless, single particles still dominated the PNC. Our approach results in reproducible and even deposition of particles on TEM grids suitable for morphological analysis and allows an estimation of the PNC in the suspensions based on the number of particles detected by TEM.
Krause, A., Häfner, F., Augustin, F., & Udert, K. M. (2021). Qualitative risk analysis for contents of dry toilets used to produce novel recycling fertilizers. Circular Economy and Sustainability, 1, 1107-1146. doi:10.1007/s43615-021-00068-3, Institutional Repository

Human excreta are a sustainable, economical source of nutrients, and can be used to produce recycling fertilizer for horticulture by collecting and processing the contents of dry toilets. Herein, we discuss the key categories of risk associated with the main groups of materials commonly found in dry toilets. The study was part of the development of a German product standard for marketable and quality-assured recycling fertilizers from human excreta for use in horticulture. Particular attention is paid to ensuring that the fertilizer is epidemiologically and environmentally harmless and that the quality of the recycling fertilizer is adequate in terms of low pollution and nutrient availability. In sum, the risk of transmissible human pathogens lies within the human excreta, particularly feces; plant materials added during composting are of particular phytosanitary relevance; pharmaceutical residues in excrements and chemical additives are potential sources of pollutants; non-biodegradable contaminants can cause pollution and injury; and the horticultural risks involve mainly the ammonia emission potential and in some cases the salinity effects of urine. These risks can be reduced significantly (i) with education of users around proper operation of dry toilets and the consequences of adding inappropriate waste, (ii) with facilitation of proper use with general waste bins and clear instructions, and importantly (iii) by using modern sanitization and cleaning processes and testing for harmful substances under the guidance of local laws and regulations, ensuring safe and high-quality fertilizers. In conclusion, the benefits of using dry toilet contents to produce fertilizers for use in horticulture are unquestionable. Our analysis highlights the need to support recycling optimization and awareness for the purpose of a sustainable circular economy and to minimize the risk of harm to humans and the environment overall.
Kuehr, S., Diehle, N., Kaegi, R., & Schlechtriem, C. (2021). Ingestion of bivalve droppings by benthic invertebrates may lead to the transfer of nanomaterials in the aquatic food chain. Environmental Sciences Europe, 33(1), 35 (16 pp.). doi:10.1186/s12302-021-00473-3, Institutional Repository

Background: Manufactured nanomaterials (MNMs) are released into the environment in increasing quantities. Consequently, MNMs also reach the aquatic environment, where they can interact with different organisms. Previous studies have already shown that filter-feeding bivalves can ingest nanomaterials from the surrounding water leading to higher concentration of the material. Furthermore, they have been shown to be vectors for environmental chemicals and pathogens to other organisms, as their feces/pseudofeces (F/pF) play a crucial role as a food source for other species. We exposed bivalves (Corbicula sp.) to MNMs and performed experiments to investigate the possible transport of MNMs by their feces to the benthic amphipod Hyalella azteca. Silver (Ag) and gold (Au) nanoparticles (NPs) as well as fluorescent polystyrene nanoparticles were used in this study. They allowed the investigation of the metal content of the bivalves’ feces and the amphipods feeding on it, as well as the localization of the fluorescent particles in the body of the animals.
Results: Examination of the feces by fluorescence microscope and determination of the total metal content by inductively coupled plasma mass spectrometry (ICP-MS) showed a high accumulation of the exposed MNMs in the F/pF. The examination of fecal matter, using transmission electron microscopy confirmed the nanoparticulate character of the metals in the examined fecal matter. After exposure of amphipods to the MNMs containing fecal matter, the fluorescent MNMs were localized in the animals gut. The chronic exposure of juvenile amphipods over 21 days to feces enriched with Au MNMs caused significant effects on the growth of the amphipods. The transfer of both metals (Ag and Au) from the fecal matter to the amphipods was confirmed after total metal measurements.
Conclusion: Probably, for the first time, it has been shown that when exposed to MNMs bivalves can transfer these particles to other benthic species. Transfer is via released F/pF upon which the benthic species feed and thus could ingest the particles. The high concentrations of MNMs in the fecal matter raises concerns about the potential accumulation and transfer of the materials and associated ecotoxicological effects in invertebrates such as benthic amphipods.
Kuehr, S., Kaegi, R., Maletzki, D., & Schlechtriem, C. (2021). Testing the bioaccumulation potential of manufactured nanomaterials in the freshwater amphipod Hyalella azteca. Chemosphere, 263, 127961 (15 pp.). doi:10.1016/j.chemosphere.2020.127961, Institutional Repository

Standardized experimental approaches for the quantification of the bioaccumulation potential of nanomaterials in general and in (benthic) invertebrates in particular are currently lacking. We examined the suitability of the benthic freshwater amphipod Hyalella azteca for the examination of the bioaccumulation potential of nanomaterials. A flow-through test system that allows the generation of bioconcentration and biomagnification factors was applied. The feasibility of the system was confirmed in a 2-lab comparison study. By carrying out bioconcentration and biomagnification studies with gold, titanium dioxide and silver nanoparticles as well as dissolved silver (AgNO3) we were able to assess the bioaccumulation potential of different types of nanomaterials and their exposure pathways. For this, the animals were examined for their total metal body burden using inductively coupled mass spectroscopy (ICP-MS) and for the presence of nanoparticulate burdens using single-particle ICP-MS. The role of released ions was highlighted as being very important for the bioavailability and bioaccumulation of metals from nanoparticles for both examined uptake paths examined (bioconcentration and biomagnification). In 2018 a tiered testing strategy for engineered nanomaterials was proposed by Handy et al. that may allow a waiver of bioaccumulation fish studies using inter alia invertebrates. Data gained in studies carried out with invertebrates like the developed Hyalella azteca test may be included in this proposed tiered testing strategy.
Larsen, T. A., Riechmann, M. E., & Udert, K. M. (2021). State of the art of urine treatment technologies: a critical review. Water Research X, 13, 100114 (20 pp.). doi:10.1016/j.wroa.2021.100114, Institutional Repository

Over the last 15 years, urine treatment technologies have developed from lab studies of a few pioneers to an interesting innovation, attracting attention from a growing number of process engineers. In this broad review, we present literature from more than a decade on biological, physical-chemical and electrochemical urine treatment processes. Like in the first review on urine treatment from 2006, we categorize the technologies according to the following objectives: stabilization, volume reduction, targeted N-recovery, targeted P-recovery, nutrient removal, sanitization, and handling of organic micropollutants. We add energy recovery as a new objective, because extensive work has been done on electrochemical energy harvesting, especially with bio-electrochemical systems. Our review reveals that biological processes are a good choice for urine stabilization. They have the advantage of little demand for chemicals and energy. Due to instabilities, however, they are not suited for bathroom applications and they cannot provide the desired volume reduction on their own. A number of physical-chemical treatment technologies are applicable at bathroom scale and can provide the necessary volume reduction, but only with a steady supply of chemicals and often with high demand for energy and maintenance. Electrochemical processes is a recent, but rapidly growing field, which could give rise to exciting technologies at bathroom scale, although energy production might only be interesting for niche applications. The review includes a qualitative assessment of all unit processes. A quantitative comparison of treatment performance was not the goal of the study and could anyway only be done for complete treatment trains. An important next step in urine technology research and development will be the combination of unit processes to set up and test robust treatment trains. We hope that the present review will help guide these efforts to accelerate the development towards a mature technology with pilot scale and eventually full-scale implementations.
Magyar, P. M., Hausherr, D., Niederdorfer, R., Stöcklin, N., Wei, J., Mohn, J., … Lehmann, M. F. (2021). Nitrogen isotope effects can be used to diagnose N transformations in wastewater anammox systems. Scientific Reports, 11(1), 7850 (12 pp.). doi:10.1038/s41598-021-87184-0, Institutional Repository

Anaerobic ammonium oxidation (anammox) plays an important role in aquatic systems as a sink of bioavailable nitrogen (N), and in engineered processes by removing ammonium from wastewater. The isotope effects anammox imparts in the N isotope signatures (15N/14N) of ammonium, nitrite, and nitrate can be used to estimate its role in environmental settings, to describe physiological and ecological variations in the anammox process, and possibly to optimize anammox-based wastewater treatment. We measured the stable N-isotope composition of ammonium, nitrite, and nitrate in wastewater cultivations of anammox bacteria. We find that the N isotope enrichment factor 15ε for the reduction of nitrite to N2 is consistent across all experimental conditions (13.5‰ ± 3.7‰), suggesting it reflects the composition of the anammox bacteria community. Values of 15ε for the oxidation of nitrite to nitrate (inverse isotope effect, - 16 to - 43‰) and for the reduction of ammonium to N2 (normal isotope effect, 19-32‰) are more variable, and likely controlled by experimental conditions. We argue that the variations in the isotope effects can be tied to the metabolism and physiology of anammox bacteria, and that the broad range of isotope effects observed for anammox introduces complications for analyzing N-isotope mass balances in natural systems.
Mehrabi, K., Kaegi, R., Günther, D., & Gundlach-Graham, A. (2021). Emerging investigator series: automated single-nanoparticle quantification and classification: a holistic study of particles into and out of wastewater treatment plants in Switzerland. Environmental Science: Nano, 8(5), 1211-1225. doi:10.1039/d0en01066a, Institutional Repository

Single particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS), in combination with online microdroplet calibration, allows for the determination of particle number concentrations (PNCs) and the amount (i.e. mass) of ICP-MS-accessible elements in individual particles. Because sp-ICP-TOFMS analyses of environmental samples produce rich datasets composed of both single-metal nanoparticles (smNPs) and many types of multi-metal NPs (mmNPs), interpretation of these data is well suited to automated analysis schemes. Here, we present a new data analysis approach that includes: 1. automatic particle detection and elemental mass determinations based on online microdroplet calibration, 2. correction of false (randomly occurring) multi-metal associations caused by measurement of coincident but distinct NPs, and 3. unsupervised clustering analysis of mmNPs to identify unique classes of NPs based on their element compositions. To demonstrate the potential of our approach, we analyzed water samples collected from the influent and effluent of five wastewater treatment plants (WWTPs) across Switzerland. We determined elemental masses in individual NPs, as well as PNCs, to estimate the NP removal efficiencies of the individual WWTPs. From WWTP samples collected at two points in time, we found an average of 90% and 94% removal efficiencies of single-metal and multi-metal NPs, respectively. Between 5% to 27% of detected NPs were multi-metal; the most abundant particle types were those rich in Ce-La, Fe-Al, Ti-Zr, and Zn-Cu. Through hierarchical clustering, we identified NP classes conserved across all WWTPs, as well as particle types that are unique to one or a few WWTPs. These uniquely occurring particle types may represent point sources of anthropogenic NPs. We describe the utility of clustering analysis of mmNPs for identifying natural, geogenic NPs, and also for the discovery of new, potentially anthropogenic, NP targets.
Mehrabi, K., Kaegi, R., Günther, D., & Gundlach-Graham, A. (2021). Quantification and clustering of inorganic nanoparticles in wastewater treatment plants across Switzerland. Chimia, 75(7-8), 642-646. doi:10.2533/chimia.2021.642, Institutional Repository

Single particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry (sp-ICP-TOFMS), in combination with online microdroplet calibration, allows the determination of particle number concentrations (PNCs) and the masses of elements in individual particles. Because sp-ICP-TOFMS analyses of environmental samples produce rich datasets composed of both single-metal nanoparticles (smNPs) and many types of multi-metal NPs (mmNPs), interpretation of these data is well suited to automated analysis schemes. Here, we present a data analysis approach that includes automatic particle detection and elemental mass determinations based on online microdroplet calibration, and unsupervised clustering analysis of mmNPs to identify unique classes of NPs based on their element compositions. To demonstrate the potential of our approach, we analyzed wastewater samples collected from the influent and effluent of five wastewater treatment plants (WWTPs) across Switzerland. We determined elemental masses in individual NPs, as well as PNCs, to estimate the NP removal efficiencies of the individual WWTPs. Through hierarchical clustering, we identified NP classes conserved across all WWTPs; the most abundant particle types were those rich in Ce-La, Fe-Al, Ti-Zr, and Zn-Cu. In addition, we found particle types that are unique to one or a few WWTPs, which could indicate point sources of anthropogenic NPs.
Moraes Schambeck, C., Ribeiro da Costa, R. H., & Derlon, N. (2021). Phosphate removal from municipal wastewater by alginate-like exopolymers hydrogels recovered from aerobic granular sludge. Bioresource Technology, 333, 125167 (10 pp.). doi:10.1016/j.biortech.2021.125167, Institutional Repository

This worked assessed the potential of alginate-like exopolymers (ALE) hydrogels recovered from aerobic granular sludge (AGS) in removing compounds commonly present in municipal wastewater. Batch sorption experiments were performed with ALE hydrogels at different operating conditions. Results showed that ALE hydrogels can only remove phosphate, at removal efficiencies of up to 90.8% and practical loadings of 1.22 ± 0.07 mg PO43--P/g TSALE. Phosphate removal was observed even in the presence of competing ions. Moreover, neutral to acidic pH values strongly impaired the phosphate removal (28.9 ± 0.8% at pH = 6.00), while basic pH at around 8.50 was the most favourable (up to 90.8% at pH = 8.67). However, ALE hydrogels contributed to the increase in COD, total nitrogen and total phosphorus in the bulk liquid, what suggests that ALE need to be further tailored. Therefore, this study demonstrates that ALE represent a relevant approach for the recovery of phosphates from municipal wastewater.
Niederdorfer, R., Fragner, L., Yuan, L., Hausherr, D., Wei, J., Magyar, P., … Bürgmann, H. (2021). Distinct growth stages controlled by the interplay of deterministic and stochastic processes in functional anammox biofilms. Water Research, 200, 117225 (14 pp.). doi:10.1016/j.watres.2021.117225, Institutional Repository

Mainstream anaerobic ammonium oxidation (anammox) represents one of the most promising energy-efficient mechanisms of fixed nitrogen elimination from wastewaters. However, little is known about the exact processes and drivers of microbial community assembly within the complex microbial biofilms that support anammox in engineered ecosystems. Here, we followed anammox biofilm development on fresh carriers in an established 8m3 mainstream anammox reactor that is exposed to seasonal temperature changes (∼25-12°C) and varying NH4+ concentrations (5-25 mg/L). We use fluorescence in situ hybridization and 16S rRNA gene sequencing to show that three distinct stages of biofilm development emerge naturally from microbial community composition and biofilm structure. Neutral modelling and network analysis are employed to elucidate the relative importance of stochastic versus deterministic processes and synergistic and antagonistic interactions in the biofilms during their development. We find that the different phases are characterized by a dynamic succession and an interplay of both stochastic and deterministic processes. The observed growth stages (Colonization, Succession and Maturation) appear to be the prerequisite for the anticipated growth of anammox bacteria and for reaching a biofilm community structure that supports the desired metabolic and functional capacities observed for biofilm carriers already present in the system (∼100gNH4-N m3 d-1). We discuss the relevance of this improved understanding of anammox-community ecology and biofilm development in the context of its practical application in the start-up, configuration, and optimization of anammox biofilm reactors.
Niederdorfer, R., Hausherr, D., Palomo, A., Wei, J., Magyar, P., Smets, B. F., … Bürgmann, H. (2021). Temperature modulates stress response in mainstream anammox reactors. Communications Biology, 4(1), 23 (12 pp.). doi:10.1038/s42003-020-01534-8, Institutional Repository

Autotrophic nitrogen removal by anaerobic ammonium oxidizing (anammox) bacteria is an energy-efficient nitrogen removal process in wastewater treatment. However, full-scale deployment under mainstream conditions remains challenging for practitioners due to the high stress susceptibility of anammox bacteria towards fluctuations in dissolved oxygen (DO) and temperature. Here, we investigated the response of microbial biofilms with verified anammox activity to DO shocks under 20 °C and 14 °C. While pulse disturbances of 0.3 mg L−1 DO prompted only moderate declines in the NH4+ removal rates, 1.0 mg L−1 DO led to complete but reversible inhibition of the NH4+ removal activity in all reactors. Genome-centric metagenomics and metatranscriptomics were used to investigate the stress response on various biological levels. We show that temperature regime and strength of DO perturbations induced divergent responses from the process level down to the transcriptional profile of individual taxa. Community-wide gene expression differed significantly depending on the temperature regime in all reactors, and we found a noticeable impact of DO disturbances on genes involved in transcription, translation, replication and posttranslational modification at 20 °C but not 14 °C. Genome-centric analysis revealed that different anammox species and other key biofilm taxa differed in their transcriptional responses to distinct temperature regimes and DO disturbances.
Reynaert, E., Hess, A., & Morgenroth, E. (2021). Making waves: why water reuse frameworks need to co-evolve with emerging small-scale technologies. Water Research X, 11, 100094 (5 pp.). doi:10.1016/j.wroa.2021.100094, Institutional Repository

Novel technologies allow to reuse or recycle water for on-site applications such as toilet flushing, showering, or hand washing at the household- or building-scale. Many of these technologies have now reached technology readiness levels that require for verification and validation testing in the field. Results from such field tests of decentralized water reuse systems have been published over the past few years, and observed performance is often compared to quality targets from water reuse frameworks (WRFs). An inspection of ten recent journal publications reveals that targets from WRFs are often misinterpreted, and the emphasis of these publications is too often on demonstrating successful aspects of the technologies rather than critically evaluating the quality of the produced water. We hypothesize that some of these misinterpretations are due to ambiguous definition of scopes of WRFs (e.g., "unrestricted urban reuse") and unclear applicability for novel recycling systems that treat the water for applications that go beyond the reuse scopes defined in current WRFs. Additional challenges are linked to the verification of WRF quality targets in small-scale and decentralized systems under economic and organizational constraints. Current WRFs are not suitable for all possible reuse cases, and there is need for a critical discussion of quality targets and associated monitoring methods. As the scope of water reuse has expanded greatly over the past years, WRFs need to address new applications and advances in technology, including in monitoring capacities.
Riechmann, M. E., Ndwandwe, B., Greenwood, E. E., Reynaert, E., Morgenroth, E., & Udert, K. M. (2021). On-site urine treatment combining Ca(OH)2 dissolution and dehydration with ambient air. Water Research X, 13, 100124 (12 pp.). doi:10.1016/j.wroa.2021.100124, Institutional Repository

We present the results of three field tests and three laboratory tests of a new physical-chemical urine treatment system, which can recover all nutrients, while pathogens are inactivated. The system consists of two steps. In the first reactor, biological processes including urea hydrolysis are prevented by mixing fresh urine with calcium hydroxide (Ca(OH)2). Due to the high pH value and the high availability of calcium, phosphate can be recovered by precipitation. The high pH value also fosters the inactivation of microorganisms, including pathogens. In the second reactor, water is evaporated at low energy consumption by blowing unheated ambient air over the stabilized urine. Stabilization in the first reactor was successful in all field and laboratory tests. The pH value remained between 12 and 13, except for short dips due to shortages of Ca(OH)2. Nearly all phosphorus (92-96%) precipitated and could be recovered as calcium phosphate in the first reactor, while nitrogen and potassium overflowed with the urine into the evaporation reactor. The efficiency of the second treatment step was very different for field and laboratory experiments and depended on the duration of the experiment. During a four-day laboratory test, nitrogen recovery was 98%. In contrast, nitrogen recovery was only around 20% in the long-term field experiments. The high nitrogen losses occurred, because biological urea hydrolysis was not inhibited anymore, when the pH value in the second reactor decreased due to the dissolution of high amounts of carbon dioxide from the ambient air. Potassium was not subject to any significant loss, and the measured recovery in the solid evaporation product was 98%. Evaporation rates ranged between 50 g m-2 h-1 (RH = 82±13%, T = 12±6°C) and 130 g m-2 h-1 (RH = 60±19%, T = 24±5°C) in the three field tests. Apart from some disturbances due to low supply of Ca(OH)2, the urine module functioned without any substantial failures and was simple to maintain. The minimum consumption of Ca(OH)2 at full capacity was 6 g·L-1 urine and the electricity demand was 150 Wh kg-1 water evaporated from urine, resulting in operational costs of 0.05 EUR pers-1 d-1.
Russo, S., Besmer, M. D., Blumensaat, F., Bouffard, D., Disch, A., Hammes, F., … Villez, K. (2021). The value of human data annotation for machine learning based anomaly detection in environmental systems. Water Research, 206, 117695 (10 pp.). doi:10.1016/j.watres.2021.117695, Institutional Repository

Anomaly detection is the process of identifying unexpected data samples in datasets. Automated anomaly detection is either performed using supervised machine learning models, which require a labelled dataset for their calibration, or unsupervised models, which do not require labels. While academic research has produced a vast array of tools and machine learning models for automated anomaly detection, the research community focused on environmental systems still lacks a comparative analysis that is simultaneously comprehensive, objective, and systematic. This knowledge gap is addressed for the first time in this study, where 15 different supervised and unsupervised anomaly detection models are evaluated on 5 different environmental datasets from engineered and natural aquatic systems. To this end, anomaly detection performance, labelling efforts, as well as the impact of model and algorithm tuning are taken into account. As a result, our analysis reveals the relative strengths and weaknesses of the different approaches in an objective manner without bias for any particular paradigm in machine learning. Most importantly, our results show that expert-based data annotation is extremely valuable for anomaly detection based on machine learning.
Sutherland, C., Reynaert, E., Sindall, R. C., Riechmann, M. E., Magwaza, F., Lienert, J., … Udert, K. M. (2021). Innovation for improved hand hygiene: field testing the Autarky handwashing station in collaboration with informal settlement residents in Durban, South Africa. Science of the Total Environment, 796, 149024 (13 pp.). doi:10.1016/j.scitotenv.2021.149024, Institutional Repository

Safe and accessible water services for hand hygiene are critical to human health and well-being. However, access to handwashing facilities is limited in cities in the Global South, where rapid urbanisation, service backlogs, lack of infrastructure and capacity, and water scarcity impact on the ability of local governments to provide them. Community participation and the co-production of knowledge in the development of innovative technologies, which are aligned with Water, Sanitation and Hygiene (WASH) principles, can lead to more sustainable and socially-acceptable hand hygiene systems. This paper presents the outcomes of the testing of the Autarky handwashing station, a technology that provides onsite treatment and recycling of handwashing water, in an informal settlement in Durban, South Africa. The transdisciplinary research approach adopted enabled the participation of multiple stakeholders with different knowledge systems in the framing, testing and evaluation of the system. The process of co-producing knowledge, as well as the outcomes of the testing, namely high levels of functionality and social acceptability of the technology, supported the WASH principles. The evaluation revealed that the Autarky handwashing station is a niche intervention that improved access to safe and appealing handwashing facilities in an informal settlement. Its novel design, socially desirable features, reliability and ability to save water increased its acceptance in the community. The testing of the system in a real-world context revealed the value of including communities in knowledge production processes for technology innovation. Further work is required to ensure that real-time monitoring of system function is feasible before such systems can be implemented at larger scale.
Sutherland, C., Reynaert, E., Dhlamini, S., Magwaza, F., Lienert, J., Riechmann, M. E., … Sindall, R. C. (2021). Socio-technical analysis of a sanitation innovation in a peri-urban household in Durban, South Africa. Science of the Total Environment, 755, 143284 (12 pp.). doi:10.1016/j.scitotenv.2020.143284, Institutional Repository

The provision of water and sanitation for all that is safe, dignified, reliable, affordable and sustainable is a major global challenge. While centralized sewer-based sanitation systems remain the dominant approach to providing sanitation, the benefits of non-sewered onsite sanitation systems are increasingly being recognised. This paper presents the outcomes of the testing of the Blue Diversion Autarky Toilet (BDAT), a sanitation system providing hygiene and dignity without relying on water and wastewater infrastructure, in a peri-urban household in Durban, South Africa. The BDAT was used by a single household as their only form of sanitation during three months of technical and social testing. An analysis based on technical data in combination with interpretive, qualitative research methods revealed that the BDAT functioned well and achieved high levels of social acceptance in the test household. The flushing, cleanliness and odour-free nature of the sanitation technology, its functionality, the household's previous sanitation experience, and their experience with and understanding of water scarcity, were the main factors underpinning their positive response to this innovation in sanitation. The testing process resulted in broader developmental benefits for the household, including improved basic services due to the upgrading of the electrical and existing sanitation system, social learning, and improved relationships between household members and the local state. A transdisciplinary research process, which emerged through the assessment, enabled the integration of different forms of knowledge from multiple actors to address the complexity of problems related to the development of socially just sanitation. The benefit of engaging with societal actors in sanitation innovation and assessing its outcomes using both the technical and social sciences is evident in this paper.
Tang, X., Pronk, W., Traber, J., Liang, H., Li, G., & Morgenroth, E. (2021). Integrating granular activated carbon (GAC) to gravity-driven membrane (GDM) to improve its flux stabilization: respective roles of adsorption and biodegradation by GAC. Science of the Total Environment, 768, 144758 (10 pp.). doi:10.1016/j.scitotenv.2020.144758, Institutional Repository

As a low-maintenance and cost-effective process, gravity-driven membrane (GDM) filtration is a promising alternative for decentralized drinking water supply, while the low flux impedes its extensive application. In order to address such issue, an integrated process consisting of granular activated carbon (GAC) layer and GDM was developed. The performance of virgin (fresh GAC) or preloaded GAC (saturated GAC) was compared. Flux stabilization was observed both in the fresh and saturated GAC/GDM process during long-term filtration and their stable fluxes were both improved by approximately 50% relative to the GDM control. Moreover, integrating GAC with GDM contributed to efficient removals for dissolved organic compounds (DOC), assimilable organic carbon (AOC) and low molecular weight substances both in fresh and saturated GAC/GDM filtration. Compared to GDM control, coupling GAC to GDM could significantly reduce the concentrations of extracellular polymeric substances (EPS) and total cell counts (TCC) within the biofouling layer, and engineer highly heterogeneous structures of biofouling layer on the membrane surface. In the fresh GAC/GDM process, the improved flux obtained was mainly related to less coverage of biofouling layer and lower EPS concentrations due to efficient removals of membrane foulants by GAC adsorption. The achieved higher stable flux can be maintained during long-term filtration (after GAC saturation) owing to the combined effects of EPS reduction and formation of highly heterogeneous structures of biofouling layer in the saturated GAC/GDM system. Overall, the integrated GAC/GDM process can hopefully facilitate improvements both in the stabilized flux and permeate quality, with practical relevance for GDM applications in decentralized drinking water supply.
Ward, B. J., Andriessen, N., Tembo, J. M., Kabika, J., Grau, M., Scheidegger, A., … Strande, L. (2021). Predictive models using "cheap and easy" field measurements: can they fill a gap in planning, monitoring, and implementing fecal sludge management solutions?. Water Research, 196, 116997 (12 pp.). doi:10.1016/j.watres.2021.116997, Institutional Repository

The characteristics of fecal sludge delivered to treatment plants are highly variable. Adapting treatment process operations accordingly is challenging due to a lack of analytical capacity for characterization and monitoring at many treatment plants. Cost-efficient and simple field measurements such as photographs and probe readings could be proxies for process control parameters that normally require laboratory analysis. To investigate this, we evaluated questionnaire data, expert assessments, and simple analytical measurements for fecal sludge collected from 421 onsite containments. This data served as inputs to models of varying complexity. Random forest and linear regression models were able to predict physical-chemical characteristics including total solids (TS) and ammonium (NH4+-N) concentrations, and solid-liquid separation performance including settling efficiency and filtration time (R2 from 0.51-0.66) based on image analysis of photographs (sludge color, supernatant color, and texture) and probe readings (conductivity (EC) and pH). Supernatant color was the best predictor of settling efficiency and filtration time, EC was the best predictor of NH4+-N, and texture was the best predictor of TS. Predictive models have the potential to be applied for real-time monitoring and process control if a database of measurements is developed and models are validated in other cities. Simple decision tree models based on the single classifier of containment type can also be used to make predictions about citywide planning, where a lower degree of accuracy is required.
Wielinski, J., Gogos, A., Voegelin, A., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Release of gold (Au), silver (Ag) and cerium dioxide (CeO2) nanoparticles from sewage sludge incineration ash. Environmental Science: Nano, 8(11), 3220-3232. doi:10.1039/D1EN00497B, Institutional Repository

Engineered nanoparticles (NPs) that are released into wastewater are retained by wastewater treatment plants (WWTPs) and accumulate in sewage sludge. Increasing shares of sludge are incinerated and landfilled, especially in industrialized countries. It is debated whether certain types of NPs can outlive the incineration process and subsequently be released from sewage sludge ash (SSA) landfills. To investigate the release of different types of NPs from SSA, we spiked gold (Au), silver (Ag) and cerium dioxide (CeO2) NPs to a pilot WWTP increasing the Au, Ag and Ce concentrations to 30, 43 and 389 mg kg-1 (dry matter basis) in the digested sludge. The spiked sludge was incinerated in a pilot fluidized bed reactor resulting in SSA with Au, Ag and Ce concentrations of 61, 103 and 854 mg kg-1. In addition, two sludge samples from a full-scale WWTP with Au concentrations of 5 and 16 mg kg-1 were incinerated, resulting in SSA with 9 mg kg-1 and 30 mg kg-1 Au. The spiked Au-NPs remain largely unaltered during the wastewater treatment and incineration process, whereas Ag-NPs and CeO2-NPs undergo transformation. During simulated landfill leaching in columns flushed with 400 to 500 pore volumes of artificial rainwater, Ag and Ce were retained in the ash, whereas about 17% of the spiked Au was released, mainly in particulate form. Lower fractions of mostly particulate Au were released from the ashes (3 and 9%) of unspiked SSA. In conclusion, unaltered Au-NPs significantly leach from landfilled SSA, whereas the incorporation of Ag-NPs and CeO2-NPs as transformed species into the SSA matrix limits the leaching of (nano)particulate and dissolved Ag and Ce compounds.
Wielinski, J., Voegelin, A., Grobéty, B., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Transformation of TiO2 (nano)particles during sewage sludge incineration. Journal of Hazardous Materials, 411, 124932 (14 pp.). doi:10.1016/j.jhazmat.2020.124932, Institutional Repository

Titanium dioxide (TiO2) (nano)particles are produced in large quantities and their potential impacts on ecosystems warrants investigations into their fate after disposal. TiO2 particles released into wastewater are retained by wastewater treatment plants and accumulate in digested sludge, which is increasingly incinerated in industrialized countries. Therefore, we investigated the changes of the Ti-speciation during incineration of as-received sludge and of sludge spiked with anatase (d=20–50 nm) or rutile (d=200–400 nm) using X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). In the as-received sludge, rutile and anatase were the dominant Ti bearing minerals and both remained unaffected by the anaerobic treatment. During incineration, Ti reacts with hematite to members of the hematite-ilmenite solid solution series (Hem-Ilm). Up to 80% of the Ti spiked as anatase transformed into Hem-Ilm, a distorted 6-fold coordinated Ti (Ti(IV)sulfate) and rutile during incineration. Up to 30% and 60% of rutile transformed into Hem-Ilm and Ti(IV)sulfate represented phases in fly and bottom ash, respectively. Fe and Ti were spatially correlated in ash derived from as-received and anatase spiked sludge, whereas only a thin layer of the spiked rutile reacted with Fe, in line with XAS data. This study highlights the transient nature of nano-Ti species during sewage sludge incineration.
Zhang, L., Graham, N., Derlon, N., Tang, Y., Siddique, M. S., Xu, L., & Yu, W. (2021). Biofouling by ultra-low pressure filtration of surface water: the paramount role of initial available biopolymers. Journal of Membrane Science, 640, 119740 (9 pp.). doi:10.1016/j.memsci.2021.119740, Institutional Repository

Biofouling layer (i.e., biofilm) is an inevitable presence for the membrane filtration processes. In this study, we elucidated biofouling formation from the perspective of affecting the attachment of bacteria for the first time, whereby the role of initial available biopolymers was revealed. Results demonstrated that the presence of initial available biopolymers increased the abundance of the genus Caulobacter, which was capable of mineralizing biopolymers; whereas, for the typically oligotrophic species of Polynucleobacter, it exhibited low abundance. Greater concentrations of polysaccharides and proteins were accumulated in the biofouling layer, when provided with initial biopolymers, and the biofilm structure was more heterogeneous with larger pore size and higher thickness. Thereby, the corresponding filtration system exhibited greater permeability and better removal performance of organics. Collectively, the initial available biopolymers altered the attachment conditions for the bacteria, which subsequently impacted the bacterial community, and in turn biofilm composition, physical structure and filtration performance.
Ziemba, C., Sharma, P., Ahrens, T., Reynaert, E., & Morgenroth, E. (2021). Disruptions in loading and aeration impact effluent chlorine demand during biological greywater recycling. Water Research X, 11, 100087 (10 pp.). doi:10.1016/j.wroa.2020.100087, Institutional Repository

Greywater recycling systems designed for high-quality applications, such as hand washing, must deliver microbially safe and aesthetically acceptable water under the challenging operating conditions present where such systems are needed most urgently. As chlorination is the most popular strategy for reducing bacterial concentrations in greywater, understanding chlorination in the context of disruptive and challenging operation is essential to designing robust treatment. In this study, we have examined how disruptions through overall increased loading, interrupted aeration and increased ammonia loading have impacted the chlorine demand of the water produced by a greywater recycling system. We also presented concentrations of significant chemicals that contributed to this chlorine demand. The results indicate that a 1 d period with 8 times (8x) the normal design loading produced a peak chlorine demand of 0.74 mg Cl2/L, which is approximately double the baseline value. While this chlorine demand can be overcome by adding more chlorine, tests involving disruptions in aeration or feeding additional ammonia into the bioreactor produced much greater increases (>30x). The risks of increased chlorine demand on microbial safety can be overcome by limiting ammonia inputs to the system, providing backup systems to ensure sufficient aeration, or through additional anti-bacterial measures that do not depend on maintaining residual chlorine.
Özel Duygan, B. D., Udert, K. M., Remmele, A., & McArdell, C. S. (2021). Removal of pharmaceuticals from human urine during storage, aerobic biological treatment, and activated carbon adsorption to produce a safe fertilizer. Resources, Conservation and Recycling, 166, 105341 (10 pp.). doi:10.1016/j.resconrec.2020.105341, Institutional Repository

Urine has great potential to be an effective fertilizer due to its high nutrient content, however, it can contain potentially worrying pharmaceuticals. Our objective was to study whether urine storage and aerobic biological treatment, i.e. nitrification, was sufficient to remove pharmaceuticals or an additional treatment with activated carbon was necessary to produce a fertilizer from urine. We investigated the abatement of twelve pharmaceuticals, including antibiotics and antivirals, in laboratory experiments representing the treatment steps of anaerobic storage of source-separated human urine, stabilization using partial and full nitrification under acclimatized and non-acclimatized conditions, and treatment of nitrified urine using powdered activated carbon (PAC). Two-month-long-term storage of urine was insufficient to substantially degrade the pharmaceuticals, except for hydrochlorothiazide (>90%). In the partial and full nitrification fed-batch reactors, atazanavir, ritonavir, and clarithromycin were rapidly removed, with biotransformation rate constants greater than 10 L gSS−1d−1. Darunavir, emtricitabine, trimethoprim, N4-acetylsulfamethoxazole, sulfamethoxazole, atenolol, diclofenac, and hydrochlorothiazide were degraded slowly, with biotransformation rate constants of < 1 L gSS−1d−1. With 200 mg PAC L−1, at least 90% of each investigated pharmaceutical was removed. Yeast estrogen screen tests and bioluminescence inhibition tests revealed efficient removal of estrogenicity (99%) and toxicity (56%) using nitrification, and a reduction of 89% and 64%, respectively, using 200 mg PAC L−1. With our study, we provide biotransformation rate constants of compounds never previously investigated. We also show that a combination of nitrification and PAC adsorption enables the production of a safe fertilizer with sufficiently low pharmaceutical concentrations and no removal of beneficial nutrients.
Al-Sid-Cheikh, M., Rowland, S. J., Kaegi, R., Henry, T. B., Cormier, M. A., & Thompson, R. C. (2020). Synthesis of 14C-labelled polystyrene nanoplastics for environmental studies. Communications Materials, 1(1), 97 (8 pp.). doi:10.1038/s43246-020-00097-9, Institutional Repository

Available analytical methods cannot detect nanoplastics at environmentally realistic concentrations in complex matrices such as biological tissues. Here, we describe a one-step polymerization method, allowing direct radiolabeling of a sulfonate end-capped nano-sized polystyrene (nPS; proposed as a model nanoplastic particle representing negatively charged nanoplastics). The method, which produces nanoplastics trackable in simulated environmental settings which have already been used to investigate the behavior of a nanoplastic in vivo in a bivalve mollusc, was developed, optimized and successfully applied to synthesis of 14C-labeled nPS of different sizes. In addition to a description of the method of synthesis, we describe the details for quantification, mass balance and recovery of the labelled particles from complex matrices offered by the radiolabelling approach. The radiolabeling approach described here, coupled to use of a highly sensitive autoradiographic method for monitoring nanoplastic body burden and distributions, may provide a valuable procedure for investigating the environmental pathways followed by negatively charged nanoplastics at low predicted environmental concentrations. Whether the behaviour of the synthetic nPS manufactured here, synthesised using a very common inititator, represents that of manufactured nPS found in the environment, remains to be seen.
Bisinella de Faria, A. B., Besson, M., Ahmadi, A., Udert, K. M., & Spérandio, M. (2020). Dynamic influent generator for alternative wastewater management with urine source separation. Journal of Sustainable Water in the Built Environment, 6(2), 04020001 (26 pp.). doi:10.1061/JSWBAY.0000904, Institutional Repository

The simulation of wastewater treatment plants allows obtaining predictive results when one needs to understand, evaluate, optimize, or design a plant. However, one of the bottlenecks of simulation feasibility is to obtain reliable and dynamic influent data. This difficulty is even more important when alternative scenarios are considered, such as source-separated streams. The present paper offers an influent generator to simulate scenarios where urine is separated at the source and at a user-specified level of retention. The proposed tool contains several blocks to include different contributions (household and industrial wastewater) and, due to its flexibility, allows the user to easily modify the parameters to fit other case studies. The tool allowed generating dynamic, long-term, and predictive data for both urine and wastewater streams. Also, the extensive set of state variables ensured the generation of influents for different modeling platforms.
Bogler, A., Packman, A., Furman, A., Gross, A., Kushmaro, A., Ronen, A., … Bar-Zeev, E. (2020). Rethinking wastewater risks and monitoring in light of the COVID-19 pandemic. Nature Sustainability, 3, 981-990. doi:10.1038/s41893-020-00605-2, Institutional Repository

The COVID-19 pandemic has severely impacted public health and the worldwide economy. Converging evidence from the current pandemic, previous outbreaks and controlled experiments indicates that SARS-CoVs are present in wastewater for several days, leading to potential health risks via waterborne and aerosolized wastewater pathways. Conventional wastewater treatment provides only partial removal of SARS-CoVs, thus safe disposal or reuse will depend on the efficacy of final disinfection. This underscores the need for a risk assessment and management framework tailored to SARS-CoV-2 transmission via wastewater, including new tools for environmental surveillance, ensuring adequate disinfection as a component of overall COVID-19 pandemic containment.
Britschgi, L., Villez, K., Schrems, P., & Udert, K. M. (2020). Electrochemical nitrite sensing for urine nitrification. Water Research X, 9, 100055 (30 pp.). doi:10.1016/j.wroa.2020.100055, Institutional Repository

Sensing nitrite in-situ in wastewater treatment processes could greatly simplify process control, especially during treatment of high-strength nitrogen wastewaters such as digester supernatant or, as in our case, urine. The two technologies available today, i.e. an on-line nitrite analyzer and a spectrophotometric sensor, have strong limitations such as sample preparation, cost of ownership and strong interferences. A promising alternative is the amperometric measurement of nitrite, which we assessed in this study. We investigated the sensor in a urine nitrification reactor and in ex-situ experiments. Based on theoretical calculations as well as a practical approach, we determined that the critical nitrite concentrations for nitrite oxidizing bacteria lie between 12 and 30 mgN/L at pH 6 to 6.8. Consequently, we decided that the sensor should be able to reliably measure concentrations up to 50 mgN/L, which is about double the value of the critical nitrite concentration. We found that the influences of various ambient conditions, such as temperature, pH, electric conductivity and aeration rate, in the ranges expected in urine nitrification systems, are negligible. For low nitrite concentrations, as expected in municipal wastewater treatment, the tested amperometric nitrite sensor was not sufficiently sensitive. Nevertheless, the sensor delivered reliable measurements for nitrite concentrations of 5-50 mgN/L or higher. This means that the amperometric nitrite sensor allows detection of critical nitrite concentrations without difficulty in high-strength nitrogen conversion processes, such as the nitrification of human urine.
Burdon, F. J., Bai, Y., Reyes, M., Tamminen, M., Staudacher, P., Mangold, S., … Stamm, C. (2020). Stream microbial communities and ecosystem functioning show complex responses to multiple stressors in wastewater. Global Change Biology, 26(11), 6363-6382. doi:10.1111/gcb.15302, Institutional Repository

Multiple anthropogenic drivers are changing ecosystems globally, with a disproportionate and intensifying impact on freshwater habitats. A major impact of urbanization are inputs from wastewater treatment plants (WWTPs). Initially designed to reduce eutrophication and improve water quality, WWTPs increasingly release a multitude of micropollutants (MPs; i.e., synthetic chemicals) and microbes (including antibiotic‐resistant bacteria) to receiving environments. This pollution may have pervasive impacts on biodiversity and ecosystem services. Viewed through multiple lenses of macroecological and ecotoxicological theory, we combined field, flume, and laboratory experiments to determine the effects of wastewater (WW) on microbial communities and organic‐matter processing using a standardized decomposition assay. First, we conducted a mensurative experiment sampling 60 locations above and below WWTP discharges in 20 Swiss streams. Microbial respiration and decomposition rates were positively influenced by WW inputs via warming and nutrient enrichment, but with a notable exception: WW decreased the activation energy of decomposition, indicating a "slowing" of this fundamental ecosystem process in response to temperature. Second, next‐generation sequencing indicated that microbial community structure below WWTPs was altered, with significant compositional turnover, reduced richness, and evidence of negative MP influences. Third, a series of flume experiments confirmed that although diluted WW generally has positive influences on microbial‐mediated processes, the negative effects of MPs are "masked" by nutrient enrichment. Finally, transplant experiments suggested that WW‐borne microbes enhance decomposition rates. Taken together, our results affirm the multiple stressor paradigm by showing that different aspects of WW (warming, nutrients, microbes, and MPs) jointly influence ecosystem functioning in complex ways. Increased respiration rates below WWTPs potentially generate ecosystem "disservices" via greater carbon evasion from streams and rivers. However, toxic MP effects may fundamentally alter ecological scaling relationships, indicating the need for a rapprochement between ecotoxicological and macroecological perspectives.
Cai, Y., Yang, T., Mitrano, D. M., Heuberger, M., Hufenus, R., & Nowack, B. (2020). Systematic study of microplastic fiber release from 12 different polyester textiles during washing. Environmental Science and Technology, 54(8), 4847-4855. doi:10.1021/acs.est.9b07395, Institutional Repository

Microplastic fibers (MPFs) have been found to be a major form of microplastics in freshwaters, and washing of synthetic textiles has been identified as one of their main sources. The aim of this work was to use a panel of 12 different textiles of representative fibers and textile types to investigate the source(s) of the MPF during washing. Using standardized washing tests, textile swatches tailored using five different cutting/sewing methods were washed up to 10 times. The MPF quantity and fiber length were determined using image analysis. The 12 textiles demonstrated great variability in MPF release, ranging from 210 to 72,000 MPF/g textile per wash. The median MPF length ranged from 165 to 841 μm. The number of released MPF was influenced by the cutting method, where scissor-cut samples released 3-21 times higher numbers of MPF than the laser-cut samples. The textiles with mechanically processed surfaces (i.e., fleece) released significantly more (p-value < 0.001) than the textiles with unprocessed surfaces. For all textiles, the MPF release decreased with repeated wash cycles, and a small continuous fiber release was observed after 5-6 washings, accompanied by a slight increase in the fiber length. The decrease in the number of MPF released is likely caused by depletion of the production-inherited MPFs trapped within the threads or the textile structure. The comparison of MPF release from laser-cut samples, which had sealed edges, and the other cutting methods allowed us to separate the contributions of the edge- and surface-sourced fibers from the textiles to the total release. On an average, 84% (range 49-95%) of the MPF release originated from the edges, highlighting the importance of the edge-to-surface ratio when comparing different release studies. The large contribution of the edges to the total release offers options for technical solutions which have the possibility to control MPF formation throughout the textile manufacturing chain by using cutting methods which minimize MPF formation.
Cai, Y., Mitrano, D. M., Heuberger, M., Hufenus, R., & Nowack, B. (2020). The origin of microplastic fiber in polyester textiles: the textile production process matters. Journal of Cleaner Production, 267, 121970 (12 pp.). doi:10.1016/j.jclepro.2020.121970, Institutional Repository

Microplastic fibers (MPF) are often detected in waste water treatment plants and environmental samples, which implies a pathway of MPF release from domestic washing of textiles into the environment. Although there are many textile washing/release studies, it is still unclear to what extent the liberated MPFs originate from processes during washing (e.g. abrasion) or rather from processes earlier in the textile supply chain. Understanding the origin of MPFs is important since different MPF formation mechanisms would lead to different mitigation strategies. Therefore, the aim of our study was to investigate the presence of MPFs in various intermediate and finished polyester textiles products. In this study, we developed a sonication extraction method to quantify and characterize extractable MPFs already present in the textiles (i.e. manufacturing related MPFs). To identify the manufacturing process responsible for the MPF formation, this study included 18 representative products along the textile production line. The extraction dynamics of MPFs for all materials were investigated by ultrasonication. The number of extracted MPFs ranged from 15 MPF/g for a filament to 45'400 MPF/g for a scissor-cut microfiber textile. We found that a rotor yarn exhibited an elevated number of extracted MPFs (4'310 MPF/g) compared to other types of yarns (160-230 MPFs/g), suggesting that the rotor spinning may be a critical step responsible for MPF formation. On average, five times more MPFs could be extracted from textiles with processed surfaces (such as Fleece, Plain brushed and Microfiber) compared to those with unprocessed surfaces. This suggests that abrasive friction during production may be another critical factor for MPF formation. Furthermore, scissor-cut textiles demonstrated three to 31 times higher number of extracted MPFs than laser-cut textiles, enabling us to quantitatively discriminate between the contribution of MPFs from the textile surface opposed to those originating from the textile edges. The majority of the extracted MPFs were found to be between 100 and 800 μm in length. The results of this study may help to reduce the MPF release from textiles by modifications throughout the production and finishing process.
Domagała, K., Jacquin, C., Borlaf, M., Sinnet, B., Julian, T., Kata, D., & Graule, T. (2020). Efficiency and stability evaluation of Cu2O/MWCNTs filters for virus removal from water. Water Research, 179, 115879 (10 pp.). doi:10.1016/j.watres.2020.115879, Institutional Repository

Both multi-walled carbon nanotubes (MWCNTs) and metal or metal oxides have demonstrated virus removal efficacy in drinking water applications. In this study, MWCNTs were coated with copper(I) oxide (Cu2O) using three distinct synthesis procedures (copper ion attachment, copper hydroxide precipitation, and [Cu(NH3)4]2+ complex attachment) and virus removal efficacy (using MS2 bacteriophages) was evaluated. All synthesis procedures resulted in the presence of adsorbed, nanosized Cu2O particles on the MWCNTs, shown using X-ray diffraction. Further, transmission electron microscopy confirmed uniform copper(I) oxide distribution along the MWCNTs for all three materials. Virus removal efficacy was assessed for all three synthesised composites both before and after material conditioning (filtering for at least 24 h/280 mL/h), and accounting for additional MS2 inactivation in the permeate due to continued copper inactivation from dissolved/desorbed copper in permeate (time-control). Material conditioning influenced virus removal, with the first litres of water containing higher concentrations of copper than the sixth litres of water, suggesting excess or non-bonded copper species dissolve from filters. Higher copper dissolution was observed for water at pH 5 than at pH 7, which decreased with time. Copper dissolution most likely caused an associated decrease in copper adsorbed to MWCNTs in the filters, which may explain the observed lower MS2 removal efficacy after conditioning. Additionally, the time-control study (immediately after filtration as compared to 2 h after filtration) highlighted continued MS2 inactivation in the permeate over time. The obtained results indicate that the synthesis procedure influences virus removal efficacy for MWCNTs coated with copper oxides and that virus removal is likely due to not only virus electrostatic adsorption to the coated MWCNTs, but also through antiviral properties of copper which continues to act in the permeate. In conclusion, it is highly important to revise the methods of testing filter materials for virus removal, as well as procedure for virus concentration evaluation.
Dörner, L., Schmutz, P., Kägi, R., Kovalenko, M. V., & Jeurgens, L. P. H. (2020). Electrophoretic deposition of nanoporous oxide coatings from concentrated CuO nanoparticle dispersions. Langmuir, 36(28), 8075-8085. doi:10.1021/acs.langmuir.0c00720, Institutional Repository

Electrophoretic deposition (EPD) of nanoporous oxide coatings is an interesting research avenue owing to the experimental simplicity and broad scope of applications and materials. In this study, the properties of concentrated (up to 5000 mg/L), nonaqueous CuO nanoparticle (NP) dispersions were tailored to produce micrometer-thick, nanoporous CuO films by EPD. In particular, we performed a systematic investigation of the electrophoretic mobilities and size distributions of dispersed CuO aggregates and developing agglomerates in different organic solvents for concentrations ranging from 50 to 5000 mg/L with and without surfactant addition. Time-resolved dynamic light scattering analyses showed that aggregate mobilities and agglomeration rates decrease with increasing hydrocarbon chain length of the organic solvent (from ethanol to hexanol) and thus with increasing viscosity. The highest electrophoretic mobility was obtained for CuO NP aggregates and agglomerates dispersed in ethanol as a solvent. However, the addition of ≥0.5 wt % acetylacetone as a surfactant is required to stabilize these dispersions for subsequent EPD and at the same time introduce a net attractive (electrostatic) interaction between neighboring agglomerates on the substrate to promote layer formation during the EPD step. The produced micrometer-thick nanoporous CuO coatings can serve as high surface area nanostructured materials or nanoporous scaffolds in catalysis, combustion, propellants, and nanojoining.
Frehland, S., Kaegi, R., Hufenus, R., & Mitrano, D. M. (2020). Long-term assessment of nanoplastic particle and microplastic fiber flux through a pilot wastewater treatment plant using metal-doped plastics. Water Research, 182, 115860 (9 pp.). doi:10.1016/j.watres.2020.115860, Institutional Repository

In recent years, several studies have investigated the flux of particulate plastic through municipal waste water treatment plants (WWTP). Challenges related to time consuming analytical methods have limited the number of sampling points and detection limits have hampered quantification of nanoplastic and microplastic fiber fluxes through WWTPs. By synthesizing nanoplastic particles and microplastic fibers labeled with a rare metal (Pd and In, respectively) which can be measured as a proxy for the plastic itself, we have circumvented major analytical pitfalls associated with (micro)plastic measurements. In this study, we spiked the labeled materials to a pilot WWTP mimicking the activated sludge process (nitrification, de-nitrification and secondary clarification). Using a mass flow model for WWTP sludge, we assessed the behavior of particulate plastic in relation to the removal of organic matter. Triplicate samples were collected from the mixed liquor and from the effluent at least twice weekly over the entire experimental run time of 40 d. Our findings show that in discrete grab samples during steady state conditions, at least 98% of particulate plastics were associated with the biosolids. A positive correlation between total suspended solids (TSS) and plastic concentrations was observed in the sludge as well as in the effluent. Because of the strong association between particulate plastic and TSS, TSS removal is likely a good indicator of plastic removal in a full scale WWTP. Therefore, additional process steps in a full-scale WWTP which further reduce the TSS load will likely retain nanoplastic particles and microplastic fibers effectively and consequently increase the removal rates.
Fringer, V. S., Fawcett, L. P., Mitrano, D. M., & Maurer-Jones, M. A. (2020). Impacts of nanoplastics on the viability and riboflavin secretion in the model bacteria Shewanella oneidensis. Frontiers in Environmental Science, 8, 97 (11 pp.). doi:10.3389/fenvs.2020.00097, Institutional Repository

Characterizing the impact of nanoplastics to organism health is important to understand the consequences of the environmental plastic waste problem. This article examines the impact of nano-polystyrene (nano-PS; 159 ± 0.9 nm diameter) to ecologically relevant bacteria Shewanella oneidensis. Bacterial viability was evaluated using a growth-based assay. Riboflavin secretion is a critical cell function of S. oneidensis, serving as an electron mediator in anaerobic respiration and/or as a signaling molecule when the bacteria are under stress. Thus, changes in cellular function were monitored through riboflavin secretion in order to evaluate toxic responses that may not result in cell death. Under aerobic and anaerobic exposures (4, 8, or 12 h), the viability of the S. oneidensis was minimally changed as compared to the control, while the concentration of riboflavin secreted varied with exposure dose. In order to determine if this was a specific response to nanoplastic particles, opposed to a response to either particles or plastic more generally, we exposed the system to colloidal TiO2 nanoparticles and polystyrene and polyethylene thin films. We confirmed that riboflavin secretion trends were specific to nano-PS and not to these other materials, which showed no significant changes. We investigated the association of the nano-PS with ICP-MS using Pd that was chemically incorporated into the model nanoplastics. While 59.2% of the nano-PS were found in the non-cellular culture media, 7.0 and 6.6% was found associated with the loosely and tightly bound extracellular polymeric substance, respectively. There was significantly more nano-PS (10.9%) strongly associated with the cells. Taken together, we found that nano-PS had minimal impacts to viability but caused a significant change in the function of S. oneidensis that can be related to the nano-PS attached or in proximity to the bacterium. These trends are consistent between aerobic and anaerobic cultures, signifying that the stress response of S. oneidensis can be generalized between different environmental compartments. This work highlights that the association of nanoplastic materials with microorganisms may modify the cellular function that could ultimately be an impact to ecosystem health.
Geitner, N. K., Ogilvie Hendren, C., Cornelis, G., Kaegi, R., Lead, J. R., Lowry, G. V., … Wiesner, M. R. (2020). Harmonizing across environmental nanomaterial testing media for increased comparability of nanomaterial datasets. Environmental Science: Nano, 7(1), 13-36. doi:10.1039/c9en00448c, Institutional Repository

The chemical composition and properties of environmental media determine nanomaterial (NM) transport, fate, biouptake, and organism response. To compare and interpret experimental data, it is essential that sufficient context be provided for describing the physical and chemical characteristics of the setting in which a nanomaterial may be present. While the nanomaterial environmental, health and safety (NanoEHS) field has begun harmonization to allow data comparison and re-use (e.g. using standardized materials, defining a minimum set of required material characterizations), there is limited guidance for standardizing test media. Since most of the NM properties driving environmental behaviour and toxicity are medium-dependent, harmonization of media is critical. A workshop in March 2016 at Duke University identified five categories of test media: aquatic testing media, soil and sediment testing media, biological testing media, engineered systems testing media and product matrix testing media. For each category of test media, a minimum set of medium characteristics to report in all NM tests is recommended. Definitions and detail level of the recommendations for specific standardized media vary across these media categories. This reflects the variation in the maturity of their use as a test medium and associated measurement techniques, variation in utility and relevance of standardizing medium properties, ability to simplify standardizing reporting requirements, and in the availability of established standard reference media. Adoption of these media harmonization recommendations will facilitate the generation of integrated comparable datasets on NM fate and effects. This will in turn allow testing of the predictive utility of functional assay measurements on NMs in relevant media, support investigation of first principles approaches to understand behavioral mechanisms, and support categorization strategies to guide research, commercial development, and policy.
Gogos, A., Wielinski, J., Voegelin, A., von der Kammer, F., & Kaegi, R. (2020). Quantification of anthropogenic and geogenic Ce in sewage sludge based on Ce oxidation state and rare earth element patterns. Water Research X, 9, 100059 (8 pp.). doi:10.1016/j.wroa.2020.100059, Institutional Repository

Emissions of Ce from anthropogenic activities (anthropogenic Ce) into urban wastewater systems and the environment result from its widespread industrial use (abrasives, catalysts, nanotechnology). Because Ce in sewage sludge can also be of geogenic origin, the quantification of anthropogenic Ce in sewage sludge remains elusive. In this study, we evaluated the suitability of Ce oxidation state and rare earth element (REE) patterns for the quantification of anthropogenic Ce fractions in sewage sludge. A diverse set of soil samples served to gain baseline information on geogenic Ce. Geogenic Ce in the soils was characterized by high Ce(III) fractions (≥70%) and their REE patterns were comparable to the REE patterns of the upper continental crust. The sewage sludges contained on average ∼80% Ce(IV) (range 18–108%), pointing to the importance of anthropogenic inputs of Ce(IV). The quantification of the anthropogenic Ce fraction based on Ce oxidation state, however, was associated with considerable uncertainty because geogenic and anthropogenic Ce cannot exclusively be assigned to Ce(III) and Ce(IV), respectively. The REE patterns of most sewage sludges indicated a clear enrichment of Ce compared to heavier REE. Based on the assumption that the industrially used Ce is free of (most) other REE, we estimated the fraction of anthropogenic Ce in the sludges based on individual Ce/REE ratios. For the individual sludges the anthropogenic contributions were very variable (10–100%) but consistent fractions were obtained for individual sludges when calculated based on Ce/Dy (dysprosium), Ce/Er (erbium) and Ce/Eu (europium) ratios. Electron microscopy analysis of sludges dominated by anthropogenic Ce revealed that the Ce was mostly contained in nanoscale particles devoid of elements characteristic of Ce-bearing minerals. Thus, anthropogenic Ce contents derived from REE patterns may be used to validate current mass flow models for engineered CeO2 nanoparticles.
Hadengue, B., Scheidegger, A., Morgenroth, E., & Larsen, T. A. (2020). Modeling the water-energy nexus in households. Energy and Buildings, 225, 110262 (10 pp.). doi:10.1016/j.enbuild.2020.110262, Institutional Repository

One third of the global carbon emissions are emitted by the building sector. Over the last decades, space heating loads have decreased in modern buildings, and domestic hot water (DHW) is now oftentimes the largest energy consumer in the household. We developed the WaterHub modeling framework to assess the potential of technologies or measures targeting DHW energy demand. The framework combines process-based technological models and stochastic water demand modeling in a modular way to allow for holistic simulations of complex DHW systems. In two rigorous tests of the modeling framework, we demonstrated the importance of water consumption dynamics in the modeling of DHW systems, showing that static modeling leads to underestimated heat losses and wrong energy consumption predictions. In an exemplary case study, we identified and quantified the synergistic interactions between water boiler temperatures and a drain water heat recovery device, demonstrating the strength of this methodology for optimizing strategies targeting DHW systems. With its modular structure, this open-source modeling framework can be extended to include any DHW-related technology, providing a useful common platform for collaboration between technology developers and water experts.
Hagemann, N., Schmidt, H. P., Kägi, R., Böhler, M., Sigmund, G., Maccagnan, A., … Bucheli, T. D. (2020). Wood-based activated biochar to eliminate organic micropollutants from biologically treated wastewater. Science of the Total Environment, 730, 138417 (11 pp.). doi:10.1016/j.scitotenv.2020.138417, Institutional Repository

Implementing advanced wastewater treatment (WWT) to eliminate organic micropollutants (OMPs) is a necessary step to protect vulnerable freshwater ecosystems and water resources. To this end, sorption of OMP by activated carbon (AC) is one viable technology among others. However, conventional AC production based on fossil precursor materials causes environmental pollution, including considerable emissions of greenhouse gases. In this study, we produced activated biochar (AB) from wood and woody residues by physical activation and evaluated their capability to eliminate OMPs in treated wastewater. Activated biochar produced under optimized conditions sorbed 15 model OMPs, of which most were dissociated at circumneutral pH, to the same or higher extent than commercial AC used as a reference. While wood quality played a minor role, the dosage of the activation agent was the main parameter controlling the capacity of ABs to eliminate OMP. Our results highlight the possibility for local production of AB from local wood or woody residues as a strategy to improve WWT avoiding negative side effects of conventional AC production.
Hess, A., Bettex, C., & Morgenroth, E. (2020). Influence of intermittent flow on removal of organics in a biological activated carbon filter (BAC) used as post-treatment for greywater. Water Research X, 9, 100078 (10 pp.). doi:10.1016/j.wroa.2020.100078, Institutional Repository

Highly variable flow has to be expected in decentralized greywater treatment and can lead to intermittent operation of the treatment system. However, few studies have addressed the influence of variable flow on the treatment performance of a biological activated carbon filter (BAC). In this study, we investigated the influence of intermittent flow using small-scale BAC columns, which treat greywater as a second treatment step following a membrane bioreactor (MBR). Three operating strategies to respond to variable flow were evaluated. The activated carbon was characterized before and after the experiments in terms of biological activity and sorption capacity. The performance of the BAC filters was assessed based on total organic carbon (TOC) removal, TOC fractions and growth potential. No significant differences were observed between constant flow compared to on-off operation with intermittent flow over the range of tested influent concentrations. Peaks with high TOC during 24 h periods were attenuated by sorption and biological degradation. Adsorbed TOC was released after switching back to normal concentrations for influent concentrations more than 5 times higher than usually observed, the BAC functioned as a temporary sink. In line with these results, the high influent TOC values led to increased biological activity in the filter but did not influence the sorption capacity. The experiments showed that intermittent flow does not negatively impact the performance of a BAC and that there is no need for additional equalization tanks to buffer the variable flow, for example in household-scale greywater treatment.
Hildebrandt, L., Mitrano, D. M., Zimmermann, T., & Pröfrock, D. (2020). A nanoplastic sampling and enrichment approach by continuous flow centrifugation. Frontiers in Environmental Science, 8, 89 (13 pp.). doi:10.3389/fenvs.2020.00089, Institutional Repository

Substantial efforts have been undertaken to isolate and characterize plastic contaminants in different sample matrices in the last years as the ubiquitous presence of particulate plastic in the environment has become evident. In comparison, plastic particles <1 µm (nanoplastic) in the environment remain mostly unexplored. Adequate techniques for the enrichment, as well as the detection of nanoplastic, are lacking but are urgently needed to assess the full scope of (potential) nanoplastic pollution. Use of Pd-doped nanoplastic particles constitutes a powerful tool to develop new analytical approaches, as they can be traced accurately and with ease in a variety of complex matrices by highly sensitive, time-efficient and robust ICP-MS(/MS) techniques. In this lab-scale study, for the first time, the capability of continuous flow centrifugation to retain nanoplastic particles (∼160 nm) from ultrapure water, as well as from filtered and unfiltered water from the German Elbe River was evaluated. Depending on the pump rate, the retention efficiency for the nanoplastic particles in ultrapure water ranged from 92% ± 8% (1 L h-1) to 53% ± 5% (5 L h-1) [uc (n = 3)] and from 75% ± 5% to 65% ± 6% (uc) (2.5 L h-1) in river water. Recirculating the water through the system two and three times at the highest tested flow rate led to retention efficiencies >90%. In a proof-of-principle setup, it was demonstrated that operating two continuous flow centrifuges sequentially at different rotational speeds bears the potential to enable size- and density-selective sampling of the colloidal fraction. A significant fraction of the spiked nanoplastic particles [76% ± 5% (uc)] could be separated from a model mixture of natural particles with a well-defined mean size of approximately 3 µm. While the certified reference plankton material used here was quantitatively retained in the first centrifuge rotor together with 23.0% ± 2.2% of the effective dose of the spiked nanoplastic, the remaining fraction of the nanoplastic could be recovered in the second rotor (53% ± 5%) and the effluent [24.4% ± 2.4% (uc)]. Based on the good retention efficiencies and the demonstrated separation potential, continuous flow centrifugation has proven to be a very promising technique for nanoplastic sampling and enrichment from natural water samples.
Hoffmann, S., Feldmann, U., Bach, P. M., Binz, C., Farrelly, M., Frantzeskaki, N., … Udert, K. M. (2020). A research agenda for the future of urban water management: exploring the potential of non-grid, small-grid, and hybrid solutions. Environmental Science and Technology, 54(9), 5312-5322. doi:10.1021/acs.est.9b05222, Institutional Repository

Recent developments in high- and middle-income countries have exhibited a shift from conventional urban water systems to alternative solutions that are more diverse in source separation, decentralization, and modularization. These solutions include non-grid, small-grid, and hybrid systems to address such pressing global challenges as climate change, eutrophication, and rapid urbanization. They close loops, recover valuable resources, and adapt quickly to changing boundary conditions such as population size. Moving to such alternative solutions requires both technical and social innovations to co-evolve over time into integrated socio-technical urban water systems. Current implementations of alternative systems in high- and middle-income countries are promising, but they also underline the need for research questions to be addressed from technical, social, and transformative perspectives. Future research should apply a transdisciplinary research approach through socio-technical "lighthouse" projects that apply alternative urban water systems at scale. Such research should leverage experience from lighthouse projects in a range of socio-economic contexts, identify their potentials and limitations from an integrated perspective, and share their successes and failures across the urban water sector.
Hoffmann, K., Bouchet, S., Christl, I., Kaegi, R., & Kretzschmar, R. (2020). Effect of NOM on copper sulfide nanoparticle growth, stability, and oxidative dissolution. Environmental Science: Nano, 7(4), 1163-1178. doi:10.1039/c9en01448a, Institutional Repository

Metal sulfide nanoparticles have recently been discovered in natural environments subject to fluctuating redox conditions such as wetlands and river floodplains, which are often very rich in natural organic matter (NOM). Strong binding of chalcophile metals like copper by NOM is expected to interfere with sulfide precipitation and is likely to affect the growth of these nanoparticles. We therefore conducted experiments on the formation of copper sulfide nanoparticles (CuxS NPs) in anoxic solutions with varying Cu (50, 500 μmol L-1) and sulfide (100, 1000 μmol L-1) concentrations in the absence and presence of Suwannee River fulvic acid (SRFA, 0, 5, 50 mg C L-1). The size development of the CuxS nanoparticles and their stability were tracked over 4 weeks using transmission electron microscopy (TEM) and size-exclusion chromatography coupled to ICP-MS (SEC-ICP-MS). Additional dissolution experiments were performed in closed containers in the absence and presence of O2 and fulvic acid over several months providing insights into the oxidative dissolution behavior of CuxS. Our results highlight the high colloidal stability of CuxS nanoparticles in anoxic environments irrespective of the NOM concentration. Median particle diameters ranged between a few and a few tens of nanometers with larger particles forming in more concentrated suspensions. At low Cu and S concentrations, fulvic acid restricted particle growth by up to 25% compared to SRFA-free suspensions and metal sulfide clusters even smaller than 1 nm were detected. The CuxS nanoparticles exhibited a remarkable chemical stability against oxidative dissolution and were only dissolved when both fulvic acid and O2 were present.
Hoffmann, K., Christl, I., Kaegi, R., & Kretzschmar, R. (2020). Effects of natural organic matter (NOM), metal-to-sulfide ratio and Mn2+ on cadmium sulfide nanoparticle growth and colloidal stability. Environmental Science: Nano, 7(11), 3385-3404. doi:10.1039/d0en00764a, Institutional Repository

Redox-dynamic environments such as river floodplains and wetlands have been identified as sources of natural metal sulfide nanoparticles (MS NPs). However, little information is available on how their growth and colloidal stability are affected by the concentrations of metals and sulfide in solution, the presence of natural organic matter (NOM), and the possible incorporation of other metal cations such as Fe2+ or Mn2+. Here, we performed experiments on the formation of CdS nanoparticles (CdS NPs) in anoxic solutions with varying Cd (50, 100, 500 μmol L-1) and sulfide (50, 100, 1000 μmol L-1) concentrations in the absence and presence of Suwannee River fulvic acid (SRFA, 0, 5, 50 mg C per L). Additionally, we studied the influence of different metal-to-sulfide ratios and varying Mn2+ (0, 0.1, 0.5, 1 mmol L−1) concentrations on CdS aggregation using dynamic light scattering (DLS), transmission electron microscopy (TEM), and electrophoretic mobility measurements. The incorporation of Mn into the crystal lattice of CdS over 8 weeks was investigated with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Our results show that after 24 hours, small CdS primary particles with median diameters of a few nanometers (d~TEM = 2-14 nm) formed large aggregates (d~TEM = 167 nm) and that increasing SRFA concentrations progressively constrained the size of these aggregates (down to 19 nm) irrespective of the initial reactant stoichiometry. When NOM was absent or at low concentration, higher metal-to-sulfide ratios (≥1) and Mn2+ concentrations (≥0.5 mmol L-1) led to reduced colloidal stability of the suspensions. We found that in suspensions containing Mn2+, 10-30% of the Cd atoms in the crystal lattice were substituted by Mn during the formation of CdS, which was prevented by NOM.
Jacquin, C., Yu, D., Sander, M., Domagala, K. W., Traber, J., Morgenroth, E., & Julian, T. R. (2020). Competitive co-adsorption of bacteriophage MS2 and natural organic matter onto multiwalled carbon nanotubes. Water Research X, 9, 100058 (12 pp.). doi:10.1016/j.wroa.2020.100058, Institutional Repository

A leading challenge in drinking water treatment is to remove small-sized viruses from the water in a simple and efficient manner. Multi-walled carbon nanotubes (MWCNT) are new generation adsorbents with previously demonstrated potential as filter media to improve virus removal. This study therefore aimed to evaluate the field applicability of MWCNT-filters for virus removal in water containing natural organic matter (NOM) as co-solute to viruses, using batch equilibrium experiments. Contrary to previous studies, our results showed with MS2 bacteriophages single-solute systems that the affinity of MWCNT for MS2 was low, since after 3 h of equilibration only 4 log10 reduction value (LRV) of MS2 (20 mL at an initial concentration of 106 PFU MS2/mL) were reached. Single solute experiments with Suwannee river NOM (SRNOM) performed with environmentally-relevant concentrations showed MWCNT surface saturation at initial SRNOM concentrations between 10 and 15 mgC/L, for water pH between 5.2 and 8.7. These results suggested that at NOM:virus ratios found in natural waters, the NOM would competitively suppress virus adsorption onto MWCNT, even at low NOM concentrations. We confirmed this expectation with SRNOM-MS2 co-solute experiments, which showed an exponential decrease of the MS2 LRV by MWCNT with an increase in the initial SRNOM concentration. More interestingly, we showed that pre-equilibrating MWCNT with a SRNOM solution at a concentration as low as 0.4 mgC/L resulted in a LRV decrease of 3 for MS2, due to the formation of a negatively charged SRNOM adlayer on the MWCNT surface. Complementary batch experiments with natural NOM-containing waters and competition experiments with SRNOM in the presence of CaCl2 confirmed that the presence of NOM in waters challenges virus removal by MWCNT-filters, irrespective of the concentration and type of NOM and also in the presence of Ca2+. We therefore conclude that MWCNT-filters produced with commercially available pristine MWCNT cannot be considered as a viable technology for drinking water virus removal.
Javier, L., Farhat, N. M., Desmond, P., Valladares Linares, R., Bucs, S., Kruithof, J. C., & Vrouwenvelder, J. S. (2020). Biofouling control by phosphorus limitation strongly depends on the assimilable organic carbon concentration. Water Research, 183, 116051 (11 pp.). doi:10.1016/j.watres.2020.116051, Institutional Repository

Nutrient limitation is a biofouling control strategy in reverse osmosis (RO) membrane systems. In seawater, the assimilable organic carbon content available for bacterial growth ranges from about 50 to 400 μg C·L-1, while the phosphorus concentration ranges from 3 to 11 μg P·L-1. Several studies monitored biofouling development, limiting either carbon or phosphorus. The effect of carbon to phosphorus ratio and the restriction of both nutrients on membrane system performance have not yet been investigated.
This study examines the impact of reduced phosphorus concentration (from 25 μg P·L-1 and 3 μg P·L-1, to a low concentration of ≤0.3 μg P·L-1), combined with two different carbon concentrations (250 C L-1 and 30 μg C·L-1), on biofilm development in an RO system. Feed channel pressure drop was measured to determine the effect of the developed biofilm on system performance. The morphology of the accumulated biomass for both carbon concentrations was characterized by optical coherence tomography (OCT) and the biomass amount and composition was quantified by measuring total organic carbon (TOC), adenosine triphosphate (ATP), total cell counts (TCC), and extracellular polymeric substances (EPS) concentration for the developed biofilms under phosphorus restricted (P-restricted) and dosed (P-dosed) conditions.
For both carbon concentrations, P-restricted conditions (≤0.3 μg P·L-1) limited bacterial growth (lower values of ATP, TCC). A faster pressure drop increase was observed for P-restricted conditions compared to P-dosed conditions when 250 μg C·L-1 was dosed. This faster pressure drop increase can be explained by a higher area covered by biofilm in the flow channel and a higher amount of produced EPS. Conversely, a slower pressure drop increase was observed for P-restricted conditions compared to P-dosed conditions when 30 μg C·L-1 was dosed. Results of this study demonstrate that P-limitation delayed biofilm formation effectively when combined with low assimilable organic carbon concentration and thereby, lengthening the overall membrane system performance.
Jimenez, J., Charnier, C., Kouas, M., Latrille, E., Torrijos, M., Harmand, J., … Steyer, J. P. (2020). Modelling hydrolysis: simultaneous versus sequential biodegradation of the hydrolysable fractions. Waste Management, 101, 150-160. doi:10.1016/j.wasman.2019.10.004, Institutional Repository

Hydrolysis is considered the limiting step during solid waste anaerobic digestion (including co-digestion of sludge and biosolids). Mechanisms of hydrolysis are mechanistically not well understood with detrimental impact on model predictive capability. The common approach to multiple substrates is to consider simultaneous degradation of the substrates. This may not have the capacity to separate the different kinetics. Sequential degradation of substrates is theoretically supported by microbial capacity and the composite nature of substrates (bioaccessibility concept). However, this has not been experimentally assessed. Sequential chemical fractionation has been successfully used to define inputs for an anaerobic digestion model. In this paper, sequential extractions of organic substrates were evaluated in order to compare both models. By removing each fraction (from the most accessible to the least accessible fraction) from three different substrates, anaerobic incubation tests showed that for physically structured substrates, such as activated sludge and wheat straw, sequential approach could better describe experimental results, while this was less important for homogeneous materials such as pulped fruit. Following this, anaerobic incubation tests were performed on five substrates. Cumulative methane production was modelled by the simultaneous and sequential approaches. Results showed that the sequential model could fit the experimental data for all the substrates whereas simultaneous model did not work for some substrates.
Keller, A. S., Jimenez-Martinez, J., & Mitrano, D. M. (2020). Transport of nano- and microplastic through unsaturated porous media from sewage sludge application. Environmental Science and Technology, 54(2), 911-920. doi:10.1021/acs.est.9b06483, Institutional Repository

Wastewater treatment plants have been identified as important hubs for small particulate plastic, down to the nanometer scale, from urban areas to the environment. The reuse of sludge as fertilizer in agricultural practices can lead to accumulation of plastic in the soil. In this study, nanoplastic particles and microplastic fibers were synthesized with a passive inorganic tracer to aid in faster and more quantitative analysis using inductively coupled plasma mass spectrometry (ICP-MS). Using the anaerobic digestate of a pilot wastewater treatment plant spiked with metal-doped plastic, the excess sludge was dewatered, ensuring realistic associations between sludge and plastic. The resulting sludge cake was affixed atop an unsaturated porous-medium column of glass beads to assess: (i) the release of particulate plastic from the sludge, and (ii) the accumulation and mobility of plastic and organic matter through the column (analogous to a soil). A total of three particulate plastic treatments were assessed, in triplicate, where the plastic and mobile organic fractions were monitored for 14 pore water volumes. Due to size-limited transport, low deattachment from the sludge and reduced mobility through the column were found for microplastic fibers (>95% retention). However, cotransport between the mobile organic fraction and nanoplastic particles was observed, with 50% of both retained in the column. These results contribute to the understanding of the fate of particulate plastics and to assessing the associated environmental risks of particle mobility and percolation, particularly for nanoplastics.
Köpping, I., McArdell, C. S., Borowska, E., Böhler, M. A., & Udert, K. M. (2020). Removal of pharmaceuticals from nitrified urine by adsorption on granular activated carbon. Water Research X, 9, 100057 (10 pp.). doi:10.1016/j.wroa.2020.100057, Institutional Repository

Nitrification and distillation of urine allow for the recovery of all nutrients in a highly concentrated fertilizer solution. However, pharmaceuticals excreted with urine are only partially removed during these two process steps. For a sustainable and safe application, more extensive removal of pharmaceuticals is necessary. To enhance the pharmaceutical removal, which is already occurring during urine storage, nitrification and distillation, an adsorption column with granular activated carbon (GAC) can be included in the treatment train. We executed a pilot-scale study to investigate the adsorption of eleven indicator pharmaceuticals on GAC. During 74 days, we treated roughly 1000 L of pre-filtered and nitrified urine spiked with pharmaceuticals in two flow-through GAC columns filled with different grain sizes. We compared the performance of these columns by calculating the number of treated bed volumes until breakthrough and carbon usage rates. The eleven spiked pharmaceuticals were candesartan, carbamazepine, clarithromycin, diclofenac, emtricitabine, hydrochlorothiazide, irbesartan, metoprolol, N4-acetylsulfamethoxazole, sulfamethoxazole and trimethoprim. At the shortest empty bed contact time (EBCT) of 25 min, immediate breakthrough was observed in both columns shortly after the start of the experiments. Strong competition by natural organic material (NOM) could have caused the low pharmaceutical removal at the EBCT of 25 min. At EBCTs of 70, 92 and 115 min, more than 660 bed volumes could be treated until breakthrough in the column with fine GAC. The earliest breakthrough was observed for candesartan and clarithromycin. On coarse GAC, only half the number of bed volumes could be treated until breakthrough compared to fine GAC. The probable reason for the later breakthrough with fine GAC is the smaller intraparticle diffusive path length. DOC and UV absorbance measurements at 265 nm indicated that both parameters can be used as indicators for the breakthrough of pharmaceuticals. In contrast to pharmaceuticals and DOC, the nutrient compounds ammonium, nitrate, phosphate, potassium and sulfate were not removed significantly. A comparison with literature values suggests that the amount of GAC needed to remove pharmaceuticals from human excreta could be reduced by nearly two orders of magnitude, if urine were treated on site instead of being discharged and treated in a centralized wastewater treatment plant.
Layer, M., Garcia Villodres, M., Hernandez, A., Reynaert, E., Morgenroth, E., & Derlon, N. (2020). Limited simultaneous nitrification-denitrification (SND) in aerobic granular sludge systems treating municipal wastewater: mechanisms and practical implications. Water Research X, 7, 100048 (13 pp.). doi:10.1016/j.wroa.2020.100048, Institutional Repository

Simultaneous nitrification-denitrification (SND) is, in theory, a key advantage of aerobic granular sludge systems over conventional activated sludge systems. But practical experience and literature suggests that SND and thus total nitrogen removal are limited during treatment of municipal wastewater using AGS systems. This study thus aims at quantifying the extent and understanding the mechanisms of SND during treatment of municipal wastewater with aerobic granular sludge (AGS) systems. Experiments (long-term and batch-tests) as well as mathematical modelling were performed. Our experimental results demonstrate that SND is significantly limited during treatment of low-strength municipal wastewater with AGS systems (14-39%), while almost full SND is observed when treating synthetic influent containing only diffusible substrate (90%). Our simulations demonstrate that the main mechanisms behind limited SND are (1) the dynamics of anoxic zone formation inside the granule, (2) the diffusibility and availability of electron-donors in those zones and (3) the aeration mode. The development of anoxic zones is driven by the utilisation of oxygen in the upper layers of the granule leading to transport limitations of oxygen inside the granule; this effect is closely linked to granule size and wastewater composition. Development of anoxic zones during the aerobic phase is limited for small granules at constant aeration at bulk dissolved oxygen (DO) concentration of 2 mgO2 L-1, and anoxic zones only develop during a brief period of the aerated phase for large granules. Modelling results further indicate that a large fraction of electron-donors are actually utilised in aerobic rather than anoxic redox zones - in the bulk or at the granule surface. Thus, full SND cannot be achieved with AGS treating low strength municipal wastewater if a constant DO is maintained during the aeration phase. Optimised aeration strategies are therefore required. 2-step and alternating aeration are tested successfully using mathematical modelling and increase TN removal to 40-79%, without compromising nitrification, and by shifting electron-donor utilisation towards anoxic redox conditions.
Layer, M., Bock, K., Ranzinger, F., Horn, H., Morgenroth, E., & Derlon, N. (2020). Particulate substrate retention in plug-flow and fully-mixed conditions during operation of aerobic granular sludge systems. Water Research X, 9, 100075 (11 pp.). doi:10.1016/j.wroa.2020.100075, Institutional Repository

Particulate substrate (XB) is the major organic substrate fraction in most municipal wastewaters. However, the impact of XB on aerobic granular sludge (AGS) systems is not fully understood. This study evaluated the physical retention of XB in AGS sequencing batch reactor (SBR) during anaerobic plug-flow and then aerobic fully-mixed conditions. The influence of different sludge types and operational variables on the extent and mechanisms of XB retention in AGS SBR were evaluated. XB mass-balancing and magnetic resonance imaging (MRI) were applied. During the anaerobic plug-flow feeding, most XB was retained in the first few cm of the settled sludge bed within the interstitial voids, where XB settled and accumulated ultimately resulting in the formation of a filter-cake. Sedimentation and surface filtration were thus the dominant XB retention mechanisms during plug-flow conditions, indicating that contact and attachment of XB to the biomass was limited. XB retention was variable and influenced by the XB influent concentration, sludge bed composition and upflow feeding velocity (vww). XB retention increased with larger XB influent concentrations and lower vww, which demonstrated the importance of sedimentation on XB retention during plug-flow conditions. Hence, large fractions of influent XB likely re-suspended during aerobic fully-mixed conditions, where XB then preferentially and rapidly attached to the flocs. During fully-mixed conditions, increasing floc fractions, longer mixing times and larger XB concentrations increased XB retention. Elevated XB retention was observed after short mixing times < 60 min when flocs were present, and the contribution of flocs towards XB retention was even more pronounced for short mixing times < 5 min. Overall, our results suggest that flocs occupy an environmental niche that results from the availability of XB during aerobic fully-mixed conditions of AGS SBR. Therefore, a complete wash-out of flocs is not desirable in AGS systems treating municipal wastewater.
Merle, T., Knappe, D. R. U., Pronk, W., Vogler, B., Hollender, J., & von Gunten, U. (2020). Assessment of the breakthrough of micropollutants in full-scale granular activated carbon adsorbers by rapid small-scale column tests and a novel pilot-scale sampling approach. Environmental Science: Water Research and Technology, 6(10), 2742-2751. doi:10.1039/D0EW00405G, Institutional Repository

This study aimed to compare three approaches for predicting the service life of full-scale GAC adsorbers for the removal of micropollutants. The approaches included (i) rapid small-scale column tests (RSSCTs), (ii) two pilot-scale sampling approaches, and (iii) predictive correlations that consider micropollutant properties and background water matrix characteristics. The RSSCT could predict full-scale performance only if a micropollutant-specific fouling index was applied. At the pilot-scale, water samples were collected (1) over time at the top sampling point only (empty bed contact time (EBCT) of 1 minute) to minimize time to breakthrough (method 1) and (2) at different column depths at a single time point (method 2). Breakthrough curves obtained with method 2 more closely matched those obtained at the full-scale. In addition, method 2 is more convenient since it requires only one sampling campaign. Method 2 was used as a prognostic tool to predict breakthrough curves for micropollutants without full-scale data and a comparison with an existing prediction model gave satisfactory results for 6 out of 13 compounds.
Mitrano, D. M., & Wohlleben, W. (2020). Microplastic regulation should be more precise to incentivize both innovation and environmental safety. Nature Communications, 11(1), 5324 (12 pp.). doi:10.1038/s41467-020-19069-1, Institutional Repository

The presence of plastic in the environment has sparked discussion amongst scientists, regulators and the general public as to how industrialization and consumerism is shaping our world. Here we discuss restrictions on the intentional use of primary microplastics: small solid polymer particles in applications ranging from agriculture to cosmetics. Microplastic hazards are uncertain, and actions are not similarly prioritized by all actors. In some instances, replacement is technically simple and easily justified, but in others substitutions may come with more uncertainty, performance questions and costs. Scientific impact assessment of primary microplastics compared to their alternatives relies on a number of factors, such as microplastic harm, existence of replacement materials and the quality, cost and hazards of alternative materials. Regulations need a precise focus and must be enforceable by these measurements. Policymakers must carefully evaluate under which contexts incentives to replace certain microplastics can stimulate innovation of new, more competitive and environmentally conscious materials.
Moraes Schambeck, C., Girbal-Neuhauser, E., Böni, L., Fischer, P., Bessière, Y., Paul, E., … Derlon, N. (2020). Chemical and physical properties of alginate-like exopolymers of aerobic granules and flocs produced from different wastewaters. Bioresource Technology, 312, 123632 (11 pp.). doi:10.1016/j.biortech.2020.123632, Institutional Repository

The influence of wastewater (WW) composition and the bioaggregates types (floccular vs. aerobic granular sludge - AGS) on the content, physical-chemical, hydrogel and rheological properties of Alginate-Like Exopolymers (ALE) was studied. Results showed that ALE are a complex mixture of proteins, humic acids and polysaccharides. Overall, rather similar ALE content and composition was observed for the different types of sludge. Only the AGS fed with acetate and propionate yielded significantly larger amount of ALE (261 ± 33 mg VSALE/g VSsludge, +49%) and of uronic sugars in ALE (254 ± 32 mgglucuronic acid/g VSALE, +62%) than bioaggregates fed with no/very little volatile fatty acids. Mannuronic acids are involved in the cohesion of the hydrogels. ALE hydrogels elasticity changed significantly with the type/origin of the bioaggregates. ALE hydrogels elasticity from AGS was always higher than from flocs when fed with real WW. Hence, different types of sludge impact the properties of the recovered ALE.
Ranzinger, F., Matern, M., Layer, M., Guthausen, G., Wagner, M., Derlon, N., & Horn, H. (2020). Transport and retention of artificial and real wastewater particles inside a bed of settled aerobic granular sludge assessed applying magnetic resonance imaging. Water Research X, 7, 100050 (9 pp.). doi:10.1016/j.wroa.2020.100050, Institutional Repository

The removal or degradation of particulate organic matter is a crucial part in biological wastewater treatment. This is even more valid with respect to aerobic granular sludge and the impact of particulate organic matter on the formation and stability of the entire granulation process. Before the organic part of the particulate matter can be hydrolyzed and finally degraded by the microorganism, the particles have to be transported towards and retained within the granulated biomass. The understanding of these processes is currently very limited. Thus, the present study aimed at visualizing the transport of particulate organic matter into and through an aerobic granular sludge bed. Magnetic Resonance Imaging (MRI) was successfully applied to resolve the different fractions of a granular sludge bed over time and space. Quantification and merging of 3D data sets allowed for a clear determination of the particle distribution within the granular sludge bed. Dextran coated super paramagnetic iron oxide nanoparticles (SPIONs, dp = 38±10 nm) served as model particles for colloidal particles. Microcrystalline cellulose particles (dp = 1-20 μm) tagged with paramagnetic iron oxide were applied as a reference for toilet paper, which is a major fraction of particulate matter in domestic wastewater. The results were supplemented by the use of real wastewater particles with a size fraction between 28 and 100 μm. Colloidal SPIONs distributed evenly over the granular sludge bed penetrating the granules up to 300 μm. Rinsing the granular sludge bed proved their immobilization. Microcrystalline cellulose and real wastewater particles in the micrometer range accumulated in the void space between settled granules. An almost full retention of the wastewater particles was observed within the first 20 mm of the granular sludge bed. Moreover, the formation of particle layers indicates that most of the micrometer-sized particles are not attached to the biomass and remain mobile. Consequently, these particles are released into the bulk phase when the granulated sludge bed is resuspended.
Reynaert, E., Greenwood, E. E., Ndwandwe, B., Riechmann, M. E., Sindall, R. C., Udert, K. M., & Morgenroth, E. (2020). Practical implementation of true on-site water recycling systems for hand washing and toilet flushing. Water Research X, 7, 100051 (13 pp.). doi:10.1016/j.wroa.2020.100051, Institutional Repository

On-site wastewater reuse can improve global access to clean water, sanitation and hygiene. We developed a treatment system (aerated bioreactor, ultrafiltration membrane, granular activated carbon and electrolysis for chlorine disinfection) that recycles hand washing and toilet flush water.
Three prototypes were field-tested in non-sewered areas, one in Switzerland (hand washing) and two in South Africa (hand washing, toilet flushing), over periods of 63, 74 and 94 days, respectively.
We demonstrated that the system is able to recycle sufficient quantities of safe and appealing hand washing and toilet flush water for domestic or public use in real-life applications. Chemical contaminants were effectively removed from the used water in all prototypes. Removal efficiencies were 99.7% for the chemical oxygen demand (COD), 98.5% for total nitrogen (TN) and 99.9% for phosphate in a prototype treating hand washing water, and 99.8% for COD, 95.7% for TN and 89.6% for phosphate in a prototype treating toilet flush water. While this system allowed for true recycling for the same application, most on-site wastewater reuse systems downcycle the treated water, i.e., reuse it for an application requiring lower water quality. An analysis of 18 selected wastewater reuse specifications revealed that at best these guidelines are only partially applicable to innovative recycling systems as they are focused on the downcycling of water to the environment (e.g., use for irrigation). We believe that a paradigm shift is necessary and advocate for the implementation of risk-based (and thus end-use dependent) system performance targets to evaluate water treatment systems, which recycle and not only downcycle water.
Russo, S., Lürig, M., Hao, W., Matthews, B., & Villez, K. (2020). Active learning for anomaly detection in environmental data. Environmental Modelling and Software, 134, 104869 (11 pp.). doi:10.1016/j.envsoft.2020.104869, Institutional Repository

Due to the growing amount of data from in-situ sensors in environmental monitoring, it becomes necessary to automatically detect anomalous data points. Nowadays, this is mainly performed using supervised machine learning models, which need a fully labelled data set for their training process. However, the process of labelling data is typically cumbersome and, as a result, a hindrance to the adoption of machine learning methods for automated anomaly detection. In this work, we propose to address this challenge by means of active learning. This method consists of querying the domain expert for the labels of only a selected subset of the full data set. We show that this reduces the time and costs associated to labelling while delivering the same or similar anomaly detection performances. Finally, we also show that machine learning models providing a nonlinear classification boundary are to be recommended for anomaly detection in complex environmental data sets.
Schambeck, C. M., Magnus, B. S., de Souza, L. C. R., Leite, W. R. M., Derlon, N., Bittencourt Guimarães, L., & Ribeiro da Costa, R. H. (2020). Biopolymers recovery: dynamics and characterization of alginate-like exopolymers in an aerobic granular sludge system treating municipal wastewater without sludge inoculum. Journal of Environmental Management, 263, 110394 (11 pp.). doi:10.1016/j.jenvman.2020.110394, Institutional Repository

Alginate-like exopolymers (ALE) are present in the extracellular polymeric substances (EPS) of biological sludge such as aerobic granular sludge (AGS). The recovery of ALE from excess sludge produced by wastewater treatment plants (WWTP) is a relevant approach for the recovery of valuable products of industrial interest. However, little is known about dynamics of ALE content in sludge and associated factors. Thus, this study aimed at assessing the dynamics of EPS and ALE in terms of content, some chemical properties and influencing environmental factors along granulation in a sequencing batch reactor treating municipal wastewater. Results indicated that the EPS content was not correlated with the development of AGS, while the ALE content was higher, more stable and steadily increased after granulation achievement. Overall, 236 ± 27 mg VSALE/g VSsludge was recovered from AGS and 187 ± 94 mg VSALE/g VSsludge from flocs. However, the lower ALE content in flocs may be compensated by the higher sludge production rate in activated sludge systems. Principal component analysis (PCA) revealed that ALE content positively correlates with the nutrient and organic substrate conversion, and with the fraction of large AGS. Microbial analyses indicated that a stable microbial community composition was associated with a higher and more stable ALE content. ALE recovered from both flocs and AGS was endowed with hydrogel property, and no clear difference in their elemental composition and functional groups was observed. Therefore, our study provides insights about quantitative and qualitative aspects of ALE which are helpful for the improvement of waste biological sludge valorization.
Schneider, M. Y., Furrer, V., Sprenger, E., Carbajal, J. P., Villez, K., & Maurer, M. (2020). Benchmarking soft sensors for remote monitoring of on-site wastewater treatment plants. Environmental Science and Technology, 54(17), 10840-10849. doi:10.1021/acs.est.9b07760, Institutional Repository

On-site wastewater treatment plants (OSTs) are usually unattended, so failures often remain undetected and lead to prolonged periods of reduced performance. To stabilize the performance of unattended plants, soft sensors could expose faults and failures to the operator. In a previous study, we developed soft sensors and showed that soft sensors with data from unmaintained physical sensors can be as accurate as soft sensors with data from maintained ones. The monitored variables were pH and dissolved oxygen (DO), and soft sensors were used to predict nitrification performance. In the present study, we use synthetic data and monitor three plants to test these soft sensors. We find that a long solids retention time and a moderate aeration rate improve the pH soft-sensor accuracy and that the aeration regime is the main operational parameter affecting the accuracy of the DO soft sensor. We demonstrate that integrated design of monitoring and control is necessary to achieve robustness when extrapolating from one OST to another in the absence of plant-specific fine-tuning. Additionally, we provide a unique labeled dataset for further feature and data-driven soft-sensor development. Our benchmarking results indicate that it is feasible to monitor OSTs with unmaintained sensors and without plant-specific tuning of the developed soft sensors. This is expected to drastically reduce monitoring costs for OST-based sanitation systems.
Suess, E., Berg, M., Bouchet, S., Cayo, L., Hug, S. J., Kaegi, R., … Buser, A. M. (2020). Mercury loads and fluxes from wastewater: a nationwide survey in Switzerland. Water Research, 175, 115708 (10 pp.). doi:10.1016/j.watres.2020.115708, Institutional Repository

Mercury (Hg) pollution threatens ecosystems and human health. Wastewater treatment plants (WWTPs) play a key role in limiting Hg discharges from wastewaters to rivers and lakes, but large-scale studies to estimate Hg loads and discharge at national levels are scarce. We assessed the concentration, flux, speciation, and removal of Hg in municipal wastewater throughout Switzerland by investigating 64 WWTPs in a pre-study and a subset of 28 WWTPs in the main study. We also studied the behavior and pathways of Hg along the various treatment steps in a state-of-the-art WWTP. The resulting dataset, representative of industrialized countries, provides an overview of (i) current Hg concentration ranges, (ii) average per capita loads, and (iii) wastewater Hg inputs into surface waters. The results allowed estimation of a total Hg (THg) load in Swiss wastewater of 130 ± 30 kg THg/year (15.7 mg/capita/y), of which 96 ± 4% is retained in sewage sludge. About 4.7 ± 0.5 kg THg/year (0.57 mg/capita/y) is discharged with the treated wastewater into surface waters. This corresponds to only 1.5-3% of the THg load carried by the major Swiss rivers, indicating that >95% of riverine Hg originates from other sources. Extrapolation to the population of Europe would yield a total amount of 11,700 kg THg/year in raw wastewater, with some 480 kg THg/year discharged to surface waters. Monomethyl mercury on average accounted for 0.23% of THg, and its fraction remained constant along the different treatment steps.
Svendsen, C., Walker, L. A., Matzke, M., Lahive, E., Harrison, S., Crossley, A., … Spurgeon, D. J. (2020). Key principles and operational practices for improved nanotechnology environmental exposure assessment. Nature Nanotechnology, 15, 731-742. doi:10.1038/s41565-020-0742-1, Institutional Repository

Nanotechnology is identified as a key enabling technology due to its potential to contribute to economic growth and societal well-being across industrial sectors. Sustainable nanotechnology requires a scientifically based and proportionate risk governance structure to support innovation, including a robust framework for environmental risk assessment (ERA) that ideally builds on methods established for conventional chemicals to ensure alignment and avoid duplication. Exposure assessment developed as a tiered approach is equally beneficial to nano-specific ERA as for other classes of chemicals. Here we present the developing knowledge, practical considerations and key principles need to support exposure assessment for engineered nanomaterials for regulatory and research applications.
ThomasArrigo, L. K., Bouchet, S., Kaegi, R., & Kretzschmar, R. (2020). Organic matter influences transformation products of ferrihydrite exposed to sulfide. Environmental Science: Nano, 7(11), 3405-3418. doi:10.1039/d0en00398k, Institutional Repository

In redox-dynamic environments, sorption to poorly-crystalline, nanometer-sized Fe(III)-(oxyhydr)oxides like ferrihydrite influences the biogeochemical cycling of nutrients and trace elements. Under sulfate-reducing conditions, the reductive dissolution of ferrihydrite leads to the release of associated constituents, which may be re-immobilized via sorption to secondary Fe minerals. To date, studies following the kinetics and transformation pathways of Fe(III)-(oxyhydr)oxides upon exposure to dissolved sulfide (S(-II)) have largely focused on pure Fe minerals. However, in nature, Fe(III)-(oxyhydr)oxides are often found in association with organic matter (OM). Because ferrihydrite-OM associations exhibit characteristics and biogeochemical reactivity differing from those of pure ferrihydrite, in this study, we compared sulfidization kinetics and transformation pathways of a pure ferrihydrite to those of ferrihydrite coprecipitated with contrasting organic ligands; polygalacturonic acid, galacturonic acid, and citric acid (C/Fe molar ratio ~0.55). Incorporating aqueous- and solid-phase S and Fe speciation analyses (via wet chemistry techniques and S and Fe X-ray absorption spectroscopy) in addition to X-ray diffraction and electron microscopy, we studied both rapid (<7 days) and long-term (12 months) mineral transformations as well as the impact of varying S(-II)/Fe molar ratios at neutral pH. Our results showed that at low S(-II)/Fe molar ratios (=0.1), poorly-crystalline Fe sulfide minerals (e.g. mackinawite) did not form in any (co)precipitate. In contrast, at higher S(-II)/Fe molar ratios (=0.5), mackinawite rapidly precipitated, with higher contributions detected in the coprecipitates than in the pure ferrihydrite. Aging of the samples led to further mineral transformations, including divergent pyrite and greigite precipitation, and an overall increase in the crystallinity of secondary mineral phases. Still, the fraction of residual ferrihydrite at 12 months was higher in the OM-containing coprecipitates, with the most ferrihydrite preservation observed in coprecipitates comprising carboxyl-poor ligands (galacturonic acid and citric acid). This suggests that the presence of OM inhibited S(-II)-induced ferrihydrite mineral transformations and that the composition of the associated OM influenced mineral transformation pathways. Collectively, these results suggest that further studies regarding sulfidization pathways should include OM in order to better represent environmental conditions.
Tu, K., Puértolas, B., Adobes-Vidal, M., Wang, Y., Sun, J., Traber, J., … Keplinger, T. (2020). Green synthesis of hierarchical metal-organic framework/wood functional composites with superior mechanical properties. Advanced Science, 7(7), 1902897 (9 pp.). doi:10.1002/advs.201902897, Institutional Repository

The applicability of advanced composite materials with hierarchical structure that conjugate metal-organic frameworks (MOFs) with macroporous materials is commonly limited by their inferior mechanical properties. Here, a universal green synthesis method for the in situ growth of MOF nanocrystals within wood substrates is introduced. Nucleation sites for different types of MOFs are readily created by a sodium hydroxide treatment, which is demonstrated to be broadly applicable to different wood species. The resulting MOF/wood composite exhibits hierarchical porosity with 130 times larger specific surface area compared to native wood. Assessment of the CO2 adsorption capacity demonstrates the efficient utilization of the MOF loading along with similar adsorption ability to that of pure MOF. Compression and tensile tests reveal superior mechanical properties, which surpass those obtained for polymer substrates. The functionalization strategy offers a stable, sustainable, and scalable platform for the fabrication of multifunctional MOF/wood-derived composites with potential applications in environmental- and energy-related fields.
Urstoeger, A., Wimmer, A., Kaegi, R., Reiter, S., & Schuster, M. (2020). Looking at silver-based nanoparticles in environmental water samples: repetitive cloud point extraction bridges gaps in electron microscopy for naturally occurring nanoparticles. Environmental Science and Technology, 54(19), 12063-12071. doi:10.1021/acs.est.0c02878, Institutional Repository

The growing use of silver-based nanoparticles (Ag-b-NPs) in everyday products goes hand in hand with their release into the environment, resulting in ng L–1 traces in natural water bodies. In order to assess their fate, possible transformations and ecotoxicology—essential information to proper risk assessment—particle size, shape, and chemical composition have to be determined. Transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDX) is a powerful tool for determining these particle characteristics, but it requires high particle concentrations in order to produce statistically reliable results. In this study, we will present the extraction of Ag-b-NPs at environmentally relevant concentrations down to 5 ng L–1 from artificial as well as environmental water samples via cloud point extraction on a repetitive basis. The combination with an on-grid centrifugation technique ensures an efficient concentration and deposition of the extracted particles onto the TEM grid for subsequent TEM-EDX measurements. Furthermore, electron microscopy investigations were supplemented by single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) measurements. Ag-b-NPs were successfully visualized and characterized at environmentally relevant concentrations of 5 ng L–1 with TEM-EDX and sp-ICP-MS measurements. Their size, shape, and chemical composition were not affected by the sample preparation.
Velimirovic, M., Wagner, S., Monikh, F. A., Uusimäki, T., Kaegi, R., Hofmann, T., & von der Kammer, F. (2020). Accurate quantification of TiO2 nanoparticles in commercial sunscreens using standard materials and orthogonal particle sizing methods for verification. Talanta, 215, 120921 (10 pp.). doi:10.1016/j.talanta.2020.120921, Institutional Repository

The implementation and enforcement of product labeling obligation as required, for example, by the cosmetic product regulation, needs simple and precise validated analytical methods. This also applies to the analysis of nanoparticles in products such as cosmetics. However, the provision of such methods is often hampered by inaccurate sizing due to unwanted nanoparticle changes, interference of matrix components with sizing and interactions between nanoparticles and analytical instrumentation. It is, therefore, necessary to develop appropriate sample preparation methods that preserve NP properties and reduce or remove matrix compounds that interfere with sizing. Further, accurate particle size analysis of samples containing unknown and possibly multiple nanoparticulate constituents is needed. In this study, we evaluated three sample preparation methods to identify and quantify TiO2 nanoparticles in sunscreens. Specifically, we used a combination of ultracentrifugation and hexane washing, thermal destruction of the matrix, and surfactant assisted particle extraction. The method accuracy was assessed by two internal reference samples: pristine TiO2 nanoparticles (NM104) and similar TiO2 nanoparticles dispersed in a sunscreen matrix. The PSDs were determined using an asymmetrical flow field-flow fractionation hyphenated with multi-angle light scattering and inductively coupled plasma-mass spectroscopy. Particle sizing was based on size calibration of the particle retention time in the AF4. Computation of radius of gyration from MALS data was used as an orthogonal particle sizing approach to verify ideal elution and particle size data from the AF4 calibration. Among the three tested sample preparation methods surfactant assisted particle extraction revealed TiO2 nanoparticle recoveries of above 90% and no increase in particle size due to sample preparation was observed. Finally, the sample preparation methods were applied to two commercial sunscreen samples revealing the existence of TiO2-NP < 100 nm. Conclusively, the surfactant assisted particle extraction method can provide valid data for TiO2-NPs in sunscreen and possibly for cosmetic samples of similar matrix.
Villez, K., Vanrolleghem, P. A., & Corominas, L. (2020). A general-purpose method for Pareto optimal placement of flow rate and concentration sensors in networked systems - with application to wastewater treatment plants. Computers and Chemical Engineering, 139, 106880 (14 pp.). doi:10.1016/j.compchemeng.2020.106880, Institutional Repository

The advent of affordable computing, low-cost sensor hardware, and high-speed and reliable communications have spurred ubiquitous installation of sensors in complex engineered systems. However, ensuring reliable data quality remains a challenge. Exploitation of redundancy among sensor signals can help improving the precision of measured variables, detecting the presence of gross errors, and identifying faulty sensors. The cost of sensor ownership, maintenance efforts in particular, can still be cost-prohibitive however. Maximizing the ability to assess and control data quality while minimizing the cost of ownership thus requires a careful sensor placement. To solve this challenge, we develop a generally applicable method to solve the multi-objective sensor placement problem in systems governed by linear and bilinear balance equations. Importantly, the method computes all Pareto-optimal sensor layouts with conventional computational resources and requires no information about the expected sensor quality.
Villez, K., Del Giudice, D., Neumann, M. B., & Rieckermann, J. (2020). Accounting for erroneous model structures in biokinetic process models. Reliability Engineering and System Safety, 203, 107075 (8 pp.). doi:10.1016/j.ress.2020.107075, Institutional Repository

In engineering practice, model-based design requires not only a good process-based model, but also a good description of stochastic disturbances and measurement errors to learn credible parameter values from observations. However, typical methods use Gaussian error models, which often cannot describe the complex temporal patterns of residuals. Consequently, this results in overconfidence in the identified parameters and, in turn, optimistic reactor designs. In this work, we assess the strengths and weaknesses of a method to statistically describe these patterns with autocorrelated error models. This method produces increased widths of the credible prediction intervals following the inclusion of the bias term, in turn leading to more conservative design choices. However, we also show that the augmented error model is not a universal tool, as its application cannot guarantee the desired reliability of the resulting wastewater reactor design.
Wielinski, J., Marafatto, F. F., Gogos, A., Scheidegger, A., Voegelin, A., Müller, C. R., … Kaegi, R. (2020). Synchrotron hard X-ray chemical imaging of trace element speciation in heterogeneous samples: development of criteria for uncertainty analysis. Journal of Analytical Atomic Spectrometry, 35, 567-579. doi:10.1039/C9JA00394K, Institutional Repository

Synchrotron hard X-ray spectroscopy with focussing optics allows recording X-ray fluorescence (XRF) maps at energies around element specific X-ray absorption edges. Stacking multiple XRF maps along the energy axis yields chemical images that contain spatially resolved information on the speciation of the absorber in the sample matrix at the micrometre scale. Short dwell times needed to keep measurement time and radiation-induced sample changes within acceptable limits result in spectral noise that affects the uncertainty in data analysis. In this study, we develop a model to quantify the uncertainty associated with the processing of XRF image stacks using Bayesian inference. To demonstrate the potential of our approach, the model is applied to stacks of XRF maps collected around the copper (Cu) K-edge (pixel size: 3 × 3 μm2, map sizes: 500 × 500 μm2). The investigated samples include digested sewage sludge spiked with either CuO nanoparticles (NP) or dissolved CuSO4 and their corresponding ashes obtained through incineration. The chemical imaging data reveal differences in species distribution between sludge spiked with CuO NP or dissolved Cu. These differences disappear during the incineration process and the resulting ashes exhibit almost identical Cu species distribution. The uncertainty analysis approach developed in this study can be used for data interpretation, but can also be used for the planning of chemical imaging experiments at synchrotron beamlines.
Wigger, H., Kägi, R., Wiesner, M., & Nowack, B. (2020). Exposure and possible risks of engineered nanomaterials in the environment - current knowledge and directions for the future. Reviews of Geophysics, 58(4), e2020RG000710 (25 pp.). doi:10.1029/2020RG000710, Institutional Repository

The consequences that engineered nanomaterials (ENMs) may cause in the environment have been under investigation for more than 15 years. Hundreds of millions of euros/dollars have been invested into safety issues of ENMs, and much progress has been made in the understanding of their fate and effects in the environment. After an initial phase of "observing the effects," research has shifted toward elucidating the mechanisms of fate and ecotoxicological effects. This also included a stronger focus on exposure issues and the development of analytical methods and computational models to predict exposure. First environmental risk assessments for ENM were performed, and much progress has been achieved on the way to nanospecific and material‐specific assessments. The release of ENM from products and their transformation in technical and natural compartments profoundly affect the form in which the ENMs are present in the environment. A crucial aspect in all areas is if there are truly nanospecific issues of the novel‐added functionalities of ENM that are different from dissolved metals, larger particles, or natural particles. This review outlines progress in understanding the environmental dimensions of ENMs and areas that merit further investigation: To what extent are ENMs different from their natural counterparts and how "long" do we need to track them in natural and technical systems? A major challenge will be in developing methods for studying particle‐mediated processes and their effects on ecosystems and organisms in a more general sense, going beyond just ENM, for example, to natural nanoparticles, microplastics, and extracellular vesicles.
Xu, J., Avellan, A., Li, H., Clark, E. A., Henkelman, G., Kaegi, R., & Lowry, G. V. (2020). Iron and sulfur precursors affect crystalline structure, speciation, and reactivity of sulfidized nanoscale zerovalent iron. Environmental Science and Technology, 54(20), 13294-13303. doi:10.1021/acs.est.0c03879, Institutional Repository

The reactivity of sulfidized nanoscale zerovalent iron (SNZVI) is affected by the amount and species of sulfur in the materials. Here, we assess the impact of the Fe (Fe2+ and Fe3+) and S (S2O42-, S2-, and S62-) precursors used to synthesize both NZVI and SNZVI on the resulting physicochemical properties and reactivity and selectivity with water and trichloroethene (TCE). X-ray diffraction indicated that the Fe precursors altered the crystalline structure of both NZVI and SNZVI. The materials made from the Fe3+ precursor had an expanded lattice in the Fe0 body-centered-cubic (BCC) structure and lower electron-transfer resistance, providing higher reactivity with water (∼2-3 fold) and TCE (∼5-13 fold) than those made from an Fe2+ precursor. The choice of the S precursor controlled the S speciation in the SNZVI particles, as indicated by X-ray absorption spectroscopy. Iron disulfide (FeS2) was the main S species of SNZVI made from S2O42-, whereas iron sulfide (FeS) was the main S species of SNZVI made from S2-/S62-. The former SNZVI was more hydrophobic, reactive with, and selective for TCE compared to the latter SNZVI. These results suggest that the Fe and S precursors can be used to select the conditions of the synthesis process and provide selected physicochemical properties (e.g., S speciation, hydrophobicity, and crystalline structure), reactivity, and selectivity of the SNZVI materials.
Xu, J., Avellan, A., Li, H., Liu, X., Noël, V., Lou, Z., … Lowry, G. V. (2020). Sulfur loading and speciation control the hydrophobicity, electron transfer, reactivity, and selectivity of sulfidized nanoscale zerovalent iron. Advanced Materials, 32(17), 1906010 (10 pp.). doi:10.1002/adma.201906910, Institutional Repository

Sulfidized nanoscale zerovalent iron (SNZVI) is a promising material for groundwater remediation. However, the relationships between sulfur content and speciation and the properties of SNZVI materials are unknown, preventing rational design. Here, the effects of sulfur on the crystalline structure, hydrophobicity, sulfur speciation, corrosion potential, and electron transfer resistance are determined. Sulfur incorporation extended the nano-Fe0 BCC lattice parameter, reduced the Fe local vacancies, and lowered the resistance to electron transfer. Impacts of the main sulfur species (FeS and FeS2) on hydrophobicity (water contact angles) are consistent with density functional theory calculations for these FeSx phases. These properties well explain the reactivity and selectivity of SNZVI during the reductive dechlorination of trichloroethylene (TCE), a hydrophobic groundwater contaminant. Controlling the amount and speciation of sulfur in the SNZVI made it highly reactive (up to 0.41 L m-2 d-1) and selective for TCE degradation over water (up to 240 moles TCE per mole H2O), with an electron efficiency of up to 70%, and these values are 54-fold, 98-fold, and 160-fold higher than for NZVI, respectively. These findings can guide the rational design of robust SNZVI with properties tailored for specific application scenarios.
Zeumer, R., Hermsen, L., Kaegi, R., Kühr, S., Knopf, B., & Schlechtriem, C. (2020). Bioavailability of silver from wastewater and planktonic food borne silver nanoparticles in the rainbow trout Oncorhynchus mykiss. Science of the Total Environment, 706, 135695 (12 pp.). doi:10.1016/j.scitotenv.2019.135695, Institutional Repository

Silver nanoparticles (AgNPs) are present in a wide field of applications and consumer products and are likely to be released into the environment, mainly via urban and industrial sewage due to their extensive use. Even though AgNPs are mostly retained within the sludge of wastewater treatment plants (WWTPs), a small amount of mainly sulfidized particles still enters the aquatic environment, where they can be taken up by various aquatic organisms and transferred along the food chain. In this study, uptake and bioavailability of Ag from AgNPs following aqueous and dietary exposure were investigated in the rainbow trout Oncorhynchus mykiss. AgNPs in the effluent of model WWTPs and in tap water were used to perform aqueous exposure studies. No significant Ag uptake into the gills and carcass of the analyzed fish could be found for wastewater-borne AgNPs. However, when added to tap water at a concentration of 12.4 μg L-1, a maximum total Ag tissue concentrations of around 100 μg kg-1 and 50 μg kg-1 in gills and carcass were measured, respectively. For the dietary exposure studies, freshwater zooplankton was exposed to AgNPs, and used for the preparation of food pellets with a total Ag concentration of 121.5 μg kg-1. During the feeding study with rainbow trout significant total Ag concentrations up to 34.3 μg kg-1 could be found in the digestive tract. However, only a limited transfer of Ag through the intestinal walls into the carcass could be detected. AgNPs in plankton and WWTP effluent were characterized by transmission electron microscopy (TEM) in combination with energy dispersive X-ray spectroscopy (EDX) and found to be sulfidized. This transformation most presumably has led to their limited bioavailability for fish. The results emphasize the importance of realistic test conditions for the risk assessment of AgNPs by the use of environmental matrices.
Ziemba, C., Larivé, O., Reynaert, E., Huisman, T., & Morgenroth, E. (2020). Linking transformations of organic carbon to post-treatment performance in a biological water recycling system. Science of the Total Environment, 721, 137489 (8 pp.). doi:10.1016/j.scitotenv.2020.137489, Institutional Repository

Ozone, electrolysis and granular activated carbon (GAC) were examined as potential post-treatments to follow a household-scale biologically activated membrane bioreactor (BAMBi), treating a wash water containing trace urine and feces contamination. Each post-treatment was evaluated for abilities and reaction preferences to remove or transform dissolved organic carbon (DOC), chemical structures that contribute color, and assimilable organic carbon (AOC), which can support bacterial regrowth. Batch treatment with each technology demonstrated an ability to remove ≥95% DOC. Ozone demonstrated a reaction selectivity through increased reaction rates with larger compounds and color-contributing compounds. Electrolysis and GAC demonstrated generally less-selective reactivity. Adding post-treatments to full-scale systems reduced DOC (55-91%), AOC (34-62%), and color (75-98%), without significant reaction selectivity. These reductions in DOC and AOC were not linked to reduction of bacterial concentrations in treated water. Reductions in bacterial concentrations were observed with ozone and electrolysis, but this is credited to oxidation chemicals produced in these systems and not the removal or transformations of organic materials.
Aeppli, M., Vranic, S., Kaegi, R., Kretzschmar, R., Brown, A. R., Voegelin, A., … Sander, M. (2019). Decreases in iron oxide reducibility during microbial reductive dissolution and transformation of ferrihydrite. Environmental Science and Technology, 53(15), 8736-8746. doi:10.1021/acs.est.9b01299, Institutional Repository

Ferrous iron formed during microbial ferric iron reduction induces phase transformations of poorly crystalline into more crystalline and thermodynamically more stable iron (oxyhydr)oxides. Yet, characterizing the resulting decreases in the reactivity of the remaining oxide ferric iron toward reduction (i.e., its reducibility) has been challenging. Here, we used the reduction of six-line ferrihydrite by Shewanella oneidensis MR-1 as a model system to demonstrate that mediated electrochemical reduction (MER) allows directly following decreases in oxide ferric iron reducibility during the transformation of ferrihydrite into goethite and magnetite which we characterized by X-ray diffraction analysis and transmission electron microscopy imaging. Ferrihydrite was fully reducible in MER at both pHMER of 5.0 and 7.5. Decreases in iron oxide reducibility associated with ferrihydrite transformation into magnetite were accessible at both pHMER because the formed magnetite was not reducible under either of these conditions. Conversely, decreases in iron oxide reducibility associated with goethite formation were apparent only at the highest tested pHMER of 7.5 and thus the thermodynamically least favorable conditions for iron oxide reductive dissolution. The unique capability to adjust the thermodynamic boundary conditions in MER to the specific reducibilities of individual iron (oxyhydr)oxides makes this electrochemical approach broadly applicable for studying changes in iron oxide reducibility in heterogeneous environmental samples such as soils and sediments.
Aeppli, M., Kaegi, R., Kretzschmar, R., Voegelin, A., Hofstetter, T. B., & Sander, M. (2019). Electrochemical analysis of changes in iron oxide reducibility during abiotic ferrihydrite transformation into goethite and magnetite. Environmental Science and Technology, 53(7), 3568-3578. doi:10.1021/acs.est.8b07190, Institutional Repository

Electron transfer to ferric iron in (oxyhydr-)oxides (hereafter iron oxides) is a critical step in many processes that are central to the biogeochemical cycling of elements and to pollutant dynamics. Understanding these processes requires analytical approaches that allow for characterizing the reactivity of iron oxides toward reduction under controlled thermodynamic boundary conditions. Here, we used mediated electrochemical reduction (MER) to follow changes in iron oxide reduction extents and rates during abiotic ferrous iron-induced transformation of six-line ferrihydrite. Transformation experiments (10 mM ferrihydrite-FeIII) were conducted over a range of solution conditions (pHtrans = 6.50 to 7.50 at 5 mM Fe2+ and for pHtrans = 7.00 also at 1 mM Fe2+) that resulted in the transformation of ferrihydrite into thermodynamically more stable goethite or magnetite. The changes in iron oxide mineralogy during the transformations were quantified using X-ray diffraction analysis. MER measurements on iron oxide suspension aliquots collected during the transformations were performed over a range of pHMER at constant applied reduction potential. The extents and rates of iron oxide reduction in MER decreased with decreasing reaction driving force resulting from both increasing pHMER and increasing transformation of ferrihydrite into thermodynamically more stable iron oxides. We show that the decreases in iron oxide reduction extents and rates during ferrihydrite transformations can be linked to the concurrent changes in iron oxide mineralogy.
Arhin, S. G., Banadda, N., Komakech, A. J., Pronk, W., & Marks, S. J. (2019). Application of hybrid coagulation–ultrafiltration for decentralized drinking water treatment: impact on flux, water quality and costs. Water Science and Technology: Water Supply, 19(7), 2163-2171. doi:10.2166/ws.2019.097, Institutional Repository

Decentralized membrane-based water treatment represents an attractive and viable approach to safe water supply in low-income areas, but its widespread adoption requires cost-effective antifouling strategies. Although the antifouling mechanisms of Al-based coagulants have been widely investigated, there is little data about their impact on costs and treatment efficiency for decentralized membrane-based systems. In this study, a comparative assessment of two decentralized ultrafiltration (UF) units with and without polyaluminum chloride (PACl) coagulation was undertaken to evaluate the influence of coagulation on the fouling, water quality, and costs nexus. The results showed that PACl suppressed both total fouling and hydraulically irreversible fouling. A matched-pair analysis also revealed that PACl improved the permeate quality by enhancing the removal of particulates and dissolved organics. Compared with the conventional UF system, the hybrid coagulation–UF system contributed to a 21% increase in the flux rate, allowing for a 27% reduction in membrane area and thus, providing cost benefits in terms of both capital and operating costs. These results suggest that PACl coagulation is potentially a cost-effective antifouling method for decentralized membrane-based water systems.
Bakshi, M., Liné, C., Bedolla, D. E., Stein, R. J., Kaegi, R., Sarret, G., … Larue, C. (2019). Assessing the impacts of sewage sludge amendment containing nano-TiO2 on tomato plants: a life cycle study. Journal of Hazardous Materials, 369, 191-198. doi:10.1016/j.jhazmat.2019.02.036, Institutional Repository

Increasing evidence indicates the presence of engineered nanoparticles (ENPs) in sewage sludge derived from wastewater treatment. Land application of sewage sludge is, therefore, considered as an important pathway for ENP transfer to the environment. The aim of this work was to understand the effects of sewage sludge containing nano-TiO2 on plants (tomato) when used as an amendment in agricultural soil. We assessed developmental parameters for the entire plant life cycle along with metabolic and bio-macromolecule changes and titanium accumulation in plants. The results suggest that the sewage sludge amendment containing nano-TiO2 increased plant growth (142% leaf biomass, 102% fruit yield), without causing changes in biochemical responses, except for a 43% decrease in leaf tannin concentration. Changes in elemental concentrations (mainly Fe, B, P, Na, and Mn) of plant stem, leaves and, to a lesser extent fruits were observed. Fourier-transformed infrared analysis showed maximum changes in plant leaves (decrease in tannins and lignins and increase in carbohydrates) but no change in fruits. No significant Ti enrichment was detected in tomato fruits. In conclusion, we evidenced no acute toxicity to plants and no major implication for food safety after one plant life cycle exposure.
Blumensaat, F., Leitão, J. P., Ort, C., Rieckermann, J., Scheidegger, A., Vanrolleghem, P. A., & Villez, K. (2019). How urban storm- and wastewater management prepares for emerging opportunities and threats: digital transformation, ubiquitous sensing, new data sources, and beyond – a horizon scan. Environmental Science and Technology, 53(15), 8488-8498. doi:10.1021/acs.est.8b06481, Institutional Repository

Ubiquitous sensing will create many opportunities and threats for urban water management, which are only poorly understood today. To identify the most relevant trends, we conducted a horizon scan regarding how ubiquitous sensing will shape the future of urban drainage and wastewater management. Our survey of the international urban water community received an active response from both the academics and the professionals from the water industry. The analysis of the responses demonstrates that emerging topics for urban water will often involve experts from different communities, including aquatic ecologists, urban water system engineers and managers, as well as information and communications technology professionals and computer scientists. Activities in topics that are identified as novel will either require (i) cross-disciplinary training, such as importing new developments from the IT sector, or (ii) research in new areas for urban water specialists, for example, to help solve open questions in aquatic ecology. These results are, therefore, a call for interdisciplinary research beyond our own discipline. They also demonstrate that the water management community is not yet prepared for the digital transformation, where we will experience a data demand, i.e. a “pull” of urban water data into external services. The results suggest that a lot remains to be done to harvest the upcoming opportunities. Horizon scanning should be repeated on a routine basis, under the umbrella of an experienced polling organization.
Burdon, F. J., Munz, N. A., Reyes, M., Focks, A., Joss, A., Räsänen, K., … Stamm, C. (2019). Agriculture versus wastewater pollution as drivers of macroinvertebrate community structure in streams. Science of the Total Environment, 659, 1256-1265. doi:10.1016/j.scitotenv.2018.12.372, Institutional Repository

Water pollution is ubiquitous globally, yet how the effects of pollutants propagate through natural ecosystems remains poorly understood. This is because the interactive effects of multiple stressors are generally hard to predict. Agriculture and municipal wastewater treatment plants (WWTPs) are often major sources of contaminants for streams, but their relative importance and the role of different pollutants (e.g. nutrients or pesticides) are largely unknown. Using a 'real world experiment' with sampling locations up- and downstream of WWTPs, we studied how effluent discharges affected water quality and macroinvertebrate communities in 23 Swiss streams across a broad land-use gradient.
Variation partitioning of community composition revealed that overall water quality explained approximately 30% of community variability, whereby nutrients and pesticides each independently explained 10% and 2%, respectively. Excluding oligochaetes (which were highly abundant downstream of the WWTPs) from the analyses, resulted in a relatively stronger influence (3%) of pesticides on the macroinvertebrate community composition, whereas nutrients had no influence. Generally, the macroinvertebrate community composition downstream of the WWTPs strongly reflected the upstream conditions, likely due to a combination of efficient treatment processes, environmental filtering and organismal dispersal. Wastewater impacts were most prominently by the Saprobic index, whereas the SPEAR index (a trait-based macroinvertebrate metrics reflecting sensitivity to pesticides) revealed a strong impact of arable cropping but only a weak impact of wastewater.
Overall, our results indicate that agriculture can have a stronger impact on headwater stream macroinvertebrate communities than discharges from WWTP. Yet, effects of wastewater-born micropollutants were clearly quantifiable among all other influence factors. Improving our ability to further quantify the impacts of micropollutants requires highly-resolved water quality and taxonomic data with adequate spatial and temporal sampling. These improvements would help to better account for the underlying causal pathways that drive observed biological responses, such as episodic contaminant peaks and dispersal-related processes.
Christiaens, M. E. R., Udert, K. M., Arends, J. B. A., Huysman, S., Vanhaecke, L., McAdam, E., & Rabaey, K. (2019). Membrane stripping enables effective electrochemical ammonia recovery from urine while retaining microorganisms and micropollutants. Water Research, 150, 349-357. doi:10.1016/j.watres.2018.11.072, Institutional Repository

Ammonia recovery from urine avoids the need for nitrogen removal through nitrification/denitrification and re-synthesis of ammonia (NH3) via the Haber-Bosch process. Previously, we coupled an alkalifying electrochemical cell to a stripping column, and achieved competitive nitrogen removal and energy efficiencies using only electricity as input, compared to other technologies such as conventional column stripping with air. Direct liquid-liquid extraction with a hydrophobic gas membrane could be an alternative to increase nitrogen recovery from urine into the absorbent while minimizing energy requirements, as well as ensuring microbial and micropollutant retention. Here we compared a column with a membrane stripping reactor, each coupled to an electrochemical cell, fed with source-separated urine and operated at 20 A m−2. Both systems achieved similar nitrogen removal rates, 0.34 ± 0.21 and 0.35 ± 0.08 mol N L−1 d−1, and removal efficiencies, 45.1 ± 18.4 and 49.0 ± 9.3%, for the column and membrane reactor, respectively. The membrane reactor improved nitrogen recovery to 0.27 ± 0.09 mol N L−1 d−1 (38.7 ± 13.5%) while lowering the operational (electrochemical and pumping) energy to 6.5 kWhe kg N−1 recovered, compared to the column reactor, which reached 0.15 ± 0.06 mol N L−1 d−1 (17.2 ± 8.1%) at 13.8 kWhe kg N−1.
Increased cell concentrations of an autofluorescent E. coli MG1655 + prpsM spiked in the urine influent were observed in the absorbent of the column stripping reactor after 24 h, but not for the membrane stripping reactor. None of six selected micropollutants spiked in the urine were found in the absorbent of both technologies.
Overall, the membrane stripping reactor is preferred as it improved nitrogen recovery with less energy input and generated an E. coli- and micropollutant-free product for potential safe reuse. Nitrogen removal rate and efficiency can be further optimized by increasing the NH3 vapor pressure gradient and/or membrane surface area.
Domagała, K., Borlaf, M., Traber, J., Kata, D., & Graule, T. (2019). Purification and functionalisation of multi-walled carbon nanotubes. Materials Letters, 253, 272-275. doi:10.1016/j.matlet.2019.06.085, Institutional Repository

Purifying and functionalising multi-walled carbon nanotubes (MWCNTs) are important processes for providing property modifications, improving handling and enhancing reactivity. The removal of impurities allows avoiding synthesis process interferences and the formation of by-products. During the process it is possible to change the MWCNT properties, e.g. providing enhanced hydrophilicity and better chemical reactivity. In this work, a two-step procedure of MWCNT functionalisation with non-oxidative and oxidative agents is presented. Firstly, hydrochloric acid was used to remove catalyst impurities, which remain after the synthesis process. Secondly, nitric acid was employed to oxidise the MWCNT surfaces and incorporate carboxylic groups onto the surface.
Dörner, L., Cancellieri, C., Rheingans, B., Walter, M., Kägi, R., Schmutz, P., … Jeurgens, L. P. H. (2019). Cost-effective sol-gel synthesis of porous CuO nanoparticle aggregates with tunable specific surface area. Scientific Reports, 9, 11758 (15 pp.). doi:10.1038/s41598-019-48020-8, Institutional Repository

CuO nanoparticles (NPs) are applied in various key technologies, such as catalysis, energy conversion, printable electronics and nanojoining. In this study, an economic, green and easy-scalable sol-gel synthesis method was adopted to produce submicron-sized nanoporous CuO NP aggregates with a specific surface area > 18 m²/g. To this end, a copper-carbonate containing precursor was precipitated from a mixed solution of copper acetate and ammonia carbonate and subsequently calcinated at T ≥ 250 °C. The thus obtained CuO nanopowder is composed of weakly-bounded agglomerates, which are constituted of aggregated CuO NPs with a tunable size in the range of 100–140 nm. The CuO aggregates, in turn, are composed of equi-axed primary crystallites with a tunable crystallite size in the range of 20–40 nm. The size and shape of the primary CuO crystallites, as well as the nanoporosity of their fused CuO aggregates, can be tuned by controlled variation of the degree of supersaturation of the solution via the pH and the carbonate concentration. The synthesized submicron-sized CuO aggregates can be more easily and safely processed in the form of a solution, dispersion or paste than individual NPs, while still offering the same enhanced reactivity due to their nanoporous architecture.
Gogos, A., Wielinski, J., Voegelin, A., Emerich, H., & Kaegi, R. (2019). Transformation of cerium dioxide nanoparticles during sewage sludge incineration. Environmental Science: Nano, 6, 1765-1776. doi:10.1039/C9EN00281B, Institutional Repository

Production volumes of cerium dioxide nanoparticles (CeO2 NP) are predicted to increase in the near future, which will result in increasing amounts of CeO2 NP discharged into wastewater systems and their accumulation in the sewage sludge. At the same time, thermal treatments of sewage sludge, especially incineration, are gaining in importance. Therefore, knowledge on the physical–chemical transformations of CeO2 NP during wastewater treatment and sludge incineration is critical for assessing possible (eco-) toxicological effects related to the increased use of CeO2 NP. We, thus, incinerated unspiked municipal sewage sludge as well as sludge spiked with CeO2 of different particle sizes (4 nm (CeO2-s1), 26 nm (CeO2-s2) and >16 μm (CeO2-s3)) in a pilot fluidized bed reactor to investigate the (size dependent) transformation of CeO2 under conditions mimicking full-scale incineration facilities. We used Ce K- and LIII-edge X-ray absorption spectroscopy (XAS) complemented by analytical electron microscopy to assess the changes in Ce speciation and to characterize the morphology of the pristine and the transformed Ce-(nano)particles. After one week of incubation in digested sludge under anaerobic conditions, CeO2-s1 already showed partial reduction (≈40%) to a Ce(III)-phase. Cerium dioxide of larger particle size (CeO2-s2 and -s3) was less reactive and did not show any detectable reduction within the same reaction time. Incineration of the sludge in general led to a further reduction of Ce, irrespective of whether the Ce was spiked (CeO2-s1, CeO2-s2, CeO2-s3) or already present in the sludge. Reduction during incineration was nearly complete for CeO2-s1 but much less pronounced for CeO2-s2 and -s3. Ce(IV) in larger (primary-) particle sizes thus was more resistant to reduction during anaerobic digestion and incineration. In addition, elemental distribution maps of the CeO2-s1 fly ash revealed elevated Ce signal intensities evenly distributed over areas of several 100 nm. The complementary results obtained from spectroscopic and microscopic analyses indicate that incineration led to the reductive decomposition of the initial CeO2-s1 NP and the sequestration of Ce(III) into a mineralogical phase with probably allanite-like local Ce(III) coordination. Our results, thus, highlight the importance of particle size and the surrounding matrix both affecting the transformation of CeO2 during sewage sludge incineration.
Gruber, W., Villez, K., Kipf, M., Wunderlin, P., Siegrist, H., Vogt, L., & Joss, A. (2019). N2O emission in full-scale wastewater treatment: proposing a refined monitoring strategy. Science of the Total Environment, 699, 134157 (9 pp.). doi:10.1016/j.scitotenv.2019.134157, Institutional Repository

Nitrous oxide (N2O) emissions from wastewater treatment contribute significantly to greenhouse gas emissions. They have been shown to exhibit a strong seasonal and daily profile in previously conducted monitoring campaigns. However, only two year-long online monitoring campaigns have been published to date. Based on three monitoring campaigns on three full-scale wastewater treatment plants (WWTPs) with different activated sludge configurations, each of which lasted at least one year, we propose a refined monitoring strategy for long-term emission monitoring with multiple flux chambers on open tanks. Our monitoring campaigns confirm that the N2O emissions exhibited a strong seasonal profile and were substantial on all three plants (1-2.4% of the total nitrogen load). These results confirm that N2O is the most important greenhouse gas emission from wastewater treatment. The temporal variation was more distinct than the spatial variation within aeration tanks. Nevertheless, multiple monitoring spots along a single lane are crucial to assess representative emission factors in flow-through systems. Sequencing batch reactor systems were shown to exhibit comparable emissions within one reactor but significant variation between parallel reactors. The results indicate that considerable emission differences between lanes are to be expected in cases of inhomogeneous loading and discontinuous feeding. For example, N2O emission could be shown to depend on the amount of treated reject water: lanes without emitted <1% of the influent load, while parallel lanes emitted around 3%. In case of inhomogeneous loading, monitoring of multiple lanes is required. Our study enables robust planning of monitoring campaigns on WWTPs with open tanks. Extensive full-scale emission monitoring campaigns are important as a basis for reliable decisions about reducing the climate impact of wastewater treatment. More specifically, such data sets help us to define general emission factors for wastewater treatment plants and to construct and critically evaluate N2O emission models.
Hoppe, M., Schlich, K., Wielinski, J., Köser, J., Rückamp, D., Kaegi, R., & Hund-Rinke, K. (2019). Long-term outdoor lysimeter study with cerium dioxide nanomaterial. NanoImpact, 14, 100170 (9 pp.). doi:10.1016/j.impact.2019.100170, Institutional Repository

Fate and impact of cerium dioxide nanomaterials (CeO2 NM) in soil remains uncertain. Most of the recent environmental studies used high doses of CeO2 NM in short-term laboratory experiments and stated soil as large sink for NM. Recent studies covering the life cycle of plants found evidence for particle uptake in crop plants, and triggered concern about NM entering the food chain. Here, we present a 25 months outdoor lysimeter study that investigates the translocation, biological impact, and transformation of CeO2 NM in soils cultivated with different crops (wheat (Triticum aestivum L.), canola (Brassica napus L.), and barley (Hordeum vulgare L.)). Low doses of CeO2 NM (NM-212, 10 and 50 mg CeO2 NM kg−1 soil) were applied to a Cambisol by sewage sludge or artificial rainwater. To simulate ploughing, the CeO2 NM was mixed into the first 20 cm of the lysimeter soil. Three weeks after the NM application by sewage sludge and five days after the latest NM application by artificial rainwater wheat seeds were sown.
We found no vertical Ce translocation to deeper soil layers as well as negligible release of Ce into percolating water, confirming that soil is a sink for CeO2 NM. Furthermore, no inhibition of the NM sensitive ammonium oxidizing bacteria (AOB) was observed which implies a low bioavailability of CeO2 NM in soil. The detected Ce root uptake for canola (Ce < 35.7 mg kg−1) and barley (Ce < 61.8 mg kg−1) indicates that physico-chemical conditions in the rhizosphere or the aging of the NM in soil can remobilize the applied CeO2 NM to some extent. One can speculate that the obtained reduction of Ce4+ to Ce3+ (≈ 50% after 25 months) was coupled to different conditions (ionic strength, pH, water content, soil organic matter content) in the rhizosphere and necessary for the root accumulation of Ce.
Due to negligible mobility in the soil-water interface, as well as non-toxicity to AOB, the environmental risk of the tested CeO2 NM appears to be low, compared to other highly mobile emergent pollutants. Nonetheless, further long-term investigations need to focus on the speciation and localization of NM in plants to clarify uptake and impact of NM to crops.
Jafari, M., Derlon, N., Desmond, P., van Loosdrecht, M. C. M., Morgenroth, E., & Picioreanu, C. (2019). Biofilm compressibility in ultrafiltration: a relation between biofilm morphology, mechanics and hydraulic resistance. Water Research, 157, 335-345. doi:10.1016/j.watres.2019.03.073, Institutional Repository

Poroelastic fluid-structure interaction models were coupled to experimental data to determine the effects of biofilm spatial distribution of mechanical and hydraulic properties on the biofilm hydraulic resistance and compressibility in membrane filtration processes. Biofilms were cultivated on ultrafiltration membranes for 20 and 30 days under high (0.28 bar) and low (0.06 bar) transmembrane pressure (TMP), in dead-end filtration mode. Subsequently, biofilms were subjected to a compression/relaxation cycles by step-wise TMP changes. Structural deformation of biofilms during compression was observed in-situ using optical coherence tomography.
Experimental results show that the observed increase in the biofilm hydraulic resistance during compression is not necessarily accompanied by a detectable biofilm thickness reduction. A dual-layer biofilm model with a dense base and porous top layer could explain these observed results. Because porosity controls indirectly the mechanical response of biofilms under compression, results could be described without assuming a gradient in mechanical properties within the biofilm. The biofilm surface roughness did not significantly influence the water flux in this study. However, the fraction of biofilm base layer directly exposed to bulk liquid could be a good indicator in the determination of water flux. The main implications of this study for the design and operation of low-pressure membrane systems (e.g., MF and UF with fouling layer being the main filtration resistance) lays in the selection of favorable operational TMP and biofilm morphology.
Laureni, M., Weissbrodt, D. G., Villez, K., Robin, O., de Jonge, N., Rosenthal, A., … Joss, A. (2019). Biomass segregation between biofilm and flocs improves the control of nitrite-oxidizing bacteria in mainstream partial nitritation and anammox processes. Water Research, 154, 104-116. doi:10.1016/j.watres.2018.12.051, Institutional Repository

The control of nitrite-oxidizing bacteria (NOB) challenges the implementation of partial nitritation and anammox (PN/A) processes under mainstream conditions. The aim of the present study was to understand how operating conditions impact microbial competition and the control of NOB in hybrid PN/A systems, where biofilm and flocs coexist. A hybrid PN/A moving-bed biofilm reactor (MBBR; also referred to as integrated fixed film activated sludge or IFAS) was operated at 15 °C on aerobically pre-treated municipal wastewater (23 mgNH4-N L–1). Ammonium-oxidizing bacteria (AOB) and NOB were enriched primarily in the flocs, and anammox bacteria (AMX) in the biofilm. After decreasing the dissolved oxygen concentration (DO) from 1.2 to 0.17 mgO2 L–1 - with all other operating conditions unchanged - washout of NOB from the flocs was observed. The activity of the minor NOB fraction remaining in the biofilm was suppressed at low DO. As a result, low effluent NO3– concentrations (0.5 mgN L–1) were consistently achieved at aerobic nitrogen removal rates (80 mgN L–1 d–1) comparable to those of conventional treatment plants. A simple dynamic mathematical model, assuming perfect biomass segregation with AOB and NOB in the flocs and AMX in the biofilm, was able to qualitatively reproduce the selective washout of NOB from the flocs in response to the decrease in DO-setpoint. Similarly, numerical simulations indicated that flocs removal is an effective operational strategy to achieve the selective washout of NOB. The direct competition for NO2– between NOB and AMX - the latter retained in the biofilm and acting as a "NO2-sink" - was identified by the model as key mechanism leading to a difference in the actual growth rates of AOB and NOB (i.e., μNOB < μAOB in flocs) and allowing for the selective NOB washout over a broad range of simulated sludge retention times (SRT = 6.8–24.5 d). Experimental results and model predictions demonstrate the increased operational flexibility, in terms of variables that can be easily controlled by operators, offered by hybrid systems as compared to solely biofilm systems for the control of NOB in mainstream PN/A applications.
Layer, M., Adler, A., Reynaert, E., Hernandez, A., Pagni, M., Morgenroth, E., … Derlon, N. (2019). Organic substrate diffusibility governs microbial community composition, nutrient removal performance and kinetics of granulation of aerobic granular sludge. Water Research X, 4, 100033 (16 pp.). doi:10.1016/j.wroa.2019.100033, Institutional Repository

Basic understanding of formation of aerobic granular sludge (AGS) has mainly been derived from lab-scale systems with simple influents containing only highly diffusible volatile fatty acids (VFA) as organic substrate. This study compares start-up of AGS systems fed by different synthetic and municipal wastewaters (WW), characterised by increasing complexity in terms of non-diffusible organic substrate. Four AGS reactors were started with the same inoculum activated sludge and operated for one year. The development of AGS, settling characteristics, nutrient and substrate removal performance as well as microbial community composition were monitored. Our results indicate that the higher the content of diffusible organic substrate in the WW, the faster the formation of AGS. The presence of non-diffusible organic substrate in the influent WW led to the formation of small granules and to the presence of 20–40% (% of total suspended solids) of flocs in the AGS. When AGS was fed with complex influent WW, the classical phosphorus and glycogen accumulating organisms (PAO, GAO) were outcompeted by their fermentative equivalents. Substrate and nutrient removal was observed in all reactors, despite the difference in physical and settling properties of the AGS, but the levels of P and N removal depended on the influent carbon composition. Mechanistically, our results indicate that increased levels of non-diffusible organic substrate in the influent lower the potential for microbial growth deep inside the granules. Additionally, non-diffusible organic substrates give a competitive advantage to the main opponents of AGS formation – ordinary heterotrophic organisms (OHO). Both of these mechanisms are suspected to limit AGS formation. The presented study has relevant implications for both practice and research. Start-up duration of AGS systems treating high complexity WW were one order of magnitude higher than a typical lab-scale system treating VFA-rich synthetic WW, and biomass as flocs persisted as a significant fraction. Finally, the complex synthetic influent WW – composed of VFA, soluble fermentable and particulate substrate - tested here seems to be a more adequate surrogate of real municipal WW for laboratory studies than 100%-VFA WW.
Mansfeldt, C., Achermann, S., Men, Y., Walser, J. C., Villez, K., Joss, A., … Fenner, K. (2019). Microbial residence time is a controlling parameter of the taxonomic composition and functional profile of microbial communities. ISME Journal, 13(6), 1589-1601. doi:10.1038/s41396-019-0371-6, Institutional Repository

A remaining challenge within microbial ecology is to understand the determinants of richness and diversity observed in environmental microbial communities. In a range of systems, including activated sludge bioreactors, the microbial residence time (MRT) has been previously shown to shape the microbial community composition. However, the physiological and ecological mechanisms driving this influence have remained unclear. Here, this relationship is explored by analyzing an activated sludge system fed with municipal wastewater. Using a model designed in this study based on Monod-growth kinetics, longer MRTs were shown to increase the range of growth parameters that enable persistence, resulting in increased richness and diversity in the modeled community. In laboratory experiments, six sequencing batch reactors treating domestic wastewater were operated in parallel at MRTs between 1 and 15 days. The communities were characterized using both 16S ribosomal RNA and non-target messenger RNA sequencing (metatranscriptomic analysis), and model-predicted monotonic increases in richness were confirmed in both profiles. Accordingly, taxonomic Shannon diversity also increased with MRT. In contrast, the diversity in enzyme class annotations resulting from the metatranscriptomic analysis displayed a non-monotonic trend over the MRT gradient. Disproportionately high abundances of transcripts encoding for rarer enzymes occur at longer MRTs and lead to the disconnect between taxonomic and functional diversity profiles.
Mitrano, D. M., Beltzung, A., Frehland, S., Schmiedgruber, M., Cingolani, A., & Schmidt, F. (2019). Synthesis of metal-doped nanoplastics and their utility to investigate fate and behaviour in complex environmental systems. Nature Nanotechnology, 14, 362-368. doi:10.1038/s41565-018-0360-3, Institutional Repository

Research on the distribution and effects of particulate plastic has intensified in recent years and yet, due to analytical challenges, our understanding of nanoplastic occurrence and behaviour has remained comparatively elusive. However, process studies could greatly aid in defining key parameters for nanoplastic interactions within and transfers between technical and environmental compartments. Here we provide a method to synthesize nanoplastic particles doped with a chemically entrapped metal used as a tracer, which provides a robust way to detect nanoplastics more easily, accurately and quantitatively in complex media. We show the utility of this approach in batch studies that simulate the activated sludge process of a municipal waste water treatment plant and so better understand the fate of nanoplastics in urban environments. We found that the majority of particles were associated with the sludge (>98%), with an average recovery of over 93% of the spiked material achieved. We believe that this approach can be developed further to study the fate, transport, mechanistic behaviour and biological uptake of nanoplastics in a variety of systems on different scales.
Németh, Z., Szekeres, G. P., Schabikowski, M., Schrantz, K., Traber, J., Pronk, W., … Graule, T. (2019). Enhanced virus filtration in hybrid membranes with MWCNT nanocomposite. Royal Society Open Science, 6(1), 181294 (14 pp.). doi:10.1098/rsos.181294, Institutional Repository

Membrane separation is proved to be a powerful tool for several applications such as wastewater treatment or the elimination of various microorganisms from drinking water. In this study, the efficiency of inorganic composite-based multi-walled carbon nanotube (MWCNT) hybrid membranes was investigated in the removal of MS2 bacteriophages from contaminated water. With this object, multi-walled carbon nanotubes were coated with copper(I) oxide, titanium(IV) oxide and iron(III) oxide nanoparticles, respectively, and their virus removal capability was tested in both batch and flow experiments. Considering the possible pH range of drinking water, the filtration tests were carried out at pH 5.0, 7.5 and 9.0 as well. The extent of MS2 removal strongly depended on the pH values for each composite, which can be due to electrostatic interactions between the membrane and the virus. The most efficient removal (greater than or equal to 99.99%) was obtained with the Cu2O-coated MWCNT membrane in the whole pH range. The fabricated nanocomposites were characterized by X-ray diffraction, specific surface area measurement, dynamic light scattering, zeta potential measurement, Raman spectroscopy, transmission electron microscopy and scanning electron microscopy. This study presents a simple route to design novel and effective nanocomposite-based hybrid membranes for virus removal.
Nürenberg, G., Kunkel, U., Wick, A., Falås, P., Joss, A., & Ternes, T. A. (2019). Nontarget analysis: a new tool for the evaluation of wastewater processes. Water Research, 163, 114842 (11 pp.). doi:10.1016/j.watres.2019.07.009, Institutional Repository

Strategies to determine the removal efficiency of micropollutants in wastewater treatment plants (WWTPs) are widely discussed. Especially the evaluation of the potential benefit of further advanced treatment steps such as an additional tertiary treatment based on ozonation or activated carbon have come into focus. Such evaluation strategies are often based on the removal behavior of known micropollutants via target or suspected analysis. The utilization of nontarget analysis is considered to lead to a more comprehensive picture as also unknown or not expected micropollutants are analyzed. Here, the results of an evaluation via target and nontarget analysis were compared for biological treatment (BT) processes of eleven full-scale WWTPs and three different post-treatments (PTs): one sand filter (SF) and two granular activated carbon (GAC) filters. The similarity of the determined removals from target and nontarget analysis of the BTs increased significantly by excluding easily degradable "features" from the nontarget evaluation. A similar ranking of the removal trends for the BTs could also be achieved by comparing this new subset of nontarget features with a set of nine readily to moderately biodegradable micropollutants. This observation suggests that a performance ranking of BTs based either on target or nontarget analysis is plausible. In contrast to the BTs, the evaluation of the three PTs revealed that the difference of feature removal between SF and the two GACs was small, but large for the target analytes with substantially higher removal effciencies for the GACs compared to the SF. In addition to the removal behavior, the nontarget analysis provided further information about the number and quantity of transformation products (TPs) in the effluent from the BTs. For all BTs more than half (55–67%) of the features detected in the effluent were not found in the influent. A comparable proportion of TPs was also detected after GAC and sand filtration due to their microbial activities.
Ohmura, K., Thürlimann, C. M., Kipf, M., Carbajal, J. P., & Villez, K. (2019). Characterizing long-term wear and tear of ion-selective pH sensors. Water Science and Technology, 80(3), 541-550. doi:10.2166/wst.2019.301, Institutional Repository

Today, the development and testing of methods for fault detection and identification in wastewater treatment research relies on two important assumptions: (i) that sensor faults appear at distinct times in different sensors and (ii) that any given sensor will function near-perfectly for a significant amount of time following installation. In this work, we show that such assumptions are unrealistic, at least for sensors built around an ion-selective measurement principle. Indeed, long-term exposure of sensors to treated wastewater shows that sensors exhibit fault symptoms that appear simultaneously and with similar intensity. Consequently, this suggests that future research should be reoriented towards methods that do not rely on the assumptions mentioned above. This study also provides the first empirically validated sensor fault model for wastewater treatment simulation, which is useful for effective benchmarking of both fault detection and identification methods and advanced control strategies. Finally, we evaluate the value of redundancy for remote sensor validation in decentralized wastewater treatment systems.
Pronk, W., Ding, A., Morgenroth, E., Derlon, N., Desmond, P., Burkhardt, M., … Fane, A. G. (2019). Gravity-driven membrane filtration for water and wastewater treatment: a review. Water Research, 149, 553-565. doi:10.1016/j.watres.2018.11.062, Institutional Repository

Gravity-driven membrane (GDM) filtration has been investigated for almost 10 years. The technology is characterized not only by relatively lower transmembrane pressures which can be achieved by gravity (extremely low energy consumption), but also by the phenomenon of flux stabilization: A biofilm is allowed to form on the membrane and a stabilization of flux occurs which is related to biological processes within the biofilm layer on the membrane. This enables stable operation during a year or longer without any cleaning or flushing. Initially, the technology was developed mainly for household drinking water treatment, but in the meantime, the research and application has expanded to the treatment of greywater, rainwater, and wastewater as well as the pretreatment of seawater for desalination. This review covers the field from the rather fundamental research on biofilm morphology and microbial community analysis to the impact of feedwater composition, process parameters and organic removal performance. Not only household applications, but also for community-scale treatment and full-scale applications are discussed. In addition, the application potential is highlighted in comparison to conventional ultrafiltration. Finally, an overall assessment is illustrated and the research and development needs are identified.
Pulido-Reyes, G., Briffa, S. M., Hurtado-Gallego, J., Yudina, T., Leganés, F., Puntes, V., … Fernández-Piñas, F. (2019). Internalization and toxicological mechanisms of uncoated and PVP-coated cerium oxide nanoparticles in the freshwater alga: Chlamydomonas reinhardtii. Environmental Science: Nano, 6(6), 1959-1972. doi:10.1039/c9en00363k, Institutional Repository

Due to the wide range of applications of cerium oxide nanoparticles (CeO2NPs), a risk assessment of their biological effects using environmentally relevant species becomes highly important. There are contradictory reports on the effects of CeO2NPs, which may be related to the use of different types of nanoparticles (NPs) and coatings. CeO2NPs may act as an oxidant causing toxicity or as an antioxidant able to scavenge free radicals. As a consequence of such complexity, the toxicological behaviour of these NPs is still poorly understood. Moreover, little is known about the internalization process of CeO2NPs in algae. There is evidence of CeO2NP-internalization by the green alga Chlamydomonas reinhardtii, but the mechanism and route of uptake are still unknown. In this study, we used uncoated and different polyvinylpyrrolidone (PVP)-coated CeO2NPs with the aim of identifying their toxicological mechanisms to C. reinhardtii and exploring their possible internalization. Our results showed that PVP coated-CeO2NPs significantly increased the formation of reactive oxygen species in exposed cells, indicating that oxidative stress is an important toxicity mechanism for these particles. Direct contact and damage of the cellular membrane was identified as the mechanism causing the toxicity of uncoated NPs. From experiments with endocytosis inhibitors, clathrin-dependent endocytosis was revealed as the main internalization route for all NPs. However, as uncoated CeO2NPs led to severe cellular membrane damage, direct passage of NPs through membrane holes could not be discarded. To our knowledge, this is the first report with evidence of direct linking between NP internalization and a specific endocytic pathway. The results presented here will help to unravel the toxicological mechanism and behaviour of CeO2NPs and provide input information for the environmental health and safety assessment of CeO2NPs.
Regmi, P., Stewart, H., Amerlinck, Y., Arnell, M., García, P. J., Johnson, B., … Rosso, D. (2019). The future of WRRF modelling – outlook and challenges. Water Science and Technology, 79(1), 3-14. doi:10.2166/wst.2018.498, Institutional Repository

The wastewater industry is currently facing dramatic changes, shifting away from energy-intensive wastewater treatment towards low-energy, sustainable technologies capable of achieving energy positive operation and resource recovery. The latter will shift the focus of the wastewater industry to how one could manage and extract resources from the wastewater, as opposed to the conventional paradigm of treatment. Debatable questions arise: can the more complex models be calibrated, or will additional unknowns be introduced? After almost 30 years using well-known International Water Association (IWA) models, should the community move to other components, processes, or model structures like 'black box' models, computational fluid dynamics techniques, etc.? Can new data sources – e.g. on-line sensor data, chemical and molecular analyses, new analytical techniques, off-gas analysis – keep up with the increasing process complexity? Are different methods for data management, data reconciliation, and fault detection mature enough for coping with such a large amount of information? Are the available calibration techniques able to cope with such complex models? This paper describes the thoughts and opinions collected during the closing session of the 6th IWA/WEF Water Resource Recovery Modelling Seminar 2018. It presents a concerted and collective effort by individuals from many different sectors of the wastewater industry to offer past and present insights, as well as an outlook into the future of wastewater modelling.
Russo, S., Li, G., & Villez, K. (2019). Automated model selection in principal component analysis: a new approach based on the cross-validated ignorance score. Industrial and Engineering Chemistry Research, 58(30), 13448-13468. doi:10.1021/acs.iecr.9b00642, Institutional Repository

Principal component analysis (PCA) is by far the most widespread tool for unsupervised learning with high-dimensional data sets. It is popularly studied for exploratory data analysis and online process monitoring. Unfortunately, fine-tuning PCA models and particularly the number of components remains a challenging task. Today, this selection is often based on a combination of guiding principles, experience, and process understanding. Unlike the case of regression, where cross-validation of the prediction error is a widespread and trusted approach for model selection, there are no tools for PCA model selection enjoying this level of acceptance. In this work, we address this challenge and evaluate the utility of the cross-validated ignorance score with both simulated and experimental data sets. Application of this model selection criterion is based on the interpretation of PCA as a density model, as in probabilistic principal component analysis. With simulation-based benchmarking, it is shown to be (a) the overall best performing criterion, (b) the preferred criterion at high noise levels, and (c) very robust to changes in noise level. Tests on experimental data sets suggest that the ignorance score is sensitive to deviations from the PCA model structure, which suggests the criterion is also useful to detect of model-reality mismatch.
Salas, P., Odzak, N., Echegoyen, Y., Kägi, R., Sancho, M. C., & Navarro, E. (2019). The role of size and protein shells in the toxicity to algal photosynthesis induced by ionic silver delivered from silver nanoparticles. Science of the Total Environment, 692, 233-239. doi:10.1016/j.scitotenv.2019.07.237, Institutional Repository

Because of their biocide properties, silver nanoparticles (AgNPs) are present in numerous consumer products. The biocidal properties of AgNPs are due to both the interactions between AgNP and cell membranes and the release of dissolved silver (Ag+). Recent studies emphasized the role of different nanoparticle coatings in complexing and storing Ag+. In this study, the availability of dissolved silver in the presence of algae was assessed for three AgNPs with different silver contents (59%, 34% and 7% of total Ag), silver core sizes and casein shell thicknesses. The impact of ionic silver on the photosynthetic yield of Chlamydomonas reinhardtii was used as a proxy to estimate the amount of ionic silver toxically active during in vivo assays. The results showed that cysteine, a strong silver ligand, mitigated the toxicity of AgNPs in all cases, demonstrating the key role of Ag+ in this toxicity. The results showed that the AgNPs presenting an intermediate level of silver (34%) were 10 times more effective in terms of total mass (EC50 ten times smaller) than those presenting more (59%) or less (7%) silver. The higher toxicity was due to the higher release of Ag+ under biotic conditions due to the high surface/mass ratio of the nanoparticle silver core. Protein shells played a minor role in altering the availability of Ag+, probably acting as intermediate reservoirs. This study highlighted the utility of a very sensitive biological endpoint (i.e., algal photosynthesis) for the optimization of ionic silver delivery by nanomaterials.
Schmiedgruber, M., Hufenus, R., & Mitrano, D. M. (2019). Mechanistic understanding of microplastic fiber fate and sampling strategies: synthesis and utility of metal doped polyester fibers. Water Research, 155, 423-430. doi:10.1016/j.watres.2019.02.044, Institutional Repository

The increased use of synthetic textiles in the last decades, coupled with recent emphasis on the accumulation of (micro)plastic across multiple environmental compartments, has garnered interest into how microplastic fibers are released into the environment. In particular, polyester textiles washed in the home have shown to release microplastic fibers but challenges with microplastic fiber analysis, including time and difficulty of sample preparation and measurement, has limited mechanistic studies on fiber fate and transport studies. In this study, we provide a method to synthesize fibers with an embedded inorganic (In) fingerprint which can be used as a tracer for ease of analysis and show the utility of this approach to assess the affinity for heteroaggregation between microplastic fibers and other particles in a heterogeneous suspension, as well as approximate the fate of microplastic fibers in batch studies using activated sludge from a municipal wastewater treatment plant (WWTP). Total In content in the fibers was measured to be 0.2 % by weight, which was low enough to not change fiber dynamics for fate and transport studies (e.g. density, etc.) but provided sensitive detection limits by ICP-MS. Fiber length was 510 μm ± 410 μm and 30 μm in diameter. The incorporated metal remained stable inside the polymer when suspended in water and in activated sludge, with < 0.1 % In leaching over two months. In batch experiments, the majority of fibers were associated with the sludge ( > 99.9 %), with a mass balance of > 95 % recovery achieved on average across batches. Fiber removal linearly increased with contact times of up to 10 min, suggesting interactions between plastics and organic matter is a metric that should be considered closely in this and other environmental contexts for fate and transport.
Schneider, M. Y., Carbajal, J. P., Furrer, V., Sterkele, B., Maurer, M., & Villez, K. (2019). Beyond signal quality: the value of unmaintained pH, dissolved oxygen, and oxidation-reduction potential sensors for remote performance monitoring of on-site sequencing batch reactors. Water Research, 161, 639-651. doi:10.1016/j.watres.2019.06.007, Institutional Repository

Sensor maintenance is time-consuming and is a bottleneck for monitoring on-site wastewater treatment systems. Hence, we compare maintained and unmaintained sensors to monitor the biological performance of a small-scale sequencing batch reactor (SBR). The sensor types are ion-selective pH, optical dissolved oxygen (DO), and oxidation-reduction potential (ORP) with platinum electrode. We created soft sensors using engineered features: ammonium valley for pH, oxidation ramp for DO, and nitrite ramp for the ORP. Four soft sensors based on unmaintained pH sensors correctly identified the completion of the ammonium oxidation (89–91 out of 107 cycles), about as many times as soft sensors based on a maintained pH sensor (91 out of 107 cycles). In contrast, the DO soft sensor using data from a maintained sensor showed slightly better (89 out of 96 cycles) detection performance than that using data from two unmaintained sensors (77, respectively 82 out of 96 correct). Furthermore, the DO soft sensor using maintained data is much less sensitive to the optimisation of cut-off frequency and slope tolerance than the soft sensor using unmaintained data. The nitrite ramp provided no useful information on the state of nitrite oxidation, so no comparison of maintained and unmaintained ORP sensors was possible in this case. We identified two hurdles when designing soft sensors for unmaintained sensors: i) Sensors’ type- and design-specific deterioration affects performance. ii) Feature engineering for soft sensors is sensor type specific, and the outcome is strongly influenced by operational parameters such as the aeration rate. In summary, the results with the provided soft sensors show that frequent sensor maintenance is not necessarily needed to monitor the performance of SBRs. Without sensor maintenance monitoring smalls-scale SBRs becomes practicable, which could improve the reliability of unstaffed on-site treatment systems substantially.
Seviour, T., Derlon, N., Simonsen Dueholm, M., Flemming, H. C., Girbal-Neuhauser, E., Horn, H., … Lin, Y. (2019). Extracellular polymeric substances of biofilms: suffering from an identity crisis. Water Research, 151, 1-7. doi:10.1016/j.watres.2018.11.020, Institutional Repository

Microbial biofilms can be both cause and cure to a range of emerging societal problems including antimicrobial tolerance, water sanitation, water scarcity and pollution. The identities of extracellular polymeric substances (EPS) responsible for the establishment and function of biofilms are poorly understood. The lack of information on the chemical and physical identities of EPS limits the potential to rationally engineer biofilm processes, and impedes progress within the water and wastewater sector towards a circular economy and resource recovery. Here, a multidisciplinary roadmap for addressing this EPS identity crisis is proposed. This involves improved EPS extraction and characterization methodologies, cross-referencing between model biofilms and full-scale biofilm systems, and functional description of isolated EPS with in situ techniques (e.g. microscopy) coupled with genomics, proteomics and glycomics. The current extraction and spectrophotometric characterization methods, often based on the principle not to compromise the integrity of the microbial cells, should be critically assessed, and more comprehensive methods for recovery and characterization of EPS need to be developed.
Silva, M. O. D., Desmond, P., Derlon, N., Morgenroth, E., & Pernthaler, J. (2019). Source community and assembly processes affect the efficiency of microbial microcystin degradation on drinking water filtration membranes. Frontiers in Microbiology, 10, 843 (15 pp.). doi:10.3389/fmicb.2019.00843, Institutional Repository

Microbial biofilms in gravity-driven membrane (GDM) filtration systems can efficiently degrade the cyanotoxin microcystin (MC), but it is unclear if this function depends on the presence of MC-producing cyanobacteria in the source water habitat. We assessed the removal of MC from added Microcystis aeruginosa biomass in GDMs fed with water from a lake with regular blooms of toxic cyanobacteria (ExpL) or from a stream without such background (ExpS). While initial MC removal was exclusively due to abiotic processes, significantly higher biological MC removal was observed in ExpL. By contrast, there was no difference in MC degradation capacity between lake and stream bacteria in separately conducted liquid enrichments on pure MC. Co-occurrence network analysis revealed a pronounced modularity of the biofilm communities, with a clear hierarchic distinction according to feed water origin and treatment type. Genotypes in the network modules associated with ExpS had significantly more links to each other, indicating that these biofilms had assembled from a more coherent source community. In turn, signals for stochastic community assembly were stronger in ExpL biofilms. We propose that the less “tightly knit” ExpL biofilm assemblages allowed for the better establishment of facultatively MC degrading bacteria, and thus for higher overall functional efficiency.
 
Surette, M. C., Nason, J. A., & Kaegi, R. (2019). The influence of surface coating functionality on the aging of nanoparticles in wastewater. Environmental Science: Nano, 6(8), 2470-2483. doi:10.1039/C9EN00376B, Institutional Repository

Efforts to predict the environmental fate of engineered nanomaterials (ENMs) are frequently based on the physiochemical properties and behavior of the ENMs in their pristine, “as-produced” state. However, it is well-established that ENMs can be physically, biologically, and chemically transformed, resulting in altered physiochemical properties and behavior. Wastewater treatment plants (WWTPs) represent an important stage in an ENM's life-cycle where they can be transformed. To better understand the properties of ENMs discharged from WWTPs into surface waters, we investigated how the transformation processes of aggregation and corona formation are influenced by the surface coating applied to ENMs during their manufacture. Using 40 nm gold nanoparticles coated with polyethylene glycol, lipoic acid, or branched polyethylenimine as model ENMs, batch experiments were performed to investigate aggregation and corona formation during the primary clarification and activated sludge treatment stages. A tangential flow filtration system was used to evaluate if the initial transformations were altered as the aquatic chemistry of the background matrix was changed, mimicking the varying conditions ENMs would experience during transport through a WWTP. Using a combination of corroborative techniques including dynamic light scattering, phase analysis light scattering, ultraviolet-visible light spectroscopy, and transmission electron microscopy, we find that the model ENMs aggregated in each wastewater matrix, regardless of the initial surface coating. Differences in the UV-vis spectra indicate that the nature of the corona acquired by the ENMs differed as a function of the surface coating of the pristine ENMs. In addition, initial ENM transformations during exposure to the influent wastewater persisted even as the background matrix changed. These results support the finding that ENMs discharged from WWTPs will not resemble their pristine analogs. Furthermore, the corona acquired by ENMs in WWTPs may vary in relation to their pristine properties and be dictated by conditions during early stage exposures.
ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2019). Ferrihydrite growth and transformation in the presence of ferrous iron and model organic ligands. Environmental Science and Technology, 53(23), 13636-13647. doi:10.1021/acs.est.9b03952, Institutional Repository

Ferrihydrite (Fh) is a poorly crystalline Fe(III)-oxyhydroxide found in abundance in soils and sediments. With a high specific surface area and sorption capacity at circumneutral pH, ferrihydrite is an important player in the biogeochemical cycling of nutrients and trace elements in redox-dynamic environments. Under reducing conditions, exposure to Fe(II) induces mineral transformations in ferrihydrite; the extent and trajectory of which may be greatly influenced by organic matter (OM). However, natural OM is heterogeneous and comprises a range of molecular weights (MWs) and varied functional group compositions. To date, the impact that the chemical composition of the associated OM has on Fe(II)-catalyzed mineral transformations is not clear. To address this knowledge gap, we coprecipitated ferrihydrite with model organic ligands selected to cover a range of MWs (25 000–50 000 vs <200 Da) as well as carboxyl content (polygalacturonic acid (PGA) > citric acid (CA) > galacturonic acid (GA)). Coprecipitates (C:Fe ≈ 0.6) were reacted with 1 mM 57Fe(II) for 1 week at pH 7, with time-resolved solid-phase analysis (via X-ray diffraction, X-ray absorption spectroscopy, and electron microscopy) revealing that all ligands inhibited Fe(II)-catalyzed ferrihydrite mineral transformations and the formation of crystalline secondary mineral phases compared to a pure ferrihydrite. For carboxyl-rich coprecipitates (Fh-PGA and Fh-CA), mineral transformations were less inhibited than in the carboxyl poor Fh-GA, and a crystalline lepidocrocite "shell" was formed surrounding the residual ferrihydrite core. However, Fe isotope analysis revealed that all coprecipitates underwent near complete atom exchange. Collectively, our results highlight that ferrihydrite is indeed an active mineral phase in redox-dynamic environments, but that its stability under reducing conditions, and thus capacity for nutrient and trace element retention, depends on the chemical characteristic of the associated OM, specifically OM-induced changes in the particle surface charge and the distribution of organic functional groups.
Thürlimann, C. M., Udert, K. M., Morgenroth, E., & Villez, K. (2019). Stabilizing control of a urine nitrification process in the presence of sensor drift. Water Research, 165, 114958 (10 pp.). doi:10.1016/j.watres.2019.114958, Institutional Repository

Sensor drift is commonly observed across engineering disciplines, particularly in harsh media such as wastewater. In this study, a novel stabilizing controller for nitrification of high strength ammonia solutions is designed based on online signal derivatives. The controller uses the derivative of a drifting nitrite signal to determine if nitrite-oxidizing bacteria (NOB) are substrate limited or substrate inhibited. To ensure a meaningful interpretation of the derivative signal, the process is excited in a cyclic manner by repeatedly exposing the NOB to substrate-limited and substrate-inhibited conditions. The resulting control system successfully prevented nitrite accumulations for a period of 72 days in a laboratory-scale reactor. Slow disturbances in the form of feed composition changes and temperature changes were successfully handled by the controller while short-term temperature disturbances are shown to pose a challenge to the current version of this controller. Most importantly, we demonstrate that drift-tolerant control for the purpose of process stabilization can be achieved without sensor redundancy by combining deliberate input excitation, qualitative trend analysis, and coarse process knowledge.
Uusimaeki, T., Wagner, T., Lipinski, H. G., & Kaegi, R. (2019). AutoEM: a software for automated acquisition and analysis of nanoparticles. Journal of Nanoparticle Research, 21(6), 122 (11 pp.). doi:10.1007/s11051-019-4555-9, Institutional Repository

The era of research on (engineered) nanomaterials (NM) has been thriving for more than a decade and has delivered many beneficial applications, but also raised concerns about potential negative impacts on human health and ecosystems. The precautionary principle, hence, calls for a regulation of certain types of NM, which in consequence requires their unambiguous identification. Most of the currently available definitions of NM rely on an evaluation of the size of the constituent particles and therefore methods have to be developed to measure this parameter. Transmission electron microscopy (TEM) is one of the most promising techniques, as its resolving power well covers the nanosize range. However, limited automation of TEM analyses and possible user bias are major drawbacks of the technique and currently put severe constraints on its broader applications in nanometrology.
Therefore, the goal of this study was to develop a software code, referred to as AutoEM, to automatically acquire TEM images, measure particle sizes and extract the respective particle size distributions (PSD) of (nano)-materials. The AutoEM software also incorporates methods for elemental analyses of individual particles using electron energy loss and energy dispersive X-ray spectroscopy (EELS/EDX) allowing the extraction of element-specific PSDs. Additionally automated acquisition of energy-filtered images (EFTEM) is implemented in the AutoEM software, which can be used, e.g., to derive thickness maps and, thus, to evaluate the thickness of individual (plate-like) particles.
Verleysen, E., Wagner, T., Lipinski, H. G., Kägi, R., Koeber, R., Boix-Sanfeliu, A., … Mast, J. (2019). Evaluation of a TEM based approach for size measurement of particulate (nano)materials. Materials, 12(14), 2274 (20 pp.). doi:10.3390/ma12142274, Institutional Repository

An approach for the size measurement of particulate (nano)materials by transmission electron microscopy was evaluated. The approach combines standard operating procedures for specimen preparation, imaging, and image analysis, and it was evaluated on a series of certified reference materials and representative test materials with varying physical properties, including particle size, shape, and agglomeration state. The measurement of the median value of the minimal external particle diameter distribution was intra-laboratory validated. The validation study included an assessment of the limit of detection, working range, selectivity, precision, trueness, robustness, and ruggedness. An uncertainty that was associated to intermediate precision in the range of 1–7% and an expanded measurement uncertainty in the range of 7–20% were obtained, depending on the material and image analysis mode. No bias was observed when assessing the trueness of the approach on the certified reference materials ERM-FD100 and ERM-FD304. The image analysis method was validated in an inter-laboratory study by 19 laboratories, which resulted in a within-laboratory precision in the range of 2–8% and a between-laboratory precision of between 2% and 14%. The automation and standardization of the proposed approach significantly improves labour and cost efficiency for the accurate and precise size measurement of the particulate materials. The approach is shown to be implementable in many other electron microscopy laboratories.
Villez, K., Billeter, J., & Bonvin, D. (2019). Incremental parameter estimation under rank-deficient measurement conditions. Processes, 7(2), 75 (33 pp.). doi:10.3390/pr7020075, Institutional Repository

The computation and modeling of extents has been proposed to handle the complexity of large-scale model identification tasks. Unfortunately, the existing extent-based framework only applies when certain conditions apply. Most typically, it is required that a unique value for each extent can be computed. This severely limits the applicability of this approach. In this work, we propose a novel procedure for parameter estimation inspired by the existing extent-based framework. A key difference with prior work is that the proposed procedure combines structural observability labeling, matrix factorization, and graph-based system partitioning to split the original model parameter estimation problem into parameter estimation problems with the least number of parameters. The value of the proposed method is demonstrated with an extensive simulation study and a study based on a historical data set collected to characterize the isomerization of a-pinene. Most importantly, the obtained results indicate that an important barrier to the application of extent-based frameworks for process modeling and monitoring tasks has been lifted.
Voegelin, A., Senn, A. C., Kaegi, R., & Hug, S. J. (2019). Reductive dissolution of As(V)-bearing Fe(III)-precipitates formed by Fe(II) oxidation in aqueous solutions. Geochemical Transactions, 20(2) (13 pp.). doi:10.1186/s12932-019-0062-2, Institutional Repository

Iron(III)-precipitates formed by the oxidation of dissolved Fe(II) are important sorbents for major and trace elements in aquatic and terrestrial systems. Their reductive dissolution in turn may result in the release of associated elements. We examined the reductive dissolution kinetics of an environmentally relevant set of Fe(II)-derived arsenate-containing Fe(III)-precipitates whose structure as function of phosphate (P) and silicate (Si) content varied between poorly-crystalline lepidocrocite, amorphous Fe(III)-phosphate, and Si-containing ferrihydrite. The experiments were performed with 0.2–0.5 mM precipitate-Fe(III) using 10 mM Na-ascorbate as reductant, 5 mM bipyridine as Fe(II)-complexing ligand, and 10 mM MOPS/5 mM NaOH as pH 7.0 buffer. Times required for the dissolution of half of the precipitate (t50%) ranged from 1.5 to 39 h; spanning a factor 25 range. At loadings up to ~ 0.2 P/Fe (molar ratio), phosphate decreased the t50% of Si-free precipitates, probably by reducing the crystallinity of lepidocrocite. The reductive dissolution of Fe(III)-phosphates formed at higher P/Fe ratios was again slower, possibly due to P-inhibited ascorbate binding to precipitate-Fe(III). The slowest reductive dissolution was observed for P-free Si-ferrihydrite with ~ 0.1 Si/Fe, suggesting that silicate binding and polymerization may reduce surface accessibility. The inhibiting effect of Si was reduced by phosphate. Dried-resuspended precipitates dissolved 1.0 to 1.8-times more slowly than precipitates that were kept wet after synthesis, most probably because drying enhanced nanoparticle aggregation. Variations in the reductive dissolution kinetics of Fe(II) oxidation products as reported from this study should be taken into account when addressing the impact of such precipitates on the environmental cycling of co-transformed nutrients and contaminants.
Ward, B. J., Traber, J., Gueye, A., Diop, B., Morgenroth, E., & Strande, L. (2019). Evaluation of conceptual model and predictors of faecal sludge dewatering performance in Senegal and Tanzania. Water Research, 167, 115101 (13 pp.). doi:10.1016/j.watres.2019.115101, Institutional Repository

Unpredictable dewatering performance is a barrier to the effective management and treatment of faecal sludge. While mechanisms of dewatering in sludges from wastewater treatment are well understood, it is not clear how dewatering of faecal sludge fits into the framework of existing knowledge. We evaluate physical-chemical parameters, including EPS and cations, and demographic (source), environmental (microbial community), and technical factors (residence time) as possible predictors of dewatering performance in faecal sludge, and make comparisons to the existing conceptual model for wastewater sludge. Faecal sludge from public toilets took longer to dewater than sludge from other sources, and had turbid supernatant after settling. Slow dewatering and turbid supernatant corresponded to high EPS and monovalent cation concentrations, conductivity, and pH, but cake solids after dewatering was not correlated with EPS or other factors. Faecal sludges with higher EPS appeared less stabilised than those with lower EPS, potentially a result of inhibition of biological degradation due to high urine concentrations. However, distinct microbial community compositions were also observed in samples with higher and lower EPS concentrations. Higher EPS faecal sludge was comparable in dewatering behaviour and EPS content to anaerobically digested and primary wastewater sludges. However lower EPS faecal sludges had different dewatering behaviour than wastewater sludges and may be governed by different mechanisms.
Wielinski, J., Gogos, A., Voegelin, A., Müller, C., Morgenroth, E., & Kaegi, R. (2019). Transformation of nanoscale and ionic Cu and Zn during the incineration of digested sewage sludge (biosolids). Environmental Science and Technology, 53(20), 11704-11713. doi:10.1021/acs.est.9b01983, Institutional Repository

Engineered nanoparticles (NP) discharged to sewers are efficiently retained by wastewater treatment plants and accumulate in the sewage sludge, which is commonly digested. The resulting biosolids are either used as fertilizer or incinerated. In this study, we address the transformation of Cu and Zn during sewage sludge incineration and evaluate whether the form of Cu or Zn (nanoparticulate versus dissolved) added to the digested sewage sludge affects the fate of the metals during incineration. We spiked CuO-NP, dissolved CuSO4, ZnO-NP, or dissolved ZnSO4 into anaerobically digested sewage sludge to reach Cu and Zn concentrations of ≈2500 and ≈3700 mg/kg and maintained the sludge under mesophilic, anaerobic conditions for 24 h. Subsequently, the sludge was incinerated in a pilot fluidized bed reactor. The speciation of Cu and Zn in the sludge, derived from X-ray absorption spectroscopy measurements, was dominated by sulfidic species, with >90% of Cu and >60% of Zn coordinated to reduced sulfur groups. In the ash, both Cu (>60%) and Zn (≈100%) were coordinated to oxygen. The chemical speciation of Cu and Zn in the ashes was independent of whether they were spiked in the dissolved or nanoparticulate form and closely matched the speciation of Cu and Zn observed in ashes from full-scale incinerators.
Worms, I. A. M., Chmiel, H. E., Traber, J., Tofield-Pasche, N., & Slaveykova, V. I. (2019). Dissolved organic matter and associated trace metal dynamics from river to lake, under ice-covered and ice-free conditions. Environmental Science and Technology, 53(24), 14134-14143. doi:10.1021/acs.est.9b02184, Institutional Repository

The present study investigates the changes in dissolved organic matter (DOM) composition and its influences on trace metal dispersion from the Shuya River (SR) in the Petrozavodsk Bay of Lake Onega during ice-covered and ice-free periods. Humic substances (HS) found in the SR dominated the composition of DOM through the river-bay-lake continuum in both periods. When the bay was ice-covered, both the aromaticity and the size of HS varied in the water column according to a horizontal stratification and decreased in the bay, while under ice-free conditions, they decreased along the river-lake gradient, suggesting in both cases a decrease in the proportion of HS with high aromatic character. These findings were associated with an overall decrease in the proportion of HS components that have the highest molecular masses. The quantification of metal bound to HS revealed that these characteristics were associated with a decrease in the binding capacity of the HS for Fe and Al but not Cu while dispersing in the bay to the lake. Pb was found to bind on HS, but its behavior in the bay could not be related to the HS dispersion nor to the changes in HS properties.
Xu, J., Wang, Y., Weng, C., Bai, W., Jiao, Y., Kaegi, R., & Lowry, G. V. (2019). Reactivity, selectivity, and long-term performance of sulfidized nanoscale zerovalent iron with different properties. Environmental Science and Technology, 53(10), 5936-5945. doi:10.1021/acs.est.9b00511, Institutional Repository

Sulfidized nanoscale zerovalent iron (SNZVI) has desirable properties for in situ groundwater remediation. However, there is limited understanding of how the sulfidation type and particle properties affect the reactivity and selectivity of SNZVI toward groundwater contaminants, or how reactivity changes as the particles age. Here, SNZVI synthesized by either a one-step (SNZVI-1) or two-step (SNZVI-2) process were characterized, and the reactivity of both fresh and aged (1d to 60 d) nanoparticles was assessed. The measured S/Fe ratio was 5.4 ± 0.5 mol % for SNZVI-1 and 0.8 ± 0.1 mol % for SNZVI-2. XPS analysis indicates S2-, S22-, and Sn2- species on the surface of both SNZVI-1 and SNZVI-2, while S22- is the dominant species inside of the SNZVI nanoparticles. SNZVI-1 particles were hydrophobic (contact angle = 103 ± 3°), while the other materials were hydrophilic (contact angles were 18 ± 2° and 36 ± 3° for NZVI and SNZVI-2, respectively). SNZVI-1, with greater S content and hydrophobicity, was less reactive with water than either NZVI or SNZVI-2 over a 60 d period, resulting in less H2 evolution. It also had the highest reactivity with TCE and the lowest reactivity with nitrate, consistent with its higher hydrophobicity. In contrast, both NZVI and SNZVI-2 were reactive with both TCE and nitrate. Both types of SNZVI remained more reactive after aging in water over 60 d than NZVI. These data suggest that the properties of the SNZVI made from a one-step synthesis procedure may provide better reactivity, selectivity, and longevity than that made from a two-step process.
Zanini, M., Cingolani, A., Hsu, C. P., Fernández-Rodríguez, M. Á., Soligno, G., Beltzung, A., … Isa, L. (2019). Mechanical phase inversion of Pickering emulsions via metastable wetting of rough colloids. Soft Matter, 15(39), 7888-7900. doi:10.1039/C9SM01352K, Institutional Repository

The possibility to invert emulsions from oil-in-water to water-in-oil (or vice versa) in a closed system, i.e. without any formulation change, remains an open fundamental challenge with many opportunities for industrial applications. Here, we propose a mechanism that exploits particle surface roughness to induce metastable wetting and obtain mechanically-responsive Pickering emulsions. We postulate that the phase inversion is driven by an in situ switch of the particle wettability from metastable positions at the interface following the input of controlled mechanical energy. Oil-in-water emulsions can be prepared at low energy using mildly hydrophobic rough colloids, which are dispersed in water and weakly pinned at the interface, and switched to water-in-oil emulsions by a second emulsification at higher energy, which triggers the relaxation of the particle contact angle. The same principle is demonstrated for the complementary emulsions using mildly hydrophilic colloids initially dispersed in oil. Our experiments and simulations support that the delicate interplay between particle surface design during synthesis and the energy of the emulsification process can encode a kinetic pathway for the phase inversion. Both organic and inorganic nanoparticles can be used, allowing for the future implementation of our strategy in a broad range of smart industrial formulations.
Zheng, Y., Mutzner, L., Ort, C., Kaegi, R., & Gottschalk, F. (2019). Modelling engineered nanomaterials in wet-weather discharges. NanoImpact, 16, 100188 (8 pp.). doi:10.1016/j.impact.2019.100188, Institutional Repository

The impacts of the unintended release of engineered nanomaterials (ENMs) and the resulting exposure to the ecosystems are still poorly understood and intensively debated. In current mass flow models, a global transfer coefficient is used to account for ENMs discharged from sewer systems to surface waters during rain events.
However, different types of sewer systems and specific ENM applications likely require a more elaborate approach to quantify ENM loads entering surface waters during rain events. Therefore, we evaluated the impact of distinguishing between different application areas of ENMs (indoor/outdoor) and different types of sewer systems (combined/separate) on the loads of selected ENMs passing through wastewater systems and reaching the surface water. We applied a dynamic mass flow analysis to eight substances (TiO2, ZnO, Ag, SiO2, FeOx, CuO, CeO2 and carbon black) for six different sewer system configurations. To estimate the runoff from streets and facades, we used a hydrological model developed for dissolved substances. For areas with separate sewer systems only and ENMs predominantly used in and released from outdoor applications (e.g. CuO, carbon black), up to ~80% of the annual loads entering the sewer systems never reach a sewage treatment plant. Those ENMs are directly discharged to surface waters via stormwater outlets. For combined sewer systems and ENMs mainly applied indoors (e.g. Ag, ZnO), the percentage of ENM bypassing sewage treatment plants remains below 2%. Although the model is setup for Switzerland and other geographical areas will show for example different rain characteristics, the relative importance of the different release pathways will broadly remain the same and the results should, therefore, be transferrable to other countries.
Ziemba, C., Khavkin, M., Priftis, D., Acar, H., Mao, J., Benami, M., … Herzberg, M. (2019). Antifouling properties of a self-assembling glutamic acid-lysine zwitterionic polymer surface coating. Langmuir, 35(5), 1699-1713. doi:10.1021/acs.langmuir.8b00181, Institutional Repository

There is a need for the development of antifouling materials to resist adsorption of biomacromolecules. Here we describe the preparation of a novel zwitterionic block copolymer with the potential to prevent or delay the formation of microbial biofilms. The block copolymer comprised a zwitterionic (hydrophilic) section of alternating glutamic acid (negatively charged) and lysine (positively charged) units and a hydrophobic polystyrene section. Cryo-TEM and dynamic-light-scattering (DLS) results showed that, on average, the block copolymer self-assembled into 7-nm-diameter micelles in aqueous solutions (0 to 100 mM NaCl, pH 6). Quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and contact angle measurements demonstrated that the block copolymer self-assembled into a brush-like monolayer on polystyrene surfaces. The brush-like monolayer produced from a 100 mg/L block copolymer solution exhibited an average distance, d, of approximately 4-8 nm between each block copolymer molecule (center to center). Once the brush-like monolayer self-assembled, it reduced EPS adsorption onto the polystyrene surface by ∼70% (mass), reduced the rate of bacterial attachment by >80%, and inhibited the development of thick biofilms. QCM-D results revealed that the EPS molecules penetrate between the chains of the brush and adsorb onto the polystyrene surface. Additionally, AFM analyses showed that the brush-like monolayer prevents the adhesion of large (>d) hydrophilic colloids onto the surface via hydration repulsion; however, molecules or colloids small enough to fit between the brush polymers (<d) were able to be adsorbed onto the surface via van der Waals interactions. Overall, we found that the penetration of extracellular organelles, as well as biopolymers through the brush, is critical for the failure of the antifouling coating, and likely could be prevented through tuning of the brush density. Stability and biofilm development testing on multiple surfaces (polypropylene, glass, and stainless steel) support practical applications of this novel block copolymer.
Ziemba, C., Larivé, O., Deck, S., Huisman, T., & Morgenroth, E. (2019). Comparing the anti-bacterial performance of chlorination and electrolysis post-treatments in a hand washing water recycling system. Water Research X, 2, 100020 (10 pp.). doi:10.1016/j.wroa.2018.100020, Institutional Repository

Innovative solutions are necessary to enable the decentralized recycling of greywater for applications requiring high-quality water, such as hand washing. While physical barriers such as ultrafiltration membranes effectively prevent the passage of bacteria, and chemical and biological treatments can effectively reduce the carbon content of the treated water, there exists a knowledge gap regarding the application of anti-bacterial strategies to prevent the growth of harmful bacteria following treatment. In this study, the effluent water from a household-scale greywater treatment system was fed to seven parallel experimental post-treatment tanks: three receiving direct chlorination with free chlorine residuals of 0.2, 1 or 5 mg Cl2/L, three with chlorine produced through electrolysis at the same residual concentrations, and one control with no chlorine added. For increasing concentrations of direct chlorination, the median total cell count (TCC) values were 9 × 104, 2.9 × 104 and 1.8 × 103 cells/mL, respectively. Electrolysis treatment produced very similar TCC concentrations, 8.8 × 104, 1.1 × 104 and 2.3 × 103 cells/mL. The TCC concentrations were lower than the concentration of the water entering each tank (~3 × 105 cells/mL). Intact cell count (ICC) measurements indicated that the viable cell concentrations, were less than 10% of the TCC values. Though electrolysis treatment can produce powerful oxidants, such as hydroxyl radical, there was no evidence that electrolysis in this system provided additional benefits beyond chlorine production for control of total or intact cell counts. Oxidation of bacteria by chlorine was the dominant anti-bacterial mechanism in our system. Monitoring of dissolved organic carbon (DOC) and assimilable organic carbon (AOC) did not suggest that carbon-limitation significantly impacted cell counts when chlorination or electrolysis treatment was applied. This work demonstrates that either direct chlorination or electrolysis treatment are able to reduce bacteria concentrations over long-term operation of a hand washing water treatment system. We recommend selecting chlorine residual targets such that a chlorine residual is maintained during periods of challenging operating conditions. We observed that a target residual of 1 mg Cl2/L, in our system, maintained the TCC below the concentration found in Zürich drinking water.
Achermann, S., Falås, P., Joss, A., Mansfeldt, C., Men, Y., Vogler, B., & Fenner, K. (2018). Trends in micropollutant biotransformation along a solids retention time gradient. Environmental Science and Technology, 52(20), 11601-11611. doi:10.1021/acs.est.8b02763, Institutional Repository

For many polar organic micropollutants, biotransformation by activated sludge microorganisms is a major removal process during wastewater treatment. However, our current understanding of how wastewater treatment operations influence microbial communities and their micropollutant biotransformation potential is limited, leaving major parts of observed variability in biotransformation rates across treatment facilities unexplained. Here, we present biotransformation rate constants for 42 micropollutants belonging to different chemical classes along a gradient of solids retention time (SRT). The geometric mean of biomass-normalized first-order rate constants shows a clear increase between 3 d and 15 d SRT by 160% and 87%, respectively, in two experiments. However, individual micropollutants show a variety of trends. Rate constants of oxidative biotransformation reactions mostly increased with SRT. Yet, nitrifying activity could be excluded as primary driver. For substances undergoing other than oxidative reactions, i.e. mostly substitution-type reactions, more diverse dependencies on SRT were observed. Most remarkably, characteristic trends were observed for groups of substances undergoing similar types of initial transformation reaction, suggesting that shared enzymes or enzyme systems that are conjointly regulated catalyze biotransformation reactions within such groups. These findings open up opportunities for correlating rate constants with measures of enzyme abundance, which in turn should help to identify genes or gene products associated with the respective biotransformation reactions.
Arhin, S. G., Banadda, N., Komakech, A. J., Pronk, W., & Marks, S. J. (2018). Optimization of hybrid coagulation-ultrafiltration process for potable water treatment using response surface methodology. Water Science and Technology: Water Supply, 18(3), 862-874. doi:10.2166/ws.2017.159, Institutional Repository

In order to optimize the operating conditions for a combined polyaluminum chloride (PACl) coagulation/flocculation and ultrafiltration process for treating potable water, the main, second order and interaction effects of PACl dose and flocculation retention time (FRT) on permeate turbidity, UV254 and membrane permeability were investigated using a 100 kDa hollow fiber membrane operated in the dead-end mode. A multilevel factorial design was used to determine the relevant ranges of the two factors for optimization. A 22 central composite design (CCD) was then used to develop mathematical correlation models for the optimum operating conditions. The main effect of PACl dose was the most significant factor on all the responses. For permeability, both the main effect of FRT and FRT – PACl dose interactions were found to be insignificant. The optimum PACl dose and FRT for the feed water were 20 mg/L and 14 min respectively. Corresponding permeate turbidity, UV254 and permeability were 0.15 ± 0.01 NTU, 0.003 ± 0.001 cm−1 and 62.0 ± 9.52 Lm−2h−1 bar−1 respectively. Experimental validation runs confirmed the reliability of the predicted optimal conditions thus implying that CCD models can be used to predict/optimize the quality and quantity of permeate from hybrid coagulation-ultrafiltration systems for potable water treatment.
Bourgin, M., Beck, B., Boehler, M., Borowska, E., Fleiner, J., Salhi, E., … McArdell, C. S. (2018). Evaluation of a full-scale wastewater treatment plant upgraded with ozonation and biological post-treatments: abatement of micropollutants, formation of transformation products and oxidation by-products. Water Research, 129, 486-498. doi:10.1016/j.watres.2017.10.036, Institutional Repository

To protect the ecosystem and drinking water resources in Switzerland and in the countries of the downstream catchments, a new Swiss water protection act entered into force in 2016 aiming to reduce the discharge of micropollutants from wastewater treatment plants (WWTPs). As a consequence, selected WWTPs must be upgraded by an advanced treatment for micropollutant abatement with suitable and economic options such as (powdered) activated carbon treatment or ozonation. WWTP Neugut (105′000 people equivalent) was the first WWTP in Switzerland to implement a long-term full-scale ozonation. Differing specific ozone doses in the range of 0.35–0.97 g O3/g DOC were applied to determine the adequate ozone dose to fulfill the requirements of the Swiss water protection act. Based on this assessment, a specific ozone dose of 0.55 g O3/g DOC is recommended at this plant to ensure an average abatement of the twelve selected indicator substances by ≥80% over the whole treatment. A monitoring of 550 substances confirmed that this dose was very efficient to abate a broad range of micropollutants by >79% on average. After ozonation, an additional biological post-treatment is required to eliminate possible negative ecotoxicological effects generated during ozonation caused by biodegradable ozonation transformation products (OTPs) and oxidation by-products (OBPs). Three biological treatments (sand filtration, moving bed, fixed bed) and granular activated carbon (GAC, fresh and pre-loaded) filtration were evaluated as post-treatments after ozonation. In parallel, a fresh GAC filter directly connected to the effluent of the secondary clarifier was assessed. Among the three purely biological post-treatments, the sand filtration performed best in terms of removal of dissolved organic carbon (DOC), assimilable organic carbon (AOC) and total suspended solids (TSS). The fresh activated carbon filtration ensured a significant additional micropollutants abatement after ozonation due to sorption. The relative abatement of the indicator substances ranged between 20 and 89% after 27′000 bed volumes (BV) and was still substantial at 50′000 BV. In an identical GAC filter running in parallel and being fed with the effluent of the secondary clarifier, the elimination was less efficient. Seven primary OTPs (chlorothiazide and six N-oxides) formed during ozonation could be quantified thanks to available reference standards. Their concentration decreased with increasing specific ozone doses with the concomitant formation of other OTPs. The seven OTPs were found to be stable compounds and were not abated in the biological post-treatments. They were sorbed in the fresh GAC filter, but less efficiently than the corresponding parent compounds. Two OBPs, bromate (BrO3−) and N-nitrosodimethylamine (NDMA), were formed during ozonation but did not exceeded 5 μg/L for bromate and 30 ng/L for NDMA at the recommended specific ozone dose of 0.55 g O3/g DOC. NDMA was well abated in all post-treatments (minimum 41% during fixed bed filtration, maximum 83% during fresh GAC filtration), while bromate was very stable as expected.
Carrel, M., Morales, V. L., Beltran, M. A., Derlon, N., Kaufmann, R., Morgenroth, E., & Holzner, M. (2018). Biofilms in 3D porous media: delineating the influence of the pore network geometry, flow and mass transfer on biofilm development. Water Research, 134, 280-291. doi:10.1016/j.watres.2018.01.059, Institutional Repository

This study investigates the functional correspondence between porescale hydrodynamics, mass transfer, pore structure and biofilm morphology during progressive biofilm colonization of a porous medium. Hydrodynamics and the structure of both the porous medium and the biofilm are experimentally measured with 3D particle tracking velocimetry and micro X-ray Computed Tomography, respectively. The analysis focuses on data obtained in a clean porous medium after 36 h of biofilm growth. Registration of the particle tracking and X-ray data sets allows to delineate the interplay between porous medium geometry, hydrodynamic and mass transfer processes on the morphology of the developing biofilm. A local analysis revealed wide distributions of wall shear stresses and concentration boundary layer thicknesses. The spatial distribution of the biofilm patches uncovered that the wall shear stresses controlled the biofilm development. Neither external nor internal mass transfer limitations were noticeable in the considered system, consistent with the excess supply of nutrient and electron acceptors. The wall shear stress remained constant in the vicinity of the biofilm but increased substantially elsewhere.
Carrel, M., Morales, V. L., Dentz, M., Derlon, N., Morgenroth, E., & Holzner, M. (2018). Pore-scale hydrodynamics in a progressively bioclogged three-dimensional porous medium: 3-D particle tracking experiments and stochastic transport modeling. Water Resources Research, 54(3), 2183-2198. doi:10.1002/2017WR021726, Institutional Repository

Biofilms are ubiquitous bacterial communities that grow in various porous media including soils, trickling, and sand filters. In these environments, they play a central role in services ranging from degradation of pollutants to water purification. Biofilms dynamically change the pore structure of the medium through selective clogging of pores, a process known as bioclogging. This affects how solutes are transported and spread through the porous matrix, but the temporal changes to transport behavior during bioclogging are not well understood. To address this uncertainty, we experimentally study the hydrodynamic changes of a transparent 3-D porous medium as it experiences progressive bioclogging. Statistical analyses of the system's hydrodynamics at four time points of bioclogging (0, 24, 36, and 48 h in the exponential growth phase) reveal exponential increases in both average and variance of the flow velocity, as well as its correlation length. Measurements for spreading, as mean-squared displacements, are found to be non-Fickian and more intensely superdiffusive with progressive bioclogging, indicating the formation of preferential flow pathways and stagnation zones. A gamma distribution describes well the Lagrangian velocity distributions and provides parameters that quantify changes to the flow, which evolves from a parallel pore arrangement under unclogged conditions, toward a more serial arrangement with increasing clogging. Exponentially evolving hydrodynamic metrics agree with an exponential bacterial growth phase and are used to parameterize a correlated continuous time random walk model with a stochastic velocity relaxation. The model accurately reproduces transport observations and can be used to resolve transport behavior at intermediate time points within the exponential growth phase considered.
Corominas, L., Garrido-Baserba, M., Villez, K., Olsson, G., Cortés, U., & Poch, M. (2018). Transforming data into knowledge for improved wastewater treatment operation: a critical review of techniques. Environmental Modelling and Software, 106, 89-103. doi:10.1016/j.envsoft.2017.11.023, Institutional Repository

The aim of this paper is to describe the state-of-the art computer-based techniques for data analysis to improve operation of wastewater treatment plants. A comprehensive review of peer-reviewed papers shows that European researchers have led academic computer-based method development during the last two decades. The most cited techniques are artificial neural networks, principal component analysis, fuzzy logic, clustering, independent component analysis and partial least squares regression. Even though there has been progress on techniques related to the development of environmental decision support systems, knowledge discovery and management, the research sector is still far from delivering systems that smoothly integrate several types of knowledge and different methods of reasoning. Several limitations that currently prevent the application of computer-based techniques in practice are highlighted.
Correia, M., Uusimäki, T., Philippe, A., & Loeschner, K. (2018). Challenges in determining the size distribution of nanoparticles in consumer products by asymmetric flow field-flow fractionation coupled to inductively coupled plasma-mass spectrometry: the example of Al2O3, TiO2, and SiO2 nanoparticles in toothpaste. Separations, 5(4), 56 (25 pp.). doi:10.3390/separations5040056, Institutional Repository

According to the current European regulation on cosmetics, any ingredient present as a nanomaterial should be indicated in the ingredient list. There is a need for analytical methods capable of determining the size of the relevant ingredients and thus assessing if these are nanomaterials or not. An analytical method based on asymmetric flow field-flow fractionation (AF4) and inductively coupled plasma-mass spectrometry (ICP-MS) was developed to determine the size of particles present in a commercial toothpaste. Multi-angle light scattering (MALS) was used for on-line size determination. The number-based particle size distributions (PSDs) of the particles were retrieved upon mathematical conversion of the mass-based PSDs recovered from the AF4-ICP-MS fractograms. AF4-ICP-MS allowed to separate and detect Al2O3 and TiO2 particles in the toothpaste and to retrieve a correct TiO2 number-based PSD. The potential presence of particles in the lower size range of the Al2O3 mass-based PSD had a strong impact on sizing and nanomaterial classification upon conversion. AF4 coupled with ICP-MS and MALS was found to be a powerful approach for characterization of different particles in a multiple-particle system such as toothpaste. Confirmation of particle size by a secondary method such as single particle ICP-MS or hydrodynamic chromatography was crucial.
Desmond, P., Best, J. P., Morgenroth, E., & Derlon, N. (2018). Linking composition of extracellular polymeric substances (EPS) to the physical structure and hydraulic resistance of membrane biofilms. Water Research, 132, 211-221. doi:10.1016/j.watres.2017.12.058, Institutional Repository

The effect of extracellular polymeric substances (EPS) on the meso-scale physical structure and hydraulic resistance of membrane biofilms during gravity driven membrane (GDM) filtration was investigated. Biofilms were developed on the surface of ultrafiltration membranes during dead-end filtration at ultra-low pressure (70 mbar). Biofilm EPS composition (total protein, polysaccharide and eDNA) was manipulated by growing biofilms under contrasting nutrient conditions. Nutrient conditions consisted of (i) a nutrient enriched condition with a nutrient ratio of 100:30:10 (C: N: P), (ii) a phosphorus limitation (C: N: P ratio: 100:30:0), and (iii) a nitrogen limitation (C: N: P ratio: 100:0:10). The structure of the biofilm was characterised at meso-scale using Optical Coherence Tomography (OCT). Biofilm composition was analysed with respect to total organic carbon, total cellular mass and extracellular concentrations of proteins, polysaccharides, and eDNA. 2D-confocal Raman mapping was used to characterise the functional group composition and micro-scale distribution of the biofilms EPS. Our study reveals that the composition of the EPS matrix can determine the meso-scale physical structure of membrane biofilms and in turn its hydraulic resistance. Biofilms grown under P limiting conditions were characterised by dense and homogeneous physical structures with high concentrations of polysaccharides and eDNA. Biofilm grown under nutrient enriched or N limiting conditions were characterised by heterogeneous physical structures with lower concentrations of polysaccharides and eDNA. For P limiting biofilms, 2D-confocal Raman microscopy revealed a homogeneous spatial distribution of anionic functional groups in homogeneous biofilm structures with higher polysaccharide and eDNA concentrations. This study links EPS composition, physical structure and hydraulic resistance of membrane biofilms, with practical relevance for the hydraulic performances of GDM ultrafiltration.
Desmond, P., Morgenroth, E., & Derlon, N. (2018). Physical structure determines compression of membrane biofilms during Gravity Driven Membrane (GDM) ultrafiltration. Water Research, 143, 539-549. doi:10.1016/j.watres.2018.07.008, Institutional Repository

Increasing transmembrane pressure (TMP) can compress and increase the hydraulic resistance of membrane biofilms. The purpose of the present study is to evaluate how compression of membrane biofilms occurs and how structural rearrangement can affect hydraulic resistance. Biofilms with heterogeneous and homogeneous physical structures were grown in membrane fouling simulators (MFS) in dead-end mode for 20 days with either (i) a nutrient enriched condition with a nutrient ratio of 100:30:10 (C: N: P), (ii) a phosphorus limitation (C: N: P ratio: 100:30:0), or (iii) river water (C: N: P ratio: ca. 100:10:1). The structural and hydraulic response of membrane biofilms to (a) changes in transmembrane pressures (0.06-0.1-0.5-0.1-0.06 bar) and (b) changes in permeate flux (10-15-20-15-10 L/m2/h) were investigated. Optical coherence tomography (OCT) was used to monitor biofilm structural response, and OCT images were processed to quantify changes in the mean biofilm thickness and relative roughness. Nutrient enriched and river water biofilms had heterogeneous physical structures with greater surface roughness (Ra' > 0.2) than homogeneous P limiting biofilms (Ra' < 0.2). Compression of biofilms with rough heterogeneous structures (Ra' > 0.2) was irreversible, indicated by irreversible decrease in surface roughness, partial relaxation in mean biofilm thickness and irreversible increase in hydraulic resistance. Compression of homogeneous biofilm (Ra' < 0.2) was on the other hand reversible, indicated by full relaxation of the biofilms structure and restoration of initial hydraulic resistance. Hydraulic response (i.e., change in the specific biofilm resistance) did not correspond with the change in physical structure of heterogeneous biofilms. The presented study provides a fundamental understanding of how biofilm physical structure can affect the biofilm's response to a change in TMP, with practical relevance for the operation of GDM filtration systems.
Desmond, P., Böni, L., Fischer, P., Morgenroth, E., & Derlon, N. (2018). Stratification in the physical structure and cohesion of membrane biofilms – implications for hydraulic resistance. Journal of Membrane Science, 564, 897-904. doi:10.1016/j.memsci.2018.07.088, Institutional Repository

This study aimed at evaluating stratification of hydraulic resistance over the depth of membrane biofilms developed during gravity driven membrane (GDM) ultrafiltration. Biofilms were grown in membrane fouling simulators (MFS) for 25 days under 3 contrasting influent conditions: nutrient enriched, phosphorus limiting, and river water influent. Shear rheology was used to determine the biofilms material characteristics (e.g., elasticity, yield stress). Optical coherence tomography (OCT) was used to determine the response of the biofilms physical structure (e.g., thickness) to increased hydraulic shear stress from 0 up to 2.6 Pa. Stratification was observed in nutrient enriched and river water biofilms and which partially detached by erosion of their rough top layer under low shear conditions. A cohesive base layer remained attached to the membrane surface under high shear conditions, indicating stratification in cohesion over the biofilms depth. Erosion of the top layer only resulted in a slight decrease in the biofilm hydraulic resistance indicating that the very cohesive and thin base layer also represent significant hydraulic resistance. Conversely, P limiting biofilms had uniform structural and mechanical characteristics, detaching by sloughing and peeling at low and high shear stress respectively. Biofilms formed under phosphorus limiting conditions had equal elasticity, yet a lower yield stress compared to nutrient enriched and river water biofilms respectively and were more susceptible to detachment. The scientific implication of the presented work demonstrates that biofilm detachment is influenced by both the structural (surface heterogeneity) and material characteristics (e.g., yield stress), with practical relevance for hydraulic resistance during GDM filtration.
Falås, P., Jewell, K. S., Hermes, N., Wick, A., Ternes, T. A., Joss, A., & Nielsen, J. L. (2018). Transformation, CO2 formation and uptake of four organic micropollutants by carrier-attached microorganisms. Water Research, 141, 405-416. doi:10.1016/j.watres.2018.03.040, Institutional Repository

A tiered process was developed to assess the transformation, CO2 formation and uptake of four organic micropollutants by carrier-attached microorganisms from two municipal wastewater treatment plants. At the first tier, primary transformation of ibuprofen, naproxen, diclofenac, and mecoprop by carrier-attached microorganisms was shown by the dissipation of the target compounds and the formation of five transformation products using LC-tandem MS. At the second tier, the microbial cleavage of the four organic micropollutants was confirmed with 14C-labeled micropollutants through liquid scintillation counting of the 14CO2 formed. At the third tier, microautoradiography coupled with fluorescence in situ hybridization (MAR-FISH) was used to screen carrier-attached microorganisms for uptake of the four radiolabeled micropollutants. Results from the MAR-FISH screening indicated that only a small fraction of the microbial community (≤1‰) was involved in the uptake of the radiolabeled micropollutants and that the responsible microorganisms differed between the compounds. At the fourth tier, the microbial community structure of the carrier-attached biofilms was analyzed by 16S rRNA gene amplicon sequencing. The sequencing results showed that the MAR-FISH screening targeted ∼80% of the microbial community and that several taxonomic families within the FISH-probed populations with MAR-positive signals (i.e. Firmicutes, Gammaproteobacteria, and Deltaproteobacteria) were present in both biofilms. From the broader perspective of organic micropollutant removal in biological wastewater treatment, the MAR-FISH results of this study indicate a high degree of microbial substrate specialization that could explain differences in transformation rates and patterns between micropollutants and microbial communities.
Giese, B., Klaessig, F., Park, B., Kaegi, R., Steinfeldt, M., Wigger, H., … Gottschalk, F. (2018). Risks, release and concentrations of engineered nanomaterial in the environment. Scientific Reports, 8(1), 1565 (8 pp.). doi:10.1038/s41598-018-19275-4, Institutional Repository

For frequently used engineered nanomaterials (ENMs) CeO2-, SiO2-, and Ag, past, current, and future use and environmental release are investigated. Considering an extended period (1950 to 2050), we assess ENMs released through commercial activity as well as found in natural and technical settings. Temporal dynamics, including shifts in release due to ENM product application, stock (delayed use), and subsequent end-of-life product treatment were taken into account. We distinguish predicted concentrations originating in ENM use phase and those originating from end-of-life release. Furthermore, we compare Ag- and CeO2-ENM predictions with existing measurements. The correlations and limitations of the model, and the analytic validity of our approach are discussed in the context of massive use of assumptive model data and high uncertainty on the colloidal material captured by the measurements. Predictions for freshwater CeO2-ENMs range from 1 pg/l (2017) to a few hundred ng/l (2050). Relative to CeO2, the SiO2-ENMs estimates are approximately 1,000 times higher, and those for Ag-ENMs 10 times lower. For most environmental compartments, ENM pose relatively low risk; however, organisms residing near ENM 'point sources' (e.g., production plant outfalls and waste treatment plants), which are not considered in the present work, may be at increased risk.
Gogos, A., Voegelin, A., & Kaegi, R. (2018). Influence of organic compounds on the sulfidation of copper oxide nanoparticles. Environmental Science: Nano, 5(11), 2560-2569. doi:10.1039/C8EN00523K, Institutional Repository

Dissolved organic matter (DOM) influences the colloidal properties of engineered nanomaterials (ENMs) and impacts their transport and transformation in the environment. Sulfidation affects the fate and the ecological effects of released chalcophile ENMs. For copper oxide nanoparticles (CuO-NPs), the sulfidation and its kinetics have been described. However, the influence of DOM on this reaction has not been investigated yet. In wastewater systems, having high bisulfide contents, the DOM mainly consists of proteins, polysaccharides and humic substances. We therefore investigated the influence of the organic compounds bovine serum albumin (BSA, model protein), alginate (ALG, model polysaccharide), and polyacrylic acid (PAA, natural organic matter analogue) as well as that of natural humic acid (HA) and filtered wastewater (FW) on the sulfidation of CuO-NPs. Experiments were conducted in solutions buffered to pH 8.0 at concentrations of 1.3 mM CuO and ∼3.2 mM HS−. Increasing amounts of organic compounds were added to reach concentrations of 10–1000 mg L−1. Reacted CuO-NPs were collected at selected time points and characterized using Cu K-edge X-ray absorption spectroscopy and analytical electron microscopy. The sulfidation of the CuO-NPs was complete after 3 h in all experiments, except in the presence of 1000 mg L−1 BSA where ∼30% of CuO remained untransformed. Complete sulfidation of the CuO-NPs as observed in experiments conducted in FW suggests quantitative sulfidation of CuO-NPs in real wastewater. Without organic compounds, initially formed amorphous CuxS transformed into covellite over time. The presence of BSA, HA, ALG, and FW (but not PAA) hampered this transformation resulting in higher fractions of CuxS after sulfidation. Different amounts of CuxS with sizes of 10 kDa up to 10 nm formed during sulfidation depending on the type of organic compound. The properties of the CuxS-NPs formed by CuO-NP sulfidation must be considered when assessing their environmental impact.
Gondikas, A., Von Der Kammer, F., Kaegi, R., Borovinskaya, O., Neubauer, E., Navratilova, J., … Hofmann, T. (2018). Where is the nano? Analytical approaches for the detection and quantification of TiO2 engineered nanoparticles in surface waters. Environmental Science: Nano, 5(2), 313-326. doi:10.1039/c7en00952f, Institutional Repository

Detecting and quantifying engineered nanoparticles (ENPs) in complex environmental matrices requires the distinction between natural nanoparticles (NNPs) and ENPs. The distinction of NNPs and ENPs for regulatory purposes calls for cost-efficient methods, but is hampered by similarities in intrinsic properties, such as particle composition, size, density, surface chemistry, etc. Titanium dioxide (TiO2) ENPs, for instance, are produced in very large quantities but Ti also commonly occurs naturally in nano-scale minerals. In this work, we focus on utilizing particle size and composition to identify ENPs in a system with a significant background concentration of the target metal. We have followed independent approaches involving both conventional and state-of-the-art analytical techniques to detect and quantify TiO2 ENPs released into surface waters from sunscreen products and to distinguish them from Ti-bearing NNPs. To achieve this, we applied single particle inductively coupled plasma mass spectrometry with single-element (spICPMS) and multi-element detection (time-of-flight) spICP-TOFMS, together with transmission electron microscopy (TEM), automated scanning electron microscopy (autoSEM), and bulk elemental analyses. A background concentration of Ti-bearing NPs (approximately 5 × 103 particles per ml), possibly of natural origin, was consistently observed outside the bathing season. This concentration increased by up to 40% during the bathing season. Multi-element analysis of individual particles using spICP-TOFMS revealed that Al, Fe, Mn, and Pb are often present in natural Ti-bearing NPs, but no specific multi-element signatures were detected for ENPs. Our data suggests that TiO2 ENPs enter the lake water during bathing activities, eventually agglomerating and sedimenting. We found adhesion of the TiO2 ENPs to the air-water interface for short time periods, depending on wind conditions. This study demonstrates that the use of spICP-TOFMS and spICPMS in combination with other conventional analytical techniques offers significant advantages for discriminating between NNPs and ENPs. The quantitative data produced in this work can be used as input for modeling studies or as a benchmark for analysis protocols and model validations.
Hagemann, N., Spokas, K., Schmidt, H. P., Kägi, R., Böhler, M. A., & Bucheli, T. D. (2018). Activated carbon, biochar and charcoal: linkages and synergies across pyrogenic carbon's ABCs. Water, 10(2), 182 (19 pp.). doi:10.3390/w10020182, Institutional Repository

Biochar and activated carbon, both carbonaceous pyrogenic materials, are important products for environmental technology and intensively studied for a multitude of purposes. A strict distinction between these materials is not always possible, and also a generally accepted terminology is lacking. However, research on both materials is increasingly overlapping: sorption and remediation are the domain of activated carbon, which nowadays is also addressed by studies on biochar. Thus, awareness of both fields of research and knowledge about the distinction of biochar and activated carbon is necessary for designing novel research on pyrogenic carbonaceous materials. Here, we describe the dividing ranges and common grounds of biochar, activated carbon and other pyrogenic carbonaceous materials such as charcoal based on their history, definition and production technologies. This review also summarizes thermochemical conversions and non-thermal pre- and post-treatments that are used to produce biochar and activated carbon. Our overview shows that biochar research should take advantage of the numerous techniques of activation and modification to tailor biochars for their intended applications.
Jafari, M., Desmond, P., van Loosdrecht, M. C. M., Derlon, N., Morgenroth, E., & Picioreanu, C. (2018). Effect of biofilm structural deformation on hydraulic resistance during ultrafiltration: A numerical and experimental study. Water Research, 145, 375-387. doi:10.1016/j.watres.2018.08.036, Institutional Repository

Biofilm formation in membrane systems negatively impacts the filtration system performances. This study evaluated how biofilm compression driven by permeate flow increases the hydraulic resistance and leads to reduction in permeate flux. We analysed the effect of biofilm compression on hydraulic resistance and permeate flux through computational models supported by experimental data. Biofilms with homogeneous surface structure were subjected to step-wise changes in flux and transmembrane pressure during compression and relaxation tests. Biofilm thickness under applied forces was measured non-invasively in-situ using optical coherence tomography (OCT). A numerical model of poroelasticity, which couples water flow through the biofilm with biofilm mechanics, was developed to correlate the structural deformation with biofilm hydraulics (permeability and resistance). The computational model enabled extracting mechanical and hydrological parameters corresponding to the experimental data. Homogeneous biofilms under elevated compression forces experienced a significant reduction in thickness while only a slight increase in resistance was observed. This shows that hydraulic resistance of homogeneous biofilms was affected more by permeability decrease due to pore closure than by a decrease in thickness. Both viscoelastic and elastoplastic models could describe well the permanent biofilm deformation. However, for biofilms under study, a simpler elastic model could also be used due to the small irreversible deformations. The elastic moduli fitting the measured data were in agreement with other reported values for biofilm under compression. Biofilm stiffening under larger flow-driven compression forces was observed and described numerically by correlating inversely the elastic modulus with biofilm porosity. The importance of this newly developed method lies in estimation of accurate biofilm mechanical parameters to be used in numerical models for both membrane filtration system and biofouling cleaning strategies. Such model can ultimately be used to identify optimal operating conditions for membrane system subjected to biofouling.
Kah, M., Kookana, R. S., Gogos, A., & Bucheli, T. D. (2018). A critical evaluation of nanopesticides and nanofertilizers against their conventional analogues. Nature Nanotechnology, 13(8), 677-684. doi:10.1038/s41565-018-0131-1, Institutional Repository

Among a wide range of possible applications of nanotechnology in agriculture, there has been a particular interest in developing novel nanoagrochemicals. While some concerns have been expressed regarding altered risk profile of the new products, many foresee a great potential to support the necessary increase in global food production in a sustainable way. A critical evaluation of nanoagrochemicals against conventional analogues is essential to assess the associated benefits and risks. In this assessment, recent literature was critically analysed to determine the extent to which nanoagrochemicals differ from conventional products. Our analysis was based on 78 published papers and shows that median gain in efficacy relative to conventional products is about 20–30%. Environmental fate of agrochemicals can be altered by nanoformulations, but changes may not necessarily translat controls. Currently, there is no comprehensive study in the literature that evaluates efficacy and environmental impact of nanoagrochemicals under field conditions. This is a crucial knowledge gap and more work will thus be necessary for a sound evaluation of the benefits and new risks that nanoagrochemicals represent relative to existing products.
Kampe, S., Kaegi, R., Schlich, K., Wasmuth, C., Hollert, H., & Schlechtriem, C. (2018). Silver nanoparticles in sewage sludge: bioavailability of sulfidized silver to the terrestrial isopod Porcellio scaber. Environmental Toxicology and Chemistry, 37(6), 1606-1613. doi:10.1002/etc.4102, Institutional Repository

Silver nanoparticles (AgNPs) are efficiently converted during the wastewater‐treatment process into sparingly soluble Ag sulfides (Ag2S). In several countries, sewage sludge is used as a fertilizer in agriculture. The bioavailability of sulfidized Ag to the terrestrial isopod Porcellio scaber was investigated. Sewage sludge containing transformed AgNPs was obtained from a laboratory‐scale sewage‐treatment plant operated according to Organisation for Economic Co‐operation and Development (OECD) guideline 303a. The results of transmission electron microscopy with energy dispersive X‐ray of sludge samples suggest that AgNPs were completely transformed to Ag2S. Adult isopods were exposed to OECD 207 soil substrate amended with the AgNP spiked sludge for 14 d (uptake phase) followed by an elimination phase in unspiked soil of equal duration. Most of the Ag measured in P. scaber at the end of the uptake phase was found in the hindgut (71%), indicating that only a minor part of the estimated Ag content was actually assimilated by the isopods with 16.3 and 12.7% found in the carcass and hepatopancreas, respectively. As a result of this, the Ag content of the animals dropped following transition to unspiked sludge within 2 d to one‐third of the previously measured Ag concentration and remained stable at this level until the end of the elimination period. The present study shows that Ag2S in sewage sludge is bioavailable to the terrestrial isopod P. scaber.
Kassotaki, E., Pijuan, M., Joss, A., Borrego, C. M., Rodriguez-Roda, I., & Buttiglieri, G. (2018). Unraveling the potential of a combined nitritation-anammox biomass towards the biodegradation of pharmaceutically active compounds. Science of the Total Environment, 624, 722-731. doi:10.1016/j.scitotenv.2017.12.116, Institutional Repository

In the past few years, anaerobic ammonium oxidation-based processes have attracted a lot of attention for their implementation at the mainstream line of wastewater treatment plants, due to the possibility of leading to energy autarky if combined with anaerobic digestion. However, little is known about the potential degradation of micropollutants by the microbial groups responsible of these processes and the few results available are inconclusive. This study aimed to assess the degradation capability of biomass withdrawn from a combined nitritation/anaerobic ammonium oxidation (combined N/A) pilot plant towards five pharmaceutically active compounds (ibuprofen, sulfamethoxazole, metoprolol, venlafaxine and carbamazepine). Batch experiments were performed under different conditions by selectively activating or inhibiting different microbial groups: i) regular combined N/A operation, ii) aerobic (optimal for nitrifying bacteria), iii) aerobic with allylthiourea (an inhibitor of ammonia monooxygenase, enzyme of ammonia oxidizing bacteria), iv) anoxic (optimal for anaerobic ammonium oxidizing bacteria), v) aerobic with acetate (optimal for heterotrophic bacteria) and vi) anoxic with acetate (optimal for heterotrophic denitrifying bacteria). Ibuprofen was the most biodegradable compound being significantly degraded (49–100%) under any condition except heterotrophic denitrification. Sulfamethoxazole, exhibited the highest removal (70%) under optimal conditions for nitrifying bacteria but in the rest of the experiments anoxic conditions were found to be slightly more favorable (up to 58%). For metoprolol the highest performance was obtained under anoxic conditions favoring anammox bacteria (62%). Finally, carbamazepine and venlafaxine were hardly removed (≤ 10% in the majority of cases). Taken together, these results suggest the specificity of different microbial groups that in combination with alternating operational parameters can lead to enhanced removal of some micropollutants.
Lindeboom, R. E. F., Ilgrande, C., Carvajal-Arroyo, J. M., Coninx, I., Van Hoey, O., Roume, H., … Vlaeminck, S. E. (2018). Nitrogen cycle microorganisms can be reactivated after Space exposure. Scientific Reports, 8(1), 13783 (7 pp.). doi:10.1038/s41598-018-32055-4, Institutional Repository

Long-term human Space missions depend on regenerative life support systems (RLSS) to produce food, water and oxygen from waste and metabolic products. Microbial biotechnology is efficient for nitrogen conversion, with nitrate or nitrogen gas as desirable products. A prerequisite to bioreactor operation in Space is the feasibility to reactivate cells exposed to microgravity and radiation. In this study, microorganisms capable of essential nitrogen cycle conversions were sent on a 44-days FOTON-M4 flight to Low Earth Orbit (LEO) and exposed to 10−3–10−4 g (gravitational constant) and 687 ± 170 µGy (Gray) d−1 (20 ± 4 °C), about the double of the radiation prevailing in the International Space Station (ISS). After return to Earth, axenic cultures, defined and reactor communities of ureolytic bacteria, ammonia oxidizing archaea and bacteria, nitrite oxidizing bacteria, denitrifiers and anammox bacteria could all be reactivated. Space exposure generally yielded similar or even higher nitrogen conversion rates as terrestrial preservation at a similar temperature, while terrestrial storage at 4 °C mostly resulted in the highest rates. Refrigerated Space exposure is proposed as a strategy to maximize the reactivation potential. For the first time, the combined potential of ureolysis, nitritation, nitratation, denitrification (nitrate reducing activity) and anammox is demonstrated as key enabler for resource recovery in human Space exploration.
Meyer, G., Frossard, E., Mäder, P., Nanzer, S., Randall, D. G., Udert, K. M., & Oberson, A. (2018). Water soluble phosphate fertilizers for crops grown in calcareous soils – an outdated paradigm for recycled phosphorus fertilizers?. Plant and Soil, 424(1-2), 367-388. doi:10.1007/s11104-017-3545-x, Institutional Repository

Background and aims The current paradigm for phosphorus (P) fertilizers applied to calcareous soil is that almost entirely water soluble P fertilizers are efficient and sparingly soluble P fertilizers are not efficient P sources for crops. We hypothesize that this paradigm does not apply to recycled P fertilizers and that other P pools can explain the plant use of recycled P fertilizers on calcareous soil.
Methods We applied 33P isotopic dilution method to evaluate recycled P fertilizers based on plant P uptake from fertilizer relative to plant uptake from a water soluble P reference fertilizer. The predictability of fertilizer effectiveness based on sequentially extracted P forms and X-ray diffraction pattern of recycled fertilizers derived from sewage sludge, human urine and organic waste was evaluated.
Results The plant experiments showed that tested recycled P fertilizers including compost were more effective than rock phosphate. The water insoluble P contained in urine based products was almost as effective as a fully water soluble P fertilizer. The tested recycled P fertilizers are characterized by complex P compounds differing in solubility which were so far not considered in the water and citric acid extraction methods. The fraction of resin- and NaHCO3 extractable fertilizer P explained effectiveness of P fertilizer applied to the calcareous and to an acidic soil.
Conclusion We concluded that water solubility is not required when P forms in recycled products are comparable to reactions products of rock phosphate based fertilizers in soil. Alternatives to fully water soluble P fertilizers are available to supply P to crops grown on calcareous soil efficiently.
Neidhardt, H., Winkel, L. H. E., Kaegi, R., Stengel, C., Trang, P. T. K., Lan, V. M., … Berg, M. (2018). Insights into arsenic retention dynamics of Pleistocene aquifer sediments by in situ sorption experiments. Water Research, 129, 123-132. doi:10.1016/j.watres.2017.11.018, Institutional Repository

The migration of arsenic (As) enriched groundwater into Pleistocene aquifers as a consequence of extensive groundwater abstraction represents an increasing threat to the precious water resources in Asian delta regions. Pleistocene aquifer sediments are typically rich in FeIII-(hydr)oxides and are capable to adsorb high amounts of As. This results in a pronounced accumulation of As in Pleistocene aquifers, where high As groundwater infiltrates from adjacent Holocene aquifers. However, As retention by Pleistocene aquifers over long-term time scales remains largely unknown. We studied As sorption in situ by placing natural Pleistocene sediments and pure mineral phases directly inside groundwater monitoring wells at a study site near Hanoi (Vietnam). This in situ exposure allows for constant flushing of the samples with unaltered groundwater and the establishment of undisturbed sorption equilibria similar to those in local aquifer sediments, which is not readily attainable in traditional laboratory sorption experiments. The groundwaters in our experimental wells were characterized by different As concentrations (0.01–6.63 μmol/L) and redox states, reaching from suboxic to anoxic conditions (Eh of +159 to −4 mV). Results show that adsorption is the dominant As retention mechanism, independent from the respective groundwater chemistry (i.e. concentrations of dissolved P, HCO3− and Si). Whilst most of the As sorbed within the first week, sorption further increased slowly but consistently by 6–189%, respectively, within six months. Hence, the As sorption behavior of Pleistocene aquifer sediments should be determined over longer periods to avoid an underestimation of the As sorption capacity. Accompanying desorption experiments revealed that about 51% of the sorbed As was remobilized within six months when exposed to low As groundwater. We therefore conclude that a considerable proportion of the As accumulated in the aquifer sediments is prone to remobilization once the As concentrations in migrating groundwater decline. Remobilization of As should be considered in local water management plans to avoid contamination of precious groundwater resources with this As legacy.
Nowack, B., & Mitrano, D. M. (2018). Procedures for the production and use of synthetically aged and product released nanomaterials for further environmental and ecotoxicity testing. NanoImpact, 10, 70-80. doi:10.1016/j.impact.2017.12.001, Institutional Repository

The use of pristine, as-produced engineered nanomaterials (ENMs) to examine environmental behavior or toxicity is convenient, but it is the aged or released ENMs that are much more likely to be present in the environment and these are the materials to which organisms will ultimately be exposed. When determining which aging processes are most relevant, a life cycle perspective can be useful to gain insight into how ENMs will be used, released from products and move through technical and environmental systems. While there are a few pristine nanomaterial standards or test materials available, procedures to create appropriate aged or released ENM standards for subsequent fate or effect studies are more rare. Whereas the aging and release processes of ENMs are studied to quite some extent, procedures for the production of these materials for further testing are still in the initial phases. Here we review the available aging and release procedures representing various stages of the product life cycle that were developed in order to collect the aged and released materials for further use. There are three main groups of aged/released materials: 1) laboratory aging of pristine ENM, 2) collection of ENMs released from nano-products, and 3) fragmentation of the product matrix combined with aging. Here, the various aging and release paradigms that may be followed are presented, each of which comes with pros and cons in terms of how close the aging parameters are to simulating real world situations and how applicable they are to different product matrices or release mechanisms. The further use of the aged/released materials in fate or effect studies is also presented when possible. We can conclude that some aging/release procedures exist which have applicability for different research questions and specific ENM/matrix/product combinations and life cycle stages, but additional research is warranted to expand the procedures for producing synthetically aged and product released ENMs to cover additional areas of interest.
Part, F., Berge, N., Baran, P., Stringfellow, A., Sun, W., Bartelt-Hunt, S., … Huber-Humer, M. (2018). A review of the fate of engineered nanomaterials in municipal solid waste streams. Waste Management, 75, 427-449. doi:10.1016/j.wasman.2018.02.012, Institutional Repository

Significant knowledge and data gaps associated with the fate of product-embedded engineered nanomaterials (ENMs) in waste management processes exist that limit our current ability to develop appropriate end-of-life management strategies. This review paper was developed as part of the activities of the IWWG ENMs in Waste Task Group. The specific objectives of this review paper are to assess the current knowledge associated with the fate of ENMs in commonly used waste management processes, including key processes and mechanisms associated with ENM fate and transport in each waste management process, and to use that information to identify the data gaps and research needs in this area. Literature associated with the fate of ENMs in wastes was reviewed and summarized. Overall, results from this literature review indicate a need for continued research in this area. No work has been conducted to quantify ENMs present in discarded materials and an understanding of ENM release from consumer products under conditions representative of those found in relevant waste management process is needed. Results also indicate that significant knowledge gaps associated with ENM behaviour exist for each waste management process investigated. There is a need for additional research investigating the fate of different types of ENMs at larger concentration ranges with different surface chemistries. Understanding how changes in treatment process operation may influence ENM fate is also needed. A series of specific research questions associated with the fate of ENMs during the management of ENM-containing wastes have been identified and used to direct future research in this area.
Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Larue, C., de Nolf, W., Reyes-Herrera, J., … Sarret, G. (2018). Searching for relevant criteria to distinguish natural vs. anthropogenic TiO2 nanoparticles in soils. Environmental Science: Nano, 5(12), 2853-2863. doi:10.1039/c8en00386f, Institutional Repository

Nanosized TiO2 is one of the most produced nanomaterials. Agricultural soils are a major compartment of accumulation of TiO2-NPs after release from consumer products into the sewer system, due to the use of sewage sludge as a soil amendment. TiO2 is naturally present in soils, and distinguishing between anthropogenic and natural TiO2 in soils is thus important to assess the risks associated with the increased use of nano-TiO2. Methods to distinguish these materials in complex matrices such as soils are currently lacking. The purpose of this study was, therefore, to search for characteristic physical and chemical properties of natural and engineered nano-TiO2, based on a combination of bulk, micro and nanofocused X-ray fluorescence and X-ray absorption spectroscopy, transmission electron microscopy, X-ray diffraction and chemical analyses. Digested sewage sludge, agricultural soil and sludge-amended soil were studied by these techniques. The particle size distribution was not a relevant criterion since the sludge and the sludge-amended soil contained a variety of nanometer- and micrometer sized Ti-containing particles. Both the sludge and the soil contained a mixture of rutile and anatase, with a minor proportion of amorphous TiO2. In the sludge, there was no trend relating particle size and Ti mineralogy. The morphology of the TiO2 particles proved to be different in the two matrices, with smooth faceted particles in the sludge and rough irregular ones in the soil. In addition, natural TiO2 particles were included in micro and macroaggregates of the soil and formed intricate assemblages with minerals and organic compounds. In the sludge, TiO2 formed homo and heteroaggregates of simpler structure, richer in organic matter. Thus, the study of the morphology of TiO2 particles and their status in unperturbed mineral-organic assemblages may provide some insights into their origin. The observed differences may attenuate over time, due to the incorporation of the sludge material within the soil structure.
Rittmann, B. E., Boltz, J. P., Brockmann, D., Daigger, G. T., Morgenroth, E., Helleshøj Sørensen, K., … Vanrolleghem, P. A. (2018). A framework for good biofilm reactor modeling practice (GBRMP). Water Science and Technology, 77(5), 1149-1164. doi:10.2166/wst.2018.021, Institutional Repository

A researcher or practitioner can employ a biofilm model to gain insight into what controls the performance of a biofilm process and for optimizing its performance. While a wide range of biofilmmodeling platforms is available, a good strategy is to choose the simplest model that includes sufficient components and processes to address the modeling goal. In most cases, a onedimensional biofilm model provides the best balance, and good choices can range from handcalculation analytical solutions, simple spreadsheets, and numerical-method platforms. What is missing today is clear guidance on how to apply a biofilm model to obtain accurate and meaningful results. Here, we present a five-step framework for good biofilm reactor modeling practice (GBRMP). The first four steps are (1) obtain information on the biofilm reactor system, (2) characterize the influent, (3) choose the plant and biofilm model, and (4) define the conversion processes. Each step demands that the model user understands the important components and processes in the system, one of the main benefits of doing biofilm modeling. The fifth step is to calibrate and validate the model: System-specific model parameters are adjusted within reasonable ranges so that model outputs match actual system performance. Calibration is not a simple 'by the numbers' process, and it requires that the modeler follows a logical hierarchy of steps. Calibration requires that the adjusted parameters remain within realistic ranges and that the calibration process be carried out in an iterative manner. Once each of steps 1 through 5 is completed satisfactorily, the calibrated model can be used for its intended purpose, such as optimizing performance, trouble-shooting poor performance, or gaining deeper understanding of what controls process performance.
Senn, A. C., Hug, S. J., Kaegi, R., Hering, J. G., & Voegelin, A. (2018). Arsenate co-precipitation with Fe(II) oxidation products and retention or release during precipitate aging. Water Research, 131, 334-345. doi:10.1016/j.watres.2017.12.038, Institutional Repository

The co-precipitation of arsenate (As(V)) with Fe(III)-precipitates is of great importance in water treatment and critically affects the fate of As in environmental systems. We studied the effects of dissolved phosphate (P; 0-1 mM), silicate (Si; 0 or 0.5 mM) and Ca (0, 0.5 and 4 mM) on the sequestration of 7 μM As(V) by Fe(III)-precipitates formed by the oxidation of 0.5 mM Fe(II) in aerated bicarbonate-buffered solutions with an initial pH of 7.0 as well as the retention or release of As(V) after precipitate aging for 30 d at 40 °C. Dissolved As(V) concentrations in fresh precipitate suspensions greatly varied as a function of the initial dissolved P/Fe ratio ((P/Fe)init) and the concentrations of Ca and Si. Limited As(V) removal was observed at (P/Fe)init that exceeded the critical ratio (P/Fe)crit above which exclusively (Ca-)Fe(III)-phosphate forms. Effective As(V) removal was observed at (P/Fe)init < (P/Fe)crit, where initial formation of (Ca-)Fe(III)-phosphate is followed by the formation of Si-ferrihydrite in Si-containing electrolytes and of poorly-crystalline lepidocrocite and hydrous ferric oxide in the Si-free electrolytes. The retention of As(V) and P by fresh Fe(III)-precipitates was most effective in systems containing both Ca and Si. In the Si- and Ca-free electrolytes at (P/Fe)init of ~0.2–0.6, the rapid onset of precipitate aging with conversion of Fe(III)-phosphate to ferrihydrite resulted in a substantial remobilization of As(V) (up to 55% of initially precipitated As(V)). Ca reduced As remobilization during aging by stabilizing Ca-Fe(III)-phosphate and promoting Ca-phosphate formation, and Si by stabilizing Si-ferrihydrite against transformation. Consequently, also after aging, the lowest dissolved As(V) and P fractions were observed in precipitate suspensions containing both Ca and Si.
Szekeres, G. P., Németh, Z., Schrantz, K., Németh, K., Schabikowski, M., Traber, J., … Graule, T. (2018). Copper-coated cellulose-based water filters for virus retention. ACS Omega, 3(1), 446-454. doi:10.1021/acsomega.7b01496, Institutional Repository

Despite recent efforts in modernization of water treatment facilities, the problem of access to healthy drinking water for hundreds of millions of people has still not been solved. A water filter based on Cu-coated nanofibrillated cellulose with controlled porosity was prepared by the "paper-making" method. We have optimized the proper mass and ratio of functionalized and pure nanofibrillated cellulose for the preparation of the filter. MS2 bacteriophages were used to model human pathogenic virions. We tested our filter material in batch experiments and the fixed filters in flow experiments. The fabricated Cu-coated nanofibrillated cellulose filters were characterized by scanning electron microscopy, X-ray diffraction, specific surface area measurement (Brunauer–Emmett–Teller), dynamic light scattering, and inductively coupled plasma mass spectroscopy. Our measurements proved that the fixation of cellulose nanofibers plays a significant role in the degree of virus retention and it greatly enhances the efficiency of the filtration. By using these functionalized water filters, we were able to achieve a virus retention of at least 5 magnitudes (5Log) at three different pH values: 5.0, 7.5, and 9.
Tang, X., Ding, A., Pronk, W., Ziemba, C., Cheng, X., Wang, J., … Liang, H. (2018). Biological pre-treatments enhance gravity-driven membrane filtration for the decentralized water supply: linking extracellular polymeric substances formation to flux stabilization. Journal of Cleaner Production, 197(1), 721-731. doi:10.1016/j.jclepro.2018.06.155, Institutional Repository

Gravity-driven membrane (GDM) filtration is a promising technology for decentralized drinking water treatment due to its low energy requirements and simple operation. The reduced flux observed in GDM systems relative to other membrane treatment techniques remains a vital obstacle to their wider application. With the goal of further improving membrane flux and permeate quality, three simple and practical technologies have been examined as pre-treatments for GDM systems, (i) slow filtration with granular activated carbon (GAC), expected to remove both biodegradable and non-biodegradable contaminants, (ii) slow filtration with modified fiber ball (MFB), expected to promote biodegradation of organic compounds and (iii) microfiltration (MF), expected to reject suspended substances and particles. Results indicated that stable permeability increased by approximately 230%, 150% and 100% in GDM systems employing GAC, MFB and MF pre-treatments compared to the control. The dissolved organic compounds (DOC) were removed by approximately 60% and 30% in GAC/GDM and MFB/GDM, while MF/GDM and GDM control were not effective at DOC removal. Correlations between the stable flux and extracellular polymeric substances (EPS) concentration (R2 > 0.9) indicated that reduction of EPS should be responsible for the flux improvements. Tracing the fate of florescent foulants illustrated that the EPS was mainly secreted/converted by the microbes colonizing within the bio-fouling layer of the GDM system. During long-term filtration, assimilable organic compounds (AOC) which can serve as nutrients for the growth of microbes within the bio-fouling layer were efficiently consumed (>50%) by the biological pre-treatments. This reduction in AOC was linked with a reduction in the growth/activity of bacteria within the bio-fouling layer of GDM system and a reduction in EPS accumulation. Overall, biological pre-treatments can significantly enhance the flux and water quality produced by a GDM system without significantly increasing the operation and maintenance. These improvements in flux and water quality can hopefully spark wider adoption of GDM as an economical and environmentally-friendly technology for decentralized drinking water treatment.
Tang, X., Pronk, W., Ding, A., Cheng, X., Wang, J., Xie, B., … Liang, H. (2018). Coupling GAC to ultra-low-pressure filtration to modify the biofouling layer and bio-community: flux enhancement and water quality improvement. Chemical Engineering Journal, 333, 289-299. doi:10.1016/j.cej.2017.09.111, Institutional Repository

An integrated gravity-driven membrane (GDM) and granular activated carbon (GAC) filtration process was operated for 193 days to investigate the influence of integrated GAC on the flux stabilization, permeate quality, composition of the biofouling layer and eukaryotic community compared with a GDM control system. The results revealed that the presence of GAC resulted in a strongly increased stable flux (6 L m−2 h−1, compared to 2 L m−2 h−1 in the GDM control). Furthermore, the GAC/GDM system exhibited a significant removal of dissolved organic compounds (DOC) (50–70%) due to the adsorption and biodegradation process. By contrast, the DOC in the permeate of the control was approximately 20–30% higher than in the raw water, which was attributed to the hydrolysis of high-MW compounds. Furthermore, the composition of the biofouling layer attached on the membrane surface was significantly influenced by the presence of GAC, leading to a reduction of accumulated organic compounds by 60%. Likewise, the extracellular polymeric substances (EPS) were obviously reduced in the GAC/GDM system, especially the tightly bound EPS in the biofilm and EPS deposited in membrane pores. Additionally, the GAC could function as a eukaryotic pre-incubator, resulting in a higher diversity of the eukaryotic community and improving predation in the biofouling layer. Furthermore, a more porous, heterogeneous and permeable biofouling layer was observed in GAC/GDM. The higher flux in GAC/GDM system was attributed to (i) lower organic foulants (especially EPS) accumulated in the biofouling layer and membrane pores and (ii) highly heterogeneous structures due to improved activity of eukaryotes in the biofouling layer. These results are essential to develop robust maintenance-free, cost-effective and energy-efficient drinking water treatments.
Thalmann, B., von Gunten, U., & Kaegi, R. (2018). Ozonation of municipal wastewater effluent containing metal sulfides and metal complexes: kinetics and mechanisms. Water Research, 134, 170-180. doi:10.1016/j.watres.2018.01.042, Institutional Repository

Ozonation can be applied to mitigate the discharge of organic micropollutants from municipal wastewater treatment plants (WWTPs) to the aquatic environment. The toxicity of metals also present in WWTP effluents strongly depends on their speciation. Therefore, knowledge on the change of the metal speciation during ozonation of a WWTP effluent is essential to assess possible negative impacts. The kinetics and the stoichiometries of the reactions of ozone with three metal sulfides (ZnS, CuS and CdS) and metal-ethylenediaminetetraacetate (EDTA)/nitriloriacetic acid (NTA) complexes of Cu(II), Cd(II), Ni(II), Zn(II), Mg(II) and Pb(II) were investigated. With a stoichiometric factor of 2.6–3.9 moles of ozone per mole of sulfide and apparent second-order rate constants at pH 8 > 104 M−1 s−1, a complete oxidation of the sulfides and a concomitant release of the respective metals is expected during ozonation of a WWTP effluent for enhanced micropollutant abatement. The apparent second-order rate constants at pH 8 for the reactions of metal-EDTA complexes with ozone ranged from 42 M−1s−1 to 2.0 × 104 M−1s−1 and increased in the order Cd(II) < Cu(II) < Mg(II) < Ni(II) < Zn(II). Approximately 40% of Cd(II)-EDTA spiked to a WWTP effluent was oxidized at typical specific ozone doses of 0.5–0.7 gO3/gDOC. For the other metal-EDTA complexes a significantly higher fraction was oxidized. The bioavailable fraction determined by the diffusive-gradient thin films (DGT) method in the WWTP effluent increased during ozonation, due to the oxidative release of the metal ions. Algal toxicity (chlamynomodas reinhardtii) tests with CuS/CdS spiked WWTP effluent revealed a high tolerance toward Cu and Cd in the respective media. A toxic response was only observed at Cu concentrations above 10 μM, which is above typical WWTP effluent concentrations. Biological post-treatment after ozonation generally reduced the bioavailability of the metals, which resulted in a lower toxicity. Therefore, the biological post-treatment serves as an additional barrier to protect the downstream ecology of receiving waters.
Thürlimann, C. M., Dürrenmatt, D. J., & Villez, K. (2018). Soft-sensing with qualitative trend analysis for wastewater treatment plant control. Control Engineering Practice, 70, 121-133. doi:10.1016/j.conengprac.2017.09.015, Institutional Repository

Ammonia control in municipal wastewater treatment plants typically requires maintenance-intensive instrumentation. A low maintenance alternative is sought for small- to medium-scale applications. To this end, a pH-based soft-sensor is proposed to detect ammonia peak load events. This soft-sensor is based on a newly developed technique for qualitative trend analysis and is combined with a rule-based controller. The use of qualitative trend analysis makes this soft-sensor tolerant towards sensor drifts and thereby reduces the maintenance effort. The method allows controlling any process in which relative changes in the measured output are informative about the system output.
Ulmer, P., Kaegi, R., & Müntener, O. (2018). Experimentally derived intermediate to silica-rich arc magmas by fractional and equilibrium crystallization at 1·0 GPa: an evaluation of phase relationships, compositions, liquid lines of descent and oxygen fugacity. Journal of Petrology, 59(1), 11-58. doi:10.1093/petrology/egy017, Institutional Repository

Differentiation of hydrous primary, mantle-derived magmas is a fundamental process to generate evolved intermediate to SiO2-rich compositions forming the bulk of the continental and island arc crust. This study focuses on the results of equilibrium and fractional crystallization experiments at 1·0 GPa using two different primary magmas representing deep (90 km) and shallow (35 km) mantle extraction depths. Experiments on a hydrous high-Mg basalt were conducted at graphite-saturated and more oxidized conditions (NNO to NNO + 2, where NNO is nickel–nickel oxide buffer) to exploit the influence of fO2 on phase assemblages and the evolution of derivative liquids. The liquid line of descent (LLD) was simulated from liquidus to near-solidus conditions ranging from 1330°C to 720°C. H2O contents varied from about 2·0 to more than 10 wt %. The LLD covers the entire compositional range from high-Mg basalt to high-silica rhyolite and evolves from metaluminous to peraluminous compositions at 56–60 wt % SiO2 under oxidizing conditions. The observed crystallization sequences and the LLD reveal contrasting behavior depending on oxidation state, H2O content and equilibrium versus fractional crystallization. Equilibrium crystallization of high-Mg basalt under reducing conditions is initially dominated by olivine fractionation followed by Cr-rich spinel, clinopyroxene (cpx), and orthopyroxene (opx). Finally, between 1060 and 1000°C, amphibole formed by a peritectic reaction consuming cpx + olivine and forming amphibole + opx, resulting in 16% silica-undersaturated trachy-basaltic liquid. Equilibrium crystallization of the same composition under oxidizing conditions is characterized by strongly enhanced olivine and cpx fractionation and suppression of opx only occurring as a result of the peritectic amphibole-forming reaction at and below 1040°C. The liquid at 980°C is a peraluminous, alkali-poor, high-Al andesite representing ∼15% residual liquid. Fractional crystallization of the high-Mg basalt under oxidizing conditions evolves through fractionation of early olivine joined by cpx at 1200°C, followed by opx and hercynitic spinel (1140–1080°C) and amphibole at 1050°C coexisting with cpx (and spinel) to 980°C. At 950°C both garnet and plagioclase (plag) join amphibole as liquidus phases. This paragenesis (plus ilmenite and apatite) persists to 750°C with 16% residual liquid relative to the initial basaltic composition. Liquids evolve continuously from basalt to rhyolite, crossing the metaluminous–peraluminous boundary at about 60 wt % SiO2. Fractional crystallization of the basaltic andesite starting material differs at high temperature, where opx and cpx are the liquidus phases (1200–1080°C), followed by amphibole at the expense of opx. Below 950°C the phase assemblage is identical except at the lowest temperature (720°C), where quartz saturates in a high-silica rhyolitic liquid representing 20% of the initial basaltic andesite. Liquid compositions of the two starting compositions converge below 950°C, with the exception of K2O, which behaves incompatibly along the liquid line of descent. The H2O-undersaturated fractional crystallization experiments on the high-Mg basaltic composition under relatively reducing conditions evolve towards tholeiitic or alkalic compositions owing to early plagioclase (at 1140°C) and abundant opx (at 1110°C) crystallization followed by garnet–cpx–plag–ilmenite at 1080°C. Closed-system equilibrium crystallization under relatively oxidized conditions is characterized by significant expansion of the olivine stability field (>250°C, 1280–1000°C) relative to more reducing conditions, causing depletion of the liquid in ferrous iron and increase of ferric iron. The resulting fO2 of the coexisting basaltic liquids increases by more than 3 log units from about NNO + 2 to NNO + 5·5 over the temperature range >1200–1040°C, potentially offering an explanation for the more oxidized character of hydrous arc magmas as opposed to low-H2O tholeiitic magmas.
Wielinski, J., Müller, C., Voegelin, A., Morgenroth, E., & Kaegi, R. (2018). Combustion of sewage sludge: kinetics and speciation of the combustible. Energy and Fuels, 32(10), 10656-10667. doi:10.1021/acs.energyfuels.8b02106, Institutional Repository

Combustion of sewage sludge has become a viable route for sewage sludge management especially as the agricultural use of sewage sludge has become increasingly difficult due to more stringent requirements regarding the quality of sewage sludge. Combustion of digested sewage sludge in dedicated monocombustion facilities is advantageous, as it substantially reduces the volume of the sludge and still allows for a recovery of phosphorus from the sewage sludge ash at a later stage. Despite increasing amounts of sewage sludge being combusted, knowledge on the respective combustion kinetics is still fragmentary. The goal of this study was, therefore, to identify the major combustion reactions of sewage sludge, assess their Arrhenius parameters (activation energy and pre-exponential factor), and assign suitable reference compounds to the individual reactions. For that purpose, experiments were conducted using a thermogravimetric analyzer (TGA). With matrix inversion, we identified 10 individual reactions. Despite the apparent kinetic compensation most likely caused by insufficient precision of the TGA temperature setting, we were able to relate the major reactions of sewage sludge combustion to the combustion of individual reference compounds. In addition to cellulose and lignin, which dominated the weight loss with 35% and 20%, respectively, hemicellulose, xylan, alginate, and calcite were identified. The dominant fraction of cellulose is consistent with recent studies identifying cellulose mainly originating from toilet paper as a major organic constituent in wastewater. As the identified model compounds explain more than 80% of the total weight loss observed, our approach allows a rough speciation of the combustibles of sewage sludge based on TGA experiments.
Ziemba, C., Larivé, O., Reynaert, E., & Morgenroth, E. (2018). Chemical composition, nutrient-balancing and biological treatment of hand washing greywater. Water Research, 144, 752-762. doi:10.1016/j.watres.2018.07.005, Institutional Repository

On-site biological hand washing water treatment can improve global access to safe hand washing water, but requires a thorough understanding of the chemical composition of the water to be treated, and an effective treatment strategy. This study first presents a detailed characterization of the individual inputs to hand washing water. We demonstrate (1) that soap is likely the most significant input in hand washing water, representing ∼90% of mass loading, and (2) that inputs to hand washing water have low concentrations of biologically-essential macro- and micro-nutrients (nitrogen, phosphorus, potassium, copper, zinc, molybdenum and cobalt) with respect to carbon, which may impair biological carbon removal. This study next formulates a recipe that recreates a representative composition of hand washing water and develops a procedure to identify and supplement nutrients in which this recipe is estimated to be deficient. Batch testing of the nutrient-supplemented hand washing water with an inoculum of planktonic bacteria demonstrated improved assimilable organic carbon removal (99% vs. 86% removal) and produced lower final DOC concentrations (1.7 mgC/L vs. 3.5 mgC/L) compared to realistic (nutrient-deficient) washing water. Supplementing nutrients did promote cell growth (50x higher final total cell count). Full-scale testing in a biologically activated membrane bioreactor (BAMBi) system treating 75 L/day of nutrient-supplemented hand washing water showed that long-term operation (100 days) can deliver effective carbon removal (95%) without detrimental fouling or other disruptions caused by cell growth. This work demonstrates that biological treatment in a BAMBi system, operated with appropriate nutrient-balancing offers an effective solution for decentralized treatment of light greywater.
Altun, A. O., Bond, T., Pronk, W., & Park, H. G. (2017). Sensitive detection of competitive molecular adsorption by surface-enhanced raman spectroscopy. Langmuir, 33(28), 6999-7006. doi:10.1021/acs.langmuir.7b01186, Institutional Repository

Surface adsorption plays a critical role in a wide variety of fields from surface catalysis to molecular separation. Despite the importance, limited access to simultaneously sensitive and selective detection mechanisms has hampered the acquisition of comprehensive and versatile experimental data needed to understand the complex aspects of mixture adsorption, calling for a molecular detection method capable of obtaining the surface adsorption isotherms over a wide range of concentrations as well as distinguishing the competitive adsorption of different adsorbates. Here, we test surface-enhanced Raman spectroscopy (SERS) as an effective analysis tool of surface adsorption phenomena. Using a sensitive SERS substrate, we characterize the adsorption isotherms of chemical species of various binding energies. We obtained the isotherms for strongly binding species in a concentration range from subpicomolar to micromolar. A log-sigmoidal dependency of the SERS signals to the analyte concentration could be modeled by surface binding theories accurately using molecular dynamics simulations, thereby bringing out the potential capability of sensitive SERS for describing a single-compound adsorption process. SERS also enabled the determination of competitive adsorption isotherms from a multiple-compound solution for the first time. The successful demonstration of the sensitive and selective characterization of surface adsorption lends SERS adaptability to a cheap, facile, and effective solution for chemical analysis.
Auvinen, H., Kaegi, R., Rousseau, D. P. L., & Du Laing, G. (2017). Fate of Silver Nanoparticles in Constructed Wetlands - a Microcosm Study. Water, Air, and Soil Pollution, 228(3) (11 pp.). doi:10.1007/s11270-017-3285-9, Institutional Repository

Nano-enabled materials are produced at growing volumes which increases the likelihood of nanoparticles being released into the environment. Constructed wetlands (CWs) are likely to receive wastewater containing nanoparticles leaching from products during usage. Therefore, we investigate the retention of silver nanoparticles (Ag-NPs) in microcosms simulating CWs treating domestic wastewater. The effects of aeration and organic matter content on the Ag-NP removal efficiencies are studied in particular. CWs remove most of the Ag (80-90%) and the largest fraction of Ag is found in/on the biofilm. Detailed electron microscopy analyses suggest that Ag-NPs are transformed into Ag2S in all microcosm experiments. The good correlation between total suspended solids (TSS) and the Ag concentration measured in the effluent indicates that Ag-NPs are bound to the solids in the effluent. Aeration of the microcosms does not affect the release of Ag-NPs from the systems but increasing organic matter leads to increased amounts of Ag passing the CWs, correlating with the increased release of TSS from the CWs. These results suggest that Ag-NPs are retained with the (suspended) solids in CWs and that the removal efficiency of TSS is an important factor determining the discharge of Ag-NPs from CWs.
Benstoem, F., Nahrstedt, A., Boehler, M., Knopp, G., Montag, D., Siegrist, H., & Pinnekamp, J. (2017). Performance of granular activated carbon to remove micropollutants from municipal wastewater - a meta-analysis of pilot- and large-scale studies. Chemosphere, 185, 105-118. doi:10.1016/j.chemosphere.2017.06.118, Institutional Repository

For reducing organic micropollutants (MP) in municipal wastewater effluents, granular activated carbon (GAC) has been tested in various studies. We did systematic literature research and found 44 studies dealing with the adsorption of MPs (carbamazepine, diclofenac, sulfamethoxazole) from municipal wastewater on GAC in pilot- and large-scale plants. Within our meta-analysis we plot the bed volumes (BV [m3 water/m3 GAC]) until the breakthrough criterion of MP-BV20% was reached, dependent on potential relevant parameters (empty bed contact time EBCT, influent DOC DOC0 and manufacturing method). Moreover, we performed statistical tests (ANOVAs) to check the results for significance. Single adsorbers operating time differs i.e. by 2500% until breakthrough of diclofenac-BV20% was reached (800-20,000 BV). There was still elimination of the “very well/well” adsorbable MPs such as carbamazepine and diclofenac even when the equilibrium of DOC had already been reached. No strong statistical significance of EBCT and DOC0 on MP-BV20% could be found due to lack of data and the high heterogeneity of the studies using GAC of different qualities. In further studies, adsorbers should be operated[20,000 BV for exact calculation of breakthrough curves, and the following parameters should be recorded: selected MPs; DOC0; UVA254; EBCT; product name, manufacturing method and raw material of GAC; suspended solids (TSS); backwash interval; backwash program and pressure drop within adsorber. Based on our investigations we generally recommend using reactivated GAC to reduce the environmental impact and to carry out tests on pilot scale to collect reliable data for process design.
Boltz, J. P., Johnson, B. R., Takács, I., Daigger, G. T., Morgenroth, E., Brockmann, D., … Derlon, N. (2017). Biofilm carrier migration model describes reactor performance. Water Science and Technology, 75(12), 2818-2828. doi:10.2166/wst.2017.160, Institutional Repository

The accuracy of a biofilm reactor model depends on the extent to which physical system conditions (particularly bulk-liquid hydrodynamics and their influence on biofilm dynamics) deviate from the ideal conditions upon which the model is based. It follows that an improved capacity to model a biofilm reactor does not necessarily rely on an improved biofilm model, but does rely on an improved mathematical description of the biofilm reactor and its components. Existing biofilm reactor models typically include a one-dimensional biofilm model, a process (biokinetic and stoichiometric) model, and a continuous flow stirred tank reactor (CFSTR) mass balance that [when organizing CFSTRs in series] creates a pseudo two-dimensional (2-D) model of bulk-liquid hydrodynamics approaching plug flow. In such a biofilm reactor model, the user-defined biofilm area is specified for each CFSTR; thereby, Xcarrier does not exit the boundaries of the CFSTR to which they are assigned or exchange boundaries with other CFSTRs in the series. The error introduced by this pseudo 2-D biofilm reactor modeling approach may adversely affect model results and limit model-user capacity to accurately calibrate a model. This paper presents a new sub-model that describes the migration of Xcarrier and associated biofilms, and evaluates the impact that Xcarrier migration and axial dispersion has on simulated system performance. Relevance of the new biofilm reactor model to engineering situations is discussed by applying it to known biofilm reactor types and operational conditions.
Boltz, J. P., Smets, B. F., Rittmann, B. E., Van Loosdrecht, M. C. M., Morgenroth, E., & Daigger, G. T. (2017). From biofilm ecology to reactors: a focused review. Water Science and Technology, 75(8), 1753-1760. doi:10.2166/wst.2017.061, Institutional Repository

Biofilms are complex biostructures that appear on all surfaces that are regularly in contact with water. They are structurally complex, dynamic systems with attributes of primordial multicellular organisms and multifaceted ecosystems. The presence of biofilms may have a negative impact on the performance of various systems, but they can also be used beneficially for the treatment of water (defined herein as potable water, municipal and industrial wastewater, fresh/brackish/salt water bodies, groundwater) as well as in water stream-based biological resource recovery systems. This review addresses the following three topics: (1) biofilm ecology, (2) biofilm reactor technology and design, and (3) biofilm modeling. In so doing, it addresses the processes occurring in the biofilm, and how these affect and are affected by the broader biofilm system. The symphonic application of a suite of biological methods has led to significant advances in the understanding of biofilm ecology. New metabolic pathways, such as anaerobic ammonium oxidation (anammox) or complete ammonium oxidation (comammox) were first observed in biofilm reactors. The functions, properties, and constituents of the biofilm extracellular polymeric substance matrix are somewhat known, but their exact composition and role in the microbial conversion kinetics and biochemical transformations are still to be resolved. Biofilm grown microorganisms may contribute to increased metabolism of micro-pollutants. Several types of biofilm reactors have been used for water treatment, with current focus on moving bed biofilm reactors, integrated fixed-film activated sludge, membrane-supported biofilm reactors, and granular sludge processes. The control and/or beneficial use of biofilms in membrane processes is advancing. Biofilm models have become essential tools for fundamental biofilm research and biofilm reactor engineering and design. At the same time, the divergence between biofilm modeling and biofilm reactor modeling approaches is recognized.
Carr, G., Blanch, A. R., Blaschke, A. P., Brouwer, R., Bucher, C., Farnleitner, A. H., … Blöschl, G. (2017). Emerging outcomes from a cross-disciplinary doctoral programme on water resource systems. Water Policy, 19(3), 463-478. doi:10.2166/wp.2017.054, Institutional Repository

Interdisciplinary research and education programmes in water science are intended to produce groundbreaking research, often with an emphasis on societal relevance, and prepare future water resource experts to work across disciplines. This paper explores the emerging outcomes from an ongoing doctoral programme currently in its seventh year. Within the programme, there is both cross-disciplinary and mono-disciplinary research. Three questions are explored: (i) whether cross-disciplinary research leads to more innovative scientific findings than monodisciplinary research, (ii) whether cross-disciplinary researchers develop professional skills that benefit their future careers, and (iii) whether cross-disciplinary research produces findings of greater societal relevance than monodisciplinary research. Various indicators are used to measure research and education outcomes. Analysis of journal impact factors and citation rates of Institute of Scientific Information indexed publications suggests that crossdisciplinary research findings are more innovative. Comparison between graduate research profile and their career destinations suggests that researchers who learn to work across the disciplines continue to work this way in their post-doctoral positions. Analysis of media interest in research findings or their impact on policy suggests that both types of research are of societal value, but researchers often expand their understanding of a societal interest topic by bringing in new research fields.
Carrel, M., Beltran, M. A., Morales, V. L., Derlon, N., Morgenroth, E., Kaufmann, R., & Holzner, M. (2017). Biofilm imaging in porous media by laboratory X-ray tomography: combining a non-destructive contrast agent with propagation-based phase-contrast imaging tools. PLoS One, 12(7), e0180374 (18 pp.). doi:10.1371/journal.pone.0180374, Institutional Repository

X-ray tomography is a powerful tool giving access to the morphology of biofilms, in 3D porous media, at the mesoscale. Due to the high water content of biofilms, the attenuation coefficient of biofilms and water are very close, hindering the distinction between biofilms and water without the use of contrast agents. Until now, the use of contrast agents such as barium sulfate, silver-coated micro-particles or 1-chloronaphtalene added to the liquid phase allowed imaging the biofilm 3D morphology. However, these contrast agents are not passive and potentially interact with the biofilm when injected into the sample. Here, we use a natural inorganic compound, namely iron sulfate, as a contrast agent progressively bounded in dilute or colloidal form into the EPS matrix during biofilm growth. By combining a very long source-to-detector distance on a X-ray laboratory source with a Lorentzian filter implemented prior to tomographic reconstruction, we substantially increase the contrast between the biofilm and the surrounding liquid, which allows revealing the 3D biofilm morphology. A comparison of this new method with the method proposed by Davit et al (Davit et al., 2011), which uses barium sulfate as a contrast agent to mark the liquid phase was performed. Quantitative evaluations between the methods revealed substantial differences for the volumetric fractions obtained from both methods. Namely, contrast agent—biofilm interactions (e.g. biofilm detachment) occurring during barium sulfate injection caused a reduction of the biofilm volumetric fraction of more than 50% and displacement of biofilm patches elsewhere in the column. Two key advantages of the newly proposed method are that passive addition of iron sulfate maintains the integrity of the biofilm prior to imaging, and that the biofilm itself is marked by the contrast agent, rather than the liquid phase as in other available methods. The iron sulfate method presented can be applied to understand biofilm development and bioclogging mechanisms in porous materials and the obtained biofilm morphology could be an ideal basis for 3D numerical calculations of hydrodynamic conditions to investigate biofilm-flow coupling.
Derlon, N., Thürlimann, C., Dürrenmatt, D., & Villez, K. (2017). Batch settling curve registration via image data modeling. Water Research, 114, 327-337. doi:10.1016/j.watres.2017.01.049, Institutional Repository

To this day, obtaining reliable characterization of sludge settling properties remains a challenging and time-consuming task. Without such assessments however, optimal design and operation of secondary settling tanks is challenging and conservative approaches will remain necessary. With this study, we show that automated sludge blanket height registration and zone settling velocity estimation is possible thanks to analysis of images taken during batch settling experiments. The experimental setup is particularly interesting for practical applications as it consists of off-the-shelf components only, no moving parts are required, and the software is released publicly. Furthermore, the proposed multivariate shape constrained spline model for image analysis appears to be a promising method for reliable sludge blanket height profile registration.
Ding, A., Liang, H., Li, G., Szivak, I., Traber, J., & Pronk, W. (2017). A low energy gravity-driven membrane bioreactor system for grey water treatment: permeability and removal performance of organics. Journal of Membrane Science, 542, 408-417. doi:10.1016/j.memsci.2017.08.037, Institutional Repository

Synthetic grey water was treated with a low-pressure gravity-driven membrane bioreactor (GDMBR) system. The system was operated without any direct shear at the membrane surface and without any cleaning or flushing. In order to reduce energy consumption, one reactor was operated without aeration and the results were compared with an aerated reactor. Although the dissolved oxygen content was low (0.4–0.6 mg/L) in the non-aerated system, a stable permeability was observed at a level of around 20 L/m2 h bar (flux of 1 L/m2 h). The fouling resistance was dominated by the bio-fouling layer, which could be removed hydraulically. In comparison to the aerated system, the bio-fouling layer grown without aeration exhibited a lower biological activity, was thicker and had a lower surface roughness. Furthermore, the stable permeability of the aerated system was higher (40 L/m2 h bar), which could be explained by a lower content and load of extracellular polymeric substances (including extracellular polysaccharides and proteins). In comparison to filtration through a non-fouled membrane, the rejection of biopolymers and humic substances was strongly enhanced, which shows that the bio-fouling layer acts as a secondary membrane. The energy consumption was 0.02–0.04 kWh/m3, which is substantially less than for normal MBRs, and even less than for the traditional activated sludge process. These results show that grey water can be treated in a membrane reactor without any cleaning and flushing and even without any aeration, which makes the process suitable for decentralized wastewater treatment and considerably reduces the energy consumption.
Fumasoli, A., Bürgmann, H., Weissbrodt, D. G., Wells, G. F., Beck, K., Mohn, J., … Udert, K. M. (2017). Growth of Nitrosococcus-related ammonia oxidizing bacteria coincides with extremely low pH values in wastewater with high ammonia content. Environmental Science and Technology, 51(12), 6857-6866. doi:10.1021/acs.est.7b00392, Institutional Repository

Ammonia oxidation decreases the pH in wastewaters where alkalinity is limited relative to total ammonia. The activity of ammonia oxidizing bacteria (AOB), however, typically decreases with pH and often ceases completely in slightly acidic wastewaters. Nevertheless, nitrification at low pH has been reported in reactors treating human urine, but it has been unclear which organisms are involved. In this study, we followed the population dynamics of ammonia oxidizing organisms and reactor performance in synthetic fully hydrolyzed urine as the pH decreased over time in response to a decrease in the loading rate. Populations of the β-proteobacterial Nitrosomonas europaea lineage were abundant at the initial pH close to 6, but the growth of a possibly novel Nitrosococcus-related AOB genus decreased the pH to the new level of 2.2, challenging the perception that nitrification is inhibited entirely at low pH values, or governed exclusively by β-proteobacterial AOB or archaea. With the pH shift, nitrite oxidizing bacteria were not further detected, but nitrous acid (HNO2) was still removed through chemical decomposition to nitric oxide (NO) and nitrate. The growth of acid-tolerant γ-proteobacterial AOB should be prevented, by keeping the pH above 5.4, which is a typical pH limit for the N. europaea lineage. Otherwise, the microbial community responsible for high-rate nitrification can be lost, and strong emissions of hazardous volatile nitrogen compounds such as NO are likely.
Gogos, A., Thalmann, B., Voegelin, A., & Kaegi, R. (2017). Sulfidation kinetics of copper oxide nanoparticles. Environmental Science: Nano, 4(8), 1733-1741. doi:10.1039/C7EN00309A, Institutional Repository

Sulfidation of copper oxide nanoparticles (CuO NPs) in urban wastewater systems is expected to influence their impact on the environment. However, the kinetics of this reaction has not been studied to date and the reaction mechanism remains largely unexplored. We therefore investigated the sulfidation kinetics of CuO NPs reacted with bisulfide (HS−) at concentrations relevant to wastewater systems. Pristine CuO NPs (50 nm, 7.7 μM) were reacted with HS− (26.4–105.6 μM) in oxic solutions buffered to pH 8.0. The reaction progress was monitored using silver nitrate to quench the reaction and selectively dissolve the copper sulfides (Cux) and zincon to spectrophotometrically quantify the released Cu2+. In addition, the reaction products were characterized at selected time points using analytical electron microscopy and X-ray absorption spectroscopy (XAS). The sulfidation rate of the CuO NPs was best described by a pseudo first order rate law and the corresponding half-life times ranged between 1 and 6 minutes. XAS results showed that crystalline CuO NPs rapidly transformed into amorphous CuxS and gradually into crystalline CuS (covellite). The comparable size of pristine and transformed primary particles, the similar morphology of their aggregates, and the initial formation of CuO–CuxS core–shell structures revealed by analytical electron microscopy suggest that the initial sulfidation occurred via a direct conversion reaction mechanism. Our findings suggest that CuO NPs released from various sources into wastewater will rapidly transform into amorphous CuxS and eventually recrystallize into covellite.
Hernandez, E., Nowack, B., & Mitrano, D. M. (2017). Polyester textiles as a source of microplastics from households: a mechanistic study to understand microfiber release during washing. Environmental Science and Technology, 51(12), 7036-7046. doi:10.1021/acs.est.7b01750, Institutional Repository

Microplastic fibers make up a large proportion of microplastics found in the environment, especially in urban areas. There is good reason to consider synthetic textiles a major source of microplastic fibers, and it will not diminish since the use of synthetic fabrics, especially polyester, continues to increase. In this study we provide quantitative data regarding the size and mass of microplastic fibers released from synthetic (polyester) textiles during simulated home washing under controlled laboratory conditions. Consideration of fabric structure and washing conditions (use of detergents, temperature, wash duration, and sequential washings) allowed us to study the propensity of fiber shedding in a mechanistic way. Thousands of individual fibers were measured (number, length) from each wash solution to provide a robust data set on which to draw conclusions. Among all the variables tested, the use of detergent appeared to affect the total mass of fibers released the most, yet the detergent composition (liquid or powder) or overdosing of detergent did not significantly influence microplastic release. Despite different release quantities due to the addition of a surfactant (approximately 0.025 and 0.1 mg fibers/g textile washed, without and with detergent, respectively), the overall microplastic fiber length profile remained similar regardless of wash condition or fabric structure, with the vast majority of fibers ranging between 100 and 800 μm in length irrespective of wash cycle number. This indicates that the fiber staple length and/or debris encapsulated inside the fabric from the yarn spinning could be directly responsible for releasing stray fibers. This study serves as a first look toward understanding the physical properties of the textile itself to better understand the mechanisms of fiber shedding in the context of microplastic fiber release into laundry wash water.
Jacquin, C., Lesage, G., Traber, J., Pronk, W., & Heran, M. (2017). Three-dimensional excitation and emission matrix fluorescence (3DEEM) for quick and pseudo-quantitative determination of protein- and humic-like substances in full-scale membrane bioreactor (MBR). Water Research, 118, 82-92. doi:10.1016/j.watres.2017.04.009, Institutional Repository

The goal of this study is to help filling the research gaps linked to the on-line application of fluorescence spectroscopy in wastewater treatment and data processing tools suitable for rapid correction and extraction of data contained in three-dimensional fluorescence excitation-emission matrix (3DEEM) for real-time studies. 3DEEM was evaluated for direct quantification of Effluent Organic Matter (EfOM) fractions in full-scale MBR bulk supernatant and permeate samples. Principal Component Analysis (PCA) was used to investigate possible correlations between conventional Lowry and Dubois methods, Liquid Chromatography coupled to Organic Carbon and Organic Nitrogen Detection (LC-OCD-OND) and 3DEEM. 3DEEM data were analyzed using the volume of fluorescence (Φ) parameter from the Fluorescence Regional Integration (FRI) method. Two mathematical correlations were established between LC-OCD-OND and 3DEEM data to quantify protein-like and humic-like substances. These correlations were validated with supplementary data from the initial full-scale MBR, and were checked with samples from other systems (a second full-scale MBR, a full-scale conventional activated sludge (CAS) and a laboratory-scale MBR). While humic-like correlation showed satisfactory prediction for a second full-scale MBR and a CAS system, further studies are required for protein-like estimation in other systems. This new approach offers interesting perspectives for the on-line application of 3DEEM for EfOM quantification (protein-like and humic-like substances), fouling prediction and MBR process control.
Kaegi, R., Englert, A., Gondikas, A., Sinnet, B., von der Kammer, F., & Burkhardt, M. (2017). Release of TiO2 – (nano) particles from construction and demolition landfills. NanoImpact, 8, 73-79. doi:10.1016/j.impact.2017.07.004, Institutional Repository

A large fraction of engineered nanomaterials (ENM) will be deposited in landfills and it is assumed that ENM are securely locked in landfill sites and cannot leach into the environment (e.g. surface waters). However, experimental evidence supporting this assumption is lacking, as current production volumes of ENM are still too small and/or analytical techniques not sensitive enough to allow for the detection and quantification of ENM in landfill leachates. TiO2 particles are currently used in large quantities, for example in construction materials such as paints and renders as white pigments and their sizes extend into the nano-size range. We, therefore, selected TiO2 particles as a surrogate to assess the potential release of ENM from construction and demolition (C & D) landfill sites. We collected leachate samples from a landfill over one year and used complementary analytical techniques, including inductively coupled plasma (ICP) – optical emission spectroscopy (OES), automated scanning electron microscopy (auto SEM), transmission electron microscopy (TEM) and single particle ICP - mass spectrometry (spICPMS) to quantify TiO2 particles in landfill leachates. Total elemental Ti contents were mostly around a few tens of μg L− 1 and were strongly correlated with total suspended solids. Based on the volumetric discharge of the landfill leachate water from the landfill, we estimate a total amount of ~ 0.5 kg of TiO2 particles that are released annually from the landfill. Ti concentrations derived from ICP-OES measurements were in good agreement with quantifications based on TiO2 particles detected by auto SEM analyses. spICPMS measurements indicated a number concentration of Ti-containing particles in the order of 105 mL− 1 and TEM analyses dominantly revealed nanoscale TiO2 particles with a spherical shape typically observed for TiO2 particles used as white pigments. In addition, angular TiO2 particles with a well-defined crystal habitus were detected, suggesting that also natural TiO2 particles of comparable sizes are present in the landfill leachates. The results from this study indicate that (nanoscale) TiO2 particles are released from C & D landfill sites (~ 5 g/year). Although the amount of TiO2 particles released from C & D landfill sites may still be rather low, these particles may serve as proxy for assessing the future release of ENM from C & D landfill sites, which may become relevant as an increasing use of ENM is predicted for construction materials in general.
Kraas, M., Schlich, K., Knopf, B., Wege, F., Kägi, R., Terytze, K., & Hund-Rinke, K. (2017). Long-term effects of sulfidized silver nanoparticles in sewage sludge on soil microflora. Environmental Toxicology and Chemistry, 36(12), 3305-3313. doi:10.1002/etc.3904, Institutional Repository

The use of silver nanoparticles (AgNPs) in consumer products such as textiles leads to their discharge into wastewater and consequently to a transfer of the AgNPs to soil ecosystems via biosolids used as fertilizer. In urban wastewater systems (e.g., sewer,wastewater treatment plant [WWTP], anaerobic digesters) AgNPs are efficiently converted into sparingly soluble silver sulfides (Ag2S), mitigating the toxicity of the AgNPs. However, long-termstudies on the bioavailability and effects of sulfidized AgNPs on soilmicroorganisms are lacking. Thus we investigated the bioavailability and long-term effects of AgNPs (spiked in a laboratory WWTP) on soil microorganisms. Before mixing the biosolids into soil, the sludges were either anaerobically digested or directly dewatered. The effects on the ammonium oxidation process were investigated over 140 d. Transmission electron microscopy (TEM) suggested an almost complete sulfidation of the AgNPs analyzed in all biosolid samples and in soil, with Ag2S predominantly detected in long-term incubation experiments. However, despite the sulfidation of the AgNPs, soil ammonium oxidation was significantly inhibited, and the degree of inhibition was independent of the sludge treatment. The results revealed that AgNPs sulfidized under environmentally relevant conditions were still bioavailable to soil microorganisms. Consequently, Ag2S may exhibit toxic effects over the long term rather than the short term.
Lepot, M., Aubin, J. B., Clemens, F. H. L. R., & Mašić, A. (2017). Outlier detection in UV/Vis spectrophotometric data. Urban Water Journal, 14(9), 908-921. doi:10.1080/1573062X.2017.1280515, Institutional Repository

UV/Vis spectrophotometers have been used to monitor water quality since the early 2000s. Calibration of these devices requires sampling campaigns to elaborate relations between recorded spectra and measured concentrations. In order to build robust calibration data sets, several spectra must be recorded per sample. This study compares two approaches – principal component analysis and data depth theory – to identify outliers and select the most representative spectrum (MRS) among the repetitively recorded spectra. Detection of samples that contain outliers is consistent between the methods in more than 70% of the samples. Identification of spectra as outliers is consistent in more than 95% of the cases. The identification of MRS differs depending on the approach used. In their current form, both of the proposed approaches can be used for outlier detection and identification. Further studies are suggested to combine the methods and develop an automated ranking and sorting system.
Mašić, A., Billeter, J., Bonvin, D., & Villez, K. (2017). Extent computation under rank-deficient conditions. In D. Dochain, D. Henrion, & D. Peaucelle (Eds.), IFAC-PapersOnLine: Vol. 50. 20th IFAC world congress. Proceedings (pp. 3929-3934). doi:10.1016/j.ifacol.2017.08.367, Institutional Repository

The identification of kinetic models can be simplified via the computation of extents of reaction on the basis of invariants such as stoichiometric balances. In the extent space, one can identify the structure and the parameters of reaction rates individually, which significantly reduces the number of parameters that need to be estimated simultaneously. So far, extent-based modeling has only been applied to cases where all the extents can be computed from measured concentrations. This generally excludes its application to many biological processes for which the number of reactions tends to be larger than the number of measured quantities. This paper shows that, in some cases, such restrictions can be lifted. In addition, this study demonstrates the applicability of extent-based model identification using laboratory experimental data.
Mašić, A., Srinivasan, S., Billeter, J., Bonvin, D., & Villez, K. (2017). Identification of biokinetic models using the concept of extents. Environmental Science and Technology, 51(13), 7520-7531. doi:10.1021/acs.est.7b00250, Institutional Repository

The development of a wide array of process technologies to enable the shift from conventional biological wastewater treatment processes to resource recovery systems is matched by an increasing demand in predictive capabilities. Mathematical models are excellent tools to meet this demand. However, obtaining reliable and fit-for-purpose models remains a cumbersome task due to the inherent complexity of biological wastewater treatment processes. In this work, we present a first study in the context of environmental biotechnology that adopts and explores the use of extents as a way to simplify and streamline the dynamic process modeling task. In addition, the extent-based modeling strategy is enhanced by optimal accounting of nonlinear algebraic equilibria and nonlinear measurement equations. Finally, a thorough discussion of our results aims at demonstrating the benefits of extent-based modeling and its potential to turn environmental process modeling into a highly automated task.
Mašić, A., Srinivasan, S., Billeter, J., Bonvin, D., & Villez, K. (2017). Shape constrained splines as transparent black-box models for bioprocess modeling. Computers and Chemical Engineering, 99, 96-105. doi:10.1016/j.compchemeng.2016.12.017, Institutional Repository

Empirical model identification for biological systems is a challenging task due to the combined effects of complex interactions, nonlinear effects, and lack of specific measurements. In this context, several researchers have provided tools for experimental design, model structure selection, and optimal parameter estimation, often packaged together in iterative model identification schemes. Still, one often has to rely on a limited number of candidate rate laws such as Contois, Haldane, Monod, Moser, and Tessier. In this work, we propose to use shape-constrained spline functions as a way to reduce the number of candidate rate laws to be considered in a model identification study, while retaining or even expanding the explanatory power in comparison to conventional sets of candidate rate laws. The shape-constrained rate laws exhibit the flexibility of typical black-box models, while offering a transparent interpretation akin to conventionally applied rate laws such as Monod and Haldane. In addition, the shape-constrained spline models lead to limited extrapolation errors despite the large number of parameters.
McCall, A. K., Palmitessa, R., Blumensaat, F., Morgenroth, E., & Ort, C. (2017). Modeling in-sewer transformations at catchment scale – implications on drug consumption estimates in wastewater-based epidemiology. Water Research, 122, 655-668. doi:10.1016/j.watres.2017.05.034, Institutional Repository

To which extent illicit drugs are transformed during in-sewer transport, depends on a number of factors: i) substance-specific transformation rates, ii) environmental conditions, iii) point of discharge (location of drug user) and iv) sewer network properties, primarily hydraulic residence time (HRT) and the ratio of biofilm contact area to wastewater volume (A/Veq).
Assessing associated uncertainties typically requires numerous simulations. Therefore, we propose a new two-step modeling framework: 1) Quantify hydrodynamic conditions. This computationally demanding step was performed once in SWMM to derive HRT and A/Veq for each potential point of discharge (node) in three catchments of different size. 2) Estimate biomarker loss. In this step, Monte Carlo simulations were performed for defined scenarios. Depending on assumptions about drug user distribution and prevalence, a number of nodes was sampled. For each node an empirical first-order transformation model was applied with flow-path-corresponding HRT and A/Veq from step 1. Biotic and abiotic transformation rates were sampled from distributions combining variability of different biofilms.
In our modeling study, median losses were >30% for amphetamine, 6-monoacetylmorphine and 6-acetylcodeine in all three catchments with high uncertainty (5%–100% loss), which would imply a systematic underestimation of consumption when neglecting in-sewer processes. Median losses for 21 other investigated biomarkers were <10% with different uncertainty ranges – “no substantial transformation” was confirmed for nine substances in a real sewer segment with a 2-h residence time. Transferability of these results must be tested for other catchments. To further reduce uncertainty, mainly additional knowledge on transformation rates, particularly in biofilm, and their distribution across a sewer network is needed to update model input objectively. Our approach allows efficient testing and, furthermore, can be expanded for many other human biomarkers. Accounting for biomarker stability during in-sewer transport will avoid biased estimates and further improve wastewater-based epidemiology.
Mehrabi, K., Nowack, B., Arroyo Rojas Dasilva, Y., & Mitrano, D. M. (2017). Improvements in nanoparticle tracking analysis to measure particle aggregation and mass distribution: a case study on engineered nanomaterial stability in incineration landfill leachates. Environmental Science and Technology, 51(10), 5611-5621. doi:10.1021/acs.est.7b00597, Institutional Repository

Numerous nanometrology techniques have been developed in recent years to determine the size, concentration, and a number of other characteristics of engineered nanomaterials (ENM) in environmental matrices. Among the many available techniques, nanoparticle tracking analysis (NTA) can measure individual particles to create a size distribution and measure the particle number. Therefore, we explore the possibility to use these data to calculate the particle mass distribution. Additionally, we further developed the NTA methodology to explore its suitability for analysis of ENM in complex matrices by measuring ENM agglomeration and sedimentation in municipal solid waste incineration landfill leachates over time. 100 nm Au ENM were spiked into DI H2O and synthetic and natural leachates. We present the possibility of measuring ENM in the presence of natural particles based on differences in particle refractivity indices, delineate the necessity of creating a calibration curve to adjust the given NTA particle number concentration, and determine the instruments linear range under different conditions. By measuring the particle size and the particle number distribution, we were able to calculate the ENM mass remaining in suspension. By combining these metrics together with transmission electron microscopy (TEM) analyses, we could assess the extent of both homo- and heteroagglomeration as well as particle sedimentation. Reporting both size and mass based metrics is common in atmospheric particle measurements, but now, the NTA can give us the possibility of applying the same approach also to aqueous samples.
Merle, T., Pronk, W., & von Gunten, U. (2017). MEMBRO3X, a novel combination of a membrane contactor with advanced oxidation (O3/H2O2) for simultaneous micropollutant abatement and bromate minimization. Environmental Science and Technology Letters, 4(5), 180-185. doi:10.1021/acs.estlett.7b00061, Institutional Repository

Ozonation is a water treatment process for disinfection and/or micropollutant abatement. However, ozonation of bromide-containing water leads to bromate (BrO3–) formation, a potential human carcinogen. A solution for mitigating BrO3– formation during abatement of micropollutants is to minimize the ozone (O3) concentration. This can be achieved by dosing ozone in numerous small portions throughout a reactor in the presence of H2O2. Under these conditions, O3 is rapidly consumed to form hydroxyl radical (·OH), which will oxidize micropollutants. To achieve this goal, a novel process (“MEMBRO3X”) was developed in which ozone is transferred to the water through the pores of polytetrafluoroethylene (PTFE) hollow fiber membranes. When compared to the conventional peroxone process (O3/H2O2), the MEMBRO3X process shows better performance in terms of micropollutant abatement and bromate minimization for groundwater and surface water treatment. For a groundwater containing 180 μg/L bromide, a 95% abatement of the ozone-resistant probe compound p-chlorobenzoic acid yielded <0.5 μg/L BrO3–, whereas in the conventional peroxone process, 8 μg/L BrO3– was formed. In addition, the efficacy of the MEMBRO3X process was demonstrated with river water and lake water.
Mkhize, N., Taylor, M., Udert, K. M., Gounden, T. G., & Buckley, C. A. (2017). Urine diversion dry toilets in eThekwini Municipality, South Africa: acceptance, use and maintenance through users' eyes. Journal of Water Sanitation and Hygiene for Development, 7(1), 111-120. doi:10.2166/washdev.2017.079, Institutional Repository

This study was part of the VUNA project aimed to develop an affordable sanitation system that produces a valuable fertiliser, reduces pollution of water resources and promotes health. Urine diversion dry toilets (UDDTs) simplify the on-site hygienisation of faeces and allow for nutrient recovery from urine. Social acceptance is vital for the implementation of the UDDT, because sanitation is only effective if the system not only provides a well-designed toilet and effective waste management, but also offers users a facility that caters to their needs and is sensitive to their cultural lifestyle. This study used qualitative and quantitative methods to investigate acceptance, use and maintenance of UDDTs. Key findings indicate lower levels of acceptance of UDDTs among the elderly, who are accustomed to traditional pit toilets. The users aspire to own a flush toilet, perceived to be indicative of household wealth. A dominant concern was emptying the pit and the quality of the building material. Community interventions are required that will promote acceptance, understanding and encourage proper use and maintenance of the UDDT, and may need some technology modification. There is an urgent need for increased community participation to address users' perceptions, attitudes and behaviour concerning the UDDT.
Moll, J., Klingenfuss, F., Widmer, F., Gogos, A., Bucheli, T. D., Hartmann, M., & van der Heijden, M. G. A. (2017). Effects of titanium dioxide nanoparticles on soil microbial communities and wheat biomass. Soil Biology and Biochemistry, 111, 85-93. doi:10.1016/j.soilbio.2017.03.019, Institutional Repository

Titanium dioxide nanoparticles (TiO2 NPs) are the most produced NPs worldwide and have great potential to be utilized in agriculture as additives for plant protection products. However, concerns have been raised that some NPs may negatively affect crops and soil microbial communities, including beneficial microbes such as arbuscular mycorrhizal fungi. Here we tested two different TiO2 NPs (P25, E171) and a bulk TiO2 (particle size >100 nm) for their effects on the diversity and community composition of soil microorganisms. In addition we tested whether increasing concentrations of TiO2 NPs had effects on wheat growth and yield. Microbial diversity was analyzed using Illumina Miseq paired-end sequencing of ribosomal markers (prokaryotic 16SV3V4 and fungal ITS2 of the ribosomal RNA operon). Application of TiO2 NPs altered the detected prokaryotic but not fungal community structure. Prokaryotic community structure differed significantly between the three NP treatments and the control treatment without NP, although differences were smaller compared to those between the positive and the negative control. Specific microbial taxa responded positively or negatively to particular TiO2 NP treatments and, thus, may be used as bio-indicators for TiO2 NPs. No negative effects on wheat growth and on arbuscular mycorrhizal root colonization were detected, and no evidence for a dose-response relationship between wheat performance and TiO2 NP concentration was found. Overall, these results reveal that prokaryotes are more sensitive than fungi to the TiO2 NP treatments.
Nguyen, M. T., Allemann, L., Ziemba, C., Larivé, O., Morgenroth, E., & Julian, T. R. (2017). Controlling bacterial pathogens in water for reuse: treatment technologies for water recirculation in the Blue Diversion Autarky Toilet. Frontiers in Environmental Science, 5, 90 (13 pp.). doi:10.3389/fenvs.2017.00090, Institutional Repository

The Blue Diversion AUTARKY Toilet is a urine-diverting toilet with on-site treatment. The toilet is being developed to provide a safe and affordable sanitation technology for people who lack access to sewer-based sanitation. Water used for personal hygiene, hand washing, and flushing to rinse urine- and feces-collection bowls is treated, stored, and recycled for reuse to reduce reliance on external water supplies. The system provides an opportunity to investigate hygiene of water for reuse following treatment. Treatment in the toilet includes a Biologically Activated Membrane Bioreactor (BAMBi) followed by a secondary treatment technology. To identify effective secondary treatment, three options, including granular activated carbon (GAC) only, GAC+chlorine (sodium hypochlorite), and GAC+electrolysis are considered based on the bacterial inactivation and growth inhibition efficiency. Four different hygiene-relevant bacteria are tested: Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, and Salmonella typhimurium. Our evaluation demonstrates that—despite treatment of water with the BAMBi—E. coli, P. aeruginosa, and S. typhimurium have the potential to grow during storage in the absence of microbial competition. Including the indigenous microbial community influences bacterial growth in different ways: E. coli growth decreases but P. aeruginosa growth increases relative to no competition. The addition of the secondary treatment options considerably improves water quality. A column of GAC after the BAMBi reduces E. coli growth potential by 2 log10, likely due to the reduction of carbon sources. Additional treatments including chlorination and electrolysis provide further safety margins, with more than 5 log10 inactivation of E. coli. However, reactivation and/or regrowth of E. coli and P. aeruginosa occurs under in the absence of residual disinfectant. Treatment including the BAMBi, GAC, and electrolysis appear to be promising technologies to control bacterial growth during storage in water intended for reuse.
Praetorius, A., Gundlach-Graham, A., Goldberg, E., Fabienke, W., Navratilova, J., Gondikas, A., … von der Kammer, F. (2017). Single-particle multi-element fingerprinting (spMEF) using inductively-coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) to identify engineered nanoparticles against the elevated natural background in soils. Environmental Science: Nano, 4(2), 307-314. doi:10.1039/c6en00455e, Institutional Repository

The discrimination of engineered nanoparticles (ENPs) from the natural geogenic background is one of the preeminent challenges for assessing their potential implications. At low ENP concentrations, most conventional analytical techniques are not able to take advantage of inherent differences (e.g. in terms of composition, isotopic signatures, element ratios, structure, shape or surface characteristics) between ENPs and naturally occurring nanoscale particles (NNPs) of similar composition. Here, we present a groundbreaking approach to overcome these limitations and enable the discrimination of man-made ENPs from NNPs through simultaneous detection of multiple elements on an individual particle level. This new analytical approach is accessible by an inductively-coupled plasma time-of-flight mass spectrometer (ICP-TOFMS) operated in single-particle mode. Machine learning is employed to classify ENPs and NNPs based on their unique elemental fingerprints and quantify their concentrations. We demonstrate the applicability of this single-particle multi-element fingerprinting (spMEF) method by distinguishing engineered cerium oxide nanoparticles (CeO2 ENPs) from natural Ce-containing nanoparticles (Ce-NNPs) in soils at environmentally relevant ENP concentrations, orders of magnitude below the natural background.
Schmitt, R. J. P., Morgenroth, E., & Larsen, T. A. (2017). Robust planning of sanitation services in urban informal settlements: an analytical framework. Water Research, 110, 297-312. doi:10.1016/j.watres.2016.12.007, Institutional Repository

New types of sanitation services are emerging to tackle the sanitation crisis in informal settlements. These services link toilet facilities to semi-decentralized treatment plants via frequent, road-based transport of excreta. However, information for the planning of such sanitation services is scarce, and their future operating conditions are highly uncertain. The key questions of this paper are therefore: a) what are the drivers behind success or failure of a service-based sanitation system in informal settlements and b) on what scales and under which conditions can such a system operate successfully? To answer these questions, already at an early stage of the planning process, we introduce a stochastic model to analyze a wide range of system designs under varying technical designs, socio-economic factors, and spatial condition. Based on these initial results, we design a sanitation service and use the numeric model to study its reliability and costs over a wide range of scales, i.e., system capacities, from very few to many hundred users per semi-decentralized treatment unit. Key findings are that such a system can only operate within a narrow, but realistic range of conditions. Key requirements are toilet facilities, which can be serviced rapidly, and a flexible workforce. A high density of facilities will also lower the costs. Under these premises, we develop a road-based sanitation service and model its functionality in different settings and under many scenarios. Results show that the developed sanitation system using a single vehicle is scalable (100–700 users), can provide reliable service, and can be cheap (<1.5 c/p/day). Hence, this paper demonstrates opportunities for road-based sanitation in informal settlements and presents a quantitative framework for designing such systems.
Senn, A. C., Kaegi, R., Hug, S. J., Hering, J. G., Mangold, S., & Voegelin, A. (2017). Effect of aging on the structure and phosphate retention of Fe(III)-precipitates formed by Fe(II) oxidation in water. Geochimica et Cosmochimica Acta, 202, 341-360. doi:10.1016/j.gca.2016.12.033, Institutional Repository

Iron(III)-precipitates formed by Fe(II) oxidation in aqueous solutions affect the cycling and impact of Fe and other co-precipitated elements in environmental systems. Fresh Fe(III)-precipitates are metastable and their transformation into more stable phases during aging may result in the release of initially co-precipitated ions. Phosphate, silicate, Mg and Ca play key roles in determining the structure and composition of fresh Fe(III)-precipitates. Here we examine how these ions affect the structure and phosphate retention of Fe(III)-precipitates formed by oxidation of 0.5 mM dissolved Fe(II) at pH 7.0 after aging for 30 days at 40 °C.
Iron K-edge X-ray absorption spectroscopy (XAS) shows that aged precipitates consist of the same structural units as fresh precipitates: Amorphous Fe(III)- or Ca-Fe(III)-phosphate, ferrihydrite, and poorly crystalline lepidocrocite. Mg, Ca, and dissolved phosphate stabilize (Ca-)Fe(III)-phosphate against transformation into ferrihydrite. Silicate further attenuates (Ca-)Fe(III)-phosphate transformation. The crystallinity of lepidocrocite formed in phosphate- and silicate-free solutions slightly increases during aging. The transformation of Fe(III)- and Ca-Fe(III)-phosphate into ferrihydrite and ongoing ferrihydrite crystallization during aging result in the release of co-precipitated phosphate. Dissolved Ca on the other hand limits phosphate concentrations to values consistent with solubility control by octacalciumphosphate. Owing to the combined effects of Ca and silicate, phosphate is most effectively retained by Fe(III)-precipitates formed and aged in Ca- and silicate-containing solutions. The results from this study contribute to an improved understanding of the formation and transformation of Fe(III)-precipitates and emphasize that the complexity of Fe(III)-precipitate dynamics in the presence of multiple interfering solutes must be considered when addressing their impact on major and trace elements in environmental systems.
Soltermann, F., Abegglen, C., Tschui, M., Stahel, S., & von Gunten, U. (2017). Options and limitations for bromate control during ozonation of wastewater. Water Research, 116, 76-85. doi:10.1016/j.watres.2017.02.026, Institutional Repository

Wastewater treatment plants (WWTPs) are important point sources for micropollutants, which are harmful to freshwater organisms. Ozonation of wastewater is a powerful option to abate micropollutants, but may result in the formation of the potentially toxic oxidation by-product bromate in bromide-containing wastewaters. This study investigates options to reduce bromate formation during wastewater ozonation by (i) reducing the bromide concentration of the wastewater, (ii) lowering the ozone dose during wastewater treatment and (iii) adding hydrogen peroxide to limit the lifetime of ozone and quench the intermediates of the bromate formation pathway. Two examples demonstrate that a high share of bromide in wastewater can originate from single point sources (e.g., municipal waste incinerators or landfills). The identification of major point sources requires laborious sampling campaigns, but may facilitate the reduction of the bromide load significantly. To reduce the bromate formation by lowering the ozone dose interferes with the aim to abate micropollutants. Therefore, an additional treatment is necessary to ensure the elimination of micropollutants. Experiments at a pilot-plant illustrate that a combined treatment (ozone/powdered activated carbon) allows to eliminate micropollutants with low bromate yields. Furthermore, the addition of hydrogen peroxide was investigated at bench-scale. The bromate yields could be reduced by ∼50% and 65% for a hydrogen peroxide dose of 5 and 10 mg L−1, respectively. In conclusion, there are options to reduce the bromate formation during wastewater ozonation, however, they are not simple with sometimes limited efficiency.
Tarpeh, W. A., Udert, K. M., & Nelson, K. L. (2017). Comparing ion exchange adsorbents for nitrogen recovery from source-separated urine. Environmental Science and Technology, 51(4), 2373-2381. doi:10.1021/acs.est.6b05816, Institutional Repository

Separate collection of urine, which is only 1% of wastewater volume but contains the majority of nitrogen humans excrete, can potentially reduce the costs and energy input of wastewater treatment and facilitate recovery of nitrogen for beneficial use. Ion exchange was investigated for recovery of nitrogen as ammonium from urine for use as a fertilizer or disinfectant. Cation adsorption curves for four adsorbents (clinoptilolite, biochar, Dowex 50, and Dowex Mac 3) were compared in pure salt solutions, synthetic urine, and real stored urine. Competition from sodium and potassium present in synthetic and real urine did not significantly decrease ammonium adsorption for any of the adsorbents. Dowex 50 and Dowex Mac 3 showed nearly 100% regeneration efficiencies. Estimated ion exchange reactor volumes to capture the nitrogen for 1 week from a four-person household were lowest for Dowex Mac 3 (5 L) and highest for biochar (19 L). Although Dowex Mac 3 had the highest adsorption capacity, material costs ($/g N removed) were lower for clinoptilolite and biochar because of their substantially lower unit cost.
Thürlimann, C. M., & Villez, K. (2017). Input estimation as a qualitative trend analysis problem. Computers and Chemical Engineering, 107, 333-342. doi:10.1016/j.compchemeng.2017.04.011, Institutional Repository

The study of techniques for qualitative trend analysis (QTA) has been a popular approach to address challenges in fault diagnosis of engineered processes. Such challenges include the lack of reliable extrapolation of available models and lack of representative data describing previously unseen circumstances. Many of these challenges appear in biological systems even when normal operation can be assumed. It is for this reason that QTA techniques have also been proposed for the purpose of fault detection, automation, and dynamic modeling. In this work, we adopt a shape-constrained spline function method for the purpose of unknown input estimation. Thanks to data collected at laboratory-scale in a biological reactor for urine nitrification, this novel approach has been demonstrated successfully for the first time.
Tobias, R., O'Keefe, M., Künzle, R., Gebauer, H., Gründl, H., Morgenroth, E., … Larsen, T. A. (2017). Early testing of new sanitation technology for urban slums: the case of the Blue Diversion Toilet. Science of the Total Environment, 576, 264-272. doi:10.1016/j.scitotenv.2016.10.057, Institutional Repository

The toilets used most in informal urban settlements have detrimental consequences for the environment and human health due to the lack of proper collection and treatment of toilet waste. Concepts for safe, sustainable and affordable sanitation systems exist, but their feasibility and acceptance have to be investigated at an early stage of development, which is difficult due to the high costs of building working models. In this paper, we present an approach to estimate acceptance in a valid and representative form with only one working model, and apply it to test an innovative zero-emission toilet with recycling of wash water. Four basic principles were specified for investigation and nine hypotheses formulated to test the feasibility and acceptance of these principles: source separation of urine and feces with subsequent collection for resource recovery; provision of wash water in a separate cycle with on-site recovery through a membrane bioreactor; a convenient and attractive overall design; and a financially sustainable business plan. In Kampala (Uganda), in 2013, data was collected from 22 regular users, 308 one-time users and a representative sample of 1538 participants. Qualitative data was collected from the users, who evaluated their likes, perceived benefits, social norms and expected ease of use based on verbal and visual information. Most of the hypotheses were confirmed, indicating the feasibility and acceptance of the basic principles. Source separation and on-site water recovery were found to be feasible and accepted, provided users can be convinced that the emptying service and water recovery process work reliably. In the survey, the toilet was evaluated favorably and 51% of the participants agreed to be placed on a bogus waiting list. However, some design challenges were revealed, such as the size of the toilet, hiding feces from view and improving the separation of urine and water
Vriens, B., Voegelin, A., Hug, S. J., Kaegi, R., Winkel, L. H. E., Buser, A. M., & Berg, M. (2017). Quantification of element fluxes in wastewaters: a nationwide survey in Switzerland. Environmental Science and Technology, 51(19), 10943-10953. doi:10.1021/acs.est.7b01731, Institutional Repository

The number and quantities of trace elements used in industry, (high-tech) consumer products, and medicine are rapidly increasing, but the resulting emissions and waste streams are largely unknown. We assessed the concentrations of 69 elements in digested sewage sludge and effluent samples from 64 municipal wastewater treatment plants as well as in major rivers in Switzerland. This data set, representative of an entire industrialized country, presents a reference point for current element concentrations, average per-capita fluxes, loads discharged to surface waters, and economic waste-stream values. The spatial distribution of many individual elements could be attributed either to predominant geogenic or to anthropogenic inputs. Per-capita element fluxes ranged from <10 μg day−1 (e.g., Au, In, and Lu) to >1 mg day−1 (e.g., Zn, Sc, Y, Nb, and Gd) and >1 g day−1 (e.g., for P, Fe, and S). Effluent loads of some elements contributed significantly to riverine budgets (e.g., 24% for Zn, 50% for P, and 83% for Gd), indicating large anthropogenic inputs via the wastewater stream. At various locations, precious metal concentrations in sludge were similar to those in profitable mining ores, with total flux values of up to 6.8 USD per capita per year or 15 USD per metric ton of dry sludge.
Völker, J., Vogt, T., Castronovo, S., Wick, A., Ternes, T. A., Joss, A., … Wagner, M. (2017). Extended anaerobic conditions in the biological wastewater treatment: higher reduction of toxicity compared to target organic micropollutants. Water Research, 116, 220-230. doi:10.1016/j.watres.2017.03.030, Institutional Repository

Extended anaerobic conditions during biological wastewater treatment may enhance the biodegradation of micropollutants. To explore this, we combined iron-reducing or substrate-limited anaerobic conditions and aerobic pilot-scale reactors directly at a wastewater treatment plant. To investigate the detoxification by these processes, we applied two in vitro bioassays for baseline toxicity (Microtox) and reactive toxicity (AREc32) as well as in vivo bioassays with aquatic model species in two laboratory experiments (Desmodesmus subspicatus, Daphnia magna) and two on-site, flow-through experiments (Potamopyrgus antipodarum, Lumbriculus variegatus). Moreover, we analyzed 31 commonly occurring micropollutants and 10 metabolites.
The baseline toxicity of raw wastewater was effectively removed in full-scale and reactor scale activated sludge treatment (>85%), while the oxidative stress response was only partially removed (>61%). A combination of an anaerobic pre-treatment under iron reducing conditions and an aerobic nitrification significantly further reduced the residual in vitro toxicities by 46–60% and outperformed the second combination consisting of an aerobic pre-treatment and an anaerobic post-treatment under substrate-limiting conditions (27–43%). Exposure to effluents of the activated sludge treatment did not induce adverse in vivo effects in aquatic invertebrates. Accordingly, no further improvement in water quality could be observed. Compared to that, the removal of persistent micropollutants was increased. However, this observation was restricted to a limited number of compounds and the removal of the sum concentration of all target micropollutants was relative low (14–17%).
In conclusion, combinations of strictly anaerobic and aerobic processes significantly enhanced the removal of specific and non-specific in vitro toxicities. Thus, an optimization of biological wastewater treatment can lead to a substantially improved detoxification. These otherwise hidden capacities of a treatment technology can only be uncovered by a complementary biological analysis.
Weissbrodt, D. G., Holliger, C., & Morgenroth, E. (2017). Modeling hydraulic transport and anaerobic uptake by PAOs and GAOs during wastewater feeding in EBPR granular sludge reactors. Biotechnology and Bioengineering, 114(8), 1688-1702. doi:10.1002/bit.26295, Institutional Repository

New-generation bioprocesses using granular sludge aim for a high-rate removal of nutrients from wastewater with low footprint. Achieving enhanced biological phosphorus removal (EBPR) relies on the design of sludge beds and wastewater feeding conditions to optimally load the biomass and to select for polyphosphate- (PAOs) over glycogen-accumulating organisms (GAOs) and over other heterotrophs. A hydraulic–metabolic mathematical model was developed to elucidate the impact of hydraulic transport patterns and environmental conditions on the PAO/GAO competition during up-flow feeding through an EBPR granular sludge bed. Tracer experiments highlighted plug-flow regimes with dispersion under both rapid (9 mh-1, Rebed = 1.6, Pez = 7.2, Pet = 4.6) and slow (0.9 mh-1, Rebed = 0.2, Pez = 21.3, Pet = 3.4) feeding. Non-turbulent regimes (Rebed << 103) promote a safe implementation of simultaneous fill/draw. Feeding time, pH, and temperature significantly impacted bacterial competition for carbon uptake under anaerobic slow feeding. Feeding duration should be designed to avoid full depletion of intracellular storage polymers within static granules. PAOs bear twice longer feeding than GAOs by using both polyphosphate and glycogen hydrolysis to sustain anaerobic C-uptake. Alkaline conditions (pH 7.25–8.0) by, e.g., dosing lime in the feed select for PAOs independently of temperature (10−30°C). A twice higher bed is required for full anaerobic conversions at 10 rather than 20°C. Biosystem responses for anaerobic C-uptake can be anticipated using the model toward designing robust anaerobic selectors to manage the microbial resource in EBPR granular sludge. Biotechnol. Bioeng. 2017;114: 1688–1702.
Wells, G. F., Shi, Y., Laureni, M., Rosenthal, A., Szivák, I., Weissbrodt, D. G., … Morgenroth, E. (2017). Comparing the resistance, resilience, and stability of replicate moving bed biofilm and suspended growth combined nitritation–anammox reactors. Environmental Science and Technology, 51(9), 5108-5117. doi:10.1021/acs.est.6b05878, Institutional Repository

Combined partial nitritation–anammox (PN/A) systems are increasingly being employed for sustainable removal of nitrogen from wastewater, but process instabilities present ongoing challenges for practitioners. The goal of this study was to elucidate differences in process stability between PN/A process variations employing two distinct aggregate types: biofilm [in moving bed biofilm reactors (MBBRs)] and suspended growth biomass. Triplicate reactors for each process variation were studied under baseline conditions and in response to a series of transient perturbations. MBBRs displayed elevated NH4+ removal rates relative to those of suspended growth counterparts over six months of unperturbed baseline operation but also exhibited significantly greater variability in performance. Transient perturbations led to strikingly divergent yet reproducible behavior in biofilm versus suspended growth systems. A temperature perturbation prompted a sharp reduction in NH4+ removal rates with no accumulation of NO2– and rapid recovery in MBBRs, compared to a similar reduction in NH4+ removal rates but a high level of accumulation of NO2– in suspended growth reactors. Pulse additions of a nitrification inhibitor (allylthiourea) prompted only moderate declines in performance in suspended growth reactors compared to sharp decreases in NH4+ removal rates in MBBRs. Quantitative fluorescence in situ hybridization demonstrated a significant enrichment of anammox in MBBRs compared to suspended growth reactors, and conversely a proportionally higher AOB abundance in suspended growth reactors. Overall, MBBRs displayed significantly increased susceptibility to transient perturbations employed in this study compared to that of suspended growth counterparts (stability parameter), including significantly longer recovery times (resilience). No significant difference in the maximal impact of perturbations (resistance) was apparent. Taken together, our results suggest that aggregate architecture (biofilm vs suspended growth) in PN/A processes exerts an unexpectedly strong influence on process stability.
Wu, B., Suwarno, S. R., Tan, H. S., Kim, L. H., Hochstrasser, F., Chong, T. H., … Fane, A. G. (2017). Gravity-driven microfiltration pretreatment for reverse osmosis (RO) seawater desalination: microbial community characterization and RO performance. Desalination, 418, 1-8. doi:10.1016/j.desal.2017.05.024, Institutional Repository

A pilot gravity-driven microfiltration (GDM) reactor was operated on-site for over 250 days to pretreat seawater for reverse osmosis (RO) desalination. The microbial community analysis indicated that the dominant species in the pilot GDM system (~ 18.6 L/m2 h) were completely different from those in the other tested GDM systems (~ 2.7–17.2 L/m2 h), operating on the same feed. This was possibly due to the differences in available space for eukaryotic movement, hydraulic retention time (i.e., different organic loadings) or operation time (250 days vs. 25–45 days). Stichotrichia, Copepoda, and Pterygota were predominant eukaryotes at genus level in the pilot GDM. Furthermore, the GDM pretreatment led to a significantly lower RO fouling potential in comparison to the ultrafiltration (UF) system. This was attributed to the fact that GDM filtration produced a permeate with less amount of assimilable organic carbon (AOC) and biopolymers. Accordingly, lower amount of organic foulants (biopolymers and low molecular weight neutrals) and less biofilm formation on the GDM-RO membrane were observed. Although α-proteobacteria were dominant in both RO fouling layers, their bacterial community compositions at genus level were significantly different. Thalassobius had higher abundance in the GDM-RO fouling layers, while Erythrobacter and Hyphomonas were more predominant in the UF-RO fouling layers.
Wu, B., Christen, T., Tan, H. S., Hochstrasser, F., Suwarno, S. R., Liu, X., … Fane, A. G. (2017). Improved performance of gravity-driven membrane filtration for seawater pretreatment: implications of membrane module configuration. Water Research, 114, 59-68. doi:10.1016/j.watres.2017.02.022, Institutional Repository

As a low energy and chemical free process, gravity-driven membrane (GDM) filtration has shown a potential for seawater pretreatment in our previous studies. In this study, a pilot submerged GDM reactor (effective volume of 720 L) was operated over 250 days and the permeate flux stabilized at 18.6 ± 1.4 L/m2h at a hydrostatic pressure of 40 mbar. This flux was higher than those in the lab-scale GDM reactor (16.3 ± 0.2 L/m2h; effective volume of 8.4 L) and in the filtration cell system (2.7 ± 0.6 L/m2h; feed side volume of 0.0046 L) when the same flat sheet membrane was used. Interestingly, when the filtration cell was submerged into the GDM reactor, the flux (17.2 L/m2h) was comparable to the submerged membrane module. Analysis of cake layer morphology and foulant properties indicated that a thicker but more porous cake layer with less accumulation of organic substances (biopolymers and humics) contributed to the improved permeate flux. This phenomenon was possibly associated with longer residence time of organic substances and sufficient space for the growth, predation, and movement of the eukaryotes in the GDM reactor. In addition, the permeate flux of the submerged hollow fibre membrane increased with decreasing packing density. It is thought that the movement of large-sized eukaryotes could be limited when the space between hollow fibres was reduced. In terms of pretreatment, the GDM systems effectively removed turbidity, viable cells, and transparent exopolymer particles from the feed seawater. Importantly, extending the reactor operation time produced a permeate with less assimilable organic carbon and biopolymers. Thus, the superior quality of the GDM permeate has the potential to alleviate subsequent reverse osmosis membrane fouling for seawater treatment.
Zöllig, H., Remmele, A., Morgenroth, E., & Udert, K. M. (2017). Removal rates and energy demand of the electrochemical oxidation of ammonia and organic substances in real stored urine. Environmental Science: Water Research and Technology, 3(3), 480-491. doi:10.1039/c7ew00014f, Institutional Repository

The separate collection and treatment of urine allows for an environmentally friendly and cost-efficient management of the nutrients contained in urine. The primary goal should be to recover all these nutrients. However, in some cases it will be economically or ecologically more sensitive to recover only the phosphorus, while nitrogen is removed together with organic substances (measured as chemical oxygen demand, COD) and pathogens. In this study, we investigated the use of galvanostatic electrolysis for the removal of nitrogen and COD from real stored urine. Non-active type boron-doped diamond (BDD) and active type thermally decomposed iridium oxide film (TDIROF) anodes were evaluated using batch experiments. On both anodes, ammonia was exclusively removed by indirect oxidation with active chlorine (AC: Cl2, HClO, and ClO−). As a consequence, ammonia was not completely removed, if chlorine was consumed by competing processes. While COD was present, ammonia removal was faster on TDIROF (227 ± 16 gN m−2 d−1 at 20 mA cm−2) than on BDD (43 ± 20 gN m−2 d−1 at 20 mA cm−2). The reason for the slower ammonia removal on BDD was the enhanced reaction of AC with organic molecules. In fact, hydroxyl radicals broke organic molecules down to shorter chain molecules which reacted with most of the AC leaving only little AC for the oxidation of ammonia. This preferential oxidation of organics resulted in very high COD removal rates on BDD (above 420 gCOD m−2 d−1 at 20 mA cm−2 for COD concentrations above 1000 mgCOD L−1). A main drawback of electrolysis with both anodes was the high energy demand (BDD: 55 W h gCOD−1 and 766 W h gN−1 for 90% and 6% removal, respectively. TDIROF: 67 W h gCOD−1 and 77 W h gN−1 for 30% and 40% removal. All at 20 mA cm−2). It can be concluded that BDD and TDIROF anodes could be combined in series for a fast, complete, and more energy efficient electrochemical urine treatment: COD could be removed on BDD before the residual ammonia would be removed on TDIROF.
Bischel, H. N., Schindelholz, S., Schoger, M., Decrey, L., Buckley, C. A., Udert, K. M., & Kohn, T. (2016). Bacteria inactivation during the drying of struvite fertilizers produced from stored urine. Environmental Science and Technology, 50(23), 13013-13023. doi:10.1021/acs.est.6b03555, Institutional Repository

Human urine can be processed into market-attractive fertilizers like struvite; however, concerns regarding the microbial safety of such products remain. The present study evaluated the inactivation of in situ heterotrophs, total bacteria as observed by flow cytometry, and inoculated Enterococcus spp. and Salmonella typhimurium during the drying of struvite under controlled temperature (from 5 to 35 °C) and relative humidity (approximately 40 and 80%) as well as dynamic field conditions. Bacteria accumulated in the struvite cake during struvite filtration. Despite the use of sublethal temperatures, all bacteria types were subsequently inactivated to some degree during struvite drying, and the inactivation typically increased with increasing drying temperature for a given relative humidity. Heterotrophic bacteria inactivation mirrored the trend in total bacteria during struvite drying. A linear relationship was observed between inactivation and sample moisture content. However, bacteria survivor curves were typically nonlinear when struvite was dried at low relative humidity, indicating bacterial persistence. Weibull model survivor curve fits indicated that a shift in the mechanism of inactivation may occur with changing humidity. For increased efficiency of bacterial inactivation during the production of struvite, initial heating under moist conditions is recommended followed by desiccation.
Burdon, F. J., Reyes, M., Alder, A. C., Joss, A., Ort, C., Räsänen, K., … Stamm, C. (2016). Environmental context and magnitude of disturbance influence trait-mediated community responses to wastewater in streams. Ecology and Evolution, 6(12), 3923-3939. doi:10.1002/ece3.2165, Institutional Repository

Human land uses and population growth represent major global threats to biodiversity and ecosystem services. Understanding how biological communities respond to multiple drivers of human-induced environmental change is fundamental for conserving ecosystems and remediating degraded habitats. Here, we used a replicated ‘real-world experiment’ to study the responses of invertebrate communities to wastewater perturbations across a land-use intensity gradient in 12 Swiss streams. We used different taxonomy and trait-based community descriptors to establish the most sensitive indicators detecting impacts and to help elucidate potential causal mechanisms of change. First, we predicted that streams in catchments adversely impacted by human land-uses would be less impaired by wastewater inputs because their invertebrate communities should be dominated by pollution-tolerant taxa (‘environmental context’). Second, we predicted that the negative effects of wastewater on stream invertebrate communities should be larger in streams that receive proportionally more wastewater (‘magnitude of disturbance’). In support of the ‘environmental context’ hypothesis, we found that change in the Saprobic Index (a trait-based indicator of tolerance to organic pollution) was associated with upstream community composition; communities in catchments with intensive agricultural land uses (e.g., arable cropping and pasture) were generally more resistant to eutrophication associated with wastewater inputs. We also found support for the ‘magnitude of disturbance’ hypothesis. The SPEAR Index (a trait-based indicator of sensitivity to pesticides) was more sensitive to the relative input of effluent, suggesting that toxic influences of wastewater scale with dilution. Whilst freshwater pollution continues to be a major environmental problem, our findings highlight that the same anthropogenic pressure (i.e., inputs of wastewater) may induce different ecological responses depending on the environmental context and community metrics used. Thus, remediation strategies aiming to improve stream ecological status (e.g., rehabilitating degraded reaches) need to consider upstream anthropogenic influences and the most appropriate indicators of restoration success.
Derlon, N., Wagner, J., Ribeiro da Costa, R. H., & Morgenroth, E. (2016). Formation of aerobic granules for the treatment of real and low-strength municipal wastewater using a sequencing batch reactor operated at constant volume. Water Research, 105, 341-350. doi:10.1016/j.watres.2016.09.007, Institutional Repository

This study aimed at evaluating the formation of aerobic granular sludge (AGS) for the treatment of real and low-strength municipal wastewater using a column sequencing batch reactor (SBR) operated in fill-draw mode (constant volume). The focus was on understanding how the wastewater upflow velocity (VWW) applied during the anaerobic feeding influenced the sludge properties and in turn the substrate conversion. Two different strategies were tested: (1) washing-out the flocs by imposing high wastewater upflow velocities (between 5.9 and 16 m h−1) during the anaerobic feeding (Approach #1) and (2) selective utilization of organic carbon during the anaerobic feeding (1 m h−1) combined with a selective sludge withdrawal (Approach #2). A column SBR of 190 L was operated in constant volume during 1500 days and fed with real and low-strength municipal wastewater. The formation of AGS with SVI30 of around 80 mL gTSS−1 was observed either at very low (1 m h−1) or at high VWW (16 m h−1). At 16 m h−1 the AGS was mainly composed of large and round granules (d > 0.63 mm) with a fluffy surface, while at 1 m h−1 the sludge was dominated by small granules (0.25 < d < 0.63 mm). The AGS contained a significant fraction of flocs during the whole operational period. A considerable and continuous washout of biomass occurred at VWW higher than 5.9 m h−1 (Approach #1) due to the lower settling velocity of the AGS fed with municipal wastewater. The low sludge retention observed at VWW higher than 5.9 m h−1 deteriorated the substrate conversion and in turn the effluent quality. High solid concentrations (and thus solid retention time) were maintained during Approach #2 (VWW of 1 m h−1), which resulted in an excellent effluent quality. The study demonstrated that the formation of AGS is possible during the treatment of real and low-strength municipal wastewater in a SBR operated at constant volume. Low wastewater upflow velocities should be applied during the anaerobic feeding phase in order to ensure enough biomass retention and efficient substrate removal.
Derlon, N., Grütter, A., Brandenberger, F., Sutter, A., Kuhlicke, U., Neu, T. R., & Morgenroth, E. (2016). The composition and compression of biofilms developed on ultrafiltration membranes determine hydraulic biofilm resistance. Water Research, 102, 63-72. doi:10.1016/j.watres.2016.06.019, Institutional Repository

This study aimed at identifying how to improve the level of permeate flux stabilisation during gravity-driven membrane filtration without control of biofilm formation. The focus was therefore on understanding (i) how the different fractions of the biofilms (inorganics particles, bacterial cells, EPS matrix) influence its hydraulic resistance and (ii) how the compression of biofilms impacts its hydraulic resistance, i.e., can water head be increased to increase the level of permeate flux stabilisation. Biofilms were developed on ultrafiltration membranes at 88 and 284 cm water heads with dead-end filtration for around 50 days. A larger water head resulted in a smaller biofilm permeability (150 and 50 L m−2 h−1 bar−1 for biofilms grown at 88 cm and 284 cm water head, respectively). Biofilms were mainly composed of EPS (>90% in volume). The comparison of the hydraulic resistances of biofilms to model fouling layers indicated that most of the hydraulic resistance is due to the EPS matrix. The compressibility of the biofilm was also evaluated by subjecting the biofilms to short-term (few minutes) and long-term variations of transmembrane pressures (TMP). A sudden change of TMP resulted in an instantaneous and reversible change of biofilm hydraulic resistance. A long-term change of TMP induced a slow change in the biofilm hydraulic resistance. Our results demonstrate that the response of biofilms to a TMP change has two components: an immediate variation of resistance (due to compression/relaxation) and a long-term response (linked to biofilm adaptation/growth). Our results provide relevant information about the relationship between the operating conditions in terms of TMP, the biofilm structure and composition and the resulting biofilm hydraulic resistance. These findings have practical implications for a broad range of membrane systems.
Ding, A., Liang, H., Li, G., Derlon, N., Szivak, I., Morgenroth, E., & Pronk, W. (2016). Impact of aeration shear stress on permeate flux and fouling layer properties in a low pressure membrane bioreactor for the treatment of grey water. Journal of Membrane Science, 510, 382-390. doi:10.1016/j.memsci.2016.03.025, Institutional Repository

Two different aeration regimes were studied in a low pressure gravity driven membrane bioreactor without any flushing or (back-) washing. In one reactor, the aeration was positioned below the membrane module, thus exposing the membranes to aeration shear stress. A second reactor was operated at low shear stress by placing the aerator in a different compartment. Flux stabilization at 2.0 L/(m2 h) occurred in the reactor with low shear stress while no flux stabilization was observed in the reactor with aeration shear stress, resulting in a flux of 0.5 L/(m2 h) after 120 days. The thickness of the bio-fouling layer in the reactor with aeration shear was smaller (129 vs. 344 µm), which implies that shear stress resulted in a thinner, denser and less permeable bio-fouling layer. The results can be explained by differences in (1) the morphology of the bio-fouling layer and (2) the EPS contents (proteins and polysaccharides) in the bio-fouling layer. The low-shear system provides a suitable solution for decentralized grey water treatment, or other conditions where maintenance and energy consumption should be minimized. Furthermore, the results can contribute to decrease the energy consumption in MBR systems.
Falås, P., Wick, A., Castronovo, S., Habermacher, J., Ternes, T. A., & Joss, A. (2016). Tracing the limits of organic micropollutant removal in biological wastewater treatment. Water Research, 95, 240-249. doi:10.1016/j.watres.2016.03.009, Institutional Repository

Removal of organic micropollutants was investigated in 15 diverse biological reactors through short and long-term experiments. Short-term batch experiments were performed with activated sludge from three parallel sequencing batch reactors (25, 40, and 80 d solid retention time, SRT) fed with synthetic wastewater without micropollutants for one year. Despite the minimal micropollutant exposure, the synthetic wastewater sludges were able to degrade several micropollutants present in municipal wastewater. The degradation occurred immediately after spiking (1–5 μg/L), showed no strong or systematic correlation to the sludge age, and proceeded at rates comparable to those of municipal wastewater sludges. Thus, the results from the batch experiments indicate that degradation of organic micropollutants in biological wastewater treatment is quite insensitive to SRT increases from 25 to 80 days, and not necessarily induced by exposure to micropollutants. Long-term experiments with municipal wastewater were performed to assess the potential for extended biological micropollutant removal under different redox conditions and substrate concentrations (carbon and nitrogen). A total of 31 organic micropollutants were monitored through influent-effluent sampling of twelve municipal wastewater reactors. In accordance with the results from the sludges grown on synthetic wastewater, several compounds such as bezafibrate, atenolol and acyclovir were significantly removed in the activated sludge processes fed with municipal wastewater. Complementary removal of two compounds, diuron and diclofenac, was achieved in an oxic biofilm treatment. A few aerobically persistent micropollutants such as venlafaxine, diatrizoate and tramadol were removed under anaerobic conditions, but a large number of micropollutants persisted in all biological treatments. Collectively, these results indicate that certain improvements in biological micropollutant removal can be achieved by combining different aerobic and anaerobic treatments, but that these improvements are restricted to a limited number of compounds.
Fumasoli, A., Etter, B., Sterkele, B., Morgenroth, E., & Udert, K. M. (2016). Operating a pilot-scale nitrification/distillation plant for complete nutrient recovery from urine. Water Science and Technology, 73(1), 215-222. doi:10.2166/wst.2015.485, Institutional Repository

Source-separated urine contains most of the excreted nutrients, which can be recovered by using nitrification to stabilize the urine before concentrating the nutrient solution with distillation. The aim of this study was to test this process combination at pilot scale. The nitrification process was efficient in a moving bed biofilm reactor with maximal rates of 930 mg N L−1 d−1. Rates decreased to 120 mg N L−1 d−1 after switching to more concentrated urine. At high nitrification rates (640 mg N L−1 d−1) and low total ammonia concentrations (1,790 mg NH4-N L−1 in influent) distillation caused the main primary energy demand of 71 W cap−1 (nitrification: 13 W cap−1) assuming a nitrogen production of 8.8 g N cap−1 d−1. Possible process failures include the accumulation of the nitrification intermediate nitrite and the selection of acid-tolerant ammonia-oxidizing bacteria. Especially during reactor start-up, the process must therefore be carefully supervised. The concentrate produced by the nitrification/distillation process is low in heavy metals, but high in nutrients, suggesting a good suitability as an integral fertilizer.
Gold, M., Dayer, P., Faye, M. C. A. S., Clair, G., Seck, A., Niang, S., … Strande, L. (2016). Locally produced natural conditioners for dewatering of faecal sludge. Environmental Technology, 37(21), 1-13. doi:10.1080/09593330.2016.1165293, Institutional Repository

In urban areas of low-income countries, treatment of faecal sludge (FS) is insufficient or non-existent. This results in large amounts of FS being dumped into the environment. Existing treatment technologies for FS, such as settling-thickening tanks and drying beds, are land intensive which is limiting in urban areas. Enhanced settling and dewatering by conditioning was evaluated in order to reduce the treatment footprint (or increase treatment capacity). Conventional wastewater conditioners, such as commercially available lime and polymers, are expensive, and commonly rely on complex supply chains for use in low-income countries. Therefore, the treatment performance of five conditioners which could be produced locally was evaluated: Moringa oleifera seeds and press cake, Jatropha curcas seeds, Jatropha Calotropis leaves and chitosan. M. oleifera seeds and press cake, and chitosan improved settling and dewatering and had a similar performance compared to lime and polymers. Optimal dosages were 400–500 kg M. oleifera/t TS, 300–800 kg lime/t TS and 25–50 kg polymer solution/t TS. In comparison, chitosan required 1.5–3.75 kg/t TS. These dosages are comparable to those recommended for wastewater (sludge). The results indicate that conditioning of FS can reduce total suspended solids (TSS) in the effluent of settling-thickening tanks by 22–81% and reduce dewatering time with drying beds by 59–97%. This means that the area of drying beds could be reduced by 59–97% with end-use as soil conditioner, or 9–26% as solid fuel. Least expensive options and availability will depend on the local context. In Dakar, Senegal, chitosan produced from shrimp waste appears to be most promising.
Habermacher, J., Benetti, A. D., Derlon, N., & Morgenroth, E. (2016). Degradation of the unbiodegradable particulate fraction (XU) from different activated sludges during batch digestion tests at ambient temperature. Water Research, 98, 206-214. doi:10.1016/j.watres.2016.04.005, Institutional Repository

One strategy for the management of excess sludge in small wastewater treatment plants (WWTPs) consists in minimizing the excess sludge production by operating the WWTP at very long solids retention times (SRTs > 30 days). A number of recent studies have suggested that sludge minimization at very long SRT results from the degradation of the unbiodegradable particulate fraction (XU) (influent unbiodegradable compounds and endogenous decay products). But the biodegradability of the unbiodegradable particulate fraction has only been evaluated during batch digestion test performed at ambient temperature with sludge fed with synthetic wastewaters. It is not clear to what extent observations made for sludge fed with synthetic influents can be transposed to sludge fed with real influent. The current study thus focused on evaluating the biodegradability of the unbiodegradable particulate fraction for sludge fed with real wastewater. Batch digestion tests (400 days, ambient temperature) were conducted with three different sludges fed with either synthetic or real influents and exposed to aerobic or intermittent aeration conditions. Our results indicate that volatile suspended solids (VSS) decreased even after complete decay of the active biomass (i.e., after 30 days of aerobic batch digestion) indicating that the unbiodegradable particulate fraction is biodegradable. However, very low degradation rates of the unbiodegradable particulate fraction were monitored after day 30 of digestion (0.7-1.7·10-3 d-1). These values were in the lower range of previously published values for synthetic wastewaters (1-7.5·10-3 d-1). The low values determined in our study indicate that the rate could decrease over time or that sludge composition influences the degradability of the unbiodegradable particulate fraction. But our results also demonstrate that extracellular polymeric substances (EPS) have a minor impact on the biodegradability of the unbiodegradable particulate fraction. Overall bound EPS were indeed biodegradable under all conditions and thus did not accumulate in the unbiodegradable particulate fraction. Different bound EPS pools (e.g., cation bound EPS) were associated with specific degradation behaviors. Besides improved mechanistic understanding of sludge degradation processes, our results have implications for the development of decentralized wastewater treatment technologies with on-site reduction of excess sludge.
Jewell, K. S., Castronovo, S., Wick, A., Falås, P., Joss, A., & Ternes, T. A. (2016). New insights into the transformation of trimethoprim during biological wastewater treatment. Water Research, 88, 550-557. doi:10.1016/j.watres.2015.10.026, Institutional Repository

The antibiotic trimethoprim (TMP), a micropollutant found at μg/L levels in raw wastewater, was investigated with regard to its (bio)transformation during biological wastewater treatment. A pilot-scale, nitrifying/denitrifying Sequencing Batch Reactor (SBR) fed with municipal wastewater was monitored for TMP removal during a 16-month monitoring study. Laboratory-scaled bioreactors spiked with TMP were applied to identify the transformation products (TPs). In total, six TPs could be identified from TMP. However, the TP formation was influenced by the spike concentration. At an initial concentration of 500 μg/L TMP, only two TPs were found, whereas at 5 μg/L a completely different transformation pathway led to four further TPs. At low concentrations, TMP was demethylated forming 4-desmethyl-TMP, which was then quickly hydroxylated, oxidized and cleaved forming 2,4-diaminopyrimidine-5-carboxylic acid (DAPC) via two intermediate TPs. DAPC was detected in the SBR effluent in a 3-d composite sample with 61 ng/L, which accounts for 52% of the attenuated TMP. The primary degradation at low spiking levels was best modelled by a pseudo-first order kinetic. Considering the SBR, the model predicted a TMP removal of 88–94% for the reactor, consistent with a monitoring campaign exhibiting an average removal of >83%. Both the TP formation profiles and kinetic modelling indicated that only the results from the bioreactor tests at low spike concentrations were representative of the transformation in the SBR.
Jewell, K. S., Falås, P., Wick, A., Joss, A., & Ternes, T. A. (2016). Transformation of diclofenac in hybrid biofilm–activated sludge processes. Water Research, 105, 559-567. doi:10.1016/j.watres.2016.08.002, Institutional Repository

The biotransformation of diclofenac during wastewater treatment was investigated. Attached growth biomass from a carrier-filled compartment of a hybrid-MBBR at the wastewater treatment plant (WWTP) in Bad Ragaz, Switzerland was used to test the biotransformation. Laboratory-scale incubation experiments were performed with diclofenac and carriers and high-resolution LC–QTof-MS was implemented to monitor the biotransformation. Up to 20 diclofenac transformation products (TPs) were detected. Tentative structures were proposed for 16 of the TPs after characterization by MS2 fragmentation and/or inferring the structure from the transformation pathway and the molecular formula given by the high resolution ionic mass. The remaining four TPs were unambiguously identified via analytical reference standards. The postulated reactions forming the TPs were: hydroxylation, decarboxylation, oxidation, amide formation, ring-opening and reductive dechlorination. Incubation experiments of individual TPs, those which were available as reference standards, provided a deeper look into the transformation pathways. It was found that the transformation consists of four main pathways but no pathway accounted for a clear majority of the transformation. A 10-day monitoring campaign of the full-scale plant confirmed an 88% removal of diclofenac (from approximately 1.6 μg/L in WWTP influent) and the formation of TPs as found in the laboratory was observed. One of the TPs, N-(2,6-dichlorophenyl)-2-indolinone detected at concentrations of around 0.25 μg/L in WWTP effluent, accounting for 16% of the influent diclofenac concentration. The biotransformation of carriers was compared to a second WWTP not utilising carriers. It was found that in contact with activated sludge, similar hydroxylation and decarboxylation reactions occurred but at much slower rates, whereas some reactions, e.g. reductive dechlorination, were not detected at all. Finally, incubation experiments were performed with attached growth biomass from a third WWTP with a similar process configuration to Bad Ragaz WWTP. A similarly effective removal of diclofenac was found with a similar presence of TPs.
Kaegi, R. (2016). Separation and analysis of nanoparticles (NP) in aqueous environmental samples. In B. Xing, C. D. Vecitis, & N. Senesi (Eds.), Wiley-IUPAC series in biophysico-chemical processes in environmental systems. Engineered nanoparticles and the environment. Biophysicochemical processes and toxicity (pp. 53-74). doi:10.1002/9781119275855.ch4, Institutional Repository

Engineered nanoparticles (NP) are defined as intentionally manufactured particles with at least one dimension between 1 and 100 nm. Colloids are roughly defined as particles with a diameter between 1 nm and 1 μm (Buffle and Leeuwen, 1992). Engineered NP, thus, represent a small subgroup of colloids. It has been suggested to distinguish between natural NP, incidental NP, and engineered NP (Christian et al. 2008; Farre et al. 2009; Hassellöv and Kaegi 2009). Several trace metals of geogenic origin are bound to colloids, such as clay minerals, or even form eigencolloids (e.g., metal hydroxides and metal sulfides). As these colloids often occur in the nanoscale range (Lead and Wilkinson 2006), they are classified as natural NP. In addition to being in the nanoscale range (1-100 nm), incidental NP are the by-products of human activities. For example, they are emitted from internal combustion engines (e.g., diesel soot) or coal-fired power plants (e.g., fly ash). Engineered NP, such as carbon nanotubes (CNT) or titanium dioxide (TiO2)-NP, can have the same elemental composition as natural or incidental NP, but they are synthesized on purpose with additional functionalities. To assess the effects of human activities on the environment, incidental and engineered NP have to be separated from natural NP and, even more specifically, to assess the impact of engineered NP on the environment, particles of this specific subgroup have to be distinguished from the other two NP types at each stage of their life cycle (Wiesner et al. 2009). Therefore, it is necessary to develop methods that allow a quantitative detection of engineered NP in complex matrices of different environmental compartments. [...]
Klein, T., Zihlmann, D., Derlon, N., Isaacson, C., Szivak, I., Weissbrodt, D. G., & Pronk, W. (2016). Biological control of biofilms on membranes by metazoans. Water Research, 88, 20-29. doi:10.1016/j.watres.2015.09.050, Institutional Repository

Traditionally, chemical and physical methods have been used to control biofouling on membranes by inactivating and removing the biofouling layer. Alternatively, the permeability can be increased using biological methods while accepting the presence of the biofouling layer. We have investigated two different types of metazoans for this purpose, the oligochaete Aelosoma hemprichi and the nematode Plectus aquatilis. The addition of these grazing metazoans in biofilm-controlled membrane systems resulted in a flux increase of 50% in presence of the oligochaetes (Aelosoma hemprichi), and a flux increase of 119–164% in presence of the nematodes (Plectus aquatilis) in comparison to the control system operated without metazoans. The change in flux resulted from (1) a change in the biofilm structure, from a homogeneous, cake-like biofilm to a more heterogeneous, porous structure and (2) a significant reduction in the thickness of the basal layer. Pyrosequencing data showed that due to the addition of the predators, also the community composition of the biofilm in terms of protists and bacteria was strongly affected. The results have implications for a range of membrane processes, including ultrafiltration for potable water production, membrane bioreactors and reverse osmosis.
Krähenbühl, M., Etter, B., & Udert, K. M. (2016). Pretreated magnesite as a source of low-cost magnesium for producing struvite from urine in Nepal. Science of the Total Environment, 542, 1155-1161. doi:10.1016/j.scitotenv.2015.08.060, Institutional Repository

Struvite is a solid phosphorus fertilizer that can be recovered easily from source-separated urine by dosing it with a soluble form of magnesium. The process is simple and low-cost, however, previous studies have shown that the cost of magnesium in low-income countries is crucial to the viability and implementation of struvite precipitation. Literature has proposed producing inexpensive magnesium locally by making magnesium oxide from magnesite. This paper aimed to investigate whether process requirements, costs, and environmental impacts would make this process viable for magnesium production in decentralized settings. Magnesite samples were calcined at temperatures between 400 °C and 800 °C and for durations between 0.5 h and 6 h. The release of magnesium was tested by dissolution in phosphate-depleted urine. The optimal processing conditions were at 700 °C for 1 h: magnesite conversion was incomplete at lower temperatures, and the formation of large crystallites caused a decrease in solubility at higher temperatures. The narrow optimal range for magnesium production from magnesite requires reliable process control. Cost estimations for Nepal showed that using local magnesite would provide the cheapest source of magnesium and that CO2 emissions from transport and production would be negligible compared to Nepal's overall CO2 emissions.
Kuroda, K., Itten, R., Kovalova, L., Ort, C., Weissbrodt, D. G., & McArdell, C. S. (2016). Hospital-use pharmaceuticals in Swiss waters modeled at high spatial resolution. Environmental Science and Technology, 50(9), 4742-4751. doi:10.1021/acs.est.6b00653, Institutional Repository

A model to predict the mass flows and concentrations of pharmaceuticals predominantly used in hospitals across a large number of sewage treatment plant (STP) effluents and river waters was developed at high spatial resolution. It comprised 427 geo-referenced hospitals and 742 STPs serving 98% of the general population in Switzerland. In the modeled base scenario, domestic, pharmaceutical use was geographically distributed according to the population size served by the respective STPs. Distinct hospital scenarios were set up to evaluate how the predicted results were modified when pharmaceutical use in hospitals was allocated differently; for example, in proportion to number of beds or number of treatments in hospitals. The hospital scenarios predicted the mass flows and concentrations up to 3.9 times greater than in the domestic scenario for iodinated X-ray contrast media (ICM) used in computed tomography (CT), and up to 6.7 times greater for gadolinium, a contrast medium used in magnetic resonance imaging (MRI). Field measurements showed that ICM and gadolinium were predicted best by the scenarios using number of beds or treatments in hospitals with the specific facilities (i.e., CT and/or MRI). Pharmaceuticals used both in hospitals and by the general population (e.g., cyclophosphamide, sulfamethoxazole, carbamazepine, diclofenac) were predicted best by the scenario using the number of beds in all hospitals, but the deviation from the domestic scenario values was only small. Our study demonstrated that the bed number-based hospital scenarios were effective in predicting the geographical distribution of a diverse range of pharmaceuticals in STP effluents and rivers, while the domestic scenario was similarly effective on the scale of large river-catchments.
Laureni, M., Falås, P., Robin, O., Wick, A., Weissbrodt, D. G., Nielsen, J. L., … Joss, A. (2016). Mainstream partial nitritation and anammox: long-term process stability and effluent quality at low temperatures. Water Research, 101, 628-639. doi:10.1016/j.watres.2016.05.005, Institutional Repository

The implementation of autotrophic anaerobic ammonium oxidation processes for the removal of nitrogen from municipal wastewater (known as “mainstream anammox”) bears the potential to bring wastewater treatment plants close to energy autarky. The aim of the present work was to assess the long-term stability of partial nitritation/anammox (PN/A) processes operating at low temperatures and their reliability in meeting nitrogen concentrations in the range of typical discharge limits below 2 mgNH4-N·L−1 and 10 mgNtot·L−1. Two main 12-L sequencing batch reactors were operated in parallel for PN/A on aerobically pre-treated municipal wastewater (21 ± 5 mgNH4-N·L−1 and residual 69 ± 19 mgCODtot·L−1) for more than one year, including over 5 months at 15 °C. The two systems consisted of a moving bed biofilm reactor (MBBR) and a hybrid MBBR (H-MBBR) with flocculent biomass. Operation at limiting oxygen concentrations (0.15–0.18 mgO2·L−1) allowed stable suppression of the activity of nitrite-oxidizing bacteria at 15 °C with a production of nitrate over ammonium consumed as low as 16% in the MBBR. Promising nitrogen removal rates of 20–40 mgN·L−1·d−1 were maintained at hydraulic retention times of 14 h. Stable ammonium and total nitrogen removal efficiencies over 90% and 70% respectively were achieved. Both reactors reached average concentrations of total nitrogen below 10 mgN·L−1 in their effluents, even down to 6 mgN·L−1 for the MBBR, with an ammonium concentration of 2 mgN·L−1 (set as operational threshold to stop aeration). Furthermore, the two PN/A systems performed almost identically with respect to the biological removal of organic micropollutants and, importantly, to a similar extent as conventional treatments. A sudden temperature drop to 11 °C resulted in significant suppression of anammox activity, although this was rapidly recovered after the temperature was increased back to 15 °C. Analyses of 16S rRNA gene-targeted amplicon sequencing revealed that the anammox guild of the bacterial communities of the two systems was composed of the genus “Candidatus Brocadia”. The potential of PN/A systems to compete with conventional treatments for biological nutrients removal both in terms of removal rates and overall effluent quality was proven.
Löwenberg, J., Zenker, A., Krahnstöver, T., Boehler, M., Baggenstos, M., Koch, G., & Wintgens, T. (2016). Upgrade of deep bed filtration with activated carbon dosage for compact micropollutant removal from wastewater in technical scale. Water Research, 94, 246-256. doi:10.1016/j.watres.2016.02.033, Institutional Repository

The removal of micropollutants from drinking and wastewater by powdered activated carbon (PAC) adsorption has received considerable attention in research over the past decade with various separation options having been investigated. With Switzerland as the first country in the world having adopted a new legislation, which forces about 100 wastewater treatment plants to be upgraded for the removal of organic micropollutants from municipal wastewater, the topic has reached practical relevance.
In this study, the process combination of powdered activated carbon (PAC) adsorption and deep bed filtration (DBF) for advanced municipal wastewater treatment was investigated over an extended period exceeding one year of operation in technical scale. The study aimed to determine optimum process conditions to achieve sufficient micropollutant removal in agreement with the new Swiss Water Ordinance under most economic process design.
It was shown that the addition of PAC and Fe3+ as combined coagulation and flocculation agent improved effluent water quality with respect to dissolved organic pollutants as well as total suspended solids (TSS), turbidity and PO4–P concentration in comparison to a DBF operated without the addition of PAC and Fe3+. Sufficient micropollutant (MP) removal of around 80% was achieved at PAC dosages of 10 mg/L revealing that PAC retained in the filter bed maintained considerable adsorption capacity. In the investigated process combination the contact reactor serves for adsorption as well as for flocculation and allowed for small hydraulic retention times of minimum 10 min while maintaining sufficient MP removal. The flocculation of two different PAC types was shown to be fully concluded after 10–15 min, which determined the flocculation reactor size while both PAC types proved suitable for the application in combination with DBF and showed no significant differences in MP removal. Finally, the capping of PAC dosage during rain water periods, which resulted in lower dosage concentrations, was efficient in limiting PAC consumption during these events without suffering from negative effects on process performance or effluent quality.
Mašić, A., Udert, K. M., & Villez, K. (2016). Global parameter optimization for biokinetic modeling of simple batch experiments. Environmental Modelling and Software, 85, 356-373. doi:10.1016/j.envsoft.2016.06.015, Institutional Repository

Environmental process modeling is challenged by the lack of high quality data, stochastic variations, and nonlinear behavior. Conventionally, parameter optimization is based on stochastic sampling techniques to deal with the nonlinear behavior of the proposed models. Despite widespread use, such tools cannot guarantee globally optimal parameter estimates. It can be especially difficult in practice to differentiate between lack of algorithm convergence, convergence to a non-global local optimum, and model structure deficits. For this reason, we use a deterministic global optimization algorithm for kinetic model identification and demonstrate it with a model describing a typical batch experiment. A combination of interval arithmetic, reformulations, and relaxations allows globally optimal identification of all (six) model parameters. In addition, the results suggest that further improvements may be obtained by modification of the optimization problem or by proof of the hypothesized pseudo-convex nature of the problem suggested by our results.
McCall, A. K., Scheidegger, A., Madry, M. M., Steuer, A. E., Weissbrodt, D. G., Vanrolleghem, P. A., … Ort, C. (2016). Influence of different sewer biofilms on transformation rates of drugs. Environmental Science and Technology, 50(24), 13351-13360. doi:10.1021/acs.est.6b04200, Institutional Repository

To estimate drug consumption more reliably, wastewater-based epidemiology would benefit from a better understanding of drug residue stability during in-sewer transport. We conducted batch experiments with real, fresh wastewater and sewer biofilms. Experimental conditions mimic small to medium-sized gravity sewers with a relevant ratio of biofilm surface area to wastewater volume (33 m2 m–3). The influences of biological, chemical, and physical processes on the transformation of 30 illicit drug and pharmaceutical residues were quantified. Rates varied among locations and over time. Three substances were not stable—that is, >20% transformation, mainly due to biological processes—at least for one type of tested biofilm for a residence time ≤2 h: amphetamine, 6-acetylcodeine, and 6-monoacetylmorphine. Cocaine, ecgonine methyl ester, norcocaine, cocaethylene, and mephedrone were mainly transformed by chemical hydrolysis and, hence, also unstable in sewers. In contrast, ketamine, norketamine, O-desmethyltramadol, diclofenac, carbamazepine, and methoxetamine were not substantially affected by in-sewer processes under all tested conditions and residence times up to 12 h. Our transformation rates include careful quantification of uncertainty and can be used to identify situations in which specific compounds are not stable. This will improve accuracy and uncertainty estimates of drug consumption when applied to the back-calculation.
Mears, L., Nørregård, R., Sin, G., Gernaey, K. V., Stocks, S. M., Albaek, M. O., & Villez, K. (2016). Functional unfold principal component regression methodology for analysis of industrial batch process data. AICHE Journal, 62(6), 1986-1994. doi:10.1002/aic.15172, Institutional Repository

This work proposes a methodology utilizing functional unfold principal component regression (FUPCR), for application to industrial batch process data as a process modeling and optimization tool. The methodology is applied to an industrial fermentation dataset, containing 30 batches of a production process operating at Novozymes A/S. Following the FUPCR methodology, the final product concentration could be predicted with an average prediction error of 7.4%. Multiple iterations of preprocessing were applied by implementing the methodology to identify the best data handling methods for the model. It is shown that application of functional data analysis and the choice of variance scaling method have the greatest impact on the prediction accuracy. Considering the vast amount of batch process data continuously generated in industry, this methodology can potentially contribute as a tool to identify desirable process operating conditions from complex industrial datasets.
Meier, C., Voegelin, A., Pradas Del Real, A., Sarret, G., Mueller, C. R., & Kaegi, R. (2016). Transformation of silver nanoparticles in sewage sludge during incineration. Environmental Science and Technology, 50(7), 3503-3510. doi:10.1021/acs.est.5b04804, Institutional Repository

Silver nanoparticles (Ag-NP) discharged into the municipal sewer system largely accumulate in the sewage sludge. Incineration and agricultural use are currently the most important strategies for sewage sludge management. Thus, the behavior of Ag-NP during sewage sludge incineration is essential for a comprehensive life cycle analysis and a more complete understanding of the fate of Ag-NP in the (urban) environment. To address the transformation of Ag-NP during sewage sludge incineration, we spiked metallic Ag0-NP to a pilot wastewater treatment plant and digested the sludge anaerobically. The sludge was then incinerated on a bench-scale fluidized bed reactor in a series of experiments under variable conditions. Complementary results from X-ray absorption spectroscopy (XAS) and electron microscopy–energy dispersive X-ray (EM–EDX) analysis revealed that Ag0-NP transformed into Ag2S-NP during the wastewater treatment, in agreement with previous studies. On the basis of a principal component analysis and subsequent target testing of the XAS spectra, Ag0 was identified as a major Ag component in the ashes, and Ag2S was clearly absent. The reformation of Ag0-NP was confirmed by EM–EDX. The fraction of Ag0 of the total Ag in the ashes was quantified by linear combination fitting (LCF) of XAS spectra, and values as high as 0.8 were found for sewage sludge incinerated at 800 °C in a synthetic flue gas atmosphere. Low LCF totals (72% to 94%) indicated that at least one relevant reference spectrum was missing in the LCF analysis. The presence of spherical Ag-NP with a diameter of <50 nm extending into the sub-nm range was revealed by electron microscopy analyses. The rapid formation of Ag0-NP from Ag2S during sewage sludge incineration, as demonstrated in this study, needs to be considered in the life cycle assessment of engineered Ag-NP.
Nathoo, J., & Randall, D. G. (2016). Thermodynamic modelling of a membrane distillation crystallisation process for the treatment of mining wastewater. Water Science and Technology, 73(3), 557-563. doi:10.2166/wst.2015.515, Institutional Repository

Membrane distillation (MD) could be applicable in zero liquid discharge applications. This is due to the fact that MD is applicable at high salinity ranges which are generally outside the scope of reverse osmosis (RO) applications, although this requires proper management of precipitating salts to avoid membrane fouling. One way of managing these salts is with MD crystallisation (MDC). This paper focuses on the applicability of MDC for the treatment of mining wastewater by thermodynamically modelling the aqueous chemistry of the process at different temperatures. The paper is based on the typical brine generated from an RO process in the South African coal mining industry and investigates the effect water recovery and operating temperature have on the salts that are predicted to crystallise out, the sequence in which they will crystallise out and purities as a function of the water recovery. The study confirmed the efficacy of using thermodynamic modelling as a tool for investigating and predicting the crystallisation aspects of the MDC process. The key finding from this work was that, for an MDC process, a purer product can be obtained at higher operating temperatures and recoveries because of the inverse solubility of calcium sulphate.
Petersen, E. J., Flores-Cervantes, D. X., Bucheli, T. D., Elliott, L. C. C., Fagan, J. A., Gogos, A., … Winchester, M. R. (2016). Quantification of carbon nanotubes in environmental matrices: current capabilities, case studies, and future prospects. Environmental Science and Technology, 50(9), 4587-4605. doi:10.1021/acs.est.5b05647, Institutional Repository

Carbon nanotubes (CNTs) have numerous exciting potential applications and some that have reached commercialization. As such, quantitative measurements of CNTs in key environmental matrices (water, soil, sediment, and biological tissues) are needed to address concerns about their potential environmental and human health risks and to inform application development. However, standard methods for CNT quantification are not yet available. We systematically and critically review each component of the current methods for CNT quantification including CNT extraction approaches, potential biases, limits of detection, and potential for standardization. This review reveals that many of the techniques with the lowest detection limits require uncommon equipment or expertise, and thus, they are not frequently accessible. Additionally, changes to the CNTs (e.g., agglomeration) after environmental release and matrix effects can cause biases for many of the techniques, and biasing factors vary among the techniques. Five case studies are provided to illustrate how to use this information to inform responses to real-world scenarios such as monitoring potential CNT discharge into a river or ecotoxicity testing by a testing laboratory. Overall, substantial progress has been made in improving CNT quantification during the past ten years, but additional work is needed for standardization, development of extraction techniques from complex matrices, and multimethod comparisons of standard samples to reveal the comparability of techniques.
Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Sinnet, B., Magnin, V., Findling, N., … Sarret, G. (2016). Fate of Ag-NPs in sewage sludge after application on agricultural soils. Environmental Science and Technology, 50(4), 1759-1768. doi:10.1021/acs.est.5b04550, Institutional Repository

The objective of this work was to investigate the fate of silver nanoparticles (Ag-NPs) in a sludge-amended soil cultivated with monocot (Wheat) and dicot (Rape) crop species. A pot experiment was performed with sludges produced in a pilot wastewater treatment plant containing realistic Ag concentrations (18 and 400 mg kg–1, 14 mg kg–1 for the control). Investigations focused on the highest dose treatment. X-ray absorption spectroscopy (XAS) showed that Ag2S was the main species in the sludge and amended soil before and after plant culture. The second most abundant species was an organic and/or amorphous Ag—S phase whose proportion slightly varied (from 24% to 36%) depending on the conditions. Micro and nano X-ray fluorescence (XRF) showed that Ag was preferentially associated with S-rich particles, including organic fragments, of the sludge and amended soils. Ag was distributed as heteroaggregates with soil components (size ranging from ≤0.5 to 1–3 μm) and as diffused zones likely corresponding to sorbed/complexed Ag species. Nano-XRF evidenced the presence of mixed metallic sulfides. Ag was weakly exchangeable and labile. However, micronutrient mobilization by plant roots and organic matter turnover may induce Ag species interconversion eventually leading to Ag release on longer time scales. Together, these data provide valuable information for risk assessment of sewage sludge application on agricultural soils.
Randall, D. G., Krähenbühl, M., Köpping, I., Larsen, T. A., & Udert, K. M. (2016). A novel approach for stabilizing fresh urine by calcium hydroxide addition. Water Research, 95, 361-369. doi:10.1016/j.watres.2016.03.007, Institutional Repository

In this study, we investigated the prevention of enzymatic urea hydrolysis in fresh urine by increasing the pH with calcium hydroxide (Ca(OH)2) powder. The amount of Ca(OH)2 dissolving in fresh urine depends significantly on the composition of the urine. The different urine compositions used in our simulations showed that between 4.3 and 5.8 g Ca(OH)2 dissolved in 1 liter of urine at 25 °C. At this temperature, the pH at saturation is 12.5 and is far above the pH of 11, which we identified as the upper limit for enzymatic urea hydrolysis. However, temperature has a strong effect on the saturation pH, with higher values being achieved at lower temperatures. Based on our results, we recommend a dosage of 10 g Ca(OH)2·L−1 of fresh urine to ensure solid Ca(OH)2 always remains in the urine reactor which ensures sufficiently high pH values. Besides providing sufficient Ca(OH)2, the temperature has to be kept in a certain range to prevent chemical urea hydrolysis. At temperatures below 14 °C, the saturation pH is higher than 13, which favors chemical urea hydrolysis. We chose a precautionary upper temperature of 40 °C because the rate of chemical urea hydrolysis increases at higher temperatures but this should be confirmed with kinetic studies. By considering the boundaries for pH and temperature developed in this study, urine can be stabilized effectively with Ca(OH)2 thereby simplifying later treatment processes or making direct use easier.
Shen, Y., Huang, C., Monroy, G. L., Janjaroen, D., Derlon, N., Lin, J., … Nguyen, T. H. (2016). Response of simulated drinking water biofilm mechanical and structural properties to long-term disinfectant exposure. Environmental Science and Technology, 50(4), 1779-1787. doi:10.1021/acs.est.5b04653, Institutional Repository

Mechanical and structural properties of biofilms influence the accumulation and release of pathogens in drinking water distribution systems (DWDS). Thus, understanding how long-term residual disinfectants exposure affects biofilm mechanical and structural properties is a necessary aspect for pathogen risk assessment and control. In this study, elastic modulus and structure of groundwater biofilms was monitored by atomic force microscopy (AFM) and optical coherence tomography (OCT) during three months of exposure to monochloramine or free chlorine. After the first month of disinfectant exposure, the mean stiffness of monochloramine- or free-chlorine-treated biofilms was 4 to 9 times higher than those before treatment. Meanwhile, the biofilm thickness decreased from 120 ± 8 μm to 93 ± 6–107 ± 11 μm. The increased surface stiffness and decreased biofilm thickness within the first month of disinfectant exposure was presumably due to the consumption of biomass. However, by the second to third month during disinfectant exposure, the biofilm mean stiffness showed a 2- to 4-fold decrease, and the biofilm thickness increased to 110 ± 7–129 ± 8 μm, suggesting that the biofilms adapted to disinfectant exposure. After three months of the disinfectant exposure process, the disinfected biofilms showed 2–5 times higher mean stiffness (as determined by AFM) and 6–13-fold higher ratios of protein over polysaccharide, as determined by differential staining and confocal laser scanning microscopy (CLSM), than the nondisinfected groundwater biofilms. However, the disinfected biofilms and nondisinfected biofilms showed statistically similar thicknesses (t test, p > 0.05), suggesting that long-term disinfection may not significantly remove net biomass. This study showed how biofilm mechanical and structural properties vary in response to a complex DWDS environment, which will contribute to further research on the risk assessment and control of biofilm-associated-pathogens in DWDS.
Shi, Y., Wells, G., & Morgenroth, E. (2016). Microbial activity balance in size fractionated suspended growth biomass from full-scale sidestream combined nitritation-anammox reactors. Bioresource Technology, 218, 38-45. doi:10.1016/j.biortech.2016.06.041, Institutional Repository

The purpose of this study was to determine the abundance, distribution and activity of aerobic ammonia-oxidizing bacteria (AOB) and anammox in size fractionated aggregates from full-scale suspended growth combined nitritation-anammox sidestream reactors. Plants with or without a cyclone device were also studied to assess a purported enrichment of anammox granules. Specific aerobic ammonium oxidation rates (p = 0.01) and specific oxygen uptake rates (p = 0.02) were significantly greater in flocs than in granules. AOB abundance measured using quantitative FISH was significantly higher in flocs than in granules (p = 0.01). Conversely, anammox abundance was significantly greater in granules (p = 0.03). The average ratio of anammox/AOB in systems employing hydrocyclone separation devices was 2.4, significantly higher (p = 0.02) than the average ratio (0.5) in a system without a hydrocyclone. Our results demonstrate substantial functional and population-level segregation between floccular and granular fractions, and provide a key corroboration that cyclone separation devices can increase anammox levels in such systems.
Thalmann, B., Voegelin, A., Morgenroth, E., & Kaegi, R. (2016). Effect of humic acid on the kinetics of silver nanoparticle sulfidation. Environmental Science: Nano, 3(1), 203-212. doi:10.1039/c5en00209e, Institutional Repository

The sulfidation of metallic silver nanoparticles (AgNP) observed in urban wastewater systems and in natural waters reduces their toxicity by several orders of magnitude. However, the reaction rate of this transformation is only poorly understood and the influence of humic acid (HA) on AgNP sulfidation has not been studied to date. We therefore investigate the sulfidation kinetics of AgNP reacted with bisulfide (HS−) in the absence and presence of HA and evaluate different kinetic models to describe the observed reaction kinetics. Citrate-stabilized AgNP of different sizes (20–200 nm) were reacted with an excess of HS− in the absence of HA as well as at HA concentrations ranging from 50 to 1000 mg L−1. The extent of AgNP sulfidation after the selected reaction times was determined by X-ray absorption spectroscopy (XAS). The overall sulfidation rate increased with decreasing AgNP size and increasing HA concentration. The sulfidation rate of the AgNP was best described by a diffusion-limited solid state reaction model (parabolic rate law). The corresponding half-lives of the AgNP ranged from minutes to hours. The increase of the sulfidation rate with increasing HA concentration may be explained by the adsorption of HA onto the AgNP surface facilitating the access of HS− to the particle surface. The results from analytical transmission electron microscopy suggest that the AgNP were sulfidized asymmetrically in the absence of HA. In the presence of HA, the initially formed concentric core–shell Ag0–Ag2S structures developed into hollow Ag2S nanoparticles with increasing reaction time, possibly via the Kirkendall effect.
Tomaszewska, J., Jakubiak, S., Michalski, J., Pronk, W., Hug, S. J., & Kurzydlowski, K. J. (2016). A polypropylene cartridge filter with hematite nanoparticles for solid particles retention and arsenic removal. Applied Surface Science, 366, 529-534. doi:10.1016/j.apsusc.2016.01.044, Institutional Repository

In this article, we report a processing route for deposition of hematite (α-Fe2O3) nanoparticles into a cartridge filter composed of polypropylene (PP) non-woven fabric by a dip-coating method. During the process, a plasma activated non-woven fabric was immersed in an electrostatically stabilized aqueous hematite suspension under low vacuum conditions. Oxygen groups introduced onto the surface of the polymer provide a strong attachment of hematite nanoparticles to the polypropylene surface, confirmed under conditions of ultrasound. Preliminary tests demonstrated the efficiency of the cartridge in treating spring water with moderate arsenic concentrations, with kinetics and extent of adsorption showing a good correlation to a Langmuir adsorption model.
Udert, K. M., Etter, B., & Gounden, T. (2016). Promoting sanitation in South Africa through nutrient recovery from urine. GAIA: Ecological Perspectives for Science and Society, 25(3), 194-196. doi:10.14512/gaia.25.3.12, Institutional Repository

The water utility of Durban, eThekwini Water and Sanitation (EWS), installed urine-diverting dry toilets to provide sanitation to under-served communities in rural and peri-urban areas. While faeces was treated by dehydration, urine was discharged into a soak away in the ground. EWS teamed up with the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and other partners in Switzerland and South Africa to valorise this resource. The VUNA project developed a sanitation system which produces a valuable fertiliser from urine, reduces pollution of water resources and promotes the acceptance of dry toilets.
Villez, K., Vanrolleghem, P. A., & Corominas, L. (2016). Optimal flow sensor placement on wastewater treatment plants. Water Research, 101, 75-83. doi:10.1016/j.watres.2016.05.068, Institutional Repository

Obtaining high quality data collected on wastewater treatment plants is gaining increasing attention in the wastewater engineering literature. Typical studies focus on recognition of faulty data with a given set of installed sensors on a wastewater treatment plant. Little attention is however given to how one can install sensors in such a way that fault detection and identification can be improved. In this work, we develop a method to obtain Pareto optimal sensor layouts in terms of cost, observability, and redundancy. Most importantly, the resulting method allows reducing the large set of possibilities to a minimal set of sensor layouts efficiently for any wastewater treatment plant on the basis of structural criteria only, with limited sensor information, and without prior data collection. In addition, the developed optimization scheme is fast. Practically important is that the number of sensors needed for both observability of all flows and redundancy of all flow sensors is only one more compared to the number of sensors needed for observability of all flows in the studied wastewater treatment plant configurations.
Villez, K., & Habermacher, J. (2016). Shape anomaly detection for process monitoring of a sequencing batch reactor. Computers and Chemical Engineering, 91, 365-379. doi:10.1016/j.compchemeng.2016.04.012, Institutional Repository

Anomaly detection is critical to process modeling, monitoring, and control since successful execution of these engineering tasks depends on access to validated data. Classical methods for data validation are quantitative in nature and require either accurate process knowledge, large representative data sets, or both. In contrast, a small section of the fault diagnosis literature has focused on qualitative data and model representations. The major benefit of such methods is that imprecise but reliable results can be obtained under previously unseen process conditions. This work continues with a line of work focused on qualitative trend analysis which is the qualitative approach to data series analysis. An existing method based on shape-constrained spline function fitting is expanded to deal explicitly with discontinuities and is applied here for the first time for anomaly detection. An experimental test case and a comparison with the principal component analysis method bear out the benefits of the qualitative approach to process monitoring.
Völker, J., Castronovo, S., Wick, A., Ternes, T. A., Joss, A., Oehlmann, J., & Wagner, M. (2016). Advancing biological wastewater treatment: extended anaerobic conditions enhance the removal of endocrine and dioxin-like activities. Environmental Science and Technology, 50(19), 10606-10615. doi:10.1021/acs.est.5b05732, Institutional Repository

Conventional activated sludge treatment of wastewater does not completely remove micropollutants. Here, extending anaerobic conditions may enhance biodegradation. To explore this, we combined iron-reducing or substrate-limiting and aerobic pilot-scale reactors directly at a wastewater treatment plant. To assess the removal of endocrine disrupting chemicals (EDCs) as group of micropollutants that adversely affects wildlife, we applied a bioanalytical approach. We used in vitro bioassays covering seven receptor-mediated mechanisms of action, including (anti)androgenicity, (anti)estrogenicity, retinoid-like, and dioxin-like activity. Untreated wastewater induced antiandrogenic, estrogenic, antiestrogenic, and retinoid-like activity. Full-scale as well as reactor-scale activated sludge treatment effectively removes the observed effects. Nevertheless, high antiandrogenic and minor dioxin-like and estrogenic effects persisted in the treated effluent that may still be environmentally relevant. The anaerobic post-treatment under substrate-limiting conditions resulted in an additional removal of endocrine activities by 17–40%. The anaerobic pre-treatment under iron-reducing conditions significantly enhanced the removal of the residual effects by 40–75%. In conclusion, this study demonstrates that a further optimization of biological wastewater treatment is possible. Here, implementing iron-reducing anaerobic conditions preceding aerobic treatment appears promising to improve the removal of receptor-mediated toxicity.
Wu, S., Bhattacharjee, A. S., Weissbrodt, D. G., Morgenroth, E., & Goel, R. (2016). Effect of short term external perturbations on bacterial ecology and activities in a partial nitritation and anammox reactor. Bioresource Technology, 219, 527-535. doi:10.1016/j.biortech.2016.07.118, Institutional Repository

This research investigated the short term effects of temperature changes (lasting 2–4 weeks each) from 35 ± 2 °C to 21 ± 2 °C and 13 ± 2 °C and sulfide toxicity on partial nitrification-anammox (PN/A) system. Temperatures below 20 °C and sulfide content as low as 5 mgS L−1 affected both aerobic and anaerobic catabolic activities of ammonia oxidation and the expression of related functional gene markers. The activity of AOB was inversely correlated with ammonium monooxygenase (amoA) gene expression. In contrast, the activity of AMX bacteria was positively correlated with the expression of their hydrazine synthase (hzsA) gene. Although the overall activities of AMX bacteria decreased at lower temperatures, the AMX bacteria were still active at the low temperatures. The inverse correlation between amoA gene expressions and the corresponding AOB activities was surprising. 16S rDNA based high throughput amplicon sequencing revealed the dominance of Chloroflexi, Planctomycetes and Proteobacteria phyla the distribution of which changed with temperature changes.
Wu, B., Hochstrasser, F., Akhondi, E., Ambauen, N., Tschirren, L., Burkhardt, M., … Pronk, W. (2016). Optimization of gravity-driven membrane (GDM) filtration process for seawater pretreatment. Water Research, 93, 133-140. doi:10.1016/j.watres.2016.02.021, Institutional Repository

Seawater pretreatment by gravity-driven membrane (GDM) filtration at 40 mbar has been investigated. In this system, a beneficial biofilm develops on the membrane that helps to stabilize flux. The effects of membrane type, prefiltration and system configuration on stable flux, biofilm layer properties and dissolved carbon removal were studied. The results show that the use of flat sheet PVDF membranes with pore sizes of 0.22 and 0.45 μm in GDM filtration achieved higher stabilized permeate fluxes (7.3–8.4 L/m2h) than that of flat sheet PES 100 kD membranes and hollow fibre PVDF 0.1 μm membranes. Pore constriction and cake filtration were identified as major membrane fouling mechanisms, but their relative contributions varied with filtration time for the various membranes. Compared to raw seawater, prefiltering of seawater with meshes at sizes of 10, 100 and 1000 μm decreased the permeate flux, which was attributed to removal of beneficial eukaryotic populations. Optical coherence tomography (OCT) showed that the porosity of the biofouling layer was more significantly related with permeate flux development rather than its thickness and roughness. To increase the contact time between the biofilm and the dissolved organics, a hybrid biofilm-submerged GDM reactor was evaluated, which displayed significantly higher permeate fluxes than the submerged GDM reactor. Although integrating the biofilm reactor with the membrane system displayed better permeate quality than the GDM filtration cells, it could not effectively reduce dissolved organic substances in the seawater. This may be attributed to the decomposition/degradation of solid organic substances in the feed and carbon fixation by the biofilm. Further studies of the dynamic carbon balance are required.
Ziemba, C., Shabtai, Y., Piatkovsky, M., & Herzberg, M. (2016). Cellulose effects on morphology and elasticity of Vibrio fischeri biofilms. npj Biofilms and Microbiomes, 2, 1 (9 pp.). doi:10.1038/s41522-016-0001-2, Institutional Repository

Cellulose effects on Vibrio fischeri biofilm morphology were tested for the wild-type and two of its isogenic mutants that eitherexhibit increased cellulose production or do not produce cellulose at all. Confocal laser scanning microscopy imaging of eachbiofilm revealed that total sessile volume increases with cellulose expression, but the size of colonies formed with cellulose wassmaller, creating a more diffuse biofilm. These morphological differences were not attributed to variations in bacterial deposition,extracellular polymeric substances affinity to the surface or bacterial growth. A positive correlation was found between celluloseexpression, Young's (elastic) modulus of the biofilm analyzed with atomic force microscope and shear modulus of the relatedextracellular polymeric substances layers analyzed with quartz crystal microbalance with dissipation monitoring. Celluloseproduction also correlated positively with concentrations of extracellular DNA. A significant negative correlation was observedbetween cellulose expression and rates of diffusion through the extracellular polymeric substances. The difference observed inbiofilm morphology is suggested as a combined result of cellulose and likely extracellular DNA (i) increasing biofilm Young'smodulus, making shear removal more difficult, and (ii) decreased diffusion rate of nutrients and wastes into and out of the biofilm,which effectively limits colony size.
Akhondi, E., Wu, B., Sun, S., Marxer, B., Lim, W., Gu, J., … Fane, A. G. (2015). Gravity-driven membrane filtration as pretreatment for seawater reverse osmosis: linking biofouling layer morphology with flux stabilization. Water Research, 70, 158-173. doi:10.1016/j.watres.2014.12.001, Institutional Repository

In this study gravity-driven membrane (GDM) ultrafiltration is investigated for the pretreatment of seawater before reverse osmosis (RO). The impacts of temperature (21 ± 1 and 29 ± 1 °C) and hydrostatic pressure (40 and 100 mbar) on dynamic flux development and biofouling layer structure were studied. The data suggested pore constriction fouling was predominant at the early stage of filtration, during which the hydrostatic pressure and temperature had negligible effects on permeate flux. With extended filtration time, cake layer fouling played a major role, during which higher hydrostatic pressure and temperature improved permeate flux. The permeate flux stabilized in a range of 3.6 L/m2 h (21 ± 1 °C, 40 mbar) to 7.3 L/m2 h (29 ± 1 °C, 100 mbar) after slight fluctuations and remained constant for the duration of the experiments (almost 3 months). An increase in biofouling layer thickness and a variable biofouling layer structure were observed over time by optical coherence tomography and confocal laser scanning microscopy. The presence of eukaryotic organisms in the biofouling layer was observed by light microscopy and the microbial community structure of the biofouling layer was analyzed by sequences of 16S rRNA genes. The magnitude of permeate flux was associated with the combined effect of the biofouling layer thickness and structure. Changes in the biofouling layer structure were attributed to (1) the movement and predation behaviour of the eukaryotic organisms which increased the heterogeneous nature of the biofouling layer; (2) the bacterial debris generated by eukaryotic predation activity which reduced porosity; (3) significant shifts of the dominant bacterial species over time that may have influenced the biofouling layer structure. As expected, most of the particles and colloids in the feed seawater were removed by the GDM process, which led to a lower RO fouling potential. However, the dissolved organic carbon in the permeate was not be reduced, possibly because some microbial species (e.g. algae) could convert CO2 into organic substances. To further improve the removal efficiency of the organic carbon, combining carrier biofilm processes with a submerged GDM filtration system is proposed.
Bischel, H. N., Schertenleib, A., Fumasoli, A., Udert, K. M., & Kohn, T. (2015). Inactivation kinetics and mechanisms of viral and bacterial pathogen surrogates during urine nitrification. Environmental Science: Water Research and Technology, 1(1), 65-76. doi:10.1039/c4ew00065j, Institutional Repository

This paper assesses the inactivation performance and mechanisms in urine nitrification reactors using bacteria and bacteriophages as surrogates for human pathogens. Two parallel continuous-flow moving bed biofilm reactors (MBBRs) were operated over a two-month period. One MBBR was used to conduct a continuous spike experiment with bacteriophage MS2. The second reactor provided the matrix for a series of batch experiments conducted to investigate the inactivation of Salmonella typhimurium, Enterococcus spp., MS2, Qβ, and ΦX174 during urine nitrification. The roles of aeration, biological activity, and solution composition in inactivation were evaluated. Whereas bacteriophages ΦX174 and MS2 remained infective following urine nitrification, partial inactivation of bacteriophage Qβ was observed. Qβ inactivation was attributed primarily to aeration with a potential additive effect of biological processes, i.e., processes that are attributable to the presence of other microorganisms such as sorption to biomass, predation or enzymatic activity. Tailing of Qβ inactivation to a plateau indicated a protective effect of the solution components in aerated nitrification reactors. In contrast to the bacteriophages, S. typhimurium and Enterococcus spp. were mainly affected by biological processes: they were inactivated in biologically active nitrification reactors while remaining stable in chemically equivalent filtered controls. The tested bacteria could, for example, be out-competed by other microbial communities or sorbed to biomass in the reactor. Microbial communities did not adapt to inactivate bacteriophage MS2 (e.g., via increased prevalence of virus predators) in the experimental time-scale evaluated, with no observed inactivation of MS2 during continuous input for 51 days in the flow-through MBBR. The compilation of these results suggests that biological nitrification as a fertilizer production process remains insufficient as a stand-alone technology for the sanitization of source-separated urine.
Bischel, H. N., Özel Duygan, B. D., Strande, L., McArdell, C. S., Udert, K. M., & Kohn, T. (2015). Pathogens and pharmaceuticals in source-separated urine in eThekwini, South Africa. Water Research, 85, 57-65. doi:10.1016/j.watres.2015.08.022, Institutional Repository

In eThekwini, South Africa, the production of agricultural fertilizers from human urine collected from urine-diverting dry toilets is being evaluated at a municipality scale as a way to help finance a decentralized, dry sanitation system. The present study aimed to assess a range of human and environmental health hazards in source-separated urine, which was presumed to be contaminated with feces, by evaluating the presence of human pathogens, pharmaceuticals, and an antibiotic resistance gene. Composite urine samples from households enrolled in a urine collection trial were obtained from urine storage tanks installed in three regions of eThekwini. Polymerase chain reaction (PCR) assays targeted 9 viral and 10 bacterial human pathogens transmitted by the fecal–oral route. The most frequently detected viral pathogens were JC polyomavirus, rotavirus, and human adenovirus in 100%, 34% and 31% of samples, respectively. Aeromonas spp. and Shigella spp. were frequently detected gram negative bacteria, in 94% and 61% of samples, respectively. The gram positive bacterium, Clostridium perfringens, which is known to survive for extended times in urine, was found in 72% of samples. A screening of 41 trace organic compounds in the urine facilitated selection of 12 priority pharmaceuticals for further evaluation. The antibiotics sulfamethoxazole and trimethoprim, which are frequently prescribed as prophylaxis for HIV-positive patients, were detected in 95% and 85% of samples, reaching maximum concentrations of 6800 μg/L and 1280 μg/L, respectively. The antiretroviral drug emtricitabine was also detected in 40% of urine samples. A sulfonamide antibiotic resistance gene (sul1) was detected in 100% of urine samples. By coupling analysis of pathogens and pharmaceuticals in geographically dispersed samples in eThekwini, this study reveals a range of human and environmental health hazards in urine intended for fertilizer production. Collection of urine offers the benefit of sequestering contaminants from environmental release and allows for targeted treatment of potential health hazards prior to agricultural application. The efficacy of pathogen and pharmaceutical inactivation, transformation or removal during urine nutrient recovery processes is thus briefly reviewed.
Boehler, M. A., Heisele, A., Seyfried, A., Grömping, M., & Siegrist, H. (2015). (NH4)2SO4 recovery from liquid side streams. Environmental Science and Pollution Research, 22(10), 7295-7305. doi:10.1007/s11356-014-3392-8, Institutional Repository

Two methods of recovering nitrogen from liquid side streams are presented in this paper. The first method was demonstrated at an ammonia stripping plant treating 5–7 m3/h sludge water at the wastewater treatment plant (WWTP) Kloten-Opfikon (CH). In addition to the usual stripping and scrubbing columns, a third column had been added in order strip CO2, thus reducing the NaOH-demand of the subsequent ammonia stripping. At first, just the stripping plant was put into operation and optimized without any pre-treatment of the supernatant. Next, the CO2-stripper column was activated and optimized by gas measurements to minimize free ammonia losses, heat losses, and energy consumption. Key operational aspects of the plant were evaluated. Finally, up to 1.4 m3/h source-separated urine was successfully fed into the stripping facility. The second ammonia removal method using hydrophobic hollow fiber membranes was tested in two small pilot systems by different manufacturers in 2012 and 2013 at WWTP Neugut. In this technology, free ammonia gas in the sludge liquid diffuses at pH >9.3 from the sludge liquid through the air-filled pores of the microporous hydrophobic membrane into concentrated sulfuric acid flowing through the hollow fibers, forming ammonium sulfate. The small pore size and the hydrophobic nature of the membrane prevent the liquid phase from entering into the pores due to the surface tension effect. Practical experience regarding operational parameters like wastewater flow rate, pH, temperature, ammonia concentration, fouling and precipitations processes, optimal flow schemes, and process configurations was collected.
Bonvin, C., Etter, B., Udert, K. M., Frossard, E., Nanzer, S., Tamburini, F., & Oberson, A. (2015). Plant uptake of phosphorus and nitrogen recycled from synthetic source-separated urine. Ambio, 44(Suppl. 2), S217-S227. doi:10.1007/s13280-014-0616-6, Institutional Repository

Urine contains about 50 % of the phosphorus (P) and about 90 % of the nitrogen (N) excreted by humans and is therefore an interesting substrate for nutrient recovery. Source-separated urine can be used to precipitate struvite or, through a newly developed technology, nitrified urine fertilizer (NUF). In this study, we prepared 33P radioisotope- and stable 15N isotope-labeled synthetic NUF (SNUF) and struvite using synthetic urine and determined P and N uptake by greenhouse-grown ryegrass (Lolium multiflorum var. Gemini) fertilized with these products. The P and N in the urine-based fertilizers were as readily plant-available in a slightly acidic soil as the P and N in reference mineral fertilizers. The ryegrass crop recovered 26 % of P applied with both urine-based fertilizers and 72 and 75 % of N applied as struvite and SNUF, respectively. Thus, NUF and urine-derived struvite are valuable N and P recycling fertilizers.
Chomiak, A., Traber, J., Morgenroth, E., & Derlon, N. (2015). Biofilm increases permeate quality by organic carbon degradation in low pressure ultrafiltration. Water Research, 85, 512-520. doi:10.1016/j.watres.2015.08.009, Institutional Repository

We investigated the influence of biofouling of ultrafiltration membranes on the removal of organic model foulants and ultimately on the quality of permeate. Gravity Driven Membrane ultrafiltration (GDM) membrane systems were operated with modified river water during five weeks without control of the biofilm formation. Three GDM systems were studied: two systems with biofilms exposed to (A) variable or (B) constant load of organic foulants, and (C) one system operated without biofilm and exposed to constant foulant loading. Biodegradable dextran or non-biodegradable polystyrene sulfonate model foulants were tested. Substrate biodegradability was confirmed by Size Exclusion Chromatography (SEC) and by degradation batch tests (D). The GDM systems (A) and (B) were fed with pre-filtered river water supplemented with dextran (Dex) of 1, 150 or 2000 kDa, or polystyrene sulfonate (PSS) of 1 or 80 kDa at concentrations of 2–3.5 mgC L−1. In exp. (C) the feed water consisted of deionized water with 25 mgC L−1 of either PSS 1, 80 kDa or Dex 2000 kDa.
The biofilm formation on UF membrane surfaces controlled the foulant permeation and thus the permeate quality. Biofilms exposed to continuous foulant loading (exp. B) degraded low molecular weight (LMW) biodegradable foulants (1 kDa Dex), which improved the permeate quality. For high molecular weight (HMW) substrates (150, 2000 kDa Dex), the improvement of the permeate quality was observed after 7 days of biofilm formation, and resulted from the foulant hydrolysis followed by degradation. For non-biodegradable foulants, an improvement of 20% of the retention was observed for the polystyrene (1, 80 kDa PSS) due to the presence of biofilms on membrane surfaces. For variable foulant loading (exp. A) the biofilms hydrolysed the large biodegradable foulants but did not degraded them fully, which resulted a deterioration of the permeate quality (except for the LMW dextran (1 kDa) that was fully degraded). Overall, the “biofilm + membrane” composite retained a larger amount of biodegradable foulant than the membrane alone, due to the activity of the biofilm. However, this resulted in an increased biofilm accumulation and reduced flux. In presence of the biofilm, the highest fluxes were observed for control (no foulant) and for small non-biodegradable foulants (PSS 1 kDa). Low fluxes were observed for the accumulating on membrane surface or degradable foulants (exp. B). But, the lowest fluxes were observed in absence of the biofilm (exp. C) due to physical accumulation of the foulants (PSS 80 kDa and Dextran 2000 kDa). Overall our study demonstrates that the presence of biofilms on membrane surfaces has some benefits: (i) biofilm helps to increase the permeate quality and (ii) biofilms protect the membrane from further fouling. Permeate flux stabilizes in the case of biofilm-membrane composite, while it continuously declines in the case of the membrane only.
Decrey, L., Kazama, S., Udert, K. M., & Kohn, T. (2015). Ammonia as an in situ sanitizer: inactivation kinetics and mechanisms of the ssRNA virus MS2 by NH3. Environmental Science and Technology, 49(2), 1060-1067. doi:10.1021/es5044529, Institutional Repository

Sanitizing human and animal waste (e.g., urine, fecal sludge, or grey water) is a critical step in reducing the spread of disease and ensuring microbially safe reuse of waste materials. Viruses are particularly persistent pathogens and can be transmitted through inadequately sanitized waste. However, adequate storage or digestion of waste can strongly reduce the number of viruses due to increases in pH and uncharged aqueous ammonia (NH3), a known biocide. In this study we investigated the kinetics and mechanisms of inactivation of the single-stranded RNA virus MS2 under temperature, pH and NH3 conditions representative of waste storage. MS2 inactivation was mainly controlled by the activity of NH3 over a pH range of 7.0–9.5 and temperatures lower than 40 °C. Other bases (e.g., hydroxide, carbonate) additionally contributed to the observed reduction of infective MS2. The loss in MS2 infectivity could be rationalized by a loss in genome integrity, which was attributed to genome cleavage via alkaline transesterification. The contribution of each base to genome transesterification, and hence inactivation, could be related to the base pKa by means of a Bronsted relationship. The Bronsted relationship in conjunction with the activity of bases in solution enabled an accurate prediction of MS2 inactivation rates.
Ding, A., Pronk, W., Qu, F., Ma, J., Li, G., Li, K., & Liang, H. (2015). Effect of calcium addition on sludge properties and membrane fouling potential of the membrane-coupled expanded granular sludge bed process. Journal of Membrane Science, 489, 55-63. doi:10.1016/j.memsci.2015.04.001, Institutional Repository

The expanded granular sludge bed reactor (EGSB) is considered a promising technology for anaerobic wastewater treatment, and the effluent quality can be further improved by membrane treatments. To mitigate membrane fouling of the membrane-coupled anaerobic process, 2.5 mM CaCl2 was added in a laboratory-scale EGSB reactor (3 L in volume). The effluent was subjected to short-term dead-end ultrafiltration (UF) tests to evaluate the membrane fouling potential. The results showed that Ca2+ addition to EGSB efficiently alleviated the fouling of the subsequent UF treatment compared with the control. The fouling potential was not diminished when Ca2+ was directly added to the effluent of the control EGSB. Further investigations revealed that the addition of Ca2+ to the EGSB resulted in an increase in the content of extracellular polymeric substances (EPS) of the granule by 24.1%. The addition of Ca2+ also reduced the concentration of the soluble extracellular polymeric substance (sEPS) (or soluble microbial product, SMP) in the effluent by 47.7–60.7% compared with the control system. Analysis of the fouling model revealed that Ca2+ addition reduced the cake resistance (Rc) by 42.8% and delayed the transition from the standard pore blocking model to the cake filtration model. The results indicate that fouling-relevant compounds, such as sEPS (aromatic proteins, tryptophan proteins and polysaccharides) and fulvic acids are included in the sludge when Ca2+ is added to the reactor, thus preventing them from reaching the membrane surface.
Fedotova, N., Kaegi, R., Koch, J., & Günther, D. (2015). Influence of dispersion agents on particle size and concentration determined by laser-induced breakdown detection. Spectrochimica Acta B: Atomic Spectroscopy, 103-104(1), 92-98. doi:10.1016/j.sab.2014.12.002, Institutional Repository

Laser-induced breakdown detection (LIBD) is a very promising analytical technique to determine the size and the concentration of nanoparticles (NPs) in aqueous suspensions. The measurement principle is based on the formation of individual plasma events selectively produced when a pulsed, focused laser beam hits a NP. The breakdown probability (BDP) is defined as the ratio of the number of plasma events detected to the total number of laser pulses applied. Energy curves are established by recording the BDP as a function of the laser energy which is increased in a stepwise manner. The size and the concentration of NPs in aqueous suspensions can be extracted from recorded energy curves. Although several studies have already documented the potential of the LIBD technique to detect NPs at trace concentrations in aqueous suspensions, the effect of dissolved matrix constituents (e.g. dispersion agents, which are frequently used to stabilize NPs in suspension) on the LIBD signal has not been addressed, yet.
We therefore recorded energy curves of ultrahigh purity (UHP) water and NP suspensions both spiked with different dispersion agents at different concentrations. An increasing shift of the energy curves towards lower energies was observed with increasing concentrations of dispersion agents. The LIBD-derived size of the NPs was less affected by the presence of dispersion agents than the LIBD-derived particle number concentrations, which deviated by up to 300% from the expected values. The effects on the calculated concentrations were most pronounced at low (2 · 107 particles mL− 1) NP concentrations and at higher NP concentrations (3 · 108 particles mL− 1), the effect of the dispersion agents on the energy curves became negligible. These results show that dissolved matrix constituents substantially affect LIBD measurements, especially at low NP concentrations.
Fumasoli, A., Morgenroth, E., & Udert, K. M. (2015). Modeling the low pH limit of Nitrosomonas eutropha in high-strength nitrogen wastewaters. Water Research, 83, 161-170. doi:10.1016/j.watres.2015.06.013, Institutional Repository

In wastewater treatment, the rate of ammonia oxidation decreases with pH and stops very often slightly below a pH of 6. Free ammonia (NH3) limitation, inhibition by nitrous acid (HNO2), limitation by inorganic carbon or direct effect of high proton concentrations have been proposed to cause the rate decrease with pH as well as the cessation of ammonia oxidation. In this study, we compare an exponential pH term common for food microbiology with conventionally applied rate laws based on Monod-type kinetics for NH3 limitation and non-competitive HNO2 inhibition as well as sigmoidal pH functions to model the low pH limit of ammonia oxidizing bacteria (AOB). For this purpose we conducted well controlled batch experiments which were then simulated with a computer model. The results showed that kinetics based on NH3 limitation and HNO2 inhibition can explain the rate decrease of ammonia oxidation between pH 7 and 6, but fail in predicting the pH limit of Nitrosomonas eutropha at pH 5.4 and rates close to that limit. This is where the exponential pH term becomes important: this term decreases the rate of ammonia oxidation to zero, as the pH limit approaches. Previously proposed sigmoidal pH functions that affect large pH regions, however, led to an overestimation of the pH effect and could therefore not be applied successfully. We show that the proposed exponential pH term can be explained quantitatively with thermodynamic principles: at low pH values, the energy available from the proton motive force is too small for the NADH production in Nitrosomonas eutropha and related AOB causing an energy limited state of the bacterial cell. Hence, energy limitation and not inhibition or limitation of enzymes is responsible for the cessation of the AOB activity at low pH values.
Habermacher, J., Benetti, A. D., Derlon, N., & Morgenroth, E. (2015). The effect of different aeration conditions in activated sludge – side-stream system on sludge production, sludge degradation rates, active biomass and extracellular polymeric substances. Water Research, 85, 46-56. doi:10.1016/j.watres.2015.08.002, Institutional Repository

On-site minimization of excess sludge production is a relevant strategy for the operation of small-scale and decentralized wastewater treatment plants. In the study, we evaluated the potential of activated sludge systems equipped with side-stream reactors (SSRs). This study especially focused on how the sequential exposure of sludge to different aeration conditions in the side-stream reactors influences the overall degradation of sludge and of its specific fractions (active biomass, extracellular polymeric substances (EPS), EPS proteins, EPS carbohydrates). We found that increasing the solid retention time from 25 to 40 and 80 days enhanced sludge degradation for all aeration conditions tested in the side-stream reactor. Also, the highest specific degradation rate and in turn the lowest sludge production were achieved when maintaining aerobic conditions in the side-stream reactors. The different sludge fractions in terms of active biomass (quantified based on adenosine tri-phosphate (ATP) measurements), EPS proteins and EPS carbohydrates were quantified before and after passage through the SSR. The relative amounts of active biomass and EPS to volatile suspended solids (VSS) did not changed when exposed to different aeration conditions in the SSRs, which indicates that long SRT and starvation in the SSRs did not promote the degradation of a specific sludge fraction. Overall, our study helps to better understand mechanisms of enhanced sludge degradation in systems operated at long SRTs.
Harris, E., Joss, A., Emmenegger, L., Kipf, M., Wolf, B., Mohn, J., & Wunderlin, P. (2015). Isotopic evidence for nitrous oxide production pathways in a partial nitritation-anammox reactor. Water Research, 83, 258-270. doi:10.1016/j.watres.2015.06.040, Institutional Repository

Nitrous oxide (N2O) production pathways in a single stage, continuously fed partial nitritation-anammox reactor were investigated using online isotopic analysis of offgas N2O with quantum cascade laser absorption spectroscopy (QCLAS). N2O emissions increased when reactor operating conditions were not optimal, for example, high dissolved oxygen concentration. SP measurements indicated that the increase in N2O was due to enhanced nitrifier denitrification, generally related to nitrite build-up in the reactor. The results of this study confirm that process control via online N2O monitoring is an ideal method to detect imbalances in reactor operation and regulate aeration, to ensure optimal reactor conditions and minimise N2O emissions.
Under normal operating conditions, the N2O isotopic site preference (SP) was much higher than expected – up to 40‰ – which could not be explained within the current understanding of N2O production pathways. Various targeted experiments were conducted to investigate the characteristics of N2O formation in the reactor. The high SP measurements during both normal operating and experimental conditions could potentially be explained by a number of hypotheses: i) unexpectedly strong heterotrophic N2O reduction, ii) unknown inorganic or anammox-associated N2O production pathway, iii) previous underestimation of SP fractionation during N2O production from NH2OH, or strong variations in SP from this pathway depending on reactor conditions. The second hypothesis – an unknown or incompletely characterised production pathway – was most consistent with results, however the other possibilities cannot be discounted. Further experiments are needed to distinguish between these hypotheses and fully resolve N2O production pathways in PN-anammox systems.
Hofacker, A. F., Behrens, S., Voegelin, A., Kaegi, R., Lösekann-Behrens, T., Kappler, A., & Kretzschmar, R. (2015). Clostridium species as metallic copper-forming bacteria in soil under reducing conditions. Geomicrobiology Journal, 32(2), 130-139. doi:10.1080/01490451.2014.933287, Institutional Repository

Recent studies have reported the formation of Cu0 nanoparticles (CuNP) by suspended bacteria in pore water of periodically flooded soils, but the bacteria have not yet been identified. The aim of this study was to identify the CuNP-forming bacteria and to determine the location of CuNP formation relative to the bacterial cell surface. Electron microscopy revealed that the bacteria were rod-shaped spore formers and suggested that CuNP were formed in the periplasm. Combined results from denaturing gradient gel electrophoresis, 16S rRNA gene clone libraries, and classic microbiological cultivation techniques provided strong evidence for a Clostridium sp. strain as the CuNP-forming bacteria. Clostridia are well-adapted to frequent flooding and drying due to their ability to form spores and may play an important role in Cu cycling and metallic Cu formation in redox-dynamic environments.
Hubaux, N., Wells, G., & Morgenroth, E. (2015). Impact of coexistence of flocs and biofilm on performance of combined nitritation-anammox granular sludge reactors. Water Research, 68, 127-139. doi:10.1016/j.watres.2014.09.036, Institutional Repository

Nitrogen (N) removal from high-strength wastewater can be accomplished in single-stage combined nitritation-anammox reactors with suspended growth biomass composed of floccular sludge, granular sludge, or of any mix of these 2 different sludge fractions. To date, the influence of floccular biomass on granular sludge reactor performance and stability has not been investigated experimentally or numerically. To address this knowledge gap, two 1D multi-species models were developed in Aquasim to assess the importance of small levels of flocs in putatively granular sludge combined nitritation-anammox reactors for different bulk oxygen concentrations and organics loads. The models included the growth and decay of aerobic ammonium-oxidizing organism (AOO), nitrite-oxidizing organisms (NOO), heterotrophic organisms (OHO), and anammox organisms (AMO) in exclusively granular sludge reactors, and in granular sludge reactors with small levels (∼5% of total biomass) of flocs. While maximum N removal efficiencies were similar for both model structures, floc addition led to a lower optimal dissolved oxygen concentration (DO) as well as a narrower maximum N removal peak, suggesting that small levels of floccular material may decrease process robustness to bulk oxygen changes. For some DO levels, this led to drastic efficiency drops. Furthermore, floc addition also led to substantial segregation in activity and microbial population distribution, with AOO, NOO and OHO concentrated in flocs and AMO concentrated in granules. Increased organic loading (COD:N = 4:3) improved maximum N removal efficiency in both model structures, but yielded substantially different predictions for optimal DO setpoint and process robustness to variations in DO. Taken together, our results indicate that even small levels of floccular biomass in biofilm reactors can have profound implications for reactor performance and optimization and for segregation of linked microbial processes, and suggest that the common practice of neglecting small levels of floccular material in biofilm models and in practice may lead to erroneous predictions.
Kaegi, R., Voegelin, A., Sinnet, B., Zuleeg, S., Siegrist, H., & Burkhardt, M. (2015). Transformation of AgCl nanoparticles in a sewer system - a field study. Science of the Total Environment, 535, 20-27. doi:10.1016/j.scitotenv.2014.12.075, Institutional Repository

Silver nanoparticles (Ag-NP) are increasingly used in consumer products and their release during the use phase may negatively affect aquatic ecosystems. Research efforts, so far, have mainly addressed the application and use of metallic Ag(0)-NP. However, as shown by recent studies on the release of Ag from textiles, other forms of Ag, especially silver chloride (AgCl), are released in much larger quantities than metallic Ag(0). In this field study, we report the release of AgCl-NP from a point source (industrial laundry that applied AgCl-NP during a piloting phase over a period of several months to protect textiles from bacterial regrowth) to the public sewer system and investigate the transformation of Ag during its transport in the sewer system and in the municipal wastewater treatment plant (WWTP). During the study period, the laundry discharged ~85 g of Ag per day, which dominated the Ag loads in the sewer system from the respective catchment (72–95%) and the Ag in the digested WWTP sludge (67%). Combined results from electron microscopy and X-ray absorption spectroscopy revealed that the Ag discharged from the laundry to the sewer consisted of about one third AgCl and two thirds Ag2S, both forms primarily occurring as nanoparticles with diameters < 100 nm. During the 800 m transport in the sewer channel to the nearby WWTP, corresponding to a travel time of ~30 min, the remaining AgCl was transformed into nanoparticulate Ag2S. Ag2S-NP also dominated the Ag speciation in the digested sludge. In line with results from earlier studies, the very low Ag concentrations measured in the effluent of the WWTP (< 0.5 μg L− 1) confirmed the very high removal efficiency of Ag from the wastewater stream (> 95%).
Künzle, R., Pronk, W., Morgenroth, E., & Larsen, T. A. (2015). An energy-efficient membrane bioreactor for on-site treatment and recovery of wastewater. Journal of Water Sanitation and Hygiene for Development, 5(3), 448-455. doi:10.2166/washdev.2015.116, Institutional Repository

The present study describes the development of a new type of aerated membrane bioreactor referred to as a biologically activated membrane bioreactor (BAMBi) for on-site treatment of high-strength wastewater. The treated wastewater is reused for flushing and personal hygiene. BAMBi is an adaptation of a gravity-driven membrane reactor, originally developed for the purpose of treating river water to drinking water quality. Initially, a series of reactor configurations were tested and it was found that the simplest possible configuration could treat the wastewater to an acceptable standard, provided that a polishing step for color removal and disinfection was introduced. A commercial electrolysis unit was utilized for polishing. The energy consumption of BAMBi is 0.8 kWh/m3 of water treated, which can be considered low for an on-site membrane bio reactor application.
Larsen, T. A., Gebauer, H., Gründl, H., Künzle, R., Lüthi, C., Messmer, U., … Ranner, B. (2015). Blue Diversion: a new approach to sanitation in informal settlements. Journal of Water Sanitation and Hygiene for Development, 5(1), 64-71. doi:10.2166/washdev.2014.115, Institutional Repository

The sanitation concept ‘Blue Diversion’ (www.bluediversiontoilet.com) was developed as a possible answer to the sanitation crisis in urban slums. It is based on two main elements: (1) diversion of urine, feces, and water at the source as the basis for efficient resource recovery, and (2) linking different scales (family toilets and semi-centralized resource recovery). Our objective was to develop an attractive ‘grid-free’ (i.e. functioning without piped water, sewer, and electrical grid) dry urine-diverting toilet, which provides water (through recycling on-site) for flushing, personal hygiene (anal cleansing and menstrual hygiene), and hand washing. This service, including the entire sanitation value chain, should eventually be made available as a profitable business with total user fees of 5 ¢/p/d. The results presented in this paper are (1) a toilet design model, (2) the development of a new type of membrane bioreactor for treating flush and wash water, (3) main results of a geographic information system-based stochastic service model to link the family-scale toilet to a community-scale Resource Recovery Plant, and (4) a business model that yields maximum profit for the local community. We conclude that the approach is feasible, but challenging from a technical as well as an organizational point of view.
Laureni, M., Weissbrodt, D. G., Szivák, I., Robin, O., Nielsen, J. L., Morgenroth, E., & Joss, A. (2015). Activity and growth of anammox biomass on aerobically pre-treated municipal wastewater. Water Research, 80, 325-336. doi:10.1016/j.watres.2015.04.026, Institutional Repository

Direct treatment of municipal wastewater (MWW) based on anaerobic ammonium oxidizing (anammox) bacteria holds promise to turn the energy balance of wastewater treatment neutral or even positive. Currently, anammox processes are successfully implemented at full scale for the treatment of high-strength wastewaters, whereas the possibility of their mainstream application still needs to be confirmed. In this study, the growth of anammox organisms on aerobically pre-treated municipal wastewater (MWWpre-treated), amended with nitrite, was proven in three parallel reactors. The reactors were operated at total N concentrations in the range 5–20 mgN∙L−1, as expected for MWW. Anammox activities up to 465 mgN∙L−1∙d−1 were reached at 29 °C, with minimum doubling times of 18 d. Lowering the temperature to 12.5 °C resulted in a marked decrease in activity to 46 mgN∙L−1∙d−1 (79 days doubling time), still in a reasonable range for autotrophic nitrogen removal from MWW. During the experiment, the biomass evolved from a suspended growth inoculum to a hybrid system with suspended flocs and wall-attached biofilm. At the same time, MWWpre-treated had a direct impact on process performance. Changing the influent from synthetic medium to MWWpre-treated resulted in a two-month delay in net anammox growth and a two to three-fold increase in the estimated doubling times of the anammox organisms. Interestingly, anammox remained the primary nitrogen consumption route, and high-throughput 16S rRNA gene-targeted amplicon sequencing analyses revealed that the shift in performance was not associated with a shift in dominant anammox bacteria ("Candidatus Brocadia fulgida"). Furthermore, only limited heterotrophic denitrification was observed in the presence of easily biodegradable organics (acetate, glucose). The observed delays in net anammox growth were thus ascribed to the acclimatization of the initial anammox population or/and the development of a side population beneficial for them. Additionally, by combining microautoradiography and fluorescence in situ hybridization it was confirmed that the anammox organisms involved in the process did not directly incorporate or store the amended acetate and glucose. In conclusion, these investigations strongly support the feasibility of MWW treatment via anammox.
Mašić, A., Santos, A. T. L., Etter, B., Udert, K. M., & Villez, K. (2015). Estimation of nitrite in source-separated nitrified urine with UV spectrophotometry. Water Research, 85, 244-254. doi:10.1016/j.watres.2015.08.031, Institutional Repository

Monitoring of nitrite is essential for an immediate response and prevention of irreversible failure of decentralized biological urine nitrification reactors. Although a few sensors are available for nitrite measurement, none of them are suitable for applications in which both nitrite and nitrate are present in very high concentrations. Such is the case in collected source-separated urine, stabilized by nitrification for long-term storage. Ultraviolet (UV) spectrophotometry in combination with chemometrics is a promising option for monitoring of nitrite. In this study, an immersible in situ UV sensor is investigated for the first time so to establish a relationship between UV absorbance spectra and nitrite concentrations in nitrified urine. The study focuses on the effects of suspended particles and saturation on the absorbance spectra and the chemometric model performance. Detailed analysis indicates that suspended particles in nitrified urine have a negligible effect on nitrite estimation, concluding that sample filtration is not necessary as pretreatment. In contrast, saturation due to very high concentrations affects the model performance severely, suggesting dilution as an essential sample preparation step. However, this can also be mitigated by simple removal of the saturated, lower end of the UV absorbance spectra, and extraction of information from the secondary, weaker nitrite absorbance peak. This approach allows for estimation of nitrite with a simple chemometric model and without sample dilution. These results are promising for a practical application of the UV sensor as an in situ nitrite measurement in a urine nitrification reactor given the exceptional quality of the nitrite estimates in comparison to previous studies.
Mimoso, J., Pronk, W., Morgenroth, E., & Hammes, F. (2015). Bacterial growth in batch-operated membrane filtration systems for drinking water treatment. Separation and Purification Technology, 156, 165-174. doi:10.1016/j.seppur.2015.09.070, Institutional Repository

Membrane filtration treats drinking water by physical removal of bacteria and other particles present in the raw water. In order to study post-filtration contamination and growth, filtered river water and wastewater were used in a controlled laboratory-scale simulation of a batch-operated membrane filtration system. Bacterial batch growth was analyzed following intentional initial contamination with a river water microbial community. Batch growth in the permeate was measured with online flow cytometry at high intervals during 10 successive 24-hour operational cycles, simulating repeated daily use (filtration followed by stagnation). Two operational mechanisms influenced the growth characteristics: (1) initial selection of bacteria adapted to batch growth conditions, and (2) biofilm formation on the surfaces of the permeate containers. The first mechanism contributed towards a stable and reproducible growth behavior (lag phase of less than 4 h, maximum growth rates of 0.37–0.42 h−1 and final total cell counts of 1.5–1.8 × 106 cells mL−1) throughout several consecutive operational cycles. When the feed water changed, the adapted bacterial communities grew rapidly and proportionally to the amount of substrate in the new water source. Biofilm development in the permeate containers resulted in a 20% reduction in the overall cell production during five operational days, suggesting this to be a potential novel strategy towards controlling biological stability in such systems.
Randall, D. G., & Nathoo, J. (2015). A succinct review of the treatment of Reverse Osmosis brines using Freeze Crystallization. Journal of Water Process Engineering, 8, 186-194. doi:10.1016/j.jwpe.2015.10.005, Institutional Repository

In recent years, various Freeze Crystallization (FC) processes have been investigated and shown to have potential as an environmentally friendly and sustainable water treatment technology towards achieving a near zero waste by producing potable water and salts (in some instances pure salt(s)) from hyper-saline brines.
This paper reviews the history and current status of FC technologies for the treatment of Reverse Osmosis (RO) brines. A number of water treatment examples and applications of FC are discussed. The review found that, although the outcomes from the FC research are promising, the adoption of this technology in mainstream desalination brine treatment has been insignificant despite the fact that FC could have niche applications in the treatment of brines generated from membrane processes such as RO. The review also found that a hybrid technology approach, such as an integrated RO-FC process, can provide the optimum treatment solution from both an equipment capital and operating cost perspective. Lastly, the paper highlights future focus areas for research and development in the field of FC that aims at making this technology part of the mainstream suite of brine treatment technologies.
Ravndal, K. T., Künzle, R., Derlon, N., & Morgenroth, E. (2015). On-site treatment of used wash-water using biologically activated membrane bioreactors operated at different solids retention times. Journal of Water Sanitation and Hygiene for Development, 5(4), 544-552. doi:10.2166/washdev.2015.174, Institutional Repository

Biologically activated membrane bioreactors (BAMBis) were operated at suspended solids retention times (SRT) of 7 and 102 days and at full solids retention. The effect of these different approaches of operation on substrate and nutrient conversion, and on permeate flux was investigated. Variations in organic loads and aeration intensities were also studied. Permeate flux stabilized during long-term operation independently of suspended SRT. Removal of organic substrate was independent of solids concentrations and remained stable over the long term. Microorganisms colonizing the surface of particles were found as the main mechanism responsible for degradation of organic substrate in the particulate form. BAMBi appeared to be a robust technology, adapted to on-site treatment of used wash-water, as it can be operated without control of suspended SRT. Thus BAMBis can be operated for long periods without any control of biofouling and sludge formation, leading to low maintenance needs. When BAMBis were operated at low aeration, the formation of anoxic zones led to combined nitrification and denitrification and thus significant nitrogen removal.
Schielke-Jenni, S., Villez, K., Morgenroth, E., & Udert, K. M. (2015). Observability of anammox activity in single-stage nitritation/anammox reactors using mass balances. Environmental Science: Water Research and Technology, 1(4), 523-534. doi:10.1039/c5ew00045a, Institutional Repository

In nitritationammox reactors, several bacterial groups contribute to the overall nitrogen conversion. Knowing the activity of the main bacterial groups, especially of anaerobic ammonium-oxidising bacteria (AMX), is extremely helpful to understand the process and optimise its operation. Mass balances of dissolved compounds such as ammonium, nitrite and nitrate commonly allow the determination of bacterial activities in a nitritationammox process, but the activity of heterotrophic bacteria (HET) is usually neglected. However, even in wastewater with a low organic substrate content, heterotrophic denitrification can contribute substantially to nitrogen removal. The goal of this study was to critically evaluate the applicability of mass balances for the determination of the relevant bacterial activities in a nitritationammox process with high HET activity. We set up and solved mass balances of different degrees of complexity. Both linear equation systems, with catabolic reactions alone and with balances according to the activated sludge model stoichiometry, do not allow estimation of any of the considered bacterial activities. When kinetic rate expressions are included, it is possible to compute the concentrations of all considered bacterial groups, but the estimation uncertainty is far too high for practical purposes: the relative standard deviation for AMX is 5280%. In a completely autotrophic system, the relative standard deviation for AMX is only 5%, which proves that the high standard deviations are due to the complexity of the nitration–anammox process with HET activity. The high standard deviations of the calculated bacterial concentrations can be significantly reduced by adding an additional mass balance for the total biomass (standard deviation for AMX activity 1210%). The required number of measurements to achieve an acceptable precision, in our example about 600 conversion rate measurements to reach a 50% standard deviation for the AMX concentration, is still far too high though for practical purposes. To conclude, mass balances including kinetics theoretically allow the observation of the bacterial activities in nitritationammox reactors with high HET activity. However, the required precision of the calculated conversion rates, the uncertainty of stoichiometric and kinetic parameters and the reactor dynamics (unsteady conditions) make mass balances unsuitable for practical estimation of AMX activity. Due to high frequency and new online instruments, mass balances might become a suitable tool in the future.
Senn, A. C., Kaegi, R., Hug, S. J., Hering, J. G., Mangold, S., & Voegelin, A. (2015). Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in water at near-neutral pH: interdependent effects of phosphate, silicate and Ca. Geochimica et Cosmochimica Acta, 162, 220-246. doi:10.1016/j.gca.2015.04.032, Institutional Repository

We studied the interdependent effects of phosphate, silicate and Ca on the formation of Fe(III)-precipitates by oxidation of 0.5 mM Fe(II) in near-neutral bicarbonate-buffered aqueous solutions at concentrations relevant for natural water resources. Complementary results obtained by a suite of analytical techniques including X-ray absorption spectroscopy and transmission electron microscopy showed that the ratio of initially dissolved phosphate over Fe(II) ((P/Fe)init) had a major impact on precipitate formation. At (P/Fe)init above a critical ratio ((P/Fe)crit) of ∼0.5 in 8 mM NaHCO3 and ∼0.8 in 4 mM Ca(HCO3)2 electrolyte, Fe(II) oxidation led to exclusive formation of amorphous basic Fe(III)-phosphate or Ca–Fe(III)-phosphate ((Ca-)Fe(III)-phosphate) with maximum precipitate P/Fe ratios ((P/Fe)ppt) of ∼0.7 in Na and ∼1.1 in Ca electrolyte. Enhanced phosphate uptake in the presence of Ca was due to phosphate-Ca interactions coupled to Fe precipitation, mainly formation of mitridatite-like Ca–Fe(III)-phosphate polymers and Ca-phosphate polymers. At (P/Fe)init < (P/Fe)crit, in the absence of silicate, (Ca-)Fe(III)-phosphate precipitation was followed by the formation of poorly crystalline lepidocrocite and concomitant transformation of the (Ca-)Fe(III)-phosphate into a phosphate-rich ferrihydrite-type precipitate with a (P/Fe)ppt of ∼0.25. In the presence of 0.5 mM silicate, initially formed (Ca-)Fe(III)-phosphate nanoparticles became coated with silicate-rich ferrihydrite during continuing Fe(II) oxidation and only limited transformation of the (Ca-)Fe(III)-phosphate occurred. The results from this study indicate the complexity of Fe(III)-precipitate formation in the presence of interfering solutes and its consequences for precipitate structure and phosphate sequestration. The findings provide a solid basis for further studies of the reactivity of different Fe(III)-precipitate types and for the systematic assessment of their impact on Fe, phosphate and trace elements dynamics in natural and engineered systems.
Shen, Y., Monroy, G. L., Derlon, N., Janjaroen, D., Huang, C., Morgenroth, E., … Nguyen, T. H. (2015). Role of biofilm roughness and hydrodynamic conditions in legionella pneumophila adhesion to and detachment from simulated drinking water biofilms. Environmental Science and Technology, 49(7), 4274-4282. doi:10.1021/es505842v, Institutional Repository

Biofilms in drinking water distribution systems (DWDS) could exacerbate the persistence and associated risks of pathogenic Legionella pneumophila (L. pneumophila), thus raising human health concerns. However, mechanisms controlling adhesion and subsequent detachment of L. pneumophila associated with biofilms remain unclear. We determined the connection between L. pneumophila adhesion and subsequent detachment with biofilm physical structure characterization using optical coherence tomography (OCT) imaging technique. Analysis of the OCT images of multispecies biofilms grown under low nutrient condition up to 34 weeks revealed the lack of biofilm deformation even when these biofilms were exposed to flow velocity of 0.7 m/s, typical flow for DWDS. L. pneumophila adhesion on these biofilm under low flow velocity (0.007 m/s) positively correlated with biofilm roughness due to enlarged biofilm surface area and local flow conditions created by roughness asperities. The preadhered L. pneumophila on selected rough and smooth biofilms were found to detach when these biofilms were subjected to higher flow velocity. At the flow velocity of 0.1 and 0.3 m/s, the ratio of detached cell from the smooth biofilm surface was from 1.3 to 1.4 times higher than that from the rough biofilm surface, presumably because of the low shear stress zones near roughness asperities. This study determined that physical structure and local hydrodynamics control L. pneumophila adhesion to and detachment from simulated drinking water biofilm, thus it is the first step toward reducing the risk of L. pneumophila exposure and subsequent infections.
Thalmann, B., Voegelin, A., von Gunten, U., Behra, R., Morgenroth, E., & Kaegi, R. (2015). Effect of ozone treatment on nano-sized silver sulfide in wastewater effluent. Environmental Science and Technology, 49(18), 10911-10919. doi:10.1021/acs.est.5b02194, Institutional Repository

Silver nanoparticles used in consumer products are likely to be released into municipal wastewater. Transformation reactions, most importantly sulfidation, lead to the formation of nanoscale silver sulfide (nano-Ag2S) particles. In wastewater treatment plants (WWTP), ozonation can enhance the effluent quality by eliminating organic micropollutants. The effect of ozonation on the fate of nano-Ag2S, however, is currently unknown. In this study, we investigate the interaction of ozone with nano-Ag2S and evaluate the effect of ozonation on the short-term toxicity of WWTP effluent spiked with nano-Ag2S. The oxidation of nano-Ag2S by ozone resulted in a stoichiometric factor (number of moles of ozone required to oxidize one mole of sulfide to sulfate) of 2.91, which is comparable to the results obtained for the reaction of bisulfide (HS–) with ozone. The second-order rate constant for the reaction of nano-Ag2S with ozone (k = 3.1 × 104 M–1 s–1) is comparable to the rate constant of fast-reacting micropollutants. Analysis of the ozonation products of nano-Ag2S by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) revealed that ozonation dominantly led to the formation of silver chloride in WWTP effluent. After ozonation of the Ag2S-spiked effluent, the short-term toxicity for the green algae Chlamydomonas reinhardtii increased and reached EC50 values comparable to Ag+. This study thus reveals that ozone treatment of WWTP effluent results in the oxidation of Ag2S and, hence, an increase of the Ag toxicity in the effluent, which may become relevant at elevated Ag concentrations.
Thürlimann, C. M., Dürrenmatt, D. J., & Villez, K. (2015). Energy and process data processing and visualisation for optimising wastewater treatment plants. Water Practice and Technology, 10(1), 10-18. doi:10.2166/wpt.2015.002, Institutional Repository

For complex systems such as wastewater treatment plants (WWTPs), effective data communication is an important step to enable operators to assess their plant. However, examples in practice show that this step is insufficiently considered. In this article, we describe a fast, relevant, and intuitive decision-support tool for operators. We have developed a key performance indicator (KPI) visualisation tool for energy and process data embedded in a larger process optimisation software. The KPI set consists of indicator values relating to energy and effluent quality. In order to ensure that the visualisation tool will be used and cover the needs of the plant staff, we developed this part of the software in collaboration with two WWTPs. At the time of writing, the tool is used in the daily operation of both plants. The operators see the tool's most important advantages as its ability to quickly assess current plant performance and to simplify the tracking and analysis of inter- and intra-process relationships and dynamics.
Topuz, E., Traber, J., Sigg, L., & Talini, I. (2015). Agglomeration of Ag and TiO2 nanoparticles in surface and wastewater: role of calcium ions and of organic carbon fractions. Environmental Pollution, 204, 313-323. doi:10.1016/j.envpol.2015.05.034, Institutional Repository

This study aims to investigate factors leading to agglomeration of citrate coated silver (AgNP-Cit), polyvinylpyrrolidone coated AgNPPVP and titanium dioxide (TiO2) nanoparticles in surface waters and wastewater. ENPs (1 mg/L) were spiked to unfiltered, filtered, ultrafiltered (<10 kDa and <1 kDa) samples. Z-average particle sizes were measured after 1 h, 1 day and 1 week. AgNP-PVP was stable in all fractions of the samples and kept their original size around 60 nm over 1 week. Agglomeration of AgNP-Cit and TiO2 was positively correlated with Ca2+ concentration, but dissolved organic carbon concentrations > 2 mg/L contributed to stabilizing these NP. Moreover, agglomeration of AgNP-Cit in the various organic matter fractions showed that high molecular weight organic compounds such as biopolymers provide stabilization in natural water. A generalized scheme for the agglomeration behavior of AgNP-Cit, AgNP-PVP and TiO2 in natural waters was proposed based on their relation with Ca2+, Mg2+ and DOC concentration.
Udert, K. M., Buckley, C. A., Wächter, M., McArdell, C. S., Kohn, T., Strande, L., … Etter, B. (2015). Technologies for the treatment of source-separated urine in the eThekwini Municipality. Water SA, 41(2), 212-221. doi:10.4314/wsa.v41i2.06, Institutional Repository

In recent years, a large number of urine-diverting dehydration toilets (UDDTs) have been installed in eThekwini to ensure access to adequate sanitation. The initial purpose of these toilets was to facilitate faeces drying, while the urine was diverted into a soak pit. This practice can lead to environmental pollution, since urine contains high amounts of nutrients. Instead of polluting the environment, these nutrients should be recovered and used as fertiliser. In 2010 the international and transdisciplinary research project VUNA was initiated in order to explore technologies and management methods for better urine management in eThekwini. Three treatment technologies have been chosen for the VUNA project. The first is struvite precipitation, a technology which has already been tested in multiple projects on urine treatment. Struvite precipitation is a simple and fast process for phosphorus recovery. Other nutrients, such as nitrogen and potassium, remain in the effluent and pathogens are not completely inactivated. Therefore, struvite precipitation has to be combined with other treatment processes to prevent environmental pollution and hygiene risks. The second process is a combination of nitrification and distillation. This process combination is more complex than struvite precipitation, but it recovers all nutrients in one concentrated solution, ensures safe sanitisation and produces only distilled water and a small amount of sludge as by-products. The third process is electrolysis. This process could be used for very small on-site reactors, because conversion rates are high and the operation is simple, as long as appropriate electrodes and voltages are used. However, nitrogen is removed and not recovered and chlorinated by-products are formed, which can be hazardous for human health. While urine electrolysis requires further research in the laboratory, struvite precipitation and nitrification/distillation have already been operated at pilot scale.
Vannecke, T. P. W., Wells, G., Hubaux, N., Morgenroth, E., & Volcke, E. I. P. (2015). Considering microbial and aggregate heterogeneity in biofilm reactor models: how far do we need to go?. Water Science and Technology, 72(10), 1692-1699. doi:10.2166/wst.2015.389, Institutional Repository

A model describing a given system should be as simple as possible – but not simpler. The appropriate level of complexity depends both on the type of system and on the intended use of the model. This paper addresses the critical question of which purposes justify increased complexity of biofilm (reactor) models. Additional model features compared to conventional models considered are: (1) the inclusion of microbial diversity, distinguishing between different species performing the same function; and (2) the distinction between flocs and granules in putatively granular sludge reactors. With a multispecies model considering interspecies diversity, it was demonstrated that a given macroscopic reactor performance does not necessarily reflect steady state conditions on the microscale. In a second case study, it was shown that the addition of a small level of flocs can have a significant impact on macroscale process performance and on microbial population and activity distributions in granular sludge reactors. It was concluded that increased complexity in biofilm models, concerning microbial diversity or mesoscale aggregate architecture, is likely more useful when the focus is on understanding fundamental microscale outputs, but under specific conditions, these additional model features can be critically informative for bulk reactor behavior prediction and general understanding.
Villez, K. (2015). Qualitative path estimation: a fast and reliable algorithm for qualitative trend analysis. AICHE Journal, 61(5), 1535-1546. doi:10.1002/aic.14736, Institutional Repository

Fault detection and identification is challenged by a lack of detailed understanding of process dynamics under anomalous circumstances as well as a lack of historical data concerning rare events in a typical process. Qualitative trend analysis (QTA) techniques provide a way out by focusing on a coarse-grained representation of time series data. Such qualitative representations are valid in a larger set of operating conditions and thus provide a robust way to handle the detection and identification of rare events. Unfortunately, available methods fail when faced with moderate noise levels or result in rather large computational efforts. For this reason, this article provides a novel method for QTA. This leads to dramatic improvements in computational efficiency compared to the previously established shape constrained splines method while the accuracy remains high.
Wagner, J., Weissbrodt, D. G., Manguin, V., Ribeiro da Costa, R. H., Morgenroth, E., & Derlon, N. (2015). Effect of particulate organic substrate on aerobic granulation and operating conditions of sequencing batch reactors. Water Research, 85, 158-166. doi:10.1016/j.watres.2015.08.030, Institutional Repository

The formation and application of aerobic granules for the treatment of real wastewaters still remains challenging. The high fraction of particulate organic matter (XS) present in real wastewaters can affect the granulation process. The present study aims at understanding to what extent the presence of XS affects the granule formation and the quality of the treated effluent. A second objective was to evaluate how the operating conditions of an aerobic granular sludge (AGS) reactor must be adapted to overcome the effects of the presence of XS. Two reactors fed with synthetic wastewaters were operated in absence (R1) or presence (R2) of starch as proxy for XS. Different operating conditions were evaluated. Our results indicated that the presence of XS in the wastewater reduces the kinetic of granule formation. After 52 d of operation, the fraction of granules reached only 21% in R2, while in R1 this fraction was of 54%. The granules grown in presence of XS had irregular and filamentous outgrowths in the surface, which affected the settleability of the biomass and therefore the quality of the effluent. An extension of the anaerobic phase in R2 led to the formation of more compact granules with a better settling ability. A high fraction of granules was obtained in both reactors after an increase of the selection pressure for fast-settling biomass, but the quality of the effluent remained low. Operating the reactors in a simultaneous fill-and-draw mode at a low selection pressure for fast-settling biomass showed to be beneficial for substrate removal efficiency and for suppressing filamentous overgrowth. Average removal efficiencies for total COD, soluble COD, ammonium, and phosphate were 87 ± 4%, 95 ± 1%, 92 ± 10%, and 87 ± 12% for R1, and 72 ± 12%, 86 ± 5%, 71 ± 12%, and 77 ± 11% for R2, respectively. Overall our study demonstrates that the operating conditions of AGS reactors must be adapted according to the wastewater composition. When treating effluents that contain XS, the selection pressure should be significantly reduced.
Wall, S. K., Gross, J. J., Kessler, E. C., Villez, K., & Bruckmaier, R. M. (2015). Blood-derived proteins in milk at start of lactation: indicators of active or passive transfer. Journal of Dairy Science, 98(11), 7748-7756. doi:10.3168/jds.2015-9440, Institutional Repository

Colostrum has a different composition compared with milk in established lactation. This difference is in part due to the partially open blood-milk barrier, which, when closed, is designed to prevent the interdiffusion of blood and milk components. In the first days of lactation, α-lactalbumin (α-LA), a milk protein, is typically present in blood and several blood-derived proteins are also present in milk, such as IgG1, IgG2, serum albumin (SA), and lactate dehydrogenase (LDH). With the exception of IgG1, which is known to be transferred by active transcellular transport, the other proteins are thought to pass paracellularly through the temporarily open barrier. Along with an exchange of blood and milk components, somatic cell count (SCC) is typically high in colostrum. The decline of these proteins and SCC can be used as indicators to determine transcellular or paracellular transport. Two hypotheses were tested. The first hypothesis was that the decline curve for a protein or SCC would be the same as IgG1, indicating transcellular transport, or the decline curve would be different than IgG1, indicating paracellular transport. The second hypothesis was that the decline curves of SCC and all proteins that are thought to have paracellular transport would be the same. Ten Holstein cows were milked at 4 h after parturition, the next 5 consecutive milkings, and the afternoon milking on d 5, 8, 10, and 14 of lactation for a total of 10 milking time points, and sequential jugular blood samples were also taken. Blood and milk samples were analyzed for the concentrations of LDH, SA, IgG1, IgG2, and α-LA and milk samples were measured for SCC. Protein concentration and SCC curves were generated from all 10 time points and were evaluated using the tau time constant model to determine the rate of decline of the slope of each protein. When examining the first hypothesis, the concentration of IgG1 declined significantly faster in the milk than the proteins IgG2 and LDH, but declined at the same rate as SA. Immunoglobulin G1 also declined significantly faster than SCC and α-LA in plasma. The second hypothesis showed that IgG2, LDH, and SA in milk were declining at the same rate, but were declining significantly faster than SCC and α-LA in plasma. These results indicate that only active transcellular transport of IgG1 occurred, with a sharp decline at parturition, compared with IgG2, SA, LDH, α-LA, and SCC, which are likely following paracellular transport.
Wittmer, A., Heisele, A., McArdell, C. S., Böhler, M., Longree, P., & Siegrist, H. (2015). Decreased UV absorbance as an indicator of micropollutant removal efficiency in wastewater treated with ozone. Water Science and Technology, 71(7), 980-985. doi:10.2166/wst.2015.053, Institutional Repository

Ozone transforms various organic compounds that absorb light within the UV and visible spectra. UV absorbance can therefore be used to detect the transformation of chemicals during ozonation. In wastewater, decolourisation can be observed after ozonation. This study investigates the correlation of the UV absorbance difference between the ozonation inlet and outlet and the removal efficiency of micropollutants in wastewater. The absorbance at 254 and 366 nm was measured at the ozonation inlet and outlet, as was the concentration of 24 representative micropollutants and the dissolved organic carbon (DOC). The results clearly showed that the relative decrease of absorbance (ΔAbs) is positively correlated with the relative removal efficiency of micropollutants. We therefore suggest that UV absorbance can be used as a feedback control parameter to achieve optimal ozone dosage in wastewater treatment plants and to gain a fast insight into the process efficiency and stability of the ozonation.
Worms, I. A. M., Adenmatten, D., Miéville, P., Traber, J., & Slaveykova, V. I. (2015). Photo-transformation of pedogenic humic acid and consequences for Cd(II), Cu(II) and Pb(II) speciation and bioavailability to green microalga. Chemosphere, 138, 908-915. doi:10.1016/j.chemosphere.2014.10.093, Institutional Repository

Humic substances (HS) play key role in toxic metal binding and protecting aquatic microorganisms from metal-induced stress. Any environmental changes that could alter HS concentration and reactivity can be expected to modify metal complexation and thus affect metal speciation and bioavailability to microalgae. The present study explores the influence of increased solar irradiance on the chemical structures and molecular weight of Elliott soil humic acid (EHA) and the associated consequences for Cd(II), Cu(II) and Pb(II) complexation and intracellular metal content in microalga. The results demonstrate that high radiance doses induce an oxidation of EHA with a formation of low molecular weight acids, an increase of –OH and –COOH group abundance, and a drop in EHA hydrodynamic size and molecular weight. The photo-induced structural changes are accompanied with a release of metal from M–EHA complexes and narrowing their size distribution, which in turn results in an increase of the intracellular Cd, Cu and Pb contents in microalga Chlamydomonas reinhardtii in agreement with the measured free metal ions concentrations.
Zöllig, H., Fritzsche, C., Morgenroth, E., & Udert, K. M. (2015). Direct electrochemical oxidation of ammonia on graphite as a treatment option for stored source-separated urine. Water Research, 69, 284-294. doi:10.1016/j.watres.2014.11.031, Institutional Repository

Electrolysis can be a viable technology for ammonia removal from source-separated urine. Compared to biological nitrogen removal, electrolysis is more robust and is highly amenable to automation, which makes it especially attractive for on-site reactors. In electrolytic wastewater treatment, ammonia is usually removed by indirect oxidation through active chlorine which is produced in-situ at elevated anode potentials. However, the evolution of chlorine can lead to the formation of chlorate, perchlorate, chlorinated organic by-products and chloramines that are toxic. This study focuses on using direct ammonia oxidation on graphite at low anode potentials in order to overcome the formation of toxic by-products. With the aid of cyclic voltammetry, we demonstrated that graphite is active for direct ammonia oxidation without concomitant chlorine formation if the anode potential is between 1.1 and 1.6 V vs. SHE (standard hydrogen electrode). A comparison of potentiostatic bulk electrolysis experiments in synthetic stored urine with and without chloride confirmed that ammonia was removed exclusively by continuous direct oxidation. Direct oxidation required high pH values (pH > 9) because free ammonia was the actual reactant. In real stored urine (pH = 9.0), an ammonia removal rate of 2.9 ± 0.3 gN·m−2·d−1 was achieved and the specific energy demand was 42 Wh·gN−1 at an anode potential of 1.31 V vs. SHE. The measurements of chlorate and perchlorate as well as selected chlorinated organic by-products confirmed that no chlorinated by-products were formed in real urine. Electrode corrosion through graphite exfoliation was prevented and the surface was not poisoned by intermediate oxidation products. We conclude that direct ammonia oxidation on graphite electrodes is a treatment option for source-separated urine with three major advantages: The formation of chlorinated by-products is prevented, less energy is consumed than in indirect ammonia oxidation and readily available and cheap graphite can be used as the electrode material.
Zöllig, H., Remmele, A., Fritzsche, C., Morgenroth, E., & Udert, K. M. (2015). Formation of chlorination byproducts and their emission pathways in chlorine mediated electro-oxidation of urine on active and nonactive type anodes. Environmental Science and Technology, 49(18), 11062-11069. doi:10.1021/acs.est.5b01675, Institutional Repository

Chlorination byproducts (CBPs) are harmful to human health and the environment. Their formation in chlorine mediated electro-oxidation is a concern for electrochemical urine treatment. We investigated the formation of chlorate, perchlorate, and organic chlorination byproducts (OCBPs) during galvanostatic (10, 15, 20 mA·cm–2) electro-oxidation of urine on boron-doped diamond (BDD) and thermally decomposed iridium oxide film (TDIROF) anodes. In the beginning of the batch experiments, the production of perchlorate was prevented by competing active chlorine and chlorate formation as well as by direct oxidation of organic substances. Perchlorate was only formed at higher specific charges (>17 Ah·L–1 on BDD and >29 Ah·L–1 on TDIROF) resulting in chlorate and perchlorate being the dominant CBPs (>90% of initial chloride). BDD produced mainly short chained OCBPs (dichloromethane, trichloromethane, and tetrachloromethane), whereas longer chained OCBPs (1,2-dichloropropane and 1,2-dichloroethane) were more frequently found on TDIROF. The OCBPs were primarily eliminated by electrochemical stripping: On BDD, this pathway accounted for 40% (dichloromethane) to 100% (tetrachloromethane) and on TDIROF for 90% (1,2-dichloroethane) to 100% (trichloromethane) of what was produced. A post-treatment of the liquid as well as the gas phase should be foreseen if CBP formation cannot be prevented by eliminating chloride or organic substances in a pretreatment.
Zöllig, H., Morgenroth, E., & Udert, K. M. (2015). Inhibition of direct electrolytic ammonia oxidation due to a change in local pH. Electrochimica Acta, 165, 348-355. doi:10.1016/j.electacta.2015.02.162, Institutional Repository

Electrochemical ammonia oxidation has gained a lot of attention recently as an efficient method for ammonia removal from wastewater, for the use in ammonia-based fuel cells and the production of high purity hydrogen. Thermally decomposed iridium oxide films (TDIROF) have been shown to be catalytically active for direct ammonia oxidation in aqueous solutions if NH3 is present. However, the process was reported to be rapidly inhibited on TDIROF. Herein, we show that this fast inhibition of direct ammonia oxidation does not result from surface poisoning by adsorbed elemental nitrogen (Nads). Instead, we propose that direct ammonia oxidation and oxygen evolution can lead to a drop of the local pH at the electrode resulting in a low availability of the actual reactant, NH3. The hypothesis was tested with cyclic voltammetry (CV) experiments on stagnant and rotating disk electrodes (RDE). The CV experiments on the stagnant electrode revealed that the decrease of the ammonia oxidation peaks was considerably reduced by introducing an idle phase at open circuit potential between subsequent scans. Furthermore, the polarization of the TDIROF electrode into the hydrogen evolution region (HER) resulted in increased ammonia oxidation peaks in the following anodic scans which can be explained with an increased local pH after the consumption of protons in the HER. On the RDE, the ammonia oxidation peaks did not decrease in immediately consecutive scans. These findings would not be expected if surface poisoning was responsible for the fast inhibition but they are in good agreement with the proposed mechanism of pH induced limitation by the reactant, NH3. The plausibility of the mechanism was also supported by our numerical simulations of the processes in the Nernstian diffusion layer. The knowledge about this inhibition mechanism of direct ammonia oxidation is especially important for the design of electrochemical cells for wastewater treatment. The mechanism is not only valid for TDIROF but also for other electrodes because it is independent of the electrode material.
Chomiak, A., Mimoso, J., Koetzsch, S., Sinnet, B., Pronk, W., Derlon, N., & Morgenroth, E. (2014). Biofilm formation and permeate quality improvement in Gravity Driven Membrane ultrafiltration. Water Science and Technology: Water Supply, 14(2), 274-282. doi:10.2166/ws.2013.197, Institutional Repository

The effects of biofilm development on ultrafiltration membranes with regards to permeate stability and permeation rates were investigated using Gravity-Driven Membrane (GDM) filtration. The first part of the study aimed at evaluating the influence of the biofilm on permeate flux quality and quantity with regards to Assimilable Organic Carbon (AOC) degradation. In addition, two types of biological pre-treatments were evaluated: slow sand filtration and packed bed bio-reactor, compared to a control (no treatment). Biofilm formation helped to decrease the AOC content of permeate water, compared to the influent. Both pre-treatments additionally reduced AOC level in permeate and thus increased its biological stability, however none of the systems were able to guarantee microbiologically stable water. Removal of AOC before the GDM filtration reduced the biofilm growth potential, which in turn influenced its physical structure and enhanced the permeation rates. Influence of inorganic particle removal by pre-sedimentation and its effect on the biofilm structure was also studied. Pre-sedimentation of particle populations selected fine and homogenous particle fractions, which lead to the formation of a homogenous biofilm structure characterized by an increased hydraulic resistance. This was clearly visible between horizontally and vertically installed membranes where the latter ones had a significantly reduced flux despite lower deposited particle mass. Presence of larger, heterogeneous particle fractions counterbalanced the negative effects of the fine particles, which overall resulted in enhanced permeation rates.
Chomiak, A., Sinnet, B., Derlon, N., & Morgenroth, E. (2014). Inorganic particles increase biofilm heterogeneity and enhance permeate flux. Water Research, 64, 177-186. doi:10.1016/j.watres.2014.06.045, Institutional Repository

This study investigated the influence of inorganic particles on the hydraulic resistance of biofilm grown on membrane surface during low-pressure dead-end ultrafiltration. Gravity-driven ultrafiltration membrane systems were operated during several weeks without any flushing or cleaning. Smaller (kaolin d0.5 = 3.6 μm) or larger (kaolin with diatomaceous earth 50/50%, d0.5 = 18.1 μm) particles were added to pre-filtered creek water or to unfiltered creek water. It was demonstrated in both experiments that presence of finer particles in the feed water (kaolin) induced formation of compact and homogeneous biofilm structure. On the other hand presence of the larger particles (diatomite) helped to counterbalance the effect of fine particles due to the formation of more heterogeneous and permeable biofilm structure. The hydraulic resistance of biofilms formed with fine particles was significantly higher than the resistance of biofilm formed in (1) absence of any inorganic particles or (2) in presence of the mixed particle population. The membrane orientation (vertical or horizontal) determined which particles were accumulating at the membrane surface, with structural differences shown by Scanning Electron Microscopy (SEM). For vertical membranes, the larger particles were selectively removed due to sedimentation and did not contribute to the biofilm development. Thus the selection of smaller particles due to vertical membrane configuration negatively affected the biofilm structure and permeation rates, and such selective accumulation of fine particles should be avoided.
Derlon, N., Mimoso, J., Klein, T., Koetzsch, S., & Morgenroth, E. (2014). Presence of biofilms on ultrafiltration membrane surfaces increases the quality of permeate produced during ultra-low pressure gravity-driven membrane filtration. Water Research, 60, 164-173. doi:10.1016/j.watres.2014.04.045, Institutional Repository

This study evaluates the effect of the presence of biofilms on membrane surfaces on the quality of permeate produced during Gravity-driven membrane ultrafiltration. GDM ultrafiltration is applied to the decentralized production of drinking water. A second objective was to evaluate to what extent permeate quality is enhanced by pre-treating feed-water (using a packed bed biofilm reactor or a slow sand filter). The influence of the ageing of the biofilm on the permeate quality was evaluated and compared to the effect of virgin membranes. Permeate quality was evaluated in terms of Assimilable Organic Carbon (AOC) content and dissolved organic carbon fractions (e.g. biopolymers). Our results indicate that virgin ultrafiltration membrane remove a small fraction of the AOC and biopolymers (rejection <10%). The presence of a young and thin biofilm on the surface of the ultrafiltration membranes increases the permeate quality due to the degradation of AOC (>80%). However, over long-term the hydrolysis of the organic matter that accumulated on membrane surfaces increases the AOC content of the permeate, thus deteriorating the permeate quality. Pre-treatment of the feed-water help to control the biofilm accumulation and thus to limit the deterioration of the permeate quality. Permeate flux stabilised at average values of 7.5–8.9 L m−2 h−1. But the presence of pre-treatment helped to increase permeate flux (+12 and 19%, with the packed bed biofilm reactor and with the slow sand filter, respectively). Overall our study demonstrates that tolerating the presence of biofilm on membrane surface has a beneficial effect on the quality of permeate even if its quantity is decreased.
Duester, L., Burkhardt, M., Gutleb, A. C., Kaegi, R., Macken, A., Meermann, B., & von der Kammer, F. (2014). Toward a comprehensive and realistic risk evaluation of engineered nanomaterials in the urban water system. Frontiers in Chemistry, 2, 39 (6 pp.). doi:10.3389/fchem.2014.00039, Institutional Repository

The European COoperation in Science and Technology (COST) Action ES1205 on the transfer of Engineered Nano materials from wastewater Treatment and stormwatEr to Rivers (ENTER) aims to create and to maintain a trans European network among scientists. This perspective article delivers a brief overview on the status quo at the beginning of the project by addressing the following aspects on engineered nano materials (ENMs) in the urban systems: (1) ENMs that need to be considered on a European level; (2) uncertainties on production-volume estimations; (3) fate of selected ENMs during waste water transport and treatment; (4) analytical strategies for ENM analysis; (5) ecotoxicity of ENMs, and (6) future needs. These six step stones deliver the derivation of the position of the ES1205 network at the beginning of the projects runtime, by defining six fundamental aspects that should be considered in future discussions on risk evaluation of ENMs in urban water systems.
Dürrenmatt, D. J., & Wanner, O. (2014). A mathematical model to predict the effect of heat recovery on the wastewater temperature in sewers. Water Research, 48(1), 548-558. doi:10.1016/j.watres.2013.10.017, Institutional Repository

Raw wastewater contains considerable amounts of energy that can be recovered by means of a heat pump and a heat exchanger installed in the sewer. The technique is well established, and there are approximately 50 facilities in Switzerland, many of which have been successfully using this technique for years. The planning of new facilities requires predictions of the effect of heat recovery on the wastewater temperature in the sewer because altered wastewater temperatures may cause problems for the biological processes used in wastewater treatment plants and receiving waters. A mathematical model is presented that calculates the discharge in a sewer conduit and the spatial profiles and dynamics of the temperature in the wastewater, sewer headspace, pipe, and surrounding soil. The model was implemented in the simulation program TEMPEST and was used to evaluate measured time series of discharge and temperatures. It was found that the model adequately reproduces the measured data and that the temperature and thermal conductivity of the soil and the distance between the sewer pipe and undisturbed soil are the most sensitive model parameters. The temporary storage of heat in the pipe wall and the exchange of heat between wastewater and the pipe wall are the most important processes for heat transfer. The model can be used as a tool to determine the optimal site for heat recovery and the maximal amount of extractable heat.
Eggen, R. I. L., Hollender, J., Joss, A., Schärer, M., & Stamm, C. (2014). Reducing the discharge of micropollutants in the aquatic environment: the benefits of upgrading wastewater treatment plants. Environmental Science and Technology, 48(14), 7683-7689. doi:10.1021/es500907n, Institutional Repository

Micropollutants (MPs) as individual compounds or in complex mixtures are relevant for water quality and may trigger unwanted ecological effects. MPs originate from different point and diffuse sources and enter water bodies via different flow paths. Effluents from conventional wastewater treatment plants (WWTPs), in which various MPs are not or not completely removed, is one major source. To improve the water quality and avoid potential negative ecological effects by micropollutants, various measures to reduce the discharge should be taken. In this feature we discuss one of these measures; the benefits of upgrading WWTPs toward reduced MP loads and toxicities from wastewater effluents, using the recently decided Swiss strategy as an example. Based on (i) full-scale case studies using ozonation or powder activated carbon treatment, showing substantial reduction of MP discharges and concomitant reduced toxicities, (ii) social and political acceptance, (iii) technical feasibility and sufficient cost-effectiveness, the Swiss authorities recently decided to implement additional wastewater treatment steps as mitigation strategy to improve water quality. Since MPs are of growing global concern, the concepts and considerations behind the Swiss strategy are explained in this feature, which could be of use for other countries as well. It should be realized that upgrading WWTPs is not the only solution to reduce the discharge of MPs entering the environment, but is part of a broader, multipronged mitigation strategy.
Gogos, A., Kaegi, R., Zenobi, R., & Bucheli, T. D. (2014). Capabilities of asymmetric flow field-flow fractionation coupled to multi-angle light scattering to detect carbon nanotubes in soot and soil. Environmental Science: Nano, 1(6), 584-594. doi:10.1039/c4en00070f, Institutional Repository

Analytical detection and quantification of multi-walled carbon nanotubes (MWCNTs) in complex matrices such as soils is very challenging. In an initial approach to this task, we identify MWCNTs by making use of their different (e.g., rod-like) shape compared to other (native) soil particles and in particular soot, which is ubiquitously present in soils. A shape factor ρ, determined using asymmetric flow field-flow fractionation coupled to multi-angle light scattering (aF4-MALS), was used to discriminate MWCNTs of different aspect ratios, as well as mixtures of soot and MWCNTs, in pure suspensions. MALS results were additionally confirmed using automated electron microscopy image analysis. We then analyzed different soil types which consistently showed ρ-values that differed from pure MWCNTs. To test the performance of the method for MWCNT detection in such complex matrices, we conducted standard additions of a MWCNT as well as soot to an agricultural soil. Extracts from these MWCNT-spiked soils showed increased ρ-values compared to soot-spiked or native soil. The method detection limit for the MWCNT was 1.6 to 4.0 mg g−1 soil and lies within the range of commonly used black carbon quantification methods, but is much higher than any currently predicted environmental concentration. Additionally, the method is currently limited by a relatively narrow dynamic range of ρ. Despite these limitations, our results suggest that aF4-MALS provides specific shape information that may be linked to an actual MWCNT presence in soils. Further method improvement potential is outlined along different steps of the workflow.
Grass, R. N., Schälchli, J., Paunescu, D., Soellner, J. O. B., Kaegi, R., & Stark, W. J. (2014). Tracking trace amounts of submicrometer silica particles in wastewaters and activated sludge using silica-encapsulated DNA barcodes. Environmental Science and Technology Letters, 1(12), 484-489. doi:10.1021/ez5003506, Institutional Repository

Although silica particles are among the widest utilized engineered nanoparticles, the measurement of silica particles at low exposure concentrations is impeded by the high background concentrations of silicates in the environment. To circumvent this analytical limitation, we describe a new method for tracing submicrometer silica particles in water by the usage of silica particles fully encapsulating unique DNA codes. Because DNA can be detected at extremely low concentrations by quantitative polymerase chain reaction (PCR), the encapsulation of DNA in silica allows an indirect measure of the concentration of silica particles down to the sub-parts per billion range (micrograms per liter). To provide insight into the capability of this novel technology, we utilized DNA-loaded submicrometer silica particles to follow the fate of silica particles in the analytically most demanding biological stages of wastewater treatment solutions (activated sludge). At various initial particle concentrations ranging from 10 ppb (10 µg/L) to 10 ppm (10 mg/L) and under both aerobic and anoxic conditions, we are able to show that >97% of the particles were removed from the wastewater by incorporation into sludge biomass.
Gulkowska, A., Thalmann, B., Hollender, J., & Krauss, M. (2014). Nonextractable residue formation of sulfonamide antimicrobials: new insights from soil incubation experiments. Chemosphere, 107, 366-372. doi:10.1016/j.chemosphere.2013.12.093, Institutional Repository

Soil incubation experiments using 14C-labelled sulfamethazine were carried out to assess the factors governing its nonextractable residue (NER) formation via nucleophilic addition reactions. Circumstantial evidence on possible mechanisms of NER formation was derived from a selective manipulation of soil samples. The amount of quinones in soil available for nucleophilic addition was a limiting factor as indicated by (i) an (initial) increase of NER formation by adding quinone precursors or enhancing their formation by manganese oxide addition and (ii) a decrease of NER formation by limiting the formation of quinones under anaerobic conditions. A slow NER formation with time under aerobic conditions is likely caused by covalent bonding as well, because no slow NER formation phase was observed under anaerobic conditions.
Hiller, R. V., Bretscher, D., DelSontro, T., Diem, T., Eugster, W., Henneberger, R., … Brunner, D. (2014). Anthropogenic and natural methane fluxes in Switzerland synthesized within a spatially explicit inventory. Biogeosciences, 11(7), 1941-1959. doi:10.5194/bg-11-1941-2014, Institutional Repository

We present the first high-resolution (500 m × 500 m) gridded methane (CH4) emission inventory for Switzerland, which integrates 90 % of the national emission totals reported to the United Nations Framework Convention on Climate Change (UNFCCC) and recent CH4 flux studies conducted by research groups across Switzerland. In addition to anthropogenic emissions, we also include natural and semi-natural CH4 fluxes, i.e., emissions from lakes and reservoirs, wetlands, wild animals as well as uptake by forest soils. National CH4 emissions were disaggregated using detailed geostatistical information on source locations and their spatial extent and process- or area-specific emission factors. In Switzerland, the highest CH4 emissions in 2011 originated from the agricultural sector (150 Gg CH4 yr−1), mainly produced by ruminants and manure management, followed by emissions from waste management (15 Gg CH4 yr−1) mainly from landfills and the energy sector (12 Gg CH4 yr−1), which was dominated by emissions from natural gas distribution. Compared with the anthropogenic sources, emissions from natural and semi-natural sources were relatively small (6 Gg CH4 yr−1), making up only 3% of the total emissions in Switzerland. CH4 fluxes from agricultural soils were estimated to be not significantly different from zero (between −1.5 and 0 Gg CH4 yr−1), while forest soils are a CH4 sink (approx. −2.8 Gg CH4 yr−1), partially offsetting other natural emissions. Estimates of uncertainties are provided for the different sources, including an estimate of spatial disaggregation errors deduced from a comparison with a global (EDGAR v4.2) and an European (TNO/MACC) CH4 inventory. This new spatially explicit emission inventory for Switzerland will provide valuable input for regional-scale atmospheric modeling and inverse source estimation.
Jenni, S., Vlaeminck, S. E., Morgenroth, E., & Udert, K. M. (2014). Successful application of nitritation/anammox towastewater with elevated organic carbon to ammonia ratios. Water Research, 49, 316-326. doi:10.1016/j.watres.2013.10.073, Institutional Repository

The nitritation/anammox process has been mainly applied to high-strength nitrogenous wastewaters with very low biodegradable organic carbon content (<0.5g COD·g N–1). However, several wastewaters have biodegradable organic carbon to nitrogen (COD/N) ratios between 0.5 and 1.7g COD·g N–1 and thus, contain elevated amounts of organic carbon but not enough for heterotrophic denitrification. In this study, the influence of elevated COD/N ratios was studied on a nitritation/anammox process with suspended sludge. In a step-wise manner, the influent COD/N ratio was increased to 1.4g COD·g N–1 by supplementing digester supernatant with acetate. The increasing availability of COD led to an increase of the nitrogen removal efficiency from around 85% with pure digester supernatant to >95% with added acetate while the nitrogen elimination rate stayed constant (275 ± 40mg N·L–1·d–1). Anammox activity and abundance of anammox bacteria (AMX) were strongly correlated, and with increasing influent COD/N ratio both decreased steadily. At the same time, heterotrophic denitrification with nitrite and the activity of ammonia oxidising bacteria (AOB) gradually increased. Simultaneously, the sludge retention time (SRT) decreased significantly with increasing COD loading to about 15 d and reached critical values for the slowly growing AMX. When the SRT was increased by reducing biomass loss with the effluent, AMX activity and abundance started to rise again, while the AOB activity remained unaltered. Fluorescent in-situ hybridisation (FISH) showed that the initial AMX community shifted within only 40 d from a mixed AMX community to "Candidatus Brocadia fulgida" as the dominant AMX type with an influent COD/N ratio of 0.8 g COD·g N–1 and higher. "Ca. Brocadia fulgida" is known to oxidise acetate, and its ability to outcompete other types of AMX indicates that AMX participated in acetate oxidation. In a later phase, glucose was added to the influent instead of acetate. The new substrate composition did not significantly influence the nitrogen removal nor the AMX activity, and "Ca. Brocadia fulgida" remained the dominant type of AMX. Overall, this study showed that AMX can coexist with heterotrophic bacteria at elevated influent COD/N ratios if a sufficiently high SRT is maintained.
Kohler, E., Villiger, J., Posch, T., Derlon, N., Shabarova, T., Morgenroth, E., … Blom, J. F. (2014). Biodegradation of microcystins during gravity-driven membrane (GDM) ultrafiltration. PLoS One, 9(11), e111794 (9 pp.). doi:10.1371/journal.pone.0111794, Institutional Repository

Gravity-driven membrane (GDM) ultrafiltration systems require little maintenance: they operate without electricity at ultra-low pressure in dead-end mode and without control of the biofilm formation. These systems are already in use for water purification in some regions of the world where adequate treatment and distribution of drinking water is not readily available. However, many water bodies worldwide exhibit harmful blooms of cyanobacteria that severely lower the water quality due to the production of toxic microcystins (MCs). We studied the performance of a GDM system during an artificial Microcystis aeruginosa bloom in lake water and its simulated collapse (i.e., the massive release of microcystins) over a period of 21 days. Presence of live or destroyed cyanobacterial cells in the feed water decreased the permeate flux in the Microcystis treatments considerably. At the same time, the microbial biofilms on the filter membranes could successfully reduce the amount of microcystins in the filtrate below the critical threshold concentration of 1 µg L−1 MC for human consumption in three out of four replicates after 15 days. We found pronounced differences in the composition of bacterial communities of the biofilms on the filter membranes. Bacterial genera that could be related to microcystin degradation substantially enriched in the biofilms amended with microcystin-containing cyanobacteria. In addition to bacteria previously characterized as microcystin degraders, members of other bacterial clades potentially involved in MC degradation could be identified.
Lackner, S., Gilbert, E. M., Vlaeminck, S. E., Joss, A., Horn, H., & van Loosdrecht, M. C. M. (2014). Full-scale partial nitritation/anammox experiences – an application survey. Water Research, 55, 292-303. doi:10.1016/j.watres.2014.02.032, Institutional Repository

Partial nitritation/anammox (PN/A) has been one of the most innovative developments in biological wastewater treatment in recent years. With its discovery in the 1990s a completely new way of ammonium removal from wastewater became available. Over the past decade many technologies have been developed and studied for their applicability to the PN/A concept and several have made it into full-scale. With the perspective of reaching 100 full-scale installations in operation worldwide by 2014 this work presents a summary of PN/A technologies that have been successfully developed, implemented and optimized for high-strength ammonium wastewaters with low C:N ratios and elevated temperatures. The data revealed that more than 50% of all PN/A installations are sequencing batch reactors, 88% of all plants being operated as single-stage systems, and 75% for sidestream treatment of municipal wastewater. Additionally an in-depth survey of 14 full-scale installations was conducted to evaluate practical experiences and report on operational control and troubleshooting. Incoming solids, aeration control and nitrate built up were revealed as the main operational difficulties. The information provided gives a unique/new perspective throughout all the major technologies and discusses the remaining obstacles.
Lin, W. C., Villez, K. R. E., & Garcia, H. E. (2014). Experimental validation of a resilient monitoring and control system. Journal of Process Control, 24, 621-639. doi:10.1016/j.jprocont.2014.03.006, Institutional Repository

Complex, high performance, engineering systems have to be closely monitored and controlled to ensure safe operation and protect public from potential hazards. One of the main challenges in designing monitoring and control algorithms for these systems is that sensors and actuators may be malfunctioning due to malicious or natural causes. To address this challenge, this paper addresses a resilient monitoring and control (ReMAC) system by expanding previously developed resilient condition assessment monitoring systems and Kalman filter-based diagnostic methods and integrating them with a supervisory controller developed here. While the monitoring and diagnostic algorithms assess plant cyber and physical health conditions, the supervisory controller selects, from a set of candidates, the best controller based on the current plant health assessments. To experimentally demonstrate its enhanced performance, the developed ReMAC system is then used for monitoring and control of a chemical reactor with a water cooling system in a hardware-in-the-loop setting, where the reactor is computer simulated and the water cooling system is implemented by a machine condition monitoring testbed at Idaho National Laboratory. Results show that the ReMAC system is able to make correct plant health assessments despite sensor malfunctioning due to cyber attacks and make decisions that achieve best control actions despite possible actuator malfunctioning. Monitoring challenges caused by mismatches between assumed system component models and actual measurements are also identified for future work.
Martin, K. J., Bolster, D., Derlon, N., Morgenroth, E., & Nerenberg, R. (2014). Effect of fouling layer spatial distribution on permeate flux: a theoretical and experimental study. Journal of Membrane Science, 471, 130-137. doi:10.1016/j.memsci.2014.07.045, Institutional Repository

Fouling layers developing on membrane filters can display significant spatial heterogeneity (roughness), yet the effect of fouling layer spatial distribution on hydraulic resistance has not been studied systematically. We used simple flux models, based on Darcy's law, to assess the impact of spatial distribution on resistance and permeate flux. Our results show that, for a given mean fouling layer thickness, greater spatial heterogeneity could increase fluxes by over an order of magnitude. The degree of error depended on the membrane resistance, fouling layer permeability, and the characteristics of the spatial distribution. We developed 1-dimensional and 2-dimensional flow models, both considering spatial heterogeneity, to improve the accuracy of the conventional model. The proposed models were validated with experimental data from a gravity driven membrane filter with a fouling layer having a high degree of spatial heterogeneity. Accounting for spatial heterogeneity significantly improved the prediction of permeate flux.
Mašić, A., & Eberl, H. J. (2014). On optimization of substrate removal in a bioreactor with wall attached and suspended bacteria. Mathematical Biosciences and Engineering, 11(5), 1139-1166. doi:10.3934/mbe.2014.11.1139, Institutional Repository

We investigate the question of optimal substrate removal in a biofilm reactor with concurrent suspended growth, both with respect to the amount of substrate removed and with respect to treatment process duration. The water to be treated is fed externally from a buffer vessel to the treatment reactor. In the two-objective optimal control problem, the flow rate between the vessels is selected as the control variable. The treatment reactor is modelled by a system of three ordinary differential equations in which a two-point boundary value problem is embedded. The solution of the associated singular optimal control problem in the class of measurable functions is impractical to determine and infeasible to implement in real reactors. Instead, we solve the simpler problem to optimize reactor performance in the class of off-on functions, a choice that is motivated by the underlying biological process. These control functions start with an initial no-flow period and then switch to a constant flow rate until the buffer vessel is empty. We approximate the Pareto Front numerically and study the behaviour of the system and its dependence on reactor and initial data. Overall, the modest potential of control strategies to improve reactor performance is found to be primarily due to an initial transient period in which the bacteria have to adapt to the environmental conditions in the reactor, i.e. depends heavily on the initial state of the dynamic system. In applications, the initial state, however, is often unknown and therefore the efficiency of reactor optimization, compared to the uncontrolled system with constant flow rate, is limited.
McConville, J. R., Künzle, R., Messmer, U., Udert, K. M., & Larsen, T. A. (2014). Decision support for redesigning wastewater treatment technologies. Environmental Science and Technology, 48(20), 12238-12246. doi:10.1021/es501854x, Institutional Repository

This paper offers a methodology for structuring the design space for innovative process engineering technology development. The methodology is exemplified in the evaluation of a wide variety of treatment technologies for source-separated domestic wastewater within the scope of the Reinvent the Toilet Challenge. It offers a methodology for narrowing down the decision-making field based on a strict interpretation of treatment objectives for undiluted urine and dry feces and macroenvironmental factors (STEEPLED analysis) which influence decision criteria. Such an evaluation identifies promising paths for technology development such as focusing on space-saving processes or the need for more innovation in low-cost, energy-efficient urine treatment methods. Critical macroenvironmental factors, such as housing density, transportation infrastructure, and climate conditions were found to affect technology decisions regarding reactor volume, weight of outputs, energy consumption, atmospheric emissions, investment cost, and net revenue. The analysis also identified a number of qualitative factors that should be carefully weighed when pursuing technology development; such as availability of O&M resources, health and safety goals, and other ethical issues. Use of this methodology allows for coevolution of innovative technology within context constraints; however, for full-scale technology choices in the field, only very mature technologies can be evaluated.
Ni, B. J., Joss, A., & Yuan, Z. (2014). Modeling nitrogen removal with partial nitritation and anammox in one floc-based sequencing batch reactor. Water Research, 67, 321-329. doi:10.1016/j.watres.2014.09.028, Institutional Repository

Full-scale application of partial nitritation and anammox in a single floc-based sequencing batch reactor (SBR) has been achieved for high-rate nitrogen (N) removal, but mechanisms resulting in reliable operation are not well understood. In this work, a mathematical model was calibrated and validated to evaluate operating conditions that lead to out-competition of nitrite oxidizers (NOB) from the SBRs and allow to maintain high anammox activity during long-term operation. The validity of the model was tested using experimental data from two independent previously reported floc-based full-scale SBRs for N-removal via partial nitritation and anammox, with different aeration strategies at aeration phase (continuous vs. intermittent aeration). The model described the SBR cycle profiles and long-term dynamic data from the two SBR plants sufficiently and provided insights into the dynamics of microbial population fractions and N-removal performance. Ammonium oxidation and anammox reaction could occur simultaneously at DO range of 0.15–0.3 mg O2 L−1 at aeration phase under continuous aeration condition, allowing simplified process control compared to intermittent aeration. The oxygen supply beyond prompt depletion by ammonium oxidizers (AOB) would lead to the growth of NOB competing with anammox for nitrite. NOB could also be washed out of the system and high anammox fractions could be maintained by controlling sludge age higher than 40 days and DO at around 0.2 mg O2 L−1. Furthermore, the results suggest that N-removal in SBR occurs via both alternating nitritation/anammox and simultaneous nitritation/anammox, supporting an alternative strategy to improve N-removal in this promising treatment process, i.e., different anaerobic phases can be implemented in the SBR-cycle configuration.
Thalmann, B., Voegelin, A., Sinnet, B., Morgenroth, E., & Kaegi, R. (2014). Sulfidation kinetics of silver nanoparticles reacted with metal sulfides. Environmental Science and Technology, 48(9), 4885-4892. doi:10.1021/es5003378, Institutional Repository

Recent studies have documented that the sulfidation of silver nanoparticles (Ag-NP), possibly released to the environment from consumer products, occurs in anoxic zones of urban wastewater systems and that sulfidized Ag-NP exhibit dramatically reduced toxic effects. However, whether Ag-NP sulfidation also occurs under oxic conditions in the absence of bisulfide has not been addressed, yet. In this study we, therefore, investigated whether metal sulfides that are more resistant toward oxidation than free sulfide, could enable the sulfidation of Ag-NP under oxic conditions.
We reacted citrate-stabilized Ag-NP of different sizes (10–100 nm) with freshly precipitated and crystalline CuS and ZnS in oxygenated aqueous suspensions at pH 7.5. The extent of Ag-NP sulfidation was derived from the increase in dissolved Cu2+ or Zn2+ over time and linked with results from X-ray absorption spectroscopy (XAS) analysis of selected samples. The sulfidation of Ag-NP followed pseudo first-order kinetics, with rate coefficients increasing with decreasing Ag-NP diameter and increasing metal sulfide concentration and depending on the type (CuS and ZnS) and crystallinity of the reacting metal sulfide. Results from analytical electron microscopy revealed the formation of complex sulfidation patterns that seemed to follow preexisting subgrain boundaries in the pristine Ag-NP. The kinetics of Ag-NP sulfidation observed in this study in combination with reported ZnS and CuS concentrations and predicted Ag-NP concentrations in wastewater and urban surface waters indicate that even under oxic conditions and in the absence of free sulfide, Ag-NP can be transformed into Ag2S within a few hours to days by reaction with metal sulfides.
Tilley, E., Strande, L., Lüthi, C., Mosler, H. J., Udert, K. M., Gebauer, H., & Hering, J. G. (2014). Looking beyond technology: an integrated approach to water, sanitation and hygiene in low income countries. Environmental Science and Technology, 48(17), 9965-9970. doi:10.1021/es501645d, Institutional Repository
Voegelin, A., Kaegi, R., Berg, M., Nitzsche, K. S., Kappler, A., Lan, V. M., … Steininger, R. (2014). Solid-phase characterisation of an effective household sand filter for As, Fe and Mn removal from groundwater in Vietnam. Environmental Chemistry, 11(5), 566-578. doi:10.1071/EN14011, Institutional Repository

Household sand filters are widely used in Vietnam to remove As, Fe and Mn from anoxic groundwater used as a drinking water resource. To expand the mechanistic knowledge of the filter functioning, we investigated the bulk and micrometre-scale distribution of Fe, As, P and Mn and the speciation of Fe, Mn and As in a sand filter after 8 years of operation using bulk and micro-focussed X-ray fluorescence spectrometry (XRF) and X-ray absorption spectroscopy (XAS) and scanning electron microscopy coupled with energy dispersive X-ray detection (SEM-EDX). Effective oxygenation of the anoxic groundwater enables the oxidative removal of Fe, As and Mn in the filter sand. Our results show that Fe is retained in the filter as a 2-line ferrihydrite-like FeIII-precipitate that coats sand grains, and that As accumulates dominantly as pentavalent arsenate. The very close spatial correlation of accumulated As and P with Fe throughout the filter sand and down to the micrometre-scale and the effective Fe, P and As retention at an estimated average water residence time of only 30 min suggest that their uptake is governed by a combination of fast sorption reactions, surface-catalysed FeII oxidation and mediated AsIII co-oxidation. In contrast, Mn is retained in separate MnIV/III-(oxyhydr)oxide coatings and concretions, probably as a result of coupled surface-catalysed and microbial MnII oxidation. Silicate sorbed to the ferrihydrite-like FeIII-coatings inhibits their crystallisation and associated remobilisation of P and As. The periodic drainage and aeration of the filter favours the oxidation of any residual FeII and AsIII and the formation of dense Fe precipitates and may thereby contribute to effective filter operation over several years.
Weissbrodt, D. G., Shani, N., & Holliger, C. (2014). Linking bacterial population dynamics and nutrient removal in the granular sludge biofilm ecosystem engineered for wastewater treatment. FEMS Microbiology Ecology, 88(3), 579-595. doi:10.1111/1574-6941.12326, Institutional Repository

Intensive nutrient removal from wastewater in anaerobic-aerobic systems using granular sludge should rely on optimal balances at biofilm and microbial ecology levels. This study targets the impacts of reactor characteristics and fluctuations in operation conditions on nutrient removal and bacterial community structures by means of microbial and numerical ecology methods. The dynamics of both predominant and accompanying populations were investigated with high resolution on temporal and phylogenetic scales in two reactors operated during 5 months with synthetic wastewater. Multivariate analyses highlighted significant correlations from process to microbial scales in the first reactor, whereas nitrification and phosphorus removal might have been affected by oxygen mass transfer limitations with no impact at population level in the second system. The bacterial community continuum of the first reactor was composed of two major antagonistic Accumulibacter-Nitrosomonas-Nitrospira and Competibacter-Cytophaga-Intrasporangiaceae clusters that prevailed under conditions leading to efficient P- (> 95%) and N-removal (> 65%) and altered P- (< 90%) and N-removal (< 60%), respectively. A third cluster independent of performances was dominated by Xanthomonadaceae affiliates that were on average more abundant at 25 °C (31 ± 5%) than at 20 °C (22 ± 4%). Starting from the physiological traits of the numerous phylotypes identified, a conceptual model is proposed as a base for functional analysis in the granular sludge microbiome and for future investigations with complex real wastewater.
Wenk, C. B., Kaegi, R., & Hug, S. J. (2014). Factors affecting arsenic and uranium removal with zero-valent iron: laboratory tests with Kanchan-type iron nail filter columns with different groundwaters. Environmental Chemistry, 11(5), 547-557. doi:10.1071/EN14020, Institutional Repository

Zero-valent iron (ZVI)-based filters are able to remove arsenic and other pollutants from drinking water, but their performance depends on the form of ZVI, filter design, water composition and operating conditions. Kanchan filters use an upper bucket with ZVI in the form of commercial iron nails, followed by a sand filter, to remove arsenic and pathogens. We evaluated factors that influence the removal of arsenic and uranium with laboratory columns containing iron nails with six different synthetic groundwaters with 500 μg L–1 AsIII, 50 μg L–1 U, 2 mg L–1 B, and with 0 and 2 mg L–1 P (added as o-phosphate), 0.25 and 2.5 mM Ca, 3.2 and 8.3 mM HCO3–, at pH 7.0 and 8.4 over 30 days. During the first 10 days, As removal was 65–95 % and strongly depended on the water composition. As removal at pH 7.0 was better than at pH 8.4 and high P combined with low Ca decreased As removal. From 10–30 days, As removal decreased to 45–60 % with all columns. Phosphate, in combination with low Ca concentrations lowered As removal, but had a slightly positive effect in combination with high Ca concentrations. U removal was only 10–70 %, but showed similar trends. The drop in performance over time can be explained by decreasing release of iron to solution due to formation of layers of FeIII phases and calcite covering the iron surface. Mobile corrosion products contained ferrihydrite, Si-containing hydrous ferric oxides, and amorphous Fe–Si–P phases. Comparisons with another type of ZVI filter (SONO-filter) were used to evaluate filter design parameters. Higher ZVI surface areas and longer contact times should lead to satisfactory As removal with Kanchan-type filters.
Wunderlin, P., Dominguez, D., & Schärer, M. (2014). In Response: what are the challenges and prospects? A governmental perspective. Environmental Toxicology and Chemistry, 33(11), 2410-2411. doi:10.1002/etc.2716, Institutional Repository
Yang, Y., Doudrick, K., Bi, X., Hristovski, K., Herckes, P., Westerhoff, P., & Kaegi, R. (2014). Characterization of food-grade titanium dioxide: the presence of nanosized particles. Environmental Science and Technology, 48(11), 6391-6400. doi:10.1021/es500436x, Institutional Repository

Titanium dioxide (TiO2) is widely used in food products, which will eventually enter wastewater treatment plants and terrestrial or aquatic environments, yet little is known about the fraction of this TiO2 that is nanoscale, or the physical and chemical properties of TiO2 that influence its human and environmental fate or toxicity. Instead of analyzing TiO2 properties in complex food or environmental samples, we procured samples of food-grade TiO2 obtained from global food suppliers and then, using spectroscopic and other analytical techniques, quantified several parameters (elemental composition, crystal structure, size, and surface composition) that are reported to influence environmental fate and toxicity. Another sample of nano-TiO2 that is generally sold for catalytic applications (P25) and widely used in toxicity studies, was analyzed for comparison. Food-grade and P25 TiO2 are engineered products, frequently synthesized from purified titanium precursors, and not milled from bulk scale minerals. Nanosized materials were present in all of the food-grade TiO2 samples, and transmission electron microscopy showed that samples 1–5 contained 35, 23, 21, 17, and 19% of nanosized primary particles (<100 nm in diameter) by number, respectively (all primary P25 particles were <100 nm in diameter). Both types of TiO2 aggregated in water with an average hydrodynamic diameter of >100 nm. Food-grade samples contained phosphorus (P), with concentrations ranging from 0.5 to 1.8 mg of P/g of TiO2. The phosphorus content of P25 was below inductively coupled plasma mass spectrometry detection limits. Presumably because of a P-based coating detected by X-ray photoelectron spectroscopy, the ζ potential of the food-grade TiO2 suspension in deionized water ranged from −10 to −45 mV around pH 7, and the iso-electric point for food-grade TiO2 (2 (Si content of 0.026–0.062% and Al content of 0.0006–0.810%) was also different from the case for P25 and would influence the environmental fate of TiO2. X-ray diffraction analysis confirmed the presence of anatase and/or rutile in the food-grade materials, and although the presence of amorphous TiO2 could not be ruled out, it is unlikely on the basis of Raman analysis. The food-grade TiO2 was solar photoactive. Cationic dyes adsorbed more readily to food-grade TiO2 than P25, indicating very different potentials for interaction with organics in the environment. This research shows that food-grade TiO2 contains engineered nanomaterials with properties quite different from those of P25, which has previously been used in many ecotoxicity studies, and because food-grade TiO2 is more likely than P25 to enter the environment (i.e., potentially higher exposure levels), there is a need to design environmental (and human) fate and toxicity studies comparing food-grade to catalytic TiO2.
Baert, A., Villez, K., & Steppe, K. (2013). Automatic drought stress detection in grapevines without using conventional threshold values. Plant and Soil, 369(1), 439-452. doi:10.1007/s11104-013-1588-1, Institutional Repository

Aims. Because the water status of grapevines strongly affects the quality of the grapes and resulting wine, automated and early drought stress detection is important. Plant measurements are very promising for detecting drought stress, but strongly depend on microclimatic changes. Therefore, conventional stress detection methods require threshold values which define when plants start sensing drought stress. There is however no unique method to define these values. In this study, we propose two techniques that overcome this limitation.
Methods. Two statistical methods were used to automatically distinguish between drought and microclimate effects, based on a short preceding full-irrigated period to extract plant behaviour under normal conditions: Unfold Principal Component Analysis (UPCA) and Functional Unfold Principal Component Analysis (FUPCA). Both techniques aimed at detecting when measured sap flow rate or stem diameter variations in grapevine deviated from their normal behaviour due to drought stress.
Results. The models based on sap flow rate had some difficulties to detect stress on days with low atmospheric demands, while those based on stem diameter variations did not show this limitation, but ceased detecting stress when the stem diameter levelled off after a period of severe shrinkage. Nevertheless, stress was successfully detected with both approaches days before visible symptoms appeared.
Conclusions. UPCA and FUPCA based on plant indicators are therefore very promising for early stress detection.
Boehler, M., Bolzonella, D., Braguglia, C. M., Gallipoli, A., Gianico, A., Levantesi, C., … Mininni, G. (2013). Innovative treatment solutions for sewage sludge recovery on a FP7 project routes. Environmental Engineering and Management Journal, 12(S11), 11-14. , Institutional Repository

ROUTES is addressed to assess new routes in wastewater and sludge treatment focusing on three main objectives:
1. optimization of the sludge quality for agricultural use with the goal to produce a clean and full stabilized sludge through intensive stabilization processes with attention to a broad spectrum of parameters including micropollutants, pathogens and their indicators.
2. minimization of the sludge to be disposed by innovative technical solutions based on different approaches, either on the water or sludge treatment lines;
3. recovery of valuable resources before sludge disposal by producing a liquid fertilizer [(NH4)2SO4], biopolymers or optimizing methane production by anaerobic treatments.
Technical and economic assessment of the investigated techniques on laboratory and pilot scale were carried out in a typical benchmarking study. The whole set of data is then provided to the partner involved in environmental assessment where different impact categories are considered (global warming potential, acidification potential, eutrophication potential and photochemical ozone creation potential).
Chon, K., Lee, Y., Traber, J., & von Gunten, U. (2013). Quantification and characterization of dissolved organic nitrogen in wastewater effluents by electrodialysis treatment followed by size-exclusion chromatography with nitrogen detection. Water Research, 47(14), 5381-5391. doi:10.1016/j.watres.2013.06.019, Institutional Repository

Dissolved organic nitrogen (DON) can act as a precursor of nitrogenous disinfection byproducts during oxidative water treatment. Quantification and characterization of DON are still challenging for waters with high concentrations of dissolved inorganic nitrogen (DIN, including ammonia, nitrate and nitrite) relative to total dissolved nitrogen (TDN) due to the cumulative analytical errors of independently measured nitrogen species (i.e., DON = TDN − NO2− − NO3− − NH4+/NH3) and interference of DIN species to TDN quantification. In this study, a novel electrodialysis (ED)-based treatment for selective DIN removal was developed and optimized with respect to type of ion-exchange membrane, sample pH, and ED duration. The optimized ED method was then coupled with size-exclusion chromatography with organic carbon, UV, and nitrogen detection (SEC-OCD-ND) for advanced DON analysis in wastewater effluents. Among the tested ion-exchange membranes, the PC-AR anion- and CMT cation-exchange membranes showed the lowest DOC loss (1–7%) during ED treatment of a wastewater effluent at ambient pH (8.0). A good correlation was found between the decrease of the DIN/TDN ratio and conductivity. Therefore, conductivity has been adopted as a convenient way to determine the optimal duration of the ED treatment. In the pH range of 7.0–8.3, ED treatment of various wastewater effluents with the PC-AR/CMT membranes showed that the relative residual conductivity could be reduced to less than 0.50 (DIN removal >90%; DIN/TDN ratio ≤0.60) with lower DOC losses (6%) than the previous dialysis and nanofiltration methods (DOC loss >10%). In addition, the ED method is shorter (0.5 h) than the previous methods (>1–24 h). The relative residual conductivity was further reduced to ∼0.20 (DIN removal >95%; DIN/TDN ratio ≤0.35) by increasing the ED duration to 0.7 h (DOC loss = 8%) for analysis by SEC-OCD-ND, which provided new information on distribution and ratio of organic carbon and nitrogen in different molecular weight fractions of effluent organic matter.
Choubert, J. M., Rieger, L., Shaw, A., Copp, J., Spérandio, M., Sørensen, K., … Gillot, S. (2013). Rethinking wastewater characterisation methods for activated sludge systems - a position paper. Water Science and Technology, 67(11), 2363-2373. doi:10.2166/wst.2013.158, Institutional Repository

Increasingly stringent effluent limits and an expanding scope of model system boundaries beyond activated sludge has led to new modelling objectives and consequently to new and often more detailed modelling concepts. Nearly three decades after the publication of Activated Sludge Model No1 (ASM1), the authors believe it is time to re-evaluate wastewater characterisation procedures and targets. The present position paper gives a brief overview of state-of-the-art methods and discusses newly developed measurement techniques on a conceptual level. Potential future paths are presented including on-line instrumentation, promising measuring techniques, and mathematical solutions to fractionation problems. This is accompanied by a discussion on standardisation needs to increase modelling efficiency in our industry.
Derlon, N., Koch, N., Eugster, B., Posch, T., Pernthaler, J., Pronk, W., & Morgenroth, E. (2013). Activity of metazoa governs biofilm structure formation and enhances permeate flux during Gravity-Driven Membrane (GDM) filtration. Water Research, 47(6), 2085-2095. doi:10.1016/j.watres.2013.01.033, Institutional Repository

The impact of different feed waters in terms of eukaryotic populations and organic carbon content on the biofilm structure formation and permeate flux during Gravity-Driven Membrane (GDM) filtration was investigated in this study. GDM filtration was performed at ultra-low pressure (65 mbar) in dead-end mode without control of the biofilm formation. Different feed waters were tested (River water, pre-treated river water, lake water, and tap water) and varied with regard to their organic substrate content and their predator community. River water was manipulated either by chemically inhibiting all eukaryotes or by filtering out macrozoobenthos (metazoan organisms). The structure of the biofilm was characterized at the meso- and micro-scale using Optical Coherence Tomography (OCT) and Confocal Laser Scanning Microscopy (CLSM), respectively. Based on Total Organic Carbon (TOC) measurements, the river waters provided the highest potential for bacterial growth whereas tap water had the lowest. An increasing content in soluble and particulate organic substrate resulted in increasing biofilm accumulation on membrane surface. However, enhanced biofilm accumulation did not result in lower flux values and permeate flux was mainly influenced by the structure of the biofilm. Metazoan organisms (in particular nematodes and oligochaetes) built-up protective habitats, which resulted in the formation of open and spatially heterogeneous biofilms composed of biomass patches. In the absence of predation by metazoan organisms, a flat and compact biofilm developed. It is concluded that the activity of metazoan organisms in natural river water and its impact on biofilm structure balances the detrimental effect of a high biofilm accumulation, thus allowing for a broader application of GDM filtration. Finally, our results suggest that for surface waters with high particulate organic carbon (POC) content, the use of worms is suitable to enhance POC removal before ultrafiltration units.
Dürrenmatt, D. J., Del Giudice, D., & Rieckermann, J. (2013). Dynamic time warping improves sewer flow monitoring. Water Research, 47(11), 3803-3816. doi:10.1016/j.watres.2013.03.051, Institutional Repository

Successful management and control of wastewater and storm water systems requires accurate sewer flow measurements. Unfortunately, the harsh sewer environment and insufficient flow meter calibration often lead to inaccurate and biased data. In this paper, we improve sewer flow monitoring by creating redundant information on sewer velocity from natural wastewater tracers. Continuous water quality measurements upstream and downstream of a sewer section are used to estimate the travel time based on i) cross-correlation (XCORR) and ii) dynamic time warping (DTW). DTW is a modern data mining technique that warps two measured time series non-linearly in the time domain so that the dissimilarity between the two is minimized. It has not been applied in this context before. From numerical experiments we can show that DTW outperforms XCORR, because it provides more accurate velocity estimates, with an error of about 7% under typical conditions, at a higher temporal resolution. In addition, we can show that pre-processing of the data is important and that tracer reaction in the sewer reach is critical. As dispersion is generally small, the distance between the sensors is less influential if it is known precisely. Considering these findings, we tested the methods on a real-world sewer to check the performance of two different sewer flow meters based on temperature measurements. Here, we were able to detect that one of two flow meters was not performing satisfactorily under a variety of flow conditions. Although theoretical analyses show that XCORR and DTW velocity estimates contain systematic errors due to dispersion and reaction processes, these are usually small and do not limit the applicability of the approach.
Falås, P., Longrée, P., La Cour Jansen, J., Siegrist, H., Hollender, J., & Joss, A. (2013). Micropollutant removal by attached and suspended growth in a hybrid biofilm-activated sludge process. Water Research, 47(13), 4498-4506. doi:10.1016/j.watres.2013.05.010, Institutional Repository

Removal of organic micropollutants in a hybrid biofilm-activated sludge process was investigated through batch experiments, modeling, and full-scale measurements. Batch experiments with carriers and activated sludge from the same full-scale reactor were performed to assess the micropollutant removal rates of the carrier biofilm under oxic conditions and the sludge under oxic and anoxic conditions. Clear differences in the micropollutant removal kinetics of the attached and suspended growth were demonstrated, often with considerably higher removal rates for the biofilm compared to the sludge. For several micropollutants, the removal rates were also affected by the redox conditions, i.e. oxic and anoxic. Removal rates obtained from the batch experiments were used to model the micropollutant removal in the full-scale process. The results from the model and plant measurements showed that the removal efficiency of the process can be predicted with acceptable accuracy (±25%) for most of the modeled micropollutants. Furthermore, the model estimations indicate that the attached growth in hybrid biofilm-activated sludge processes can contribute significantly to the removal of individual compounds, such as diclofenac.
Guo, B., Zhang, Y., Yu, G., Lee, W. H., Jin, Y. S., & Morgenroth, E. (2013). Two-stage acidic-alkaline hydrothermal pretreatment of lignocellulose for the high recovery of cellulose and hemicellulose sugars. Applied Biochemistry and Biotechnology, 169(4), 1069-1087. doi:10.1007/s12010-012-0038-5, Institutional Repository

The focus of this work was to develop a combined acid and alkaline hydrothermal pretreatment of lignocellulose that ensures high recovery of both hexose and pentose. Dilute sulfuric acid and lime pretreatments were employed sequentially. Process performance was optimized in terms of catalyst concentration, retention time, and temperature using response surface methodology. Medium operational conditions in the acid stage and harsh conditions in the alkaline stage were desirable with optimal performance at 0.73 wt% H2SO4, 150 °C, 6.1 min in the first stage, and 0.024 g lime/g biomass, 202 °C, 30 min in the second stage. In comparison to single-stage pretreatments with high recovery of either glucose or xylose, two-stage process showed great promises with >80 % glucose and >70 % xylose recovery. In addition, the method greatly improved ethanol fermentation with yields up to 0.145 g/g Miscanthus, due to significantly reduced formation of inhibitory by-products such as weak acids, furans, and phenols. Supplementing biomimetic acids would further increase glucose yield by up to 15 % and xylose yield by 25 %.
Hofacker, A. F., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2013). Mercury mobilization in a flooded soil by incorporation into metallic copper and metal sulfide nanoparticles. Environmental Science and Technology, 47(14), 7739-7746. doi:10.1021/es4010976, Institutional Repository

Mercury is a highly toxic priority pollutant that can be released from wetlands as a result of biogeochemical redox processes. To investigate the temperature-dependent release of colloidal and dissolved Hg induced by flooding of a contaminated riparian soil, we performed laboratory microcosm experiments at 5, 14, and 23 °C. Our results demonstrate substantial colloidal Hg mobilization concomitant with Cu prior to the main period of sulfate reduction. For Cu, we previously showed that this mobilization was due to biomineralization of metallic Cu nanoparticles associated with suspended bacteria. X-ray absorption spectroscopy at the Hg LIII-edge showed that colloidal Hg corresponded to Hg substituting for Cu in the metallic Cu nanoparticles. Over the course of microbial sulfate reduction, colloidal Hg concentrations decreased but continued to dominate total Hg in the pore water for up to 5 weeks of flooding at all temperatures. Transmission electron microscopy (TEM) suggested that Hg became associated with Cu-rich mixed metal sulfide nanoparticles. The formation of Hg-containing metallic Cu and metal sulfide nanoparticles in contaminated riparian soils may influence the availability of Hg for methylation or volatilization processes and has substantial potential to drive Hg release into adjacent water bodies.
Hofacker, A. F., Voegelin, A., Kaegi, R., Weber, F. A., & Kretzschmar, R. (2013). Temperature-dependent formation of metallic copper and metal sulfide nanoparticles during flooding of a contaminated soil. Geochimica et Cosmochimica Acta, 103, 316-332. doi:10.1016/j.gca.2012.10.053, Institutional Repository

Riparian floodplains in temperate regions are affected by pronounced seasonal variations in soil and water temperature. This affects the rates and interplay of microbial and abiotic geochemical processes that control the fate of metals in contaminated floodplain soils, including potential release into surface and groundwater during periodic flooding. Here, we investigated how temperature affects chalcophile trace metal contaminants (Cu, Cd, Pb) upon flooding of a riparian soil contaminated by past mining activities. In soil microcosms incubated at 23, 14, and 5 °C, the reductive dissolution of Mn(III,IV) and Fe(III) (oxyhydr)oxides and the release of dissolved Mn2+ and Fe2+ were significantly slower and less intense at the lower temperatures, which was reflected in a decrease of trace metal mobilization via the dissolution of metal oxide sorbents and cation competition for sorption sites. The onset of sulfate reduction was significantly delayed at lower temperatures and the apparent rate of sulfate reduction was decreased, especially at 5 °C. This resulted in elevated high dissolved Cu, Cd, and Pb concentrations over weeks of flooding at 5 °C, whereas colloidal metal sulfide formation dominated Cu, Cd, and Pb pore water dynamics at higher temperatures of 14 and 23 °C due to fast sulfate reduction. Cu K-edge X-ray absorption fine structure spectroscopy revealed metallic Cu(0) as the main colloidal Cu species prior to sulfate reduction at all three temperatures. Analytical electron microscopy showed that Cu(0) particles were associated with suspended bacteria, suggesting biomineralization of Cu(0). Upon onset of sulfate reduction, metallic Cu particles were transformed into CuxS with incorporation of smaller amounts of Cd and Pb. Concomitantly, freely dispersed mixed Cu–Cd–Pb sulfide nanoparticles precipitated in the pore water. Other metals with higher metal sulfide solubility products did not react with the limited amounts of biogenic sulfide. The median size of the mixed metal sulfide nanoparticles increased from 21 nm at 23 °C to 70 nm at 5 °C. During ∼30 days of soil flooding at 23 and 14 °C, Cu speciation in the soil matrix changed from Cu(II) bound to soil organic matter in the oxic soil to 66% CuxS, with intermittent formation of about 14% metallic Cu(0). In contrast, at 5 °C, sulfate reduction and formation of Cu(0) were strongly retarded. After ∼30 days of flooding at 23 and 14 °C, nearly all Cd and about 25% of total Pb in the soil, were precipitated in mixed metal sulfides. Our results demonstrate that temperature controls trace metal dynamics during soil flooding via its influence on microbial reduction of terminal electron acceptors. Even at low temperatures, soil flooding may trigger the release of chalcophile metals from contaminated floodplain soils by sorbent reduction, competitive sorption, and formation of nanoparticulate metal-bearing colloids.
Hug, A., & Udert, K. M. (2013). Struvite precipitation from urine with electrochemical magnesium dosage. Water Research, 47(1), 289-299. doi:10.1016/j.watres.2012.09.036, Institutional Repository

When magnesium is added to source-separated urine, struvite (MgNH4PO4·6H2O) precipitates and phosphorus can be recovered. Up to now, magnesium salts have been used as the main source of magnesium. Struvite precipitation with these salts works well but is challenging in decentralized reactors, where high automation of the dosage and small reactor sizes are required. In this study, we investigated a novel approach for magnesium dosage: magnesium was electrochemically dissolved from a sacrificial magnesium electrode. We demonstrated that this process is technically simple and economically feasible and thus interesting for decentralized reactors. Linear voltammetry and batch experiments at different anode potentials revealed that the anode potential must be higher than −0.9 V vs. NHE (normal hydrogen electrode) to overcome the strong passivation of the anode. An anode potential of −0.6 V vs. NHE seemed to be suitable for active magnesium dissolution. For 13 subsequent cycles at this potential, we achieved an average phosphate removal rate of 3.7 mg P cm−2 h−1, a current density of 5.5 mA cm−2 and a current efficiency of 118%. Some magnesium carbonate (nesquehonite) accumulated on the anode surface; as a consequence, the current density decreased slightly, but the current efficiency was not affected. The energy consumption for these experiments was 1.7 W h g P−1. A cost comparison showed that sacrificial magnesium electrodes are competitive with easily soluble magnesium salts such as MgCl2 and MgSO4, but are more expensive than dosing with MgO. Energy costs for the electrochemical process were insignificant. Dosing magnesium electrochemically could thus be a worthwhile alternative to dosing magnesium salts. Due to the simple reactor and handling of magnesium, this may well be a particularly interesting approach for decentralized urine treatment.
Janjaroen, D., Ling, F., Monroy, G., Derlon, N., Morgenroth, E., Boppart, S. A., … Nguyen, T. H. (2013). Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces. Water Research, 47(7), 2531-2542. doi:10.1016/j.watres.2013.02.032, Institutional Repository

Mechanisms of Escherichia coli attachment on biofilms grown on PVC coupons were investigated. Biofilms were grown in CDC reactors using groundwater as feed solution over a period up to 27 weeks. Biofilm physical structure was characterized at the micro- and meso-scales using Scanning Electron Microscopy (SEM) and Optical Coherence Tomography (OCT), respectively. Microbial community diversity was analyzed with Terminal Restricted Fragment Length Polymorphism (T-RFLP). Both physical structure and microbial community diversity of the biofilms were shown to be changing from 2 weeks to 14 weeks, and became relatively stable after 16 weeks. A parallel plate flow chamber coupled with an inverted fluorescent microscope was also used to monitor the attachment of fluorescent microspheres and E. coli on clean PVC surfaces and biofilms grown on PVC surfaces for different ages. Two mechanisms of E. coli attachment were identified. The adhesion rate coefficients (kd) of E. coli on nascent PVC surfaces and 2-week biofilms increased with ionic strength. However, after biofilms grew for 8 weeks, the adhesion was found to be independent of solution chemistry. Instead, a positive correlation between kd and biofilm roughness as determined by OCT was obtained, indicating that the physical structure of biofilms could play an important role in facilitating the adhesion of E. coli cells.
Kaegi, R., Voegelin, A., Ort, C., Sinnet, B., Thalmann, B., Krismer, J., … Mueller, E. (2013). Fate and transformation of silver nanoparticles in urban wastewater systems. Water Research, 47(12), 3866-3877. doi:10.1016/j.watres.2012.11.060, Institutional Repository

Discharge of silver nanoparticles (Ag-NP) from textiles and cosmetics, todays major application areas for metallic Ag-NP, into wastewater is inevitable. Transformation and removal processes in sewers and wastewater treatment plants (WWTP) will determine the impact of Ag-NP on aquatic and terrestrial environments, via the effluents of the WWTP and via the use of digested sludge as fertilizer. We thus conducted experiments addressing the behavior of Ag-NP in sewers and in WWTP.
We spiked Ag-NP to a 5 km long main trunk sewer and collected 40 wastewater samples after 500 m, 2400 m and 5000 m each according to the expected travel times of the Ag-NP. Excellent mass closure of the Ag derived by multiplying the measured Ag concentrations times the volumetric flow rates indicate an efficient transport of the Ag-NP without substantial losses to the sewer biofilm. Ag-NP reacted with raw wastewater in batch experiments were sulfidized to roughly 15% after 5 h reaction time as revealed by X-ray absorption spectroscopy (XAS). However, acid volatile sulfide (AVS) concentrations were substantially higher in the sewer channel (100 μM) compared to the batch experiments (3 μM; still sufficient to sulfidize spiked 2 μM Ag) possibly resulting in a higher degree of sulfidation in the sewer channel. We further investigated the removal efficiency of 10 nm and 100 nm Ag- and gold (Au)-NP coated with citrate or polyvinylpyrrolidone in activated sludge batch experiments. We obtained very high removal efficiencies (∼99%) irrespective of size and coating for Ag- and Au-NP, the latter confirming that the particle type was of minor importance with respect to the degree of NP removal. We observed a strong size dependence of the sulfidation kinetics. We conclude that Ag-NP discharged to the wastewater stream will become sulfidized to various degrees in the sewer system and are efficiently transported to the WWTP. The sulfidation of the Ag-NP will continue in the WWTP, but primarily depending on the size the Ag-NP, may not be complete. Very high removal efficiencies in the WWTP will divert most of the Ag-NP mass flow to the digester and only a small fraction of the Ag will be released to surface waters.
Kaiser, H. P., Köster, O., Gresch, M., Périsset, P. M. J., Jäggi, P., Salhi, E., & von Gunten, U. (2013). Process control for ozonation systems: a novel real-time approach. Ozone: Science and Engineering, 35(3), 168-185. doi:10.1080/01919512.2013.772007, Institutional Repository

For real-time control of ozonation processes in water works, a sequencing batch reactor was constructed to measure the ozone decay rate constant (kO3) in short time intervals of about 15 min. The batch reactor is filled during the production process, immediately after dissolving ozone in water by a static mixer. On the basis of kO3 and the initial ozone concentration ([O3]0), and the experimentally determined ratio of the concentrations of ·OH radicals to ozone (Rct), the degradation of micropollutants in ozone reactors (modeled as Continuously Stirred Tank Reactors - CSTRs) were calculated for compounds with known reaction rate constants with ozone and ·OH radicals. Calculated degradation of atrazine, iopromide, benzotriazole and acesulfame are in good agreement with measured data. For acesulfame the following rate constants were determined in this study at 20 °C: reaction rate constant with ozone = 88 M−1s−1, reaction rate constant with ·OH radical = 4.55 × 109 M−1s−1. For the ozone reaction an activation energy of 35 kJ/mol was determined. Similarly to micropollutants, the relative inactivation of microorganisms (N/N0) can be calculated based on the inactivation rate constant for ozone and if applicable the lag phase. The pI-value (= −logN/N0) was introduced and implemented in the process management system to calculate online the log inactivation of reference microorganisms such as B. subtilis spores. The system was tested for variation of pH (6.5–8.5), DOC (1.2–4.2 mg/L) flowrate 3.2–12 m3/h and temperature (5.7–9 °C). Furthermore, a given pI-value, e.g. 1 for a 1-log inactivation of B. subtilis spores, can be set as control parameter in the process management system. The ozone gas flow is then adjusted until the set pI-value is reached. The process control concept was validated with B. subtilis spores. Generally, a good agreement was found between calculated and measured inactivation data. It was also demonstrated, that a constant ozone residual may lead to insufficient disinfection or overdosing of ozone. The new process control concept for ozonations based on onsite measurement of the ozone decay rate constant and the pI-value allows to assess disinfection and degradation processes quantitatively in real-time.
Kim, T. S., Jeong, J. Y., Wells, G. F., & Park, H. D. (2013). General and rare bacterial taxa demonstrating different temporal dynamic patterns in an activated sludge bioreactor. Applied Microbiology and Biotechnology, 97(4), 1755-1765. doi:10.1007/s00253-012-4002-7, Institutional Repository

Temporal variation of general and rare bacterial taxa was investigated using pyrosequencing of 16S rRNA gene from activated sludge samples collected bimonthly for a two-year period. Most of operational taxonomic units (OTUs) were allocated to rare taxa (89.6%), but the rare taxa comprised a small portion of the community in terms of abundance of sequences analyzed (28.6%). Temporal variations in OTUs richness significantly differed between the two taxa groups in which the rare taxa showed a higher diversity and a more fluctuating pattern than the general taxa. Furthermore, the two taxa groups were constrained by different explanatory variables: influent BOD, effluent BOD, and DO were the significant (P<0.05) parameters affecting the pattern of the general taxa, while temperature was the factor for the rare taxa. Over the test period, the general taxa persisted for a longer time (i.e., lower turnover rate) in the bioreactor than the rare taxa. In conclusion, this study demonstrated clear differences in temporal dynamic patterns for the general and rare bacterial taxa in an activated sludge bioreactor, which would be a foundation for better understanding the bacterial ecology of activated sludge.
Kovalova, L., Siegrist, H., von Gunten, U., Eugster, J., Hagenbuch, M., Wittmer, A., … McArdell, C. S. (2013). Elimination of micropollutants during post-treatment of hospital wastewater with powdered activated carbon, ozone, and UV. Environmental Science and Technology, 47(14), 7899-7908. doi:10.1021/es400708w, Institutional Repository

A pilot-scale hospital wastewater treatment plant consisting of a primary clarifier, membrane bioreactor, and five post-treatment technologies including ozone (O3), O3/H2O2, powdered activated carbon (PAC), and low pressure UV light with and without TiO2 was operated to test the elimination efficiencies for 56 micropollutants. The extent of the elimination of the selected micropollutants (pharmaceuticals, metabolites and industrial chemicals) was successfully correlated to physical-chemical properties or molecular structure. By mass loading, 95% of all measured micropollutants in the biologically treated hospital wastewater feeding the post-treatments consisted of iodinated contrast media (ICM). The elimination of ICM by the tested post-treatment technologies was 50–65% when using 1.08 g O3/gDOC, 23 mg/L PAC, or a UV dose of 2400 J/m2 (254 nm). For the total load of analyzed pharmaceuticals and metabolites excluding ICM the elimination by ozonation, PAC, and UV at the same conditions was 90%, 86%, and 33%, respectively. Thus, the majority of analyzed substances can be efficiently eliminated by ozonation (which also provides disinfection) or PAC (which provides micropollutants removal, not only transformation). Some micropollutants recalcitrant to those two post-treatments, such as the ICM diatrizoate, can be substantially removed only by high doses of UV (96% at 7200 J/m2). The tested combined treatments (O3/H2O2 and UV/TiO2) did not improve the elimination compared to the single treatments (O3 and UV).
Margot, J., Kienle, C., Magnet, A., Weil, M., Rossi, L., de Alencastro, L. F., … Barry, D. A. (2013). Treatment of micropollutants in municipal wastewater: ozone or powdered activated carbon?. Science of the Total Environment, 461-462, 480-498. doi:10.1016/j.scitotenv.2013.05.034, Institutional Repository

Many organic micropollutants present in wastewater, such as pharmaceuticals and pesticides, are poorly removed in conventional wastewater treatment plants (WWTPs). To reduce the release of these substances into the aquatic environment, advanced wastewater treatments are necessary. In this context, two large-scale pilot advanced treatments were tested in parallel over more than one year at the municipal WWTP of Lausanne, Switzerland. The treatments were: i) oxidation by ozone followed by sand filtration (SF) and ii) powdered activated carbon (PAC) adsorption followed by either ultrafiltration (UF) or sand filtration. More than 70 potentially problematic substances (pharmaceuticals, pesticides, endocrine disruptors, drug metabolites and other common chemicals) were regularly measured at different stages of treatment. Additionally, several ecotoxicological tests such as the Yeast Estrogen Screen, a combined algae bioassay and a fish early life stage test were performed to evaluate effluent toxicity. Both treatments significantly improved the effluent quality. Micropollutants were removed on average over 80% compared with raw wastewater, with an average ozone dose of 5.7 mg O3 l−1 or a PAC dose between 10 and 20 mg l−1. Depending on the chemical properties of the substances (presence of electron-rich moieties, charge and hydrophobicity), either ozone or PAC performed better. Both advanced treatments led to a clear reduction in toxicity of the effluents, with PAC-UF performing slightly better overall. As both treatments had, on average, relatively similar efficiency, further criteria relevant to their implementation were considered, including local constraints (e.g., safety, sludge disposal, disinfection), operational feasibility and cost. For sensitive receiving waters (drinking water resources or recreational waters), the PAC-UF treatment, despite its current higher cost, was considered to be the most suitable option, enabling good removal of most micropollutants and macropollutants without forming problematic by-products, the strongest decrease in toxicity and a total disinfection of the effluent.
Morales, N., Boehler, M. A., Buettner, S., Liebi, C., & Siegrist, H. (2013). Recovery of N and P from urine by struvite precipitation followed by combined stripping with digester sludge liquid at full scale. Water, 5(3), 1262-1278. doi:10.3390/w5031262, Institutional Repository

A novel ammonia stripping method, including a CO2 pre-stripper was used to treat a mix of supernatant liquor from an anaerobic digester and urine in order to recycle nitrogen as ammonium sulfate at full-scale in the WWTP Kloten/Opfikon. Waste streams were not generated, since the ammonia was recovered as a marketable nitrogen fertilizer, turning a waste product into a valuable product. The efficiency of this system was increased by means of the addition of pre-treated urine collected separately at EAWAG building. The separation step was performed by the use of water free urinals and urine diversion flush toilets. An increase of 10% in the liquid flux with the addition of the urine translated into a 40% increase of the ammonia concentration in the inlet of the stripping unit. The achievement of these percentages generated a proportional increase in the fertilizer production. The urine pre-treatment was carried out by adding magnesium to produce a precipitate of struvite. The first experiments with the combined treatment showed the feasibility of the combination of the separation and pre-treatment steps.
Neumann, A., Kaegi, R., Voegelin, A., Hussam, A., Munir, A. K. M., & Hug, S. J. (2013). Arsenic removal with composite iron matrix filters in Bangladesh: a field and laboratory study. Environmental Science and Technology, 47(9), 4544-4554. doi:10.1021/es305176x, Institutional Repository

The main arsenic mitigation measures in Bangladesh, well-switching and deep tube wells, have reduced As exposure, but water treatment is important where As-free water is not available. Zero-valent iron (ZVI) based SONO household filters, developed in Bangladesh, remove As by corrosion of locally available inexpensive surplus iron and sand filtration in two buckets. We investigated As removal in SONO filters in the field and laboratory, covering a range of typical groundwater concentrations (in mg/L) of As (0.14–0.96), Fe (0–17), P (0–4.4), Ca (45–162), and Mn (0–2.8). Depending on influent Fe(II) concentrations, 20–80% As was removed in the top sand layer, but As removal to safe levels occurred in the ZVI-layer of the first bucket. Residual As, Fe, and Mn were removed after re-aeration in the sand of the second bucket. New and over 8-year-old filters removed As to <50 μg/L and mostly to <10 μg/L and Mn to <0.2 mg/L. Vertical concentration profiles revealed formation of Fe(II) by corrosion of Fe(0) with O2 and incorporation of As into forming amorphous Fe phases in the composite iron matrix (CIM) of newer filters and predominantly magnetite in older filters. As mass balances indicated that users filtered less than reported volumes of water, pointing to the need for more educational efforts. All tested SONO filters provided safe drinking water without replacement for up to over 8 years of use.
Perona, P., Dürrenmatt, D. J., & Characklis, G. W. (2013). Obtaining natural-like flow releases in diverted river reaches from simple riparian benefit economic models. Journal of Environmental Management, 118, 161-169. doi:10.1016/j.jenvman.2013.01.010, Institutional Repository

We propose a theoretical river modeling framework for generating variable flow patterns in diverted-streams (i.e., no reservoir). Using a simple economic model and the principle of equal marginal utility in an inverse fashion we first quantify the benefit of the water that goes to the environment in relation to that of the anthropic activity. Then, we obtain exact expressions for optimal water allocation rules between the two competing uses, as well as the related statistical distributions. These rules are applied using both synthetic and observed streamflow data, to demonstrate that this approach may be useful in 1) generating more natural flow patterns in the river reach downstream of the diversion, thus reducing the ecodeficit; 2) obtaining a more enlightened economic interpretation of Minimum Flow Release (MFR) strategies, and; 3) comparing the long-term costs and benefits of variable versus MFR policies and showing the greater ecological sustainability of this new approach.
Schwyzer, I., Kaegi, R., Sigg, L., & Nowack, B. (2013). Colloidal stability of suspended and agglomerate structures of settled carbon nanotubes in different aqueous matrices. Water Research, 47(12), 3910-3920. doi:10.1016/j.watres.2013.01.057, Institutional Repository

Carbon nanotubes (CNTs) are often processed in suspended form and therefore a release of CNT-suspensions into the aquatic environment is plausible. In this study, the behaviour of two physico-chemically very different CNT types in the presence of varying, environmentally relevant calcium-containing media was investigated, including the long-term colloidal stability and the sedimentary structures of settled CNTs. Calcium induced CNT flocculation, however, the stability of the CNTs in the medium did not monotonously decrease with increasing calcium concentration. At intermediate calcium concentrations (0.5–1.5 mM Ca) pre-dispersed CNTs were stabilized in humic acid medium to similar, temporarily even to higher degree than in the absence of calcium. Between pH 5 and 8 only at the highest pH an influence on CNT stability was observed by either promoting flocculation or stabilisation depending on the CNT type. Humic acid stabilized CNTs much better than fulvic acid. Generally, the colloidal stability of the long, thick CNTs with higher surface oxygen content was less affected by the media composition.
An investigation of the settled CNT material using analytical electron microscopy revealed the presence of spheroidal, bundle-like and net like CNT-agglomerate structures. Calcium possibly acted as bridging agent linking CNTs in a network like manner, temporarily increasing the CNT concentrations stabilized in the supernatants due to the low density of these structures. With increasing settling time the CNTs formed a fluffy sediment layer at the bottom of the reaction vessels. Bundle-like CNT agglomerates were also observed within that layer of settled CNTs, possibly caused by calcium neutralizing the surface charges. Furthermore, the CNT suspensions contained spheroidal CNT agglomerates, most likely residues from the original dry powder that were not disaggregated. The analysis of settled CNT material is a novelty and illustrates CNT agglomerate structures possibly accumulating in the sediments of aquatic systems subsequent to CNT emissions.
Stewart, T. J., Traber, J., Kroll, A., Behra, R., & Sigg, L. (2013). Characterization of extracellular polymeric substances (EPS) from periphyton using liquid chromatography-organic carbon detection–organic nitrogen detection (LC-OCD-OND). Environmental Science and Pollution Research, 20(5), 3214-3223. doi:10.1007/s11356-012-1228-y, Institutional Repository

A protocol was developed to extract, fractionate, and quantitatively analyze periphyton extracellular polymeric substances (EPS), which obtains both information on the molecular weight (Mr) distribution and protein and polysaccharide content. The EPS were extracted from freshwater periphyton between July and December 2011. Organic carbon (OC) compounds from different EPS extracts were analyzed using liquid chromatography-organic carbon detection–organic nitrogen detection (LC-OCD-OND), and total protein and polysaccharide content were quantified. Four distinct OC fractions, on the basis of Mr, were identified in all extracts, corresponding to high Mr biopolymers (≥80–4 kDa), degradation products of humic substances (Mr not available), low Mr acids (10–0.7 kDa), and small amphiphilic/neutral compounds (3–0.5 kDa). Low C/N ratios (4.3 ± 0.8) were calculated for the biopolymer fractions, which represented 16–38 % of the measured dissolved organic carbon (DOC), indicating a significant presence of high Mr proteins in the EPS. Protein and polysaccharide represented the two major components of EPS and, when combined, accounted for the measured DOC in extracts. Differences in specific OC fractions of EPS extracts over the course of the study could be quantified using this method. This study suggests that LC-OCD-OND is a new valuable tool in EPS characterization of periphyton.
Villez, K., Venkatasubramanian, V., & Rengaswamy, R. (2013). Generalized shape constrained spline fitting for qualitative analysis of trends. Computers and Chemical Engineering, 58, 116-134. doi:10.1016/j.compchemeng.2013.06.005, Institutional Repository

In this work, we present a generalized method for analysis of data series based on shape constraint spline fitting which constitutes the first step toward a statistically optimal method for qualitative analysis of trends. The presented method is based on a branch-and-bound (B&B) algorithm which is applied for globally optimal fitting of a spline function subject to shape constraints. More specifically, the B&B algorithm searches for optimal argument values in which the sign of the fitted function and/or one or more of its derivatives change. We derive upper and lower bounding procedures for the B&B algorithm to efficiently converge to the global optimum. These bounds are based on existing solutions for shape constraint spline estimation via Second Order Cone Programs (SOCPs). The presented method is demonstrated with three different examples which are indicative of both the strengths and weaknesses of this method.
Voegelin, A., Senn, A. C., Kaegi, R., Hug, S. J., & Mangold, S. (2013). Dynamic Fe-precipitate formation induced by Fe(II) oxidation in aerated phosphate-containing water. Geochimica et Cosmochimica Acta, 117, 216-231. doi:10.1016/j.gca.2013.04.022, Institutional Repository

We studied the effect of phosphate on the precipitation of Fe during the oxidation of 1 mM Fe(II) in aerated 8 mM NaHCO3–CO2 buffered aqueous solutions at near-neutral pH. The structure and morphology of the precipitates were analyzed by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe K-edge, and transmission electron microscopy (TEM). Up to an initial dissolved P/Fe ratio of ∼0.55, most phosphate was incorporated into the fresh Fe(III)-precipitates. At dissolved P/Fe ratios from 0.55 to 1.91, the precipitate P/Fe ratios only exhibited a minor increase from 0.56 to 0.72. XRD patterns and Fe EXAFS spectra indicated a shift in precipitate type from mostly poorly-crystalline lepidocrocite in the absence of phosphate to amorphous Fe(III)–phosphate (mostly monomeric and oligomeric Fe(III) coordinated with phosphate) at dissolved P/Fe ratios >0.55. A time-resolved oxidation experiment at an initial dissolved P/Fe ratio of 0.29 revealed that amorphous Fe(III)–phosphate formed during Fe(II) oxidation until phosphate was nearly depleted from solution. During continuing Fe(II) oxidation, about half of the newly formed Fe(III) contributed to the polymerization of Fe–phosphate into phosphate-rich hydrous ferric oxide with a maximum P/Fe ratio of 0.25 (HFO-P; edge-sharing linkage of Fe(III) octahedra) and about half precipitated as poorly-crystalline lepidocrocite in the phosphate-depleted solution. At initial P/Fe ratios <0.2, initially formed Fe(III)–phosphate was fully transformed into HFO-P during continuing Fe(II) oxidation. The dynamic interactions between phosphate and Fe described in this study impact the structure of fresh Fe(III)-precipitates at redox transitions in environmental and technical systems. The modulating effects of other dissolved species such as silicate and Ca on Fe precipitate formation and implications for co-transformed trace elements require further study.
Weissbrodt, D. G., Neu, T. R., Kuhlicke, U., Rappaz, Y., & Holliger, C. (2013). Assessment of bacterial and structural dynamics in aerobic granular biofilms. Frontiers in Microbiology, 4, 175 (18 pp.). doi:10.3389/fmicb.2013.00175, Institutional Repository

Aerobic granular sludge (AGS) is based on self-granulated flocs forming mobile biofilms with a gel-like consistence. Bacterial and structural dynamics from flocs to granules were followed in anaerobic-aerobic sequencing batch reactors (SBR) fed with synthetic wastewater, namely a bubble column (BC-SBR) operated under wash-out conditions for fast granulation, and two stirred-tank enrichments of Accumulibacter (PAO-SBR) and Competibacter (GAO-SBR) operated at steady-state. In the BC-SBR, granules formed within 2 weeks by swelling of Zoogloea colonies around flocs, developing subsequently smooth zoogloeal biofilms. However, Zoogloea predominance (37–79%) led to deteriorated nutrient removal during the first months of reactor operation. Upon maturation, improved nitrification (80–100%), nitrogen removal (43–83%), and high but unstable dephosphatation (75–100%) were obtained. Proliferation of dense clusters of nitrifiers, Accumulibacter, and Competibacter from granule cores outwards resulted in heterogeneous bioaggregates, inside which only low abundance Zoogloea (<5%) were detected in biofilm interstices. The presence of different extracellular glycoconjugates detected by fluorescence lectin-binding analysis showed the complex nature of the intracellular matrix of these granules. In the PAO-SBR, granulation occurred within two months with abundant and active Accumulibacter populations (56 ± 10%) that were selected under full anaerobic uptake of volatile fatty acids and that aggregated as dense clusters within heterogeneous granules. Flocs self-granulated in the GAO-SBR after 480 days during a period of over-aeration caused by biofilm growth on the oxygen sensor. Granules were dominated by heterogeneous clusters of Competibacter (37 ± 11%). Zoogloea were never abundant in biomass of both PAO- and GAO-SBRs. This study showed that Zoogloea, Accumulibacter, and Competibacter affiliates can form granules, and that the granulation mechanisms rely on the dominant population involved.
Wunderlin, P., Lehmann, M. F., Siegrist, H., Tuzson, B., Joss, A., Emmenegger, L., & Mohn, J. (2013). Isotope signatures of N2O in a mixed microbial population system: constraints on N2O producing pathways in wastewater treatment. Environmental Science and Technology, 47(3), 1339-1348. doi:10.1021/es303174x, Institutional Repository

We present measurements of site preference (SP) and bulk 15N/14N ratios (δ15NbulkN2O) of nitrous oxide (N2O) by quantum cascade laser absorption spectroscopy (QCLAS) as a powerful tool to investigate N2O production pathways in biological wastewater treatment. QCLAS enables high-precision N2O isotopomer analysis in real time. This allowed us to trace short-term fluctuations in SP and δ15NbulkN2O and, hence, microbial transformation pathways during individual batch experiments with activated sludge from a pilot-scale facility treating municipal wastewater. On the basis of previous work with microbial pure cultures, we demonstrate that N2O emitted during ammonia (NH4+) oxidation with a SP of −5.8 to 5.6 ‰ derives mostly from nitrite (NO2–) reduction (e.g., nitrifier denitrification), with a minor contribution from hydroxylamine (NH2OH) oxidation at the beginning of the experiments. SP of N2O produced under anoxic conditions was always positive (1.2 to 26.1 ‰), and SP values at the high end of this spectrum (24.9 to 26.1 ‰) are indicative of N2O reductase activity. The measured δ15NbulkN2O at the initiation of the NH4+ oxidation experiments ranged between −42.3 and −57.6 ‰ (corresponding to a nitrogen isotope effect Δδ15N = δ15Nsubstrate – δ15NbulkN2O of 43.5 to 58.8 ‰), which is considerably higher than under denitrifying conditions (δ15NbulkN2O 2.4 to −17 ‰; Δδ15N = 0.1 to 19.5 ‰). During the course of all NH4+ oxidation and nitrate (NO3–) reduction experiments, δ15NbulkN2O increased significantly, indicating net 15N enrichment in the dissolved inorganic nitrogen substrates (NH4+, NO3–) and transfer into the N2O pool. The decrease in δ15NbulkN2O during NO2– and NH2OH oxidation experiments is best explained by inverse fractionation during the oxidation of NO2– to NO3–.
Ye, X., Zhang, X., Morgenroth, E., & Finneran, K. T. (2013). Exogenous anthrahydroquinone-2,6-disulfonate specifically increases xylose utilization during mixed sugar fermentation by Clostridium beijerinckii NCIMB 8052. International Journal of Hydrogen Energy, 38(6), 2719-2727. doi:10.1016/j.ijhydene.2012.11.149, Institutional Repository

The influence of a reduced extracellular electron shuttle (anthrahydroquinone-2,6-disulfonate, AH2QDS) on substrate utilization and H2 production was investigated at different glucose:xylose ratios using the fermentative culture Clostridium beijerinckii NCIMB 8052. Adding 250 μM AH2QDS increased the total substrate utilization by 23–66%, and specifically xylose utilization by 20–54% at glucose:xylose ratios of 1:1, 1:3 and 1:9. Adding 250 μM AH2QDS also increased the substrate utilization by 40–88% at all tested glucose:xylose ratios (which ranged from 1:9 to 9:1). Increasing AH2QDS concentrations from 250 μM to 2 mM increased xylose utilization (>99% xylose consumed) as well as cumulative hydrogen production during mixed sugar fermentation. The extent of glucose utilization was consistent amongst all tests, which was expected. However, hydroquinone amendment specifically increased the extent of xylose utilized irrespective of the starting glucose:xylose ratio. To the best of our knowledge this is the first report of 100% xylose utilization by C. beijerinckii NCIMB 8052 grown under mixed sugar conditions. These data demonstrate that the substrate utilization, particularly xylose utilization, can be manipulated by amending extracellular redox active compounds. This will improve pentose utilization during fermentation of hydrolyzates that result from pre-treatment of lignocellulosic materials with wild type (non-GMO) cultures.
Zhang, X., Ye, X., Finneran, K. T., Zilles, J. L., & Morgenroth, E. (2013). Interactions between Clostridium beijerinckii and Geobacter metallireducens in co-culture fermentation with anthrahydroquinone-2, 6-disulfonate (AH2QDS) for enhanced biohydrogen production from xylose. Biotechnology and Bioengineering, 110(1), 164-172. doi:10.1002/bit.24627, Institutional Repository

To enhance biohydrogen production, Clostridium beijerinckii was co-cultured with Geobacter metallireducens in the presence of the reduced extracellular electron shuttle anthrahydroquinone-2, 6-disulfonate (AH2QDS). In the co-culture system, increases of up to 52.3% for maximum cumulative hydrogen production, 38.4% for specific hydrogen production rate, 15.4% for substrate utilization rate, 39.0% for substrate utilization extent, and 34.8% for hydrogen molar yield in co-culture fermentation were observed compared to a pure culture of C. beijerinckii without AH2QDS. G. metallireducens grew in the co-culture system, resulting in a decrease in acetate concentration under co-culture conditions and a presumed regeneration of AH2QDS from AQDS. These co-culture results demonstrate metabolic crosstalk between the fermentative bacterium C. beijerinckii and the respiratory bacterium G. metallireducens and suggest a strategy for industrial biohydrogen production.
Zhang, X., Ye, X., Guo, B., Finneran, K. T., Zilles, J. L., & Morgenroth, E. (2013). Lignocellulosic hydrolysates and extracellular electron shuttles for H2 production using co-culture fermentation with Clostridium beijerinckii and Geobacter metallireducens. Bioresource Technology, 147, 89-95. doi:10.1016/j.biortech.2013.07.106, Institutional Repository

A co-culture of Clostridium beijerinckii and Geobacter metallireducens with AH2QDS produced hydrogen from lignocellulosic hydrolysates (biomass of Miscanthus prepared by hydrothermal treatment with dilute acids). This co-culture system enhanced hydrogen production from lignocellulosic hydrolysates by improving substrate utilization and diminishing acetate accumulation, despite the presence of fermentation inhibitors in the hydrolysates. The improvements were greater for xylose-rich hydrolysates. The increase in maximum cumulative hydrogen production for hydrolysates with glucose:xylose mass ratios of 1:0.2, 1:1 and 1:10g/g was 0%, 22% and 11%, respectively. Alternative extracellular electron shuttles (EES), including indigo dye, juglone, lawsone, fulvic acids and humic acids, were able to substitute for AH2QDS, improving hydrogen production in the co-culture system using xylose as model substrate. Increased utilization of xylose-rich hydrolysates and substitution of alternative EES make the co-culture with EES system a more attractive strategy for industrial biohydrogen production.
Amstutz, V., Katsaounis, A., Kapalka, A., Comninellis, C., & Udert, K. M. (2012). Effects of carbonate on the electrolytic removal of ammonia and urea from urine with thermally prepared IrO2 electrodes. Journal of Applied Electrochemistry, 42(9), 787-795. doi:10.1007/s10800-012-0444-y, Institutional Repository

Recent studies have shown that electrolysis can be an efficient process for nitrogen removal from urine. These studies have been conducted with urea solutions or fresh urine, but urine collected in NoMix toilets and urinals has a substantially different composition, because bacteria hydrolyse urea quickly to ammonia and carbonate. In this study, we compared electrochemical removal of nitrogen from synthetic solutions of fresh and stored urine using IrO2 anodes. We could show that in fresh urine both ammonia and urea are efficiently eliminated, mainly through chlorine-mediated oxidation. However, in stored urine the presence of carbonate, arising from urea hydrolysis, leads to an inhibition of ammonia oxidation. We suggest two parallel mechanisms to explain this effect: the competition between chloride and carbonate oxidation at the anode and the competition between chlorate formation, enhanced by the buffering effect of carbonate, and ammonia oxidation for the consumption of active chlorine in the bulk. However, further experiments are needed to support the latter mechanism. In conclusion, this study highlights the negative consequences of the presence of carbonate in urine solutions, but also in other wastewaters, when subjected to an electrolytic treatment on IrO2 in alkaline media.
Ashauer, R., Hintermeister, A., O'Connor, I., Elumelu, M., Hollender, J., & Escher, B. I. (2012). Significance of xenobiotic metabolism for bioaccumulation kinetics of organic chemicals in Gammarus pulex. Environmental Science and Technology, 46(6), 3498-3508. doi:10.1021/es204611h, Institutional Repository

Bioaccumulation and biotransformation are key toxicokinetic processes that modify toxicity of chemicals and sensitivity of organisms. Bioaccumulation kinetics vary greatly among organisms and chemicals; thus, we investigated the influence of biotransformation kinetics on bioaccumulation in a model aquatic invertebrate using fifteen 14C-labeled organic xenobiotics from diverse chemical classes and physicochemical properties (1,2,3-trichlorobenzene, imidacloprid, 4,6-dinitro-o-cresol, ethylacrylate, malathion, chlorpyrifos, aldicarb, carbofuran, carbaryl, 2,4-dichlorophenol, 2,4,5-trichlorophenol, pentachlorophenol, 4-nitrobenzyl-chloride, 2,4-dichloroaniline, and sea-nine (4,5-dichloro-2-octyl-3-isothiazolone)). We detected and identified metabolites using HPLC with UV and radio-detection as well as high resolution mass spectrometry (LTQ-Orbitrap). Kinetics of uptake, biotransformation, and elimination of parent compounds and metabolites were modeled with a first-order one-compartment model. Bioaccumulation factors were calculated for parent compounds and metabolite enrichment factors for metabolites. Out of 19 detected metabolites, we identified seven by standards or accurate mass measurements and two via pathway analysis and analogies to other compounds. 1,2,3-Trichlorobenzene, imidacloprid, and 4,6-dinitro-o-cresol were not biotransformed. Dietary uptake contributed little to overall uptake. Differentiation between parent and metabolites increased accuracy of bioaccumulation parameters compared to total 14C measurements. Biotransformation dominated toxicokinetics and strongly affected internal concentrations of parent compounds and metabolites. Many metabolites reached higher internal concentrations than their parents, characterized by large metabolite enrichment factors.
Biller, S. J., Mosier, A. C., Wells, G. F., & Francis, C. A. (2012). Global biodiversity of aquatic ammonia-oxidizing archaea is partitioned by habitat. Frontiers in Microbiology, 3, 252 (15 pp.). doi:10.3389/fmicb.2012.00252, Institutional Repository

Archaea play an important role in nitrification and are, thus, inextricably linked to the global carbon and nitrogen cycles. Since the initial discovery of an ammonia monooxygenase α-subunit (amoA) gene associated with an archaeal metagenomic fragment, archaeal amoA sequences have been detected in a wide variety of nitrifying environments. Recent sequencing efforts have revealed extensive diversity of archaeal amoA sequences within different habitats. In this study, we have examined over 8000 amoA sequences from the literature and public databases in an effort to understand the ecological factors influencing the distribution and diversity of ammonia-oxidizing archaea (AOA), with a particular focus on sequences from aquatic habitats. This broad survey provides strong statistical support for the hypothesis that different environments contain distinct clusters of AOA amoA sequences, as surprisingly few sequences are found in more than one habitat type. Within aquatic environments, salinity, depth in the water column, and temperature were significantly correlated with the distribution of sequence types. These findings support the existence of multiple distinct aquatic AOA populations in the environment and suggest some possible selective pressures driving the partitioning of AOA amoA diversity.
Boehler, M., Zwickenpflug, B., Hollender, J., Ternes, T., Joss, A., & Siegrist, H. (2012). Removal of micropollutants in municipal wastewater treatment plants by powder-activated carbon. Water Science and Technology, 66(10), 2115-2121. doi:10.2166/wst.2012.353, Institutional Repository

Micropollutants (MP) are only partly removed from municipal wastewater by nutrient removal plants and are seen increasingly as a threat to aquatic ecosystems and to the safety of drinking water resources. The addition of powder activated carbon (PAC) is a promising technology to complement municipal nutrient removal plants in order to achieve a significant reduction of MPs and ecotoxicity in receiving waters. This paper presents the salient outcomes of pilot- and full-scale applications of PAC addition in different flow schemes for micropollutant removal in municipal wastewater treatment plants (WWTPs). The sorption efficiency of PAC is reduced with increasing dissolved organic carbon (DOC). Adequate treatment of secondary effluent with 5–10 g DOC m−3 requires 10–20 g PAC m−3 of effluent. Counter-current use of PAC by recycling waste PAC from post-treatment in a contact tank with an additional clarifier to the biology tank improved the overall MP removal by 10 to 50% compared with effluent PAC application alone. A dosage of 15 g PAC m−3 to a full-scale flocculation sand filtration system and recycling the backwash water to the biology tank showed similar MP elimination. Due to an adequate mixing regime and the addition of adapted flocculants, a good retention of the fine fraction of the PAC in the deep-bed filter were observed (1–3 g TSS m−3; TSS: total suspended solids). With double use of PAC, only half of the PAC was required to reach MP removal efficiencies similar to the direct single dosage of PAC to the biology tank. Overall, the application of PAC in WWTPs seems to be an adequate and feasible technology for efficient MP elimination (>80%) from wastewater comparable with post ozonation.
Boltz, J. P., Morgenroth, E., Daigger, G. T., deBarbadillo, C., Murthy, S., Sørensen, K. H., & Stinson, B. (2012). Method to identify potential phosphorus rate-limiting conditions in post-denitrification biofilm reactors within systems designed for simultaneous low-level effluent nitrogen and phosphorus concentrations. Water Research, 46(19), 6228-6238. doi:10.1016/j.watres.2012.08.020, Institutional Repository

Water-quality standards requiring simultaneous low level effluent N and P concentrations are increasingly common in Europe and the United States of America. Moving bed biofilm reactors (MBBRs) and biologically active filters (BAFs) have been used as post-denitrification biofilm reactors in processes designed and operated for this purpose (Boltz et al., 2010a). There is a paucity of information describing systematic design and operational protocols that will minimize the potential for phosphorus rate-limited conditions as well as a lack of information describing the interaction between these post-denitrification biofilm reactors and unit processes that substantially alter phosphorus speciation (e.g., chemically enhanced clarification). In this paper, a simple mathematical model for estimating the threshold below which P becomes rate-limiting, and the model is presented and evaluated by comparing its predictions with operational data from post-denitrification MBBRs and BAFs. Ortho-phosphorus (PO4–P), which is the dissolved reactive component of total phosphorus, was a primary indicator of P rate-limiting conditions in the evaluated post-denitrification biofilm reactors. The threshold below which PO4–P becomes the rate-limiting substrate is defined: SPO4–P:SNOx–N = 0.0086 g P/g N and SPO4–P : SM = 0.0013 g P/g COD. Additional analyses indicate JavgNOx-N =0.48g/m2/d when SPO4–P:SNOx–N > 0.0086, and JavgNOx-N=0.06g/m2/d when SPO4–P:SNOx–N < 0.0086. Effluent nitrate–nitrogen plus nitrite–nitrogen concentration (SNOx–N)(SNOx–N) from the evaluated post-denitrification biofilm reactors began to rapidly increase when SPO4–P:SNOx–N:SNOx–N was 0.01, approximately (consistent with the rate-limitation threshold of SPO4–P:SNOx–N < 0.0086 predicted by the mathematical model described in this paper). Depending on the processes used at a given WWTP, optimizing chemically enhanced clarification to increase the amount of PO4–P that remains in the clarifiers effluent stream, dosing phosphoric acid in the MBBR or BAF influent stream, and/or optimizing secondary process EBPR may overcome phosphorus rate-limitations in the biofilm-based post-denitrification process.
Boulestreau, M., Hoa, E., Peter-Verbanets, M., Pronk, W., Rajagopaul, R., & Lesjean, B. (2012). Operation of gravity-driven ultrafiltration prototype for decentralised water supply. Desalination and Water Treatment, 42, 125-130. doi:10.1080/19443994.2012.683073, Institutional Repository

The study aims at assessing in long-term trials a gravity-driven ultrafiltration pilot plant designed for a capacity of 5 m3 d-1. The unit was operated in South Africa with Ogunjini surface water and was run with restricted chemical intervention or maintenance (no backflush, no aeration, no crossflow and no chemical). Under South African environmental conditions and with direct filtration of the river water and only one manual drainage of the membrane reactor every weekday, the unit could fulfil the design specification in terms of water production (5 m3 d-1) as long as the turbidity of the raw water remained in a reasonable level (up to 160 NTU), with a filtration flux typically 4-6 l h m-2 (corrected at 20°C). This value was in the same range as the lab results and was consistent with the first phase results (around 5-7 l h-1 m-2 after biosand filtration). However, the flux dropped significantly to a range of 2-4 l h-1 m-2 after a rain event resulting in a turbidity peak over several days up to >600 NTU. This demonstrated that for variable raw water types with expected turbidity peaks above 100 NTU, a pre-treatment would be required for the system (biosand filter or other). The performance of microbiological tests confirmed the integrity of the membrane and the ability of the system to achieve advanced disinfection.
Derlon, N., Peter-Varbanets, M., Scheidegger, A., Pronk, W., & Morgenroth, E. (2012). Predation influences the structure of biofilm developed on ultrafiltration membranes. Water Research, 46(10), 3323-3333. doi:10.1016/j.watres.2012.03.031, Institutional Repository

This study investigates the impact of predation by eukaryotes on the development of specific biofilm structures in gravity-driven dead-end ultrafiltration systems. Filtration systems were operated under ultra-low pressure conditions (65 mbar) without the control of biofilm formation. Three different levels of predation were evaluated: (1) inhibition of eukaryotic organisms, (2) addition of cultured protozoa (Tetrahymena pyriformis), and (3) no modification of microbial community as a control. The system performance was evaluated based on permeate flux and structures of the biofilm. It was found that predation had a significant influence on both the total amount and also the structure of the biofilm. An open and heterogeneous structure developed in systems with predation whereas a flat, compact, and thick structure that homogeneously covered the membrane surface developed in absence of predation. Permeate flux was correlated with the structure of the biofilm with increased fluxes for smaller membrane coverage. Permeate fluxes in the presence or absence of the predators was 10 and 5 L m−2 h−1, respectively. It was concluded that eukaryotic predation is a key factor influencing the performance of gravity-driven ultrafiltration systems.
Dürrenmatt, D. J., & Gujer, W. (2012). Automatic reactor model synthesis with genetic programming. Water Science and Technology, 65(4), 765-772. doi:10.2166/wst.2012.913, Institutional Repository

Successful modeling of wastewater treatment plant (WWTP) processes requires an accurate description of the plant hydraulics. Common methods such as tracer experiments are difficult and costly and thus have limited applicability in practice; engineers are often forced to rely on their experience only. An implementation of grammar-based genetic programming with an encoding to represent hydraulic reactor models as program trees should fill this gap: The encoding enables the algorithm to construct arbitrary reactor models compatible with common software used for WWTP modeling by linking building blocks, such as continuous stirred-tank reactors. Discharge measurements and influent and effluent concentrations are the only required inputs. As shown in a synthetic example, the technique can be used to identify a set of reactor models that perform equally well. Instead of being guided by experience, the most suitable model can now be chosen by the engineer from the set. In a second example, temperature measurements at the influent and effluent of a primary clarifier are used to generate a reactor model. A virtual tracer experiment performed on the reactor model has good agreement with a tracer experiment performed on-site.
Dürrenmatt, D. J., & Gujer, W. (2012). Data-driven modeling approaches to support wastewater treatment plant operation. Environmental Modelling and Software, 30, 47-56. doi:10.1016/j.envsoft.2011.11.007, Institutional Repository

Data-driven modeling techniques are applied to process data from wastewater treatment plants to provide valuable additional information for optimal plant control. The application of data-driven modeling techniques, however, bears some risk because the generated models are of non-mechanistic nature and they thus do not always describe the plant processes appropriately. In this study, a procedure to build software sensors based on sensor data available in the process information system is defined and used to compare several techniques suitable for data-driven modeling, including generalized least squares regression, artificial neural networks, self-organizing maps and random forests. Three different degrees of expert knowledge are defined and considered mainly for optimum input signal selection and model interpretation. In two full-scale experiments, software sensors are created. The experiments reveal that even with linear modeling techniques, it is possible to automatically generate accurate software sensors. Hence, this justifies the selection of the most parsimonious and transparent models and to motivate their investigation by taking into account available expert knowledge. A high degree of expert knowledge is valuable for long-term accuracy, but can lead to performance decreases in short-term predictions. With regard to safe on-site deployment, the consideration of uncertainty measures is crucial to prevent misinterpretation of software-sensor outputs in the cases of rare events or model input failures.
Ghasemian, M., Amin, M. M., Morgenroth, E., & Jaafarzadeh, N. (2012). Anaerobic biodegradation of methyl tert-butyl ether and tert-butyl alcohol in petrochemical wastewater. Environmental Technology, 33(16), 1937-1943. doi:10.1080/09593330.2012.655313, Institutional Repository

A laboratory-scale anaerobic sequencing batch reactor was used to evaluate treatment of a synthetic substrate mixture representing petrochemical wastewater containing methyl tert-butyl ether (MTBE), ethanol and acetic acid. Influent MTBE concentrations were 5, 10 and 50 mg/l (corresponding to MTBE loading rates of 0.2, 0.4 and 2 mg/l.d) with overall organic loading rates (OLRs) of 1.51, 3.23 and 3.25 g COD/l.d, respectively. These OLRs resulted in removal efficiencies for MTBE of 78%, 98% and 88%. Removal efficiencies for chemical oxygen demand were 85% and 90% with influent MTBE concentrations of 5 and 10 mg/l, but were significantly reduced to 72% with influent MTBE concentrations of 50 mg/l. During all reactor runs, effluent concentrations of tert-butyl alcohol (TBA) were below the detection limit. Batch degradation of the organic substrate mixture demonstrated initial inhibitory effects when exposed to MTBE concentrations of 50 mg/l and complete inhibition with MTBE concentrations above 2000 mg/l. It is interesting to note that in batch tests using MTBE as the sole organic substrate (initial MTBE concentrations of 50, 100 and 200 mg/l), the specific methanogenic activity decreased to below detection within the first 96 hours, but following a 72-hour lag phase the methane production increased again. Based on low volatile fatty acid (VFA) concentration, disappearance of TBA peaks and no findings of any other intermediate via gas chromatography/mass spectrometry, while the MTBE concentration is still high, it can be suggested that during the batch tests the breakdown of gas production and the following lag phase were the direct effect of higher MTBE concentrations (more than 50 mg/l) and not because of the TBA or VFA accumulations.
Guo, B., Zhang, Y., Ha, S. J., Jin, Y. S., & Morgenroth, E. (2012). Combined biomimetic and inorganic acids hydrolysis of hemicellulose in Miscanthus for bioethanol production. Bioresource Technology, 110, 278-287. doi:10.1016/j.biortech.2012.01.133, Institutional Repository

Combined acid catalysis was employed as a pretreatment alternative with combined acid catalysts blending sulfuric acid with two biomimetic acids, trifluoroacetic acid (TFA) and maleic acid (MA), respectively. The influences of acid blending ratio, temperature, and acid dosage on pretreatment performance were investigated. A synergistic effect on hemicellulose decomposition was observed in the combined acid hydrolysis, which greatly increased xylose yield, although TFA/MA would induce more total phenols. Besides, combined TFA pretreatment could efficiently prevent xylose degradation. Fermentation tests of the acid-catalyzed hydrolysates with overliming showed that compared to H2SO4 pretreatment, TFA and MA pretreatments improved overall ethanol yield with an increase by 27–54%. Combined acid catalysis was shown as a feasible pretreatment method for its improved sugar yield, reduced phenols production and catalyst costs.
Hagendorfer, H., Kaegi, R., Parlinska, M., Sinnet, B., Ludwig, C., & Ulrich, A. (2012). Characterization of silver nanoparticle products using asymmetric flow field flow fractionation with a multidetector approach - a comparison to transmission electron microscopy and batch dynamic light scattering. Analytical Chemistry, 84(6), 2678-2685. doi:10.1021/ac202641d, Institutional Repository

Due to the already prevalent and increasing use of silver-nanoparticle (Ag-NP) products and the raised concerns in particular for the aquatic environment, analytical techniques for the characterization of such products are of need. However, because Ag-NP products are of different compositions and polydispersities, analysis especially of the size distribution is challenging. In this work, an asymmetric flow field flow fractionation (A4F) multidetector system (UV/vis, light scattering, inductively coupled plasma mass spectrometry - ICPMS), in combination with a method to distinguish and quantify the particle and dissolved Ag fractions (ICPMS after ultracentrifugation), for the characterization of Ag-NP products with different degrees of polydispersities is presented. For validation and to outline benefits and limitations, results obtained from batch dynamic light scattering (batch-DLS) and transmission electron microscopy (TEM) were compared. With the developed method a comprehensive understanding in terms of dissolved Ag and Ag-NP concentration as well as an element selective, mass- and number particle size distribution (PSD) was obtained. In relation to batch-DLS, the reliability of the data was improved significantly. In comparison to TEM, faster measurement times and the ability to determine the samples directly in dispersions are clearly advantageous. The proposed setup shows potential for a rapid- and reliable characterization method of virtually any polydisperse metallic NP dispersion, many of them available on the market already.
Jenni, S., Mohn, J., Emmenegger, L., & Udert, K. M. (2012). Temperature dependence and interferences of NO and N2O microelectrodes used in wastewater treatment. Environmental Science and Technology, 46(4), 2257-2266. doi:10.1021/es2032357, Institutional Repository

Electrodes for nitric and nitrous oxide have been on the market for some time, but have not yet been tested for an application in wastewater treatment processes. Both sensors were therefore assessed with respect to their (non)linear response, temperature dependence and potential cross sensitivity to dissolved compounds, which are present and highly dynamic in nitrogen conversion processes (nitric oxide, nitrous oxide, nitrogen dioxide, ammonia, hydrazine, hydroxylamine, nitrous acid, oxygen, and carbon dioxide). Off-gas measurements were employed to differentiate between cross sensitivity to interfering components and chemical nitric oxide or nitrous oxide production. Significant cross sensitivities were detected for both sensors: by the nitrous oxide sensor to nitric oxide and by the nitric oxide sensor to ammonia, hydrazine, hydroxylamine and nitrous acid. These interferences could, however, be removed by correction functions. Temperature fluctuations in the range of ±1 °C lead to artifacts of ±3.5% for the nitric oxide and ±3.9% for the nitrous oxide sensor and can be corrected with exponential equations. The results from this study help to significantly shorten and optimize the determination of the correction functions and are therefore relevant for all users of nitric and nitrous oxide electrodes.
Kovalova, L., Siegrist, H., Singer, H., Wittmer, A., & McArdell, C. S. (2012). Hospital wastewater treatment by membrane bioreactor: performance and efficiency for organic micropollutant elimination. Environmental Science and Technology, 46(3), 1536-1545. doi:10.1021/es203495d, Institutional Repository

A pilot-scale membrane bioreactor (MBR) was installed and operated for one year at a Swiss hospital. It was fed an influent directly from the hospital’s sanitary collection system. To study the efficiency of micropollutant elimination in raw hospital wastewater that comprises a complex matrix with micropollutant concentrations ranging from low ng/L to low mg/L, an automated online SPE-HPLC-MS/MS analytical method was developed. Among the 68 target analytes were the following: 56 pharmaceuticals (antibiotics, antimycotics, antivirals, iodinated X-ray contrast media, antiinflamatory, cytostatics, diuretics, beta blockers, anesthetics, analgesics, antiepileptics, antidepressants, and others), 10 metabolites, and 2 corrosion inhibitors. The MBR influent contained the majority of those target analytes. The micropollutant elimination efficiency was assessed through continuous flow-proportional sampling of the MBR influent and continuous time-proportional sampling of the MBR effluent. An overall load elimination of all pharmaceuticals and metabolites in the MBR was 22%, as over 80% of the load was due to persistent iodinated contrast media. No inhibition by antibacterial agents or disinfectants from the hospital was observed in the MBR. The hospital wastewater was found to be a dynamic system in which conjugates of pharmaceuticals deconjugate and biological transformation products are formed, which in some cases are pharmaceuticals themselves.
Li, X., Yuen, W., Morgenroth, E., & Raskin, L. (2012). Backwash intensity and frequency impact the microbial community structure and function in a fixed-bed biofilm reactor. Applied Microbiology and Biotechnology, 96(3), 815-827. doi:10.1007/s00253-011-3838-6, Institutional Repository

Linkages among bioreactor operation and performance and microbial community structure were investigated for a fixed-bed biofilm system designed to remove perchlorate from drinking water. Perchlorate removal was monitored to evaluate reactor performance during and after the frequency and intensity of the backwash procedure were changed, while the microbial community structure was studied using clone libraries and quantitative PCR targeting the 16S rRNA gene. When backwash frequency was increased from once per month to once per day, perchlorate removal initially deteriorated and then recovered, and the relative abundance of perchlorate-reducing bacteria (PRB) initially increased and then decreased. This apparent discrepancy suggested that bacterial populations other than PRB played an indirect role in perchlorate removal, likely by consuming dissolved oxygen, a competing electron acceptor. When backwash intensity was increased, the reactor gradually lost its ability to remove perchlorate, and concurrently the relative abundance of PRB decreased. The results indicated that changes in reactor operation had a profound impact on reactor performance through altering the microbial community structure. Backwashing is an important yet poorly characterized procedure when operating fixed-bed biofilm reactors. Compared to backwash intensity, changes in backwash frequency exerted less disturbance on the microbial community in the current study. If this finding can be confirmed in future work, backwash frequency may serve as the primary parameter when optimizing backwash procedures.
Lotito, A. M., Wunderlin, P., Joss, A., Kipf, M., & Siegrist, H. (2012). Nitrous oxide emissions from the oxidation tank of a pilot activated sludge plant. Water Research, 46(11), 3563-3573. doi:10.1016/j.watres.2012.03.067, Institutional Repository

This study discusses the results of the continuous monitoring of nitrous oxide emissions from the oxidation tank of a pilot conventional wastewater treatment plant. Nitrous oxide emissions from biological processes for nitrogen removal in wastewater treatment plants have drawn great attention over the last years, due to the high greenhouse effect. However, even if several studies have been carried out to quantify nitrous oxide emission rates from different types of treatment, quite wide ranges have been reported. Only grab samples or continuous measurements over limited periods were considered in previous studies, which can account for the wide variability of the obtained results. Through continuous monitoring over several months, our work tries to fill this gap of knowledge and get a deeper insight into nitrous oxide daily and weekly emission dynamics. Moreover, the influence of some operating conditions (sludge age, dissolved oxygen concentration in the oxidation tank, nitrogen load) was studied to determine good practices for wastewater treatment plant operation aiming at the reduction of nitrous oxide emissions. The dissolved oxygen set-point is shown to play a major role in nitrous oxide emissions. Low sludge ages and high nitrogen loads are responsible for higher emissions as well. An interesting pattern has been observed, with quite negligible emissions during most of the day and a peak with a bell-like shape in the morning in the hours of maximum nitrogen load in the plant, correlated to the ammonia and nitrite peaks in the tank.
Maurer, M., Bufardi, A., Tilley, E., Zurbrügg, C., & Truffer, B. (2012). A compatibility-based procedure designed to generate potential sanitation system alternatives. Journal of Environmental Management, 104(Aug), 51-61. doi:10.1016/j.jenvman.2012.03.023, Institutional Repository

Regarding multi-criteria decision analysis (MCDA), the problem of generating alternatives has not received the attention it deserves. Most research is currently devoted to the problem of alternative selection, where it is assumed that a set of appropriate alternatives is already given. This paper addresses the generation of potential alternatives in the domain of sanitation systems planning and decision-making. A compatibility assessment procedure is proposed to determine the set of technically feasible or potential sanitation system alternatives. This is based on a clear definition of such an alternative containing sub-processes that include a user interface, storage, conveyance treatment and reuse/disposal. A newly developed compatibility matrix is applied to identify incompatibilities between the options of the sub-processes.
A potential sanitation system alternative is therefore defined by the absence of two-by-two incompatibility between all its options.
The compatibility assessment acts as a first filter on the set of sanitation system alternatives to eliminate those that are inoperable before the feasibility assessment. The objective of both steps is to obtain a set of alternatives that are of reasonable and manageable size from which the final solution may be selected.
Mertens, J., Rose, J., Kägi, R., Chaurand, P., Plötze, M., Wehrli, B., & Furrer, G. (2012). Adsorption of arsenic on polyaluminum granulate. Environmental Science and Technology, 46(13), 7310-7317. doi:10.1021/es204508t, Institutional Repository

The kinetics and efficiencies of arsenite and arsenate removal from water were evaluated using polyaluminum granulates (PAG) with high content of aluminum nanoclusters. PAG was characterized to be meso- and macroporous, with a specific surface area of 35 ± 1 m2 g–1. Adsorption experiments were conducted at pH 7.5 in deionized water and synthetic water with composition of As-contaminated groundwater in the Pannonian Basin. As(III) and As(V) sorption was best described by the Freundlich and Langmuir isotherm, respectively, with a maximum As(V) uptake capacity of 200 μmol g–1 in synthetic water. While As(III) removal reached equilibrium within 40 h, As(V) was removed almost entirely within 20 h. Micro X-ray fluorescence and electron microscopy revealed that As(III) was distributed uniformly within the grain, whereas As(V) diffused up to 81 μm into PAG. The results imply that As(V) is adsorbed 3 times faster while being transported 105 times slower than As(III) in Al hydroxide materials.
Mueller, N. C., van der Bruggen, B., Keuter, V., Luis, P., Melin, T., Pronk, W., … Nowack, B. (2012). Nanofiltration and nanostructured membranes-should they be considered nanotechnology or not?. Journal of Hazardous Materials, 211-212, 275-280. doi:10.1016/j.jhazmat.2011.10.096, Institutional Repository

Nanofiltration is frequently associated with nanotechnology – obviously because of its name. However, the term "nano" in nanofiltration refers – according to the definition of the International Union of Pure and Applied Chemistry (IUPAC) – to the size of the particles rejected and not to a nanostructure as defined by the International Organisation of Standardisation (ISO) in the membrane. Evidently, the approach to standardisation of materials differs significantly between membrane technology and nanotechnology which leads to considerable confusion and inconsistent use of the terminology. There are membranes that can be unambiguously attributed to both membrane technology and nanotechnology such as those that are functionalized with nanoparticles, while the classification of hitherto considered to be conventional membranes as nanostructured material is questionable. A driving force behind the efforts to define nanomaterials is not least the urgent need for the regulation of the use of nanomaterials. Since risk estimation is the basis for nanotechnology legislation, the risk associated with nanomaterials should also be reflected in the underlying standards and definitions. This paper discusses the impacts of the recent attempts to define nanomaterials on membrane terminology in the light of risk estimations and the need for regulation.
Neumann, M. B. (2012). Comparison of sensitivity analysis methods for pollutant degradation modelling: a case study from drinking water treatment. Science of the Total Environment, 433, 530-537. doi:10.1016/j.scitotenv.2012.06.026, Institutional Repository

Five sensitivity analysis methods based on derivatives, screening, regression, variance decomposition and entropy are introduced, applied and compared for a model predicting micropollutant degradation in drinking water treatment. The sensitivity analysis objectives considered are factors prioritisation (detecting important factors), factors fixing (detecting non-influential factors) and factors mapping (detecting which factors are responsible for causing pollutant limit exceedances). It is shown how the applicability of methods changes in view of increasing interactions between model factors and increasing non-linearity between the model output and the model factors. A high correlation is observed between the indices obtained for the objectives factors prioritisation and factors mapping due to the positive skewness of the probability distributions of the predicted residual pollutant concentrations. The entropy-based method which uses the Kullback–Leibler divergence is found to be particularly suited when assessing pollutant limit exceedances.
Peter, S., Koetzsch, S., Traber, J., Bernasconi, S. M., Wehrli, B., & Durisch-Kaiser, E. (2012). Intensified organic carbon dynamics in the ground water of a restored riparian zone. Freshwater Biology, 57(8), 1603-1616. doi:10.1111/j.1365-2427.2012.02821.x, Institutional Repository

1.River restoration projects usually aim at improving the physical habitat for aquatic organisms. The extent to which biogeochemical processes and microbial activities are intensified in restored river reaches remains uncertain.
2. Here, we investigated the relationships between the distribution and composition of organic carbon (OC), bacterial secondary carbon production and extracellular enzymatic activity (EEA) in the ground water below a restored riparian section of the River Thur, Switzerland, relative to a channelised section. The spatiotemporal variability in the stable C isotopic ratio, dissolved OC polydispersity (the distribution of molecular mass in a mixture of molecules) as well as bacterial abundance, EEA and secondary production were investigated in different process zones.
3. At high river discharge, humic as well as low molecular weight amphiphilic substances infiltrated into the subsurface in a zone dominated by the pioneer plants Salix viminalis (willow bush). Concurrently, bacterial abundance, EEA and secondary carbon production increased at this location.
4. The willow plants leached bioavailable substrates into the ground water when the water table was high. The flood-driven soil–groundwater coupling stimulated EEA and bacterial secondary production of the suspended groundwater bacterial community.
5. Establishing riparian habitat diversity adds hot spots of OC inputs during flood events, potentially providing valuable ecosystem services (e.g. degradation of organic pollutants) that accompany.
Peter-Varbanets, M., Gujer, W., & Pronk, W. (2012). Intermittent operation of ultra-low pressure ultrafiltration for decentralized drinking water treatment. Water Research, 46(10), 3272-3282. doi:10.1016/j.watres.2012.03.020, Institutional Repository

River water was treated by ultrafiltration at a relatively low transmembrane pressure (40 mbar). As observed before, flux stabilization occurred after several days of operation although no back-flushing or cross flow was applied. Interruptions in flux were applied by temporary offset of the transmembrane pressure. After restoration of the transmembrane pressure, the initial flux was higher than the stable flux level, and the flux recovery depended on the standstill time. Furthermore, if a short cross flow was applied after standstill, the flux was restored to an even higher level. In all cases, the flux decreased again during operation to reach finally the same stable level as before standstill. In order to evaluate the influence of intermittent operation as practiced for water treatment on a household level, daily interruptions of flux were applied. An optimum of total daily water production rate was obtained at 21 h of operation and 3 h of standstill per day. A model was developed which can describe the impact of intermittent operation on the flux depending on the duration of the standstill and operating periods. This enables the prediction of production capacity of the system operated intermittently. The flux increase during standstill could be explained by a relaxation and expansion of the biofouling layer, while the higher flux after forward-flushing was caused by this layer being partially sloughed off. Household water treatment with the process presented here will generally be operated on a discontinuous basis. The results show that such operation schemes do not compromise the permeability of the system, but actually lead to higher fluxes after standstill.
Rattier, M., Reungoat, J., Gernjak, W., Joss, A., & Keller, J. (2012). Investigating the role of adsorption and biodegradation in the removal of organic micropollutants during biological activated carbon filtration of treated wastewater. Journal of Water Reuse and Desalination, 2(3), 127-139. doi:10.2166/wrd.2012.012, Institutional Repository

Municipal water recycling may expose humans and the environment to trace organic contaminants. We assessed biological activated carbon (BAC) filtration for removal of organic micropollutants (MPs). Adsorption experiments were carried out in batch reactors containing secondary effluent and new granular activated carbon (GAC) and preloaded BAC media. Results show that BAC has good potential for removal of dissolved organic carbon (40%) and MPs (60–95%). The primary objective was to better understand removal mechanisms of representative MPs at environmentally relevant concentrations. Adsorption and biodegradation of 20 compounds of varying physico-chemical properties were investigated by inhibiting the biomass with azide. Average removal of compounds by adsorption on GAC was 88 ± 5% with no influence of azide. Average BAC removal was 72 ± 15%, reduced to 59 ± 20% after azide addition, showing that biological activity is important for MP removal. Comparison of MP removal by BAC and BAC + azide showed a more important impact of the inhibition on the removal of negatively charged compounds. Sustained removal of recalcitrant compounds showed that BAC maintained sorption capacity. These results highlight the advantage of a combination of adsorption and biodegradation as compared to other biofiltration techniques for the long-term attenuation of MPs.
Rieger, L., Takács, I., & Siegrist, H. (2012). Improving nutrient removal while reducing energy use at three Swiss WWTPs using advanced control. Water Environment Research, 84(2), 170-188. doi:10.2175/106143011X13233670703684, Institutional Repository

Aeration consumes about 60% of the total energy use of a wastewater treatment plant (WWTP) and therefore is a major contributor to its carbon footprint. Introducing advanced process control can help plants to reduce their carbon footprint and at the same time improve effluent quality through making available unused capacity for denitrification, if the ammonia concentration is below a certain set-point. Monitoring and control concepts are cost-saving alternatives to the extension of reactor volume. However, they also involve the risk of violation of the effluent limits due to measuring errors, unsuitable control concepts or inadequate implementation of the monitoring and control system. Dynamic simulation is a suitable tool to analyze the plant and to design tailored measuring and control systems. During this work, extensive data collection, modeling and fullscale implementation of aeration control algorithms were carried out at three conventional activated sludge plants with fixed pre-denitrification and nitrification reactor zones. Full-scale energy savings in the range of 16-20% could be achieved together with an increase of total nitrogen removal of 40%.
Sakthivel, S. R., Tilley, E., & Udert, K. M. (2012). Wood ash as a magnesium source for phosphorus recovery from source-separated urine. Science of the Total Environment, 419, 68-75. doi:10.1016/j.scitotenv.2011.12.065, Institutional Repository

Struvite precipitation is a simple technology for phosphorus recovery from source-separated urine. However, production costs can be high if expensive magnesium salts are used as precipitants. Therefore, waste products can be interesting alternatives to industrially-produced magnesium salts. We investigated the technical and financial feasibility of wood ash as a magnesium source in India. In batch experiments with source-separated urine, we could precipitate 99% of the phosphate with a magnesium dosage of 2.7 mol Mg mol P− 1. The availability of the magnesium from the wood ash used in our experiment was only about 50% but this could be increased by burning the wood at temperatures well above 600 °C. Depending on the wood ash used, the precipitate can contain high concentrations of heavy metals. This could be problematic if the precipitate were used as fertilizer depending on the applicable fertilizer regulations. The financial study revealed that wood ash is considerably cheaper than industrially-produced magnesium sources and even cheaper than bittern. However, the solid precipitated with wood ash is not pure struvite. Due to the high calcite and the low phosphorus content (3%), the precipitate would be better used as a phosphorus-enhanced conditioner for acidic soils. The estimated fertilizer value of the precipitate was actually slightly lower than wood ash, because 60% of the potassium dissolved into solution during precipitation and was not present in the final product. From a financial point of view and due to the high heavy metal content, wood ash is not a very suitable precipitant for struvite production. Phosphate precipitation from urine with wood ash can be useful if (1) a strong need for a soil conditioner that also contains phosphate exists, (2) potassium is abundant in the soil and (3) no other cheap precipitant, such as bittern or magnesium oxide, is available.
Schreiber, F., Wunderlin, P., Udert, K. M., & Wells, G. F. (2012). Nitric oxide and nitrous oxide turnover in natural and engineered microbial communities: biological pathways, chemical reactions, and novel technologies. Frontiers in Microbiology, 3(372), 372 (24 pp.). doi:10.3389/fmicb.2012.00372, Institutional Repository

Nitrous oxide (N2O) is an environmentally important atmospheric trace gas because it is an effective greenhouse gas and it leads to ozone depletion through photo-chemical nitric oxide (NO) production in the stratosphere. Mitigating its steady increase in atmospheric concentration requires an understanding of the mechanisms that lead to its formation in natural and engineered microbial communities. N2O is formed biologically from the oxidation of hydroxylamine (NH2OH) or the reduction of nitrite (NO−2) to NO and further to N2O. Our review of the biological pathways for N2O production shows that apparently all organisms and pathways known to be involved in the catabolic branch of microbial N-cycle have the potential to catalyze the reduction of NO−2 to NO and the further reduction of NO to N2O, while N2O formation from NH2OH is only performed by ammonia oxidizing bacteria (AOB). In addition to biological pathways, we review important chemical reactions that can lead to NO and N2O formation due to the reactivity of NO−2, NH2OH, and nitroxyl (HNO). Moreover, biological N2O formation is highly dynamic in response to N-imbalance imposed on a system. Thus, understanding NO formation and capturing the dynamics of NO and N2O build-up are key to understand mechanisms of N2O release. Here, we discuss novel technologies that allow experiments on NO and N2O formation at high temporal resolution, namely NO and N2O microelectrodes and the dynamic analysis of the isotopic signature of N2O with quantum cascade laser absorption spectroscopy (QCLAS). In addition, we introduce other techniques that use the isotopic composition of N2O to distinguish production pathways and findings that were made with emerging molecular techniques in complex environments. Finally, we discuss how a combination of the presented tools might help to address important open questions on pathways and controls of nitrogen flow through complex microbial communities that eventually lead to N2O build-up.
Schwyzer, I., Kaegi, R., Sigg, L., Smajda, R., Magrez, A., & Nowack, B. (2012). Long-term colloidal stability of 10 carbon nanotube types in the absence/presence of humic acid and calcium. Environmental Pollution, 169(1), 64-73. doi:10.1016/j.envpol.2012.05.004, Institutional Repository

The colloidal stabilities of ten carbon nanotubes (CNTs) having varying physico-chemical properties were compared in long-term experiments. The presence of Suwannee River Humic Acid (SRHA) increased the fraction of CNTs in the supernatants (4–88% for the various CNT types) after addition in pre-dispersed form and 20 days of shaking and 5 days of settling. These suspensions were monomodal, containing individually suspended CNTs with highly negative surface charges. Calcium (2 mM) removed most of the CNT types from the supernatant, due to CNT-agglomerate formation initiated by reduction in surface charge. The amount of SRHA adsorbed to the different CNT types did not correlate (r2 < 0.1) with the percentage of CNTs remaining in suspension. Multiple linear regression analysis revealed that the oxygen content and the diameter of the CNTs significantly influenced the percentage of stabilized CNTs, resulting in an increased fraction of functionalized and large-diameter CNTs that remained in suspension.
Siegrist, H., & Joss, A. (2012). Review on the fate of organic micropollutants in wastewater treatment and water reuse with membranes. Water Science and Technology, 66(6), 1369-1376. doi:10.2166/wst.2012.285, Institutional Repository

A brief review of the fate of micropollutants in membrane-based wastewater treatment due to sorption, stripping, biological degradation/transformation and membrane separation is discussed, to give an overview of these technologies due to the growing importance for water reuse purposes. Compared with conventional activated sludge treatment (CAS) micropollutant removal in membrane bioreactor (MBR) is slightly improved due to complete suspended solids removal and increased sludge age. For discharge to sensitive receiving waters advanced treatment, such as post-ozonation or activated carbon adsorption, is recommended. In water reuse plants nanofiltration (NF) and reverse osmosis (RO) efficiently reject micropollutants due to size exclusions as well as electrostatic and hydrophobic effects reaching potable quality. To remove micropollutants fully, additionally post-ozone or the addition of powdered activated carbon (PAC) have to be applied, which in parallel also reduce NDMA precursors. The concentrate has to be treated if disposed to sensitive receiving waters due to its high micropollutant concentration and ecotoxicity potential. The present review summarizes principles and capabilities for the most important membrane-based applications for wastewater treatment, i.e. porous membranes in MBRs (micro- or ultrafiltration) and dense membrane applications (NF and RO) for water reuse.
Stasinakis, A. S. (2012). Review on the fate of emerging contaminants during sludge anaerobic digestion. Bioresource Technology, 121, 432-440. doi:10.1016/j.biortech.2012.06.074, Institutional Repository

Several research papers have been published during the last years investigating the occurrence, fate and effects of emerging contaminants (ECs) on sludge anaerobic digestion (AD). Literature review revealed that research has been mainly focused on specific groups of compounds (linear alkylbenzene sulphonates, nonylphenol ethoxylates, some pharmaceuticals, estrogens, phthalates), while there are fewer or no data for others (personal care products, perfluorinated compounds, brominated flame retardants, organotins, benzotriazoles, benzothiazoles, nanoparticles). AD operational parameters (sludge residence time, temperature), sludge characteristics (type of sludge, adaptation on the compound), physicochemical properties of ECs and co-metabolic phenomena seem to affect compounds' biodegradation. The use of sludge pretreatment methods does not seem to enhance ECs removal; whereas encouraging results have been reported when AD was combined with other treatment methods. Future efforts should be focused on better understanding of biotransformation processes and sorption phenomena occurred in anaerobic digesters, as well as on identification of (bio)transformation products.
Sternitzke, V., Kaegi, R., Audinot, J. N., Lewin, E., Hering, J. G., & Johnson, C. A. (2012). Uptake of fluoride from aqueous solution on nano-sized hydroxyapatite: examination of a fluoridated surface layer. Environmental Science and Technology, 46(2), 802-809. doi:10.1021/es202750t, Institutional Repository

Hydroxyapatite (Ca10(PO4)6(OH)2, HAP), both as a synthetic material and as a constituent of bone char, can serve as an effective and relatively inexpensive filter material for fluoride (F–) removal from drinking water in low-income countries. Fluoride uptake on HAP can occur through different mechanisms, which are, in principle, influenced by solution composition. Suspensions of HAP (2 g L–1) were equilibrated under controlled pH conditions (pH 6.5, 7.3, 9.5) at 25 °C for 28 d after the addition of different F– concentrations (0.5–7.0 mM). The reacted HAP solids were examined with Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Nano Secondary Ion Mass Spectroscopy (NanoSIMS). Fluoride uptake on HAP was dependent on pH, with the highest capacity at pH 6.5; the lowest uptake was found at pH 9.5. Under all experimental conditions, the thermodynamically stable mineral phase was fluorapatite, (Ca10(PO4)6F2, FAP). Fluoride uptake capacity was quantified on the basis of FTIR and XPS analysis, which was consistent with F– uptake from solution. The results of XPS and NanoSIMS analyses indicate that a fluoridated surface layer with a thickness of several nanometers is formed on nanosized HAP.
Udert, K. M., & Wächter, M. (2012). Complete nutrient recovery from source-separated urine by nitrification and distillation. Water Research, 46(2), 453-464. doi:10.1016/j.watres.2011.11.020, Institutional Repository

In this study we present a method to recover all nutrients from source-separated urine in a dry solid by combining biological nitrification with distillation. In a first process step, a membrane-aerated biofilm reactor was operated stably for more than 12 months, producing a nutrient solution with a pH between 6.2 and 7.0 (depending on the pH set-point), and an ammonium to nitrate ratio between 0.87 and 1.15 gN gN−1. The maximum nitrification rate was 1.8 ± 0.3 gN m−2 d−1. Process stability was achieved by controlling the pH via the influent. In the second process step, real nitrified urine and synthetic solutions were concentrated in lab-scale distillation reactors. All nutrients were recovered in a dry powder except for some ammonia (less than 3% of total nitrogen). We estimate that the primary energy demand for a simple nitrification/distillation process is four to five times higher than removing nitrogen and phosphorus in a conventional wastewater treatment plant and producing the equivalent amount of phosphorus and nitrogen fertilizers. However, the primary energy demand can be reduced to values very close to conventional treatment, if 80% of the water is removed with reverse osmosis and distillation is operated with vapor compression. The ammonium nitrate content of the solid residue is below the limit at which stringent EU safety regulations for fertilizers come into effect; nevertheless, we propose some additional process steps that will increase the thermal stability of the solid product.
Wunderlin, P., Mohn, J., Joss, A., Emmenegger, L., & Siegrist, H. (2012). Mechanisms of N2O production in biological wastewater treatment under nitrifying and denitrifying conditions. Water Research, 46(4), 1027-1037. doi:10.1016/j.watres.2011.11.080, Institutional Repository

Nitrous oxide (N2O) is an important greenhouse gas and a major sink for stratospheric ozone. In biological wastewater treatment, microbial processes such as autotrophic nitrification and heterotrophic denitrification have been identified as major sources; however, the underlying pathways remain unclear. In this study, the mechanisms of N2O production were investigated in a laboratory batch-scale system with activated sludge for treating municipal wastewater. This relatively complex mixed population system is well representative for full-scale activated sludge treatment under nitrifying and denitrifying conditions.
Under aerobic conditions, the addition of nitrite resulted in strongly nitrite-dependent N2O production, mainly by nitrifier denitrification of ammonia-oxidizing bacteria (AOB). Furthermore, N2O is produced via hydroxylamine oxidation, as has been shown by the addition of hydroxylamine. In both sets of experiments, N2O production was highest at the beginning of the experiment, then decreased continuously and ceased when the substrate (nitrite, hydroxylamine) had been completely consumed. In ammonia oxidation experiments, N2O peaked at the beginning of the experiment when the nitrite concentration was lowest. This indicates that N2O production via hydroxylamine oxidation is favored at high ammonia and low nitrite concentrations, and in combination with a high metabolic activity of ammonia-oxidizing bacteria (at 2 to 3 mgO2/l); the contribution of nitrifier denitrification by AOB increased at higher nitrite and lower ammonia concentrations towards the end of the experiment.
Under anoxic conditions, nitrate reducing experiments confirmed that N2O emission is low under optimal growth conditions for heterotrophic denitrifiers (e.g. no oxygen input and no limitation of readily biodegradable organic carbon). However, N2O and nitric oxide (NO) production rates increased significantly in the presence of nitrite or low dissolved oxygen concentrations.
Ye, X., Zhang, X., Morgenroth, E., & Finneran, K. T. (2012). Anthrahydroquinone-2,6-disulfonate increases the rate of hydrogen production during Clostridium beijerinckii fermentation with glucose, xylose, and cellobiose. International Journal of Hydrogen Energy, 37(16), 11701-11709. doi:10.1016/j.ijhydene.2012.05.018, Institutional Repository

Fermentative hydrogen production is considered a reasonable alternative for generating H2 as an energy carrier for electricity production using hydrogen fuel cells. The kinetics of hydrogen production from glucose, xylose and cellobiose were investigated using pure culture Clostridium beijerinckii NCIMB 8052. Adding anthrahydroquinone-2,6-disulfonate (AH2QDS) at concentrations ranging from 100 μM to 500 μM increased the hydrogen production rates from 0.80 to 1.35 mmol/L-hr to 1.20–2.70 mmol/L-hr with glucose, xylose, or cellobiose as the primary substrates. AH2QDS amendment also increased the substrate utilization rate and biomass growth rate by at least two times. These findings suggest that adding hydroquinone reducing equivalents influence cellular metabolism with hydrogen production rate, substrate utilization rate, and growth rate being simultaneously affected. Resting cell suspensions were conducted to investigate the influence of AH2QDS on the hydrogen production rate from glyceraldehyde 3-phosphate, which is a shared intermediate in both glycolysis and pentose phosphate pathway. Data demonstrated that hydrogen production rate increased by 1.5 times when glyceraldehyde 3-phosphate was the sole carbon source, suggesting that the hydroquinone may alter reactions starting with or after glyceraldehyde 3-phosphate in central metabolism. These data demonstrate that adding hydroquinones increased overall metabolic activity of C. beijerinckii. This will eventually increase the efficiency of industrial scale production once appropriate hydroquinone equivalents are identified that work well in large-scale operations, since fermentation rate is one of the two critical factors (production rate and yield) influencing efficiency and cost.
Bonalumi, M., Anselmetti, F. S., Kaegi, R., & Wüest, A. (2011). Particle dynamics in high-Alpine proglacial reservoirs modified by pumped-storage operation. Water Resources Research, 47(9), 1-15. doi:10.1029/2010WR010262, Institutional Repository

Temperature and suspended particle distribution were surveyed and modeled in two high-Alpine reservoirs in Switzerland, connected by pumped-storage operations for ∼30 years. Due to different glacier coverage of the catchments, the two reservoirs exhibit different particle concentrations and temperatures. After ice-breakup, the lower reservoir with a higher glacier cover in its catchment experiences a higher particle input becoming more turbid than the upper reservoir, which in contrast becomes warmer and thermally more stratified. The pumped-storage operations, which replace the basin volumes annually at least 6 (larger lower basin) to 10 (smaller upper basin) times, modify the physical characteristics of the two reservoirs. This is especially so in winter, when they are ice-covered, without riverine input and at low water level. Our reservoir investigations between 2007 and 2009 and the subsequent particle-balance model show that the upper and lower basins have become more and less turbid, respectively. Pumped-storage operations modify the stratification and particle distribution in both reservoirs and therefore alter the particle outflow and sedimentation. However, on the basis of particle concentrations and reservoir volumes, it is evident that the annually integrated particle release to downstream (∼40% of total) and to overall sedimentation (∼60%) have hardly changed. The budget model was useful in the prediction of particle distribution and sedimentation dynamics in the pumped-storage system. It implies that this approach can be useful for further employment during planning stages of power plants in order to modify and mitigate downstream particle loads in reservoir operations.
Bukowiecki, N., Zieger, P., Weingartner, E., Jurányi, Z., Gysel, M., Neininger, B., … Baltensperger, U. (2011). Ground-based and airborne in-situ measurements of the Eyjafjallajökull volcanic aerosol plume in Switzerland in spring 2010. Atmospheric Chemistry and Physics, 11(19), 10011-10030. doi:10.5194/acp-11-10011-2011, Institutional Repository

The volcanic aerosol plume resulting from the Eyjafjallajökull eruption in Iceland in April and May 2010 was detected in clear layers above Switzerland during two periods (17–19 April 2010 and 16–19 May 2010). In-situ measurements of the airborne volcanic plume were performed both within ground-based monitoring networks and with a research aircraft up to an altitude of 6000 m a.s.l. The wide range of aerosol and gas phase parameters studied at the high altitude research station Jungfraujoch (3580 m a.s.l.) allowed for an in-depth characterization of the detected volcanic aerosol. Both the data from the Jungfraujoch and the aircraft vertical profiles showed a consistent volcanic ash mode in the aerosol volume size distribution with a mean optical diameter around 3 ± 0.3 μm. These particles were found to have an average chemical composition very similar to the trachyandesite-like composition of rock samples collected near the volcano. Furthermore, chemical processing of volcanic sulfur dioxide into sulfate clearly contributed to the accumulation mode of the aerosol at the Jungfraujoch. The combination of these in-situ data and plume dispersion modeling results showed that a significant portion of the first volcanic aerosol plume reaching Switzerland on 17 April 2010 did not reach the Jungfraujoch directly, but was first dispersed and diluted in the planetary boundary layer. The maximum PM10 mass concentrations at the Jungfraujoch reached 30 μg m−3 and 70 μg m−3 (for 10-min mean values) during the April and May episode, respectively. Even low-altitude monitoring stations registered up to 45 μg m−3 of volcanic ash related PM10 (Basel, Northwestern Switzerland, 18/19 April 2010). The flights with the research aircraft on 17 April 2010 showed one order of magnitude higher number concentrations over the northern Swiss plateau compared to the Jungfraujoch, and a mass concentration of 320 (200–520) μg m−3 on 18 May 2010 over the northwestern Swiss plateau. The presented data significantly contributed to the time-critical assessment of the local ash layer properties during the initial eruption phase. Furthermore, dispersion models benefited from the detailed information on the volcanic aerosol size distribution and its chemical composition.
Bürgmann, H., Jenni, S., Vazquez, F., & Udert, K. M. (2011). Regime shift and microbial dynamics in a sequencing batch reactor for nitrification and anammox treatment of urine. Applied and Environmental Microbiology, 77(17), 5897-5907. doi:10.1128/AEM.02986-10, Institutional Repository

The microbial population and physicochemical process parameters of a sequencing batch reactor for nitrogen removal from urine were monitored over a 1.5-year period. Microbial community fingerprinting (automated ribosomal intergenic spacer analysis), 16S rRNA gene sequencing, and quantitative PCR on nitrogen cycle functional groups were used to characterize the microbial population. The reactor combined nitrification (ammonium oxidation)/anammox with organoheterotrophic denitrification. The nitrogen elimination rate initially increased by 400%, followed by an extended period of performance degradation. This phase was characterized by accumulation of nitrite and nitrous oxide, reduced anammox activity, and a different but stable microbial community. Outwashing of anammox bacteria or their inhibition by oxygen or nitrite was insufficient to explain reactor behavior. Multiple lines of evidence, e.g., regime-shift analysis of chemical and physical parameters and cluster and ordination analysis of the microbial community, indicated that the system had experienced a rapid transition to a new stable state that led to the observed inferior process rates. The events in the reactor can thus be interpreted to be an ecological regime shift. Constrained ordination indicated that the pH set point controlling cycle duration, temperature, airflow rate, and the release of nitric and nitrous oxides controlled the primarily heterotrophic microbial community. We show that by combining chemical and physical measurements, microbial community analysis and ecological theory allowed extraction of useful information about the causes and dynamics of the observed process instability.
Decrey, L., Udert, K. M., Tilley, E., Pecson, B. M., & Kohn, T. (2011). Fate of the pathogen indicators phage ΦX174 and Ascaris suum eggs during the production of struvite fertilizer from source-separated urine. Water Research, 45(16), 4960-4972. doi:10.1016/j.watres.2011.06.042, Institutional Repository

Human urine has the potential to be a sustainable, locally and continuously available source of nutrients for agriculture. Phosphate can be efficiently recovered from human urine in the form of the mineral struvite (MgNH4PO4·6H2O). However, struvite formation may be coupled with the precipitation of other constituents present in urine including pathogens, pharmaceuticals, and heavy metals. To determine if struvite fertilizer presents a microbiological health risk to producers and end users, we characterized the fate of a human virus surrogate (phage ΦX174) and the eggs of the helminth Ascaris suum during a low-cost struvite recovery process. While the concentration of phages was similar in both the struvite and the urine, Ascaris eggs accumulated within the solid during the precipitation and filtration process. Subsequent air-drying of the struvite filter cake partially inactivated both microorganisms; however, viable Ascaris eggs and infective phages were still detected after several days of drying. The infectivity of both viruses and eggs was affected by the specific struvite drying conditions: higher inactivation generally occurred with increased air temperature and decreased relative humidity. On a log–log scale, phage inactivation increased linearly with decreasing moisture content of the struvite, while Ascaris inactivation occurred only after achieving a minimum moisture threshold. Sunlight exposure did not directly affect the infectivity of phages or Ascaris eggs in struvite cakes, though the resultant rise in temperature accelerated the drying of the struvite cake, which contributed to inactivation.
Dominguez, D., Truffer, B., & Gujer, W. (2011). Tackling uncertainties in infrastructure sectors through strategic planning: the contribution of discursive approaches in the urban water sector. Water Policy, 13(3), 299-316. doi:10.2166/wp.2010.109, Institutional Repository

Several strategic planning approaches have been proposed for dealing with future uncertainties in the urban water infrastructure sector. We identify three well established perspectives that address uncertainties in strategic decisions: an adaptive perspective, focusing on an incremental adaptation of existing structures as a reaction to unforeseen developments, a modeling perspective, focusing on an improved characterization of future context conditions and a managerial perspective, focusing on increasing the flexibility of the infrastructure organization. Despite their virtues, these approaches have definite weaknesses in their approach to uncertainty: they often consider a restricted scope of alternatives, they face substantial difficulties in predicting context conditions over time periods of decades and often consider objectives and tradeoffs only implicitly. We elaborate and illustrate with a case study a fourth perspective that may compensate for these specific weaknesses and complement the established strategic planning approaches. This perspective is based on a discursive, qualitative assessment of key elements in the strategic planning process among a selected set of local stakeholders and decision makers. We maintain that this approach leads to a more explicit and reflexive treatment of future uncertainty, conflicting objectives and a broadening of the considered alternatives and therefore to a more robust decision-making process.
Dürrenmatt, D. J., & Gujer, W. (2011). Identification of industrial wastewater by clustering wastewater treatment plant influent ultraviolet visible spectra. Water Science and Technology, 63(6), 1153-1159. doi:10.2166/wst.2011.354, Institutional Repository

A procedure is proposed which allows the detection of industrial discharge events at the inlet of a wastewater treatment plant without the need for measurements performed at the industry, for special equipment and for exact knowledge of the industrial sewage. By performing UV/Vis measurements at the inlet of a plant and analyzing them with a two-staged clustering method consisting of the self-organizing map algorithm and the Ward clustering method, typical sewage clusters can be found. In an experiment performed at a mid-sized Swiss plant, one cluster of a cluster model with five clusters could be attributed to an industrial laundry. Out of 95 laundry discharging events measured in a validation period, 93 were correctly detected by the proposed algorithm, two were false positives and five were false negatives.
Etter, B., Tilley, E., Khadka, R., & Udert, K. M. (2011). Low-cost struvite production using source-separated urine in Nepal. Water Research, 45(11), 852-862. doi:10.1016/j.watres.2010.10.007, Institutional Repository

This research investigated the possibility of transferring phosphorus from human urine into a concentrated form that can be used as fertilizer in agriculture. The community of Siddhipur in Nepal was chosen as a research site, because there is a strong presence and acceptance of the urine-diverting dry toilets needed to collect urine separately at the source. Furthermore, because the mainly agricultural country is landlocked and depends on expensive, imported fertilizers, the need for nutrient security is high. We found that struvite (MgNH4PO4·6H2O) precipitation from urine is an efficient and simple approach to produce a granulated phosphorus fertilizer. Bittern, a waste stream from salt production, is a practical magnesium source for struvite production, but it has to be imported from India. Calculations show that magnesium oxide produced from locally available magnesite would be a cheaper magnesium source. A reactor with an external filtration system was capable of removing over 90% of phosphorus with a low magnesium dosage (1.1 mol Mg mol P), with coarse nylon filters (pore width up to 160 ± 50 μm) and with only one hour total treatment time. A second reactor setup based on sedimentation only achieved 50% phosphate removal, even when flocculants were added. Given the current fertilizer prices, high volumes of urine must be processed, if struvite recovery should be financially sustainable. Therefore, it is important to optimize the process. Our calculations showed that collecting the struvite and calcium phosphate precipitated spontaneously due to urea hydrolysis could increase the overall phosphate recovery by at least 40%. The magnesium dosage can be optimized by estimating the phosphate concentration by measuring electrical conductivity. An important source of additional revenue could be the effluent of the struvite reactor. Further research should be aimed at finding methods and technologies to recover the nutrients from the effluent.
Gresch, M., Armbruster, M., Braun, D., & Gujer, W. (2011). Effects of aeration patterns on the flow field in wastewater aeration tanks. Water Research, 45(2), 810-818. doi:10.1016/j.watres.2010.09.009, Institutional Repository

Due to the high energy input of aeration, the spatial distribution of air diffusers largely determines the flow field in aeration tanks. This has consequences on the efficiency of the aeration system, the performance of the aeration tank and on tank operation and control. This paper deals with these effects applying both Computational Fluid Dynamics (CFD) enhanced with a biokinetic model and full scale validation using velocity and reactive tracer measurements with high temporal and spatial resolution. It is shown that small changes in the diffuser arrangement drastically change the overall flow field. Using different aeration patterns in the same tank may lead to large scale instabilities in the flow field that lower plant performance and produce strong variations in concentration signals impeding their use for plant control. CFD is a valuable tool to analyze the interaction of flow field and aeration and their effects on plant performance and operation. But, in complex flow situations experimental validation is needed and strongly suggested.
Gresch, M., Braun, D., & Gujer, W. (2011). Using reactive tracers to detect flow field anomalies in water treatment reactors. Water Research, 45(5), 1984-1994. doi:10.1016/j.watres.2010.11.017, Institutional Repository

The hydraulics of water and wastewater treatment reactors has a major impact on their performance and control. The residence time distribution as a measure for the hydraulics represents macroscopic mixing in an integrated way with no spatial information. However, with regard to optimal sensor location for process control and for process optimisation measures, spatial information about macro-mixing is helpful. Spatially distributed measurements of reactive tracers can provide this information. In this paper we generally discuss how reactive tracers can be used to detect and characterize distinct large scale flow structures. It is shown that tracer substances are particularly suited if their reaction time scale is similar to the time scale of the large scale flow structure. For nitrifying activated sludge systems, ammonium is identified to be a suitable tracer. In a comprehensive experimental study at a real aeration tank, two distinct large scale flow features were identified by distributed ammonium measurements. Flow velocity measurements using acoustic Doppler velocimetry clearly supported the nature of these flow field anomalies. Ion selective electrodes are a well suited device for ammonium measurements providing the temporal resolution that is needed for such an analysis.
Hagendorfer, H., Kaegi, R., Traber, J., Mertens, S. F. L., Scherrers, R., Ludwig, C., & Ulrich, A. (2011). Application of an asymmetric flow field flow fractionation multi-detector approach for metallic engineered nanoparticle characterization - prospects and limitations demonstrated on Au nanoparticles. Analytica Chimica Acta, 706(2), 367-378. doi:10.1016/j.aca.2011.08.014, Institutional Repository

In this work we discuss about the method development, applicability and limitations of an asymmetric flow field flow fractionation (A4F) system in combination with a multi-detector setup consisting of UV/vis, light scattering, and inductively coupled plasma mass spectrometry (ICPMS). The overall aim was to obtain a size dependent-, element specific-, and quantitative method appropriate for the characterization of metallic engineered nanoparticle (ENP) dispersions. Thus, systematic investigations of crucial method parameters were performed by employing well characterized Au nanoparticles (Au-NPs) as a defined model system.
For good separation performance, the A4F flow-, membrane-, and carrier conditions were optimized. To obtain reliable size information, the use of laser light scattering based detectors was evaluated, where an online dynamic light scattering (DLS) detector showed good results for the investigated Au-NP up to a size of 80 nm in hydrodynamic diameter. To adapt large sensitivity differences of the various detectors, as well as to guarantee long term stability and minimum contamination of the mass spectrometer a split-flow concept for coupling ICPMS was evaluated. To test for reliable quantification, the ICPMS signal response of ionic Au standards was compared to that of Au-NP. Using proper stabilization with surfactants, no difference for concentrations of 1–50 μg Au L−1 in the size range from 5 to 80 nm for citrate stabilized dispersions was observed. However, studies using different A4F channel membranes showed unspecific particle–membrane interaction resulting in retention time shifts and unspecific loss of nanoparticles, depending on the Au-NP system as well as membrane batch and type. Thus, reliable quantification and discrimination of ionic and particular species was performed using ICPMS in combination with ultracentrifugation instead of direct quantification with the A4F multi-detector setup.
Figures of merit were obtained, by comparing the results from the multi detector approach outlined above, with results from batch-DLS and transmission electron microscopy (TEM). Furthermore, validation performed with certified NIST Au-NP showed excellent agreement. The developed methods show potential for characterization of other commonly used and important metallic engineered nanoparticles.
Huber, S. A., Balz, A., Abert, M., & Pronk, W. (2011). Characterisation of aquatic humic and non-humic matter with size-exclusion chromatography – organic carbon detection – organic nitrogen detection (LC-OCD-OND). Water Research, 45(2), 879-885. doi:10.1016/j.watres.2010.09.023, Institutional Repository

Size-exclusion chromatography in combination with organic carbon detection (SEC-OCD) is an established method to separate the pool of NOM into major fractions of different sizes and chemical functions and to quantify these on the basis of organic carbon. One specific approach, also known as LC-OCD-OND, is based on the Gräntzel thin-film UV-reactor. This approach is described with recent improvements in fraction assignation (humic substances, biopolymers, building blocks, low molecular weight organic acids and neutrals, hydrophobic organic carbon), the coupling of a novel organic nitrogen detector (OND), and an improved diagram for the characterisation of aquatic humic substances (HS-diagram). The diagram replaces the operational distinction between humic and fulvic acids by a continuum ranging from aquagenic fulvic acids to pedogenic humic acids.
Joss, A., Derlon, N., Cyprien, C., Burger, S., Szivak, I., Traber, J., … Morgenroth, E. (2011). Combined nitritation–anammox: advances in understanding process stability. Environmental Science and Technology, 45(22), 9735-9742. doi:10.1021/es202181v, Institutional Repository

Efficient nitrogen removal from wastewater containing high concentrations of ammonium but little organic substrate has recently been demonstrated by several full-scale applications of the combined nitritation–anammox process. While the process efficiency is in most cases very good, process instabilities have been observed to result in temporary process failures. In the current study, conditions resulting in instability and strategies to regain efficient operation were evaluated. First, data from full-scale operation is presented, showing a sudden partial loss of activity followed by recovery within less than 1 month. Results from laboratory-scale experiments indicate that these dynamics observed in full scale can be caused by partial inhibition of the ammonia oxidizing bacteria (AOB), while anammox inhibition is a secondary effect due to temporarily reduced O2 depletion. Complete anammox inhibition is observed at 0.2 mg O2·L–1, resulting in NO2– accumulation. However, this inhibition of anammox is reversible within minutes after O2 depletion. Thus, variable AOB activity was identified as the key to reactor stability. With appropriate interpretation of the online NH4+ signal, accumulation of NO2– can be detected indirectly and used to signal an imbalance of O2 supply and AOB activity (no suitable online NO2– electrode is currently available). Second, increased abundance of nitrite-oxidizing bacteria (NOB; competing with anammox for NO2–) is known as another cause of instability. Based on a comparison of parallel full-scale reactors, it is suggested that an infrequent and short-term increased O2 supply (e.g., for maintenance of aerators) that exceeds prompt depletion of oxygen by AOB may have caused increased NOB abundance. The volumetric air supply as a proxy for O2 supply thus needs to be linked to AOB activity. Further, NOB can be washed out of the system during regular operation if the system is operated at a sludge age in the range of 45 days and by controlling the air supply according to the NO3– concentration in the treated effluent. Early detection of growing NOB abundance while the population is still low can help guide process operation and it is suggested that molecular methods of quantifying NOB abundance should be tested.
Joss, A., Baenninger, C., Foa, P., Koepke, S., Krauss, M., McArdell, C. S., … Siegrist, H. (2011). Water reuse: >90% water yield in MBR/RO through concentrate recycling and CO2 addition as scaling control. Water Research, 45(18), 6141-6151. doi:10.1016/j.watres.2011.09.011, Institutional Repository

Over 1.5 years continuous piloting of a municipal wastewater plant upgraded with a double membrane system (ca. 0.6 m3 d−1 of product water produced) have demonstrated the feasibility of achieving high water quality with a water yield of 90% by combining a membrane bioreactor (MBR) with a submerged ultrafiltration membrane followed by a reverse osmosis membrane (RO). The novelty of the proposed treatment scheme consists of the appropriate conditioning of MBR effluent prior to the RO and in recycling the RO concentrates back to the biological unit.
All the 15 pharmaceuticals measured in the influent municipal sewage were retained below 100 ng L−1, a proposed quality parameter, and mostly below detection limits of 10 ng L−1. The mass balance of the micropollutants shows that these are either degraded or discharged with the excess concentrate, while only minor quantities were found in the excess sludge. The micropollutant load in the concentrate can be significantly reduced by ozonation. A low treated water salinity (<10 mM inorganic salts; 280 ± 70 μS cm−1) also confirms that the resulting product has a high water quality.
Solids precipitation and inorganic scaling are effectively mitigated by lowering the pH in the RO feed water with CO2 conditioning, while the concentrate from the RO is recycled to the biological unit where CO2 is stripped by aeration. This causes precipitation to occur in the bioreactor bulk, where it is much less of a process issue. SiO2 is the sole exception. Equilibrium modeling of precipitation reactions confirms the effectiveness of this scaling-mitigation approach for CaCO3 precipitation, calcium phosphate and sulfate minerals.
Kaegi, R., Voegelin, A., Sinnet, B., Zuleeg, S., Hagendorfer, H., Burkhardt, M., & Siegrist, H. (2011). Behavior of metallic silver nanoparticles in a pilot wastewater treatment plant. Environmental Science and Technology, 45(9), 3902-3908. doi:10.1021/es1041892, Institutional Repository

We investigated the behavior of metallic silver nanoparticles (Ag-NP) in a pilot wastewater treatment plant (WWTP) fed with municipal wastewater. The treatment plant consisted of a nonaerated and an aerated tank and a secondary clarifier. The average hydraulic retention time including the secondary clarifier was 1 day and the sludge age was 14 days. Ag-NP were spiked into the nonaerated tank and samples were collected from the aerated tank and from the effluent. Ag concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) were in good agreement with predictions based on mass balance considerations. Transmission electron microscopy (TEM) analyses confirmed that nanoscale Ag particles were sorbed to wastewater biosolids, both in the sludge and in the effluent. Freely dispersed nanoscale Ag particles were only observed in the effluent during the initial pulse spike. X-ray absorption spectroscopy (XAS) measurements indicated that most Ag in the sludge and in the effluent was present as Ag2S. Results from batch experiments suggested that Ag-NP transformation to Ag2S occured in the nonaerated tank within less than 2 h. Physical and chemical transformations of Ag-NP in WWTPs control the fate, the transport and also the toxicity and the bioavailability of Ag-NP and therefore must be considered in future risk assessments.
Kapałka, A., Fierro, S., Frontistis, Z., Katsaounis, A., Neodo, S., Frey, O., … Comninellis, C. (2011). Electrochemical oxidation of ammonia (NH4+/NH3) on thermally and electrochemically prepared IrO2 electrodes. Electrochimica Acta, 56(3), 1361-1365. doi:10.1016/j.electacta.2010.10.071, Institutional Repository

The electrochemical oxidation of ammonia (NH4+/NH3) in sodium perchlorate was investigated on IrO2 electrodes prepared by two techniques: the thermal decomposition of H2IrCl6 precursor and the anodic oxidation of metallic iridium. The electrochemical behaviour of Ir(IV)/Ir(III) surface redox couple differs between the electrodes indicating that on the anodic iridium oxide film (AIROF) both, the surface and the interior of the electrode are electrochemically active whereas on the thermally decomposed iridium oxide films (TDIROF), mainly the electrode surface participates in the electrochemical processes.
On both electrodes, ammonia is oxidized in the potential region of Ir(V)/Ir(IV) surface redox couple activity, thus, may involve Ir(V). During ammonia oxidation, TDIROF is deactivated, probably by adsorbed products of ammonia oxidation. To regenerate TDIROF, it is necessary to polarize the electrode in the hydrogen evolution region. On the contrary, AIROF seems not to be blocked during ammonia oxidation indicating its fast regeneration during the potential scan. The difference between both electrodes results from the difference in the activity of the iridium oxide surface redox couples.
Lorenz, C., Hagendorfer, H., von Goetz, N., Kaegi, R., Gehrig, R., Ulrich, A., … Hungerbühler, K. (2011). Nanosized aerosols from consumer sprays: experimental analysis and exposure modeling for four commercial products. Journal of Nanoparticle Research, 13, 3377-3391. doi:10.1007/s11051-011-0256-8, Institutional Repository

Consumer spray products are already on the market in the cosmetics and household sector, which suggest by their label that they contain engineered nanoparticles (ENP). Sprays are considered critical for human health, because the lungs represent a major route for the uptake of ENP into the human body. To contribute to the exposure assessment of ENP in consumer spray products, we analyzed ENP in four commercially available sprays: one antiperspirant, two shoe impregnation sprays, and one plant-strengthening agent. The spray dispersions were analyzed by inductively coupled plasma mass spectrometry (ICPMS) and (scanning-) transmission electron microscopy ((S)TEM). Aerosols were generated by using the original vessels, and analyzed by scanning mobility particle sizer (SMPS) and (S)TEM. On the basis of SMPS results, the nanosized aerosol depositing in the respiratory tract was modeled for female and male consumers. The derived exposure levels reflect a single spray application. We identified ENP in the dispersions of two products (shoe impregnation and plant spray). Nanosized aerosols were observed in three products that contained propellant gas. The aerosol number concentration increased linearly with the sprayed amount, with the highest concentration resulting from the antiperspirant. Modeled aerosol exposure levels were in the range of 1010 nanosized aerosol components per person and application event for the antiperspirant and the impregnation sprays, with the largest fraction of nanosized aerosol depositing in the alveolar region. Negligible exposure from the application of the plant spray (pump spray) was observed.
Peter-Varbanets, M., Margot, J., Traber, J., & Pronk, W. (2011). Mechanisms of membrane fouling during ultra-low pressure ultrafiltration. Journal of Membrane Science, 377(Feb), 42-53. doi:10.1016/j.memsci.2011.03.029, Institutional Repository

Gravity-driven, dead-end ultrafiltration of surface water, performed at ultra-low pressures without backflushing, cross-flow or chemical cleaning, results in flux stabilization during extended periods of time. This principle can be used for direct ultrafiltration of surface water without an external energy supply and low maintenance for decentralized drinking-water treatment. Here we investigate the mechanisms of membrane fouling and flux stabilization during gravity-driven, ultra low-pressure UF (ULP-UF). The impact of natural organic matter on the structure and resistance of the fouling layer is studied for different types of water, namely river water, pre-treated river water, river water with addition of sodium azide, aerobic diluted wastewater, diluted wastewater with a low dissolved oxygen content and river water spiked with humic acids or kaolin. Our results show that the deposition of non-dissolved material, biologically induced structural changes in the fouling layer and development of irremovable fouling are three major processes determining the fouling and flux stabilization in ULP-UF. The biologically induced structural changes in the fouling layer lead to heterogeneous structures and channel networks there and cause a decrease of the specific resistance of this layer over time. Flux stabilization occurs when the decrease of the resistance due to structural changes in the fouling layer balances the increase of resistance due to deposition and irremovable fouling.
Ramseier, M. K., Peter, A., Traber, J., & von Gunten, U. (2011). Formation of assimilable organic carbon during oxidation of natural waters with ozone, chlorine dioxide, chlorine, permanganate, and ferrate. Water Research, 45(5), 2002-2010. doi:10.1016/j.watres.2010.12.002, Institutional Repository

Five oxidants, ozone, chlorine dioxide, chlorine, permanganate, and ferrate were studied with regard to the formation of assimilable organic carbon (AOC) and oxalate in absence and presence of cyanobacteria in lake water matrices. Ozone and ferrate formed significant amounts of AOC, i.e. more than 100 μg/L AOC were formed with 4.6 mg/L ozone and ferrate in water with 3.8 mg/L dissolved organic carbon. In the same water samples chlorine dioxide, chlorine, and permanganate produced no or only limited AOC. When cyanobacterial cells (Aphanizomenon gracile) were added to the water, an AOC increase was detected with ozone, permanganate, and ferrate, probably due to cell lysis. This was confirmed by the increase of extracellular geosmin, a substance found in the selected cyanobacterial cells. AOC formation by chlorine and chlorine dioxide was not affected by the presence of the cells. The formation of oxalate upon oxidation was found to be a linear function of the oxidant consumption for all five oxidants. The following molar yields were measured in three different water matrices based on oxidant consumed: 2.4–4.4% for ozone, 1.0–2.8% for chlorine dioxide and chlorine, 1.1–1.2% for ferrate, and 11–16% for permanganate. Furthermore, oxalate was formed in similar concentrations as trihalomethanes during chlorination (~ 1% based on chlorine consumed). Oxalate formation kinetics and stoichiometry did not correspond to the AOC formation. Therefore, oxalate cannot be used as a surrogate for AOC formation during oxidative water treatment.
Schwyzer, I., Kaegi, R., Sigg, L., Magrez, A., & Nowack, B. (2011). Influence of the initial state of carbon nanotubes on their colloidal stability under natural conditions. Environmental Pollution, 159(6), 1641-1648. doi:10.1016/j.envpol.2011.02.044, Institutional Repository

The colloidal stability of dry and suspended carbon nanotubes (CNTs) in the presence of amphiphilic compounds (i.e. natural organic matter or surfactants) at environmentally realistic concentrations was investigated over several days. The suspensions were analyzed for CNT concentration (UV–vis spectroscopy), particle size (nanoparticle tracking analysis), and CNT length and dispersion quality (TEM). When added in dry form, around 1% of the added CNTs remained suspended. Pre-dispersion in organic solvent or anionic detergent stabilized up to 65% of the added CNTs after 20 days of mild shaking and 5 days of settling. The initial state of the CNTs (dry vs. suspended) and the medium composition hence are critical determinants for the partitioning of CNTs between sediment and the water column. TEM analysis revealed that single suspended CNTs were present in all suspensions and that shaking and settling resulted in a fractionation of the CNTs with shorter CNTs remaining predominantly in suspension.
Shimada, T., Li, X., Zilles, J. L., Morgenroth, E., & Raskin, L. (2011). Effects of the antimicrobial tylosin on the microbial community structure of an anaerobic sequencing batch reactor. Biotechnology and Bioengineering, 108(2), 296-305. doi:10.1002/bit.22934, Institutional Repository

The effects of the antimicrobial tylosin on a methanogenic microbial community were studied in a glucose-fed laboratory-scale anaerobic sequencing batch reactor (ASBR) exposed to stepwise increases of tylosin (0, 1.67, and 167 mg/L). The microbial community structure was determined using quantitative fluorescence in situ hybridization (FISH) and phylogenetic analyses of bacterial 16S ribosomal RNA (rRNA) gene clone libraries of biomass samples. During the periods without tylosin addition and with an influent tylosin concentration of 1.67 mg/L, 16S rRNA gene sequences related to Syntrophobacter were detected and the relative abundance of Methanosaeta species was high. During the highest tylosin dose of 167 mg/L, 16S rRNA gene sequences related to Syntrophobacter species were not detected and the relative abundance of Methanosaeta decreased considerably. Throughout the experimental period, Propionibacteriaceae and high GC Gram-positive bacteria were present, based on 16S rRNA gene sequences and FISH analyses, respectively. The accumulation of propionate and subsequent reactor failure after long-term exposure to tylosin are attributed to the direct inhibition of propionate-oxidizing syntrophic bacteria closely related to Syntrophobacter and the indirect inhibition of Methanosaeta by high propionate concentrations and low pH.
Shimada, T., Morgenroth, E., Tandukar, M., Pavlostathis, S. G., Smith, A., Raskin, I., & Kilian, R. F. (2011). Syntrophic acetate oxidation in two-phase (acid–methane) anaerobic digesters. Water Science and Technology, 64(9), 1812-1820. doi:10.2166/wst.2011.748, Institutional Repository

The microbial processes involved in two-phase anaerobic digestion were investigated by operating a laboratory-scale acid-phase (AP) reactor and analyzing two full-scale, two-phase anaerobic digesters operated under mesophilic (35 °C) conditions. The digesters received a blend of primary sludge and waste activated sludge (WAS). Methane levels of 20% in the laboratory-scale reactor indicated the presence of methanogenic activity in the AP. A phylogenetic analysis of an archaeal 16S rRNA gene clone library of one of the full-scale AP digesters showed that 82% and 5% of the clones were affiliated with the orders Methanobacteriales and Methanosarcinales, respectively. These results indicate that substantial levels of aceticlastic methanogens (order Methanosarcinales) were not maintained at the low solids retention times and acidic conditions (pH 5.2–5.5) of the AP, and that methanogenesis was carried out by hydrogen-utilizing methanogens of the order Methanobacteriales. Approximately 43, 31, and 9% of the archaeal clones from the methanogenic phase (MP) digester were affiliated with the orders Methanosarcinales, Methanomicrobiales, and Methanobacteriales, respectively. A phylogenetic analysis of a bacterial 16S rRNA gene clone library suggested the presence of acetate-oxidizing bacteria (close relatives of Thermacetogenium phaeum, ‘Syntrophaceticus schinkii,’ and Clostridium ultunense). The high abundance of hydrogen consuming methanogens and the presence of known acetate-oxidizing bacteria suggest that acetate utilization by acetate oxidizing bacteria in syntrophic interaction with hydrogen-utilizing methanogens was an important pathway in the second-stage of the two-phase digestion, which was operated at high ammonium-N concentrations (1.0 and 1.4 g/L). A modified version of the IWA Anaerobic Digestion Model No. 1 (ADM1) with extensions for syntrophic acetate oxidation and weak-acid inhibition adequately described the dynamic profiles of volatile acid production/degradation and methane generation observed in the laboratory-scale AP reactor. The model was validated with historical data from the full-scale digesters.
Sin, G., Gernaey, K. V., Neumann, M. B., van Loosdrecht, M. C. M., & Gujer, W. (2011). Global sensitivity analysis in wastewater treatment plant model applications: prioritizing sources of uncertainty. Water Research, 45(2), 639-651. doi:10.1016/j.watres.2010.08.025, Institutional Repository

This study demonstrates the usefulness of global sensitivity analysis in wastewater treatment plant (WWTP) design to prioritize sources of uncertainty and quantify their impact on performance criteria. The study, which is performed with the Benchmark Simulation Model no. 1 plant design, complements a previous paper on input uncertainty characterisation and propagation (Sin et al., 2009). A sampling-based sensitivity analysis is conducted to compute standardized regression coefficients. It was found that this method is able to decompose satisfactorily the variance of plant performance criteria (with R2 > 0.9) for effluent concentrations, sludge production and energy demand. This high extent of linearity means that the plant performance criteria can be described as linear functions of the model inputs under the defined plant conditions. In effect, the system of coupled ordinary differential equations can be replaced by multivariate linear models, which can be used as surrogate models. The importance ranking based on the sensitivity measures demonstrates that the most influential factors involve ash content and influent inert particulate COD among others, largely responsible for the uncertainty in predicting sludge production and effluent ammonium concentration. While these results were in agreement with process knowledge, the added value is that the global sensitivity methods can quantify the contribution of the variance of significant parameters, e.g., ash content explains 70% of the variance in sludge production. Further the importance of formulating appropriate sensitivity analysis scenarios that match the purpose of the model application needs to be highlighted. Overall, the global sensitivity analysis proved a powerful tool for explaining and quantifying uncertainties as well as providing insight into devising useful ways for reducing uncertainties in the plant performance. This information can help engineers design robust WWTP plants.
Velten, S., Knappe, D. R. U., Traber, J., Kaiser, H. P., von Gunten, U., Boller, M., & Meylan, S. (2011). Characterization of natural organic matter adsorption in granular activated carbon adsorbers. Water Research, 45(13), 3951-3959. doi:10.1016/j.watres.2011.04.047, Institutional Repository

The removal of natural organic matter (NOM) from lake water was studied in two pilot-scale adsorbers containing granular activated carbon (GAC) with different physical properties. To study the adsorption behavior of individual NOM fractions as a function of time and adsorber depth, NOM was fractionated by size exclusion chromatography (SEC) into biopolymers, humics, building blocks, and low molecular weight (LMW) organics, and NOM fractions were quantified by both ultraviolet and organic carbon detectors. High molecular weight biopolymers were not retained in the two adsorbers. In contrast, humic substances, building blocks and LMW organics were initially well and irreversibly removed, and their effluent concentrations increased gradually in the outlet of the adsorbers until a pseudo-steady state concentration was reached. Poor removal of biopolymers was likely a result of their comparatively large size that prevented access to the internal pore structure of the GACs. In both GAC adsorbers, adsorbability of the remaining NOM fractions, compared on the basis of partition coefficients, increased with decreasing molecular size, suggesting that increasingly larger portions of the internal GAC surface area could be accessed as the size of NOM decreased. Overall DOC uptake at pseudo-steady state differed between the two tested GACs (18.9 and 28.6 g-C/kg GAC), and the percent difference in DOC uptake closely matched the percent difference in the volume of pores with widths in the 1–50 nm range that was measured for the two fresh GACs. Despite the differences in NOM uptake capacity, individual NOM fractions were removed in similar proportions by the two GACs.
Wittmer, I. K., Scheidegger, R., Stamm, C., Gujer, W., & Bader, H. P. (2011). Modelling biocide leaching from facades. Water Research, 45(11), 3453-3460. doi:10.1016/j.watres.2011.04.003, Institutional Repository

Biocides leach from facades during rain events and subsequently enter the aquatic environment with storm water. Little is known about the losses of an entire settlement, since most studies referred to wash-off experiments conducted under laboratory conditions. Their results show a fast decrease of concentrations in the beginning, which subsequently slows down. The aim of this study is to develop a simple model to understand the mechanisms leading to these losses as well as to simulate losses under various rainfall and application conditions.
We developed a four-box model based on the knowledge gained from fits of an exponential function to an existing experimental data set of a wash-off experiment. The model consists of two mobile stocks from which biocides are washed off during a rain event. These mobile stocks are supplied with biocides from storage stocks by diffusion-type processes. The model accurately reproduced the measured data of wash-off during single cycles as well as peak wash-offs over all cycles.
Our model results for diuron losses showed that a large proportion (~70%) of the applied biocides are still in the stocks even after a rain volume corresponding to several years (1100 mm y−1, Swiss Plateau). Applications to realistic outdoor conditions showed that losses can not be neglected for urban environments and that knowledge about the amount of rainfall turned into runoff and the decay constants of the biocides in the facades are crucial. The model increased our understanding of the processes leading to the observed dynamic in laboratory experiments and was used to simulate losses for various rainfall and application conditions.
Zimmermann, S. G., Wittenwiler, M., Hollender, J., Krauss, M., Ort, C., Siegrist, H., & von Gunten, U. (2011). Kinetic assessment and modeling of an ozonation step for full-scale municipal wastewater treatment: micropollutant oxidation, by-product formation and disinfection. Water Research, 45(2), 605-617. doi:10.1016/j.watres.2010.07.080, Institutional Repository

The kinetics of oxidation and disinfection processes during ozonation in a full-scale reactor treating secondary wastewater effluent were investigated for seven ozone doses ranging from 0.21 to 1.24 g O3 g−1 dissolved organic carbon (DOC). Substances reacting fast with ozone, such as diclofenac or carbamazepine (kP,O3 > 104 M−1), were eliminated within the gas bubble column, except for the lowest ozone dose of 0.21 g O3 g−1 DOC. For this low dose, this could be attributed to short-circuiting within the reactor. Substances with lower ozone reactivity (kP,O3 < 104 M−1 s−1) were only fully eliminated for higher ozone doses.
The predictions of micropollutant oxidation based on coupling reactor hydraulics with ozone chemistry and reaction kinetics were up to a factor of 2.5 higher than full-scale measurements. Monte Carlo simulations showed that the observed differences were higher than model uncertainties. The overestimation of micropollutant oxidation was attributed to a protection of micropollutants from ozone attack by the interaction with aquatic colloids. Laboratory-scale batch experiments using wastewater from the same full-scale treatment plant could predict the oxidation of slowly-reacting micropollutants on the full-scale level within a factor of 1.5. The Rct value, the experimentally determined ratio of the concentrations of hydroxyl radicals and ozone, was identified as a major contribution to this difference.
An increase in the formation of bromate, a potential human carcinogen, was observed with increasing ozone doses. The final concentration for the highest ozone dose of 1.24 g O3 g−1 DOC was 7.5 μg L−1, which is below the drinking water standard of 10 μg L−1. N-Nitrosodimethylamine (NDMA) formation of up to 15 ng L−1 was observed in the first compartment of the reactor, followed by a slight elimination during sand filtration. Assimilable organic carbon (AOC) increased up to 740 μg AOC L−1, with no clear trend when correlated to the ozone dose, and decreased by up to 50% during post-sand filtration. The disinfection capacity of the ozone reactor was assessed to be 1–4.5 log units in terms of total cell counts (TCC) and 0.5 to 2.5 log units for Escherichia coli (E. coli). Regrowth of up to 2.5 log units during sand filtration was observed for TCC while no regrowth occurred for E. coli. E. coli inactivation could not be accurately predicted by the model approach, most likely due to shielding of E. coli by flocs.
Battilani, A., Steiner, M., Andersen, M., Back, S. N., Lorenzen, J., Schweitzer, A., … Andersen, M. N. (2010). Decentralised water and wastewater treatment technologies to produce functional water for irrigation. Agricultural Water Management, 98(3), 385-402. doi:10.1016/j.agwat.2010.10.010, Institutional Repository

The EU project SAFIR aimed to help farmers solve problems related to the use of low quality water for irrigation in a context of increasing scarcity of conventional freshwater resources. New decentralised water treatment devices (prototypes) were developed to allow a safe direct or indirect reuse of wastewater produced by small communities/industries or the use of polluted surface water. Water treatment technologies were coupled with irrigation strategies and technologies to obtain a flexible, easy to use, integrated management of the system. The challenge is to apply new strategies and technologies which allow using the lowest irrigation water quality without harming food safety or yield and fruit or derivatives quality. This study presents the results of prototype testing of a small-scale compact pressurized membrane bioreactor and of a modular field treatment system including commercial gravel filters and heavy-metal specific adsorption materials. Decentralised compact pressurised membrane biobooster (MBR), was able to remove up to 99.99% of the inlet Escherichia coli and 98.52% of total coliforms. E. coli was completely removed from irrigation water in 53% of the samples by the last MBR prototype version. In 2008, 100% of samples fulfilled WHO standards (1989) and Global Gap requirement for faecal contamination. MBR removed from inlet flow in the average 82% of arsenic, 82% of cadmium, 97% of chromium, 93% of copper and 99% of lead. Boron and manganese were not removed from permeate. The field treatment system (FT'S) proved to be effective against faecal contamination when applied with its complete set up including UV treatment. The sole gravel filter and heavy metal removal device (HMR) cannot provide sufficient and steadily treatment for microbial contamination. Nevertheless, gravel filter can remove up to 60% of E. coli but the removal process was not stable nor predictable. FTS removed 76% of arsenic, 80% of cadmium and copper, 88% of chromium and lead, and up to 97% of zinc. Like the MBR. boron and manganese were not removed from the irrigation water. Gravel filter directly fed with secondary treated wastewater was found able to remove 41% of arsenic, 36% of cadmium and lead, 48% of chromium and 46% of copper. The residual heavy metals concentration after the gravel filter was further reduced by the HMR: 35% for arsenic, 22% for cadmium, 25% for chromium, 33% for copper and 53% for lead.
Boltz, J. P., Morgenroth, E., & Sen, D. (2010). Mathematical modelling of biofilms and biofilm reactors for engineering design. Water Science and Technology, 62(8), 1821-1836. doi:10.2166/wst.2010.076, Institutional Repository

Mathematical models are critical to modern environmental biotechnology—both in research and in the engineering practice. Wastewater treatment plant (WWTP) simulators are used by consulting engineers and WWTP operators when planning, designing, optimizing, and evaluating the unit processes that comprise municipal and industrial WWTPs. Many WWTP simulators have been expanded to include a submerged completely-mixed biofilm reactor module that is based on the mathematical description of a one-dimensional biofilm. Leading consultants, equipment manufacturers, and WWTP modelling software developers have made meaningful contributions to advancing the use of biofilm models in engineering practice, but the bulk of the engineering community either does not use the now readily available biofilm reactor modules or utilizes them as ‘black-box’ design tools. The latter approach results in the mathematical biofilm models being no more useful than the empirical design criteria and formulations that have been historically applied to biofilm reactor design. The present work provides a consensus report on the state-of-the art, areas of uncertainty, and future needs for advancing the use of biofilm models in engineering design.
Bradac, P., Wagner, B., Kistler, D., Traber, J., Behra, R., & Sigg, L. (2010). Cadmium speciation and accumulation in periphyton in a small stream with dynamic concentration variations. Environmental Pollution, 158(3), 641-648. doi:10.1016/j.envpol.2009.10.031, Institutional Repository

Accumulation of cadmium in periphyton was investigated under field conditions while Cd concentration and speciation were dynamically varying in a small stream during rain events. Speciation in water was determined in situ by diffusion gradient in thin-films (DGT) and by modeling of complexation with fulvic acids. During the rain events, dissolved Cd concentrations increased from 0.17 nM to 0.27-0.36 nM, and 70-97% were DGT-labile. Cd content in periphyton closely followed Cd concentrations in water, despite higher concentrations of Zn and Mn, and may be controlled by either free or DGT-labile Cd concentrations. Decrease of Cd content in periphyton after the rain events was slower than the decrease of Cd concentration in water. Concentrations of Zn, Mn, Cu, Pb and Fe in periphyton also followed the dynamic variations of metal concentrations in water. Repeated exposure of periphyton to elevated dissolved Cd may lead to Cd accumulation.
Burkhardt, M., Zuleeg, S., Kägi, R., Sinnet, B., Eugster, J., Boller, M., & Siegrist, H. (2010). Verhalten von Nanosilber in Kläranlagen und dessen Einfluss auf die Nitrifikationsleistung in Belebtschlamm. Fate of nanosilver in wastewater treatment plants and their impact on nitrification activity in sewage sludge. Umweltwissenschaften und Schadstoff-Forschung, 22(5), 529-540. doi:10.1007/s12302-010-0153-2, Institutional Repository

Background, aim and scope The application of nanosilver is increasing. Knowledge on the fate and behavior of nanosilver in wastewater and wastewater treatment plants is scarce. Studies under real world conditions are completely lacking. We studied (1) the impact of nanosilver on the nitrification of sewage sludge, (2) quantified the mass flow of nanosilver in a pilot-plant, and (3) verified the mass balance in a full-scale municipal wastewater treatment plant where nanosilver is introduced to the municipal plant by an indirect discharger.
Materials and Methods The addition of four different nanosilver additives on ammonia oxidation in activated sludge has been studied in batch-reactors at two concentrations (1, 100 mg/L Ag) with two exposure times (2 h, 6 days). The pilot-plant treating 70 population equivalents of domestic wastewater is operated with a 12 day sludge age. Nanosilver was applied to the activated sludge tank within two sludge ages. The silver concentrations were measured in sludge and effluent samples during dosing and the following two sludge ages. The adsorption and speciation of silver particles has been analyzed using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Influent, effluent and sludge were sampled on a full-scale plant (60 000 equivalent inhabitants) and analyzed for silver.
Results Silver nitrate, metallic nanosilver, nano-scaled silver chloride and microcomposite silver did not show any effect on ammonia oxidation after the addition of 1 mg/L Ag to the activated sludge (corresponding to 250 mg Ag per kg solids). In contrast, 100 mg/L Ag inhibited the nitrification process by 100 % after the addition of silver nitrate and 20–30 % after addition of colloidal polymer-coated nanosilver. A complete mass balance of the pilot-plant, a steady-state system with known fluxes, demonstrates significant enrichment of silver in the sewage sludge (96 %) after the addition of silver chloride to the plant and small losses of silver into the secondary effluent (4 %). The mass fluxes are similar to metallic colloidal nanosilver investigated under the same conditions. The mass balance has been consistently confirmed by the full-scale study in a municipal wastewater treatment plant. The silver fluxes correspond to the fluxes of the suspended solids in sludge and effluent. Overall, it is estimated that from public wastewater treatment plants about 4–40 mg/a Ag per inhabitant equivalent are discharged annually to the receiving water. The analysis by SEM-EDX demonstrates adsorption and incorporation of nanosilver on biological flocs. This method yields first insight into complex building and transformation of silver associated with sulfide after adding metallic nanosilver and silver chloride to wastewater.
Discussion Silver ions released from nanosilver react immediately with large amounts of chloride present in wastewater to form silver chloride. Silver ions may react with organic ligands or sulfide groups additionally. Consequently, even silver nitrate added with 1 mg/L Ag (250 mg Ag/kg TS) to activated sludge did not inhibit nitrification activity. Very high amounts of nanosilver, i. e. 100 mg/L Ag, overburdened the system and equilibrium condition between silver ion release and ligands was not reached. The mass balance reflects the excellent attachment of nanosilver to activated sludge and biological flocs. Therefore, the main elimination process of nanosilver is attachment to the activated sludge. The elimination of nanosilver is high compared to organic and inorganic micro pollutants omnipresent in wastewater. Any further reduction of suspended solids in the effluent water will reduce the silver load.
Conclusions Generally, in wastewater nanosilver occurs bonded to activated sludge flocs and therefore the elimination of nanosilver is efficient under operation conditions typical for wastewater treatment plants. The major fraction of nanosilver is removed from the system by the excess sludge withdrawal. Nonetheless, the efficiency may be further improved by a tertiary filtration step. All analyses of influent, effluent and sludge confirmed that silver exists as silver sulfide. Due to a negligible water solubility of this silver species, silver ions are not subsequently released.
Recommendations and perspectives Nanosilver research should be driven to the identification of transformation processes in real environmental matrices and the influence of coatings on the adsorption behavior. There is no need for action to take special measures for nanosilver removal in the area of municipal wastewater treatment plants compared to ubiquitous hazardous organic pollutants may present in wastewater. Nevertheless, source control measures following the precautionary principle should be performed.
Glaus, R., Kaegi, R., Krumeich, F., & Günther, D. (2010). Phenomenological studies on structure and elemental composition of nanosecond and femtosecond laser-generated aerosols with implications on laser ablation inductively coupled plasma mass spectrometry. Spectrochimica Acta B: Atomic Spectroscopy, 65(9–10), 812-822. doi:10.1016/j.sab.2010.07.005, Institutional Repository

In laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), the properties of laser-generated aerosols, such as size and composition, are crucial for matrix-independent quantification. In this study, the aerosol particle morphology and elemental composition generated by two state-of-the-art laser systems (ArF excimer nanosecond-UV laser and Ti:sapphire femtosecond-IR laser) were investigated by electron microscopic techniques. Electrostatic sampling of the aerosols directly onto transmission electron microscopy (TEM) grids allowed us to study the morphology and elemental composition of the aerosols using TEM and TEM–EDX (energy dispersive X-ray spectroscopy) analyses, respectively. The results of the electron microscopic studies were finally compared to the LA-ICPMS signals of the main matrix components. The investigations were carried out for non-conducting materials (glass and zircon), metallic samples (steel and brass) and semiconductors (sulfides). The studies confirm that ns-LA-generated aerosols dominantly consist of nanoparticle agglomerates while conducting samples additionally contain larger spherical particles (diameter typically 50 to 500 nm). In contrast to ns-laser ablation, fs-LA-generated aerosols consist of a mixture of spherical particles and nanoparticle agglomerates for all investigated samples. Surprisingly, the differences in elemental composition between nanoparticle agglomerates and spherical particles produced with fs-LA were much more pronounced than in the case of ns-LA, especially for zircon (Si/Zr fractionation) and brass (Cu/Zn fractionation). These observations indicate different ablation and particle formation mechanisms for ns- and fs-LA. The particle growth mechanism for ns-LA is most likely a gas-to-particle conversion followed by agglomeration and additional hydrodynamic sputtering for conducting samples. On the other hand, phase explosion is assumed to be responsible for the mixture of large spherical particles and nanoparticle agglomerates as found for fs-LA-generated aerosols. Based on these mechanisms, the overall temporal elemental fractionation effects in ns-LA-ICPMS seem to occur mainly during the ablation. This effect was not observed for fs-LA-ICPMS despite the element separation into different particle fractions, which, on the other hand, could induce severe ICP-induced fractionation.
Gresch, M., Braun, D., & Gujer, W. (2010). The role of the flow pattern in wastewater aeration tanks. Water Science and Technology, 61(2), 407-414. doi:10.2166/wst.2010.803, Institutional Repository

Reactor hydraulics is one of the key factors for plant performance and plant control. The residence time distribution is a good but limited indicator of reactor hydraulics. A more detailed view is obtained by direct observations within the reactor. Two different techniques (conservative tracer, reactive tracer) are discussed to detect major anomalies in the flow field of a wastewater aeration tank. Experiments with conservative tracers give valuable information over a very limited period of time making the analysis of the flow field difficult. On the other hand, reactive tracers can be monitored long term which helps identifying the flow pattern provided that a high spatial and temporal resolution of the measurements is applied. Experimental data is used to determine the structure and the parameters of a compartment model that corresponds well with the measurements.
Gujer, W. (2010). Nitrification and me – a subjective review. Water Research, 44(1), 1-19. doi:10.1016/j.watres.2009.08.038, Institutional Repository

Based on the subjective experience of the author it is discussed how the nitrification processes served as an important basis for the development of today's understanding and mathematical models for many wastewater treatment processes (activated sludge, biofilm reactors) and self-purification processes in rivers. Besides being an important process for the protection of receiving waters, nitrification served as a proxy for the understanding of the behavior of a narrowly defined group of microorganisms growing on known substrates under environmental conditions. Until the upcoming of readily available microbial genetic techniques, nitrification was the single most studied microbial process in environmental engineering.
Kaegi, R., Voegelin, A., Folini, D., & Hug, S. (2010). Effect of phosphate, silicate, and Ca on the morphology, structure and elemental composition of Fe(III)-precipitates formed in aerated Fe(II) and As(III) containing water. Geochimica et Cosmochimica Acta, 74(20), 5798-5816. doi:10.1016/j.gca.2010.07.017, Institutional Repository

We investigated Fe(III)-precipitates formed from Fe(II) oxidation in water at pH 7 as a function of dissolved Fe(II), As(III), phosphate, and silicate in the absence and presence of Ca. We used transmission electron microscopy (TEM), including selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) to characterize the morphology, structure and elemental composition of the precipitates. Results from our companion X-ray absorption spectroscopy (XAS) study suggested that the oxidation of Fe(II) leads to the sequential formation of distinct polymeric units in the following order: Fe(III)–phosphate oligomers in the presence of phosphate, silicate-rich hydrous ferric oxide (HFO-Si) at high Si/Fe (>0.5) or 2-line ferrihydrite (2L-Fh) at lower Si/Fe (0.1–0.5), and lepidocrocite (Lp) in the absence of phosphate at low Si/Fe (<0.1). Results from this study show that the size of the polymeric units increased along the same sequence and that the aggregation of these polymeric units resulted in spherical particles with characteristic surface textures changing from smooth to coarse. The diameter of the spherical particles increased from 15 to 380 nm as the molar ratio (P + Si + As)/Fe(II) in the starting solution decreased and larger spherical particles precipitated from Ca-containing than from Ca-free solutions. These trends suggested that the size of the spherical particles was controlled by the charge of the polymeric units. Spherical particles coagulated into flocs whose size was larger in the presence than in the absence of Ca. Further observations pointed to the importance of Fe(II) oxidation and polymerization versus polymer aggregation and floc formation kinetics in controlling the spatial arrangement of the different polymeric units within Fe(III)-precipitates. The resulting structural and compositional heterogeneity of short-range-ordered Fe(III)-precipitates likely affects their colloidal stability and their chemical reactivity and needs to be considered when addressing the fate of co-transformed trace elements such as arsenic.
Kaegi, R., Sinnet, B., Zuleeg, S., Hagendorfer, H., Mueller, E., Vonbank, R., … Burkhardt, M. (2010). Release of silver nanoparticles from outdoor facades. Environmental Pollution, 158(9), 2900-2905. doi:10.1016/j.envpol.2010.06.009, Institutional Repository

In this study we investigate the release of metallic silver nanoparticles (Ag-NP) from paints used for outdoor applications. A facade panel mounted on a model house was exposed to ambient weather conditions over a period of one year. The runoff volume of individual rain events was determined and the silver and titanium concentrations of 36 out of 65 runoff events were measured. Selected samples were prepared for electron microscopic analysis. A strong leaching of the Ag-NP was observed during the initial runoff events with a maximum concentration of 145 μ Ag/l. After a period of one year, more than 30% of the Ag-NP were released to the environment. Particles were mostly <15 nm and are released as composite colloids attached to the organic binders of the paint. Microscopic results indicate that the Ag-NP are likely transformed to considerably less toxic forms such as Ag2S.
Kapałka, A., Katsaounis, A., Michels, N. L., Leonidova, A., Souentie, S., Comninellis, C., & Udert, K. M. (2010). Ammonia oxidation to nitrogen mediated by electrogenerated active chlorine on Ti/PtOx-IrO2. Electrochemistry Communications, 12(9), 1203-1205. doi:10.1016/j.elecom.2010.06.019, Institutional Repository

The electrochemical oxidation of ammonia (NH3 and/or NH4+) in the presence of chloride was investigated on a Ti/PtOx–IrO2 electrode. It was shown that ammonia is effectively removed from solution via electrogenerated active chlorine. Based on mass balances, nitrogen is postulated to be the main product of ammonia electrolysis. In the bulk, the concentration of chloramines was low. This could be explained by the fact that the oxidation of ammonia takes place close to the electrode surface where an excess of chlorine relative to ammonia is ensured during the process. This results in the oxidation of ammonia to N2 and in a local pH decrease. As a result, chloramines were decomposed in the proximity of the electrode prior to diffusing into the bulk.
Kapałka, A., Joss, L., Anglada, Á., Comninellis, C., & Udert, K. M. (2010). Direct and mediated electrochemical oxidation of ammonia on boron-doped diamond electrode. Electrochemistry Communications, 12(12), 1714-1717. doi:10.1016/j.elecom.2010.10.004, Institutional Repository

Direct (non-mediated) electrochemical oxidation of ammonia on boron-doped diamond (BDD) electrode proceeds mainly at high pH (>8) via free ammonia (NH3) oxidation. To enhance ammonia oxidation on BDD at low pH (<8), where mainly ammonium (NH4+) is present, oxidation of ammonia was mediated by active free chlorine. In this process, electro-generated in situ active chlorine rapidly reacts with ammonia instead of being further electro-oxidized to chlorate at the electrode surface. Thus, active chlorine effectively removes ammonia from an acidic solution, while the formation of by-products such as chlorate and possibly perchlorate is minimized.
Kapałka, A., Cally, A., Neodo, S., Comninellis, C., Wächter, M., & Udert, K. M. (2010). Electrochemical behavior of ammonia at Ni/Ni(OH)2 electrode. Electrochemistry Communications, 12(1), 18-21. doi:10.1016/j.elecom.2009.10.026, Institutional Repository

The electrochemical oxidation of ammonia was investigated on a Ni/Ni(OH)2 electrode prepared by potential cycling of a Ni electrode in 1 M NaClO4. It was found that oxidation of ammonia is strongly pH dependent and proceeds mainly at pH values above 7. This indicates that NH3 rather than NH4+ is oxidized on nickel electrodes. Oxidation of ammonia occurs in the potential region of Ni(II)/Ni(III) redox activity resulting in formation of a clear peak. Ni/Ni(OH)2 is not deactivated during ammonia oxidation even at high ammonia concentrations. A considerable fraction of the ammonia was oxidized to nitrate (11%), while the rest were gaseous nitrogen compounds. It is postulated that nitrogen was formed via a mechanism involving direct electron transfer from ammonia to the anode whereas the formation of nitrate involved oxygen transfer from water to an ammonia molecule.
Larsen, T. A., Maurer, M., Eggen, R. I. L., Pronk, W., & Lienert, J. (2010). Decision support in urban water management based on generic scenarios: the example of NoMix technology. Journal of Environmental Management, 91(12), 2676-2687. doi:10.1016/j.jenvman.2010.07.032, Institutional Repository

Urine source separation (NoMix technology) followed by processing the concentrated nutrient solution has the potential to become a cost-efficient alternative to conventional end-of-pipe nutrient elimination. A choice of processing technologies can only be made for specific scenarios, and there is currently no methodology for analyzing generic situations. In setting up a formalized decision-support methodology (based on STEEPLED analysis), we discuss how to create such generic scenarios, how to couple them with process engineering objectives, how to define the technology requirements, and finally how to produce a realistic subset of technology alternatives. The methodology is tested in five real scenarios. We also touch on the criteria for a final choice of technology taking into account large uncertainties about the performance of real technologies. We conclude that technology development is one of the most important requirements for implementing urine source separation in practice. There is an urgent need to develop cost-efficient processing technologies that satisfy the requirements of stakeholders.
Latkoczy, C., Kägi, R., Fierz, M., Ritzmann, M., Günther, D., & Boller, M. (2010). Development of a mobile fast-screening laser-induced breakdown detection (LIBD) system for field-based measurements of nanometre sized particles in aqueous solutions. Journal of Environmental Monitoring, 12(7), 1422-1429. doi:10.1039/c002020f, Institutional Repository

Laser-induced breakdown detection (LIBD) is a promising method to detect trace amounts of nanoparticles (NP, <100 nm) in aqueous suspensions. Based on available systems, we developed a mobile LIBD, designed for on-site and on-line measurements. We used the energy ratio of every laser pulse before and after passing the laser beam through the aqueous sample as a new method to detect laser-induced plasma events. The particle size and the particle number density are derived from recorded energy curves. Our LIBD is operated with a Nd:YAG laser at 100 Hz significantly reducing the measurement times compared to other LIBD systems operated at 20 Hz and increasing the capabilities for monitoring purposes. Long-term experiments on water samples revealed losses of NP up to 75% in 15 mL and 35% in 5 L sample containers after 3 months. The size of the particles remained constant (5 L) or slightly decreased (15 mL) indicating significant adsorption of NP to the walls of the sampling containers. Furthermore, we monitored the NP content of water after different purification steps at a drinking water plant (Maennedorf, Lake Zurich, Switzerland). Activated carbon filtration resulted in an increase of the particle size from ∼20 nm to ∼75 nm possibly caused by the release of organic fragments derived from the biology within the activated carbon tank. After the final ultrafiltration step the particle size was around 10 nm in agreement with the nominal cutoff of 100 kDa of the membrane. The results underline the strength of a fast-screening LIBD to detect relative changes in NP size and concentration.
Leemann, A., Lothenbach, B., Siegrist, H., & Hoffmann, C. (2010). Influence of water hardness on concrete surface deterioration caused by nitrifying biofilms in wastewater treatment plants. International Biodeterioration and Biodegradation, 64(6), 489-498. doi:10.1016/j.ibiod.2010.03.009, Institutional Repository

In aeration tanks of wastewater treatment plants (WWTP), biodeterioration can lead to a partial dissolution and ensuing erosion of the concrete due to an acid attack caused by the nitrifying biofilm covering the tank surface. In this study, concrete samples were exposed in four different WWTP. The CaO content of the cement used, the water-to-cement ratio, and curing affect the resistance of the concrete to acid attack. However, both experimental data and thermodynamic modeling show that water hardness is the dominating parameter for surface erosion. In the presence of high water hardness, the protons produced by the nitrifiers are buffered and the calcite precipitation occurring in all concrete samples is increased. This results in a decrease of porosity near the surface and higher mass transfer resistance against carbon dioxide and therefore in lower deterioration rates of the concrete.
Leisinger, S. M., Lothenbach, B., Saout, G. L., Kägi, R., Wehrli, B., & Johnson, C. A. (2010). Solid solutions between CrO4- and SO4-ettringite Ca6(Al(OH)6)2[(CrO4)x(SO4)1-x]3*26 H2O. Environmental Science and Technology, 44(23), 8983-8988. doi:10.1021/es100554v, Institutional Repository

Chromate is a toxic contaminant of potential concern, as it is quite soluble in the alkaline pH range and could be released to the environment. In cementitous systems, CrO42− is thought to be incorporated as a solid solution with SO42− in ettringite. The formation of a solid solution (SS) could lower the soluble CrO42− concentrations.
Ettringite containing SO42− or CrO42− and mixtures thereof have been synthesized. The resulting solids and their solubility after an equilibration time of 3 months have been characterized. For CrO4-ettringite at 25 °C, a solubility product log KS0 of −40.2 ± 0.4 was calculated: log KCrO4−ettringite = 6log{Ca2+} + 2log{Al(OH)4−} + 3log{CrO42−} + 4log{OH−} + 26log{H2O}. X-ray diffraction and the analysis of the solution indicated the formation of a regular solid solution between SO4- and CrO4-ettringite with a miscibility gap between 0.4 ≤ XCrO4 ≤ 0.6. The miscibility gap of the SO4- and CrO4-ettringite solid solution could be reproduced with a dimensionless Guggenheim fitting parameter (a0) of 2.03.
The presence of a solid solution between SO4- and CrO4-ettringite results in a stabilization of the solids compared to the pure ettringites and thus in an increased uptake of CrO42− in cementitious systems.
Li, X., Upadhyaya, G., Yuen, W., Brown, J., Morgenroth, E., & Raskin, L. (2010). Changes in the structure and function of microbial communities in drinking water treatment bioreactors upon addition of phosphorus. Applied and Environmental Microbiology, 76(22), 7473-7481. doi:10.1128/AEM.01232-10, Institutional Repository

Phosphorus was added as a nutrient to bench-scale and pilot-scale biologically active carbon (BAC) reactors operated for perchlorate and nitrate removal from contaminated groundwater. The two bioreactors responded similarly to phosphorus addition in terms of microbial community function (i.e., reactor performance), while drastically different responses in microbial community structure were detected. Improvement in reactor performance with respect to perchlorate and nitrate removal started within a few days after phosphorus addition for both reactors. Microbial community structures were evaluated using molecular techniques targeting 16S rRNA genes. Clone library results showed that the relative abundance of perchlorate-reducing bacteria (PRB) Dechloromonas and Azospira in the bench-scale reactor increased from 15.2% and 0.6% to 54.2% and 11.7% after phosphorus addition, respectively. Real-time quantitative PCR (qPCR) experiments revealed that these increases started within a few days after phosphorus addition. In contrast, after phosphorus addition, the relative abundance of Dechloromonas in the pilot-scale reactor decreased from 7.1 to 0.6%, while Zoogloea increased from 17.9 to 52.0%. The results of this study demonstrated that similar operating conditions for bench-scale and pilot-scale reactors resulted in similar contaminant removal performances, despite dramatically different responses from microbial communities. These findings suggest that it is important to evaluate the microbial community compositions inside bioreactors used for drinking water treatment, as they determine the microbial composition in the effluent and impact downstream treatment requirements for drinking water production. This information could be particularly relevant to drinking water safety, if pathogens or disinfectant-resistant bacteria are detected in the bioreactors.
Mikutta, C., Frommer, J., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2010). Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation. Geochimica et Cosmochimica Acta, 74(19), 5574-5592. doi:10.1016/j.gca.2010.06.024, Institutional Repository

In oxic environments contaminated with arsenate (As(V)), small polyhydroxycarboxylates such as citrate may impact the structure of precipitating ferrihydrite (Fh) and thus the surface speciation of As(V). In this study, ‘2-line’ Fh was precipitated from ferric nitrate solutions that were neutralized to pH 6.5 in the presence of increasing citrate concentrations and in the absence or presence of As(V). The initial citrate/Fe and As/Fe ratios were 0–50 mol% and 5 mol%, respectively. The reaction products, enriched with up to 0.32 mol citrate per mole Fe, were characterized by X-ray diffraction, transmission electron microscopy, and Fe and As K-edge X-ray absorption spectroscopy. Citrate decreased the particle size of Fh by impairing the polymerization of Fe(O,OH)6 octahedra via edge and corner linkages. In the presence of citrate and As(V), coordination numbers of Fe decreased by up to 28% relative to pure Fh. Citrate significantly reduced the static disorder of Fe–O bonds, implying a decreased octahedral distortion in Fh. Mean bond distances in Fh were not affected by citrate and remained constant within error at 1.98 Å for Fe–O, 3.03 Å for Fe–Fe1, and 3.45 Å for Fe–Fe2. Likewise, citrate had no effect on the As–Fe (3.31 Å) bond distance in As(V) coprecipitated with Fh. The As K-edge EXAFS data comply with the formation of (i) only monodentate binuclear (2C) As(V) surface complexes and (ii) combinations of 2C, monodentate mononuclear (1V), and outersphere As(V) surface complexes. Our results suggest that increasing citrate concentrations led to a decreasing 1V/2C ratio and/or that citrate increasingly impaired the formation of outersphere As(V) complexes. Moreover, citrate stabilized colloidal suspensions of Fh (pH 4.3–6.6, I 0.45 M) and reduced Fh formation at the expense of soluble Fe(III)-citrate complexes. At initial citrate/Fe ratios 25 mol%, between 8% and 41% of total Fe was bound in Fe(III)-citrate complexes after Fh formation. Polynuclear Fe(III)-citrate species were found to bind As(V) via surface complexes indistinguishable by EXAFS from those of As(V) adsorbed to or coprecipitated with Fh. Our study implies that low molecular weight polyhydroxycarboxylates may enhance the mobility of As(V) in aqueous systems of high ionic strength (e.g., neutralizing acid mine drainage) by colloidal stabilization of suspended Fh particles and the formation of ternary As(V) complexes.
Ort, C., Lawrence, M. G., Rieckermann, J., & Joss, A. (2010). Sampling for pharmaceuticals and personal care products (PPCPs) and illicit drugs in wastewater systems: are your conclusions valid? A critical review. Environmental Science and Technology, 44(16), 6024-6035. doi:10.1021/es100779n, Institutional Repository

The analysis of 87 peer-reviewed journal articles reveals that sampling for pharmaceuticals and personal care products (PPCPs) and illicit drugs in sewers and sewage treatment plant influents is mostly carried out according to existing tradition or standard laboratory protocols. Less than 5% of all studies explicitly consider internationally acknowledged guidelines or methods for the experimental design of monitoring campaigns. In the absence of a proper analysis of the system under investigation, the importance of short-term pollutant variations was typically not addressed. Therefore, due to relatively long sampling intervals, potentially inadequate sampling modes, or insufficient documentation, it remains unclear for the majority of reviewed studies whether observed variations can be attributed to “real” variations or if they simply reflect sampling artifacts. Based on results from previous and current work, the present paper demonstrates that sampling errors can lead to overinterpretation of measured data and ultimately, wrong conclusions. Depending on catchment size, sewer type, sampling setup, substance of interest, and accuracy of analytical method, avoidable sampling artifacts can range from “not significant” to “100% or more” for different compounds even within the same study. However, in most situations sampling errors can be reduced greatly, and sampling biases can be eliminated completely, by choosing an appropriate sampling mode and frequency. This is crucial, because proper sampling will help to maximize the value of measured data for the experimental assessment of the fate of PPCPs as well as for the formulation and validation of mathematical models. The trend from reporting presence or absence of a compound in “clean” water samples toward the quantification of PPCPs in raw wastewater requires not only sophisticated analytical methods but also adapted sampling methods. With increasing accuracy of chemical analyses, inappropriate sampling increasingly represents the major source of inaccuracy. A condensed step-by-step Sampling Guide is proposed as a starting point for future studies.
Peter-Varbanets, M., Hammes, F., Vital, M., & Pronk, W. (2010). Stabilization of flux during dead-end ultra-low pressure ultrafiltration. Water Research, 44(12), 3607-3616. doi:10.1016/j.watres.2010.04.020, Institutional Repository

Gravity driven ultrafiltration was operated in dead-end mode without any flushing or cleaning. In contrary to general expectations, the flux value stabilized after about one week of operation and remained constant during an extended period of time (several months). Different surface water types and diluted wastewater were used as feed water and, depending on the feed water composition, stable flux values were in the range of 4–10 L h−1 m−2. When sodium azide was added to the feed water to diminish the biological activity, no stabilization of flux occurred, indicating that biological processes play an important role in the flux stabilization process. Confocal laser scanning microscopy revealed the presence of a biofouling layer, of which the structure changed over time, leading to relatively heterogeneous structures. It is assumed that the stabilization of flux is related to the development of heterogeneous structures in the fouling layer, due to biological processes in the layer. The phenomenon of flux stabilization opens interesting possibilities for application, for instance in simple and low-cost ultrafiltration systems for decentralized drinking water treatment in developing and transition countries, independent of energy supply, chemicals, or complex process control.
Rieckermann, J., Borsuk, M. E., Sydler, D., Gujer, W., & Reichert, P. (2010). Bayesian experimental design of tracer studies to monitor wastewater leakage from sewer networks. Water Resources Research, 46(8), 1-14. doi:10.1029/2009WR008630, Institutional Repository

Despite more than a decade of research, the magnitude of wastewater leakage from defective sewer systems into groundwater supplies is still largely unknown, partly because reliable measurement methods are lacking. Although recently suggested in-sewer tracer studies present a promising solution, it is unclear how to optimally design such studies in network settings. In this study we present a formal experimental design procedure, which uses Bayesian data analysis to improve the diagnosis of sewer leakage by combining tracer test data with prior knowledge on network topology and condition. From a simulation study, we show that (1) if a single sewer section is expected to have high leakage, that section should be distinguished in measurement layouts through isolated tests or appropriate overlapping of multiple tests; (2) if multiple sections are expected to have high leakage, layouts with tests that cover more than one high-leakage section should be avoided; and (3) if a robust experimental design is desired, a balanced layout of tests that overlap multiple sections of high leakage, yet minimizes stretch length, should be chosen. This design will have the additional benefit of inducing covariance in the posterior distribution of exfiltration estimates, which can be used to advantage in subsequent studies. We apply these guidelines to a case study of a catchment in Zurich, Switzerland, and find that optimal layout design can improve the anticipated gain of information substantially relative to designs based on practical considerations alone. Remaining concerns regarding the procedure include (1) the generally poor understanding of the mechanisms governing sewer leakage, which can hamper reliable prior information on exfiltration; (2) the currently low measurement precision of sewer tracer studies, which might only allow for the detection of large leaks; and (3) the need for numerical implementation of the Bayesian inference procedure, which requires careful tuning and long computation times. In general, we were able to demonstrate that the incorporation of prior information through a Bayesian procedure adds significant value to experimental design, especially in situations with few "hard" data but good site-specific knowledge, which is common in water resources research.
Rieger, L., Takács, I., Villez, K., Siegrist, H., Lessard, P., Vanrolleghem, P. A., & Comeau, Y. (2010). Data reconciliation for wastewater treatment plant simulation studies-planning for high-quality data and typical sources of errors. Water Environment Research, 82(5), 426-433. doi:10.2175/106143009X12529484815511, Institutional Repository

Model results are only as good as the data fed as input or used for calibration. Data reconciliation for wastewater treatment modeling is a demanding task, and standardized approaches are lacking. This paper suggests a procedure to obtain high-quality data sets for model-based studies. The proposed approach starts with the collection of existing historical data, followed by the planning of additional measurements for reliability checks, a data reconciliation step, and it ends with an intensive measuring campaign. With the suggested method, it should be possible to detect, isolate, and finally identify systematic measurement errors leading to verified and qualitative data sets.
To allow mass balances to be calculated or other reliability checks to be applied, few additional measurements must be introduced in addition to routine measurements. The intensive measurement campaign should be started only after all mass balances applied to the historical data are closed or the faults have been detected, isolated, and identified. In addition to the procedure itself, an overview of typical sources of errors is given.
Ronteltap, M., Maurer, M., Hausherr, R., & Gujer, W. (2010). Struvite precipitation from urine - influencing factors on particle size. Water Research, 44(6), 2038-2046. doi:10.1016/j.watres.2009.12.015, Institutional Repository

Struvite crystallisation is a fast and reliable phosphorus removal and recovery process for concentrated waste streams – such as hydrolysed human urine. In order to optimise P-elimination efficiency, it is beneficial to obtain larger particle sizes: they are easier to separate and less prone to wash-out than smaller particles. This paper presents the results of a study on the effect of process parameters on particle size in a single step struvite precipitation. Crystals formed in batch experiments with real hydrolysed urine were shown to have an average size of >90 μm at pH 9 and 20 °C. This is reduced to 45 μm when changing stirrer type. Particle size increases with lower supersaturation. The results showed that under otherwise constant conditions, particle size decreases with lower temperature and has a minimum between pH 9 and 10. Deviating trends are observed at pH <8. Struvite formation in a CSTR (continuously stirred tank reactor) process was shown to be a reliable stable process that does not require any pH control. A method based on conductivity measurement is presented to estimate ionic strength, which is needed for equilibrium calculations.
Schmid Neset, T. S., Singer, H., Longrée, P., Bader, H. P., Scheidegger, R., Wittmer, A., & Andersson, J. C. M. (2010). Understanding consumption-related sucralose emissions - a conceptual approach combining substance-flow analysis with sampling analysis. Science of the Total Environment, 408(16), 3261-3269. doi:10.1016/j.scitotenv.2010.04.003, Institutional Repository

This paper explores the potential of combining substance-flow modelling with water and wastewater sampling to trace consumption-related substances emitted through the urban wastewater. The method is exemplified on sucralose. Sucralose is a chemical sweetener that is 600 times sweeter than sucrose and has been on the European market since 2004. As a food additive, sucralose has recently increased in usage in a number of foods, such as soft drinks, dairy products, candy and several dietary products. In a field campaign, sucralose concentrations were measured in the inflow and outflow of the local wastewater treatment plant in Linköping, Sweden, as well as upstream and downstream of the receiving stream and in Lake Roxen. This allows the loads emitted from the city to be estimated. A method consisting of solid-phase extraction followed by liquid chromatography and high resolution mass spectrometry was used to quantify the sucralose in the collected surface and wastewater samples. To identify and quantify the sucralose sources, a consumption analysis of households including small business enterprises was conducted as well as an estimation of the emissions from the local food industry.
The application of a simple model including uncertainty and sensitivity analysis indicates that at present not one large source but rather several small sources contribute to the load coming from households, small business enterprises and industry. This is in contrast to the consumption pattern seen two years earlier, which was dominated by one product. The inflow to the wastewater treatment plant decreased significantly from other measurements made two years earlier. The study shows that the combination of substance-flow modelling with the analysis of the loads to the receiving waters helps us to understand consumption-related emissions.
Voegelin, A., Kaegi, R., Frommer, J., Vantelon, D., & Hug, S. J. (2010). Effect of phosphate, silicate, and Ca on Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water studied by X-ray absorption spectroscopy. Geochimica et Cosmochimica Acta, 74(1), 164-186. doi:10.1016/j.gca.2009.09.020, Institutional Repository

We studied the local coordination and structure of Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water (buffered to pH 7 by 8 mM bicarbonate) using synchrotron-based X-ray absorption spectroscopy (XAS) at the K-edges of Fe, P, Ca, and As. Dissolved phosphate, silicate, and Ca at different ratios relative to each other and to Fe affect the forming Fe(III)-phases in a complex manner. The high affinity of phosphate for Fe(III) results in the predominant precipitation of Fe(III)-phosphate as long as dissolved phosphate is present, with Fe(III) polymerization limited to small oligomers. In Ca-containing solution, Ca uptake by Fe(III)–Ca-phosphate involves the linkage and coagulation of negatively charged Fe(III)-phosphate oligomers via Ca–O–P bonds. In the absence of phosphate, dissolved silicate at Si/Fe ratios above ~0.5 results in the formation of hydrous ferric oxide (HFO) with mainly edge-sharing Fe–Fe linkage. At lower Si/Fe ratios of ~0.5–0.1, mainly 2-line ferrihydrite (2L-Fh) with both edge- and corner-sharing Fe–Fe linkage forms. Only in the absence of phosphate at low Si/Fe ratio, lepidocrocite (Lp) forms. In solutions containing sufficient Fe(II), aeration results in the sequential precipitation of Fe(III)-(Ca-)phosphate, HFO or 2L-Fh (depending on solution Si/Fe), and finally Lp. The amount and oxidation state of As co-precipitated with Fe(III) are controlled by the co-oxidation of As(III) with Fe(II), which increases with initial Fe/As ratio, and the competitive uptake of phosphate, As(V) and less strongly sorbing silicate and As(III). This study demonstrates that the diversity and sequence of short-range-ordered Fe(III)-precipitates forming by Fe(II) oxidation in near-neutral natural waters depend on water chemistry. Because differences in the colloidal stability and biogeochemical reactivity of these phases will affect the fate of associated major and trace elements, the different Fe(III)-precipitates and their specific biogeochemical properties must be taken into account when addressing nutrient and contaminant dynamics at redox boundaries in natural and engineered systems.
Worms, I. A. M., Al-Gorani Szigeti, Z., Dubascoux, S., Lespes, G., Traber, J., Sigg, L., & Slaveykova, V. I. (2010). Colloidal organic matter from wastewater treatment plant effluents: characterization and role in metal distribution. Water Research, 44(1), 340-350. doi:10.1016/j.watres.2009.09.037, Institutional Repository

Colloidal organic matter from wastewater treatment plants was characterized and examined with respect to its role in metal distribution by using tangential flow ultrafiltration, liquid chromatography coupled with organic carbon and UV detectors, and an asymmetrical flow field-flow fractionation (AFlFFF) multidetection platform. Results revealed that a humic-like fraction of low aromaticity with an average molar mass ranging from 1600 to 2600 Da was the main colloidal component. High molar mass fractions (HMM), with molar mass ranges between 20 and 200 kDa, were present in lower proportions. Ag, Cd, Cu, Cr, Mn and Zn were found mainly in the dissolved phase (<0.45 μm) and their distribution between colloidal and truly dissolved fractions was strongly influenced by the distribution of dissolved organic carbon. AFlFFF coupled to ICP-MS showed that Ag, Cd, Cu, Cr, Mn and Zn associate to the low molar mass fraction of the colloidal pool, whereas Al, Fe and Pb were equally bound to low and high molar mass fractions.
Worms, I. A. M., Traber, J., Kistler, D., Sigg, L., & Slaveykova, V. I. (2010). Uptake of Cd(II) and Pb(II) by microalgae in presence of colloidal organic matter from wastewater treatment plant effluents. Environmental Pollution, 158(2), 369-374. doi:10.1016/j.envpol.2009.09.007, Institutional Repository

The present study addresses the key issue of linking the chemical speciation to the uptake of priority pollutants Cd(II) and Pb(II) in the wastewater treatment plant effluents, with emphasis on the role of the colloidal organic matter (EfOM). Binding of Cd(II) and Pb(II) by EfOM was examined by an ion exchange technique and flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry in parallel to bioassays with green microalga Chlorella kesslerii in ultrafiltrate (<1 kDa) and colloidal isolates (1 kDa to 0.45 μm). The uptake of Cd by C. kesslerii was consistent with the speciation analysis and measured free metal ion concentrations, while Pb uptake was much greater than that expected from the speciation measurement. Better understanding of the differences in the effects of the EfOM on Cd(II) and Pb(II) uptake required to take into account the size dependence of metal binding by EfOM.
Abegglen, C., Joss, A., Boehler, M., Buetzer, S., & Siegrist, H. (2009). Reducing the natural color of membrane bioreactor permeate with activated carbon or ozone. Water Science and Technology, 60(1), 155-165. doi:10.2166/wst.2009.331, Institutional Repository

The suitability of two membrane bioreactors for on-site wastewater treatment and reuse in Switzerland was investigated. The treated wastewater was used for toilet flushing and gardening, with water recycling rates of 30% (single family house) and almost 100% (toilets in a cable car station) respectively. Due to the recycling, an increase in a natural yellowish-brown color was observed, leading to double flushing of the toilets, higher cleaning requirements and increased permeate production. Color removal with ozone, powdered (PAC) and granulated (GAC) activated carbon was assessed in laboratory and field experiments. PAC was added directly into the MBR, whereas ozonation and GAC were applied to the permeate. The dosage of ozone or activated carbon depended on the recycling rate and color intensity. If color removal is necessary, PAC is the option best suited to small treatment plants, with a requirement of 30–50 g m-3 for 30% and 100 g m-3 for 100% water recycling.
Abegglen, C., Joss, A., McArdell, C. S., Fink, G., Schlüsener, M. P., Ternes, T. A., & Siegrist, H. (2009). The fate of selected micropollutants in a single-house MBR. Water Research, 43(7), 2036-2046. doi:10.1016/j.watres.2009.02.005, Institutional Repository

Membrane bioreactor (MBR) technology is an interesting option for single-house wastewater treatment or small communities. Because typically a very high effluent quality is achieved with respect to pathogens, suspended solids, organics and nitrogen, the permeate is well suited for reuse. Little is known about the fate of micropollutants in such small systems. The differences between centralized and decentralized biological wastewater treatment with respect to micropollutants are manifold: besides the operational parameters like hydraulic and sludge retention time, the main difference is in the load variation. While the influent load is expected to be more or less constant in large catchments, it varies strongly in small MBRs due to irregular consumption (e.g. of medication by individuals). Concentrations of micropollutants are higher by a factor 50–1000 than in centralized treatment. It is also unknown how reliable degradation of micropollutants is in case of irregular exposure.
In this study, two experiments were conducted in a small MBR treating the wastewater of a three-person household. During normal operation of the treatment plant, 25 pharmaceuticals (antibiotics, antiphlogistics, lipid regulators, iodinated contrast media and hormones) that had not been used by members of the household were added in concentrations typical for municipal wastewater. The removal of most substances was in the same range as for centralized wastewater treatment. It was shown that biological transformation was the main elimination process while adsorption to the activated sludge was negligible for most substances due to the low sludge production at high sludge retention time. No appreciable lag for inducing biological degradation was observed. The high hydraulic and sludge residence time had a positive effect on the elimination of slowly degradable substances, but this was partly compensated by the lower biological activity.
An experiment with antibiotics concentrations typical for decentralized treatment (between 500 and 1000 μg l−1; sulfamethoxazole, sulfapyridine, trimethoprim, clarithromycin, roxithromycin) did not show an inhibitory effect on either nitrification or denitrification.
Belia, E., Amerlinck, Y., Benedetti, L., Johnson, B., Sin, G., Vanrolleghem, P. A., … Villez, K. (2009). Wastewater treatment modelling: dealing with uncertainties. Water Science and Technology, 60(8), 1929-1941. doi:10.2166/wst.2009.225, Institutional Repository

This paper serves as a problem statement of the issues surrounding uncertainty in wastewater treatment modelling. The paper proposes a structure for identifying the sources of uncertainty introduced during each step of an engineering project concerned with model-based design or optimisation of a wastewater treatment system. It briefly references the methods currently used to evaluate prediction accuracy and uncertainty and discusses the relevance of uncertainty evaluations in model applications. The paper aims to raise awareness and initiate a comprehensive discussion among professionals on model prediction accuracy and uncertainty issues. It also aims to identify future research needs. Ultimately the goal of such a discussion would be to generate transparent and objective methods of explicitly evaluating the reliability of model results, before they are implemented in an engineering decision-making context.
Boltz, J. P., Morgenroth, E., deBarbadillo, C., Dempsey, M. J., McQuarrie, J. P., Ghylin, T., … Nerenberg, R. (2009). Biofilm reactor technology and design. In T. L. Krause & A. B. Pincince (Eds.), WEF manual of practice No. 8 ASCE manuals and reports on engineering practice No. 76: Vol. 2. Design of municipal wastewater treatment plants. Liquid treatment processes (p. (238 pp.). Retrieved from https://www.accessengineeringlibrary.com/content/book/9780071663588/toc-chapter/chapter13/section/section1, Institutional Repository

Biological systems treating municipal wastewater require (1) the accumulation of active microorganisms in a bioreactor and (2) the separation of microorganisms from treated effluent. In suspended growth reactors, such as the activated sludge process, microorganisms grow and bioflocculate, and the resultant flocs are suspended freely in the bulk phase. Flocculated bacteria are then separated from the bulk-liquid by sedimentation or membranes. Clarifier-coupled suspended growth reactors rely on return activated sludge, or underflow, from the clarifier to provide the desired active biomass concentration in the bioreactor. Consequently, clarification units may be hydraulically or solids limited (see Chapter 14 for additional information). Biofilm reactors retain bacterial cells in a biofilm attached to fixed or movable carriers. The biofilm matrix consists of water and a variety of soluble and particulate components that include soluble microbial products, inert material, and extracellular polymeric substances (EPS). [...]
Escher, B. I., Bramaz, N., & Ort, C. (2009). JEM Spotlight: monitoring the treatment efficiency of a full scale ozonation on a sewage treatment plant with a mode-of-action based test battery. Journal of Environmental Monitoring, 11(10), 1836-1846. doi:10.1039/b907093a, Institutional Repository

Tertiary treatment of wastewater with ozone is a promising technique for removing residual micropollutants that remain after secondary biological treatment. We monitored the performance of a full-scale ozonation reactor on a sewage treatment plant in Switzerland with a screening battery of bioassays. Six toxicity endpoints were selected that covered non-specific toxicity, as well as selected receptor-mediated modes of action and reactive toxicity. Non-specific toxicity was assessed with two bioassays, the bioluminescence inhibition of the marine luminescent bacterium Vibrio Fischeri and the growth inhibition of the green algae Pseudokirchneriella subcapitata. Treatment efficiency was around 90% for the secondary treatment, but only 65% and 76% for the ozonation step in the two non-specific endpoints, respectively. This finding is consistent with this type of oxidation reaction because ozone only modifies the organic molecules but does not mineralize them fully leaving residual toxicity of the transformation products. In contrast, the specific receptor-mediated endpoints of inhibition of photosystem II in algae and estrogenicity were largely reduced by ozonation. While compounds inhibiting photosynthesis proved to be rather recalcitrant toward biological treatment with only 47% removal, an additional 86% removal by ozonation yielded an overall treatment efficiency in the entire treatment chain of 89%. The effect on estrogenicity, quantified with the yeast estrogen screen, was even more significant: A treatment efficiency of 95% in the secondary treatment, 86% during ozonation plus a small effect by biological sand filtration yielded an overall treatment efficiency of 99.5%. Insecticides that inhibit acetylcholinesterase were fairly resistant to degradation, but an overall treatment efficiency of 91% was achieved in two steps: 72% in biological treatment and 60% during ozonation. Finally, no significant genotoxicity was observed with the umuC test after ozonation, while the influent showed a genotoxic response when it was enriched by a factor of 15 to 60. Treatment efficiency increased with the ozone dose and remained virtually unchanged over ozone doses above 500 g ozone per kg dissolved organic carbon. The reduction of toxicity can be rationalized by the chemical oxidation processes likely to occur for each group of chemicals that are typical for a given mode of toxic action. For comparison, tertiary treatment with powdered activated carbon was also evaluated, which poses a viable alternative to ozonation with respect to removal of micropollutants.
Gresch, M., Brügger, R., Meyer, A., & Gujer, W. (2009). Compartmental models for continuous flow reactors derived from CFD simulations. Environmental Science and Technology, 43(7), 2381-2387. doi:10.1021/es801651j, Institutional Repository

Reactor modeling is of major interest in environmental technology. In this context, new contaminants with higher degradation requirements increase the importance of reactor hydraulics. CFD (Computational Fluid Dynamics) may meet this challenge but is expensive for everyday use. In this paper, we provide research and practice with a methodology designed to automatically reduce the complexity of such a high-dimensional flow model to a compartmental model. The derivation is based on the concentration field of a reacting species which is included in the steady state CFD simulation. While still capturing the most important flow features, the compartmental model is fast, easy to use, and open for process modeling with yet unknown compounds. The inherent overestimation of diffusion by compartmental models has been corrected by locally adjusting turbulent fluxes. We successfully applied the methodology to the ozonation process and experimentally verified it with tracer experiments. The loss of information was quantified as a deviation from CFD performance prediction for different reactions. With increasing discretisation of the compartmental model, these deviations diminish. General advice on the necessary discretisation is given.
Hollender, J., Zimmermann, S. G., Koepke, S., Krauss, M., McArdell, C. S., Ort, C., … Siegrist, H. (2009). Elimination of organic micropollutants in a municipal wastewater treatment plant upgraded with a full-scale post-ozonation followed by sand filtration. Environmental Science and Technology, 43(20), 7862-7869. doi:10.1021/es9014629, Institutional Repository

The removal efficiency for 220 micropollutants was studied at the scale of a municipal wastewater treatment plant (WWTP) upgraded with post-ozonation followed by sand filtration. During post-ozonation, compounds with activated aromatic moieties, amine functions, or double bonds such as sulfamethoxazole, diclofenac, or carbamazepine with second-order rate constants for the reaction with ozone >104 M−1 s−1 at pH 7 (fast-reacting) were eliminated to concentrations below the detection limit for an ozone dose of 0.47 g O3 g−1 dissolved organic carbon (DOC). Compounds more resistant to oxidation by ozone such as atenolol and benzotriazole were increasingly eliminated with increasing ozone doses, resulting in >85% removal for a medium ozone dose (0.6 g O3 g−1 DOC). Only a few micropollutants such as some X-ray contrast media and triazine herbicides with second-order rate constants <102 M−1 s−1 (slowly reacting) persisted to a large extent. With a medium ozone dose, only 11 micropollutants of 55 detected in the secondary effluent were found at >100 ng L−1. The combination of reaction kinetics and reactor hydraulics, based on laboratory- and full-scale data, enabled a quantification of the results by model calculations. This conceptual approach allows a direct upscaling from laboratory- to full-scale systems and can be applied to other similar systems. The carcinogenic by-products N-nitrosodimethylamine (NDMA) (≤14 ng L−1) and bromate (<10 μg L−1) were produced during ozonation, however their concentrations were below or in the range of the drinking water standards. Furthermore, it could be demonstrated that biological sand filtration is an efficient additional barrier for the elimination of biodegradable compounds formed during ozonation such as NDMA. The energy requirement for the additional post-ozonation step is about 0.035 kWh m−3, which corresponds to 12% of a typical medium-sized nutrient removal plant (5 g DOC m−3).
Jermann, D., Pronk, W., Boller, M., & Schäfer, A. I. (2009). The role of NOM fouling for the retention of estradiol and ibuprofen during ultrafiltration. Journal of Membrane Science, 329(1–2), 75-84. doi:10.1016/j.memsci.2008.12.016, Institutional Repository

The impact of membrane fouling by natural organic matter (NOM) on the behavior of micropollutants during ultrafiltration (UF) was investigated. Batch experiments with radioactively labeled estradiol and ibuprofen in the presence of NOM model compounds (alginate, Nordic aquatic and Aldrich humic acid) were performed using a hydrophilic and a hydrophobic membrane. The results indicate that the impact of the NOM fractions studied on micropollutant retention correlated with the fouling mechanism of the individual NOM fractions. NOM substances of high molecular weight such as alginate and Aldrich HA that foul the membrane by pore blocking and cake/gel formation had a greater impact than the Nordic aquatic humic acid of lower molecular weight. The effect of cake formation was attributed partly to micropollutant-NOM partitioning and subsequent NOM retention and partly to the effect of the fouling layer itself acting as a kind of second membrane. Fouling by NOM cake/gel formation led to a significantly increased retention of estradiol, whereas the impact of fouling on ibuprofen retention was negligible due to significantly lower log Koc values of ibuprofen compared to estradiol. Moreover, NOM adsorption on the membrane can lower the adsorption of hydrophobic micropollutants. Membrane adsorption of estradiol was in the order of mg/m2 and was largely reversible with caustic solutions. The results of this study may prove useful for predicting the mass flow of micropollutants in UF applications.
Joss, A., Salzgeber, D., Eugster, J., König, R., Rottermann, K., Burger, S., … Siegrist, H. (2009). Full-scale nitrogen removal from digester liquid with partial nitritation and anammox in one SBR. Environmental Science and Technology, 43(14), 5301-5306. doi:10.1021/es900107w, Institutional Repository

Full-scale application of partial nitritation and anammox in a single suspended-growth sequencing batch (SBR) reactor presented here confirm the process suitable for removing nitrogen from ammonium-rich wastewater with low concentrations of BOD and suspended solids: details of simple and robust process control based on online ammonium or conductivity signals are discussed by describing the full-scale startup at three municipal plants (five reactors in total). Ammonium oxidation rates of up to 500 gN m−3d−1 with conversion to N2 of over 90% are achieved in a full-scale plant, but pilot results indicate that significantly higher rates are feasible. With continuous aeration at dissolved oxygen concentrations <1 mgO2·L−1, the nitrite oxidation and the anammox reaction occur simultaneously, allowing increased overall performance and simplified process control compared to separate aerobic and anaerobic phases (segregated either temporally or in different reactors). Sedimentation of the sludge requires special attention only during startup. Although the observed N2O emissions were slightly higher than in conventional nitrogen removal, the overall greenhouse gas emissions were lower, mainly due to energy-saving.
Joss, A., Böhler, M., Wedi, D., & Siegrist, H. (2009). Proposing a method for online permeability monitoring in membrane bioreactors. Water Science and Technology, 60(2), 497-506. doi:10.2166/wst.2009.370, Institutional Repository

Reliable and efficient operation of membrane bioreactors (MBR) for centralized municipal wastewater treatment strongly depends on a good monitoring of the membrane permeability, a value often used to quantify the transmissibility (i.e. the inverse of the flow resistance) of the membrane. By directly or indirectly evaluating this parameter the operator normally plans on the necessity and effectivity of maintenance activities. To allow the operator monitoring the membrane performance closely, the present paper proposes a method for online permeability based on the measurements of permeate flow, transmembrane pressure and water temperature. The theoretical background of the method is discussed and a data set of 250 days of continuous pilot operation of a municipal MBR equipped with three different standard membrane modules is used for testing. The method is numerically simple enough to allow being implemented on any programmable logical controller.
Kaelin, D., Manser, R., Rieger, L., Eugster, J., Rottermann, K., & Siegrist, H. (2009). Extension of ASM3 for two-step nitrification and denitrification and its calibration and validation with batch tests and pilot scale data. Water Research, 43(6), 1680-1692. doi:10.1016/j.watres.2008.12.039, Institutional Repository

Although traditionally not taken into account by most of activated sludge models the production of nitrite as an intermediate of the nitrification–denitrification processes becomes of interest in some specific plant operational situations or in case of high sensitivity of the receiving ecosystems. The Activated Sludge Model No.3 (ASM3) was therefore extended for two-step nitrification and two-step denitrification in order to better describe nitrite dynamics especially during the treatment of communal wastewater. Nitrite was included as a new model compound and as an intermediate product of biological processes, both for heterotrophic and autotrophic bacteria. Two new model compounds replace XA, the original autotrophic biomass: Ammonium Oxidizing Bacteria, XAOB and Nitrite Oxidizing Bacteria, XNOB. Growth and decay processes of nitrifiers were split into AOB and NOB processes (3 additional processes) and heterotrophic anoxic processes were also doubled in order to account for two-step denitrification (4 additional processes).
Default values from literature as well as laboratory measurements were considered for the choice of kinetic and stoichiometric parameters. The model was calibrated and validated with laboratory scale tests in batch reactors and with data from an Eawag activated sludge pilot plant configured conventionally with nitrification and pre-denitrification for the treatment of communal wastewater.
Kapałka, A., Fierro, S., Frontistis, Z., Katsaounis, A., Frey, O., Koudelka, M., … Udert, K. M. (2009). Electrochemical behaviour of ammonia (NH4+/NH3) on electrochemically grown anodic iridium oxide film (AIROF) electrode. Electrochemistry Communications, 11(8), 1590-1592. doi:10.1016/j.elecom.2009.06.003, Institutional Repository

The electrochemical behaviour of ammonia (NH4+/NH3) in sodium perchlorate at pH 9 has been investigated on electrochemically grown anodic iridium oxide film (AIROF) electrode. In base electrolyte at pH 9, the Ir(IV)/Ir(III) surface redox couple exhibits unusually large separation of the oxidation/reduction peaks (ΔEp~ 750 mV) due to the local pH changes within the oxide film. These local pH changes are induced by protons released/consumed during the Ir(IV)/Ir(III) redox activity. As a consequence, the local pH within AIROF changed up to 10 units during potential cycling. The presence of ammonia at pH 9 prevents these local pH changes because NH4+/NH3 buffer the solution inside the electrode. As a consequence, ΔEp of Ir(IV)/Ir(III) was reduced to 100 mV. It has been shown further that ammonia oxidation is mediated by Ir(V), resulting in the appearance of anodic peaks in forward and backward scans.
Krauss, M., Longrée, P., Dorusch, F., Ort, C., & Hollender, J. (2009). Occurrence and removal of N-nitrosamines in wastewater treatment plants. Water Research, 43(17), 4381-4391. doi:10.1016/j.watres.2009.06.048, Institutional Repository

The presence of nitrosamines in wastewater might pose a risk to water resources even in countries where chlorination or chloramination are hardly used for water disinfection. We studied the variation of concentrations and removal efficiencies of eight N-nitrosamines among 21 full-scale sewage treatment plants (STPs) in Switzerland and temporal variations at one of these plants. N-nitrosodimethylamine (NDMA) was the predominant compound in STP primary effluents with median concentrations in the range of 5–20 ng/L, but peak concentrations up to 1 μg/L. N-nitrosomorpholine (NMOR) was abundant in all plants at concentrations of 5–30 ng/L, other nitrosamines occurred at a lower number of plants at similar levels. From concentrations in urine samples and domestic wastewater we estimated that human excretion accounted for levels of <5 ng/L of NDMA and <1 ng/L of the other nitrosamines in municipal wastewater, additional domestic sources for <5 ng/L of NMOR. Levels above this domestic background are probably caused by industrial or commercial discharges, which results in highly variable concentrations in sewage. Aqueous removal efficiencies in activated sludge treatment were in general above 40% for NMOR and above 60% for the other nitrosamines, but could be lower if concentrations were below 8–15 ng/L in primary effluent. We hypothesize that substrate competition in the cometabolic degradation explains the occurrence of such threshold concentrations. An additional sand filtration step resulted in a further removal of nitrosamines from secondary effluents even at low concentrations. Concentrations released to surface waters were largely below 10 ng/L, suggesting a low impact on Swiss water resources and drinking water generation considering the generally high environmental dilution and possible degradation. However, local impacts in case a larger fraction of wastewater is present cannot be ruled out.
Mahmoud, M., Liu, Y., Hartmann, H., Stewart, S., Wagener, T., Semmens, D., … Winter, L. (2009). A formal framework for scenario development in support of environmental decision-making. Environmental Modelling and Software, 24(7), 798-808. doi:10.1016/j.envsoft.2008.11.010, Institutional Repository

Scenarios are possible future states of the world that represent alternative plausible conditions under different assumptions. Often, scenarios are developed in a context relevant to stakeholders involved in their applications since the evaluation of scenario outcomes and implications can enhance decision-making activities. This paper reviews the state-of-the-art of scenario development and proposes a formal approach to scenario development in environmental decision-making. The discussion of current issues in scenario studies includes advantages and obstacles in utilizing a formal scenario development framework, and the different forms of uncertainty inherent in scenario development, as well as how they should be treated. An appendix for common scenario terminology has been attached for clarity. Major recommendations for future research in this area include proper consideration of uncertainty in scenario studies in particular in relation to stakeholder relevant information, construction of scenarios that are more diverse in nature, and sharing of information and resources among the scenario development research community.
Morgenroth, E., & Milferstedt, K. (2009). Biofilm engineering: linking biofilm development at different length and time scales. Reviews in Environmental Science and Biotechnology, 8(3), 203-208. doi:10.1007/s11157-009-9163-1, Institutional Repository

Biofilms are heterogeneous and dynamic systems. Evaluation of biofilm structure and function at the microscale has been greatly advanced through the application of multidimensional imaging, in-situ identification of the microbial community composition, function, and genetic regulation. Biofilm reactors are being applied for advanced biological treatment processes and their overall (macroscale) operation is well understood and controlled. What is missing is the link between micro and macroscale. In this horizon paper we suggest how understanding the overall biofilm ecosystem will require an integrated evaluation of the different length and time scales.
Neale, P. A., Pronk, W., & Schäfer, A. I. (2009). Influence of pH on losses of analyte estradiol in sample prefiltration. Environmental Engineering Science, 26(6), 1157-1161. doi:10.1089/ees.2008.0291, Institutional Repository

Cellulose acetate 0.45-μm syringe filters could be used to filter environmental samples containing steroidal hormones, such as estradiol, prior to analysis. Such pretreatment may result in significant loss of analyte due to either adsorption of analyte to the filter material or association with retained colloidal and particulate materials. To determine the quantity of such losses, several experiments were performed by filtering water spiked with estradiol at different concentrations (50, 100, and 500ng/L) and pH (3–12) through cellulose acetate syringe filters. Further, the influence of added organic matter was studied. At all concentrations the experiments indicated that below pH 11, up to 50% of estradiol in the feed was adsorbed on the filter. This occurred regardless of the presence of bulk organic matter in solution, and was related to dissociation of estradiol with pH and subsequent changes in filter interaction. As a consequence, pretreatment of solutions containing estradiol should be adjusted to greater than pH 11 prior to filtration with 0.45-μm cellulose acetate filters.
Neumann, M. B., Gujer, W., & von Gunten, U. (2009). Global sensitivity analysis for model-based prediction of oxidative micropollutant transformation during drinking water treatment. Water Research, 43(4), 997-1004. doi:10.1016/j.watres.2008.11.049, Institutional Repository

This study quantifies the uncertainty involved in predicting micropollutant oxidation during drinking water ozonation in a pilot plant reactor. The analysis is conducted for geosmin, methyl tert-butyl ether (MTBE), isopropylmethoxypyrazine (IPMP), bezafibrate, β-cyclocitral and ciprofloxazin. These compounds are representative for a wide range of substances with second order rate constants between 0.1 and 1.9 × 104 M−1 s−1 for the reaction with ozone and between 2 × 109 and 8 × 109 M−1 s−1 for the reaction with OH-radicals. Uncertainty ranges are derived for second order rate constants, hydraulic parameters, flow- and ozone concentration data, and water characteristic parameters. The uncertain model factors are propagated via Monte Carlo simulation and the resulting probability distributions of the relative residual micropollutant concentrations are assessed. The importance of factors in determining model output variance is quantified using Extended Fourier Amplitude Sensitivity Testing (Extended-FAST). For substances that react slowly with ozone (MTBE, IPMP, geosmin) the water characteristic Rct-value (ratio of ozone- to OH-radical concentration) is the most influential factor explaining 80% of the output variance. In the case of bezafibrate the Rct-value and the second order rate constant for the reaction with ozone each contribute about 30% to the output variance. For β-cyclocitral and ciprofloxazin (fast reacting with ozone) the second order rate constant for the reaction with ozone and the hydraulic model structure become the dominating sources of uncertainty.
Ort, C., & Siegrist, H. (2009). Assessing wastewater dilution in small rivers with high resolution conductivity probes. Water Science and Technology, 59(8), 1593-1601. doi:10.2166/wst.2009.174, Institutional Repository

Installation and maintenance of flow gauging stations to assess wastewater dilution in small creeks is expensive. The method outlined in this paper provides a flexible and cheap alternative for situations with dilution factors smaller than 10 and unambiguous flow direction. It is shown that conductivity profiles from three sampling locations enable accurate identification of the dilution factor with an uncertainty of ±10–30%. Furthermore, much insight can be gained on the temporal behavior of both, the receiving water and the wastewater treatment system by combined analysis of conductivity and temperature data. In this case study the data also enabled identification and tracking down of illegal polluters.
Ort, C., Hollender, J., Schaerer, M., & Siegrist, H. (2009). Model-based evaluation of reduction strategies for micropollutants from wastewater treatment plants in complex river networks. Environmental Science and Technology, 43(9), 3214-3220. doi:10.1021/es802286v, Institutional Repository

A model based on graph theory was developed to efficiently evaluate the impact of the effluent from 742 wastewater treatment plants (WWTPs) on micropollutant loading throughout all river catchments in Switzerland. Model results agree well with measured loads for 12 compounds in river water samples, revealing mean predictive accuracy factors between 0.8 and 3.4. Subsequently, pollutant concentrations were predicted for river sections downstream from 543 WWTPs where hydrological information was available, and compared with recent recommendations for water quality criteria. At base flow conditions, carbamazepine concentrations (parent compound only) are ubiquitously below a water quality criterion of 0.5 μg L−1. In contrast, the sum of diclofenac and its metabolites is expected to exceed the corresponding water quality criterion of 0.1 μg L−1 in 224 river sections. If diclofenac cannot be eliminated at the source, the model suggests a directed upgrade of 173 WWTPs to meet the condition that concentrations are never to exceed this water quality criterion.
Peter-Varbanets, M., Zurbrügg, C., Swartz, C., & Pronk, W. (2009). Decentralized systems for potable water and the potential of membrane technology. Water Research, 43(2), 245-265. doi:10.1016/j.watres.2008.10.030, Institutional Repository

Decentralized drinking-water systems are an important element in the process of reaching the Millennium Development Goals, as centralized systems are often deficient or non-existent in developing and transition countries (DC and TC). Most water-quality problems are due to hygiene factors and pathogens. A range of decentralized systems is available to counter these problems, including thermal and/or UV methods, physical removal and chemical treatment.
This review focuses on decentralized systems that treat the potable water (drinking and cooking) of a single household (point-of-use systems) or a community (small-scale systems). For application in DC and TC, important boundary conditions for decentralized systems include low costs, ease of use, sustainability, low maintenance and independence of utilities (energy sources). Although some low-cost systems are available, their application is limited by time-consuming daily operation and maintenance. Other systems are too expensive for the poor populations of DC and TC and in most cases do not fulfill the system requirements described above. Point-of-use systems based on membranes are commercially available and are designed to operate on tap pressure or gravity.
Membrane systems are attractive since they provide an absolute barrier for pathogens and remove turbidity, thus increasing the palatability of the water. The costs of membrane have decreased rapidly during the last decades and therefore membrane systems have also become within reach for application in low-cost applications in DC and TC. Some membrane systems rely on gravity as a driving force, thereby avoiding the use of pumps and electricity. On the basis of the present literature data, no small-scale systems could be identified which meet all the requirements for successful implementation. Furthermore, in the available literature the performance of highly fouling water types has not been reported. For such cases, more extensive studies are required and a need for suitable pre-treatment was identified.
It can be concluded that there are good prospects for decentralized systems based on membranes, but that a need exists for research and development of systems with low costs and low maintenance, specifically designed for DC and TC.
Pronk, W., & Koné, D. (2009). Options for urine treatment in developing countries. Desalination, 248(1–3), 360-368. doi:10.1016/j.desal.2008.05.076, Institutional Repository

Interesting prospects of a urine-based product exist as a fertilizer in agricultural applications in developing countries. However, removal of pharmaceutical residues is essential to prevent long-termenvironmental hazards. In this paper, the perspectives of urine collection and treatment are discussed with a perspective of the developing countries. Scenarios are drawn up and discussed around the processes of electrodialysis, precipitation and evaporation. A new process combination is presented consisting of nitrification in sand filters and solar evaporation, which could potentially be implemented in developing countries. Such a scenario enables good perspectives for local business development, which is an important prerequisite for the implementation of new technologies in the developing countries.
Sin, G., Gernaey, K. V., Neumann, M. B., van Loosdrecht, M. C. M., & Gujer, W. (2009). Uncertainty analysis in WWTP model applications: a critical discussion using an example from design. Water Research, 43(11), 2894-2906. doi:10.1016/j.watres.2009.03.048, Institutional Repository

This study focuses on uncertainty analysis of WWTP models and analyzes the issue of framing and how it affects the interpretation of uncertainty analysis results. As a case study, the prediction of uncertainty involved in model-based design of a wastewater treatment plant is studied. The Monte Carlo procedure is used for uncertainty estimation, for which the input uncertainty is quantified through expert elicitation and the sampling is performed using the Latin hypercube method. Three scenarios from engineering practice are selected to examine the issue of framing: (1) uncertainty due to stoichiometric, biokinetic and influent parameters; (2) uncertainty due to hydraulic behaviour of the plant and mass transfer parameters; (3) uncertainty due to the combination of (1) and (2). The results demonstrate that depending on the way the uncertainty analysis is framed, the estimated uncertainty of design performance criteria differs significantly. The implication for the practical applications of uncertainty analysis in the wastewater industry is profound: (i) as the uncertainty analysis results are specific to the framing used, the results must be interpreted within the context of that framing; and (ii) the framing must be crafted according to the particular purpose of uncertainty analysis/model application. Finally, it needs to be emphasised that uncertainty analysis is no doubt a powerful tool for model-based design among others, however clear guidelines for good uncertainty analysis in wastewater engineering practice are needed.
Vernooij, M. G. C., Mohr, M., Tzvetkov, G., Zelenay, V., Huthwelker, T., Kaegi, R., … Grobéty, B. (2009). On source identification and alteration of single diesel and wood smoke soot particles in the atmosphere; an X-Ray microspectroscopy study. Environmental Science and Technology, 43(14), 5339-5344. doi:10.1021/es800773h, Institutional Repository

Diesel and wood combustion are major sources of carbonaceous particles in the atmosphere. It is very hard to distinguish between the two sources by looking at soot particle morphology, but clear differences in the chemical structure of single particles are revealed by C(1s) NEXAFS (near edge X-ray absorption fine structure) microspectroscopy. Soot from diesel combustion has a dominant spectral signature at ~285 eV from aromatic π-bonds, whereas soot from wood combustion has the strongest signature at ~287 eV from phenolic carbon bonds. To investigate if it is possible to use these signatures for source apportionment purposes, we collected atmospheric samples with either diesel or wood combustion as a dominant particle source. No spectra obtained from the atmospheric particles completely matched the emission spectra. Especially particles from the wood dominated location underwent large modifications; the phenolic spectral signature at ~287 eV is greatly suppressed and surpassed by the peak attributed to the aromatic carbon groups at ~285 eV. Comparison with spectra from diesel soot samples experimentally aged with ozone show that very fast modification of the carbon structure of soot particles occurs as soon as they enter the atmosphere. Source attribution of single soot particles with microspectroscopy is thus hardly possible, but NEXAFS remains a powerful tool to study aging effects.
Weber, F. A., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2009). Contaminant mobilization by metallic copper and metal sulphide colloids in flooded soil. Nature Geoscience, 2, 267-271. doi:10.1038/NGEO476, Institutional Repository

Colloids, such as submicrometre mineral particles or bacterial cells, can act as carriers enhancing the mobility of poorly soluble contaminants in subsurface environments1,2. In sulphate-reducing soils and sediments, metal sulphide precipitation has been proposed3-6 to generate contaminant-bearing sulphide colloids, which could transport contaminants traditionally thought to be immobilized by metal sulphide formation7. However, direct evidence for such a process is lacking. Here, we report the composition and morphology of pore-water colloids formed in contaminated floodplain soil when flooded with synthetic river water over a four-week period. We show that, on flooding, bacteria dispersed in the pore water mobilize copper by inducing biomineralization of metallic copper(0). We suggest that copper(0) crystals form by disproportionation of copper(I), which is released by copper-stressed bacteria to maintain copper homeostasis8,9. Sulphate reduction, which started on the fourth day of flooding, resulted in the mobilization of cadmium and lead, which were partitioned to copper-rich sulphide colloids showing two types of morphology: bacterium-associated 50–150-nm-diameter hollow particles formed through copper(0) transformation, and dispersed <50 nm nanoparticles, probably formed through homogeneous precipitation. The slow deposition of both types of sulphide colloid ensured elevated contaminant concentrations in the pore water for weeks. Our findings imply that colloid formation can enhance contaminant release from periodically sulphate-reducing soils and sediments, potentially polluting surface- and groundwaters.
Weissbrodt, D., Kovalova, L., Ort, C., Pazhepurackel, V., Moser, R., Hollender, J., … McArdell, C. S. (2009). Mass flows of X-ray contrast media and cytostatics in hospital wastewater. Environmental Science and Technology, 43(13), 4810-4817. doi:10.1021/es8036725, Institutional Repository

Little is known about the significance of hospitals as point sources for emission of organic micropollutants into the aquatic environment. A mass flow analysis of pharmaceuticals and diagnostics used in hospitals was performed on the site of a representative Swiss cantonal hospital. Specifically, we analyzed the consumption of iodinated X-ray contrast media (ICM) and cytostatics in their corresponding medical applications of radiology and oncology, respectively, and their discharge into hospital wastewater and eventually into the wastewater of the municipal wastewater treatment plant. Emission levels within one day and over several days were found to correlate with the pharmacokinetic excretion pattern and the consumed amounts in the hospital during these days. ICM total emissions vary substantially from day to day from 255 to 1259 g/d, with a maximum on the day when the highest radiology treatment occurred. Parent cytostatic compounds reach maximal emissions of 8−10 mg/d. A total of 1.1%, 1.4%, and 3.7% of the excreted amounts of the cytostatics 5-fluorouracil, gemcitabine, and 2′,2′-difluorodeoxyuridine (main metabolite of gemcitabine), respectively, were found in the hospital wastewater, whereas 49% of the total ICM was detected, showing a high variability among the compounds. These recoveries can essentially be explained by the high amount administered to out-patients (70% for cytostatics and 50% for ICM); therefore, only part of this dose is expected to be excreted on-site. In addition, this study emphasizes critical issues to consider when sampling in hospital sewer systems. Flow proportional sampling over a longer period is crucial to compute robust hospital mass flows.
Wick, A., Fink, G., Joss, A., Siegrist, H., & Ternes, T. A. (2009). Fate of beta blockers and psycho-active drugs in conventional wastewater treatment. Water Research, 43(4), 1060-1074. doi:10.1016/j.watres.2008.11.031, Institutional Repository

The removal of beta blockers and psycho-active drugs was investigated in a representative conventional German WWTP by long-term measurement campaigns along different biological treatment processes. The activated sludge treatment with an elevated SRT of 18 d was the only process which led to a significant removal of certain beta blockers and psycho-active drugs. The removal efficiency was below 60% for all compounds except for the natural opium alkaloids codeine and morphine being removed by more than 80%. Primary biological transformation and sorption onto sludge as the main removal mechanisms were examined in lab-scale batch experiments. Sorption onto activated sludge was found to be negligible (<3%). The biological transformation could be described by pseudo-first order kinetics and the transformation constants kbiol were used to predict the removal of beta blockers and psycho-active drugs in an activated sludge unit with a model. For most compounds the removal efficiencies measured on the full-scale WWTP were within the 95% confidence intervals predicted by the model. The results from full-scale measurements and modeling indicate that biological transformation in the nitrification tank together with parameters such as the sludge retention time and the temperature is crucial regarding the biological transformation of beta blockers and psycho-active drugs in conventional WWTPs.
Abegglen, C., Ospelt, M., & Siegrist, H. (2008). Biological nutrient removal in a small-scale MBR treating household wastewater. Water Research, 42(1–2), 338-346. doi:10.1016/j.watres.2007.07.020, Institutional Repository

The biological nutrient-removal potential of an on-site Membrane bioreactor (MBR) located in the basement of a four-person house treating domestic wastewater was investigated. The reactor consists of two tanks in series. This treatment plant differs from other conventional MBRs by a highly fluctuating influent water flow and a lack of pretreatment. During the first period, the first reactor was operated as a primary clarifier, resulting in nitrogen and phosphorus removals of 50% and 25%, respectively. Primary sludge production and bad odors in the basement were further disadvantages. When using the first reactor as an anaerobic/anoxic reactor by recycling activated sludge and mixing the first reactor, nitrogen and phosphorus removals of over 90% and 70% were achieved, respectively. By applying a dynamic model of the plant, the return sludge ratio was identified as the most important parameter. With a return sludge ratio of about 1.2, optimal PAO growth and phosphorous removal up to 90% was reached. Since only activated sludge is produced with this operational mode, on-site sludge dewatering is possible. During vacation periods without loading, the Bio-P activity is kept constant if the aeration is reduced to 5–20 min d–1.
Al-Halbouni, D., Traber, J., Lyko, S., Wintgens, T., Melin, T., Tacke, D., … Hollender, J. (2008). Correlation of EPS content in activated sludge at different sludge retention times with membrane fouling phenomena. Water Research, 42(6–7), 1475-1488. doi:10.1016/j.watres.2007.10.026, Institutional Repository

In this study, activated sludge characteristics were studied with regard to membrane fouling in membrane bioreactors (MBRs) for two pilot plants and one full-scale plant treating municipal wastewater. For the full-scale MBR, concentrations of extracellular polymeric substances (EPS) bound to sludge flocs were shown to have seasonal variations from as low as 17 mg g−1 dry matter (DM) in summer up to 51 mg (gDM)−1 in winter, which correlated with an increased occurrence of filamentous bacteria in the colder season. Therefore, it was investigated at pilot-scale MBRs with different sludge retention times (SRTs) whether different EPS contents and corresponding sludge properties influence membrane fouling. Activated sludge from the pilot MBR with low SRT (23 d) was found to have worse filterability, settleability and dewaterability. Photometric analysis of EPS extracts as well as LC-OCD measurements showed that it contained significantly higher concentrations of floc-bound EPS than sludge at higher SRT (40 d) The formation of fouling layers on the membranes, characterised by SEM-EDX as well as photometric analysis of EPS extracts, was more distinct at lower SRT where concentrations of deposited EPS were 40-fold higher for proteins and 5-fold higher for carbohydrates compared with the membrane at higher SRT. Floc-bound EPS and metals were suggested to play a role in the fouling process at the full-scale MBR and this was confirmed by the pilot-scale study. However, despite the different sludge properties, the permeability of membranes was found to be similar.
Braun, D., & Gujer, W. (2008). Reactive tracers reveal hydraulic and control instabilities in full-scale activated sludge plant. Water Science and Technology, 57(7), 1001-1007. doi:10.2166/wst.2008.210, Institutional Repository

The hydraulic characteristics of aeration tanks in WWTPs have a major impact on the degradation of pollutants, as well as on the control of the aeration. In particular in long reactors, which are not separated by baffles, hydraulic shortcuts or large scale recirculation can lead to a loss of performance. This work demonstrates that reactive tracers such as ammonium and oxygen can be used to investigate the hydraulics of aeration tanks in detail. With the use of electrochemical sensors it is possible to investigate effects in a broad range of time scales.
In the present case study a slow oscillation of the aeration control loop was investigated. Large scale recirculation in the aeration tank and fast fluctuations of the ammonium concentrations close to the oxygen sensor were identified as the cause of these oscillations. Both, the recirculation as well as the fluctuation of the ammonium have a substantial influence on the performance of the aeration tank and the aeration control loop.
Brepols, C., Dorgeloh, E., Frechen, F. B., Fuchs, W., Haider, S., Joss, A., … Wozniak, T. (2008). Upgrading and retrofitting of municipal wastewater treatment plants by means of membrane bioreactor (MBR) technology. Desalination, 231(1–3), 20-26. doi:10.1016/j.desal.2007.11.035, Institutional Repository

In the future, upgrading of existing wastewater treatment plants (wwtps) will become the more challenging task than erection of wholly new plants, as most of the plants (e.g. necessary in Germany) do exist already. Since some time, MBR technology has been taken into consideration and has been realised as an alternative for wwtp upgrading. This paper gives an overview about some relevant preconditions, basic upgrading concepts and examples of already upgraded wwtps using MBR technology.
Clauwaert, P., Tolêdo, R., van der Ha, D., Crab, R., Verstraete, W., Hu, H., … Rabaey, K. (2008). Combining biocatalyzed electrolysis with anaerobic digestion. Water Science and Technology, 57(4), 575-579. doi:10.2166/wst.2008.084, Institutional Repository

Biocatalyzed electrolysis is a microbial fuel cell based technology for the generation of hydrogen gas and other reduced products out of electron donors. Examples of electron donors are acetate and wastewater. An external power supply can support the process and therefore circumvent thermodynamical constraints that normally render the generation of compounds such as hydrogen unlikely. We have investigated the possibility of biocatalyzed electrolysis for the generation of methane. The cathodically produced hydrogen could be converted into methane at a ratio of 0.41 mole methane mole-1 acetate, at temperatures of 22 ± 2°C. The anodic oxidation of acetate was not hampered by ammonium concentrations up to 5gNL-1. An overview is given of potential applications for biocatalyzed electrolysis.
Dodd, M. C., Zuleeg, S., von Gunten, U., & Pronk, W. (2008). Ozonation of source-separated urine for resource recovery and waste minimization: process modeling, reaction chemistry, and operational considerations. Environmental Science and Technology, 42(24), 9329-9337. doi:10.1021/es800560r, Institutional Repository

Bench-scale, semibatch experiments were performed to examine physical−chemical constraints on ozone (O3) absorption and micropollutant oxidation during ozonation of source-separated hydrolyzed urine and the concentrate and diluate streams produced via electrodialysis of hydrolyzed urine. O3 consumption by each matrix was found to occur within a fast pseudo-first-order kinetic regime. Critical constraints on micropollutant oxidation were found through mass transfer modeling to be (i) micropollutant diffusion from the bulk solution into the gas−liquid interfacial film for compounds recalcitrant toward O3 (i.e., kO′′3,app ≤ 103 M−1 s−1), and (ii) aqueous-phase mixing for compounds highly reactive toward O3 (i.e., kO′′3,app > 103 M−1 s−1). Homogeneous chemical reaction modeling indicated that aqueous reaction chemistry is significantly influenced by the degree to which incidentally produced hydroxyl radicals are consumed by NH3 in each matrix, in terms of (a) micropollutant oxidation efficiencies, and (b) potential yields of oxidation byproducts. On the basis of the experimental data reported here, per capita energy requirements were estimated for treatment of source-separated urine via (1) ozonation, (2) ozonation with postelectrodialysis, and (3) electrodialysis with postozonation. These estimates indicate that scenario (1) would likely be less energy efficient than ozonation of municipal wastewater effluent in achieving equivalent reductions in urine-derived micropollutant loads, whereas scenarios (2 and 3) could be more efficient than equivalent centralized wastewater treatment strategies in achieving equivalent levels of urine-derived nutrient and micropollutant attenuation. Furthermore, experimental and model data suggest that urine ozonation efficiency may be substantially improved by optimizing aqueous-phase mixing and specific gas−liquid interfacial area.
Huset, C. A., Chiaia, A. C., Barofsky, D. F., Jonkers, N., Kohler, H. P. E., Ort, C., … Field, J. A. (2008). Occurrence and mass flows of fluorochemicals in the Glatt Valley watershed, Switzerland. Environmental Science and Technology, 42(17), 6369-6377. doi:10.1021/es703062f, Institutional Repository

Fluorochemicals are persistent contaminants that are globally distributed in air, water, sediments, and biota. Wastewater treatment plants (WWTPs) play an important role in mitigating pollutant releases from municipalities to aquatic and terrestrial environments. However, because WWTPs are point sources of fluorochemicals, it is important to understand their contribution to fluorochemical burdens in the greater context of watersheds. To this end, over a 1 week period, the mass flows of 11 fluorochemicals from seven WWTPs that discharge effluent into the Glatt River in Switzerland were measured and compared to the measured mass flows within the Glatt River. Overall, the fluorochemicals were not removed efficiently during wastewater treatment. Effluents from WWTPs and Glatt River water were dominated by perfluorooctane sulfonate, which was detected in all samples, followed by perfluorohexane sulfonate and perfluorooctanoate. The mass flows of fluorochemicals emanating from WWTPs were found to be conserved within the 35 km Glatt River, which indicates that input from the WWTPs is additive and that removal within the Glatt River is not significant. Per capita discharges of fluorochemicals were calculated from the populations served by the WWTPs studied; the values determined also account for the fluorochemical content of Lake Greifen (Greifensee), which is a lake at the headwaters of the Glatt River that also receives treated wastewater.
Jermann, D., Pronk, W., & Boller, M. (2008). Mutual influences between natural organic matter and inorganic particles and their combined effect on ultrafiltration membrane fouling. Environmental Science and Technology, 42(24), 9129-9136. doi:10.1021/es800654p, Institutional Repository

Fouling is one of the most critical aspects of membrane technology and is strongly influenced by natural water characteristics. This study focuses on a mechanistic understanding of the impact of interactions between natural organic matter (NOM) and particles on fouling. The model substances used were humic acid, alginate (polysaccharide), and kaolinite. NOM−kaolinite adsorption experiments, particle characterization, and dead-end ultrafiltration (UF) batch experiments were performed. The adsorption experiments indicated particle stabilization at low NOM equilibrium concentrations, whereas calcium induced significant aggregation, especially with alginate. UF experiments implicated a synergistic fouling effect of particle−NOM combinations, which was greatly reduced by calcium. Moreover, irreversible NOM fouling was only prevented by particles in the presence of calcium. On the basis of our results, we present a mechanistic model suggesting that synergistic fouling effects occur due to particle stabilization by NOM adsorption, especially shown for HA, and antagonistic effects due to particle destabilization by calcium. However, synergistic fouling can also be based on sterical interferences between larger NOM in the form of polysaccharides and particles during simultaneous pore blocking and cake formation. A heterogeneous NOM−particle fouling layer is ultimately formed with membrane associations dominated by NOM. The combined fouling is conclusively determined by the type of NOM, its specific fouling mechanisms, and its particle interactions prior to and during the filtration process.
Joss, A., Siegrist, H., & Ternes, T. A. (2008). Are we about to upgrade wastewater treatment for removing organic micropollutants?. Water Science and Technology, 57(2), 251-255. doi:10.2166/wst.2008.825, Institutional Repository

Activated sludge treatment allows only for a partial removal of micropollutants, mainly via sorption and biological degradation. Ozonation and activated carbon filtration are processes bearing the potential to drastically reduce the micropollutant load discharged to the environment after (centralized) biological treatment. The estimated total costs between 0.05 and 0.20€ per m3 treated water (depending on plant size and effluent DOC content) represent only a small fraction of the total costs for urban wastewater management and are therefore considered feasible. Full scale testing is currently planned or under way with the aim to a) confirm this cost estimation and b) to demonstrate the benefit by quantification of the effect of removal and by documenting the impact on the ecology of receiving waters. Ozonation would have the additional advantage of achieving partial disinfection. Another issue currently being intensively studied is the byproducts formed during ozonation and their toxicity. Evidence is needed that the formed ozonation byproducts are either harmless or easily degradable. Since a 5% to 20% loss of sewage is occurring due to sewer leakage and combined sewer overflow an improved reduction of micropollutant input to the aquatic environment requires that advanced centralized treatment is complemented with measures taken before discharge into the sewer. Options hereto may be waste design, labeling of compounds according to environmental friendliness or separate treatment of quantitatively significant point sources (e.g. hospital wastewater, nursery homes, industrial wastewater).
Kaegi, R., Wagner, T., Hetzer, B., Sinnet, B., Tzvetkov, G., & Boller, M. (2008). Size, number and chemical composition of nanosized particles in drinking water determined by analytical microscopy and LIBD. Water Research, 42(10–11), 2778-2786. doi:10.1016/j.watres.2008.02.009, Institutional Repository

In this paper we comprehensively characterized particles in drinking water originating from a lake water source. We focused on particles smaller than a few hundred nm. Several analytical techniques were applied to obtain information on number concentration, size distribution, morphology and chemical composition of the particles. Morphological information was obtained by atomic force microscopy (AFM) analysis. Two types of particles, spherical aggregates up to a few tens of nm and elongated fibers were identified. Similar structures were also observed in transmission electron microscope (TEM) images. A size distribution of the particles was obtained by applying image analysis (IA) tools on the TEM images. IA results showed an exponential increase of the particle number concentration down to 40 nm, which is the lower detection limit of our setup. The total number of particles down to 10 nm and the average particle diameter were determined with the laser-induced breakdown detection (LIBD) method. The results were in good agreement with the TEM-IA data and showed a total number concentration of roughly 108 particles/mL in the purified water. The carbon of the particles was investigated with scanning transmission X-ray microscopy (STXM), which revealed that most particles were organic matter; the C-1s spectra were typical for dissolved organic matter.
The methods were applied to characterize the particles from two different drinking waters treated with different methods (conventional vs. ultrafiltration (cut-off 100 kDa)). The results showed that the particle number density following ultrafiltration was lower by a factor of 5–10, compared to conventional treatment. However, the average particle diameter in the finished water of both treatment trains was roughly the same.
Kaegi, R., Ulrich, A., Sinnet, B., Vonbank, R., Wichser, A., Zuleeg, S., … Boller, M. (2008). Synthetic TiO2 nanoparticle emission from exterior facades into the aquatic environment. Environmental Pollution, 156(2), 233-239. doi:10.1016/j.envpol.2008.08.004, Institutional Repository

We present direct evidence of the release of synthetic nanoparticles from urban applications into the aquatic environment. We investigated TiO2 particles as these particles are used in large quantities in exterior paints as whitening pigments and are to some extent also present in the nano-size range.
TiO2 particles were traced from exterior facade paints to the discharge into surface waters. We used a centrifugation based sample preparation which recovers TiO2 particles between roughly 20 and 300 nm. Analytical electron microscopy revealed that TiO2 particles are detached from new and aged facade paints by natural weather conditions and are then transported by facade runoff and are discharged into natural, receiving waters. Microscopic investigations are confirmed by bulk chemical analysis. By combining results from microscopic investigations with bulk chemical analysis we calculated the number densities of synthetic TiO2 particles in the runoff.
Kaelin, D., Rieger, L., Eugster, J., Rottermann, K., Bänninger, C., & Siegrist, H. (2008). Potential of in-situ sensors with ion-selective electrodes for aeration control at wastewater treatment plants. Water Science and Technology, 58(3), 629-637. doi:10.2166/wst.2008.433, Institutional Repository

A pilot-scale activated sludge wastewater treatment plant (WWTP) operated with nitrification and pre-denitrification was monitored with a set of on-line sensors for over 3 years. Wet-chemistry ex-situ analyzers, UV and UV-Visible in-situ sensors and in-situ sensors based on ion-selective electrodes (ISE) were used. New ISE sensors for ammonium, nitrate and nitrite, adapted to water and wastewater matrices, have been released in recent years, With adequate quality control they proved to be highly accurate and reliable in WWTP influents and activated sludge (AS) reactors even at the end of the biological treatment zone, working at low ammonium concentrations (1–2 mgN/l). The ammonium measurement was used to test several feed-forward and feed-back aeration control strategies. The first aim was to keep inorganic nitrogen compounds, i.e. ammonium, nitrate and particularly nitrite, as low as possible in the effluent, and within Swiss national standards (<2.0 mgNH4-N/l, <0.3 mgNO2-N/l, 24 h average). All the strategies were successful at keeping ammonium low and subsequently at gaining denitrification capacity to significantly reduce the total nitrogen discharge. Some control strategies however generated temporary peaks of ammonium or even accumulation of nitrite.
Kracht, O., Gresch, M., & Gujer, W. (2008). Innovative tracer methods for sewer infiltration monitoring. Urban Water Journal, 5(3), 173-185. doi:10.1080/15730620802180802, Institutional Repository

Two innovative tracer methods for the quantification of extraneous discharges in sewers have been proposed as routine applications within the scope of the European research project APUSS (Assessing Infiltration and Exfiltration on the Performance of Urban Sewer Systems). In order to improve the accuracy of wastewater hydrograph separation compared to conventional practice, the novel approaches use intrinsic physicochemical characteristics (stable isotopes, pollutographs) of the wastewater as a natural tracer for the differentiation of its constituting components. The methods were evaluated and tested under field conditions and have been validated in the course of a comparative experimental study. We analyse the state of development achieved and demonstrate the application of the protocols with data from a reference experiment conducted in a combined sewer catchment housing 5400 inhabitants. The article details the requirements for suitable boundary conditions and presents a comprehensive assessment of measurement uncertainties.
Navarro, E., Piccapietra, F., Wagner, B., Marconi, F., Kaegi, R., Odzak, N., … Behra, R. (2008). Toxicity of silver nanoparticles to Chlamydomonas reinhardtii. Environmental Science and Technology, 42(23), 8959-8964. doi:10.1021/es801785m, Institutional Repository

Silver nanoparticles (AgNP) are likely to enter the aquatic environment because of their multiple uses. We have examined the short-term toxicity of AgNP and ionic silver (Ag+) to photosynthesis in Chlamydomonas reinhardtii using fluorometry. AgNP ranged in size from 10 to 200 nm with most particles around 25 nm. As determined by DGT (diffusive gradients in thin films), by ion-selective electrode, and by centrifugal ultrafiltration, about 1% of the AgNP was present as Ag+ ions. Based on total Ag concentration, toxicity was 18 times higher for AgNO3 than for AgNP (in terms of EC50). However, when compared as a function of the Ag+ concentration, toxicity of AgNP appeared to be much higher than that of AgNO3. The ionic Ag+ measured in the AgNP suspensions could not fully explain the observed toxicity. Cysteine, a strong Ag+ ligand, abolished the inhibitory effects on photosynthesis of both AgNP and Ag+. Together, the results indicate that the interaction of these particles with algae influences the toxicity of AgNP, which is mediated by Ag+. Particles contributed to the toxicity as a source of Ag+ which is formed in presence of algae.
Neumann, M. B., & Gujer, W. (2008). Underestimation of uncertainty in statistical regression of environmental models: influence of model structure uncertainty. Environmental Science and Technology, 42(11), 4037-4043. doi:10.1021/es702397q, Institutional Repository

As the quality of sensors increases, systematic discrepancies between measurements and model outputs become more apparent. Applying regression type analysis in these cases leads to autocorrelated residuals, biased parameter estimates, and underestimation of uncertainty. This paper examines how parameter estimates are affected by model structure uncertainty for an application from wastewater treatment. A Monod model is fitted to synthetic data generated by a reference system exhibiting predefined Tessier kinetics and a known error process. A range of methods are suggested to test if the resulting residuals fulfill the IID (independent and identically distributed)—requirement: visual examination of time series, autocorrelation, and partial autocorrelation functions, the Jarque−Bera normality test, the Runs test for independence, and the BDS test for IID. The tests are shown to perform well at low measurement noise but not at higher levels of noise where transferring the parameter estimates gained from a batch system leads to erroneous estimation of steady state concentrations in a completely stirred tank reactor. Additional diagnostics are suggested which include second order autocorrelation functions of the residuals in the case of a single experiment and examination of moving averages of residuals in the case of multiple experiments.
Ort, C., & Gujer, W. (2008). Sorption and high dynamics of micropollutants in sewers. Water Science and Technology, 57(11), 1791-1797. doi:10.2166/wst.2008.309, Institutional Repository

Down-the-drain household chemicals are mostly discharged intermittently (i.e. with water pulses, e.g. pharmaceuticals from toilet flushing) and well soluble micropollutants can, therefore, be subject to significantly high short-term fluctuations. It is not known how these fluctuations are attenuated by sorption to sewer sediments or biofilm. First, we investigated in this paper the effect of sorption for substances with high, medium and low affinity to particulate matter based on computational experiments. For substances with high Koc we found that the additional attenuation of a load pattern due to sorption is in the same order of magnitude as caused by dispersion in a typical main sewer. The mass flux between wastewater and the first biofilm layer was identified as the most sensitive parameter. Furthermore, the interplay of systematic, slow diurnal variations does not affect short-term fluctuations. Second, during rain events partial erosion of the biofilm can lead to increased micropollutant loads for substances with high Koc. This increase is in the same order of magnitude as diurnal variations of the loads in the liquid phase and the TSS.
Rieger, L., Langergraber, G., Kaelin, D., Siegrist, H., & Vanrolleghem, P. A. (2008). Long-term evaluation of a spectral sensor for nitrite and nitrate. Water Science and Technology, 57(10), 1563-1569. doi:10.2166/wst.2008.146, Institutional Repository

A spectral in-situ UV sensor was investigated to measure nitrite and nitrate concentrations in the effluent of the EAWAG pilot-scale plant. The sensor was used with a calibration that was based on data from another WWTP and was operated over a period of 1.5 years. The results showed constant accuracy although the sensor was operated with minimal maintenance (manual cleaning once a month). It could be shown that the sensor was able to accurately predict the nitrite and nitrate concentration with a precision of 0.32 mg N/l (95% prediction interval at mean lab value of 1.15 mg N/l) and 1.08 mg N/l (at 5.55 mg N/l) for nitrite and nitrate, respectively. The UV sensor showed good results for nitrite in the low concentration range and very accurate results for higher concentrations (up to 10 mg N/l). This allows using the sensor for alarm systems as well as for control concepts at WWTPs.
Siegrist, H., Salzgeber, D., Eugster, J., & Joss, A. (2008). Anammox brings WWTP closer to energy autarky due to increased biogas production and reduced aeration energy for N-removal. Water Science and Technology, 57(3), 383-388. doi:10.2166/wst.2008.048, Institutional Repository

Fifty years ago when only BOD was removed at municipal WWTPs primary clarifiers were designed with 2–3 hours hydraulic retention time (HRT). This changed with the introduction of nitrogen removal in activated sludge treatment that needed more BOD for denitrification. The HRT of primary clarification was reduced to less than one hour for dry weather flow with the consequence that secondary sludge had to be separately thickened and biogas production was reduced. Only recently the ammonia rich digester liquid (15–20% of the inlet ammonia load) could be treated with the very economic autotrophic nitritation/anammox process requiring half of the aeration energy and no organic carbon source compared to nitrification and heterotrophic denitrification. With the introduction of this new innovative digester liquid treatment the situation reverts, allowing us to increase HRT of the primary clarifier to improve biogas production and reduce aeration energy for BOD removal and nitrification at similar overall N-removal.
Sin, G., Kaelin, D., Kampschreur, M. J., Takács, I., Wett, B., Gernaey, K. V., … van Loosdrecht, M. C. M. (2008). Modelling nitrite in wastewater treatment systems: a discussion of different modelling concepts. Water Science and Technology, 58(6), 1155-1171. doi:10.2166/wst.2008.485, Institutional Repository

Originally presented at the 1st IWA/WEF Wastewater Treatment Modelling Seminar (WWTmod 2008), this contribution has been updated to also include the valuable feedback that was received during the Modelling Seminar. This paper addresses a number of basic issues concerning the modelling of nitrite in key processes involved in biological wastewater water treatment. To this end, we review different model concepts (together with model structures and corresponding parameter sets) proposed for processes such as two-step nitrification/denitrification, anaerobic ammonium oxidation and phosphorus uptake processes. After critically discussing these models with respect to their assumptions and parameter sets, common points of agreement as well as disagreement were elucidated. From this discussion a general picture of the state-of-the-art in the modelling of nitrite is provided. Taking this into account, a number of recommendations are provided to focus further research and development on nitrite modelling in biological wastewater treatment.
Stamm, C., Alder, A. C., Fenner, K., Hollender, J., Krauss, M., McArdell, C. S., … Schneider, M. K. (2008). Spatial and temporal patterns of pharmaceuticals in the aquatic environment: a review. Geography Compass, 2(3), 920-955. doi:10.1111/j.1749-8198.2008.00104.x, Institutional Repository

In recent years, human and veterinary pharmaceuticals have received much attention as pollutants of water bodies or drinking water resources due to possible negative effects on humans or the ecosystem even at very low concentrations. Over the last 10 years, considerable progress has been made regarding the knowledge of the exposure of water bodies to those drugs. This review summarizes the present understanding in this broad and interdisciplinary field incorporating contributions ranging from trace analytics to spatially distributed modelling of point-source and diffuse pollution. It discusses the main factors and processes controlling the environmental fate of pharmaceuticals from their usage to their spatial and temporal occurrence in water bodies. The current research is still rather phenomenological and further advancement of the field requires more integrated, quantitative mass flux analyses. Such analyses should also consider the explicit incorporation of uncertainties that appropriately reflect the current limited understanding and data availability.
Udert, K. M., Kind, E., Teunissen, M., Jenni, S., & Larsen, T. A. (2008). Effect of heterotrophic growth on nitritation/anammox in a single sequencing batch reactor. Water Science and Technology, 58(2), 277-284. doi:10.2166/wst.2008.389, Institutional Repository

The combination of nitritation and autotrophic denitrification (anammox) in a single sequencing batch reactor (SBR) is an energy efficient process for nitrogen removal from high-strength ammonia wastewaters. So far, the process has been successfully applied to digester supernatant. However, the process could also be suitable to treat source-separated urine, which has very high ammonium and organic substrate concentrations (up to 8,200 gN/m3 and 10,000 gCOD/m3). In this study, reactor performance was tested for digester supernatant and diluted source-separated urine. Ammonium concentrations in both solutions were similar (between 611 and 642 gN/m3), thus reactor performance could be directly compared. Differences were mainly due to higher activity of heterotrophic bacteria in urine. Nitrogen removal was slightly higher for source-separated urine, because heterotrophic bacteria denitrified the nitrate that was produced by anammox bacteria. In spite of higher heterotrophic growth with source-separated urine, calculated sludge concentrations at steady state were higher with digester supernatant due to accumulation of inert particulate organic matter from the influent. Although the sludge concentrations are less problematic for source-separated urine, process instabilities are more likely, because lower pH values are reached and heterotrophic denitrification can cause sudden increases of nitrite concentrations and/or nitric oxide. Both compounds inhibit aerobic ammonium oxidizing bacteria, heterotrophic bacteria and, most importantly, anammox bacteria. Nitrite and nitric oxide production by heterotrophic denitrification must be better understood to optimize nitritation/anammox for source-separated urine.
Wedi, D., & Joss, A. (2008). Dimensioning of membrane bioreactors for municipal wastewater treatment. Water Science and Technology, 57(6), 829-835. doi:10.2166/wst.2008.117, Institutional Repository

A basic procedure is proposed for dimensioning membrane bioreactors that is generally applicable. It evaluates the required membrane surface with particular consideration of loading combinations and hydraulic loading characteristics; it also takes into account ranges of minimum temperatures and corresponding fluxes as given by suppliers. The procedures, while likely to require further improvement, should make MBR design more transparent and aid the comparison of design variants
Boehler, M., & Siegrist, H. (2007). Potential of activated sludge ozonation. Water Science and Technology, 55(12), 181-187. doi:10.2166/wst.2007.407, Institutional Repository

The disposal of sewage sludge and the agricultural use of stabilised sludge are decreasing due to more stringent regulations in Europe. An increasing fraction of sewage sludge must,therefore be dewatered, dried, incinerated and the ashes disposed of in landfills. These processes are cost-intensive and also lead to the loss of the valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Partial ozonation of the return sludge of an activated sludge system significantly reduces excess sludge production, improves the settling properties of the sludge and reduces bulking and scumming. The solubilised COD will also improve denitrification if the treated sludge is recycled to the anoxic zone. However, ozonation partly kills nitrifiers and could therefore lead to a decrease of the effective solid retention time of the nitrifier, thus reducing the safety of the nitrification. This paper discusses the effect of ozonation on sludge reduction, the operating stability of nitrification, the improvement of denitrification and also presents an energy and cost evaluation.
Boehler, M., Joss, A., Buetzer, S., Holzapfel, M., Mooser, H., & Siegrist, H. (2007). Treatment of toilet wastewater for reuse in a membrane bioreactor. Water Science and Technology, 56(5), 63-70. doi:10.2166/wst.2007.557, Institutional Repository

Toilet wastewater is treated and reused on site at Europe's highest membrane bioreactor (MBR), located in a cable car mountain station in the ski resort of Zermatt. Negative impacts on the sensitive mountain environment are minimised by reusing close to 100% of the treated wastewater for toilet flushing. Besides 100% nitrogen removal, 80% of phosphorus was also eliminated. This paper presents operational results, optimisations of sludge management, decoloration and long-term maintenance of biomass in the very low-loaded summer season. From a global view the experiences and results of the project are of great importance, proposing a solution to a problem existing 100-fold in the Alps as well as in and regions all over the world: reducing water consumption for sanitation by reuse.
Daebel, H., Manser, R., & Gujer, W. (2007). Exploring temporal variations of oxygen saturation constants of nitrifying bacteria. Water Research, 41(5), 1094-1102. doi:10.1016/j.watres.2006.11.011, Institutional Repository

Activated sludge models (ASM) are generally accepted as state-of-the-art in modeling wastewater treatment plants. In this paper, we assess the temporal variability of an ASM parameter – the oxygen half-saturation constant of autotrophic bacteria (KO,AUT). A series of respirometric experiments is performed for conventional activated sludge and sludge from a membrane bioreactor. KO values are estimated for both ammonium-oxidizing and nitrite-oxidizing bacteria. For parameter estimation, the Monod kinetic model structure is extended by a sensor model. Still remaining systematic deviations between data and model are considered by a thorough residual analysis: (1) uncertainty estimates of KO are corrected to reflect model structure deficiencies and (2) the inter-experimental cross-correlation of residuals is taken into account to assess temporal changes. We conclude that KO,AUT is a time variable parameter and should be considered accordingly.
Dytczak, M. A., Londry, K. L., Siegrist, H., & Oleszkiewicz, J. A. (2007). Ozonation reduces sludge production and improves denitrification. Water Research, 41(3), 543-550. doi:10.1016/j.watres.2006.11.009, Institutional Repository

The effectiveness of partial ozonation of return activated sludge for enhancing denitrification and waste sludge minimization were examined. A pair of nitrifying sequencing batch reactors was operated in either aerobic or alternating anoxic/aerobic conditions, with one control and one ozonated reactor in each set. The amount of solids produced decreased with the ozone dose. Biomass in the anoxic/aerobic reactor was easier to destroy (up to 25% of the initial excess sludge) than in the aerobic (10%) one, generating approximately twice as much soluble COD by cell lysis. Denitrification rate improved up to 60% due to additional carbon released by ozonation. Nitrification rates deteriorated much more in the aerobic than in the alternating reactor, possibly as a result of direct destruction of nitrifying autotrophs as well as competition created by growth of heterotrophs receiving the additional COD. Overall, ozonation provided the expected benefits in denitrification and had less impact on nitrification in the alternating reactors.
Göbel, A., McArdell, C. S., Joss, A., Siegrist, H., & Giger, W. (2007). Fate of sulfonamides, macrolides, and trimethoprim in different wastewater treatment technologies. Science of the Total Environment, 372(2–3), 361-371. doi:10.1016/j.scitotenv.2006.07.039, Institutional Repository

The elimination of sulfonamides, macrolides and trimethoprim from raw wastewater was investigated in several municipal wastewater treatment plants. Primary treatment provided no significant elimination for the investigated substances. Similar eliminations were observed in the secondary treatment of two conventional activated sludge (CAS) systems and a fixed-bed reactor (FBR). Sulfamethoxazole, including the fraction present as N4-acetyl-sulfamethoxazole, was eliminated by approximately 60% in comparison to about 80% in a membrane bioreactor (MBR) independently of the solid retention time (SRT), indicating a positive correlation of the observed elimination to the organic substrate concentration. The elimination for macrolides and trimethoprim varied significantly between the different sampling campaigns in the two CAS systems and in the FBR. In the MBR, these analytes were eliminated up to 50% at SRT of 16 ± 2 and 33 ± 3 d. Trimethoprim, clarithromycin and dehydro-erythromycin showed a higher elimination of up to 90% at a SRT of 60-80 d indicating a correlation with reduced substrate loading (SL). Together with the high SRT, the SL may lead to an increased biodiversity of the active biomass, resulting in a broader range of degradation pathways available. Two investigated sand filters showed different elimination behavior. One led to a significant elimination of most macrolides (17–23%) and trimethoprim (74 ± 14%), while no elimination was observed in the other sand filter investigated.
Huang, D. B., Bader, H. P., Scheidegger, R., Schertenleib, R., & Gujer, W. (2007). Confronting limitations: new solutions required for urban water management in Kunming City. Journal of Environmental Management, 84(1), 49-61. doi:10.1016/j.jenvman.2006.05.004, Institutional Repository

Despite continuous investment and various efforts to control pollution, urban water environments are worsening in large parts of the developing world. In order to reveal potential constraints and limitations of current practices of urban water management and to stimulate proactive intervention, we conducted a material flow analysis of the urban water system in Kunming City. The results demonstrate that the current efficiency of wastewater treatment is only around 25% and the emission of total phosphorous from the city into its receiving water, Dianchi Lake, is more than 25 times higher than its estimated tolerance. With regard to the crisis of water quantity and quality, the goal of a sustainable urban water environment cannot be attained with the current problem-solving approach in the region due to the technical limitations of the conventional urban drainage and treatment systems. A set of strategies is therefore proposed. The urban drainage system in Zurich is used as a reference for a potential best-available technology for conventional urban water management (BAT) scenario in terms of its low combined frequency of sewer overflow.
Huang, D. B., Scholz, R. W., Gujer, W., Chitwood, D. E., Loukopoulos, P., Schertenleib, R., & Siegrist, H. (2007). Discrete event simulation for exploring strategies: an urban water management case. Environmental Science and Technology, 41(3), 915-921. doi:10.1021/es061370b, Institutional Repository

This paper presents a model structure aimed at offering an overview of the various elements of a strategy and exploring their multidimensional effects through time in an efficient way. It treats a strategy as a set of discrete events planned to achieve a certain strategic goal and develops a new form of causal networks as an interfacing component between decision makers and environment models, e.g., life cycle inventory and material flow models. The causal network receives a strategic plan as input in a discrete manner and then outputs the updated parameter sets to the subsequent environmental models. Accordingly, the potential dynamic evolution of environmental systems caused by various strategies can be stepwise simulated. It enables a way to incorporate discontinuous change in models for environmental strategy analysis, and enhances the interpretability and extendibility of a complex model by its cellular constructs. It is exemplified using an urban water management case in Kunming, a major city in Southwest China. By utilizing the presented method, the case study modeled the cross-scale interdependencies of the urban drainage system and regional water balance systems, and evaluated the effectiveness of various strategies for improving the situation of Dianchi Lake.
Jermann, D., Pronk, W., Meylan, S., & Boller, M. (2007). Interplay of different NOM fouling mechanisms during ultrafiltration for drinking water production. Water Research, 41(8), 1713-1722. doi:10.1016/j.watres.2006.12.030, Institutional Repository

Ultrafiltration is an emerging technology for drinking water production, but a main challenge remains the lack of understanding about fouling. This paper investigates the impact of molecular interactions between different natural organic matter (NOM) compounds on ultrafiltration fouling mechanisms. We performed dead-end filtration experiments with individual and mixed humic acid and alginate (polysaccharide). Alginate showed detrimental, but mostly reversible, flux decline and high solute retention. Our results indicate that this was caused by pore blocking transformed into cake building and weak molecular foulant-membrane and foulant-foulant interactions. In the presence of calcium, aggravated fouling was observed, related to complexation of alginate and its subsequently induced gel formation. With humic acid, more severe irreversible fouling occurred due to humic acid adsorption. Minor adsorption of alginate onto the membrane was also observed, which probably caused the substantial irreversible flux decline. The fouling characteristics in the mixtures reflected a combination of the individual humic acid and alginate experiments and we conclude, that the individual fouling mechanisms mutually influence each other. A model elucidates this interplay of the individual fouling mechanisms via hydrophobic and electrostatic interactions. In our study such an interplay resulted in an alginate cake, or gel in the presence of calcium, which is relatively irreversibly adsorbed onto the membrane by humic acid associations. This study shows the importance of mutual influences between various foulants for improved understanding of fouling phenomena. Furthermore it shows that substances with a minor individual influence might have a large impact in mixed systems such as natural water.
Kracht, O., Gresch, M., & Gujer, W. (2007). A stable isotope approach for the quantification of sewer infiltration. Environmental Science and Technology, 41(16), 5839-5845. doi:10.1021/es062960c, Institutional Repository

Extraneous flows in wastewater collection systems are conventionally evaluated solely on the consideration of discharge hydrographs, which often involves a great degree of subjectivity and oversimplification. To obtain reliable information on the material fluxes within the urban environment, the use of intrinsic tracers can be the optimal choice. We demonstrate the successful use of naturally occurring stable isotopes of water (18O/16O and D/H) to accurately quantify extraneous discharge of groundwater in a combined sewer network. Fresh water supply from a distant hydrological regime provided usable isotopic separations between drinking water (proxy for real foul sewage) and local groundwater (proxy for sewer infiltration) of 1.8‰ in δ18O and 11.7‰ in δ2H. Diurnal variation of wastewater isotopic composition reflected both the varying rates of foul sewage production and irregular dispersion effects in the pipe network. The latter suggest the existence of larger cumulative backwater zone volumes, which have not been attended to yet. Infiltrating groundwater contributed 39% (95% confidence interval = ±2.5%) of the total daily dry weather wastewater discharge. This paper discusses all relevant aspects for practical application of the method. It presents a comprehensive framework for uncertainty analysis and details on the detection and discrimination of possibly interfering effects.
Larsen, T. A., Maurer, M., Udert, K. M., & Lienert, J. (2007). Nutrient cycles and resource management: implications for the choice of wastewater treatment technology. Water Science and Technology, 56(5), 229-237. doi:10.2166/wst.2007.576, Institutional Repository

We look at the most important issues of the global nitrogen and phosphorus cycle and conclude that the nutrients from human metabolism are of no importance for the global nitrogen cycle and of minor importance for the global phosphorus cycle. However, for water pollution control, N and P from the human metabolism are of extreme importance. Nitrogen is mainly an issue for coastal waters, whereas P is an issue for freshwater and coastal areas alike. It is by now generally recognised that coastal ecosystems are exceedingly important for human well-being and at the same time highly endangered. The recycling issue is of high importance in areas where nutrient application is low due to economic constraints. NoMix technology (urine source separation) holds a large promise to become an efficient mainstream technology. The largest short-term potential is found in densely populated areas in coastal areas without existing infrastructure and in areas with nutrient deficiency, especially in urban areas with a large nutrient potential. We believe, however, that these technologies will, with time, also become competitive in Europe.
Meylan, S., Hammes, F., Traber, J., Salhi, E., von Gunten, U., & Pronk, W. (2007). Permeability of low molecular weight organics through nanofiltration membranes. Water Research, 41(17), 3968-3976. doi:10.1016/j.watres.2007.05.031, Institutional Repository

The removal of natural organic matter (NOM) using nanofiltration (NF) is increasingly becoming an option for drinking water treatment. Low molecular weight (LMW) organic compounds are nevertheless only partially retained by such membranes. Bacterial regrowth and biofilm formation in the drinking water distribution system is favoured by the presence of such compounds, which in this context are considered as the assimilable organic carbon (AOC). In this study, the question of whether NF produces microbiologically stable water was addressed. Two NF membranes (cut-off of about 300 Da) were tested with different natural and synthetic water samples in a cross-flow filtration unit. NOM was characterised by liquid chromatography with organic carbon detection (LC-OCD) using a size-exclusion column in addition to specific organic acid measurements, while AOC was measured in a batch growth bioassay.
Similarly to high molecular weight organic compounds like polysaccharides or humic substances that have a permeability lower than 1%, charged LMW organic compounds were efficiently retained by the NF membranes tested and showed a permeability lower than 3%. However, LMW neutrals and hydrophobic organic compounds permeate to a higher extent through the membranes and have a permeability of up to 6% and 12%, respectively. Furthermore, AOC was poorly retained by NF and the apparent AOC concentration measured in the permeated water was above the proposed limit for microbiologically stable water. This indicates that the drinking water produced by NF might be biologically unstable in the distribution system. Nevertheless, in comparison with the raw water, NF significantly reduced the AOC concentration.
Neumann, M. B., von Gunten, U., & Gujer, W. (2007). Sources of parameter uncertainty in predicting treatment performance: the case of preozonation in drinking water engineering. Environmental Science and Technology, 41(11), 3991-3996. doi:10.1021/es062566e, Institutional Repository

This study investigates the factors that determine parameter uncertainty when applying predefined, existing models to predict the performance of a full scale treatment system from environmental engineering. The analysis is performed for ozonation of surface water, a technology applied in drinking water treatment for disinfection and oxidation of micropollutants. The pseudo first order rate constant of ozone decay k03 is characterized as a time dependent parameter and estimated from data obtained from three experimental setups representing upscaling stages in engineering design. To obtain meaningful uncertainty estimates, various factors need to be acknowledged: uncertainty about the model structure, uncertainty of other model parameters, uncertainty due to non-representative sampling, and errors in chemical analysis. It is concluded that an on-site automated sequencing batch reactor is best suited for estimating kinetics during operation of the full scale system. Furthermore, the transferability of information in upscaling from laboratory experiments to the full scale system is found to be critical. Although uncertainty analysis enhances the understanding of the system, it is also shown to be a subjective process depending on the knowledge and assumptions of the modeler and the availability and quality of data.
Neumann, M. B., von Gunten, U., & Gujer, W. (2007). Uncertainty in prediction of disinfection performance. Water Research, 41(11), 2371-2378. doi:10.1016/j.watres.2007.02.022, Institutional Repository

Predicting the disinfection performance of a full-scale reactor in drinking water treatment is associated with considerable uncertainty. In view of quantitative risk analysis, this study assesses the uncertainty involved in predicting inactivation of Cryptosporidium parvum oocysts for an ozone reactor treating lake water. A micromodel is suggested which quantifies inactivation by stochastic sampling from density distributions of ozone exposure and lethal ozone dose. The ozone exposure distribution is computed with a tank in series model that is derived from tracer data and measurements of flow, ozone concentration and ozone decay. The distribution of lethal ozone doses is computed with a delayed Chick–Watson model which was calibrated by Sivaganesan and Marinas [2005. Development of a Ct equation taking into consideration the effect of Lot variability on the inactivation of Cryptosporidium parvum oocysts with ozone. Water Res. 39(11), 2429–2437] utilizing a large number of inactivation studies. Parameter uncertainty is propagated with Monte Carlo simulation and the probability of attaining given inactivation levels is assessed. Regional sensitivity analysis based on variance decomposition ranks the influence of parameters in determining the variance of the model result. The lethal dose model turns out to be responsible for over 90% of the output variance. The entire analysis is re-run for three exemplary scenarios to assess the robustness of the results in view of changing inputs, differing operational parameters or revised assumptions about the appropriate model. We argue that the suggested micromodel is a versatile approach for characterization of disinfection reactors. The scheme developed for uncertainty assessment is optimal for model diagnostics and effectively supports the management of uncertainty.
Pronk, W., Zuleeg, S., Lienert, J., Escher, B., Koller, M., Berner, A., … Boller, M. (2007). Pilot experiments with electrodialysis and ozonation for the production of a fertiliser from urine. Water Science and Technology, 56(5), 219-227. doi:10.2166/wst.2007.575, Institutional Repository

Pilot tests were performed with a process combination of electrodialysis and ozonation for the removal of micropollutants and the concentration of nutrients in urine. In continuous and batch experiments, maximum concentration factors up to 3.5 and 4.1 were obtained, respectively. The desalination capacity did not decrease significantly during continuous operation periods of several weeks. Membrane cleaning after 195 days resulted in approximately 35% increase in desalination rate. The Yeast Estrogen Screen (YES), a bioassay that selectively detects oestrogenic compounds, confirmed that about 90% of the oestrogenic activity was removed by electrodialysis. HPLC analysis showed that ibuprofen was removed to a high extent, while other micropollutants were below the detection limit. In view of the fact that ibuprofen is among the most rapidly transported micropollutants in electrodialysis processes, this result indicates that electrodialysis provides an effective barrier for micropollutants. Standardised plant growth tests were performed in the field with the salt solution resulting from the treatment by electrodialysis and subsequent ozonation. The results show that the plant height is comparable to synthetic fertilisers, but the crop yield is slightly lower. The latter is probably caused by volatilisation losses during field application, which can be prevented by improved application technologies.
Rieckermann, J., Bareš, V., Kracht, O., Braun, D., & Gujer, W. (2007). Estimating sewer leakage from continuous tracer experiments. Water Research, 41(9), 1960-1972. doi:10.1016/j.watres.2007.01.024, Institutional Repository

Direct measurements of sewer leakage with continuous dosing of tracers are often considered too imprecise for practical applications. However, no mathematical framework for data analysis is reported in literature. In this paper, we present an improved experimental design and data analysis procedure together with a comprehensive framework for uncertainty assessment. Test runs in a 700 m-long watertight sewer showed no significant bias and a very high precision of the methodology. The standard error in the results was assessed to 2.6% of the labeled flow with a simplified model. It could be reduced to 1.2% when a dynamic data analysis procedure was applied. The major error contribution was caused by transient transport phenomena, which suggests that careful choosing of the experimental time is more important than the choice of a very specific tracer substance. Although the method is not intended to replace traditional CCTV inspections, it can provide complementary information for rational rehabilitation planning.
Ronteltap, M., Maurer, M., & Gujer, W. (2007). Struvite precipitation thermodynamics in source-separated urine. Water Research, 41(5), 977-984. doi:10.1016/j.watres.2006.11.046, Institutional Repository

Struvite (MgNH4PO4·6H2O) precipitation eliminates phosphate efficiently from urine, a small but highly concentrated stream in the total flux of domestic wastewater. Precipitation experiments with hydrolysed urine evaluated the solubility product of struvite. The stored and fully hydrolysed urine had an ionic strength of between 0.33 and 0.56 M and required the estimation of activity coefficients. From our data, we identified the Davies approximation with the two constants A=0.509 and B=0.3 as agreeing best with our laboratory results. The standard solubility product Ks0=f1[NH4+]f2[Mg2+]f3[PO43−] ([ ]=concentration of the species; fx=corresponding activity coefficient) of struvite in urine was found to be 10−13.26±0.057 at 25 °C and the enthalpy of struvite formation ΔH was 22.6(±1.1) kJ mol−1. The equilibrium calculations required the following dissolved complexes: [MgCO3]aq, [MgHCO3]+, [MgPO4]−, [NH4HPO4]−, and [NaHPO4]− and to a lesser extent [MgSO4]aq and [NH4SO4]−. Organic complexes do not seem to influence the solubility product substantially.
For practical purposes, a conditional solubility product Kscond=[Mgaq]·[NH4++NH3]·[Portho]=10−7.57 M3 was derived to calculate struvite solubility in urine at 25 °C, pH=9.0 and ionic strength I=0.4 M directly from measured concentrations.
Ronteltap, M., Maurer, M., & Gujer, W. (2007). The behaviour of pharmaceuticals and heavy metals during struvite precipitation in urine. Water Research, 41(9), 1859-1868. doi:10.1016/j.watres.2007.01.026, Institutional Repository

Separating urine from wastewater at the source reduces the costs of extensive wastewater treatment. Recovering the nutrients from urine and reusing them for agricultural purposes adds resource saving to the benefits. Phosphate can be recovered in the form of struvite (magnesium ammonium phosphate). In this paper, the behaviour of pharmaceuticals and heavy metals during the precipitation of struvite in urine is studied.
When precipitating struvite in urine spiked with hormones and non-ionic, acidic and basic pharmaceuticals, the hormones and pharmaceuticals remain in solution for more than 98%.
For heavy metals, initial experiments were performed to study metal solubility in urine. Solubility is shown to be affected by the chemical conditions of stored and therefore hydrolysed urine. Thermodynamic modelling reveals low or very low equilibrium solute concentrations for cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni) and lead (Pb). Experiments confirmed Cd, Cu and Pb carbonate and hydroxide precipitation upon metal addition in stored urine with a reaction half-life of ca. 7 days.
For all metals considered, the maximum specific metal concentrations per gram phosphate or nitrogen showed to be typically several orders of magnitudes lower in urine than in commercially available fertilizers and manure. Heavy metals in struvite precipitated from normal stored urine could not be detected.
Phosphate recovery from urine over struvite precipitation is shown to render a product free from most organic micropollutants and containing only a fraction of the already low amounts of heavy metals in urine.
Steiner, M., Boller, M., Schulz, T., & Pronk, W. (2007). Modelling heavy metal fluxes from traffic into the environment. Journal of Environmental Monitoring, 9(8), 847-854. doi:10.1039/b703509h, Institutional Repository

A new method is presented which allows emissions of traffic into the environment to be described as a function of road distance. The method distinguishes different types of emissions (runoff, spray and drift), which are determined by measurements and mass balances of a specified road section. The measurement of two-dimensional pollutant concentrations in the road shoulder is an important part of the method. In a case study performed at Burgdorf, Switzerland, the method was applied to the determination of the spatial distribution of heavy metal emissions. The results show that between 36 and 65% of the heavy metals Cd, Cr, Cu, Pb and Zn are present in runoff and spray and between 35 and 64% are dispersed diffusely in the environment (defined as drift). The runoff infiltrates into the vegetated road shoulder up to a distance of approx. 1 m from the road. The distribution of spray shows a maximum at 1 m and decreases steadily up to a distance of 5 m. This information can serve as a basis for the quantitative evaluation of road-runoff treatment scenarios. Although the results of the Burgdorf study are case-specific, several general guidelines for the reduction of traffic-related emissions can be derived from it.
Yang, T., Holzer, L., Kägi, R., Winnefeld, F., & Keller, B. (2007). In situ nanomanipulators as a tool to separate individual tobermorite crystals for AFM studies. Ultramicroscopy, 107(10–11), 1068-1077. doi:10.1016/j.ultramic.2007.02.042, Institutional Repository

Atomic force microscopy (AFM) studies of cementitious materials are limited, mainly due to the lack of appropriate sample preparation techniques. In porous autoclaved aerated concrete (AAC), calcium silicate hydrate (C–S–H) is produced in its crystalline form, tobermorite. The crystals are lath-like with a length of several micrometers. In this work, we demonstrate the application of nanomanipulators to separate an individual tobermorite crystal from the bulk AAC for subsequent AFM investigations. The nanomanipulators are operated directly in an environmental scanning electron microscope (ESEM). We studied the interaction between moisture and the tobermorite surface under controlled relative humidity (RH). The results of topography and adhesion force measurements with AFM suggest that the surface of tobermorite is hydrophobic, which contrasts the macroscopic material properties (e.g. moisture transport in capillary pores).
Zennegg, M., Kohler, M., Hartmann, P. C., Sturm, M., Gujer, E., Schmid, P., … Giger, W. (2007). The historical record of PCB and PCDD/F deposition at Greifensee, a lake of the Swiss plateau, between 1848 and 1999. Chemosphere, 67(9), 1754-1761. doi:10.1016/j.chemosphere.2006.05.115, Institutional Repository

Dated sediment cores provide an excellent way to investigate the historical input of persistent organic pollutants into the environment and to identify possible sources of pollution. The vertical distribution of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/F) and polychlorinated biphenlys (PCB) was investigated in a sediment core from Greifensee to elucidate the historical trends of PCDD/F and PCB inputs between 1848 and 1999. Concentrations of PCB and PCDD/F increased by more than one order of magnitude between 1930 and 1960. PCB and PCDD/F concentrations were 5700 ng/kg dry weight (dw) and 160 ng/kg dw, respectively, in sediments originating from the late 1930s and reached a maximum of 130 000 ng/kg dw and 2400 ng/kg dw, respectively, in the early 1960s. From 1960 on, concentrations decreased to the 1930s level by the mid 1980s. A remarkable shift in the PCDD/F pattern was observed after the early 1940s. Before 1940, the PCDD/F pattern was PCDF dominated (ratio of PCDD to PCDF = 0.41 ± 0.11), while the PCDD started to be the major species after the early 1940s (ratio of PCDD to PCDF = 1.46 ± 0.38).
The temporal trends of PCB and PCDD/F correlate surprisingly well with each other. This might be due to the coincidence of two factors. The introduction of PCB on the market in the 1930s resulted in emissions due to the widespread use of these industrial chemicals. In the same time period, waste incineration became an increasingly popular way to get rid of garbage, boosting the PCDD/F emissions significantly. The rapid decline of PCDD/F and PCB concentrations in the sediment starting in the early 1960s reflects the result of better emission control techniques in thermal processes and the improvement of waste water treatment in the catchment of Greifensee.
Abegglen, C., & Siegrist, H. (2006). Domestic wastewater treatment with a small-scale membrane bioreactor. Water Science and Technology, 53(3), 69-78. doi:10.2166/wst.2006.077, Institutional Repository

A small-scale membrane plant for treating the domestic wastewater of a four-person household is presented. The membrane bioreactor has been in operation for 6 months and achieves elimination rates of 90, 95 and 80% for total organic carbon, chemical oxygen demand and total nitrogen, respectively. Only a small amount sludge is produced. The permeate is reused for flushing toilets and has a yellowish colour. After investigations of the effluent quality, decolourisation of the permeate, energy efficiency and control strategies in the first year, urine will be treated separately in an automated precipitation reactor where struvite is produced to improve the overall phosphate removal of the plant.
Boehler, M., & Siegrist, H. (2006). Potential of activated sludge disintegration. Water Science and Technology, 53(12), 207-216. doi:10.2166/wst.2006.423, Institutional Repository

The disposal of sewage sludge and the agricultural use of stabilized sludge are decreasing due to more stringent regulations in Europe. An increasing fraction of sewage sludge must therefore be dewatered, dried, incinerated and the ashes disposed of in landfills. These processes are cost-intensive and also lead to the loss of the valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Disintegration of biological sludge by mechanical, thermal and physical methods could significantly reduce excess sludge production, improve the settling properties of the sludge and reduce bulking and scumming. The solubilized COD could also improve denitrification if the treated sludge is recycled to the anoxic zone. However, disintegration partly inhibits and kills nitrifiers and could therefore shorten their effective solid retention time, thus reducing the safety of the nitrification. This paper discusses the potential of disintegration on sludge reduction, the operating stability of nitrification, the improvement of denitrification and also presents an energy and cost evaluation.
Dominguez, D., Truffer, B., & Gujer, W. (2006). Driving forces in the long range development of wastewater treatment plants. In A. Voinov, A. J. Jakeman, & A. E. Rizzoli (Eds.), Proceedings of the iEMSs third biennial meeting. Summit on environmental modelling and software (p. 302 (6 pp.). Burlington, VT, USA: International Environmental Modelling and Software Society. , Institutional Repository

Wastewater treatment plants (WWTP) are planned and designed for a lifespan of 25 to 40 years. The catchment area, discharge requirements, available technology, institutional conditions, operational procedures etc. of these plants may change drastically over this long time period. In the private sector such dynamic development would possibly be considered in the planning and design phase based on a scenario analysis. However, conducting a scenario process requires knowledge about the driving forces of this dynamic, which at the moment is very limited in the field of urban drainage. In this paper we take a first step in closing this gap. In a case study we analyzed the development of a WWTP and its environment for a time period of over a decade. From this investigation we identified the driving forces responsible for the observed strong dynamic and their effect on the development of the WWTP. Based on the analysis of these forces, we deduce important aspects that will have to be considered in the future if scenario planning is to be applied routinely in the field of urban drainage.
Dominguez, D., & Gujer, W. (2006). Evolution of a wastewater treatment plant challenges traditional design concepts. Water Research, 40(7), 1389-1396. doi:10.1016/j.watres.2006.01.034, Institutional Repository

Traditional design and upgrade concepts for wastewater treatment plants (WWTPs) are based on the forecasting of load parameters over a period of 25-40 years. This approach is adequate as long as the environment of a WWTP is stable or predictable over this long time period. However, these conditions are usually not met, as the catchment area, discharge requirements, available technology and institutional conditions of a WWTP may change drastically over time. The complexity and consequences of these dynamics are shown exemplarily in a case study analyzing the historical development of a plant from the initial planning steps to the current date. We conclude that the dynamics and complexity of the wastewater system makes reliable predictions impossible, and therefore question the current design and upgrade approach. Instead, we propose to improve the planning and design of wastewater infrastructures through methodologies that systematically account for future uncertainty, like, e.g. scenario planning.
Dytczak, M. A., Londry, K., Siegrist, H., & Oleszkiewicz, J. A. (2006). Extracellular polymers in partly ozonated return activated sludge: impact on flocculation and dewaterability. Water Science and Technology, 54(9), 155-164. doi:10.2166/wst.2006.873, Institutional Repository

The purpose of this study was to evaluate the influence of partial ozonation of return activated sludge on settling properties and dewaterability of sludge. Sequencing batch reactors with two sets of aerobic and alternating anoxic/aerobic conditions were used. In each set, one reactor served as a control and the other was subject to the ozone treatment (doses in the range of 0.016-0.080 mg O3/mg TSS of initial excess sludge). The level of total suspended solids (TSS) in each reactor was controlled at 1,800 mg/l. To evaluate settleability and dewaterability, settling kinetic studies, sludge volume index (SVI) and capillary suction time test (CST) were used. For extraction and quantifying sludge biopolymers, thermal-ethanolic extraction was employed. The ratio of bound-to-total extracellular polymer substances (EPS) was higher for the strictly aerobic reactor than for the alternating anoxic/aerobic one, indicating the stronger structure of the aerobic flocs. After ozone treatment, the fraction of bound EPS was released and solubilized, increasing soluble EPS. Increased apparent food-to-microorganism (F/M) ratio favoured production of EPS in ozonated reactors, enhancing flocculation, which had potential to improve settling. Dewaterability, measured by CST test, was better in alternating anoxic/aerobic reactors than in aerobic ones, indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation.
Escher, B. I., Pronk, W., Suter, M. J. F., & Maurer, M. (2006). Monitoring the removal efficiency of pharmaceuticals and hormones in different treatment processes of source-separated urine with bioassays. Environmental Science and Technology, 40(16), 5095-5101. doi:10.1021/es060598w, Institutional Repository

Urine can be collected separately from the general wastewater with the aim of recycling the nutrients. Urine source-separation not only prevents wasting nutrients but also prevents potentially hazardous micropollutants from entering the wastewater stream and tainting a final fertilizer product. We assessed various urine treatment technologies for their performance to remove micropollutants such as pharmaceuticals, natural and synthetic steroid hormones, and their human biotransformation products. Removal efficiencies were determined with a combination of bioassays and chemical target analysis. The yeast estrogen screen yielded information on estrogenicity. Specific phytotoxicity and nonspecific baseline toxicity was determined with an algae chlorophyll fluorescence test. Filtration methods, such as nanofiltration and electrodialysis, were highly efficient with respect to toxicity reduction. Micropollutant degradation during biological treatment in a sequencing batch reactor was very compound specific. Ozonation removed the target analytes and the estrogenicity completely, but the baseline toxicity was only reduced by 50-60% depending on the ozone doses. Struvite precipitation produced a very "clean" fertilizer product that is ready to use. The examples show that bioassays and chemical analysis yield complementary information, but are very useful to monitor treatment efficiencies and to assess the ecotoxicological potential of byproducts of urine treatment processes. The results of this study present a method to assess the micropollutant removal efficiency, and therefore, support the choice of an appropriate urine processing technique for real-world applications.
Gujer, W. (2006). Activated sludge modelling: past, present and future. Water Science and Technology, 53(3), 111-119. doi:10.2166/wst.2006.082, Institutional Repository

Model complexity in activated sludge modelling has increased over 30 years in parallel with the computational power of computers. Today, the complexity of biokinetics has reached a practical limit. Future advances may be in the direction of enhanced spacial resolution (CFD, single organisms) respectively, in repetitive computations (MC simulation, parameter identification). Further model development may be in niches such as population dynamics, micropollutants, etc.
Hug, T., Gujer, W., & Siegrist, H. (2006). Modelling seasonal dynamics of "Microthrix parvicella". Water Science and Technology, 54(1), 189-198. doi:10.2166/wst.2006.387, Institutional Repository

The filamentous bacteria "Microthrix parvicella" can cause serious bulking and scumming in wastewater treatment plants (WWTPs) all over the world. Decades of research have identified Microthrix as a specialized lipid consumer but could not clarify the processes that allow this organism to successfully compete in activated sludge systems. In this study we developed a model, based on ASM3, that describes the pronounced seasonal variations of Microthrix abundance observed in a full-scale WWTP. We hypothesize that low temperatures reduce the solubility of lipids and inhibit their uptake by non-specialized bacteria. The presented model structure and parameters successfully fit the measured data; however they do not necessarily reflect the only and true selection mechanism for Microthrix. This model is not yet to be used for prediction; it is rather a valuable research tool to coordinate the discussion and plan future research activities in order to identify the relevant selection mechanisms favoring Microthrix in activated sludge systems.
Joss, A., Zabczynski, S., Göbel, A., Hoffmann, B., Löffler, D., McArdell, C. S., … Siegrist, H. (2006). Biological degradation of pharmaceuticals in municipal wastewater treatment: proposing a classification scheme. Water Research, 40(8), 1686-1696. doi:10.1016/j.watres.2006.02.014, Institutional Repository

A simple classification scheme is suggested to characterize the biological degradation of micropollutants such as pharmaceuticals, musk fragrances and estrogens during wastewater treatment. The scheme should be a basis for the discussion about potential removal efficiencies. Hence, the biological degradation of 25 pharmaceuticals, hormones and fragrances was studied in batch experiments at typical concentration levels using activated sewage sludge originating from nutrient-eliminating municipal wastewater treatment plants.
Since pseudo first-order degradation kinetics was observed for all compounds down to ng L-1 levels, the removal rates can be predicted for various reactor configurations. Therefore dilution of wastewater (e.g. by extraneous water) is expected to reduce the degree of biological removal. Wastewater segregation and treatment at the source are therefore to be favoured for elimination of persistent micropollutants over centralized end-of-pipe treatment. For reactor configurations typical for nutrient removal in municipal wastewater, the derived formula for predicting removal allows the identification of three groups of micropollutants according to their degradation constant kbiol: compounds with kbiol<0.1 L gSS-1 d-1 are not removed to a significant extent (<20%), compounds with kbiol>10 L gSS-1 d-1 transformed by >90% and in-between moderate removal is expected. Based on the degradation of a heterogeneous group of 35 compounds (including literature data), state of the art biological treatment schemes for municipal wastewater are not efficient in degrading pharmaceuticals: only 4 out of 35 compounds are degraded by more than 90% while 17 compounds are removed by less than 50%.
Joss, A., Carballa, M., Kreuzinger, N., Siegrist, H., & Zabczynski, S. (2006). Wastewater treatment. In T. A. Ternes & A. Joss (Eds.), Human pharmaceuticals, hormones and fragrances. The challenge of micropollutants in urban water management (pp. 243-292). London, UK: IWA Publishing. , Institutional Repository
Kaegi, R., & Gasser, P. (2006). Application of the focused ion beam technique in aerosol science: detailed investigation of selected, airborne particles. Journal of Microscopy, 224(2), 140-145. doi:10.1111/j.1365-2818.2006.01669.x, Institutional Repository

The focused ion beam technique was used to fabricate transmission electron microscope lamellas of selected, micrometre-sized airborne particles. Particles were sampled from ambient air on Nuclepore polycarbonate filters and analysed with an environmental scanning electron microscope. A large number of particles between 0.6 and 10 μm in diameter (projected optical equivalent diameter) were detected and analysed using computer-controlled scanning electron microscopy. From the resulting dataset, where the chemistry, morphology and position of each individual particle are stored, two particles were selected for a more detailed investigation. For that purpose, the particle-loaded filter was transferred from the environmental scanning electron microscope to the focused ion beam, where lamellas of the selected particles were fabricated. The definition of a custom coordinate system enabled the relocation of the particles after the transfer. The lamellas were finally analysed with an analytical transmission electron microscope. Internal structure and elemental distribution maps of the interior of the particles provided additional information about the particles, which helped to assign the particles to their sources. The combination of computer-controlled scanning electron microscopy, focused ion beam and transmission electron microscopy offers new possibilities for characterizing airborne particles in great detail, eventually enabling a detailed source apportionment of specific particles. The particle of interest can be selected from a large dataset (e.g. based on chemistry and/or morphology) and then investigated in more detail in the transmission electron microscope.
Manser, R., Gujer, W., & Siegrist, H. (2006). Decay processes of nitrifying bacteria in biological wastewater treatment systems. Water Research, 40(12), 2416-2426. doi:10.1016/j.watres.2006.04.019, Institutional Repository

A knowledge of the decay rates of autotrophic bacteria is important for reliably modeling nitrification in activated sludge plants. The introduction of nitrite to activated sludge models also requires the separate determination of the kinetics of ammonia- and nitrite-oxidizing bacteria. Batch experiments were carried out in order to study the effects of different oxidiation-reduction potential conditions and membrane separation on the separate decay of these bacteria. It was found that decay is negligible in both cases under anoxic conditions. No significant differences were detected between the membrane and conventional activated sludge. The aerobic decay of these two types of bacteria did not diverge significantly either. However, the measured loss of autotrophic activity was only partly explained by the endogenous respiration concept as incorporated in activated sludge model no. 3 (ASM3). In contrast to nitrite-oxidizing bacteria, ammonia-oxidizing bacteria needed 1-2 h after substrate addition to reach their maximum growth rate measured as a maximum OUR. This pattern could be successfully modeled using the ASM3 extended by enzyme kinetics. The significance of these findings on wastewater treatment is discussed on the basis of the extended ASM3.
Maurer, M., Rothenberger, D., & Larsen, T. A. (2006). Decentralised wastewater treatment technologies from a national perspective: At what cost are they competitive?. Water Science and Technology: Water Supply, 5(6), 145-154. doi:10.2166/ws.2005.0059, Institutional Repository

In this paper we estimate at what cost decentralised wastewater treatment can be competitive compared with conventional centralised technologies. For the current wastewater infrastructure in Western Europe and North America, typical replacement costs are 2,600 US$/cap for large countries and 4,800 US$/cap for small ones. In the same literature, average annual operating costs are reported to be 3.8% of replacement costs. However, if a long-term interest rate of 3% is consistently applied, this value increases to 4.7% for small countries and 5.5% for large ones. Assuming that alternative wastewater systems will only be accepted if their costs are similar to existing ones, the possible investments for alternative wastewater treatment technologies are calculated. Between 640 and 2,170 US$/cap can be invested in new technologies for scenarios without a sewer system. The corresponding figures for scenarios with sewer systems are between 260 and 680 US$/cap. Acceptable maintenance requirements are calculated on the basis of unit size. Transition periods are not accounted for.
Maurer, M., Pronk, W., & Larsen, T. A. (2006). Treatment processes for source-separated urine. Water Research, 40(17), 3151-3166. doi:10.1016/j.watres.2006.07.012, Institutional Repository

The separate collection and treatment of urine has attracted considerable attention in the engineering community in the last few years and is seen as a viable option for enhancing the flexibility of wastewater treatment systems. This comprehensive review focuses on the status of current urine treatment processes and summarises the properties of collected urine. We distinguish between seven main purposes of urine-treatment processes: hygienisation (storage), volume reduction (evaporation, freeze-thaw, reverse osmosis), stabilisation (acidification, nitrification), P-recovery (struvite formation), N-recovery (ion treatment exchange, ammonia stripping, isobutylaldehyde-diurea (IBDU) precipitation), nutrient removal (anammox) and handling of micropollutants (electrodialysis, nanofiltration, ozonation). The review shows clearly that a wide range of technical options is available to treat collected urine effectively, but that none of these single options can accomplish all seven purposes. Depending on the overall goal of the treatment process, a specific technical solution or a combination of solutions can be found to meet the requirements. Such combinations are not discussed in this paper unless they are explicitly presented in the literature. Except for 'evaporation' and 'storage', none of the processes described have so far advanced beyond the laboratory stage. Considerable development work remains to be done to optimise urine-processing techniques in order to create marketable products.
Ort, C., & Gujer, W. (2006). Sampling for representative micropollutant loads in sewer systems. Water Science and Technology, 54(6-7), 169-176. doi:10.2166/wst.2006.591, Institutional Repository

Most commercially available auto-sampling devices do not support a continuous flow-proportional sampling mode, which would conceptually be the best for collecting representative composite samples. Instead different discrete sampling modes are available. Household chemicals can show considerable random short-term variations. With the anticorrosive benzotriazole, relating to a middle-frequent household activity, we show that, besides an accurate flow meter, mainly three factors are decisive for the representativeness of a substance's average load: the substance's load pattern, the sampling frequency and the length of the composite sample. When the sampling intervals are 10 minutes or longer, errors in the order of ±40% (standard deviation) or more have to be accepted, if the substance of interest is contained in a low number of wastewater pulses (i.e. the level of household activity). This particularly holds true for specific pharmaceuticals e.g. carbamazepine. Ammonium would be less critical, because it relates to a larger number of sources in the same catchment.
Pronk, W., Sinnet, B., Meylan, S., & Boller, M. (2006). Characterization of nano- and microparticles in Swiss waters and their role in potable water production. Water Science and Technology: Water Supply, 6(1), 21-29. doi:10.2166/ws.2006.004, Institutional Repository

Particles in lake water samples originating from the Swiss lakes of Zurich and Constance were analysed, showing an exponential increase of particle number with decreasing particle size down to the detection limit (350 nm). Investigation of nanoparticles in Lake Zurich by microscopic methods showed that relatively large numbers of clay particles are present with different Al/Si composition and sizes. The small-sized clay particles (ca. 80 nm) tend to build aggregates with a size of 500-1,000 nm. In karstic spring water, the particle count and size distribution is strongly dependent on the precipitation rate. At high precipitation rates, channel flow occurs in the subsoil, leading to high particle counts among the whole size range and a larger average particle size. In membrane treatment by microfiltration and ultrafiltration this leads to membrane fouling due to pore blocking and cake formation, the latter being associated with the presence of organic compounds.
Pronk, W., Biebow, M., & Boller, M. (2006). Electrodialysis for recovering salts from a urine solution containing micropollutants. Environmental Science and Technology, 40(7), 2414-2420. doi:10.1021/es051921i, Institutional Repository

Electrodialysis was investigated for the separation of micropollutants from nutrients in anthropogenic urine. In a continuously operated process, the nutrients were concentrated up to a factor of 3.2. The concentration factor was limited by water transport across the membrane. Water transport was caused by osmosis and electroosmosis, and a model was developed to describe these phenomena. The removal of several spiked micropollutants was investigated in continuous electrodialysis experiments, Ethinylestradiol was removed completely during the whole operating period. Diclofenac and carbamazepine were initially retained, but limited permeation (5-10%) occurred after longer operating times (90 days). Retentions of propranolol and ibuprofen were also high initially, but substantial breakthroughs occurred during extended operation. Considerable adsorption on the membranes was observed for all compounds. The permeation mechanism of several compounds appears to depend on the adsorbed amount on the membrane, which indicates that partitioning and diffusion mechanisms play an important role in the permeation transport. Partial desorption occurred in leaching experiments with polarity reversal, and almost quantitative desorption was observed after incubation of the membranes with Filter Count Gel Solution. Because environmental concentrations are much lower than the concentrations spiked here, it can be anticipated that operation without significant permeation is possible in practice during extended periods of time.
Pronk, W., Palmquist, H., Biebow, M., & Boller, M. (2006). Nanofiltration for the separation of pharmaceuticals from nutrients in source-separated urine. Water Research, 40(7), 1405-1412. doi:10.1016/j.watres.2006.01.038, Institutional Repository

The potential of nanofiltration for the separation of pharmaceutical and estrogenic compounds from salts in urine was investigated with the aim of producing a micropollutant-free nutrient solution that can be used as a fertilizer. A fresh urine solution and a synthetic solution of similar inorganic composition were tested at different pH values in order to investigate their separation behavior. These solutions were spiked with the micropollutants propranolol, ethinylestradiol, ibuprofen, diclofenac and carbamazepine. Among the membranes tested, NF270 showed the best performance with respect to the retention of micropollutants. The optimum retention of micropollutants was obtained at values of around pH 5. At this point, the retention of all micropollutants in non-hydrolysed urine was above 92%, while the corresponding value for the synthetic urine solution was above 73%. From the results, it can be concluded that the retention mechanism is determined by steric and electrostatic effects as well as by the partitioning of the micropollutants in the membrane. The nutrients urea and ammonia were well permeated, but phosphate and sulfate were almost completely retained. Nanofiltration can consequently be used to produce a permeate which contains most of the nitrogen and a greatly reduced proportion of micropollutants.
Pronk, W., Biebow, M., & Boller, M. (2006). Treatment of source-separated urine by a combination of bipolar electrodialysis and a gas transfer membrane. Water Science and Technology, 53(3), 139-146. doi:10.2166/wst.2006.086, Institutional Repository

Urine contains nutrients which can be applied usefully as a fertiliser in agriculture, but the relatively high pH can lead to ammonia evaporation. Electrodialysis with bipolar membranes was combined with an additional mass transfer unit in order to render a product containing ammonium and phosphate at a low pH. In one case, the additional mass transfer unit consisted of bubble columns placed in acid and basic concentrate streams, connected with a circulating gas phase. In the other case, the unit consisted of a gas-filled (hydrophobic) membrane placed in between the circulating acid and basic concentrate streams. The results showed that ammonia was transferred through the gas phase, but also carbonate, which is present in stored urine originating from the hydrolysis of urea. Although the pH in the product stream decreases initially, it rises above pH 7 at longer operation times. This pH increase can be attributed to a combination of proton compensating effects. The use of ammonia-selective membranes for the transfer into the acid concentrate could provide a solution to generate an ammonium phosphate product at low pH and high recoveries.
Rieckermann, J., Borsuk, M. E., & Gujer, W. (2006). Using decision analysis to determine optimal experimental design for monitoring sewer exfiltration with tracers. Water Science and Technology, 54(6-7), 161-168. doi:10.2166/wst.2006.615, Institutional Repository

The tracer methods developed to assess exfiltration from sewers in the European project APUSS (assessment of the performance of sewer systems) have a high degree of freedom with regard to the choice of tracer and the dosing strategy. These can lead to very different degrees of uncertainty in the measured exfiltration ratio. In this study, we demonstrate how to select an optimal experimental design using decision analysis, which accounts for this uncertainty and its associated costs. Although the results are site-specific, we can conclude generally that, when NaCl is used as the tracer, the accuracy of the exfiltration estimate is most sensitive to the amount of tracer used and the starting time of the experiment.
Rieger, L., Alex, J., Gujer, W., & Siegrist, H. (2006). Modelling of aeration systems at wastewater treatment plants. Water Science and Technology, 53(4-5), 439-447. doi:10.2166/wst.2006.100, Institutional Repository

A model for the response time of aeration systems at WWTPs is proposed. It includes the delays caused by the air supply system (consisting of blowers, throttles and pipes), the rise time of the air bubbles and all control loops except the master DO controller. Beside a description of the required step-change experiments, different approaches for model calibration are given depending on the available data. Moreover, the parameters for the oxygen transfer and the response time of the aeration system model are not clearly identifiable. The model can be used for simulation studies which compare different types of controllers under changing loading and process conditions. The results from full-scale experiments at three different plants show that the response times of the aeration systems are in the range of 4 - 5 min. Taking all processes and time constants into account, some 30 min are needed to reach a new steady state after a step change of the airflow rate.
Rieger, L., Langergraber, G., & Siegrist, H. (2006). Uncertainties of spectral in-situ measurements in wastewater using different calibration approaches. Water Science and Technology, 53(12), 187-197. doi:10.2166/wst.2006.421, Institutional Repository

Three calibration methods were applied to UV/VIS spectra recorded in the influent of six wastewater treatment plants (WWTPs) to measure total COD (CODtot), filtered COD (CODfil), nitrate and nitrite nitrogen (NOx-N) and total suspended solids (TSS). It could be shown that a calibration of the sensor using data sets from four Swiss WWTPs leads to an improvement of the precision in comparison to the global calibration provided by the manufacturer. A calibration to the specific wastewater matrix always improves the results and gives the highest accuracy. For CODtot a mean coefficient of variation CVx of 12.5% could be reached, whereas for NOx-N only weak results were achieved (average CVx = 36%).
Rossi, L., Fankhauser, R., & Chèvre, N. (2006). Water quality criteria for total suspended solids (TSS) in urban wet-weather discharges. Water Science and Technology, 54(6-7), 355-362. doi:10.2166/wst.2006.623, Institutional Repository

Total suspended solids (TSS) from combined sewer overflows (CSOs) and stormwater discharges represent a crucial parameter for evaluating wet-weather pollution in urban areas. In fact, the increase of TSS in water during rain events can have ecotoxic effects on aquatic organisms. Furthermore, major potentially harmful substances such as heavy metals, PAHs and organic matter are adsorbed onto TSS and later settle on sediment. Water quality criteria for TSS consequently enable the risk of wet-weather pollution to be assessed, for instance to avoid detrimental effects on aquatic organisms. The criteria proposed in this study cover the short-term impact of TSS on fish (acute quality criteria AQC), taking into account the duration of their exposure in the receiving water. The concentration-exposure duration-effect curve proposed here thus predicts "ill effects" on fish for different exposure times and TSS concentrations. The ecotoxic effects of adsorbed pollutants are also taken into account with an additional safety factor. We implement this TSS criteria in a software that allows us to estimate the number of rain events that exceed a given morbidity threshold for fishes per year.
Rutsch, M., Rieckermann, J., & Krebs, P. (2006). Quantification of sewer leakage: a review. Water Science and Technology, 54(6-7), 135-144. doi:10.2166/wst.2006.616, Institutional Repository

One of the goals of the APUSS project (assessing infiltration and exfiltration on the performance of urban sewer systems) is to assess sewer exfiltration, in order to support cities and operators to define problem-oriented rehabilitation strategies. In this paper, we review various methods currently used for the estimation of exfiltration and discuss data needs and applicability for rehabilitation planning. Although each approach has its individual advantages and drawbacks, we identified pressure tests and tracer methods to have the highest potential for decision support in rehabilitation planning. With regard to future challenges (e.g. micropollutants) such methods might play a key role in integrated sewer management.
Steiner, M., Pronk, W., & Boller, M. (2006). Modeling of copper sorption onto GFH and design of full-scale GFH adsorbers. Environmental Science and Technology, 40(5), 1629-1635. doi:10.1021/es051324w, Institutional Repository

During rain events, copper wash-off occurring from copper roofs results in environmental hazards. In this study, columns filled with granulated ferric hydroxide (GFH) were used to treat copper-containing roof runoff. It was shown that copper could be removed to a high extent. A model was developed to describe this removal process. The model was based on the Two Region Model (TRM), extended with an additional diffusion zone. The extended model was able to describe the copper removal in long-term experiments (up to 125 days) with variable flow rates reflecting realistic runoff events. The four parameters of the model were estimated based on data gained with specific column experiments according to maximum sensitivity for each parameter. After model validation, the parameter set was used for the design of full-scale adsorbers. These full-scale adsorbers show high removal rates during extended periods of time.
Udert, K. M., Larsen, T. A., & Gujer, W. (2006). Fate of major compounds in source-separated urine. Water Science and Technology, 54(11-12), 413-420. doi:10.2166/wst.2006.921, Institutional Repository

Urine separation is a promising alternative to present-day’s waste water management. It can help to manage our nutrient flows in a sustainable way. Currently, techniques are being developed to recycle and treat source-separated urine. These techniques, however, must consider the spontaneous processes that change the separated urine. The initial cause of changes is the contamination with microorganisms, which can hardly be avoided in urine-collecting systems. The most important transformation processes are microbial urea hydrolysis, mineral precipitation and ammonia volatilisation. Additionally, a variety of microorganisms, including pathogens, may grow in source-separated urine. In this paper we give an overview of the effects that the spontaneous transformation processes may have. We focus on nitrogen, phosphorus, magnesium, calcium, potassium, sulphur, organic substances, pathogens and the buffering capacity. The discussion is based on own research results and literature reviews. This overview will help to develop appropriate technologies for urine recycling.

Not Peer Reviewed Publications

Gruber, W., Niederdorfer, R., Ganesanandamoorthy, P., Bürgmann, H., Morgenroth, E., & Joss, A. (2024). Nitrit-Akkumulation auf Nitrifizierenden Belebtschlammanlagen. Wie kann der NO2– - Richtwert eingehalten werden?. Aqua & Gas, 104(1), 18-24. , Institutional Repository

Nitrit ist eine ökotoxikologisch problematische Substanz und führt auf Kläranlagen zur Bildung von klimaschädlichem Lachgas. Auf nitrifizierenden Belebtschlammanlagen kann Nitrit saisonal akkumulieren und erhöhte Ablaufwerte treten auf. Hier diskutieren wir die Häufigkeit von Überschreitungen des Nitrit-Richtwerts auf Schweizer ARA und schlagen Gegenmassnahmen vor.
Ballikaya, P., Brunner, I., Cocozza, C., Grolimund, D., Kaegi, R., Murazzi, M. E., … Cherubini, P. (2023). Nanoparticles are everywhere, even inside trees. Chimia, 77(4), 256. doi:10.2533/chimia.2023.256, Institutional Repository
Derlon, N., & Villez, K. (2023). Editorial: water resource recovery modelling 2021 (WRRmod2021 conference). Water Science and Technology, 87(12), III-IV. doi:10.2166/wst.2023.175, Institutional Repository
Dieziger, C., Freimann, R., Durisch-Kaiser, E., & Joss, A. (2023). Lachgasemissionen aus Faulwasserbehandlung. Beprobung und Einordnung 12 Schweizer Anlagen. Aqua & Gas, 103(3), 50-54. , Institutional Repository

Lachgas ist neben Kohlendioxid und Methan eines der potentesten Treibhausgase und hauptverantwortlich für den Abbau der stratosphärischen Ozonschicht. Auf Schweizer Abwasserreinigungsanlagen (ARA) ist die Faulwasserbehandlung, die hauptsächlich mit dem ein- oder zweistufigen anaeroben Ammonium-Oxidation-Verfahren (Anammox) durchgeführt wird, eine mögliche Quelle für Lachgas. Messungen zeigen, dass die Lachgasemissionen im klimarelevanten Bereich liegen und Reduktionsmassnahmen zu empfehlen sind.
Joss, A., Kipf, M., Morgenroth, E., Baggenstos, M., & Salzgeber, D. (2023). Modifiziertes Anammox-Verfahren. Faulwasserbehandlungen mit stabiler Prozessführung. Aqua & Gas, 103(1), 24-29. , Institutional Repository

Bei der anaeroben Ammonium-Oxidation, kurz Anammox, werden Ammonium und Nitrit im Faulwasser zu Stickstoffgas umgewandelt. Das Verfahren ist auch auf einigen Schweizer ARA im Einsatz. Da aber nicht alle Anlagen die Sollleistung erfüllten, wurde das Anammox-Verfahren untersucht und weiterentwickelt. Mit dem Wechsel von der ein- zur zweistufigen Verfahrensführung wurde nicht nur eine höhere Betriebsstabilität bei der biologischen Entstickung von Rückläufen aus der Schlammentwässerung, sondern teils auch höhere Leistungen erreicht.
Maurer, M., Tilley, E., & Udert, K. (2023). Andere Wege für das Abwasser. Globe, 23(2), 26-28. , Institutional Repository

Die Wasserwirtschaft mit Kanalisation und zentralen Kläranlagen ist nicht mehr zukunftsfähig und global keine Lösung. Umweltingenieur:innen der ETH Zürich und der Eawag bereiten den Weg zu einer kreislauffähigen und dezentraleren Wasserinfrastruktur.
Niederdorfer, R., Gruber, W., Joss, A., & Bürgmann, H. (2023). MicROcensus: zeitnahe Mikrobiom-Analysen auf ARA. Aqua & Gas, 103(9), 54-59. , Institutional Repository

Ein zeitnahes Biomonitoring mit Nanopore-Sequenzierung gewährt neue Einblicke in die biologischen Prozesse einer Abwasserreinigungsanlage (ARA). Im Rahmen des Projekts «MicROcensus» wurde an verschiedenen ARA die Einsatzfähigkeit solcher Mikrobiom-Analysen als Diagnoseinstrument evaluiert. So unterstützen Momentaufnahmemessungen die Ursachenfindung von Prozessinstabilitäten oder Begleitphänomenen. Während wöchentliche Analysen des Mikrobioms – bei Bekanntsein der jahreszeitlichen Dynamiken - als Frühwarnsystem dienen und praxisrelevante Daten für den ARA-Betrieb liefern können.
Pulido-Reyes, G., Bianco, C., Magherini, L., Sethi, R., von Gunten, U., Kaegi, R., & Mitrano, D. M. (2023). Rückhalt von Nanoplastik-Partikeln bei der Wasseraufbereitung. Aqua & Gas, 103(7-8), 30-35. , Institutional Repository

Nanoplastik-Partikel (NP) werden bei einer klassischen Wasseraufbereitung bestehend aus Schnell- und Langsamsandfiltration sowie Aktivkohlefiltration gut aus Seewasser entfernt. Eine simulation einer Wasseraufbereitungsanlage ergab ein Eliminationseffizient von > 99,9%. Der Biofilm des Langsamsandfilters ist dabei das wichtigste Element. Die Ozonbehandlung verändert die NP kaum und hat somit keinen Einfluss auf den Rückhalt der NP bei der nachgeschalteten Sandund Aktivkohlefiltration.
Schäfer, R., Dönni, A., Thomann, M., Gulde, R., Eugster, F., Joss, A., & Piazzoli, A. (2023). Entwicklung des AIA-Tests. Alternativer inhärenter Abbautest für Industrieabwasser. Aqua & Gas, 103(4), 68-75. , Institutional Repository

Um den biologischen Abbau einer Abwasserprobe zu untersuchen und die refraktäre organische Fracht zu quantifizieren, werden Abbautests eingesetzt. Die Charakterisierung der Abwasserströme führt zu Entscheidungen bezüglich Entsorgung und allfälliger benötigter Vorbehandlungen. Der gängige Zahn-Wellens-Test wurde optimiert, um einen zeiteffizienteren Abbautest zu entwickeln: den alternativen inhärenten Abbautest (AIA-Test).
Braun, D., von Känel, L., Biolley, L., Bauer, H., Gahler, D., Gruber, W., … Morgenroth, E. (2022). Dynamische Regelung der ARA Hofen. Infrawatt-Innovationspreis für mehr Leistung und weniger Emissionen. Aqua & Gas, 102(1), 26-31. , Institutional Repository

Die ARA Hofen hat den Infrawatt Innovationspreis 2021 für die Ertüchtigung ihrer Biologiebecken mit dem Konzept der dynamischen Regelung erhalten. Die Leistung der ARA konnte dadurch signifikant erhöht werden, bei stark vermindertem Energieverbrauch und gleichzeitig sehr geringen Lachgasemissionen.
Böhler, M. A., Joss, A., & McArdell, C. S. (2022). GAK-Filter für die Spurenstoffentfernung. Erfahrungen und Betriebsergebnisse der Pilotstudien ARA Furt/Bülach und Glarnerland. Aqua & Gas, 102(1), 48-54. , Institutional Repository

Auf den Kläranlagen Furt/Bülach und Glarnerland des Abwasserverbandes Glarnerland (AVG, Bilten) wurden zwischen 2014 und 2019 umfangreiche Untersuchungen zur Elimination von Mikroverunreinigungen mittels granulierter Aktivkohle (GAK) durchgeführt. Ziel war es, unter Schweizer Praxisbedingungen die Machbarkeit, Effizienz und Wirtschaftlichkeit des Verfahrens zu evaluieren. Fazit beider Forschungsprojekte ist, dass sich die GAK-Filtration zur Spurenstoffelimination gemäss Schweizer Gesetzgebung eignet. Das Verfahren ist technisch und wirtschaftlich realisierbar und hat sich als praxistauglich erwiesen.
Gruber, W., Joss, A., von Känel, L., Biolley, L., Braun, D., & Morgenroth, E. (2022). Abluftmessungen in der biologischen Abwasserreinigung. Aqua & Gas, 102(1), 24-25. , Institutional Repository

Neue Leistungsanforderungen an Abwasserreinigungsanlagen hinsichtlich Ablaufqualität, Energieeffizienz und Treibhausgasemission werden immer bedeutender. Um dabei Zielkonflikte zu vermeiden, ist bei der Optimierung die genaue Überwachung der Prozesse erforderlich. So ist die Messung von Gaskonzentrationen in der Abluft aus biologischen Reinigungsstufen ein nützliches Werkzeug, um verschiedene Zielsetzungen einer ARA hochaufgelöst und wartungsarm zu überwachen.
Gruber, W., Niederdorfer, R., Bürgmann, H., Joss, A., von Känel, L., Braun, D., … Morgenroth, E. (2022). Lachgasemissionen aus ARA. Reduktionsmassnahmen zeichnen sich ab. Aqua & Gas, 102(1), 14-22. , Institutional Repository

Lachgas (N2O) ist ein starkes Treibhausgas und die wichtigste ozonzerstörende Substanz in der Stratosphäre. Auf Abwasserreinigungsanlagen wird N2O während des biologischen Stickstoffabbaus gebildet, der somit die grösste Treibhausgasquelle während des Reinigungsprozesses darstellt. Reduktionsmassnahmen sind deshalb von grosser Bedeutung und gemäss neuen Erkenntnissen durch eine Optimierung der Nitrifikation und Denitrifikation auch erreichbar.
Kerkez, B., Villez, K., & Volcke, E. I. P. (2022). Editorial: themed issue on data-intensive water systems management and operation. Environmental Science: Water Research and Technology, 8(10), 2032-2033. doi:10.1039/d2ew90029g, Institutional Repository
Kessler, M., Löwenberg, J., Böhler, M., & Strebel, P. (2022). Neue Reinigungsstufe für die ARA Muri. Aqua & Gas, 102(12), 74-79. , Institutional Repository

Zukünftig werden auf der ARA Muri dank einer neuen Reinigungsstufe Mikroverunreinigungen aus dem Abwasser entfernt. Die GAK-Filtration bietet viele Vorteile und wird nicht nur verfahrenstechnisch, sondern auch ästhetisch optimal in die bestehenden Strukturen der ARA Muri eingebunden. Zur sicheren Umsetzung wurden in einer Pilotierung wichtige Fragen beantwortet, insbesondere wie die Filterzellen möglichst ideal mit einer Parallelschaltung für eine maximale Beladung zu verschalten sind.
Benstöm, F., Meda, A., Baumann, P., Derlon, N., Lackner, S., Layer, M., … Wichern, M. (2021). Aerobe Verfahren mit granuliertem Schlamm zur Abwasserbehandlung - Arbeitsbericht der DWA­Arbeitsgruppe KA­6.3. "Biofilmverfahren"*) - Teil 1. KA: Korrespondenz Abwasser Abfall, 68(4), 281-288. , Institutional Repository

Unter bestimmten Prozessbedingungen entsteht in der konventionellen Abwasserreinigung aus flockenförmigem Belebtschlamm (FloS) aerober granulierter Schlamm (AGS), der in der Regel ohne Zugabe von Aufwuchskörpern gebildet wird. Prinzipiell können mit AGS die gleichen Reinigungsleistungen wie mit FloS erzielt werden. Im Vergleich zu konventionellen Anlagen ohne AGS können jedoch vergleichsweise höhere Biomassenkonzentrationen und kürzere Absetzzeiten des Schlamms erreicht und damit potenziell Reaktorvolumina eingespart werden. Somit können Verfahren mit AGS eine interessante Alternative zu etablierten Verfahren sein. Der vorliegende Arbeitsbericht erläutert die derzeit verfügbaren AGS-Verfahrensvarianten (diskontinuierlich und kontinuierlich), diskutiert erstmalig typische Verfahrenskennwerte und gibt Hinweise zu planerischen Aspekten und noch offenen Fragen.
Berg, M., Suess, E., Cayo, L., Bouchet, S., Hug, S. J., Kaegi, R., … Buser, A. M. (2021). Quecksilber im Schweizer Abwasser. Konzentrationen, Massenflüsse, Speziierung und Rückhalt. Aqua & Gas, 101(1), 14-20. , Institutional Repository

In einer landesweiten Studie wurde Quecksilber in Abwässern und Klärschlämmen analysiert, jährliche Gesamtmengen des abwasserbürtigen Quecksilbers ermittelt und die Einhaltung der gesetzlichen Vorgaben überprüft. Ebenso wurde die durchschnittliche Fracht pro Einwohner und der Beitrag der Abwasserreinigungsanlagen zur Quecksilberbelastung der Oberflächengewässer ermittelt. Auf nationaler Ebene waren diese Kennzahlen bisher nicht bekannt.
Doll, C., Larsen, T. A., Strande, L., Udert, K. M., & Morgenroth, E. (2020). Water Hub im NEST-Gebäude. Eine Plattform zum Testen von innovativen ressourcenorientierten Sanitärsystemen. Aqua & Gas, 100(2), 52-57. , Institutional Repository

Mit innovativen Technologien werden im Water Hub unter realen Bedingungen Ressourcen aus dem Abwasser gewonnen und Kreisläufe geschlossen. Die Forschung in diesem Living Lab erlaubt es, praxisnahe Erfahrungen zu machen, Schwachstellen schnell zu identifizieren und das System zu optimieren. Bei der Implementierung dieser dezentralen Technologien spielen die lokalen Herausforderungen und Begebenheiten stets eine wichtige Rolle.
Helleshøj Sørensen, K., & Morgenroth, E. (2020). Biofilm reactors. In G. Chen, G. A. Ekama, M. C. M. van Loosdrecht, & D. Brdjanovic (Eds.), Biological wastewater treatment: principles, modeling and design (pp. 813-839). London: IWA Publishing. , Institutional Repository
Mast, J., Verleysen, E., Hodoroaba, V. D., & Kaegi, R. (2020). Characterization of nanomaterials by transmission electron microscopy: measurement procedures. In V. D. Hodoroaba, W. E. S. Unger, & A. G. Shard (Eds.), Micro and nano technologies. Characterization of nanoparticles. Measurement processes for nanoparticles (pp. 29-48). doi:10.1016/B978-0-12-814182-3.00004-3, Institutional Repository
Morgenroth, E. (2020). Modelling biofilms. In G. H. Chen, M. C. M. van Loosdrecht, G. A. Ekama, & D. Brdjanovic (Eds.), Biological wastewater treatment. principles, modeling and design (pp. 757-812). London: IWA Publishing. , Institutional Repository
Fumasoli, A., Bützer, S., Kraft, T., Derlon, N., Lüdin, K., Behl, M., & Maissen, B. (2019). Trommelsieb als Vorklärbecken-Ersatz. Erkenntnisse aus einem Pilotversuch auf der ARA Sihltal. Aqua & Gas, 99(10), 76-82. , Institutional Repository

Die ARA Sihltal wird heute ohne Vorklärung betrieben, soll jedoch aufgrund der zukünftigen Bevölkerungsentwicklung und zur energetischen Optimierung mit einer Vorklärung erweitert werden. Wegen der sehr engen Platzverhältnisse kann eine maschinelle Vorklärung (Trommelsieb) einfacher realisiert werden als eine konventionelle Vorklärung. Die Pilotversuche bestätigen, dass das Trommelsieb aus betrieblicher Sicht und bezüglich Abscheideleistung eine gleichwertige Vorklärung bietet.
Hagemann, N., Bucheli, T. D., Schmidt, H. P., Kägi, R., Böhler, M., & McArdell, C. S. (2019). Aktivkohle - Made in Switzerland!. Aqua & Gas, 99(1), 32-38. , Institutional Repository

Die Elimination von Mikroverunreinigungen in der Abwasserreinigung mit Aktivkohle oder Ozon ist eine wichtige Massnahme zum vorbeugenden Schutz der Gewässer und der Trinkwasserressourcen der Schweiz. Während der Einsatz von Ozon mit einem hohen Energieverbrauch einhergeht, führt der Einsatz von Aktivkohle andernorts zu negativen Umweltauswirkungen, da die Aktivkohle zum Teil aus fossilen Ausgangsstoffen wie Stein- oder Braunkohle hergestellt und zudem über weite Strecken transportiert wird. Aktivkohlen mit sehr guten Eliminationsleistungen könnten aber auch in der Schweiz aus einheimischen erneuerbaren Roh- und Reststoffen hergestellt werden.
Horisberger, M., Casazza, R., Grelot, J., & Joss, A. (2019). Elimination von Mikroverunreinigungen. Pilotversuche: Einsatz von granulierter Aktivkohle im Wirbelbett auf der Ara Penthaz. Aqua & Gas, 99(1), 39-45. , Institutional Repository

Im Rahmen der Erweiterung der ARA Penthaz VD um eine Reinigungsstufe zur Elimination von Mikroverunreinigungen wurden Pilotversuche mit granulierter Aktivkohle im Wirbelbett (CarboPlus®-Verfahren) durchgeführt. Sie zeigten, dass sich mit diesem Verfahren die Anforderungen der Schweizer Gesetzgebung an die Elimination von Mikroverunreinigungen erfüllen lassen. Zudem konnten in den Versuchen Parameter zur Überwachung des Betriebs ermittelt werden. Aufgrund der vielversprechenden Ergebnisse wurde das Verfahren auf der ARA Penthaz grosstechnisch realisiert und im Herbst 2018 in Betrieb genommen.
Meier, A., & Böhler, M. (2019). Pulveraktivkohle - Welche passt? Wahl, Beschaffung und Qualitätssicherung von Pak zur Elimination von Mikroverunreinigungen. Aqua & Gas, 99(1), 22-31. , Institutional Repository

Fünf bis zehn Gramm Pulveraktivkohle weisen die Oberfläche eines Fussballfeldes auf. Das faszinierende schwarze Pulver kann vielerorts eingesetzt werden, zum Beispiel auf Abwasserreinigungsanlagen, um Mikroverunreinigungen aus dem Abwasser zu eliminieren – und dies immer häufiger. Auf dem Markt sind zahlreiche PAK-Sorten verfügbar, die zwar äusserlich nicht zu unterscheiden sind, aber dennoch unterschiedliche Eigenschaften aufweisen. Dieser Artikel soll Betreiber und Ingenieure bei der Entscheidung unterstützen, welche Pulveraktivkohle für ihr Abwasser optimal ist und wie sie die Qualität neuer Lieferungen überprüfen können.
Siegrist, H., Joss, A., Boehler, M., McArdell, C. S., & Ternes, T. (2019). Organic micropollutant control. In G. Mannina, G. Ekama, H. Ødegaard, & G. Olsson (Eds.), Advances in wastewater treatment (pp. 231-260). doi:10.2166/9781780409719_0231, Institutional Repository

About 100,000 chemical substances have economic uses, of which 4,600 substances are produced annually in quantities exceeding 1,000 tons in the OECD member states. During production and disposal, as well as after regular use, a significant portion of these substances will unavoidably enter the aquatic environment, where they can have ecotoxicological effects, such as fish feminization. Organic compounds are increasingly being detected in water bodies and in sewage sludge in low concentration ranges (μg/L and ng/L), being referred to as organic micropollutants. T he removal of micropollutants by conventional municipal wastewater treatment is incomplete and a multitude of compounds are only slightly abated. To significantly reduce eco-toxicological effects of micropollutants in receiving waters and water resources, additional treatment steps (e.g. ozonation or activated carbon adsorption) are required in combination with measures taken at the source. Ozonation requires complete nitrification and it might not be suitable for wastewater with high industrial wastewater fractions and high bromide concentrations due to the production of bromate and increased oxidation by-products. Powdered activated carbon (PAC) addition is already broadly applied. PAC can be recycled to the activated sludge treatment to improve micropollutant removal and therefore reduce PAC consumption. Recently granular activated carbon (GAC) filters are increasingly investigated and built in full scale for micropollutant and dissolved organic carbon (DOC) removal. Additional measures in wastewater treatment should be based on careful micropollutant mass flux studies to identify critical catchment areas so that relevant hot spots can be addressed.
Derlon, N., Layer, M., Morgenroth, E., Adler, A., Gelb, A., & Holliger, C. (2018). Boues granulaires aérobies. État de l'art de la recherche actuelle et future. Aqua & Gas, 98(1), 14-19. , Institutional Repository

Les boues granulaires aérobies offrent plusieurs avantages pour le traitement biologique des eaux usées municipales par rapport au procédé à boues activées conventionnels. Cependant, malgré un nombre croissant d’applications industrielles et municipales, notre recul sur les boues granulaires aérobies reste limité. L’EPFL et l’Eawag ont évalué au cours des dernières années les mécanismes, performances et limites des systèmes de boues granulaires aérobies. Dans cet article, nous résumons notre compréhension des facteurs influençant les propriétés des boues granulaires aérobies et fournissons une appréciation globale de cette nouvelle technologie.
Derlon, N., Pronk, W., & Morgenroth, E. (2018). Membranes d'ultrafiltration. La présence de biofilms: un avantage pour stabiliser le flux et augmenter la qualité du perméat. Aqua & Gas, 98(5), 30-35. , Institutional Repository

L’utilisation de systèmes composites combinant une couche biologique (le biofilm) supportée par une barrière physique (la membrane) a de multiples avantages pour le traitement des eaux (production d’eau potable, recyclage des eaux grises). Cet article présente comment tirer profit de la microbiologie des biofilms afin d’améliorer la qualité du perméat et faire fonctionner des systèmes membranaires à flux constant pendant plusieurs années, et ce sans maintenance.
Horisberger, M., Casazza, R., Grelot, J., & Joss, A. (2018). Élimination des micropolluants. Essais pilotes: traitement par charbon actif en grain en lit fluidisé à la step de Penthaz. Aqua & Gas, 98(10), 44-50. , Institutional Repository

En vue de la construction d’un traitement des micropolluants à la STEP de Penthaz (VD), des essais pilotes avec du charbon actif en grain (CAG) en lit fluidisé (procédé CarboPlus®) ont été réalisés. Ces essais pilotes ont montré que ce procédé permet d'éliminer les micropolluants des eaux usées selon les bases légales suisses. Ils ont de plus permis de développer des mesures pertinentes pour le suivi de l’installation. En raison des résultats prometteurs, ce procédé a été validé. L'installation est en cours de réalisation et sera mise en service en automne 2018.
Thalmann, B., Kägi, R., & von Gunten, U. (2018). Metalle in der Ozonung. Verhalten von ausgewählten Metallen: Oxidation von Metallsulfiden und Metallkomplexen. Aqua & Gas, 98(4), 68-77. , Institutional Repository

Metallsulfide (CuS, ZnS, CdS) werden während der Ozonbehandlung von geklärtem Abwasser nahezu vollständig in Metallionen und Sulfat umgewandelt. Auch organische Komplexbildner, wie EDTA oder NTA, werden durch die Ozonung teilweise zerstört. Dies führt zu einer Freisetzung der entsprechenden Metallionen. Toxische Effekte, hervorgerufen durch erhöhte Konzentrationen von Metallionen, wurden jedoch nur für sehr hohe Kupferkonzentrationen, die dem Abwasser als Kupfersulfide zugegeben worden waren, beobachtet und sind deshalb im «normalen» Abwasser nicht zu erwarten.
Udert, K. M. (2018). Phosphorus as a resource. In C. Schaum (Ed.), Integrated environmental technology series. Phosphorus: polluter and resource of the future – removal and recovery from wastewater (pp. 57-80). doi:10.2166/9781780408361_057, Institutional Repository
Vriens, B., Voegelin, A., Hug, S., Kaegi, R., Berg, M., & Winkel, L. (2018). Spurenelemente in Schweizer Abwasser. Aktuelle Konzentrationen und Frachten. Aqua & Gas, 98(1), 40-46. , Institutional Repository

In einem landesweiten Screening wurden in 64 Schweizer Kläranlagen die aktuellen Konzentrationsbereiche und Frachten von Spurenelementen erfasst. Anhand dieser Werte wurde die Einhaltung der gesetzlichen Vorgaben überprüft sowie die gegenwärtigen durchschnittlichen Pro-Kopf-Elementfrachten und der ökonomische Wert der Elementfrachten berechnet. Bisher waren für viele Spurenelemente diese Kennzahlen nicht bekannt.
Ward, B. J., Sam, S., Andriessen, N., Morgenroth, E., & Strande, L. (2018). Research priorities and progress in faecal sludge dewatering. Sandec News, 19, 10-11. , Institutional Repository

Difficulties in dewatering of faecal sludge are a crucial barrier to implementation of effective faecal sludge management. This article focuses on progress with locally available conditioners and the next steps toward implementing high-throughput, low-footprint dewatering technologies.
Böhler, M., Fleiner, J., McArdell, C. S., Teichler, R., Siegrist, H., Kienle, C., … Wunderlin, P. (2017). Projekt ReTREAT. Untersuchungen zu Verfahren für die biologische Nachbehandlung nach Ozonung. Aqua & Gas, 97(5), 54-63. , Institutional Repository

Im Rahmen des Projekts ReTREAT wurden verschiedene Verfahren auf deren Eignung als biologische Nachbehandlung nach einer Ozonung getestet. Der Fokus lag dabei – neben allgemeinen Reinigungseffekten – insbesondere auf dem Abbau von labilen Reaktionsprodukten sowie deren ökotoxikologischen Wirkungen.
Stamm, C., Burdon, F., Fischer, S., Kienle, C., Munz, N., Tlili, A., … Eggen, R. (2017). Einfluss von Mikroverunreinigungen. Aqua & Gas, 97(6), 90-95. , Institutional Repository

Im Projekt EcoImpact wurden die ökotoxikologischen und ökologischen Effekte von Mikroverunreinigungen aus Kläranlagen auf aquatische Lebensgemeinschaften untersucht. Chemische und biologische Untersuchungen oberhalb und unterhalb von Kläranlagen deuten auf Effekte dieser Stoffe hin, die von physiologischen Antworten der Organismen bis hin zu veränderten Ökosystemfunktionen wie z. B. dem Laubabbau reichen. Gezielte Rinnenexperimente mit kontrollierter Wasserqualität unterstützen diese Befunde.
von Gunten, U., Merle, T., Lee, M., Pronk, W., Hollender, J., Vogler, B., … Meier, T. (2017). Aufbereitung von Trinkwasser im Hardwald. Einschätzung der jetzigen Situation und möglicher zusätzlicher Aufbereitungsstufen. Aqua & Gas, 97(2), 21-28. , Institutional Repository

Im Hardwald bei Muttenz wird zur Trinkwasseraufbereitung Rheinwasser versickert. Während der Bodenpassage wird rund die Hälfte der vorhandenen Spurenstoffe im Rheinwasser entfernt. Ein Grossteil der restlichen Substanzen wird durch die Aktivkohlefiltration des angereicherten Grundwassers entfernt. Wie gut die Spurenstoffe im Aktivkohlefilter zurückgehalten werden und ob eine vor- oder nachgeschaltete Oxidation zu einer besseren Entfernung führen kann, wird in der nachfolgend vorgestellten Studie aufgezeigt. Die Studie wurde im Rahmen des Projekts "Regionale Wasserversorgung Basel-Landschaft 21" realisiert.
Krampe, J., & Böhler, M. (2016). Ein Projekt mit Leuchtturm-Charakter. Gas- und Wasserfach: Wasser, Abwasser, 157(1), 28-31. , Institutional Repository

Stickstoffelimination im Seitenstrom – damit beschäftigen sich aktuell zwei Fallstudien im Rahmen von PowerStep: Prof. Dr.-Ing. Jörg Krampe (Vorstand des Forschungsbereiches Wassergütewirtschaft des Instituts für Wassergüte, Ressourcenmanagement und Abfallwirtschaft der Technischen Universität Wien) arbeitet dazu an der Case Study 5 in Zusammenarbeit mit dem Abwasserverband Wörgl-Kirchbichl an der Kläranlage Kirchbichl in Österreich (100 000 EW); Auf der Kläranlage Altenrhein in der Schweiz (120 000 EW) ist Marc Böhler (Eidgenössische Anstalt für Wasserversorgung, Abwasserreinigung und Gewässerschutz, Eawag) zusammen mit dem Abwasserverband Altenrhein für die Case Study 6 verantwortlich. Im Interview mit gwf-Wasser | Abwasser sprechen Prof. Dr.-Ing. Jörg Krampe und Marc Böhler über ihre Hintergründe, Aussichten und Ziele.
Lieberherr, E., Truffer, B., & Dominguez, D. (2016). Innovation and public management. Comparing dynamic capabilities in two Swiss wastewater utilities. In M. Finger & C. Jaag (Eds.), Routledge companions in business, management and accounting. The Routledge companion to network industries (pp. 389-402). Retrieved from https://www.taylorfrancis.com/chapters/edit/10.4324/9781315768984-37/innovation-public-management-comparing-dynamic-capabilities-two-swiss-wastewater-utilities-eva-lieberherr-bernhard-truffer-damian-dominguez?context=ubx&refId=d80e4bc7-1ccd-47a0-9f4c, Institutional Repository

Potable water and flushing toilets in households are taken for granted in today's Organization for Economic Co-operation and Development (OECD) countries. Close to 100 percent of the population in most OECD countries has access to safe drinking water, and ca. 70 percent is connected to wastewater treatment plants (Aubin and Varone, 2007; OECD, 2011; OECD Environment Directorate, 2008). This taken-for-granted situation is largely possible due to extensive governmental planning, management, and investments in water and wastewater infrastructure (OECD, 2009). The expansion of domestic water service provision occurred via public subsidies, with service provision provided by primarily local and regional governments and, hence, predominantly public organizations (Citroni, 2010). Indeed, the water and wastewater sectors in OECD countries have been developed as centralized systems of treatment plants and waterworks with vast, integrated networks of water supply mains and wastewater pipes. Accordingly, these sectors can be considered 'typical' public network utility sectors (Luis-Manso, 2007: 2). [...]
Stamm, C., Räsänen, K., Burdon, F. J., Altermatt, F., Jokela, J., Joss, A., … Eggen, R. I. L. (2016). Unravelling the impacts of micropollutants in aquatic ecosystems: interdisciplinary studies at the interface of large-scale ecology. In A. J. Dumbrell, R. L. Kordas, & G. Woodward (Eds.), Advances in ecological research: Vol. 55. Large-scale ecology: model systems to global perspectives (pp. 183-223). doi:10.1016/bs.aecr.2016.07.002, Institutional Repository

Human-induced environmental changes are causing major shifts in ecosystems around the globe. To support environmental management, scientific research has to infer both general trends and context dependency in these shifts at global and local scales. Combining replicated real-world experiments, which take advantage of implemented mitigation measures or other forms of human impact, with research-led experimental manipulations can provide powerful scientific tools for inferring causal drivers of ecological change and the generality of their effects. Additionally, combining these two approaches can facilitate communication with stakeholders involved in implementing management strategies. We demonstrate such an integrative approach using the case study EcoImpact, which aims at empirically unravelling the impacts of wastewater-born micropollutants on aquatic ecosystems.
Udert, K. M., & Etter, B. (2016). Vom Urin zum Dünger. Projekt VUNA - Sanitäre Grundversorgung und Separatbehandlung von Urin in Durban/Südafrika. Aqua & Gas, 96(3), 62-69. , Institutional Repository

In Durban/Südafrika werden urinseparierende Toiletten zur Grundversorgung der Bevölkerung in den Vorstadtgebieten eingesetzt. Die Eawag, das Wasserforschungsinstitut des ETH-Bereichs, hat mit dem VUNA-Projekt (www.vuna.ch) die Stadtwerke von Durban dabei unterstützt, die im Urin enthaltenen Wertstoffe zu nutzen. Ziel des Projektes war es, die Akzeptanz der Trockentoiletten zu erhöhen, die Nährstoffe in Form eines wertvollen Düngers wiederzugewinnen und Umweltverschmutzung zu verhindern.
Burkhardt, M., Dietschweiler, C., Schmidt, S., Englert, A., Hemmann, J., Sinnet, B., & Kägi, R. (2015). Titandioxid. Leitsubstanz für Nanopartikel im Deponiesickerwasser. Aqua & Gas, 95(12), 40-47. , Institutional Repository

Nanopartikel können auf Deponien und von dort mit dem Sickerwasser in Vorfluter gelangen. Als Leitsubstanz für Nanopartikel wurde das Weisspigment Titandioxid in Wasserproben der lnertstoffdeponien Bruni und Schwanental untersucht. Vorgestellt werden insbesondere die Herausforderungen an die analytischen Methoden zur Erfassung von Nanopartikeln in Wasserproben und die ermittelten Massenflüsse.
Etter, B., & Udert, K. M. (2015). Aus Urin wird Flüssigdünger. Eawag News [dtsch. Ausg.] (1), 1-8. Retrieved from http://www.eawag.ch/de/news-agenda/news-plattform/news/news/aus-urin-wird-fluessigduenger/?tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&cHash=a15131c1f98586a1529ff21f31b9ea0e, Institutional Repository

Ein neuartiges Recyclingverfahren gewinnt aus Urin wertvolle Nährstoffe zurück, die sich als Dünger verkaufen lassen. Das schont natürliche Ressourcen, entlastet Kläranlagen und macht Sanitärsysteme in Entwicklungsländern wirtschaftlich attraktiver. Drei Anlagen sind schon in Betrieb: eine an der Eawag in Dübendorf und zwei in der südafrikanischen Stadt Durban.
Etter, B., & Udert, K. M. (2015). Converting urine into liquid fertilizer. Eawag News [engl. ed.] (1), 1-8. Retrieved from http://www.eawag.ch/en/news-agenda/news-portal/news-detail/news/aus-urin-wird-fluessigduenger/?tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&cHash=a15131c1f98586a1529ff21f31b9ea0e, Institutional Repository

With an innovative recycling method, valuable nutrients recovered from urine can be sold as fertilizers. As well as conserving natural resources, this reduces water pollution and makes sanitation systems in developing countries economically more attractive. Three pilot plants are already in operation – one at Eawag in Dübendorf and two in the South African city of Durban.
Etter, B., & Udert, K. M. (2015). Quand l’urine se change en engrais. Eawag News [éd. fr.] (1), 1-8. Retrieved from http://www.eawag.ch/fr/news-agenda/actualites/detail/news/aus-urin-wird-fluessigduenger/?tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&cHash=a15131c1f98586a1529ff21f31b9ea0e, Institutional Repository

Une nouvelle technique de valorisation permet d'extraire les éléments nutritifs de l'urine et de fabriquer un fertilisant commercialisable. Cette approche préserve les ressources naturelles, limite les charges à traiter dans les stations d'épuration et augmente la rentabilité des systèmes d'assainissement dans les pays en développement. Trois stations pilotes sont déjà en fonction: une à Dübendorf et deux dans la ville sud-africaine de Durban
Fux, C., Kienle, C., Joss, A., Wittmer, A., & Frei, R. (2015). Ausbau der ARA Basel mit 4. Reinigungsstufe. Pilotstudie: Elimination Mikroverunreinigungen und ökotoxikologische Wirkungen. Aqua & Gas, 95(7/8), 10-17. , Institutional Repository

Auf der ARA Basel der ProRheno AG, die hauptsächlich kommunales Abwasser reinigt, wird aufgrund ihrer Grösse eine zusätzliche Stufe zur Elimination von Mikroverunreinigungen nötig sein. Während mehreren Monaten wurde in einer Pilotanlage untersucht, ob sich die Verfahren Zugabe von Pulveraktivkohle (PAK) und Ozonung grundsätzlich auf der ARA Basel eignen. Zusätzlich wurde die Reinigungsleistung der weitergehenden Abwasserbehandlung für kommunales Abwasser der ARA Basel getestet, das einen gewissen Anteil biologisch gereinigtes Industrieabwasser enthielt.
Kaufmann, M., Dürrenmatt, D., & Villez, K. (2015). Verstecktes Potenzial in Kläranlagendaten. Anlageoptimierung dank systematischer Datenauswertung. Aqua & Gas, 95(2), 76-81. , Institutional Repository

Auf einer durchschnittlichen Kläranlage werden Tausende Signale aufgezeichnet. Ihr Potenzial für einen besseren Anlagebetrieb ist beachtlich. Dennoch werden sie selten systematisch genutzt und ausgewertet. Dank einer spezialisierten Software ist es jetzt möglich, eine Anlage und ihre Prozesse schneller und besser zu verstehen, zu überwachen und zu optimieren.
Stamm, C., Eggen, R. I. L., Hering, J. G., Hollender, J., Joss, A., & Schärer, M. (2015). Micropollutant removal from wastewater: facts and decision-making despite uncertainty. Environmental Science and Technology, 49(11), 6374-6375. doi:10.1021/acs.est.5b02242, Institutional Repository
Ternes, T., Joss, A., & Oehlmann, J. (2015). Occurrence, fate, removal and assessment of emerging contaminants in water in the water cycle (from wastewater to drinking water). Water Research, 72, 1-2. doi:10.1016/j.watres.2015.02.055, Institutional Repository
Wunderlin, P., Mestankova, H., Salhi, E., Schindler Wildhaber, Y., Schärer, M., Schirmer, K., & von Gunten, U. (2015). Behandelbarkeit von Abwasser mit Ozon. Testverfahren zur Beurteilung. Aqua & Gas, 95(7-8), 28-38. , Institutional Repository

Eine Ozonung als zusätzliche Reinigungsstufe auf einer kommunalen Abwasserreinigungsanlage (ARA) bewirkt eine deutliche Abnahme der Mikroverunreinigungen. Bei speziellen Belastungen, z.B. aufgrund bedeutender Industrie- oder Gewerbeabwassereinleitungen, können durch die Ozonung jedoch neue Stoffe, sogenannte Transformationsprodukte, gebildet werden. Daher soll künftig im Einzelfall ein Testverfahren aus fünf Modulen prüfen, ob sich ein bestimmtes Abwasser für eine Ozonbehandlung eignet oder nicht.
Wunderlin, P., Joss, A., Siegrist, H., Abegglen, C., & Schärer, M. (2015). Verfahrenstechnik Mikroverunreinigungen. www.micropoll.ch - Wissensplattform des VSA. Aqua & Gas, 95(2), 14-19. , Institutional Repository

Noch liegen in der Schweiz erst wenige grosstechnische Erfahrungen mit den Technologien zur Elimination organischer Spurenstoffe auf Abwasserreinigungsanlagen vor. Deswegen wurde 2012 die Plattform «Verfahrenstechnik Mikroverunreinigungen» gegründet und innerhalb des Verbands der Schweizer Abwasser- und Gewässerschutzfachleute (VSA) angesiedelt. Sie soll helfen, Wissen aufzubauen, den Austausch unter den Akteuren zu fördern sowie offene Fragen zu bearbeiten.
Etter, B., Gounden, T., & Udert, K. M. (2014). VUNA: harvesting nutrients from urine for agriculture. Sandec News, 15, 10-11. , Institutional Repository

VUNA is a trans-disciplinary project that is developing a system to collect source-separated urine and process it into fertiliser. Collection logistics, treatment technologies, and social and economic assessments of nutrient recovery are some of the activities worked on by the VUNA team.
Larsen, T. A., Udert, K. M., & Lienert, J. (2014). Abwassertrennung und Dezentralisierung. Aqua & Gas, 94(1), 52-54. , Institutional Repository

Ist eine ressourcenschonende Abwasserreinigung durch Abwassertrennung und Dezentralisierung realistisch? Rund 40 international bekannte Wissenschafter und Wissenschafterinnen behandeln auf 520 Seiten in einem 2013 erschienenen Buch nuanciert diese Fragestellung. Die Editoren der Eawag diskutieren das Thema des Buches im Schweizer Kontext.
Udert, K. M. (2014). Electrochemical treatment of urine. In G. Kreysa, Kichiro Ota, & R. F. Savinell (Eds.), Encyclopedia of applied electrochemistry (pp. 654-658). doi:10.1007/978-1-4419-6996-5_109, Institutional Repository

Separation at the source and decentralized treatment of urine, feces, and greywater is a novel concept for wastewater management. This approach is particularly suitable for regions where the availability of water resources is low or the infrastructure for centralized wastewater treatment is missing. Urine is the main contributor of nutrients to municipal wastewater (80 % of nitrogen and 50 % of phosphorus). Since the urine volume is small (1.3 L · s-1 · d-1), nutrient removal (or recovery) could be achieved in small decentralized reactors.
Some properties of electrochemical processes make them particularly suitable for urine treatment in a small decentralized reactor: no chemicals have to be added, the reaction can be easily started and terminated, a wide range of compounds can be oxidized or reduced, and the electric parameters current and voltage can be used for process automation and remote process control. However, electrochemical processes also have some drawbacks: the energy consumption is higher than for comparable biological processes, side reactions can produce unwanted by-products, and efficient electrodes are often expensive.
The main focus of this article is on the electrochemical removal of nitrogen and phosphorus from source-separated urine. Bioelectrochemical systems for urine treatment will not be discussed, because the research is still at an early stage. Some possible applications of bioelectrochemical systems for urine treatment have been presented in Udert et al..
Weissbrodt, D. G., Wells, G. F., Johnson, D. R., Bürgmann, H., Joss, A., Laureni, M., & Morgenroth, E. (2014). Towards community systems microbiology for the optimization of aerobic-anaerobic ammonium oxidation processes. In Vol. 1. 87th annual water environment federation technical exhibition and conference (WEFTEC 2014) (pp. 2645-2649). doi:10.2175/193864714815942567, Institutional Repository
Kabdaşlı, I., Tünay, O., & Udert, K. M. (2013). Transfer into the solid phase. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 351-365). London: IWA Publishing. , Institutional Repository

Several treatment methods can be used to transfer dissolved compounds from source-separated wastewater streams onto or into a solid phase. A critical review of these methods will be given here. The emphasis will be placed on the recovery of nutrients, especially from human urine; the treatment of other waste streams will be described in brief.
Larsen, T. A., Udert, K. M., & Lienert, J. (2013). Editorial. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 1-10). London: IWA Publishing. , Institutional Repository

Why are we editing a book about source separation and decentralization? We live in Switzerland, an industrialized country with a highly advanced and well-functioning wastewater management system. But even in Switzerland, the central system is reaching its limits, shortcomings, which become very obvious from a global perspective. We are proud to have been able to assemble contributions from renowned authors worldwide from both research and practice. They share with us their experience and thoughts about the current wastewater system. They analyze its advantages, but also deficiencies and they have the courage to breach the paradigm that central wastewater treatment is the only possible approach in urban areas. Many of the authors of this book are pioneers in the field and have been paving the way to a more sustainable and equitable handling of wastewater. We are greatly indebted to all the authors for their contributions to this book, but even more so for their continuous research on source separation and decentralization. We hope that this book will help develop this new area into a mature field in science as well as in practice. [...]
Larsen, T. A., & Gujer, W. (2013). Implementation of source separation and decentralization in cities. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 135-150). London: IWA Publishing. , Institutional Repository

In the next decades, global population growth will be dominated by an increasing urban population. As seen from Figure 10.1, this growth will primarily take place in "less developed" regions. Maintaining urban hygiene and healthy water resources in these regions will be a formidable, expensive and time consuming task. In Switzerland, water pollution control had a very high public priority in the period from 1960 to 1990 and the construction of sewers and centralized wastewater treatment plants was highly subsidized by federal and state agencies in order to speed up the construction process. Nevertheless it took about 27 years to increase the connection of the population and industry to first-generation wastewater treatment plants (BOD removal only) from 10% to 90%. Second-generation treatment, which includes nutrient removal, is still in progress. Thus, experience tells us that under ideal conditions, in a rich country, with a well established engineering community and well organized state agencies, the establishment of efficient and stable wastewater treatment infrastructure is subject to a time constant of at least 50 years. [...]
Martin, K. J., Derlon, N., Morgenroth, E., & Nerenberg, R. (2013). Fouling layer surface heterogeneity improves permeate flux. In 86th Annual Water Environment Federation Technical Exhibition and Conference, WEFTEC 2013: Vol. 1. 86th annual water environment federation technical exhibition and conference (WEFTEC 2013) (pp. 621-629). doi:10.2175/193864713813668079, Institutional Repository

In this research, we used modeling to assess the impact of irregular fouling-layer surface morphology (i.e., roughness) on permeate fluxes. Two membrane filtration models, each based on Darcy's Law, were used to predict fluxes for fouling layers with varying degrees of surface irregularity. One of the models considered the arithmetic mean thickness of the fouling layer, while the other accounted for the actual, irregular surface morphology assuming one-dimensional permeate flow. Surface morphology and permeate-flux data from an ultra-low pressure gravity-driven membrane filter were used to test the models. The models that accounted for the surface morphology were more accurate, especially for highly irregular surface morphologies. These models were also able to correctly predict greater permeate fluxes exhibited by highly irregular surface morphologies despite their having greater mean thicknesses. Our results show that models based on the mean thickness may not accurately characterize the effect of the fouling layer on fluxes. Future research should consider the surface morphology of the fouling layer when devising fouling mitigation strategies.
Siegrist, H., Laureni, M., & Udert, K. M. (2013). Transfer into the gas phase: ammonia stripping. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 337-350). London: IWA Publishing. , Institutional Repository

Stripping is the most common process for the selective recovery of ammonia from wastewater. Two stripping technologies have been used for source-separated urine: first, air stripping of ammonia with subsequent ammonia adsorption in acid, and second, steam stripping with ammonia recovery in the condensate. In this chapter, we discuss the basic concepts of air stripping, because it is probably more suitable for decentralized reactors than steam stripping. We will also present results of air stripping/acid adsorption and steam stripping experiments with urine. Furthermore, we will discuss the conditions that can lead to passive ammonia stripping in urine-collecting systems. In the future, passive stripping could be a low-energy option for ammonia recovery in on-site systems.
The focus of this chapter is on the treatment of source-separated urine. However, we will also refer to the treatment of digester supernatant during the discussion of the basic concepts of air stripping. Since our literature review did not reveal any report about ammonia stripping from blackwater, we will not discuss this application.
Throughout the text, we will use the term ammonia for the sum of free ammonia (NH3) and ammonium (NH4+). To specifically address the two forms of ammonia, we will use the chemical formula NH3 and NH4+. The terms for carbonate and phosphate will be used accordingly.
Strähl, S., Ort, C., Siegrist, H., Thomann, M., Obrecht, J., & Kurz, E. (2013). Stickstoffelimination in Schweizer ARA. Weitere Entlastung der Oberflächengewässer. Aqua & Gas, 93(5), 74-84. , Institutional Repository

Mit dem Abwasser gelangen pro Jahr rund 41 000 t Stickstoff (N) in die Schweizer Kläranlagen. Davon werden heute etwa 18 000 t in den ARA eliminiert. Mit Hilfe einer Kombination von neu entwickelten Reinigungsverfahren, die zum Teil bereits gut etabliert und auf dem Stand der Technik sind, liessen sich die Oberflächengewässer im Inland um weitere 6600 t Stickstoff entlasten, wie die vorliegende Studie zeigt. Bei Ausschöpfung des Reduktionspotenzials in den 160 grösseren ARA ist mit Gesamtinvestitionen von 344 Mio. Franken und jährlichen Betriebskosten von 27 Mio. Franken zu rechnen.
Udert, K. M., & Jenni, S. (2013). Biological nitrogen conversion processes. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 291-305). London: IWA Publishing. , Institutional Repository

Biological processes are the gold standard for nitrogen removal in municipal wastewater treatment, because they are more energy-efficient and require fewer resources than physico-chemical processes. Several studies have shown that biological processes can also be used for nitrogen removal from urine and blackwater, the two source-separated waste streams with the highest nitrogen loads. However, biological processes are not only used for nitrogen removal but also for nitrogen recovery: with nitrification the volatile ammonia in urine can be stabilized as nitrate or ammonium nitrate. This is a suitable pretreatment step for the evaporative recovery of all nutrients in one solid product.
In this chapter, we present the basic processes for biological nitrogen conversion in wastewater treatment and we discuss laboratory and pilot-scale experiments of nitrogen conversion in urine and blackwater.
Udert, K. M., Brown-Malker, S., & Keller, J. (2013). Electrochemical systems. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 321-335). London: IWA Publishing. , Institutional Repository

Electrochemical processes offer many possibilities for decentralized wastewater treatment. Besides the direct oxidation and reduction of major pollutants they can also be used for coagulation and precipitation processes, disinfection or targeted micropollutant removal. While those processes require energy, wastewater can also be used as a direct source for electricity, either in purely chemical fuel cells or in bioelectrochemical systems. Several processes have been tested for source-separated waste streams, especially for urine. However, no pilot plants or long-term experiences have been reported so far. In this chapter, we present basic concepts of electrochemical treatment, possible applications for source-separated waste streams and we summarize and discuss existing data especially with respect to energy.
Wunderlin, P., Siegrist, H., & Joss, A. (2013). Online N2O measurement: the next standard for controlling biological ammonia oxidation?. Environmental Science and Technology, 47(17), 9567-9568. doi:10.1021/es402971p, Institutional Repository
Böhler, M., Büttner, S., Liebi, C., & Siegrist, H. (2012). Dünger aus Abwasser. Ammoniakstrippung mittels Luft zur Behandlung von Faulwasser und Urin auf der Kläranlage Kloten/Opfikon. Aqua & Gas, 92(1), 26-31. , Institutional Repository

Auf der Kläranlage Kloten/Opfikon wurde erstmals in der Schweiz das Verfahren der Luftstrippung zur Stickstoffrückgewinnung aus Faulwasser volltechnisch umgesetzt. Das Verfahren beinhaltet neben der Ammoniakstrippung eine Faulwasservorbehandlung in Form eines CO2-Strippers, welche eine 50%ige Reduktion des Laugenbedarfs erlaubt und eine deutliche Effizienzsteigerung des nachhaltigen Verfahrens erbringt. Die Idee der vorgängigen CO2-Strippung zur pH-Wert-Anhebung wurde von der Eawag entwickelt und ist grosstechnisch einzigartig.
Johnston, R., Derksen-Müller, S., Peter-Varbanets, M., Pronk, W., & Krohn, M. (2012). Building a better filter – combining research and design. Sandec News, 13, 20. , Institutional Repository

Engineers, designers and end users contributed to the development of a new generation household water treatment filters.
Kazner, C., Joss, A., Ternes, T., van Houtte, E., & Wintgens, T. (2012). Membrane based treatment trains for managed aquifer recharge. In C. Kazner, T. Wintgens, & P. Dillon (Eds.), Water reclamation technologies for safe managed aquifer recharge (pp. 259-282). London: IWA Publishing. , Institutional Repository

Activated carbon-nanofiltration as well as MBR/NF hybrid processes are promising alternatives to existing treatment trains. They are well suited for high-grade water reuse applications. The present study demonstrated the feasibility of all processes and identified advantages and disadvantages of the processes. The optimum process combination depends on local boundary conditions such as size of plant, raw water characteristics and plant location. In the light of growing water scarcity and increasing concerns about organic micropollutants activated carbon treatment in combination with nanofiltration could be applied in an increasing number of cases with appropriate boundary conditions.
Future applications should be embedded in integrated wastewater treatment concepts including concentrate treatment. Particularly combinations with membrane bioreactors are interesting options for innovative sustainable water recycling solutions.
Abegglen, C., Beier, S., Pinnekamp, J., Mauer, C., & Siegrist, H. (2011). Mikroverunreinigungen. Energieverbrauch und Kosten weitergehender Verfahren auf kommunalen ARA. GWA Gas, Wasser, Abwasser, 91(7), 479-486. , Institutional Repository

Micropollutants. Energy Consumption and Costs of Advanced. Technologies in WWTP By upgrading around 100 out of 700 wastewater treatment plants (WWTP) with an advanced treatment (e.g. ozonation or powdered activated carbon adsorption), the input of organic micropollutants into Swiss surface waters can be significantly reduced and the water quality is further improved. However, such processes increase both the energy demand and the costs of wastewater treatment. In general, the increase is around 5–25%, and it depends on the technology and local circumstances like the plant size, the wastewater composition and the existing infrastructure.
Etter, B., Tilley, E., & Udert, K. M. (2011). Urine as a resource in Nepal. Sandec News, 12, 16. , Institutional Repository

Depleting fertiliser supplies call for alternative nutrient sources. Promising low-cost technologies to recover nutrients from urine were therefore field-tested in Nepal.
Peter-Varbanets, M., Johnston, R., Meierhofer, R., & Pronk, W. (2011). GDM technology for household water disinfection. Sandec News, 12, 5. , Institutional Repository

The Gravity-driven Membrane (GDM) technology reveals a high implementation potential for efficient, robust, durable, low cost, and virtually maintenance-free household water filters. A project was recently launched in Kenya to establish filter efficiency in the field and develop a market-based approach for their sustainable use.
Abegglen, C., Böhler, M., Hollender, J., Zimmermann, S., Zwickenpflug, B., von Gunten, U., … Thonney, D. (2010). Mikroverunreinigungen in Kläranlagen. Technische Verfahren zur Elimination von organischen Spurenstoffen. GWA Gas, Wasser, Abwasser, 90(7), 587-594. , Institutional Repository

Micropollutants in Wastewater Treatment Plants. Technologies to Eliminate Organic Trace Contaminants. Today’s mechanical-biological treatment plants only inadequately remove organic micropollutants. Advanced technologies are necessary such as ozonation or adsorption on powdered active carbon (PAC) in order to increase removal capacity. These two techniques are being evaluated in various tests on the laboratory level, but also on a large scale. Both ozonation and PA C adsorption are suitable for reducing the emission of organic trace elements from settlement drainage systems into the various bodies of water. This article presents the current knowledge of both technologies for application in municipal wastewater treatment systems.
Abegglen, C., Escher, B., Hollender, J., Siegrist, H., von Gunten, U., Zimmermann, S., … Schärer, M. (2010). Ozonung von gereinigtem Abwasser zur Elimination von organischen Spurenstoffen. Großtechnischer Pilotversuch Regensdorf (Schweiz). KA: Korrespondenz Abwasser Abfall, 57(2), 155-160. doi:10.3242/kae2010.02.004, Institutional Repository

Within the framework of the “Micropoll Strategy” project of the Swiss Federal Environmental Agency, the suitability of ozonation as an additional treatment stage for the removal of organic trace elements was tested at the Regensdorf wastewater treatment plant. With ozone doses of 0.60 g O3/g DOC already, a large portion of the organic trace elements could no longer be detected in the plant run-off. Only for a few, very persistent compounds (like iodized radio-opaque substances or atrazine), the removal rates amounted to only about 50 percent, even with high ozone doses (1.16 g O3 /g DOC). Eco-toxicological methods were used to prove that a clear reduction in summary effects (like e.g. oestrogen effects or the effect of insecticides) took place. In two tests, negative effects were measured directly after ozonation, but they disappeared again after the final sand filter. Oxidation by-products (such as assimilable organic carbon or N-Nitrosodimethylamine [NDMA]) were also reduced through sand filtration. This underlines the importance of a biologically active stage downstream of the ozonation stage, for example a sand filtration stage. The pilot operation also showed that an ozonation stage at a municipal wastewater treatment plant is technically feasible and economically reasonable.
Götz, C. W., Abegglen, C., McArdell, C. S., Koller, M., Siegrist, H., Hollender, J., & Schärer, M. (2010). Mikroverunreinigungen. Beurteilung weitergehender Abwasserreinigungsverfahren anhand Indikatorsubstanzen. GWA Gas, Wasser, Abwasser, 90(4), 325-333. , Institutional Repository

Recently, advanced treatment steps for the elimination of organic micropollutants in municipal wastewater are investigated intensively in largescale experiments. One of the key issues is to assess the elimination performance of different advanced treatments routinely in practice. In this article, a concept for the assessment of the elimination of organic micropollutants in municipal wastewater treatment plants using five indicatorsubstances is presented. The selected indicatorsubstances represent larger groups of chemicals, occur in surface waters across Switzerland and are quantifiable with established analytical methods.
Klahre, J., Bitz, S., Traber, J., & Pronk, W. (2010). Ultrafiltration von Karstquellen. Flockung erweitert den Einsatzbereich. GWA Gas, Wasser, Abwasser, 90(1), 23-30. , Institutional Repository

At present in Switzerland drinking water is obtained from karstic spring water in more than 35 plants – often in only one processing stage. Most plants are located in the Valais, in the foothills of the Alps in central Switzerland, in the Jura or in the area around the Säntis mountain. They have an output of less than 1000 m3/day. Apart from pre-filtration at 200 μ they can be operated without any other pre-treatment, however some natural water contains such high levels of organic material after thunderstorms or when the snow melts that pre-treatment becomes necessary. Initial results from a research project show that by determining a fouling index, which is underpinned by LC-OCD analysis, useful information on the feasibility of ultra-filtration as well as the best type of pre-treatment with flocking agents or powdered coal can be obtained.
Morgenroth, E., Buergmann, H., & Udert, K. (2010). Functional diversity in wastewater treatment. Eawag News [engl. ed.], 69, 15-17. , Institutional Repository

Variations in influent loads pose major challenges for biological wastewater treatment. Could increased biodiversity allow for more stable operation, and does this mean that biodiversity should also be protected in wastewater treatment plants? Using molecular biological methods, we can now quantify biodiversity and specific groups of microorganisms in complex systems.
Morgenroth, E., Bürgmann, H., & Udert, K. (2010). Funktionelle Vielfalt in der Abwasserreinigung. Eawag News [dtsch. Ausg.], 69, 15-17. , Institutional Repository

Schwankende Zulauffrachten stellen die biologische Abwasserreinigung vor grosse Herausforderungen. Kann hier eine erhöhte Biodiversität helfen und ist Biodiversität also auch in der Kläranlage erstrebenswert? Molekularbiologische Methoden erlauben es uns heute, die Artenvielfalt und spezifische Organismengruppen in komplexen Systemen zu quantifizieren.
Pronk, W., & Peter-Varbanets, M. (2010). Schwerkraftgetriebene Ultrafiltration. Für die dezentrale Trinkwasseraufbereitung. GWA Gas, Wasser, Abwasser, 90(1), 19-22. , Institutional Repository

Membrane technology has enormous potential in water preparation and the treatment of waste water. However, conventionally constructed membrane plants are relatively expensive for decentralised applications. A cheaper solution for the preparation of drinking water is gravity ultra-filtration under low pressure conditions. This does not require any pumps or regulating systems, which leads to a reduction in costs and also makes the application independent of electricity or other energy resources. Tests were carried out in the laboratory and on a pilot scale with a series of different natural waters. In doing so it was discovered that the flow rate stabilised after a few days and remained stable for several months. This new technology means that the costs for water preparation using ultra-filtration are also acceptable for use in developing countries.
Schärer, M., & Abegglen, C. (2010). Schweizer Projekt „Strategie Micropoll“. Reduktion von Mikroverunreinigungen. Wasserwirtschaft Wassertechnik wwt, 3, 18-20. Retrieved from http:www.wwt-online.de, Institutional Repository
Abegglen, C., Joss, A., & Siegrist, H. (2009). Eliminating micropollutants: wastewater treatment methods. Eawag News [engl. ed.], 67, 25-27. , Institutional Repository

In many cases, micropollutants are only partly eliminated at wastewater treatment plants. The remaining fraction, together with any transformation products, enters receiving waters with the treated effluents. What options can modern process engineering offer to improve elimination performance?
Abegglen, C., Joss, A., & Siegrist, H. (2009). Eliminer des micropolluants: techniques d'épuration. Eawag News [éd. fr.], 67, 25-27. , Institutional Repository

Les micropolluants ne sont souvent que partiellement retenus dans les stations d’épuration. La partie restante et les éventuels sous-produits de dégradation sont alors rejetés dans le milieu naturel avec les effluents d’épuration. Quelles sont les options actuellement disponibles pour améliorer le rendement d’élimination de ces composés?
Abegglen, C., Joss, A., & Siegrist, H. (2009). Spurenstoffe eliminieren: Kläranlagentechnik. Eawag News [dtsch. Ausg.], 67, 25-27. , Institutional Repository

Vielfach werden Spurenstoffe in Kläranlagen nur teilweise zurückgehalten. Der restliche Teil und mögliche Abbauprodukte gelangen mit dem geklärten Abwasser in die Gewässer. Welche technischen Optionen stehen zur Verfügung, um die Eliminationsleistung zu verbessern? Ein Einblick in die moderne Verfahrenstechnik.
Abegglen, C., Rosenstiel, R., Ort, C., & Schärer, M. (2009). Weitergehende Verfahren zur Elimination von organischen Spurenstoffen bei kommunalen Abwasserreinigungsanlagen. KA: Korrespondenz Abwasser Abfall, 56(6), 584-592. doi:10.3242/kae2009.06.003, Institutional Repository

Der Eintrag von organischen Spurenstoffen aus der Siedlungsentwässerung ist aktuell eine besondere Herausforderung für den Gewässerschutz. Im Rahmen des Projekts "Strategie Micro-Poll" des Schweizer Bundesamts für Umwelt werden weitergehende Maßnahmen auf Kläranlagen zur Reduktion des Eintrags problematischer Stoffe diskutiert. Dabei stehen zurzeit die Ozonung und die Behandlung mit Pulveraktivkohle im Vordergrund. In einer Teilstudie des Projekts wurden für sechs ausgewählte Kläranlagen unterschiedlicher Größe die Kosten für Bau und Betrieb dieser zwei Verfahren berechnet sowie die Kosten für Kläranlagen anderer Größen interpoliert. Die Mehrkosten gegenüber der herkömmlichen Reinigung belaufen sich, je nach Anlagengröße, auf 5 bis 25 Prozent. Anschließend wurden die Gesamtkosten für die Schweiz für verschiedene Szenarien bestimmt. Die Gesamtkosten für den Ausbau der größten Anlagen sowie der Ausbau aller Anlagen, bei denen das Qualitätsziel für Diclofenac im Gewässer überschritten ist, würden für die Schweiz auf 115 bis 180 Millionen Schweizer Franken pro Jahr oder 15 bis 24 Schweizer Franken pro Einwohner jährlich geschätzt. Die Mehrkosten werden somit als vertretbar angesehen. Für eine konkrete Umsetzung müssen im Einzelfall jedoch sorgfältige Kosten-Nutzen-Betrachtungen vorgenommen werden.
Behra, R., Kägi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Effects of engineered nanoparticles. Eawag News [engl. ed.], 67, 22-24. , Institutional Repository

As nanoparticles are already widely used, it was only too likely that they would ultimately find their way into the environment. This has now been demonstrated for the first time by Eawag studies - which also show how engineered nanoparticles can exert toxic effects on aquatic organisms.
Behra, R., Kaegi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Les nanoparticules synthétiques et leurs effets. Eawag News [éd. fr.], 67, 22-24. , Institutional Repository

Les nanoparticules sont déjà employées dans un grand nombre de domaines. Il semble donc hautement probable qu’elles se retrouvent tôt ou tard dans l’environnement. Des études de l’Eawag ont démontré pour la première fois la réalité de ce phénomène et ­montrent d’autre part de quelle manière les nanoparticules synthétiques peuvent perturber les organismes aquatiques.
Behra, R., Kaegi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Synthetische Nanopartikel und ihre Wirkung. Eawag News [dtsch. Ausg.], 67, 22-24. , Institutional Repository

Nanopartikel werden heute bereits breit eingesetzt. Da ist es nur wahrscheinlich, dass sie früher oder später auch in der Umwelt landen. Studien der Eawag wiesen dies nun erstmals nach und zeigen darüber hinaus, auf welche Weise sich synthetische Nanopartikel negativ auf Gewässerorganismen auswirken können.
Goosse, P., Steiner, M., Udert, K. M., & Neuenschwander, W. (2009). NoMix Toilettensystem. Erste Monitoringergebnisse im Forum Chriesbach. GWA Gas, Wasser, Abwasser, 89(7), 567-574. , Institutional Repository

The NoMix toilet system of Eawag’s main building «Forum Chriesbach» has been in operation for three years. So far, NoMix toilets, waterless urinals and urine pipes do not show any clogging problems. Clogging was only observed in the siphons of some of the urinals. Due to the simple handling of exchanging the siphons, the problems could be solved easily. Toilets and urinals did not cause odour problems inside the building. However, outside the building (on the roof), odour problems occurred. The cause is ammonia gas emissions from the urine pipes. At the moment, the most important remaining problem for an efficient separation of urine and feces is the correct use of the NoMix toilets by non-acquainted users. New users have to be informed accordingly. A close collaboration with the maintenance service provider proved to be a critical factor for an optimal operation of the NoMix toilet system.
Hassellöv, M., & Kaegi, R. (2009). Analysis and characterization of manufactured nanoparticles in aquatic environments. In J. R. Lead & E. Smith (Eds.), Environmental and human health impacts of nanotechnology (pp. 211-266). doi:10.1002/9781444307504.ch6, Institutional Repository

This chapter aims to discuss the minimum set of key properties that describe nanoparticles (NPs) in aquatic environments, and to review suitable analysis and characterization methods. Special focus is on characterization of manufactured NPs and associated nanoscale processes (Gilbert and Banfield, 2005). Manufactured NPs have recently raised concerns because of their potential effects on human health and the environment (Colvin, 2003; Donaldson et al., 2004; Handy et al., 2008; Nel et al., 2006; Oberdorster et al., 2005). Therefore, the analytical demands related to both exposure and effect assessment are discussed. Atmospheric NPs and airborne exposure are not covered in this chapter, but within Chapters 5 and 8, and also reviewed elsewhere (Burleson et al., 2004; Maynard, 2000); Powers et al., 2007). One aim has been to bring together concepts and knowledge from analytical chemistry, (e.g. quantitative determination of chemical composition in nanoparticle ensembles, such as size fractions or on a single NP), the mature field of particle size analysis (mainly developed for micron particles) (Barth and Flippen, 1995), environmental colloid science (Wilkinson and Lead, 2007) and the young field of nanometrology (Graham, 2007).
Kaegi, R., Wenk, C., & Hug, S. (2009). Elimination de l'arsenic par le fer colloïdal. Eawag News [éd. fr.], 66, 13-15. , Institutional Repository

Face à une contamination de l’eau potable par l’arsenic, la filtration est un bon moyen de lutte. Les systèmes employés sont basés sur la capacité des colloïdes de fer à piéger l’arsenic. Mais selon la composition chimique de l’eau, le fonctionnement des filtres est plus ou moins efficace. L’Eawag a recherché les causes potentielles de perturbation et étudié les possibilités d’optimisation technique des filtres.
Kaegi, R. (2009). Les nanoparticules dans l'eau potable. Eawag News [éd. fr.], 66, 7-9. , Institutional Repository

De plus en plus de produits du quotidien renferment des nanoparticules synthétiques. Nos connaissances sur leur émission et leur comportement dans l’environnement sont cependant encore très limitées. En outre, on ignore aussi très largement quelles sont les quantités de nanoparticules naturellement présentes, notamment dans l’eau potable. Nous avons tenté de dresser un état des lieux.
Kaegi, R., & Sinnet, B. (2009). Nanoparticles in drinking water. Eawag News [engl. ed.], 66, 7-9. , Institutional Repository

Synthetic nanoparticles are increasingly being used in everyday products, but little is known about environmental releases of these materials. Our knowledge of how many natural nanoparticles occur in drinking water is also inadequate. An initial assessment is presented here.
Kägi, R., Wenk, C., & Hug, S. (2009). Arsenentfernung mittels Eisenkolloiden. Eawag News [dtsch. Ausg.], 66, 13-15. , Institutional Repository

Ist Trinkwasser mit Arsen belastet, können Filtersysteme Abhilfe schaffen. Darin bindet das Arsen an Eisenkolloide. Doch je nach Wasserzusammensetzung funktionieren die Filter nicht optimal. Die Eawag erforschte nun, woran das liegt und wie zukünftige Filter konstruiert sein müssen.
Kägi, R., Wenk, C., & Hug, S. (2009). Arsenic removal using iron colloids. Eawag News [engl. ed.], 66, 13-15. , Institutional Repository

Drinking water contaminated with arsenic can be treated using filters in which arsenic is adsorbed onto iron colloids. However, the performance of these systems may not be optimal, depending on the composition of the water. Eawag has now investigated the processes involved - and how the design of future filters could be optimized.
Kägi, R., & Sinnet, B. (2009). Nanopartikel im Trinkwasser. Eawag News [dtsch. Ausg.], 66, 7-9. , Institutional Repository

Immer mehr Produkte in unserem Alltag enthalten synthetische Nanopartikel. Noch aber ist wenig über ihren Eintrag in die Umwelt bekannt. Genauso wenig weiss man, wie viele natürliche Nanopartikel überhaupt im Trinkwasser vorkommen. Eine erste Bestandsaufnahme.
Tilley, E., Etter, B., Gantenbein, B., Khadka, R., & Udert, K. M. (2009). Struvite from urine in Nepal (STUN). Sandec News, 10, 4-5. , Institutional Repository

A new project in Nepal examines whether the production of fertiliser from urine can inspire residents to take up improved sanitation, while reducing their dependency on imported chemicals. By harvesting urine and converting it to “struvite”, the farmers of Siddhipur may better resist the coming years of fertiliser shortages.
Udert, K. M., & Siegrist, H. (2009). Anorganische Ausfällungen. In Trinkwasser- und Faulwasserleitungen. GWA Gas, Wasser, Abwasser, 89(11), 881-886. , Institutional Repository

Deposits and blockages from inorganic precipitation can adversely affect the operation of sewage treatment plants and domestic water supplies and result in substantial costs. Whilst the problem is generally well-known for hard drinking water, there is an increasing number of reports on precipitation in sludge water treatment in sewage plants, particularly plants with biological elimination of phosphates. This article discusses the chemical conditions for precipitation. Using the examples of drinking water and digester supernatant, it examines the most important chemical parameters and the key environmental influences – solubility of the solid phases, the composition of the water, pH value, release of carbon dioxide, biological decomposition processes, temperature and ionic strength. This article shows how the supersaturation of mineral solutions can be calculated.
Zurbrügg, C., Bufardi, A., Tilley, E., Maurer, M., & Truffer, B. (2009). Decision-making for sanitation systems. Sandec News, 10, 20-21. , Institutional Repository

This Eawag project addresses the various decision-making aspects in sanitation system and technology selection as a support tool for choosing the best available options to secure sustainable sanitation systems.
Burkhardt, M., Kägi, R., Sinnet, B., Zuleeg, S., Simmler, H., Vonbank, R., … Boller, M. (2008). Biozide - Suche nach Alternativen. Nanopartikel in Fassadenbeschichtungen. Coviss, 4, 14-17. , Institutional Repository

Gegen Algen und Pilze auf Fassaden werden in der Regel Biozide eingesetzt. Ob Nanosilber und photoaktives Nanotitandioxid unproblematische Alternativen oder Ergänzungen zu Bioziden darstellen, ist unklar. Die Eawag und Empa, zwei Forschungsinstitute des ETH-Bereichs, untersuchen erstmals die Auswaschung aus Fassadenanstrichen im Labor und unter Feldbedingungen. Damit werden wesentliche Grundlagen zur Dauerhaftigkeit und Risikobewertung erarbeitet.
Jermann, D., Pronk, W., & Boller, M. (2008). Membranfouling. Forschungsergebnisse zu den Mechanismen. GWA Gas, Wasser, Abwasser, 88(1), 37-44. , Institutional Repository

Membrane fouling (deposition of water substances on the membrane surface) is a crucial problem during ultrafiltration for drinking water production. Despite many international research efforts the phenomenon of fouling is only partly understood, mainly because of the complexity and variety of influencing factors. These reasons are described in the following article which shows, how mechanistic studies can provide new insight into membrane fouling. Fouling models gained from lab experiments are presented and compared to first results from a pilot plant. The main outcome of the presented study: Interactions between different foulants can impact fouling significantly.
Pronk, W., & Kaiser, H. P. (2008). Trinkwasseraufbereitung der Zukunft. Eawag News [dtsch. Ausg.], 65, 28-31. , Institutional Repository

Ein Grossteil der Wasserversorgungsanlagen, die Mitte des 20. Jahrhunderts gebaut wurden, muss erneuert werden. Im Rahmen des Eawag-Querprojekts Wave 21 «Wasserversorgung im 21. Jahrhundert» wurden zwei neue Verfahrenskombinationen mit Membranfiltration getestet.
Burkhardt, M., Kupper, T., Eugster, J., Rossi, L., & Boller, M. (2007). Biozide und Additive in Gebäudehüllen: ein Risiko für die Gewässer?. Eawag Jahresbericht, 2006, 49. , Institutional Repository

Mit dem Niederschlag können problematische Stoffe aus Fassaden- und Dachmaterialien ausgewaschen werden und in die Gewässer gelangen. Im Rahmen des Projekts URBIC werden die Freisetzung von Bioziden und Additiven sowie deren Transportverhalten in der Siedlungsentwässerung erstmals systematisch untersucht.
Burkhardt, M., Kägi, R., Simmler, H., Ulrich, A., & Boller, M. (2007). Nanopartikel auf Fassaden erforschen. Thema Umwelt, 2, 12-13. , Institutional Repository

Nanosilber und Nanotitandioxid haben das Potenzial, problematische Biozide zur Bekämpfung von Algen und Pilzen auf Fassaden zu ergänzen oder zu ersetzen. Allerdings ist bis heute völlig unklar, ob und in welchem Umfang diese Nanopartikel die Umwelt und die menschliche Gesundheit beeinträchtigen können. Um die Chancen und Risiken dieser Technologie abwägen und mit den heute üblichen Bioziden vergleichen zu können, haben Eawag und Empa, zwei Forschungsinstitute des ETH-Bereichs, ein Forschungsprojekt lanciert.
Herlyn, A., & Maurer, M. (2007). Was ARA und Kanalisation kosten. Umwelt-Perspektiven, 2007(1), 2-3. , Institutional Repository

Die Abwasserentsorgung gehört auf kommunaler Ebene zu den anlagenintensivsten Dienstleistungen mit hohen langfristig gebundenen Kapitalbeträgen. Für eine strategische Investitionsplanung in der Schweiz fehlte bis anhin eine umfassende Datengrundlage, die jetzt vorliegt.
Larsen, T. A., Bader, H. P., Mosler, H. J., Gujer, W., Medilanski, E., Scheidegger, R., … Schertenleib, R. (2007). Applying traditional Chinese knowledge. Eawag News [engl. ed.], 63, 26-28. , Institutional Repository

Kunming, Zurich's sister city in China, is determined to tackle its wastewater problem. In the development of measures based on nutrient recycling - a long-established principle in China - it is receiving support from Eawag in technical as well as social issues.
Maurer, M. (2007). Urine treatment - absolute flexibility. Eawag News [engl. ed.], 63, 14-16. , Institutional Repository

What happens to urine after it has been collected? The particular characteristics of this liquid permit a wide range of treatment methods. These can be used to modify the unusual resource as required - e. g. to remove specific pollutants or to produce a fertilizer. The suitability of a number of processes has been assessed by Eawag.
Moser, R., McArdell, C. S., & Weissbrodt, D. (2007). Mikroverunreinigungen. Vorbehandlung von Spitalabwasser. GWA Gas, Wasser, Abwasser, 87(11), 869-875. , Institutional Repository

ln the framework of elimination of micropollutants, resiclua of pharmaceuticals in waste water require special attention. ln Switzerland, 18 % of all sold drugs are given out in hospitals. lt is selfeviclent that hospitals are regarded as point source of residua of pharmaceuticals in waste water. However, there are only a few drugs significantly more often used in hospitals: contrast media and cytostatics. ln order to eliminate the residua, there are two strategies: upgrading the communal waste water treatment plants and, as a special case, the separate treatment of hospital waste water.
Ort, C., Siegrist, H., Hosbach, H., Studer, C., Morf, L., & Scheringer, M. (2007). Mikroverunreinigungen. Nationales Stoffflussmodell. GWA Gas, Wasser, Abwasser, 87(11), 853-859. , Institutional Repository

Sampling and analytical chemistry are costly, and therefore, measurements can only provide limited information in space and time on the occurrence of micropollutants in surface waters. What would the picture look like, if one measured in rivers downstream of all wastewater treatment plants? To make a prediction of pollutant loads from urban drainage a national mass flux model has been developed. For more than 100 wastewater treatment plants, the dilution factor of treated wastewater during dry weather conditions is smaller than 10. For specific substances, this can lead to the exceedance of critical concentrations in rivers. Furthermore, the model allows the calculation of different scenarios. Whole river catchments are taken inter consideration.
Pronk, W. (2007). Urinaufbereitung: vom Labor zur Praxis. Eawag News [dtsch. Ausg.], 63, 20-22. , Institutional Repository

Die Kombination von Elektrodialyse und Ozonierung ist eine mögliche Verfahrenstechnik, um wertvolle Nährstoffe aus dem Urin aufzukonzentrieren. Gleichzeitig können damit Risikostoffe entfernt und einwandfreier Dünger produziert werden. Das an der Eawag entwickelte Verfahren wird derzeit im Kanton Basel-Landschaft getestet.
Pronk, W. (2007). Urine treatment: from laboratory to practice. Eawag News [engl. ed.], 63, 20-22. , Institutional Repository

The combination of electrodialysis and ozonation is a possible method for recovering valuable nutrients from urine in a concentrated form. At the same time, hazardous substances can be removed, yielding a perfectly acceptable fertilizer. The processes developed at Eawag are currently being tested at a pilot plant in Canton Basel-Landschaft.
Salzgeber, D., Joss, A., & Siegrist, H. (2007). Autotrophe Schlammwasserentstickung (Nitritation/Anammox). Im SBR-Verfahren (Sequencing batch reactor). GWA Gas, Wasser, Abwasser, 87(3), 205-209. , Institutional Repository

For six months, Eawag has in operated in a stable fashion a 400 litre SBR for autotrophic denitrification of ammonium rich sludge. In so doing, a part of the ammonium is oxidised with oxygen into a nitrite (partial nitrification) and the remaining ammonium is oxidised using the created nitrites into molecular nitrogen. With a nitrogen elimination rate of up to 680 gN m-3 d-1 and hydraulic delay times of somewhat under a day with a clear N-elimination rate of 90 %, a good level of elimination is achieved. The processes can be controlled via conductivity, pH or the nitrite signal.
Siegrist, H., & Joss, A. (2007). Mikroverunreinigungen. Technische Verfahren zur Elimination. GWA Gas, Wasser, Abwasser, 87(11), 861-867. , Institutional Repository

Due to improved chem ical analysis, pharmaceuticals, pesticides and endocrine disrupters are increasingly detected in waters. The waste water treatment plant removes parts of the substances by sorption and biological decomposition. The other part reaches river and lakes together with the treated waste water. This article presents possible measures to eliminate the remaining substances. On the one hand, via sustainable measures on the source, and on the other hand, with technical measures like ozone or activated carbon dosages.
Udert, K. (2007). NoMix begins in the bathroom. Eawag News [engl. ed.], 63, 11-13. , Institutional Repository

The basic idea of the NoMix toilet is simple: urine is drained - separately from other wastewater - into a collection tank. However, urine pipes can easily be blocked by mineral precipitates, and nutrient concentrations in the urine collected may be lower than expected. The results of our laboratory experiments and computer simulations should facilitate the development of improved appliances in collaboration with the sanitary technology sector.
Fletcher, H., Kekre, K., Guihe, T., Seah, H., Guglielmi, G., Andreottola, G., … Siegrist, H. (2006). Design. In S. Judd & C. Judd (Eds.), The MBR Book. Principles and applications of membrane bioreactors in water and wastewater treatment (pp. 123-162). doi:10.1016/B978-185617481-7/50005-2, Institutional Repository
Gianella, S., & Maurer, M. (2006). Infrastrukturmanagement. Internationale Standortbestimmung für den Wasser- und Abwassersektor. GWA Gas, Wasser, Abwasser, 86(9), 733-742. , Institutional Repository

In the last years, many Swiss municipalities developed extensive information systems for the collection and use of manifold infrastructure data. Facing the high investments for the realization of these systems and the data value for an optimal infrastructure management, the municipalities must define a suitable data maintenance strategy. The experiences of different municipalities are used in this article to illustrate a procedure for the development of data maintenance strategies. The problems to solve are described and the goals and success factors of a data maintenance strategy are defined.
Gianella, S., & Gujer, W. (2006). Nachführungsstrategie für Infrastrukturdaten. Ziele und Erfolgsfaktoren. GWA Gas, Wasser, Abwasser, 86(11), 887-893. , Institutional Repository

In the last years, many Swiss municipalities developed extensive information systems for the collection and use of manifold infrastructure data. Facing the high investments for the realization of these systems and the data value for an optimal infrastructure management, the municipalities must define a suitable data maintenance strategy. The experiences of different municipalities are used in this article to illustrate a procedure for the development of data maintenance strategies. The problems to solve are described and the goals and success factors of a data maintenance strategy are defined.
Schärer, M., Müller, S., Carrard, M., Ort, C., Siegrist, H., Escher, B., … McArdell-Bürgisser, C. (2006). Projekt "Strategie MicroPoll". Strategie zur Reduktion von Mikroverunreinigungen. GWA Gas, Wasser, Abwasser, 86(7), 551-555. , Institutional Repository

In urbanized areas large quantities of synthetic organic compounds are being used which can inevitably enter both municipai waste water end receiving water bodies. Many of these substances can be detected in aqueous systems at very low concentrations (nano- to microgram per litre). These so-called rnicropollutants are seen as a further challenge tor the field of water protection. The new project «Strategy MicroPoll» of the Swiss Federal Office tor the Environment (FOEN) is gathering evidence to determine a basis for policy decision-making with regard to micropollutants in municipal waste water.
Störmer, E., & Herlyn, A. (2006). Nachhaltige Strategieplanung für die kommunale Abwasserentsorgung. Zukunftssichere Strategien. Umwelt-Perspektiven, 2006(5), 11-15. , Institutional Repository

Die Mehrzahl der Schweizer Abwasserentsorgungsanlagen wurde mit Bundeszuschuss in den 1960er-und 70er-Jahren gebaut. Heute sind viele Anlagen in die Jahre gekommen. Für die Entscheidung über eine Erneuerung der Anlage müssen die möglichen Entwicklungen von Abwassermenge und Reinigungsansprüchen sowie die Wirtschaftlichkeit der Lösung über die gesamte Laufzeit der Investition berücksichtigt werden. In einem vom Schweizerischen Nationalfonds geförderten Forschungsvorhaben entwickelt die Eawag, das Wasserforschungsinstitut des ETH-Bereichs, eine Planungsmethode, mit der mögliche zukünftige Herausforderungen für die kommunale Siedlungswasserwirtschah abgeschätzt werden und verschiedene Handlungsoptionen bewertet und zu einem nachhaltigen Strategieplan zusammengefügt werden.

Publications arranged by authors

Eberhard Morgenroth

Hu, Y., Morgenroth, E., & Jacquin, C. (2025). Online monitoring of greywater reuse system using excitation-emission matrix (EEM) and K-PARAFACs. Water Research, 268, 122604 (13 pp.). doi:10.1016/j.watres.2024.122604, Institutional Repository

A currently increasing interest in water reuse is met with the concern about water quality. Excitation-emission matrix (EEM) measurements, which are widely implemented in laboratory analysis, emerge as a promising tool for characterizing both microbial and chemical water qualities in the online monitoring of water reuse systems. However, the robustness of EEM measurements has been rarely validated in actual online monitoring campaigns where predictions are made for new samples independent of those used to establish EEM analysis models, including the popular parallel factor analysis (PARAFAC). In this study, two strategies of conducting PARAFAC were examined for the online monitoring of a greywater reuse system using two EEM datasets from two monitoring periods for model establishment and model testing respectively. With the first strategy that is commonly used in laboratory analyses, an entire EEM datasets from one period was used to establish one PARAFAC model, and the maximum fluorescence intensity (Fmax) of a PARAFAC component was used to predict total cell count (TCC) in another period. However, under the disturbance of dissolved organic matter (DOM) fluorescence in the background, Fmax gave unreliable predictions in model testing. To address this problem, a second and novel strategy was proposed using an EEM clustering and PARAFAC component shift mining technique. This unsupervised algorithm, named K-PARAFACs, automatically groups EEMs into K clusters and on each cluster establishes a cluster-specific PARAFAC model with distinct component shapes. With this method, multiple PARAFAC models were established on one EEM dataset, with each model representing samples with certain TCC ranges and DOM compositions. In model testing, these cluster-specific PARAFAC models served as EEM classifiers. A new sample was not characterized by Fmax but by the cluster-specific model that best fitted the EEM signal of the sample with the least numerical error. The proposed strategy demonstrates its robustness by successfully predicting the TCC trend in test datasets. Our findings suggest that K-PARAFACs is a promising tool that enables robust qualitative monitoring of water reuse systems with background DOM variability.
Binz, C., Sedlak, D., O’Callaghan, P., Truffer, B., Nesi, M., Morgenroth, E., … Wellauer, S. (2024). Mainstreaming decentralized urban water management solutions for sustainable cities. doi:10.55408/eawag:33039, Institutional Repository

Climate change, rapid urbanization and other grand challenges increasingly force cities to rethink their urban (water) infrastructure. In particular, decentralized urban water management solutions, which can recover valuable resources close to the source are increasingly applied to remediate water scarcity, sanitation or environmental pollution challenges. Yet, although interesting demonstration projects with decentralized solutions (from here on labeled ‘decentralized UWM solutions’) are underway in several world regions, actors developing and implementing this transformative innovation are not effectively coordinating their efforts and sharing the latest knowledge. While effective technologies, business models, or regulative frameworks increasingly exist that could inform, inspire and improve similar activities elsewhere, details of local successes and failures are still (too) rarely shared or transferred across space. Drawing from experience on the mainstreaming of other transformative infrastructure solutions (like renewable energies, electric mobility or circular waste management), we posit that the global diffusion of decentralized UWM solutions has been significantly slowed down by this lack of interaction among key stakeholders, and the resulting lack of an effective innovation ecosystem.
Gruber, W., Niederdorfer, R., Ganesanandamoorthy, P., Bürgmann, H., Morgenroth, E., & Joss, A. (2024). Nitrit-Akkumulation auf Nitrifizierenden Belebtschlammanlagen. Wie kann der NO2– - Richtwert eingehalten werden?. Aqua & Gas, 104(1), 18-24. , Institutional Repository

Nitrit ist eine ökotoxikologisch problematische Substanz und führt auf Kläranlagen zur Bildung von klimaschädlichem Lachgas. Auf nitrifizierenden Belebtschlammanlagen kann Nitrit saisonal akkumulieren und erhöhte Ablaufwerte treten auf. Hier diskutieren wir die Häufigkeit von Überschreitungen des Nitrit-Richtwerts auf Schweizer ARA und schlagen Gegenmassnahmen vor.
Knabl, M., Rist, B., & Morgenroth, E. (2024). Réutilisation de l’eau en Suisse. Besoins, opportunités, risques et recommandations dérivées à l’attention des responsables. doi:10.55408/eawag:33722, Institutional Repository

La réutilisation planifiée des eaux usées épurées peut soulager les ressources en eau conventionnelles et réduire la consommation d'eau. Elle constitue une option d'action possible dans la gestion intégrée des ressources en eau, si les avantages dans le contexte local l'emportent sur les dépenses nécessaires (traitement supplémentaire, infrastructure, coûts, énergie). Le présent projet a cherché à savoir si la réutilisation de l'eau pouvait être une option pertinente pour la gestion des ressources en eau en Suisse. Pour ce faire, les données existantes sur la disponibilité et la consommation d'eau ont été analysées et une enquête sur le sujet a été menée auprès des services cantonaux de l'environnement. En raison du changement climatique, les périodes de fortes chaleurs sont de plus en plus fréquentes en Suisse, notamment en été. Les épisodes de sécheresse qui en découlent entraînent une augmentation des besoins en eau pour différentes applications (irrigation pour l'agriculture et dans les villes, eau de refroidissement, etc.). Au niveau local, les représentants de 19 des 26 cantons ont identifié un besoin de réutilisation de l'eau pour diverses applications, en particulier pour l'irrigation. De plus, on s'attend à une augmentation de ces besoins avec le changement climatique en cours. En outre, la réutilisation de l'eau présente des synergies avec d'autres mesures de gestion des ressources en eau, par exemple le stockage de l'eau pour les périodes où les besoins sont plus importants. Bien entendu, la réutilisation de l'eau doit être soumise à des exigences claires en termes de qualité et de quantité utilisable et des directives techniques doivent être établies, afin de ne pas mettre en danger l'homme et l'environnement. De plus, pour que les projets de réutilisation de l'eau puissent être mis en oeuvre avec succès à long terme, l'acceptation sociale doit être garantie. Actuellement, la réutilisation de l'eau n'est pas explicitement réglementée dans le droit suisse ; seule l'irrigation est implicitement interdite, alors que toutes les autres applications sont autorisées, mais sans directives concernant la mise en oeuvre ou la qualité. En outre, la Suisse manque d'expérience, de connaissances et de compétences pour la mise en place de la réutilisation de l’eau. Il est donc recommandé d’acquérir de l’expérience par le biais de projets pilotes et d’évaluer les informations spécifiques au projet (coûts, infrastructure nécessaire, etc.). En parallèle, un processus coordonné d'adaptation de la législation est nécessaire pour encadrer une mise en oeuvre sûre de la pratique en Suisse. Cela permettra de garantir que la réutilisation de l'eau soit une mesure fiable et contrôlée pour la gestion future des ressources en eau.

Die geplante Wiederverwendung von gereinigtem Abwasser kann konventionelle Wasserressourcen entlasten und den Wasserverbrauch senken. Sie ist eine mögliche Handlungsoption im integralen Wasserressourcenmanagement, wenn der Nutzen im lokalen Kontext den notwendigen Aufwand (zusätzliche Aufbereitung, Infrastruktur, Kosten, Energie) überwiegt. Im vorliegenden Projekt wurde untersucht, ob die Wasserwiederverwendung eine relevante Option für das Wasserressourcenmanagement in der Schweiz sein könnte. Dazu wurden bestehende Daten zur Wasserverfügbarkeit und zum -Verbrauch analysiert und eine Umfrage zum Thema bei den kantonalen Umweltfachstellen durchgeführt. Aufgrund des Klimawandels kommt es in der Schweiz bereits heute häufiger zu Trockenheitsperioden, insbesondere im Sommer. Die damit verbundenen Hitzeereignisse führen zu einem Anstieg des Wasserbedarfs für verschiedene Anwendungen (Bewässerung in der Landwirtschaft und in den Städten, Kühlwasser etc.). Auf lokaler Ebene haben Vertretende von 19 der 26 Kantone einen Bedarf für die Wasserwiederverwendung für verschiedene Anwendungen, besonders für die Bewässerung, festgestellt. Zudem wird erwartet, dass dieser Bedarf mit dem fortschreitenden Klimawandel ansteigen wird. Ausserdem weist die Wasserwiederverwendung Synergien mit anderen Massnahmen im Wasserressourcenmanagement auf, z.B. mit der Speicherung von Wasser für Zeiten mit erhöhtem Bedarf. Für die Wiederverwendung von Wasser müssen klare Vorgaben bezüglich Qualität, nutzbarer Menge und technischer Rahmenbedingungen definiert werden, um Mensch und Umwelt nicht zu gefährden. Um Wasserwiederverwendungsprojekte langfristig erfolgreich umzusetzen zu können, muss zudem die soziale Akzeptanz gewährleistet sein. Derzeit ist die Wasserwiederverwendung im Schweizer Recht nicht explizit geregelt; im Prinzip ist nur die Bewässerung implizit verboten, während alle anderen Anwendungen grundsätzlich erlaubt sind, jedoch ohne Vorgaben zur Umsetzung oder Qualität. Zudem fehlen in der Schweiz Erfahrungen, Wissen und Kompetenzen für ihre Umsetzung. Daher wird empfohlen, in praktischen Pilotprojekten Erfahrungen zu sammeln und projektspezifische Informationen zu ermitteln (Kosten, benötigte Infrastruktur etc.). Parallel dazu sollte ein koordinierter Gesetzesanpassungsprozess stattfinden, der einen sicheren Umsetzungsrahmen für die Praxis in der Schweiz schafft. Damit wird sichergestellt, dass die Wasserwiederverwendung als sichere und kontrollierte Massnahme im zukünftigen Wasserressourcenmanagement zur Verfügung steht.

The planned reuse of treated wastewater can relieve the pressure on conventional water resources and reduce water consumption. It is a possible option for action in integrated water resource management if the benefits in the local context outweigh the necessary effort (additional treatment, infrastructure, costs, energy). This project analysed whether water reuse could be a relevant option for water resource management in Switzerland. To this end, existing data on water availability and consumption were analysed and a survey on the topic was conducted among the cantonal environmental agencies. Due to climate change, Switzerland is already experiencing more frequent periods of drought, particularly in summer. The associated heat events lead to an increase in water demand for various applications (irrigation in agriculture and cities, cooling water, etc.). At local level, representatives from 19 of the 26 cantons have identified a need for water reuse for various applications, particularly irrigation. This demand is also expected to increase as climate change progresses. In addition, water reuse has synergies with other water resource management measures, such as storing water for times of increased demand. Clear specifications regarding quality, usable quantity and technical framework conditions must be defined for the reuse of water so as not to jeopardise people and the environment. In order to successfully implement water reuse projects on the long term, social acceptance must also be guaranteed. Currently, water reuse is not explicitly regulated in Swiss law; in principle, only irrigation is implicitly prohibited, while all other applications are permitted in principle, but without specifications regarding implementation or quality. In addition, there is a lack of experience, knowledge and expertise for their implementation in Switzerland. It is therefore recommended to gather experience in practical pilot projects and to determine project-specific information (costs, required infrastructure, etc.). At the same time, a coordinated legislative amendment process should take place to create a secure implementation framework for water reuse in Switzerland. This will ensure that water reuse is available as a safe and controlled measure in future water resource management.
Knabl, M., Rist, B., & Morgenroth, E. (2024). Wasserwiederverwendung in der Schweiz. Bedarf, Chancen, Risiken und abgeleitete Handlungsempfehlungen für Verantwortliche. doi:10.55408/eawag:32884, Institutional Repository

Die geplante Wiederverwendung von gereinigtem Abwasser kann konventionelle Wasserressourcen entlasten und den Wasserverbrauch senken. Sie ist eine mögliche Handlungsoption im integralen Wasserressourcenmanagement, wenn der Nutzen im lokalen Kontext den notwendigen Aufwand (zusätzliche Aufbereitung, Infrastruktur, Kosten, Energie) überwiegt. Im vorliegenden Projekt wurde untersucht, ob die Wasserwiederverwendung eine relevante Option für das Wasserressourcenmanagement in der Schweiz sein könnte. Dazu wurden bestehende Daten zur Wasserverfügbarkeit und zum -Verbrauch analysiert und eine Umfrage zum Thema bei den kantonalen Umweltfachstellen durchgeführt. Aufgrund des Klimawandels kommt es in der Schweiz bereits heute häufiger zu Trockenheitsperioden, insbesondere im Sommer. Die damit verbundenen Hitzeereignisse führen zu einem Anstieg des Wasserbedarfs für verschiedene Anwendungen (Bewässerung in der Landwirtschaft und in den Städten, Kühlwasser etc.). Auf lokaler Ebene haben Vertretende von 19 der 26 Kantone einen Bedarf für die Wasserwiederverwendung für verschiedene Anwendungen, besonders für die Bewässerung, festgestellt. Zudem wird erwartet, dass dieser Bedarf mit dem fortschreitenden Klimawandel ansteigen wird. Ausserdem weist die Wasserwiederverwendung Synergien mit anderen Massnahmen im Wasserressourcenmanagement auf, z.B. mit der Speicherung von Wasser für Zeiten mit erhöhtem Bedarf. Für die Wiederverwendung von Wasser müssen klare Vorgaben bezüglich Qualität, nutzbarer Menge und technischer Rahmenbedingungen definiert werden, um Mensch und Umwelt nicht zu gefährden. Um Wasserwiederverwendungsprojekte langfristig erfolgreich umzusetzen zu können, muss zudem die soziale Akzeptanz gewährleistet sein. Derzeit ist die Wasserwiederverwendung im Schweizer Recht nicht explizit geregelt; im Prinzip ist nur die Bewässerung implizit verboten, während alle anderen Anwendungen grundsätzlich erlaubt sind, jedoch ohne Vorgaben zur Umsetzung oder Qualität. Zudem fehlen in der Schweiz Erfahrungen, Wissen und Kompetenzen für ihre Umsetzung. Daher wird empfohlen, in praktischen Pilotprojekten Erfahrungen zu sammeln und projektspezifische Informationen zu ermitteln (Kosten, benötigte Infrastruktur etc.). Parallel dazu sollte ein koordinierter Gesetzesanpassungsprozess stattfinden, der einen sicheren Umsetzungsrahmen für die Praxis in der Schweiz schafft. Damit wird sichergestellt, dass die Wasserwiederverwendung als sichere und kontrollierte Massnahme im zukünftigen Wasserressourcenmanagement zur Verfügung steht.
 
La réutilisation planifiée des eaux usées épurées peut soulager les ressources en eau conventionnelles et réduire la consommation d'eau. Elle constitue une option d'action possible dans la gestion intégrée des ressources en eau, si les avantages dans le contexte local l'emportent sur les dépenses nécessaires (traitement supplémentaire, infrastructure, coûts, énergie). Le présent projet a cherché à savoir si la réutilisation de l'eau pouvait être une option pertinente pour la gestion des ressources en eau en Suisse. Pour ce faire, les données existantes sur la disponibilité et la consommation d'eau ont été analysées et une enquête sur le sujet a été menée auprès des services cantonaux de l'environnement. En raison du changement climatique, les périodes de fortes chaleurs sont de plus en plus fréquentes en Suisse, notamment en été. Les épisodes de sécheresse qui en découlent entraînent une augmentation des besoins en eau pour différentes applications (irrigation pour l'agriculture et dans les villes, eau de refroidissement, etc.). Au niveau local, les représentants de 19 des 26 cantons ont identifié un besoin de réutilisation de l'eau pour diverses applications, en particulier pour l'irrigation. De plus, on s'attend à une augmentation de ces besoins avec le changement climatique en cours. En outre, la réutilisation de l'eau présente des synergies avec d'autres mesures de gestion des ressources en eau, par exemple le stockage de l'eau pour les périodes où les besoins sont plus importants. Bien entendu, la réutilisation de l'eau doit être soumise à des exigences claires en termes de qualité et de quantité utilisable et des directives techniques doivent être établies, afin de ne pas mettre en danger l'homme et l'environnement. De plus, pour que les projets de réutilisation de l'eau puissent être mis en oeuvre avec succès à long terme, l'acceptation sociale doit être garantie. Actuellement, la réutilisation de l'eau n'est pas explicitement réglementée dans le droit suisse ; seule l'irrigation est implicitement interdite, alors que toutes les autres applications sont autorisées, mais sans directives concernant la mise en oeuvre ou la qualité. En outre, la Suisse manque d'expérience, de connaissances et de compétences pour la mise en place de la réutilisation de l’eau. Il est donc recommandé d’acquérir de l’expérience par le biais de projets pilotes et d’évaluer les informations spécifiques au projet (coûts, infrastructure nécessaire, etc.). En parallèle, un processus coordonné d'adaptation de la législation est nécessaire pour encadrer une mise en oeuvre sûre de la pratique en Suisse. Cela permettra de garantir que la réutilisation de l'eau soit une mesure fiable et contrôlée pour la gestion future des ressources en eau.
 
The planned reuse of treated wastewater can relieve the pressure on conventional water resources and reduce water consumption. It is a possible option for action in integrated water resource management if the benefits in the local context outweigh the necessary effort (additional treatment, infrastructure, costs, energy). This project analysed whether water reuse could be a relevant option for water resource management in Switzerland. To this end, existing data on water availability and consumption were analysed and a survey on the topic was conducted among the cantonal environmental agencies. Due to climate change, Switzerland is already experiencing more frequent periods of drought, particularly in summer. The associated heat events lead to an increase in water demand for various applications (irrigation in agriculture and cities, cooling water, etc.). At local level, representatives from 19 of the 26 cantons have identified a need for water reuse for various applications, particularly irrigation. This demand is also expected to increase as climate change progresses. In addition, water reuse has synergies with other water resource management measures, such as storing water for times of increased demand. Clear specifications regarding quality, usable quantity and technical framework conditions must be defined for the reuse of water so as not to jeopardise people and the environment. In order to successfully implement water reuse projects on the long term, social acceptance must also be guaranteed. Currently, water reuse is not explicitly regulated in Swiss law; in principle, only irrigation is implicitly prohibited, while all other applications are permitted in principle, but without specifications regarding implementation or quality. In addition, there is a lack of experience, knowledge and expertise for their implementation in Switzerland. It is therefore recommended to gather experience in practical pilot projects and to determine project-specific information (costs, required infrastructure, etc.). At the same time, a coordinated legislative amendment process should take place to create a secure implementation framework for water reuse in Switzerland. This will ensure that water reuse is available as a safe and controlled measure in future water resource management.
Reynaert, E., Nagappa, D., Sigrist, J. A., & Morgenroth, E. (2024). Ensuring microbial water quality for on-site water reuse: importance of online sensors for reliable operation. Water Research X, 22, 100215 (8 pp.). doi:10.1016/j.wroa.2024.100215, Institutional Repository

A growing number of cities and regions are promoting or mandating on-site treatment and reuse of wastewater, which has resulted in the implementation of several thousand on-site water reuse systems on a global scale. However, there is only limited information on the (microbial) water quality from implemented systems. The focus of this study was on two best-in-class on-site water reuse systems in Bengaluru, India, which typically met the local water quality requirements during monthly compliance testing. This study aimed to (i) assess the microbial quality of the reclaimed water at a high temporal resolution (daily or every 15 min), and (ii) explore whether measurements from commercially available sensors can be used to improve the operation of such systems. The monitoring campaign revealed high variations in microbial water quality, even in these best-in-class systems, rendering the water inadequate for the intended reuse applications (toilet flushing and landscape irrigation). These variations were attributed to two key factors: (1) the low frequency of chlorination, and (2) fluctuations of the chlorine demand of the water, in particular of ammonium concentrations. Such fluctuations are likely inherent to on-site systems, which rely on a low level of process control. The monitoring campaign showed that the microbial water quality was most closely related to oxidation–reduction potential (ORP) and free chlorine sensors. Due to its relatively low cost and low need for maintenance, the ORP emerges as a compelling candidate for automating the chlorination to effectively manage variations in chlorine demand and ensure safe water reuse. Overall, this study underscores the necessity of integrating treatment trains, operation, and monitoring for safe on-site water reuse.
Reynaert, E., Sylvestre, É., Morgenroth, E., & Julian, T. R. (2024). Greywater recycling for diverse collection scales and appliances: enteric pathogen log-removal targets and treatment trains. Water Research, 264, 122216 (13 pp.). doi:10.1016/j.watres.2024.122216, Institutional Repository

In light of increasingly diverse greywater reuse applications, this study proposes risk-based log-removal targets (LRTs) to aid the selection of treatment trains for greywater recycling at different collection scales, including appliance-scale reuse of individual greywater streams. An epidemiology-based model was used to simulate the concentrations of prevalent and treatment-resistant reference pathogens (protozoa: Giardia and Cryptosporidium spp., bacteria: Salmonella and Campylobacter spp., viruses: rotavirus, norovirus, adenovirus, and Coxsackievirus B5) in the greywater streams for collection scales of 5-, 100-, and a 1000-people. Using quantitative microbial risk assessment (QMRA), we calculated LRTs to meet a health benchmark of 10–4 infections per person per year over 10′000 Monte Carlo iterations. LRTs were highest for norovirus at the 5-people scale and for adenovirus at the 100- and 1000-people scales. Example treatment trains were designed to meet the 95 % quantiles of LRTs. Treatment trains consisted of an aerated membrane bioreactor, chlorination, and, if required, UV disinfection. In most cases, rotavirus, norovirus, adenovirus and Cryptosporidium spp. determined the overall treatment train requirements. Norovirus was most often critical to dimension the chlorination (concentration × time values) and adenovirus determined the required UV dose. Smaller collection scales did not generally allow for simpler treatment trains due to the high LRTs associated with viruses, with the exception of recirculating washing machines and handwashing stations. Similarly, treating greywater sources individually resulted in lower LRTs, but the lower required LRTs nevertheless did not generally allow for simpler treatment trains. For instance, LRTs for a recirculating washing machine were around 3-log units lower compared to LRTs for indoor reuse of combined greywater (1000-people scale), but both scenarios necessitated treatment with a membrane bioreactor, chlorination and UV disinfection. However, simpler treatment trains may be feasible for small-scale and application-scale reuse if: (i) less conservative health benchmarks are used for household-based systems, considering the reduced relative importance of treated greywater in pathogen transmission in households, and (ii) higher log-removal values (LRVs) can be validated for unit processes, enabling simpler treatment trains for a larger number of appliance-scale reuse systems.
Sylvestre, É., Jahne, M. A., Reynaert, E., Morgenroth, E., & Julian, T. R. (2024). A critical evaluation of parametric models for predicting faecal indicator bacteria concentrations in greywater. Microbial Risk Analysis, 26, 100297 (8 pp.). doi:10.1016/j.mran.2024.100297, Institutional Repository

Greywater reuse is a strategy to address water scarcity, necessitating the selection of treatment processes that balance cost-efficiency and human health risks. A key aspect in evaluating these risks is understanding pathogen contamination levels in greywater, a complex task due to intermittent pathogen occurrences. To address this, faecal indicator organisms like E. coli are often monitored as proxies to evaluate faecal contamination levels and infer pathogen concentrations. However, the wide variability in faecal indicator concentrations poses challenges in their modelling for quantitative microbial risk assessment (QMRA). Our study critically assesses the adequacy of parametric models in predicting the variability in E. coli concentrations in greywater. We found that models that build on summary statistics, like medians and standard deviations, can substantially underestimate the variability in E. coli concentrations. More appropriate models may provide more accurate estimations of, and uncertainty around, peak E. coli concentrations. To demonstrate this, a Poisson lognormal distribution model is fit to a data set of E. coli concentrations measured in shower and laundry greywater sources. This model estimated arithmetic mean E. coli concentrations in laundry waters at approximately 1.0E + 06 MPN 100 mL−1. These results are around 2.0 log10 units higher than estimations from a previously used hierarchical lognormal model based on aggregated summary data from multiple studies. Such differences are considerable when assessing human health risks and setting pathogen reduction targets for greywater reuse. This research highlights the importance of making raw monitoring data available for more accurate statistical evaluations than those based on summary statistics. It also emphasizes the crucial role of model comparison, selection, and validation to inform policy-relevant outcomes.
Joss, A., Kipf, M., Morgenroth, E., Baggenstos, M., & Salzgeber, D. (2023). Modifiziertes Anammox-Verfahren. Faulwasserbehandlungen mit stabiler Prozessführung. Aqua & Gas, 103(1), 24-29. , Institutional Repository

Bei der anaeroben Ammonium-Oxidation, kurz Anammox, werden Ammonium und Nitrit im Faulwasser zu Stickstoffgas umgewandelt. Das Verfahren ist auch auf einigen Schweizer ARA im Einsatz. Da aber nicht alle Anlagen die Sollleistung erfüllten, wurde das Anammox-Verfahren untersucht und weiterentwickelt. Mit dem Wechsel von der ein- zur zweistufigen Verfahrensführung wurde nicht nur eine höhere Betriebsstabilität bei der biologischen Entstickung von Rückläufen aus der Schlammentwässerung, sondern teils auch höhere Leistungen erreicht.
Kizgin, A., Schmidt, D., Joss, A., Hollender, J., Morgenroth, E., Kienle, C., & Langer, M. (2023). Application of biological early warning systems in wastewater treatment plants: Introducing a promising approach to monitor changing wastewater composition. Journal of Environmental Management, 347, 119001 (12 pp.). doi:10.1016/j.jenvman.2023.119001, Institutional Repository

Wastewater treatment plants (WWTPs) are a major source of micropollutants to surface waters. Currently, their chemical or biological monitoring is realized by using grab or composite samples, which provides only snapshots of the current wastewater composition. Especially in WWTPs with industrial input, the wastewater composition can be highly variable and a continuous assessment would be advantageous, but very labor and cost intensive. A promising concept are automated real-time biological early warning systems (BEWS), where living organisms are constantly exposed to the water and an alarm is triggered if the organism's responses exceed a harmful threshold of acute toxicity. Currently, BEWS are established for drinking water and surface water but are seldom applied to monitor wastewater. This study demonstrates that a battery of BEWS using algae (Chlorella vulgaris in the Algae Toximeter, bbe Moldaenke), water flea (Daphnia magna in the DaphTox II, bbe Moldaenke) and gammarids (Gammarus pulex in the Sensaguard, REMONDIS Aqua) can be adapted for wastewater surveillance. For continuous low-maintenance operation, a back-washable membrane filtration system is indispensable for adequate preparation of treated wastewater. Only minor deviations in the reaction of the organisms towards treated and filtered wastewater compared to surface waters were detected. After spiking treated wastewater with two concentrations of the model compounds diuron, chlorpyrifos methyl, and sertraline, the organisms in the different BEWS showed clear responses depending on the respective compound, concentration and mode of action. Immediate effects on photosynthetic activity of algae were detected for diuron exposure, and strong behavioral changes in water flea and gammarids after exposure to chlorpyrifos methyl or sertraline were observed, which triggered automated alarms. Different types of data analysis were applied to extract more information out of the specific behavioral traits, than only provided by the vendors algorithms. To investigate, whether behavioral movement changes can be linked to impact other endpoints, the effects on feeding activity of G. pulex were evaluated and results indicated significant differences between the exposures. Overall, these findings provide an important basis indicating that BEWS have the potential to act as alarm systems for pollution events in the wastewater sector.
Kollmann, J., Nath, S., Singh, S., Balasubramanian, S., Reynaert, E., Morgenroth, E., & Contzen, N. (2023). Acceptance of on-site wastewater treatment and reuse in Bengaluru, India: the role of perceived costs, risks, and benefits. Science of the Total Environment, 895, 165042 (11 pp.). doi:10.1016/j.scitotenv.2023.165042, Institutional Repository

In dealing with water pollution and freshwater scarcity, on-site treatment and reuse of domestic wastewater has shown to be a promising solution. To increase on-site wastewater treatment and reuse, some cities, among them Bengaluru in India, have mandated the installation and use of the necessary technology in certain building types. However, even with a mandate, a successful and sustainable implementation of the technology, including reliable operation, monitoring, and maintenance, depends on the acceptance (i.e. positive valuation) of the technology and its use by the (prospective) users. Literature on technology acceptance indicates perceived costs, risks, and benefits of the respective technology as key predictors of acceptance. Therefore, the present online study assessed this relationship for on-site systems in Bengaluru. The relation was analysed separately for mandated users of on-site systems (N = 103) and current non-users (i.e. potential prospective users, should the mandate be expanded; N = 232), as the perceptions might differ between the two groups, due to the personal experience with the technology among users. The results show that for mandated users and non-users, acceptance of on-site systems is explained by perceived benefits only, namely a positive image of users, environmental benefits, and, only for non-users, also financial benefits for the city. The findings suggest that interventions aimed at promoting on-site systems should include emphasis on the benefits of on-site systems. Whenever possible, interventions should be tailored to the target group's individual cost, risk, and benefit perception.
Reynaert, E., Steiner, P., Yu, Q., D'Olif, L., Joller, N., Schneider, M. Y., & Morgenroth, E. (2023). Predicting microbial water quality in on-site water reuse systems with online sensors. Water Research, 240, 120075 (13 pp.). doi:10.1016/j.watres.2023.120075, Institutional Repository

Widespread implementation of on-site water reuse is hindered by the limited availability of monitoring approaches that ensure microbial quality during operation. In this study, we developed a methodology for monitoring microbial water quality in on-site water reuse systems using inexpensive and commercially available online sensors. An extensive dataset containing sensor and microbial water quality data for six of the most critical types of disruptions in membrane bioreactors with chlorination was collected. We then tested the ability of three typological machine learning algorithms - logistic regression, support-vector machine, and random forest - to predict the microbial water quality as "safe" or "unsafe" for reuse. The main criteria for model optimization was to ensure a low false positive rate (FPR) - the percentage of safe predictions when the actual condition is unsafe - which is essential to protect users health. This resulted in enforcing a fixed FPR ≤ 2%. Maximizing the true positive rate (TPR) - the percentage of safe predictions when the actual condition is safe - was given second priority. Our results show that logistic-regression-based models using only two out of the six sensors (free chlorine and oxidation-reduction potential) achieved the highest TPR. Including sensor slopes as engineered features allowed to reach similar TPRs using only one sensor instead of two. Analysis of the occurrence of false predictions showed that these were mostly early alarms, a characteristic that could be regarded as an asset in alarm management. In conclusion, the simplest algorithm in combination with only one or two sensors performed best at predicting the microbial water quality. This result provides useful insights for water quality modeling or for applications where small datasets are a common challenge and a general advantage might be gained by using simpler models that reduce the risk of overfitting, allow better interpretability, and require less computational power.
Reynaert, E., Nagappa, D., & Morgenroth, E. (2023). Research brief: using sensors and automated chlorination to improve the microbial water quality of on-site sewage treatment plants in Bengaluru. doi:10.3929/ethz-b-000603755, Institutional Repository

More than 3,000 on-site sewage treatment plants (STPs) recycle water for landscaping and toilet flushing in Bengaluru. Microbial water quality is essential to protect user health, even for non-potable water reuse applications. However, there is lack of information on short-term variability of the microbial quality of the water. This research brief presents monitoring results from two on-site STPs in Bengaluru, and makes recommendations on how to optimize STP operation to ensure microbiologically safe water at all times.
Reynaert, E., Gretener, F., Julian, T. R., & Morgenroth, E. (2023). Sensor setpoints that ensure compliance with microbial water quality targets for membrane bioreactor and chlorination treatment in on-site water reuse systems. Water Research X, 18, 100164 (13 pp.). doi:10.1016/j.wroa.2022.100164, Institutional Repository

Widespread implementation of on-site water reuse systems is hindered by the limited ability to ensure the level of treatment and protection of human health during operation. In this study, we tested the ability of five commercially available online sensors (free chlorine (FC), oxidation-reduction potential (ORP), pH, turbidity, UV absorbance at 254 nm) to predict the microbial water quality in membrane bioreactors followed by chlorination using logistic regression-based and mechanism-based models. The microbial water quality was assessed in terms of removal of enteric bacteria from the wastewater, removal of enteric viruses, and regrowth of bacteria in the treated water. We found that FC and ORP alone could predict the microbial water quality well, with ORP-based models generally performing better. We further observed that prediction accuracy did not increase when data from multiple sensors were integrated. We propose a methodology to link online sensor measurements to risk-based water quality targets, providing operation setpoints protective of human health for specific combinations of wastewaters and reuse applications. For instance, we recommend a minimum ORP of 705 mV to ensure a virus log-removal of 5, and an ORP of 765 mV for a log-removal of 6. These setpoints were selected to ensure that the percentage of events where the water is predicted to meet the quality target but it does not remains below 5%. Such a systematic approach to set sensor setpoints could be used in the development of water reuse guidelines and regulations that aim to cover a range of reuse applications with differential risks to human health.
Sam, S. B., Morgenroth, E., & Strande, L. (2023). Changes in organic fractions, cations, and stabilization from feces to fecal sludge: implications for dewatering performance and management solutions. Journal of Water Sanitation and Hygiene for Development, 13(9), 699-710. doi:10.2166/washdev.2023.086, Institutional Repository

Reliable dewatering performance remains a key challenge in fecal sludge management, and the controlling factors or mechanisms are not well understood. There remain limited studies on constituents in feces and fecal sludge and how they affect the dewaterability of fecal sludge. This study aimed at evaluating a range of constituents in feces, and to gain empirical knowledge toward a mechanistic understanding of how they influence dewaterability. In this study, cellulose reduced capillary suction time, decreased supernatant turbidity, and increased cake solids. While hemicellulose decreased supernatant turbidity, lignin increased supernatant turbidity, capillary suction time, and cake solids. Extracellular polymeric substances (EPS) increased both capillary suction time and supernatant turbidity and decreased cake solids, whereas lipids increased turbidity. Cations had no significant effect on dewatering properties. Overall, fecal sludge stored in containments had better dewatering performance than ‘fresh’ fecal sludge, which was attributed to stabilization. Field fecal sludge had a higher relative abundance of Pseudomonas, which is associated with better aggregation, and fewer small particles (<10 μm) that clog filters to reduce dewatering performance. Further understanding of stabilization and developing an agreed-upon metrics of stabilization are essential for predicting fecal sludge dewatering performance, and developing smaller footprint dewatering treatment technologies.
Stoffel, D., Derlon, N., Traber, J., Staaks, C., Heijnen, M., Morgenroth, E., & Jacquin, C. (2023). Gravity-driven membrane filtration with compact second-life modules daily backwashed: an alternative to conventional ultrafiltration for centralized facilities. Water Research X, 18, 100178 (12 pp.). doi:10.1016/j.wroa.2023.100178, Institutional Repository

Gravity-driven membrane (GDM) filtration is a strategic alternative to conventional ultrafiltration (UF) for the resilient production of drinking water via ultrafiltration when resources become scarce, given the low dependency on energy and chemicals, and longer membrane lifetime. Implementation at large scale requires the use of compact and low-cost membrane modules with high biopolymer removal capacity. We therefore evaluated (1) to what extent stable flux can be obtained with compact membrane modules, i.e., inside-out hollow fiber membranes, and frequent gravity-driven backwash, (2) whether we can reduce membrane expenses by effectively utilizing second-life UF modules, i.e., modules that have been discarded by treatment plant operators because they are no longer under warranty, (3) if biopolymer removal could be maintained when applying a frequent backwash and with second-life modules and (4) which GDM filtration scenarios are economically viable compared to conventional UF, when considering the influence of new or second-life modules, membrane lifetime, stable flux value and energy pricing. Our findings showed that it was possible to maintain stable fluxes around 10 L/m2/h with both new and second-life modules for 142 days, but a daily gravity-driven backwash was necessary and sufficient to compensate the continuous flux drop observed with compact modules. In addition, the backwash did not affect the biopolymer removal. Costs calculations revealed two significant findings: (1) using second-life modules made GDM filtration membrane investment less expensive than conventional UF, despite the higher module requirements for GDM filtration and (2) overall costs of GDM filtration with a gravity-driven backwash were unaffected by energy prices rise, while conventional UF costs rose significantly. The later increased the number of economically viable GDM filtration scenarios, including scenarios with new modules. In summary, we proposed an approach that could make GDM filtration in centralized facilities feasible and increase the range of UF operating conditions to better adapt to increasing environmental and societal constraints.
Ward, B. J., Nguyen, M. T., Sam, S. B., Korir, N., Niwagaba, C. B., Morgenroth, E., & Strande, L. (2023). Particle size as a driver of dewatering performance and its relationship to stabilization in fecal sludge. Journal of Environmental Management, 326, 116801 (12 pp.). doi:10.1016/j.jenvman.2022.116801, Institutional Repository

Poor and unpredictable dewatering performance of fecal sludge is a major barrier to sanitation provision in urban areas not served by sewers. Fecal sludge comprises everything that accumulates in onsite containments, and its characteristics are distinct from wastewater sludges and from feces. There is little fundamental understanding of what causes poor dewatering in fecal sludge. For the first time, we demonstrate that particle size distribution is a driver of dewatering performance in fecal sludge, and is associated with level of stabilization. Higher concentrations of small particles (<10 μm) and smaller median aggregate size (D50) corresponded to poor dewatering performance (measured by capillary suction time (CST) and supernatant turbidity) in field samples from Kenya and Uganda and in controlled laboratory anaerobic storage experiments. More stabilized fecal sludge (higher C/N, lower VSS/TSS) had better dewatering performance, corresponding to lower concentrations of small particles. Samples with the largest aggregates (D50 > 90 μm) had higher abundance of Gammaproteobacteria Pseudomonas, and samples with the smallest aggregates (D50 ≤ 50 μm) were characterized by higher abundance of Bacteroidetes Vadin HA17 and Rikenellaceae. Contrary to common perceptions, stabilization, particle size distribution, and dewatering performance were not dependent on time intervals between emptying of onsite containments or on time in controlled anaerobic storage experiments. Our results suggest that the stabilization process in onsite containments, and hence the dewaterability of sludge arriving at treatment facilities, is not dependent on time in containment but is more likely associated with specific microbial populations and the in-situ environmental conditions which promote or discourage their growth.
Braun, D., von Känel, L., Biolley, L., Bauer, H., Gahler, D., Gruber, W., … Morgenroth, E. (2022). Dynamische Regelung der ARA Hofen. Infrawatt-Innovationspreis für mehr Leistung und weniger Emissionen. Aqua & Gas, 102(1), 26-31. , Institutional Repository

Die ARA Hofen hat den Infrawatt Innovationspreis 2021 für die Ertüchtigung ihrer Biologiebecken mit dem Konzept der dynamischen Regelung erhalten. Die Leistung der ARA konnte dadurch signifikant erhöht werden, bei stark vermindertem Energieverbrauch und gleichzeitig sehr geringen Lachgasemissionen.
Derlon, N., Desmond, P., Rühs, P. A., & Morgenroth, E. (2022). Cross flow frequency determines the physical structure and cohesion of membrane biofilms developed during gravity-driven membrane ultrafiltration of river water: implication for hydraulic resistance. Journal of Membrane Science, 643, 120079 (10 pp.). doi:10.1016/j.memsci.2021.120079, Institutional Repository

We evaluated how intermittent shear influences the physical structure, material properties and hydraulic resistance of membrane biofilms developed during gravity-driven ultrafiltration of river water, with the ultimate goal of increasing the filtration performances. Our results indicate intermittent shear helps slowing-down the flux decline but does not help to increase the level of stabilisation of the permeate flux. After several weeks, the biofilms exposed to different shear regimes were indeed characterised by similar hydraulic resistance. But the characteristic time to achieve a stable flux increased from 7 d to 25d when increasing the shear frequency. Also, most of the hydraulic resistance (up to 95%) was governed by the base layer that remained attached after erosion tests. With increasing exposure to shear conditions, the biofilms became more cohesive and more elastic, thus resisting better to cross flow conditions. Overall, our results demonstrate that engineering membrane biofilms with a desired permeability is not feasible using intermittent shear due to significant adaptability of the biofilms to their hydraulic environment.
Derlon, N., Garcia Villodres, M., Kovács, R., Brison, A., Layer, M., Takács, I., & Morgenroth, E. (2022). Modelling of aerobic granular sludge reactors: the importance of hydrodynamic regimes, selective sludge removal and gradients. Water Science and Technology, 86(3), 410-431. doi:10.2166/wst.2022.220, Institutional Repository

Hydraulic selection is a key feature of aerobic granular sludge (AGS) systems but existing aerobic granular sludge (AGS) models neglect those mechanisms: gradients over reactor height (Hreactor), selective removal of slow settling sludge, etc. This study aimed at evaluating to what extent integration of those additional processes into AGS models is needed, i.e., at demonstrating that model predictions (biomass inventory, microbial activities and effluent quality) are affected by such additional model complexity. We therefore developed a new AGS model that includes key features of full-scale AGS systems: fill-draw operation, selective sludge removal, distinct settling models for flocs/granules. We then compared predictions of our model to those of a fully mixed AGS model. Our results demonstrate that hydraulic selection can be predicted with an assembly of four continuous stirred tank reactors in series together with a correction code for plug-flow. Concentration gradients over the reactor height during settling/plug-flow feeding strongly impact the predictions of aerobic granular sludge models in terms of microbial selection, microbial activities and ultimately effluent quality. Hydraulic selection is a key to predict selection of storing microorganisms (phosphorus-accumulating organisms (PAO) and glycogen-accumulating organisms (GAO)) and in turn effluent quality in terms of total phosphorus, and for predicting effluent solid concentration and dynamic during plug-flow feeding.
Gruber, W., Joss, A., von Känel, L., Biolley, L., Braun, D., & Morgenroth, E. (2022). Abluftmessungen in der biologischen Abwasserreinigung. Aqua & Gas, 102(1), 24-25. , Institutional Repository

Neue Leistungsanforderungen an Abwasserreinigungsanlagen hinsichtlich Ablaufqualität, Energieeffizienz und Treibhausgasemission werden immer bedeutender. Um dabei Zielkonflikte zu vermeiden, ist bei der Optimierung die genaue Überwachung der Prozesse erforderlich. So ist die Messung von Gaskonzentrationen in der Abluft aus biologischen Reinigungsstufen ein nützliches Werkzeug, um verschiedene Zielsetzungen einer ARA hochaufgelöst und wartungsarm zu überwachen.
Gruber, W., Niederdorfer, R., Bürgmann, H., Joss, A., von Känel, L., Braun, D., … Morgenroth, E. (2022). Lachgasemissionen aus ARA. Reduktionsmassnahmen zeichnen sich ab. Aqua & Gas, 102(1), 14-22. , Institutional Repository

Lachgas (N2O) ist ein starkes Treibhausgas und die wichtigste ozonzerstörende Substanz in der Stratosphäre. Auf Abwasserreinigungsanlagen wird N2O während des biologischen Stickstoffabbaus gebildet, der somit die grösste Treibhausgasquelle während des Reinigungsprozesses darstellt. Reduktionsmassnahmen sind deshalb von grosser Bedeutung und gemäss neuen Erkenntnissen durch eine Optimierung der Nitrifikation und Denitrifikation auch erreichbar.
Gruber, W., Magyar, P. M., Mitrovic, I., Zeyer, K., Vogel, M., von Känel, L., … Mohn, J. (2022). Tracing N2O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings. Water Research X, 15, 100130 (11 pp.). doi:10.1016/j.wroa.2022.100130, Institutional Repository

Nitrous oxide (N2O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N2O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N2O mitigation strategies require an improved understanding of nitrogen transformation pathways and their modulating controls. Analyses of the nitrogen (N) and oxygen (O) isotopic composition of N2O and its substrates at natural abundance have been shown to provide valuable information on formation and reduction pathways in laboratory settings, but have rarely been applied to full-scale WWTPs.
Here we show that N-species isotope ratio measurements at natural abundance level, combined with long-term N2O monitoring, allow identification of the N2O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). Heterotrophic denitrification appears as the main N2O production pathway under all tested process conditions (0-2 mgO2/l, high and low loading conditions), while nitrifier denitrification was less important, and more variable. N2O production by hydroxylamine oxidation was not observed. Fractional N2O elimination by reduction to dinitrogen (N2) during anoxic conditions was clearly indicated by a concomitant increase in site preference, δ18O(N2O) and δ15N(N2O). N2O reduction increased with decreasing availability of dissolved inorganic N and organic substrates, which represents the link between diurnal N2O emission dynamics and organic substrate fluctuations. Consequently, dosing ammonium-rich reject water under low-organic-substrate conditions is unfavorable, as it is very likely to cause high net N2O emissions.
Our results demonstrate that monitoring of the N2O isotopic composition holds a high potential to disentangle N2O formation mechanisms in engineered systems, such as full-scale WWTP. Our study serves as a starting point for advanced campaigns in the future combining isotopic technologies in WWTP with complementary approaches, such as mathematical modeling of N2O formation or microbial assays to develop efficient N2O mitigation strategies.
Hadengue, B., Morgenroth, E., & Larsen, T. A. (2022). How to get your feet wet: Integrating urban water and building engineering for low-energy domestic hot water systems. Energy and Buildings, 271, 112318 (6 pp.). doi:10.1016/j.enbuild.2022.112318, Institutional Repository

Thanks to intense research efforts, modern low-energy buildings consume only a fraction of the space heating loads of their older counterparts. However, reducing their energy footprint further requires optimization of domestic hot water systems. This is a difficult task, because the relationship between water and energy in domestic systems is intricate and complex. In general, the intrinsic uncertainty and variability of water demand makes the planning and assessment of new technologies challenging, but also risks related for instance to water pathogens like Legionella pneumophila impose trade-offs that diminish the performance of energy-saving measures. In this short communication, we argue that truly sustainable solutions will only be found if a multi-scale, multi-disciplinary mindset is adopted by the community. We show how the collaboration and knowledge integration between experts of various fields, notably urban water specialists and building engineers, is a prerequisite to resolve some of the most pressing issues on the way to optimizing domestic hot water systems. Through concrete examples, we describe how a new, common modeling framework has already triggered the required knowledge integration, and how it could be expanded further to integrate additional disciplines.
Hadengue, B., Morgenroth, E., Larsen, T. A., & Baldini, L. (2022). Performance and dynamics of active greywater heat recovery in buildings. Applied Energy, 305, 117677 (13 pp.). doi:10.1016/j.apenergy.2021.117677, Institutional Repository

In the effort to de-carbonize the building stock, heat pumps are increasingly utilized in Switzerland, with 70% of the fast-growing heat pump market using ambient air as heat source. Inexpensive and easy to implement, these heat pumps are, however, less efficient than their ground- or water-source counterparts. In this modeling study, we aim at increasing the efficiency of air-source heat pumps using domestic greywater-contained heat. We assess the performance improvement relative to standard heat pump configurations across various climates, seasons, building envelopes, and domestic hot water consumption patterns. The results show that the annually-averaged coefficient of performance improves by 4.1% on average - ranging from 0.6% to 7.5%. This efficiency gain translates on average to 1.8 kWh/week of compressor electricity savings. Although attractive due to its simplicity, the proposed open-loop configuration - preheating of an external heat source - only leads to moderate performance improvement of air-source heat pumps. Based on these results, we extensively discuss and compare alternative system configurations and identify several fundamental differences in the heat recovery dynamics of each configuration. We show that closed-loop systems - using greywater as direct heat source - show the largest performance improvement potential, although being more expensive and complex to implement.
Hadengue, B., Morgenroth, E., & Larsen, T. A. (2022). Screening innovative technologies for energy-efficient domestic hot water systems. Journal of Environmental Management, 320, 115713 (9 pp.). doi:10.1016/j.jenvman.2022.115713, Institutional Repository

Domestic hot water systems are large energy consumers. With the aim of reducing the energy footprint of these systems, we selected and simulated five technologies across a wide range of technology readiness levels: established technologies - pipe insulation and low-flow faucets -, relatively new technologies - shower drain heat exchangers and an innovative pipe system - and a novel experimental technology - a heat exchanger connected to membrane bioreactor for on-site greywater treatment. Using the WaterHub modeling framework, we simulated the technologies alone and in combination and compared the energetic performance of fifteen scenarios with a validated reference domestic hot water system. Low-flow appliances as standalone technologies performed best with 30% less energy required for the boiler tank, but combining low-flow appliances with a membrane bioreactor heat exchanger performed best overall (50% reduction). Deep insights into the temperature dynamics at all locations in the system led to the identification of technological competition patterns to prevent and synergies to exploit. Through our results, we are able to discuss and recommend further investigations regarding critical aspects like hygiene and economic performance.
Hausherr, D., Niederdorfer, R., Bürgmann, H., Lehmann, M. F., Magyar, P., Mohn, J., … Joss, A. (2022). Successful mainstream nitritation through NOB inactivation. Science of the Total Environment, 822, 153546 (11 pp.). doi:10.1016/j.scitotenv.2022.153546, Institutional Repository

The development of new wastewater treatment processes can assist in reducing the impact of wastewater treatment on the environment. The recently developed partial nitritation anammox (PNA) process, for example, consumes less energy for aeration and reduces nitrate in the effluent without requiring additional organic carbon. However, achieving stable nitritation (ammonium oxidation; NH4+ → NO2−) at mainstream conditions (T = 10–25 °C, C:N > 10, influent ammonium < 50 mgNH4-N/L and effluent < 1 mgNH4-N/L) remains challenging. This study explores the potential and mechanism of nitrite-oxidizing bacteria (NOB) suppression in a bottom-fed sequencing batch reactor (SBR). Two bench-scale (11 L) reactors and a pilot-scale reactor (8 m3) were operated for over a year and were fed with organic substrate depleted municipal wastewater. Initially, nitratation (nitrite oxidation; NO2− → NO3−) occurred occasionally until an anaerobic phase was integrated into the operating cycle. The introduction of the anaerobic phase effectively suppressed the regrowth of NOB while nitritation was stable over 300 days, down to 8 °C and at ammonium influent concentrations < 25 mgNH4-N/L. Batch experiments and process data revealed that parameters typically affecting NOB growth (e.g., dissolved oxygen, alkalinity, trace elements, lag-phase after anoxia, free nitrous acid (FNA), free ammonia (FA), pH, sulfide, or solids retention time (SRT)) could not fully explain the suppression of nitratation. Experiments in which fresh nitrifying microbial biomass was added to the nitritation system indicated that NOB inactivation explained NOB suppression better than NOB washout at high SRT. This study concludes that bottom-fed SBRs with anaerobic phases allow for stable nitritation over a broad range of operational parameters. Coupling this type of SBR to an anammox reactor can enable efficient mainstream anammox-based wastewater treatment.
Hausherr, D., Niederdorfer, R., Bürgmann, H., Lehmann, M. F., Magyar, P., Mohn, J., … Joss, A. (2022). Successful year-round mainstream partial nitritation anammox: assessment of effluent quality, performance and N2O emissions. Water Research X, 16, 100145 (11 pp.). doi:10.1016/j.wroa.2022.100145, Institutional Repository

For two decades now, partial nitritation anammox (PNA) systems were suggested to more efficiently remove nitrogen (N) from mainstream municipal wastewater. Yet to date, only a few pilot-scale systems and even fewer full-scale implementations of this technology have been described. Process instability continues to restrict the broad application of PNA. Especially problematic are insufficient anammox biomass retention, the growth of undesired aerobic nitrite-oxidizers, and nitrous oxide (N2O) emissions. In this study, a two-stage mainstream pilot-scale PNA system, consisting of three reactors (carbon pre-treatment, nitritation, anammox - 8 m3 each), was operated over a year, treating municipal wastewater. The aim was to test whether both, robust autotrophic N removal and high effluent quality, can be achieved throughout the year. A second aim was to better understand rate limiting processes, potentially affecting the overall performance of PNA systems. In this pilot study, excellent effluent quality, in terms of inorganic nitrogen, was accomplished (average effluent concentrations: 0.4 mgNH4-N/L, 0.1 mgNO2-N/L, 0.9 mgNO3-N/L) even at wastewater temperatures previously considered problematic (as low as 8 °C). N removal was limited by nitritation rates (84 ± 43 mgNH4-N/L/d), while surplus anammox activity was observed at all times (178 ± 43 mgN/L/d). Throughout the study, nitrite-oxidation was maintained at a low level (<2.5% of ammonium consumption rate). Unfortunately, high N2O emissions from the nitritation stage (1.2% of total nitrogen in the influent) were observed, and, based on natural isotope abundance measurements, could be attributed to heterotrophic denitrification. In situ batch experiments were conducted to identify the role of dissolved oxygen (DO) and organic substrate availability in N2O emission-mitigation. The addition of organic substrate, to promote complete denitrification, was not successful in decreasing N2O emission, but increasing the DO from 0.3 to 2.9 mgO2/L decreased N2O emissions by a factor of 3.4.
Layer, M., Brison, A., Garcia Villodres, M., Stähle, M., Házi, F., Takács, I., … Derlon, N. (2022). Microbial conversion pathways of particulate organic substrate conversion of aerobic granular sludge systems: limited anaerobic conversion and the essential role of flocs. Environmental Science: Water Research and Technology, 8(6), 1236-1251. doi:10.1039/D1EW00841B, Institutional Repository

Particulate organic substrate (XB) represents the major fraction of organic substrate in low-strength municipal wastewater (MWW) but its hydrolysis, conversion and utilisation in aerobic granular sludge (AGS) are not well understood. We systematically analysed through modelling the microbial conversion pathways of XB in AGS systems operated as sequencing batch reactors and treating municipal wastewater. Based on our current understanding of AGS systems, we developed an AGS model in Sumo® to better understand (1) during which phases of the SBR cycle (anaerobic plug-flow feeding or aerobic fully-mixed conditions), (2) by what biomass fraction (granules or flocs) and (3) via which microbial processes XB is converted into soluble organic substrate (SB) and volatile fatty acids (SVFA) and further utilised. The validity of all our results was evaluated by assessing the sensitivity of findings on the biomass distribution (floc fraction) (SCENARIO #1), SBR cycle (SCENARIO #2), and biofilm properties (SCENARIO #3). Our results indicate that only 20% of influent XB was hydrolysed and 11% of influent XB was then used for internal carbon-storage during 90 min anaerobic plug-flow feeding. The major fraction of influent XB (80%) leaked into the aerobic SBR phase, where XB was then hydrolysed and oxidised aerobically by ordinary heterotrophic organisms (OHOs). Under aerobic fully-mixed conditions, the flocs successfully competed for XB with the granules. Aerobic XB hydrolysis and its further utilisation by OHOs occurred mainly in flocs despite their minor biomass fraction (13% of total suspended solids), preventing excessive OHO growth on granules and demonstrating that flocs are beneficial for AGS systems treating MWW. Also, the model allowed us to better understand that the SBR sequence can be optimised to make better use of XB under anaerobic conditions and to reduce the leakage of XB to aerobic conditions. The introduction of a 60 min anaerobic idle phase after a 60 min plug-flow feeding phase almost doubled the anaerobic XB hydrolysis and internal carbon-storage by phosphorus and glycogen accumulating organisms (PAOs and GAOs), respectively, compared to 90 min plug-flow feeding. Nonetheless, most influent XB was still utilised by OHOs during the aerobic SBR phase.
Morgenroth, E., & Derlon, N. (2022). Entwicklung der biologischen Abwasserreinigung: Belebtschlamm vs Biofilmsysteme. In T. Wintgens & J. Pinnekamp (Eds.), Gewässerschutz, Wasser, Abwasser. 55. Essener Tagung für Wasserwirtschaft. Wasserwirtschaft im Klimawandel (p. 31 (12 pp.). Aachen: Gesellschaft zur Förderung des Instituts für Siedlungswasserwirtschaft an der RWTH Aachen. , Institutional Repository
Sam, S. B., Ward, B. J., Niederdorfer, R., Morgenroth, E., & Strande, L. (2022). Elucidating the role of extracellular polymeric substances (EPS) in dewaterability of fecal sludge from onsite sanitation systems, and changes during anaerobic storage. Water Research, 222, 118915 (12 pp.). doi:10.1016/j.watres.2022.118915, Institutional Repository

As the importance of fecal sludge management (FSM) is increasingly being realized, the need for adequately designed and functioning fecal sludge (FS) treatment plants is also increasing. Research to fill this gap is only emerging and dewatering is a key challenge for developing sustainable treatment solutions. This study evaluated the effect of extracellular polymeric substances (EPS) on dewaterability of FS, and how EPS and dewaterability change during anaerobic storage (as a proxy for time in onsite containment). EPS was extracted from FS and activated sludge using Na2CO3 and sonication and added to sludge samples to determine the effect on dewaterability. The results confirmed that an increase in EPS had a direct impact of decreasing FS dewaterability (as capillary suction time). In this context, we evaluated FS degradation during anaerobic storage, the effect of anaerobic storage time on EPS, EPS fractions and particle size distribution, and the effect of variations in these factors on FS dewaterability. Variations in EPS, EPS fraction and particle size distribution during anaerobic storage were less than expected and average VS reduction of 20% was recorded over 7 weeks. Although anaerobic digestion was verified (biogas production), the results indicate that kinetics of degradation of FS is different from wastewater sludges. Comparatively, EPS fractions in FS were 70 – 75% lower and with higher fractions of humic-like substances than wastewater sludges. Although EPS significantly affects FS dewaterability, anaerobic storage time is not a predictor of dewaterability.
Stoffel, D., Rigo, E., Derlon, N., Staaks, C., Heijnen, M., Morgenroth, E., & Jacquin, C. (2022). Low maintenance gravity-driven membrane filtration using hollow fibers: effect of reducing space for biofilm growth and control strategies on permeate flux. Science of the Total Environment, 811, 152307 (13 pp.). doi:10.1016/j.scitotenv.2021.152307, Institutional Repository

The implementation of centralized drinking water treatment systems necessitates lower operational costs and improved biopolymer removal during ultrafiltration (UF), which can be afforded by gravity-driven membrane (GDM) filtration. However, prior to implementing GDM filtration in centralized systems, biofilm growth in compacted membrane configurations, such as inside-out hollow fiber (HF), and its impact on permeate flux need to be investigated. To this end, we operated modules with distinct limits on available space for biofilm growth: (1) outside-in 1.5 mm 7-capillary HF (non-limited), (2) inside-out 1.5 mm 7-capillary HF (limited), and (3) inside-out 0.9 mm 7-capillary HF (very limited). Here, we observed that the lower the space available for biofilm growth, the lower the permeate flux. To improve GDM performance with inside-out HF, we applied daily shear stress to the biofilm surface with forward flush (FF) or combined relaxation and forward flush (R+FF). We showed that applying shear stress to the biofilm surface was insufficient for controlling flux loss due to low available space for biofilm growth. At the experimental endpoint, we backwashed with a stepwise transmembrane pressure (TMP) increase or a single TMP on all inside-out HF modules, which removed the biofilm from its base. Afterwards, higher fluxes were yielded. We also showed that all modules exhibited a gradual increase in biopolymer removal followed by stabilization between 70 and 90%. Additionally, control of biofilm growth with surface shear stress did not affect biopolymer removal. In summary, the implementation of inside-out HF with GDM filtration is challenged by low available space for biofilm growth, but may be remedied with a regular backwash to remove biofilm from its base. We showed that a wider range of GDM applications are available; making GDM potentially compatible with implementation in centralized systems, if space limitation is taken into consideration for operation optimization.
Ward, B. J. (2022). Settling and dewatering of fecal sludge: building fundamental knowledge for improved global sanitation (Doctoral dissertation). ETH Zurich, Zurich, 206 p. , Institutional Repository

More than 1/3 of the global population relies on onsite sanitation systems, and in some cases entire urban areas in low- and middle-income countries are not served by sewers. Improved options for the management of fecal sludge that accumulates in these onsite systems are required immediately, as the majority of it is currently discharged untreated into the urban environment, placing a huge burden on public and environmental health. One of the greatest obstacles to establishing more reliable and accessible fecal sludge treatment is inconsistent and unpredictable solid-liquid separation. Extreme influent variability in influent fecal sludge poses operational problems with settling and dewatering, reducing the capacity of existing centralized and semi-centralized treatment facilities and hindering the transfer of low-footprint technologies which could extend decentralized and community-scale sanitation coverage in high-density urban areas. [...]
Benstöm, F., Meda, A., Baumann, P., Derlon, N., Lackner, S., Layer, M., … Wichern, M. (2021). Aerobe Verfahren mit granuliertem Schlamm zur Abwasserbehandlung - Arbeitsbericht der DWA­Arbeitsgruppe KA­6.3. "Biofilmverfahren"*) - Teil 1. KA: Korrespondenz Abwasser Abfall, 68(4), 281-288. , Institutional Repository

Unter bestimmten Prozessbedingungen entsteht in der konventionellen Abwasserreinigung aus flockenförmigem Belebtschlamm (FloS) aerober granulierter Schlamm (AGS), der in der Regel ohne Zugabe von Aufwuchskörpern gebildet wird. Prinzipiell können mit AGS die gleichen Reinigungsleistungen wie mit FloS erzielt werden. Im Vergleich zu konventionellen Anlagen ohne AGS können jedoch vergleichsweise höhere Biomassenkonzentrationen und kürzere Absetzzeiten des Schlamms erreicht und damit potenziell Reaktorvolumina eingespart werden. Somit können Verfahren mit AGS eine interessante Alternative zu etablierten Verfahren sein. Der vorliegende Arbeitsbericht erläutert die derzeit verfügbaren AGS-Verfahrensvarianten (diskontinuierlich und kontinuierlich), diskutiert erstmalig typische Verfahrenskennwerte und gibt Hinweise zu planerischen Aspekten und noch offenen Fragen.
Gruber, W., von Känel, L., Vogt, L., Luck, M., Biolley, L., Feller, K., … Joss, A. (2021). Estimation of countrywide N2O emissions from wastewater treatment in Switzerland using long-term monitoring data. Water Research X, 13, 100122 (12 pp.). doi:10.1016/j.wroa.2021.100122, Institutional Repository

Nitrous oxides (N2O) emissions contribute to climate change and stratospheric ozone depletion. Wastewater treatment is an important, yet likely underestimated, source of N2O emissions, as recent, long-term monitoring campaigns have demonstrated. However, the available data are insufficient to representatively estimate countrywide emission due to the brevity of most monitoring campaigns. This study showed that the emission estimates can be significantly improved using an advanced approach based on multiple continuous, long-term monitoring campaigns. In monitoring studies on 14 full-scale wastewater treatment plants (WWTPs), we found a strong variability in the yearly emission factors (EFs) (0.1 to 8% of the incoming nitrogen load) which exhibited a good correlation with effluent nitrite. But countrywide data on nitrite effluent concentrations is very limited and unavailable for emission estimation in many countries. Hence, we propose a countrywide emission factor calculated from the weighted EFs of three WWTP categories (carbon removal, EF: 0.1-8%, nitrification only: 1.8%, and full nitrogen removal: 0.9%). However, EF of carbon removal WWTPs are still highly uncertain given the expected variability in performance.
The newly developed approach allows representative, country-specific estimations of the N2O emissions from WWTP. Applied to Switzerland, the estimations result in an average EF of 0.9 to 3.6% and total emissions of 410 to 1690 tN2O-N/year, which corresponds to 0.3-1.4% of the total greenhouse gas emissions in Switzerland. Our results demonstrate that better data availability and an improved understanding of long-term monitoring campaigns is crucial to improve current emission estimations. Finally, our results confirm several measures to mitigate N2O emissions from wastewater treatment; year-round denitrification, limiting nitrite accumulation, and stringent control of sludge age in carbon removal plants.
Gruber, W., Niederdorfer, R., Ringwald, J., Morgenroth, E., Bürgmann, H., & Joss, A. (2021). Linking seasonal N2O emissions and nitrification failures to microbial dynamics in a SBR wastewater treatment plant. Water Research X, 11, 100098 (13 pp.). doi:10.1016/j.wroa.2021.100098, Institutional Repository

Nitrous oxide (N2O) is a strong greenhouse gas and causal for stratospheric ozone depletion. During biological nitrogen removal in wastewater treatment plants (WWTP), high N2O fluxes to the atmosphere can occur, typically exhibiting a seasonal emission pattern. Attempts to explain the peak emission phases in winter and spring using physico-chemical process data from WWTP were so far unsuccessful and new approaches are required. The complex and diverse microbial community of activated sludge used in biological treatment systems also exhibit substantial seasonal patterns. However, a potentially causal link between the seasonal patterns of microbial diversity and N2O emissions has not yet been investigated. Here we show that in a full-scale WWTP nitrification failure and N2O peak emissions, bad settleability of the activated sludge and a turbid effluent strongly correlate with a significant reduction in the microbial community diversity and shifts in community composition. During episodes of impaired performance, we observed a significant reduction in abundance for filamentous and nitrite oxidizing bacteria in all affected reactors. In some reactors that did not exhibit nitrification and settling failures, we observed a stable microbial community and no drastic loss of species. Standard engineering approaches to stabilize nitrification, such as increasing the aerobic sludge age and oxygen availability failed to improve the plant performance on this particular WWTP and replacing the activated sludge was the only measure applied by the operators to recover treatment performance in affected reactors. Our results demonstrate that disturbances of the sludge microbiome affect key structural and functional microbial groups, which lead to seasonal N2O emission patterns. To reduce N2O emissions from WWTP, it is therefore crucial to understand the drivers that lead to the microbial population dynamics in the activated sludge.
Gruber, W. J. (2021). Long-term N2O emission monitoring in biological wastewater treatment: methods, applications and relevance (Doctoral dissertation). doi:10.3929/ethz-b-000537321, Institutional Repository

Nitrous oxide (N2O) emissions substantially contribute to global, environmental issues: climate change and stratospheric ozone depletion. Wastewater treatment plants (WWTPs) are potent point sources and significant contributors to anthropogenic N2O emissions. However, emissions are currently underestimated in most greenhouse gas inventories due to overly simplified emission processes of WWTPs in the IPCC guidelines. Key limitations towards more realistic estimations are the low availability of representative monitoring campaigns and a limited understanding of N2O formation mechanism during biological nitrogen removal in WWTPs. In particular, N2O emission patterns assessed in long-term full-scale monitoring campaigns have shown strong seasonal variations, highlighting the requirement for long-term monitoring campaigns as basis for representative emission factor estimation. But underlying causes for the seasonal dynamics are unclear. Therefore, this thesis investigated (i) methods for long-term emission monitoring and the assessment of representative emission factors (EFs), (ii) methodologies for a more realistic estimation of countrywide N2O emissions and (iii) causes of the seasonal emission pattern to ultimately propose mitigation measures. [...]

Lachgasemissionen (N2O) tragen substantiell zu bedeutenden, globalen Umweltproblemen bei: dem Klimawandel und der stratosphärischen Zerstörung von Ozon. Kläranlagen (ARAs) sind relevante N2O Punktquellen und verursachen einen relevanten Teil der anthropogenen Emissionen. Gegenwärtig werden die N2O Emissionen aus ARAs in den meisten Treibhausgasinventaren jedoch unterschätzt, da die Emissionsprozesse in den üblicherweise verwendeten IPCC Richtlinien unzureichend abgebildet werden. Die Hauptgründe dafür sind eine limitierte Verfügbarkeit an repräsentativen Langzeitdaten und ein fehlendes Verständnis der N2O Bildung während der biologischen Stickstoffelimination auf ARAs. Insbesondere die Ursachen für die saisonale Variabilität der Emission sind unbekannt. Die hohe Variabilität im Jahresverlauf unterstreicht die Notwendigkeit von Langzeitmess-kampagnen als Grundlage für eine repräsentative Schätzung der Emissionsfaktoren. Deshalb hatte die vorliegende Doktorarbeit folgende Zielsetzung: (i) Entwicklung und Anwendung einer Methode zur langfristigen Emissions-überwachung und zur Abschätzung repräsentativer Emissionsfaktoren (EFs), (ii) Erarbeitung eine Methode für eine realistischere Abschätzung der landesweiten N2O Emissionen ARAs sowie (iii) Charakterisierung von ursächlichen Faktoren für die saisonale Variabilität, um schließlich Maßnahmen zur Emissionsminderung vorzuschlagen. [...]
Hausherr, D., Niederdorfer, R., Morgenroth, E., & Joss, A. (2021). Robustness of mainstream anammox activity at bench and pilot scale. Science of the Total Environment, 796, 148920 (11 pp.). doi:10.1016/j.scitotenv.2021.148920, Institutional Repository

New technologies and processes, such as mainstream anammox, aim to reduce energy requirements of wastewater treatment and improve effluent quality. However, in municipal wastewater (MWW) anammox system are often unstable due to process control disturbance, influent variability, or unwanted nitrite oxidizing bacteria (NOB). This study examines the anammox system by focusing on anammox activity and its robustness in a mainstream environment. An 8 m3 pilot-scale sequencing batch reactor (SBR) receiving pretreated MWW (with external nitrite addition) was seeded with pre-colonized carriers. Within six months at 12–20 °C an anammox activity of 200 gN·m−3·d−1 was achieved. After the startup an anammox activity of 260 ± 83 gN·m−3·d−1 was maintained over 450 days. The robustness of the anammox activity was analyzed through three disturbance experiments. Anammox biofilm on carriers were exposed to dissolved oxygen (DO = 1.6 mg·L−1, intermittent aeration), organic loading rate (OLR, C/N increased from 2:1 to 5:1) and temperature disturbances (20 °C to 12 °C) in triplicate 12 L bench scale reactors. The anammox activity and microbial community was monitored during these disturbances. The DO and OLR disturbance experiments were replicated at pilot scale to investigate upscaling effects. Bench and pilot scale anammox activity were unaffected by the DO disturbance. Similarly, an increase in OLR did not deteriorate the bench and pilot scale anammox activity, if nitrate was available. When, at bench scale, the reactor temperature was reduced from 20 °C to 12 °C overnight, anammox activity decreased significantly, this was not the case for the slow seasonal temperature changes (12–25 °C) at pilot scale where no strong temperature dependency was detected in winter. Metagenomic analysis revealed a broad range of Brocadiaceae species with no single dominant anammox species. Anammox thrive under mainstream conditions and can withstand typical process disruptions.
Hess, A., & Morgenroth, E. (2021). Biological activated carbon filter for greywater post-treatment: Long-term TOC removal with adsorption and biodegradation. Water Research X, 13, 100113 (9 pp.). doi:10.1016/j.wroa.2021.100113, Institutional Repository

Biological activated carbon (BAC) filters can be used to remove residual total organic carbon (TOC) from greywater after a membrane bioreactor. The two main TOC removal processes are adsorption to the granular activated carbon (GAC) and biological degradation. Biodegradation leads to the growth of microorganisms in the filter bed, which can lead to increased pressure loss over the filter bed. However, the roles of sorption and biodegradation in long-term TOC removal and how they complement each other are unclear. We monitored TOC removal from greywater in a BAC filter installed following a membrane bioreactor over more than 900 days. Removal performance depended on the operational time of the BAC filter, the influent TOC concentration, and in the upper part of the filter on the empty bed contact time (EBCT). Across the overall filter, the EBCT did not significantly influence TOC removal, showing that the filter was sufficiently large for the range of flow rates observed. Analysis of the long-term data revealed the equal importance of sorption and biodegradation over the whole operation period and the whole filter bed. Most of the TOC was removed in the upper part of the filter, where biodegradation was the dominant mechanism. In the lower part of the filter, sorption capacity remained and allowed high influent TOC concentrations to be buffered. The generous filter design with low average filtration rates ensured long-term TOC removal. The only maintenance needed was backwashing, which was required only after more than 800 days of operation. Backwashing effectively reduced the pressure loss but had no significant influence on the effluent water quality. Our study shows that BAC filters are a suitable post-treatment step for the treatment of greywater with highly variable flow and TOC concentrations.
Hess, A., Baum, C., Schiessl, K., Besmer, M. D., Hammes, F., & Morgenroth, E. (2021). Stagnation leads to short-term fluctuations in the effluent water quality of biofilters: a problem for greywater reuse?. Water Research X, 13, 100120 (9 pp.). doi:10.1016/j.wroa.2021.100120, Institutional Repository

A key characteristic of decentralized greywater treatment and reuse is high variability in both nutrient concentrations and flow. This variability in flow leads to stagnant water in the system and causes short-term fluctuations in the effluent water quality. Automated monitoring tools provide data to understand the mechanisms underlying the dynamics and to adapt control strategies accordingly. We investigated the fluctuations in a building-scale greywater treatment system comprising a membrane bioreactor followed by a biological activated carbon filter. Short-term dynamics in the effluent of the biological activated carbon filter were monitored with automated flow cytometry and turbidity, and the impact of these fluctuations on various hygiene-relevant parameters in the reuse water was evaluated. Continuous biofilm detachment into the stagnant water in the biological activated carbon filter led to temporarily increased turbidity and cell concentrations in the effluent after periods of stagnation. The fluctuations in cell concentrations were consistent with a model assuming higher detachment rates during flow than during times with stagnant water. For this system, total cell concentration and turbidity were strongly correlated. We also showed that the observed increase in cell concentration was not related to either an increase of organic carbon concentration or the concentration of two opportunistic pathogens, P. aeruginosa and L. pneumophila. Our findings demonstrate that turbidity measurements are sensitive to changes in the effluent water quality and can be used to monitor the fluctuations caused by intermittent flow. Intermittent flow did not lead to an increase in opportunistic pathogens, and this study provides no indications that stagnant water in biological activated carbon filters need be prevented.
Reynaert, E., Hess, A., & Morgenroth, E. (2021). Making waves: why water reuse frameworks need to co-evolve with emerging small-scale technologies. Water Research X, 11, 100094 (5 pp.). doi:10.1016/j.wroa.2021.100094, Institutional Repository

Novel technologies allow to reuse or recycle water for on-site applications such as toilet flushing, showering, or hand washing at the household- or building-scale. Many of these technologies have now reached technology readiness levels that require for verification and validation testing in the field. Results from such field tests of decentralized water reuse systems have been published over the past few years, and observed performance is often compared to quality targets from water reuse frameworks (WRFs). An inspection of ten recent journal publications reveals that targets from WRFs are often misinterpreted, and the emphasis of these publications is too often on demonstrating successful aspects of the technologies rather than critically evaluating the quality of the produced water. We hypothesize that some of these misinterpretations are due to ambiguous definition of scopes of WRFs (e.g., "unrestricted urban reuse") and unclear applicability for novel recycling systems that treat the water for applications that go beyond the reuse scopes defined in current WRFs. Additional challenges are linked to the verification of WRF quality targets in small-scale and decentralized systems under economic and organizational constraints. Current WRFs are not suitable for all possible reuse cases, and there is need for a critical discussion of quality targets and associated monitoring methods. As the scope of water reuse has expanded greatly over the past years, WRFs need to address new applications and advances in technology, including in monitoring capacities.
Riechmann, M. E., Ndwandwe, B., Greenwood, E. E., Reynaert, E., Morgenroth, E., & Udert, K. M. (2021). On-site urine treatment combining Ca(OH)2 dissolution and dehydration with ambient air. Water Research X, 13, 100124 (12 pp.). doi:10.1016/j.wroa.2021.100124, Institutional Repository

We present the results of three field tests and three laboratory tests of a new physical-chemical urine treatment system, which can recover all nutrients, while pathogens are inactivated. The system consists of two steps. In the first reactor, biological processes including urea hydrolysis are prevented by mixing fresh urine with calcium hydroxide (Ca(OH)2). Due to the high pH value and the high availability of calcium, phosphate can be recovered by precipitation. The high pH value also fosters the inactivation of microorganisms, including pathogens. In the second reactor, water is evaporated at low energy consumption by blowing unheated ambient air over the stabilized urine. Stabilization in the first reactor was successful in all field and laboratory tests. The pH value remained between 12 and 13, except for short dips due to shortages of Ca(OH)2. Nearly all phosphorus (92-96%) precipitated and could be recovered as calcium phosphate in the first reactor, while nitrogen and potassium overflowed with the urine into the evaporation reactor. The efficiency of the second treatment step was very different for field and laboratory experiments and depended on the duration of the experiment. During a four-day laboratory test, nitrogen recovery was 98%. In contrast, nitrogen recovery was only around 20% in the long-term field experiments. The high nitrogen losses occurred, because biological urea hydrolysis was not inhibited anymore, when the pH value in the second reactor decreased due to the dissolution of high amounts of carbon dioxide from the ambient air. Potassium was not subject to any significant loss, and the measured recovery in the solid evaporation product was 98%. Evaporation rates ranged between 50 g m-2 h-1 (RH = 82±13%, T = 12±6°C) and 130 g m-2 h-1 (RH = 60±19%, T = 24±5°C) in the three field tests. Apart from some disturbances due to low supply of Ca(OH)2, the urine module functioned without any substantial failures and was simple to maintain. The minimum consumption of Ca(OH)2 at full capacity was 6 g·L-1 urine and the electricity demand was 150 Wh kg-1 water evaporated from urine, resulting in operational costs of 0.05 EUR pers-1 d-1.
Russo, S., Besmer, M. D., Blumensaat, F., Bouffard, D., Disch, A., Hammes, F., … Villez, K. (2021). The value of human data annotation for machine learning based anomaly detection in environmental systems. Water Research, 206, 117695 (10 pp.). doi:10.1016/j.watres.2021.117695, Institutional Repository

Anomaly detection is the process of identifying unexpected data samples in datasets. Automated anomaly detection is either performed using supervised machine learning models, which require a labelled dataset for their calibration, or unsupervised models, which do not require labels. While academic research has produced a vast array of tools and machine learning models for automated anomaly detection, the research community focused on environmental systems still lacks a comparative analysis that is simultaneously comprehensive, objective, and systematic. This knowledge gap is addressed for the first time in this study, where 15 different supervised and unsupervised anomaly detection models are evaluated on 5 different environmental datasets from engineered and natural aquatic systems. To this end, anomaly detection performance, labelling efforts, as well as the impact of model and algorithm tuning are taken into account. As a result, our analysis reveals the relative strengths and weaknesses of the different approaches in an objective manner without bias for any particular paradigm in machine learning. Most importantly, our results show that expert-based data annotation is extremely valuable for anomaly detection based on machine learning.
Sutherland, C., Reynaert, E., Sindall, R. C., Riechmann, M. E., Magwaza, F., Lienert, J., … Udert, K. M. (2021). Innovation for improved hand hygiene: field testing the Autarky handwashing station in collaboration with informal settlement residents in Durban, South Africa. Science of the Total Environment, 796, 149024 (13 pp.). doi:10.1016/j.scitotenv.2021.149024, Institutional Repository

Safe and accessible water services for hand hygiene are critical to human health and well-being. However, access to handwashing facilities is limited in cities in the Global South, where rapid urbanisation, service backlogs, lack of infrastructure and capacity, and water scarcity impact on the ability of local governments to provide them. Community participation and the co-production of knowledge in the development of innovative technologies, which are aligned with Water, Sanitation and Hygiene (WASH) principles, can lead to more sustainable and socially-acceptable hand hygiene systems. This paper presents the outcomes of the testing of the Autarky handwashing station, a technology that provides onsite treatment and recycling of handwashing water, in an informal settlement in Durban, South Africa. The transdisciplinary research approach adopted enabled the participation of multiple stakeholders with different knowledge systems in the framing, testing and evaluation of the system. The process of co-producing knowledge, as well as the outcomes of the testing, namely high levels of functionality and social acceptability of the technology, supported the WASH principles. The evaluation revealed that the Autarky handwashing station is a niche intervention that improved access to safe and appealing handwashing facilities in an informal settlement. Its novel design, socially desirable features, reliability and ability to save water increased its acceptance in the community. The testing of the system in a real-world context revealed the value of including communities in knowledge production processes for technology innovation. Further work is required to ensure that real-time monitoring of system function is feasible before such systems can be implemented at larger scale.
Sutherland, C., Reynaert, E., Dhlamini, S., Magwaza, F., Lienert, J., Riechmann, M. E., … Sindall, R. C. (2021). Socio-technical analysis of a sanitation innovation in a peri-urban household in Durban, South Africa. Science of the Total Environment, 755, 143284 (12 pp.). doi:10.1016/j.scitotenv.2020.143284, Institutional Repository

The provision of water and sanitation for all that is safe, dignified, reliable, affordable and sustainable is a major global challenge. While centralized sewer-based sanitation systems remain the dominant approach to providing sanitation, the benefits of non-sewered onsite sanitation systems are increasingly being recognised. This paper presents the outcomes of the testing of the Blue Diversion Autarky Toilet (BDAT), a sanitation system providing hygiene and dignity without relying on water and wastewater infrastructure, in a peri-urban household in Durban, South Africa. The BDAT was used by a single household as their only form of sanitation during three months of technical and social testing. An analysis based on technical data in combination with interpretive, qualitative research methods revealed that the BDAT functioned well and achieved high levels of social acceptance in the test household. The flushing, cleanliness and odour-free nature of the sanitation technology, its functionality, the household's previous sanitation experience, and their experience with and understanding of water scarcity, were the main factors underpinning their positive response to this innovation in sanitation. The testing process resulted in broader developmental benefits for the household, including improved basic services due to the upgrading of the electrical and existing sanitation system, social learning, and improved relationships between household members and the local state. A transdisciplinary research process, which emerged through the assessment, enabled the integration of different forms of knowledge from multiple actors to address the complexity of problems related to the development of socially just sanitation. The benefit of engaging with societal actors in sanitation innovation and assessing its outcomes using both the technical and social sciences is evident in this paper.
Tang, X., Pronk, W., Traber, J., Liang, H., Li, G., & Morgenroth, E. (2021). Integrating granular activated carbon (GAC) to gravity-driven membrane (GDM) to improve its flux stabilization: respective roles of adsorption and biodegradation by GAC. Science of the Total Environment, 768, 144758 (10 pp.). doi:10.1016/j.scitotenv.2020.144758, Institutional Repository

As a low-maintenance and cost-effective process, gravity-driven membrane (GDM) filtration is a promising alternative for decentralized drinking water supply, while the low flux impedes its extensive application. In order to address such issue, an integrated process consisting of granular activated carbon (GAC) layer and GDM was developed. The performance of virgin (fresh GAC) or preloaded GAC (saturated GAC) was compared. Flux stabilization was observed both in the fresh and saturated GAC/GDM process during long-term filtration and their stable fluxes were both improved by approximately 50% relative to the GDM control. Moreover, integrating GAC with GDM contributed to efficient removals for dissolved organic compounds (DOC), assimilable organic carbon (AOC) and low molecular weight substances both in fresh and saturated GAC/GDM filtration. Compared to GDM control, coupling GAC to GDM could significantly reduce the concentrations of extracellular polymeric substances (EPS) and total cell counts (TCC) within the biofouling layer, and engineer highly heterogeneous structures of biofouling layer on the membrane surface. In the fresh GAC/GDM process, the improved flux obtained was mainly related to less coverage of biofouling layer and lower EPS concentrations due to efficient removals of membrane foulants by GAC adsorption. The achieved higher stable flux can be maintained during long-term filtration (after GAC saturation) owing to the combined effects of EPS reduction and formation of highly heterogeneous structures of biofouling layer in the saturated GAC/GDM system. Overall, the integrated GAC/GDM process can hopefully facilitate improvements both in the stabilized flux and permeate quality, with practical relevance for GDM applications in decentralized drinking water supply.
Ward, B. J., Andriessen, N., Tembo, J. M., Kabika, J., Grau, M., Scheidegger, A., … Strande, L. (2021). Predictive models using "cheap and easy" field measurements: can they fill a gap in planning, monitoring, and implementing fecal sludge management solutions?. Water Research, 196, 116997 (12 pp.). doi:10.1016/j.watres.2021.116997, Institutional Repository

The characteristics of fecal sludge delivered to treatment plants are highly variable. Adapting treatment process operations accordingly is challenging due to a lack of analytical capacity for characterization and monitoring at many treatment plants. Cost-efficient and simple field measurements such as photographs and probe readings could be proxies for process control parameters that normally require laboratory analysis. To investigate this, we evaluated questionnaire data, expert assessments, and simple analytical measurements for fecal sludge collected from 421 onsite containments. This data served as inputs to models of varying complexity. Random forest and linear regression models were able to predict physical-chemical characteristics including total solids (TS) and ammonium (NH4+-N) concentrations, and solid-liquid separation performance including settling efficiency and filtration time (R2 from 0.51-0.66) based on image analysis of photographs (sludge color, supernatant color, and texture) and probe readings (conductivity (EC) and pH). Supernatant color was the best predictor of settling efficiency and filtration time, EC was the best predictor of NH4+-N, and texture was the best predictor of TS. Predictive models have the potential to be applied for real-time monitoring and process control if a database of measurements is developed and models are validated in other cities. Simple decision tree models based on the single classifier of containment type can also be used to make predictions about citywide planning, where a lower degree of accuracy is required.
Wielinski, J., Gogos, A., Voegelin, A., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Release of gold (Au), silver (Ag) and cerium dioxide (CeO2) nanoparticles from sewage sludge incineration ash. Environmental Science: Nano, 8(11), 3220-3232. doi:10.1039/D1EN00497B, Institutional Repository

Engineered nanoparticles (NPs) that are released into wastewater are retained by wastewater treatment plants (WWTPs) and accumulate in sewage sludge. Increasing shares of sludge are incinerated and landfilled, especially in industrialized countries. It is debated whether certain types of NPs can outlive the incineration process and subsequently be released from sewage sludge ash (SSA) landfills. To investigate the release of different types of NPs from SSA, we spiked gold (Au), silver (Ag) and cerium dioxide (CeO2) NPs to a pilot WWTP increasing the Au, Ag and Ce concentrations to 30, 43 and 389 mg kg-1 (dry matter basis) in the digested sludge. The spiked sludge was incinerated in a pilot fluidized bed reactor resulting in SSA with Au, Ag and Ce concentrations of 61, 103 and 854 mg kg-1. In addition, two sludge samples from a full-scale WWTP with Au concentrations of 5 and 16 mg kg-1 were incinerated, resulting in SSA with 9 mg kg-1 and 30 mg kg-1 Au. The spiked Au-NPs remain largely unaltered during the wastewater treatment and incineration process, whereas Ag-NPs and CeO2-NPs undergo transformation. During simulated landfill leaching in columns flushed with 400 to 500 pore volumes of artificial rainwater, Ag and Ce were retained in the ash, whereas about 17% of the spiked Au was released, mainly in particulate form. Lower fractions of mostly particulate Au were released from the ashes (3 and 9%) of unspiked SSA. In conclusion, unaltered Au-NPs significantly leach from landfilled SSA, whereas the incorporation of Ag-NPs and CeO2-NPs as transformed species into the SSA matrix limits the leaching of (nano)particulate and dissolved Ag and Ce compounds.
Wielinski, J., Voegelin, A., Grobéty, B., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Transformation of TiO2 (nano)particles during sewage sludge incineration. Journal of Hazardous Materials, 411, 124932 (14 pp.). doi:10.1016/j.jhazmat.2020.124932, Institutional Repository

Titanium dioxide (TiO2) (nano)particles are produced in large quantities and their potential impacts on ecosystems warrants investigations into their fate after disposal. TiO2 particles released into wastewater are retained by wastewater treatment plants and accumulate in digested sludge, which is increasingly incinerated in industrialized countries. Therefore, we investigated the changes of the Ti-speciation during incineration of as-received sludge and of sludge spiked with anatase (d=20–50 nm) or rutile (d=200–400 nm) using X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). In the as-received sludge, rutile and anatase were the dominant Ti bearing minerals and both remained unaffected by the anaerobic treatment. During incineration, Ti reacts with hematite to members of the hematite-ilmenite solid solution series (Hem-Ilm). Up to 80% of the Ti spiked as anatase transformed into Hem-Ilm, a distorted 6-fold coordinated Ti (Ti(IV)sulfate) and rutile during incineration. Up to 30% and 60% of rutile transformed into Hem-Ilm and Ti(IV)sulfate represented phases in fly and bottom ash, respectively. Fe and Ti were spatially correlated in ash derived from as-received and anatase spiked sludge, whereas only a thin layer of the spiked rutile reacted with Fe, in line with XAS data. This study highlights the transient nature of nano-Ti species during sewage sludge incineration.
Ziemba, C., Sharma, P., Ahrens, T., Reynaert, E., & Morgenroth, E. (2021). Disruptions in loading and aeration impact effluent chlorine demand during biological greywater recycling. Water Research X, 11, 100087 (10 pp.). doi:10.1016/j.wroa.2020.100087, Institutional Repository

Greywater recycling systems designed for high-quality applications, such as hand washing, must deliver microbially safe and aesthetically acceptable water under the challenging operating conditions present where such systems are needed most urgently. As chlorination is the most popular strategy for reducing bacterial concentrations in greywater, understanding chlorination in the context of disruptive and challenging operation is essential to designing robust treatment. In this study, we have examined how disruptions through overall increased loading, interrupted aeration and increased ammonia loading have impacted the chlorine demand of the water produced by a greywater recycling system. We also presented concentrations of significant chemicals that contributed to this chlorine demand. The results indicate that a 1 d period with 8 times (8x) the normal design loading produced a peak chlorine demand of 0.74 mg Cl2/L, which is approximately double the baseline value. While this chlorine demand can be overcome by adding more chlorine, tests involving disruptions in aeration or feeding additional ammonia into the bioreactor produced much greater increases (>30x). The risks of increased chlorine demand on microbial safety can be overcome by limiting ammonia inputs to the system, providing backup systems to ensure sufficient aeration, or through additional anti-bacterial measures that do not depend on maintaining residual chlorine.
Bogler, A., Packman, A., Furman, A., Gross, A., Kushmaro, A., Ronen, A., … Bar-Zeev, E. (2020). Rethinking wastewater risks and monitoring in light of the COVID-19 pandemic. Nature Sustainability, 3, 981-990. doi:10.1038/s41893-020-00605-2, Institutional Repository

The COVID-19 pandemic has severely impacted public health and the worldwide economy. Converging evidence from the current pandemic, previous outbreaks and controlled experiments indicates that SARS-CoVs are present in wastewater for several days, leading to potential health risks via waterborne and aerosolized wastewater pathways. Conventional wastewater treatment provides only partial removal of SARS-CoVs, thus safe disposal or reuse will depend on the efficacy of final disinfection. This underscores the need for a risk assessment and management framework tailored to SARS-CoV-2 transmission via wastewater, including new tools for environmental surveillance, ensuring adequate disinfection as a component of overall COVID-19 pandemic containment.
Doll, C., Larsen, T. A., Strande, L., Udert, K. M., & Morgenroth, E. (2020). Water Hub im NEST-Gebäude. Eine Plattform zum Testen von innovativen ressourcenorientierten Sanitärsystemen. Aqua & Gas, 100(2), 52-57. , Institutional Repository

Mit innovativen Technologien werden im Water Hub unter realen Bedingungen Ressourcen aus dem Abwasser gewonnen und Kreisläufe geschlossen. Die Forschung in diesem Living Lab erlaubt es, praxisnahe Erfahrungen zu machen, Schwachstellen schnell zu identifizieren und das System zu optimieren. Bei der Implementierung dieser dezentralen Technologien spielen die lokalen Herausforderungen und Begebenheiten stets eine wichtige Rolle.
Hadengue, B., Scheidegger, A., Morgenroth, E., & Larsen, T. A. (2020). Modeling the water-energy nexus in households. Energy and Buildings, 225, 110262 (10 pp.). doi:10.1016/j.enbuild.2020.110262, Institutional Repository

One third of the global carbon emissions are emitted by the building sector. Over the last decades, space heating loads have decreased in modern buildings, and domestic hot water (DHW) is now oftentimes the largest energy consumer in the household. We developed the WaterHub modeling framework to assess the potential of technologies or measures targeting DHW energy demand. The framework combines process-based technological models and stochastic water demand modeling in a modular way to allow for holistic simulations of complex DHW systems. In two rigorous tests of the modeling framework, we demonstrated the importance of water consumption dynamics in the modeling of DHW systems, showing that static modeling leads to underestimated heat losses and wrong energy consumption predictions. In an exemplary case study, we identified and quantified the synergistic interactions between water boiler temperatures and a drain water heat recovery device, demonstrating the strength of this methodology for optimizing strategies targeting DHW systems. With its modular structure, this open-source modeling framework can be extended to include any DHW-related technology, providing a useful common platform for collaboration between technology developers and water experts.
Helleshøj Sørensen, K., & Morgenroth, E. (2020). Biofilm reactors. In G. Chen, G. A. Ekama, M. C. M. van Loosdrecht, & D. Brdjanovic (Eds.), Biological wastewater treatment: principles, modeling and design (pp. 813-839). London: IWA Publishing. , Institutional Repository
Hess, A., Bettex, C., & Morgenroth, E. (2020). Influence of intermittent flow on removal of organics in a biological activated carbon filter (BAC) used as post-treatment for greywater. Water Research X, 9, 100078 (10 pp.). doi:10.1016/j.wroa.2020.100078, Institutional Repository

Highly variable flow has to be expected in decentralized greywater treatment and can lead to intermittent operation of the treatment system. However, few studies have addressed the influence of variable flow on the treatment performance of a biological activated carbon filter (BAC). In this study, we investigated the influence of intermittent flow using small-scale BAC columns, which treat greywater as a second treatment step following a membrane bioreactor (MBR). Three operating strategies to respond to variable flow were evaluated. The activated carbon was characterized before and after the experiments in terms of biological activity and sorption capacity. The performance of the BAC filters was assessed based on total organic carbon (TOC) removal, TOC fractions and growth potential. No significant differences were observed between constant flow compared to on-off operation with intermittent flow over the range of tested influent concentrations. Peaks with high TOC during 24 h periods were attenuated by sorption and biological degradation. Adsorbed TOC was released after switching back to normal concentrations for influent concentrations more than 5 times higher than usually observed, the BAC functioned as a temporary sink. In line with these results, the high influent TOC values led to increased biological activity in the filter but did not influence the sorption capacity. The experiments showed that intermittent flow does not negatively impact the performance of a BAC and that there is no need for additional equalization tanks to buffer the variable flow, for example in household-scale greywater treatment.
Hoffmann, S., Feldmann, U., Bach, P. M., Binz, C., Farrelly, M., Frantzeskaki, N., … Udert, K. M. (2020). A research agenda for the future of urban water management: exploring the potential of non-grid, small-grid, and hybrid solutions. Environmental Science and Technology, 54(9), 5312-5322. doi:10.1021/acs.est.9b05222, Institutional Repository

Recent developments in high- and middle-income countries have exhibited a shift from conventional urban water systems to alternative solutions that are more diverse in source separation, decentralization, and modularization. These solutions include non-grid, small-grid, and hybrid systems to address such pressing global challenges as climate change, eutrophication, and rapid urbanization. They close loops, recover valuable resources, and adapt quickly to changing boundary conditions such as population size. Moving to such alternative solutions requires both technical and social innovations to co-evolve over time into integrated socio-technical urban water systems. Current implementations of alternative systems in high- and middle-income countries are promising, but they also underline the need for research questions to be addressed from technical, social, and transformative perspectives. Future research should apply a transdisciplinary research approach through socio-technical "lighthouse" projects that apply alternative urban water systems at scale. Such research should leverage experience from lighthouse projects in a range of socio-economic contexts, identify their potentials and limitations from an integrated perspective, and share their successes and failures across the urban water sector.
Jacquin, C., Yu, D., Sander, M., Domagala, K. W., Traber, J., Morgenroth, E., & Julian, T. R. (2020). Competitive co-adsorption of bacteriophage MS2 and natural organic matter onto multiwalled carbon nanotubes. Water Research X, 9, 100058 (12 pp.). doi:10.1016/j.wroa.2020.100058, Institutional Repository

A leading challenge in drinking water treatment is to remove small-sized viruses from the water in a simple and efficient manner. Multi-walled carbon nanotubes (MWCNT) are new generation adsorbents with previously demonstrated potential as filter media to improve virus removal. This study therefore aimed to evaluate the field applicability of MWCNT-filters for virus removal in water containing natural organic matter (NOM) as co-solute to viruses, using batch equilibrium experiments. Contrary to previous studies, our results showed with MS2 bacteriophages single-solute systems that the affinity of MWCNT for MS2 was low, since after 3 h of equilibration only 4 log10 reduction value (LRV) of MS2 (20 mL at an initial concentration of 106 PFU MS2/mL) were reached. Single solute experiments with Suwannee river NOM (SRNOM) performed with environmentally-relevant concentrations showed MWCNT surface saturation at initial SRNOM concentrations between 10 and 15 mgC/L, for water pH between 5.2 and 8.7. These results suggested that at NOM:virus ratios found in natural waters, the NOM would competitively suppress virus adsorption onto MWCNT, even at low NOM concentrations. We confirmed this expectation with SRNOM-MS2 co-solute experiments, which showed an exponential decrease of the MS2 LRV by MWCNT with an increase in the initial SRNOM concentration. More interestingly, we showed that pre-equilibrating MWCNT with a SRNOM solution at a concentration as low as 0.4 mgC/L resulted in a LRV decrease of 3 for MS2, due to the formation of a negatively charged SRNOM adlayer on the MWCNT surface. Complementary batch experiments with natural NOM-containing waters and competition experiments with SRNOM in the presence of CaCl2 confirmed that the presence of NOM in waters challenges virus removal by MWCNT-filters, irrespective of the concentration and type of NOM and also in the presence of Ca2+. We therefore conclude that MWCNT-filters produced with commercially available pristine MWCNT cannot be considered as a viable technology for drinking water virus removal.
Jimenez, J., Charnier, C., Kouas, M., Latrille, E., Torrijos, M., Harmand, J., … Steyer, J. P. (2020). Modelling hydrolysis: simultaneous versus sequential biodegradation of the hydrolysable fractions. Waste Management, 101, 150-160. doi:10.1016/j.wasman.2019.10.004, Institutional Repository

Hydrolysis is considered the limiting step during solid waste anaerobic digestion (including co-digestion of sludge and biosolids). Mechanisms of hydrolysis are mechanistically not well understood with detrimental impact on model predictive capability. The common approach to multiple substrates is to consider simultaneous degradation of the substrates. This may not have the capacity to separate the different kinetics. Sequential degradation of substrates is theoretically supported by microbial capacity and the composite nature of substrates (bioaccessibility concept). However, this has not been experimentally assessed. Sequential chemical fractionation has been successfully used to define inputs for an anaerobic digestion model. In this paper, sequential extractions of organic substrates were evaluated in order to compare both models. By removing each fraction (from the most accessible to the least accessible fraction) from three different substrates, anaerobic incubation tests showed that for physically structured substrates, such as activated sludge and wheat straw, sequential approach could better describe experimental results, while this was less important for homogeneous materials such as pulped fruit. Following this, anaerobic incubation tests were performed on five substrates. Cumulative methane production was modelled by the simultaneous and sequential approaches. Results showed that the sequential model could fit the experimental data for all the substrates whereas simultaneous model did not work for some substrates.
Layer, M., Garcia Villodres, M., Hernandez, A., Reynaert, E., Morgenroth, E., & Derlon, N. (2020). Limited simultaneous nitrification-denitrification (SND) in aerobic granular sludge systems treating municipal wastewater: mechanisms and practical implications. Water Research X, 7, 100048 (13 pp.). doi:10.1016/j.wroa.2020.100048, Institutional Repository

Simultaneous nitrification-denitrification (SND) is, in theory, a key advantage of aerobic granular sludge systems over conventional activated sludge systems. But practical experience and literature suggests that SND and thus total nitrogen removal are limited during treatment of municipal wastewater using AGS systems. This study thus aims at quantifying the extent and understanding the mechanisms of SND during treatment of municipal wastewater with aerobic granular sludge (AGS) systems. Experiments (long-term and batch-tests) as well as mathematical modelling were performed. Our experimental results demonstrate that SND is significantly limited during treatment of low-strength municipal wastewater with AGS systems (14-39%), while almost full SND is observed when treating synthetic influent containing only diffusible substrate (90%). Our simulations demonstrate that the main mechanisms behind limited SND are (1) the dynamics of anoxic zone formation inside the granule, (2) the diffusibility and availability of electron-donors in those zones and (3) the aeration mode. The development of anoxic zones is driven by the utilisation of oxygen in the upper layers of the granule leading to transport limitations of oxygen inside the granule; this effect is closely linked to granule size and wastewater composition. Development of anoxic zones during the aerobic phase is limited for small granules at constant aeration at bulk dissolved oxygen (DO) concentration of 2 mgO2 L-1, and anoxic zones only develop during a brief period of the aerated phase for large granules. Modelling results further indicate that a large fraction of electron-donors are actually utilised in aerobic rather than anoxic redox zones - in the bulk or at the granule surface. Thus, full SND cannot be achieved with AGS treating low strength municipal wastewater if a constant DO is maintained during the aeration phase. Optimised aeration strategies are therefore required. 2-step and alternating aeration are tested successfully using mathematical modelling and increase TN removal to 40-79%, without compromising nitrification, and by shifting electron-donor utilisation towards anoxic redox conditions.
Layer, M., Bock, K., Ranzinger, F., Horn, H., Morgenroth, E., & Derlon, N. (2020). Particulate substrate retention in plug-flow and fully-mixed conditions during operation of aerobic granular sludge systems. Water Research X, 9, 100075 (11 pp.). doi:10.1016/j.wroa.2020.100075, Institutional Repository

Particulate substrate (XB) is the major organic substrate fraction in most municipal wastewaters. However, the impact of XB on aerobic granular sludge (AGS) systems is not fully understood. This study evaluated the physical retention of XB in AGS sequencing batch reactor (SBR) during anaerobic plug-flow and then aerobic fully-mixed conditions. The influence of different sludge types and operational variables on the extent and mechanisms of XB retention in AGS SBR were evaluated. XB mass-balancing and magnetic resonance imaging (MRI) were applied. During the anaerobic plug-flow feeding, most XB was retained in the first few cm of the settled sludge bed within the interstitial voids, where XB settled and accumulated ultimately resulting in the formation of a filter-cake. Sedimentation and surface filtration were thus the dominant XB retention mechanisms during plug-flow conditions, indicating that contact and attachment of XB to the biomass was limited. XB retention was variable and influenced by the XB influent concentration, sludge bed composition and upflow feeding velocity (vww). XB retention increased with larger XB influent concentrations and lower vww, which demonstrated the importance of sedimentation on XB retention during plug-flow conditions. Hence, large fractions of influent XB likely re-suspended during aerobic fully-mixed conditions, where XB then preferentially and rapidly attached to the flocs. During fully-mixed conditions, increasing floc fractions, longer mixing times and larger XB concentrations increased XB retention. Elevated XB retention was observed after short mixing times < 60 min when flocs were present, and the contribution of flocs towards XB retention was even more pronounced for short mixing times < 5 min. Overall, our results suggest that flocs occupy an environmental niche that results from the availability of XB during aerobic fully-mixed conditions of AGS SBR. Therefore, a complete wash-out of flocs is not desirable in AGS systems treating municipal wastewater.
Morgenroth, E. (2020). Modelling biofilms. In G. H. Chen, M. C. M. van Loosdrecht, G. A. Ekama, & D. Brdjanovic (Eds.), Biological wastewater treatment. principles, modeling and design (pp. 757-812). London: IWA Publishing. , Institutional Repository
Reynaert, E., Greenwood, E. E., Ndwandwe, B., Riechmann, M. E., Sindall, R. C., Udert, K. M., & Morgenroth, E. (2020). Practical implementation of true on-site water recycling systems for hand washing and toilet flushing. Water Research X, 7, 100051 (13 pp.). doi:10.1016/j.wroa.2020.100051, Institutional Repository

On-site wastewater reuse can improve global access to clean water, sanitation and hygiene. We developed a treatment system (aerated bioreactor, ultrafiltration membrane, granular activated carbon and electrolysis for chlorine disinfection) that recycles hand washing and toilet flush water.
Three prototypes were field-tested in non-sewered areas, one in Switzerland (hand washing) and two in South Africa (hand washing, toilet flushing), over periods of 63, 74 and 94 days, respectively.
We demonstrated that the system is able to recycle sufficient quantities of safe and appealing hand washing and toilet flush water for domestic or public use in real-life applications. Chemical contaminants were effectively removed from the used water in all prototypes. Removal efficiencies were 99.7% for the chemical oxygen demand (COD), 98.5% for total nitrogen (TN) and 99.9% for phosphate in a prototype treating hand washing water, and 99.8% for COD, 95.7% for TN and 89.6% for phosphate in a prototype treating toilet flush water. While this system allowed for true recycling for the same application, most on-site wastewater reuse systems downcycle the treated water, i.e., reuse it for an application requiring lower water quality. An analysis of 18 selected wastewater reuse specifications revealed that at best these guidelines are only partially applicable to innovative recycling systems as they are focused on the downcycling of water to the environment (e.g., use for irrigation). We believe that a paradigm shift is necessary and advocate for the implementation of risk-based (and thus end-use dependent) system performance targets to evaluate water treatment systems, which recycle and not only downcycle water.
Wielinski, J. J. (2020). Investigations into the fate of engineered transition metal nano particles during sewage sludge incineration (Doctoral dissertation). doi:10.3929/ethz-b-000473625, Institutional Repository

Engineered nanoparticles (ENP) are applied in consumer products and industrial processes to increase profitability and sustainability through reduced resource consumption, e.g., TiO2-NP in sun screens, ZnO-NP in cosmetics and paints or Ag-NP and CuO-NP as anti-microbial agents. However, critical discussions about unintended, adverse effects of ENP on humans, soil- and aquatic organisms have always accompanied their usage. Therefore, investigations into the fate of ENP after their use phase are necessary to enable a reliable assessment of the risks associated with the use of such novel materials. Previous research efforts showed that after usage, large shares of ENP applied in consumer products are discharged to wastewater and transported to wastewater treatment plants (WWTPs). WWTPs retain > 95% of ENP leading to their accumulation in sewage sludge. In Switzerland, sewage sludge is incinerated preferably in mono-combustion fluidized bed reactors (FBRs) and the resulting ashes are landfilled for resource recovery in the future. To contribute to a better understanding of the fate and behavior of ENP in the urban environment, the following research questions were addressed: (i) how can the kinetics of sewage sludge devolatilization be quantified, (ii) what chemical and physical transformations of ENP occur during the sewage sludge combustion, (iii) what are the possibilities of synchrotron hard X-ray chemical imaging to study transformation products of ENP, and lastly (iv) to what extent are ENP released from sewage sludge ash landfill sites? [...]

Künstlich produzierte Nanopartikel (NP) werden in Konsumgütern und industriellen Prozessen zur Steigerung von Effizienz und Nachhaltigkeit durch reduzierten Ressourceneinsatz verwendet, z.B. TiO2-NP in Sonnencreme, ZnO-NP in Kosmetika und Farbe oder Ag-NP und CuO-NP zu antimikrobiellen Zwecken. Allerdings ist stets vor ungewollten, nachteiligen Effekten solcher NP gegenüber Menschen, sowie Boden- und Wasserorganismen gewarnt worden. Daher sind Studien über die Transformation und den Verbleib von NP nach ihrer Nutzungsphase notwendig um die oben genannten Risiken der Nutzung solcher neuartigen Materialen zuverlässig abschätzen zu können. Vorangegangene Studien haben gezeigt, dass ein grosser Teil der NP in Konsumgütern in Abwasserkanäle entlassen wird und in Abwasserreinigungsanlangen (ARAs) gelangt. ARAs halten über 95% der einkommenden NP zurück, welche folglich im Faulschlamm aufkonzentriert werden. In der Schweiz wird Faulschlamm vorzugsweise in speziell dafür errichteten Wirbelbettreaktoren verbrannt und die anfallende Asche wird von Asche aus anderen Brennstoffen getrennt deponiert um daraus in der Zukunft Ressourcen rückzugewinnen.
Um ein besseres Verständnis des Verhaltens von NP in städtischen Abwassersystemen und insbesondere während der Klärschlammverbrennung zu gewinnen, wurden die folgenden Forschungsfragen adressiert: (i)Wie lässt sich die Verbrennungskinetik von Klärschlamm quantifizieren, (ii) welche physikalischen und chemischen Transformationsprozesse unterlaufen NP während der Klärschlammverbrennung, (iii) wie können Transformationsprodukte von NP mithilfe synchrotronbasierter, chemische Bildgebung identifiziert werden und (iv) wie gross ist das Freisetzungspotential von NP aus Klärschlammaschedeponien? [...]
Wielinski, J., Marafatto, F. F., Gogos, A., Scheidegger, A., Voegelin, A., Müller, C. R., … Kaegi, R. (2020). Synchrotron hard X-ray chemical imaging of trace element speciation in heterogeneous samples: development of criteria for uncertainty analysis. Journal of Analytical Atomic Spectrometry, 35, 567-579. doi:10.1039/C9JA00394K, Institutional Repository

Synchrotron hard X-ray spectroscopy with focussing optics allows recording X-ray fluorescence (XRF) maps at energies around element specific X-ray absorption edges. Stacking multiple XRF maps along the energy axis yields chemical images that contain spatially resolved information on the speciation of the absorber in the sample matrix at the micrometre scale. Short dwell times needed to keep measurement time and radiation-induced sample changes within acceptable limits result in spectral noise that affects the uncertainty in data analysis. In this study, we develop a model to quantify the uncertainty associated with the processing of XRF image stacks using Bayesian inference. To demonstrate the potential of our approach, the model is applied to stacks of XRF maps collected around the copper (Cu) K-edge (pixel size: 3 × 3 μm2, map sizes: 500 × 500 μm2). The investigated samples include digested sewage sludge spiked with either CuO nanoparticles (NP) or dissolved CuSO4 and their corresponding ashes obtained through incineration. The chemical imaging data reveal differences in species distribution between sludge spiked with CuO NP or dissolved Cu. These differences disappear during the incineration process and the resulting ashes exhibit almost identical Cu species distribution. The uncertainty analysis approach developed in this study can be used for data interpretation, but can also be used for the planning of chemical imaging experiments at synchrotron beamlines.
Ziemba, C., Larivé, O., Reynaert, E., Huisman, T., & Morgenroth, E. (2020). Linking transformations of organic carbon to post-treatment performance in a biological water recycling system. Science of the Total Environment, 721, 137489 (8 pp.). doi:10.1016/j.scitotenv.2020.137489, Institutional Repository

Ozone, electrolysis and granular activated carbon (GAC) were examined as potential post-treatments to follow a household-scale biologically activated membrane bioreactor (BAMBi), treating a wash water containing trace urine and feces contamination. Each post-treatment was evaluated for abilities and reaction preferences to remove or transform dissolved organic carbon (DOC), chemical structures that contribute color, and assimilable organic carbon (AOC), which can support bacterial regrowth. Batch treatment with each technology demonstrated an ability to remove ≥95% DOC. Ozone demonstrated a reaction selectivity through increased reaction rates with larger compounds and color-contributing compounds. Electrolysis and GAC demonstrated generally less-selective reactivity. Adding post-treatments to full-scale systems reduced DOC (55-91%), AOC (34-62%), and color (75-98%), without significant reaction selectivity. These reductions in DOC and AOC were not linked to reduction of bacterial concentrations in treated water. Reductions in bacterial concentrations were observed with ozone and electrolysis, but this is credited to oxidation chemicals produced in these systems and not the removal or transformations of organic materials.
Hadengue, B., Scheidegger, A., Morgenroth, E., & Larsen, T. A. (2019). The waterhub modules: material and energy flow analysis of domestic hot water systems. In A. Haumer (Ed.), Linköping Electronic Conference Proceedings: Vol. 157. Proceedings of the 13th international modelica conference (pp. 639-646). doi:10.3384/ecp19157639, Institutional Repository

Domestic Hot Water (DHW) systems are large energy consumers in newly-built residential buildings. Mitigation measures involve more efficient hot water appliances and distribution systems, waste heat recovery systems, or changes in consumer habits. However, the implementation of these measures must be investigated carefully, as combinations may lead to unforeseen systemic interactions limiting their potential. In this article, we present tools to identify and optimize these interactions. The WaterHub modules were developed for Material and Energy Flow Analyses (MEFA) of domestic hot water systems. Two modules are available: (i) the WaterHub Modelica library includes models for MEFA system definition, and (ii) The HydroGen Python module provides methods for the stochastic generation of appliance-specific hydrographs, used as input data for the simulation of the system energy and water flows. First, we describe the technical aspects of these modules. Second, we provide an example of how they may be used in a didactic scenario analysis of a heat recovery device.
Jafari, M., Derlon, N., Desmond, P., van Loosdrecht, M. C. M., Morgenroth, E., & Picioreanu, C. (2019). Biofilm compressibility in ultrafiltration: a relation between biofilm morphology, mechanics and hydraulic resistance. Water Research, 157, 335-345. doi:10.1016/j.watres.2019.03.073, Institutional Repository

Poroelastic fluid-structure interaction models were coupled to experimental data to determine the effects of biofilm spatial distribution of mechanical and hydraulic properties on the biofilm hydraulic resistance and compressibility in membrane filtration processes. Biofilms were cultivated on ultrafiltration membranes for 20 and 30 days under high (0.28 bar) and low (0.06 bar) transmembrane pressure (TMP), in dead-end filtration mode. Subsequently, biofilms were subjected to a compression/relaxation cycles by step-wise TMP changes. Structural deformation of biofilms during compression was observed in-situ using optical coherence tomography.
Experimental results show that the observed increase in the biofilm hydraulic resistance during compression is not necessarily accompanied by a detectable biofilm thickness reduction. A dual-layer biofilm model with a dense base and porous top layer could explain these observed results. Because porosity controls indirectly the mechanical response of biofilms under compression, results could be described without assuming a gradient in mechanical properties within the biofilm. The biofilm surface roughness did not significantly influence the water flux in this study. However, the fraction of biofilm base layer directly exposed to bulk liquid could be a good indicator in the determination of water flux. The main implications of this study for the design and operation of low-pressure membrane systems (e.g., MF and UF with fouling layer being the main filtration resistance) lays in the selection of favorable operational TMP and biofilm morphology.
Laureni, M., Weissbrodt, D. G., Villez, K., Robin, O., de Jonge, N., Rosenthal, A., … Joss, A. (2019). Biomass segregation between biofilm and flocs improves the control of nitrite-oxidizing bacteria in mainstream partial nitritation and anammox processes. Water Research, 154, 104-116. doi:10.1016/j.watres.2018.12.051, Institutional Repository

The control of nitrite-oxidizing bacteria (NOB) challenges the implementation of partial nitritation and anammox (PN/A) processes under mainstream conditions. The aim of the present study was to understand how operating conditions impact microbial competition and the control of NOB in hybrid PN/A systems, where biofilm and flocs coexist. A hybrid PN/A moving-bed biofilm reactor (MBBR; also referred to as integrated fixed film activated sludge or IFAS) was operated at 15 °C on aerobically pre-treated municipal wastewater (23 mgNH4-N L–1). Ammonium-oxidizing bacteria (AOB) and NOB were enriched primarily in the flocs, and anammox bacteria (AMX) in the biofilm. After decreasing the dissolved oxygen concentration (DO) from 1.2 to 0.17 mgO2 L–1 - with all other operating conditions unchanged - washout of NOB from the flocs was observed. The activity of the minor NOB fraction remaining in the biofilm was suppressed at low DO. As a result, low effluent NO3– concentrations (0.5 mgN L–1) were consistently achieved at aerobic nitrogen removal rates (80 mgN L–1 d–1) comparable to those of conventional treatment plants. A simple dynamic mathematical model, assuming perfect biomass segregation with AOB and NOB in the flocs and AMX in the biofilm, was able to qualitatively reproduce the selective washout of NOB from the flocs in response to the decrease in DO-setpoint. Similarly, numerical simulations indicated that flocs removal is an effective operational strategy to achieve the selective washout of NOB. The direct competition for NO2– between NOB and AMX - the latter retained in the biofilm and acting as a "NO2-sink" - was identified by the model as key mechanism leading to a difference in the actual growth rates of AOB and NOB (i.e., μNOB < μAOB in flocs) and allowing for the selective NOB washout over a broad range of simulated sludge retention times (SRT = 6.8–24.5 d). Experimental results and model predictions demonstrate the increased operational flexibility, in terms of variables that can be easily controlled by operators, offered by hybrid systems as compared to solely biofilm systems for the control of NOB in mainstream PN/A applications.
Layer, M., Adler, A., Reynaert, E., Hernandez, A., Pagni, M., Morgenroth, E., … Derlon, N. (2019). Organic substrate diffusibility governs microbial community composition, nutrient removal performance and kinetics of granulation of aerobic granular sludge. Water Research X, 4, 100033 (16 pp.). doi:10.1016/j.wroa.2019.100033, Institutional Repository

Basic understanding of formation of aerobic granular sludge (AGS) has mainly been derived from lab-scale systems with simple influents containing only highly diffusible volatile fatty acids (VFA) as organic substrate. This study compares start-up of AGS systems fed by different synthetic and municipal wastewaters (WW), characterised by increasing complexity in terms of non-diffusible organic substrate. Four AGS reactors were started with the same inoculum activated sludge and operated for one year. The development of AGS, settling characteristics, nutrient and substrate removal performance as well as microbial community composition were monitored. Our results indicate that the higher the content of diffusible organic substrate in the WW, the faster the formation of AGS. The presence of non-diffusible organic substrate in the influent WW led to the formation of small granules and to the presence of 20–40% (% of total suspended solids) of flocs in the AGS. When AGS was fed with complex influent WW, the classical phosphorus and glycogen accumulating organisms (PAO, GAO) were outcompeted by their fermentative equivalents. Substrate and nutrient removal was observed in all reactors, despite the difference in physical and settling properties of the AGS, but the levels of P and N removal depended on the influent carbon composition. Mechanistically, our results indicate that increased levels of non-diffusible organic substrate in the influent lower the potential for microbial growth deep inside the granules. Additionally, non-diffusible organic substrates give a competitive advantage to the main opponents of AGS formation – ordinary heterotrophic organisms (OHO). Both of these mechanisms are suspected to limit AGS formation. The presented study has relevant implications for both practice and research. Start-up duration of AGS systems treating high complexity WW were one order of magnitude higher than a typical lab-scale system treating VFA-rich synthetic WW, and biomass as flocs persisted as a significant fraction. Finally, the complex synthetic influent WW – composed of VFA, soluble fermentable and particulate substrate - tested here seems to be a more adequate surrogate of real municipal WW for laboratory studies than 100%-VFA WW.
Pronk, W., Ding, A., Morgenroth, E., Derlon, N., Desmond, P., Burkhardt, M., … Fane, A. G. (2019). Gravity-driven membrane filtration for water and wastewater treatment: a review. Water Research, 149, 553-565. doi:10.1016/j.watres.2018.11.062, Institutional Repository

Gravity-driven membrane (GDM) filtration has been investigated for almost 10 years. The technology is characterized not only by relatively lower transmembrane pressures which can be achieved by gravity (extremely low energy consumption), but also by the phenomenon of flux stabilization: A biofilm is allowed to form on the membrane and a stabilization of flux occurs which is related to biological processes within the biofilm layer on the membrane. This enables stable operation during a year or longer without any cleaning or flushing. Initially, the technology was developed mainly for household drinking water treatment, but in the meantime, the research and application has expanded to the treatment of greywater, rainwater, and wastewater as well as the pretreatment of seawater for desalination. This review covers the field from the rather fundamental research on biofilm morphology and microbial community analysis to the impact of feedwater composition, process parameters and organic removal performance. Not only household applications, but also for community-scale treatment and full-scale applications are discussed. In addition, the application potential is highlighted in comparison to conventional ultrafiltration. Finally, an overall assessment is illustrated and the research and development needs are identified.
Silva, M. O. D., Desmond, P., Derlon, N., Morgenroth, E., & Pernthaler, J. (2019). Source community and assembly processes affect the efficiency of microbial microcystin degradation on drinking water filtration membranes. Frontiers in Microbiology, 10, 843 (15 pp.). doi:10.3389/fmicb.2019.00843, Institutional Repository

Microbial biofilms in gravity-driven membrane (GDM) filtration systems can efficiently degrade the cyanotoxin microcystin (MC), but it is unclear if this function depends on the presence of MC-producing cyanobacteria in the source water habitat. We assessed the removal of MC from added Microcystis aeruginosa biomass in GDMs fed with water from a lake with regular blooms of toxic cyanobacteria (ExpL) or from a stream without such background (ExpS). While initial MC removal was exclusively due to abiotic processes, significantly higher biological MC removal was observed in ExpL. By contrast, there was no difference in MC degradation capacity between lake and stream bacteria in separately conducted liquid enrichments on pure MC. Co-occurrence network analysis revealed a pronounced modularity of the biofilm communities, with a clear hierarchic distinction according to feed water origin and treatment type. Genotypes in the network modules associated with ExpS had significantly more links to each other, indicating that these biofilms had assembled from a more coherent source community. In turn, signals for stochastic community assembly were stronger in ExpL biofilms. We propose that the less “tightly knit” ExpL biofilm assemblages allowed for the better establishment of facultatively MC degrading bacteria, and thus for higher overall functional efficiency.
 
Thürlimann, C. M. (2019). Soft-sensing, automation, and diagnosis for nitrification (Doctoral dissertation). doi:10.3929/ethz-b-000347049, Institutional Repository

Nitrification of wastewater requires control for the purposes of efficiency and of stability. However, first, the highly complex microbial community in wastewater treatment plants and very different compositions of wastewaters impede a complete understanding of nitrification. Second, the determination of the states of the process is seldom exact because sensors are subject to a high level of wear and tear. Consequently, instrumentation, control, and automation (ICA) of nitrification processes are a challenge. I hypothesize that soft-sensors - based on the signals of robust, physical sensors - and specially designed control loops, which do not need redundant information to correct for drift, can reduce the maintenance needs for the control of nitrification. Consequently, the econonomical application range for ICA of nitrification processes can be extended.
A large part of this thesis is dedicated to the stabilisation of urine nitrification as a pretreatment for nutrient recovery. To this end, an online nitrite detection and an according control of the process are required. Furthermore, the thesis comprises an ammonia aeration controller, which is based on pH signals, to be used in municipal wastewater. The four chapters of the thesis focus on the following topics.
The first chapter investigates calibration experiments for in-line UV-Vis sensors. Such sensors can serve as soft-sensors for numerous substances. With differently designed experiments, data for the calibration of UV-Vis based nitrite models in high strength wastewater was recorded. Online experiments executed in-situ allow calibrating similarly exact models like experiments which are conducted by spiking additional nitrite. The good performance of the models being based on online experiments is explained by the correlation of other light-absorbing substances in the process with nitrite.
The second chapter evaluates the potential of a stoichiometry-based soft-sensor for nitrite. The stoichiometry of nitrification theoretically allows distinguishing the ammonia and the nitrite oxidation rates by means of the derivatives of the dissolved oxygen and of the pH signal and in turn detecting nitrite accumulations. We show that under relatively ideal conditions the dynamics in the ratio of the two derivatives show similarities with the dynamics in the nitrite concentration. Factors that deteriorate this information quality are identified.
The third part of this thesis investigates how drifting sensor signals can be used as an input for a feedback controller without relying on redundant information to correct this drift. The controller shall prevent uncontrolled nitrite accumulation in a urine nitrification system. To this end, the controller does not use the absolute value of the nitrite signal, but its 1st and 2nd derivative as inputs. By controlled accumulation and degradation of nitrite, the controller can keep the derivatives continuously informative. The switch from substrate inhibition to substrate limitation of the nitrite oxidising bacteria can be identified by means of the inflection point in the signal. The developed controller is tested successfully on a lab-scale reactor.
The fourth chapter of this thesis describes an ammonia based aeration controller. These controllers usually require maintenance intensive instrumentation. Therefore a new ammonia soft sensor for continuously operated municipal wastewater treatment plants is developed. It relies on the 1st derivative of a pH difference measured over the aerated zone. This soft sensor is successfully tested in a controller deployed on various municipal wastewater treatment plants. The controller was designed to increase its robustness towards drift in the pH signals.
Thürlimann, C. M., Udert, K. M., Morgenroth, E., & Villez, K. (2019). Stabilizing control of a urine nitrification process in the presence of sensor drift. Water Research, 165, 114958 (10 pp.). doi:10.1016/j.watres.2019.114958, Institutional Repository

Sensor drift is commonly observed across engineering disciplines, particularly in harsh media such as wastewater. In this study, a novel stabilizing controller for nitrification of high strength ammonia solutions is designed based on online signal derivatives. The controller uses the derivative of a drifting nitrite signal to determine if nitrite-oxidizing bacteria (NOB) are substrate limited or substrate inhibited. To ensure a meaningful interpretation of the derivative signal, the process is excited in a cyclic manner by repeatedly exposing the NOB to substrate-limited and substrate-inhibited conditions. The resulting control system successfully prevented nitrite accumulations for a period of 72 days in a laboratory-scale reactor. Slow disturbances in the form of feed composition changes and temperature changes were successfully handled by the controller while short-term temperature disturbances are shown to pose a challenge to the current version of this controller. Most importantly, we demonstrate that drift-tolerant control for the purpose of process stabilization can be achieved without sensor redundancy by combining deliberate input excitation, qualitative trend analysis, and coarse process knowledge.
Ward, B. J., Traber, J., Gueye, A., Diop, B., Morgenroth, E., & Strande, L. (2019). Evaluation of conceptual model and predictors of faecal sludge dewatering performance in Senegal and Tanzania. Water Research, 167, 115101 (13 pp.). doi:10.1016/j.watres.2019.115101, Institutional Repository

Unpredictable dewatering performance is a barrier to the effective management and treatment of faecal sludge. While mechanisms of dewatering in sludges from wastewater treatment are well understood, it is not clear how dewatering of faecal sludge fits into the framework of existing knowledge. We evaluate physical-chemical parameters, including EPS and cations, and demographic (source), environmental (microbial community), and technical factors (residence time) as possible predictors of dewatering performance in faecal sludge, and make comparisons to the existing conceptual model for wastewater sludge. Faecal sludge from public toilets took longer to dewater than sludge from other sources, and had turbid supernatant after settling. Slow dewatering and turbid supernatant corresponded to high EPS and monovalent cation concentrations, conductivity, and pH, but cake solids after dewatering was not correlated with EPS or other factors. Faecal sludges with higher EPS appeared less stabilised than those with lower EPS, potentially a result of inhibition of biological degradation due to high urine concentrations. However, distinct microbial community compositions were also observed in samples with higher and lower EPS concentrations. Higher EPS faecal sludge was comparable in dewatering behaviour and EPS content to anaerobically digested and primary wastewater sludges. However lower EPS faecal sludges had different dewatering behaviour than wastewater sludges and may be governed by different mechanisms.
Wielinski, J., Gogos, A., Voegelin, A., Müller, C., Morgenroth, E., & Kaegi, R. (2019). Transformation of nanoscale and ionic Cu and Zn during the incineration of digested sewage sludge (biosolids). Environmental Science and Technology, 53(20), 11704-11713. doi:10.1021/acs.est.9b01983, Institutional Repository

Engineered nanoparticles (NP) discharged to sewers are efficiently retained by wastewater treatment plants and accumulate in the sewage sludge, which is commonly digested. The resulting biosolids are either used as fertilizer or incinerated. In this study, we address the transformation of Cu and Zn during sewage sludge incineration and evaluate whether the form of Cu or Zn (nanoparticulate versus dissolved) added to the digested sewage sludge affects the fate of the metals during incineration. We spiked CuO-NP, dissolved CuSO4, ZnO-NP, or dissolved ZnSO4 into anaerobically digested sewage sludge to reach Cu and Zn concentrations of ≈2500 and ≈3700 mg/kg and maintained the sludge under mesophilic, anaerobic conditions for 24 h. Subsequently, the sludge was incinerated in a pilot fluidized bed reactor. The speciation of Cu and Zn in the sludge, derived from X-ray absorption spectroscopy measurements, was dominated by sulfidic species, with >90% of Cu and >60% of Zn coordinated to reduced sulfur groups. In the ash, both Cu (>60%) and Zn (≈100%) were coordinated to oxygen. The chemical speciation of Cu and Zn in the ashes was independent of whether they were spiked in the dissolved or nanoparticulate form and closely matched the speciation of Cu and Zn observed in ashes from full-scale incinerators.
Ziemba, C., Larivé, O., Deck, S., Huisman, T., & Morgenroth, E. (2019). Comparing the anti-bacterial performance of chlorination and electrolysis post-treatments in a hand washing water recycling system. Water Research X, 2, 100020 (10 pp.). doi:10.1016/j.wroa.2018.100020, Institutional Repository

Innovative solutions are necessary to enable the decentralized recycling of greywater for applications requiring high-quality water, such as hand washing. While physical barriers such as ultrafiltration membranes effectively prevent the passage of bacteria, and chemical and biological treatments can effectively reduce the carbon content of the treated water, there exists a knowledge gap regarding the application of anti-bacterial strategies to prevent the growth of harmful bacteria following treatment. In this study, the effluent water from a household-scale greywater treatment system was fed to seven parallel experimental post-treatment tanks: three receiving direct chlorination with free chlorine residuals of 0.2, 1 or 5 mg Cl2/L, three with chlorine produced through electrolysis at the same residual concentrations, and one control with no chlorine added. For increasing concentrations of direct chlorination, the median total cell count (TCC) values were 9 × 104, 2.9 × 104 and 1.8 × 103 cells/mL, respectively. Electrolysis treatment produced very similar TCC concentrations, 8.8 × 104, 1.1 × 104 and 2.3 × 103 cells/mL. The TCC concentrations were lower than the concentration of the water entering each tank (~3 × 105 cells/mL). Intact cell count (ICC) measurements indicated that the viable cell concentrations, were less than 10% of the TCC values. Though electrolysis treatment can produce powerful oxidants, such as hydroxyl radical, there was no evidence that electrolysis in this system provided additional benefits beyond chlorine production for control of total or intact cell counts. Oxidation of bacteria by chlorine was the dominant anti-bacterial mechanism in our system. Monitoring of dissolved organic carbon (DOC) and assimilable organic carbon (AOC) did not suggest that carbon-limitation significantly impacted cell counts when chlorination or electrolysis treatment was applied. This work demonstrates that either direct chlorination or electrolysis treatment are able to reduce bacteria concentrations over long-term operation of a hand washing water treatment system. We recommend selecting chlorine residual targets such that a chlorine residual is maintained during periods of challenging operating conditions. We observed that a target residual of 1 mg Cl2/L, in our system, maintained the TCC below the concentration found in Zürich drinking water.
Carrel, M., Morales, V. L., Beltran, M. A., Derlon, N., Kaufmann, R., Morgenroth, E., & Holzner, M. (2018). Biofilms in 3D porous media: delineating the influence of the pore network geometry, flow and mass transfer on biofilm development. Water Research, 134, 280-291. doi:10.1016/j.watres.2018.01.059, Institutional Repository

This study investigates the functional correspondence between porescale hydrodynamics, mass transfer, pore structure and biofilm morphology during progressive biofilm colonization of a porous medium. Hydrodynamics and the structure of both the porous medium and the biofilm are experimentally measured with 3D particle tracking velocimetry and micro X-ray Computed Tomography, respectively. The analysis focuses on data obtained in a clean porous medium after 36 h of biofilm growth. Registration of the particle tracking and X-ray data sets allows to delineate the interplay between porous medium geometry, hydrodynamic and mass transfer processes on the morphology of the developing biofilm. A local analysis revealed wide distributions of wall shear stresses and concentration boundary layer thicknesses. The spatial distribution of the biofilm patches uncovered that the wall shear stresses controlled the biofilm development. Neither external nor internal mass transfer limitations were noticeable in the considered system, consistent with the excess supply of nutrient and electron acceptors. The wall shear stress remained constant in the vicinity of the biofilm but increased substantially elsewhere.
Carrel, M., Morales, V. L., Dentz, M., Derlon, N., Morgenroth, E., & Holzner, M. (2018). Pore-scale hydrodynamics in a progressively bioclogged three-dimensional porous medium: 3-D particle tracking experiments and stochastic transport modeling. Water Resources Research, 54(3), 2183-2198. doi:10.1002/2017WR021726, Institutional Repository

Biofilms are ubiquitous bacterial communities that grow in various porous media including soils, trickling, and sand filters. In these environments, they play a central role in services ranging from degradation of pollutants to water purification. Biofilms dynamically change the pore structure of the medium through selective clogging of pores, a process known as bioclogging. This affects how solutes are transported and spread through the porous matrix, but the temporal changes to transport behavior during bioclogging are not well understood. To address this uncertainty, we experimentally study the hydrodynamic changes of a transparent 3-D porous medium as it experiences progressive bioclogging. Statistical analyses of the system's hydrodynamics at four time points of bioclogging (0, 24, 36, and 48 h in the exponential growth phase) reveal exponential increases in both average and variance of the flow velocity, as well as its correlation length. Measurements for spreading, as mean-squared displacements, are found to be non-Fickian and more intensely superdiffusive with progressive bioclogging, indicating the formation of preferential flow pathways and stagnation zones. A gamma distribution describes well the Lagrangian velocity distributions and provides parameters that quantify changes to the flow, which evolves from a parallel pore arrangement under unclogged conditions, toward a more serial arrangement with increasing clogging. Exponentially evolving hydrodynamic metrics agree with an exponential bacterial growth phase and are used to parameterize a correlated continuous time random walk model with a stochastic velocity relaxation. The model accurately reproduces transport observations and can be used to resolve transport behavior at intermediate time points within the exponential growth phase considered.
Derlon, N., Layer, M., Morgenroth, E., Adler, A., Gelb, A., & Holliger, C. (2018). Boues granulaires aérobies. État de l'art de la recherche actuelle et future. Aqua & Gas, 98(1), 14-19. , Institutional Repository

Les boues granulaires aérobies offrent plusieurs avantages pour le traitement biologique des eaux usées municipales par rapport au procédé à boues activées conventionnels. Cependant, malgré un nombre croissant d’applications industrielles et municipales, notre recul sur les boues granulaires aérobies reste limité. L’EPFL et l’Eawag ont évalué au cours des dernières années les mécanismes, performances et limites des systèmes de boues granulaires aérobies. Dans cet article, nous résumons notre compréhension des facteurs influençant les propriétés des boues granulaires aérobies et fournissons une appréciation globale de cette nouvelle technologie.
Derlon, N., Pronk, W., & Morgenroth, E. (2018). Membranes d'ultrafiltration. La présence de biofilms: un avantage pour stabiliser le flux et augmenter la qualité du perméat. Aqua & Gas, 98(5), 30-35. , Institutional Repository

L’utilisation de systèmes composites combinant une couche biologique (le biofilm) supportée par une barrière physique (la membrane) a de multiples avantages pour le traitement des eaux (production d’eau potable, recyclage des eaux grises). Cet article présente comment tirer profit de la microbiologie des biofilms afin d’améliorer la qualité du perméat et faire fonctionner des systèmes membranaires à flux constant pendant plusieurs années, et ce sans maintenance.
Desmond, P., Best, J. P., Morgenroth, E., & Derlon, N. (2018). Linking composition of extracellular polymeric substances (EPS) to the physical structure and hydraulic resistance of membrane biofilms. Water Research, 132, 211-221. doi:10.1016/j.watres.2017.12.058, Institutional Repository

The effect of extracellular polymeric substances (EPS) on the meso-scale physical structure and hydraulic resistance of membrane biofilms during gravity driven membrane (GDM) filtration was investigated. Biofilms were developed on the surface of ultrafiltration membranes during dead-end filtration at ultra-low pressure (70 mbar). Biofilm EPS composition (total protein, polysaccharide and eDNA) was manipulated by growing biofilms under contrasting nutrient conditions. Nutrient conditions consisted of (i) a nutrient enriched condition with a nutrient ratio of 100:30:10 (C: N: P), (ii) a phosphorus limitation (C: N: P ratio: 100:30:0), and (iii) a nitrogen limitation (C: N: P ratio: 100:0:10). The structure of the biofilm was characterised at meso-scale using Optical Coherence Tomography (OCT). Biofilm composition was analysed with respect to total organic carbon, total cellular mass and extracellular concentrations of proteins, polysaccharides, and eDNA. 2D-confocal Raman mapping was used to characterise the functional group composition and micro-scale distribution of the biofilms EPS. Our study reveals that the composition of the EPS matrix can determine the meso-scale physical structure of membrane biofilms and in turn its hydraulic resistance. Biofilms grown under P limiting conditions were characterised by dense and homogeneous physical structures with high concentrations of polysaccharides and eDNA. Biofilm grown under nutrient enriched or N limiting conditions were characterised by heterogeneous physical structures with lower concentrations of polysaccharides and eDNA. For P limiting biofilms, 2D-confocal Raman microscopy revealed a homogeneous spatial distribution of anionic functional groups in homogeneous biofilm structures with higher polysaccharide and eDNA concentrations. This study links EPS composition, physical structure and hydraulic resistance of membrane biofilms, with practical relevance for the hydraulic performances of GDM ultrafiltration.
Desmond, P. (2018). Linking hydraulic resistance to the physical structure of membrane biofilms (Doctoral dissertation). doi:10.3929/ethz-b-000296862, Institutional Repository

Gravity driven membrane (GDM) ultrafiltration is a continuous dead-end filtration process for potable and non-potable water production. GDM operates on the principle of tolerating biofilm development on the membranes surface for the benefit of minimum membrane maintenance, stable flux production, and improved permeate quality. The biological activity afforded by the tolerated biofilm allows degradation of foulants that would otherwise accumulate on the surface of the membrane, decreasing permeate flux. However, membrane biofilms are not without problems. The presence of a biofilm increases the hydraulic resistance, which exceeds the intrinsic resistance of the membrane, leading to low yet stable permeate flux. The purpose of the presented thesis is to evaluate what structural feature of the biofilm can exert a resistance to hydraulic passage and how hydraulic resistance is influenced by the biofilms mechanical response to changes in process operation (e.g., transmembrane pressure (TMP), cross-flow). Towards this goal, the approach taken to determine the link between hydraulic resistance and the biofilms structural and mechanical characteristics shall examine: (a) how different biofilm physical structures affect hydraulic resistance; (b) how compression affect physical structure and related hydraulic resistance; (c) how hydraulic resistance changes over the biofilms depth. A key advancement of the current study is evaluating the link between biofilm physical structure and resulting hydraulic resistance using in-situ and non-invasive methods for chemical, structural and mechanical characterization, using 2D confocal Raman microscopy and optical coherence tomography, respectively.

Results of the presented thesis indicate that the formation of GDM biofilms is influenced by the nutrient availability (carbon, nitrogen, and phosphorus), which determined composition and micro-scale spatial distribution of extracellular polymeric substances (EPS). High concentrations of anionic polymers, homogeneously distributed in space, led to the formation of thin dense homogenous physical structures which had a higher hydraulic resistance. Low concentration of anionic polymers, heterogeneously distributed in space, led to the formation of thick heterogeneous physical structures with a low hydraulic resistance. Taken together, it is demonstrated that thicker heterogeneous structures imposed less hydraulic resistance than thin dense homogeneous structure, indicating density rather than thickness is the structural determinant of a biofilms hydraulic resistance.

The hydraulic resistance of membrane biofilms is also linked to their structural response to perpendicular and parallel flow. With increasing perpendicular flow, heterogeneous biofilms became irreversibly compressed, while homogeneous biofilms were reversibly compressed. Irreversible compression results from the reduction of the biofilm roughness and porosity and led to an irreversible increase in hydraulic resistance. With increasing hydraulic shear stress (flow parallel to the membrane), we demonstrated stratification in the physical structure, cohesion and hydraulic resistance of GDM biofilms. Detachment of a thick surface layer roughness had limited impact on hydraulic resistance due to retention of a cohesive base layer with a high hydraulic resistance.

The presented thesis provides a fundamental understanding of how hydraulic resistance is linked to a biofilms composition, physical structure and mechanical strength. Our evaluation of biofilm physical structure and hydraulic resistance in GDM systems has demonstrated that heterogeneous physical structures exert limited hydraulic resistance and have a low mechanical strength. Greater hydraulic resistance is exerted by thin dense base layer at the surface of the membrane. We suggest GDM membrane operators (a) maintain constant transmembrane pressure to avoided compaction of heterogeneous structure, (b) avoid hydraulic shear due to limited effect on resistance due to retention of thin and dense cohesive base layer and (c) focus on efforts to decrease the hydraulic resistance by increasing structural heterogeneity "in-place" by way of predation and/or nutrient enrichment.
Desmond, P., Morgenroth, E., & Derlon, N. (2018). Physical structure determines compression of membrane biofilms during Gravity Driven Membrane (GDM) ultrafiltration. Water Research, 143, 539-549. doi:10.1016/j.watres.2018.07.008, Institutional Repository

Increasing transmembrane pressure (TMP) can compress and increase the hydraulic resistance of membrane biofilms. The purpose of the present study is to evaluate how compression of membrane biofilms occurs and how structural rearrangement can affect hydraulic resistance. Biofilms with heterogeneous and homogeneous physical structures were grown in membrane fouling simulators (MFS) in dead-end mode for 20 days with either (i) a nutrient enriched condition with a nutrient ratio of 100:30:10 (C: N: P), (ii) a phosphorus limitation (C: N: P ratio: 100:30:0), or (iii) river water (C: N: P ratio: ca. 100:10:1). The structural and hydraulic response of membrane biofilms to (a) changes in transmembrane pressures (0.06-0.1-0.5-0.1-0.06 bar) and (b) changes in permeate flux (10-15-20-15-10 L/m2/h) were investigated. Optical coherence tomography (OCT) was used to monitor biofilm structural response, and OCT images were processed to quantify changes in the mean biofilm thickness and relative roughness. Nutrient enriched and river water biofilms had heterogeneous physical structures with greater surface roughness (Ra' > 0.2) than homogeneous P limiting biofilms (Ra' < 0.2). Compression of biofilms with rough heterogeneous structures (Ra' > 0.2) was irreversible, indicated by irreversible decrease in surface roughness, partial relaxation in mean biofilm thickness and irreversible increase in hydraulic resistance. Compression of homogeneous biofilm (Ra' < 0.2) was on the other hand reversible, indicated by full relaxation of the biofilms structure and restoration of initial hydraulic resistance. Hydraulic response (i.e., change in the specific biofilm resistance) did not correspond with the change in physical structure of heterogeneous biofilms. The presented study provides a fundamental understanding of how biofilm physical structure can affect the biofilm's response to a change in TMP, with practical relevance for the operation of GDM filtration systems.
Desmond, P., Böni, L., Fischer, P., Morgenroth, E., & Derlon, N. (2018). Stratification in the physical structure and cohesion of membrane biofilms – implications for hydraulic resistance. Journal of Membrane Science, 564, 897-904. doi:10.1016/j.memsci.2018.07.088, Institutional Repository

This study aimed at evaluating stratification of hydraulic resistance over the depth of membrane biofilms developed during gravity driven membrane (GDM) ultrafiltration. Biofilms were grown in membrane fouling simulators (MFS) for 25 days under 3 contrasting influent conditions: nutrient enriched, phosphorus limiting, and river water influent. Shear rheology was used to determine the biofilms material characteristics (e.g., elasticity, yield stress). Optical coherence tomography (OCT) was used to determine the response of the biofilms physical structure (e.g., thickness) to increased hydraulic shear stress from 0 up to 2.6 Pa. Stratification was observed in nutrient enriched and river water biofilms and which partially detached by erosion of their rough top layer under low shear conditions. A cohesive base layer remained attached to the membrane surface under high shear conditions, indicating stratification in cohesion over the biofilms depth. Erosion of the top layer only resulted in a slight decrease in the biofilm hydraulic resistance indicating that the very cohesive and thin base layer also represent significant hydraulic resistance. Conversely, P limiting biofilms had uniform structural and mechanical characteristics, detaching by sloughing and peeling at low and high shear stress respectively. Biofilms formed under phosphorus limiting conditions had equal elasticity, yet a lower yield stress compared to nutrient enriched and river water biofilms respectively and were more susceptible to detachment. The scientific implication of the presented work demonstrates that biofilm detachment is influenced by both the structural (surface heterogeneity) and material characteristics (e.g., yield stress), with practical relevance for hydraulic resistance during GDM filtration.
Jafari, M., Desmond, P., van Loosdrecht, M. C. M., Derlon, N., Morgenroth, E., & Picioreanu, C. (2018). Effect of biofilm structural deformation on hydraulic resistance during ultrafiltration: A numerical and experimental study. Water Research, 145, 375-387. doi:10.1016/j.watres.2018.08.036, Institutional Repository

Biofilm formation in membrane systems negatively impacts the filtration system performances. This study evaluated how biofilm compression driven by permeate flow increases the hydraulic resistance and leads to reduction in permeate flux. We analysed the effect of biofilm compression on hydraulic resistance and permeate flux through computational models supported by experimental data. Biofilms with homogeneous surface structure were subjected to step-wise changes in flux and transmembrane pressure during compression and relaxation tests. Biofilm thickness under applied forces was measured non-invasively in-situ using optical coherence tomography (OCT). A numerical model of poroelasticity, which couples water flow through the biofilm with biofilm mechanics, was developed to correlate the structural deformation with biofilm hydraulics (permeability and resistance). The computational model enabled extracting mechanical and hydrological parameters corresponding to the experimental data. Homogeneous biofilms under elevated compression forces experienced a significant reduction in thickness while only a slight increase in resistance was observed. This shows that hydraulic resistance of homogeneous biofilms was affected more by permeability decrease due to pore closure than by a decrease in thickness. Both viscoelastic and elastoplastic models could describe well the permanent biofilm deformation. However, for biofilms under study, a simpler elastic model could also be used due to the small irreversible deformations. The elastic moduli fitting the measured data were in agreement with other reported values for biofilm under compression. Biofilm stiffening under larger flow-driven compression forces was observed and described numerically by correlating inversely the elastic modulus with biofilm porosity. The importance of this newly developed method lies in estimation of accurate biofilm mechanical parameters to be used in numerical models for both membrane filtration system and biofouling cleaning strategies. Such model can ultimately be used to identify optimal operating conditions for membrane system subjected to biofouling.
Rittmann, B. E., Boltz, J. P., Brockmann, D., Daigger, G. T., Morgenroth, E., Helleshøj Sørensen, K., … Vanrolleghem, P. A. (2018). A framework for good biofilm reactor modeling practice (GBRMP). Water Science and Technology, 77(5), 1149-1164. doi:10.2166/wst.2018.021, Institutional Repository

A researcher or practitioner can employ a biofilm model to gain insight into what controls the performance of a biofilm process and for optimizing its performance. While a wide range of biofilmmodeling platforms is available, a good strategy is to choose the simplest model that includes sufficient components and processes to address the modeling goal. In most cases, a onedimensional biofilm model provides the best balance, and good choices can range from handcalculation analytical solutions, simple spreadsheets, and numerical-method platforms. What is missing today is clear guidance on how to apply a biofilm model to obtain accurate and meaningful results. Here, we present a five-step framework for good biofilm reactor modeling practice (GBRMP). The first four steps are (1) obtain information on the biofilm reactor system, (2) characterize the influent, (3) choose the plant and biofilm model, and (4) define the conversion processes. Each step demands that the model user understands the important components and processes in the system, one of the main benefits of doing biofilm modeling. The fifth step is to calibrate and validate the model: System-specific model parameters are adjusted within reasonable ranges so that model outputs match actual system performance. Calibration is not a simple 'by the numbers' process, and it requires that the modeler follows a logical hierarchy of steps. Calibration requires that the adjusted parameters remain within realistic ranges and that the calibration process be carried out in an iterative manner. Once each of steps 1 through 5 is completed satisfactorily, the calibrated model can be used for its intended purpose, such as optimizing performance, trouble-shooting poor performance, or gaining deeper understanding of what controls process performance.
Ward, B. J., Sam, S., Andriessen, N., Morgenroth, E., & Strande, L. (2018). Research priorities and progress in faecal sludge dewatering. Sandec News, 19, 10-11. , Institutional Repository

Difficulties in dewatering of faecal sludge are a crucial barrier to implementation of effective faecal sludge management. This article focuses on progress with locally available conditioners and the next steps toward implementing high-throughput, low-footprint dewatering technologies.
Wielinski, J., Müller, C., Voegelin, A., Morgenroth, E., & Kaegi, R. (2018). Combustion of sewage sludge: kinetics and speciation of the combustible. Energy and Fuels, 32(10), 10656-10667. doi:10.1021/acs.energyfuels.8b02106, Institutional Repository

Combustion of sewage sludge has become a viable route for sewage sludge management especially as the agricultural use of sewage sludge has become increasingly difficult due to more stringent requirements regarding the quality of sewage sludge. Combustion of digested sewage sludge in dedicated monocombustion facilities is advantageous, as it substantially reduces the volume of the sludge and still allows for a recovery of phosphorus from the sewage sludge ash at a later stage. Despite increasing amounts of sewage sludge being combusted, knowledge on the respective combustion kinetics is still fragmentary. The goal of this study was, therefore, to identify the major combustion reactions of sewage sludge, assess their Arrhenius parameters (activation energy and pre-exponential factor), and assign suitable reference compounds to the individual reactions. For that purpose, experiments were conducted using a thermogravimetric analyzer (TGA). With matrix inversion, we identified 10 individual reactions. Despite the apparent kinetic compensation most likely caused by insufficient precision of the TGA temperature setting, we were able to relate the major reactions of sewage sludge combustion to the combustion of individual reference compounds. In addition to cellulose and lignin, which dominated the weight loss with 35% and 20%, respectively, hemicellulose, xylan, alginate, and calcite were identified. The dominant fraction of cellulose is consistent with recent studies identifying cellulose mainly originating from toilet paper as a major organic constituent in wastewater. As the identified model compounds explain more than 80% of the total weight loss observed, our approach allows a rough speciation of the combustibles of sewage sludge based on TGA experiments.
Ziemba, C., Larivé, O., Reynaert, E., & Morgenroth, E. (2018). Chemical composition, nutrient-balancing and biological treatment of hand washing greywater. Water Research, 144, 752-762. doi:10.1016/j.watres.2018.07.005, Institutional Repository

On-site biological hand washing water treatment can improve global access to safe hand washing water, but requires a thorough understanding of the chemical composition of the water to be treated, and an effective treatment strategy. This study first presents a detailed characterization of the individual inputs to hand washing water. We demonstrate (1) that soap is likely the most significant input in hand washing water, representing ∼90% of mass loading, and (2) that inputs to hand washing water have low concentrations of biologically-essential macro- and micro-nutrients (nitrogen, phosphorus, potassium, copper, zinc, molybdenum and cobalt) with respect to carbon, which may impair biological carbon removal. This study next formulates a recipe that recreates a representative composition of hand washing water and develops a procedure to identify and supplement nutrients in which this recipe is estimated to be deficient. Batch testing of the nutrient-supplemented hand washing water with an inoculum of planktonic bacteria demonstrated improved assimilable organic carbon removal (99% vs. 86% removal) and produced lower final DOC concentrations (1.7 mgC/L vs. 3.5 mgC/L) compared to realistic (nutrient-deficient) washing water. Supplementing nutrients did promote cell growth (50x higher final total cell count). Full-scale testing in a biologically activated membrane bioreactor (BAMBi) system treating 75 L/day of nutrient-supplemented hand washing water showed that long-term operation (100 days) can deliver effective carbon removal (95%) without detrimental fouling or other disruptions caused by cell growth. This work demonstrates that biological treatment in a BAMBi system, operated with appropriate nutrient-balancing offers an effective solution for decentralized treatment of light greywater.
Boltz, J. P., Johnson, B. R., Takács, I., Daigger, G. T., Morgenroth, E., Brockmann, D., … Derlon, N. (2017). Biofilm carrier migration model describes reactor performance. Water Science and Technology, 75(12), 2818-2828. doi:10.2166/wst.2017.160, Institutional Repository

The accuracy of a biofilm reactor model depends on the extent to which physical system conditions (particularly bulk-liquid hydrodynamics and their influence on biofilm dynamics) deviate from the ideal conditions upon which the model is based. It follows that an improved capacity to model a biofilm reactor does not necessarily rely on an improved biofilm model, but does rely on an improved mathematical description of the biofilm reactor and its components. Existing biofilm reactor models typically include a one-dimensional biofilm model, a process (biokinetic and stoichiometric) model, and a continuous flow stirred tank reactor (CFSTR) mass balance that [when organizing CFSTRs in series] creates a pseudo two-dimensional (2-D) model of bulk-liquid hydrodynamics approaching plug flow. In such a biofilm reactor model, the user-defined biofilm area is specified for each CFSTR; thereby, Xcarrier does not exit the boundaries of the CFSTR to which they are assigned or exchange boundaries with other CFSTRs in the series. The error introduced by this pseudo 2-D biofilm reactor modeling approach may adversely affect model results and limit model-user capacity to accurately calibrate a model. This paper presents a new sub-model that describes the migration of Xcarrier and associated biofilms, and evaluates the impact that Xcarrier migration and axial dispersion has on simulated system performance. Relevance of the new biofilm reactor model to engineering situations is discussed by applying it to known biofilm reactor types and operational conditions.
Boltz, J. P., Smets, B. F., Rittmann, B. E., Van Loosdrecht, M. C. M., Morgenroth, E., & Daigger, G. T. (2017). From biofilm ecology to reactors: a focused review. Water Science and Technology, 75(8), 1753-1760. doi:10.2166/wst.2017.061, Institutional Repository

Biofilms are complex biostructures that appear on all surfaces that are regularly in contact with water. They are structurally complex, dynamic systems with attributes of primordial multicellular organisms and multifaceted ecosystems. The presence of biofilms may have a negative impact on the performance of various systems, but they can also be used beneficially for the treatment of water (defined herein as potable water, municipal and industrial wastewater, fresh/brackish/salt water bodies, groundwater) as well as in water stream-based biological resource recovery systems. This review addresses the following three topics: (1) biofilm ecology, (2) biofilm reactor technology and design, and (3) biofilm modeling. In so doing, it addresses the processes occurring in the biofilm, and how these affect and are affected by the broader biofilm system. The symphonic application of a suite of biological methods has led to significant advances in the understanding of biofilm ecology. New metabolic pathways, such as anaerobic ammonium oxidation (anammox) or complete ammonium oxidation (comammox) were first observed in biofilm reactors. The functions, properties, and constituents of the biofilm extracellular polymeric substance matrix are somewhat known, but their exact composition and role in the microbial conversion kinetics and biochemical transformations are still to be resolved. Biofilm grown microorganisms may contribute to increased metabolism of micro-pollutants. Several types of biofilm reactors have been used for water treatment, with current focus on moving bed biofilm reactors, integrated fixed-film activated sludge, membrane-supported biofilm reactors, and granular sludge processes. The control and/or beneficial use of biofilms in membrane processes is advancing. Biofilm models have become essential tools for fundamental biofilm research and biofilm reactor engineering and design. At the same time, the divergence between biofilm modeling and biofilm reactor modeling approaches is recognized.
Carr, G., Blanch, A. R., Blaschke, A. P., Brouwer, R., Bucher, C., Farnleitner, A. H., … Blöschl, G. (2017). Emerging outcomes from a cross-disciplinary doctoral programme on water resource systems. Water Policy, 19(3), 463-478. doi:10.2166/wp.2017.054, Institutional Repository

Interdisciplinary research and education programmes in water science are intended to produce groundbreaking research, often with an emphasis on societal relevance, and prepare future water resource experts to work across disciplines. This paper explores the emerging outcomes from an ongoing doctoral programme currently in its seventh year. Within the programme, there is both cross-disciplinary and mono-disciplinary research. Three questions are explored: (i) whether cross-disciplinary research leads to more innovative scientific findings than monodisciplinary research, (ii) whether cross-disciplinary researchers develop professional skills that benefit their future careers, and (iii) whether cross-disciplinary research produces findings of greater societal relevance than monodisciplinary research. Various indicators are used to measure research and education outcomes. Analysis of journal impact factors and citation rates of Institute of Scientific Information indexed publications suggests that crossdisciplinary research findings are more innovative. Comparison between graduate research profile and their career destinations suggests that researchers who learn to work across the disciplines continue to work this way in their post-doctoral positions. Analysis of media interest in research findings or their impact on policy suggests that both types of research are of societal value, but researchers often expand their understanding of a societal interest topic by bringing in new research fields.
Carrel, M., Beltran, M. A., Morales, V. L., Derlon, N., Morgenroth, E., Kaufmann, R., & Holzner, M. (2017). Biofilm imaging in porous media by laboratory X-ray tomography: combining a non-destructive contrast agent with propagation-based phase-contrast imaging tools. PLoS One, 12(7), e0180374 (18 pp.). doi:10.1371/journal.pone.0180374, Institutional Repository

X-ray tomography is a powerful tool giving access to the morphology of biofilms, in 3D porous media, at the mesoscale. Due to the high water content of biofilms, the attenuation coefficient of biofilms and water are very close, hindering the distinction between biofilms and water without the use of contrast agents. Until now, the use of contrast agents such as barium sulfate, silver-coated micro-particles or 1-chloronaphtalene added to the liquid phase allowed imaging the biofilm 3D morphology. However, these contrast agents are not passive and potentially interact with the biofilm when injected into the sample. Here, we use a natural inorganic compound, namely iron sulfate, as a contrast agent progressively bounded in dilute or colloidal form into the EPS matrix during biofilm growth. By combining a very long source-to-detector distance on a X-ray laboratory source with a Lorentzian filter implemented prior to tomographic reconstruction, we substantially increase the contrast between the biofilm and the surrounding liquid, which allows revealing the 3D biofilm morphology. A comparison of this new method with the method proposed by Davit et al (Davit et al., 2011), which uses barium sulfate as a contrast agent to mark the liquid phase was performed. Quantitative evaluations between the methods revealed substantial differences for the volumetric fractions obtained from both methods. Namely, contrast agent—biofilm interactions (e.g. biofilm detachment) occurring during barium sulfate injection caused a reduction of the biofilm volumetric fraction of more than 50% and displacement of biofilm patches elsewhere in the column. Two key advantages of the newly proposed method are that passive addition of iron sulfate maintains the integrity of the biofilm prior to imaging, and that the biofilm itself is marked by the contrast agent, rather than the liquid phase as in other available methods. The iron sulfate method presented can be applied to understand biofilm development and bioclogging mechanisms in porous materials and the obtained biofilm morphology could be an ideal basis for 3D numerical calculations of hydrodynamic conditions to investigate biofilm-flow coupling.
Fumasoli, A., Bürgmann, H., Weissbrodt, D. G., Wells, G. F., Beck, K., Mohn, J., … Udert, K. M. (2017). Growth of Nitrosococcus-related ammonia oxidizing bacteria coincides with extremely low pH values in wastewater with high ammonia content. Environmental Science and Technology, 51(12), 6857-6866. doi:10.1021/acs.est.7b00392, Institutional Repository

Ammonia oxidation decreases the pH in wastewaters where alkalinity is limited relative to total ammonia. The activity of ammonia oxidizing bacteria (AOB), however, typically decreases with pH and often ceases completely in slightly acidic wastewaters. Nevertheless, nitrification at low pH has been reported in reactors treating human urine, but it has been unclear which organisms are involved. In this study, we followed the population dynamics of ammonia oxidizing organisms and reactor performance in synthetic fully hydrolyzed urine as the pH decreased over time in response to a decrease in the loading rate. Populations of the β-proteobacterial Nitrosomonas europaea lineage were abundant at the initial pH close to 6, but the growth of a possibly novel Nitrosococcus-related AOB genus decreased the pH to the new level of 2.2, challenging the perception that nitrification is inhibited entirely at low pH values, or governed exclusively by β-proteobacterial AOB or archaea. With the pH shift, nitrite oxidizing bacteria were not further detected, but nitrous acid (HNO2) was still removed through chemical decomposition to nitric oxide (NO) and nitrate. The growth of acid-tolerant γ-proteobacterial AOB should be prevented, by keeping the pH above 5.4, which is a typical pH limit for the N. europaea lineage. Otherwise, the microbial community responsible for high-rate nitrification can be lost, and strong emissions of hazardous volatile nitrogen compounds such as NO are likely.
McCall, A. K., Palmitessa, R., Blumensaat, F., Morgenroth, E., & Ort, C. (2017). Modeling in-sewer transformations at catchment scale – implications on drug consumption estimates in wastewater-based epidemiology. Water Research, 122, 655-668. doi:10.1016/j.watres.2017.05.034, Institutional Repository

To which extent illicit drugs are transformed during in-sewer transport, depends on a number of factors: i) substance-specific transformation rates, ii) environmental conditions, iii) point of discharge (location of drug user) and iv) sewer network properties, primarily hydraulic residence time (HRT) and the ratio of biofilm contact area to wastewater volume (A/Veq).
Assessing associated uncertainties typically requires numerous simulations. Therefore, we propose a new two-step modeling framework: 1) Quantify hydrodynamic conditions. This computationally demanding step was performed once in SWMM to derive HRT and A/Veq for each potential point of discharge (node) in three catchments of different size. 2) Estimate biomarker loss. In this step, Monte Carlo simulations were performed for defined scenarios. Depending on assumptions about drug user distribution and prevalence, a number of nodes was sampled. For each node an empirical first-order transformation model was applied with flow-path-corresponding HRT and A/Veq from step 1. Biotic and abiotic transformation rates were sampled from distributions combining variability of different biofilms.
In our modeling study, median losses were >30% for amphetamine, 6-monoacetylmorphine and 6-acetylcodeine in all three catchments with high uncertainty (5%–100% loss), which would imply a systematic underestimation of consumption when neglecting in-sewer processes. Median losses for 21 other investigated biomarkers were <10% with different uncertainty ranges – “no substantial transformation” was confirmed for nine substances in a real sewer segment with a 2-h residence time. Transferability of these results must be tested for other catchments. To further reduce uncertainty, mainly additional knowledge on transformation rates, particularly in biofilm, and their distribution across a sewer network is needed to update model input objectively. Our approach allows efficient testing and, furthermore, can be expanded for many other human biomarkers. Accounting for biomarker stability during in-sewer transport will avoid biased estimates and further improve wastewater-based epidemiology.
Nguyen, M. T., Allemann, L., Ziemba, C., Larivé, O., Morgenroth, E., & Julian, T. R. (2017). Controlling bacterial pathogens in water for reuse: treatment technologies for water recirculation in the Blue Diversion Autarky Toilet. Frontiers in Environmental Science, 5, 90 (13 pp.). doi:10.3389/fenvs.2017.00090, Institutional Repository

The Blue Diversion AUTARKY Toilet is a urine-diverting toilet with on-site treatment. The toilet is being developed to provide a safe and affordable sanitation technology for people who lack access to sewer-based sanitation. Water used for personal hygiene, hand washing, and flushing to rinse urine- and feces-collection bowls is treated, stored, and recycled for reuse to reduce reliance on external water supplies. The system provides an opportunity to investigate hygiene of water for reuse following treatment. Treatment in the toilet includes a Biologically Activated Membrane Bioreactor (BAMBi) followed by a secondary treatment technology. To identify effective secondary treatment, three options, including granular activated carbon (GAC) only, GAC+chlorine (sodium hypochlorite), and GAC+electrolysis are considered based on the bacterial inactivation and growth inhibition efficiency. Four different hygiene-relevant bacteria are tested: Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, and Salmonella typhimurium. Our evaluation demonstrates that—despite treatment of water with the BAMBi—E. coli, P. aeruginosa, and S. typhimurium have the potential to grow during storage in the absence of microbial competition. Including the indigenous microbial community influences bacterial growth in different ways: E. coli growth decreases but P. aeruginosa growth increases relative to no competition. The addition of the secondary treatment options considerably improves water quality. A column of GAC after the BAMBi reduces E. coli growth potential by 2 log10, likely due to the reduction of carbon sources. Additional treatments including chlorination and electrolysis provide further safety margins, with more than 5 log10 inactivation of E. coli. However, reactivation and/or regrowth of E. coli and P. aeruginosa occurs under in the absence of residual disinfectant. Treatment including the BAMBi, GAC, and electrolysis appear to be promising technologies to control bacterial growth during storage in water intended for reuse.
Schmitt, R. J. P., Morgenroth, E., & Larsen, T. A. (2017). Robust planning of sanitation services in urban informal settlements: an analytical framework. Water Research, 110, 297-312. doi:10.1016/j.watres.2016.12.007, Institutional Repository

New types of sanitation services are emerging to tackle the sanitation crisis in informal settlements. These services link toilet facilities to semi-decentralized treatment plants via frequent, road-based transport of excreta. However, information for the planning of such sanitation services is scarce, and their future operating conditions are highly uncertain. The key questions of this paper are therefore: a) what are the drivers behind success or failure of a service-based sanitation system in informal settlements and b) on what scales and under which conditions can such a system operate successfully? To answer these questions, already at an early stage of the planning process, we introduce a stochastic model to analyze a wide range of system designs under varying technical designs, socio-economic factors, and spatial condition. Based on these initial results, we design a sanitation service and use the numeric model to study its reliability and costs over a wide range of scales, i.e., system capacities, from very few to many hundred users per semi-decentralized treatment unit. Key findings are that such a system can only operate within a narrow, but realistic range of conditions. Key requirements are toilet facilities, which can be serviced rapidly, and a flexible workforce. A high density of facilities will also lower the costs. Under these premises, we develop a road-based sanitation service and model its functionality in different settings and under many scenarios. Results show that the developed sanitation system using a single vehicle is scalable (100–700 users), can provide reliable service, and can be cheap (<1.5 c/p/day). Hence, this paper demonstrates opportunities for road-based sanitation in informal settlements and presents a quantitative framework for designing such systems.
Tobias, R., O'Keefe, M., Künzle, R., Gebauer, H., Gründl, H., Morgenroth, E., … Larsen, T. A. (2017). Early testing of new sanitation technology for urban slums: the case of the Blue Diversion Toilet. Science of the Total Environment, 576, 264-272. doi:10.1016/j.scitotenv.2016.10.057, Institutional Repository

The toilets used most in informal urban settlements have detrimental consequences for the environment and human health due to the lack of proper collection and treatment of toilet waste. Concepts for safe, sustainable and affordable sanitation systems exist, but their feasibility and acceptance have to be investigated at an early stage of development, which is difficult due to the high costs of building working models. In this paper, we present an approach to estimate acceptance in a valid and representative form with only one working model, and apply it to test an innovative zero-emission toilet with recycling of wash water. Four basic principles were specified for investigation and nine hypotheses formulated to test the feasibility and acceptance of these principles: source separation of urine and feces with subsequent collection for resource recovery; provision of wash water in a separate cycle with on-site recovery through a membrane bioreactor; a convenient and attractive overall design; and a financially sustainable business plan. In Kampala (Uganda), in 2013, data was collected from 22 regular users, 308 one-time users and a representative sample of 1538 participants. Qualitative data was collected from the users, who evaluated their likes, perceived benefits, social norms and expected ease of use based on verbal and visual information. Most of the hypotheses were confirmed, indicating the feasibility and acceptance of the basic principles. Source separation and on-site water recovery were found to be feasible and accepted, provided users can be convinced that the emptying service and water recovery process work reliably. In the survey, the toilet was evaluated favorably and 51% of the participants agreed to be placed on a bogus waiting list. However, some design challenges were revealed, such as the size of the toilet, hiding feces from view and improving the separation of urine and water
Weissbrodt, D. G., Holliger, C., & Morgenroth, E. (2017). Modeling hydraulic transport and anaerobic uptake by PAOs and GAOs during wastewater feeding in EBPR granular sludge reactors. Biotechnology and Bioengineering, 114(8), 1688-1702. doi:10.1002/bit.26295, Institutional Repository

New-generation bioprocesses using granular sludge aim for a high-rate removal of nutrients from wastewater with low footprint. Achieving enhanced biological phosphorus removal (EBPR) relies on the design of sludge beds and wastewater feeding conditions to optimally load the biomass and to select for polyphosphate- (PAOs) over glycogen-accumulating organisms (GAOs) and over other heterotrophs. A hydraulic–metabolic mathematical model was developed to elucidate the impact of hydraulic transport patterns and environmental conditions on the PAO/GAO competition during up-flow feeding through an EBPR granular sludge bed. Tracer experiments highlighted plug-flow regimes with dispersion under both rapid (9 mh-1, Rebed = 1.6, Pez = 7.2, Pet = 4.6) and slow (0.9 mh-1, Rebed = 0.2, Pez = 21.3, Pet = 3.4) feeding. Non-turbulent regimes (Rebed << 103) promote a safe implementation of simultaneous fill/draw. Feeding time, pH, and temperature significantly impacted bacterial competition for carbon uptake under anaerobic slow feeding. Feeding duration should be designed to avoid full depletion of intracellular storage polymers within static granules. PAOs bear twice longer feeding than GAOs by using both polyphosphate and glycogen hydrolysis to sustain anaerobic C-uptake. Alkaline conditions (pH 7.25–8.0) by, e.g., dosing lime in the feed select for PAOs independently of temperature (10−30°C). A twice higher bed is required for full anaerobic conversions at 10 rather than 20°C. Biosystem responses for anaerobic C-uptake can be anticipated using the model toward designing robust anaerobic selectors to manage the microbial resource in EBPR granular sludge. Biotechnol. Bioeng. 2017;114: 1688–1702.
Wells, G. F., Shi, Y., Laureni, M., Rosenthal, A., Szivák, I., Weissbrodt, D. G., … Morgenroth, E. (2017). Comparing the resistance, resilience, and stability of replicate moving bed biofilm and suspended growth combined nitritation–anammox reactors. Environmental Science and Technology, 51(9), 5108-5117. doi:10.1021/acs.est.6b05878, Institutional Repository

Combined partial nitritation–anammox (PN/A) systems are increasingly being employed for sustainable removal of nitrogen from wastewater, but process instabilities present ongoing challenges for practitioners. The goal of this study was to elucidate differences in process stability between PN/A process variations employing two distinct aggregate types: biofilm [in moving bed biofilm reactors (MBBRs)] and suspended growth biomass. Triplicate reactors for each process variation were studied under baseline conditions and in response to a series of transient perturbations. MBBRs displayed elevated NH4+ removal rates relative to those of suspended growth counterparts over six months of unperturbed baseline operation but also exhibited significantly greater variability in performance. Transient perturbations led to strikingly divergent yet reproducible behavior in biofilm versus suspended growth systems. A temperature perturbation prompted a sharp reduction in NH4+ removal rates with no accumulation of NO2– and rapid recovery in MBBRs, compared to a similar reduction in NH4+ removal rates but a high level of accumulation of NO2– in suspended growth reactors. Pulse additions of a nitrification inhibitor (allylthiourea) prompted only moderate declines in performance in suspended growth reactors compared to sharp decreases in NH4+ removal rates in MBBRs. Quantitative fluorescence in situ hybridization demonstrated a significant enrichment of anammox in MBBRs compared to suspended growth reactors, and conversely a proportionally higher AOB abundance in suspended growth reactors. Overall, MBBRs displayed significantly increased susceptibility to transient perturbations employed in this study compared to that of suspended growth counterparts (stability parameter), including significantly longer recovery times (resilience). No significant difference in the maximal impact of perturbations (resistance) was apparent. Taken together, our results suggest that aggregate architecture (biofilm vs suspended growth) in PN/A processes exerts an unexpectedly strong influence on process stability.
Zöllig, H., Remmele, A., Morgenroth, E., & Udert, K. M. (2017). Removal rates and energy demand of the electrochemical oxidation of ammonia and organic substances in real stored urine. Environmental Science: Water Research and Technology, 3(3), 480-491. doi:10.1039/c7ew00014f, Institutional Repository

The separate collection and treatment of urine allows for an environmentally friendly and cost-efficient management of the nutrients contained in urine. The primary goal should be to recover all these nutrients. However, in some cases it will be economically or ecologically more sensitive to recover only the phosphorus, while nitrogen is removed together with organic substances (measured as chemical oxygen demand, COD) and pathogens. In this study, we investigated the use of galvanostatic electrolysis for the removal of nitrogen and COD from real stored urine. Non-active type boron-doped diamond (BDD) and active type thermally decomposed iridium oxide film (TDIROF) anodes were evaluated using batch experiments. On both anodes, ammonia was exclusively removed by indirect oxidation with active chlorine (AC: Cl2, HClO, and ClO−). As a consequence, ammonia was not completely removed, if chlorine was consumed by competing processes. While COD was present, ammonia removal was faster on TDIROF (227 ± 16 gN m−2 d−1 at 20 mA cm−2) than on BDD (43 ± 20 gN m−2 d−1 at 20 mA cm−2). The reason for the slower ammonia removal on BDD was the enhanced reaction of AC with organic molecules. In fact, hydroxyl radicals broke organic molecules down to shorter chain molecules which reacted with most of the AC leaving only little AC for the oxidation of ammonia. This preferential oxidation of organics resulted in very high COD removal rates on BDD (above 420 gCOD m−2 d−1 at 20 mA cm−2 for COD concentrations above 1000 mgCOD L−1). A main drawback of electrolysis with both anodes was the high energy demand (BDD: 55 W h gCOD−1 and 766 W h gN−1 for 90% and 6% removal, respectively. TDIROF: 67 W h gCOD−1 and 77 W h gN−1 for 30% and 40% removal. All at 20 mA cm−2). It can be concluded that BDD and TDIROF anodes could be combined in series for a fast, complete, and more energy efficient electrochemical urine treatment: COD could be removed on BDD before the residual ammonia would be removed on TDIROF.
Bertram, K. (2016). Reverse osmosis of nitrified urine to concentrate the nutrients (Master thesis). 29 p. , Institutional Repository

Urine contributes a major part of the nitrogen, phosphorus and potassium in municipal wastewater. Since the concentrations are much lower than in commercial fertilizers, volume reduction can reduce costs for transport and storage. A combination of nitrification and distillation has been tested at Eawag and was found to produce a valuable fertilizer. The energy consumption of the process is high. Reverse osmosis is another option for volume reduction, which is expected to consume less energy. This thesis deals with the question, whether it is beneficial to use reverse osmosis as a preconcentration step before distillation.
Experiments were conducted in a lab-scale reverse osmosis system and the experimental observations were used to implement a model. The model was used to predict the concentration factor that can be reached with reverse osmosis and the ion loss that has to be expected.
The solution-diffusion model and the concentration polarization model with the equation of Schock and Miquel for the concentration polarization mass transfer coefficient were found to describe the experimental observations well and were used in the model. The parameters of the solution-diffusion model were determined experimentally.
In this study the model was not solved for each ion individually but only for the total ion concentration. This allowed a prediction of the overall concentration factor and ion loss but not for the individual ions.
It was found that a single-step reverse osmosis system can reach a concentration factor of 1.9 while losing about 5 % of the ions. For higher concentration factors, higher ion losses occur. Multi-stage systems have higher ion recovery and require less membrane area than single-stage systems. However, the recovery was found to improve only slightly with two- and three-stage systems. Two-pass systems lead to very high ion recoveries but require high membrane areas and consume more energy.
It was estimated that the energy consumption of the distillation process can be reduced to about 30 % when using a two-pass reverse osmosis system up to a concentration factor of about 4.8. However, about 4 % ion loss has to be expected in the reverse osmosis system.
In this study, the observations from the experiments were extrapolated to higher concentration factors and higher pressures. For the model assumptions and simplifications were made. Therefore, further research should be conducted to verify the model predictions from this study.
For the optimization of the process chain, all costs and benefits should be considered. A value would have to be assigned to the fertilizer produced and also to the ions that are lost. For this, it is important to predict the ion loss for each ion individually.
Cunningham, M. (2016). Particulate substrate (Xs) retention mechanisms during feeding of an aerobic granular sludge (AGS) system (Master thesis). 35 p. , Institutional Repository

Aerobic granular sludge (AGS) has been proposed as a lower cost alternative to activated sludge in municipal wastewater treatment. AGS has a settling velocity up to twenty times greater than activated sludge (Rocktaschel, 2013). Granules have multiple redox zones which potentially allows for carbon, nitrogen, and phosphorous removal to occur in a single reactor (Giesen et al., 2013). These benefits reduce AGS reactor tank volume, equipment and aeration requirements—resulting in cost savings. However, growing AGS with wastewater and other feed waters with high particulate substrate (Xs) results in undesirable fluffy less dense granules and floc growth (de Kreuk et al., 2010).
A proposed solution is maximizing Xs attachment, hydrolysis and consumption during the anaerobic plug flow feeding phase of a sequencing batch reactor (SBR) cycle (de Kreuk et al., 2010). This thesis aims to better understand how biomass composition (ratio of granules to flocs), Xs size, and feeding velocity influence Xs retention. The secondary objective is to compare Xs retention by flocs and granules under fully mixed conditions.
A column test was developed to compare cellulose and wastewater Xs attachment to granules, flocs and granular sludge under plug flow conditions. A feed velocity of 1.4 m/h resulted in greater Xs retention compared to 3 and 5 m/h by all types of biomass; the outlier scenario is wastewater fed at 3 m/h, which could be attributed to Xs wastewater concentration in those tests. Granules performed better than flocs, which was surprising given that in granular media filtration a smaller media diameter leads to better particle retention (Yao et al., 1971; Darby et al., 1990). Abrupt changes to the biomass bed structure through channel formation or fractioning into multiple segments is proposed as an explanation. Furthermore, channeling and fractioning affected the distribution of retained Xs in the bed. The hydrolysis rate is a function of biomass and Xs concentration; therefore, the distribution of retained Xs in the bed is an important topic for potential future research (Morgenroth et al., 2002).
The jar tests also further emphasize the importance of maximizing Xs retention and consumption by granules during the anaerobic phase. Flocs performed better than granules at capturing Xs in fully mixed conditions. This indicates that flocs are likely to survive on Xs that is available in the supernatant, or was retained by the bed of granules but becomes available during the aerobic cycle because it was not fully consumed.
Overall, this thesis provides a first step into understanding the fate of Xs in AGS systems treating municipal wastewater. This topic involves physical (Xs retention) and biological (Xs hydrolysis and degradation) processes. Previous research on granular media filtration and contact stabilization is helpful for developing experimental procedures. Continued research into this topic can help maximize the economic benefits of AGS for wastewater treatment by improving granule morphology and limiting floc growth.
Derlon, N., Wagner, J., Ribeiro da Costa, R. H., & Morgenroth, E. (2016). Formation of aerobic granules for the treatment of real and low-strength municipal wastewater using a sequencing batch reactor operated at constant volume. Water Research, 105, 341-350. doi:10.1016/j.watres.2016.09.007, Institutional Repository

This study aimed at evaluating the formation of aerobic granular sludge (AGS) for the treatment of real and low-strength municipal wastewater using a column sequencing batch reactor (SBR) operated in fill-draw mode (constant volume). The focus was on understanding how the wastewater upflow velocity (VWW) applied during the anaerobic feeding influenced the sludge properties and in turn the substrate conversion. Two different strategies were tested: (1) washing-out the flocs by imposing high wastewater upflow velocities (between 5.9 and 16 m h−1) during the anaerobic feeding (Approach #1) and (2) selective utilization of organic carbon during the anaerobic feeding (1 m h−1) combined with a selective sludge withdrawal (Approach #2). A column SBR of 190 L was operated in constant volume during 1500 days and fed with real and low-strength municipal wastewater. The formation of AGS with SVI30 of around 80 mL gTSS−1 was observed either at very low (1 m h−1) or at high VWW (16 m h−1). At 16 m h−1 the AGS was mainly composed of large and round granules (d > 0.63 mm) with a fluffy surface, while at 1 m h−1 the sludge was dominated by small granules (0.25 < d < 0.63 mm). The AGS contained a significant fraction of flocs during the whole operational period. A considerable and continuous washout of biomass occurred at VWW higher than 5.9 m h−1 (Approach #1) due to the lower settling velocity of the AGS fed with municipal wastewater. The low sludge retention observed at VWW higher than 5.9 m h−1 deteriorated the substrate conversion and in turn the effluent quality. High solid concentrations (and thus solid retention time) were maintained during Approach #2 (VWW of 1 m h−1), which resulted in an excellent effluent quality. The study demonstrated that the formation of AGS is possible during the treatment of real and low-strength municipal wastewater in a SBR operated at constant volume. Low wastewater upflow velocities should be applied during the anaerobic feeding phase in order to ensure enough biomass retention and efficient substrate removal.
Derlon, N., Grütter, A., Brandenberger, F., Sutter, A., Kuhlicke, U., Neu, T. R., & Morgenroth, E. (2016). The composition and compression of biofilms developed on ultrafiltration membranes determine hydraulic biofilm resistance. Water Research, 102, 63-72. doi:10.1016/j.watres.2016.06.019, Institutional Repository

This study aimed at identifying how to improve the level of permeate flux stabilisation during gravity-driven membrane filtration without control of biofilm formation. The focus was therefore on understanding (i) how the different fractions of the biofilms (inorganics particles, bacterial cells, EPS matrix) influence its hydraulic resistance and (ii) how the compression of biofilms impacts its hydraulic resistance, i.e., can water head be increased to increase the level of permeate flux stabilisation. Biofilms were developed on ultrafiltration membranes at 88 and 284 cm water heads with dead-end filtration for around 50 days. A larger water head resulted in a smaller biofilm permeability (150 and 50 L m−2 h−1 bar−1 for biofilms grown at 88 cm and 284 cm water head, respectively). Biofilms were mainly composed of EPS (>90% in volume). The comparison of the hydraulic resistances of biofilms to model fouling layers indicated that most of the hydraulic resistance is due to the EPS matrix. The compressibility of the biofilm was also evaluated by subjecting the biofilms to short-term (few minutes) and long-term variations of transmembrane pressures (TMP). A sudden change of TMP resulted in an instantaneous and reversible change of biofilm hydraulic resistance. A long-term change of TMP induced a slow change in the biofilm hydraulic resistance. Our results demonstrate that the response of biofilms to a TMP change has two components: an immediate variation of resistance (due to compression/relaxation) and a long-term response (linked to biofilm adaptation/growth). Our results provide relevant information about the relationship between the operating conditions in terms of TMP, the biofilm structure and composition and the resulting biofilm hydraulic resistance. These findings have practical implications for a broad range of membrane systems.
Ding, A., Liang, H., Li, G., Derlon, N., Szivak, I., Morgenroth, E., & Pronk, W. (2016). Impact of aeration shear stress on permeate flux and fouling layer properties in a low pressure membrane bioreactor for the treatment of grey water. Journal of Membrane Science, 510, 382-390. doi:10.1016/j.memsci.2016.03.025, Institutional Repository

Two different aeration regimes were studied in a low pressure gravity driven membrane bioreactor without any flushing or (back-) washing. In one reactor, the aeration was positioned below the membrane module, thus exposing the membranes to aeration shear stress. A second reactor was operated at low shear stress by placing the aerator in a different compartment. Flux stabilization at 2.0 L/(m2 h) occurred in the reactor with low shear stress while no flux stabilization was observed in the reactor with aeration shear stress, resulting in a flux of 0.5 L/(m2 h) after 120 days. The thickness of the bio-fouling layer in the reactor with aeration shear was smaller (129 vs. 344 µm), which implies that shear stress resulted in a thinner, denser and less permeable bio-fouling layer. The results can be explained by differences in (1) the morphology of the bio-fouling layer and (2) the EPS contents (proteins and polysaccharides) in the bio-fouling layer. The low-shear system provides a suitable solution for decentralized grey water treatment, or other conditions where maintenance and energy consumption should be minimized. Furthermore, the results can contribute to decrease the energy consumption in MBR systems.
Fumasoli, A., Etter, B., Sterkele, B., Morgenroth, E., & Udert, K. M. (2016). Operating a pilot-scale nitrification/distillation plant for complete nutrient recovery from urine. Water Science and Technology, 73(1), 215-222. doi:10.2166/wst.2015.485, Institutional Repository

Source-separated urine contains most of the excreted nutrients, which can be recovered by using nitrification to stabilize the urine before concentrating the nutrient solution with distillation. The aim of this study was to test this process combination at pilot scale. The nitrification process was efficient in a moving bed biofilm reactor with maximal rates of 930 mg N L−1 d−1. Rates decreased to 120 mg N L−1 d−1 after switching to more concentrated urine. At high nitrification rates (640 mg N L−1 d−1) and low total ammonia concentrations (1,790 mg NH4-N L−1 in influent) distillation caused the main primary energy demand of 71 W cap−1 (nitrification: 13 W cap−1) assuming a nitrogen production of 8.8 g N cap−1 d−1. Possible process failures include the accumulation of the nitrification intermediate nitrite and the selection of acid-tolerant ammonia-oxidizing bacteria. Especially during reactor start-up, the process must therefore be carefully supervised. The concentrate produced by the nitrification/distillation process is low in heavy metals, but high in nutrients, suggesting a good suitability as an integral fertilizer.
Gold, M., Dayer, P., Faye, M. C. A. S., Clair, G., Seck, A., Niang, S., … Strande, L. (2016). Locally produced natural conditioners for dewatering of faecal sludge. Environmental Technology, 37(21), 1-13. doi:10.1080/09593330.2016.1165293, Institutional Repository

In urban areas of low-income countries, treatment of faecal sludge (FS) is insufficient or non-existent. This results in large amounts of FS being dumped into the environment. Existing treatment technologies for FS, such as settling-thickening tanks and drying beds, are land intensive which is limiting in urban areas. Enhanced settling and dewatering by conditioning was evaluated in order to reduce the treatment footprint (or increase treatment capacity). Conventional wastewater conditioners, such as commercially available lime and polymers, are expensive, and commonly rely on complex supply chains for use in low-income countries. Therefore, the treatment performance of five conditioners which could be produced locally was evaluated: Moringa oleifera seeds and press cake, Jatropha curcas seeds, Jatropha Calotropis leaves and chitosan. M. oleifera seeds and press cake, and chitosan improved settling and dewatering and had a similar performance compared to lime and polymers. Optimal dosages were 400–500 kg M. oleifera/t TS, 300–800 kg lime/t TS and 25–50 kg polymer solution/t TS. In comparison, chitosan required 1.5–3.75 kg/t TS. These dosages are comparable to those recommended for wastewater (sludge). The results indicate that conditioning of FS can reduce total suspended solids (TSS) in the effluent of settling-thickening tanks by 22–81% and reduce dewatering time with drying beds by 59–97%. This means that the area of drying beds could be reduced by 59–97% with end-use as soil conditioner, or 9–26% as solid fuel. Least expensive options and availability will depend on the local context. In Dakar, Senegal, chitosan produced from shrimp waste appears to be most promising.
Habermacher, J., Benetti, A. D., Derlon, N., & Morgenroth, E. (2016). Degradation of the unbiodegradable particulate fraction (XU) from different activated sludges during batch digestion tests at ambient temperature. Water Research, 98, 206-214. doi:10.1016/j.watres.2016.04.005, Institutional Repository

One strategy for the management of excess sludge in small wastewater treatment plants (WWTPs) consists in minimizing the excess sludge production by operating the WWTP at very long solids retention times (SRTs > 30 days). A number of recent studies have suggested that sludge minimization at very long SRT results from the degradation of the unbiodegradable particulate fraction (XU) (influent unbiodegradable compounds and endogenous decay products). But the biodegradability of the unbiodegradable particulate fraction has only been evaluated during batch digestion test performed at ambient temperature with sludge fed with synthetic wastewaters. It is not clear to what extent observations made for sludge fed with synthetic influents can be transposed to sludge fed with real influent. The current study thus focused on evaluating the biodegradability of the unbiodegradable particulate fraction for sludge fed with real wastewater. Batch digestion tests (400 days, ambient temperature) were conducted with three different sludges fed with either synthetic or real influents and exposed to aerobic or intermittent aeration conditions. Our results indicate that volatile suspended solids (VSS) decreased even after complete decay of the active biomass (i.e., after 30 days of aerobic batch digestion) indicating that the unbiodegradable particulate fraction is biodegradable. However, very low degradation rates of the unbiodegradable particulate fraction were monitored after day 30 of digestion (0.7-1.7·10-3 d-1). These values were in the lower range of previously published values for synthetic wastewaters (1-7.5·10-3 d-1). The low values determined in our study indicate that the rate could decrease over time or that sludge composition influences the degradability of the unbiodegradable particulate fraction. But our results also demonstrate that extracellular polymeric substances (EPS) have a minor impact on the biodegradability of the unbiodegradable particulate fraction. Overall bound EPS were indeed biodegradable under all conditions and thus did not accumulate in the unbiodegradable particulate fraction. Different bound EPS pools (e.g., cation bound EPS) were associated with specific degradation behaviors. Besides improved mechanistic understanding of sludge degradation processes, our results have implications for the development of decentralized wastewater treatment technologies with on-site reduction of excess sludge.
Laureni, M., Falås, P., Robin, O., Wick, A., Weissbrodt, D. G., Nielsen, J. L., … Joss, A. (2016). Mainstream partial nitritation and anammox: long-term process stability and effluent quality at low temperatures. Water Research, 101, 628-639. doi:10.1016/j.watres.2016.05.005, Institutional Repository

The implementation of autotrophic anaerobic ammonium oxidation processes for the removal of nitrogen from municipal wastewater (known as “mainstream anammox”) bears the potential to bring wastewater treatment plants close to energy autarky. The aim of the present work was to assess the long-term stability of partial nitritation/anammox (PN/A) processes operating at low temperatures and their reliability in meeting nitrogen concentrations in the range of typical discharge limits below 2 mgNH4-N·L−1 and 10 mgNtot·L−1. Two main 12-L sequencing batch reactors were operated in parallel for PN/A on aerobically pre-treated municipal wastewater (21 ± 5 mgNH4-N·L−1 and residual 69 ± 19 mgCODtot·L−1) for more than one year, including over 5 months at 15 °C. The two systems consisted of a moving bed biofilm reactor (MBBR) and a hybrid MBBR (H-MBBR) with flocculent biomass. Operation at limiting oxygen concentrations (0.15–0.18 mgO2·L−1) allowed stable suppression of the activity of nitrite-oxidizing bacteria at 15 °C with a production of nitrate over ammonium consumed as low as 16% in the MBBR. Promising nitrogen removal rates of 20–40 mgN·L−1·d−1 were maintained at hydraulic retention times of 14 h. Stable ammonium and total nitrogen removal efficiencies over 90% and 70% respectively were achieved. Both reactors reached average concentrations of total nitrogen below 10 mgN·L−1 in their effluents, even down to 6 mgN·L−1 for the MBBR, with an ammonium concentration of 2 mgN·L−1 (set as operational threshold to stop aeration). Furthermore, the two PN/A systems performed almost identically with respect to the biological removal of organic micropollutants and, importantly, to a similar extent as conventional treatments. A sudden temperature drop to 11 °C resulted in significant suppression of anammox activity, although this was rapidly recovered after the temperature was increased back to 15 °C. Analyses of 16S rRNA gene-targeted amplicon sequencing revealed that the anammox guild of the bacterial communities of the two systems was composed of the genus “Candidatus Brocadia”. The potential of PN/A systems to compete with conventional treatments for biological nutrients removal both in terms of removal rates and overall effluent quality was proven.
McCall, A. K., Scheidegger, A., Madry, M. M., Steuer, A. E., Weissbrodt, D. G., Vanrolleghem, P. A., … Ort, C. (2016). Influence of different sewer biofilms on transformation rates of drugs. Environmental Science and Technology, 50(24), 13351-13360. doi:10.1021/acs.est.6b04200, Institutional Repository

To estimate drug consumption more reliably, wastewater-based epidemiology would benefit from a better understanding of drug residue stability during in-sewer transport. We conducted batch experiments with real, fresh wastewater and sewer biofilms. Experimental conditions mimic small to medium-sized gravity sewers with a relevant ratio of biofilm surface area to wastewater volume (33 m2 m–3). The influences of biological, chemical, and physical processes on the transformation of 30 illicit drug and pharmaceutical residues were quantified. Rates varied among locations and over time. Three substances were not stable—that is, >20% transformation, mainly due to biological processes—at least for one type of tested biofilm for a residence time ≤2 h: amphetamine, 6-acetylcodeine, and 6-monoacetylmorphine. Cocaine, ecgonine methyl ester, norcocaine, cocaethylene, and mephedrone were mainly transformed by chemical hydrolysis and, hence, also unstable in sewers. In contrast, ketamine, norketamine, O-desmethyltramadol, diclofenac, carbamazepine, and methoxetamine were not substantially affected by in-sewer processes under all tested conditions and residence times up to 12 h. Our transformation rates include careful quantification of uncertainty and can be used to identify situations in which specific compounds are not stable. This will improve accuracy and uncertainty estimates of drug consumption when applied to the back-calculation.
Meili, N. (2016). Improvement of permeate quality after gravity-driven membrane filtration (Master thesis). 42 p. , Institutional Repository

Removal of bacteria and reduction of the assimilable organic carbon (AOC) are two of the main goals in drinking water treatment. In a gravity‐driven membrane (GDM) system the bacteria are retained by an ultrafiltration membrane while the biofilm on top of the membrane reduces the AOC concentration. But with the ageing of the biofilm, the AOC concentration in the permeate increases and the drinking water quality deteriorates (Derlon et al., 2014).
In this thesis, the influence of multiple GDMs in series on the permeate quality is investigated. An experiment with five GDMs in series, fed with a 5 mg C L‐1 acetate feed, is conducted. The permeate after each GDM was analyzed for its acetate concentration, total organic carbon (TOC) concentration and total cell count (TCC). The biofilm on each GDM was analyzed for its TOC, TCC and adenosine triphosphate (ATP) content as well as its biofilm resistance. The mean biofilm thickness was measured with optical coherence tomography.
The results of the experiment showed a decrease of TCC in the permeate at the time of sampling, as well as after three days of incubation at 30 °C, over the number of GDMs. The TOC, TCC and ATP in the biofilm decreased over the number of GDMs. So did the biofilm resistance and the mean biofilm thickness. These results indicate a decrease of AOC over the number of GDMs.
No flux stabilization over the five GDMs in series was observed. The flux varied between 3 L m‐2 h‐1 and 4 L m‐2 h‐1. This flux is higher than expected and can be explained by the low biofilm resistance of the GDM 2 to 5. Biofilm 1 displays by far the highest biofilm resistance to flux.
Overall, multiple GDMs in series result in a decrease of TCC in the permeate and therefore in an increase of the permeate quality. The flux obtained was higher than expected. Hence, multiple GDMs in series should be further investigated for drinking water treatment.
Niadiodava, H. (2016). Mechanisms governing simultaneous nitrification-denitrification in aerobic granular sludge (Master thesis). 28 p. , Institutional Repository

Aerobic granular sludge (AGS) is a new technology for biological treatment of wastewater. Simultaneous removal of organic matter, nitrogen and phosphorus is possible in an AGS reactor due to the large physical size of granules and their heterogeneous structure. While sufficient removal efficiencies of C and P have been achieved, N removal from municipal wastewaters using AGS still remains a challenge.
To address this knowledge gap, a model was developed in SUMO software to assess the mechanisms driving simultaneous nitrification and denitrification (SND) in a granular sludge reactor. Nitrification and denitrification can be accomplished in a single reactor due to coexistence of aerobic and anoxic zone in granules. Therefore, the objective of this master’s thesis is to evaluate the influence of oxygen concentration and anoxic volume in the granules on SND performance. Another objective is to evaluate the contribution of phosphorous accumulating organisms (PAO) on SND as PAOs are mainly responsible for the denitrification in AGS.
The granular sequenced batch reactor (SBR) module in SUMO was used to simulate mass transport and conversion processes occurring in the reactor. A low-strength influent with particulate organic carbon, which is typical for the municipal wastewater, was used in the study. A total COD concentration was 420 gCOD.m-3. The model included growth and decay of nitrifiers, ordinary heterotrophs and PAO. Three case studies were analyzed with low, intermediate and high granulation. The simulations were performed under different airflow resulting in different dissolved oxygen concentration in the bulk.
The highest SND of 96% was achieved for the simulation with intermediate granulation and oxygen concentration in the bulk reaching 1.2 gO2.m-3. Complete nitrification occurred in this simulation. The fraction of anoxic volume in the granule reached 100% and remained high during most of the aerobic period, which is significantly higher than the anoxic volume in cases with low or high granulation. In case with intermediate granulation, high PHA concentrations are found in anoxic layers of the granule. Therefore, there is a sufficient amount of organic carbon for denitrification by PAOs. In cases with low and high granulation, most of the PHA was concentrated in the aerobic layers and was not available for denitrification by PAOs.
To conclude, this study shows that aerobic granular sludge can be an effective technology for treatment of municipal wastewater, achieving high nitrification and SND efficiencies. However, special consideration shall be paid to oxygen concentration, anoxic volume in the granule and organic carbon availability in the anoxic zone.
Shen, Y., Huang, C., Monroy, G. L., Janjaroen, D., Derlon, N., Lin, J., … Nguyen, T. H. (2016). Response of simulated drinking water biofilm mechanical and structural properties to long-term disinfectant exposure. Environmental Science and Technology, 50(4), 1779-1787. doi:10.1021/acs.est.5b04653, Institutional Repository

Mechanical and structural properties of biofilms influence the accumulation and release of pathogens in drinking water distribution systems (DWDS). Thus, understanding how long-term residual disinfectants exposure affects biofilm mechanical and structural properties is a necessary aspect for pathogen risk assessment and control. In this study, elastic modulus and structure of groundwater biofilms was monitored by atomic force microscopy (AFM) and optical coherence tomography (OCT) during three months of exposure to monochloramine or free chlorine. After the first month of disinfectant exposure, the mean stiffness of monochloramine- or free-chlorine-treated biofilms was 4 to 9 times higher than those before treatment. Meanwhile, the biofilm thickness decreased from 120 ± 8 μm to 93 ± 6–107 ± 11 μm. The increased surface stiffness and decreased biofilm thickness within the first month of disinfectant exposure was presumably due to the consumption of biomass. However, by the second to third month during disinfectant exposure, the biofilm mean stiffness showed a 2- to 4-fold decrease, and the biofilm thickness increased to 110 ± 7–129 ± 8 μm, suggesting that the biofilms adapted to disinfectant exposure. After three months of the disinfectant exposure process, the disinfected biofilms showed 2–5 times higher mean stiffness (as determined by AFM) and 6–13-fold higher ratios of protein over polysaccharide, as determined by differential staining and confocal laser scanning microscopy (CLSM), than the nondisinfected groundwater biofilms. However, the disinfected biofilms and nondisinfected biofilms showed statistically similar thicknesses (t test, p > 0.05), suggesting that long-term disinfection may not significantly remove net biomass. This study showed how biofilm mechanical and structural properties vary in response to a complex DWDS environment, which will contribute to further research on the risk assessment and control of biofilm-associated-pathogens in DWDS.
Shi, Y., Wells, G., & Morgenroth, E. (2016). Microbial activity balance in size fractionated suspended growth biomass from full-scale sidestream combined nitritation-anammox reactors. Bioresource Technology, 218, 38-45. doi:10.1016/j.biortech.2016.06.041, Institutional Repository

The purpose of this study was to determine the abundance, distribution and activity of aerobic ammonia-oxidizing bacteria (AOB) and anammox in size fractionated aggregates from full-scale suspended growth combined nitritation-anammox sidestream reactors. Plants with or without a cyclone device were also studied to assess a purported enrichment of anammox granules. Specific aerobic ammonium oxidation rates (p = 0.01) and specific oxygen uptake rates (p = 0.02) were significantly greater in flocs than in granules. AOB abundance measured using quantitative FISH was significantly higher in flocs than in granules (p = 0.01). Conversely, anammox abundance was significantly greater in granules (p = 0.03). The average ratio of anammox/AOB in systems employing hydrocyclone separation devices was 2.4, significantly higher (p = 0.02) than the average ratio (0.5) in a system without a hydrocyclone. Our results demonstrate substantial functional and population-level segregation between floccular and granular fractions, and provide a key corroboration that cyclone separation devices can increase anammox levels in such systems.
Thalmann, B., Voegelin, A., Morgenroth, E., & Kaegi, R. (2016). Effect of humic acid on the kinetics of silver nanoparticle sulfidation. Environmental Science: Nano, 3(1), 203-212. doi:10.1039/c5en00209e, Institutional Repository

The sulfidation of metallic silver nanoparticles (AgNP) observed in urban wastewater systems and in natural waters reduces their toxicity by several orders of magnitude. However, the reaction rate of this transformation is only poorly understood and the influence of humic acid (HA) on AgNP sulfidation has not been studied to date. We therefore investigate the sulfidation kinetics of AgNP reacted with bisulfide (HS−) in the absence and presence of HA and evaluate different kinetic models to describe the observed reaction kinetics. Citrate-stabilized AgNP of different sizes (20–200 nm) were reacted with an excess of HS− in the absence of HA as well as at HA concentrations ranging from 50 to 1000 mg L−1. The extent of AgNP sulfidation after the selected reaction times was determined by X-ray absorption spectroscopy (XAS). The overall sulfidation rate increased with decreasing AgNP size and increasing HA concentration. The sulfidation rate of the AgNP was best described by a diffusion-limited solid state reaction model (parabolic rate law). The corresponding half-lives of the AgNP ranged from minutes to hours. The increase of the sulfidation rate with increasing HA concentration may be explained by the adsorption of HA onto the AgNP surface facilitating the access of HS− to the particle surface. The results from analytical transmission electron microscopy suggest that the AgNP were sulfidized asymmetrically in the absence of HA. In the presence of HA, the initially formed concentric core–shell Ag0–Ag2S structures developed into hollow Ag2S nanoparticles with increasing reaction time, possibly via the Kirkendall effect.
Wu, S., Bhattacharjee, A. S., Weissbrodt, D. G., Morgenroth, E., & Goel, R. (2016). Effect of short term external perturbations on bacterial ecology and activities in a partial nitritation and anammox reactor. Bioresource Technology, 219, 527-535. doi:10.1016/j.biortech.2016.07.118, Institutional Repository

This research investigated the short term effects of temperature changes (lasting 2–4 weeks each) from 35 ± 2 °C to 21 ± 2 °C and 13 ± 2 °C and sulfide toxicity on partial nitrification-anammox (PN/A) system. Temperatures below 20 °C and sulfide content as low as 5 mgS L−1 affected both aerobic and anaerobic catabolic activities of ammonia oxidation and the expression of related functional gene markers. The activity of AOB was inversely correlated with ammonium monooxygenase (amoA) gene expression. In contrast, the activity of AMX bacteria was positively correlated with the expression of their hydrazine synthase (hzsA) gene. Although the overall activities of AMX bacteria decreased at lower temperatures, the AMX bacteria were still active at the low temperatures. The inverse correlation between amoA gene expressions and the corresponding AOB activities was surprising. 16S rDNA based high throughput amplicon sequencing revealed the dominance of Chloroflexi, Planctomycetes and Proteobacteria phyla the distribution of which changed with temperature changes.
Bogler, A. (2015). Effect of a feed spacer on biofouling in a forward osmosis membrane system (Master thesis). 35 p. , Institutional Repository

Fresh water sources are getting scarcer and innovative technologies are necessary to treat other water sources, for example wastewater. Forward Osmosis (FO) has been met with increasing interest over the past decades as it shows different advantages over pressure driven membrane processes. One advantage is a lower fouling propensity that gives FO high potential in treating feed waters with high fouling capacity. Literature on biofouling in FO is sparse. The objective of this thesis was therefore to investigate the e ect of feed spacers on biofouling in a FO system.
Pseudomonas aerigunosa was used as a model strain to biofoul a closed-loop custom-made flow system with a polyamide thin-film composite FO membrane. Synthetic wastewater mimicking secondary effluent was circulated as the feed solution, while 0.5M sodium chloride solution was used on the draw side to generate an initial flux of 20L/m2/h. Baselines were recorded over 24h to account for dilution, followed by the biofouling run lasting again 24h. After the biofouling membrane and feed spacer were analyzed for bacterial concentration via plate counts, for total organic carbon and protein and with confocal laser scanning microscopy for further characterization of the biofilm.
Results show that flow rate and spacer configuration on the draw side infuence the flux decline due to dilution, which varied from 9% to 24% at 500mL cumulative volume. This effect was not captured by the calculation of the water flux and was attributed to changes in the mass transfer coecient on the draw side, which was used as a fitting parameter. Those changes could be caused by the used spacer type and stagnant zones between spacer laments, but more experiments are necessary to investigate this further.
No flux decline due to biofouling was observed and the application of a feed spacer did not lead to significant differences. Flux decline during the baseline and biofouling without a feed spacer was 23±2% at a cumulative volume of 600mL. With a feed spacer flux decline was 26±4% during the baseline and 251% during biofouling. There was no difference between the biofilm grown in experiments with and without a feed spacer.
An equation was developed for the estimation of water flux influenced by bio lm growth. It represents the biofilm analogously to the membrane support layer relying on the concept of cake-enhanced concentration polarization. The equation predicted a flux decline of 5% due to biofouling. Biofilm growth was probably reduced by high shear forces and short experiment durations and its effect on flux might have been lessened by low feed solution concentrations. The equation did not represent the biofilm or the mechanism correctly and again more experiments are necessary to nd out what caused the biofilm to be without influence on the flux and how it can be represented correctly.
Briner, K. (2015). Calibration of a UV-Vis spectrophotometer for simultaneous estimation of nitrate and nitrite in nitrified urine (Master thesis). 26 p. , Institutional Repository

In the context of nutrient recovery research, urine is collected separately at Eawag Dübendorf (CH) and treated with biological nitrification. It is important to have an appropriate technique to measure the nitrite concentration in the reactor as nitrite, which is the intermediate product of nitrification, inhibits the process.
The objective of this project is to test UV-Vis spectrophotometry for the simultaneous estimation of nitrite and nitrate in the nitrified urine. For this purpose, the influence of changing nitrite and nitrate concentrations and of the urine background composition on the absorbance spectrum and the estimation accuracy is analysed. Furthermore, the stability of the estimation performance of the linear model under changes in the urine composition is evaluated. [...]
Chomiak, A., Traber, J., Morgenroth, E., & Derlon, N. (2015). Biofilm increases permeate quality by organic carbon degradation in low pressure ultrafiltration. Water Research, 85, 512-520. doi:10.1016/j.watres.2015.08.009, Institutional Repository

We investigated the influence of biofouling of ultrafiltration membranes on the removal of organic model foulants and ultimately on the quality of permeate. Gravity Driven Membrane ultrafiltration (GDM) membrane systems were operated with modified river water during five weeks without control of the biofilm formation. Three GDM systems were studied: two systems with biofilms exposed to (A) variable or (B) constant load of organic foulants, and (C) one system operated without biofilm and exposed to constant foulant loading. Biodegradable dextran or non-biodegradable polystyrene sulfonate model foulants were tested. Substrate biodegradability was confirmed by Size Exclusion Chromatography (SEC) and by degradation batch tests (D). The GDM systems (A) and (B) were fed with pre-filtered river water supplemented with dextran (Dex) of 1, 150 or 2000 kDa, or polystyrene sulfonate (PSS) of 1 or 80 kDa at concentrations of 2–3.5 mgC L−1. In exp. (C) the feed water consisted of deionized water with 25 mgC L−1 of either PSS 1, 80 kDa or Dex 2000 kDa.
The biofilm formation on UF membrane surfaces controlled the foulant permeation and thus the permeate quality. Biofilms exposed to continuous foulant loading (exp. B) degraded low molecular weight (LMW) biodegradable foulants (1 kDa Dex), which improved the permeate quality. For high molecular weight (HMW) substrates (150, 2000 kDa Dex), the improvement of the permeate quality was observed after 7 days of biofilm formation, and resulted from the foulant hydrolysis followed by degradation. For non-biodegradable foulants, an improvement of 20% of the retention was observed for the polystyrene (1, 80 kDa PSS) due to the presence of biofilms on membrane surfaces. For variable foulant loading (exp. A) the biofilms hydrolysed the large biodegradable foulants but did not degraded them fully, which resulted a deterioration of the permeate quality (except for the LMW dextran (1 kDa) that was fully degraded). Overall, the “biofilm + membrane” composite retained a larger amount of biodegradable foulant than the membrane alone, due to the activity of the biofilm. However, this resulted in an increased biofilm accumulation and reduced flux. In presence of the biofilm, the highest fluxes were observed for control (no foulant) and for small non-biodegradable foulants (PSS 1 kDa). Low fluxes were observed for the accumulating on membrane surface or degradable foulants (exp. B). But, the lowest fluxes were observed in absence of the biofilm (exp. C) due to physical accumulation of the foulants (PSS 80 kDa and Dextran 2000 kDa). Overall our study demonstrates that the presence of biofilms on membrane surfaces has some benefits: (i) biofilm helps to increase the permeate quality and (ii) biofilms protect the membrane from further fouling. Permeate flux stabilizes in the case of biofilm-membrane composite, while it continuously declines in the case of the membrane only.
Chomiak, A. (2015). Influence of inorganic and organic matter in gravity driven membrane ultrafilatration (Doctoral dissertation). doi:10.3929/ethz-a-010453952, Institutional Repository

The main advantage of membrane filtration processes is efficiency of separation, which allows to reach very high quality treated water. However, main disadvantages are cost of the treatment (electricity, chemicals) and membrane fouling, which can severely reduce the efficiency of the filtration process. Biofouling and biofilm formation is a major type of fouling due to biological deposition and activity on any membrane type surface. Biofilms on membranes significantly reduce permeation rates, and as such are removed and controlled by using chemical treatments (Flemming 2002). [...]

Die Membranfiltration ist attraktiv für die Trinkwasseraufbereitung, da sie Partikel sicher zurückhalten kann. Nachteile der Membranfiltration sind die hohen Kosten, verursacht durch den Energie‐ und Chemikalienverbrauch, sowie das sogenannte Fouling, welches die Effizienz der Filtration stark beeinträchtigen kann. Eine wichtige Form des Foulings ist das Biofouling bzw. Biofilmwachstum. Biofilme können die Permeabilität der Membran stark beeinträchtigen und werden in der Regel durch regelmässige, chemische Reinigung entfernt (Flemming 2002). [...]
Del Giudice, D. (2015). Improving output and input statistical error descriptions in urban hydrological modeling (Doctoral dissertation). doi:10.3929/ethz-a-010536371, Institutional Repository

Hydrological or drainage models can be valuable tools to support water management in urban environments. They can help to assess the characteristics of a catchment and to make predictions about its response (e.g. discharge). Unfortunately, parameters and results of these models are not perfect. These inaccuracies manifest themselves as model discrepancy, the so-called bias. Model bias represents the systematic deviation between model output and the real system response. There are two main causes of bias. First, there are errors in the input estimates, e.g. due to the insufficient coverage of pluviometers. Second, there are deficits in the model structure, e.g. due to the use of oversimplified empirical equations. Besides model bias, there are output measurement errors, e.g. due to imprecise flowmeters.
Until now, a large proportion of hydrological studies implicitly neglected input and structural errors. Neglecting these can lead to: i) misrepresented output measurement errors, ii) incorrect parameter estimates which compensate for model discrepancy, and iii) predictions which underestimate the uncertainty. Furthermore, these approaches do not provide guidance for finding the reasons for bias. Therefore, they cannot support its reduction. This inappropriate error consideration can finally lead to faulty risk assessment, flawed evaluation of decision alternatives, and, consequently, impaired urban water management. More advanced error assessment techniques are therefore called for.
The main goal of this thesis is to better represent input, structural, and output measurement errors. This can meliorate parameter estimation and prediction generation. The main thesis contributions are two. The first is a realistic description of the uncertainties in stormwater, wastewater, and sediment transport predictions. The second is a sound representation of errors in the rainfall inputs. Additionally, we discuss and compare different statistical methods used for hydrological inference. Finally, we also present a new tool to improve sewer flow monitoring. [...]
Egger, C. S. (2015). Sewer rehabilitation planning under uncertainty (Doctoral dissertation). doi:10.3929/ethz-a-010532893, Institutional Repository

The need for renewal of sewer systems will increase in coming decades. However, efficient and effective rehabilitation involves substantial planning challenges. These challenges are due to the typically limited degree of documentation of existing infrastructure, variability of input data and deterioration processes, lack of knowledge on the current and indeed future structural condition of sewer systems and unpredictable external influences. Planning challenges are even more pronounced in small utilities as (i) the rehabilitation demand will increase more markedly and (ii) informational, personal and financial planning resources are typically more restricted. Furthermore, it is necessary to make the planning process transparent as a wide range of stakeholders is involved and affected by the planning decisions. [...]

Der Erneuerungsbedarf von Kanalisationen wird in den nächsten Jahren vielerorts ansteigen. Eine effiziente und effektive Umsetzung dieses Bedarfs beinhaltet jedoch substanzielle planerische Herausforderungen. Diese sind begründet in limitiertem Dokumentationsgrad bestehender Infrastruktur, Variabilität von Eingangsgrössen und Alterungsprozessen, fehlendem Wissen über den heutigen und zukünftigen baulichen Zustand der Infrastruktur, sowie in hohem Masse unbekannten äusseren Einflussfaktoren. Insbesondere kleine Kanalnetzbetreiber sind von diesen Herausforderungen betroffen, da im ländlichen Raum oftmals (i) der Erneuerungsbedarf ausgeprägter ansteigen wird und (ii) dessen Planung informationell, personell wie finanziell noch stärkeren Einschränkungen unterliegt. Weiterhin gilt es entsprechende Planungen transparent zu gestalten, da ein breites Spektrum an Akteuren an Entscheidungen beteiligt und betroffen ist. [...]
Fumasoli, A., Morgenroth, E., & Udert, K. M. (2015). Modeling the low pH limit of Nitrosomonas eutropha in high-strength nitrogen wastewaters. Water Research, 83, 161-170. doi:10.1016/j.watres.2015.06.013, Institutional Repository

In wastewater treatment, the rate of ammonia oxidation decreases with pH and stops very often slightly below a pH of 6. Free ammonia (NH3) limitation, inhibition by nitrous acid (HNO2), limitation by inorganic carbon or direct effect of high proton concentrations have been proposed to cause the rate decrease with pH as well as the cessation of ammonia oxidation. In this study, we compare an exponential pH term common for food microbiology with conventionally applied rate laws based on Monod-type kinetics for NH3 limitation and non-competitive HNO2 inhibition as well as sigmoidal pH functions to model the low pH limit of ammonia oxidizing bacteria (AOB). For this purpose we conducted well controlled batch experiments which were then simulated with a computer model. The results showed that kinetics based on NH3 limitation and HNO2 inhibition can explain the rate decrease of ammonia oxidation between pH 7 and 6, but fail in predicting the pH limit of Nitrosomonas eutropha at pH 5.4 and rates close to that limit. This is where the exponential pH term becomes important: this term decreases the rate of ammonia oxidation to zero, as the pH limit approaches. Previously proposed sigmoidal pH functions that affect large pH regions, however, led to an overestimation of the pH effect and could therefore not be applied successfully. We show that the proposed exponential pH term can be explained quantitatively with thermodynamic principles: at low pH values, the energy available from the proton motive force is too small for the NADH production in Nitrosomonas eutropha and related AOB causing an energy limited state of the bacterial cell. Hence, energy limitation and not inhibition or limitation of enzymes is responsible for the cessation of the AOB activity at low pH values.
Habermacher, J., Benetti, A. D., Derlon, N., & Morgenroth, E. (2015). The effect of different aeration conditions in activated sludge – side-stream system on sludge production, sludge degradation rates, active biomass and extracellular polymeric substances. Water Research, 85, 46-56. doi:10.1016/j.watres.2015.08.002, Institutional Repository

On-site minimization of excess sludge production is a relevant strategy for the operation of small-scale and decentralized wastewater treatment plants. In the study, we evaluated the potential of activated sludge systems equipped with side-stream reactors (SSRs). This study especially focused on how the sequential exposure of sludge to different aeration conditions in the side-stream reactors influences the overall degradation of sludge and of its specific fractions (active biomass, extracellular polymeric substances (EPS), EPS proteins, EPS carbohydrates). We found that increasing the solid retention time from 25 to 40 and 80 days enhanced sludge degradation for all aeration conditions tested in the side-stream reactor. Also, the highest specific degradation rate and in turn the lowest sludge production were achieved when maintaining aerobic conditions in the side-stream reactors. The different sludge fractions in terms of active biomass (quantified based on adenosine tri-phosphate (ATP) measurements), EPS proteins and EPS carbohydrates were quantified before and after passage through the SSR. The relative amounts of active biomass and EPS to volatile suspended solids (VSS) did not changed when exposed to different aeration conditions in the SSRs, which indicates that long SRT and starvation in the SSRs did not promote the degradation of a specific sludge fraction. Overall, our study helps to better understand mechanisms of enhanced sludge degradation in systems operated at long SRTs.
Haupt, C. (2015). Feasibility of granular activated carbon (GAC) filtration as an alternative for electrolysis in the post-treatment of the Blue Diversion Toilet (Master thesis). 82 p. , Institutional Repository

The Blue Diversion Toilet (BDT) was developed as a possible answer to the sanita-tion crisis in urban slums. It is a urine-diverting dry toilet with an integrated water cycle that provides water for handwashing, personal hygiene and flushing the urine bowl. The recovery of the water happens in a so called water wall, based on a biolog-ically activated membrane bioreactor (BAMBi) together with an electrolysis module as the post-treatment. In order to primarily minimize the costs and the energy de-mand of the toilet, granular activated carbon (GAC) filters were investigated as an alternative to the electrolysis. For this purpose, four water walls with different post-treatments were monitored and compared: a control without any treatment, one drained and one flooded GAC bed and an electrolysis module. This study focused on the produced water quality from a hygienic point of view as well as with regard to the aesthetic, namely the colour. In order to investigate the possibility of the presence of pathogens in the recycled water, faecal indicators (E. coli and total coliforms) were monitored. Moreover, surrogates for organic content and therefore, the potential for microbial growth were investigated by measuring the amount of total organic carbon (TOC) and assimilable organic carbon (AOC). Further, a spiking experiment with a viral indicator (MS2) was conducted in order to examine the retention of vi-ruses within the water wall. Finally, the absorbance of the water was measured in order to investigate the colour removal. It was found that with both applications, GAC and electrolysis, the absence of E. coli in the effluent in most of the times was guaranteed and thus the risk of bacterial pathogens could be most probably excluded. While drained GAC and flooded GAC yielded to a significant TOC removal, no sig-nificant TOC removal by the electrolysis was observed. Further, no significant AOC removal by the post-treatments could be measured; neither for the electrolysis nor for GAC. All median AOC concentrations in the effluents exceeded the proposed limits for a biological stability at least for drinking water. In order to draw reliable conclu-sions of the impact of the post-treatments on the removal of viruses, further research is needed. With regard to the aesthetic, both, electrolysis and GAC, yielded to a sig-nificant reduction of absorbance of the water and did not significantly differ in their ability to reduce the colour. From those results it can be concluded that at the current settings of the electrolysis, GAC constitutes a feasible alternative. Due to the fact that both, electrolysis and GAC alone, only partly achieved a satisfying water quality, the combination of both should be considered, since this could achieve a better water quality and save energy.
Hubaux, N., Wells, G., & Morgenroth, E. (2015). Impact of coexistence of flocs and biofilm on performance of combined nitritation-anammox granular sludge reactors. Water Research, 68, 127-139. doi:10.1016/j.watres.2014.09.036, Institutional Repository

Nitrogen (N) removal from high-strength wastewater can be accomplished in single-stage combined nitritation-anammox reactors with suspended growth biomass composed of floccular sludge, granular sludge, or of any mix of these 2 different sludge fractions. To date, the influence of floccular biomass on granular sludge reactor performance and stability has not been investigated experimentally or numerically. To address this knowledge gap, two 1D multi-species models were developed in Aquasim to assess the importance of small levels of flocs in putatively granular sludge combined nitritation-anammox reactors for different bulk oxygen concentrations and organics loads. The models included the growth and decay of aerobic ammonium-oxidizing organism (AOO), nitrite-oxidizing organisms (NOO), heterotrophic organisms (OHO), and anammox organisms (AMO) in exclusively granular sludge reactors, and in granular sludge reactors with small levels (∼5% of total biomass) of flocs. While maximum N removal efficiencies were similar for both model structures, floc addition led to a lower optimal dissolved oxygen concentration (DO) as well as a narrower maximum N removal peak, suggesting that small levels of floccular material may decrease process robustness to bulk oxygen changes. For some DO levels, this led to drastic efficiency drops. Furthermore, floc addition also led to substantial segregation in activity and microbial population distribution, with AOO, NOO and OHO concentrated in flocs and AMO concentrated in granules. Increased organic loading (COD:N = 4:3) improved maximum N removal efficiency in both model structures, but yielded substantially different predictions for optimal DO setpoint and process robustness to variations in DO. Taken together, our results indicate that even small levels of floccular biomass in biofilm reactors can have profound implications for reactor performance and optimization and for segregation of linked microbial processes, and suggest that the common practice of neglecting small levels of floccular material in biofilm models and in practice may lead to erroneous predictions.
Künzle, R., Pronk, W., Morgenroth, E., & Larsen, T. A. (2015). An energy-efficient membrane bioreactor for on-site treatment and recovery of wastewater. Journal of Water Sanitation and Hygiene for Development, 5(3), 448-455. doi:10.2166/washdev.2015.116, Institutional Repository

The present study describes the development of a new type of aerated membrane bioreactor referred to as a biologically activated membrane bioreactor (BAMBi) for on-site treatment of high-strength wastewater. The treated wastewater is reused for flushing and personal hygiene. BAMBi is an adaptation of a gravity-driven membrane reactor, originally developed for the purpose of treating river water to drinking water quality. Initially, a series of reactor configurations were tested and it was found that the simplest possible configuration could treat the wastewater to an acceptable standard, provided that a polishing step for color removal and disinfection was introduced. A commercial electrolysis unit was utilized for polishing. The energy consumption of BAMBi is 0.8 kWh/m3 of water treated, which can be considered low for an on-site membrane bio reactor application.
Larsen, T. A., Gebauer, H., Gründl, H., Künzle, R., Lüthi, C., Messmer, U., … Ranner, B. (2015). Blue Diversion: a new approach to sanitation in informal settlements. Journal of Water Sanitation and Hygiene for Development, 5(1), 64-71. doi:10.2166/washdev.2014.115, Institutional Repository

The sanitation concept ‘Blue Diversion’ (www.bluediversiontoilet.com) was developed as a possible answer to the sanitation crisis in urban slums. It is based on two main elements: (1) diversion of urine, feces, and water at the source as the basis for efficient resource recovery, and (2) linking different scales (family toilets and semi-centralized resource recovery). Our objective was to develop an attractive ‘grid-free’ (i.e. functioning without piped water, sewer, and electrical grid) dry urine-diverting toilet, which provides water (through recycling on-site) for flushing, personal hygiene (anal cleansing and menstrual hygiene), and hand washing. This service, including the entire sanitation value chain, should eventually be made available as a profitable business with total user fees of 5 ¢/p/d. The results presented in this paper are (1) a toilet design model, (2) the development of a new type of membrane bioreactor for treating flush and wash water, (3) main results of a geographic information system-based stochastic service model to link the family-scale toilet to a community-scale Resource Recovery Plant, and (4) a business model that yields maximum profit for the local community. We conclude that the approach is feasible, but challenging from a technical as well as an organizational point of view.
Laureni, M., Weissbrodt, D. G., Szivák, I., Robin, O., Nielsen, J. L., Morgenroth, E., & Joss, A. (2015). Activity and growth of anammox biomass on aerobically pre-treated municipal wastewater. Water Research, 80, 325-336. doi:10.1016/j.watres.2015.04.026, Institutional Repository

Direct treatment of municipal wastewater (MWW) based on anaerobic ammonium oxidizing (anammox) bacteria holds promise to turn the energy balance of wastewater treatment neutral or even positive. Currently, anammox processes are successfully implemented at full scale for the treatment of high-strength wastewaters, whereas the possibility of their mainstream application still needs to be confirmed. In this study, the growth of anammox organisms on aerobically pre-treated municipal wastewater (MWWpre-treated), amended with nitrite, was proven in three parallel reactors. The reactors were operated at total N concentrations in the range 5–20 mgN∙L−1, as expected for MWW. Anammox activities up to 465 mgN∙L−1∙d−1 were reached at 29 °C, with minimum doubling times of 18 d. Lowering the temperature to 12.5 °C resulted in a marked decrease in activity to 46 mgN∙L−1∙d−1 (79 days doubling time), still in a reasonable range for autotrophic nitrogen removal from MWW. During the experiment, the biomass evolved from a suspended growth inoculum to a hybrid system with suspended flocs and wall-attached biofilm. At the same time, MWWpre-treated had a direct impact on process performance. Changing the influent from synthetic medium to MWWpre-treated resulted in a two-month delay in net anammox growth and a two to three-fold increase in the estimated doubling times of the anammox organisms. Interestingly, anammox remained the primary nitrogen consumption route, and high-throughput 16S rRNA gene-targeted amplicon sequencing analyses revealed that the shift in performance was not associated with a shift in dominant anammox bacteria ("Candidatus Brocadia fulgida"). Furthermore, only limited heterotrophic denitrification was observed in the presence of easily biodegradable organics (acetate, glucose). The observed delays in net anammox growth were thus ascribed to the acclimatization of the initial anammox population or/and the development of a side population beneficial for them. Additionally, by combining microautoradiography and fluorescence in situ hybridization it was confirmed that the anammox organisms involved in the process did not directly incorporate or store the amended acetate and glucose. In conclusion, these investigations strongly support the feasibility of MWW treatment via anammox.
Mimoso, J., Pronk, W., Morgenroth, E., & Hammes, F. (2015). Bacterial growth in batch-operated membrane filtration systems for drinking water treatment. Separation and Purification Technology, 156, 165-174. doi:10.1016/j.seppur.2015.09.070, Institutional Repository

Membrane filtration treats drinking water by physical removal of bacteria and other particles present in the raw water. In order to study post-filtration contamination and growth, filtered river water and wastewater were used in a controlled laboratory-scale simulation of a batch-operated membrane filtration system. Bacterial batch growth was analyzed following intentional initial contamination with a river water microbial community. Batch growth in the permeate was measured with online flow cytometry at high intervals during 10 successive 24-hour operational cycles, simulating repeated daily use (filtration followed by stagnation). Two operational mechanisms influenced the growth characteristics: (1) initial selection of bacteria adapted to batch growth conditions, and (2) biofilm formation on the surfaces of the permeate containers. The first mechanism contributed towards a stable and reproducible growth behavior (lag phase of less than 4 h, maximum growth rates of 0.37–0.42 h−1 and final total cell counts of 1.5–1.8 × 106 cells mL−1) throughout several consecutive operational cycles. When the feed water changed, the adapted bacterial communities grew rapidly and proportionally to the amount of substrate in the new water source. Biofilm development in the permeate containers resulted in a 20% reduction in the overall cell production during five operational days, suggesting this to be a potential novel strategy towards controlling biological stability in such systems.
Morgenroth, E., Derlon, N., Pronk, W., & Larsen, T. A. (2015). Von der Grundlagenforschung zur Anwendung: Trinkwasseraufbereitung und Sanitärversorgung (p. (14 pp.). Presented at the 48. Essener Tagung für Wasser- und Abfallwirtschaft "Forschung trifft Praxis". Aachen, Germany. , Institutional Repository
Ravndal, K. T., Künzle, R., Derlon, N., & Morgenroth, E. (2015). On-site treatment of used wash-water using biologically activated membrane bioreactors operated at different solids retention times. Journal of Water Sanitation and Hygiene for Development, 5(4), 544-552. doi:10.2166/washdev.2015.174, Institutional Repository

Biologically activated membrane bioreactors (BAMBis) were operated at suspended solids retention times (SRT) of 7 and 102 days and at full solids retention. The effect of these different approaches of operation on substrate and nutrient conversion, and on permeate flux was investigated. Variations in organic loads and aeration intensities were also studied. Permeate flux stabilized during long-term operation independently of suspended SRT. Removal of organic substrate was independent of solids concentrations and remained stable over the long term. Microorganisms colonizing the surface of particles were found as the main mechanism responsible for degradation of organic substrate in the particulate form. BAMBi appeared to be a robust technology, adapted to on-site treatment of used wash-water, as it can be operated without control of suspended SRT. Thus BAMBis can be operated for long periods without any control of biofouling and sludge formation, leading to low maintenance needs. When BAMBis were operated at low aeration, the formation of anoxic zones led to combined nitrification and denitrification and thus significant nitrogen removal.
Schielke-Jenni, S. (2015). Decentralised urine treatment with the nitritationammox process (Doctoral dissertation). doi:10.3929/ethz-a-010479901, Institutional Repository

Urine contains over 80% of the total nitrogen but accounts for less than 1% of the total wastewater volume. Due to higher concentrations, nitrogen removal from source-separated urine is potentially much cheaper and less energy intensive than from wastewater. For many cities, removing nitrogen in small decentralized reactors could be more efficient and affordable than in large treatment plants situated at the end of extensive sewer networks. However, due to a lack of personnel and expensive instruments, process control of small on-site reactors is potentially critical. In addition, process stability and resilience tend to be low due to a lower microbial diversity. Therefore, the main goal of this thesis is to contribute to the development of a reliable and simple process configuration for decentralised nitrogen removal from urine. [...]

Urin beinhaltet über 80% des gesamten Stickstoffs und macht aber nur etwas weniger als 1% des gesamten Abwasservolumens aus. Aufgrund der höheren Konzentrationen ist Stickstoffentfernung aus separat gesammeltem Urin potentiell günstiger und verbraucht weniger Energie als Stickstoffentfernung aus dem gesamten Abwasser. Stickstoffentfernung in kleinen dezentralen Reaktoren könnte deshalb für viele Städte effizienter und erschwinglicher sein als in grossen Reinigungsanlagen am Ende von weitläufigen Kanalisationsnetzen. Da aber kein Personal und keine teuren Instrumente zur Verfügung stehen, kann die Prozesskontrolle von kleinen, dezentralen Reaktoren kritisch sein. Aufgrund der niedrigeren mikrobiellen Diversität, ist in kleinen Systemen tendenziell auch mit einer geringeren Stabilität und Belastbarkeit der Prozesse zu rechnen. Das Hauptziel dieser Arbeit war deshalb, einen Beitrag zur Entwicklung eines einfachen und robusten Prozesses zur dezentralen Stickstoffentfernung aus Urin zu leisten. [...]
Schielke-Jenni, S., Villez, K., Morgenroth, E., & Udert, K. M. (2015). Observability of anammox activity in single-stage nitritation/anammox reactors using mass balances. Environmental Science: Water Research and Technology, 1(4), 523-534. doi:10.1039/c5ew00045a, Institutional Repository

In nitritationammox reactors, several bacterial groups contribute to the overall nitrogen conversion. Knowing the activity of the main bacterial groups, especially of anaerobic ammonium-oxidising bacteria (AMX), is extremely helpful to understand the process and optimise its operation. Mass balances of dissolved compounds such as ammonium, nitrite and nitrate commonly allow the determination of bacterial activities in a nitritationammox process, but the activity of heterotrophic bacteria (HET) is usually neglected. However, even in wastewater with a low organic substrate content, heterotrophic denitrification can contribute substantially to nitrogen removal. The goal of this study was to critically evaluate the applicability of mass balances for the determination of the relevant bacterial activities in a nitritationammox process with high HET activity. We set up and solved mass balances of different degrees of complexity. Both linear equation systems, with catabolic reactions alone and with balances according to the activated sludge model stoichiometry, do not allow estimation of any of the considered bacterial activities. When kinetic rate expressions are included, it is possible to compute the concentrations of all considered bacterial groups, but the estimation uncertainty is far too high for practical purposes: the relative standard deviation for AMX is 5280%. In a completely autotrophic system, the relative standard deviation for AMX is only 5%, which proves that the high standard deviations are due to the complexity of the nitration–anammox process with HET activity. The high standard deviations of the calculated bacterial concentrations can be significantly reduced by adding an additional mass balance for the total biomass (standard deviation for AMX activity 1210%). The required number of measurements to achieve an acceptable precision, in our example about 600 conversion rate measurements to reach a 50% standard deviation for the AMX concentration, is still far too high though for practical purposes. To conclude, mass balances including kinetics theoretically allow the observation of the bacterial activities in nitritationammox reactors with high HET activity. However, the required precision of the calculated conversion rates, the uncertainty of stoichiometric and kinetic parameters and the reactor dynamics (unsteady conditions) make mass balances unsuitable for practical estimation of AMX activity. Due to high frequency and new online instruments, mass balances might become a suitable tool in the future.
Schönenberger, U. (2015). Data reconciliation and gross error detection for wastewater treatment processes (Master thesis). 34 p. , Institutional Repository

Sensors on wastewater treatment plants are often influenced by measurement errors. These errors can seriously affect the control and monitoring of the processes occurring in these facilities. In this thesis it is investigated to which extent mass balancing methods can be used to reduce random errors and to detect gross errors in the measurements of hydraulic flows and TSS concentrations of wastewater treatment plants.
Therefore, a bilinear data reconciliation technique is implemented and evaluated by means of the Benchmark Simulation model No. 1 – Long Term (BSM1_LT). The BSM1_LT is a wastewater treatment plant simulation platform which was developed to compare different error detection methods. In this thesis the following gross error detection methods are assessed using the BSM1_LT: Global test, univariate CUSUM charts and multivariate CUSUM charts.
The results show that bilinear data reconciliation is able to reduce random errors in the measurements of hydraulic flows and TSS component flows. CUSUM charts are found to show a much higher gross error detection power than the global test. Furthermore, it is revealed that accounting for TSS storage and TSS reaction processes is essential for the success of the implemented data reconciliation and gross error detection methods.
Shen, Y., Monroy, G. L., Derlon, N., Janjaroen, D., Huang, C., Morgenroth, E., … Nguyen, T. H. (2015). Role of biofilm roughness and hydrodynamic conditions in legionella pneumophila adhesion to and detachment from simulated drinking water biofilms. Environmental Science and Technology, 49(7), 4274-4282. doi:10.1021/es505842v, Institutional Repository

Biofilms in drinking water distribution systems (DWDS) could exacerbate the persistence and associated risks of pathogenic Legionella pneumophila (L. pneumophila), thus raising human health concerns. However, mechanisms controlling adhesion and subsequent detachment of L. pneumophila associated with biofilms remain unclear. We determined the connection between L. pneumophila adhesion and subsequent detachment with biofilm physical structure characterization using optical coherence tomography (OCT) imaging technique. Analysis of the OCT images of multispecies biofilms grown under low nutrient condition up to 34 weeks revealed the lack of biofilm deformation even when these biofilms were exposed to flow velocity of 0.7 m/s, typical flow for DWDS. L. pneumophila adhesion on these biofilm under low flow velocity (0.007 m/s) positively correlated with biofilm roughness due to enlarged biofilm surface area and local flow conditions created by roughness asperities. The preadhered L. pneumophila on selected rough and smooth biofilms were found to detach when these biofilms were subjected to higher flow velocity. At the flow velocity of 0.1 and 0.3 m/s, the ratio of detached cell from the smooth biofilm surface was from 1.3 to 1.4 times higher than that from the rough biofilm surface, presumably because of the low shear stress zones near roughness asperities. This study determined that physical structure and local hydrodynamics control L. pneumophila adhesion to and detachment from simulated drinking water biofilm, thus it is the first step toward reducing the risk of L. pneumophila exposure and subsequent infections.
Thalmann, B., Voegelin, A., von Gunten, U., Behra, R., Morgenroth, E., & Kaegi, R. (2015). Effect of ozone treatment on nano-sized silver sulfide in wastewater effluent. Environmental Science and Technology, 49(18), 10911-10919. doi:10.1021/acs.est.5b02194, Institutional Repository

Silver nanoparticles used in consumer products are likely to be released into municipal wastewater. Transformation reactions, most importantly sulfidation, lead to the formation of nanoscale silver sulfide (nano-Ag2S) particles. In wastewater treatment plants (WWTP), ozonation can enhance the effluent quality by eliminating organic micropollutants. The effect of ozonation on the fate of nano-Ag2S, however, is currently unknown. In this study, we investigate the interaction of ozone with nano-Ag2S and evaluate the effect of ozonation on the short-term toxicity of WWTP effluent spiked with nano-Ag2S. The oxidation of nano-Ag2S by ozone resulted in a stoichiometric factor (number of moles of ozone required to oxidize one mole of sulfide to sulfate) of 2.91, which is comparable to the results obtained for the reaction of bisulfide (HS–) with ozone. The second-order rate constant for the reaction of nano-Ag2S with ozone (k = 3.1 × 104 M–1 s–1) is comparable to the rate constant of fast-reacting micropollutants. Analysis of the ozonation products of nano-Ag2S by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) revealed that ozonation dominantly led to the formation of silver chloride in WWTP effluent. After ozonation of the Ag2S-spiked effluent, the short-term toxicity for the green algae Chlamydomonas reinhardtii increased and reached EC50 values comparable to Ag+. This study thus reveals that ozone treatment of WWTP effluent results in the oxidation of Ag2S and, hence, an increase of the Ag toxicity in the effluent, which may become relevant at elevated Ag concentrations.
Thalmann, B. A. D. (2015). Transformations of silver nanoparticles in urban wastewater and water systems (Doctoral dissertation). doi:10.3929/ethz-a-010579189, Institutional Repository

Metallic silver nanoparticles (AgNP) are increasingly applied in consumer products from which they are probably released to the urban wastewater and water system. Due to the antimicrobial activity of AgNP, they are of high ecotoxicological concern and an engineered nanomaterial of priority for environmental risk assessment. Transformations of AgNP can have large efects on their toxicity toward aquatic organism. Most importantly, the sulidation of AgNP is known to reduce the toxicity of Ag by several orders of magnitude. Thus, a proper understanding of the sulidation of AgNP in the urban wastewater and water system is crucial for in-depth environmental risk assessments. Furthermore, the ozonation of the eluent of wastewater treatment plant (WWTP) to mitigate micropollutants is likely to further change the Ag speciation. he irst objective of this thesis was to understand the sulidation kinetics of AgNP with bisulide (HS-) and metal sulides. The second objective was to study the impact of ozone treatment on sulidized AgNP. [...]

Silber Nanopartikel (AgNP) werden vermehrt in Konsumgütern angewandt, von welchen die Partikel durch den Gebrauch in das urbane Abwasser und Wasser ausgewaschen werden können. Aufgrund ihrer antimikrobieller Wirkung stellen sie ein potentielles Risiko für die Umwelt dar, welches abgeschätzt werden sollte. Durch Umwandlung in der Umwelt ändert sich die Speziierung der AgNP was die Toxizität gegenüber aquatischen Organismen und Planzen beeinlusst. Die Reaktion von AgNP mit Suliden, genannt Sulidierung, zum Beispiel reduziert die Ag Toxizität um mehrere Grössenordnungen. Deshalb ist es für eine Risikoeinschätzung der AgNP in der Umwelt wichtig die Sulidierung im urbanen Abwasser und Wasser zu verstehen. Im Abwasser ist die dominante Sulid Quelle Bisulid (HS-), welches in erhöhten Konzentrationen zu inden ist. Für das Oberlächengewässer hingegen ist die Sulidierung mit Metallsuliden wahrscheinlicher, da sie persistenter gegen die Oxidation mit Sauerstof sind. Das erste Ziel dieser Dissertation war deshalb die Sulidierung von AgNP mit HS- und Metallsuliden zu verstehen. [...]
Trottmann, C. (2015). Simultaneous nitrification and denitrification with aerobic granules in municipal wastewater (Master thesis). 31 p. , Institutional Repository

This study aims at the question why SND is only working with very low efficiency for granules fed with municipal wastewaster. Therefore three hypotheses were set up: (i) Absence of anoxic zone within the aerobic granules due to deep penetration of oxygen, (ii) low availability of electron donor (carbon source) for denitrification and (iii) low denitrification rate as fraction of large granules is too small.
Experiments with batch reactors were performed, with aerobic granular sludge (40-60 % granules) from a column sequencing batch reactor fed with municipal wastewater, to verify the hypotheses.
To analyze the influence of a carbon source a distinction of two cases was done. In Case 1 the granules were fed with extra added acetate in a first anaerobic phase. Phosphate,- and glycogenaccumulating bacteria (PAOs and GAOs) stored this acetate intracellular as polyhydroxyalkanoates (PHA) before the aerobic phase started. For Case 2 only particular carbon stored in the matrix of the granules, as extracellular polymeric substances (EPS), was available.
Beside that the oxygen concentration was varied between 0.5-2.2 mgO2l-1 and separate tests with extra added nitrate were done to evaluate the denitrification rate.
For Case 1 the intracellular stored acetate (PHA) caused a stable simultaneous nitrification and denitrification process whereas for Case 2 unstable situations sometimes caused no denitrifaciton at all. The oxygen concentration was found to be a very important and sensitive parameter.
It has a direct impact to the anoxic volume in the granules due to its mass transport limitation by diffusion which is limiting the penetration depth (causing an aerobic surface were nitrification is performed and an anoxic core with denitrifying bacteria).
Highest SND ratios were found in Case 1 at an oxygen concentration level of 0.5-1.0 mgO2l-1 and completely taken up and intracellular stored acetate of 100 mgCODl-1. An average SND efficiency of 26.4±13.6 % was reached therefore.
Denitrification rates of 1.22±0.16 mgN∙gVSS-1∙h-1 (Case 1) and 0.89±0.05 mgN∙gVSS-1∙h-1 (Case 2) were observed.
The fraction of large granules (d>0.63 mm) of only 10 % by weight (gVSS) was relatively low. Therefore it is affirmed that denitrification is low due to this, but not that the denitrification rate is lower than for smaller granules.
Vannecke, T. P. W., Wells, G., Hubaux, N., Morgenroth, E., & Volcke, E. I. P. (2015). Considering microbial and aggregate heterogeneity in biofilm reactor models: how far do we need to go?. Water Science and Technology, 72(10), 1692-1699. doi:10.2166/wst.2015.389, Institutional Repository

A model describing a given system should be as simple as possible – but not simpler. The appropriate level of complexity depends both on the type of system and on the intended use of the model. This paper addresses the critical question of which purposes justify increased complexity of biofilm (reactor) models. Additional model features compared to conventional models considered are: (1) the inclusion of microbial diversity, distinguishing between different species performing the same function; and (2) the distinction between flocs and granules in putatively granular sludge reactors. With a multispecies model considering interspecies diversity, it was demonstrated that a given macroscopic reactor performance does not necessarily reflect steady state conditions on the microscale. In a second case study, it was shown that the addition of a small level of flocs can have a significant impact on macroscale process performance and on microbial population and activity distributions in granular sludge reactors. It was concluded that increased complexity in biofilm models, concerning microbial diversity or mesoscale aggregate architecture, is likely more useful when the focus is on understanding fundamental microscale outputs, but under specific conditions, these additional model features can be critically informative for bulk reactor behavior prediction and general understanding.
Wagner, J., Weissbrodt, D. G., Manguin, V., Ribeiro da Costa, R. H., Morgenroth, E., & Derlon, N. (2015). Effect of particulate organic substrate on aerobic granulation and operating conditions of sequencing batch reactors. Water Research, 85, 158-166. doi:10.1016/j.watres.2015.08.030, Institutional Repository

The formation and application of aerobic granules for the treatment of real wastewaters still remains challenging. The high fraction of particulate organic matter (XS) present in real wastewaters can affect the granulation process. The present study aims at understanding to what extent the presence of XS affects the granule formation and the quality of the treated effluent. A second objective was to evaluate how the operating conditions of an aerobic granular sludge (AGS) reactor must be adapted to overcome the effects of the presence of XS. Two reactors fed with synthetic wastewaters were operated in absence (R1) or presence (R2) of starch as proxy for XS. Different operating conditions were evaluated. Our results indicated that the presence of XS in the wastewater reduces the kinetic of granule formation. After 52 d of operation, the fraction of granules reached only 21% in R2, while in R1 this fraction was of 54%. The granules grown in presence of XS had irregular and filamentous outgrowths in the surface, which affected the settleability of the biomass and therefore the quality of the effluent. An extension of the anaerobic phase in R2 led to the formation of more compact granules with a better settling ability. A high fraction of granules was obtained in both reactors after an increase of the selection pressure for fast-settling biomass, but the quality of the effluent remained low. Operating the reactors in a simultaneous fill-and-draw mode at a low selection pressure for fast-settling biomass showed to be beneficial for substrate removal efficiency and for suppressing filamentous overgrowth. Average removal efficiencies for total COD, soluble COD, ammonium, and phosphate were 87 ± 4%, 95 ± 1%, 92 ± 10%, and 87 ± 12% for R1, and 72 ± 12%, 86 ± 5%, 71 ± 12%, and 77 ± 11% for R2, respectively. Overall our study demonstrates that the operating conditions of AGS reactors must be adapted according to the wastewater composition. When treating effluents that contain XS, the selection pressure should be significantly reduced.
Wu, S., Weissbrodt, D. G., Morgenroth, E., & Goel, R. (2015). Resiliency of anammox against external stress factors – Effects of temperature and wastewater constituents. In Vol. 3. 88th annual water environment federation technical exhibition and conference (WEFTEC 2015) (pp. 1476-1483). doi:10.2175/193864715819540054, Institutional Repository

Nitrogen r emoval based on anaerobic a mmonium oxidation (anammox) has g ained tremendous popularity as it is energy efficient and environmentally friendly. In this case, anammox is c oupled w ith p artial n itrification (collectively called p artial n itritation-anammox or P N/A systems) t o a ccomplish ne arly 80–90% t otal i norganic ni trogen removal. Despite s ignificant k nowledge gained ab out t he p rocess en gineering an d microbiology related to PN/A systems, very little is known about the effect of external perturbations on P N/A s ystems e specially in a s ystem b iology f ramework. I n this research w e first evaluated t he effects o f m etal an d t oxic l oading o n an en riched anammox community. Thereafter, we operated a single-stage PN/A lab-scale reactor to evaluate the effect of temperature on t he process efficiency and system microbiology. Mercury led to a 50% reduction and lead caused a 20% reduction in specific anammox activity a t 0.8 m g/L concentrations. Cyanide, used as a t oxic ch emical, caused significant anammox activity inhibition at 50 pp b concentration. The results related to temperature changes showed that ammonium oxidizing bacteria (Nitrosomonas sp.) can maintain a relatively stable activity at lower temperatures (13~21°C), while anammox bacteria (Candidatus Brocadia) are more sensitive to temperature reductions.
Zöllig, H., Fritzsche, C., Morgenroth, E., & Udert, K. M. (2015). Direct electrochemical oxidation of ammonia on graphite as a treatment option for stored source-separated urine. Water Research, 69, 284-294. doi:10.1016/j.watres.2014.11.031, Institutional Repository

Electrolysis can be a viable technology for ammonia removal from source-separated urine. Compared to biological nitrogen removal, electrolysis is more robust and is highly amenable to automation, which makes it especially attractive for on-site reactors. In electrolytic wastewater treatment, ammonia is usually removed by indirect oxidation through active chlorine which is produced in-situ at elevated anode potentials. However, the evolution of chlorine can lead to the formation of chlorate, perchlorate, chlorinated organic by-products and chloramines that are toxic. This study focuses on using direct ammonia oxidation on graphite at low anode potentials in order to overcome the formation of toxic by-products. With the aid of cyclic voltammetry, we demonstrated that graphite is active for direct ammonia oxidation without concomitant chlorine formation if the anode potential is between 1.1 and 1.6 V vs. SHE (standard hydrogen electrode). A comparison of potentiostatic bulk electrolysis experiments in synthetic stored urine with and without chloride confirmed that ammonia was removed exclusively by continuous direct oxidation. Direct oxidation required high pH values (pH > 9) because free ammonia was the actual reactant. In real stored urine (pH = 9.0), an ammonia removal rate of 2.9 ± 0.3 gN·m−2·d−1 was achieved and the specific energy demand was 42 Wh·gN−1 at an anode potential of 1.31 V vs. SHE. The measurements of chlorate and perchlorate as well as selected chlorinated organic by-products confirmed that no chlorinated by-products were formed in real urine. Electrode corrosion through graphite exfoliation was prevented and the surface was not poisoned by intermediate oxidation products. We conclude that direct ammonia oxidation on graphite electrodes is a treatment option for source-separated urine with three major advantages: The formation of chlorinated by-products is prevented, less energy is consumed than in indirect ammonia oxidation and readily available and cheap graphite can be used as the electrode material.
Zöllig, H. (2015). Electrolysis for the treatment of stored source-separated urine (Doctoral dissertation). doi:10.3929/ethz-a-010549050, Institutional Repository

Electrolysis is a promising technology for the on-site treatment of source-separated urine. It is the many degrees of freedom (electrode material, electrode potential, current density, cell design), the electrical conductivity of urine and the high amenability to automation which make electrolysis attractive. It was the objective of this thesis to understand the electro-oxidation of organic substances and ammonia to apply electrolysis successfully for the removal of these compounds from stored source-separated urine. To achieve this goal, a variety of electrochemical experiments were conducted with anodes consisting of boron-doped diamond (BDD), thermally decomposed iridium oxide film (TDIROF) or graphite and a new experimental procedure was developed to assess the time dependent production of volatile organic chlorination by-products (OCBPs). [...]

Die Elektrolyse ist eine vielversprechende Technologie für die Behandlung von Urin. Es sind die vielen Freiheitsgrade (Elektrodenmaterialien, Elektrodenpotential, Stromdichte, Zellendesign), die elektrische Leitfähigkeit des Urins sowie das hohe Automatisierungspotential, welche die Elektrolyse attraktiv machen. Es war das Ziel dieser Arbeit, die elektrochemische Oxidation von organischen Substanzen und Ammoniak zu verstehen, um diese für die dezentrale Behandlung von gelagertem Urin anzuwenden. Es wurden elektrochemische Experimente mit Bor-versetzten Diamant-(BDD), thermisch hergestellten Iridiumoxidfilm- (TDIROF) und Graphitanoden durchgeführt. Um dabei die Entstehung von leichtflüchtigen, chlorierten Nebenprodukten (CNPs) zu verfolgen, wurde eine neue experimentelle Methode entwickelt. [...]
Zöllig, H., Remmele, A., Fritzsche, C., Morgenroth, E., & Udert, K. M. (2015). Formation of chlorination byproducts and their emission pathways in chlorine mediated electro-oxidation of urine on active and nonactive type anodes. Environmental Science and Technology, 49(18), 11062-11069. doi:10.1021/acs.est.5b01675, Institutional Repository

Chlorination byproducts (CBPs) are harmful to human health and the environment. Their formation in chlorine mediated electro-oxidation is a concern for electrochemical urine treatment. We investigated the formation of chlorate, perchlorate, and organic chlorination byproducts (OCBPs) during galvanostatic (10, 15, 20 mA·cm–2) electro-oxidation of urine on boron-doped diamond (BDD) and thermally decomposed iridium oxide film (TDIROF) anodes. In the beginning of the batch experiments, the production of perchlorate was prevented by competing active chlorine and chlorate formation as well as by direct oxidation of organic substances. Perchlorate was only formed at higher specific charges (>17 Ah·L–1 on BDD and >29 Ah·L–1 on TDIROF) resulting in chlorate and perchlorate being the dominant CBPs (>90% of initial chloride). BDD produced mainly short chained OCBPs (dichloromethane, trichloromethane, and tetrachloromethane), whereas longer chained OCBPs (1,2-dichloropropane and 1,2-dichloroethane) were more frequently found on TDIROF. The OCBPs were primarily eliminated by electrochemical stripping: On BDD, this pathway accounted for 40% (dichloromethane) to 100% (tetrachloromethane) and on TDIROF for 90% (1,2-dichloroethane) to 100% (trichloromethane) of what was produced. A post-treatment of the liquid as well as the gas phase should be foreseen if CBP formation cannot be prevented by eliminating chloride or organic substances in a pretreatment.
Zöllig, H., Morgenroth, E., & Udert, K. M. (2015). Inhibition of direct electrolytic ammonia oxidation due to a change in local pH. Electrochimica Acta, 165, 348-355. doi:10.1016/j.electacta.2015.02.162, Institutional Repository

Electrochemical ammonia oxidation has gained a lot of attention recently as an efficient method for ammonia removal from wastewater, for the use in ammonia-based fuel cells and the production of high purity hydrogen. Thermally decomposed iridium oxide films (TDIROF) have been shown to be catalytically active for direct ammonia oxidation in aqueous solutions if NH3 is present. However, the process was reported to be rapidly inhibited on TDIROF. Herein, we show that this fast inhibition of direct ammonia oxidation does not result from surface poisoning by adsorbed elemental nitrogen (Nads). Instead, we propose that direct ammonia oxidation and oxygen evolution can lead to a drop of the local pH at the electrode resulting in a low availability of the actual reactant, NH3. The hypothesis was tested with cyclic voltammetry (CV) experiments on stagnant and rotating disk electrodes (RDE). The CV experiments on the stagnant electrode revealed that the decrease of the ammonia oxidation peaks was considerably reduced by introducing an idle phase at open circuit potential between subsequent scans. Furthermore, the polarization of the TDIROF electrode into the hydrogen evolution region (HER) resulted in increased ammonia oxidation peaks in the following anodic scans which can be explained with an increased local pH after the consumption of protons in the HER. On the RDE, the ammonia oxidation peaks did not decrease in immediately consecutive scans. These findings would not be expected if surface poisoning was responsible for the fast inhibition but they are in good agreement with the proposed mechanism of pH induced limitation by the reactant, NH3. The plausibility of the mechanism was also supported by our numerical simulations of the processes in the Nernstian diffusion layer. The knowledge about this inhibition mechanism of direct ammonia oxidation is especially important for the design of electrochemical cells for wastewater treatment. The mechanism is not only valid for TDIROF but also for other electrodes because it is independent of the electrode material.
Chomiak, A., Mimoso, J., Koetzsch, S., Sinnet, B., Pronk, W., Derlon, N., & Morgenroth, E. (2014). Biofilm formation and permeate quality improvement in Gravity Driven Membrane ultrafiltration. Water Science and Technology: Water Supply, 14(2), 274-282. doi:10.2166/ws.2013.197, Institutional Repository

The effects of biofilm development on ultrafiltration membranes with regards to permeate stability and permeation rates were investigated using Gravity-Driven Membrane (GDM) filtration. The first part of the study aimed at evaluating the influence of the biofilm on permeate flux quality and quantity with regards to Assimilable Organic Carbon (AOC) degradation. In addition, two types of biological pre-treatments were evaluated: slow sand filtration and packed bed bio-reactor, compared to a control (no treatment). Biofilm formation helped to decrease the AOC content of permeate water, compared to the influent. Both pre-treatments additionally reduced AOC level in permeate and thus increased its biological stability, however none of the systems were able to guarantee microbiologically stable water. Removal of AOC before the GDM filtration reduced the biofilm growth potential, which in turn influenced its physical structure and enhanced the permeation rates. Influence of inorganic particle removal by pre-sedimentation and its effect on the biofilm structure was also studied. Pre-sedimentation of particle populations selected fine and homogenous particle fractions, which lead to the formation of a homogenous biofilm structure characterized by an increased hydraulic resistance. This was clearly visible between horizontally and vertically installed membranes where the latter ones had a significantly reduced flux despite lower deposited particle mass. Presence of larger, heterogeneous particle fractions counterbalanced the negative effects of the fine particles, which overall resulted in enhanced permeation rates.
Chomiak, A., Sinnet, B., Derlon, N., & Morgenroth, E. (2014). Inorganic particles increase biofilm heterogeneity and enhance permeate flux. Water Research, 64, 177-186. doi:10.1016/j.watres.2014.06.045, Institutional Repository

This study investigated the influence of inorganic particles on the hydraulic resistance of biofilm grown on membrane surface during low-pressure dead-end ultrafiltration. Gravity-driven ultrafiltration membrane systems were operated during several weeks without any flushing or cleaning. Smaller (kaolin d0.5 = 3.6 μm) or larger (kaolin with diatomaceous earth 50/50%, d0.5 = 18.1 μm) particles were added to pre-filtered creek water or to unfiltered creek water. It was demonstrated in both experiments that presence of finer particles in the feed water (kaolin) induced formation of compact and homogeneous biofilm structure. On the other hand presence of the larger particles (diatomite) helped to counterbalance the effect of fine particles due to the formation of more heterogeneous and permeable biofilm structure. The hydraulic resistance of biofilms formed with fine particles was significantly higher than the resistance of biofilm formed in (1) absence of any inorganic particles or (2) in presence of the mixed particle population. The membrane orientation (vertical or horizontal) determined which particles were accumulating at the membrane surface, with structural differences shown by Scanning Electron Microscopy (SEM). For vertical membranes, the larger particles were selectively removed due to sedimentation and did not contribute to the biofilm development. Thus the selection of smaller particles due to vertical membrane configuration negatively affected the biofilm structure and permeation rates, and such selective accumulation of fine particles should be avoided.
Derlon, N., Mimoso, J., Klein, T., Koetzsch, S., & Morgenroth, E. (2014). Presence of biofilms on ultrafiltration membrane surfaces increases the quality of permeate produced during ultra-low pressure gravity-driven membrane filtration. Water Research, 60, 164-173. doi:10.1016/j.watres.2014.04.045, Institutional Repository

This study evaluates the effect of the presence of biofilms on membrane surfaces on the quality of permeate produced during Gravity-driven membrane ultrafiltration. GDM ultrafiltration is applied to the decentralized production of drinking water. A second objective was to evaluate to what extent permeate quality is enhanced by pre-treating feed-water (using a packed bed biofilm reactor or a slow sand filter). The influence of the ageing of the biofilm on the permeate quality was evaluated and compared to the effect of virgin membranes. Permeate quality was evaluated in terms of Assimilable Organic Carbon (AOC) content and dissolved organic carbon fractions (e.g. biopolymers). Our results indicate that virgin ultrafiltration membrane remove a small fraction of the AOC and biopolymers (rejection <10%). The presence of a young and thin biofilm on the surface of the ultrafiltration membranes increases the permeate quality due to the degradation of AOC (>80%). However, over long-term the hydrolysis of the organic matter that accumulated on membrane surfaces increases the AOC content of the permeate, thus deteriorating the permeate quality. Pre-treatment of the feed-water help to control the biofilm accumulation and thus to limit the deterioration of the permeate quality. Permeate flux stabilised at average values of 7.5–8.9 L m−2 h−1. But the presence of pre-treatment helped to increase permeate flux (+12 and 19%, with the packed bed biofilm reactor and with the slow sand filter, respectively). Overall our study demonstrates that tolerating the presence of biofilm on membrane surface has a beneficial effect on the quality of permeate even if its quantity is decreased.
Gruber, W. (2014). Modellierung der Lachgasemissionen aus der biologischen Abwasserreinigung (Master thesis). 34 p. , Institutional Repository

Lachgas (N2O) ist ein Treibhausgas (ca. 300 Mal stärker als CO2) und bedeutend an der Zerstörung der stratosphärischen Ozonschicht beteiligt. In der biologischen Stufe von Abwasserreinigungsanlagen (ARA) werden relevante Mengen an N2O emittiert. Die N2OBildung ist sehr komplex und nur ansatzweise verstanden. Es wird aber davon ausgegangen, dass hauptsächlich die Nitrifikation eine dominante Quelle darstellt.
In der vorliegenden Masterarbeit wurde anhand von qualitativen Modellierungen versucht die Dynamik der N2O-Emissionen auf der ARA Real nachzuvollziehen und Strategien zur Reduktion der Emissionen zu entwickeln.
Anhand von Daten aus einer Langzeit Messkampagne auf der ARA Real über die N2OEmissionen konnte gezeigt werden, dass die N2O-Emissionen im Winter und Frühling einen bedeutenden Einfluss auf die Treibhausgasbilanz der Anlage hat. Berechnungen ergaben, dass die Emissionen bei über 1.5% der Ammoniumfracht im Zulauf der Anlage liegen. Es wurde abgeschätzt, dass die Emissionen ca. je zur Hälfte auf die Haupt- und die Nachbelüftung der Anlage entfallen. Dieses Ergebnis ist erstaunlich, da üblicherweise vor allem in der Hauptbelüftung der Grossteil der N2O-Emissionen ausgestossen wird.
Für die Entwicklung von N2O reduzierenden Massnahmen auf Kläranlagen können Modellierungen wichtige Hilfestellungen bieten. Allerdings kann mit den bereits publizierten mechanistischen Modellen über die N2O-Bildung nur ein Teil der N2O-Dynamik erklärt werden. Daher wurde in der vorliegenden Studie die N2O-Bildung basierend auf den Daten aus einer Langzeit-Messkampagne auf der ARA Real mit empirischen Ansätzen modelliert. Die N2O-Emissionen zeigen starke Korrelationen zur NO2--Konzentration in der Belüftungszone, Temperatur und zum Niederschlag. Darauf aufbauend wurde das ASM3-Modell mit Stickstofferweiterung um die Lachgasbildung in der Nitrifikation durch die Nitrifikaten Denitrifikation und die hetrotrophe Denitrifikation erweitert und kalibriert. Der dritte bekannte Prozess zur N2O-Bildung (Oxidation von NH2OH) wurde weggelassen.
Die Resultate der Modellierungen zeigen, dass mit dem Modell die Emissionen im Winter qualitativ gut reproduziert und erklärt werden können. Im Sommer bei höheren Temperaturen sind die modellierten Konzentrationen zu hoch. Insbesondere für die Modell Prozesse der Denitrifikation sind Anpassungen möglicherweise vorzusehen.
Anhand des Modells wurden für den Winter Betriebsoptimierungen getestet. In Kombination mit den Resultaten aus der Analyse der Daten aus der Messkampange wurden verschiedene Optimierungsmassnahmen entwickelt. Am vielversprechendsten sind die Erhöhung der O2-Konzentration in der Hauptbelüftung, die Verlängerung der Belüftungsphasen, ein dosierterer Betrieb der Belüftungseinheit der Nachbelüftung und die separate Behandlung von Rückläufen aus der Schlammbehandlung. Teilweise entstehen aber Konflikte mit anderen Zielgrössen, wie der Stickstoffelimination und dem Energieverbrauch der Anlage. Dabei kann das Modell in Zukunft interessante Hilfestellungen bieten und verbunden mit Ökobilanz-Tools könnten die gestellten Optimierungsprobleme gelöst werden.
Jenni, S., Vlaeminck, S. E., Morgenroth, E., & Udert, K. M. (2014). Successful application of nitritation/anammox towastewater with elevated organic carbon to ammonia ratios. Water Research, 49, 316-326. doi:10.1016/j.watres.2013.10.073, Institutional Repository

The nitritation/anammox process has been mainly applied to high-strength nitrogenous wastewaters with very low biodegradable organic carbon content (<0.5g COD·g N–1). However, several wastewaters have biodegradable organic carbon to nitrogen (COD/N) ratios between 0.5 and 1.7g COD·g N–1 and thus, contain elevated amounts of organic carbon but not enough for heterotrophic denitrification. In this study, the influence of elevated COD/N ratios was studied on a nitritation/anammox process with suspended sludge. In a step-wise manner, the influent COD/N ratio was increased to 1.4g COD·g N–1 by supplementing digester supernatant with acetate. The increasing availability of COD led to an increase of the nitrogen removal efficiency from around 85% with pure digester supernatant to >95% with added acetate while the nitrogen elimination rate stayed constant (275 ± 40mg N·L–1·d–1). Anammox activity and abundance of anammox bacteria (AMX) were strongly correlated, and with increasing influent COD/N ratio both decreased steadily. At the same time, heterotrophic denitrification with nitrite and the activity of ammonia oxidising bacteria (AOB) gradually increased. Simultaneously, the sludge retention time (SRT) decreased significantly with increasing COD loading to about 15 d and reached critical values for the slowly growing AMX. When the SRT was increased by reducing biomass loss with the effluent, AMX activity and abundance started to rise again, while the AOB activity remained unaltered. Fluorescent in-situ hybridisation (FISH) showed that the initial AMX community shifted within only 40 d from a mixed AMX community to "Candidatus Brocadia fulgida" as the dominant AMX type with an influent COD/N ratio of 0.8 g COD·g N–1 and higher. "Ca. Brocadia fulgida" is known to oxidise acetate, and its ability to outcompete other types of AMX indicates that AMX participated in acetate oxidation. In a later phase, glucose was added to the influent instead of acetate. The new substrate composition did not significantly influence the nitrogen removal nor the AMX activity, and "Ca. Brocadia fulgida" remained the dominant type of AMX. Overall, this study showed that AMX can coexist with heterotrophic bacteria at elevated influent COD/N ratios if a sufficiently high SRT is maintained.
Kohler, E., Villiger, J., Posch, T., Derlon, N., Shabarova, T., Morgenroth, E., … Blom, J. F. (2014). Biodegradation of microcystins during gravity-driven membrane (GDM) ultrafiltration. PLoS One, 9(11), e111794 (9 pp.). doi:10.1371/journal.pone.0111794, Institutional Repository

Gravity-driven membrane (GDM) ultrafiltration systems require little maintenance: they operate without electricity at ultra-low pressure in dead-end mode and without control of the biofilm formation. These systems are already in use for water purification in some regions of the world where adequate treatment and distribution of drinking water is not readily available. However, many water bodies worldwide exhibit harmful blooms of cyanobacteria that severely lower the water quality due to the production of toxic microcystins (MCs). We studied the performance of a GDM system during an artificial Microcystis aeruginosa bloom in lake water and its simulated collapse (i.e., the massive release of microcystins) over a period of 21 days. Presence of live or destroyed cyanobacterial cells in the feed water decreased the permeate flux in the Microcystis treatments considerably. At the same time, the microbial biofilms on the filter membranes could successfully reduce the amount of microcystins in the filtrate below the critical threshold concentration of 1 µg L−1 MC for human consumption in three out of four replicates after 15 days. We found pronounced differences in the composition of bacterial communities of the biofilms on the filter membranes. Bacterial genera that could be related to microcystin degradation substantially enriched in the biofilms amended with microcystin-containing cyanobacteria. In addition to bacteria previously characterized as microcystin degraders, members of other bacterial clades potentially involved in MC degradation could be identified.
Martin, K. J., Bolster, D., Derlon, N., Morgenroth, E., & Nerenberg, R. (2014). Effect of fouling layer spatial distribution on permeate flux: a theoretical and experimental study. Journal of Membrane Science, 471, 130-137. doi:10.1016/j.memsci.2014.07.045, Institutional Repository

Fouling layers developing on membrane filters can display significant spatial heterogeneity (roughness), yet the effect of fouling layer spatial distribution on hydraulic resistance has not been studied systematically. We used simple flux models, based on Darcy's law, to assess the impact of spatial distribution on resistance and permeate flux. Our results show that, for a given mean fouling layer thickness, greater spatial heterogeneity could increase fluxes by over an order of magnitude. The degree of error depended on the membrane resistance, fouling layer permeability, and the characteristics of the spatial distribution. We developed 1-dimensional and 2-dimensional flow models, both considering spatial heterogeneity, to improve the accuracy of the conventional model. The proposed models were validated with experimental data from a gravity driven membrane filter with a fouling layer having a high degree of spatial heterogeneity. Accounting for spatial heterogeneity significantly improved the prediction of permeate flux.
Renggli, S. (2014). Influence of dry phases on gravity-driven membrane performance (Master thesis). 63 p. , Institutional Repository

The global water challenge still stands. What often works best for the treatment of water in developing countries are decentralized, point of use, low priced, low maintenance and systems independent of utilities. Membranes fulfill all of those criteria if it was not for the auxiliary equipment needed, to avoid fouling, leading to a reduction of flux. In 2010 it was found, that the buildup of a biofilm does not stop the flux entirely. The flux stabilizes at a range of about 4-10 l/m2/h, with gravity as the only driving force towards the membrane, thus Gravity-Driven Membrane. This is enough flux to provide a family of five with the drinking water needed with less than half a square meter of membrane area. Those findings led to the development of a prototype. In field tests it was seen that the users operate the system intermittent. Resulting in half of the membrane being exposed to air regularly, which is very unconventional for membranes.
To different setups, one with self-constructed immersed membranes and one with Flow Cells in two corresponding intermittent operation scenarios are chosen to simulate this. All the units are operated during 3 hours per day before going into standstill time for the next 21 hours. While one system is fully immersed during standstill time, the other is immersed only 50% during standstill. Flux is measured to see the difference in the performance of the different systems. To explain the flux differences the structure, coverage and biological activity of the biofilm is investigated. [...]
Thalmann, B., Voegelin, A., Sinnet, B., Morgenroth, E., & Kaegi, R. (2014). Sulfidation kinetics of silver nanoparticles reacted with metal sulfides. Environmental Science and Technology, 48(9), 4885-4892. doi:10.1021/es5003378, Institutional Repository

Recent studies have documented that the sulfidation of silver nanoparticles (Ag-NP), possibly released to the environment from consumer products, occurs in anoxic zones of urban wastewater systems and that sulfidized Ag-NP exhibit dramatically reduced toxic effects. However, whether Ag-NP sulfidation also occurs under oxic conditions in the absence of bisulfide has not been addressed, yet. In this study we, therefore, investigated whether metal sulfides that are more resistant toward oxidation than free sulfide, could enable the sulfidation of Ag-NP under oxic conditions.
We reacted citrate-stabilized Ag-NP of different sizes (10–100 nm) with freshly precipitated and crystalline CuS and ZnS in oxygenated aqueous suspensions at pH 7.5. The extent of Ag-NP sulfidation was derived from the increase in dissolved Cu2+ or Zn2+ over time and linked with results from X-ray absorption spectroscopy (XAS) analysis of selected samples. The sulfidation of Ag-NP followed pseudo first-order kinetics, with rate coefficients increasing with decreasing Ag-NP diameter and increasing metal sulfide concentration and depending on the type (CuS and ZnS) and crystallinity of the reacting metal sulfide. Results from analytical electron microscopy revealed the formation of complex sulfidation patterns that seemed to follow preexisting subgrain boundaries in the pristine Ag-NP. The kinetics of Ag-NP sulfidation observed in this study in combination with reported ZnS and CuS concentrations and predicted Ag-NP concentrations in wastewater and urban surface waters indicate that even under oxic conditions and in the absence of free sulfide, Ag-NP can be transformed into Ag2S within a few hours to days by reaction with metal sulfides.
Uhlmann, C. (2014). Dynamics of complete and partial nitrification of source-separated urine (Master thesis). 32 p. , Institutional Repository

In this thesis the resilience of complete and partial nitrification of source-separated urine under dynamic conditions were investigated and compared. The process stability of nitrification reactors is important for their commercial application. In partial nitrification the alkalinity contained in urine allows nitrifying 50% of the ammonia whereas in complete nitrification the dosage of a base allows the nitrification of almost 100% of the ammonia. Due to considerations about Monod kinetic substrate limitation of Ammonia Oxidizing Bacteria (AOB) it was hypothesized that complete nitrification is more prone to nitrite accumulation and therefore less stable than partial nitrification. A computer model based on Monod kinetics should help to understand the processes and the resilience of urine nitrification reactors. Laboratory experiments were conducted in 7 L moving bed biofilm reactors (MBBR) to analyze the behavior of the two processes in respect to changes in temperature and inflow. The total ammonia concentration in the inflow was on average 1750±150 mg N L-1. Complete nitrification has at same conditions a lower nitrification rate than partial nitrification due to the lower ammonia concentration in the reactor. In order to reach comparable nitrification rates complete and partial nitrification reactors were therefore operated at two different pH values of 7 and 6 respectively. The average nitrification rate in complete nitrification was 1.08±0.17 g N m-2 d-1 and in parital nitrification 0.90±0.25 g N m-2 d-1 with regard to biofilm carrier surface (Kaldnes®). During all experiments no essential difference of process stability between complete and partial nitrification were observed. Both processes remained stable during temperature fluctuations between 20 °C and 32 °C when urine inflow was constant. pH-diven inflow control led to substantial nitrite accumulation and to a break down of nitrification due to an increase of the inflow caused by increasing AOB activity at higher temperatures. It could be shown that the dynamics of bacterial growth due to temperature changes are damped when pH is not controlled. Instantaneous increase of the inflow caused severe nitrite accumulations in both processes. A reliable process control should therefore consider the effects of temperature and restrict load fluctuations to a minimum. The developed model was able to describe the dynamics of nitrogen conversion due to temperature changes but failed in the prediction of process instabilities caused by increasing inflow.
Weissbrodt, D. G., Wells, G. F., Johnson, D. R., Bürgmann, H., Joss, A., Laureni, M., & Morgenroth, E. (2014). Towards community systems microbiology for the optimization of aerobic-anaerobic ammonium oxidation processes. In Vol. 1. 87th annual water environment federation technical exhibition and conference (WEFTEC 2014) (pp. 2645-2649). doi:10.2175/193864714815942567, Institutional Repository
Böhler, M., Morgenroth, E., Siegrist, H., Haueter, R., Rensch, D., Sterkele, B., … Beurer, I. (2013). Machbarkeits‐ und Vergleichsstudie zur Umstellung der chemischen Phosphorelimination mittels Eisen‐ auf Aluminium‐Produkte auf kommunalen Abwasserreinigungsanlagen. Dübendorf: Eawag. , Institutional Repository

Stand und (Mehr-) Kosten der Fällung im Kanton Zürich

Alle Kläranlagen des Kanton Zürichs betreiben eine chemische Phosphor-Fällung. Zeitweise werden auch sogenannte Kombi-Produkte bestehend aus Eisen und Aluminium zur Bekämpfung schlechter Absetzeigenschaften angewendet. Eine reine Aluminium-Fällung wird auf keiner Kläranlage im Kanton vorgenommen, so dass hier keine Langzeiterfahrungen zum Einsatz von reinen Aluminium-Produkten vorliegen.

Die derzeitigen Kosten für Fällmittel (Basis AWEL-Daten-Erhebung B5) auf den Kläranlagen des Kantons sind sehr unterschiedlich. In Abhängigkeit der Verfahrenswahl, des verwendeten Fällmittel-Produkte und der geforderten Einleitwerte ergeben sich derzeit reale Kosten in einer Spannweite von 4 bis 15 Sfr. je Kilogramm Phosphor, welches über eine Fällung eliminiert wird. Hohe Kosten entstehen insbesondere bei Verwendung von Kombi-Produkten und für kleine Kläranlagen. Die günstigste Variante und zugleich mengenmässig der bedeutendste Anteil stellt die Verwendung von Grünsalz (Fe(II) dar, welches von 5 Kläranlagen, darunter den zwei grössten des Kantons eingesetzt werden.

Auf Grundlage einer Preisanfrage der grössten Fällmittel-Lieferanten des Kantons wurde eine Kostenabschätzung der Mehrkosten bei Umstellung auf ein reines Aluminium-Produkt vorgenommen. Im Vergleich zu Fe(II)-Produkten bzw. Fe(III)-Produkten ergibt sich ein um rund 2.4 respektive um 1.3-fach höherer Einkaufspreis für das Fällmittel. Auf Basis einer Phosphor-Massenbilanz wurden in Abhängigkeit der derzeit verwendeten Fällmittelmengen (Beta-Wert 1.9 mol/mol) eine Abschätzung der Mehrkosten für die Fällmittelbeschaffung der Kläranlagen berechnet. [...]
Carrel, M. (2013). Membrane ultrafiltration: a study of the combined use of iron chloride for coagulation and of hypochlorite for disinfection (Master thesis). 47 p. , Institutional Repository

Fouling is the main issue related to the use of ultrafiltration membranes, a promising technology arising in the drinking water field. The topic of this work was suggested by results of pilot tests performed by the Swiss company Membratec. This company holds a leading position in the water treatment field in Switzerland and is an industry partner of Eawag. They observed that the irreversible fouling caused by high waters with humic substances loads could almost be totally mitigated while combining inline iron chloride coagulation and hypochlorite disinfection twice a day. A further observation is that iron chloride had a positive effect regarding NOM retention.
Several experiments were performed at Eawag with Swiss natural waters in order to reproduce the results obtained by Membratec. The main focus of this work was to investigate whether the strong fouling mitigation observed was caused by the combination of optimal pre-treatment and disinfection processes, or whether these results were caused by direct chemical interactions occuring between iron chloride and hypochorite.
The results of these tests show that iron chloride is a powerful coagulant for the treatment of waters with high humic substances loads in terms of fouling mitigation (50 % hydraulically reversible fouling reduction when comparing with addition of iron chloride and without for short filtration experiments). Hypochlorite disinfection also allows important permability recovery. However, the fouling mitigation obtained here was not as strong as the one observed by Membratec. This could be explained by the higher NOM content of the water used in this work. With humic substances and biopolymers retention of more than 90 % respectively 80%, even at underdose, iron chloride can provide excellent and promising results in terms of NOM removal. Fouling quantification and analysis is a key step in order to compare different pre-treatments and cleaning strategies. Since the different fouling quantification approaches used in this work all represent limitations,the use of a multi-criteria analysis strategy combining them is suggested. Jar-tests showed that hypochlorite reacts with iron chloride flocs, suggesting that the cake layer produced by iron chloride coagulation can be removed very efficiently. These results underline the importance of understanding the mechanisms leading to the cake layer build up and of the necessity to adapt pre-treatment and disinfection to the water to be filtered.
Choubert, J. M., Rieger, L., Shaw, A., Copp, J., Spérandio, M., Sørensen, K., … Gillot, S. (2013). Rethinking wastewater characterisation methods for activated sludge systems - a position paper. Water Science and Technology, 67(11), 2363-2373. doi:10.2166/wst.2013.158, Institutional Repository

Increasingly stringent effluent limits and an expanding scope of model system boundaries beyond activated sludge has led to new modelling objectives and consequently to new and often more detailed modelling concepts. Nearly three decades after the publication of Activated Sludge Model No1 (ASM1), the authors believe it is time to re-evaluate wastewater characterisation procedures and targets. The present position paper gives a brief overview of state-of-the-art methods and discusses newly developed measurement techniques on a conceptual level. Potential future paths are presented including on-line instrumentation, promising measuring techniques, and mathematical solutions to fractionation problems. This is accompanied by a discussion on standardisation needs to increase modelling efficiency in our industry.
Derlon, N., Koch, N., Eugster, B., Posch, T., Pernthaler, J., Pronk, W., & Morgenroth, E. (2013). Activity of metazoa governs biofilm structure formation and enhances permeate flux during Gravity-Driven Membrane (GDM) filtration. Water Research, 47(6), 2085-2095. doi:10.1016/j.watres.2013.01.033, Institutional Repository

The impact of different feed waters in terms of eukaryotic populations and organic carbon content on the biofilm structure formation and permeate flux during Gravity-Driven Membrane (GDM) filtration was investigated in this study. GDM filtration was performed at ultra-low pressure (65 mbar) in dead-end mode without control of the biofilm formation. Different feed waters were tested (River water, pre-treated river water, lake water, and tap water) and varied with regard to their organic substrate content and their predator community. River water was manipulated either by chemically inhibiting all eukaryotes or by filtering out macrozoobenthos (metazoan organisms). The structure of the biofilm was characterized at the meso- and micro-scale using Optical Coherence Tomography (OCT) and Confocal Laser Scanning Microscopy (CLSM), respectively. Based on Total Organic Carbon (TOC) measurements, the river waters provided the highest potential for bacterial growth whereas tap water had the lowest. An increasing content in soluble and particulate organic substrate resulted in increasing biofilm accumulation on membrane surface. However, enhanced biofilm accumulation did not result in lower flux values and permeate flux was mainly influenced by the structure of the biofilm. Metazoan organisms (in particular nematodes and oligochaetes) built-up protective habitats, which resulted in the formation of open and spatially heterogeneous biofilms composed of biomass patches. In the absence of predation by metazoan organisms, a flat and compact biofilm developed. It is concluded that the activity of metazoan organisms in natural river water and its impact on biofilm structure balances the detrimental effect of a high biofilm accumulation, thus allowing for a broader application of GDM filtration. Finally, our results suggest that for surface waters with high particulate organic carbon (POC) content, the use of worms is suitable to enhance POC removal before ultrafiltration units.
Faust, V. (2013). Aufenthaltszeit von Urin in einem Urinsammelsystem (Bachelor thesis). 16 p. , Institutional Repository

Im Forum Chriesbach der Eawag ist ein NoMix-System installiert, das den Urin sammelt und getrennt vom restlichen Abwasser abführt. Da der Urin einen Grossteil an Nährstoffen wie Stickstoff enthält, kann er separat aufbereitet und anschliessend als landwirtschaftlicher Dünger genutzt werden. Im Leitungssystem wird der Harnstoff, welcher die grösste Stickstoffkomponente im Urin bildet, durch Bakterien abgebaut. Für ein besseres Verständnis der Harnstoffhydrolyse muss bekannt sein, wie lange der Urin im Leitungssystem verweilt. Um die Aufenthaltszeit von Urin zu quantifizieren wurden in dieser Arbeit Tracerversuche mit Bromid durchgeführt. Dabei wurden neben einer mittleren Aufenthaltszeit auch der Einfluss der Benutzerfrequenz und der Distanz, also dem Stockwerk aus dem der Urin kommt, untersucht. Zusätzlich wurde die Aufenthaltszeit mit Hilfe einer Urinbilanz berechnet, bei der die summierten Input und Output Kurven des Urins aufgezeichnet wurden. Die zeitliche Verschiebung der beiden Kurven beschreibt eine mittlere Verweilzeit.
Die Tracerversuche zeigten, dass sich die Aufenthaltszeit des Bromids und des eigentlichen Urins deutlich unterscheiden. Der Tracer repräsentiert somit nicht wie ursprünglich angenommen den Grundstrom. Wie aus der Urinbilanz hervorging hat der Urin eine mittlere Verweilzeit von 31 Minuten mit einer Standartabweichung von 12 Minuten. Die mittlere Aufenthaltszeit des Bromids ist gemäss den Tracerversuchen etwa viermal grösser. Das unterschiedliche Verhalten ist dadurch zu erklären, dass das Bromid im Leitungsrohr in den Biofilm diffundiert und deshalb mehr Zeit als der Urin benötigt. Mit zunehmender Benutzerfrequenz gleichen sich die beiden Aufenthaltszeiten an, da mehr Urin vorhanden ist, in welches das Bromid zurückdiffundieren kann. Das Stockwerk beeinflusst die Aufenthaltszeit des Urins und des Bromids. Der Einfluss auf das Bromid ist jedoch grösser, da die Diffusion in den Biofilm in den vertikalen Leitungen grösser ist als in den horizontalen.
Auf die Verweilzeit des Harnstoffs konnte aus den Ergebnissen auf Grund der Diffusion nicht geschlossen werden, da weder der Urin noch das Bromid repräsentativ sind. Es kann aber mit grosser Wahrscheinlichkeit gesagt werden, dass auch der Harnstoff und weitere gelöste Stoffe in den Biofilm diffundieren und damit eine grössere Aufenthaltszeit als der Urin besitzen.
Florin, A. (2013). Full nitrification of urine by adding a base (Master thesis). 38 p. , Institutional Repository

With the goal of nutrient recovery, full nitrification of human urine is investigated for its stabilization in simple, decentralized reactors. In a first part of this work, undiluted urine was completely nitrified in a laboratory-scale moving-bed biofilm reactor (MBBR), with automated dosage of a KHCO3 solution keeping the pH at 7.0-7.1. The effluent contained up to 2706 mg-N/L of nitrate; on average > 99% of the total nitrogen. Maintaining low concentrations of ammonium and nitrite (generally below 1 ‰ and 4.7‰ respectively of the influent total ammonia) proved to reduce the risks of dramatic process instabilities due to inhibition with nitrous acid and free ammonia. Although full nitrification by adding a base presents several advantages, for decentralized applications, it is recommended to add alkalinity in a way requiring less expensive and complex material than by dosing a basic solution.
Hoping that calcite (CaCO3) could be a simple alternative to buffer nitrification, in a second part we studied the dissolution of chalk powder in synthetic urine solutions, both in the presence and absence of phosphate. Experiments and simulations with PHREEQC verified the hypothesis that phosphate may precipitate on the surface of calcite, and thus slow down dissolution. In the absence of phosphate, calcite dissolved rapidly until saturation of the solution. By contrast, with the high phosphate concentrations in stored urine (around 200-250 mgP/L), calcite dissolution was inhibited by the rapid formation of  amorphous calcium-phosphate (ACP; eventually converting into hydroxyapatite, HAP) directly on the particle’s surface, as was revealed by XRD and REM analysis. To prevent calcite passivation, precipitation of struvite (MgNH4PO4•6H2O) is suggested before the full nitrification reactor.  In real urine, the effect of biofilm growth directly on calcite may be of advantage to compensate possibly too slow calcite dissolution, and should inform further work.
Guo, B., Zhang, Y., Yu, G., Lee, W. H., Jin, Y. S., & Morgenroth, E. (2013). Two-stage acidic-alkaline hydrothermal pretreatment of lignocellulose for the high recovery of cellulose and hemicellulose sugars. Applied Biochemistry and Biotechnology, 169(4), 1069-1087. doi:10.1007/s12010-012-0038-5, Institutional Repository

The focus of this work was to develop a combined acid and alkaline hydrothermal pretreatment of lignocellulose that ensures high recovery of both hexose and pentose. Dilute sulfuric acid and lime pretreatments were employed sequentially. Process performance was optimized in terms of catalyst concentration, retention time, and temperature using response surface methodology. Medium operational conditions in the acid stage and harsh conditions in the alkaline stage were desirable with optimal performance at 0.73 wt% H2SO4, 150 °C, 6.1 min in the first stage, and 0.024 g lime/g biomass, 202 °C, 30 min in the second stage. In comparison to single-stage pretreatments with high recovery of either glucose or xylose, two-stage process showed great promises with >80 % glucose and >70 % xylose recovery. In addition, the method greatly improved ethanol fermentation with yields up to 0.145 g/g Miscanthus, due to significantly reduced formation of inhibitory by-products such as weak acids, furans, and phenols. Supplementing biomimetic acids would further increase glucose yield by up to 15 % and xylose yield by 25 %.
Janjaroen, D., Ling, F., Monroy, G., Derlon, N., Morgenroth, E., Boppart, S. A., … Nguyen, T. H. (2013). Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces. Water Research, 47(7), 2531-2542. doi:10.1016/j.watres.2013.02.032, Institutional Repository

Mechanisms of Escherichia coli attachment on biofilms grown on PVC coupons were investigated. Biofilms were grown in CDC reactors using groundwater as feed solution over a period up to 27 weeks. Biofilm physical structure was characterized at the micro- and meso-scales using Scanning Electron Microscopy (SEM) and Optical Coherence Tomography (OCT), respectively. Microbial community diversity was analyzed with Terminal Restricted Fragment Length Polymorphism (T-RFLP). Both physical structure and microbial community diversity of the biofilms were shown to be changing from 2 weeks to 14 weeks, and became relatively stable after 16 weeks. A parallel plate flow chamber coupled with an inverted fluorescent microscope was also used to monitor the attachment of fluorescent microspheres and E. coli on clean PVC surfaces and biofilms grown on PVC surfaces for different ages. Two mechanisms of E. coli attachment were identified. The adhesion rate coefficients (kd) of E. coli on nascent PVC surfaces and 2-week biofilms increased with ionic strength. However, after biofilms grew for 8 weeks, the adhesion was found to be independent of solution chemistry. Instead, a positive correlation between kd and biofilm roughness as determined by OCT was obtained, indicating that the physical structure of biofilms could play an important role in facilitating the adhesion of E. coli cells.
Martin, K. J., Derlon, N., Morgenroth, E., & Nerenberg, R. (2013). Fouling layer surface heterogeneity improves permeate flux. In 86th Annual Water Environment Federation Technical Exhibition and Conference, WEFTEC 2013: Vol. 1. 86th annual water environment federation technical exhibition and conference (WEFTEC 2013) (pp. 621-629). doi:10.2175/193864713813668079, Institutional Repository

In this research, we used modeling to assess the impact of irregular fouling-layer surface morphology (i.e., roughness) on permeate fluxes. Two membrane filtration models, each based on Darcy's Law, were used to predict fluxes for fouling layers with varying degrees of surface irregularity. One of the models considered the arithmetic mean thickness of the fouling layer, while the other accounted for the actual, irregular surface morphology assuming one-dimensional permeate flow. Surface morphology and permeate-flux data from an ultra-low pressure gravity-driven membrane filter were used to test the models. The models that accounted for the surface morphology were more accurate, especially for highly irregular surface morphologies. These models were also able to correctly predict greater permeate fluxes exhibited by highly irregular surface morphologies despite their having greater mean thicknesses. Our results show that models based on the mean thickness may not accurately characterize the effect of the fouling layer on fluxes. Future research should consider the surface morphology of the fouling layer when devising fouling mitigation strategies.
Remmele, A. (2013). The influence of anode material and current density on the emissions of disinfection by-products (DBPs) during electrolytic treatment of stored urine (Master thesis). 33 p. , Institutional Repository

Electrolysis of source separated urine is an efficient technology for COD and ammonia removal. Despite a huge of research about electrochemical treatment of wastewater the formation and emission of toxic and carcinogenic disinfection by-products (DBPs), is still not understoood in detail. The aim of this masterthesis is to contribute to the optimisation of the electrolysis of stored urine by a better understanding of the DBP formation.
For this purpose two control variables, anode material and current density, are investigated. DBP formation was analysed in nine galvanostatic experiments with the anode materials boron-doped diamond (BDD), iridium dioxide (Ti/IrO2) and graphite. Current densities of 5, 10, 15 and 20 mA cm-2 were applied to a discontinuous electrolysis cell filled with 350 mL of stored urine. The gas above the electrolyte was extracted and drawn through two traps in series filled with dodecane by a gas pump. Periodically taken samples from the reactor were analysed with GCMS, IC and Hach Dr. Lange tests for concentrations of six selected DBPs, COD, ammonia, Chloride and Chlorate. Samples from the raps were analysed for DBP concentrations. [...]
Ye, X., Zhang, X., Morgenroth, E., & Finneran, K. T. (2013). Exogenous anthrahydroquinone-2,6-disulfonate specifically increases xylose utilization during mixed sugar fermentation by Clostridium beijerinckii NCIMB 8052. International Journal of Hydrogen Energy, 38(6), 2719-2727. doi:10.1016/j.ijhydene.2012.11.149, Institutional Repository

The influence of a reduced extracellular electron shuttle (anthrahydroquinone-2,6-disulfonate, AH2QDS) on substrate utilization and H2 production was investigated at different glucose:xylose ratios using the fermentative culture Clostridium beijerinckii NCIMB 8052. Adding 250 μM AH2QDS increased the total substrate utilization by 23–66%, and specifically xylose utilization by 20–54% at glucose:xylose ratios of 1:1, 1:3 and 1:9. Adding 250 μM AH2QDS also increased the substrate utilization by 40–88% at all tested glucose:xylose ratios (which ranged from 1:9 to 9:1). Increasing AH2QDS concentrations from 250 μM to 2 mM increased xylose utilization (>99% xylose consumed) as well as cumulative hydrogen production during mixed sugar fermentation. The extent of glucose utilization was consistent amongst all tests, which was expected. However, hydroquinone amendment specifically increased the extent of xylose utilized irrespective of the starting glucose:xylose ratio. To the best of our knowledge this is the first report of 100% xylose utilization by C. beijerinckii NCIMB 8052 grown under mixed sugar conditions. These data demonstrate that the substrate utilization, particularly xylose utilization, can be manipulated by amending extracellular redox active compounds. This will improve pentose utilization during fermentation of hydrolyzates that result from pre-treatment of lignocellulosic materials with wild type (non-GMO) cultures.
Zhang, X., Ye, X., Finneran, K. T., Zilles, J. L., & Morgenroth, E. (2013). Interactions between Clostridium beijerinckii and Geobacter metallireducens in co-culture fermentation with anthrahydroquinone-2, 6-disulfonate (AH2QDS) for enhanced biohydrogen production from xylose. Biotechnology and Bioengineering, 110(1), 164-172. doi:10.1002/bit.24627, Institutional Repository

To enhance biohydrogen production, Clostridium beijerinckii was co-cultured with Geobacter metallireducens in the presence of the reduced extracellular electron shuttle anthrahydroquinone-2, 6-disulfonate (AH2QDS). In the co-culture system, increases of up to 52.3% for maximum cumulative hydrogen production, 38.4% for specific hydrogen production rate, 15.4% for substrate utilization rate, 39.0% for substrate utilization extent, and 34.8% for hydrogen molar yield in co-culture fermentation were observed compared to a pure culture of C. beijerinckii without AH2QDS. G. metallireducens grew in the co-culture system, resulting in a decrease in acetate concentration under co-culture conditions and a presumed regeneration of AH2QDS from AQDS. These co-culture results demonstrate metabolic crosstalk between the fermentative bacterium C. beijerinckii and the respiratory bacterium G. metallireducens and suggest a strategy for industrial biohydrogen production.
Zhang, X., Ye, X., Guo, B., Finneran, K. T., Zilles, J. L., & Morgenroth, E. (2013). Lignocellulosic hydrolysates and extracellular electron shuttles for H2 production using co-culture fermentation with Clostridium beijerinckii and Geobacter metallireducens. Bioresource Technology, 147, 89-95. doi:10.1016/j.biortech.2013.07.106, Institutional Repository

A co-culture of Clostridium beijerinckii and Geobacter metallireducens with AH2QDS produced hydrogen from lignocellulosic hydrolysates (biomass of Miscanthus prepared by hydrothermal treatment with dilute acids). This co-culture system enhanced hydrogen production from lignocellulosic hydrolysates by improving substrate utilization and diminishing acetate accumulation, despite the presence of fermentation inhibitors in the hydrolysates. The improvements were greater for xylose-rich hydrolysates. The increase in maximum cumulative hydrogen production for hydrolysates with glucose:xylose mass ratios of 1:0.2, 1:1 and 1:10g/g was 0%, 22% and 11%, respectively. Alternative extracellular electron shuttles (EES), including indigo dye, juglone, lawsone, fulvic acids and humic acids, were able to substitute for AH2QDS, improving hydrogen production in the co-culture system using xylose as model substrate. Increased utilization of xylose-rich hydrolysates and substitution of alternative EES make the co-culture with EES system a more attractive strategy for industrial biohydrogen production.
Boltz, J. P., Morgenroth, E., Daigger, G. T., deBarbadillo, C., Murthy, S., Sørensen, K. H., & Stinson, B. (2012). Method to identify potential phosphorus rate-limiting conditions in post-denitrification biofilm reactors within systems designed for simultaneous low-level effluent nitrogen and phosphorus concentrations. Water Research, 46(19), 6228-6238. doi:10.1016/j.watres.2012.08.020, Institutional Repository

Water-quality standards requiring simultaneous low level effluent N and P concentrations are increasingly common in Europe and the United States of America. Moving bed biofilm reactors (MBBRs) and biologically active filters (BAFs) have been used as post-denitrification biofilm reactors in processes designed and operated for this purpose (Boltz et al., 2010a). There is a paucity of information describing systematic design and operational protocols that will minimize the potential for phosphorus rate-limited conditions as well as a lack of information describing the interaction between these post-denitrification biofilm reactors and unit processes that substantially alter phosphorus speciation (e.g., chemically enhanced clarification). In this paper, a simple mathematical model for estimating the threshold below which P becomes rate-limiting, and the model is presented and evaluated by comparing its predictions with operational data from post-denitrification MBBRs and BAFs. Ortho-phosphorus (PO4–P), which is the dissolved reactive component of total phosphorus, was a primary indicator of P rate-limiting conditions in the evaluated post-denitrification biofilm reactors. The threshold below which PO4–P becomes the rate-limiting substrate is defined: SPO4–P:SNOx–N = 0.0086 g P/g N and SPO4–P : SM = 0.0013 g P/g COD. Additional analyses indicate JavgNOx-N =0.48g/m2/d when SPO4–P:SNOx–N > 0.0086, and JavgNOx-N=0.06g/m2/d when SPO4–P:SNOx–N < 0.0086. Effluent nitrate–nitrogen plus nitrite–nitrogen concentration (SNOx–N)(SNOx–N) from the evaluated post-denitrification biofilm reactors began to rapidly increase when SPO4–P:SNOx–N:SNOx–N was 0.01, approximately (consistent with the rate-limitation threshold of SPO4–P:SNOx–N < 0.0086 predicted by the mathematical model described in this paper). Depending on the processes used at a given WWTP, optimizing chemically enhanced clarification to increase the amount of PO4–P that remains in the clarifiers effluent stream, dosing phosphoric acid in the MBBR or BAF influent stream, and/or optimizing secondary process EBPR may overcome phosphorus rate-limitations in the biofilm-based post-denitrification process.
Derlon, N., Peter-Varbanets, M., Scheidegger, A., Pronk, W., & Morgenroth, E. (2012). Predation influences the structure of biofilm developed on ultrafiltration membranes. Water Research, 46(10), 3323-3333. doi:10.1016/j.watres.2012.03.031, Institutional Repository

This study investigates the impact of predation by eukaryotes on the development of specific biofilm structures in gravity-driven dead-end ultrafiltration systems. Filtration systems were operated under ultra-low pressure conditions (65 mbar) without the control of biofilm formation. Three different levels of predation were evaluated: (1) inhibition of eukaryotic organisms, (2) addition of cultured protozoa (Tetrahymena pyriformis), and (3) no modification of microbial community as a control. The system performance was evaluated based on permeate flux and structures of the biofilm. It was found that predation had a significant influence on both the total amount and also the structure of the biofilm. An open and heterogeneous structure developed in systems with predation whereas a flat, compact, and thick structure that homogeneously covered the membrane surface developed in absence of predation. Permeate flux was correlated with the structure of the biofilm with increased fluxes for smaller membrane coverage. Permeate fluxes in the presence or absence of the predators was 10 and 5 L m−2 h−1, respectively. It was concluded that eukaryotic predation is a key factor influencing the performance of gravity-driven ultrafiltration systems.
Fritzsche, C. (2012). The formation of chlorinated organics during electrolytic urine treatment (Master thesis). 74 p. , Institutional Repository

This master thesis is part of the VUNA project which aims for nutrient recovery and treatment of urine in decentralized treatment facilities. Electrolysis is used to remove nitrogen through electrolytic ammonia oxidation. It is a promising treatment option because it is not susceptible to inflow variations. However, a disadvantage of electrolysis is that chlorinated organics, which are dangerous for environmental and human health, might be formed.
The overall goal of this master thesis is to analyze the processes of chlorinated organics formation during electrolytic treatment of stored urine. The subgoals are to choose four chlorinated, organic substances of interest, to develop a measurement method for these substances, to quantify the current efficiency in experiments with urine and to either accept or reject the following hypotheses: 1) Chlorinated organics are formed during the electrolytic treatment of stored urine. 2) If the electrode potential applied in electrolytic urine treatment is lower than the potential needed for chloride oxidation, no chlorinated organics are formed. [...]
Ghasemian, M., Amin, M. M., Morgenroth, E., & Jaafarzadeh, N. (2012). Anaerobic biodegradation of methyl tert-butyl ether and tert-butyl alcohol in petrochemical wastewater. Environmental Technology, 33(16), 1937-1943. doi:10.1080/09593330.2012.655313, Institutional Repository

A laboratory-scale anaerobic sequencing batch reactor was used to evaluate treatment of a synthetic substrate mixture representing petrochemical wastewater containing methyl tert-butyl ether (MTBE), ethanol and acetic acid. Influent MTBE concentrations were 5, 10 and 50 mg/l (corresponding to MTBE loading rates of 0.2, 0.4 and 2 mg/l.d) with overall organic loading rates (OLRs) of 1.51, 3.23 and 3.25 g COD/l.d, respectively. These OLRs resulted in removal efficiencies for MTBE of 78%, 98% and 88%. Removal efficiencies for chemical oxygen demand were 85% and 90% with influent MTBE concentrations of 5 and 10 mg/l, but were significantly reduced to 72% with influent MTBE concentrations of 50 mg/l. During all reactor runs, effluent concentrations of tert-butyl alcohol (TBA) were below the detection limit. Batch degradation of the organic substrate mixture demonstrated initial inhibitory effects when exposed to MTBE concentrations of 50 mg/l and complete inhibition with MTBE concentrations above 2000 mg/l. It is interesting to note that in batch tests using MTBE as the sole organic substrate (initial MTBE concentrations of 50, 100 and 200 mg/l), the specific methanogenic activity decreased to below detection within the first 96 hours, but following a 72-hour lag phase the methane production increased again. Based on low volatile fatty acid (VFA) concentration, disappearance of TBA peaks and no findings of any other intermediate via gas chromatography/mass spectrometry, while the MTBE concentration is still high, it can be suggested that during the batch tests the breakdown of gas production and the following lag phase were the direct effect of higher MTBE concentrations (more than 50 mg/l) and not because of the TBA or VFA accumulations.
Guo, B., Zhang, Y., Ha, S. J., Jin, Y. S., & Morgenroth, E. (2012). Combined biomimetic and inorganic acids hydrolysis of hemicellulose in Miscanthus for bioethanol production. Bioresource Technology, 110, 278-287. doi:10.1016/j.biortech.2012.01.133, Institutional Repository

Combined acid catalysis was employed as a pretreatment alternative with combined acid catalysts blending sulfuric acid with two biomimetic acids, trifluoroacetic acid (TFA) and maleic acid (MA), respectively. The influences of acid blending ratio, temperature, and acid dosage on pretreatment performance were investigated. A synergistic effect on hemicellulose decomposition was observed in the combined acid hydrolysis, which greatly increased xylose yield, although TFA/MA would induce more total phenols. Besides, combined TFA pretreatment could efficiently prevent xylose degradation. Fermentation tests of the acid-catalyzed hydrolysates with overliming showed that compared to H2SO4 pretreatment, TFA and MA pretreatments improved overall ethanol yield with an increase by 27–54%. Combined acid catalysis was shown as a feasible pretreatment method for its improved sugar yield, reduced phenols production and catalyst costs.
Larsen, T., Gebauer, H., Künzle, R., Lüthi, C., McConville, J., Messmer, U., … Tumwebaze, I. K. (2012). Final report. Reinvent the toilet challenge. Round 1. Diversion for safe saniation. Dübendorf: Eawag. , Institutional Repository
Li, X., Yuen, W., Morgenroth, E., & Raskin, L. (2012). Backwash intensity and frequency impact the microbial community structure and function in a fixed-bed biofilm reactor. Applied Microbiology and Biotechnology, 96(3), 815-827. doi:10.1007/s00253-011-3838-6, Institutional Repository

Linkages among bioreactor operation and performance and microbial community structure were investigated for a fixed-bed biofilm system designed to remove perchlorate from drinking water. Perchlorate removal was monitored to evaluate reactor performance during and after the frequency and intensity of the backwash procedure were changed, while the microbial community structure was studied using clone libraries and quantitative PCR targeting the 16S rRNA gene. When backwash frequency was increased from once per month to once per day, perchlorate removal initially deteriorated and then recovered, and the relative abundance of perchlorate-reducing bacteria (PRB) initially increased and then decreased. This apparent discrepancy suggested that bacterial populations other than PRB played an indirect role in perchlorate removal, likely by consuming dissolved oxygen, a competing electron acceptor. When backwash intensity was increased, the reactor gradually lost its ability to remove perchlorate, and concurrently the relative abundance of PRB decreased. The results indicated that changes in reactor operation had a profound impact on reactor performance through altering the microbial community structure. Backwashing is an important yet poorly characterized procedure when operating fixed-bed biofilm reactors. Compared to backwash intensity, changes in backwash frequency exerted less disturbance on the microbial community in the current study. If this finding can be confirmed in future work, backwash frequency may serve as the primary parameter when optimizing backwash procedures.
Menniti, A., Rieger, L., Boltz, J. P., Johnson, B., Daigger, G., Habermacher, J., … Morgenroth, E. (2012). Critical review on the degradability of endogenous decay products. In Vol. 12. 85th annual water environment federation technical exhibition and conference (WEFTEC 2012) (pp. 7406-7408). Virginia, USA: Water Environment Federation (WEF). , Institutional Repository

Sludge disposal is one of the main cost factors in wastewater treatment. Endogenous processes produce inert materials (endogenous decay products) which contribute a large fraction of the sludge produced in activated sludge treatment. There is evidence that endogenous decay products are degradable under certain conditions. However, a serious knowledge gap exists for the detailed understanding of endogenous processes and specific treatment options influencing the degradability of endogenous decay products. Before models can be applied to describe sludge reduction through degradation of endogenous decay products, we must first understand the endogenous processes producing them and the conditions influencing their degradability. This paper provides a review of the key literature on the degradability of endogenous decay products and summarizes the primary
mechanistic hypotheses based on these observations. These hypotheses are evaluated based on performance of three proposed model structures to predict the sludge production performance of a CannibalTM system.
Sägesser, D. (2012). Transformation von Mikroverunreinigungen in der Kanalisation. Erstellung eines hydraulischen Modells als Grundlage (Bachelor thesis). 32 p. , Institutional Repository

Über die Transformation von Mikroverunreinigungen in Kanalisationssystemen ist bislang wenig bekannt. Aus diesem Grund will die vorliegende Bachelorarbeit aufzuzeigen, wie gross Abbauraten von solchen anthropogenen Stoffen sein müssten, damit am Ende eines Versuchskanals ein Abbau messbar ist. Dazu wurden mehrere Tracerexperimente ausgewertet. Die Tracerexperimente waren vorgängig von der EAWAG durchgeführt worden. Als Versuchskanal diente der fünf Kilometer lange Glattstollen, welcher das Abwasser durch den Zürichberg zur Abwasserreinigungsanlage Werdhölzli transportiert. Der Abwasserkanal ist für die Experimente ideal, da keine seitlichen Zuflüsse vorhanden sind.
Für die Auswertung der Tracerexperimente wurde das Computerprogramm Aquasim 2.1 verwendet. Der Abwasserkanal wurde sowohl als Advective-Diffusive Reactor Compartment (Modell 1) als auch als River-Section Compartment (Modell 2) modelliert. Anschliessend wurden die Modelle mittels Daten aus den Tracerexperimenten kalibriert. Als Grundlage dazu diente das Massenerhaltungsgesetz. Für die hydraulische Kalibrierung wurde bei beiden Modellen die Dispersion geschätzt. Zusätzlich wurde beim Modell 1 die Geschwindigkeit und beim Modell 2 der hydraulischen Widerstandsbeiwert nach Strickler ermittelt. Anschliessend wurde ein linearer Abbauprozess hinzugefügt. Durch das Variieren verschiedener Abbauraten konnte die verbleibende Konzentration fünf Kilometer nach Zudosierung berechnet und verglichen werden.
Das Modell 1 und 2 unterscheiden sich prinzipiell in der Wahl des Kompartiments. Gewisse Variablen müssen dadurch unterschiedlich definiert werden. Die Resultate zum Abbau indizieren, dass das Modell 2 genauere Ergebnisse liefert. Beide Modelle zeigen bei der Parameterschätzung ähnliche Resultate. Dies zeigt, dass auch die Modellierung des Kanals als Advektive-Diffusive Reactor Compartment (Modell 1) für eine solide Abschätzung der Parameter sowie zur Quantifizierung des Abbaus verwendet werden kann. Modell 1 ist insbesondere vorzuziehen, falls Angaben zum Durchmesser oder Gefälle fehlen.
Die Auswertung der Tracerversuche ergab, dass sich der Dispersionskoeffizient zwischen 0.11 – 0.29 m2/s befindet. Nach Rieckermann et al. (2005) ist in Abwasserkanälen ein mittlerer Dispersionskoeffizient von 0.16 m2/s üblich. Die ermittelten Werte sind somit durchaus realistisch.
Für die Quantifizierung des Abbaus wurden Abbauraten zwischen 0.1/d und 24/d betrachtet. Die Berechnungen ergaben, dass bei einer Abbaurate von 24/d am Ende des Versuchskanals etwa 90 % der Zudosiermenge abgebaut werden. Allerdings sind die Abbauraten von Mikroverunreinigungen viel geringer. Eine Abbaurate von 0.1/d oder noch kleiner ist realistischer (Joss et al., 2006). Dabei würden ungefähr 1.2 % abgebaut werden. Dies entspricht keinem erheblichen Abbau und könnte, je nach Substanz und Genauigkeit des Messinstruments, knapp oder gar nicht registriert werden.
Bei der Transformation von Mikroverunreinigungen in Abwasserkanälen spielt, neben dem Abbau, auch die Sorption eine Rolle. Durch die Erweiterung der Modelle mit einem Biofilm - Reaktor sowie einem Prozess, der die Sorption beschreibt, könnte das Verhalten der Mikroverunreinigungen in Kanalisationssytemen noch detaillierter betrachtet werden.
Ye, X., Zhang, X., Morgenroth, E., & Finneran, K. T. (2012). Anthrahydroquinone-2,6-disulfonate increases the rate of hydrogen production during Clostridium beijerinckii fermentation with glucose, xylose, and cellobiose. International Journal of Hydrogen Energy, 37(16), 11701-11709. doi:10.1016/j.ijhydene.2012.05.018, Institutional Repository

Fermentative hydrogen production is considered a reasonable alternative for generating H2 as an energy carrier for electricity production using hydrogen fuel cells. The kinetics of hydrogen production from glucose, xylose and cellobiose were investigated using pure culture Clostridium beijerinckii NCIMB 8052. Adding anthrahydroquinone-2,6-disulfonate (AH2QDS) at concentrations ranging from 100 μM to 500 μM increased the hydrogen production rates from 0.80 to 1.35 mmol/L-hr to 1.20–2.70 mmol/L-hr with glucose, xylose, or cellobiose as the primary substrates. AH2QDS amendment also increased the substrate utilization rate and biomass growth rate by at least two times. These findings suggest that adding hydroquinone reducing equivalents influence cellular metabolism with hydrogen production rate, substrate utilization rate, and growth rate being simultaneously affected. Resting cell suspensions were conducted to investigate the influence of AH2QDS on the hydrogen production rate from glyceraldehyde 3-phosphate, which is a shared intermediate in both glycolysis and pentose phosphate pathway. Data demonstrated that hydrogen production rate increased by 1.5 times when glyceraldehyde 3-phosphate was the sole carbon source, suggesting that the hydroquinone may alter reactions starting with or after glyceraldehyde 3-phosphate in central metabolism. These data demonstrate that adding hydroquinones increased overall metabolic activity of C. beijerinckii. This will eventually increase the efficiency of industrial scale production once appropriate hydroquinone equivalents are identified that work well in large-scale operations, since fermentation rate is one of the two critical factors (production rate and yield) influencing efficiency and cost.
Arreaza Bauer, A. S. (2011). Robust elicitation of imprecise expert knowledge for water infrastructure management (Master thesis). 32 p. , Institutional Repository

A project lead by SWIP (Sustainable Water Infrastructure Planning) at Eawag is working on the development of probabilistic pipe decay models to support mid- and longterm infrastructure management and rehabilitation planning. Lack of data is one of the diculties this group is facing, but methods exist to collect information of experienced experts with the help of elicitation. To develop an appropriate elicitation procedure was the goal of this thesis, especially comparing the imprecise method of elicitation, which is in development, with the traditional precise method.
First, a brieng was developed for the experts to be informed about the intention and the procedure of the elicitation. The interview itself was conducted with 15 experts in water infrastructure management, eight in the drinking water sector and seven in the wastewater sector. The interviews were designed to elicit pipe lifetime distributions of dierent pipe types. Important psychological and statistical aspects as the basic axioms of probability theory, possible pitfalls, calibrating the expert and give feedback to recognize inconsistencies in the experts answers, are some among the important considerations.
To evaluate if experts have a distinct preference regarding the precise and imprecise method of elicitation, subjective questions were posed to the experts after the elicitations. To additionally see if the choice of the method had an inuence on the time needed for elicitation or the adaptations done for each probability, these were measured and compared. Finally, to recognize if both methods expressed the same information with regard to the lifetime of the pipes, the elicited precise and imprecise estimates for each pipe type were compared. The intention of this work was to evaluate if the imprecise method is equal or even better than the precise method. If this case was conrmed, then the imprecise method could be recommended for future elicitations.
The answers given for the questions posed after the elicitation, state a preference of the imprecise method (8 experts out of 14). Most experts also found it easier (9 out of 14). Interestingly, a majority thought in a precise way (8 out of 14), but this did not seem to infuence the preference of the method as half of those experts prefered the imprecise method. The results showed that the methods had no inuence on time nor on adaptation. The comparison of the methods with regard to the elicited pipe types showed, that the inuence factors of the dierent areas in Switzerland or the experience of the experts were dominating the elicited estimations.
To sum up, the imprecise method can be recommended for future elicitations, as it is considered equal or better than the precise method. More than half of the experts preferred this method. This is also supported by the easiness of doing the elicitation.
Boltz, J. P., Morgenroth, E., Brockmann, D., Bott, C., Gellner, W. J., & Vanrolleghem, P. A. (2011). Systematic evaluation of biofilm models for engineering practice: components and critical assumptions. Water Science and Technology, 64(4), 930-944. doi:10.2166/wst.2011.709, Institutional Repository

Biofilm models are valuable tools for the design and evaluation of biofilm-based processes despite several uncertainties including the dynamics and rate of biofilm detachment, concentration gradients external to the biofilm surface, and undefined biofilm reactor model calibration protocol. The present investigation serves to (1) systematically evaluate critical biofilm model assumptions and components and (2) conduct a sensitivity analysis with the aim of identifying parameter subsets for biofilm reactor model calibration. AQUASIM was used to describe submerged-completely mixed combined carbon oxidation and nitrification IFAS and MBBR systems, and tertiary nitrification and denitrification MBBRs. The influence of uncertainties in model parameters on relevant model outputs was determined for simulated scenarios by means of a local sensitivity analysis. To obtain reasonable simulation results for partially penetrated biofilms that accumulated a substantial thickness in the modelled biofilm reactor (e.g. 1,000 mm), an appropriate biofilm discretization was applied to properly model soluble substrate concentration gradients and, consistent with the assumed mechanism for describing biofilm biomass distribution, biofilm biomass spatial variability. The MTBL thickness had a significant impact on model results for each of the modelled reactor configurations. Further research is needed to develop a mathematical description (empirical or otherwise) of the MTBL thickness that is relevant to modern biofilm reactors. No simple recommendations for a generally applicable calibration protocol are provided, but sensitivity analysis has been proven to be a powerful tool for the identification of highly sensitive parameter subsets for biofilm (reactor) model calibration.
Dürrenmatt, D. J. (2011). Data mining and data-driven modelling approaches to support wastewater treatment plant operation (Doctoral dissertation). doi:10.3929/ethz-a-006717398, Institutional Repository

In wastewater treatment plants (WWTPs), much effort and money is invested in operating and maintaining dense plant-wide measuring networks. The network primarily serves as input for the advanced control scenarios that are implemented in the supervisory control and data acquisition (SCADA) system to satisfy the stringent effluent quality constraints. Due to new developments in information technology, long-term archiving has become practicable, and specialized process information systems are now available. The steadily growing amount of plant data available, however, is not systematically exploited for plant optimization because of the lack of specialized tools that allow operators and engineers alike to extract meaningful and valuable information efficiently from the massive amount of high-dimensional data. As a result, most information contained in the data is eventually lost. [...]

In Kläranlagen wird viel Aufwand und Geld in den Betrieb und die Wartung eines anlagenweiten Messnetzes gesteckt. Dieses Messnetz dient in erster Linie als Input für die Regelungsvorgänge, die im Prozessleitsystem definiert sind, um die strengen Grenzwerte bezüglich der Ablaufqualität zu erfüllen. Neue Errungenschaften im Bereich der Informationstechnologie ermöglichen nun eine wirtschaftliche Langzeitarchivierung und es stehen mittlerweile sogar spezialisierte Prozessinformationssysteme zur Verfügung. Allerdings wird die stetig wachsende Menge an verfügbaren Anlagedaten nicht systematisch ausgenutzt und zur Optimierung der Anlagen herangezogen. Dies ist auf das Fehlen von spezialisierten Instrumenten zurückzuführen, die es sowohl Betreibern als auch Ingenieuren ermöglichten, aussagekräftige und wertvolle Informationen aus der gewaltigen Menge hochdimensionaler Daten zu extrahieren. Folglich geht ein Grossteil der in den Daten enthaltenen Informationen verloren. [...]
Huber, S. J. (2011). Temperature dependent removal of sodium chloride (NaCl) from synthetic nitrified urine (Master thesis). 46 p. , Institutional Repository

Urine is the source of the major part of plant nutrients in municipal wastewater. Therefore, full nutrient recovery from source-separated urine is an attractive option for both treating wastewater and gaining a valuable fertilizer product. Full nutrient recovery can be achieved by first stabilizing collected urine by nitrification and then concentrating the urine by distillation. Since concentrations of all salts in urine increase with increasing removal of water also the sodium chloride (NaCl) content is high in the end. There are two problems related to NaCl, the first being the synergistic decomposition of ammonium nitrate by chloride and the second being soil salinity and sodicity related problems when applying the product as fertilizer. [...]
Joss, A., Derlon, N., Cyprien, C., Burger, S., Szivak, I., Traber, J., … Morgenroth, E. (2011). Combined nitritation–anammox: advances in understanding process stability. Environmental Science and Technology, 45(22), 9735-9742. doi:10.1021/es202181v, Institutional Repository

Efficient nitrogen removal from wastewater containing high concentrations of ammonium but little organic substrate has recently been demonstrated by several full-scale applications of the combined nitritation–anammox process. While the process efficiency is in most cases very good, process instabilities have been observed to result in temporary process failures. In the current study, conditions resulting in instability and strategies to regain efficient operation were evaluated. First, data from full-scale operation is presented, showing a sudden partial loss of activity followed by recovery within less than 1 month. Results from laboratory-scale experiments indicate that these dynamics observed in full scale can be caused by partial inhibition of the ammonia oxidizing bacteria (AOB), while anammox inhibition is a secondary effect due to temporarily reduced O2 depletion. Complete anammox inhibition is observed at 0.2 mg O2·L–1, resulting in NO2– accumulation. However, this inhibition of anammox is reversible within minutes after O2 depletion. Thus, variable AOB activity was identified as the key to reactor stability. With appropriate interpretation of the online NH4+ signal, accumulation of NO2– can be detected indirectly and used to signal an imbalance of O2 supply and AOB activity (no suitable online NO2– electrode is currently available). Second, increased abundance of nitrite-oxidizing bacteria (NOB; competing with anammox for NO2–) is known as another cause of instability. Based on a comparison of parallel full-scale reactors, it is suggested that an infrequent and short-term increased O2 supply (e.g., for maintenance of aerators) that exceeds prompt depletion of oxygen by AOB may have caused increased NOB abundance. The volumetric air supply as a proxy for O2 supply thus needs to be linked to AOB activity. Further, NOB can be washed out of the system during regular operation if the system is operated at a sludge age in the range of 45 days and by controlling the air supply according to the NO3– concentration in the treated effluent. Early detection of growing NOB abundance while the population is still low can help guide process operation and it is suggested that molecular methods of quantifying NOB abundance should be tested.
Mutzner, L. (2011). GIS based assessment of the fate of micropollutants in combined sewerages (Master thesis). 45 p. , Institutional Repository

Only little is known about the micropollutants from urban areas discharged via combined sewer overflows during rain events. In urban catchments various sources of micropollution
occur that change over time and with different kind of land uses. In Switzerland different rain regions and various land use types have to be considered to characterise the large variability of urban drainage systems. Thus a geographical information system based analysis of the urban areas in Switzerland combined with the modelling of the amount of pollutants released via combined sewer over flows during rain events is feasible to asses the dominant sources. Therefore a model was developed to determine the combined sewer over flow emissions loads of micropollutants for Switzerland. This model accounts for the main urban sources of micropollutants and the variation in the urban area of Switzerland.
The overall model results show, that combined sewer over flow emissions of urban areas are an important contribution to the pollutant load in surface water. Especially for pollutants
washed-off impervious areas, such as roofs or traffic surfaces, the load discharged via combined sewer over flow was estimated to be in the same range as the load discharged to the wastewater treatment plant. Thus the discharge via combined sewer over flow can result in acute effects on the environment. The result also emphasizes the importance of mitigation measures at the pollutant source rather then end-of-pipe measures.
Shimada, T., Li, X., Zilles, J. L., Morgenroth, E., & Raskin, L. (2011). Effects of the antimicrobial tylosin on the microbial community structure of an anaerobic sequencing batch reactor. Biotechnology and Bioengineering, 108(2), 296-305. doi:10.1002/bit.22934, Institutional Repository

The effects of the antimicrobial tylosin on a methanogenic microbial community were studied in a glucose-fed laboratory-scale anaerobic sequencing batch reactor (ASBR) exposed to stepwise increases of tylosin (0, 1.67, and 167 mg/L). The microbial community structure was determined using quantitative fluorescence in situ hybridization (FISH) and phylogenetic analyses of bacterial 16S ribosomal RNA (rRNA) gene clone libraries of biomass samples. During the periods without tylosin addition and with an influent tylosin concentration of 1.67 mg/L, 16S rRNA gene sequences related to Syntrophobacter were detected and the relative abundance of Methanosaeta species was high. During the highest tylosin dose of 167 mg/L, 16S rRNA gene sequences related to Syntrophobacter species were not detected and the relative abundance of Methanosaeta decreased considerably. Throughout the experimental period, Propionibacteriaceae and high GC Gram-positive bacteria were present, based on 16S rRNA gene sequences and FISH analyses, respectively. The accumulation of propionate and subsequent reactor failure after long-term exposure to tylosin are attributed to the direct inhibition of propionate-oxidizing syntrophic bacteria closely related to Syntrophobacter and the indirect inhibition of Methanosaeta by high propionate concentrations and low pH.
Shimada, T., Morgenroth, E., Tandukar, M., Pavlostathis, S. G., Smith, A., Raskin, I., & Kilian, R. F. (2011). Syntrophic acetate oxidation in two-phase (acid–methane) anaerobic digesters. Water Science and Technology, 64(9), 1812-1820. doi:10.2166/wst.2011.748, Institutional Repository

The microbial processes involved in two-phase anaerobic digestion were investigated by operating a laboratory-scale acid-phase (AP) reactor and analyzing two full-scale, two-phase anaerobic digesters operated under mesophilic (35 °C) conditions. The digesters received a blend of primary sludge and waste activated sludge (WAS). Methane levels of 20% in the laboratory-scale reactor indicated the presence of methanogenic activity in the AP. A phylogenetic analysis of an archaeal 16S rRNA gene clone library of one of the full-scale AP digesters showed that 82% and 5% of the clones were affiliated with the orders Methanobacteriales and Methanosarcinales, respectively. These results indicate that substantial levels of aceticlastic methanogens (order Methanosarcinales) were not maintained at the low solids retention times and acidic conditions (pH 5.2–5.5) of the AP, and that methanogenesis was carried out by hydrogen-utilizing methanogens of the order Methanobacteriales. Approximately 43, 31, and 9% of the archaeal clones from the methanogenic phase (MP) digester were affiliated with the orders Methanosarcinales, Methanomicrobiales, and Methanobacteriales, respectively. A phylogenetic analysis of a bacterial 16S rRNA gene clone library suggested the presence of acetate-oxidizing bacteria (close relatives of Thermacetogenium phaeum, ‘Syntrophaceticus schinkii,’ and Clostridium ultunense). The high abundance of hydrogen consuming methanogens and the presence of known acetate-oxidizing bacteria suggest that acetate utilization by acetate oxidizing bacteria in syntrophic interaction with hydrogen-utilizing methanogens was an important pathway in the second-stage of the two-phase digestion, which was operated at high ammonium-N concentrations (1.0 and 1.4 g/L). A modified version of the IWA Anaerobic Digestion Model No. 1 (ADM1) with extensions for syntrophic acetate oxidation and weak-acid inhibition adequately described the dynamic profiles of volatile acid production/degradation and methane generation observed in the laboratory-scale AP reactor. The model was validated with historical data from the full-scale digesters.
Ye, X., Morgenroth, E., Zhang, X., & Finneran, K. T. (2011). Anthrahydroquinone-2,6,-disulfonate (AH2QDS) increases hydrogen molar yield and xylose utilization in growing cultures of Clostridium beijerinckii. Applied Microbiology and Biotechnology, 92(4), 855-864. doi:10.1007/s00253-011-3571-1, Institutional Repository

H2 production and xylose utilization were investigated using the fermentative culture Clostridium beijerinckii NCIMB 8052. Adding anthrahydroquinone-2,6-disulfonate (AH2QDS) increased the extent of xylose utilization by 56% and hydrogen molar yield by 24–37%. Enhanced hydrogen molar yield correlated with increased xylose utilization and increases in the acetate/butyrate product ratio. An electron balance indicated that AH2QDS shifted the electrons from the butyric acid pathway (NADH-dependent pathway) to the acetic acid pathway (non-NADH-dependent pathway), putatively creating a surplus of reducing equivalents that were then available for hydrogen production. These data demonstrate that hydrogen yield and xylose utilization can be manipulated by amending redox active molecules into growing cultures. This will impact biohydrogen/biofuel production by allowing physiological manipulations of growing cells for increased (or decreased) output of selected metabolites using amendments that are not consumed during the reactions. Although the current yield increases are small, they suggest a target for cellular alterations. In addition, increased xylose utilization will be critical to the fermentation of pretreated lignocellulosic feedstocks, which may have higher xylose content.
Boltz, J. P., Morgenroth, E., & Sen, D. (2010). Mathematical modelling of biofilms and biofilm reactors for engineering design. Water Science and Technology, 62(8), 1821-1836. doi:10.2166/wst.2010.076, Institutional Repository

Mathematical models are critical to modern environmental biotechnology—both in research and in the engineering practice. Wastewater treatment plant (WWTP) simulators are used by consulting engineers and WWTP operators when planning, designing, optimizing, and evaluating the unit processes that comprise municipal and industrial WWTPs. Many WWTP simulators have been expanded to include a submerged completely-mixed biofilm reactor module that is based on the mathematical description of a one-dimensional biofilm. Leading consultants, equipment manufacturers, and WWTP modelling software developers have made meaningful contributions to advancing the use of biofilm models in engineering practice, but the bulk of the engineering community either does not use the now readily available biofilm reactor modules or utilizes them as ‘black-box’ design tools. The latter approach results in the mathematical biofilm models being no more useful than the empirical design criteria and formulations that have been historically applied to biofilm reactor design. The present work provides a consensus report on the state-of-the art, areas of uncertainty, and future needs for advancing the use of biofilm models in engineering design.
Brockmann, D., & Morgenroth, E. (2010). Evaluating operating conditions for outcompeting nitrite oxidizers and maintaining partial nitrification in biofilm systems using biofilm modeling and Monte Carlo filtering. Water Research, 44(6), 1995-2009. doi:10.1016/j.watres.2009.12.010, Institutional Repository

In practice, partial nitrification to nitrite in biofilms has been achieved with a range of different operating conditions, but mechanisms resulting in reliable partial nitrification in biofilms are not well understood. In this study, mathematical biofilm modeling combined with Monte Carlo filtering was used to evaluate operating conditions that (1) lead to outcompetition of nitrite oxidizers from the biofilm, and (2) allow to maintain partial nitrification during long-term operation. Competition for oxygen was found to be the main mechanism for displacing nitrite oxidizers from the biofilm, and preventing re-growth of nitrite oxidizers in the long-term. To maintain partial nitrification in the model, a larger oxygen affinity (i.e., smaller half saturation constant) for ammonium oxidizers compared to nitrite oxidizers was required, while the difference in maximum growth rate was not important for competition under steady state conditions. Thus, mechanisms for washout of nitrite oxidizing bacteria from biofilms are different from suspended cultures where the difference in maximum growth rate is a key mechanism. Inhibition of nitrite oxidizers by free ammonia was not required to outcompete nitrite oxidizers from the biofilm, and to maintain partial nitrification to nitrite. But inhibition by free ammonia resulted in faster washout of nitrite oxidizers.
Hug, A. (2010). Phosphate recovery from urine by electrocoagulation (Master thesis). 38 p. , Institutional Repository

Phosphorus is an essential compound for plants. But the major phosphorus source for fertilizers - phosphate rock - is a limited resource. To close the nutrient cycle, phosphorus should be recovered from waste streams. Urine has a high phosphate content, which can be recovered as struvite.
Struvite is a magnesium-ammonium-phosphate (NH4MgPO4 · 6 H2O) and can be used as a slow release fertilizer in agriculture. As magnesium is the limited compound in urine, a magnesium source has to be added for struvite precipitation. Conventional methods consist in the dosage of a magnesium salt. Electrocoagulation on the other hand dissolves magnesium electrochemically from a magnesium electrode.
For electrocoagulation magnesium is oxidized to magnesium ions at the magnesium anode, water is reduced to hydrogen gas at the steel cathode. To enhance the reaction speed a voltage source can be added. The voltage source can either be applied between the magnesium and a reference electrode (magnesium potential, three electrode configuration) or between the magnesium and the steel electrode (cell voltage, two electrode configuration). The advantage of the three electrode configuration being that the magnesium potential determines directly the reactions that can take place at the magnesium electrode.
Two sets of experiments have been conducted: voltammetry and batch experiments. For voltammetry the applied magnesium potential was changed with time to detect electrode characteristics. For the batch experiments the voltage source (magnesium potential or cell voltage) was kept constant over time.
Voltammetry and batch experiments showed that the magnesium electrode is sensitive to layer formation at magnesium potentials below -800 mV. An electrode potential of -600 mV seemed to be a very appropriate potential concerning reaction speed and energy consumption. An electrocoagulation reactor can either be operated by applying an electrode potential or a cell voltage. Applying a cell voltage will be the easier configuration, as no potentiostat is needed. A cell voltage of at least 1000 mV should be applied to prevent layer formation.
The monitored cell voltage/electrode potential (depending on electrode configuration) showed a maximum/minimum as phosphate was removed from urine. It can therefore be used as a parameter to control the magnesium dissolution in order to not waste magnesium. A continuous reactor could then be operated in sequencing batch mode, using three tanks:
storage tank, electrocoagulation reactor and settling tank.
It has been shown that electrocoagulation is a very functional method to recover struvite from natural urine. The advantage of electrocoagulation against chemical dosing will be found in a high magnesium efficiency and in a high automation possibility.
Li, X., Upadhyaya, G., Yuen, W., Brown, J., Morgenroth, E., & Raskin, L. (2010). Changes in the structure and function of microbial communities in drinking water treatment bioreactors upon addition of phosphorus. Applied and Environmental Microbiology, 76(22), 7473-7481. doi:10.1128/AEM.01232-10, Institutional Repository

Phosphorus was added as a nutrient to bench-scale and pilot-scale biologically active carbon (BAC) reactors operated for perchlorate and nitrate removal from contaminated groundwater. The two bioreactors responded similarly to phosphorus addition in terms of microbial community function (i.e., reactor performance), while drastically different responses in microbial community structure were detected. Improvement in reactor performance with respect to perchlorate and nitrate removal started within a few days after phosphorus addition for both reactors. Microbial community structures were evaluated using molecular techniques targeting 16S rRNA genes. Clone library results showed that the relative abundance of perchlorate-reducing bacteria (PRB) Dechloromonas and Azospira in the bench-scale reactor increased from 15.2% and 0.6% to 54.2% and 11.7% after phosphorus addition, respectively. Real-time quantitative PCR (qPCR) experiments revealed that these increases started within a few days after phosphorus addition. In contrast, after phosphorus addition, the relative abundance of Dechloromonas in the pilot-scale reactor decreased from 7.1 to 0.6%, while Zoogloea increased from 17.9 to 52.0%. The results of this study demonstrated that similar operating conditions for bench-scale and pilot-scale reactors resulted in similar contaminant removal performances, despite dramatically different responses from microbial communities. These findings suggest that it is important to evaluate the microbial community compositions inside bioreactors used for drinking water treatment, as they determine the microbial composition in the effluent and impact downstream treatment requirements for drinking water production. This information could be particularly relevant to drinking water safety, if pathogens or disinfectant-resistant bacteria are detected in the bioreactors.
Marti, B. (2010). Bioelectrochemical removal of sulfur from source-separated urine (Master thesis). 32 p. , Institutional Repository

All of the sulfur in human excreta ends up as dissolved sulfate in the urine. If released to the environment, sulfate is not problematic because it is stable. However, if it comes in contact with water containing a large amount of organics, sulfate transformation to sulfide starts as soon as the water is depleted of oxygen and nitrate, producing a bad smell and intoxicating the microbiology. The largest problem in wastewater treatment is probably the corrosion in anaerobic sewer systems due to sulfide oxidation. Another problem is the H2S production during biogas generation, which necessitates gas washing. Since it is an essential plant nutrient [18] and a widely applied element in industry [23], recovering sulfur from urine can be of interest. Within the scope of a master thesis of 16 weeks the bioelectrochemical sulfate removal from stored, source-separated urine was analyzed. The iodometric method was applied to urine in order to measure dissolved sulfide, thiosulfate, and sulfite. In a microbial electrolysis cell a sulfate load of 4.10 ± 0.17 g SO2−4 -S m−2 biofilm surface d−1 was microbially transformed to sulfide which was subsequently oxidized to elemental sulfur at an anode potential of 0.06 V. Comparison between dissimilatory sulfate reduction with and without electrochemical sulfide oxidation showed an increase of the sulfate degradation rate of 30 % to 1.48 g SO2−4 -S m−2 biofilm surface d−1 when sulfide was electrochemically oxidized. A mass balance of sulfur over the reactor showed that dissolved sulfur disappeared in the reactor. Based on the sulfur balance, a sulfide oxidation rate was estimated yielding 0.35 g SH−-S m−2d−1. The process combination of biological sulfate reduction and subsequent partial sulfide oxidation to elemental sulfur was applied successfully to stored, source-separated urine. In a future work, the process parameters need to be improved, first of all the tradeoff between biofilm surface on the anode and free anode surface for sulfide oxidation. A separation of the biological and electrochemical processes would be suitable for further experiments on the bioelectrochemical sulfate reduction. Additionally a more throughout analysis of the conversion of the sulfur species in the reactor should be done. The limitations of the sulfate degradation need to be analyzed.
Menniti, A., & Morgenroth, E. (2010). Mechanisms of SMP production in membrane bioreactors: choosing an appropriate mathematical model structure. Water Research, 44(18), 5240-5251. doi:10.1016/j.watres.2010.06.040, Institutional Repository

Being able to predict the soluble microbial product (SMP) concentration, an important foulant in membrane bioreactors (MBRs), with mathematical models provides the opportunity to use foulant production as an MBR design and optimization parameter. This study examined the ability of three mathematical model structures to describe two distinct mechanisms of SMP production. The production mechanisms evaluated are (1) the erosion or hydrolysis of floc-associated extracellular polymeric substance (EPS) and (2) decay of active cells. The models were compared based on their ability to predict SMP concentrations observed in an MBR system during a period of increased SMP and floc-associated EPS production due to increased predation. Predation was an important contributor to overall biomass decay. Short-term batch experiments were also preformed to examine model assumptions related to the (1) production of SMP due to decay of active cells, (2) production of SMP due to erosion of floc-associated EPS, (3) degradability of SMP present in the MBR mixed liquor during increased predation and (4) degradability of eroded floc-associated EPS. Both erosion of floc-associated EPS and decay of active cells were shown to be important independent mechanisms of SMP production. Therefore, a mathematical model used to predict SMP concentrations should provide the ability to capture both mechanisms independently. SMP produced during increased predation were slowly degradable while eroded floc-associated EPS was rapidly degradable. Model results demonstrate that the slowly biodegradable SMP fraction will dominate the bulk phase SMP concentration.
Menniti, A., & Morgenroth, E. (2010). The influence of aeration intensity on predation and EPS production in membrane bioreactors. Water Research, 44(8), 2541-2553. doi:10.1016/j.watres.2009.12.024, Institutional Repository

Shear, in the form of vigorous aeration, is used to control fouling in membrane bioreactor (MBR) systems. However, shear also influences the physicochemical and biological properties of MBR biomass. The current study examines the relationship between the aeration intensity and extracellular polymeric substance (EPS) production in MBRs. Two identical submerged MBRs were operated in parallel but the aeration rate was three times greater in one of the MBRs. The concentrations of floc-associated and soluble EPS were monitored for the duration of the experiment. Microscopic images and floc-size measurements were also collected regularly. The membrane fouling potential of the biomass was quantified using the flux-step method. Increased aeration did not have a direct effect on soluble or floc-associated EPS production in the microfiltration MBRs. However, aeration intensity had a significant effect on predatory organisms. Large aquatic earthworms, Aeolosoma hemprichi, proliferated under lower shear conditions but were never observed in the high shear reactor. Predation by A. hemprichi resulted in increased floc-associated and soluble EPS production. Thus, the mixing conditions in the low shear MBR indirectly resulted in increased soluble EPS concentrations and higher fouling potential. This research suggests that predation can have a significant impact on the production rates of floc-associated and soluble EPS – key parameters driving membrane fouling in MBRs.
Morgenroth, E., Buergmann, H., & Udert, K. (2010). Functional diversity in wastewater treatment. Eawag News [engl. ed.], 69, 15-17. , Institutional Repository

Variations in influent loads pose major challenges for biological wastewater treatment. Could increased biodiversity allow for more stable operation, and does this mean that biodiversity should also be protected in wastewater treatment plants? Using molecular biological methods, we can now quantify biodiversity and specific groups of microorganisms in complex systems.
Morgenroth, E., Bürgmann, H., & Udert, K. (2010). Funktionelle Vielfalt in der Abwasserreinigung. Eawag News [dtsch. Ausg.], 69, 15-17. , Institutional Repository

Schwankende Zulauffrachten stellen die biologische Abwasserreinigung vor grosse Herausforderungen. Kann hier eine erhöhte Biodiversität helfen und ist Biodiversität also auch in der Kläranlage erstrebenswert? Molekularbiologische Methoden erlauben es uns heute, die Artenvielfalt und spezifische Organismengruppen in komplexen Systemen zu quantifizieren.
Obrecht, J. (2010). Online Überwachung biologischer Abwasserreinigungsprozesse (Master thesis). 75 p. , Institutional Repository

Der Anammox-Prozess (anaerobe Ammoniumoxidierung) ist eine Möglichkeit Stickstoff biologisch abzubauen. Anammox hat im Gegensatz zu Nitrifikation/Denitrifikation den Vorteil, dass kein leicht abbaubarer Kohlenstoff verbraucht wird. Die Anwendung dieses Prozesses in dezentralen Urinbehandlungsanlagen wird an der Eawag in Dübendorf seit 2008 in einer Pilotanlage getestet. Die Messungen mit einer Sauerstoff-, einer Leitfähigkeits- und einer pHSonde haben gezeigt, dass die Signale während eines Zyklus einen charakteristischen Verlauf aufweisen.
Das führte zur Vermutung, dass sich der Prozess anhand dieser drei Sondensignale überwachen lässt. Das Ziel war die Untersuchung folgender Frage: Können anhand einer Kombination der drei Parameter Sauerstoff, pH-Wert und Leitfähigkeit biologische Prozesse identifiziert und quantifiziert werden?
In der vorliegenden Arbeit werden folgende vier Hauptaufgaben vorgestellt:
• Tabelle zur quantitativen Bewertung der Sondensignale
• Quantifizierung des Stickstoffabbaus mittels der Leitfähigkeit
• Modellierung der Leitfähigkeit
• Unterscheidung von Anammox und heterotropher Denitrifikation anhand des pH-Werts und der Leitfähigkeit.
Die Tabelle zur qualitativen Bewertung der Sondensignale ist ein nützliches Mittel um rasch eine Aussage zum Zustand des Systems machen zu können. In der zur Verfügung stehenden Zeit, konnten nicht alle Störfälle beurteilt werden. Sie müssen noch modelliert werden, damit man die Tabelle vervollständigen kann.
Die Quantifizierung des Stickstoffabbaus durch die Leitfähigkeitsabnahme ist ein interessanter Ansatz. Bedingt durch einige Parameter - das Strippen von CO2 und der Abbau von organischen Stoffen zu Beginn des Zyklus - ist die Unsicherheit der Bestimmung des Stickstoffabbaus derzeit noch zu gross, um eine zuverlässige Aussage machen zu können. Es sind weitere Untersuchungen nötig um festlegen zu können, wie diese Parameter miteinzubeziehen sind.
Die Leitfähigkeit lässt sich mit der allgemeinen Formel gut berechnen. Werden bei der Berechnung alle gemessenen Ionen miteinbezogen, wird die Leitfähigkeit durch das Ergebnis der Modelle deutlich überschätzt. Ein besseres Resultat wird erzielt, wenn man die Leitfähigkeit mit der Aktivität modelliert.
Eine Unterscheidung von heterotropher Denitrifikation und Anammox ist zurzeit (noch) nicht möglich. Bei beiden Prozessen nimmt der pH-Wert zu und die Leitfähigkeit nimmt ab. Die modellierten Veränderungen sind so gering, dass die Sondensignale unter Einbezug der Messunsicherheit schwierig zu interpretieren sind. Zudem ist die Frage des Einflusses von Puffern noch nicht geklärt.
Zusammenfassend ist zu sagen, dass die Onlineüberwachung mit Sonden, die die beschriebenen drei Schlüsselsignale ermitteln, ein guter Ansatz ist. Dieses Vorgehen ermöglicht eine Prozessüberwachung ohne grossen Messaufwand. Der pH-Wert wird bereits heute für die Steuerung der Zykluslänge verwendet. Die Sauerstoffkonzentration gibt Auskunft über die Funktion der Belüftung und die Messdaten der Leitfähigkeit können evtl. in Zukunft für die Quantifizierung des Stickstoffabbaus verwendet werden.
Boltz, J. P., Morgenroth, E., deBarbadillo, C., Dempsey, M. J., McQuarrie, J. P., Ghylin, T., … Nerenberg, R. (2009). Biofilm reactor technology and design. In T. L. Krause & A. B. Pincince (Eds.), WEF manual of practice No. 8 ASCE manuals and reports on engineering practice No. 76: Vol. 2. Design of municipal wastewater treatment plants. Liquid treatment processes (p. (238 pp.). Retrieved from https://www.accessengineeringlibrary.com/content/book/9780071663588/toc-chapter/chapter13/section/section1, Institutional Repository

Biological systems treating municipal wastewater require (1) the accumulation of active microorganisms in a bioreactor and (2) the separation of microorganisms from treated effluent. In suspended growth reactors, such as the activated sludge process, microorganisms grow and bioflocculate, and the resultant flocs are suspended freely in the bulk phase. Flocculated bacteria are then separated from the bulk-liquid by sedimentation or membranes. Clarifier-coupled suspended growth reactors rely on return activated sludge, or underflow, from the clarifier to provide the desired active biomass concentration in the bioreactor. Consequently, clarification units may be hydraulically or solids limited (see Chapter 14 for additional information). Biofilm reactors retain bacterial cells in a biofilm attached to fixed or movable carriers. The biofilm matrix consists of water and a variety of soluble and particulate components that include soluble microbial products, inert material, and extracellular polymeric substances (EPS). [...]
Menniti, A., Kang, S., Elimelech, M., & Morgenroth, E. (2009). Influence of shear on the production of extracellular polymeric substances in membrane bioreactors. Water Research, 43(17), 4305-4315. doi:10.1016/j.watres.2009.06.052, Institutional Repository

Shear is used to control fouling in membrane bioreactor (MBR) systems. However, shear also influences the physicochemical and biological properties of MBR biomass. The current study examines the relationship between the level of shear and extracellular polymeric substance (EPS) production in MBRs. Two identical MBRs were operated in parallel where the biomass in one reactor was exposed to seven times greater shear forces. The concentrations of floc-associated and soluble EPS were monitored for the duration of the experiment. The stickiness of extracted floc-associated EPS from each reactor was also characterized using atomic force microscopy. A mathematical model of floc-associated and soluble EPS production was applied to quantitatively describe changes in EPS production with shear. Biomass grown in a high shear environment has lower floc-associated EPS production compared to biomass grown in a lower shear environment. This decrease in floc-associated EPS production also corresponds to a decrease in soluble EPS production, which can be explained by both the lower concentration of floc-associated EPS and the production of stickier floc-associated EPS that is more erosion resistant in the high shear reactor. This research suggests that mechanical stresses can have a significant impact on the production rates of floc-associated and soluble EPS—key parameters governing membrane fouling in MBRs.
Morgenroth, E., & Milferstedt, K. (2009). Biofilm engineering: linking biofilm development at different length and time scales. Reviews in Environmental Science and Biotechnology, 8(3), 203-208. doi:10.1007/s11157-009-9163-1, Institutional Repository

Biofilms are heterogeneous and dynamic systems. Evaluation of biofilm structure and function at the microscale has been greatly advanced through the application of multidimensional imaging, in-situ identification of the microbial community composition, function, and genetic regulation. Biofilm reactors are being applied for advanced biological treatment processes and their overall (macroscale) operation is well understood and controlled. What is missing is the link between micro and macroscale. In this horizon paper we suggest how understanding the overall biofilm ecosystem will require an integrated evaluation of the different length and time scales.
Wanner, O., Eberl, H., Morgenroth, E., Noguera, D., Picioreanu, C., Rittmann, B., & van Loosdrecht, M. (2006). Mathematical modeling of biofilms. Scientific and technical report: Vol. 18. doi:10.2166/9781780402482, Institutional Repository
Eberl, H. J., van Loosdrecht, M. C. M., Morgenroth, E., Noguera, D. R., Perez, J., Picioreanu, C., … Wanner, O. (2004). Modelling a spatially heterogeneous biofilm and the bulk fluid: selected results from Benchmark Problem 2 (BM2). Water Science and Technology, 49(11-12), 155-162. doi:10.2166/wst.2004.0829, Institutional Repository

The numerical simulation of mass transfer and conversion in spatially heterogeneous biofilms on the meso-scale requires an accurate description of the hydrodynamics in the biofilm systems and of spatial effects. This leads to systems of three-dimensional nonlinear partial differential equations that are numerically very expensive to solve and to data requirements that are not easy to meet. In this paper several modeling approaches to reduce the physical complexity and, hence, accelerate the computation are compared. They range from a mere reduction of dimensionality by lumping the problem along a secondary flow direction to global mass balances or empirical correlations, at the core of which a one-dimensional boundary value problem must be solved. It is found that even strongly simplified models can describe the qualitative behaviour of the model with regard to variations in the geometrical and hydrodynamic model parameters quite well. In order to obtain also quantitatively reliable results the hydrodynamics must be considered in an appropriate manner.
Morgenroth, E., Eberl, H. J., van Loosdrecht, M. C. M., Noguera, D. R., Pizarro, G. E., Picioreanu, C., … Wanner, O. (2004). Comparing biofilm models for a single species biofilm system. Water Science and Technology, 49(11-12), 145-154. doi:10.2166/wst.2004.0826, Institutional Repository

A benchmark problem was defined to evaluate the performance of different mathematical biofilm models. The biofilm consisted of heterotrophic bacteria degrading organic substrate and oxygen. Mathematical models tested ranged from simple analytical to multidimensional numerical models. For simple and more or less flat biofilms it was shown that analytical biofilm models provide very similar results compared to more complex numerical solutions. When considering a heterogeneous biofilm morphology it was shown that the effect of an increased external mass transfer resistance was much more significant compared to the effect of an increased surface area inside the biofilm.
Rittmann, B. E., Schwarz, A. O., Eberl, H. J., Morgenroth, E., Perez, J., van Loosdrecht, M. C. M., & Wanner, O. (2004). Results from the multi-species Benchmark Problem (BM3) using one-dimensional models. Water Science and Technology, 49(11-12), 163-168. doi:10.2166/wst.2004.0831, Institutional Repository

The IWA's Biofilm Modeling Task Group created a multi-species benchmark problem in which heterotrophic bacteria, nitrifying bacteria, and inert biomass coexist in a biofilm. Members of the Task Group submitted solutions from nine different one-dimensional models. The most important distinctions among the models were (1) whether the model required a full numerical solution or was solved with a spreadsheet, and (2) the way the biomass types were distributed in the biofilm. The models that protected the slow-growing species by having them accumulate away from the outer surface always had the largest surface coverage by nitrifiers and inerts, but the heterotroph coverage declined to compensate. Coverage by heterotrophs and removal of substrate COD were most strongly affected by dilution from nitrifiers and inerts near the outer surface. Models that did not allow the nitrifiers and inerts to dilute the heterotrophs significantly in the outer layer predicted more removal of COD than did the other models. The choice of the model to use depends on the user's needs and the relative importance of including protection of slow-growing species and/or dilution of fast-growing species.
Wanner, O., & Morgenroth, E. (2004). Biofilm modeling with AQUASIM. Water Science and Technology, 49(11-12), 137-144. doi:10.2166/wst.2004.0824, Institutional Repository

AQUASIM is a computer program for the identification and simulation of aquatic systems. The program includes a one-dimensional multisubstrate and multispecies biofilm model and represents a suitable tool for biofilm simulation. The program can be used to calculate substrate removal in biofilm reactors for any user specified microbial system. One-dimensional spatial profiles of substrates and microbial species in the biofilm can be predicted. The program also calculates the development of the biofilm thickness and of the substrates and microbial species in the biofilm and in the bulk fluid over time. Detachment and attachment of microbial cells at the biofilm surface and in the biofilm interior can be considered, and simulations of sloughing events can be performed. Furthermore, AQUASIM allows pseudo two-dimensional modeling of plug flow biofilm reactors by a series of biofilm reactor compartments. The most significant limitation of the model is that it only considers spatial gradients of substrates and microbial species in the biofilm in the direction perpendicular to the substratum.
Morgenroth, E., van Loosdrecht, M. C. M., & Wanner, O. (2000). Biofilm models for the practitioner. Water Science and Technology, 41(4-5), 509-512. doi:10.2166/wst.2000.0486, Institutional Repository

Even though mathematical biofilm models are extensively used in biofilm research, there has been very little application of these models in the engineering practice so far. However, practitioners would be interested in models that can be used as tools to control plant operation under dynamic conditions or to help them handle complex interactions between particle removal, carbon oxidation, nitrification, denitrification and biological phosphorus removal. But even though there is a whole range of biofilm models available, it is difficult for the practitioner to select the appropriate modeling approach. Practitioners, experimenters and modelers should work together to identify the important processes that shoud be included in models. Guidance for model selection, calibration and application should be provided.

Kai Udert

Akert, F., Aebischer, P., Udert, K. M., & Reidy, B. (2024). Aurin, ein Dünger aus menschlichem Urin im Praxistest auf Sportrasen. Rasen: Turf: Gazon: European Journal of Turfgrass Science, 55(1), 16-21. , Institutional Repository

Um Nährstoffkreisläufe möglichst zu schließen und Nährstoffe effizient zu nutzen, wurde ein aus menschlichem Urin produzierter Dünger (Aurin) auf einem für Fußball genutzten Sportrasen getestet. Dabei wurde die Rasenfläche in drei Teilflächen unterteilt und von April bis Oktober mit herkömmlichem Handelsdünger (HD), Aurin (A) und Aurin mit Ergänzungsdüngung von Kalium, Phosphor und Magnesium (A+) gedüngt. Die Teilflächen wurden zwischen April und November regelmäßig bonitiert und mittels Multispektralbildanalyse untersucht. Im April, September und Oktober wurden Bodenproben entnommen, um den Nmin Gehalt im Boden zu bestimmen. Aus den Ergebnissen der Untersuchungen zeigten sich nur bei der Rasenfarbe und beim Nmin Gehalt des Bodens geringe Unterschiede. Dabei schien die Nährstoffergänzung von Aurin einen positiven Effekt auf die Stickstoffaufnahme in die Pflanze zu haben. Dies wirkte sich vor allem während Trockenperioden positiv auf die Rasenfarbe aus. Praktische Beobachtungen durch die Pflegeverantwortlichen zeigten, dass ein höheres Ausbringungsintervall mit geringeren Aurin-Mengen sinnvoll war. So konnten die Vernässung der Fläche und die kurzzeitige Verätzung des Rasens verhindert werden. Auch das Stoßwachstum in den Tagen nach der Düngung konnte so gebremst werden. Dieser Praxistest zeigt auf, dass Dünger aus menschlichem Urin eine interessante Option für eine kreislauffähige Bewirtschaftung von Sportrasen oder andere Kulturen mit hohem Stickstoffbedarf darstellen kann. Dies ist allerdings mit einem höheren Arbeitsaufwand in der Bewirtschaftung verbunden.
Faust, V., Markus, P., Schielke-Jenni, S., Timmer, M. J., De Paepe, J., Ganigué, R., … Udert, K. M. (2024). Conditions for successful nitrogen removal from source-separated urine by partial nitritation/anammox. PLoS Water, 3(5), e0000235 (23 pp.). doi:10.1371/journal.pwat.0000235, Institutional Repository

Partial nitritation/anammox (PN/A) of source-separated urine is less energy-intensive and potentially cheaper and more environmentally friendly than conventional nitrogen removal from mixed sewage. However, PN/A of undiluted source-separated urine has not yet been established. In this study, the feasibility of PN/A for source-separated urine (total nitrogen 2 to 3 g-N L-1). To evaluate the influence of different factors, one- and two-stage configurations were operated using different influents, i.e. source-separated urine, synthetic urine, and urine with additional divalent cations. While partial nitritation was successfully achieved in both configurations with digester supernatant and urine, anammox activity was lost shortly after switching from digester supernatant to the urine influents. Toxic organic compounds or pharmaceuticals and the high monovalent to divalent cation ratio were suspected as causes of anammox failure, but were ruled out due to the different reactor configurations and influent compositions tested. Other suspected factors such as COD/N ratio, phosphate and sulfate inhibition, nitrogen compound inhibition, metal inhibition, pH and dissolved oxygen were also systematically excluded. Instead, the high salt concentration in urine compared to the digester supernatant most likely caused the reactor to fail due to the disintegration of large flocs, and the resulting challenge of biomass retention. The shortcomings of the floccular sludge system were overcome by using biofilm carriers, resulting in successful PN/A. This hybrid system ran for 140 days with nitrogen removal rates of up to 1000 mg-N L-1 d-1 with an average of 410 ± 220 mg-N L-1 d-1, and a nitrogen removal efficiency of 93 ± 3% at 30C.
Faust, V., Vlaeminck, S. E., Ganigué, R., & Udert, K. M. (2024). Influence of pH on urine nitrification: community shifts of ammonia-oxidizing bacteria and inhibition of nitrite-oxidizing bacteria. ACS ES&T Engineering, 4(2), 342-353. doi:10.1021/acsestengg.3c00320, Institutional Repository

Urine nitrification is pH-sensitive due to limited alkalinity and high residual ammonium concentrations. This study aimed to investigate how the pH affects nitrogen conversion and the microbial community of urine nitrification with a pH-based feeding strategy. First, kinetic parameters for NH3, HNO2, and NO2- limitation and inhibition were determined for nitrifiers from a urine nitrification reactor. The turning point for ammonia-oxidizing bacteria (AOB), i.e., the substrate concentration at which a further increase would lead to a decrease in activity due to inhibitory effects, was at an NH3 concentration of 12 mg-N L-1, which was reached only at pH values above 7. The total nitrite turning point for nitrite-oxidizing bacteria (NOB) was pH-dependent, e.g., 18 mg-N L-1 at pH 6.3. Second, four years of data from two 120 L reactors were analyzed, showing that stable nitrification with low nitrite was most likely between pH 5.8 and 6.7. And third, six 12 L urine nitrification reactors were operated at total nitrogen concentrations of 1300 and 3600 mg-N L-1 and pH values between 2.5 and 8.5. At pH 6, the AOB Nitrosomonas europaea was found, and the NOB belonged to the genus Nitrobacter. At pH 7, nitrite accumulated, and Nitrosomonas halophila was the dominant AOB. NOB were inhibited by HNO2 accumulation. At pH 8.5, the AOB Nitrosomonas stercoris became dominant, and NH3 inhibited NOB. Without influent, the pH dropped to 2.5 due to the growth of the acid-tolerant AOB “Candidatus Nitrosacidococcus urinae”. In conclusion, pH is a decisive process control parameter for urine nitrification by influencing the selection and kinetics of nitrifiers.
Frossard, E., Crain, G., Giménez de Azcárate Bordóns, I., Hirschvogel, C., Oberson, A., Paille, C., … Udert, K. M. (2024). Recycling nutrients from organic waste for growing higher plants in the Micro Ecological Life Support System Alternative (MELiSSA) loop during long-term space missions. Life Sciences in Space Research, 40, 176-185. doi:10.1016/j.lssr.2023.08.005, Institutional Repository

Space agencies are developing Bioregenerative Life Support Systems (BLSS) in view of upcoming long-term crewed space missions. Most of these BLSS plan to include various crops to produce different types of foods, clean water, and O2 while capturing CO2 from the atmosphere. However, growing these plants will require the appropriate addition of nutrients in forms that are available. As shipping fertilizers from Earth would be too costly, it will be necessary to use waste-derived nutrients. Using the example of the MELiSSA (Micro-Ecological Life Support System Alternative) loop of the European Space Agency, this paper reviews what should be considered so that nutrients recycled from waste streams could be used by plants grown in a hydroponic system. Whereas substantial research has been conducted on nitrogen and phosphorus recovery from human urine, much work remains to be done on recovering nutrients from other liquid and solid organic waste. It is essential to continue to study ways to efficiently remove sodium and chloride from urine and other organic waste to prevent the spread of these elements to the rest of the MELiSSA loop. A full nitrogen balance at habitat level will have to be achieved; on one hand, sufficient N2 will be needed to maintain atmospheric pressure at a proper level and on the other, enough mineral nitrogen will have to be provided to the plants to ensure biomass production. From a plant nutrition point of view, we will need to evaluate whether the flux of nutrients reaching the hydroponic system will enable the production of nutrient solutions able to sustain a wide variety of crops. We will also have to assess the nutrient use efficiency of these crops and how that efficiency might be increased. Techniques and sensors will have to be developed to grow the plants, considering low levels or the total absence of gravity, the limited volume available to plant growth systems, variations in plant needs, the recycling of nutrient solutions, and eventually the ultimate disposal of waste that can no longer be used.
Heusser, A., Dax, A., McArdell, C. S., & Udert, K. M. (2024). Comparing the adsorption of micropollutants on activated carbon from anaerobically stored, organics-depleted, and nitrified urine. Water Research, 257, 121615 (12 pp.). doi:10.1016/j.watres.2024.121615, Institutional Repository

Separate collection and treatment of urine optimizes nutrient recovery and enhances micropollutant removal from municipal wastewater. One typical urine treatment train includes nutrient recovery in three biological processes: anaerobic storage, followed by aerobic organics degradation concurrently with nitrification. These are usually followed by activated carbon adsorption to remove micropollutants. However, removing micropollutants prior to nitrification would protect nitrifiers from potential inhibition by pharmaceuticals. In addition, combining simplified biological treatment with activated carbon adsorption could offer a cheap and robust process for removing micropollutants where nutrient recovery is not the first priority, as a partial loss of ammonia occurs without nitrification. In this study, we investigated whether activated carbon adsorption could also take place between the three biological treatment steps. We tested the effectiveness of micropollutant removal with activated carbon after each biological treatment step by conducting experiments with anaerobically stored urine, organics-depleted urine, and nitrified urine. The urine solutions were spiked with 19 pharmaceuticals: amisulpride, atenolol, atenolol acid, candesartan, carbamazepine, citalopram, clarithromycin, darunavir, diclofenac, emtricitabine, fexofenadine, hydrochlorothiazide, irbesartan, lidocaine, metoprolol, N4-acetylsulfamethoxazole, sulfamethoxazole, trimethoprim, venlafaxine, and two artificial sweeteners, acesulfame and sucralose. Batch experiments were conducted with powdered activated carbon (PAC) to determine how much activated carbon achieve which degree of micropollutant removal and how organics, pH, and speciation change from ammonium to nitrate influence adsorption. Micropollutant removal was also tested in granular activated carbon (GAC) columns, which is the preferred technology for micropollutant removal from urine. The carbon usage rates (CUR) per person were lower for all urine solutions than for municipal wastewater. The results showed that organics depletion would be needed when micropollutant removal was the sole aim of urine treatment, as the degradation of easily biodegradable organics prevented clogging of GAC columns. However, CUR did hardly improve with organics-depleted urine compared to stored urine. The lowest CUR was achieved with nitrified urine. This resulted from the additional organics removal during nitrification and not the lower pH or the partial conversion of ammonium to nitrate. In addition, we showed that the relative pharmaceutical removal in all solutions was independent of the initial pharmaceutical concentration unless the background organics matrix changed considerably. We conclude that removal of micropollutants in GAC columns from organics-depleted urine can be performed without clogging, but with the drawback of a higher carbon usage compared to removal from nitrified urine.
Heusser, A., Wackernagel, I., Reinmann, M., & Udert, K. M. (2024). Increasing urine nitrification performance with sequential membrane aerated biofilm reactors. Water Research, 261, 122019 (10 pp.). doi:10.1016/j.watres.2024.122019, Institutional Repository

This study aimed to investigate whether separating organics depletion from nitrification increases the overall performance of urine nitrification. Separate organics depletion was facilitated with membrane aerated biofilm reactors (MABRs). The high pH and ammonia concentration in stored urine inhibited nitrification in the first stage and therewith allowed the separation of organics depletion from nitrification. An organics removal of 70 % was achieved at organic loading rates in the influent of 3.7 gCOD d−1 m−2. Organics depletion in a continuous flow stirred tank reactor (CSTR) for organics depletion led to ammonia stripping through diffused aeration of up to 13 %. Using an MABR, diffusion into the lumen amounted for 4 % ammonia loss only. In the MABR, headspace volume and therefore ammonia loss through the headspace was negligible. By aerating the downstream MABR for nitrification with the off-gas of the MABR for organics depletion, 96 % of the ammonia stripped in the first stage could be recovered in the second stage, so that the overall ammonia loss was negligibly low. Nitrification of the organics-depleted urine was studied in MABRs, CSTRs, and sequencing batch reactors in fed batch mode (FBRs), the latter two operated with suspended biomass. The experiments demonstrated that upstream organics depletion can double the nitrification rate. In a laboratory-scale MABR, nitrification rates were recorded of up to 830 mgN L−1 d−1 (3.1 gN m−2 d−1) with ambient air and over 1500 mgN L−1 d−1 (6.7 gN m−2 d−1) with oxygen-enriched air. Experiments with a laboratory-scale MABR showed that increasing operational parameters such as pH, recirculation flow, scouring frequency, and oxygen content increased the nitrification rate. The nitrification in the MABR was robust even at high pH setpoints of 6.9 and was robust against process failures arising from operational mistakes. The hydraulic retention time (HRT) required for nitrification was only 1 to 2 days. With the preceding organics depletion, the HRT for our system requires 2 to 3 days in total, whereas a combined activated sludge system requires 4 to 8 days. The N2O concentration in the off-gas increases with increasing nitrification rates; however, the N2O emission factor was 2.8 % on average and independent of nitrification rates. These results indicate that the MABR technology has a high potential for efficient and robust production of ammonium nitrate from source-separated urine.
Timmer, M. J., De Paepe, J., Van Winckel, T., Spiller, M., Spacova, I., De Paepe, K., … Vlaeminck, S. E. (2024). Resource-efficient nitrogen removal from source-separated urine with partial nitritation/anammox in a membrane-aerated biofilm reactor. ACS ES&T Engineering, 4(7), 1609-1621. doi:10.1021/acsestengg.4c00058, Institutional Repository

Source separation and decentralized urine treatment can cut costs in centralized wastewater treatment by diverting 80% of the nitrogen load in sewage. One promising approach for nitrogen removal from source-separated urine is partial nitritation/anammox (PN/A), reducing the aeration demand by 67% and organic dosage by 100% compared to nitrification/denitrification. While previous studies with suspended biomass have encountered stability issues during PN/A treatment of urine, a PN/A biofilm was hypothesized to be more resilient. Its use for urine treatment has been pioneered here for maximum rates and efficiencies in an energy-efficient membrane-aerated biofilm reactor (MABR). Nitrogen removal rates of 1.0 g N L-1 d-1 and removal efficiencies of 80-95% were achieved during a 335-day operational period at 28 °C on stabilized (pH > 11.5), diluted urine (10%). A balance between N2 and NO3- formation was observed while optimizing the supply of O2 through intermittent aeration and was rate limiting for the conversion toward N2. A short-term operation on less- and undiluted urine yielded N removal rates of 0.6-0.8 g N L-1 d-1 and removal efficiencies of 93% on 66% urine and 85% on undiluted urine. Metataxonomic analysis and fluorescence in situ hybridization confirmed the presence in the biofilm of nitrifiers (Nitrosomonas, Nitrospira) at the membrane side and anammox bacteria ("Candidatus Brocadia") at the anoxic bulk side. The findings suggest that a biofilm approach to PN/A treatment of urine overcomes stability issues and that a PN/A-MABR has significant potential for resource-efficient decentralized urine treatment. In human long-duration deep-space missions, this gravity-independent technology could produce N2 to compensate artificial atmosphere losses while facilitating water recovery from urine.
Faust, V. (2023). Effects of pH on urine nitrification: from microbial selection to process performance (Doctoral dissertation). doi:10.3929/ethz-b-000648527, Institutional Repository

Separation of urine at the source allows for the efficient recovery of nitrogen, phosphorus and other nutrients and reduces the load of these nutrients on wastewater treatment plants. Before urine can be used as a fertilizer, a treatment for nitrogen stabilization is required. Nitrification is a well-suited process for urine stabilization and is also the targeted approach in bioregenerative life support systems for Space such as in the MELiSSA project. However, due to the limited alkalinity and the high residual ammonium concentration, urine nitrification without alkalinity addition is very pH sensitive, which can compromise stable urine nitrification. Usually, the pH is controlled with the influent. Nevertheless, process failures can occur, namely nitrite accumulation, complete cessation of nitrification, and the growth of acid-tolerant ammonia-oxidizing bacteria (AOB), which can further lower the pH during periods of limited urine and lead to the emission of harmful nitrogen oxide gases. [...]

Die Urinseparierung ermöglicht eine effiziente Rückgewinnung von Stickstoff, Phosphor und anderen Nährstoffen und führt zur Entlastung der Kläranlagen. Bevor Urin als Düngemittel verwendet werden kann, ist jedoch eine Stickstoffbehandlung erforderlich. Dafür bietet sich die Nitrifikation an, welche auch im Rahmen der bioregenerative Lebenserhaltungssysteme für Weltraumanwendungen wie das MELiSSA Projekt untersucht werden. Aufgrund der begrenzten Alkalinität und der hohen Ammoniumkonzentration ist die Nitrifikation von Urin ohne Erhöhung der Alkalinität jedoch sehr pH-empfindlich, was die Stabilität der Urinnitrifikation gefährdet. Normalerweise wird der pH-Wert mit dem Zufluss geregelt. Dennoch kann es zu Prozessstörungen kommen, wie zur Akkumulation von Nitrit, zum vollständigen Erlegen der Nitrifikation und zum Wachstum säuretoleranter Ammoniakoxidierenden Bakterien (AOB), die den pH-Wert bei geringem Urinzuflus weiter senken und zur Emission schädlicher Stickoxidgase führen können. [...]
Faust, V., Boon, N., Ganigué, R., Vlaeminck, S. E., & Udert, K. M. (2023). Optimizing control strategies for urine nitrification: narrow pH control band enhances process stability and reduces nitrous oxide emissions. Frontiers in Environmental Science, 11, 1275152 (14 pp.). doi:10.3389/fenvs.2023.1275152, Institutional Repository

Nitrification is well-suited for urine stabilization. No base dosage is required if the pH is controlled within an appropriate operating range by urine feeding, producing an ammonium-nitrate fertilizer. However, the process is highly dependent on the selected pH set-points and is susceptible to process failures such as nitrite accumulation or the growth of acid-tolerant ammonia-oxidizing bacteria. To address the need for a robust and reliable process in decentralized applications, two different strategies were tested: operating a two-position pH controller (inflow on/off) with a narrow pH control band at 6.20/6.25 (∆pH = 0.05, narrow-pH) vs. a wider pH control band at 6.00/6.50 (∆pH = 0.50, wide-pH). These variations in pH also cause variations in the chemical speciation of ammonia and nitrite and, as shown, the microbial production of nitrite. It was hypothesized that the higher fluctuations would result in greater microbial diversity and, thus, a more robust process. The diversity of nitrifiers was higher in the wide-pH reactor, while the diversity of the entire microbiome was similar in both systems. However, the wide-pH reactor was more susceptible to tested process disturbances caused by increasing pH or temperature, decreasing dissolved oxygen, or an influent stop. In addition, with an emission factor of 0.47%, the nitrous oxide (N2O) emissions from the wide-pH reactor were twice as high as the N2O emissions from the narrow-pH reactor, most likely due to the nitrite fluctuations. Based on these results, a narrow control band is recommended for pH control in urine nitrification.
Heusser, A., Dax, A., McArdell, C. S., & Udert, K. M. (2023). High content of low molecular weight organics does not always affect pharmaceutical adsorption on activated carbon: the case of acetate, propionate and ethanol in source-separated urine. Water Research X, 21, 100199 (10 pp.). doi:10.1016/j.wroa.2023.100199, Institutional Repository

Adsorption on activated carbon is a common process to remove pharmaceuticals in wastewater treatment. Activated carbon adsorption is usually applied to wastewater with a low content of biological degradable organics, i.e. after biological treatment. Especially low molecular weight (LMW) compounds are known to compete with pharmaceuticals for adsorption sites. The goal of this study was to test the hypothesis that biological treatment is necessary for efficient pharmaceutical removal. Source-separated urine after anaerobic storage (anaerobically stored urine) and after aerobic biological removal of organics without nitrification (organics-depleted urine) were used in this study. In anaerobically stored urine 60% of the organic compounds were LMW organics, of which about 40% were acetate and propionate. 74% of the DOC and 100% of acetate and propionate were removed during aerobic biological treatment. To investigate the effect of the organic compounds on pharmaceutical removal, sorption experiments with 19 spiked pharmaceuticals and one artificial sweetener were conducted with powdered activated carbon. Ethanol, another LMW organic, was included in the study, as it is regularly used for pharmaceutical spiking thereby strongly increasing the DOC content. The experiments showed that the adsorption of the pharmaceuticals and the sweetener were hardly affected by the easily biodegradable LMW organics or ethanol. Therefore, it was concluded that biological pre-treatment is not necessary for efficient pharmaceutical adsorption. Since acetate, propionate and ethanol contribute substantially to the DOC content but do not absorb UV light, the latter is recommended as indicator for pharmaceutical removal in solutions with high contents of biodegradable LMW organics.
Maurer, M., Tilley, E., & Udert, K. (2023). Andere Wege für das Abwasser. Globe, 23(2), 26-28. , Institutional Repository

Die Wasserwirtschaft mit Kanalisation und zentralen Kläranlagen ist nicht mehr zukunftsfähig und global keine Lösung. Umweltingenieur:innen der ETH Zürich und der Eawag bereiten den Weg zu einer kreislauffähigen und dezentraleren Wasserinfrastruktur.
Faust, V., van Alen, T. A., Op den Camp, H. J. M., Vlaeminck, S. E., Ganigué, R., Boon, N., & Udert, K. M. (2022). Ammonia oxidation by novel "Candidatus Nitrosacidococcus urinae" is sensitive to process disturbances at low pH and to iron limitation at neutral pH. Water Research X, 17, 100157 (11 pp.). doi:10.1016/j.wroa.2022.100157, Institutional Repository

Acid-tolerant ammonia-oxidizing bacteria (AOB) can open the door to new applications, such as partial nitritation at low pH. However, they can also be problematic because chemical nitrite oxidation occurs at low pH, leading to the release of harmful nitrogen oxide gases. In this publication, the role of acid-tolerant AOB in urine treatment was explored. On the one hand, the technical feasibility of ammonia oxidation under acidic conditions for source-separated urine with total nitrogen concentrations up to 3.5 g-N L-1 was investigated. On the other hand, the abundance and growth of acid-tolerant AOB at more neutral pH was explored. Under acidic conditions (pH of 5), ammonia oxidation rates of 500 mg-N L-1 d-1 and 10 g-N g-VSS-1 d-1 were observed, despite high concentrations of 15 mg-N L-1 of the AOB-inhibiting compound nitrous acid and low concentration of 0.04 mg-N L-1 of the substrate ammonia. However, ammonia oxidation under acidic conditions was very sensitive to process disturbances. Even short periods of less than 12 h without oxygen or without influent resulted in a complete cessation of ammonia oxidation with a recovery time of up to two months, which is a problem for low maintenance applications such as decentralized treatment. Furthermore, undesirable nitrogen losses of about 10% were observed. Under acidic conditions, a novel AOB strain was enriched with a relative abundance of up to 80%, for which the name “Candidatus (Ca.) Nitrosacidococcus urinae” is proposed. While Nitrosacidococcus members were present only to a small extent (0.004%) in urine nitrification reactors operated at pH values between 5.8 and 7, acid-tolerant AOB were always enriched during long periods without influent, resulting in an uncontrolled drop in pH to as low as 2.5. Long-term experiments at different pH values showed that the activity of “Ca. Nitrosacidococcus urinae” decreased strongly at a pH of 7, where they were also outcompeted by the acid-sensitive AOB Nitrosomonas halophila. The experiment results showed that the decreased activity of “Ca. Nitrosacidococcus urinae” correlated with the limited availability of dissolved iron at neutral pH.
Faust, V., Gruber, W., Ganigué, R., Vlaeminck, S. E., & Udert, K. M. (2022). Nitrous oxide emissions and carbon footprint of decentralized urine fertilizer production by nitrification and distillation. ACS ES&T Engineering, 2(9), 1745-1755. doi:10.1021/acsestengg.2c00082, Institutional Repository

Combining partial nitrification, granular activated carbon (GAC) filtration, and distillation is a well-studied approach to convert urine into a fertilizer. To evaluate the environmental sustainability of a technology, the operational carbon footprint and therefore nitrous oxide (N2O) emissions should be known, but N2O emissions from urine nitrification have not been assessed yet. Therefore, N2O emissions of a decentralized urine nitrification reactor were monitored for 1 month. During nitrification, 0.4-1.2% of the total nitrogen load was emitted as N2O-N with an average N2O emission factor (EFN2O) of 0.7%. Additional N2O was produced during anoxic storage between nitrification and GAC filtration with an estimated EFN2O of 0.8%, resulting in an EFN2O of 1.5% for the treatment chain. N2O emissions during nitrification can be mitigated by 60% by avoiding low dissolved oxygen or anoxic conditions and nitrite concentrations above 5 mg-N L-1. Minimizing the hydraulic retention time between nitrification and GAC filtration can reduce N2O formation during intermediate storage by 100%. Overall, the N2O emissions accounted for 45% of the operational carbon footprint of 14 kg-CO2,equiv kg-N-1 for urine fertilizer production. Using electricity from renewable sources and applying the proposed N2O mitigation strategies could potentially lower the carbon footprint by 85%.
Randall, D. G., Brison, A., & Udert, K. M. (2022). High temperatures and CO2 dissolution can cause nitrogen losses from urine stabilized with base. Frontiers in Environmental Science, 10, 998743 (13 pp.). doi:10.3389/fenvs.2022.998743, Institutional Repository

Human urine is rich in valuable nitrogen which can easily be lost due to biological urea hydrolysis and subsequent ammonia volatilization. While this enzymatic reaction can be prevented by alkalizing the urine, recent studies suggest that chemical urea hydrolysis can result in substantial nitrogen losses when drying alkalinized urine at high temperatures. Furthermore, it was previously suggested that CO2 dissolution from the air used to evaporate water from alkalinized urine could result in a pH decrease to values which allows for biological urea hydrolysis and subsequent ammonia losses. This study aimed to determine the kinetics of chemical urea hydrolysis in alkalinized human urine and confirm the effect of CO2 dissolution with controlled laboratory experiments. We measured the change in urea concentration at different temperatures and pH values for real human urine and determined the corresponding rate constants for chemical urea hydrolysis. We showed that the rate constant increases as a function of temperature and that pH has a negligible effect on the rate of chemical urea hydrolysis in the high pH range of alkalized urine (>11). The rate constants for chemical urea hydrolysis in a saturated calcium hydroxide solution were found to be 0.00147 d-1, 0.00595 d-1, 0.0204 d-1 and 0.0848 d-1 for temperatures of 25°C, 40°C, 55°C and 70°C, respectively. The effect of CO2 dissolution on urea hydrolysis was determined by aerating human urine alkalinized with calcium hydroxide (Ca(OH)2). In order to represent biological urea hydrolysis, urease was added to the solution. The computer simulations of the experimental results showed that CO2 dissolution and the subsequent dissociation of carbonic acid to carbonate ions, bicarbonate ions and protons is the main cause of the pH decrease, but CaCO3 precipitation, and NH3 volatilization foster the pH decrease. However, biological urea hydrolysis prevents the pH from decreasing below 9. Residual undissolved Ca(OH)2 was shown to substantially delay the pH decrease. Overall, this work provides valuable insights into the mechanisms of urea hydrolysis in alkalinized urine during dehydration, which can be used to design more efficient decentralized sanitation systems and minimize nitrogen losses.
Stamm, C., Binder, C. R., Frossard, E., Haygarth, P. M., Oberson, A., Richardson, A. E., … Udert, K. M. (2022). Towards circular phosphorus: the need of inter- and transdisciplinary research to close the broken cycle. Ambio, 51, 611-622. doi:10.1007/s13280-021-01562-6, Institutional Repository

Phosphorus (P) is an essential element to all living beings but also a finite resource. P-related problems center around broken P cycles from local to global scales. This paper presents outcomes from the 9th International Phosphorus Workshop (IPW9) held 2019 on how to move towards a sustainable P management. It is based on two sequential discussion rounds with all participants. Important progress was reported regarding the awareness of P as finite mineable resource, technologies to recycle P, and legislation towards a circular P economy. Yet, critical deficits were identified such as how to handle legacy P, how climate change may affect ecosystem P cycling, or working business models to up-scale existing recycling models. Workshop participants argued for more transdisciplinary networks to narrow a perceived science-practice/policy gap. While this gap may be smaller in reality as illustrated with a Swiss example, we formulate recommendations how to bridge this gap more effectively.
Krause, A., Häfner, F., Augustin, F., & Udert, K. M. (2021). Qualitative risk analysis for contents of dry toilets used to produce novel recycling fertilizers. Circular Economy and Sustainability, 1, 1107-1146. doi:10.1007/s43615-021-00068-3, Institutional Repository

Human excreta are a sustainable, economical source of nutrients, and can be used to produce recycling fertilizer for horticulture by collecting and processing the contents of dry toilets. Herein, we discuss the key categories of risk associated with the main groups of materials commonly found in dry toilets. The study was part of the development of a German product standard for marketable and quality-assured recycling fertilizers from human excreta for use in horticulture. Particular attention is paid to ensuring that the fertilizer is epidemiologically and environmentally harmless and that the quality of the recycling fertilizer is adequate in terms of low pollution and nutrient availability. In sum, the risk of transmissible human pathogens lies within the human excreta, particularly feces; plant materials added during composting are of particular phytosanitary relevance; pharmaceutical residues in excrements and chemical additives are potential sources of pollutants; non-biodegradable contaminants can cause pollution and injury; and the horticultural risks involve mainly the ammonia emission potential and in some cases the salinity effects of urine. These risks can be reduced significantly (i) with education of users around proper operation of dry toilets and the consequences of adding inappropriate waste, (ii) with facilitation of proper use with general waste bins and clear instructions, and importantly (iii) by using modern sanitization and cleaning processes and testing for harmful substances under the guidance of local laws and regulations, ensuring safe and high-quality fertilizers. In conclusion, the benefits of using dry toilet contents to produce fertilizers for use in horticulture are unquestionable. Our analysis highlights the need to support recycling optimization and awareness for the purpose of a sustainable circular economy and to minimize the risk of harm to humans and the environment overall.
Larsen, T. A., Riechmann, M. E., & Udert, K. M. (2021). State of the art of urine treatment technologies: a critical review. Water Research X, 13, 100114 (20 pp.). doi:10.1016/j.wroa.2021.100114, Institutional Repository

Over the last 15 years, urine treatment technologies have developed from lab studies of a few pioneers to an interesting innovation, attracting attention from a growing number of process engineers. In this broad review, we present literature from more than a decade on biological, physical-chemical and electrochemical urine treatment processes. Like in the first review on urine treatment from 2006, we categorize the technologies according to the following objectives: stabilization, volume reduction, targeted N-recovery, targeted P-recovery, nutrient removal, sanitization, and handling of organic micropollutants. We add energy recovery as a new objective, because extensive work has been done on electrochemical energy harvesting, especially with bio-electrochemical systems. Our review reveals that biological processes are a good choice for urine stabilization. They have the advantage of little demand for chemicals and energy. Due to instabilities, however, they are not suited for bathroom applications and they cannot provide the desired volume reduction on their own. A number of physical-chemical treatment technologies are applicable at bathroom scale and can provide the necessary volume reduction, but only with a steady supply of chemicals and often with high demand for energy and maintenance. Electrochemical processes is a recent, but rapidly growing field, which could give rise to exciting technologies at bathroom scale, although energy production might only be interesting for niche applications. The review includes a qualitative assessment of all unit processes. A quantitative comparison of treatment performance was not the goal of the study and could anyway only be done for complete treatment trains. An important next step in urine technology research and development will be the combination of unit processes to set up and test robust treatment trains. We hope that the present review will help guide these efforts to accelerate the development towards a mature technology with pilot scale and eventually full-scale implementations.
Riechmann, M. E., Ndwandwe, B., Greenwood, E. E., Reynaert, E., Morgenroth, E., & Udert, K. M. (2021). On-site urine treatment combining Ca(OH)2 dissolution and dehydration with ambient air. Water Research X, 13, 100124 (12 pp.). doi:10.1016/j.wroa.2021.100124, Institutional Repository

We present the results of three field tests and three laboratory tests of a new physical-chemical urine treatment system, which can recover all nutrients, while pathogens are inactivated. The system consists of two steps. In the first reactor, biological processes including urea hydrolysis are prevented by mixing fresh urine with calcium hydroxide (Ca(OH)2). Due to the high pH value and the high availability of calcium, phosphate can be recovered by precipitation. The high pH value also fosters the inactivation of microorganisms, including pathogens. In the second reactor, water is evaporated at low energy consumption by blowing unheated ambient air over the stabilized urine. Stabilization in the first reactor was successful in all field and laboratory tests. The pH value remained between 12 and 13, except for short dips due to shortages of Ca(OH)2. Nearly all phosphorus (92-96%) precipitated and could be recovered as calcium phosphate in the first reactor, while nitrogen and potassium overflowed with the urine into the evaporation reactor. The efficiency of the second treatment step was very different for field and laboratory experiments and depended on the duration of the experiment. During a four-day laboratory test, nitrogen recovery was 98%. In contrast, nitrogen recovery was only around 20% in the long-term field experiments. The high nitrogen losses occurred, because biological urea hydrolysis was not inhibited anymore, when the pH value in the second reactor decreased due to the dissolution of high amounts of carbon dioxide from the ambient air. Potassium was not subject to any significant loss, and the measured recovery in the solid evaporation product was 98%. Evaporation rates ranged between 50 g m-2 h-1 (RH = 82±13%, T = 12±6°C) and 130 g m-2 h-1 (RH = 60±19%, T = 24±5°C) in the three field tests. Apart from some disturbances due to low supply of Ca(OH)2, the urine module functioned without any substantial failures and was simple to maintain. The minimum consumption of Ca(OH)2 at full capacity was 6 g·L-1 urine and the electricity demand was 150 Wh kg-1 water evaporated from urine, resulting in operational costs of 0.05 EUR pers-1 d-1.
Sutherland, C., Reynaert, E., Sindall, R. C., Riechmann, M. E., Magwaza, F., Lienert, J., … Udert, K. M. (2021). Innovation for improved hand hygiene: field testing the Autarky handwashing station in collaboration with informal settlement residents in Durban, South Africa. Science of the Total Environment, 796, 149024 (13 pp.). doi:10.1016/j.scitotenv.2021.149024, Institutional Repository

Safe and accessible water services for hand hygiene are critical to human health and well-being. However, access to handwashing facilities is limited in cities in the Global South, where rapid urbanisation, service backlogs, lack of infrastructure and capacity, and water scarcity impact on the ability of local governments to provide them. Community participation and the co-production of knowledge in the development of innovative technologies, which are aligned with Water, Sanitation and Hygiene (WASH) principles, can lead to more sustainable and socially-acceptable hand hygiene systems. This paper presents the outcomes of the testing of the Autarky handwashing station, a technology that provides onsite treatment and recycling of handwashing water, in an informal settlement in Durban, South Africa. The transdisciplinary research approach adopted enabled the participation of multiple stakeholders with different knowledge systems in the framing, testing and evaluation of the system. The process of co-producing knowledge, as well as the outcomes of the testing, namely high levels of functionality and social acceptability of the technology, supported the WASH principles. The evaluation revealed that the Autarky handwashing station is a niche intervention that improved access to safe and appealing handwashing facilities in an informal settlement. Its novel design, socially desirable features, reliability and ability to save water increased its acceptance in the community. The testing of the system in a real-world context revealed the value of including communities in knowledge production processes for technology innovation. Further work is required to ensure that real-time monitoring of system function is feasible before such systems can be implemented at larger scale.
Sutherland, C., Reynaert, E., Dhlamini, S., Magwaza, F., Lienert, J., Riechmann, M. E., … Sindall, R. C. (2021). Socio-technical analysis of a sanitation innovation in a peri-urban household in Durban, South Africa. Science of the Total Environment, 755, 143284 (12 pp.). doi:10.1016/j.scitotenv.2020.143284, Institutional Repository

The provision of water and sanitation for all that is safe, dignified, reliable, affordable and sustainable is a major global challenge. While centralized sewer-based sanitation systems remain the dominant approach to providing sanitation, the benefits of non-sewered onsite sanitation systems are increasingly being recognised. This paper presents the outcomes of the testing of the Blue Diversion Autarky Toilet (BDAT), a sanitation system providing hygiene and dignity without relying on water and wastewater infrastructure, in a peri-urban household in Durban, South Africa. The BDAT was used by a single household as their only form of sanitation during three months of technical and social testing. An analysis based on technical data in combination with interpretive, qualitative research methods revealed that the BDAT functioned well and achieved high levels of social acceptance in the test household. The flushing, cleanliness and odour-free nature of the sanitation technology, its functionality, the household's previous sanitation experience, and their experience with and understanding of water scarcity, were the main factors underpinning their positive response to this innovation in sanitation. The testing process resulted in broader developmental benefits for the household, including improved basic services due to the upgrading of the electrical and existing sanitation system, social learning, and improved relationships between household members and the local state. A transdisciplinary research process, which emerged through the assessment, enabled the integration of different forms of knowledge from multiple actors to address the complexity of problems related to the development of socially just sanitation. The benefit of engaging with societal actors in sanitation innovation and assessing its outcomes using both the technical and social sciences is evident in this paper.
Özel Duygan, B. D., Udert, K. M., Remmele, A., & McArdell, C. S. (2021). Removal of pharmaceuticals from human urine during storage, aerobic biological treatment, and activated carbon adsorption to produce a safe fertilizer. Resources, Conservation and Recycling, 166, 105341 (10 pp.). doi:10.1016/j.resconrec.2020.105341, Institutional Repository

Urine has great potential to be an effective fertilizer due to its high nutrient content, however, it can contain potentially worrying pharmaceuticals. Our objective was to study whether urine storage and aerobic biological treatment, i.e. nitrification, was sufficient to remove pharmaceuticals or an additional treatment with activated carbon was necessary to produce a fertilizer from urine. We investigated the abatement of twelve pharmaceuticals, including antibiotics and antivirals, in laboratory experiments representing the treatment steps of anaerobic storage of source-separated human urine, stabilization using partial and full nitrification under acclimatized and non-acclimatized conditions, and treatment of nitrified urine using powdered activated carbon (PAC). Two-month-long-term storage of urine was insufficient to substantially degrade the pharmaceuticals, except for hydrochlorothiazide (>90%). In the partial and full nitrification fed-batch reactors, atazanavir, ritonavir, and clarithromycin were rapidly removed, with biotransformation rate constants greater than 10 L gSS−1d−1. Darunavir, emtricitabine, trimethoprim, N4-acetylsulfamethoxazole, sulfamethoxazole, atenolol, diclofenac, and hydrochlorothiazide were degraded slowly, with biotransformation rate constants of < 1 L gSS−1d−1. With 200 mg PAC L−1, at least 90% of each investigated pharmaceutical was removed. Yeast estrogen screen tests and bioluminescence inhibition tests revealed efficient removal of estrogenicity (99%) and toxicity (56%) using nitrification, and a reduction of 89% and 64%, respectively, using 200 mg PAC L−1. With our study, we provide biotransformation rate constants of compounds never previously investigated. We also show that a combination of nitrification and PAC adsorption enables the production of a safe fertilizer with sufficiently low pharmaceutical concentrations and no removal of beneficial nutrients.
Bisinella de Faria, A. B., Besson, M., Ahmadi, A., Udert, K. M., & Spérandio, M. (2020). Dynamic influent generator for alternative wastewater management with urine source separation. Journal of Sustainable Water in the Built Environment, 6(2), 04020001 (26 pp.). doi:10.1061/JSWBAY.0000904, Institutional Repository

The simulation of wastewater treatment plants allows obtaining predictive results when one needs to understand, evaluate, optimize, or design a plant. However, one of the bottlenecks of simulation feasibility is to obtain reliable and dynamic influent data. This difficulty is even more important when alternative scenarios are considered, such as source-separated streams. The present paper offers an influent generator to simulate scenarios where urine is separated at the source and at a user-specified level of retention. The proposed tool contains several blocks to include different contributions (household and industrial wastewater) and, due to its flexibility, allows the user to easily modify the parameters to fit other case studies. The tool allowed generating dynamic, long-term, and predictive data for both urine and wastewater streams. Also, the extensive set of state variables ensured the generation of influents for different modeling platforms.
Britschgi, L., Villez, K., Schrems, P., & Udert, K. M. (2020). Electrochemical nitrite sensing for urine nitrification. Water Research X, 9, 100055 (30 pp.). doi:10.1016/j.wroa.2020.100055, Institutional Repository

Sensing nitrite in-situ in wastewater treatment processes could greatly simplify process control, especially during treatment of high-strength nitrogen wastewaters such as digester supernatant or, as in our case, urine. The two technologies available today, i.e. an on-line nitrite analyzer and a spectrophotometric sensor, have strong limitations such as sample preparation, cost of ownership and strong interferences. A promising alternative is the amperometric measurement of nitrite, which we assessed in this study. We investigated the sensor in a urine nitrification reactor and in ex-situ experiments. Based on theoretical calculations as well as a practical approach, we determined that the critical nitrite concentrations for nitrite oxidizing bacteria lie between 12 and 30 mgN/L at pH 6 to 6.8. Consequently, we decided that the sensor should be able to reliably measure concentrations up to 50 mgN/L, which is about double the value of the critical nitrite concentration. We found that the influences of various ambient conditions, such as temperature, pH, electric conductivity and aeration rate, in the ranges expected in urine nitrification systems, are negligible. For low nitrite concentrations, as expected in municipal wastewater treatment, the tested amperometric nitrite sensor was not sufficiently sensitive. Nevertheless, the sensor delivered reliable measurements for nitrite concentrations of 5-50 mgN/L or higher. This means that the amperometric nitrite sensor allows detection of critical nitrite concentrations without difficulty in high-strength nitrogen conversion processes, such as the nitrification of human urine.
Doll, C., Larsen, T. A., Strande, L., Udert, K. M., & Morgenroth, E. (2020). Water Hub im NEST-Gebäude. Eine Plattform zum Testen von innovativen ressourcenorientierten Sanitärsystemen. Aqua & Gas, 100(2), 52-57. , Institutional Repository

Mit innovativen Technologien werden im Water Hub unter realen Bedingungen Ressourcen aus dem Abwasser gewonnen und Kreisläufe geschlossen. Die Forschung in diesem Living Lab erlaubt es, praxisnahe Erfahrungen zu machen, Schwachstellen schnell zu identifizieren und das System zu optimieren. Bei der Implementierung dieser dezentralen Technologien spielen die lokalen Herausforderungen und Begebenheiten stets eine wichtige Rolle.
Hoffmann, S., Feldmann, U., Bach, P. M., Binz, C., Farrelly, M., Frantzeskaki, N., … Udert, K. M. (2020). A research agenda for the future of urban water management: exploring the potential of non-grid, small-grid, and hybrid solutions. Environmental Science and Technology, 54(9), 5312-5322. doi:10.1021/acs.est.9b05222, Institutional Repository

Recent developments in high- and middle-income countries have exhibited a shift from conventional urban water systems to alternative solutions that are more diverse in source separation, decentralization, and modularization. These solutions include non-grid, small-grid, and hybrid systems to address such pressing global challenges as climate change, eutrophication, and rapid urbanization. They close loops, recover valuable resources, and adapt quickly to changing boundary conditions such as population size. Moving to such alternative solutions requires both technical and social innovations to co-evolve over time into integrated socio-technical urban water systems. Current implementations of alternative systems in high- and middle-income countries are promising, but they also underline the need for research questions to be addressed from technical, social, and transformative perspectives. Future research should apply a transdisciplinary research approach through socio-technical "lighthouse" projects that apply alternative urban water systems at scale. Such research should leverage experience from lighthouse projects in a range of socio-economic contexts, identify their potentials and limitations from an integrated perspective, and share their successes and failures across the urban water sector.
Köpping, I., McArdell, C. S., Borowska, E., Böhler, M. A., & Udert, K. M. (2020). Removal of pharmaceuticals from nitrified urine by adsorption on granular activated carbon. Water Research X, 9, 100057 (10 pp.). doi:10.1016/j.wroa.2020.100057, Institutional Repository

Nitrification and distillation of urine allow for the recovery of all nutrients in a highly concentrated fertilizer solution. However, pharmaceuticals excreted with urine are only partially removed during these two process steps. For a sustainable and safe application, more extensive removal of pharmaceuticals is necessary. To enhance the pharmaceutical removal, which is already occurring during urine storage, nitrification and distillation, an adsorption column with granular activated carbon (GAC) can be included in the treatment train. We executed a pilot-scale study to investigate the adsorption of eleven indicator pharmaceuticals on GAC. During 74 days, we treated roughly 1000 L of pre-filtered and nitrified urine spiked with pharmaceuticals in two flow-through GAC columns filled with different grain sizes. We compared the performance of these columns by calculating the number of treated bed volumes until breakthrough and carbon usage rates. The eleven spiked pharmaceuticals were candesartan, carbamazepine, clarithromycin, diclofenac, emtricitabine, hydrochlorothiazide, irbesartan, metoprolol, N4-acetylsulfamethoxazole, sulfamethoxazole and trimethoprim. At the shortest empty bed contact time (EBCT) of 25 min, immediate breakthrough was observed in both columns shortly after the start of the experiments. Strong competition by natural organic material (NOM) could have caused the low pharmaceutical removal at the EBCT of 25 min. At EBCTs of 70, 92 and 115 min, more than 660 bed volumes could be treated until breakthrough in the column with fine GAC. The earliest breakthrough was observed for candesartan and clarithromycin. On coarse GAC, only half the number of bed volumes could be treated until breakthrough compared to fine GAC. The probable reason for the later breakthrough with fine GAC is the smaller intraparticle diffusive path length. DOC and UV absorbance measurements at 265 nm indicated that both parameters can be used as indicators for the breakthrough of pharmaceuticals. In contrast to pharmaceuticals and DOC, the nutrient compounds ammonium, nitrate, phosphate, potassium and sulfate were not removed significantly. A comparison with literature values suggests that the amount of GAC needed to remove pharmaceuticals from human excreta could be reduced by nearly two orders of magnitude, if urine were treated on site instead of being discharged and treated in a centralized wastewater treatment plant.
Reynaert, E., Greenwood, E. E., Ndwandwe, B., Riechmann, M. E., Sindall, R. C., Udert, K. M., & Morgenroth, E. (2020). Practical implementation of true on-site water recycling systems for hand washing and toilet flushing. Water Research X, 7, 100051 (13 pp.). doi:10.1016/j.wroa.2020.100051, Institutional Repository

On-site wastewater reuse can improve global access to clean water, sanitation and hygiene. We developed a treatment system (aerated bioreactor, ultrafiltration membrane, granular activated carbon and electrolysis for chlorine disinfection) that recycles hand washing and toilet flush water.
Three prototypes were field-tested in non-sewered areas, one in Switzerland (hand washing) and two in South Africa (hand washing, toilet flushing), over periods of 63, 74 and 94 days, respectively.
We demonstrated that the system is able to recycle sufficient quantities of safe and appealing hand washing and toilet flush water for domestic or public use in real-life applications. Chemical contaminants were effectively removed from the used water in all prototypes. Removal efficiencies were 99.7% for the chemical oxygen demand (COD), 98.5% for total nitrogen (TN) and 99.9% for phosphate in a prototype treating hand washing water, and 99.8% for COD, 95.7% for TN and 89.6% for phosphate in a prototype treating toilet flush water. While this system allowed for true recycling for the same application, most on-site wastewater reuse systems downcycle the treated water, i.e., reuse it for an application requiring lower water quality. An analysis of 18 selected wastewater reuse specifications revealed that at best these guidelines are only partially applicable to innovative recycling systems as they are focused on the downcycling of water to the environment (e.g., use for irrigation). We believe that a paradigm shift is necessary and advocate for the implementation of risk-based (and thus end-use dependent) system performance targets to evaluate water treatment systems, which recycle and not only downcycle water.
Christiaens, M. E. R., Udert, K. M., Arends, J. B. A., Huysman, S., Vanhaecke, L., McAdam, E., & Rabaey, K. (2019). Membrane stripping enables effective electrochemical ammonia recovery from urine while retaining microorganisms and micropollutants. Water Research, 150, 349-357. doi:10.1016/j.watres.2018.11.072, Institutional Repository

Ammonia recovery from urine avoids the need for nitrogen removal through nitrification/denitrification and re-synthesis of ammonia (NH3) via the Haber-Bosch process. Previously, we coupled an alkalifying electrochemical cell to a stripping column, and achieved competitive nitrogen removal and energy efficiencies using only electricity as input, compared to other technologies such as conventional column stripping with air. Direct liquid-liquid extraction with a hydrophobic gas membrane could be an alternative to increase nitrogen recovery from urine into the absorbent while minimizing energy requirements, as well as ensuring microbial and micropollutant retention. Here we compared a column with a membrane stripping reactor, each coupled to an electrochemical cell, fed with source-separated urine and operated at 20 A m−2. Both systems achieved similar nitrogen removal rates, 0.34 ± 0.21 and 0.35 ± 0.08 mol N L−1 d−1, and removal efficiencies, 45.1 ± 18.4 and 49.0 ± 9.3%, for the column and membrane reactor, respectively. The membrane reactor improved nitrogen recovery to 0.27 ± 0.09 mol N L−1 d−1 (38.7 ± 13.5%) while lowering the operational (electrochemical and pumping) energy to 6.5 kWhe kg N−1 recovered, compared to the column reactor, which reached 0.15 ± 0.06 mol N L−1 d−1 (17.2 ± 8.1%) at 13.8 kWhe kg N−1.
Increased cell concentrations of an autofluorescent E. coli MG1655 + prpsM spiked in the urine influent were observed in the absorbent of the column stripping reactor after 24 h, but not for the membrane stripping reactor. None of six selected micropollutants spiked in the urine were found in the absorbent of both technologies.
Overall, the membrane stripping reactor is preferred as it improved nitrogen recovery with less energy input and generated an E. coli- and micropollutant-free product for potential safe reuse. Nitrogen removal rate and efficiency can be further optimized by increasing the NH3 vapor pressure gradient and/or membrane surface area.
Thürlimann, C. M. (2019). Soft-sensing, automation, and diagnosis for nitrification (Doctoral dissertation). doi:10.3929/ethz-b-000347049, Institutional Repository

Nitrification of wastewater requires control for the purposes of efficiency and of stability. However, first, the highly complex microbial community in wastewater treatment plants and very different compositions of wastewaters impede a complete understanding of nitrification. Second, the determination of the states of the process is seldom exact because sensors are subject to a high level of wear and tear. Consequently, instrumentation, control, and automation (ICA) of nitrification processes are a challenge. I hypothesize that soft-sensors - based on the signals of robust, physical sensors - and specially designed control loops, which do not need redundant information to correct for drift, can reduce the maintenance needs for the control of nitrification. Consequently, the econonomical application range for ICA of nitrification processes can be extended.
A large part of this thesis is dedicated to the stabilisation of urine nitrification as a pretreatment for nutrient recovery. To this end, an online nitrite detection and an according control of the process are required. Furthermore, the thesis comprises an ammonia aeration controller, which is based on pH signals, to be used in municipal wastewater. The four chapters of the thesis focus on the following topics.
The first chapter investigates calibration experiments for in-line UV-Vis sensors. Such sensors can serve as soft-sensors for numerous substances. With differently designed experiments, data for the calibration of UV-Vis based nitrite models in high strength wastewater was recorded. Online experiments executed in-situ allow calibrating similarly exact models like experiments which are conducted by spiking additional nitrite. The good performance of the models being based on online experiments is explained by the correlation of other light-absorbing substances in the process with nitrite.
The second chapter evaluates the potential of a stoichiometry-based soft-sensor for nitrite. The stoichiometry of nitrification theoretically allows distinguishing the ammonia and the nitrite oxidation rates by means of the derivatives of the dissolved oxygen and of the pH signal and in turn detecting nitrite accumulations. We show that under relatively ideal conditions the dynamics in the ratio of the two derivatives show similarities with the dynamics in the nitrite concentration. Factors that deteriorate this information quality are identified.
The third part of this thesis investigates how drifting sensor signals can be used as an input for a feedback controller without relying on redundant information to correct this drift. The controller shall prevent uncontrolled nitrite accumulation in a urine nitrification system. To this end, the controller does not use the absolute value of the nitrite signal, but its 1st and 2nd derivative as inputs. By controlled accumulation and degradation of nitrite, the controller can keep the derivatives continuously informative. The switch from substrate inhibition to substrate limitation of the nitrite oxidising bacteria can be identified by means of the inflection point in the signal. The developed controller is tested successfully on a lab-scale reactor.
The fourth chapter of this thesis describes an ammonia based aeration controller. These controllers usually require maintenance intensive instrumentation. Therefore a new ammonia soft sensor for continuously operated municipal wastewater treatment plants is developed. It relies on the 1st derivative of a pH difference measured over the aerated zone. This soft sensor is successfully tested in a controller deployed on various municipal wastewater treatment plants. The controller was designed to increase its robustness towards drift in the pH signals.
Thürlimann, C. M., Udert, K. M., Morgenroth, E., & Villez, K. (2019). Stabilizing control of a urine nitrification process in the presence of sensor drift. Water Research, 165, 114958 (10 pp.). doi:10.1016/j.watres.2019.114958, Institutional Repository

Sensor drift is commonly observed across engineering disciplines, particularly in harsh media such as wastewater. In this study, a novel stabilizing controller for nitrification of high strength ammonia solutions is designed based on online signal derivatives. The controller uses the derivative of a drifting nitrite signal to determine if nitrite-oxidizing bacteria (NOB) are substrate limited or substrate inhibited. To ensure a meaningful interpretation of the derivative signal, the process is excited in a cyclic manner by repeatedly exposing the NOB to substrate-limited and substrate-inhibited conditions. The resulting control system successfully prevented nitrite accumulations for a period of 72 days in a laboratory-scale reactor. Slow disturbances in the form of feed composition changes and temperature changes were successfully handled by the controller while short-term temperature disturbances are shown to pose a challenge to the current version of this controller. Most importantly, we demonstrate that drift-tolerant control for the purpose of process stabilization can be achieved without sensor redundancy by combining deliberate input excitation, qualitative trend analysis, and coarse process knowledge.
Lindeboom, R. E. F., Ilgrande, C., Carvajal-Arroyo, J. M., Coninx, I., Van Hoey, O., Roume, H., … Vlaeminck, S. E. (2018). Nitrogen cycle microorganisms can be reactivated after Space exposure. Scientific Reports, 8(1), 13783 (7 pp.). doi:10.1038/s41598-018-32055-4, Institutional Repository

Long-term human Space missions depend on regenerative life support systems (RLSS) to produce food, water and oxygen from waste and metabolic products. Microbial biotechnology is efficient for nitrogen conversion, with nitrate or nitrogen gas as desirable products. A prerequisite to bioreactor operation in Space is the feasibility to reactivate cells exposed to microgravity and radiation. In this study, microorganisms capable of essential nitrogen cycle conversions were sent on a 44-days FOTON-M4 flight to Low Earth Orbit (LEO) and exposed to 10−3–10−4 g (gravitational constant) and 687 ± 170 µGy (Gray) d−1 (20 ± 4 °C), about the double of the radiation prevailing in the International Space Station (ISS). After return to Earth, axenic cultures, defined and reactor communities of ureolytic bacteria, ammonia oxidizing archaea and bacteria, nitrite oxidizing bacteria, denitrifiers and anammox bacteria could all be reactivated. Space exposure generally yielded similar or even higher nitrogen conversion rates as terrestrial preservation at a similar temperature, while terrestrial storage at 4 °C mostly resulted in the highest rates. Refrigerated Space exposure is proposed as a strategy to maximize the reactivation potential. For the first time, the combined potential of ureolysis, nitritation, nitratation, denitrification (nitrate reducing activity) and anammox is demonstrated as key enabler for resource recovery in human Space exploration.
Meyer, G., Frossard, E., Mäder, P., Nanzer, S., Randall, D. G., Udert, K. M., & Oberson, A. (2018). Water soluble phosphate fertilizers for crops grown in calcareous soils – an outdated paradigm for recycled phosphorus fertilizers?. Plant and Soil, 424(1-2), 367-388. doi:10.1007/s11104-017-3545-x, Institutional Repository

Background and aims The current paradigm for phosphorus (P) fertilizers applied to calcareous soil is that almost entirely water soluble P fertilizers are efficient and sparingly soluble P fertilizers are not efficient P sources for crops. We hypothesize that this paradigm does not apply to recycled P fertilizers and that other P pools can explain the plant use of recycled P fertilizers on calcareous soil.
Methods We applied 33P isotopic dilution method to evaluate recycled P fertilizers based on plant P uptake from fertilizer relative to plant uptake from a water soluble P reference fertilizer. The predictability of fertilizer effectiveness based on sequentially extracted P forms and X-ray diffraction pattern of recycled fertilizers derived from sewage sludge, human urine and organic waste was evaluated.
Results The plant experiments showed that tested recycled P fertilizers including compost were more effective than rock phosphate. The water insoluble P contained in urine based products was almost as effective as a fully water soluble P fertilizer. The tested recycled P fertilizers are characterized by complex P compounds differing in solubility which were so far not considered in the water and citric acid extraction methods. The fraction of resin- and NaHCO3 extractable fertilizer P explained effectiveness of P fertilizer applied to the calcareous and to an acidic soil.
Conclusion We concluded that water solubility is not required when P forms in recycled products are comparable to reactions products of rock phosphate based fertilizers in soil. Alternatives to fully water soluble P fertilizers are available to supply P to crops grown on calcareous soil efficiently.
Udert, K. M. (2018). Phosphorus as a resource. In C. Schaum (Ed.), Integrated environmental technology series. Phosphorus: polluter and resource of the future – removal and recovery from wastewater (pp. 57-80). doi:10.2166/9781780408361_057, Institutional Repository
Baeriswyl, P., Carisch, M., Etter, B., Holliger, U., Hug, T., Konz, N., … Udert, K. (2017). Leitfaden: Abwasser im ländlichen Raum. Glattbrugg: Verband Schweizer Abwasser und Gewässerschutzfachleute (VSA). , Institutional Repository

Der Gewässerschutz in der Schweiz und damit die Qualität der ober- und unterirdischen Gewässer haben allgemein einen beachtlichen Stand erreicht. Diese erfreuliche Tatsache darf nicht darüber hinwegtäuschen, dass lokal im ländlichen Raum und ausserhalb erschlossener Baugebiete weiterhin Handlungsbedarf besteht. Einerseits gibt es bei bestehenden dezentralen Abwasserinfrastrukturen nach wie vor Anlagen, welche die Einleitungsbedingungen nicht erfüllen.

Der vorliegende Leitfaden soll helfen, diese bestehenden Lücken im Gewässerschutz zu schliessen und eine einheitliche Abwasserentsorgung im ländlichen Raum zu gewährleisten. Er wurde von einer breit abgestützten Projektgruppe des VSA erarbeitet, in welcher Vertreter aus Bund, Kantonen und der Eawag mitwirkten.

Das Dokument ersetzt den VSA-Leitfaden "Abwasser im ländlichen Raum" vom Oktober 2005 und die 1995 publizierte "Richtlinie für den Einsatz, die Auswahl und die Bemessung von Kleinkläranlagen" des VSA. Der Leitfaden 2017 ist neu strukturiert und enthält aktuelle Komponenten der ländlichen Abwasserentsorgung insbesondere für: - Das Vorgehen der Lösungsfindung
- Die Spezielle Abwasserarten
- Die Speicher- und Anschlusssysteme
- Die Reinigungssysteme
- Den Betrieb und Unterhalt von Kleinkläranlagen (KLARA)

Im Weiteren berücksichtigt die vorliegende Version zwischenzeitlich veröffentlichte Vollzugshilfen von BAFU und BLW ("Baulicher Umweltschutz in der Landwirtschaft", 2011 und "Nährstoffe und Verwendung von Düngern in der Landwirtschaft", 2012) sowie etablierte Hilfsmittel der Kantone. Auch Ausführungsmöglichkeiten zu den jeweiligen Themen sind im Dokument enthalten. Das Massnahmenspektrum ist bewusst weit gehalten: Obwohl mit dem Anschluss der Liegenschaften an die öffentliche Kanalisation mit zentraler Abwasserreinigung das Abwasserproblem weitgehend gelöst sein kann, drängen sich auch im ländlichen Raum häufig Massnahmen an der Quelle auf.

Der Leitfaden richtet sich an Vollzugsbehörden, Planungsbüros, Gemeinden und weitere interessierte Stellen. Bei der Suche nach einer spezifischen Abwasserlösung wird empfohlen, sich im Vorfeld bei der kantonalen Fachstelle zu erkundigen. Dasselbe gilt analog auf Gemeindeebene.
Fumasoli, A., Bürgmann, H., Weissbrodt, D. G., Wells, G. F., Beck, K., Mohn, J., … Udert, K. M. (2017). Growth of Nitrosococcus-related ammonia oxidizing bacteria coincides with extremely low pH values in wastewater with high ammonia content. Environmental Science and Technology, 51(12), 6857-6866. doi:10.1021/acs.est.7b00392, Institutional Repository

Ammonia oxidation decreases the pH in wastewaters where alkalinity is limited relative to total ammonia. The activity of ammonia oxidizing bacteria (AOB), however, typically decreases with pH and often ceases completely in slightly acidic wastewaters. Nevertheless, nitrification at low pH has been reported in reactors treating human urine, but it has been unclear which organisms are involved. In this study, we followed the population dynamics of ammonia oxidizing organisms and reactor performance in synthetic fully hydrolyzed urine as the pH decreased over time in response to a decrease in the loading rate. Populations of the β-proteobacterial Nitrosomonas europaea lineage were abundant at the initial pH close to 6, but the growth of a possibly novel Nitrosococcus-related AOB genus decreased the pH to the new level of 2.2, challenging the perception that nitrification is inhibited entirely at low pH values, or governed exclusively by β-proteobacterial AOB or archaea. With the pH shift, nitrite oxidizing bacteria were not further detected, but nitrous acid (HNO2) was still removed through chemical decomposition to nitric oxide (NO) and nitrate. The growth of acid-tolerant γ-proteobacterial AOB should be prevented, by keeping the pH above 5.4, which is a typical pH limit for the N. europaea lineage. Otherwise, the microbial community responsible for high-rate nitrification can be lost, and strong emissions of hazardous volatile nitrogen compounds such as NO are likely.
Mkhize, N., Taylor, M., Udert, K. M., Gounden, T. G., & Buckley, C. A. (2017). Urine diversion dry toilets in eThekwini Municipality, South Africa: acceptance, use and maintenance through users' eyes. Journal of Water Sanitation and Hygiene for Development, 7(1), 111-120. doi:10.2166/washdev.2017.079, Institutional Repository

This study was part of the VUNA project aimed to develop an affordable sanitation system that produces a valuable fertiliser, reduces pollution of water resources and promotes health. Urine diversion dry toilets (UDDTs) simplify the on-site hygienisation of faeces and allow for nutrient recovery from urine. Social acceptance is vital for the implementation of the UDDT, because sanitation is only effective if the system not only provides a well-designed toilet and effective waste management, but also offers users a facility that caters to their needs and is sensitive to their cultural lifestyle. This study used qualitative and quantitative methods to investigate acceptance, use and maintenance of UDDTs. Key findings indicate lower levels of acceptance of UDDTs among the elderly, who are accustomed to traditional pit toilets. The users aspire to own a flush toilet, perceived to be indicative of household wealth. A dominant concern was emptying the pit and the quality of the building material. Community interventions are required that will promote acceptance, understanding and encourage proper use and maintenance of the UDDT, and may need some technology modification. There is an urgent need for increased community participation to address users' perceptions, attitudes and behaviour concerning the UDDT.
Tarpeh, W. A., Udert, K. M., & Nelson, K. L. (2017). Comparing ion exchange adsorbents for nitrogen recovery from source-separated urine. Environmental Science and Technology, 51(4), 2373-2381. doi:10.1021/acs.est.6b05816, Institutional Repository

Separate collection of urine, which is only 1% of wastewater volume but contains the majority of nitrogen humans excrete, can potentially reduce the costs and energy input of wastewater treatment and facilitate recovery of nitrogen for beneficial use. Ion exchange was investigated for recovery of nitrogen as ammonium from urine for use as a fertilizer or disinfectant. Cation adsorption curves for four adsorbents (clinoptilolite, biochar, Dowex 50, and Dowex Mac 3) were compared in pure salt solutions, synthetic urine, and real stored urine. Competition from sodium and potassium present in synthetic and real urine did not significantly decrease ammonium adsorption for any of the adsorbents. Dowex 50 and Dowex Mac 3 showed nearly 100% regeneration efficiencies. Estimated ion exchange reactor volumes to capture the nitrogen for 1 week from a four-person household were lowest for Dowex Mac 3 (5 L) and highest for biochar (19 L). Although Dowex Mac 3 had the highest adsorption capacity, material costs ($/g N removed) were lower for clinoptilolite and biochar because of their substantially lower unit cost.
Zöllig, H., Remmele, A., Morgenroth, E., & Udert, K. M. (2017). Removal rates and energy demand of the electrochemical oxidation of ammonia and organic substances in real stored urine. Environmental Science: Water Research and Technology, 3(3), 480-491. doi:10.1039/c7ew00014f, Institutional Repository

The separate collection and treatment of urine allows for an environmentally friendly and cost-efficient management of the nutrients contained in urine. The primary goal should be to recover all these nutrients. However, in some cases it will be economically or ecologically more sensitive to recover only the phosphorus, while nitrogen is removed together with organic substances (measured as chemical oxygen demand, COD) and pathogens. In this study, we investigated the use of galvanostatic electrolysis for the removal of nitrogen and COD from real stored urine. Non-active type boron-doped diamond (BDD) and active type thermally decomposed iridium oxide film (TDIROF) anodes were evaluated using batch experiments. On both anodes, ammonia was exclusively removed by indirect oxidation with active chlorine (AC: Cl2, HClO, and ClO−). As a consequence, ammonia was not completely removed, if chlorine was consumed by competing processes. While COD was present, ammonia removal was faster on TDIROF (227 ± 16 gN m−2 d−1 at 20 mA cm−2) than on BDD (43 ± 20 gN m−2 d−1 at 20 mA cm−2). The reason for the slower ammonia removal on BDD was the enhanced reaction of AC with organic molecules. In fact, hydroxyl radicals broke organic molecules down to shorter chain molecules which reacted with most of the AC leaving only little AC for the oxidation of ammonia. This preferential oxidation of organics resulted in very high COD removal rates on BDD (above 420 gCOD m−2 d−1 at 20 mA cm−2 for COD concentrations above 1000 mgCOD L−1). A main drawback of electrolysis with both anodes was the high energy demand (BDD: 55 W h gCOD−1 and 766 W h gN−1 for 90% and 6% removal, respectively. TDIROF: 67 W h gCOD−1 and 77 W h gN−1 for 30% and 40% removal. All at 20 mA cm−2). It can be concluded that BDD and TDIROF anodes could be combined in series for a fast, complete, and more energy efficient electrochemical urine treatment: COD could be removed on BDD before the residual ammonia would be removed on TDIROF.
Bischel, H. N., Schindelholz, S., Schoger, M., Decrey, L., Buckley, C. A., Udert, K. M., & Kohn, T. (2016). Bacteria inactivation during the drying of struvite fertilizers produced from stored urine. Environmental Science and Technology, 50(23), 13013-13023. doi:10.1021/acs.est.6b03555, Institutional Repository

Human urine can be processed into market-attractive fertilizers like struvite; however, concerns regarding the microbial safety of such products remain. The present study evaluated the inactivation of in situ heterotrophs, total bacteria as observed by flow cytometry, and inoculated Enterococcus spp. and Salmonella typhimurium during the drying of struvite under controlled temperature (from 5 to 35 °C) and relative humidity (approximately 40 and 80%) as well as dynamic field conditions. Bacteria accumulated in the struvite cake during struvite filtration. Despite the use of sublethal temperatures, all bacteria types were subsequently inactivated to some degree during struvite drying, and the inactivation typically increased with increasing drying temperature for a given relative humidity. Heterotrophic bacteria inactivation mirrored the trend in total bacteria during struvite drying. A linear relationship was observed between inactivation and sample moisture content. However, bacteria survivor curves were typically nonlinear when struvite was dried at low relative humidity, indicating bacterial persistence. Weibull model survivor curve fits indicated that a shift in the mechanism of inactivation may occur with changing humidity. For increased efficiency of bacterial inactivation during the production of struvite, initial heating under moist conditions is recommended followed by desiccation.
Fumasoli, A., Etter, B., Sterkele, B., Morgenroth, E., & Udert, K. M. (2016). Operating a pilot-scale nitrification/distillation plant for complete nutrient recovery from urine. Water Science and Technology, 73(1), 215-222. doi:10.2166/wst.2015.485, Institutional Repository

Source-separated urine contains most of the excreted nutrients, which can be recovered by using nitrification to stabilize the urine before concentrating the nutrient solution with distillation. The aim of this study was to test this process combination at pilot scale. The nitrification process was efficient in a moving bed biofilm reactor with maximal rates of 930 mg N L−1 d−1. Rates decreased to 120 mg N L−1 d−1 after switching to more concentrated urine. At high nitrification rates (640 mg N L−1 d−1) and low total ammonia concentrations (1,790 mg NH4-N L−1 in influent) distillation caused the main primary energy demand of 71 W cap−1 (nitrification: 13 W cap−1) assuming a nitrogen production of 8.8 g N cap−1 d−1. Possible process failures include the accumulation of the nitrification intermediate nitrite and the selection of acid-tolerant ammonia-oxidizing bacteria. Especially during reactor start-up, the process must therefore be carefully supervised. The concentrate produced by the nitrification/distillation process is low in heavy metals, but high in nutrients, suggesting a good suitability as an integral fertilizer.
Krähenbühl, M., Etter, B., & Udert, K. M. (2016). Pretreated magnesite as a source of low-cost magnesium for producing struvite from urine in Nepal. Science of the Total Environment, 542, 1155-1161. doi:10.1016/j.scitotenv.2015.08.060, Institutional Repository

Struvite is a solid phosphorus fertilizer that can be recovered easily from source-separated urine by dosing it with a soluble form of magnesium. The process is simple and low-cost, however, previous studies have shown that the cost of magnesium in low-income countries is crucial to the viability and implementation of struvite precipitation. Literature has proposed producing inexpensive magnesium locally by making magnesium oxide from magnesite. This paper aimed to investigate whether process requirements, costs, and environmental impacts would make this process viable for magnesium production in decentralized settings. Magnesite samples were calcined at temperatures between 400 °C and 800 °C and for durations between 0.5 h and 6 h. The release of magnesium was tested by dissolution in phosphate-depleted urine. The optimal processing conditions were at 700 °C for 1 h: magnesite conversion was incomplete at lower temperatures, and the formation of large crystallites caused a decrease in solubility at higher temperatures. The narrow optimal range for magnesium production from magnesite requires reliable process control. Cost estimations for Nepal showed that using local magnesite would provide the cheapest source of magnesium and that CO2 emissions from transport and production would be negligible compared to Nepal's overall CO2 emissions.
Mašić, A., Udert, K. M., & Villez, K. (2016). Global parameter optimization for biokinetic modeling of simple batch experiments. Environmental Modelling and Software, 85, 356-373. doi:10.1016/j.envsoft.2016.06.015, Institutional Repository

Environmental process modeling is challenged by the lack of high quality data, stochastic variations, and nonlinear behavior. Conventionally, parameter optimization is based on stochastic sampling techniques to deal with the nonlinear behavior of the proposed models. Despite widespread use, such tools cannot guarantee globally optimal parameter estimates. It can be especially difficult in practice to differentiate between lack of algorithm convergence, convergence to a non-global local optimum, and model structure deficits. For this reason, we use a deterministic global optimization algorithm for kinetic model identification and demonstrate it with a model describing a typical batch experiment. A combination of interval arithmetic, reformulations, and relaxations allows globally optimal identification of all (six) model parameters. In addition, the results suggest that further improvements may be obtained by modification of the optimization problem or by proof of the hypothesized pseudo-convex nature of the problem suggested by our results.
Randall, D. G., Krähenbühl, M., Köpping, I., Larsen, T. A., & Udert, K. M. (2016). A novel approach for stabilizing fresh urine by calcium hydroxide addition. Water Research, 95, 361-369. doi:10.1016/j.watres.2016.03.007, Institutional Repository

In this study, we investigated the prevention of enzymatic urea hydrolysis in fresh urine by increasing the pH with calcium hydroxide (Ca(OH)2) powder. The amount of Ca(OH)2 dissolving in fresh urine depends significantly on the composition of the urine. The different urine compositions used in our simulations showed that between 4.3 and 5.8 g Ca(OH)2 dissolved in 1 liter of urine at 25 °C. At this temperature, the pH at saturation is 12.5 and is far above the pH of 11, which we identified as the upper limit for enzymatic urea hydrolysis. However, temperature has a strong effect on the saturation pH, with higher values being achieved at lower temperatures. Based on our results, we recommend a dosage of 10 g Ca(OH)2·L−1 of fresh urine to ensure solid Ca(OH)2 always remains in the urine reactor which ensures sufficiently high pH values. Besides providing sufficient Ca(OH)2, the temperature has to be kept in a certain range to prevent chemical urea hydrolysis. At temperatures below 14 °C, the saturation pH is higher than 13, which favors chemical urea hydrolysis. We chose a precautionary upper temperature of 40 °C because the rate of chemical urea hydrolysis increases at higher temperatures but this should be confirmed with kinetic studies. By considering the boundaries for pH and temperature developed in this study, urine can be stabilized effectively with Ca(OH)2 thereby simplifying later treatment processes or making direct use easier.
Udert, K. M., Etter, B., & Gounden, T. (2016). Promoting sanitation in South Africa through nutrient recovery from urine. GAIA: Ecological Perspectives for Science and Society, 25(3), 194-196. doi:10.14512/gaia.25.3.12, Institutional Repository

The water utility of Durban, eThekwini Water and Sanitation (EWS), installed urine-diverting dry toilets to provide sanitation to under-served communities in rural and peri-urban areas. While faeces was treated by dehydration, urine was discharged into a soak away in the ground. EWS teamed up with the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and other partners in Switzerland and South Africa to valorise this resource. The VUNA project developed a sanitation system which produces a valuable fertiliser from urine, reduces pollution of water resources and promotes the acceptance of dry toilets.
Udert, K. M., & Etter, B. (2016). Vom Urin zum Dünger. Projekt VUNA - Sanitäre Grundversorgung und Separatbehandlung von Urin in Durban/Südafrika. Aqua & Gas, 96(3), 62-69. , Institutional Repository

In Durban/Südafrika werden urinseparierende Toiletten zur Grundversorgung der Bevölkerung in den Vorstadtgebieten eingesetzt. Die Eawag, das Wasserforschungsinstitut des ETH-Bereichs, hat mit dem VUNA-Projekt (www.vuna.ch) die Stadtwerke von Durban dabei unterstützt, die im Urin enthaltenen Wertstoffe zu nutzen. Ziel des Projektes war es, die Akzeptanz der Trockentoiletten zu erhöhen, die Nährstoffe in Form eines wertvollen Düngers wiederzugewinnen und Umweltverschmutzung zu verhindern.
Bischel, H. N., Schertenleib, A., Fumasoli, A., Udert, K. M., & Kohn, T. (2015). Inactivation kinetics and mechanisms of viral and bacterial pathogen surrogates during urine nitrification. Environmental Science: Water Research and Technology, 1(1), 65-76. doi:10.1039/c4ew00065j, Institutional Repository

This paper assesses the inactivation performance and mechanisms in urine nitrification reactors using bacteria and bacteriophages as surrogates for human pathogens. Two parallel continuous-flow moving bed biofilm reactors (MBBRs) were operated over a two-month period. One MBBR was used to conduct a continuous spike experiment with bacteriophage MS2. The second reactor provided the matrix for a series of batch experiments conducted to investigate the inactivation of Salmonella typhimurium, Enterococcus spp., MS2, Qβ, and ΦX174 during urine nitrification. The roles of aeration, biological activity, and solution composition in inactivation were evaluated. Whereas bacteriophages ΦX174 and MS2 remained infective following urine nitrification, partial inactivation of bacteriophage Qβ was observed. Qβ inactivation was attributed primarily to aeration with a potential additive effect of biological processes, i.e., processes that are attributable to the presence of other microorganisms such as sorption to biomass, predation or enzymatic activity. Tailing of Qβ inactivation to a plateau indicated a protective effect of the solution components in aerated nitrification reactors. In contrast to the bacteriophages, S. typhimurium and Enterococcus spp. were mainly affected by biological processes: they were inactivated in biologically active nitrification reactors while remaining stable in chemically equivalent filtered controls. The tested bacteria could, for example, be out-competed by other microbial communities or sorbed to biomass in the reactor. Microbial communities did not adapt to inactivate bacteriophage MS2 (e.g., via increased prevalence of virus predators) in the experimental time-scale evaluated, with no observed inactivation of MS2 during continuous input for 51 days in the flow-through MBBR. The compilation of these results suggests that biological nitrification as a fertilizer production process remains insufficient as a stand-alone technology for the sanitization of source-separated urine.
Bischel, H. N., Özel Duygan, B. D., Strande, L., McArdell, C. S., Udert, K. M., & Kohn, T. (2015). Pathogens and pharmaceuticals in source-separated urine in eThekwini, South Africa. Water Research, 85, 57-65. doi:10.1016/j.watres.2015.08.022, Institutional Repository

In eThekwini, South Africa, the production of agricultural fertilizers from human urine collected from urine-diverting dry toilets is being evaluated at a municipality scale as a way to help finance a decentralized, dry sanitation system. The present study aimed to assess a range of human and environmental health hazards in source-separated urine, which was presumed to be contaminated with feces, by evaluating the presence of human pathogens, pharmaceuticals, and an antibiotic resistance gene. Composite urine samples from households enrolled in a urine collection trial were obtained from urine storage tanks installed in three regions of eThekwini. Polymerase chain reaction (PCR) assays targeted 9 viral and 10 bacterial human pathogens transmitted by the fecal–oral route. The most frequently detected viral pathogens were JC polyomavirus, rotavirus, and human adenovirus in 100%, 34% and 31% of samples, respectively. Aeromonas spp. and Shigella spp. were frequently detected gram negative bacteria, in 94% and 61% of samples, respectively. The gram positive bacterium, Clostridium perfringens, which is known to survive for extended times in urine, was found in 72% of samples. A screening of 41 trace organic compounds in the urine facilitated selection of 12 priority pharmaceuticals for further evaluation. The antibiotics sulfamethoxazole and trimethoprim, which are frequently prescribed as prophylaxis for HIV-positive patients, were detected in 95% and 85% of samples, reaching maximum concentrations of 6800 μg/L and 1280 μg/L, respectively. The antiretroviral drug emtricitabine was also detected in 40% of urine samples. A sulfonamide antibiotic resistance gene (sul1) was detected in 100% of urine samples. By coupling analysis of pathogens and pharmaceuticals in geographically dispersed samples in eThekwini, this study reveals a range of human and environmental health hazards in urine intended for fertilizer production. Collection of urine offers the benefit of sequestering contaminants from environmental release and allows for targeted treatment of potential health hazards prior to agricultural application. The efficacy of pathogen and pharmaceutical inactivation, transformation or removal during urine nutrient recovery processes is thus briefly reviewed.
Bonvin, C., Etter, B., Udert, K. M., Frossard, E., Nanzer, S., Tamburini, F., & Oberson, A. (2015). Plant uptake of phosphorus and nitrogen recycled from synthetic source-separated urine. Ambio, 44(Suppl. 2), S217-S227. doi:10.1007/s13280-014-0616-6, Institutional Repository

Urine contains about 50 % of the phosphorus (P) and about 90 % of the nitrogen (N) excreted by humans and is therefore an interesting substrate for nutrient recovery. Source-separated urine can be used to precipitate struvite or, through a newly developed technology, nitrified urine fertilizer (NUF). In this study, we prepared 33P radioisotope- and stable 15N isotope-labeled synthetic NUF (SNUF) and struvite using synthetic urine and determined P and N uptake by greenhouse-grown ryegrass (Lolium multiflorum var. Gemini) fertilized with these products. The P and N in the urine-based fertilizers were as readily plant-available in a slightly acidic soil as the P and N in reference mineral fertilizers. The ryegrass crop recovered 26 % of P applied with both urine-based fertilizers and 72 and 75 % of N applied as struvite and SNUF, respectively. Thus, NUF and urine-derived struvite are valuable N and P recycling fertilizers.
Decrey, L., Kazama, S., Udert, K. M., & Kohn, T. (2015). Ammonia as an in situ sanitizer: inactivation kinetics and mechanisms of the ssRNA virus MS2 by NH3. Environmental Science and Technology, 49(2), 1060-1067. doi:10.1021/es5044529, Institutional Repository

Sanitizing human and animal waste (e.g., urine, fecal sludge, or grey water) is a critical step in reducing the spread of disease and ensuring microbially safe reuse of waste materials. Viruses are particularly persistent pathogens and can be transmitted through inadequately sanitized waste. However, adequate storage or digestion of waste can strongly reduce the number of viruses due to increases in pH and uncharged aqueous ammonia (NH3), a known biocide. In this study we investigated the kinetics and mechanisms of inactivation of the single-stranded RNA virus MS2 under temperature, pH and NH3 conditions representative of waste storage. MS2 inactivation was mainly controlled by the activity of NH3 over a pH range of 7.0–9.5 and temperatures lower than 40 °C. Other bases (e.g., hydroxide, carbonate) additionally contributed to the observed reduction of infective MS2. The loss in MS2 infectivity could be rationalized by a loss in genome integrity, which was attributed to genome cleavage via alkaline transesterification. The contribution of each base to genome transesterification, and hence inactivation, could be related to the base pKa by means of a Bronsted relationship. The Bronsted relationship in conjunction with the activity of bases in solution enabled an accurate prediction of MS2 inactivation rates.
Etter, B., & Udert, K. M. (2015). Aus Urin wird Flüssigdünger. Eawag News [dtsch. Ausg.] (1), 1-8. Retrieved from http://www.eawag.ch/de/news-agenda/news-plattform/news/news/aus-urin-wird-fluessigduenger/?tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&cHash=a15131c1f98586a1529ff21f31b9ea0e, Institutional Repository

Ein neuartiges Recyclingverfahren gewinnt aus Urin wertvolle Nährstoffe zurück, die sich als Dünger verkaufen lassen. Das schont natürliche Ressourcen, entlastet Kläranlagen und macht Sanitärsysteme in Entwicklungsländern wirtschaftlich attraktiver. Drei Anlagen sind schon in Betrieb: eine an der Eawag in Dübendorf und zwei in der südafrikanischen Stadt Durban.
Etter, B., & Udert, K. M. (2015). Converting urine into liquid fertilizer. Eawag News [engl. ed.] (1), 1-8. Retrieved from http://www.eawag.ch/en/news-agenda/news-portal/news-detail/news/aus-urin-wird-fluessigduenger/?tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&cHash=a15131c1f98586a1529ff21f31b9ea0e, Institutional Repository

With an innovative recycling method, valuable nutrients recovered from urine can be sold as fertilizers. As well as conserving natural resources, this reduces water pollution and makes sanitation systems in developing countries economically more attractive. Three pilot plants are already in operation – one at Eawag in Dübendorf and two in the South African city of Durban.
Etter, B., & Udert, K. M. (2015). Quand l’urine se change en engrais. Eawag News [éd. fr.] (1), 1-8. Retrieved from http://www.eawag.ch/fr/news-agenda/actualites/detail/news/aus-urin-wird-fluessigduenger/?tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&cHash=a15131c1f98586a1529ff21f31b9ea0e, Institutional Repository

Une nouvelle technique de valorisation permet d'extraire les éléments nutritifs de l'urine et de fabriquer un fertilisant commercialisable. Cette approche préserve les ressources naturelles, limite les charges à traiter dans les stations d'épuration et augmente la rentabilité des systèmes d'assainissement dans les pays en développement. Trois stations pilotes sont déjà en fonction: une à Dübendorf et deux dans la ville sud-africaine de Durban
Etter, B., Udert, K. M., & Gounden, T. (2015). Valorisation of urine nutrients. Promoting sanitation & nutrient recovery through urine separation. Laufenburg: Binkert Buag AG. , Institutional Repository
Fumasoli, A., Morgenroth, E., & Udert, K. M. (2015). Modeling the low pH limit of Nitrosomonas eutropha in high-strength nitrogen wastewaters. Water Research, 83, 161-170. doi:10.1016/j.watres.2015.06.013, Institutional Repository

In wastewater treatment, the rate of ammonia oxidation decreases with pH and stops very often slightly below a pH of 6. Free ammonia (NH3) limitation, inhibition by nitrous acid (HNO2), limitation by inorganic carbon or direct effect of high proton concentrations have been proposed to cause the rate decrease with pH as well as the cessation of ammonia oxidation. In this study, we compare an exponential pH term common for food microbiology with conventionally applied rate laws based on Monod-type kinetics for NH3 limitation and non-competitive HNO2 inhibition as well as sigmoidal pH functions to model the low pH limit of ammonia oxidizing bacteria (AOB). For this purpose we conducted well controlled batch experiments which were then simulated with a computer model. The results showed that kinetics based on NH3 limitation and HNO2 inhibition can explain the rate decrease of ammonia oxidation between pH 7 and 6, but fail in predicting the pH limit of Nitrosomonas eutropha at pH 5.4 and rates close to that limit. This is where the exponential pH term becomes important: this term decreases the rate of ammonia oxidation to zero, as the pH limit approaches. Previously proposed sigmoidal pH functions that affect large pH regions, however, led to an overestimation of the pH effect and could therefore not be applied successfully. We show that the proposed exponential pH term can be explained quantitatively with thermodynamic principles: at low pH values, the energy available from the proton motive force is too small for the NADH production in Nitrosomonas eutropha and related AOB causing an energy limited state of the bacterial cell. Hence, energy limitation and not inhibition or limitation of enzymes is responsible for the cessation of the AOB activity at low pH values.
Mašić, A., Santos, A. T. L., Etter, B., Udert, K. M., & Villez, K. (2015). Estimation of nitrite in source-separated nitrified urine with UV spectrophotometry. Water Research, 85, 244-254. doi:10.1016/j.watres.2015.08.031, Institutional Repository

Monitoring of nitrite is essential for an immediate response and prevention of irreversible failure of decentralized biological urine nitrification reactors. Although a few sensors are available for nitrite measurement, none of them are suitable for applications in which both nitrite and nitrate are present in very high concentrations. Such is the case in collected source-separated urine, stabilized by nitrification for long-term storage. Ultraviolet (UV) spectrophotometry in combination with chemometrics is a promising option for monitoring of nitrite. In this study, an immersible in situ UV sensor is investigated for the first time so to establish a relationship between UV absorbance spectra and nitrite concentrations in nitrified urine. The study focuses on the effects of suspended particles and saturation on the absorbance spectra and the chemometric model performance. Detailed analysis indicates that suspended particles in nitrified urine have a negligible effect on nitrite estimation, concluding that sample filtration is not necessary as pretreatment. In contrast, saturation due to very high concentrations affects the model performance severely, suggesting dilution as an essential sample preparation step. However, this can also be mitigated by simple removal of the saturated, lower end of the UV absorbance spectra, and extraction of information from the secondary, weaker nitrite absorbance peak. This approach allows for estimation of nitrite with a simple chemometric model and without sample dilution. These results are promising for a practical application of the UV sensor as an in situ nitrite measurement in a urine nitrification reactor given the exceptional quality of the nitrite estimates in comparison to previous studies.
Schielke-Jenni, S. (2015). Decentralised urine treatment with the nitritationammox process (Doctoral dissertation). doi:10.3929/ethz-a-010479901, Institutional Repository

Urine contains over 80% of the total nitrogen but accounts for less than 1% of the total wastewater volume. Due to higher concentrations, nitrogen removal from source-separated urine is potentially much cheaper and less energy intensive than from wastewater. For many cities, removing nitrogen in small decentralized reactors could be more efficient and affordable than in large treatment plants situated at the end of extensive sewer networks. However, due to a lack of personnel and expensive instruments, process control of small on-site reactors is potentially critical. In addition, process stability and resilience tend to be low due to a lower microbial diversity. Therefore, the main goal of this thesis is to contribute to the development of a reliable and simple process configuration for decentralised nitrogen removal from urine. [...]

Urin beinhaltet über 80% des gesamten Stickstoffs und macht aber nur etwas weniger als 1% des gesamten Abwasservolumens aus. Aufgrund der höheren Konzentrationen ist Stickstoffentfernung aus separat gesammeltem Urin potentiell günstiger und verbraucht weniger Energie als Stickstoffentfernung aus dem gesamten Abwasser. Stickstoffentfernung in kleinen dezentralen Reaktoren könnte deshalb für viele Städte effizienter und erschwinglicher sein als in grossen Reinigungsanlagen am Ende von weitläufigen Kanalisationsnetzen. Da aber kein Personal und keine teuren Instrumente zur Verfügung stehen, kann die Prozesskontrolle von kleinen, dezentralen Reaktoren kritisch sein. Aufgrund der niedrigeren mikrobiellen Diversität, ist in kleinen Systemen tendenziell auch mit einer geringeren Stabilität und Belastbarkeit der Prozesse zu rechnen. Das Hauptziel dieser Arbeit war deshalb, einen Beitrag zur Entwicklung eines einfachen und robusten Prozesses zur dezentralen Stickstoffentfernung aus Urin zu leisten. [...]
Schielke-Jenni, S., Villez, K., Morgenroth, E., & Udert, K. M. (2015). Observability of anammox activity in single-stage nitritation/anammox reactors using mass balances. Environmental Science: Water Research and Technology, 1(4), 523-534. doi:10.1039/c5ew00045a, Institutional Repository

In nitritationammox reactors, several bacterial groups contribute to the overall nitrogen conversion. Knowing the activity of the main bacterial groups, especially of anaerobic ammonium-oxidising bacteria (AMX), is extremely helpful to understand the process and optimise its operation. Mass balances of dissolved compounds such as ammonium, nitrite and nitrate commonly allow the determination of bacterial activities in a nitritationammox process, but the activity of heterotrophic bacteria (HET) is usually neglected. However, even in wastewater with a low organic substrate content, heterotrophic denitrification can contribute substantially to nitrogen removal. The goal of this study was to critically evaluate the applicability of mass balances for the determination of the relevant bacterial activities in a nitritationammox process with high HET activity. We set up and solved mass balances of different degrees of complexity. Both linear equation systems, with catabolic reactions alone and with balances according to the activated sludge model stoichiometry, do not allow estimation of any of the considered bacterial activities. When kinetic rate expressions are included, it is possible to compute the concentrations of all considered bacterial groups, but the estimation uncertainty is far too high for practical purposes: the relative standard deviation for AMX is 5280%. In a completely autotrophic system, the relative standard deviation for AMX is only 5%, which proves that the high standard deviations are due to the complexity of the nitration–anammox process with HET activity. The high standard deviations of the calculated bacterial concentrations can be significantly reduced by adding an additional mass balance for the total biomass (standard deviation for AMX activity 1210%). The required number of measurements to achieve an acceptable precision, in our example about 600 conversion rate measurements to reach a 50% standard deviation for the AMX concentration, is still far too high though for practical purposes. To conclude, mass balances including kinetics theoretically allow the observation of the bacterial activities in nitritationammox reactors with high HET activity. However, the required precision of the calculated conversion rates, the uncertainty of stoichiometric and kinetic parameters and the reactor dynamics (unsteady conditions) make mass balances unsuitable for practical estimation of AMX activity. Due to high frequency and new online instruments, mass balances might become a suitable tool in the future.
Udert, K. M., Buckley, C. A., Wächter, M., McArdell, C. S., Kohn, T., Strande, L., … Etter, B. (2015). Technologies for the treatment of source-separated urine in the eThekwini Municipality. Water SA, 41(2), 212-221. doi:10.4314/wsa.v41i2.06, Institutional Repository

In recent years, a large number of urine-diverting dehydration toilets (UDDTs) have been installed in eThekwini to ensure access to adequate sanitation. The initial purpose of these toilets was to facilitate faeces drying, while the urine was diverted into a soak pit. This practice can lead to environmental pollution, since urine contains high amounts of nutrients. Instead of polluting the environment, these nutrients should be recovered and used as fertiliser. In 2010 the international and transdisciplinary research project VUNA was initiated in order to explore technologies and management methods for better urine management in eThekwini. Three treatment technologies have been chosen for the VUNA project. The first is struvite precipitation, a technology which has already been tested in multiple projects on urine treatment. Struvite precipitation is a simple and fast process for phosphorus recovery. Other nutrients, such as nitrogen and potassium, remain in the effluent and pathogens are not completely inactivated. Therefore, struvite precipitation has to be combined with other treatment processes to prevent environmental pollution and hygiene risks. The second process is a combination of nitrification and distillation. This process combination is more complex than struvite precipitation, but it recovers all nutrients in one concentrated solution, ensures safe sanitisation and produces only distilled water and a small amount of sludge as by-products. The third process is electrolysis. This process could be used for very small on-site reactors, because conversion rates are high and the operation is simple, as long as appropriate electrodes and voltages are used. However, nitrogen is removed and not recovered and chlorinated by-products are formed, which can be hazardous for human health. While urine electrolysis requires further research in the laboratory, struvite precipitation and nitrification/distillation have already been operated at pilot scale.
Zöllig, H., Fritzsche, C., Morgenroth, E., & Udert, K. M. (2015). Direct electrochemical oxidation of ammonia on graphite as a treatment option for stored source-separated urine. Water Research, 69, 284-294. doi:10.1016/j.watres.2014.11.031, Institutional Repository

Electrolysis can be a viable technology for ammonia removal from source-separated urine. Compared to biological nitrogen removal, electrolysis is more robust and is highly amenable to automation, which makes it especially attractive for on-site reactors. In electrolytic wastewater treatment, ammonia is usually removed by indirect oxidation through active chlorine which is produced in-situ at elevated anode potentials. However, the evolution of chlorine can lead to the formation of chlorate, perchlorate, chlorinated organic by-products and chloramines that are toxic. This study focuses on using direct ammonia oxidation on graphite at low anode potentials in order to overcome the formation of toxic by-products. With the aid of cyclic voltammetry, we demonstrated that graphite is active for direct ammonia oxidation without concomitant chlorine formation if the anode potential is between 1.1 and 1.6 V vs. SHE (standard hydrogen electrode). A comparison of potentiostatic bulk electrolysis experiments in synthetic stored urine with and without chloride confirmed that ammonia was removed exclusively by continuous direct oxidation. Direct oxidation required high pH values (pH > 9) because free ammonia was the actual reactant. In real stored urine (pH = 9.0), an ammonia removal rate of 2.9 ± 0.3 gN·m−2·d−1 was achieved and the specific energy demand was 42 Wh·gN−1 at an anode potential of 1.31 V vs. SHE. The measurements of chlorate and perchlorate as well as selected chlorinated organic by-products confirmed that no chlorinated by-products were formed in real urine. Electrode corrosion through graphite exfoliation was prevented and the surface was not poisoned by intermediate oxidation products. We conclude that direct ammonia oxidation on graphite electrodes is a treatment option for source-separated urine with three major advantages: The formation of chlorinated by-products is prevented, less energy is consumed than in indirect ammonia oxidation and readily available and cheap graphite can be used as the electrode material.
Zöllig, H. (2015). Electrolysis for the treatment of stored source-separated urine (Doctoral dissertation). doi:10.3929/ethz-a-010549050, Institutional Repository

Electrolysis is a promising technology for the on-site treatment of source-separated urine. It is the many degrees of freedom (electrode material, electrode potential, current density, cell design), the electrical conductivity of urine and the high amenability to automation which make electrolysis attractive. It was the objective of this thesis to understand the electro-oxidation of organic substances and ammonia to apply electrolysis successfully for the removal of these compounds from stored source-separated urine. To achieve this goal, a variety of electrochemical experiments were conducted with anodes consisting of boron-doped diamond (BDD), thermally decomposed iridium oxide film (TDIROF) or graphite and a new experimental procedure was developed to assess the time dependent production of volatile organic chlorination by-products (OCBPs). [...]

Die Elektrolyse ist eine vielversprechende Technologie für die Behandlung von Urin. Es sind die vielen Freiheitsgrade (Elektrodenmaterialien, Elektrodenpotential, Stromdichte, Zellendesign), die elektrische Leitfähigkeit des Urins sowie das hohe Automatisierungspotential, welche die Elektrolyse attraktiv machen. Es war das Ziel dieser Arbeit, die elektrochemische Oxidation von organischen Substanzen und Ammoniak zu verstehen, um diese für die dezentrale Behandlung von gelagertem Urin anzuwenden. Es wurden elektrochemische Experimente mit Bor-versetzten Diamant-(BDD), thermisch hergestellten Iridiumoxidfilm- (TDIROF) und Graphitanoden durchgeführt. Um dabei die Entstehung von leichtflüchtigen, chlorierten Nebenprodukten (CNPs) zu verfolgen, wurde eine neue experimentelle Methode entwickelt. [...]
Zöllig, H., Remmele, A., Fritzsche, C., Morgenroth, E., & Udert, K. M. (2015). Formation of chlorination byproducts and their emission pathways in chlorine mediated electro-oxidation of urine on active and nonactive type anodes. Environmental Science and Technology, 49(18), 11062-11069. doi:10.1021/acs.est.5b01675, Institutional Repository

Chlorination byproducts (CBPs) are harmful to human health and the environment. Their formation in chlorine mediated electro-oxidation is a concern for electrochemical urine treatment. We investigated the formation of chlorate, perchlorate, and organic chlorination byproducts (OCBPs) during galvanostatic (10, 15, 20 mA·cm–2) electro-oxidation of urine on boron-doped diamond (BDD) and thermally decomposed iridium oxide film (TDIROF) anodes. In the beginning of the batch experiments, the production of perchlorate was prevented by competing active chlorine and chlorate formation as well as by direct oxidation of organic substances. Perchlorate was only formed at higher specific charges (>17 Ah·L–1 on BDD and >29 Ah·L–1 on TDIROF) resulting in chlorate and perchlorate being the dominant CBPs (>90% of initial chloride). BDD produced mainly short chained OCBPs (dichloromethane, trichloromethane, and tetrachloromethane), whereas longer chained OCBPs (1,2-dichloropropane and 1,2-dichloroethane) were more frequently found on TDIROF. The OCBPs were primarily eliminated by electrochemical stripping: On BDD, this pathway accounted for 40% (dichloromethane) to 100% (tetrachloromethane) and on TDIROF for 90% (1,2-dichloroethane) to 100% (trichloromethane) of what was produced. A post-treatment of the liquid as well as the gas phase should be foreseen if CBP formation cannot be prevented by eliminating chloride or organic substances in a pretreatment.
Zöllig, H., Morgenroth, E., & Udert, K. M. (2015). Inhibition of direct electrolytic ammonia oxidation due to a change in local pH. Electrochimica Acta, 165, 348-355. doi:10.1016/j.electacta.2015.02.162, Institutional Repository

Electrochemical ammonia oxidation has gained a lot of attention recently as an efficient method for ammonia removal from wastewater, for the use in ammonia-based fuel cells and the production of high purity hydrogen. Thermally decomposed iridium oxide films (TDIROF) have been shown to be catalytically active for direct ammonia oxidation in aqueous solutions if NH3 is present. However, the process was reported to be rapidly inhibited on TDIROF. Herein, we show that this fast inhibition of direct ammonia oxidation does not result from surface poisoning by adsorbed elemental nitrogen (Nads). Instead, we propose that direct ammonia oxidation and oxygen evolution can lead to a drop of the local pH at the electrode resulting in a low availability of the actual reactant, NH3. The hypothesis was tested with cyclic voltammetry (CV) experiments on stagnant and rotating disk electrodes (RDE). The CV experiments on the stagnant electrode revealed that the decrease of the ammonia oxidation peaks was considerably reduced by introducing an idle phase at open circuit potential between subsequent scans. Furthermore, the polarization of the TDIROF electrode into the hydrogen evolution region (HER) resulted in increased ammonia oxidation peaks in the following anodic scans which can be explained with an increased local pH after the consumption of protons in the HER. On the RDE, the ammonia oxidation peaks did not decrease in immediately consecutive scans. These findings would not be expected if surface poisoning was responsible for the fast inhibition but they are in good agreement with the proposed mechanism of pH induced limitation by the reactant, NH3. The plausibility of the mechanism was also supported by our numerical simulations of the processes in the Nernstian diffusion layer. The knowledge about this inhibition mechanism of direct ammonia oxidation is especially important for the design of electrochemical cells for wastewater treatment. The mechanism is not only valid for TDIROF but also for other electrodes because it is independent of the electrode material.
Etter, B., Gounden, T., & Udert, K. M. (2014). VUNA: harvesting nutrients from urine for agriculture. Sandec News, 15, 10-11. , Institutional Repository

VUNA is a trans-disciplinary project that is developing a system to collect source-separated urine and process it into fertiliser. Collection logistics, treatment technologies, and social and economic assessments of nutrient recovery are some of the activities worked on by the VUNA team.
Jenni, S., Vlaeminck, S. E., Morgenroth, E., & Udert, K. M. (2014). Successful application of nitritation/anammox towastewater with elevated organic carbon to ammonia ratios. Water Research, 49, 316-326. doi:10.1016/j.watres.2013.10.073, Institutional Repository

The nitritation/anammox process has been mainly applied to high-strength nitrogenous wastewaters with very low biodegradable organic carbon content (<0.5g COD·g N–1). However, several wastewaters have biodegradable organic carbon to nitrogen (COD/N) ratios between 0.5 and 1.7g COD·g N–1 and thus, contain elevated amounts of organic carbon but not enough for heterotrophic denitrification. In this study, the influence of elevated COD/N ratios was studied on a nitritation/anammox process with suspended sludge. In a step-wise manner, the influent COD/N ratio was increased to 1.4g COD·g N–1 by supplementing digester supernatant with acetate. The increasing availability of COD led to an increase of the nitrogen removal efficiency from around 85% with pure digester supernatant to >95% with added acetate while the nitrogen elimination rate stayed constant (275 ± 40mg N·L–1·d–1). Anammox activity and abundance of anammox bacteria (AMX) were strongly correlated, and with increasing influent COD/N ratio both decreased steadily. At the same time, heterotrophic denitrification with nitrite and the activity of ammonia oxidising bacteria (AOB) gradually increased. Simultaneously, the sludge retention time (SRT) decreased significantly with increasing COD loading to about 15 d and reached critical values for the slowly growing AMX. When the SRT was increased by reducing biomass loss with the effluent, AMX activity and abundance started to rise again, while the AOB activity remained unaltered. Fluorescent in-situ hybridisation (FISH) showed that the initial AMX community shifted within only 40 d from a mixed AMX community to "Candidatus Brocadia fulgida" as the dominant AMX type with an influent COD/N ratio of 0.8 g COD·g N–1 and higher. "Ca. Brocadia fulgida" is known to oxidise acetate, and its ability to outcompete other types of AMX indicates that AMX participated in acetate oxidation. In a later phase, glucose was added to the influent instead of acetate. The new substrate composition did not significantly influence the nitrogen removal nor the AMX activity, and "Ca. Brocadia fulgida" remained the dominant type of AMX. Overall, this study showed that AMX can coexist with heterotrophic bacteria at elevated influent COD/N ratios if a sufficiently high SRT is maintained.
Larsen, T. A., Udert, K. M., & Lienert, J. (2014). Abwassertrennung und Dezentralisierung. Aqua & Gas, 94(1), 52-54. , Institutional Repository

Ist eine ressourcenschonende Abwasserreinigung durch Abwassertrennung und Dezentralisierung realistisch? Rund 40 international bekannte Wissenschafter und Wissenschafterinnen behandeln auf 520 Seiten in einem 2013 erschienenen Buch nuanciert diese Fragestellung. Die Editoren der Eawag diskutieren das Thema des Buches im Schweizer Kontext.
McConville, J. R., Künzle, R., Messmer, U., Udert, K. M., & Larsen, T. A. (2014). Decision support for redesigning wastewater treatment technologies. Environmental Science and Technology, 48(20), 12238-12246. doi:10.1021/es501854x, Institutional Repository

This paper offers a methodology for structuring the design space for innovative process engineering technology development. The methodology is exemplified in the evaluation of a wide variety of treatment technologies for source-separated domestic wastewater within the scope of the Reinvent the Toilet Challenge. It offers a methodology for narrowing down the decision-making field based on a strict interpretation of treatment objectives for undiluted urine and dry feces and macroenvironmental factors (STEEPLED analysis) which influence decision criteria. Such an evaluation identifies promising paths for technology development such as focusing on space-saving processes or the need for more innovation in low-cost, energy-efficient urine treatment methods. Critical macroenvironmental factors, such as housing density, transportation infrastructure, and climate conditions were found to affect technology decisions regarding reactor volume, weight of outputs, energy consumption, atmospheric emissions, investment cost, and net revenue. The analysis also identified a number of qualitative factors that should be carefully weighed when pursuing technology development; such as availability of O&M resources, health and safety goals, and other ethical issues. Use of this methodology allows for coevolution of innovative technology within context constraints; however, for full-scale technology choices in the field, only very mature technologies can be evaluated.
Tilley, E., Strande, L., Lüthi, C., Mosler, H. J., Udert, K. M., Gebauer, H., & Hering, J. G. (2014). Looking beyond technology: an integrated approach to water, sanitation and hygiene in low income countries. Environmental Science and Technology, 48(17), 9965-9970. doi:10.1021/es501645d, Institutional Repository
Udert, K. M. (2014). Electrochemical treatment of urine. In G. Kreysa, Kichiro Ota, & R. F. Savinell (Eds.), Encyclopedia of applied electrochemistry (pp. 654-658). doi:10.1007/978-1-4419-6996-5_109, Institutional Repository

Separation at the source and decentralized treatment of urine, feces, and greywater is a novel concept for wastewater management. This approach is particularly suitable for regions where the availability of water resources is low or the infrastructure for centralized wastewater treatment is missing. Urine is the main contributor of nutrients to municipal wastewater (80 % of nitrogen and 50 % of phosphorus). Since the urine volume is small (1.3 L · s-1 · d-1), nutrient removal (or recovery) could be achieved in small decentralized reactors.
Some properties of electrochemical processes make them particularly suitable for urine treatment in a small decentralized reactor: no chemicals have to be added, the reaction can be easily started and terminated, a wide range of compounds can be oxidized or reduced, and the electric parameters current and voltage can be used for process automation and remote process control. However, electrochemical processes also have some drawbacks: the energy consumption is higher than for comparable biological processes, side reactions can produce unwanted by-products, and efficient electrodes are often expensive.
The main focus of this article is on the electrochemical removal of nitrogen and phosphorus from source-separated urine. Bioelectrochemical systems for urine treatment will not be discussed, because the research is still at an early stage. Some possible applications of bioelectrochemical systems for urine treatment have been presented in Udert et al..
Uhlmann, C. (2014). Dynamics of complete and partial nitrification of source-separated urine (Master thesis). 32 p. , Institutional Repository

In this thesis the resilience of complete and partial nitrification of source-separated urine under dynamic conditions were investigated and compared. The process stability of nitrification reactors is important for their commercial application. In partial nitrification the alkalinity contained in urine allows nitrifying 50% of the ammonia whereas in complete nitrification the dosage of a base allows the nitrification of almost 100% of the ammonia. Due to considerations about Monod kinetic substrate limitation of Ammonia Oxidizing Bacteria (AOB) it was hypothesized that complete nitrification is more prone to nitrite accumulation and therefore less stable than partial nitrification. A computer model based on Monod kinetics should help to understand the processes and the resilience of urine nitrification reactors. Laboratory experiments were conducted in 7 L moving bed biofilm reactors (MBBR) to analyze the behavior of the two processes in respect to changes in temperature and inflow. The total ammonia concentration in the inflow was on average 1750±150 mg N L-1. Complete nitrification has at same conditions a lower nitrification rate than partial nitrification due to the lower ammonia concentration in the reactor. In order to reach comparable nitrification rates complete and partial nitrification reactors were therefore operated at two different pH values of 7 and 6 respectively. The average nitrification rate in complete nitrification was 1.08±0.17 g N m-2 d-1 and in parital nitrification 0.90±0.25 g N m-2 d-1 with regard to biofilm carrier surface (Kaldnes®). During all experiments no essential difference of process stability between complete and partial nitrification were observed. Both processes remained stable during temperature fluctuations between 20 °C and 32 °C when urine inflow was constant. pH-diven inflow control led to substantial nitrite accumulation and to a break down of nitrification due to an increase of the inflow caused by increasing AOB activity at higher temperatures. It could be shown that the dynamics of bacterial growth due to temperature changes are damped when pH is not controlled. Instantaneous increase of the inflow caused severe nitrite accumulations in both processes. A reliable process control should therefore consider the effects of temperature and restrict load fluctuations to a minimum. The developed model was able to describe the dynamics of nitrogen conversion due to temperature changes but failed in the prediction of process instabilities caused by increasing inflow.
Faust, V. (2013). Aufenthaltszeit von Urin in einem Urinsammelsystem (Bachelor thesis). 16 p. , Institutional Repository

Im Forum Chriesbach der Eawag ist ein NoMix-System installiert, das den Urin sammelt und getrennt vom restlichen Abwasser abführt. Da der Urin einen Grossteil an Nährstoffen wie Stickstoff enthält, kann er separat aufbereitet und anschliessend als landwirtschaftlicher Dünger genutzt werden. Im Leitungssystem wird der Harnstoff, welcher die grösste Stickstoffkomponente im Urin bildet, durch Bakterien abgebaut. Für ein besseres Verständnis der Harnstoffhydrolyse muss bekannt sein, wie lange der Urin im Leitungssystem verweilt. Um die Aufenthaltszeit von Urin zu quantifizieren wurden in dieser Arbeit Tracerversuche mit Bromid durchgeführt. Dabei wurden neben einer mittleren Aufenthaltszeit auch der Einfluss der Benutzerfrequenz und der Distanz, also dem Stockwerk aus dem der Urin kommt, untersucht. Zusätzlich wurde die Aufenthaltszeit mit Hilfe einer Urinbilanz berechnet, bei der die summierten Input und Output Kurven des Urins aufgezeichnet wurden. Die zeitliche Verschiebung der beiden Kurven beschreibt eine mittlere Verweilzeit.
Die Tracerversuche zeigten, dass sich die Aufenthaltszeit des Bromids und des eigentlichen Urins deutlich unterscheiden. Der Tracer repräsentiert somit nicht wie ursprünglich angenommen den Grundstrom. Wie aus der Urinbilanz hervorging hat der Urin eine mittlere Verweilzeit von 31 Minuten mit einer Standartabweichung von 12 Minuten. Die mittlere Aufenthaltszeit des Bromids ist gemäss den Tracerversuchen etwa viermal grösser. Das unterschiedliche Verhalten ist dadurch zu erklären, dass das Bromid im Leitungsrohr in den Biofilm diffundiert und deshalb mehr Zeit als der Urin benötigt. Mit zunehmender Benutzerfrequenz gleichen sich die beiden Aufenthaltszeiten an, da mehr Urin vorhanden ist, in welches das Bromid zurückdiffundieren kann. Das Stockwerk beeinflusst die Aufenthaltszeit des Urins und des Bromids. Der Einfluss auf das Bromid ist jedoch grösser, da die Diffusion in den Biofilm in den vertikalen Leitungen grösser ist als in den horizontalen.
Auf die Verweilzeit des Harnstoffs konnte aus den Ergebnissen auf Grund der Diffusion nicht geschlossen werden, da weder der Urin noch das Bromid repräsentativ sind. Es kann aber mit grosser Wahrscheinlichkeit gesagt werden, dass auch der Harnstoff und weitere gelöste Stoffe in den Biofilm diffundieren und damit eine grössere Aufenthaltszeit als der Urin besitzen.
Florin, A. (2013). Full nitrification of urine by adding a base (Master thesis). 38 p. , Institutional Repository

With the goal of nutrient recovery, full nitrification of human urine is investigated for its stabilization in simple, decentralized reactors. In a first part of this work, undiluted urine was completely nitrified in a laboratory-scale moving-bed biofilm reactor (MBBR), with automated dosage of a KHCO3 solution keeping the pH at 7.0-7.1. The effluent contained up to 2706 mg-N/L of nitrate; on average > 99% of the total nitrogen. Maintaining low concentrations of ammonium and nitrite (generally below 1 ‰ and 4.7‰ respectively of the influent total ammonia) proved to reduce the risks of dramatic process instabilities due to inhibition with nitrous acid and free ammonia. Although full nitrification by adding a base presents several advantages, for decentralized applications, it is recommended to add alkalinity in a way requiring less expensive and complex material than by dosing a basic solution.
Hoping that calcite (CaCO3) could be a simple alternative to buffer nitrification, in a second part we studied the dissolution of chalk powder in synthetic urine solutions, both in the presence and absence of phosphate. Experiments and simulations with PHREEQC verified the hypothesis that phosphate may precipitate on the surface of calcite, and thus slow down dissolution. In the absence of phosphate, calcite dissolved rapidly until saturation of the solution. By contrast, with the high phosphate concentrations in stored urine (around 200-250 mgP/L), calcite dissolution was inhibited by the rapid formation of  amorphous calcium-phosphate (ACP; eventually converting into hydroxyapatite, HAP) directly on the particle’s surface, as was revealed by XRD and REM analysis. To prevent calcite passivation, precipitation of struvite (MgNH4PO4•6H2O) is suggested before the full nitrification reactor.  In real urine, the effect of biofilm growth directly on calcite may be of advantage to compensate possibly too slow calcite dissolution, and should inform further work.
Hug, A., & Udert, K. M. (2013). Struvite precipitation from urine with electrochemical magnesium dosage. Water Research, 47(1), 289-299. doi:10.1016/j.watres.2012.09.036, Institutional Repository

When magnesium is added to source-separated urine, struvite (MgNH4PO4·6H2O) precipitates and phosphorus can be recovered. Up to now, magnesium salts have been used as the main source of magnesium. Struvite precipitation with these salts works well but is challenging in decentralized reactors, where high automation of the dosage and small reactor sizes are required. In this study, we investigated a novel approach for magnesium dosage: magnesium was electrochemically dissolved from a sacrificial magnesium electrode. We demonstrated that this process is technically simple and economically feasible and thus interesting for decentralized reactors. Linear voltammetry and batch experiments at different anode potentials revealed that the anode potential must be higher than −0.9 V vs. NHE (normal hydrogen electrode) to overcome the strong passivation of the anode. An anode potential of −0.6 V vs. NHE seemed to be suitable for active magnesium dissolution. For 13 subsequent cycles at this potential, we achieved an average phosphate removal rate of 3.7 mg P cm−2 h−1, a current density of 5.5 mA cm−2 and a current efficiency of 118%. Some magnesium carbonate (nesquehonite) accumulated on the anode surface; as a consequence, the current density decreased slightly, but the current efficiency was not affected. The energy consumption for these experiments was 1.7 W h g P−1. A cost comparison showed that sacrificial magnesium electrodes are competitive with easily soluble magnesium salts such as MgCl2 and MgSO4, but are more expensive than dosing with MgO. Energy costs for the electrochemical process were insignificant. Dosing magnesium electrochemically could thus be a worthwhile alternative to dosing magnesium salts. Due to the simple reactor and handling of magnesium, this may well be a particularly interesting approach for decentralized urine treatment.
Kabdaşlı, I., Tünay, O., & Udert, K. M. (2013). Transfer into the solid phase. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 351-365). London: IWA Publishing. , Institutional Repository

Several treatment methods can be used to transfer dissolved compounds from source-separated wastewater streams onto or into a solid phase. A critical review of these methods will be given here. The emphasis will be placed on the recovery of nutrients, especially from human urine; the treatment of other waste streams will be described in brief.
Larsen, T. A., Udert, K. M., & Lienert, J. (2013). Editorial. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 1-10). London: IWA Publishing. , Institutional Repository

Why are we editing a book about source separation and decentralization? We live in Switzerland, an industrialized country with a highly advanced and well-functioning wastewater management system. But even in Switzerland, the central system is reaching its limits, shortcomings, which become very obvious from a global perspective. We are proud to have been able to assemble contributions from renowned authors worldwide from both research and practice. They share with us their experience and thoughts about the current wastewater system. They analyze its advantages, but also deficiencies and they have the courage to breach the paradigm that central wastewater treatment is the only possible approach in urban areas. Many of the authors of this book are pioneers in the field and have been paving the way to a more sustainable and equitable handling of wastewater. We are greatly indebted to all the authors for their contributions to this book, but even more so for their continuous research on source separation and decentralization. We hope that this book will help develop this new area into a mature field in science as well as in practice. [...]
Remmele, A. (2013). The influence of anode material and current density on the emissions of disinfection by-products (DBPs) during electrolytic treatment of stored urine (Master thesis). 33 p. , Institutional Repository

Electrolysis of source separated urine is an efficient technology for COD and ammonia removal. Despite a huge of research about electrochemical treatment of wastewater the formation and emission of toxic and carcinogenic disinfection by-products (DBPs), is still not understoood in detail. The aim of this masterthesis is to contribute to the optimisation of the electrolysis of stored urine by a better understanding of the DBP formation.
For this purpose two control variables, anode material and current density, are investigated. DBP formation was analysed in nine galvanostatic experiments with the anode materials boron-doped diamond (BDD), iridium dioxide (Ti/IrO2) and graphite. Current densities of 5, 10, 15 and 20 mA cm-2 were applied to a discontinuous electrolysis cell filled with 350 mL of stored urine. The gas above the electrolyte was extracted and drawn through two traps in series filled with dodecane by a gas pump. Periodically taken samples from the reactor were analysed with GCMS, IC and Hach Dr. Lange tests for concentrations of six selected DBPs, COD, ammonia, Chloride and Chlorate. Samples from the raps were analysed for DBP concentrations. [...]
Siegrist, H., Laureni, M., & Udert, K. M. (2013). Transfer into the gas phase: ammonia stripping. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 337-350). London: IWA Publishing. , Institutional Repository

Stripping is the most common process for the selective recovery of ammonia from wastewater. Two stripping technologies have been used for source-separated urine: first, air stripping of ammonia with subsequent ammonia adsorption in acid, and second, steam stripping with ammonia recovery in the condensate. In this chapter, we discuss the basic concepts of air stripping, because it is probably more suitable for decentralized reactors than steam stripping. We will also present results of air stripping/acid adsorption and steam stripping experiments with urine. Furthermore, we will discuss the conditions that can lead to passive ammonia stripping in urine-collecting systems. In the future, passive stripping could be a low-energy option for ammonia recovery in on-site systems.
The focus of this chapter is on the treatment of source-separated urine. However, we will also refer to the treatment of digester supernatant during the discussion of the basic concepts of air stripping. Since our literature review did not reveal any report about ammonia stripping from blackwater, we will not discuss this application.
Throughout the text, we will use the term ammonia for the sum of free ammonia (NH3) and ammonium (NH4+). To specifically address the two forms of ammonia, we will use the chemical formula NH3 and NH4+. The terms for carbonate and phosphate will be used accordingly.
Udert, K. M., & Jenni, S. (2013). Biological nitrogen conversion processes. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 291-305). London: IWA Publishing. , Institutional Repository

Biological processes are the gold standard for nitrogen removal in municipal wastewater treatment, because they are more energy-efficient and require fewer resources than physico-chemical processes. Several studies have shown that biological processes can also be used for nitrogen removal from urine and blackwater, the two source-separated waste streams with the highest nitrogen loads. However, biological processes are not only used for nitrogen removal but also for nitrogen recovery: with nitrification the volatile ammonia in urine can be stabilized as nitrate or ammonium nitrate. This is a suitable pretreatment step for the evaporative recovery of all nutrients in one solid product.
In this chapter, we present the basic processes for biological nitrogen conversion in wastewater treatment and we discuss laboratory and pilot-scale experiments of nitrogen conversion in urine and blackwater.
Udert, K. M., Brown-Malker, S., & Keller, J. (2013). Electrochemical systems. In T. A. Larsen, K. M. Udert, & J. Lienert (Eds.), Source separation and decentralization for wastewater management (pp. 321-335). London: IWA Publishing. , Institutional Repository

Electrochemical processes offer many possibilities for decentralized wastewater treatment. Besides the direct oxidation and reduction of major pollutants they can also be used for coagulation and precipitation processes, disinfection or targeted micropollutant removal. While those processes require energy, wastewater can also be used as a direct source for electricity, either in purely chemical fuel cells or in bioelectrochemical systems. Several processes have been tested for source-separated waste streams, especially for urine. However, no pilot plants or long-term experiences have been reported so far. In this chapter, we present basic concepts of electrochemical treatment, possible applications for source-separated waste streams and we summarize and discuss existing data especially with respect to energy.
Larsen, T. A., Udert, K. M., & Lienert, J. (Eds.). (2013). Source separation and decentralization for wastewater management. doi:10.2166/9781780401072, Institutional Repository

Is sewer-based wastewater treatment really the optimal technical solution in urban water management? This paradigm is increasingly being questioned. Growing water scarcity and the insight that water will be an important limiting factor for the quality of urban life are main drivers for new approaches in wastewater management. Source Separation and Decentralization for Wastewater Management sets up a comprehensive view of the resources involved in urban water management. It explores the potential of source separation and decentralization to provide viable alternatives to sewerbased urban water management.
During the 1990s, several research groups started working on sourceseparating technologies for wastewater treatment. Source separation was not new, but had only been propagated as a cheap and environmentally friendly technology for the poor. The novelty was the discussion whether source separation could be a sustainable alternative to existing end-of-pipe systems, even in urban areas and industrialized countries.
Since then, sustainable resource management and many different sourceseparating technologies have been investigated. The theoretical framework and also possible technologies have now developed to a more mature state. At the same time, many interesting technologies to process combined or concentrated wastewaters have evolved, which are equally suited for the treatment of source-separated domestic wastewater.
The book presents a comprehensive view of the state of the art of source separation and decentralization. It discusses the technical possibilities and practical experience with source separation in different countries around the world. The area is in rapid development, but many of the fundamental insights presented in this book will stay valid.
Source Separation and Decentralization for Wastewater Management is intended for all professionals and researchers interested in wastewater mamagement, wheter or not they are familiar with source separation.
Amstutz, V., Katsaounis, A., Kapalka, A., Comninellis, C., & Udert, K. M. (2012). Effects of carbonate on the electrolytic removal of ammonia and urea from urine with thermally prepared IrO2 electrodes. Journal of Applied Electrochemistry, 42(9), 787-795. doi:10.1007/s10800-012-0444-y, Institutional Repository

Recent studies have shown that electrolysis can be an efficient process for nitrogen removal from urine. These studies have been conducted with urea solutions or fresh urine, but urine collected in NoMix toilets and urinals has a substantially different composition, because bacteria hydrolyse urea quickly to ammonia and carbonate. In this study, we compared electrochemical removal of nitrogen from synthetic solutions of fresh and stored urine using IrO2 anodes. We could show that in fresh urine both ammonia and urea are efficiently eliminated, mainly through chlorine-mediated oxidation. However, in stored urine the presence of carbonate, arising from urea hydrolysis, leads to an inhibition of ammonia oxidation. We suggest two parallel mechanisms to explain this effect: the competition between chloride and carbonate oxidation at the anode and the competition between chlorate formation, enhanced by the buffering effect of carbonate, and ammonia oxidation for the consumption of active chlorine in the bulk. However, further experiments are needed to support the latter mechanism. In conclusion, this study highlights the negative consequences of the presence of carbonate in urine solutions, but also in other wastewaters, when subjected to an electrolytic treatment on IrO2 in alkaline media.
Fritzsche, C. (2012). The formation of chlorinated organics during electrolytic urine treatment (Master thesis). 74 p. , Institutional Repository

This master thesis is part of the VUNA project which aims for nutrient recovery and treatment of urine in decentralized treatment facilities. Electrolysis is used to remove nitrogen through electrolytic ammonia oxidation. It is a promising treatment option because it is not susceptible to inflow variations. However, a disadvantage of electrolysis is that chlorinated organics, which are dangerous for environmental and human health, might be formed.
The overall goal of this master thesis is to analyze the processes of chlorinated organics formation during electrolytic treatment of stored urine. The subgoals are to choose four chlorinated, organic substances of interest, to develop a measurement method for these substances, to quantify the current efficiency in experiments with urine and to either accept or reject the following hypotheses: 1) Chlorinated organics are formed during the electrolytic treatment of stored urine. 2) If the electrode potential applied in electrolytic urine treatment is lower than the potential needed for chloride oxidation, no chlorinated organics are formed. [...]
Jenni, S., Mohn, J., Emmenegger, L., & Udert, K. M. (2012). Temperature dependence and interferences of NO and N2O microelectrodes used in wastewater treatment. Environmental Science and Technology, 46(4), 2257-2266. doi:10.1021/es2032357, Institutional Repository

Electrodes for nitric and nitrous oxide have been on the market for some time, but have not yet been tested for an application in wastewater treatment processes. Both sensors were therefore assessed with respect to their (non)linear response, temperature dependence and potential cross sensitivity to dissolved compounds, which are present and highly dynamic in nitrogen conversion processes (nitric oxide, nitrous oxide, nitrogen dioxide, ammonia, hydrazine, hydroxylamine, nitrous acid, oxygen, and carbon dioxide). Off-gas measurements were employed to differentiate between cross sensitivity to interfering components and chemical nitric oxide or nitrous oxide production. Significant cross sensitivities were detected for both sensors: by the nitrous oxide sensor to nitric oxide and by the nitric oxide sensor to ammonia, hydrazine, hydroxylamine and nitrous acid. These interferences could, however, be removed by correction functions. Temperature fluctuations in the range of ±1 °C lead to artifacts of ±3.5% for the nitric oxide and ±3.9% for the nitrous oxide sensor and can be corrected with exponential equations. The results from this study help to significantly shorten and optimize the determination of the correction functions and are therefore relevant for all users of nitric and nitrous oxide electrodes.
Sakthivel, S. R., Tilley, E., & Udert, K. M. (2012). Wood ash as a magnesium source for phosphorus recovery from source-separated urine. Science of the Total Environment, 419, 68-75. doi:10.1016/j.scitotenv.2011.12.065, Institutional Repository

Struvite precipitation is a simple technology for phosphorus recovery from source-separated urine. However, production costs can be high if expensive magnesium salts are used as precipitants. Therefore, waste products can be interesting alternatives to industrially-produced magnesium salts. We investigated the technical and financial feasibility of wood ash as a magnesium source in India. In batch experiments with source-separated urine, we could precipitate 99% of the phosphate with a magnesium dosage of 2.7 mol Mg mol P− 1. The availability of the magnesium from the wood ash used in our experiment was only about 50% but this could be increased by burning the wood at temperatures well above 600 °C. Depending on the wood ash used, the precipitate can contain high concentrations of heavy metals. This could be problematic if the precipitate were used as fertilizer depending on the applicable fertilizer regulations. The financial study revealed that wood ash is considerably cheaper than industrially-produced magnesium sources and even cheaper than bittern. However, the solid precipitated with wood ash is not pure struvite. Due to the high calcite and the low phosphorus content (3%), the precipitate would be better used as a phosphorus-enhanced conditioner for acidic soils. The estimated fertilizer value of the precipitate was actually slightly lower than wood ash, because 60% of the potassium dissolved into solution during precipitation and was not present in the final product. From a financial point of view and due to the high heavy metal content, wood ash is not a very suitable precipitant for struvite production. Phosphate precipitation from urine with wood ash can be useful if (1) a strong need for a soil conditioner that also contains phosphate exists, (2) potassium is abundant in the soil and (3) no other cheap precipitant, such as bittern or magnesium oxide, is available.
Schreiber, F., Wunderlin, P., Udert, K. M., & Wells, G. F. (2012). Nitric oxide and nitrous oxide turnover in natural and engineered microbial communities: biological pathways, chemical reactions, and novel technologies. Frontiers in Microbiology, 3(372), 372 (24 pp.). doi:10.3389/fmicb.2012.00372, Institutional Repository

Nitrous oxide (N2O) is an environmentally important atmospheric trace gas because it is an effective greenhouse gas and it leads to ozone depletion through photo-chemical nitric oxide (NO) production in the stratosphere. Mitigating its steady increase in atmospheric concentration requires an understanding of the mechanisms that lead to its formation in natural and engineered microbial communities. N2O is formed biologically from the oxidation of hydroxylamine (NH2OH) or the reduction of nitrite (NO−2) to NO and further to N2O. Our review of the biological pathways for N2O production shows that apparently all organisms and pathways known to be involved in the catabolic branch of microbial N-cycle have the potential to catalyze the reduction of NO−2 to NO and the further reduction of NO to N2O, while N2O formation from NH2OH is only performed by ammonia oxidizing bacteria (AOB). In addition to biological pathways, we review important chemical reactions that can lead to NO and N2O formation due to the reactivity of NO−2, NH2OH, and nitroxyl (HNO). Moreover, biological N2O formation is highly dynamic in response to N-imbalance imposed on a system. Thus, understanding NO formation and capturing the dynamics of NO and N2O build-up are key to understand mechanisms of N2O release. Here, we discuss novel technologies that allow experiments on NO and N2O formation at high temporal resolution, namely NO and N2O microelectrodes and the dynamic analysis of the isotopic signature of N2O with quantum cascade laser absorption spectroscopy (QCLAS). In addition, we introduce other techniques that use the isotopic composition of N2O to distinguish production pathways and findings that were made with emerging molecular techniques in complex environments. Finally, we discuss how a combination of the presented tools might help to address important open questions on pathways and controls of nitrogen flow through complex microbial communities that eventually lead to N2O build-up.
Udert, K. M., & Wächter, M. (2012). Complete nutrient recovery from source-separated urine by nitrification and distillation. Water Research, 46(2), 453-464. doi:10.1016/j.watres.2011.11.020, Institutional Repository

In this study we present a method to recover all nutrients from source-separated urine in a dry solid by combining biological nitrification with distillation. In a first process step, a membrane-aerated biofilm reactor was operated stably for more than 12 months, producing a nutrient solution with a pH between 6.2 and 7.0 (depending on the pH set-point), and an ammonium to nitrate ratio between 0.87 and 1.15 gN gN−1. The maximum nitrification rate was 1.8 ± 0.3 gN m−2 d−1. Process stability was achieved by controlling the pH via the influent. In the second process step, real nitrified urine and synthetic solutions were concentrated in lab-scale distillation reactors. All nutrients were recovered in a dry powder except for some ammonia (less than 3% of total nitrogen). We estimate that the primary energy demand for a simple nitrification/distillation process is four to five times higher than removing nitrogen and phosphorus in a conventional wastewater treatment plant and producing the equivalent amount of phosphorus and nitrogen fertilizers. However, the primary energy demand can be reduced to values very close to conventional treatment, if 80% of the water is removed with reverse osmosis and distillation is operated with vapor compression. The ammonium nitrate content of the solid residue is below the limit at which stringent EU safety regulations for fertilizers come into effect; nevertheless, we propose some additional process steps that will increase the thermal stability of the solid product.
Bürgmann, H., Jenni, S., Vazquez, F., & Udert, K. M. (2011). Regime shift and microbial dynamics in a sequencing batch reactor for nitrification and anammox treatment of urine. Applied and Environmental Microbiology, 77(17), 5897-5907. doi:10.1128/AEM.02986-10, Institutional Repository

The microbial population and physicochemical process parameters of a sequencing batch reactor for nitrogen removal from urine were monitored over a 1.5-year period. Microbial community fingerprinting (automated ribosomal intergenic spacer analysis), 16S rRNA gene sequencing, and quantitative PCR on nitrogen cycle functional groups were used to characterize the microbial population. The reactor combined nitrification (ammonium oxidation)/anammox with organoheterotrophic denitrification. The nitrogen elimination rate initially increased by 400%, followed by an extended period of performance degradation. This phase was characterized by accumulation of nitrite and nitrous oxide, reduced anammox activity, and a different but stable microbial community. Outwashing of anammox bacteria or their inhibition by oxygen or nitrite was insufficient to explain reactor behavior. Multiple lines of evidence, e.g., regime-shift analysis of chemical and physical parameters and cluster and ordination analysis of the microbial community, indicated that the system had experienced a rapid transition to a new stable state that led to the observed inferior process rates. The events in the reactor can thus be interpreted to be an ecological regime shift. Constrained ordination indicated that the pH set point controlling cycle duration, temperature, airflow rate, and the release of nitric and nitrous oxides controlled the primarily heterotrophic microbial community. We show that by combining chemical and physical measurements, microbial community analysis and ecological theory allowed extraction of useful information about the causes and dynamics of the observed process instability.
Decrey, L., Udert, K. M., Tilley, E., Pecson, B. M., & Kohn, T. (2011). Fate of the pathogen indicators phage ΦX174 and Ascaris suum eggs during the production of struvite fertilizer from source-separated urine. Water Research, 45(16), 4960-4972. doi:10.1016/j.watres.2011.06.042, Institutional Repository

Human urine has the potential to be a sustainable, locally and continuously available source of nutrients for agriculture. Phosphate can be efficiently recovered from human urine in the form of the mineral struvite (MgNH4PO4·6H2O). However, struvite formation may be coupled with the precipitation of other constituents present in urine including pathogens, pharmaceuticals, and heavy metals. To determine if struvite fertilizer presents a microbiological health risk to producers and end users, we characterized the fate of a human virus surrogate (phage ΦX174) and the eggs of the helminth Ascaris suum during a low-cost struvite recovery process. While the concentration of phages was similar in both the struvite and the urine, Ascaris eggs accumulated within the solid during the precipitation and filtration process. Subsequent air-drying of the struvite filter cake partially inactivated both microorganisms; however, viable Ascaris eggs and infective phages were still detected after several days of drying. The infectivity of both viruses and eggs was affected by the specific struvite drying conditions: higher inactivation generally occurred with increased air temperature and decreased relative humidity. On a log–log scale, phage inactivation increased linearly with decreasing moisture content of the struvite, while Ascaris inactivation occurred only after achieving a minimum moisture threshold. Sunlight exposure did not directly affect the infectivity of phages or Ascaris eggs in struvite cakes, though the resultant rise in temperature accelerated the drying of the struvite cake, which contributed to inactivation.
Etter, B., Tilley, E., Khadka, R., & Udert, K. M. (2011). Low-cost struvite production using source-separated urine in Nepal. Water Research, 45(11), 852-862. doi:10.1016/j.watres.2010.10.007, Institutional Repository

This research investigated the possibility of transferring phosphorus from human urine into a concentrated form that can be used as fertilizer in agriculture. The community of Siddhipur in Nepal was chosen as a research site, because there is a strong presence and acceptance of the urine-diverting dry toilets needed to collect urine separately at the source. Furthermore, because the mainly agricultural country is landlocked and depends on expensive, imported fertilizers, the need for nutrient security is high. We found that struvite (MgNH4PO4·6H2O) precipitation from urine is an efficient and simple approach to produce a granulated phosphorus fertilizer. Bittern, a waste stream from salt production, is a practical magnesium source for struvite production, but it has to be imported from India. Calculations show that magnesium oxide produced from locally available magnesite would be a cheaper magnesium source. A reactor with an external filtration system was capable of removing over 90% of phosphorus with a low magnesium dosage (1.1 mol Mg mol P), with coarse nylon filters (pore width up to 160 ± 50 μm) and with only one hour total treatment time. A second reactor setup based on sedimentation only achieved 50% phosphate removal, even when flocculants were added. Given the current fertilizer prices, high volumes of urine must be processed, if struvite recovery should be financially sustainable. Therefore, it is important to optimize the process. Our calculations showed that collecting the struvite and calcium phosphate precipitated spontaneously due to urea hydrolysis could increase the overall phosphate recovery by at least 40%. The magnesium dosage can be optimized by estimating the phosphate concentration by measuring electrical conductivity. An important source of additional revenue could be the effluent of the struvite reactor. Further research should be aimed at finding methods and technologies to recover the nutrients from the effluent.
Etter, B., Tilley, E., & Udert, K. M. (2011). Urine as a resource in Nepal. Sandec News, 12, 16. , Institutional Repository

Depleting fertiliser supplies call for alternative nutrient sources. Promising low-cost technologies to recover nutrients from urine were therefore field-tested in Nepal.
Huber, S. J. (2011). Temperature dependent removal of sodium chloride (NaCl) from synthetic nitrified urine (Master thesis). 46 p. , Institutional Repository

Urine is the source of the major part of plant nutrients in municipal wastewater. Therefore, full nutrient recovery from source-separated urine is an attractive option for both treating wastewater and gaining a valuable fertilizer product. Full nutrient recovery can be achieved by first stabilizing collected urine by nitrification and then concentrating the urine by distillation. Since concentrations of all salts in urine increase with increasing removal of water also the sodium chloride (NaCl) content is high in the end. There are two problems related to NaCl, the first being the synergistic decomposition of ammonium nitrate by chloride and the second being soil salinity and sodicity related problems when applying the product as fertilizer. [...]
Kapałka, A., Fierro, S., Frontistis, Z., Katsaounis, A., Neodo, S., Frey, O., … Comninellis, C. (2011). Electrochemical oxidation of ammonia (NH4+/NH3) on thermally and electrochemically prepared IrO2 electrodes. Electrochimica Acta, 56(3), 1361-1365. doi:10.1016/j.electacta.2010.10.071, Institutional Repository

The electrochemical oxidation of ammonia (NH4+/NH3) in sodium perchlorate was investigated on IrO2 electrodes prepared by two techniques: the thermal decomposition of H2IrCl6 precursor and the anodic oxidation of metallic iridium. The electrochemical behaviour of Ir(IV)/Ir(III) surface redox couple differs between the electrodes indicating that on the anodic iridium oxide film (AIROF) both, the surface and the interior of the electrode are electrochemically active whereas on the thermally decomposed iridium oxide films (TDIROF), mainly the electrode surface participates in the electrochemical processes.
On both electrodes, ammonia is oxidized in the potential region of Ir(V)/Ir(IV) surface redox couple activity, thus, may involve Ir(V). During ammonia oxidation, TDIROF is deactivated, probably by adsorbed products of ammonia oxidation. To regenerate TDIROF, it is necessary to polarize the electrode in the hydrogen evolution region. On the contrary, AIROF seems not to be blocked during ammonia oxidation indicating its fast regeneration during the potential scan. The difference between both electrodes results from the difference in the activity of the iridium oxide surface redox couples.
Bourgeois, A. (2010). Electro-coagulation of phosphate frome urine (Master thesis). 43 p. , Institutional Repository

Problem: The most wastewater produced in modern countries is treated by centralised wastewater treatment plants which have a low technological flexibility and high financial costs. The phosphate in the wastewater, a nutrient, is burned and diverted into the rivers. Since the reserves of phosphate rock are limited this thesis tries to define a way to recover it by electro-coagulation.
Solution: Novaquatis (EAWAG) propose to separate the urine from wastewater and to treat it separately in a small scale reactor to recover the phosphate.
A method for the phosphate recovery from urine is the struvite precipitation. Struvite is usually obtained by the addition of magnesium mineral. The dosage control and storage of the powder aren’t well adapted to small reactors. The electro-coagulation of phosphate has potential to be a better solution at the household scale.
Process: The electro-coagulation of phosphate from urine is based on the electro-dissolution of a magnesium electrode. The dissolved magnesium reacts with phosphate and ammonium, present in urine, to struvite. The struvite is recovered and sold as fertilizer.
Thesis: The electro-coagulation isn’t yet a well known process. The thesis tried to define and to optimize the whole process. The design of a small scale reactor, a simple controlling and monitoring possibilities are studied. Finally the economical and technical suitability of the process is evaluated.
Method: Two metal plates, used as electrodes, are put into a one litre reactor filled with a synthetic solution simulating urine. The working electrode is made of magnesium and the counter-electrode of stainless steel. A constant voltage was applied, inducing the dissolution of magnesium. Many variables were measured during the phosphate elimination, like pH, current, conductivity, etc. A series of experiments was set up to optimize the process.
Experiment: To understand the process some basic experiments were done. Afterwards the electro-coagulation was performed with different voltages to find out an optimal one. It appeared that in some conditions the magnesium plate was covered with a white layer, a struvite layer, which inhibits the electro-coagulation process. How to prevent the formation of this layer is described.
Results: The first results were promising, the struvite was actually produced and the phosphate almost completely removed. The optimal voltage was defined in the range of +1.0V to +1.25V avoiding the struvite layer formation on the working electrode by lower voltage and the electrolysis of the solution at higher voltage.
A nice way to monitor the process is to follow the changes of the conductivity of the solution and the change of the working electrode potential. The rate of electro-dissolution of magnesium is dependent on the current, so by setting the current, we can control the process well, even stop it.
Suitability: The different experiments showed the process of electro-coagulation is undoubtedly a technologically suitable way to recover phosphate from urine. The process can only be profitable considering the saving costs by the wastewater treatment plant. The cost of the production of the magnesium electrode is difficult to be compensated by the selling of the struvite fertilizer.
Conclusion: The result of this thesis will certainly promote the process of electro-coagulation, since the process is working well and easy to control. The different open points are mentioned in order to confirm the promising results described in this project.
Hug, A. (2010). Phosphate recovery from urine by electrocoagulation (Master thesis). 38 p. , Institutional Repository

Phosphorus is an essential compound for plants. But the major phosphorus source for fertilizers - phosphate rock - is a limited resource. To close the nutrient cycle, phosphorus should be recovered from waste streams. Urine has a high phosphate content, which can be recovered as struvite.
Struvite is a magnesium-ammonium-phosphate (NH4MgPO4 · 6 H2O) and can be used as a slow release fertilizer in agriculture. As magnesium is the limited compound in urine, a magnesium source has to be added for struvite precipitation. Conventional methods consist in the dosage of a magnesium salt. Electrocoagulation on the other hand dissolves magnesium electrochemically from a magnesium electrode.
For electrocoagulation magnesium is oxidized to magnesium ions at the magnesium anode, water is reduced to hydrogen gas at the steel cathode. To enhance the reaction speed a voltage source can be added. The voltage source can either be applied between the magnesium and a reference electrode (magnesium potential, three electrode configuration) or between the magnesium and the steel electrode (cell voltage, two electrode configuration). The advantage of the three electrode configuration being that the magnesium potential determines directly the reactions that can take place at the magnesium electrode.
Two sets of experiments have been conducted: voltammetry and batch experiments. For voltammetry the applied magnesium potential was changed with time to detect electrode characteristics. For the batch experiments the voltage source (magnesium potential or cell voltage) was kept constant over time.
Voltammetry and batch experiments showed that the magnesium electrode is sensitive to layer formation at magnesium potentials below -800 mV. An electrode potential of -600 mV seemed to be a very appropriate potential concerning reaction speed and energy consumption. An electrocoagulation reactor can either be operated by applying an electrode potential or a cell voltage. Applying a cell voltage will be the easier configuration, as no potentiostat is needed. A cell voltage of at least 1000 mV should be applied to prevent layer formation.
The monitored cell voltage/electrode potential (depending on electrode configuration) showed a maximum/minimum as phosphate was removed from urine. It can therefore be used as a parameter to control the magnesium dissolution in order to not waste magnesium. A continuous reactor could then be operated in sequencing batch mode, using three tanks:
storage tank, electrocoagulation reactor and settling tank.
It has been shown that electrocoagulation is a very functional method to recover struvite from natural urine. The advantage of electrocoagulation against chemical dosing will be found in a high magnesium efficiency and in a high automation possibility.
Kapałka, A., Katsaounis, A., Michels, N. L., Leonidova, A., Souentie, S., Comninellis, C., & Udert, K. M. (2010). Ammonia oxidation to nitrogen mediated by electrogenerated active chlorine on Ti/PtOx-IrO2. Electrochemistry Communications, 12(9), 1203-1205. doi:10.1016/j.elecom.2010.06.019, Institutional Repository

The electrochemical oxidation of ammonia (NH3 and/or NH4+) in the presence of chloride was investigated on a Ti/PtOx–IrO2 electrode. It was shown that ammonia is effectively removed from solution via electrogenerated active chlorine. Based on mass balances, nitrogen is postulated to be the main product of ammonia electrolysis. In the bulk, the concentration of chloramines was low. This could be explained by the fact that the oxidation of ammonia takes place close to the electrode surface where an excess of chlorine relative to ammonia is ensured during the process. This results in the oxidation of ammonia to N2 and in a local pH decrease. As a result, chloramines were decomposed in the proximity of the electrode prior to diffusing into the bulk.
Kapałka, A., Joss, L., Anglada, Á., Comninellis, C., & Udert, K. M. (2010). Direct and mediated electrochemical oxidation of ammonia on boron-doped diamond electrode. Electrochemistry Communications, 12(12), 1714-1717. doi:10.1016/j.elecom.2010.10.004, Institutional Repository

Direct (non-mediated) electrochemical oxidation of ammonia on boron-doped diamond (BDD) electrode proceeds mainly at high pH (>8) via free ammonia (NH3) oxidation. To enhance ammonia oxidation on BDD at low pH (<8), where mainly ammonium (NH4+) is present, oxidation of ammonia was mediated by active free chlorine. In this process, electro-generated in situ active chlorine rapidly reacts with ammonia instead of being further electro-oxidized to chlorate at the electrode surface. Thus, active chlorine effectively removes ammonia from an acidic solution, while the formation of by-products such as chlorate and possibly perchlorate is minimized.
Kapałka, A., Cally, A., Neodo, S., Comninellis, C., Wächter, M., & Udert, K. M. (2010). Electrochemical behavior of ammonia at Ni/Ni(OH)2 electrode. Electrochemistry Communications, 12(1), 18-21. doi:10.1016/j.elecom.2009.10.026, Institutional Repository

The electrochemical oxidation of ammonia was investigated on a Ni/Ni(OH)2 electrode prepared by potential cycling of a Ni electrode in 1 M NaClO4. It was found that oxidation of ammonia is strongly pH dependent and proceeds mainly at pH values above 7. This indicates that NH3 rather than NH4+ is oxidized on nickel electrodes. Oxidation of ammonia occurs in the potential region of Ni(II)/Ni(III) redox activity resulting in formation of a clear peak. Ni/Ni(OH)2 is not deactivated during ammonia oxidation even at high ammonia concentrations. A considerable fraction of the ammonia was oxidized to nitrate (11%), while the rest were gaseous nitrogen compounds. It is postulated that nitrogen was formed via a mechanism involving direct electron transfer from ammonia to the anode whereas the formation of nitrate involved oxygen transfer from water to an ammonia molecule.
Marti, B. (2010). Bioelectrochemical removal of sulfur from source-separated urine (Master thesis). 32 p. , Institutional Repository

All of the sulfur in human excreta ends up as dissolved sulfate in the urine. If released to the environment, sulfate is not problematic because it is stable. However, if it comes in contact with water containing a large amount of organics, sulfate transformation to sulfide starts as soon as the water is depleted of oxygen and nitrate, producing a bad smell and intoxicating the microbiology. The largest problem in wastewater treatment is probably the corrosion in anaerobic sewer systems due to sulfide oxidation. Another problem is the H2S production during biogas generation, which necessitates gas washing. Since it is an essential plant nutrient [18] and a widely applied element in industry [23], recovering sulfur from urine can be of interest. Within the scope of a master thesis of 16 weeks the bioelectrochemical sulfate removal from stored, source-separated urine was analyzed. The iodometric method was applied to urine in order to measure dissolved sulfide, thiosulfate, and sulfite. In a microbial electrolysis cell a sulfate load of 4.10 ± 0.17 g SO2−4 -S m−2 biofilm surface d−1 was microbially transformed to sulfide which was subsequently oxidized to elemental sulfur at an anode potential of 0.06 V. Comparison between dissimilatory sulfate reduction with and without electrochemical sulfide oxidation showed an increase of the sulfate degradation rate of 30 % to 1.48 g SO2−4 -S m−2 biofilm surface d−1 when sulfide was electrochemically oxidized. A mass balance of sulfur over the reactor showed that dissolved sulfur disappeared in the reactor. Based on the sulfur balance, a sulfide oxidation rate was estimated yielding 0.35 g SH−-S m−2d−1. The process combination of biological sulfate reduction and subsequent partial sulfide oxidation to elemental sulfur was applied successfully to stored, source-separated urine. In a future work, the process parameters need to be improved, first of all the tradeoff between biofilm surface on the anode and free anode surface for sulfide oxidation. A separation of the biological and electrochemical processes would be suitable for further experiments on the bioelectrochemical sulfate reduction. Additionally a more throughout analysis of the conversion of the sulfur species in the reactor should be done. The limitations of the sulfate degradation need to be analyzed.
Morgenroth, E., Buergmann, H., & Udert, K. (2010). Functional diversity in wastewater treatment. Eawag News [engl. ed.], 69, 15-17. , Institutional Repository

Variations in influent loads pose major challenges for biological wastewater treatment. Could increased biodiversity allow for more stable operation, and does this mean that biodiversity should also be protected in wastewater treatment plants? Using molecular biological methods, we can now quantify biodiversity and specific groups of microorganisms in complex systems.
Morgenroth, E., Bürgmann, H., & Udert, K. (2010). Funktionelle Vielfalt in der Abwasserreinigung. Eawag News [dtsch. Ausg.], 69, 15-17. , Institutional Repository

Schwankende Zulauffrachten stellen die biologische Abwasserreinigung vor grosse Herausforderungen. Kann hier eine erhöhte Biodiversität helfen und ist Biodiversität also auch in der Kläranlage erstrebenswert? Molekularbiologische Methoden erlauben es uns heute, die Artenvielfalt und spezifische Organismengruppen in komplexen Systemen zu quantifizieren.
Obrecht, J. (2010). Online Überwachung biologischer Abwasserreinigungsprozesse (Master thesis). 75 p. , Institutional Repository

Der Anammox-Prozess (anaerobe Ammoniumoxidierung) ist eine Möglichkeit Stickstoff biologisch abzubauen. Anammox hat im Gegensatz zu Nitrifikation/Denitrifikation den Vorteil, dass kein leicht abbaubarer Kohlenstoff verbraucht wird. Die Anwendung dieses Prozesses in dezentralen Urinbehandlungsanlagen wird an der Eawag in Dübendorf seit 2008 in einer Pilotanlage getestet. Die Messungen mit einer Sauerstoff-, einer Leitfähigkeits- und einer pHSonde haben gezeigt, dass die Signale während eines Zyklus einen charakteristischen Verlauf aufweisen.
Das führte zur Vermutung, dass sich der Prozess anhand dieser drei Sondensignale überwachen lässt. Das Ziel war die Untersuchung folgender Frage: Können anhand einer Kombination der drei Parameter Sauerstoff, pH-Wert und Leitfähigkeit biologische Prozesse identifiziert und quantifiziert werden?
In der vorliegenden Arbeit werden folgende vier Hauptaufgaben vorgestellt:
• Tabelle zur quantitativen Bewertung der Sondensignale
• Quantifizierung des Stickstoffabbaus mittels der Leitfähigkeit
• Modellierung der Leitfähigkeit
• Unterscheidung von Anammox und heterotropher Denitrifikation anhand des pH-Werts und der Leitfähigkeit.
Die Tabelle zur qualitativen Bewertung der Sondensignale ist ein nützliches Mittel um rasch eine Aussage zum Zustand des Systems machen zu können. In der zur Verfügung stehenden Zeit, konnten nicht alle Störfälle beurteilt werden. Sie müssen noch modelliert werden, damit man die Tabelle vervollständigen kann.
Die Quantifizierung des Stickstoffabbaus durch die Leitfähigkeitsabnahme ist ein interessanter Ansatz. Bedingt durch einige Parameter - das Strippen von CO2 und der Abbau von organischen Stoffen zu Beginn des Zyklus - ist die Unsicherheit der Bestimmung des Stickstoffabbaus derzeit noch zu gross, um eine zuverlässige Aussage machen zu können. Es sind weitere Untersuchungen nötig um festlegen zu können, wie diese Parameter miteinzubeziehen sind.
Die Leitfähigkeit lässt sich mit der allgemeinen Formel gut berechnen. Werden bei der Berechnung alle gemessenen Ionen miteinbezogen, wird die Leitfähigkeit durch das Ergebnis der Modelle deutlich überschätzt. Ein besseres Resultat wird erzielt, wenn man die Leitfähigkeit mit der Aktivität modelliert.
Eine Unterscheidung von heterotropher Denitrifikation und Anammox ist zurzeit (noch) nicht möglich. Bei beiden Prozessen nimmt der pH-Wert zu und die Leitfähigkeit nimmt ab. Die modellierten Veränderungen sind so gering, dass die Sondensignale unter Einbezug der Messunsicherheit schwierig zu interpretieren sind. Zudem ist die Frage des Einflusses von Puffern noch nicht geklärt.
Zusammenfassend ist zu sagen, dass die Onlineüberwachung mit Sonden, die die beschriebenen drei Schlüsselsignale ermitteln, ein guter Ansatz ist. Dieses Vorgehen ermöglicht eine Prozessüberwachung ohne grossen Messaufwand. Der pH-Wert wird bereits heute für die Steuerung der Zykluslänge verwendet. Die Sauerstoffkonzentration gibt Auskunft über die Funktion der Belüftung und die Messdaten der Leitfähigkeit können evtl. in Zukunft für die Quantifizierung des Stickstoffabbaus verwendet werden.
Assumpta Ngozi, A. M. (2009). Nitrification of human urine using a membrane aerated biofilm reactor (MABR) (Master thesis). 49 p. , Institutional Repository

Membrane aerated bioreactors (MABR) provide attachment for biofilm and supply air for biological processes.
An MABR operated in coninously stirred tank reactor (CSTR) treats undiluted urine (high ammonium, pH value around 9) to produce NH4-NO3 with a pH value around 6. The main influence factors investigated in the system were mainly the free ammonia (FA), free nitrous acid (FNA) and carbonate concentration.
The experiment was designed into 3 phases. Phase 1 was operated in batch-mode using tapwater as start-up medium. Phases 2 and 3 were started with a conditioning saline solution and then switched to the CSTR mode. Activated sludge was used as inoculum for biofilm in phase 1. Sludge used to build conditioned biofilm in phase 2 was a mixture of equal volumes of activated sludge and sludge from a partial nitratation and anammox (PNAA) system. In phase 3, the biofilm was grown from activated sludge and the NOB of the biofilm were selectively cultured using 10ml batch doses of 0.5M NaNO2 .
Influent paramenters analysed were NH4, NO2, NO3, dissolved COD, total inorganic carbon (TIC) whilst in the effluent, the parameters determined were NH4, NO2, NO3 and TIC. Dissolved oxygen (DO) concentration and pH in the reactor were taken daily.
During phase 1, COD degradation and ammonium loss were observed. Nitrification was inhibited by FA concentration of above 300mg/l though the value later decreased to 40mg/l. Average oxygen concentration was 9mg/l and pH of the medium averaged above 8.0. Effect of FNA was not observed. During phase 2, a constant load of 0.12gN/d was supplied. FA concentration gradually increased to 40mg/l and eventually inhibited NOB activity but the AOB continuously produced nitrite. There was no FNA effect. Average oxygen concentration was 8mg/l and pH ranged between 7 and 8. In phase 3, varying loads of 0.05 to 0.22gN/d was delivered. Maximum concentration of FA was 0.07mg/l and the highest value of FNA was 0. 09mg/l. Average oxygen concentration was 7.0mg/l and pH averaged 6.5. There was hardly measurable carbonate in the system though NOB and AOB continuously functioned that a solution of ammonium nitrate (1:3) was produced at non-steady state.
Etter, B. (2009). Process optimization of low-cost struvite recovery (Master thesis). 53 p. , Institutional Repository

Struvite (MgNH4PO4·6H2O) recovery from wastewater streams has been known as an efficient nutrient recycling method. However, current research has predominantly addressed high-end solutions to overcome fertilizer shortages in agriculture and prevent eutrophication in receiving waters.
The present study focused on low-cost struvite recovery from stored human urine, by optimizing a process developed at pilot scale in the peri-urban settlement of Siddhipur in the Kathmandu Valley (Nepal). A combination of laboratory and field experiments were conducted to develop a design for an improved cost-effective struvite production reactor – completely constructed with locally available materials. [...]

La récupération de struvite (MgNH4PO4·6H2O) à partir d'eaux usées est connue en tant que méthode de recyclage de nutriments efficace. Néanmoins, la recherche actuelle se concentre principalement sur des solutions de haute gamme, afin de surmonter les pénuries d'engrais en agriculture ou de réduire l'eutrophisation de cours d'eaux récepteurs.
À travers l'optimisation d'un procédé développé à échelle pilote dans le village périurbain de Siddhipur dans la Vallée de Kathmandou (Népal), la présente étude vise à une récupération de struvite à bas coûts à partir d'urine humaine. La combinaison d'expérience de terrain et en laboratoire a conduit à la conception d'un réacteur – construit entièrement avec des matériaux locaux – de production de struvite amélioré. [...]
Goosse, P., Steiner, M., Udert, K. M., & Neuenschwander, W. (2009). NoMix Toilettensystem. Erste Monitoringergebnisse im Forum Chriesbach. GWA Gas, Wasser, Abwasser, 89(7), 567-574. , Institutional Repository

The NoMix toilet system of Eawag’s main building «Forum Chriesbach» has been in operation for three years. So far, NoMix toilets, waterless urinals and urine pipes do not show any clogging problems. Clogging was only observed in the siphons of some of the urinals. Due to the simple handling of exchanging the siphons, the problems could be solved easily. Toilets and urinals did not cause odour problems inside the building. However, outside the building (on the roof), odour problems occurred. The cause is ammonia gas emissions from the urine pipes. At the moment, the most important remaining problem for an efficient separation of urine and feces is the correct use of the NoMix toilets by non-acquainted users. New users have to be informed accordingly. A close collaboration with the maintenance service provider proved to be a critical factor for an optimal operation of the NoMix toilet system.
Kapałka, A., Fierro, S., Frontistis, Z., Katsaounis, A., Frey, O., Koudelka, M., … Udert, K. M. (2009). Electrochemical behaviour of ammonia (NH4+/NH3) on electrochemically grown anodic iridium oxide film (AIROF) electrode. Electrochemistry Communications, 11(8), 1590-1592. doi:10.1016/j.elecom.2009.06.003, Institutional Repository

The electrochemical behaviour of ammonia (NH4+/NH3) in sodium perchlorate at pH 9 has been investigated on electrochemically grown anodic iridium oxide film (AIROF) electrode. In base electrolyte at pH 9, the Ir(IV)/Ir(III) surface redox couple exhibits unusually large separation of the oxidation/reduction peaks (ΔEp~ 750 mV) due to the local pH changes within the oxide film. These local pH changes are induced by protons released/consumed during the Ir(IV)/Ir(III) redox activity. As a consequence, the local pH within AIROF changed up to 10 units during potential cycling. The presence of ammonia at pH 9 prevents these local pH changes because NH4+/NH3 buffer the solution inside the electrode. As a consequence, ΔEp of Ir(IV)/Ir(III) was reduced to 100 mV. It has been shown further that ammonia oxidation is mediated by Ir(V), resulting in the appearance of anodic peaks in forward and backward scans.
Kashekya, E. J. (2009). Struvite production from source separated urine in Nepal: the reuse potential of the effluent (Master thesis). 67 p. , Institutional Repository

Important amounts of nutrients excreted by humans are found in human urine. This provides the motivation for separating urine and recycling it, as fertilizer, back to agricultural land for food production. Urine diverting toilets have been increasingly being promoted in Nepal and more than 500 units have been installed since 2002 (Das and Kumar, 2008). However, potential drawbacks to urine handling systems are the risk of ammonia evaporation and the relatively large volumes to be handled. In that situation struvite technology has been established to trap the phosphates in a solid fertilizer. Using the technology could reduce the huge volume of urine and transporting cost. However, struvite production also generates effluent. Struvite effluent reuse has significant potential benefits on both a local and global scale, such as re-circulating plant nutrients like nitrogen and potassium back to agriculture.
This thesis explores the potential reuse of struvite effluent in Siddhipur Nepal. The hypotheses being investigated are that 1) preliminary struvite precipitation prevents clogging during drip fertigation with urine and 2) that drip-fertigation with urine is superior to bucket spreading, because the ammonia volatilization is strongly reduced.
When the nutrients in effluent are beneficially utilized through irrigation some amount of pollutants discharged into our waterways can be reduced.
In this study the small plots for drip irrigation and ammonia volatilization were established. The amount of clogging was based on measurements of head loss in the tank and time of application. The ammonia volatilization measurements were collected in each hour after application.
Boric acid was used to trap the ammonia volatilized in the plots. The method was successfully used to determine that more ammonia volatilized in the plot of the bucket application for up to 2.3 times as compared with drip effluent plot. The largest loss (11% of the applied N) was measured after application of 45 L of urine per plot. Virtually no volatilizations were detected (on the first 6hrs) when the urine was applied to the freshly tilled soil. The results also suggest that reuse of struvite effluent through drip irrigation is possible without full clogging (only 30% decrease of flow rate).
The reuse of effluent from a struvite reactor is beneficial in terms of the nutrients that are made available and when applied through drip irrigation the loss of ammonia is reduced. In addition, the reuse of effluent can contribute towards the reduction of importing the commercial fertilizers.
Kaufmann, M. (2009). Process parameters of a Microbial Electrolysis Cell (MEC) (Master thesis). 37 p. , Institutional Repository

Decentralized systems which treat separated wastewater streams according to their specific properties are quite promising according to the newest research results. The use of a microbial electrolysis cell (MEC) to treat urine and produce hydrogen gas is such a novel technology. The MEC consists of two chambers which are connected via a cation exchange membrane. By applying voltage, the oxidation of organic substrate (assisted by exoelectrogens) at the anode can be coupled with a proton reduction at the cathode. EAWAG takes part in the investigations and set a MEC into operation in February 2009. The goal of this Master project is to understand and quantify the influence of some of the most important process parameters such as applied voltage, temperature and pH.
The chronoamperometry measures the current at stepwise higher applied voltages. The influence of the applied voltage on the system performance was linear before reaching slowly a limit. The needed minimum voltage was determined to 238 mV. Those chronoamperometric curves gave indications that the system got diffusion limited with time. The coulombic efficiency represents the ratio between produced hydrogen according to the measured current and the theoretical possible hydrogen production calculated with a COD balance. The low coulombic efficiency of 57.7% leads as well to the assumption, that other bacteria degrade the organic substrate. Once the MEC was opened and a biofilm consisting of two layers could be observed: the wanted exoelectrogens and undesired other bacteria. By analyzing samples from the anode and the cathode chamber the sulphate degrading bacteria could be quantified to contribute 3% to the COD-consumption. Additional measures such as installing an oxygen-sensor to judge the possibility of aerobic growth or off-gas measurements to quantify the methanogenic growth should be considered. After classifying the bacteria, parameters to damage them uniquely should be investigated.
The temperature experiment presented a linear increase in performance of 2.3% per degree. As the system is probably diffusion limited, the effect was caused by a bigger diffusive flux due to a temperature-dependent diffusion coefficient. The reaction at the cathode was not limiting at a pH between 6 and 9. When the pH was changed and the anode potential was fixed, the measured current increased 25% per pH unit. The growth curve of the exoelectrogens depends therefore linearly on the pH. If the applied voltage was constant, the current increase reached a limit, as due to the higher pH, the anode potential decreased. Sample analysis from the anode and cathode chamber proved, that the proton transport via the membrane is insignificant. The pH is therefore controlled in both chambers by adding sodium hydroxide solution or hydrochloric acid. If some day a perfect proton-exchange membrane is developed, proton-gradients might play a role and the before mentioned results from the pH-experiments might change. Nowadays, instead of adding chemicals, the effluent of the anode could be connected to the influent of the cathode. At the same time, this would unfortunately decrease the hydrogen purity. Some improvements are still needed, before the first full-scale reactor can be built. Another problem will be that resistances get bigger in a full-scale reactor. The measured resistances during the experiment decreased linearly with temperature and plotted against the applied voltage, a minimum resistance at 650 mV was found. For a full-scale reactor it would pay off to choose the operation parameters such that resistances get minimized.
So there is still a long way to go before the first full-scale reactor will be set into operation. The biggest problems for the analyzed reactor at the moment are the growing competition and the insignificant proton-diffusion.
Tilley, E., Gantenbein, B., Khadka, R., Zurbrügg, C., & Udert, K. M. (2009). Social and economic feasibility of struvite recovery from urine at the community level in Nepal. In K. Ashley, D. Mavinic, & F. Koch (Eds.), International conference on nutrient recovery from wastewater streams (pp. 169-178). Retrieved from https://www.susana.org/en/knowledge-hub/resources-and-publications/library/details/1123, Institutional Repository

In the face of increasing phosphorus prices, Nepal, like all agrarian societies is in imminent need of a low-cost, sustainable source of phosphorus and nitrogen.
The town of Siddhipur in the Kathmandu valley was selected as a study site to determine the feasibility of establishing a community-scale struvite processing centre using source-separated urine as a feedstock. Focus groups, workshops and household questionnaires were used to determine cultural acceptability and willingness to pay. Urine quality and quantity measurements, along with fertilizer cost analysis were used to determine the economic feasibility. A regression analysis using the current, local value of the nutrients was used to calculate the theoretical value of struvite; the estimated nutrient value of struvite was found to be 24–41 NRp per kilogram, which is in the same range as locally available Diammonium Phosphate (DAP). The production of struvite would currently cost about 25 NRp/kg due to high prices of available magnesium sources. Nevertheless, struvite precipitation can be economically feasible for at least three reasons. First, Nepal possesses own magnesite deposits, which might allow to produce cheaper magnesium sources. Second, customers are likely to pay more for locally produced struvite than for imported synthetic fertilizers Third, the effluent from struvite precipitation can also be used as a valuable and efficient nitrogen and potassium fertilizer. Despite shadow-pricing based on the constituent nutrients, the true value of struvite can not be known until it is produced and sold.
Tilley, E., Etter, B., Gantenbein, B., Khadka, R., & Udert, K. M. (2009). Struvite from urine in Nepal (STUN). Sandec News, 10, 4-5. , Institutional Repository

A new project in Nepal examines whether the production of fertiliser from urine can inspire residents to take up improved sanitation, while reducing their dependency on imported chemicals. By harvesting urine and converting it to “struvite”, the farmers of Siddhipur may better resist the coming years of fertiliser shortages.
Udert, K. M., & Siegrist, H. (2009). Anorganische Ausfällungen. In Trinkwasser- und Faulwasserleitungen. GWA Gas, Wasser, Abwasser, 89(11), 881-886. , Institutional Repository

Deposits and blockages from inorganic precipitation can adversely affect the operation of sewage treatment plants and domestic water supplies and result in substantial costs. Whilst the problem is generally well-known for hard drinking water, there is an increasing number of reports on precipitation in sludge water treatment in sewage plants, particularly plants with biological elimination of phosphates. This article discusses the chemical conditions for precipitation. Using the examples of drinking water and digester supernatant, it examines the most important chemical parameters and the key environmental influences – solubility of the solid phases, the composition of the water, pH value, release of carbon dioxide, biological decomposition processes, temperature and ionic strength. This article shows how the supersaturation of mineral solutions can be calculated.
Winkler, R. (2009). Urine treatment with microbial fuel cells. Inhibition effects of ammonia compounds (Master thesis). 32 p. , Institutional Repository

Microbial fuel cells (MFC's) have been operated with manifold substances. Experiments with municipal wastewater, swine wastewater and even brewery wastewater had been successfully conducted. In previous studies the application of separated urine, with its comparable high energy content, showed breakdown of electricity generation. Studies with MFCs showed inhibition e ects due to salinity, ammonium concentration or pH. Which of these factors in urine is limiting, was to determine in this study.
For these experiments a two chamber MFC with graphite electrodes was used. At the cathode a ferricyanide solution was used as nal electron acceptor. In the startup ammonium concentration was low in the anode solution and pH was set to 7 with the help of a phosphate bu er. Ionic strength was from the beginning as high as in urine. Acetate was used as substrate and electron donor. After a certain power output was reached ammonium was continuously increased until the maximal concentration of 6.35 gN/l. In the next experiment pH was stepwise increased from pH 7 to pH 9.
Current generation showed a strong temperature dependence. It could be modeled well by the arrhenius approach. Power output was therefore doubled by an increase of temperature from 15 °C to 25 °C. Maximal power density of the cell was 180 mW/m2. An increase of ammonium concentration to 6.35 gN/l did not lead to a breakdown in power output as in earlier studies. Though a slight decrease in power output was observed, it is not clear if that was caused by the ammonium concentration. The increase of pH from 7 to 9 lead to an increase of power output from 1.3 to 8.2 mW/m2. An ammonia concentration up to 3.4 gN/l did apparently not have an e ect on exoelectrogenic bacteria.
All the tested parameters did not inhibit power output substantially. Therefore urine treatment with microbial fuel cells still seems to be a practicable solution even tough other possible inhibitory factors must be checked and stored urine has to be applied as well.
Clauwaert, P., Tolêdo, R., van der Ha, D., Crab, R., Verstraete, W., Hu, H., … Rabaey, K. (2008). Combining biocatalyzed electrolysis with anaerobic digestion. Water Science and Technology, 57(4), 575-579. doi:10.2166/wst.2008.084, Institutional Repository

Biocatalyzed electrolysis is a microbial fuel cell based technology for the generation of hydrogen gas and other reduced products out of electron donors. Examples of electron donors are acetate and wastewater. An external power supply can support the process and therefore circumvent thermodynamical constraints that normally render the generation of compounds such as hydrogen unlikely. We have investigated the possibility of biocatalyzed electrolysis for the generation of methane. The cathodically produced hydrogen could be converted into methane at a ratio of 0.41 mole methane mole-1 acetate, at temperatures of 22 ± 2°C. The anodic oxidation of acetate was not hampered by ammonium concentrations up to 5gNL-1. An overview is given of potential applications for biocatalyzed electrolysis.
Neuenschwander, W. (2008). Stickstoffbilanz der NoMix Anlage zur Abwasserstoffstromtrennung (Master thesis). 58 p. , Institutional Repository

In Nordeuropa wurde ein energieintensives System aufgebaut, das einerseits Ammonium und Nitrat für die Landwirtschaft herstellt, anderseits die gleichen Moleküle in der Kläranlage eliminiert. Da in häuslichem Abwasser nahezu 80% des gesamten Stickstoffs aus menschlichem Urin stammen, zielen neuartige Sanitärkonzepte auf Urintrennung und -verwertung ab, um den N-Kreislauf zu schliessen. Jedoch sind mehrere Pilotprojekte zu dem Ergebnis gekommen, dass die Stickstoffkonzentrationen in gelagertem Urin im Vergleich zu frischem Urin stark abnehmen. Dies haben Beobachtungen an der Eawag in Dübendorf bestätigt, wo im Jahre 2005 15 Trenntoiletten und 2 Lagertanks installiert wurden (NoMix-Anlage).
Die Untersuchungen dieser Diplomarbeit haben ergeben, dass die Ausgasung von NH3 während des Transports und der Lagerung für 30-60% Stickstoffverlust verantwortlichist. Der Kamineffekt treibt Ammoniak aus der natürlichen Belüftungsleitung heraus. Dieses Gas wurde mit Hilfe von „Impinger“ erfasst und sein Massenstrom in Beziehung zur Aussentemperatur gesetzt, um die Ausgasung über Zeit modellieren zu können. Als Beitrag zur Konzentrationsabnahme spielt auch die Verdünnung mit Spülwasser eine Rolle. Diese beruht auf einer Designschwäche der eingesetzten Trenntoilette, die bei Anwenderfehlbenutzung Spülwasser durch ein Ventil zum Urintank fließen lässt. Die Bilanz der Stickstofffracht zeigt die Schwäche der bestehenden NoMix-Anlage hinsichtlich der Urinwiederverwertung auf. Im Kapitel "Systembeurteilung" werden leichte  Umbaumöglichkeiten aufgezeigt, die die Effizienz dieses Abwassertrennkonzeptes steigern und den Eintrag von Ammoniak in der Umwelt mindern können.

In Northern Europe industrial food production relies on synthetic nitrogen fertilizer, the massive application of which has adverse effects on the environment. On the other hand the same compounds naturally present in urban wastewater are removed in expensive treatment plants. Urine source separation technology seems to be a promising concept that could recover 80% of nitrogen from the urban wastewater and close the nutriment cycle. However, a significant number of pilot projects showed that the nitrogen concentration of the stored urine is much lower than expected. The EAWAG confirmed the same finding through investigation of the installed urine collecting system, composed of 15 NoMix toilets and 2 collecting tanks.
The analysis of this diploma thesis shows that the ammonia volatilisation during the transport and storage of the urine is largely responsible for the low concentration in the tank. Between 30 and 60 % of total nitrogen input gas out of the ventilation pipe,depending on the outdoor temperature (stack effect). The ammonia flow could be measured with “Impinger” and modelled over the time. The weak design of that toilet prototype combined with wrong use let flush water reach the tank and enhance the decrease of concentration. The nitrogen balance reveals the low N-recovery of urine in that NoMix plant. The concluding remarks of this thesis point at improvements regarding the efficiency of the system and the ammonia diffusion in the environment.
Udert, K. M., Kind, E., Teunissen, M., Jenni, S., & Larsen, T. A. (2008). Effect of heterotrophic growth on nitritation/anammox in a single sequencing batch reactor. Water Science and Technology, 58(2), 277-284. doi:10.2166/wst.2008.389, Institutional Repository

The combination of nitritation and autotrophic denitrification (anammox) in a single sequencing batch reactor (SBR) is an energy efficient process for nitrogen removal from high-strength ammonia wastewaters. So far, the process has been successfully applied to digester supernatant. However, the process could also be suitable to treat source-separated urine, which has very high ammonium and organic substrate concentrations (up to 8,200 gN/m3 and 10,000 gCOD/m3). In this study, reactor performance was tested for digester supernatant and diluted source-separated urine. Ammonium concentrations in both solutions were similar (between 611 and 642 gN/m3), thus reactor performance could be directly compared. Differences were mainly due to higher activity of heterotrophic bacteria in urine. Nitrogen removal was slightly higher for source-separated urine, because heterotrophic bacteria denitrified the nitrate that was produced by anammox bacteria. In spite of higher heterotrophic growth with source-separated urine, calculated sludge concentrations at steady state were higher with digester supernatant due to accumulation of inert particulate organic matter from the influent. Although the sludge concentrations are less problematic for source-separated urine, process instabilities are more likely, because lower pH values are reached and heterotrophic denitrification can cause sudden increases of nitrite concentrations and/or nitric oxide. Both compounds inhibit aerobic ammonium oxidizing bacteria, heterotrophic bacteria and, most importantly, anammox bacteria. Nitrite and nitric oxide production by heterotrophic denitrification must be better understood to optimize nitritation/anammox for source-separated urine.
Walker, M. (2008). Phosphorus removal and recovery in source separated urine through adsorption and electrochemical magnesium dissolution (Master thesis). 28 p. , Institutional Repository

Urine separation is a very interesting process to recover phosphate from wastewater because it contains 550 mg PO4-P l-1. The preferred technology at the moment is struvite precipitation by the addition of MgCl2 or MgO. This is not ideal at the household level, as the particularly dosage of the correct amount of magnesium salts is not very easy. Thus the technical feasibility of two alternative technologies was estimated in batch experiments at the lab-scale: adsorption of phosphate on GFH and calcite, or phosphate precipitation by electrochemical dissolution of magnesium.
The adsorption of phosphate out of untreated synthetic urine (pH=8.9) on a typical GFH/calcite mix (7:3) obtained maximally a load of 9 mg PO4-P g-1 adsorbent which was considered to be insufficient.
Further tests were conducted on synthetic urine after nitrogen removal (pH=6.3). GFH showed very good adsorption capacity of 47.5 mg PO4-P g-1 GFH according to a Langmuir isotherm and high affinity to phosphate (32 mg PO4-P g-1 can be reached at 25 mg PO4-P l-1 in solution). However, the adsorption kinetics was rather slow, as 7 days were needed with grain size 0.8-1.25 mm to get in equilibrium. The application of a surface diffusion model could not well approximate the equilibrium time due to the high solute concentrations. 75% of the adsorbed phosphate could be recovered by 7 days desorption in 0.1 M Na(OH).
The addition of calcite was shown not to decrease the adsorption/desorption properties of GFH at pH=6.3 while its maximal phosphate load at that pH was maximally 7.4 mg PO4-P g-1, thus too small.
The process of electrochemical magnesium dissolution is shown to be a technically feasible process. Very good magnesium (99%) and current (over 100 %) efficiencies were obtained by applying a constant current (1.95/3.9 mA cm-2] on two magnesium electrodes plunged in untreated synthetic urine when the polarity was changing every 30 minutes until phosphate was depleted. Current efficiencies above 100% are thought to be due to Local Cell Action which leads to magnesium electrode self-dissolution. A reduction of current efficiency was observed with time, as a precipitation layer formed on the electrodes. This layer had an impact on the energy needed to resolve the magnesium (up to 4 Wh g-1 P) but also on the current efficiency which decreased with time in otherwise equal experiments.
The same passivation behaviour of the sacrificial magnesium was observed when stainless steel was used as cathode. By their intrinsic potential difference (measured as 1.2 V) , elimination rates of 0.29 mg PO4-P l-1 h-1cm-2 were observed. The current efficiencies were lower than in the experiments with two magnesium electrodes, ranging around 50%, depending negatively on the period the magnesium electrode was used and on the applied current intensity. This is thought to be due to the passivation of the electrode and to the fact that more self-dissolution could occur if the electrodes are longer in contact with urine. One series of measurements furthermore suggests that the oxidation of chloride to chlorine gas could account for a substantial part of the inefficiencies.
No of pH, conductivity and voltage measurement could be identified as process control master variable, as it a difference in absolute value cannot be estimated,
Unfortunately, neither of pH, conductivity and voltage measurement could be identified as potential process control because their behaviour was not observed to change when phosphate in solution was depleted.
Zöllig, H. (2008). Urine treatment in microbial fuel cells (Master thesis). 52 p. , Institutional Repository

The identification of decentralized urine treatment processes is a crucial issue considering source separating sanitary systems (NoMix technology). In this work the suitability of urine treatment with microbial fuel cells (MFCs) has been tested in the laboratory. MFCs hold great promises for urine treatment, since organic substances and nitrogen can be eliminated at the anode and cathode respectively.
First, a MFC was started based on synthetic wastewater containing acetate in the anodic and nitrate in the cathodic influent to eliminate COD using a denitrifing cathode. Unfortunately, the denitrification process at the cathode never started. Instead of nitrate oxygen was the electron acceptor, although oxygen was only present in small amounts of approximately 0.3 mgO2/L .
In a second experiment the anode was fed with 30-,10- and 3-times diluted synthetic urine solutions, corresponding to urine after storage, again containing acetate as COD. At the cathode oxygen was supplied as electron acceptor by aeration of the catholyte. The cell was characterized in each operation state by means of electrode measurements, current interruption tests, cell polarization and power curves.
For a reference measurement taken when the anode was fed with synthetic wastewater prior to the changeover to 30-times diluted synthetic urine, the maximum power point (MPP) was 11.6 W/m3NAC. In the transition state from synthetic wastewater to 30-times diluted synthetic urine, a MPP of 16.0 W/m3NAC was reached. At close to steady state conditions with 30-times diluted synthetic urine as anolyte, the MPP was 14.3 W/m3NACC. With a MPP of 11.8 W/m3NAC, the maximum attainable power in the case of a 10-times diluted synthetic urine, went back to a level similar to the reference case. The reduction in maximum attainable power with decreasing dilution can be explained with a higher internal resistance of the cell, compensating the positive effect of increasing pH on the anodic reaction reduction potential. Furthermore, an increased overpotential at the anode was calculated for a 10-times diluted synthetic urine anolyte. When a 3-times diluted solution was fed to the anode, the power density collapsed and could not be recovered by going back to a 10-times diluted solution.
These findings suggest that anodic bacteria grown in synthetic wastewater are not able to sustain COD elimination even in diluted synthetic urine.
Kind, E. (2007). Simultane Ammoniumoxidation von aeroben und anoxischen Ammoniumoxidierern. Experimente und Modellierung mit Faulwasser und Urin (Master thesis). 67 p. , Institutional Repository

Urin macht weniger als 1% des Abwasservolumens aus, ist aber für rund 80% der Stickstoffbelastung verantwortlich. Würde Urin nicht ins Abwasser gelangen, sondern bereits in der Toilette getrennt gesammelt und anschliessend dezentral behandelt, so wären die Stickstofffrachten in die Kläranlagen bedeutend geringer. Die in der Kläranlage eingesetzte Technik könnte dadurch vereinfacht und verbilligt werden und die gesetzlichen Grenzwerte zur Belastung der Gewässer mit Nährstoffen könnten mit geringerem Aufwand eingehalten werden. Um ein solches System dezentral zu betreiben, bedarf es einerseits kleiner, selbständig funktionierender Anlagen und andererseits braucht es ein geeignetes Verfahren. In der vorliegenden Arbeit wurde im Blick auf diese zwei Anforderungen einer solchen Anlage in einem einstufigen Reaktor im SBR-Betrieb die simultane Ammoniumoxidation von aeroben und anoxischen Ammonium Oxidierern (AOB und Anammoxbakterien) zur Stickstoff-entfernung aus Faulwasser und Urin untersucht. Dazu wurden Versuche zur Bestimmung der Vorgänge im Reaktor unter verschiedenen Belüftungsraten und Substraten durchgeführt und ein mathematisches Modell erstellt um die Abläufe im Reaktor zu simulieren. Im Modell wurden neben den biologischen Prozessen die chemischen Gleichgewichte berücksichtigt und zusätzlich der pH und die Leitfähigkeit simuliert. Implementiert wurde das Modell in Berkeley Madonna. In der Arbeit konnte gezeigt werden, dass Anammoxbakterien durchaus mit Sauerstoffkonzentrationen im tieferen Bereich (<0.2 gO2m-3) umgehen können. Die Modellierung hat gezeigt, dass die Anammoxbakterien nicht nur eine aerobe Phase ungeschädigt überstehen, sondern in dieser sogar aktiven Stoffumsatz zeigen. Simultane aerobe und anoxische Ammoniumoxidation ist somit möglich. Dies bedeutet für die Praxis, dass beide Bakteriengruppen in einer einstufigen Anlage vorhanden sein können. Für die Simulation der Leitfähigkeit und des pHs wurde ersichtlich, dass bei der Leitfähigkeit die Ionenstärke im Reaktor berücksichtigt werden muss und dass der pH stark durch chemische und physikalische Prozesse beeinflusst wird. Im Bezug zum längerfristigen Betrieb mit Urin konnte keine abschliessende Aussage gemacht werden. Es scheint aber, dass das Anammoxverfahren ideal zur Entstickung geeignet ist, da mit dem Substrat aus dem Urin eine vollkommene Eliminierung des Stickstoffes möglich wird.
Larsen, T. A., Maurer, M., Udert, K. M., & Lienert, J. (2007). Nutrient cycles and resource management: implications for the choice of wastewater treatment technology. Water Science and Technology, 56(5), 229-237. doi:10.2166/wst.2007.576, Institutional Repository

We look at the most important issues of the global nitrogen and phosphorus cycle and conclude that the nutrients from human metabolism are of no importance for the global nitrogen cycle and of minor importance for the global phosphorus cycle. However, for water pollution control, N and P from the human metabolism are of extreme importance. Nitrogen is mainly an issue for coastal waters, whereas P is an issue for freshwater and coastal areas alike. It is by now generally recognised that coastal ecosystems are exceedingly important for human well-being and at the same time highly endangered. The recycling issue is of high importance in areas where nutrient application is low due to economic constraints. NoMix technology (urine source separation) holds a large promise to become an efficient mainstream technology. The largest short-term potential is found in densely populated areas in coastal areas without existing infrastructure and in areas with nutrient deficiency, especially in urban areas with a large nutrient potential. We believe, however, that these technologies will, with time, also become competitive in Europe.
Teunissen, M. (2007). Nitrogen removal from urine. Optimization of simultaneous ammonium oxidation by AOB, Anammox and heterotrophic bacteria (Master thesis). 33 p. , Institutional Repository

Up to 80 percent of the nitrogen and 50 percent of the phosphorus in the wastewater streams that enter the wastewater treatment plant (WWTP) comes from urine but urine accounts for only one percent of the wastewater stream. If urine is collected and treated separately, water pollution can be controlled better, it might be possible to close nutrient cycles and WWTP’s can be dimensioned smaller and the risk of ammonium discharges from combined sewer overflows can be reduced.
In this work the possibilities are investigated to remove nitrogen from urine in a sequencing batch reactor (SBR) with the help of ammonium oxidizing bacteria, Anammox bacteria and heterotrophic bacteria.
The SBR was first operated with digester supernatant to replace the bulk volume. Hereafter it was operated with five time diluted urine. The urine was diluted five times to have about the same concentrations as in the digester supernatant. In the beginning of the operation of the reactor each batch started with an anoxic phase to facilitate the use of nitrate for the degradation of dissolved organic substrate. The goal was to reduce nitrite and COD concentrations concomitantly.
With experiments it could be shown that in increase of the air flow from 40 mL/min to 50 mL/min
did not increase the oxygen concentration in the reactor. It could also be shown that during the aerobic phases nitrite build up takes place; the Anammox bacteria are too slow to reduce all the nitrite that is produced by the ammonium oxidizing bacteria. In anoxic phases nitrite reduction takes place.
The efficiency of the reactor can be enhanced by operating the system with continuous aeration. In this way nitrifying bacteria and Anammox bacteria can work continuously what makes the batches shorter. However, when the system was changed to continuous aeration the nitrite concentration in the reactor increased a lot. This was caused by reduction of nitrate to nitrite by heterotrophic bacteria and nitrite production in the sedimentation phase. The initial anoxic phase was deleted and the batches ended with an anoxic phase for the Anammox to reduce the nitrite concentrations. It was not possible to operate the reactor with continuous aeration.
Higher pH values in the reactor have positive effects on the nitrogen removal rate but not at the reduction of the total nitrogen concentration. The pH in the reactor can be increased by exchanging more of the volume with urine, by adding basic chemicals or by stripping of CO2. It could also be shown that long batches (about 30 hours) are not better for the nitrogen degradation compared to shorter batches (about 15 hours) because in the second half of the batch only seven percent more degradation is reached.
Udert, K. (2007). NoMix begins in the bathroom. Eawag News [engl. ed.], 63, 11-13. , Institutional Repository

The basic idea of the NoMix toilet is simple: urine is drained - separately from other wastewater - into a collection tank. However, urine pipes can easily be blocked by mineral precipitates, and nutrient concentrations in the urine collected may be lower than expected. The results of our laboratory experiments and computer simulations should facilitate the development of improved appliances in collaboration with the sanitary technology sector.
Udert, K. M., Larsen, T. A., & Gujer, W. (2006). Fate of major compounds in source-separated urine. Water Science and Technology, 54(11-12), 413-420. doi:10.2166/wst.2006.921, Institutional Repository

Urine separation is a promising alternative to present-day’s waste water management. It can help to manage our nutrient flows in a sustainable way. Currently, techniques are being developed to recycle and treat source-separated urine. These techniques, however, must consider the spontaneous processes that change the separated urine. The initial cause of changes is the contamination with microorganisms, which can hardly be avoided in urine-collecting systems. The most important transformation processes are microbial urea hydrolysis, mineral precipitation and ammonia volatilisation. Additionally, a variety of microorganisms, including pathogens, may grow in source-separated urine. In this paper we give an overview of the effects that the spontaneous transformation processes may have. We focus on nitrogen, phosphorus, magnesium, calcium, potassium, sulphur, organic substances, pathogens and the buffering capacity. The discussion is based on own research results and literature reviews. This overview will help to develop appropriate technologies for urine recycling.
Udert, K. M., Lienert, J., & Larsen, T. A. (2006). Novaquatis – Neue Wege in der Siedlungswasserwirtschaft. In J. Pinnekamp (Ed.), Gewässerschutz - Wasser & Abwasser - GWA: Vol. 204. 1. Aachener Kongress dezentrale Infrastruktur Wasser - Energie - Abfall (p. (13 pp.). Aachen: Gesellschaft zur Förderung der Siedlungswasserwirtschaft an der RWTH Aachen e.V. , Institutional Repository
Udert, K. M., Larsen, T. A., & Gujer, W. (2005). Chemical nitrite oxidation in acid solutions as a consequence of microbial ammonium oxidation. Environmental Science and Technology, 39(11), 4066-4075. doi:10.1021/es048422m, Institutional Repository

In long-term experiments with membrane aerated biofilm reactors we observed complete nitrite oxidation in highly concentrated ammonium nitrite solutions with a contaminant pH decrease to values below 3. The maximum initial concentration for ammonium was 42 mM and for nitrite was 41 mM. We hypothesized that (1) acid-tolerant ammonium oxidizing bacteria were responsible for the pH decrease, and (2) chemical processes caused complete nitrite oxidation at low pH values. To test this hypothesis we set up a mechanistic computer model based on kinetic data from literature and we validated the model with additional experiments. The simulations fitted the measurements very well. Additionally, an experiment with the inhibitor allylthiourea showed that ammonium-oxidizing bacteria were active at pH values far below 5.5. Experiments in a sterile reactor confirmed the chemical nitrite oxidation to nitrate. Nitrogen balances revealed that 8 ± 4% of the initial nitrogen (ammonium, nitrite, and nitrate) were lost during the cycles. On the basis of measurements and simulations we concluded that volatilization was responsible for the significant nitrogen loss. We estimated that about half of the lost nitrogen volatilized as nitrous acid HNO2. The rest mainly volatilized as dinitrogen N2 and nitrous oxide N2O.
Udert, K. M., Larsen, T. A., Gujer, W., & Högger, R. (2004). Fällungsprodukte in Urinalen und NoMix-Toiletten. GWA Gas, Wasser, Abwasser, 84(12), 913-920. , Institutional Repository

Precipitates from urine cause severe blockages in urinals of public restrooms, waterless urinals and NoMix toilets.
This paper presents a study in which the precipitation phenomena were investigated in detail.
The results show:
- the precipitates mainly consist of the phosphate minerals struvite and hydroxylapatite
- the bacterial degradation of urea triggers precipitation
- the use of flushing water reduces the formation of precipitates and is not the promoter
The study helps to develop processes that prevent blockages caused by urine precipitation. Possible approaches are presented in this paper.
Udert, K. M., Högger, R., Larsen, T. A., & Gujer, W. (2004). Urinausfällungen in Urinalen und NoMix-Toiletten. Installateur, 11, 46-48. , Institutional Repository

Die Siphons und Leitungen von öffentlichen, hochfrequentierten Urinalen können sehr rasch verstopfen. Ein gutes Beispiel dafür sind die Urinale im Ankunftsterminal A des Flughafens Zürich. Die Siphons und Leitungen dieser Urinale müssen rund alle drei Monate ausgewechselt bzw. gereinigt werden.
Udert, K. M., Larsen, T. A., & Gujer, W. (2003). Biologically induced precipitation in urine-collecting systems. Water Science and Technology: Water Supply, 3(3), 71-78. doi:10.2166/ws.2003.0010, Institutional Repository

Precipitation in urine-separating toilets (NoMix toilets), waterless urinals, and conventional urinals causes severe maintenance problems. Additionally, the partial fixation of nutrients in precipitates may affect the later use and treatment of source-separated urine. The goal of this study was to characterise the mineral composition of the precipitates and to identify the main causes for precipitation. X-ray diffraction analysis showed that the main crystalline compounds are struvite, hydroxyapatite, and calcite. We measured concentrations in the solutions of the traps and of the urine collection tank for estimating saturation indices, extent of urea degradation, urine dilution, and elimination of solutes. Our results indicate that bacterial urea degradation triggers precipitation. The composition of the precipitates depends on the urine dilution with flushing water: in low diluted urine, struvite is the main compound, while calcite dominates in systems with high urine dilution. HAP occurs over a wide range of dilution factors. A high fraction of phosphate is incorporated into the precipitates. Dilution with tap water increases this fraction by providing the limiting calcium and magnesium ions. Currently, constructing exchangeable traps seems to be the best solution to deal with problematic precipitation.
Udert, K. M., Larsen, T. A., & Gujer, W. (2003). Estimating the precipitation potential in urine-collecting systems. Water Research, 37(11), 2667-2677. doi:10.1016/S0043-1354(03)00071-X, Institutional Repository

Precipitation in urine-separating toilets (NoMix toilets) and waterless urinals causes severe maintenance problems and can strongly reduce the content of soluble phosphate. In this study, we present a computer model for estimating the precipitation potential (PP) in urine-collecting systems. Calculating the PP enables to predict the composition and mass concentration of precipitates. We used our computer model for investigating how urea hydrolysis and dilution with flushing water affect precipitation. In a previous study, we found that microbial urea hydrolysis (ureolysis) triggers precipitation and that the amount of precipitates is limited by calcium and magnesium. With the present simulations, we could confirm these findings. We determined that only a small fraction of urea has to be hydrolysed for reaching 95% of the maximum PP. Since urease-positive bacteria are abundant in urine-collecting systems, strong precipitation is very likely. In further simulations, we determined that struvite (MgNH4PO4·6H2O) and hydroxyapatite (HAP, Ca10(PO4)6(OH)2) are the main precipitate compounds. If urine is highly diluted with tapwater, calcite (CaCO3) occurs as well. HAP is the only calcium phosphate mineral, although several others were supersaturated. Additionally, the simulations indicated that urine dilution diminishes the risk of blockages, since the mass concentration of precipitates decreases with the volume of flushing water. Rainwater flushing is more effective than flushing with tapwater. Moreover, flushing with tapwater leads to high phosphate fixation, because the total amount of calcium and magnesium ions increases, while the total amount of phosphate keeps constant. Finally, we compared simulation results with field measurements and found good agreement at low and very high urine dilution.
Udert, K. M., Fux, C., Münster, M., Larsen, T. A., Siegrist, H., & Gujer, W. (2003). Nitrification and autotrophic denitrification of source-separated urine. Water Science and Technology, 48(1), 119-130. doi:10.2166/wst.2003.0031, Institutional Repository

In laboratory experiments, source-separated urine was stabilised with nitrification and denitrified via nitritation and anaerobic ammonium oxidation. The highest total ammonia concentration in the influent was 7,300 gN/m3, the maximum pH 9.2. In a moving bed biofilm reactor (MBBR) with Kaldnes® biofilm carriers, we stabilised urine as a 1:1 ammonium nitrate solution. The maximum nitrification rate was 380 gN/m3/d corresponding to 1.7 gN/m2 biofilm/d. Nitrite ammonium solutions were produced in a continuous flow stirred tank reactor (CSTR) with 4.8 days sludge retention time (SRT) at 30°C and in a sequencing batch reactor (SBR) with more than 30 days SRT. Nitrate build-up was negligible in both reactors. Nitritation rates were 780 gN/m3/d in the CSTR and 280 gN/m3/d in the SBR, respectively. However, shortening the cycles would increase nitritation in the SBR. High concentrations of nitrous acid, salts, and presumably hydroxylamine suppressed nitrite oxidation in the nitritation reactors. In all three nitrification reactors, maximally 50% of the influent total ammonia was oxidised without pH control. None of the common inhibition or limitation approaches could explain why ammonia oxidation always stopped at pH values around 6. In a batch experiment, we showed that source-separated urine can be denitrified autotrophically by anammox bacteria.
Udert, K. M., Larsen, T. A., Biebow, M., & Gujer, W. (2003). Urea hydrolysis and precipitation dynamics in a urine-collecting system. Water Research, 37(11), 2571-2582. doi:10.1016/S0043-1354(03)00065-4, Institutional Repository

Blockages caused by inorganic precipitates are a major problem of urine-collecting systems. The trigger of precipitation is the hydrolysis of urea by bacterial urease. While the maximum amount of precipitates, i.e. the precipitation potential, can be estimated with equilibrium calculations, little is known about the dynamics of ureolysis and precipitation. To gain insight in these processes, we performed batch experiments with precipitated solids and stored urine from a urine-collecting system and later simulated the results with a computer model. We found that urease-active bacteria mainly grow in the pipes and are flushed into the collection tank. Both, bacteria and free urease, hydrolyse urea. Only few days are necessary for complete urea depletion in the collection tank. Two experiments with precipitated solids from the pipes showed that precipitation sets in soon after ureolysis has started. At the end of the experiments, 11% and 24% of urea was hydrolysed while the mass concentration of newly formed precipitates already corresponded to 87% and 97% of the precipitation potential, respectively. We could simulate ureolysis and precipitation with a computer model based on the surface dislocation approach. The simulations showed that struvite and octacalcium phosphate (OCP) are the precipitating minerals. While struvite precipitates already at low supersaturation, OCP precipitation starts not until a high level of supersaturation is reached. Since measurements and computer simulations show that hydroxyapatite (HAP) is the final calcium phosphate mineral in urine solutions, OCP is only a precursor phase which slowly transforms into HAP.
Udert, K. M. (2002). The fate of nitrogen and phosphorus in source-separated urine (Doctoral dissertation). doi:10.3929/ethz-a-004541820, Institutional Repository

Introduction
Intensive agriculture and urban sewage burden the environment with high nutrient loads. An improved nutrient management is necessary to remove present damages and to prevent future impacts. Nutrient losses to the environment can be strongly reduced, if nutrients from waste water are recycled to agriculture.
Human urine is the most important nutrient source of household waste water. It contributes about 80% of nitrogen and 60% of phosphorus, but accounts for less than one percent of the waste water volume. Separate collection of human urine would strongly reduce the demands on waste water treatment, because no enhanced nutrient elimination would be necessary to prevent eutrophication. Furthermore the separate collection and application of urine would be an efficient method to recycle nutrients from urban sewerage to agriculture.
Waterless urinals and NoMix toilets are available for urine separation. In urine-collecting systems the separated urine is directed to a collection tank where it is stored for later transport to a treatment facility.
In existing systems biological and chemical processes hamper the technical realisation of urine separation. By hydrolysing urea, bacteria cause a strong increase of ammonia and pH. Under these conditions large amounts of phosphate minerals precipitate, which can lead to pipe blockages. The produced ammonia is volatile. Degassing of ammonia can cause odour problems and significant nitrogen losses. [...]

Einleitung
Intensive Landwirtschaft und Siedlungsabwässer belasten die Umwelt mit hohen Nährstoffeinträgen. Ein besseres Nährstoffmanagement ist notwendig, um entstandene Schäden zu beheben und künftige zu verhindern. Nährstoffverluste in die Umwelt können stark verringert werden, wenn die Nährstoffe aus dem Abwasser in die Landwirtschaft rezykliert werden.
Menschlicher Urin ist die wichtigste Nährstoffquelle des kommunalen Abwassers. Er liefert ca. 80% des Stickstoffs und 60% des Phosphors, macht aber weniger als ein Prozent des Abwasservolumens aus. Die getrennte Sammlung von Urin würde die Abwasserreinigung stark entlasten, weil in Kläranlagen keine erweiterte Nährstoffelimination mehr notwendig wäre, um die Gewässereutrophierung zu bekämpfen. Die separate Sammlung und Ausbringung von Urin wäre zudem eine sehr effiziente Massnahme, um Nährstoffe von der Siedlungswasserwirtschaft in die Landwirtschaft zu rezyklieren.
Für die separate Sammlung von Urin stehen wasserlose Urinale und NoMix-Toiletten zur Verfügung. In Urinsammelanlagen wird der Urin nach der Abtrennung in einen Sammeltank geleitet und dort zwischengelagert, bevor er zur Weiterverarbeitung abtransportiert wird.
In bestehenden Systemen erschweren allerdings biologische und chemische Prozesse die Urinseparierung. Bakterien hydrolisieren den im Urin enthaltenen Harnstoff und erhöhen dadurch die Ammoniakkonzentration und den pH. Unter diesen Bedingungen fallen grosse Mengen an Phosphatmineralien aus, was zu Verstopfungen der Leitungen führen kann. Das produzierte Ammoniak ist flüchtig. Ausgasungen können Geruchsbelästigungen und erheblichen Stickstoffverluste verursachen. [...]
Udert, K. (2000). Charakterisierung von Urinausfällungen in wassergespülten und wasserlosen Urinalen sowie in No-Mix-Toiletten. Jona; Dübendorf: GEBERIT Technik AG; Eawag. , Institutional Repository

Urinausfällungen treten in Urinalen und No-Mix-Toiletten auf und führen häufig zu Verstopfungen. Trotz der grossen Bedeutung der Urinausfällungen für die Funktionsfähigkeit von Urinalen, gibt es bisher kaum wissenschaftliche Untersuchungen zu diesem Thema. Ziel des gemeinsamen Projektes der GEBERIT Technik AG und der EAWAG war es, erste qualitative Aussagen zur Zusammensetzung und zu den Ursachen der Urinausfällungen zu erhalten. Drei verschiedene Toilettentypen wurden untersucht: herkömmliche wassergespülte Urinale, wasserlose Urinale der Firma URIMAT und eine No-Mix-Toilette, die an der EAWAG installiert ist. [...]
Udert, K. (2000). Urinsteinbildung in Urinalen des Flughafens Kloten. Analyseergebnisse. Jona; Dübendorf: GEBERIT Technik AG, Eawag. , Institutional Repository

Als Fortsetzung des Projektes "Charakterisierung von Urinausfällungen in wassergespülten und wasserlosen Urinalen sowie in No-Mix-Toiletten" (Geberit und EAWAG 2000) wurden mehrere Urinale einer Toilettenanlage des Flughafens Kloten untersucht. Ziel der Messungen war es, die Erkenntnisse des ersten Projektes durch weitere Daten zu überprüfen und zu erganzen. [...]
Larsen, T. A., & Udert, K. M. (1999). Urinseparierung - ein Konzept zur Schliessung der Nährstoffkreisläufe. Wasser und Boden, 51(11), 6-9. , Institutional Repository

Nutrient control is generally acknowledged to be an important part of domestic wastewater treatment. However, it is not as widely recognised that nutrient control is only necessary due to the presence of urine in wastewater. With urine separation and a subsequent treatment or recycling, only solids and organic matter need to be removed for the treatment of domestic wastewater. Urine separation combined with recycling of primary and secondary sludge would make it possible to close nutrient cycles. Problems with pharmaceutics and hormones in the receiving waters would be alleviated. From a technical point of view, the separate collection of urine is possible with a so-called 'No-Mix'-Toilet: after separation the urine is stored in the household and in the night, when the sewers are more or less empty, it is led through the sewers are more or less empty, it is led through the sewers to the treatment plant. Just before it reaches the treatment plant, the urine must be collected and separately treated or recycled.
Moser-Engeler, R., Udert, K. M., Wild, D., & Siegrist, H. (1998). Products from primary sludge fermentation and their suitability for nutrient removal. Water Science and Technology, 38(1), 265-273. doi:10.1016/S0273-1223(98)00411-9, Institutional Repository

Both denitrification and biological phosphorus removal depend on the presence of readily biodegradable carbon. Primary sludge fermentation is one way of producing such substrates. Soluble products of sludge fermentation are mainly short-chain fatty acids with two to five carbon atoms (84% of dissolved COD). In considering molar degradation rates by denitrifying organisms in batch experiments, the acids can be divided into two groups: the preferentially degraded linear forms of C2 to C5 acids and the branched C4 and C5 acids. The non-identified fraction (16% COD) which might contain acids with more than five carbon atoms is also removed by the activated sludge either by degradation or adsorption. In batch experiments with anaerobic and aerobic cycles, the uptake rate for short-chain fatty acids by phosphorus accumulating organisms and the ratio of phosphorus release to substrate uptake are determined. Acetate and propionate are taken up much faster than the C4 and C5 acids, which show very similar rates. For the ratio of phosphorus release to substrate uptake the situation is more complicated. The acids with four carbon atoms show by far the highest values.

Adriano Joss

Ganesanandamoorthy, P., Joss, A., Gruber, W., Bührer, T., & Thomann, M. (2024). Online-Nitritmessung. Vergleich von Online-Nitritsensoren für die Abwassereinigung. Aqua & Gas, 104(1), 26-31. , Institutional Repository

Nitrit ist eine ökotoxikologisch problematische Substanz und führt auf Kläranlagen ausserdem zur Bildung von klimaschädlichem Lachgas. In der hier vorgestellten Studie werden verschiedene Online-Sensoren verglichen und deren Messunsicherheit in Ablauf und Belebtschlamm erfasst.
Gruber, W., Niederdorfer, R., Ganesanandamoorthy, P., Bürgmann, H., Morgenroth, E., & Joss, A. (2024). Nitrit-Akkumulation auf Nitrifizierenden Belebtschlammanlagen. Wie kann der NO2– - Richtwert eingehalten werden?. Aqua & Gas, 104(1), 18-24. , Institutional Repository

Nitrit ist eine ökotoxikologisch problematische Substanz und führt auf Kläranlagen zur Bildung von klimaschädlichem Lachgas. Auf nitrifizierenden Belebtschlammanlagen kann Nitrit saisonal akkumulieren und erhöhte Ablaufwerte treten auf. Hier diskutieren wir die Häufigkeit von Überschreitungen des Nitrit-Richtwerts auf Schweizer ARA und schlagen Gegenmassnahmen vor.
Meynet, P., Joss, A., Davenport, R. J., & Fenner, K. (2024). Impact of long-term temperature shifts on activated sludge microbiome dynamics and micropollutant removal. Water Research, 258, 121790 (10 pp.). doi:10.1016/j.watres.2024.121790, Institutional Repository

Micropollutants removal efficiency strongly vary across different aerobic wastewater treatment plants, resulting in their frequent detection in surface and ground waters. Seasonal temperature variation is a major factor influencing plant performance, but it is still unclear how prolonged periods of temperature change impact microbiome and micropollutant biotransformation. This work investigates the effect of long-term temperature variation on the microbial dynamics in an activated sludge system, and the impact on micropollutant biotransformation. Sequencing batch reactors were used as model system and 4–40 °C temperature range was studied. 16S rRNA amplicon sequencing showed that temperature drives microbial structure (gDNA) and activity (RNA), rather than time, and this was stronger below 15 °C and above 25 °C. The microbial community was richest and more diverse at 20 °C, while rarer and more specific taxa became predominant over time, at more extreme temperatures. This suggested that less abundant taxa might be responsible for maintaining the biotransformation capability in the activated sludge at extreme temperatures. Micropollutant biotransformation rates mostly deviated from the classic Arrhenius model below 15 °C and above 25 °C, indicating that prolonged exposure to temperature changes leads to temperature-induced taxonomic shifts, resulting in the emerging of different sets of biotransformation pathways over different temperature ranges.
Böhler, M. A., Carl, F., Zhu, M., McArdell, C. S., Frömelt, A., & Joss, A. (2023). Spurenstoffelimination bei stark verdünnter Abwassermatrix – Erfahrungen, Kenntnisstand und Herausforderungen. In M. Wessling & T. Wintgens (Eds.), 15. Aachener Tagung Wassertechnologie. Verfahren der Abwasserbehandlung und Wasseraufbereitung (pp. 14-23). Aachen: RWTH Aachen University. , Institutional Repository

Das Qualitätsziel einer 80%igen Elimination von Mikroverunreinigungen ist in der Schweiz für ausgewählte ARA auch bei Regenwetterverhältnissen stets einzuhalten. Hohe Niederschläge verursachen hohe Mischwasserzuläufe zur ARA, die in der Menge häufig das Doppelte der Trockenwettermenge übersteigt. Der Schmutzwasseranteil (Abwassermatrix) ist dann um das Vielfache verdünnt. Dieser Umstand verursacht hydraulische Effekte wie verkürzte hydraulische Aufenthaltszeiten in den Behandlungsstufen und führt zu verkürzten Kontakt- und Reaktionszeiten in den Reaktoren. U.a. können Kurzschlussströme entstehen, die die EMV erniedrigen können. Die EMVStufen in der Schweiz sind auf Mischwasserzulauf ausgelegt und es wurden über die letzten Jahre angepasste Betriebsstrategien für die verschiedenen
EMV-Verfahren erarbeitet, so dass in aller Regel das Qualitätsziel erreicht wird. Dennoch bleibt der sichere, wirtschaftliche sowie nachhaltige Betrieb der Anlagen anspruchsvoll mit hohen Herausforderungen.
Aktuelle Untersuchungen der Eawag zum Verhalten höher beladener GAK im Einzelfilter zeigten bei Kontakt mit stark verdünntem Abwasser trotz 20-minütiger Kontaktzeit verringerte Sorptionsleistung bis hin zur Desorption von Einzelsubstanzen. Ob dieser Umstand auch bei einem Parallelbetrieb zu beobachten ist, sollen weiterführende Untersuchungen im Praxisbetrieb von GAK-Filtrationen zeigen. Im Fall der GAK-Filtration der ARA Glarnerland mit langanhaltenden Regennachläufen und Schmelzwasserzulauf wurde eine PAK-Dosierung in die Biologie vorgeschaltet bzw. wird aktuell realisiert, um allenfalls Einbussen durch verdünnte Abwassermatrix abzufangen.
Dieziger, C., Freimann, R., Durisch-Kaiser, E., & Joss, A. (2023). Lachgasemissionen aus Faulwasserbehandlung. Beprobung und Einordnung 12 Schweizer Anlagen. Aqua & Gas, 103(3), 50-54. , Institutional Repository

Lachgas ist neben Kohlendioxid und Methan eines der potentesten Treibhausgase und hauptverantwortlich für den Abbau der stratosphärischen Ozonschicht. Auf Schweizer Abwasserreinigungsanlagen (ARA) ist die Faulwasserbehandlung, die hauptsächlich mit dem ein- oder zweistufigen anaeroben Ammonium-Oxidation-Verfahren (Anammox) durchgeführt wird, eine mögliche Quelle für Lachgas. Messungen zeigen, dass die Lachgasemissionen im klimarelevanten Bereich liegen und Reduktionsmassnahmen zu empfehlen sind.
Huang, K., Eschenbach, W., Wei, J., Hausherr, D., Frey, C., Kupferschmid, A., … Mohn, J. (2023). Simultaneous 15N online analysis in NH4+, NO2-, NO3-, and N2O to trace N2O production pathways in nitrogen-polluted aqueous environments. ACS ES&T Water, 3(11), 3485-3495. doi:10.1021/acsestwater.3c00216, Institutional Repository

Engineered nitrogen (N) removal processes in water treatment plants and N-transformation reactions in polluted environments represent prominent sources of the potent greenhouse gas, nitrous oxide (N2O). The relevance of microbial and abiotic formation pathways can be assessed by using 15N tracer techniques. While 15N-N2O analysis with optical analyzers is straightforward, the quantification of atom % 15N of inorganic N compounds, such as ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-), requires discrete sample analyses that are time-consuming and labor-intensive. In this study, we developed an automated sample preparation unit, coupled to a membrane inlet quadrupole mass spectrometer, for the online, quasi-simultaneous analysis of atom % 15N in NH4+, NO2-, and NO3-. This technique was designed and validated for 15N-spiking applications at moderate (100-200 μmol L-1, 1 atom % 15N) to high (2-3 mmol L-1, 33 atom % 15N) dissolved inorganic N concentrations typically encountered in sewer systems or contaminated watersheds. The high potential of the developed system, in combination with 15N-N2O analysis by Fourier-transform infrared spectroscopy, to constrain N transformations and sources of N2O was demonstrated in a feasibility study, where nitrifier denitrification was identified as the primary N2O formation pathway during the partial NH4+ oxidation to NO2- in a lab-scale sequencing batch reactor.
Joss, A., Kipf, M., Morgenroth, E., Baggenstos, M., & Salzgeber, D. (2023). Modifiziertes Anammox-Verfahren. Faulwasserbehandlungen mit stabiler Prozessführung. Aqua & Gas, 103(1), 24-29. , Institutional Repository

Bei der anaeroben Ammonium-Oxidation, kurz Anammox, werden Ammonium und Nitrit im Faulwasser zu Stickstoffgas umgewandelt. Das Verfahren ist auch auf einigen Schweizer ARA im Einsatz. Da aber nicht alle Anlagen die Sollleistung erfüllten, wurde das Anammox-Verfahren untersucht und weiterentwickelt. Mit dem Wechsel von der ein- zur zweistufigen Verfahrensführung wurde nicht nur eine höhere Betriebsstabilität bei der biologischen Entstickung von Rückläufen aus der Schlammentwässerung, sondern teils auch höhere Leistungen erreicht.
Kizgin, A., Schmidt, D., Joss, A., Hollender, J., Morgenroth, E., Kienle, C., & Langer, M. (2023). Application of biological early warning systems in wastewater treatment plants: Introducing a promising approach to monitor changing wastewater composition. Journal of Environmental Management, 347, 119001 (12 pp.). doi:10.1016/j.jenvman.2023.119001, Institutional Repository

Wastewater treatment plants (WWTPs) are a major source of micropollutants to surface waters. Currently, their chemical or biological monitoring is realized by using grab or composite samples, which provides only snapshots of the current wastewater composition. Especially in WWTPs with industrial input, the wastewater composition can be highly variable and a continuous assessment would be advantageous, but very labor and cost intensive. A promising concept are automated real-time biological early warning systems (BEWS), where living organisms are constantly exposed to the water and an alarm is triggered if the organism's responses exceed a harmful threshold of acute toxicity. Currently, BEWS are established for drinking water and surface water but are seldom applied to monitor wastewater. This study demonstrates that a battery of BEWS using algae (Chlorella vulgaris in the Algae Toximeter, bbe Moldaenke), water flea (Daphnia magna in the DaphTox II, bbe Moldaenke) and gammarids (Gammarus pulex in the Sensaguard, REMONDIS Aqua) can be adapted for wastewater surveillance. For continuous low-maintenance operation, a back-washable membrane filtration system is indispensable for adequate preparation of treated wastewater. Only minor deviations in the reaction of the organisms towards treated and filtered wastewater compared to surface waters were detected. After spiking treated wastewater with two concentrations of the model compounds diuron, chlorpyrifos methyl, and sertraline, the organisms in the different BEWS showed clear responses depending on the respective compound, concentration and mode of action. Immediate effects on photosynthetic activity of algae were detected for diuron exposure, and strong behavioral changes in water flea and gammarids after exposure to chlorpyrifos methyl or sertraline were observed, which triggered automated alarms. Different types of data analysis were applied to extract more information out of the specific behavioral traits, than only provided by the vendors algorithms. To investigate, whether behavioral movement changes can be linked to impact other endpoints, the effects on feeding activity of G. pulex were evaluated and results indicated significant differences between the exposures. Overall, these findings provide an important basis indicating that BEWS have the potential to act as alarm systems for pollution events in the wastewater sector.
Niederdorfer, R., Gruber, W., Joss, A., & Bürgmann, H. (2023). MicROcensus: zeitnahe Mikrobiom-Analysen auf ARA. Aqua & Gas, 103(9), 54-59. , Institutional Repository

Ein zeitnahes Biomonitoring mit Nanopore-Sequenzierung gewährt neue Einblicke in die biologischen Prozesse einer Abwasserreinigungsanlage (ARA). Im Rahmen des Projekts «MicROcensus» wurde an verschiedenen ARA die Einsatzfähigkeit solcher Mikrobiom-Analysen als Diagnoseinstrument evaluiert. So unterstützen Momentaufnahmemessungen die Ursachenfindung von Prozessinstabilitäten oder Begleitphänomenen. Während wöchentliche Analysen des Mikrobioms – bei Bekanntsein der jahreszeitlichen Dynamiken - als Frühwarnsystem dienen und praxisrelevante Daten für den ARA-Betrieb liefern können.
Schäfer, R., Dönni, A., Thomann, M., Gulde, R., Eugster, F., Joss, A., & Piazzoli, A. (2023). Entwicklung des AIA-Tests. Alternativer inhärenter Abbautest für Industrieabwasser. Aqua & Gas, 103(4), 68-75. , Institutional Repository

Um den biologischen Abbau einer Abwasserprobe zu untersuchen und die refraktäre organische Fracht zu quantifizieren, werden Abbautests eingesetzt. Die Charakterisierung der Abwasserströme führt zu Entscheidungen bezüglich Entsorgung und allfälliger benötigter Vorbehandlungen. Der gängige Zahn-Wellens-Test wurde optimiert, um einen zeiteffizienteren Abbautest zu entwickeln: den alternativen inhärenten Abbautest (AIA-Test).
Braun, D., von Känel, L., Biolley, L., Bauer, H., Gahler, D., Gruber, W., … Morgenroth, E. (2022). Dynamische Regelung der ARA Hofen. Infrawatt-Innovationspreis für mehr Leistung und weniger Emissionen. Aqua & Gas, 102(1), 26-31. , Institutional Repository

Die ARA Hofen hat den Infrawatt Innovationspreis 2021 für die Ertüchtigung ihrer Biologiebecken mit dem Konzept der dynamischen Regelung erhalten. Die Leistung der ARA konnte dadurch signifikant erhöht werden, bei stark vermindertem Energieverbrauch und gleichzeitig sehr geringen Lachgasemissionen.
Böhler, M. A., Joss, A., & McArdell, C. S. (2022). GAK-Filter für die Spurenstoffentfernung. Erfahrungen und Betriebsergebnisse der Pilotstudien ARA Furt/Bülach und Glarnerland. Aqua & Gas, 102(1), 48-54. , Institutional Repository

Auf den Kläranlagen Furt/Bülach und Glarnerland des Abwasserverbandes Glarnerland (AVG, Bilten) wurden zwischen 2014 und 2019 umfangreiche Untersuchungen zur Elimination von Mikroverunreinigungen mittels granulierter Aktivkohle (GAK) durchgeführt. Ziel war es, unter Schweizer Praxisbedingungen die Machbarkeit, Effizienz und Wirtschaftlichkeit des Verfahrens zu evaluieren. Fazit beider Forschungsprojekte ist, dass sich die GAK-Filtration zur Spurenstoffelimination gemäss Schweizer Gesetzgebung eignet. Das Verfahren ist technisch und wirtschaftlich realisierbar und hat sich als praxistauglich erwiesen.
Carles, L., Wullschleger, S., Joss, A., Eggen, R. I. L., Schirmer, K., Schuwirth, N., … Tlili, A. (2022). Wastewater microorganisms impact microbial diversity and important ecological functions of stream periphyton. Water Research, 225, 119119 (13 pp.). doi:10.1016/j.watres.2022.119119, Institutional Repository

Effluents of wastewater treatment plants can impact microbial communities in the receiving streams. However, little is known about the role of microorganisms in wastewater as opposed to other wastewater constituents, such as nutrients and micropollutants. We aimed therefore at determining the impact of wastewater microorganisms on the microbial diversity and function of periphyton, key microbial communities in streams. We used a flow-through channel system to grow periphyton upon exposure to a mixture of stream water and unfiltered or ultra-filtered wastewater. Impacts were assessed on periphyton biomass, activities and tolerance to micropollutants, as well as on microbial diversity. Our results showed that wastewater microorganisms colonized periphyton and modified its community composition, resulting for instance in an increased abundance of Chloroflexi and a decreased abundance of diatoms and green algae. This led to shifts towards heterotrophy, as suggested by the changes in nutrient stoichiometry and the increased mineralization potential of carbon substrates. An increased tolerance towards micropollutants was only found for periphyton exposed to unfiltered wastewater but not to ultra-filtered wastewater, suggesting that wastewater microorganisms were responsible for this increased tolerance. Overall, our results highlight the need to consider the role of wastewater microorganisms when studying potential impacts of wastewater on the receiving water body.
Desiante, W. L., Carles, L., Wullschleger, S., Joss, A., Stamm, C., & Fenner, K. (2022). Wastewater microorganisms impact the micropollutant biotransformation potential of natural stream biofilms. Water Research, 217, 118413 (13 pp.). doi:10.1016/j.watres.2022.118413, Institutional Repository

Biotransformation is the most important process removing manmade chemicals from the environment, yet mechanisms governing this essential ecosystem function are underexplored. To understand these mechanisms, we conducted experiments in flow-through systems, by colonizing stream biofilms under different conditions of mixing river water with treated (and ultrafiltered) wastewater. We performed biotransformation experiments with those biofilms, using a set of 75 micropollutants, and could disentangle potential mechanisms determining the biotransformation potential of stream biofilms. We showed that the increased biotransformation potential downstream of wastewater treatment plants that we observed for specific micropollutants contained in household wastewaters (downstream effect) is caused by microorganisms released with the treated effluent, rather than by the in-stream exposure to those micropollutants. Complementary data from 16S rRNA amplicon-sequencing revealed 146 amplicon sequence variants (ASVs) that followed the observed biotransformation patterns. Our results align with findings for community tolerance, and provide clear experimental evidence that microorganisms released with treated wastewater integrate into downstream biofilms and impact crucial ecosystem functions.
Gruber, W., Joss, A., von Känel, L., Biolley, L., Braun, D., & Morgenroth, E. (2022). Abluftmessungen in der biologischen Abwasserreinigung. Aqua & Gas, 102(1), 24-25. , Institutional Repository

Neue Leistungsanforderungen an Abwasserreinigungsanlagen hinsichtlich Ablaufqualität, Energieeffizienz und Treibhausgasemission werden immer bedeutender. Um dabei Zielkonflikte zu vermeiden, ist bei der Optimierung die genaue Überwachung der Prozesse erforderlich. So ist die Messung von Gaskonzentrationen in der Abluft aus biologischen Reinigungsstufen ein nützliches Werkzeug, um verschiedene Zielsetzungen einer ARA hochaufgelöst und wartungsarm zu überwachen.
Gruber, W., Niederdorfer, R., Bürgmann, H., Joss, A., von Känel, L., Braun, D., … Morgenroth, E. (2022). Lachgasemissionen aus ARA. Reduktionsmassnahmen zeichnen sich ab. Aqua & Gas, 102(1), 14-22. , Institutional Repository

Lachgas (N2O) ist ein starkes Treibhausgas und die wichtigste ozonzerstörende Substanz in der Stratosphäre. Auf Abwasserreinigungsanlagen wird N2O während des biologischen Stickstoffabbaus gebildet, der somit die grösste Treibhausgasquelle während des Reinigungsprozesses darstellt. Reduktionsmassnahmen sind deshalb von grosser Bedeutung und gemäss neuen Erkenntnissen durch eine Optimierung der Nitrifikation und Denitrifikation auch erreichbar.
Gruber, W., Magyar, P. M., Mitrovic, I., Zeyer, K., Vogel, M., von Känel, L., … Mohn, J. (2022). Tracing N2O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings. Water Research X, 15, 100130 (11 pp.). doi:10.1016/j.wroa.2022.100130, Institutional Repository

Nitrous oxide (N2O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N2O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N2O mitigation strategies require an improved understanding of nitrogen transformation pathways and their modulating controls. Analyses of the nitrogen (N) and oxygen (O) isotopic composition of N2O and its substrates at natural abundance have been shown to provide valuable information on formation and reduction pathways in laboratory settings, but have rarely been applied to full-scale WWTPs.
Here we show that N-species isotope ratio measurements at natural abundance level, combined with long-term N2O monitoring, allow identification of the N2O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). Heterotrophic denitrification appears as the main N2O production pathway under all tested process conditions (0-2 mgO2/l, high and low loading conditions), while nitrifier denitrification was less important, and more variable. N2O production by hydroxylamine oxidation was not observed. Fractional N2O elimination by reduction to dinitrogen (N2) during anoxic conditions was clearly indicated by a concomitant increase in site preference, δ18O(N2O) and δ15N(N2O). N2O reduction increased with decreasing availability of dissolved inorganic N and organic substrates, which represents the link between diurnal N2O emission dynamics and organic substrate fluctuations. Consequently, dosing ammonium-rich reject water under low-organic-substrate conditions is unfavorable, as it is very likely to cause high net N2O emissions.
Our results demonstrate that monitoring of the N2O isotopic composition holds a high potential to disentangle N2O formation mechanisms in engineered systems, such as full-scale WWTP. Our study serves as a starting point for advanced campaigns in the future combining isotopic technologies in WWTP with complementary approaches, such as mathematical modeling of N2O formation or microbial assays to develop efficient N2O mitigation strategies.
Hausherr, D., Niederdorfer, R., Bürgmann, H., Lehmann, M. F., Magyar, P., Mohn, J., … Joss, A. (2022). Successful mainstream nitritation through NOB inactivation. Science of the Total Environment, 822, 153546 (11 pp.). doi:10.1016/j.scitotenv.2022.153546, Institutional Repository

The development of new wastewater treatment processes can assist in reducing the impact of wastewater treatment on the environment. The recently developed partial nitritation anammox (PNA) process, for example, consumes less energy for aeration and reduces nitrate in the effluent without requiring additional organic carbon. However, achieving stable nitritation (ammonium oxidation; NH4+ → NO2−) at mainstream conditions (T = 10–25 °C, C:N > 10, influent ammonium < 50 mgNH4-N/L and effluent < 1 mgNH4-N/L) remains challenging. This study explores the potential and mechanism of nitrite-oxidizing bacteria (NOB) suppression in a bottom-fed sequencing batch reactor (SBR). Two bench-scale (11 L) reactors and a pilot-scale reactor (8 m3) were operated for over a year and were fed with organic substrate depleted municipal wastewater. Initially, nitratation (nitrite oxidation; NO2− → NO3−) occurred occasionally until an anaerobic phase was integrated into the operating cycle. The introduction of the anaerobic phase effectively suppressed the regrowth of NOB while nitritation was stable over 300 days, down to 8 °C and at ammonium influent concentrations < 25 mgNH4-N/L. Batch experiments and process data revealed that parameters typically affecting NOB growth (e.g., dissolved oxygen, alkalinity, trace elements, lag-phase after anoxia, free nitrous acid (FNA), free ammonia (FA), pH, sulfide, or solids retention time (SRT)) could not fully explain the suppression of nitratation. Experiments in which fresh nitrifying microbial biomass was added to the nitritation system indicated that NOB inactivation explained NOB suppression better than NOB washout at high SRT. This study concludes that bottom-fed SBRs with anaerobic phases allow for stable nitritation over a broad range of operational parameters. Coupling this type of SBR to an anammox reactor can enable efficient mainstream anammox-based wastewater treatment.
Hausherr, D., Niederdorfer, R., Bürgmann, H., Lehmann, M. F., Magyar, P., Mohn, J., … Joss, A. (2022). Successful year-round mainstream partial nitritation anammox: assessment of effluent quality, performance and N2O emissions. Water Research X, 16, 100145 (11 pp.). doi:10.1016/j.wroa.2022.100145, Institutional Repository

For two decades now, partial nitritation anammox (PNA) systems were suggested to more efficiently remove nitrogen (N) from mainstream municipal wastewater. Yet to date, only a few pilot-scale systems and even fewer full-scale implementations of this technology have been described. Process instability continues to restrict the broad application of PNA. Especially problematic are insufficient anammox biomass retention, the growth of undesired aerobic nitrite-oxidizers, and nitrous oxide (N2O) emissions. In this study, a two-stage mainstream pilot-scale PNA system, consisting of three reactors (carbon pre-treatment, nitritation, anammox - 8 m3 each), was operated over a year, treating municipal wastewater. The aim was to test whether both, robust autotrophic N removal and high effluent quality, can be achieved throughout the year. A second aim was to better understand rate limiting processes, potentially affecting the overall performance of PNA systems. In this pilot study, excellent effluent quality, in terms of inorganic nitrogen, was accomplished (average effluent concentrations: 0.4 mgNH4-N/L, 0.1 mgNO2-N/L, 0.9 mgNO3-N/L) even at wastewater temperatures previously considered problematic (as low as 8 °C). N removal was limited by nitritation rates (84 ± 43 mgNH4-N/L/d), while surplus anammox activity was observed at all times (178 ± 43 mgN/L/d). Throughout the study, nitrite-oxidation was maintained at a low level (<2.5% of ammonium consumption rate). Unfortunately, high N2O emissions from the nitritation stage (1.2% of total nitrogen in the influent) were observed, and, based on natural isotope abundance measurements, could be attributed to heterotrophic denitrification. In situ batch experiments were conducted to identify the role of dissolved oxygen (DO) and organic substrate availability in N2O emission-mitigation. The addition of organic substrate, to promote complete denitrification, was not successful in decreasing N2O emission, but increasing the DO from 0.3 to 2.9 mgO2/L decreased N2O emissions by a factor of 3.4.
Walpen, N., Joss, A., & von Gunten, U. (2022). Application of UV absorbance and electron-donating capacity as surrogates for micropollutant abatement during full-scale ozonation of secondary-treated wastewater. Water Research, 209, 117858 (11 pp.). doi:10.1016/j.watres.2021.117858, Institutional Repository

Ozonation of secondary-treated wastewater for the abatement of micropollutants requires a reliable control of ozone doses. Changes in the UV absorbance of dissolved organic matter (DOM) during ozonation allow to estimate micropollutant abatement on-line and were therefore identified as feed-back control parameter. In this study, the suitability of the electron-donating capacity (EDC) as an additional surrogate parameter which is independent of optical DOM properties was evaluated during full-scale ozonation. For this purpose, a recently developed EDC analyzer was enhanced to enable continuous on-line EDC and UV absorbance measurements. During a multi-week monitoring campaign at the wastewater treatment plant of Zurich, Switzerland, specific ozone doses were varied from 0.13 to 0.91 mgO3⋅mgDOC-1 and selected micropollutants with different ozone reactivities were analyzed by LC-MS in conjunction with bromate analysis by IC-MS. In agreement with previous laboratory studies, the relative residual UV absorbance and EDC both decreased exponentially as a function of the specific ozone dose and, in comparison to the residual UV absorbance, residual EDC values showed a more pronounced decrease at low specific ozone doses ≤0.34 mgO3⋅mgDOC-1. Logistic regression models allowed to estimate relative residual micropollutant concentrations in the ozonation effluent using either the residual UV absorbance or EDC as explanatory variable. Averaging those models along the explanatory variables allowed to estimate target values in relative residual UV absorbances and EDC for specific micropollutant abatement targets. In addition, both parameters allowed to identify conditions with elevated conversions of bromide to bromate. Taken together, these findings show that the integration of relative residual EDC values as a second control parameter can improve existing absorbance-based ozonation control systems to meet micropollutant abatement targets, particularly for treatment systems where low ozone doses are applied.
Brander, A., Böhler, M., McArdell, C., & Joss, A. (2021). Hinweise zur Planung und Auslegung von diskontinuierlich gespülten GAK-Filtern zur Elimination organischer Spurenstoffe aus kommunalem Abwasser unter besonderer Berücksichtigung der Anforderungen und Erfahrungen in der Schweiz (p. (6 pp.). Presented at the 14. Aachener Tagung Wassertechnologie. Verfahren der Wasseraufbereitung und Abwasserbehandlung. Aachen, Deutschland. , Institutional Repository
Carles, L., Wullschleger, S., Joss, A., Eggen, R. I. L., Schirmer, K., Schuwirth, N., … Tlili, A. (2021). Impact of wastewater on the microbial diversity of periphyton and its tolerance to micropollutants in an engineered flow-through channel system. Water Research, 203, 117486 (14 pp.). doi:10.1016/j.watres.2021.117486, Institutional Repository

Wastewater treatment plants (WWTPs) play an important role in retaining organic matter and nutrients but to a lesser extent micropollutants. Therefore, treated wastewater is recognized as a major source of multiple stressors, including complex mixtures of micropollutants. These can potentially affect microbial communities in the receiving water bodies and the ecological functions they provide. In this study, we evaluated in flow-through channels the consequences of an exposure to a mixture of stream water and different percentages of urban WWTP effluent, ranging from 0% to 80%, on the microbial diversity and function of periphyton communities. Assuming that micropollutants exert a selective pressure for tolerant microorganisms within communities, we further examined the periphyton sensitivity to a micropollutant mixture extracted from passive samplers that were immersed in the wastewater effluent. As well, micropollutants in water and in periphyton were comprehensively quantified. Our results show that micropollutants detected in periphyton differed from those found in water, both in term of concentration and composition. Especially photosystem II inhibitors accumulated in periphyton more than other pesticides. Although effects of other substances cannot be excluded, this accumulation may have contributed to the observed higher tolerance of phototrophic communities to micropollutants upon exposure to 30% and 80% of wastewater. On the contrary, no difference in tolerance was observed for heterotrophic communities. Exposure to the gradient of wastewater led to structural differences in both prokaryotic and eukaryotic communities. For instance, the relative abundance of cyanobacteria was higher with increasing percentage of wastewater effluent, whereas the opposite was observed for diatoms. Such results could indicate that differences in community structure do not necessarily lead to higher tolerance. This highlights the need to consider other wastewater constituents such as nutrients and wastewater-derived microorganisms that can modulate community structure and tolerance. By using engineered flow-through channels that mimic to some extent the required field conditions for the development of tolerance in periphyton, our study constitutes a base to investigate the mechanisms underlying the increased tolerance, such as the potential role of microorganisms originating from wastewater effluents, and different treatment options to reduce the micropollutant load in effluents.
Gruber, W., Joss, A., Luck, M., Kupper, T., Bühler, M., & Bührer, T. (2021). Elaboration of a data basis on greenhouse gas emissions from wastewater management - Final report N2OklimARA. Bern: Federal Office for the Environment (FOEN). , Institutional Repository

The currently applied approaches to estimate direct greenhouse gas (GHG) emissions of nitrous oxide (N2O) and methane (CH4) from wastewater treatment (sector 5D) in the national greenhouse gas inventories of Switzerland are based on the IPCC guidelines (IPCC 2006). A review of the Swiss application of guidelines showed that the guidelines are only partly representative for Switzerland (Eawag 2018). Hence, an extended study was performed including extensive monitoring campaigns on Swiss wastewater treatment plants (WWTPs), analysis of existing data sets and literature reviews. The present document summarizes the study and suggests an improved methodology for an assessment of the GHG emissions of sector 5D.
N2O emission are drastically underestimated with the current methodology. Additionally, source allocation of emissions is not representative. Hence, we suggest a new methodology based on 17 (14 Swiss and 3 from literature) long-term monitoring campaigns on full-scale WWTPs and an analysis of nitrogen flows in Swiss WWTPs. The decreasing N2O emissions since 1990 link to improvements of nitrogen removal rates on WWTPs. Further reductions are expected in the coming decades because of further planned improvements of nitrogen removal on Swiss WWTPs. Major uncertainties within the new methodology can be linked to the emission factor of WWTPs with carbon removal only. The occurrence of such plants decreased substantially between 1990 and 2020.
CH4 emissions are overestimated with the current methodology. Additionally, source allocation of emissions is not representative. Hence, we propose a new methodology based on monitoring campaigns and a literature review. Emissions increased moderately since 1990 along with an increase in population.
Gruber, W., von Känel, L., Vogt, L., Luck, M., Biolley, L., Feller, K., … Joss, A. (2021). Estimation of countrywide N2O emissions from wastewater treatment in Switzerland using long-term monitoring data. Water Research X, 13, 100122 (12 pp.). doi:10.1016/j.wroa.2021.100122, Institutional Repository

Nitrous oxides (N2O) emissions contribute to climate change and stratospheric ozone depletion. Wastewater treatment is an important, yet likely underestimated, source of N2O emissions, as recent, long-term monitoring campaigns have demonstrated. However, the available data are insufficient to representatively estimate countrywide emission due to the brevity of most monitoring campaigns. This study showed that the emission estimates can be significantly improved using an advanced approach based on multiple continuous, long-term monitoring campaigns. In monitoring studies on 14 full-scale wastewater treatment plants (WWTPs), we found a strong variability in the yearly emission factors (EFs) (0.1 to 8% of the incoming nitrogen load) which exhibited a good correlation with effluent nitrite. But countrywide data on nitrite effluent concentrations is very limited and unavailable for emission estimation in many countries. Hence, we propose a countrywide emission factor calculated from the weighted EFs of three WWTP categories (carbon removal, EF: 0.1-8%, nitrification only: 1.8%, and full nitrogen removal: 0.9%). However, EF of carbon removal WWTPs are still highly uncertain given the expected variability in performance.
The newly developed approach allows representative, country-specific estimations of the N2O emissions from WWTP. Applied to Switzerland, the estimations result in an average EF of 0.9 to 3.6% and total emissions of 410 to 1690 tN2O-N/year, which corresponds to 0.3-1.4% of the total greenhouse gas emissions in Switzerland. Our results demonstrate that better data availability and an improved understanding of long-term monitoring campaigns is crucial to improve current emission estimations. Finally, our results confirm several measures to mitigate N2O emissions from wastewater treatment; year-round denitrification, limiting nitrite accumulation, and stringent control of sludge age in carbon removal plants.
Gruber, W., Niederdorfer, R., Ringwald, J., Morgenroth, E., Bürgmann, H., & Joss, A. (2021). Linking seasonal N2O emissions and nitrification failures to microbial dynamics in a SBR wastewater treatment plant. Water Research X, 11, 100098 (13 pp.). doi:10.1016/j.wroa.2021.100098, Institutional Repository

Nitrous oxide (N2O) is a strong greenhouse gas and causal for stratospheric ozone depletion. During biological nitrogen removal in wastewater treatment plants (WWTP), high N2O fluxes to the atmosphere can occur, typically exhibiting a seasonal emission pattern. Attempts to explain the peak emission phases in winter and spring using physico-chemical process data from WWTP were so far unsuccessful and new approaches are required. The complex and diverse microbial community of activated sludge used in biological treatment systems also exhibit substantial seasonal patterns. However, a potentially causal link between the seasonal patterns of microbial diversity and N2O emissions has not yet been investigated. Here we show that in a full-scale WWTP nitrification failure and N2O peak emissions, bad settleability of the activated sludge and a turbid effluent strongly correlate with a significant reduction in the microbial community diversity and shifts in community composition. During episodes of impaired performance, we observed a significant reduction in abundance for filamentous and nitrite oxidizing bacteria in all affected reactors. In some reactors that did not exhibit nitrification and settling failures, we observed a stable microbial community and no drastic loss of species. Standard engineering approaches to stabilize nitrification, such as increasing the aerobic sludge age and oxygen availability failed to improve the plant performance on this particular WWTP and replacing the activated sludge was the only measure applied by the operators to recover treatment performance in affected reactors. Our results demonstrate that disturbances of the sludge microbiome affect key structural and functional microbial groups, which lead to seasonal N2O emission patterns. To reduce N2O emissions from WWTP, it is therefore crucial to understand the drivers that lead to the microbial population dynamics in the activated sludge.
Gruber, W. J. (2021). Long-term N2O emission monitoring in biological wastewater treatment: methods, applications and relevance (Doctoral dissertation). doi:10.3929/ethz-b-000537321, Institutional Repository

Nitrous oxide (N2O) emissions substantially contribute to global, environmental issues: climate change and stratospheric ozone depletion. Wastewater treatment plants (WWTPs) are potent point sources and significant contributors to anthropogenic N2O emissions. However, emissions are currently underestimated in most greenhouse gas inventories due to overly simplified emission processes of WWTPs in the IPCC guidelines. Key limitations towards more realistic estimations are the low availability of representative monitoring campaigns and a limited understanding of N2O formation mechanism during biological nitrogen removal in WWTPs. In particular, N2O emission patterns assessed in long-term full-scale monitoring campaigns have shown strong seasonal variations, highlighting the requirement for long-term monitoring campaigns as basis for representative emission factor estimation. But underlying causes for the seasonal dynamics are unclear. Therefore, this thesis investigated (i) methods for long-term emission monitoring and the assessment of representative emission factors (EFs), (ii) methodologies for a more realistic estimation of countrywide N2O emissions and (iii) causes of the seasonal emission pattern to ultimately propose mitigation measures. [...]

Lachgasemissionen (N2O) tragen substantiell zu bedeutenden, globalen Umweltproblemen bei: dem Klimawandel und der stratosphärischen Zerstörung von Ozon. Kläranlagen (ARAs) sind relevante N2O Punktquellen und verursachen einen relevanten Teil der anthropogenen Emissionen. Gegenwärtig werden die N2O Emissionen aus ARAs in den meisten Treibhausgasinventaren jedoch unterschätzt, da die Emissionsprozesse in den üblicherweise verwendeten IPCC Richtlinien unzureichend abgebildet werden. Die Hauptgründe dafür sind eine limitierte Verfügbarkeit an repräsentativen Langzeitdaten und ein fehlendes Verständnis der N2O Bildung während der biologischen Stickstoffelimination auf ARAs. Insbesondere die Ursachen für die saisonale Variabilität der Emission sind unbekannt. Die hohe Variabilität im Jahresverlauf unterstreicht die Notwendigkeit von Langzeitmess-kampagnen als Grundlage für eine repräsentative Schätzung der Emissionsfaktoren. Deshalb hatte die vorliegende Doktorarbeit folgende Zielsetzung: (i) Entwicklung und Anwendung einer Methode zur langfristigen Emissions-überwachung und zur Abschätzung repräsentativer Emissionsfaktoren (EFs), (ii) Erarbeitung eine Methode für eine realistischere Abschätzung der landesweiten N2O Emissionen ARAs sowie (iii) Charakterisierung von ursächlichen Faktoren für die saisonale Variabilität, um schließlich Maßnahmen zur Emissionsminderung vorzuschlagen. [...]
Hausherr, D., Niederdorfer, R., Morgenroth, E., & Joss, A. (2021). Robustness of mainstream anammox activity at bench and pilot scale. Science of the Total Environment, 796, 148920 (11 pp.). doi:10.1016/j.scitotenv.2021.148920, Institutional Repository

New technologies and processes, such as mainstream anammox, aim to reduce energy requirements of wastewater treatment and improve effluent quality. However, in municipal wastewater (MWW) anammox system are often unstable due to process control disturbance, influent variability, or unwanted nitrite oxidizing bacteria (NOB). This study examines the anammox system by focusing on anammox activity and its robustness in a mainstream environment. An 8 m3 pilot-scale sequencing batch reactor (SBR) receiving pretreated MWW (with external nitrite addition) was seeded with pre-colonized carriers. Within six months at 12–20 °C an anammox activity of 200 gN·m−3·d−1 was achieved. After the startup an anammox activity of 260 ± 83 gN·m−3·d−1 was maintained over 450 days. The robustness of the anammox activity was analyzed through three disturbance experiments. Anammox biofilm on carriers were exposed to dissolved oxygen (DO = 1.6 mg·L−1, intermittent aeration), organic loading rate (OLR, C/N increased from 2:1 to 5:1) and temperature disturbances (20 °C to 12 °C) in triplicate 12 L bench scale reactors. The anammox activity and microbial community was monitored during these disturbances. The DO and OLR disturbance experiments were replicated at pilot scale to investigate upscaling effects. Bench and pilot scale anammox activity were unaffected by the DO disturbance. Similarly, an increase in OLR did not deteriorate the bench and pilot scale anammox activity, if nitrate was available. When, at bench scale, the reactor temperature was reduced from 20 °C to 12 °C overnight, anammox activity decreased significantly, this was not the case for the slow seasonal temperature changes (12–25 °C) at pilot scale where no strong temperature dependency was detected in winter. Metagenomic analysis revealed a broad range of Brocadiaceae species with no single dominant anammox species. Anammox thrive under mainstream conditions and can withstand typical process disruptions.
Magyar, P. M., Hausherr, D., Niederdorfer, R., Stöcklin, N., Wei, J., Mohn, J., … Lehmann, M. F. (2021). Nitrogen isotope effects can be used to diagnose N transformations in wastewater anammox systems. Scientific Reports, 11(1), 7850 (12 pp.). doi:10.1038/s41598-021-87184-0, Institutional Repository

Anaerobic ammonium oxidation (anammox) plays an important role in aquatic systems as a sink of bioavailable nitrogen (N), and in engineered processes by removing ammonium from wastewater. The isotope effects anammox imparts in the N isotope signatures (15N/14N) of ammonium, nitrite, and nitrate can be used to estimate its role in environmental settings, to describe physiological and ecological variations in the anammox process, and possibly to optimize anammox-based wastewater treatment. We measured the stable N-isotope composition of ammonium, nitrite, and nitrate in wastewater cultivations of anammox bacteria. We find that the N isotope enrichment factor 15ε for the reduction of nitrite to N2 is consistent across all experimental conditions (13.5‰ ± 3.7‰), suggesting it reflects the composition of the anammox bacteria community. Values of 15ε for the oxidation of nitrite to nitrate (inverse isotope effect, - 16 to - 43‰) and for the reduction of ammonium to N2 (normal isotope effect, 19-32‰) are more variable, and likely controlled by experimental conditions. We argue that the variations in the isotope effects can be tied to the metabolism and physiology of anammox bacteria, and that the broad range of isotope effects observed for anammox introduces complications for analyzing N-isotope mass balances in natural systems.
Niederdorfer, R., Hausherr, D., Palomo, A., Wei, J., Magyar, P., Smets, B. F., … Bürgmann, H. (2021). Temperature modulates stress response in mainstream anammox reactors. Communications Biology, 4(1), 23 (12 pp.). doi:10.1038/s42003-020-01534-8, Institutional Repository

Autotrophic nitrogen removal by anaerobic ammonium oxidizing (anammox) bacteria is an energy-efficient nitrogen removal process in wastewater treatment. However, full-scale deployment under mainstream conditions remains challenging for practitioners due to the high stress susceptibility of anammox bacteria towards fluctuations in dissolved oxygen (DO) and temperature. Here, we investigated the response of microbial biofilms with verified anammox activity to DO shocks under 20 °C and 14 °C. While pulse disturbances of 0.3 mg L−1 DO prompted only moderate declines in the NH4+ removal rates, 1.0 mg L−1 DO led to complete but reversible inhibition of the NH4+ removal activity in all reactors. Genome-centric metagenomics and metatranscriptomics were used to investigate the stress response on various biological levels. We show that temperature regime and strength of DO perturbations induced divergent responses from the process level down to the transcriptional profile of individual taxa. Community-wide gene expression differed significantly depending on the temperature regime in all reactors, and we found a noticeable impact of DO disturbances on genes involved in transcription, translation, replication and posttranslational modification at 20 °C but not 14 °C. Genome-centric analysis revealed that different anammox species and other key biofilm taxa differed in their transcriptional responses to distinct temperature regimes and DO disturbances.
Burdon, F. J., Bai, Y., Reyes, M., Tamminen, M., Staudacher, P., Mangold, S., … Stamm, C. (2020). Stream microbial communities and ecosystem functioning show complex responses to multiple stressors in wastewater. Global Change Biology, 26(11), 6363-6382. doi:10.1111/gcb.15302, Institutional Repository

Multiple anthropogenic drivers are changing ecosystems globally, with a disproportionate and intensifying impact on freshwater habitats. A major impact of urbanization are inputs from wastewater treatment plants (WWTPs). Initially designed to reduce eutrophication and improve water quality, WWTPs increasingly release a multitude of micropollutants (MPs; i.e., synthetic chemicals) and microbes (including antibiotic‐resistant bacteria) to receiving environments. This pollution may have pervasive impacts on biodiversity and ecosystem services. Viewed through multiple lenses of macroecological and ecotoxicological theory, we combined field, flume, and laboratory experiments to determine the effects of wastewater (WW) on microbial communities and organic‐matter processing using a standardized decomposition assay. First, we conducted a mensurative experiment sampling 60 locations above and below WWTP discharges in 20 Swiss streams. Microbial respiration and decomposition rates were positively influenced by WW inputs via warming and nutrient enrichment, but with a notable exception: WW decreased the activation energy of decomposition, indicating a "slowing" of this fundamental ecosystem process in response to temperature. Second, next‐generation sequencing indicated that microbial community structure below WWTPs was altered, with significant compositional turnover, reduced richness, and evidence of negative MP influences. Third, a series of flume experiments confirmed that although diluted WW generally has positive influences on microbial‐mediated processes, the negative effects of MPs are "masked" by nutrient enrichment. Finally, transplant experiments suggested that WW‐borne microbes enhance decomposition rates. Taken together, our results affirm the multiple stressor paradigm by showing that different aspects of WW (warming, nutrients, microbes, and MPs) jointly influence ecosystem functioning in complex ways. Increased respiration rates below WWTPs potentially generate ecosystem "disservices" via greater carbon evasion from streams and rivers. However, toxic MP effects may fundamentally alter ecological scaling relationships, indicating the need for a rapprochement between ecotoxicological and macroecological perspectives.
Böhler, M., Hernandez, A., McArdell, C. S., Siegrist, H., Joss, A., & Baggenstos, M. (2020). Elimination von Spurenstoffen durch granulierte Aktivkohle-Filtration (GAK). Grosstechnische Untersuchungen auf der ARA Furt, Bülach. Schlussbericht. Dübendorf: Eawag. , Institutional Repository
Böhler, M., Joss, A., McArdell, C., & Meier, A. (2020). Hinweise zur Planung und Auslegung von diskontinuierlich gespülten GAK-Filtern zur Elimination organischer Spurenstoffe aus kommunalem Abwasser. Konsenspapier zum Ergebnis des Workshops vom 9.12.2019 an der Eawag. Dübendorf: Eawag; VSA. , Institutional Repository
Böhler, M., Joss, A., McArdell, C., & Meier, A. (2020). Notice explicative pour la planification et le dimensionnement de filtres à charbon actif en grains (CAG) rétrolavés discontinuellement pour l'élimination des composés traces organiques dans les eaux usées communales. Document de synthèse suite au workshop du 9.12.2019 à l'Eawag. Dübendorf: Eawag; VSA. , Institutional Repository
Burdon, F. J., Munz, N. A., Reyes, M., Focks, A., Joss, A., Räsänen, K., … Stamm, C. (2019). Agriculture versus wastewater pollution as drivers of macroinvertebrate community structure in streams. Science of the Total Environment, 659, 1256-1265. doi:10.1016/j.scitotenv.2018.12.372, Institutional Repository

Water pollution is ubiquitous globally, yet how the effects of pollutants propagate through natural ecosystems remains poorly understood. This is because the interactive effects of multiple stressors are generally hard to predict. Agriculture and municipal wastewater treatment plants (WWTPs) are often major sources of contaminants for streams, but their relative importance and the role of different pollutants (e.g. nutrients or pesticides) are largely unknown. Using a 'real world experiment' with sampling locations up- and downstream of WWTPs, we studied how effluent discharges affected water quality and macroinvertebrate communities in 23 Swiss streams across a broad land-use gradient.
Variation partitioning of community composition revealed that overall water quality explained approximately 30% of community variability, whereby nutrients and pesticides each independently explained 10% and 2%, respectively. Excluding oligochaetes (which were highly abundant downstream of the WWTPs) from the analyses, resulted in a relatively stronger influence (3%) of pesticides on the macroinvertebrate community composition, whereas nutrients had no influence. Generally, the macroinvertebrate community composition downstream of the WWTPs strongly reflected the upstream conditions, likely due to a combination of efficient treatment processes, environmental filtering and organismal dispersal. Wastewater impacts were most prominently by the Saprobic index, whereas the SPEAR index (a trait-based macroinvertebrate metrics reflecting sensitivity to pesticides) revealed a strong impact of arable cropping but only a weak impact of wastewater.
Overall, our results indicate that agriculture can have a stronger impact on headwater stream macroinvertebrate communities than discharges from WWTP. Yet, effects of wastewater-born micropollutants were clearly quantifiable among all other influence factors. Improving our ability to further quantify the impacts of micropollutants requires highly-resolved water quality and taxonomic data with adequate spatial and temporal sampling. These improvements would help to better account for the underlying causal pathways that drive observed biological responses, such as episodic contaminant peaks and dispersal-related processes.
Böhler, M. A., Remy, C., Löwenberg, J., Hagemann, N., Hernandez, A., Joss, A., & McArdell, C. S. (2019). Kann die Kohle nachhaltig sein? – Einsatz von Aktivkohle zur Elimination von Spurenstoffen aus kommunalem Abwasser. In M. Wessling & J. Pinnekamp (Eds.), 13. Aachener Tagung Wassertechnologie. Verfahren der Wasseraufbereitung und Abwasserbehandlung (pp. 51-62). Aachen: RWTH Aachen. , Institutional Repository
Gruber, W., Villez, K., Kipf, M., Wunderlin, P., Siegrist, H., Vogt, L., & Joss, A. (2019). N2O emission in full-scale wastewater treatment: proposing a refined monitoring strategy. Science of the Total Environment, 699, 134157 (9 pp.). doi:10.1016/j.scitotenv.2019.134157, Institutional Repository

Nitrous oxide (N2O) emissions from wastewater treatment contribute significantly to greenhouse gas emissions. They have been shown to exhibit a strong seasonal and daily profile in previously conducted monitoring campaigns. However, only two year-long online monitoring campaigns have been published to date. Based on three monitoring campaigns on three full-scale wastewater treatment plants (WWTPs) with different activated sludge configurations, each of which lasted at least one year, we propose a refined monitoring strategy for long-term emission monitoring with multiple flux chambers on open tanks. Our monitoring campaigns confirm that the N2O emissions exhibited a strong seasonal profile and were substantial on all three plants (1-2.4% of the total nitrogen load). These results confirm that N2O is the most important greenhouse gas emission from wastewater treatment. The temporal variation was more distinct than the spatial variation within aeration tanks. Nevertheless, multiple monitoring spots along a single lane are crucial to assess representative emission factors in flow-through systems. Sequencing batch reactor systems were shown to exhibit comparable emissions within one reactor but significant variation between parallel reactors. The results indicate that considerable emission differences between lanes are to be expected in cases of inhomogeneous loading and discontinuous feeding. For example, N2O emission could be shown to depend on the amount of treated reject water: lanes without emitted <1% of the influent load, while parallel lanes emitted around 3%. In case of inhomogeneous loading, monitoring of multiple lanes is required. Our study enables robust planning of monitoring campaigns on WWTPs with open tanks. Extensive full-scale emission monitoring campaigns are important as a basis for reliable decisions about reducing the climate impact of wastewater treatment. More specifically, such data sets help us to define general emission factors for wastewater treatment plants and to construct and critically evaluate N2O emission models.
Horisberger, M., Casazza, R., Grelot, J., & Joss, A. (2019). Elimination von Mikroverunreinigungen. Pilotversuche: Einsatz von granulierter Aktivkohle im Wirbelbett auf der Ara Penthaz. Aqua & Gas, 99(1), 39-45. , Institutional Repository

Im Rahmen der Erweiterung der ARA Penthaz VD um eine Reinigungsstufe zur Elimination von Mikroverunreinigungen wurden Pilotversuche mit granulierter Aktivkohle im Wirbelbett (CarboPlus®-Verfahren) durchgeführt. Sie zeigten, dass sich mit diesem Verfahren die Anforderungen der Schweizer Gesetzgebung an die Elimination von Mikroverunreinigungen erfüllen lassen. Zudem konnten in den Versuchen Parameter zur Überwachung des Betriebs ermittelt werden. Aufgrund der vielversprechenden Ergebnisse wurde das Verfahren auf der ARA Penthaz grosstechnisch realisiert und im Herbst 2018 in Betrieb genommen.
Laureni, M., Weissbrodt, D. G., Villez, K., Robin, O., de Jonge, N., Rosenthal, A., … Joss, A. (2019). Biomass segregation between biofilm and flocs improves the control of nitrite-oxidizing bacteria in mainstream partial nitritation and anammox processes. Water Research, 154, 104-116. doi:10.1016/j.watres.2018.12.051, Institutional Repository

The control of nitrite-oxidizing bacteria (NOB) challenges the implementation of partial nitritation and anammox (PN/A) processes under mainstream conditions. The aim of the present study was to understand how operating conditions impact microbial competition and the control of NOB in hybrid PN/A systems, where biofilm and flocs coexist. A hybrid PN/A moving-bed biofilm reactor (MBBR; also referred to as integrated fixed film activated sludge or IFAS) was operated at 15 °C on aerobically pre-treated municipal wastewater (23 mgNH4-N L–1). Ammonium-oxidizing bacteria (AOB) and NOB were enriched primarily in the flocs, and anammox bacteria (AMX) in the biofilm. After decreasing the dissolved oxygen concentration (DO) from 1.2 to 0.17 mgO2 L–1 - with all other operating conditions unchanged - washout of NOB from the flocs was observed. The activity of the minor NOB fraction remaining in the biofilm was suppressed at low DO. As a result, low effluent NO3– concentrations (0.5 mgN L–1) were consistently achieved at aerobic nitrogen removal rates (80 mgN L–1 d–1) comparable to those of conventional treatment plants. A simple dynamic mathematical model, assuming perfect biomass segregation with AOB and NOB in the flocs and AMX in the biofilm, was able to qualitatively reproduce the selective washout of NOB from the flocs in response to the decrease in DO-setpoint. Similarly, numerical simulations indicated that flocs removal is an effective operational strategy to achieve the selective washout of NOB. The direct competition for NO2– between NOB and AMX - the latter retained in the biofilm and acting as a "NO2-sink" - was identified by the model as key mechanism leading to a difference in the actual growth rates of AOB and NOB (i.e., μNOB < μAOB in flocs) and allowing for the selective NOB washout over a broad range of simulated sludge retention times (SRT = 6.8–24.5 d). Experimental results and model predictions demonstrate the increased operational flexibility, in terms of variables that can be easily controlled by operators, offered by hybrid systems as compared to solely biofilm systems for the control of NOB in mainstream PN/A applications.
Mansfeldt, C., Achermann, S., Men, Y., Walser, J. C., Villez, K., Joss, A., … Fenner, K. (2019). Microbial residence time is a controlling parameter of the taxonomic composition and functional profile of microbial communities. ISME Journal, 13(6), 1589-1601. doi:10.1038/s41396-019-0371-6, Institutional Repository

A remaining challenge within microbial ecology is to understand the determinants of richness and diversity observed in environmental microbial communities. In a range of systems, including activated sludge bioreactors, the microbial residence time (MRT) has been previously shown to shape the microbial community composition. However, the physiological and ecological mechanisms driving this influence have remained unclear. Here, this relationship is explored by analyzing an activated sludge system fed with municipal wastewater. Using a model designed in this study based on Monod-growth kinetics, longer MRTs were shown to increase the range of growth parameters that enable persistence, resulting in increased richness and diversity in the modeled community. In laboratory experiments, six sequencing batch reactors treating domestic wastewater were operated in parallel at MRTs between 1 and 15 days. The communities were characterized using both 16S ribosomal RNA and non-target messenger RNA sequencing (metatranscriptomic analysis), and model-predicted monotonic increases in richness were confirmed in both profiles. Accordingly, taxonomic Shannon diversity also increased with MRT. In contrast, the diversity in enzyme class annotations resulting from the metatranscriptomic analysis displayed a non-monotonic trend over the MRT gradient. Disproportionately high abundances of transcripts encoding for rarer enzymes occur at longer MRTs and lead to the disconnect between taxonomic and functional diversity profiles.
Nürenberg, G., Kunkel, U., Wick, A., Falås, P., Joss, A., & Ternes, T. A. (2019). Nontarget analysis: a new tool for the evaluation of wastewater processes. Water Research, 163, 114842 (11 pp.). doi:10.1016/j.watres.2019.07.009, Institutional Repository

Strategies to determine the removal efficiency of micropollutants in wastewater treatment plants (WWTPs) are widely discussed. Especially the evaluation of the potential benefit of further advanced treatment steps such as an additional tertiary treatment based on ozonation or activated carbon have come into focus. Such evaluation strategies are often based on the removal behavior of known micropollutants via target or suspected analysis. The utilization of nontarget analysis is considered to lead to a more comprehensive picture as also unknown or not expected micropollutants are analyzed. Here, the results of an evaluation via target and nontarget analysis were compared for biological treatment (BT) processes of eleven full-scale WWTPs and three different post-treatments (PTs): one sand filter (SF) and two granular activated carbon (GAC) filters. The similarity of the determined removals from target and nontarget analysis of the BTs increased significantly by excluding easily degradable "features" from the nontarget evaluation. A similar ranking of the removal trends for the BTs could also be achieved by comparing this new subset of nontarget features with a set of nine readily to moderately biodegradable micropollutants. This observation suggests that a performance ranking of BTs based either on target or nontarget analysis is plausible. In contrast to the BTs, the evaluation of the three PTs revealed that the difference of feature removal between SF and the two GACs was small, but large for the target analytes with substantially higher removal effciencies for the GACs compared to the SF. In addition to the removal behavior, the nontarget analysis provided further information about the number and quantity of transformation products (TPs) in the effluent from the BTs. For all BTs more than half (55–67%) of the features detected in the effluent were not found in the influent. A comparable proportion of TPs was also detected after GAC and sand filtration due to their microbial activities.
Siegrist, H., Joss, A., Boehler, M., McArdell, C. S., & Ternes, T. (2019). Organic micropollutant control. In G. Mannina, G. Ekama, H. Ødegaard, & G. Olsson (Eds.), Advances in wastewater treatment (pp. 231-260). doi:10.2166/9781780409719_0231, Institutional Repository

About 100,000 chemical substances have economic uses, of which 4,600 substances are produced annually in quantities exceeding 1,000 tons in the OECD member states. During production and disposal, as well as after regular use, a significant portion of these substances will unavoidably enter the aquatic environment, where they can have ecotoxicological effects, such as fish feminization. Organic compounds are increasingly being detected in water bodies and in sewage sludge in low concentration ranges (μg/L and ng/L), being referred to as organic micropollutants. T he removal of micropollutants by conventional municipal wastewater treatment is incomplete and a multitude of compounds are only slightly abated. To significantly reduce eco-toxicological effects of micropollutants in receiving waters and water resources, additional treatment steps (e.g. ozonation or activated carbon adsorption) are required in combination with measures taken at the source. Ozonation requires complete nitrification and it might not be suitable for wastewater with high industrial wastewater fractions and high bromide concentrations due to the production of bromate and increased oxidation by-products. Powdered activated carbon (PAC) addition is already broadly applied. PAC can be recycled to the activated sludge treatment to improve micropollutant removal and therefore reduce PAC consumption. Recently granular activated carbon (GAC) filters are increasingly investigated and built in full scale for micropollutant and dissolved organic carbon (DOC) removal. Additional measures in wastewater treatment should be based on careful micropollutant mass flux studies to identify critical catchment areas so that relevant hot spots can be addressed.
Achermann, S., Falås, P., Joss, A., Mansfeldt, C., Men, Y., Vogler, B., & Fenner, K. (2018). Trends in micropollutant biotransformation along a solids retention time gradient. Environmental Science and Technology, 52(20), 11601-11611. doi:10.1021/acs.est.8b02763, Institutional Repository

For many polar organic micropollutants, biotransformation by activated sludge microorganisms is a major removal process during wastewater treatment. However, our current understanding of how wastewater treatment operations influence microbial communities and their micropollutant biotransformation potential is limited, leaving major parts of observed variability in biotransformation rates across treatment facilities unexplained. Here, we present biotransformation rate constants for 42 micropollutants belonging to different chemical classes along a gradient of solids retention time (SRT). The geometric mean of biomass-normalized first-order rate constants shows a clear increase between 3 d and 15 d SRT by 160% and 87%, respectively, in two experiments. However, individual micropollutants show a variety of trends. Rate constants of oxidative biotransformation reactions mostly increased with SRT. Yet, nitrifying activity could be excluded as primary driver. For substances undergoing other than oxidative reactions, i.e. mostly substitution-type reactions, more diverse dependencies on SRT were observed. Most remarkably, characteristic trends were observed for groups of substances undergoing similar types of initial transformation reaction, suggesting that shared enzymes or enzyme systems that are conjointly regulated catalyze biotransformation reactions within such groups. These findings open up opportunities for correlating rate constants with measures of enzyme abundance, which in turn should help to identify genes or gene products associated with the respective biotransformation reactions.
Falås, P., Jewell, K. S., Hermes, N., Wick, A., Ternes, T. A., Joss, A., & Nielsen, J. L. (2018). Transformation, CO2 formation and uptake of four organic micropollutants by carrier-attached microorganisms. Water Research, 141, 405-416. doi:10.1016/j.watres.2018.03.040, Institutional Repository

A tiered process was developed to assess the transformation, CO2 formation and uptake of four organic micropollutants by carrier-attached microorganisms from two municipal wastewater treatment plants. At the first tier, primary transformation of ibuprofen, naproxen, diclofenac, and mecoprop by carrier-attached microorganisms was shown by the dissipation of the target compounds and the formation of five transformation products using LC-tandem MS. At the second tier, the microbial cleavage of the four organic micropollutants was confirmed with 14C-labeled micropollutants through liquid scintillation counting of the 14CO2 formed. At the third tier, microautoradiography coupled with fluorescence in situ hybridization (MAR-FISH) was used to screen carrier-attached microorganisms for uptake of the four radiolabeled micropollutants. Results from the MAR-FISH screening indicated that only a small fraction of the microbial community (≤1‰) was involved in the uptake of the radiolabeled micropollutants and that the responsible microorganisms differed between the compounds. At the fourth tier, the microbial community structure of the carrier-attached biofilms was analyzed by 16S rRNA gene amplicon sequencing. The sequencing results showed that the MAR-FISH screening targeted ∼80% of the microbial community and that several taxonomic families within the FISH-probed populations with MAR-positive signals (i.e. Firmicutes, Gammaproteobacteria, and Deltaproteobacteria) were present in both biofilms. From the broader perspective of organic micropollutant removal in biological wastewater treatment, the MAR-FISH results of this study indicate a high degree of microbial substrate specialization that could explain differences in transformation rates and patterns between micropollutants and microbial communities.
Horisberger, M., Casazza, R., Grelot, J., & Joss, A. (2018). Élimination des micropolluants. Essais pilotes: traitement par charbon actif en grain en lit fluidisé à la step de Penthaz. Aqua & Gas, 98(10), 44-50. , Institutional Repository

En vue de la construction d’un traitement des micropolluants à la STEP de Penthaz (VD), des essais pilotes avec du charbon actif en grain (CAG) en lit fluidisé (procédé CarboPlus®) ont été réalisés. Ces essais pilotes ont montré que ce procédé permet d'éliminer les micropolluants des eaux usées selon les bases légales suisses. Ils ont de plus permis de développer des mesures pertinentes pour le suivi de l’installation. En raison des résultats prometteurs, ce procédé a été validé. L'installation est en cours de réalisation et sera mise en service en automne 2018.
Kassotaki, E., Pijuan, M., Joss, A., Borrego, C. M., Rodriguez-Roda, I., & Buttiglieri, G. (2018). Unraveling the potential of a combined nitritation-anammox biomass towards the biodegradation of pharmaceutically active compounds. Science of the Total Environment, 624, 722-731. doi:10.1016/j.scitotenv.2017.12.116, Institutional Repository

In the past few years, anaerobic ammonium oxidation-based processes have attracted a lot of attention for their implementation at the mainstream line of wastewater treatment plants, due to the possibility of leading to energy autarky if combined with anaerobic digestion. However, little is known about the potential degradation of micropollutants by the microbial groups responsible of these processes and the few results available are inconclusive. This study aimed to assess the degradation capability of biomass withdrawn from a combined nitritation/anaerobic ammonium oxidation (combined N/A) pilot plant towards five pharmaceutically active compounds (ibuprofen, sulfamethoxazole, metoprolol, venlafaxine and carbamazepine). Batch experiments were performed under different conditions by selectively activating or inhibiting different microbial groups: i) regular combined N/A operation, ii) aerobic (optimal for nitrifying bacteria), iii) aerobic with allylthiourea (an inhibitor of ammonia monooxygenase, enzyme of ammonia oxidizing bacteria), iv) anoxic (optimal for anaerobic ammonium oxidizing bacteria), v) aerobic with acetate (optimal for heterotrophic bacteria) and vi) anoxic with acetate (optimal for heterotrophic denitrifying bacteria). Ibuprofen was the most biodegradable compound being significantly degraded (49–100%) under any condition except heterotrophic denitrification. Sulfamethoxazole, exhibited the highest removal (70%) under optimal conditions for nitrifying bacteria but in the rest of the experiments anoxic conditions were found to be slightly more favorable (up to 58%). For metoprolol the highest performance was obtained under anoxic conditions favoring anammox bacteria (62%). Finally, carbamazepine and venlafaxine were hardly removed (≤ 10% in the majority of cases). Taken together, these results suggest the specificity of different microbial groups that in combination with alternating operational parameters can lead to enhanced removal of some micropollutants.
Bitterwolf, S., Böhler, M., Siegrist, H., & Joss, A. (2017). Elimination von Spurenstoffen durch granulierte Aktivkohle (GAK) Filtration: Grosstechnische Untersuchungen auf der ARA Furt-Bülach. Zwischenbericht. Dübendorf: Eawag. , Institutional Repository
Stamm, C., Burdon, F., Fischer, S., Kienle, C., Munz, N., Tlili, A., … Eggen, R. (2017). Einfluss von Mikroverunreinigungen. Aqua & Gas, 97(6), 90-95. , Institutional Repository

Im Projekt EcoImpact wurden die ökotoxikologischen und ökologischen Effekte von Mikroverunreinigungen aus Kläranlagen auf aquatische Lebensgemeinschaften untersucht. Chemische und biologische Untersuchungen oberhalb und unterhalb von Kläranlagen deuten auf Effekte dieser Stoffe hin, die von physiologischen Antworten der Organismen bis hin zu veränderten Ökosystemfunktionen wie z. B. dem Laubabbau reichen. Gezielte Rinnenexperimente mit kontrollierter Wasserqualität unterstützen diese Befunde.
Völker, J., Vogt, T., Castronovo, S., Wick, A., Ternes, T. A., Joss, A., … Wagner, M. (2017). Extended anaerobic conditions in the biological wastewater treatment: higher reduction of toxicity compared to target organic micropollutants. Water Research, 116, 220-230. doi:10.1016/j.watres.2017.03.030, Institutional Repository

Extended anaerobic conditions during biological wastewater treatment may enhance the biodegradation of micropollutants. To explore this, we combined iron-reducing or substrate-limited anaerobic conditions and aerobic pilot-scale reactors directly at a wastewater treatment plant. To investigate the detoxification by these processes, we applied two in vitro bioassays for baseline toxicity (Microtox) and reactive toxicity (AREc32) as well as in vivo bioassays with aquatic model species in two laboratory experiments (Desmodesmus subspicatus, Daphnia magna) and two on-site, flow-through experiments (Potamopyrgus antipodarum, Lumbriculus variegatus). Moreover, we analyzed 31 commonly occurring micropollutants and 10 metabolites.
The baseline toxicity of raw wastewater was effectively removed in full-scale and reactor scale activated sludge treatment (>85%), while the oxidative stress response was only partially removed (>61%). A combination of an anaerobic pre-treatment under iron reducing conditions and an aerobic nitrification significantly further reduced the residual in vitro toxicities by 46–60% and outperformed the second combination consisting of an aerobic pre-treatment and an anaerobic post-treatment under substrate-limiting conditions (27–43%). Exposure to effluents of the activated sludge treatment did not induce adverse in vivo effects in aquatic invertebrates. Accordingly, no further improvement in water quality could be observed. Compared to that, the removal of persistent micropollutants was increased. However, this observation was restricted to a limited number of compounds and the removal of the sum concentration of all target micropollutants was relative low (14–17%).
In conclusion, combinations of strictly anaerobic and aerobic processes significantly enhanced the removal of specific and non-specific in vitro toxicities. Thus, an optimization of biological wastewater treatment can lead to a substantially improved detoxification. These otherwise hidden capacities of a treatment technology can only be uncovered by a complementary biological analysis.
Wells, G. F., Shi, Y., Laureni, M., Rosenthal, A., Szivák, I., Weissbrodt, D. G., … Morgenroth, E. (2017). Comparing the resistance, resilience, and stability of replicate moving bed biofilm and suspended growth combined nitritation–anammox reactors. Environmental Science and Technology, 51(9), 5108-5117. doi:10.1021/acs.est.6b05878, Institutional Repository

Combined partial nitritation–anammox (PN/A) systems are increasingly being employed for sustainable removal of nitrogen from wastewater, but process instabilities present ongoing challenges for practitioners. The goal of this study was to elucidate differences in process stability between PN/A process variations employing two distinct aggregate types: biofilm [in moving bed biofilm reactors (MBBRs)] and suspended growth biomass. Triplicate reactors for each process variation were studied under baseline conditions and in response to a series of transient perturbations. MBBRs displayed elevated NH4+ removal rates relative to those of suspended growth counterparts over six months of unperturbed baseline operation but also exhibited significantly greater variability in performance. Transient perturbations led to strikingly divergent yet reproducible behavior in biofilm versus suspended growth systems. A temperature perturbation prompted a sharp reduction in NH4+ removal rates with no accumulation of NO2– and rapid recovery in MBBRs, compared to a similar reduction in NH4+ removal rates but a high level of accumulation of NO2– in suspended growth reactors. Pulse additions of a nitrification inhibitor (allylthiourea) prompted only moderate declines in performance in suspended growth reactors compared to sharp decreases in NH4+ removal rates in MBBRs. Quantitative fluorescence in situ hybridization demonstrated a significant enrichment of anammox in MBBRs compared to suspended growth reactors, and conversely a proportionally higher AOB abundance in suspended growth reactors. Overall, MBBRs displayed significantly increased susceptibility to transient perturbations employed in this study compared to that of suspended growth counterparts (stability parameter), including significantly longer recovery times (resilience). No significant difference in the maximal impact of perturbations (resistance) was apparent. Taken together, our results suggest that aggregate architecture (biofilm vs suspended growth) in PN/A processes exerts an unexpectedly strong influence on process stability.
Burdon, F. J., Reyes, M., Alder, A. C., Joss, A., Ort, C., Räsänen, K., … Stamm, C. (2016). Environmental context and magnitude of disturbance influence trait-mediated community responses to wastewater in streams. Ecology and Evolution, 6(12), 3923-3939. doi:10.1002/ece3.2165, Institutional Repository

Human land uses and population growth represent major global threats to biodiversity and ecosystem services. Understanding how biological communities respond to multiple drivers of human-induced environmental change is fundamental for conserving ecosystems and remediating degraded habitats. Here, we used a replicated ‘real-world experiment’ to study the responses of invertebrate communities to wastewater perturbations across a land-use intensity gradient in 12 Swiss streams. We used different taxonomy and trait-based community descriptors to establish the most sensitive indicators detecting impacts and to help elucidate potential causal mechanisms of change. First, we predicted that streams in catchments adversely impacted by human land-uses would be less impaired by wastewater inputs because their invertebrate communities should be dominated by pollution-tolerant taxa (‘environmental context’). Second, we predicted that the negative effects of wastewater on stream invertebrate communities should be larger in streams that receive proportionally more wastewater (‘magnitude of disturbance’). In support of the ‘environmental context’ hypothesis, we found that change in the Saprobic Index (a trait-based indicator of tolerance to organic pollution) was associated with upstream community composition; communities in catchments with intensive agricultural land uses (e.g., arable cropping and pasture) were generally more resistant to eutrophication associated with wastewater inputs. We also found support for the ‘magnitude of disturbance’ hypothesis. The SPEAR Index (a trait-based indicator of sensitivity to pesticides) was more sensitive to the relative input of effluent, suggesting that toxic influences of wastewater scale with dilution. Whilst freshwater pollution continues to be a major environmental problem, our findings highlight that the same anthropogenic pressure (i.e., inputs of wastewater) may induce different ecological responses depending on the environmental context and community metrics used. Thus, remediation strategies aiming to improve stream ecological status (e.g., rehabilitating degraded reaches) need to consider upstream anthropogenic influences and the most appropriate indicators of restoration success.
Falås, P., Wick, A., Castronovo, S., Habermacher, J., Ternes, T. A., & Joss, A. (2016). Tracing the limits of organic micropollutant removal in biological wastewater treatment. Water Research, 95, 240-249. doi:10.1016/j.watres.2016.03.009, Institutional Repository

Removal of organic micropollutants was investigated in 15 diverse biological reactors through short and long-term experiments. Short-term batch experiments were performed with activated sludge from three parallel sequencing batch reactors (25, 40, and 80 d solid retention time, SRT) fed with synthetic wastewater without micropollutants for one year. Despite the minimal micropollutant exposure, the synthetic wastewater sludges were able to degrade several micropollutants present in municipal wastewater. The degradation occurred immediately after spiking (1–5 μg/L), showed no strong or systematic correlation to the sludge age, and proceeded at rates comparable to those of municipal wastewater sludges. Thus, the results from the batch experiments indicate that degradation of organic micropollutants in biological wastewater treatment is quite insensitive to SRT increases from 25 to 80 days, and not necessarily induced by exposure to micropollutants. Long-term experiments with municipal wastewater were performed to assess the potential for extended biological micropollutant removal under different redox conditions and substrate concentrations (carbon and nitrogen). A total of 31 organic micropollutants were monitored through influent-effluent sampling of twelve municipal wastewater reactors. In accordance with the results from the sludges grown on synthetic wastewater, several compounds such as bezafibrate, atenolol and acyclovir were significantly removed in the activated sludge processes fed with municipal wastewater. Complementary removal of two compounds, diuron and diclofenac, was achieved in an oxic biofilm treatment. A few aerobically persistent micropollutants such as venlafaxine, diatrizoate and tramadol were removed under anaerobic conditions, but a large number of micropollutants persisted in all biological treatments. Collectively, these results indicate that certain improvements in biological micropollutant removal can be achieved by combining different aerobic and anaerobic treatments, but that these improvements are restricted to a limited number of compounds.
Jewell, K. S., Castronovo, S., Wick, A., Falås, P., Joss, A., & Ternes, T. A. (2016). New insights into the transformation of trimethoprim during biological wastewater treatment. Water Research, 88, 550-557. doi:10.1016/j.watres.2015.10.026, Institutional Repository

The antibiotic trimethoprim (TMP), a micropollutant found at μg/L levels in raw wastewater, was investigated with regard to its (bio)transformation during biological wastewater treatment. A pilot-scale, nitrifying/denitrifying Sequencing Batch Reactor (SBR) fed with municipal wastewater was monitored for TMP removal during a 16-month monitoring study. Laboratory-scaled bioreactors spiked with TMP were applied to identify the transformation products (TPs). In total, six TPs could be identified from TMP. However, the TP formation was influenced by the spike concentration. At an initial concentration of 500 μg/L TMP, only two TPs were found, whereas at 5 μg/L a completely different transformation pathway led to four further TPs. At low concentrations, TMP was demethylated forming 4-desmethyl-TMP, which was then quickly hydroxylated, oxidized and cleaved forming 2,4-diaminopyrimidine-5-carboxylic acid (DAPC) via two intermediate TPs. DAPC was detected in the SBR effluent in a 3-d composite sample with 61 ng/L, which accounts for 52% of the attenuated TMP. The primary degradation at low spiking levels was best modelled by a pseudo-first order kinetic. Considering the SBR, the model predicted a TMP removal of 88–94% for the reactor, consistent with a monitoring campaign exhibiting an average removal of >83%. Both the TP formation profiles and kinetic modelling indicated that only the results from the bioreactor tests at low spike concentrations were representative of the transformation in the SBR.
Jewell, K. S., Falås, P., Wick, A., Joss, A., & Ternes, T. A. (2016). Transformation of diclofenac in hybrid biofilm–activated sludge processes. Water Research, 105, 559-567. doi:10.1016/j.watres.2016.08.002, Institutional Repository

The biotransformation of diclofenac during wastewater treatment was investigated. Attached growth biomass from a carrier-filled compartment of a hybrid-MBBR at the wastewater treatment plant (WWTP) in Bad Ragaz, Switzerland was used to test the biotransformation. Laboratory-scale incubation experiments were performed with diclofenac and carriers and high-resolution LC–QTof-MS was implemented to monitor the biotransformation. Up to 20 diclofenac transformation products (TPs) were detected. Tentative structures were proposed for 16 of the TPs after characterization by MS2 fragmentation and/or inferring the structure from the transformation pathway and the molecular formula given by the high resolution ionic mass. The remaining four TPs were unambiguously identified via analytical reference standards. The postulated reactions forming the TPs were: hydroxylation, decarboxylation, oxidation, amide formation, ring-opening and reductive dechlorination. Incubation experiments of individual TPs, those which were available as reference standards, provided a deeper look into the transformation pathways. It was found that the transformation consists of four main pathways but no pathway accounted for a clear majority of the transformation. A 10-day monitoring campaign of the full-scale plant confirmed an 88% removal of diclofenac (from approximately 1.6 μg/L in WWTP influent) and the formation of TPs as found in the laboratory was observed. One of the TPs, N-(2,6-dichlorophenyl)-2-indolinone detected at concentrations of around 0.25 μg/L in WWTP effluent, accounting for 16% of the influent diclofenac concentration. The biotransformation of carriers was compared to a second WWTP not utilising carriers. It was found that in contact with activated sludge, similar hydroxylation and decarboxylation reactions occurred but at much slower rates, whereas some reactions, e.g. reductive dechlorination, were not detected at all. Finally, incubation experiments were performed with attached growth biomass from a third WWTP with a similar process configuration to Bad Ragaz WWTP. A similarly effective removal of diclofenac was found with a similar presence of TPs.
Laureni, M., Falås, P., Robin, O., Wick, A., Weissbrodt, D. G., Nielsen, J. L., … Joss, A. (2016). Mainstream partial nitritation and anammox: long-term process stability and effluent quality at low temperatures. Water Research, 101, 628-639. doi:10.1016/j.watres.2016.05.005, Institutional Repository

The implementation of autotrophic anaerobic ammonium oxidation processes for the removal of nitrogen from municipal wastewater (known as “mainstream anammox”) bears the potential to bring wastewater treatment plants close to energy autarky. The aim of the present work was to assess the long-term stability of partial nitritation/anammox (PN/A) processes operating at low temperatures and their reliability in meeting nitrogen concentrations in the range of typical discharge limits below 2 mgNH4-N·L−1 and 10 mgNtot·L−1. Two main 12-L sequencing batch reactors were operated in parallel for PN/A on aerobically pre-treated municipal wastewater (21 ± 5 mgNH4-N·L−1 and residual 69 ± 19 mgCODtot·L−1) for more than one year, including over 5 months at 15 °C. The two systems consisted of a moving bed biofilm reactor (MBBR) and a hybrid MBBR (H-MBBR) with flocculent biomass. Operation at limiting oxygen concentrations (0.15–0.18 mgO2·L−1) allowed stable suppression of the activity of nitrite-oxidizing bacteria at 15 °C with a production of nitrate over ammonium consumed as low as 16% in the MBBR. Promising nitrogen removal rates of 20–40 mgN·L−1·d−1 were maintained at hydraulic retention times of 14 h. Stable ammonium and total nitrogen removal efficiencies over 90% and 70% respectively were achieved. Both reactors reached average concentrations of total nitrogen below 10 mgN·L−1 in their effluents, even down to 6 mgN·L−1 for the MBBR, with an ammonium concentration of 2 mgN·L−1 (set as operational threshold to stop aeration). Furthermore, the two PN/A systems performed almost identically with respect to the biological removal of organic micropollutants and, importantly, to a similar extent as conventional treatments. A sudden temperature drop to 11 °C resulted in significant suppression of anammox activity, although this was rapidly recovered after the temperature was increased back to 15 °C. Analyses of 16S rRNA gene-targeted amplicon sequencing revealed that the anammox guild of the bacterial communities of the two systems was composed of the genus “Candidatus Brocadia”. The potential of PN/A systems to compete with conventional treatments for biological nutrients removal both in terms of removal rates and overall effluent quality was proven.
Stamm, C., Räsänen, K., Burdon, F. J., Altermatt, F., Jokela, J., Joss, A., … Eggen, R. I. L. (2016). Unravelling the impacts of micropollutants in aquatic ecosystems: interdisciplinary studies at the interface of large-scale ecology. In A. J. Dumbrell, R. L. Kordas, & G. Woodward (Eds.), Advances in ecological research: Vol. 55. Large-scale ecology: model systems to global perspectives (pp. 183-223). doi:10.1016/bs.aecr.2016.07.002, Institutional Repository

Human-induced environmental changes are causing major shifts in ecosystems around the globe. To support environmental management, scientific research has to infer both general trends and context dependency in these shifts at global and local scales. Combining replicated real-world experiments, which take advantage of implemented mitigation measures or other forms of human impact, with research-led experimental manipulations can provide powerful scientific tools for inferring causal drivers of ecological change and the generality of their effects. Additionally, combining these two approaches can facilitate communication with stakeholders involved in implementing management strategies. We demonstrate such an integrative approach using the case study EcoImpact, which aims at empirically unravelling the impacts of wastewater-born micropollutants on aquatic ecosystems.
Völker, J., Castronovo, S., Wick, A., Ternes, T. A., Joss, A., Oehlmann, J., & Wagner, M. (2016). Advancing biological wastewater treatment: extended anaerobic conditions enhance the removal of endocrine and dioxin-like activities. Environmental Science and Technology, 50(19), 10606-10615. doi:10.1021/acs.est.5b05732, Institutional Repository

Conventional activated sludge treatment of wastewater does not completely remove micropollutants. Here, extending anaerobic conditions may enhance biodegradation. To explore this, we combined iron-reducing or substrate-limiting and aerobic pilot-scale reactors directly at a wastewater treatment plant. To assess the removal of endocrine disrupting chemicals (EDCs) as group of micropollutants that adversely affects wildlife, we applied a bioanalytical approach. We used in vitro bioassays covering seven receptor-mediated mechanisms of action, including (anti)androgenicity, (anti)estrogenicity, retinoid-like, and dioxin-like activity. Untreated wastewater induced antiandrogenic, estrogenic, antiestrogenic, and retinoid-like activity. Full-scale as well as reactor-scale activated sludge treatment effectively removes the observed effects. Nevertheless, high antiandrogenic and minor dioxin-like and estrogenic effects persisted in the treated effluent that may still be environmentally relevant. The anaerobic post-treatment under substrate-limiting conditions resulted in an additional removal of endocrine activities by 17–40%. The anaerobic pre-treatment under iron-reducing conditions significantly enhanced the removal of the residual effects by 40–75%. In conclusion, this study demonstrates that a further optimization of biological wastewater treatment is possible. Here, implementing iron-reducing anaerobic conditions preceding aerobic treatment appears promising to improve the removal of receptor-mediated toxicity.
Eckstein, D. T. (2015). Einfluss von biologisch abbaubarem Kohlenstoff auf die Aktivität und die räumliche Verteilung Nitrit oxidierender Bakterien im einstufigen Nitritations/Anammox-Prozess (Master thesis). 69 p. , Institutional Repository

Der einstufige Nitritations/Anammox-Prozess hat sich in den vergangenen Jahren als effektive Methode zur biologischen Behandlung ammoniumreicher Abwässer etabliert. Aufgrund seiner ökologischen und ökonomischen Vorteile gegenüber der Nitrifikation mit anschließender Denitrifikation leistet er bereits heute einen wertvollen Beitrag zur qualitativen Verbesserung unserer Gewässer.
Eine der größten Herausforderungen beim Betrieb des Verfahrens besteht darin, die Population Nitrit oxidierender Bakterien im Reaktor möglichst gering zu halten. Diese konkurrieren mit den Anammoxbakterien um Nitrit und sind daher in der Lage die Entstickungsleistung des Prozesses maßgeblich zu verringern. Mittlerweile ist bekannt, dass Nitritoxidierer genetisch dazu befähigt sind Enzyme zu produzieren, welche für den Abbau niedermolekularer, leicht abbaubarer organischer Kohlenstoffverbindungen notwendig sind. Ob sich diese Fähigkeit auf die praktische Anwendung des Verfahrens auswirkt, ist derzeit jedoch nicht bekannt. [...]

In recent years the nitritation/anammox-process has proven to be one of the most viable strategies for biological treatment of high strength wastewaters. An important contribution to the purification of receiving water bodies has been made by using this novel approach. The process has also shown to be more sustainable and cost effective compared to conventional nitrification with subsequent denitrification.
One of the most important drawback of this technique is the confinement of nitrite oxidizing bacteria in the reactor. These bacteria compete with anammox bacteria for nitrite and are therefore able to reduce the nitrogen removal rate significantly. While it is known that nitrite oxidizers are genetically capable to produce enzymes involved in the degradation of low molecular organic carbon compounds, it remains unknown whether this ability could negatively affect the process performance. [...]
Fux, C., Kienle, C., Joss, A., Wittmer, A., & Frei, R. (2015). Ausbau der ARA Basel mit 4. Reinigungsstufe. Pilotstudie: Elimination Mikroverunreinigungen und ökotoxikologische Wirkungen. Aqua & Gas, 95(7/8), 10-17. , Institutional Repository

Auf der ARA Basel der ProRheno AG, die hauptsächlich kommunales Abwasser reinigt, wird aufgrund ihrer Grösse eine zusätzliche Stufe zur Elimination von Mikroverunreinigungen nötig sein. Während mehreren Monaten wurde in einer Pilotanlage untersucht, ob sich die Verfahren Zugabe von Pulveraktivkohle (PAK) und Ozonung grundsätzlich auf der ARA Basel eignen. Zusätzlich wurde die Reinigungsleistung der weitergehenden Abwasserbehandlung für kommunales Abwasser der ARA Basel getestet, das einen gewissen Anteil biologisch gereinigtes Industrieabwasser enthielt.
Harris, E., Joss, A., Emmenegger, L., Kipf, M., Wolf, B., Mohn, J., & Wunderlin, P. (2015). Isotopic evidence for nitrous oxide production pathways in a partial nitritation-anammox reactor. Water Research, 83, 258-270. doi:10.1016/j.watres.2015.06.040, Institutional Repository

Nitrous oxide (N2O) production pathways in a single stage, continuously fed partial nitritation-anammox reactor were investigated using online isotopic analysis of offgas N2O with quantum cascade laser absorption spectroscopy (QCLAS). N2O emissions increased when reactor operating conditions were not optimal, for example, high dissolved oxygen concentration. SP measurements indicated that the increase in N2O was due to enhanced nitrifier denitrification, generally related to nitrite build-up in the reactor. The results of this study confirm that process control via online N2O monitoring is an ideal method to detect imbalances in reactor operation and regulate aeration, to ensure optimal reactor conditions and minimise N2O emissions.
Under normal operating conditions, the N2O isotopic site preference (SP) was much higher than expected – up to 40‰ – which could not be explained within the current understanding of N2O production pathways. Various targeted experiments were conducted to investigate the characteristics of N2O formation in the reactor. The high SP measurements during both normal operating and experimental conditions could potentially be explained by a number of hypotheses: i) unexpectedly strong heterotrophic N2O reduction, ii) unknown inorganic or anammox-associated N2O production pathway, iii) previous underestimation of SP fractionation during N2O production from NH2OH, or strong variations in SP from this pathway depending on reactor conditions. The second hypothesis – an unknown or incompletely characterised production pathway – was most consistent with results, however the other possibilities cannot be discounted. Further experiments are needed to distinguish between these hypotheses and fully resolve N2O production pathways in PN-anammox systems.
Laureni, M., Weissbrodt, D. G., Szivák, I., Robin, O., Nielsen, J. L., Morgenroth, E., & Joss, A. (2015). Activity and growth of anammox biomass on aerobically pre-treated municipal wastewater. Water Research, 80, 325-336. doi:10.1016/j.watres.2015.04.026, Institutional Repository

Direct treatment of municipal wastewater (MWW) based on anaerobic ammonium oxidizing (anammox) bacteria holds promise to turn the energy balance of wastewater treatment neutral or even positive. Currently, anammox processes are successfully implemented at full scale for the treatment of high-strength wastewaters, whereas the possibility of their mainstream application still needs to be confirmed. In this study, the growth of anammox organisms on aerobically pre-treated municipal wastewater (MWWpre-treated), amended with nitrite, was proven in three parallel reactors. The reactors were operated at total N concentrations in the range 5–20 mgN∙L−1, as expected for MWW. Anammox activities up to 465 mgN∙L−1∙d−1 were reached at 29 °C, with minimum doubling times of 18 d. Lowering the temperature to 12.5 °C resulted in a marked decrease in activity to 46 mgN∙L−1∙d−1 (79 days doubling time), still in a reasonable range for autotrophic nitrogen removal from MWW. During the experiment, the biomass evolved from a suspended growth inoculum to a hybrid system with suspended flocs and wall-attached biofilm. At the same time, MWWpre-treated had a direct impact on process performance. Changing the influent from synthetic medium to MWWpre-treated resulted in a two-month delay in net anammox growth and a two to three-fold increase in the estimated doubling times of the anammox organisms. Interestingly, anammox remained the primary nitrogen consumption route, and high-throughput 16S rRNA gene-targeted amplicon sequencing analyses revealed that the shift in performance was not associated with a shift in dominant anammox bacteria ("Candidatus Brocadia fulgida"). Furthermore, only limited heterotrophic denitrification was observed in the presence of easily biodegradable organics (acetate, glucose). The observed delays in net anammox growth were thus ascribed to the acclimatization of the initial anammox population or/and the development of a side population beneficial for them. Additionally, by combining microautoradiography and fluorescence in situ hybridization it was confirmed that the anammox organisms involved in the process did not directly incorporate or store the amended acetate and glucose. In conclusion, these investigations strongly support the feasibility of MWW treatment via anammox.
Stamm, C., Eggen, R. I. L., Hering, J. G., Hollender, J., Joss, A., & Schärer, M. (2015). Micropollutant removal from wastewater: facts and decision-making despite uncertainty. Environmental Science and Technology, 49(11), 6374-6375. doi:10.1021/acs.est.5b02242, Institutional Repository
Ternes, T., Joss, A., & Oehlmann, J. (2015). Occurrence, fate, removal and assessment of emerging contaminants in water in the water cycle (from wastewater to drinking water). Water Research, 72, 1-2. doi:10.1016/j.watres.2015.02.055, Institutional Repository
Wunderlin, P., Joss, A., Siegrist, H., Abegglen, C., & Schärer, M. (2015). Verfahrenstechnik Mikroverunreinigungen. www.micropoll.ch - Wissensplattform des VSA. Aqua & Gas, 95(2), 14-19. , Institutional Repository

Noch liegen in der Schweiz erst wenige grosstechnische Erfahrungen mit den Technologien zur Elimination organischer Spurenstoffe auf Abwasserreinigungsanlagen vor. Deswegen wurde 2012 die Plattform «Verfahrenstechnik Mikroverunreinigungen» gegründet und innerhalb des Verbands der Schweizer Abwasser- und Gewässerschutzfachleute (VSA) angesiedelt. Sie soll helfen, Wissen aufzubauen, den Austausch unter den Akteuren zu fördern sowie offene Fragen zu bearbeiten.
Eggen, R. I. L., Hollender, J., Joss, A., Schärer, M., & Stamm, C. (2014). Reducing the discharge of micropollutants in the aquatic environment: the benefits of upgrading wastewater treatment plants. Environmental Science and Technology, 48(14), 7683-7689. doi:10.1021/es500907n, Institutional Repository

Micropollutants (MPs) as individual compounds or in complex mixtures are relevant for water quality and may trigger unwanted ecological effects. MPs originate from different point and diffuse sources and enter water bodies via different flow paths. Effluents from conventional wastewater treatment plants (WWTPs), in which various MPs are not or not completely removed, is one major source. To improve the water quality and avoid potential negative ecological effects by micropollutants, various measures to reduce the discharge should be taken. In this feature we discuss one of these measures; the benefits of upgrading WWTPs toward reduced MP loads and toxicities from wastewater effluents, using the recently decided Swiss strategy as an example. Based on (i) full-scale case studies using ozonation or powder activated carbon treatment, showing substantial reduction of MP discharges and concomitant reduced toxicities, (ii) social and political acceptance, (iii) technical feasibility and sufficient cost-effectiveness, the Swiss authorities recently decided to implement additional wastewater treatment steps as mitigation strategy to improve water quality. Since MPs are of growing global concern, the concepts and considerations behind the Swiss strategy are explained in this feature, which could be of use for other countries as well. It should be realized that upgrading WWTPs is not the only solution to reduce the discharge of MPs entering the environment, but is part of a broader, multipronged mitigation strategy.
Gruber, W. (2014). Modellierung der Lachgasemissionen aus der biologischen Abwasserreinigung (Master thesis). 34 p. , Institutional Repository

Lachgas (N2O) ist ein Treibhausgas (ca. 300 Mal stärker als CO2) und bedeutend an der Zerstörung der stratosphärischen Ozonschicht beteiligt. In der biologischen Stufe von Abwasserreinigungsanlagen (ARA) werden relevante Mengen an N2O emittiert. Die N2OBildung ist sehr komplex und nur ansatzweise verstanden. Es wird aber davon ausgegangen, dass hauptsächlich die Nitrifikation eine dominante Quelle darstellt.
In der vorliegenden Masterarbeit wurde anhand von qualitativen Modellierungen versucht die Dynamik der N2O-Emissionen auf der ARA Real nachzuvollziehen und Strategien zur Reduktion der Emissionen zu entwickeln.
Anhand von Daten aus einer Langzeit Messkampagne auf der ARA Real über die N2OEmissionen konnte gezeigt werden, dass die N2O-Emissionen im Winter und Frühling einen bedeutenden Einfluss auf die Treibhausgasbilanz der Anlage hat. Berechnungen ergaben, dass die Emissionen bei über 1.5% der Ammoniumfracht im Zulauf der Anlage liegen. Es wurde abgeschätzt, dass die Emissionen ca. je zur Hälfte auf die Haupt- und die Nachbelüftung der Anlage entfallen. Dieses Ergebnis ist erstaunlich, da üblicherweise vor allem in der Hauptbelüftung der Grossteil der N2O-Emissionen ausgestossen wird.
Für die Entwicklung von N2O reduzierenden Massnahmen auf Kläranlagen können Modellierungen wichtige Hilfestellungen bieten. Allerdings kann mit den bereits publizierten mechanistischen Modellen über die N2O-Bildung nur ein Teil der N2O-Dynamik erklärt werden. Daher wurde in der vorliegenden Studie die N2O-Bildung basierend auf den Daten aus einer Langzeit-Messkampagne auf der ARA Real mit empirischen Ansätzen modelliert. Die N2O-Emissionen zeigen starke Korrelationen zur NO2--Konzentration in der Belüftungszone, Temperatur und zum Niederschlag. Darauf aufbauend wurde das ASM3-Modell mit Stickstofferweiterung um die Lachgasbildung in der Nitrifikation durch die Nitrifikaten Denitrifikation und die hetrotrophe Denitrifikation erweitert und kalibriert. Der dritte bekannte Prozess zur N2O-Bildung (Oxidation von NH2OH) wurde weggelassen.
Die Resultate der Modellierungen zeigen, dass mit dem Modell die Emissionen im Winter qualitativ gut reproduziert und erklärt werden können. Im Sommer bei höheren Temperaturen sind die modellierten Konzentrationen zu hoch. Insbesondere für die Modell Prozesse der Denitrifikation sind Anpassungen möglicherweise vorzusehen.
Anhand des Modells wurden für den Winter Betriebsoptimierungen getestet. In Kombination mit den Resultaten aus der Analyse der Daten aus der Messkampange wurden verschiedene Optimierungsmassnahmen entwickelt. Am vielversprechendsten sind die Erhöhung der O2-Konzentration in der Hauptbelüftung, die Verlängerung der Belüftungsphasen, ein dosierterer Betrieb der Belüftungseinheit der Nachbelüftung und die separate Behandlung von Rückläufen aus der Schlammbehandlung. Teilweise entstehen aber Konflikte mit anderen Zielgrössen, wie der Stickstoffelimination und dem Energieverbrauch der Anlage. Dabei kann das Modell in Zukunft interessante Hilfestellungen bieten und verbunden mit Ökobilanz-Tools könnten die gestellten Optimierungsprobleme gelöst werden.
Lackner, S., Gilbert, E. M., Vlaeminck, S. E., Joss, A., Horn, H., & van Loosdrecht, M. C. M. (2014). Full-scale partial nitritation/anammox experiences – an application survey. Water Research, 55, 292-303. doi:10.1016/j.watres.2014.02.032, Institutional Repository

Partial nitritation/anammox (PN/A) has been one of the most innovative developments in biological wastewater treatment in recent years. With its discovery in the 1990s a completely new way of ammonium removal from wastewater became available. Over the past decade many technologies have been developed and studied for their applicability to the PN/A concept and several have made it into full-scale. With the perspective of reaching 100 full-scale installations in operation worldwide by 2014 this work presents a summary of PN/A technologies that have been successfully developed, implemented and optimized for high-strength ammonium wastewaters with low C:N ratios and elevated temperatures. The data revealed that more than 50% of all PN/A installations are sequencing batch reactors, 88% of all plants being operated as single-stage systems, and 75% for sidestream treatment of municipal wastewater. Additionally an in-depth survey of 14 full-scale installations was conducted to evaluate practical experiences and report on operational control and troubleshooting. Incoming solids, aeration control and nitrate built up were revealed as the main operational difficulties. The information provided gives a unique/new perspective throughout all the major technologies and discusses the remaining obstacles.
Ni, B. J., Joss, A., & Yuan, Z. (2014). Modeling nitrogen removal with partial nitritation and anammox in one floc-based sequencing batch reactor. Water Research, 67, 321-329. doi:10.1016/j.watres.2014.09.028, Institutional Repository

Full-scale application of partial nitritation and anammox in a single floc-based sequencing batch reactor (SBR) has been achieved for high-rate nitrogen (N) removal, but mechanisms resulting in reliable operation are not well understood. In this work, a mathematical model was calibrated and validated to evaluate operating conditions that lead to out-competition of nitrite oxidizers (NOB) from the SBRs and allow to maintain high anammox activity during long-term operation. The validity of the model was tested using experimental data from two independent previously reported floc-based full-scale SBRs for N-removal via partial nitritation and anammox, with different aeration strategies at aeration phase (continuous vs. intermittent aeration). The model described the SBR cycle profiles and long-term dynamic data from the two SBR plants sufficiently and provided insights into the dynamics of microbial population fractions and N-removal performance. Ammonium oxidation and anammox reaction could occur simultaneously at DO range of 0.15–0.3 mg O2 L−1 at aeration phase under continuous aeration condition, allowing simplified process control compared to intermittent aeration. The oxygen supply beyond prompt depletion by ammonium oxidizers (AOB) would lead to the growth of NOB competing with anammox for nitrite. NOB could also be washed out of the system and high anammox fractions could be maintained by controlling sludge age higher than 40 days and DO at around 0.2 mg O2 L−1. Furthermore, the results suggest that N-removal in SBR occurs via both alternating nitritation/anammox and simultaneous nitritation/anammox, supporting an alternative strategy to improve N-removal in this promising treatment process, i.e., different anaerobic phases can be implemented in the SBR-cycle configuration.
Weissbrodt, D. G., Wells, G. F., Johnson, D. R., Bürgmann, H., Joss, A., Laureni, M., & Morgenroth, E. (2014). Towards community systems microbiology for the optimization of aerobic-anaerobic ammonium oxidation processes. In Vol. 1. 87th annual water environment federation technical exhibition and conference (WEFTEC 2014) (pp. 2645-2649). doi:10.2175/193864714815942567, Institutional Repository
Wunderlin, P., Siegrist, H., Kipf, M., Gruber, W., & Joss, A. (2014). Energieoptimierung um jeden Preis? – Potentielle Risiken für den Umweltschutz. In H. Steinmetz & C. Meyer (Eds.), Stuttgarter Berichte zur Siedlungswasserwirtschaft: Vol. 221. Energiepotenziale kommunaler Kläranlagen erkennen, nutzen und kritisch bewerten (pp. 1-26). München: DIV Deutscher Industrieverlag. , Institutional Repository

Lachgas (N2O) ist ein starkes Treibhausgas und bedeutend an der Zerstörung der stratosphärischen Ozonschicht beteiligt. Seine Bildung und Freisetzung in die Atmosphäre hat deshalb eine grosse Umweltrelevanz. In der biologischen Abwasserreinigung kann N2O sowohl während der Nitrifikation (Oxidation von Ammonium zu Nitrat), wie auch durch die heterotrophe Denitrifikation (Reduktion von Nitrat zu Luftstickstoff) gebildet werden. Diese Prozesse laufen häufig gleichzeitig ab. Daher lässt sich ihr individueller Beitrag zur N2O Bildung nur schwer abschätzen. Für diese Studie wurde ein neuartiger Ansatz angewandt, der eine bessere Beurteilung der N2O Bildung auf Abwasserreinigungsanlagen erlaubt. Anhand der Analyse der stabilen Stickstoffisotopen wurde gezeigt, dass unter aeroben Bedingungen die Nitrifikation die N2O Bildung dominiert. Dabei fördern sowohl hohe Ammonium (NH4+) wie auch Nitrit (NO2-) Konzentrationen die N2O Bildung. Ausserdem ist zu beachten, dass die Entstehung von N2O räumlich und zeitlich sehr variabel ist und durch viele Parameter beeinflusst wird. Die aktuellen Emissionsschätzungen sind daher mit einer grossen Unsicherheit verbunden, was eine Bestimmung von präzisen Emissionsfaktoren schwierig macht. Untersuchungen zeigen aber, dass die N2O Emissionen die Treibhausgasbilanz der gesamten Anlage dominieren können, welche ansonsten vor allem durch die indirekten Emissionen der Belüftungenergie der biologischen Reinigungsstufe beeinflusst wird.
In Anbetracht der negativen Umweltauswirkungen von N2O und der langen Aufenthaltszeit in der Atmosphäre (rund 120 Jahre) sollte unbedingt eine möglichst weitgehende Reduktion der Emissionen angestrebt werden. Das gegenwärtige Verständnis der relevanten Bildungsmechanismen deutet darauf hin, dass bei einer möglichst vollständigen Nitrifikation betrieben mit Sauerstoffkonzentrationen von mehr als 2 mgO2/L und einer weitgehenden Denitrifikation unter Vermeidung von Sauerstoffeinträgen, gleichzeitig auch die Nitrit und damit die N2O Bildung minimiert werden kann. Aus diesem Grund sollte sowohl bei der Auslegung wie auch bei der energetischen Optimierung und beim Betrieb von Belebtschlamm-Anlagen (z.B. Regelung der Belüftung, O2-Sollwert) die N2O Bildung mitberücksichtigt werden.
Falås, P., Longrée, P., La Cour Jansen, J., Siegrist, H., Hollender, J., & Joss, A. (2013). Micropollutant removal by attached and suspended growth in a hybrid biofilm-activated sludge process. Water Research, 47(13), 4498-4506. doi:10.1016/j.watres.2013.05.010, Institutional Repository

Removal of organic micropollutants in a hybrid biofilm-activated sludge process was investigated through batch experiments, modeling, and full-scale measurements. Batch experiments with carriers and activated sludge from the same full-scale reactor were performed to assess the micropollutant removal rates of the carrier biofilm under oxic conditions and the sludge under oxic and anoxic conditions. Clear differences in the micropollutant removal kinetics of the attached and suspended growth were demonstrated, often with considerably higher removal rates for the biofilm compared to the sludge. For several micropollutants, the removal rates were also affected by the redox conditions, i.e. oxic and anoxic. Removal rates obtained from the batch experiments were used to model the micropollutant removal in the full-scale process. The results from the model and plant measurements showed that the removal efficiency of the process can be predicted with acceptable accuracy (±25%) for most of the modeled micropollutants. Furthermore, the model estimations indicate that the attached growth in hybrid biofilm-activated sludge processes can contribute significantly to the removal of individual compounds, such as diclofenac.
Wunderlin, P., Lehmann, M. F., Siegrist, H., Tuzson, B., Joss, A., Emmenegger, L., & Mohn, J. (2013). Isotope signatures of N2O in a mixed microbial population system: constraints on N2O producing pathways in wastewater treatment. Environmental Science and Technology, 47(3), 1339-1348. doi:10.1021/es303174x, Institutional Repository

We present measurements of site preference (SP) and bulk 15N/14N ratios (δ15NbulkN2O) of nitrous oxide (N2O) by quantum cascade laser absorption spectroscopy (QCLAS) as a powerful tool to investigate N2O production pathways in biological wastewater treatment. QCLAS enables high-precision N2O isotopomer analysis in real time. This allowed us to trace short-term fluctuations in SP and δ15NbulkN2O and, hence, microbial transformation pathways during individual batch experiments with activated sludge from a pilot-scale facility treating municipal wastewater. On the basis of previous work with microbial pure cultures, we demonstrate that N2O emitted during ammonia (NH4+) oxidation with a SP of −5.8 to 5.6 ‰ derives mostly from nitrite (NO2–) reduction (e.g., nitrifier denitrification), with a minor contribution from hydroxylamine (NH2OH) oxidation at the beginning of the experiments. SP of N2O produced under anoxic conditions was always positive (1.2 to 26.1 ‰), and SP values at the high end of this spectrum (24.9 to 26.1 ‰) are indicative of N2O reductase activity. The measured δ15NbulkN2O at the initiation of the NH4+ oxidation experiments ranged between −42.3 and −57.6 ‰ (corresponding to a nitrogen isotope effect Δδ15N = δ15Nsubstrate – δ15NbulkN2O of 43.5 to 58.8 ‰), which is considerably higher than under denitrifying conditions (δ15NbulkN2O 2.4 to −17 ‰; Δδ15N = 0.1 to 19.5 ‰). During the course of all NH4+ oxidation and nitrate (NO3–) reduction experiments, δ15NbulkN2O increased significantly, indicating net 15N enrichment in the dissolved inorganic nitrogen substrates (NH4+, NO3–) and transfer into the N2O pool. The decrease in δ15NbulkN2O during NO2– and NH2OH oxidation experiments is best explained by inverse fractionation during the oxidation of NO2– to NO3–.
Wunderlin, P., Siegrist, H., & Joss, A. (2013). Online N2O measurement: the next standard for controlling biological ammonia oxidation?. Environmental Science and Technology, 47(17), 9567-9568. doi:10.1021/es402971p, Institutional Repository
Boehler, M., Zwickenpflug, B., Hollender, J., Ternes, T., Joss, A., & Siegrist, H. (2012). Removal of micropollutants in municipal wastewater treatment plants by powder-activated carbon. Water Science and Technology, 66(10), 2115-2121. doi:10.2166/wst.2012.353, Institutional Repository

Micropollutants (MP) are only partly removed from municipal wastewater by nutrient removal plants and are seen increasingly as a threat to aquatic ecosystems and to the safety of drinking water resources. The addition of powder activated carbon (PAC) is a promising technology to complement municipal nutrient removal plants in order to achieve a significant reduction of MPs and ecotoxicity in receiving waters. This paper presents the salient outcomes of pilot- and full-scale applications of PAC addition in different flow schemes for micropollutant removal in municipal wastewater treatment plants (WWTPs). The sorption efficiency of PAC is reduced with increasing dissolved organic carbon (DOC). Adequate treatment of secondary effluent with 5–10 g DOC m−3 requires 10–20 g PAC m−3 of effluent. Counter-current use of PAC by recycling waste PAC from post-treatment in a contact tank with an additional clarifier to the biology tank improved the overall MP removal by 10 to 50% compared with effluent PAC application alone. A dosage of 15 g PAC m−3 to a full-scale flocculation sand filtration system and recycling the backwash water to the biology tank showed similar MP elimination. Due to an adequate mixing regime and the addition of adapted flocculants, a good retention of the fine fraction of the PAC in the deep-bed filter were observed (1–3 g TSS m−3; TSS: total suspended solids). With double use of PAC, only half of the PAC was required to reach MP removal efficiencies similar to the direct single dosage of PAC to the biology tank. Overall, the application of PAC in WWTPs seems to be an adequate and feasible technology for efficient MP elimination (>80%) from wastewater comparable with post ozonation.
Kazner, C., Joss, A., Ternes, T., van Houtte, E., & Wintgens, T. (2012). Membrane based treatment trains for managed aquifer recharge. In C. Kazner, T. Wintgens, & P. Dillon (Eds.), Water reclamation technologies for safe managed aquifer recharge (pp. 259-282). London: IWA Publishing. , Institutional Repository

Activated carbon-nanofiltration as well as MBR/NF hybrid processes are promising alternatives to existing treatment trains. They are well suited for high-grade water reuse applications. The present study demonstrated the feasibility of all processes and identified advantages and disadvantages of the processes. The optimum process combination depends on local boundary conditions such as size of plant, raw water characteristics and plant location. In the light of growing water scarcity and increasing concerns about organic micropollutants activated carbon treatment in combination with nanofiltration could be applied in an increasing number of cases with appropriate boundary conditions.
Future applications should be embedded in integrated wastewater treatment concepts including concentrate treatment. Particularly combinations with membrane bioreactors are interesting options for innovative sustainable water recycling solutions.
Lotito, A. M., Wunderlin, P., Joss, A., Kipf, M., & Siegrist, H. (2012). Nitrous oxide emissions from the oxidation tank of a pilot activated sludge plant. Water Research, 46(11), 3563-3573. doi:10.1016/j.watres.2012.03.067, Institutional Repository

This study discusses the results of the continuous monitoring of nitrous oxide emissions from the oxidation tank of a pilot conventional wastewater treatment plant. Nitrous oxide emissions from biological processes for nitrogen removal in wastewater treatment plants have drawn great attention over the last years, due to the high greenhouse effect. However, even if several studies have been carried out to quantify nitrous oxide emission rates from different types of treatment, quite wide ranges have been reported. Only grab samples or continuous measurements over limited periods were considered in previous studies, which can account for the wide variability of the obtained results. Through continuous monitoring over several months, our work tries to fill this gap of knowledge and get a deeper insight into nitrous oxide daily and weekly emission dynamics. Moreover, the influence of some operating conditions (sludge age, dissolved oxygen concentration in the oxidation tank, nitrogen load) was studied to determine good practices for wastewater treatment plant operation aiming at the reduction of nitrous oxide emissions. The dissolved oxygen set-point is shown to play a major role in nitrous oxide emissions. Low sludge ages and high nitrogen loads are responsible for higher emissions as well. An interesting pattern has been observed, with quite negligible emissions during most of the day and a peak with a bell-like shape in the morning in the hours of maximum nitrogen load in the plant, correlated to the ammonia and nitrite peaks in the tank.
Rattier, M., Reungoat, J., Gernjak, W., Joss, A., & Keller, J. (2012). Investigating the role of adsorption and biodegradation in the removal of organic micropollutants during biological activated carbon filtration of treated wastewater. Journal of Water Reuse and Desalination, 2(3), 127-139. doi:10.2166/wrd.2012.012, Institutional Repository

Municipal water recycling may expose humans and the environment to trace organic contaminants. We assessed biological activated carbon (BAC) filtration for removal of organic micropollutants (MPs). Adsorption experiments were carried out in batch reactors containing secondary effluent and new granular activated carbon (GAC) and preloaded BAC media. Results show that BAC has good potential for removal of dissolved organic carbon (40%) and MPs (60–95%). The primary objective was to better understand removal mechanisms of representative MPs at environmentally relevant concentrations. Adsorption and biodegradation of 20 compounds of varying physico-chemical properties were investigated by inhibiting the biomass with azide. Average removal of compounds by adsorption on GAC was 88 ± 5% with no influence of azide. Average BAC removal was 72 ± 15%, reduced to 59 ± 20% after azide addition, showing that biological activity is important for MP removal. Comparison of MP removal by BAC and BAC + azide showed a more important impact of the inhibition on the removal of negatively charged compounds. Sustained removal of recalcitrant compounds showed that BAC maintained sorption capacity. These results highlight the advantage of a combination of adsorption and biodegradation as compared to other biofiltration techniques for the long-term attenuation of MPs.
Siegrist, H., & Joss, A. (2012). Review on the fate of organic micropollutants in wastewater treatment and water reuse with membranes. Water Science and Technology, 66(6), 1369-1376. doi:10.2166/wst.2012.285, Institutional Repository

A brief review of the fate of micropollutants in membrane-based wastewater treatment due to sorption, stripping, biological degradation/transformation and membrane separation is discussed, to give an overview of these technologies due to the growing importance for water reuse purposes. Compared with conventional activated sludge treatment (CAS) micropollutant removal in membrane bioreactor (MBR) is slightly improved due to complete suspended solids removal and increased sludge age. For discharge to sensitive receiving waters advanced treatment, such as post-ozonation or activated carbon adsorption, is recommended. In water reuse plants nanofiltration (NF) and reverse osmosis (RO) efficiently reject micropollutants due to size exclusions as well as electrostatic and hydrophobic effects reaching potable quality. To remove micropollutants fully, additionally post-ozone or the addition of powdered activated carbon (PAC) have to be applied, which in parallel also reduce NDMA precursors. The concentrate has to be treated if disposed to sensitive receiving waters due to its high micropollutant concentration and ecotoxicity potential. The present review summarizes principles and capabilities for the most important membrane-based applications for wastewater treatment, i.e. porous membranes in MBRs (micro- or ultrafiltration) and dense membrane applications (NF and RO) for water reuse.
Wunderlin, P., Mohn, J., Joss, A., Emmenegger, L., & Siegrist, H. (2012). Mechanisms of N2O production in biological wastewater treatment under nitrifying and denitrifying conditions. Water Research, 46(4), 1027-1037. doi:10.1016/j.watres.2011.11.080, Institutional Repository

Nitrous oxide (N2O) is an important greenhouse gas and a major sink for stratospheric ozone. In biological wastewater treatment, microbial processes such as autotrophic nitrification and heterotrophic denitrification have been identified as major sources; however, the underlying pathways remain unclear. In this study, the mechanisms of N2O production were investigated in a laboratory batch-scale system with activated sludge for treating municipal wastewater. This relatively complex mixed population system is well representative for full-scale activated sludge treatment under nitrifying and denitrifying conditions.
Under aerobic conditions, the addition of nitrite resulted in strongly nitrite-dependent N2O production, mainly by nitrifier denitrification of ammonia-oxidizing bacteria (AOB). Furthermore, N2O is produced via hydroxylamine oxidation, as has been shown by the addition of hydroxylamine. In both sets of experiments, N2O production was highest at the beginning of the experiment, then decreased continuously and ceased when the substrate (nitrite, hydroxylamine) had been completely consumed. In ammonia oxidation experiments, N2O peaked at the beginning of the experiment when the nitrite concentration was lowest. This indicates that N2O production via hydroxylamine oxidation is favored at high ammonia and low nitrite concentrations, and in combination with a high metabolic activity of ammonia-oxidizing bacteria (at 2 to 3 mgO2/l); the contribution of nitrifier denitrification by AOB increased at higher nitrite and lower ammonia concentrations towards the end of the experiment.
Under anoxic conditions, nitrate reducing experiments confirmed that N2O emission is low under optimal growth conditions for heterotrophic denitrifiers (e.g. no oxygen input and no limitation of readily biodegradable organic carbon). However, N2O and nitric oxide (NO) production rates increased significantly in the presence of nitrite or low dissolved oxygen concentrations.
Houweling, D., Wunderlin, P., Dold, P., Bye, C., Joss, A., & Siegrist, H. (2011). N2O emissions: modeling the effect of process configuration and diurnal loading patterns. Water Environment Research, 83(12), 2131-2139. doi:10.2175/106143011X13176499923775, Institutional Repository

The objective of this research was to develop a mechanistic model for quantifying N2O emissions from activated sludge plants and demonstrate how this may be used to evaluate the effects of process configuration and diurnal loading patterns. The model describes the mechanistic link between the factors recognized to correlate positively with N2O emissions. The primary factors are the presence of ammonia and nitrite accumulation. Low dissolved oxygen concentrations also may be implicated through differential impacts on ammonia-oxidizing bacteria (AOB) versus nitrite-oxidizing bacteria (NOB) activity. Factors promoting N2O emissions at treatment plants are discussed below. The model was applied to data from laboratory and pilot-scale systems. From a practical standpoint, plant configuration (e.g., plug-flow versus complete-mix), influent loading patterns (and peak load), and certain operating strategies (e.g., handling of return streams) are all important in determining N2O emissions.
Joss, A., Derlon, N., Cyprien, C., Burger, S., Szivak, I., Traber, J., … Morgenroth, E. (2011). Combined nitritation–anammox: advances in understanding process stability. Environmental Science and Technology, 45(22), 9735-9742. doi:10.1021/es202181v, Institutional Repository

Efficient nitrogen removal from wastewater containing high concentrations of ammonium but little organic substrate has recently been demonstrated by several full-scale applications of the combined nitritation–anammox process. While the process efficiency is in most cases very good, process instabilities have been observed to result in temporary process failures. In the current study, conditions resulting in instability and strategies to regain efficient operation were evaluated. First, data from full-scale operation is presented, showing a sudden partial loss of activity followed by recovery within less than 1 month. Results from laboratory-scale experiments indicate that these dynamics observed in full scale can be caused by partial inhibition of the ammonia oxidizing bacteria (AOB), while anammox inhibition is a secondary effect due to temporarily reduced O2 depletion. Complete anammox inhibition is observed at 0.2 mg O2·L–1, resulting in NO2– accumulation. However, this inhibition of anammox is reversible within minutes after O2 depletion. Thus, variable AOB activity was identified as the key to reactor stability. With appropriate interpretation of the online NH4+ signal, accumulation of NO2– can be detected indirectly and used to signal an imbalance of O2 supply and AOB activity (no suitable online NO2– electrode is currently available). Second, increased abundance of nitrite-oxidizing bacteria (NOB; competing with anammox for NO2–) is known as another cause of instability. Based on a comparison of parallel full-scale reactors, it is suggested that an infrequent and short-term increased O2 supply (e.g., for maintenance of aerators) that exceeds prompt depletion of oxygen by AOB may have caused increased NOB abundance. The volumetric air supply as a proxy for O2 supply thus needs to be linked to AOB activity. Further, NOB can be washed out of the system during regular operation if the system is operated at a sludge age in the range of 45 days and by controlling the air supply according to the NO3– concentration in the treated effluent. Early detection of growing NOB abundance while the population is still low can help guide process operation and it is suggested that molecular methods of quantifying NOB abundance should be tested.
Joss, A., Baenninger, C., Foa, P., Koepke, S., Krauss, M., McArdell, C. S., … Siegrist, H. (2011). Water reuse: >90% water yield in MBR/RO through concentrate recycling and CO2 addition as scaling control. Water Research, 45(18), 6141-6151. doi:10.1016/j.watres.2011.09.011, Institutional Repository

Over 1.5 years continuous piloting of a municipal wastewater plant upgraded with a double membrane system (ca. 0.6 m3 d−1 of product water produced) have demonstrated the feasibility of achieving high water quality with a water yield of 90% by combining a membrane bioreactor (MBR) with a submerged ultrafiltration membrane followed by a reverse osmosis membrane (RO). The novelty of the proposed treatment scheme consists of the appropriate conditioning of MBR effluent prior to the RO and in recycling the RO concentrates back to the biological unit.
All the 15 pharmaceuticals measured in the influent municipal sewage were retained below 100 ng L−1, a proposed quality parameter, and mostly below detection limits of 10 ng L−1. The mass balance of the micropollutants shows that these are either degraded or discharged with the excess concentrate, while only minor quantities were found in the excess sludge. The micropollutant load in the concentrate can be significantly reduced by ozonation. A low treated water salinity (<10 mM inorganic salts; 280 ± 70 μS cm−1) also confirms that the resulting product has a high water quality.
Solids precipitation and inorganic scaling are effectively mitigated by lowering the pH in the RO feed water with CO2 conditioning, while the concentrate from the RO is recycled to the biological unit where CO2 is stripped by aeration. This causes precipitation to occur in the bioreactor bulk, where it is much less of a process issue. SiO2 is the sole exception. Equilibrium modeling of precipitation reactions confirms the effectiveness of this scaling-mitigation approach for CaCO3 precipitation, calcium phosphate and sulfate minerals.
Ante, S., Böhler, M., Ellerhorst, S., Fink, G., Knacker, T., Joss, A., … Zwickenpflug, B. (2010). NEPTUNE. New sustainable concepts and processes for optimization and upgrading municipal wastewater and sludge treatment. A specific targeted research project under the thematic priority 'Global change and ecosystems'. Work packages 1 and 3. Deliverable 1.1 and 3.3 · Fate and occurrence of micropollutants, microorganisms and viruses and strategies to minimize their release in plant effluent. sine loco: Eawag. , Institutional Repository

Analytical methods, compound occurrence and transformation products
The palette of analytical methods available for analyzing micropollutants in wastewater covers a wide variety of compounds: 152 compounds belonging to 16 different classes were applied within this project. Of relevance due to their occurrence and toxic potency are the new methods developed for biocides, UV-filters, benzothiazoles and antivirals: the majority persist wastewater treatment and many are found in surface waters at concentrations justifying more attention within the micropollutant discussion.
A major break through of the project is the development of methods for systematic transformation product identification. These are applicable for biological degradation as well as for chemical oxidative treatment. [...]
Corominas, Ll., Flores-Alsina, X., Joss, A., Lettl, W., Roels, J., Siegrist, H., … Vanrolleghem, P. A. (2010). NEPTUNE. New sustainable concepts and processes for optimization and upgrading municipal wastewater and sludge treatment. A specific targeted research project under the thematic priority 'Global change and ecosystems'. Work package 1 · Technologies for WWTP upgrading. Deliverable 1.2 · Strategies to improve nutrient removal. sine loco: Eawag. , Institutional Repository
Morgan-Sagastume, F., Karlsson, A., Werker, A., De Gussem, K., Roels, J., Weemaes, M., … Petrova, S. (2010). NEPTUNE. New sustainable concepts and processes for optimization and upgrading municipal wastewater and sludge treatment. A specific targeted research project under the thematic priority 'Global change and ecosystems'. Work package 5 · Dissemination. Deliverable 5.4 · Catalogue with criteria for evaluating technologies. sine loco: Eawag. , Institutional Repository
Ort, C., Lawrence, M. G., Rieckermann, J., & Joss, A. (2010). Sampling for pharmaceuticals and personal care products (PPCPs) and illicit drugs in wastewater systems: are your conclusions valid? A critical review. Environmental Science and Technology, 44(16), 6024-6035. doi:10.1021/es100779n, Institutional Repository

The analysis of 87 peer-reviewed journal articles reveals that sampling for pharmaceuticals and personal care products (PPCPs) and illicit drugs in sewers and sewage treatment plant influents is mostly carried out according to existing tradition or standard laboratory protocols. Less than 5% of all studies explicitly consider internationally acknowledged guidelines or methods for the experimental design of monitoring campaigns. In the absence of a proper analysis of the system under investigation, the importance of short-term pollutant variations was typically not addressed. Therefore, due to relatively long sampling intervals, potentially inadequate sampling modes, or insufficient documentation, it remains unclear for the majority of reviewed studies whether observed variations can be attributed to “real” variations or if they simply reflect sampling artifacts. Based on results from previous and current work, the present paper demonstrates that sampling errors can lead to overinterpretation of measured data and ultimately, wrong conclusions. Depending on catchment size, sewer type, sampling setup, substance of interest, and accuracy of analytical method, avoidable sampling artifacts can range from “not significant” to “100% or more” for different compounds even within the same study. However, in most situations sampling errors can be reduced greatly, and sampling biases can be eliminated completely, by choosing an appropriate sampling mode and frequency. This is crucial, because proper sampling will help to maximize the value of measured data for the experimental assessment of the fate of PPCPs as well as for the formulation and validation of mathematical models. The trend from reporting presence or absence of a compound in “clean” water samples toward the quantification of PPCPs in raw wastewater requires not only sophisticated analytical methods but also adapted sampling methods. With increasing accuracy of chemical analyses, inappropriate sampling increasingly represents the major source of inaccuracy. A condensed step-by-step Sampling Guide is proposed as a starting point for future studies.
Siegrist, H., Joss, A., & Miladinovic, N. (2010). NEPTUNE. New sustainable concepts and processes for optimization and upgrading municipal wastewater and sludge treatment. A specific targeted research project under the thematic priority 'Global change and ecosystems'. Final activity report. sine loco: Eawag. , Institutional Repository

The scope of sewage treatment is changing: more and more seen as an interface between sanitation and environment, WWTP are delivering resources to the environment and for human activities (e.g. recharge drinking water reservoirs, recycling of nutrient, efficient energy use). This focus shift has implications on the quality goals for WWTP products: [...]
Ternes, T., Joss, A., Knacker, T., Oehlmann, J., von Gunten, U., & Siegrist, H. (2010). NEPTUNE. New sustainable concepts and processes for optimization and upgrading municipal wastewater and sludge treatment. A specific targeted research project under the thematic priority 'Global change and ecosystems'. Work package 5 · Dissemination. Deliverable 5.2: Conclusions of the workshop about the revision of the WFD priority substances based on the Neptune outcome. sine loco: Eawag. , Institutional Repository
Zwickenpflug, B., Böhler, M., Sterkele, B., Joss, A., Siegrist, H., Traber, J., … Fink, G. (2010). Einsatz von Pulveraktivkohle zur Elimination von Mikroverunreinigungen aus kommunalem Abwasser. Dübendorf: Eawag. , Institutional Repository

Der vorliegende Abschlussbericht des Micropoll-Teilprojektes zur Elimination von Spurenstoffen aus kommunalem Abwasser mittels Pulveraktivkohle (PAK) fasst die zentralen Ergebnisse der Pilotierungen und Einzelversuche aller Projektphasen der letzten drei Jahren zusammen.
Hauptziel des Projektes war es durch den Betrieb von halbtechnischen Pilotanlagen und zielgerichteten Einzeluntersuchungen weitere Klärung und Erfahrungen zum Einsatz von Aktivkohle zur Spurenstoffelimination in der kommunalen Abwasserbehandlung zu liefern. Während der ersten Projektphase wurden im Wesentlichen Grundlagen evaluiert (1. - 2. Zwischenbericht), während in den Versuchsphasen zwei und drei empirische und praxisorientierte Untersuchungen vorgenommen wurden. [...]
Abegglen, C., Joss, A., & Siegrist, H. (2009). Eliminating micropollutants: wastewater treatment methods. Eawag News [engl. ed.], 67, 25-27. , Institutional Repository

In many cases, micropollutants are only partly eliminated at wastewater treatment plants. The remaining fraction, together with any transformation products, enters receiving waters with the treated effluents. What options can modern process engineering offer to improve elimination performance?
Abegglen, C., Joss, A., & Siegrist, H. (2009). Eliminer des micropolluants: techniques d'épuration. Eawag News [éd. fr.], 67, 25-27. , Institutional Repository

Les micropolluants ne sont souvent que partiellement retenus dans les stations d’épuration. La partie restante et les éventuels sous-produits de dégradation sont alors rejetés dans le milieu naturel avec les effluents d’épuration. Quelles sont les options actuellement disponibles pour améliorer le rendement d’élimination de ces composés?
Abegglen, C., Joss, A., Boehler, M., Buetzer, S., & Siegrist, H. (2009). Reducing the natural color of membrane bioreactor permeate with activated carbon or ozone. Water Science and Technology, 60(1), 155-165. doi:10.2166/wst.2009.331, Institutional Repository

The suitability of two membrane bioreactors for on-site wastewater treatment and reuse in Switzerland was investigated. The treated wastewater was used for toilet flushing and gardening, with water recycling rates of 30% (single family house) and almost 100% (toilets in a cable car station) respectively. Due to the recycling, an increase in a natural yellowish-brown color was observed, leading to double flushing of the toilets, higher cleaning requirements and increased permeate production. Color removal with ozone, powdered (PAC) and granulated (GAC) activated carbon was assessed in laboratory and field experiments. PAC was added directly into the MBR, whereas ozonation and GAC were applied to the permeate. The dosage of ozone or activated carbon depended on the recycling rate and color intensity. If color removal is necessary, PAC is the option best suited to small treatment plants, with a requirement of 30–50 g m-3 for 30% and 100 g m-3 for 100% water recycling.
Abegglen, C., Joss, A., & Siegrist, H. (2009). Spurenstoffe eliminieren: Kläranlagentechnik. Eawag News [dtsch. Ausg.], 67, 25-27. , Institutional Repository

Vielfach werden Spurenstoffe in Kläranlagen nur teilweise zurückgehalten. Der restliche Teil und mögliche Abbauprodukte gelangen mit dem geklärten Abwasser in die Gewässer. Welche technischen Optionen stehen zur Verfügung, um die Eliminationsleistung zu verbessern? Ein Einblick in die moderne Verfahrenstechnik.
Abegglen, C., Joss, A., McArdell, C. S., Fink, G., Schlüsener, M. P., Ternes, T. A., & Siegrist, H. (2009). The fate of selected micropollutants in a single-house MBR. Water Research, 43(7), 2036-2046. doi:10.1016/j.watres.2009.02.005, Institutional Repository

Membrane bioreactor (MBR) technology is an interesting option for single-house wastewater treatment or small communities. Because typically a very high effluent quality is achieved with respect to pathogens, suspended solids, organics and nitrogen, the permeate is well suited for reuse. Little is known about the fate of micropollutants in such small systems. The differences between centralized and decentralized biological wastewater treatment with respect to micropollutants are manifold: besides the operational parameters like hydraulic and sludge retention time, the main difference is in the load variation. While the influent load is expected to be more or less constant in large catchments, it varies strongly in small MBRs due to irregular consumption (e.g. of medication by individuals). Concentrations of micropollutants are higher by a factor 50–1000 than in centralized treatment. It is also unknown how reliable degradation of micropollutants is in case of irregular exposure.
In this study, two experiments were conducted in a small MBR treating the wastewater of a three-person household. During normal operation of the treatment plant, 25 pharmaceuticals (antibiotics, antiphlogistics, lipid regulators, iodinated contrast media and hormones) that had not been used by members of the household were added in concentrations typical for municipal wastewater. The removal of most substances was in the same range as for centralized wastewater treatment. It was shown that biological transformation was the main elimination process while adsorption to the activated sludge was negligible for most substances due to the low sludge production at high sludge retention time. No appreciable lag for inducing biological degradation was observed. The high hydraulic and sludge residence time had a positive effect on the elimination of slowly degradable substances, but this was partly compensated by the lower biological activity.
An experiment with antibiotics concentrations typical for decentralized treatment (between 500 and 1000 μg l−1; sulfamethoxazole, sulfapyridine, trimethoprim, clarithromycin, roxithromycin) did not show an inhibitory effect on either nitrification or denitrification.
Goosse, P., Steiner, M., & Joss, A. (2009). Safe and high quality food production using low quality waters and improved irrigation systems and management (SAFIR). A specific targeted research project under the thematic priority "Food quality and safety". Work package 1 · Water treatment and irrigation technology. D1_5(extra deliverable): evaluation of alternative water resources for irrigation in agriculture. sine loco: sine nomine. , Institutional Repository
Joss, A., Salzgeber, D., Eugster, J., König, R., Rottermann, K., Burger, S., … Siegrist, H. (2009). Full-scale nitrogen removal from digester liquid with partial nitritation and anammox in one SBR. Environmental Science and Technology, 43(14), 5301-5306. doi:10.1021/es900107w, Institutional Repository

Full-scale application of partial nitritation and anammox in a single suspended-growth sequencing batch (SBR) reactor presented here confirm the process suitable for removing nitrogen from ammonium-rich wastewater with low concentrations of BOD and suspended solids: details of simple and robust process control based on online ammonium or conductivity signals are discussed by describing the full-scale startup at three municipal plants (five reactors in total). Ammonium oxidation rates of up to 500 gN m−3d−1 with conversion to N2 of over 90% are achieved in a full-scale plant, but pilot results indicate that significantly higher rates are feasible. With continuous aeration at dissolved oxygen concentrations <1 mgO2·L−1, the nitrite oxidation and the anammox reaction occur simultaneously, allowing increased overall performance and simplified process control compared to separate aerobic and anaerobic phases (segregated either temporally or in different reactors). Sedimentation of the sludge requires special attention only during startup. Although the observed N2O emissions were slightly higher than in conventional nitrogen removal, the overall greenhouse gas emissions were lower, mainly due to energy-saving.
Joss, A., Böhler, M., Wedi, D., & Siegrist, H. (2009). Proposing a method for online permeability monitoring in membrane bioreactors. Water Science and Technology, 60(2), 497-506. doi:10.2166/wst.2009.370, Institutional Repository

Reliable and efficient operation of membrane bioreactors (MBR) for centralized municipal wastewater treatment strongly depends on a good monitoring of the membrane permeability, a value often used to quantify the transmissibility (i.e. the inverse of the flow resistance) of the membrane. By directly or indirectly evaluating this parameter the operator normally plans on the necessity and effectivity of maintenance activities. To allow the operator monitoring the membrane performance closely, the present paper proposes a method for online permeability based on the measurements of permeate flow, transmembrane pressure and water temperature. The theoretical background of the method is discussed and a data set of 250 days of continuous pilot operation of a municipal MBR equipped with three different standard membrane modules is used for testing. The method is numerically simple enough to allow being implemented on any programmable logical controller.
Wick, A., Fink, G., Joss, A., Siegrist, H., & Ternes, T. A. (2009). Fate of beta blockers and psycho-active drugs in conventional wastewater treatment. Water Research, 43(4), 1060-1074. doi:10.1016/j.watres.2008.11.031, Institutional Repository

The removal of beta blockers and psycho-active drugs was investigated in a representative conventional German WWTP by long-term measurement campaigns along different biological treatment processes. The activated sludge treatment with an elevated SRT of 18 d was the only process which led to a significant removal of certain beta blockers and psycho-active drugs. The removal efficiency was below 60% for all compounds except for the natural opium alkaloids codeine and morphine being removed by more than 80%. Primary biological transformation and sorption onto sludge as the main removal mechanisms were examined in lab-scale batch experiments. Sorption onto activated sludge was found to be negligible (<3%). The biological transformation could be described by pseudo-first order kinetics and the transformation constants kbiol were used to predict the removal of beta blockers and psycho-active drugs in an activated sludge unit with a model. For most compounds the removal efficiencies measured on the full-scale WWTP were within the 95% confidence intervals predicted by the model. The results from full-scale measurements and modeling indicate that biological transformation in the nitrification tank together with parameters such as the sludge retention time and the temperature is crucial regarding the biological transformation of beta blockers and psycho-active drugs in conventional WWTPs.
Brepols, C., Dorgeloh, E., Frechen, F. B., Fuchs, W., Haider, S., Joss, A., … Wozniak, T. (2008). Upgrading and retrofitting of municipal wastewater treatment plants by means of membrane bioreactor (MBR) technology. Desalination, 231(1–3), 20-26. doi:10.1016/j.desal.2007.11.035, Institutional Repository

In the future, upgrading of existing wastewater treatment plants (wwtps) will become the more challenging task than erection of wholly new plants, as most of the plants (e.g. necessary in Germany) do exist already. Since some time, MBR technology has been taken into consideration and has been realised as an alternative for wwtp upgrading. This paper gives an overview about some relevant preconditions, basic upgrading concepts and examples of already upgraded wwtps using MBR technology.
Joss, A., Siegrist, H., & Ternes, T. A. (2008). Are we about to upgrade wastewater treatment for removing organic micropollutants?. Water Science and Technology, 57(2), 251-255. doi:10.2166/wst.2008.825, Institutional Repository

Activated sludge treatment allows only for a partial removal of micropollutants, mainly via sorption and biological degradation. Ozonation and activated carbon filtration are processes bearing the potential to drastically reduce the micropollutant load discharged to the environment after (centralized) biological treatment. The estimated total costs between 0.05 and 0.20€ per m3 treated water (depending on plant size and effluent DOC content) represent only a small fraction of the total costs for urban wastewater management and are therefore considered feasible. Full scale testing is currently planned or under way with the aim to a) confirm this cost estimation and b) to demonstrate the benefit by quantification of the effect of removal and by documenting the impact on the ecology of receiving waters. Ozonation would have the additional advantage of achieving partial disinfection. Another issue currently being intensively studied is the byproducts formed during ozonation and their toxicity. Evidence is needed that the formed ozonation byproducts are either harmless or easily degradable. Since a 5% to 20% loss of sewage is occurring due to sewer leakage and combined sewer overflow an improved reduction of micropollutant input to the aquatic environment requires that advanced centralized treatment is complemented with measures taken before discharge into the sewer. Options hereto may be waste design, labeling of compounds according to environmental friendliness or separate treatment of quantitatively significant point sources (e.g. hospital wastewater, nursery homes, industrial wastewater).
Siegrist, H., Salzgeber, D., Eugster, J., & Joss, A. (2008). Anammox brings WWTP closer to energy autarky due to increased biogas production and reduced aeration energy for N-removal. Water Science and Technology, 57(3), 383-388. doi:10.2166/wst.2008.048, Institutional Repository

Fifty years ago when only BOD was removed at municipal WWTPs primary clarifiers were designed with 2–3 hours hydraulic retention time (HRT). This changed with the introduction of nitrogen removal in activated sludge treatment that needed more BOD for denitrification. The HRT of primary clarification was reduced to less than one hour for dry weather flow with the consequence that secondary sludge had to be separately thickened and biogas production was reduced. Only recently the ammonia rich digester liquid (15–20% of the inlet ammonia load) could be treated with the very economic autotrophic nitritation/anammox process requiring half of the aeration energy and no organic carbon source compared to nitrification and heterotrophic denitrification. With the introduction of this new innovative digester liquid treatment the situation reverts, allowing us to increase HRT of the primary clarifier to improve biogas production and reduce aeration energy for BOD removal and nitrification at similar overall N-removal.
Wedi, D., & Joss, A. (2008). Dimensioning of membrane bioreactors for municipal wastewater treatment. Water Science and Technology, 57(6), 829-835. doi:10.2166/wst.2008.117, Institutional Repository

A basic procedure is proposed for dimensioning membrane bioreactors that is generally applicable. It evaluates the required membrane surface with particular consideration of loading combinations and hydraulic loading characteristics; it also takes into account ranges of minimum temperatures and corresponding fluxes as given by suppliers. The procedures, while likely to require further improvement, should make MBR design more transparent and aid the comparison of design variants
Boehler, M., Joss, A., Buetzer, S., Holzapfel, M., Mooser, H., & Siegrist, H. (2007). Treatment of toilet wastewater for reuse in a membrane bioreactor. Water Science and Technology, 56(5), 63-70. doi:10.2166/wst.2007.557, Institutional Repository

Toilet wastewater is treated and reused on site at Europe's highest membrane bioreactor (MBR), located in a cable car mountain station in the ski resort of Zermatt. Negative impacts on the sensitive mountain environment are minimised by reusing close to 100% of the treated wastewater for toilet flushing. Besides 100% nitrogen removal, 80% of phosphorus was also eliminated. This paper presents operational results, optimisations of sludge management, decoloration and long-term maintenance of biomass in the very low-loaded summer season. From a global view the experiences and results of the project are of great importance, proposing a solution to a problem existing 100-fold in the Alps as well as in and regions all over the world: reducing water consumption for sanitation by reuse.
De Wilde, W., Besancon, A., Joss, A., Sharma, S., Amy, G., Pollice, A., … Ng, H. Y. (2007). Reclaim water. A specific targeted research project under the thematic priority "Global change and ecosystems". Work package 1 assessment and development of water reclamation technology. Deliverable D 1.1 characterisation of unit operations for wastewater reclamation in terms of upgrading capability, reliability and flexibility. sine loco: sine nomine. , Institutional Repository
Göbel, A., McArdell, C. S., Joss, A., Siegrist, H., & Giger, W. (2007). Fate of sulfonamides, macrolides, and trimethoprim in different wastewater treatment technologies. Science of the Total Environment, 372(2–3), 361-371. doi:10.1016/j.scitotenv.2006.07.039, Institutional Repository

The elimination of sulfonamides, macrolides and trimethoprim from raw wastewater was investigated in several municipal wastewater treatment plants. Primary treatment provided no significant elimination for the investigated substances. Similar eliminations were observed in the secondary treatment of two conventional activated sludge (CAS) systems and a fixed-bed reactor (FBR). Sulfamethoxazole, including the fraction present as N4-acetyl-sulfamethoxazole, was eliminated by approximately 60% in comparison to about 80% in a membrane bioreactor (MBR) independently of the solid retention time (SRT), indicating a positive correlation of the observed elimination to the organic substrate concentration. The elimination for macrolides and trimethoprim varied significantly between the different sampling campaigns in the two CAS systems and in the FBR. In the MBR, these analytes were eliminated up to 50% at SRT of 16 ± 2 and 33 ± 3 d. Trimethoprim, clarithromycin and dehydro-erythromycin showed a higher elimination of up to 90% at a SRT of 60-80 d indicating a correlation with reduced substrate loading (SL). Together with the high SRT, the SL may lead to an increased biodiversity of the active biomass, resulting in a broader range of degradation pathways available. Two investigated sand filters showed different elimination behavior. One led to a significant elimination of most macrolides (17–23%) and trimethoprim (74 ± 14%), while no elimination was observed in the other sand filter investigated.
Jenni, S. (2007). Modellierung der autotrophen Deammonifikation (Master thesis). 98 p. , Institutional Repository

Mit dem Schlammwasser aus der anaeroben Schlammfaulung werden 15-20% der Gesamtstickstofffracht in den Zulauf der Abwasserreinigungsanlage zurückgeführt. Mit einer separaten Schlammwasserbehandlung kann die Stickstofffracht im Zulauf der Anlage verkleinert und somit die Stickstoffelimination signifikant gesteigert werden. Die autotrophe Deammonifikation bietet dabei eine Reihe von Vorteilen gegenüber der konventionellen Schlammwasserbehandlung mit Nitrifikation und Denitrifikation. In einem Sequencing Batch Reaktor (SBR) kann die autotrophe Deammonifikation in einem Reaktor kombiniert werden. Das Verfahren wurde so im Pilotmassstab an der EAWAG bereits über mehrere Monate erfolgreich betrieben. Ausstehend ist noch die Umsetzung des Verfahrens im Vollmassstab, die auf den Kläranlagen Werdhölzli (Zürich) und St. Gallen geplant ist.
In der vorliegenden Arbeit ist die Umsetzung des Verfahrens auf der Kläranlage Werdhölzli im Pilotmassstab getestet worden. Der 400L-Reaktor wurde dazu mit Schlamm aus der konventionellen Schlammwasserbehandlung des Werdhölzlis gefüllt und im Verhältnis 1:40 mit Anammoxschlamm aus der EAWAG angeimpft. Die Anammoxorganismen konnten allerdings nicht einwachsen, da der Schlamm eine zu hohe Nitritoxidationsaktivität aufwies. Innerhalb von vier Wochen konnte mit einer Substratlimitierung keine entscheidende Verminderung der Nitritoxidierer erreicht werden.
Für die Modellierung der einstufigen autotrophen Deammonifikation ist ein dynamisches Modell entwickelt und in AQUASIM implementiert worden. Experimentelle Untersuchungen einzelner kinetischer Parameter ergaben, dass der Nitritsättigungsbeiwert der Anammoxorganismen bei ungefähr 0.5 mgNO2-N/L liegt und dass weder die Nitritoxidierer noch die Anammoxorganismen durch hohe Ammoniakkonzentrationen gehemmt werden. Das Modell ist mit Messdaten aus dem Betrieb der Pilotanlage kalibriert worden. Die beste Übereinstimmung zwischen den gemessenen und den modellierten Stickstoffzehrungsraten resultiert mit einer maximalen Wachstumsgeschwindigkeit der Anammoxorganismen von 0.083 d-1.
Mit dem Modell wurde die Einwachsphase mit einer geringen Anfangsnitritoxidationsaktivität bei 35 und 25°C simuliert. Der Reaktor kann bei beiden Betriebstemperaturen problemlos eingefahren werden. Nach rund 30 bzw. 60 Tagen kann der Reak-tor mit einer hydraulischen Aufenthaltszeit von einem Tag und einem Schlammalter von rund 21 Tagen stabil betrieben werden. Die Konzentration der Nitritoxidierer nimmt dabei ab. Aus dieser und ähnlichen Simulationen lassen sich wichtige Erkenntnisse für den optimalen Betrieb eines Reaktors gewinnen.
Salzgeber, D., Joss, A., & Siegrist, H. (2007). Autotrophe Schlammwasserentstickung (Nitritation/Anammox). Im SBR-Verfahren (Sequencing batch reactor). GWA Gas, Wasser, Abwasser, 87(3), 205-209. , Institutional Repository

For six months, Eawag has in operated in a stable fashion a 400 litre SBR for autotrophic denitrification of ammonium rich sludge. In so doing, a part of the ammonium is oxidised with oxygen into a nitrite (partial nitrification) and the remaining ammonium is oxidised using the created nitrites into molecular nitrogen. With a nitrogen elimination rate of up to 680 gN m-3 d-1 and hydraulic delay times of somewhat under a day with a clear N-elimination rate of 90 %, a good level of elimination is achieved. The processes can be controlled via conductivity, pH or the nitrite signal.
Salzgeber, D. (2007). Biologische Schlammwasserentstickung mit Anammox im einstufigen SBR (Master thesis). 59 p. , Institutional Repository

Die autotrophe Entstickung von ammoniumreichem Schlammwasser wird in einem 400L SBR-Reaktor während eines halben Jahres ohne Unterbruch betrieben. Dabei wird ein Teil des Ammoniums zu Nitrit oxidiert (Teilnitritation) und das restliche Ammonium mit Hilfe des gebildeten Nitrits zu molekularem Stickstoff oxidiert (Anammox: anaerob Ammoniumoxidation). Die Stickstoffeliminationsleistung liegt bei bis zu 680 gN m-3 d-1 bei einer Elimination von 90 % des Stickstoffs. Der Reaktor wird bei 30°C, 25°C und 20°C betrieben. Die tiefsten hydraulischen Aufenthaltszeiten (HRT) von unter einem Tag werden bei 30°C erreicht, wobei bei dieser Temperatur die Anammoxbakterien auch die höchsten Aktivitäten von über 2000 gN m-3 d-1 aufweisen. Der Betrieb kann bei 25°C und 20°C ebenfalls stabil aufrechterhalten werden, die HRT kann bei 20°C aber nicht mehr unter 1.5 Tage gesenkt werden. Während der ersten drei Monate kann für die Anammoxbakterien eine Wachstumsrate von 0.029 d-1 beobachtet werden.
Der Ammoniumabbau kann sowohl in einem getakteten Betrieb durchgeführt werden, bei
dem auf jede 15-30 Minuten dauernde belüftete Phase eine unbelüftete Phase folgt, als auch
mit einer kontinuierlichen Belüftung, bei welcher die Ammoniumoxidation und die
Anammoxreaktion simultan ablaufen. Das Verfahren kann über das Leitfähigkeits-, pH- oder
Nitritsignal geregelt werden und wird im Sommer `07 in der ARA Werdhölzli in einem 1400
m3-Becken implementiert.

The autotrophic deammonification of ammonium-rich digester supernatant in a 400L SBR-reactor has been carried out for a half year without any interruptions. In this process a part of the ammonium is oxidized to nitrite. The remaining ammonium is oxidized under anoxic conditions with the formed nitrite to molecular nitrogen (Anammox: anaerobic ammonium oxidation). The nitrogen removal capacity is up to 680 gN m-3 d-1 with a elimination of 90 % of the nitrogen. The reactor is operated at 30°C, 25°C and 20°C. The shortest hydraulic
retention time (HRT) of less than one day is achieved at 30°C. At 30°C the Anammox-bacteria also exhibits the highest activity by removing over to 2000 gN m-3 d-1. Likewise, the operation can be stably maintained at 25°C and 20°C, but the HRT can not be shortened to less than 1.5 days at 20°C. Over the period of the first three months a growth rate of 0.029 d-1 for the Anammox bacteria could be observed.
The ammonium degradation can be accomplished two ways: in an alternating mode where the reactor is aerated for a period of 15-30 minutes and then stirred, or in a continuous mode where the aeration is constant. The ammonium oxidation runs in this mode simultaneously to the Anammox-reaction. The procedure can be regulated using the conductivity, the pH-value or the nitrite concentration. This procedure will be implemented in the ARA Werdhoelzli/Zürich in the summer of 2007 in a 1400 m3-reactor.
Siegrist, H., Joss, A., & Ternes, T. (2007). Fate of micropollutants in drinking and wastewater treatment and consequences for process design (p. (8 pp.). Presented at the 4th leading edge conference on water and wastewater technologies. Singapore. , Institutional Repository

Through improved methods of chemical analysis, micropollutants, e.g. pharmaceuticals and endocrine disrupting compounds are increasingly being detected in our water bodies. In most cases these enter the wastewater after being excreted in urine and feces. In the sewage plant, a part of the substances is eliminated via sorption and biological degradation. The rest is discharged with the treated effluent. In surface water and during bank infiltration further elimination is observed but some micropollutants persist, acting as wastewater tracer in groundwater and are also detected in drinking water. This article describes possible measures for eliminating trace organics in waste and drinking water treatment. These include on the one hand, permanent measures at the source such as an eco-label for pharmaceuticals and personal care products as well as the separate treatment of strongly polluted wastewater, e.g. in hospital or industry. However, as most of these measures can only be implemented over the long term, it is expedient on the other hand, to also consider technical measures such as increasing the sludge age in the activated sludge tanks of WWTP and for crucial locations, additional treatment with ozone or activated carbon.
Siegrist, H., & Joss, A. (2007). Mikroverunreinigungen. Technische Verfahren zur Elimination. GWA Gas, Wasser, Abwasser, 87(11), 861-867. , Institutional Repository

Due to improved chem ical analysis, pharmaceuticals, pesticides and endocrine disrupters are increasingly detected in waters. The waste water treatment plant removes parts of the substances by sorption and biological decomposition. The other part reaches river and lakes together with the treated waste water. This article presents possible measures to eliminate the remaining substances. On the one hand, via sustainable measures on the source, and on the other hand, with technical measures like ozone or activated carbon dosages.
de Mes, T. (2007). Fate of estrogens in biological treatment of concentrated black water (Doctoral dissertation). 154 p. , Institutional Repository

Sewage treatment plants (STPs) effluents were found to have estrogenic character which is mainly due to the presence of estrone (E1), 17β-estradiol (E2) and 17α-ethynylestradiol (EE2). E1 and E2 are natural hormones excreted by mammals in urine and faeces, whereas EE2 is a synthetic hormone present in the contraceptive pill. The largest part of the estrogens is excreted via urine as glucuronide or sulphate conjugate with no estrogenic properties. These conjugates can be cleaved back to their original form by bacterial enzymes, where deconjugation of glucuronide conjugates is faster than of sulphate conjugates.
Human excreted estrogens are insufficiently removed in conventional treatment systems designed to remove bulk organic matter and nutrients. Maximum reported concentrations in STP effluents are 76 ng/l for E1, 64 ng/l for E2 and 42 ng/l for EE2. Effects on fish were already prevalent at 3.3 ng E1/l, 1 ng E2/l and 0.03 ng EE2/l, values that are often exceeded in surface waters.
Present research focused on the fate of estrogens in sanitation concepts with source separated collection and treatment of domestic wastewater i.e. black water (toilet), grey water (personal hygiene, kitchen) and rain water. Source separated collection offer benefits in terms of energy and resource conservation. By applying vacuum toilets in these concepts, the black water volume containing estrogens is about 7 L per person per day, whereas in conventional sanitation concepts this volume (including rain water) is about 200 L per person per day.
Adsorption and biodegradation are considered the most important processes for the removal of estrogens in biological wastewater treatment systems, and therefore adsorption constants and first order degradation rates were determined. Besides, their fate was investigated in a concentrated black water pilot treatment system consisting of UASB septic tank, with aerobic post-treatment. Determination was established by HPLC with UV, fluorescence and diode array detection and GC-MS for environmental relevant concentrations.
The highest degradation rates were obtained under aerobic redox conditions for all three estrogens, with EE2 being the most persistent as was also confirmed in literature. Increasing sludge retention time had a positive effect on the biological removal rates, whilst nitrifiers did not contribute significantly to it. The results showed that reduced bioavailability, e.g. desorption of adsorbed estrogens, can suppress the conversion rate. During anaerobic conditions, a reduction of E1 to E2 was observed but no decline for the sum of E1 and E2 nor EE2 was observed in various types of sludge.
In the pilot UASB septic tank effluent, total concentrations of 4.02 μg E1/l and 18.69 μg E2/l, of which >70% for E1 and >80% for E2 were in conjugated form. EE2 concentrations were below the detection limit. In the effluent of the post-treatment E1 and E2 were present in concentrations of 1.37±1.45 μg/l and 0.65±0.78 μg/l, respectively. The limited deconjugation of conjugated estrogens during treatment was demonstrated when UASB septic tank was spiked with the sulphate conjugate of E2, revealing that 99% of the detected E2 in the final effluent is in conjugated form.
Even though the application of source separation can prevent storm water overflow and reduce the volume of the wastewater in which estrogens are present, high effluent concentrations after biological treatment necessitate additional treatment. Besides, there is a need for information on the deconjugation rates and the behaviour of conjugated estrogens in general.
Alder, A. C., Bruchet, A., Carballa, M., Clara, M., Joss, A., Löffler, D., … Ternes, T. A. (2006). Consumption and occurrence. In T. A. Ternes & A. Joss (Eds.), Human pharmaceuticals, hormones and fragrances. The challenge of micropollutants in urban water management (pp. 15-54). Retrieved from https://iwaponline.com/ebooks/book/19/Human-Pharmaceuticals-Hormones-and-Fragrances-The, Institutional Repository

The several studies in Europe and North America exhibited the ubiquitous occurrence of pharmaceuticals, contrast media and estrogens in wastewater and in the aquatic environment. Since the major part of PPCPs is only partially eliminated during wastewater treatment, residual amounts are usually present in wastewater effluents and can reach ambient waters or groundwater. Certain pharmaceuticals are persistent and pass through the STP without major elimination, such as the lipid regulator clofibric acid, the antiepileptic carbamazepine or the contrast medium diatrizoate. Additionally, direct inputs into natural waters are also possible through storm water overflow and leakages in the sewer system. (...)
Amy, G., Cheng, X., de Heyder, B., Hein, A., Jefferson, B., Joss, A., … Kazner, C. (2006). Reclaim water. A specific targeted research project under the thematic priority "Global change and ecosystems". Work package 1 · assessment and development of water reclamation technology. Milestone M 1.2 · Set up of all required analytical skills or contact to the corresponding labs. sine loco: sine nomine. , Institutional Repository
Fletcher, H., Kekre, K., Guihe, T., Seah, H., Guglielmi, G., Andreottola, G., … Siegrist, H. (2006). Design. In S. Judd & C. Judd (Eds.), The MBR Book. Principles and applications of membrane bioreactors in water and wastewater treatment (pp. 123-162). doi:10.1016/B978-185617481-7/50005-2, Institutional Repository
Joss, A., Zabczynski, S., Göbel, A., Hoffmann, B., Löffler, D., McArdell, C. S., … Siegrist, H. (2006). Biological degradation of pharmaceuticals in municipal wastewater treatment: proposing a classification scheme. Water Research, 40(8), 1686-1696. doi:10.1016/j.watres.2006.02.014, Institutional Repository

A simple classification scheme is suggested to characterize the biological degradation of micropollutants such as pharmaceuticals, musk fragrances and estrogens during wastewater treatment. The scheme should be a basis for the discussion about potential removal efficiencies. Hence, the biological degradation of 25 pharmaceuticals, hormones and fragrances was studied in batch experiments at typical concentration levels using activated sewage sludge originating from nutrient-eliminating municipal wastewater treatment plants.
Since pseudo first-order degradation kinetics was observed for all compounds down to ng L-1 levels, the removal rates can be predicted for various reactor configurations. Therefore dilution of wastewater (e.g. by extraneous water) is expected to reduce the degree of biological removal. Wastewater segregation and treatment at the source are therefore to be favoured for elimination of persistent micropollutants over centralized end-of-pipe treatment. For reactor configurations typical for nutrient removal in municipal wastewater, the derived formula for predicting removal allows the identification of three groups of micropollutants according to their degradation constant kbiol: compounds with kbiol<0.1 L gSS-1 d-1 are not removed to a significant extent (<20%), compounds with kbiol>10 L gSS-1 d-1 transformed by >90% and in-between moderate removal is expected. Based on the degradation of a heterogeneous group of 35 compounds (including literature data), state of the art biological treatment schemes for municipal wastewater are not efficient in degrading pharmaceuticals: only 4 out of 35 compounds are degraded by more than 90% while 17 compounds are removed by less than 50%.
Joss, A., Klaschka, U., Knacker, T., Liebig, M., Lienert, J., Ternes, T. A., & Wennmalm, A. (2006). Source control, source separation. In T. A. Ternes & A. Joss (Eds.), Human pharmaceuticals, hormones and fragrances. The challenge of micropollutants in urban water management (pp. 353-384). Retrieved from https://iwaponline.com/ebooks/book/19/Human-Pharmaceuticals-Hormones-and-Fragrances-The, Institutional Repository

The reduction of the micropollutant emission into the environment is to be achieved by complementing end-of-pipe advanced wastewater treatment steps in centralized municipal plants with measures taken at the source. A significant reduction in terms of consumed quantities as well as in terms of the ecotoxicity of the selected compounds is feasible if the stakeholders can be successfully involved:
• patients and the general public represent the starting point on which a shift of production (i.e. towards more environmentally friendly compounds) as well as legislative issues are based on
• industry is a central player able to influence the pace at which new solutions are introduced on the market
• physicians and health care personnel play a key role in the therapeutic choice as well as in supporting complementary strategies to reduce medical consumption (e.g. hygienic standard in hospitals, empirical vs. targeted therapy)
• legislative authorities are required if solutions are to be implemented beyond voluntary choice (e.g. composition of industrial or hospital wastewater discharged into the sewer)
Ecolabelling may represent a tool to initiate the required public discourse for phasing in of new products or production methods. However, it ought to be substituted or backed up by legislation to achieve broader compliance or general validity. (...)
Joss, A., Carballa, M., Kreuzinger, N., Siegrist, H., & Zabczynski, S. (2006). Wastewater treatment. In T. A. Ternes & A. Joss (Eds.), Human pharmaceuticals, hormones and fragrances. The challenge of micropollutants in urban water management (pp. 243-292). London, UK: IWA Publishing. , Institutional Repository
Siegrist, H., & Joss, A. (2006). Leading-edge processes on urban wastewater treatment - presentation of the European Project NEPTUNE (p. (6 pp.). Presented at the 10a fiera internazionale del recupero di materia ed energia e dello sviluppo sostenibile (Ecomondo 2006). Rimini, Italy. , Institutional Repository

The scope of sewage treatment is changing: There is a shift from today's end of pipe treatment, having the aim to avoid eutrophication and hygienic health hazard in surface water, towards resource recovery (water, energy, nutrients, sludge), that demand an improved control and removal of micropollutants. The EU project NEPTUNE will focus its research mainly on centralized wastewater treatment via upgrading of existing infrastructure as well as new technologies.
Siegrist, H., & Joss, A. (2006). Leistung der heutigen Abwasserreinigung und innovative Ansätze für das zukünftige Design (p. (9 pp.). Presented at the DWA Tagung "Elimination organischer Spurenstoffe und Mikroorganismen". Koblenz, Germany. , Institutional Repository

Heute sind in der Europäischen Union (EU) etwa 100'000 verschiedene Chemikalien gemeldet, von denen rund 30'000 in einer Menge von mehr als einer Tonne auf dem Markt vertrieben werden [1]. Es ist unvermeidlich, dass bei der Herstellung und Entsorgung sowie beim Gebrauch der Stoffe auch Anteile in die Umwelt gelangen.

Durch die sich die ständig verbessernde chemische Analytik findet man im Abwasser, in den Gewässern und im Klärschlamm vermehrt Verbindungen in sehr niedrigen Konzentrationsbereichen (Mikro- und Nanogramm pro Liter), die als Mikroverunreinigungen bezeichnet werden. Dazu gehören bekannte Vertreter wie das Pestizid Atrazin, der Kunststoffzusatz Bispenol A und das Benzinantiklopfmittel Methyl-tertiär-butylmethyläther. Weniger bekannt ist, dass sich darunter auch sehr viele Verbindungen für den täglichen Gebrauch wie z.B. Arzneimittel befinden. Heute werden in der EU ca. 3'300 verschiedene Stoffe als Arzneimittel verwendet. Mengenmässig bedeutsam sind Wirkstoffe, die u.a. als Analgetika, Antibiotika, Antidiabetika, Betablocker, Kontrazeptiva, Lipidsenker, Psychopharmaka oder Zytostatika eingesetzt werden.

Arzneimittel gelangen in der Regel über die natürlichen Ausscheidungen wie Urin oder Fäkalien in das Abwassersystem. Ein nicht zu vernachlässigender Anteil der im Abwasser enthaltenen Arzneimittel wird aber auch durch unsachgemässe Entsorgung über die Toilette eingetragen. Eine deutsche Studie [2] untersuchte das Vorkommen von 55 Arzneimittelwirkstoffen und 9 Metaboliten im Ablauf von 49 Kläranlagen sowie in den jeweiligen Gewässern, in die die geklärten Abwässer eingeleitet werden (Vorfluter). Dabei konnten in den Kläranlagenabläufen 36 Wirkstoffe und 5 Metaboliten in Konzentrationen bis zu mehreren μg/l nachgewiesen werden. In den Gewässern wurden noch Spitzenkonzentrationen von über 1 μg/l (z.B. Betablocker und Antiepileptika) gemessen.

Darüber hinaus machen in den letzten Jahren neuartige Umwelteffekte, wie die Verweiblichung von Fischen, von sich reden. Sie werden zum Teil auf den chronischen Eintrag hormonaktiver (endokriner) Substanzen zurückgeführt. Dazu gehören neben den körpereigenen Hormonen, die ebenso mit dem Urin ausgeschieden werden, auch diejenigen Arzneimittel, die aufgrund ihrer hormonellen Wirkung eingesetzt werden wie z.B. die Kontrazeptiva und Antidiabetika. Einigen anderen Arzneimittelwirkstoffen, wie z.B. β-Sitosterol (zur Senkung des Cholesterinspiegels) und Clenbuterol (Asthmamittel), wird zusätzlich zu ihrer nichthormonellen Hauptwirkung, eine hormonelle Nebenwirkung zugeschrieben. Für die meisten Arzneimittel sind jedoch keine endokrinen Wirkungen bekannt. Das mag aber auch daran liegen, dass sie niemals auf etwaige hormonelle Wirkungen getestet wurden. Es ist daher nicht ausgeschlossen, dass die Gruppe der Arzneimittelwirkstoffe mit ungewollten hormonellen Nebenwirkungen viel grösser ist als angenommen.

Der vorliegende Artikel gibt anhand ausgewahlter Beispiele einen Überblick über die Eliminationsprozesse und stellt mogliche Massnahmen zur Diskussion.
Ternes, T. A., & Joss, A. (Eds.). (2006). Human pharmaceuticals, hormones and fragrances. The challenge of micropollutants in urban water management. doi:10.2166/9781780402468, Institutional Repository
Göbel, A., Thomsen, A., McArdell, C. S., Joss, A., & Giger, W. (2005). Occurrence and sorption behavior of sulfonamides, macrolides, and trimethoprim in activated sludge treatment. Environmental Science and Technology, 39(11), 3981-3989. doi:10.1021/es048550a, Institutional Repository

The occurrence of sulfonamide and macrolide antimicrobials, as well as trimethoprim, was investigated in conventional activated sludge treatment. Average daily loads in untreated wastewater correlated well with those estimated from annual consumption data and pharmacokinetic behavior. Considerable variations were found during a day, and seasonal differences seem to occur for the macrolides, probably caused by a higher consumption of these substances in winter. The most predominant macrolide and sulfonamide antimicrobials were clarithromycin and sulfamethoxazole, respectively. In the case of sulfamethoxazole, the main human metabolite, N4- acetylsulfamethoxazole, was included as an analyte, accounting for up to 86% of the total load in untreated wastewater. The results obtained illustrate the importance of considering retransformable substances, for example human metabolites, when investigating the behavior and fate of pharmaceuticals, Average concentrations of sulfapyridine, sulfamethoxazole, trimethoprim, azithromycin, and clarithromycin in activated sludge ranged between 28 and 68 μg/kg of dry weight. Overall the sorption to activated sludge was shown to be low for the investigated antimicrobials, with estimated sorption constants for activated sludge below 500 L/kg. Elimination in activated sludge treatment was found to be incomplete for all investigated compounds. In final effluents, the median concentrations for sulfamethoxazole and clarithromycin were 290 and 240 ng/L, respectively.
Huber, M. M., Göbel, A., Joss, A., Hermann, N., Löffler, D., McArdell, C. S., … von Gunten, U. (2005). Oxidation of pharmaceuticals during ozonation of municipal wastewater effluents: a pilot study. Environmental Science and Technology, 39(11), 4290-4299. doi:10.1021/es048396s, Institutional Repository

To reduce the release of pharmaceuticals and endocrine disruptors into the aquatic environment or to remove them from wastewater intended for direct or indirect reuse, the application of advanced wastewater treatment may be required. In the present study, municipal wastewater effluents were treated with ozone (O3) in a pilot-scale plant consisting of two bubble columns. The investigated effluents, which varied in suspended solids concentrations, comprised an effluent of conventional activated sludge treatment (CAS), the same effluent dosed with 15 mg of TSS L-1 of activated sludge (CAS + SS), and the effluent of a membrane bioreactor pilot plant (MBR). Selected classes of pharmaceuticals were spiked in the wastewater at realistic levels ranging from 0.5 to 5 μg L-1. Samples taken at the inlet and the outlet of the pilot plant were analyzed with liquid chromatography (LC)-electrospray tandem mass spectrometry (MS). Macrolide and sulfonamide antibiotics, estrogens, and the acidic pharmaceuticals diclofenac, naproxen, and indomethacin were oxidized by more than 90-99% for O3 doses ≥ 2 mg L-1 in all effluents. X-ray contrast media and a few acidic pharmaceuticals were only partly oxidized, but no significant differences were observed among the three effluents. These results show that many pharmaceuticals present in wastewater can be efficiently oxidized with O3 and that suspended solids have only a minor influence on the oxidation efficiency of nonsorbing micropollutants.
Joss, A., Goosse, P., Cao, T. A., & Siegrist, H. (2005). Langzeitverhalten der Permeabilität von getauchten Membranmodulen für die kommunale Abwasserreinigung. In T. Melin (Ed.), Membrantechnik in der Wasseraufbereitung und Abwasserbehandlung. Perspektiven, Neuentwicklungen und Betriebserfahrungen im In- und Ausland. Begleitbuch zur 6. Aachener Tagung Siedlungswasserwirtschaft und Verfahrenstechnik, 26. - 27.10.2005 (p. (15 pp.). Retrieved from https://www.avt.rwth-aachen.de/cms/AVT/Forschung/Sonstiges/Publikationen/~iavo/Details/?file=47592, Institutional Repository

Für die kommunale Abwasserreinigung mittels Membranbioreaktor werden heute sowohl Plattenmembranen wie auch Hohlfasermembranen eingesetzt. Während Anschaffungskosten und Packungsdichte der Membran relative einfach anhand der Hersteller- und Lieferantenangaben verglichen werden können, ist das Langzeitverhalten der Permeabilität und somit die zu dimensionierende Permeatleistung nur mittels Langzeiterfahrung zu ermitteln. Diese Studie soll zur Deckung dieser Wissenslücke beitragen, indem über Jahre beobachtete Permeabilitätswerte der Plattenmembran (Kubota) vorgestellt und anhand einiger Begleituntersuchungen diskutiert werden. Betriebserfahrungen mit den Hohlfasermodulen von Mitsubishi und Zenon werden als Vergleich herangezogen, nicht aber im Detail diskutiert.
Joss, A., Keller, E., Alder, A. C., Göbel, A., McArdell, C. S., Ternes, T., & Siegrist, H. (2005). Removal of pharmaceuticals and fragrances in biological wastewater treatment. Water Research, 39(14), 3139-3152. doi:10.1016/j.watres.2005.05.031, Institutional Repository

The removal of seven pharmaceuticals and two fragrances in the biological units of various full-scale municipal wastewater treatment plants was studied. The observed removal of pharmaceuticals was mainly due to biological transformation and varied from insignificant (<10%, carbamazepine) to>90% (ibuprofen). However, no quantitative relationship between structure and activity can be set up for the biological transformation. Overall, it can be concluded that for compounds showing a sorption coefficient (Kd) of below 300 L kg-1, sorption onto secondary sludge is not relevant and their transformation can consequently be assessed simply by comparing influent and effluent concentrations. The two fragrances (HHCB, AHTN) studied were mainly removed by sorption onto sludge. For the compounds studied, comparable transformation and sorption was seen for different reactor types (conventional activated sludge, membrane bioreactor and fixed bed reactor) as well as for sludge ages between 10 and 60-80 days and temperatures between 12 °C and 21 °C. However, some significant variations in the observed removal currently lack an explanation. The observed incoming daily load of iopromide and roxithromycin in medium-sized municipal wastewater treatment plants (up to 80,000 population equivalents) is generated by only a small number of patients: the consequences for representative 24 h composite sampling are discussed. Generally, the paper presents a method for setting up mass balances for micropollutants over entire wastewater treatment plants, including an estimation of the accuracy of the quantified fate (i.e. removal by sorption and biological transformation).
Siegrist, H., Joss, A., Ternes, T., & Oehlmann, J. (2005). Fate of EDCS in wastewater treatment and EU perspective on EDC regulation (pp. 3142-3165). Presented at the 78th annual technical exhibition and conference, Water Environment Federation, WEFTEC.05®. Alexandria, VA: Water Environment Federation. , Institutional Repository

Municipal wastewater is one of the main exposure routes that brings the most important EDCs like natural and artificial hormones via urine, ingredients of personal care products and detergent via grey water (e.g. alkylphenol) and ubiquitous industrial chemicals (e.g. Bisphenyl A) into the environment.
Whether trace pollutants can be eliminated in a WWTP depends on the biological treatment standard (Ternes et al., 2004). In Europe, mainly activated sludge systems are installed for biological treatment. Biological treatment has been developed step by step during the past 50 years starting from only BOD removal with short sludge retention times (SRT <4 days), followed by nitrification and denitrification with an extension of the SRT to 10-15 d and finally, in the last 15 years, introduction of anaerobic zones for P removal with total SRT 15-25 d. Degradation of EDCs is strongly improved with increasing SRT. Whereas natural hormones (E1 and E2) are partly degraded at SRT <5 days, EE2 is only significantly removed at SRT >10 days (Andersen et al., 2003). Biofiltration reaches similar removal efficiencies if designed for nutrient removal (Joss et al. 2004). With membrane bioreactors having SRT of more than 30 days an increased alkylphenol degradation (>95%) was observed (Wettstein, 2004). Sorption plays only a minor role if a compound is degraded. [...]
Ternes, T., Joss, A., Kreuzinger, N., Miksch, K., Lema, J. M., von Gunten, U., … Siegrist, H. (2005). Removal of pharmaceuticals and personal care products - results of the poseidon project. Presented at the 78th Annual Technical Exhibition and Conference, Water Environment Federation WEFTEC. Washington DC, USA: 2005 Water Environment Federation. , Institutional Repository

Municipal wastewater is highly contaminated by pharmaceuticals and personal care products (PPCPs) and (subtle) effects such as feminization of fish have already been found in the receiving waters of wastewater treatment plants. Due to the wide spread of PPCPs in rivers and groundwater also a contamination of drinking water is known in some cases. The EU project POSEIDON established a basic knowledge on the removal of PPCPs and estrogens in wastewater and drinking water treatment. Both wastewater technology and drinking water technology optimized for the removal of domestic chemicals can be applied world-wide for indirect water reuse. Based on the POSEIDON outcome, a form of BAT (Best Available Technology) for water treatment concerning PPCP removal was proposed and will provide a basis to implement administrative measures with regard to persistent domestic chemicals as contaminants of reclaimed wastewater treatment plant (WWTP) discharges. [...]
Joss, A., Alder, A., Huber, M., Göbel, A., von Gunten, U., Keller, E., … Siegrist, H. (2004). Abbau von Mikroverunreinigungen in der kommunalen Abwasserreinigung. In Mikroverunreinigungen in der Abwasserreinigung (p. (18 pp.). Glattbrugg: Verband Schweizer Abwasser- und Gewässerschutzfachleute. , Institutional Repository

Zwei wichtige Aspekte haben dazu geführt, dass Mikroverunreinigungen in der aquatischen Umwelt gegenwärtig ein wichtiges Thema ist: Einerseits ist mit der Reduktion des Nährstoffeintrages in die Gewässer das Problem der Eutrophierung seit den 70er Jahre weitgehend entschärft worden. In der Folge konnte festgestellt werden, dass auch ohne Überdüngung der Gewässer einige Schadensbilder nicht aus unseren Fliessgewässern verschwunden sind (siehe Beitrag Patricia Holm). Andererseits haben die Weiterentwicklungen des letzten Jahrzehnts in der analytischen Chemie die Nachweisgrenze um etwa einen Faktor 1000 gesenkt. Dadurch konnten diese Stoffe nicht nur in der Umwelt, sondern teilweise auch im Trinkwasser quantifiziert werden und haben somit die Diskussion betreffend deren Bedeutung in Gang gesetzt. Abbildung 1 zeigt die gemessenen Arzneimittelkonzentration im Ablauf einer deutschen nährstoffeliminierenden Kläranlage (ARA Wiesbaden, 300'000 Einwohnergleichwerte, 11-13 Tage Schlammalter). Diese Daten zeigen exemplarisch, dass im gereinigten kommunalen Abwasser Arzneimittel typischerweise in Konzentrationen bis zu 5 μg L-1 gemessen werden. Im vorliegenden Beitrag wird diskutiert, welchen Eliminationsbeitrag durch die kommunale Abwasserreinigung zu erwarten ist bzw. wie man diesen möglicherweise noch verbessern kann. Anhand der gegenwärtig vorliegenden Informationen zeichnet sich ab, dass Hochlastanlangen nur Stoffe mit guten Sorptionseigenschaften über den Schlamm entfernen, während bei nährstoffeliminierenden Anlagen zusätzlich eine bedeutende Anzahl Arzneimittel biologisch abgebaut werden. Das Schlammalter scheint hierfür die massgebende Grösse zu sein. Bei weiter steigendem Schlammalter scheint die Vielfalt an abgebauten Stoffen nur noch leicht zuzunehmen. Hingegen konnte gezeigt werden, dass mit Zusatzkosten von ~0.05 Fr m-3Abwasser durch Ozonierung eine breite Palette von Stoffen abgebaut wird. Obwohl die dabei entstehenden Abbauprodukte noch wenig bekannt sind, ist zu erwarten, dass dieser chemischen Nachbehandlung eine grosse Bedeutung zukommen wird, falls die Elimination bei der kommunalen Abwasserreinigung weiter verbessert werden soll.
Joss, A., Goosse, P., & Siegrist, H. (2004). Betriebliche Details von Membran Belebungsanlagen (MBR). Module für die kommunalen Abwasserreinigung. In MBR in der kommunalen Abwasserreinigung (p. (14 pp.). Glattbrugg: Verband Schweizer Abwasser- und Gewässerschutzfachleute. , Institutional Repository
Joss, A., Andersen, H., Ternes, T., Richle, P. R., & Siegrist, H. (2004). Removal of estrogens in municipal wastewater treatment under aerobic and anaerobic conditions: consequences for plant optimization. Environmental Science and Technology, 38(11), 3047-3055. doi:10.1021/es0351488, Institutional Repository

The removal of estrogens (estrone El, estradiol E2, and ethinylestradiol EE2) was studied in various municipal wastewater treatment processes equipped for nutrient removal. A biological degradation model is formulated, and kinetic parameters are evaluated with batch experiments under various redox conditions. The resulting model calculations are then compared with sampling campaigns performed on different types of full-scale plant: conventional activated-sludge treatment, a membrane bioreactor, and a fixed-bed reactor. The results show a >90% removal of all estrogens in the activated sludge processes. (Due to the analytical quantification limit and low influent concentrations, however, this removal efficiency represents only an observable minimum.) The removal efficiencies of 77% and ≥90% for E1 and E2, respectively, in the fixed-bed reactor represent a good performance in view of the short hydraulic retention time of 35 min. The first-order removal-rate constant in batch experiments observed for E2 varied from 150 to 950 d-1 for a 1 gSS L-1 sludge suspension. The removal efficiency of E1 and EE2 clearly depends on the redox conditions, the maximum removal rate occurring under aerobic conditions when E1 was reduced to E2. Sampling campaigns on full-scale plants indicate that the kinetic values identified in batch experiments (without substrate addition) for the natural estrogens may overestimate the actual removal rates. Although this paper does not give direct experimental evidence, it seems that the substrate present in the raw influent competitively inhibits the degradation of E1 and E2. These compounds are therefore removed mainly in activated sludge compartments with low substrate loading. Theoretical evaluation leads us to expect that diffusive mass transfer inside the floc (but not across the laminar boundary layer) appreciably influences the observed degradation rates of E1 and E2, but not of EE2.
Larsen, T. A., Lienert, J., Joss, A., & Siegrist, H. (2004). How to avoid pharmaceuticals in the aquatic environment. Journal of Biotechnology, 113(1-3), 295-304. doi:10.1016/j.jbiotec.2004.03.033, Institutional Repository

Pharmaceuticals and other micropollutants in wastewater pose a new challenge to wastewater professionals as well as to the pharmaceutical industry. Although there is a great deal of uncertainty concerning the possible detrimental effects on the aquatic ecosystems, the precautionary principle — or possibly new scientific evidence — may give rise to more stringent demands on wastewater treatment in the future. In conventional wastewater treatment plants, a combination of biological treatment with high sludge residence times and ozonation of the effluent seems to be the most promising technology. Ozonation, however, is an energy-intensive technology. Moreover, in conventional end-of-pipe systems a large part of the pollutants will always be lost to the environment due to leaking, primarily during rain. In the long term, source separation offers the more sustainable solution to the entire wastewater problem, including organic micropollutants. Urine source separation is an elegant solution to the problems of nutrients and pharmaceuticals alike and losses of untreated pollutants to the environment can be minimized. Although few technologies for the separate treatment of urine have been developed to date, the 100-500 times higher concentrations of micropollutants promise more efficient conditions for all removal technologies known from conventional wastewater treatment.
Rieger, L., Thomann, M., Joss, A., Gujer, W., & Siegrist, H. (2004). Computer-aided monitoring and operation of continuous measuring devices. Water Science and Technology, 50(11), 31-39. doi:10.2166/wst.2004.0668, Institutional Repository

Extended studies of measuring and control systems in activated sludge plants at EAWAG revealed that the measuring devices remain the weakest point in control applications. To overcome this problem, a software package was developed which analyses and evaluates the residuals between a reference measurement and the sensor and collects the information in a database. The underlying monitoring concept is based on a two-step evaluation of the residuals by means of statistical evaluations using control charts with two different sets of criteria. The first step is a warning phase in which hints on probable errors trigger an increase in the monitoring frequency. In the second step, the alarm phase, the error hypothesis has to be validated and should allow immediate and targeted reactions from the operator. This procedure enables an optimized and flexible monitoring effort combined with an increased probability of early detection of systematic measuring errors. Beside the monitoring concept, information about the measuring device, the performed servicing actions and the responsibilities is stored. Statistical values for the quantitative characterization of the measuring system during operation will be given. They are needed to parameterise controllers or to guarantee the accuracy of the instrument in order to allow reliable calculations of effluent tax. In contrast to other concepts, not only is the measuring device examined under standard conditions, but so is the entire measuring chain from the liquid to be analysed to the value stored in the database of the supervisory system. The knowledge of the response time of the measuring system is then required in order to allow a comparison of the corresponding values.
Siegrist, H., & Joss, A. (2004). Membranverfahren in der Abwasserreinigung (p. (47 pp.). Presented at the 58. VSA Fortbildungskurs. Glattbrugg: Verband Schweizer Abwasser- und Gewässerschutzfachleute. , Institutional Repository

Durch die vollständige Abtrennung der Feststoffe kann mit Membranbelebungsanlagen im Vergleich zu konventionellen Belebungsanlagen eine sehr gute Ablaufqualität erreicht werden. Dies betrifft insbesondere zu für die Parameter CSB und P. Die Membranbelebungsanlage ist also vergleichbar mit bzw. erreicht höhere Leistungen als konventionelle Anlagen mit nachgeschalteter Flockungsfiltration. Das höhere Schlammalter und der Rückhalt der Feststoffe erlaubt zudem eine bessere Elimination von Spurenstoffen. [...]
Ternes, T. A., Herrmann, N., Bonerz, M., Knacker, T., Siegrist, H., & Joss, A. (2004). A rapid method to measure the solid-water distribution coefficient (Kd) for pharmaceuticals and musk fragrances in sewage sludge. Water Research, 38(19), 4075-4084. doi:10.1016/j.watres.2004.07.015, Institutional Repository

Pharmaceuticals and personal care products are omnipresent in wastewater world-wide. In order to predict their sorption quantities onto sludge in wastewater treatment plants (WWTPs), the solid-water distribution coefficients (Kd values) of selected pharmaceuticals (antiphlogistics, estrogens, lipid regulators, anti-epileptic and cytostatic agents) and polycyclic musk fragrances (HHCB, AHTN) were determined in primary and secondary sludges taken from a German municipal WWTP. For the Kd determination, batches of primary and secondary sludge slurries were spiked with the respective target compounds and slowly stirred under defined conditions (e.g. an argon atmosphere). Finally, the water and solid sludge phases were analysed. The Kd values of pharmaceuticals ranged from <1 to 500 L kg-1, while those for the polycyclic musk fragrances AHTN and HHCB proved to be up to 5300 and 4900 L kg-1, respectively. The primary and secondary sludge showed significant differences for some pharmaceuticals such as Diclofenac and Cyclophosphamide due to the different pH and composition of the two sludges. The removal rate from the water phase caused by sorption in a WWTP can be reasonably predicted on the basis of the Kd values.
Ternes, T. A., Joss, A., & Siegrist, H. (2004). Scrutinizing pharmaceuticals and personal care products in wastewater treatment. Environmental Science and Technology, 38(20), 392A-399A. doi:10.1021/es040639t, Institutional Repository
Siegrist, H., Joss, A., Alder, A., McArdell-Bürgisser, C., Göbel, A., Keller, E., & Ternes, T. (2003). Micropolluants - le traitement des eaux usées face à un nouveau défi?. Eawag News [éd. fr.], 57, 7-10. , Institutional Repository

Grâce aux progrès réalisés au niveau de la chimie analytique, la présence de produits pharmaceutiques et de substances à effets endocriniens est de plus en plus fréquemment constatée dans le milieu naturel aquatique. Dans leur grande majorité, ces composés s’incorporent aux eaux usées par le biais des urines. Une partie de ces substances est éliminée dans les stations d’épuration par sorption et par biodégradation. Le reste est déversé dans le milieu naturel avec les eaux traitées. Le présent article fait état de solutions durables appliquées à la source pour tenter d’éliminer ces substances restantes. Comme ces mesures ne peuvent être achevées qu’en l’espace de quelques décennies, il est judicieux de développer en outre pour le court et le moyen terme des procédés plus poussés de traitement physico-chimique des eaux usées.
Siegrist, H., Joss, A., Alder, A., McArdell-Bürgisser, C., Göbel, A., Keller, E., & Ternes, T. (2003). Micropollutants - new challenge in wastewater disposal?. Eawag News [engl. ed.], 57, 7-10. , Institutional Repository

Through improved methods of chemical analysis, pharmaceutical and hormone-active substances are increasingly being detected in our water bodies. In most cases, they enter the waste water after being excreted in urine. In the sewage plant, a fraction of the substances is eliminated through sorption and biological degradation. The remaining part enters water bodies with the treated waste water. This article describes possible measures aiming at eliminating the residual substances. These include on the one hand, permanent measures at the source such as an eco label for pharmaceuticals, the pre-treatment of hospital waste waters and the separate treatment of urine. However, on the other hand, as the measures at the source can only be implemented over the long term, it is expedient to also consider technical measures such as raising the sludge age in the activated sludge tanks of sewage treatment plants and, for critical cases, the ozonation of the purified waste water.
Siegrist, H., Joss, A., Alder, A., McArdell-Bürgisser, C., Göbel, A., Keller, E., & Ternes, T. (2003). Mikroverunreinigungen - Abwasserentsorgung vor neuen Anforderungen?. Eawag News [dtsch. Ausg.], 57, 7-10. , Institutional Repository

Durch eine verbesserte chemische Analytik werden in den Gewässern vermehrt Arzneimittel und hormonaktive Stoffe nachgewiesen. Sie werden grösstenteils über den Urin ausgeschieden und gelangen so ins Abwasser. In der Kläranlage wird ein Teil der Stoffe durch Sorption und biologischen Abbau eliminiert. Der andere Teil gelangt mit dem geklärten Abwasser in die Gewässer. Dieser Artikel zeigt mögliche Massnahmen auf, mit denen auch die verbleibenden Stoffe eliminiert werden können. Dazu gehören einerseits nachhaltige Massnahmen an der Quelle wie ein Umweltlabel für Arzneimittel, die Vorbehandlung von Spitalabwässern und die getrennte Behandlung von Urin. Da diese jedoch nur längerfristig umgesetzt werden können, ist es anderseits sinnvoll, auch technische Massnahmen wie die Erhöhung des Schlammalters im Belebungsbecken der Kläranlagen und bei kritischen Fällen die Ozonierung des gereinigten Abwassers zu erwägen.
Joss, A., & Siegrist, H. (2002). Membranen - Material, Module, Betrieb. GWA Gas, Wasser, Abwasser, 82(1), 7-11. , Institutional Repository

It is to be expected that micro- and ultrafiltration will continue to find increasing use in communal water and sewage treatment over the coming years. The following article discusses the design of a membrane module and some of the most important aspects of membrane operation.
Fuchs, W., Braun, R., & Joss, A. (2001). Status and development of MBR-technology. H2O: Tijdschrift voor Watervoorziening en Waterbeheer, 34, 58-59. , Institutional Repository
Joss, A., Monti, A., Fux, C., Manser, R., Rozzi, A., & Siegrist, H. (2001). Anaerobic ammonia oxidation (anammox) with a submerged membrane system (p. (8 pp.). Presented at the International water conference on membrane technology for waste water reclaimation and reuse. London: IWA Publishing. , Institutional Repository

The biological treatment of the supernatant from a municipal sewage sludge digester (700 g NH4-N m-3 and 1000 g m-3 CODtotal) consisting of a partial nitritation in a chemostat followed by anaerobic ammonia oxidation (anammox) in a submersed membrane reactor was investigated at pilot scale. The anammox membrane reactor (volume = 0.14 m3) contained a Zenon hollow fiber ZW-10 ultrafiltration membrane module (total surface = 0.8 m2). Average transmembrane pressure was 0.32±0.02 bar. Nitrogen gas sparging (3 Nm3 m-2membrane h-1) was used in combination with intermittent filtration (4 min interval) and backwashing (20 s every 4 min) to prevent fouling. Reactor start-up and membrane performance under anaerobic conditions were tested at various operating conditions. During the whole operation period (150 days; suspended solids in the range of 4 up to 12 g TSS m-3) the membrane performed constantly at a flux of 10.5±1.5 l m-2 h-1. At hydraulic retention times HRT ≥ 0.7 days the nitrite was completely consumed and the ammonia reduced by 90% For stable plant operation, a solid retention time above 16 days was required.
The experimental results of the anammox reactor were compared with modeling data of the mathematical model of Koch et al. (2000).
Joss, A. (2001). Mikroverunreinigungen. Umwelt-Focus, 27-31. , Institutional Repository

Aufgrund laufender Forschungsprojekte erhärten sich die Hinweise, dass im gereinigten kommunalen Abwasser verschiedene Stoffe wie beispielsweise natürliche Hormone, Biozide oder Pharmaka enthalten sind, welche negative Auswirkungen auf Umwelt und Mensch zur Folge haben. Die Forschung will abklären, ob die Elimination der Mikroverunreinigungen (MV) durch Optimierung bestehender Verfahren, durch neue Reinigungsmethoden oder durch Massnahmen an der Quelle erreicht werden kann.
Joss, A., & Siegrist, H. (2001). Mikroverunreinigungen - brauchen wir neue Kläranlagen?. GWA Gas, Wasser, Abwasser, 81(3), 151-157. , Institutional Repository

Current research projects show that the effluent of municipal wastewater treatment plants contain micropollutants harming the environment at concentrations (≤ µg l-1). Actually it is not possible to compile a definitive list of environmentally relevant micropollutants. Nevertheless engineers are seeking wastewater treatment processes and source control methods capable to reduce micropollutant immission. For this purpose different treatment processes (activated sludge, membrane bioreactor and biofilter) shall be compared concerning elimination efficiency of micropollutant and the impact of single operating parameters will be evaluated. Some possible optimization mechanisms are being discussed.
Joss, A., & Siegrist, H. (2001). Mikroverunreinigungen: Brauchen wir neue Kläranlagen?. Kommunalmagazin, 18(12) (8 pp.). , Institutional Repository

Laufende Forschungsprojekte zeigen, dass gereinigtes Abwasser Verunreinigungen enthält, die sich bereits in kleinsten Konzentrationen negativ auf die Umwelt auswirken. Obwohl das Wissen über solche Stoffe noch unvollständig ist, sollte man heute schon darüber nachdenken, wie sie sich von unseren Gewässern fern halten lassen. Inwiefern verschiedene Verfahren Möglichkeiten bieten, wird in laufenden Projekten untersucht. Massnahmen an der Quelle müssen ebenfalls in Betracht gezogen werden.

Ralf Kägi

Rothwell, K. A., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2025). Low molecular weight organic acids stabilise siderite against oxidation and influence the composition of iron (oxyhydr)oxide oxidation products. Environmental Science: Processes and Impacts (13 pp.). doi:10.1039/d4em00363b, Institutional Repository

Siderite (FeCO3) is an important reservoir of mineral-bound ferrous iron in non-sulfidic, reducing soils and sediments. It is redox sensitive, and its oxidation may facilitate the reduction of a range of pollutants, produce reactive oxygen species, or induce the formation of oxidation products with large surface areas for contaminant sorption. However, there is currently a limited understanding of the stability of siderite in complex environments such as soils and sediments. Here, we use a series of batch experiments complemented with thorough characterisation of mineral oxidation products to investigate the oxidation of siderite in the presence and absence of the low molecular weight organic acids (LMWOAs) citrate, tiron, salicylate, and EDTA as analogues for naturally occurring compounds or functional groups of natural organic matter that ubiquitously coexist with siderite. Our results show that siderite alone at pH 7.5 was completely oxidised to form ferrihydrite, nanocrystalline lepidocrocite, and nanocrystalline goethite in less than 6 hours. However, in the presence of LMWOAs, up to 48% of the siderite was preserved for more than 500 hours and the formation of goethite was inhibited in favour of ferrihydrite and lepidocrocite. Using experimental data from electron microscopy and chemical speciation modelling, we hypothesise that the siderite may be preserved through the formation of an Fe(iii)-passivation layer at the siderite surface.
Galgani, F., Lusher, A. L., Strand, J., Haarr, M. L., Vinci, M., Molina Jack, E., … van Bavel, B. (2024). Revisiting the strategy for marine litter monitoring within the european marine strategy framework directive (MSFD). Ocean and Coastal Management, 255, 107254 (11 pp.). doi:10.1016/j.ocecoaman.2024.107254, Institutional Repository

Marine litter and non-degradable plastic pollution is of global concern. Regular monitoring programs are being established to assess and understand the scale of this pollution. In Europe, the goal of the European Marine Strategy Framework Directive (MSFD) is to assess trends in Good Environmental Status and support large-scale actions at the regional level. Marine litter monitoring requires tailored sampling strategies, protocols and indicators, that align with specific objectives and are tailored for local or regional needs. In addition, the uneven spatial and temporal distributions of marine litter present a challenge when designing a statistically powerful monitoring program. In this paper, we critically review the existing marine litter monitoring programs in Europe. We discuss the main constraints, including environmental, logistical, scientific, and ethical factors. Additionally, we outline the critical gaps and shortcomings in monitoring MSFD beaches/shorelines, floating litter, seafloor litter, microplastics, and harm. Several priorities must be established to shape the future of monitoring within the MSFD. Recent developments in analytical approaches, including optimizing protocols and sampling strategies, gaining a better understanding of the spatiotemporal heterogeneity of litter and its implications for survey design and replication, and the inclusion of newly validated methodologies that have achieved sufficient technical readiness, must be considered. Although there are well-established methods for assessing beaches, floating and seafloor litter, it will be necessary to implement monitoring schemes for microplastics in sediments and invertebrates as robust analytical methods become available for targeting smaller particle size classes. Furthermore, the inclusion of indicators for entanglement and injury to marine organisms will have to be considered in the near future. Moreover, the following actions will enhance the effectiveness of monitoring efforts: (1) creating an inventory of accumulation areas and sources of specific types of litter (e.g., fishing gear), (2) monitoring riverine inputs of litter, (3) monitoring atmospheric inputs including microplastics, (4) accidental inputs during extreme weather events, and (5) studying how species at risk may be transported by litter. We provide recommendations to support long-term, effective, and well-coordinated marine litter monitoring within the MSFD to achieve a comprehensive and accurate understanding of marine litter in EU waters. This will allow the development of measures to mitigate the impacts of marine pollution and eventually to evaluate the success of the respective measures.
Grigg, A. R. C., Notini, L., Kaegi, R., ThomasArrigo, L. K., & Kretzschmar, R. (2024). Aluminium substitution affects jarosite transformation to iron oxyhydroxides in the presence of aqueous Fe(II). Geochimica et Cosmochimica Acta, 374, 72-84. doi:10.1016/j.gca.2024.04.008, Institutional Repository

Jarosite is an abundant mineral in acidic environments, often found in acid sulfate soil (ASS) and acid-mine drainage (AMD). As a store of Fe, K, S and acidity, and a scavenger for major and trace elements, jarosite plays an important role in the biogeochemistry of acid sulfate environments. When ASS and AMD become anoxic, reducing conditions can set in, producing conditions that are outside the thermodynamic stability field of jarosite. In this study, we investigated the transformation of synthetic and natural jarosite with various degrees of Al-for-Fe substitution under circumneutral anoxic conditions in the presence of Fe(II), to understand the rates and pathways of jarosite and Al-jarosite transformation, the role of competing transformation pathways, the fate of Al during transformation and the different reactivity of natural and synthetic Al-jarosite. Synthetic jarosite (containing 0 %–7 % Al-for-Fe substitution) and a natural Al-substituted jarosite sample from an ASS in Thailand were suspended in solutions of 57Fe(II) at pH 7 for 24 h under anoxic conditions. The chosen experimental conditions mimic the Fe(II) concentrations and pH found in flooded ASS under reducing conditions. Changes in mineral composition of the suspensions were determined by Rietveld analysis of X-ray diffraction patterns at six time points. The fate of Al was determined by XRD, Raman spectroscopy and energy dispersive X-ray spectroscopy analysis of the jarosite and product minerals. Different transformation pathways that occurred simultaneously were traced by using 57Fe Mössbauer spectroscopy and aqueous Fe isotope composition. The analysis showed that 7 % Al-for-Fe substitution in jarosite more than halved the mineral transformation rate compared to unsubstituted jarosite, regardless of the Fe(II) concentrations. Indeed, 7 % Al-for-Fe substitution had a greater effect on the transformation rate than an order-of-magnitude decrease in the Fe(II) concentrations in all Al-for-Fe substitution treatments. The transformation products in all samples were goethite, lepidocrocite and ferrihydrite, with minor amounts of magnetite forming from jarosite with no or low Al-for-Fe substitution reacted with high Fe(II) concentrations. Lepidocrocite was the dominant product in reactors without aluminium, but lepidocrocite was not strongly enriched in 57Fe, suggesting that it may not have formed exclusively from Fe in solution during the Fe(II)-catalysed transformation of other minerals. In high-Al systems, lepidocrocite appeared to be a sink for Al, although its formation in Al-rich samples was suppressed. Natural jarosite reacted more than an order of magnitude more slowly than the synthetic jarosite and Al-jarosite, indicating that the properties of the synthetic jarosite do not completely account for the stability of natural jarosite under anoxic circumneutral conditions. The results provide an important baseline for understanding the drivers of jarosite transformation or stability in ASS and AMD.
Grigg, A. R. C., Notini, L., Kaegi, R., ThomasArrigo, L. K., & Kretzschmar, R. (2024). Structural effects of aluminum and iron occupancy in minerals of the jarosite-alunite solid solution. ACS Earth and Space Chemistry, 8(2), 194-206. doi:10.1021/acsearthspacechem.3c00174, Institutional Repository

The alunite supergroup of minerals contains several hydroxysulfate mineral phases that commonly occur in acidic natural and engineered environments. The main division of the mineral supergroup defines two minerals, jarosite and alunite, based on the relative structural occupancy by Al or Fe, respectively. However, intermediate members of the jarosite-alunite solid solution have not been extensively characterized, especially in the environment. Here, we link the mineral unit cell sizes measured by X-ray diffraction, peak shifts in Raman spectra, fitting parameters in Mössbauer spectroscopy, and elemental quantification by EDX spectroscopy to known amounts of Al substitution in two synthetic series of Al-substituted jarosite (up to Al-for-Fe substitution of 9.5%) and unknown Al substitution in a natural jarosite isolated from an acid sulfate soil. Strong correlations were observed between the Al substitution of the jarosite samples and unit cell size, position of several vibrational peaks in Raman spectroscopy, and the temperature of magnetic ordering. In addition, elemental mapping provided a robust way to characterize the Al content of jarosite. As the techniques were effective in quantifying the Al or Fe content of jarosite-alunite supergroup mineral samples, without the need for sample dissolution, the findings support the application of these spectroscopy techniques to characterize natural jarosite-alunite samples. Using these techniques, we demonstrate at least 5% Al-for-Fe substitution in a jarosite sample from an acid sulfate soil. Application to environmental samples is especially useful in cases where it is otherwise difficult to directly measure the Al content of a mineral sample or when Al-for-Fe substitution influences the spectral responses to substitution at other sites in the crystal structure.
Kaiser, S., Kaegi, R., & Rhein, F. (2024). Influence of aging, morphology and particle size on the behavior of microplastics during magnetic seeded filtration. Science of the Total Environment, 957, 177353 (12 pp.). doi:10.1016/j.scitotenv.2024.177353, Institutional Repository

Magnetic seeded filtration (MSF) is a solid-liquid separation process based on the formation of hetero-agglomerates between target (non-magnetic) particles and added magnetic particles, followed by magnetic separation. Previous experimental studies reported high separation efficiencies for hydrophobic microplastic particles (MP) and focused mainly on the polymer type. This study investigates the influence of the particle size, morphology and aging on the separation efficiency of different polymer types. Surface morphology and particle size only marginally affect the separation of particles larger than 30μm. However, the agglomeration of particles in the lower micron range is increasingly dominated by repulsive electrostatic interactions. After oxidative treatment with Fenton's reagent, separation efficiencies for most MP remain between 55% and 96%. Exposure to UV light results in a significant decrease in separation efficiency, particularly for polystyrene, where the separation efficiency decreases from 86% to 9%. Mechanical aging, simulated by mixing MP in a sand matrix on a horizontal shaker, reduces the separation to below 50% for all polymer types. Exposure to UV light causes surface oxidation, as evidenced by the formation of carbonyl peaks in the Fourier transformed infrared spectra. Mechanical treatment results in the deposition of small silica particles on the MP surface, as revealed by electron microscopy. Both mechanisms render the polymer surface more hydrophilic and reduce the tendency to form hetero-agglomerates with (hydrophobic) magnetic seed particles. MSF is a promising technique for MP separation but also offers the possibility to probe surface properties of (environmentally aged) MPs. This study demonstrates that environmental aging can significantly affect the behavior of MP and highlights the importance of environmental aging in MP fate studies.
Kuehr, S., Kaegi, R., Raths, J., Sinnet, B., Kipf, M., Rehkämper, M., … Georgantzopoulou, A. (2024). Reduced bioavailability of Au and isotopically enriched 109Ag nanoparticles transformed through a pilot wastewater treatment plant in Hyalella azteca under environmentally relevant exposure scenarios. Science of the Total Environment, 949, 174768 (13 pp.). doi:10.1016/j.scitotenv.2024.174768, Institutional Repository

Wastewater Treatment Plants (WWTP) are a major repository and entrance path of nanoparticles (NP) in the environment and hence play a major role in the final NP fate and toxicity. Studies on silver nanoparticles (AgNP) transport via the WWTP system and uptake by aquatic organisms have so far been carried out using unrealistically high AgNP concentrations, unlikely to be encountered in the aquatic environment. The use of high AgNP concentrations is necessitated by both the low sensitivity of the detection methods used and the need to distinguish background Ag from spiked AgNP.
In this study, isotopically enriched 109AgNP were synthesized to overcome these shortcomings and characterized by a broad range of methods including transmission electron microscopy, dynamic and electrophoretic light scattering. 109AgNP and gold NP (AuNP) were spiked to a pilot wastewater treatment plant fed with municipal wastewater for up to 21 days. AuNP were used as chemically less reactive tracer. The uptake of the pristine and transformed NP present in the effluent was assessed using the benthic amphipod Hyalella azteca in fresh- and brackish water exposures at environmentally relevant concentrations of 30 to 500 ng Au/L and 39 to 260 ng Ag/L. The unique isotopic signature of the 109AgNP allowed to detect the material at environmentally relevant concentrations in the presence of a much higher natural Ag background. The results show that the transformations reduce the NP uptake at environmentally relevant exposure concentrations. For 109Ag, lower accumulation factors (AF) were obtained after exposure to transformed NP (250–350) compared to the AF values obtained for pristine 109AgNP (750–840). The reduced AF values observed for H. azteca exposed to effluent from the AuNP-spiked WWTP indicate that biological transformation processes (e.g. eco-corona formation) seem to be involved in addition to chemical transformation.
Käser, D., Kägi, R., Hattendorf, B., & Günther, D. (2024). Fundamental studies of laser ablation ICPMS using a nitrogen plasma source and helium, argon and nitrogen as carrier gas. Journal of Analytical Atomic Spectrometry, 39(12), 3069-3081. doi:10.1039/d4ja00327f, Institutional Repository

Laser-generated aerosols in helium, argon and nitrogen were directly compared using a nitrogen microwave inductively coupled plasma in combination with a mass spectrometer. An increased surface darkening of the sample was observed during ablation in nitrogen, suggesting a more pronounced particle deposition in comparison to helium, but only 30% lower sensitivities were obtained for nitrogen. Crater depth measurements proved that these variations were not the consequence of a difference in ablation rate (271 ± 17 nm per pulse for He vs. 267 ± 12 nm per pulse for N2). Particle size measurements and electron microscopy images indicated that the aerosol generated in nitrogen or argon tends to form smaller agglomerates in comparison to helium. This dependence in agglomeration however appeared to be dependent on the ablation cell used. Furthermore, the fluence of the 193 nm laser system used for the experiments significantly influenced the temporal stability of the signals (e.g.238U+/232Th+). Finally, the quantification capabilities of nitrogen as an ablation environment and carrier gas were studied and compared to helium generated aerosols transported in nitrogen. A selection of samples (NIST SRM 612, USGS BCR-2G, USGS GSD-1G and GSE-1G) were quantified using NIST SRM 610 as an external standard. The potential of nitrogen as an alternative carrier gas was highlighted with deviations from the reference values calculated between −13% and +16% in comparison to the deviations between −15% and +17% obtained with helium in a cylindrical ablation cell for most elements in the different reference materials analyzed.
Nopp-Mayr, U., Layendecker, S., Sittenthaler, M., Philipp, M., Kägi, R., & Weinberger, I. (2024). Microplastic loads in Eurasian otter (Lutra lutra) feces - targeting a standardized protocol and first results from an alpine stream, the River Inn. Environmental Monitoring and Assessment, 196(8), 707 (14 pp.). doi:10.1007/s10661-024-12791-z, Institutional Repository

Microplastics (MP) are omnipresent in a wide range of environments, constituting a potential threat for aquatic and terrestrial wildlife. Effects in consumers range from physical injuries to pathological reactions. Due to potential bioaccumulation of MP, predators are of particular concern for MP induced health effects. The Eurasian otter is an apex predator in (semi-)aquatic habitats feeding primarily on fish. Furthermore, the species is classified as “near threatened” on the IUCN Red List. Thus, the Eurasian otter is of conservation concern and may serve as a bioindicator for MP pollution. Feces can be used to detect pollutants, including MP. Initial studies confirmed the presence of MP in otter feces (= spraints). However, as specific, validated protocols targeting at an efficient and standardized extraction of MP from otter spraints are missing, experimental results reported from different groups are challenging to compare. Therefore, we (i) present steps towards a standardized protocol for the extraction of MP from otter feces, (ii) give recommendations for field sample collection of otter spraints, and (iii) provide a user-friendly step-by-step workflow for MP extraction and analysis. Applying this framework to field samples from five study sites along the River Inn (n = 50), we detected MP of different sizes and shapes (ranging from microfibers to road abrasion and tire wear) in all otter spraint samples.
Schwarzfischer, M., Ruoss, T. S., Niechcial, A., Lee, S. S., Wawrzyniak, M., Laimbacher, A., … Spalinger, M. R. (2024). Impact of nanoplastic particles on macrophage inflammation and intestinal health in a mouse model of inflammatory bowel disease. Nanomaterials, 14(16), 1350 (15 pp.). doi:10.3390/nano14161350, Institutional Repository

Background: The increasing presence of plastics in the human diet is raising public concern about the potential risks posed by nanoplastic (NP) particles, which can emerge from the degradation of plastic debris. NP ingestion poses particular risks to individuals with inflammatory bowel disease (IBD), as compromised epithelial barriers may facilitate NP translocation. Methods: In vitro, bone-marrow-derived macrophages (BMDMs) were exposed to 25 nm polymethacrylate (PMMA) or 50 nm polystyrene (PS) particles to assess morphological changes and alterations in pro- and anti-inflammatory gene expression. In vivo, mice received PMMA NP particles for 6 months before acute dextran sodium sulfate (DSS) colitis was induced to investigate NP impacts on intestinal health and inflammation. Results: PMMA and PS NP exposure in BMDMs induced morphological changes indicative of a proinflammatory phenotype characterized by enlarged amoeboid cell shapes. It also triggered an inflammatory response, indicated by increased expression of proinflammatory cytokines such as Tnfa and Il6. Unexpectedly, long-term PMMA NP administration did not affect the intestinal epithelial barrier or exacerbate acute DSS-induced colitis in mice. Colonoscopy and histological analysis revealed no NP-related changes, suggesting adverse effects on intestinal health or inflammation. Conclusion: Our findings from animal models offer some reassurance to IBD patients regarding the effects of NP ingestion. However, variations in lifestyle and dietary habits may lead to significantly higher plastic intake in certain individuals, raising concerns about potential long-term gastrointestinal effects of lifelong plastic consumption.
Stetten, L., Kaegi, R., Hofmann, T., & von der Kammer, F. (2024). Depth-dependent transformation of ZnO and Ag nanoparticles in sulfate-reducing sediments tracked using scanning transmission electron microscopy. Environmental Science: Nano, 11(1), 136-148. doi:10.1039/d3en00550j, Institutional Repository

Studies on the transformation of engineered nanomaterials (ENMs) based on relevant environmental exposure scenarios are scarce. In this context, we investigated the use of Transmission Electron Microscopy (TEM) grids to expose minute amounts of ZnO and Ag nanoparticles (NPs) to artificial and natural aqueous media and follow their transformation using scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy. Short-term experiments conducted with inorganic sulfides confirmed the potential of using TEM grids to monitor the transformation of ENMs at the single particle level. After 30 min, Ag NPs transformed into Ag-sulfides, with Ag : S ratios ≈ 2 : 1, while ZnO NPs showed little evidence of Zn-sulfides precipitation after 6 hours. Ag NPs and ZnO NPs were also exposed to depth-dependent pore water concentration gradients in freshwater sediment columns. After three days and four weeks, all the Ag NPs observed were transformed into Ag-sulfides with various morphologies and Ag : S ratios (1 ≤ Ag/S ≤ 2), depending on the depth and duration of the exposure. Furthermore, a depth-dependent transformation was observed for ZnO NPs. At low sulfide concentration, in the first millimeters below the water-sediment interface, ZnO NPs were completely transformed into ZnS harboring empty shell structures, together with smaller particles in their vicinity. By contrast, ZnO cores persisted in the deeper layers, indicating that ZnO NPs dissolution was inhibited at high sulfide concentrations. Our results demonstrate the advantage of experimental and analytical strategies adapted to study the transformation of ENMs under environmentally relevant conditions, to unravel transformation rates and products not yet considered in risk assessment studies.
la Cecilia, D., Philipp, M., Kaegi, R., Schirmer, M., & Moeck, C. (2024). Microplastics attenuation from surface water to drinking water: impact of treatment and managed aquifer recharge – and identification uncertainties. Science of the Total Environment, 908, 168378 (12 pp.). doi:10.1016/j.scitotenv.2023.168378, Institutional Repository

River water can be used to recharge aquifers exploited for drinking water production. Several recent studies reported microplastics (MPs) in river water, and therefore, the potential contamination of groundwater by MPs is a growing concern among stakeholders and citizens. In this research, we investigate the fate of MPs (> 20 μm) along six different stages of a major Managed Aquifer Recharge (MAR)-water supply system in Switzerland. About 20 l of water were filtered using steel meshes at each location in triplicates. In the laboratory, MPs deposited on the anodisc filters were identified using Focal Plane Array (FPA) micro-Fourier-Transform-InfraRed (μFTIR) spectroscopy. The obtained hyperspectral data were processed using the imaging software Microplastics Finder for MPs identification and classification. Our results revealed a 20-fold decrease in MPs concentration from the Rhine River bed water (112 ± 27.4 MPs/l) to after the coagulation, flocculation and sedimentation (5.5 ± 2.2 MPs/l), a further 3-fold decrease to after the sand-filtration system (1.8 ± 0.9 MPs/l), corresponding to an overall removal efficiency of 98.4 %. The MPs concentrations remained low following MAR (2.7 ± 0.7 MPs/l) through a Quaternary gravel aquifer. Activated carbon filters did not substantially further reduce MPs concentrations. The percentage of fragments (≈95 %) prevailed over fibers (≈5 %) at all locations, with fibers being longer and more abundant in the river water. Overall, this study demonstrates the effectiveness of the treatment systems to remove MPs larger than 20 μm. Finally, we calculated an uncertainty in MPs concentrations of one order of magnitude depending on the user-defined parameters inside the MPs identification and classification model. The Quality Assurance/Quality Control approach followed during laboratory analysis highlighted an accumulation of surrogate particles at the edges of the disc, which would have an impact for MPs number upscaling.
Ballikaya, P., Brunner, I., Cocozza, C., Grolimund, D., Kaegi, R., Murazzi, M. E., … Cherubini, P. (2023). First evidence of nanoparticle uptake through leaves and roots in beech (Fagus sylvatica L.) and pine (Pinus sylvestris L.). Tree Physiology, 43(2), 262-276. doi:10.1093/treephys/tpac117, Institutional Repository

Trees have been used for phytoremediation and as biomonitors of air pollution. However, the mechanisms by which trees mitigate nanoparticle pollution in the environment are still unclear. We investigated whether two important tree species, European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.), are able to take up and transport differently charged gold nanoparticles (Au-NPs) into their stem by comparing leaf-to-root and root-to-leaf pathways. Au-NPs were taken up by roots and leaves, and a small fraction was transported to the stem in both species. Au-NPs were transported from leaves to roots but not vice versa. Leaf Au uptake was higher in beech than in pine, probably because of the higher stomatal density and wood characteristics of beech. Confocal (3D) analysis confirmed the presence of Au-NPs in trichomes and leaf blade, about 20–30 μm below the leaf surface in beech. Most Au-NPs likely penetrated into the stomatal openings through diffusion of Au-NPs as suggested by the 3D XRF scanning analysis. However, trichomes were probably involved in the uptake and internal immobilization of NPs, besides their ability to retain them on the leaf surface. The surface charge of Au-NPs may have played a role in their adhesion and uptake, but not in their transport to different tree compartments. Stomatal conductance did not influence the uptake of Au-NPs. This is the first study that shows nanoparticle uptake and transport in beech and pine, contributing to a better understanding of the interactions of NPs with different tree species.
Ballikaya, P., Brunner, I., Cocozza, C., Grolimund, D., Kaegi, R., Murazzi, M. E., … Cherubini, P. (2023). Nanoparticles are everywhere, even inside trees. Chimia, 77(4), 256. doi:10.2533/chimia.2023.256, Institutional Repository
Gottschalk, F., Debray, B., Klaessig, F., Park, B., Lacome, J. M., Vignes, A., … Kaegi, R. (2023). Predicting accidental release of engineered nanomaterials to the environment. Nature Nanotechnology, 18, 412-418. doi:10.1038/s41565-022-01290-2, Institutional Repository

Challenges in distinguishing between natural and engineered nanomaterials (ENMs) and the lack of historical records on ENM accidents have hampered attempts to estimate the accidental release and associated environmental impacts of ENMs. Building on knowledge from the nuclear power industry, we provide an assessment of the likelihood of accidental release rates of ENMs within the next 10 and 30 years. We evaluate risk predictive methodology and compare the results with empirical evidence, which enables us to propose modelling approaches to estimate accidental release risk probabilities. Results from two independent modelling approaches based on either assigning 0.5% of reported accidents to ENM-releasing accidents (M1) or based on an evaluation of expert opinions (M2) correlate well and predict severe accidental release of 7% (M1) in the next 10 years and of 10% and 20% for M2 and M1, respectively, in the next 30 years. We discuss the relevance of these results in a regulatory context.
Joëlle Kubeneck, L., ThomasArrigo, L. K., Rothwell, K. A., Kaegi, R., & Kretzschmar, R. (2023). Competitive incorporation of Mn and Mg in vivianite at varying salinity and effects on crystal structure and morphology. Geochimica et Cosmochimica Acta, 346, 231-244. doi:10.1016/j.gca.2023.01.029, Institutional Repository

Vivianite, a ferrous phosphate mineral, can be an important phosphorus (P) sink in non-sulfidic, reducing coastal sediments. The Fe in the crystal structure of vivianite can be substituted by other divalent metal cations such as Mn2+ or Mg2+. Since Mg is much more abundant in coastal porewaters than Mn, the more frequent reports of Mn substitution in vivianites of coastal sediments has been suggested to indicate a preferential incorporation of Mn over Mg into the crystal structure of vivianite. However, although both Mn and Mg substitution in vivianite are environmentally relevant, it is yet unknown whether Mn or Mg is preferentially incorporated and how these isomorphic substitutions alter the crystal structure and morphology of vivianite, parameters which may influence vivianite reactivity. Here, we studied the incorporation of Mn and/or Mg in vivianites formed by co-precipitation at pH 7 in the presence of varying dissolved Mn and/or Mg concentrations and solution salinities resembling an estuarine gradient from 0 to 9 psu. In total, 19 different vivianites were synthesized, with up to 50% of Fe substituted by Mn and Mg. Thermodynamic equilibrium calculations showed that aqueous Mg speciation was altered with increasing salinity, while Mn speciation was less affected, likely explaining the preferential incorporation of Mn in the vivianite structure at higher salinities. 57Fe-Mössbauer spectroscopy revealed that both Mn and Mg were preferentially incorporated in the double-octahedral Fe position, at which intervalence charge transfer is possible during the oxidation of vivianite. In contrast to Mg, which is redox inactive, incorporated Mn can participate in heteronuclear intervalence charge transfer with Fe. Thus, incorporation of either cation may impact the reactivity of vivianite under oxidizing conditions in element specific ways. Results of complementary analyses including X-ray diffraction, electron microscopy and Fe K-edge X-ray absorption spectroscopy further showed that incorporation of Mn and/or Mg led to smaller particle size, increased crystal roughness and thinner crystals, as well as systematic changes in unit cell parameters. These observed changes in crystal morphology might impact the reactivity of vivianite in natural environments and thus the effect of cation incorporation in vivianite should be considered when studying Fe and P cycling in coastal sediments.
Nenonen, V. V., Kaegi, R., Hug, S. J., Göttlicher, J., Mangold, S., Winkel, L. H. E., & Voegelin, A. (2023). Formation and transformation of Fe(III)- and Ca-precipitates in aqueous solutions and effects on phosphate retention over time. Geochimica et Cosmochimica Acta, 360, 207-230. doi:10.1016/j.gca.2023.09.004, Institutional Repository

Exfiltration of anoxic phosphate-rich groundwater into surface water leads to the oxidation of dissolved Fe(II) and the formation of Fe(III)-precipitates that can retain phosphate (PO4) and thereby attenuate eutrophication. Fresh Fe(III)-precipitates transform into more stable phases over time, and retained PO4 may be released again. In parallel, CO2 outgassing can promote the formation of Ca-phosphates or -carbonates that also sequester PO4. In laboratory experiments, we studied the effects of Mg, Ca, silicate (SiO4) and PO4 on these processes. Fresh Fe(III)-precipitates were formed in bicarbonate-buffered aqueous solutions at pH ∼ 7.0 via the oxidation of 0.5 mM Fe(II) in the presence of 0.15 or 0.025 mM PO4, at Mg or Ca concentrations of 0, 0.4, 1.2 or 4 mM and in the absence or presence of 0.5 mM SiO4. After CO2 outgassing, the suspensions were allowed to age for 100 d at pH ∼ 8. Changes in the composition and structure of Fe(III)- and Ca-precipitates over time were probed with spectroscopic and microscopic techniques and were linked to variations in the retention of PO4. The oxidation of Fe(II) led to effective PO4 removal via the formation of Fe(III)-precipitates that consisted of amorphous (Ca-)Fe(III)-phosphate ((Ca)FeP), ferrihydrite (Fh) and, in SiO4-free treatments, lepidocrocite (Lp). During aging, FeP and Fh that had formed in the absence of Mg, Ca and SiO4 rapidly and nearly completely transformed into Lp. Via effects on molecular- and nanoscale precipitate structure, Mg slowed down FeP transformation into Fh, stabilized Fh, and decreased the crystallinity of Lp (in SiO4-free suspensions), Ca stabilized CaFeP against transformation into Fh, and SiO4 stabilized Fh and (Ca)FeP. Core/shell CaFeP/Fh particles formed in electrolytes that contained Ca and SiO4 hardly transformed within 100 d. Calcite only formed at low dissolved PO4 concentrations and, by incorporation of PO4, contributed to PO4 retention. Higher levels of dissolved PO4 inhibited calcite formation but could induce Ca-phosphate precipitation. Differences in precipitate formation and transformation pathways and kinetics were reflected in the extents of PO4 release over the 100-d aging period, ranging from rapid release of 77% of the total PO4 in the treatment without Mg, Ca and SiO4 at 0.15 mM total PO4 to slow release of only 0.1% of the total PO4 at initial concentrations of 4 mM Ca, 0.5 mM SiO4, and 0.025 mM PO4. In summary, this study reveals the conditions and the extents and timescales over which Fe(III)- and Ca-precipitates form and transform and how these processes affect PO4 immobilization in near-neutral natural waters. The detailed new insights into the coupling between Fe(III)- and Ca-precipitate formation and into the interdependent effects of Mg, Ca, SiO4 and PO4 are not only relevant with respect to PO4 but also with respect to the cycling of trace elements in natural and engineered systems.
Pulido-Reyes, G., Bianco, C., Magherini, L., Sethi, R., von Gunten, U., Kaegi, R., & Mitrano, D. M. (2023). Rückhalt von Nanoplastik-Partikeln bei der Wasseraufbereitung. Aqua & Gas, 103(7-8), 30-35. , Institutional Repository

Nanoplastik-Partikel (NP) werden bei einer klassischen Wasseraufbereitung bestehend aus Schnell- und Langsamsandfiltration sowie Aktivkohlefiltration gut aus Seewasser entfernt. Eine simulation einer Wasseraufbereitungsanlage ergab ein Eliminationseffizient von > 99,9%. Der Biofilm des Langsamsandfilters ist dabei das wichtigste Element. Die Ozonbehandlung verändert die NP kaum und hat somit keinen Einfluss auf den Rückhalt der NP bei der nachgeschalteten Sandund Aktivkohlefiltration.
Sodnikar, K., Kaegi, R., Christl, I., Schroth, M. H., & Sander, M. (2023). Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries. Environmental Science: Processes and Impacts, 25(12), 2067-2080. doi:10.1039/d3em00294b, Institutional Repository

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.
Xu, J., Chen, C., Hu, X., Chen, D., Bland, G., Wielinski, J., … Lowry, G. V. (2023). Particle-scale understanding of arsenic interactions with sulfidized nanoscale zerovalent iron and their impacts on dehalogenation reactivity. Environmental Science and Technology, 57(51), 21917-21926. doi:10.1021/acs.est.3c08635, Institutional Repository

Co-occurrence of organic contaminants and arsenic oxoanions occurs often at polluted groundwater sites, but the effect of arsenite on the reactivity of sulfidized nanoscale zerovalent iron (SNZVI) used to remediate groundwater has not been evaluated. Here, we study the interaction of arsenite [As(III)] with SNZVI at the individual-particle scale to better understand the impacts on the SNZVI properties and reactivity. Surface and intraparticle accumulation of As was observed on hydrophilic FeS-Fe0 and hydrophobic FeS2-Fe0 particles, respectively. X-ray absorption spectroscopy indicated the presence of realgar-like As-S and elemental As0 species at low and high As/Fe concentration ratios, respectively. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis identified As-containing particles both with and without Fe. The probability of finding As-containing particles without Fe increased with the S-induced hydrophobicity of SNZVI. The interactions of SNZVI materials with coexisting arsenite inhibited their reactivity with water (∼5.8-230.7-fold), trichloroethylene (∼3.6-67.5-fold), and florfenicol (∼1.1-5.9-fold). However, the overall selectivity toward trichloroethylene and florfenicol relative to water was improved (up to 9.0-fold) because the surface-associated As increased the SNZVI hydrophobicity. These results indicate that reactions of SNZVI with arsenite can remove As from groundwater and improve the properties of SNZVI for dehalogenation selectivity.
Grigg, A. R. C., ThomasArrigo, L. K., Schulz, K., Rothwell, K. A., Kaegi, R., & Kretzschmar, R. (2022). Ferrihydrite transformations in flooded paddy soils: rates, pathways, and product spatial distributions. Environmental Science: Processes and Impacts, 24(10), 1867-1882. doi:10.1039/d2em00290f, Institutional Repository

Complex interactions between redox-driven element cycles in soils influence iron mineral transformation processes. The rates and pathways of iron mineral transformation processes have been studied intensely in model systems such as mixed suspensions, but transformation in complex heterogeneous porous media is not well understood. Here, mesh bags containing 0.5 g of ferrihydrite were incubated in five water-saturated paddy soils with contrasting microbial iron-reduction potential for up to twelve weeks. Using X-ray diffraction analysis, we show near-complete transformation of the ferrihydrite to lepidocrocite and goethite within six weeks in the soil with the highest iron(II) release, and slower transformation with higher ratios of goethite to lepidocrocite in soils with lower iron(II) release. In the least reduced soil, no mineral transformations were observed. In soils where ferrihydrite transformation occurred, the transformation rate was one to three orders of magnitude slower than transformation in comparable mixed-suspension studies. To interpret the spatial distribution of ferrihydrite and its transformation products, we developed a novel application of confocal micro-Raman spectroscopy in which we identified and mapped minerals on selected cross sections of mesh bag contents. After two weeks of flooded incubation, ferrihydrite was still abundant in the core of some mesh bags, and as a rim at the mineral–soil interface. The reacted outer core contained unevenly mixed ferrihydrite, goethite and lepidocrocite on the micrometre scale. The slower rate of transformation and uneven distribution of product minerals highlight the influence of biogeochemically complex matrices and diffusion processes on the transformation of minerals, and the importance of studying iron mineral transformation in environmental media.
Kocic, J., Dirin, D. N., Kägi, R., Kovalenko, M. V., Günther, D., & Hattendorf, B. (2022). Direct analysis of nanoparticles in organic solvents by ICPMS with microdroplet injection. Journal of Analytical Atomic Spectrometry, 37(8), 1738-1750. doi:10.1039/d1ja00358e, Institutional Repository

In recent years, the capabilities for characterizing inorganic nanoparticles (NPs) in aqueous solvents with respect to their elemental composition, mass and particle number concentration have been expanded using single particle inductively coupled plasma mass spectrometry (sp-ICPMS). However, NPs with high monodispersity, size, shape and surface chemistry control are frequently synthesized using hot-injection methods, utilizing hydrophobic organic ligands which are only soluble in non-polar organic solvents. Due to several instrumental limitations, suspensions in organic solvents are not commonly analysed by sp-ICPMS. In this study, we investigated the direct introduction of toluene and mesitylene into an ICPMS using a microdroplet generator. With this configuration the solvent load in the ICP is substantially reduced and soot formation, causing instrumental drift, was minimized while maintaining a transport efficiency (TE) of 100%. Furthermore, the effect of different vacuum interface configurations and the addition of oxygen or nitrogen on the detection efficiency (DE) and instrumental background signals was investigated for Al, Si, Ti, Fe Cu, Ag, Cd, and Pb. The highest DE was obtained for a “Jet” interface with the addition of nitrogen at a flow rate of 10 mL min−1, resulting in an increase by a factor of 2-8 depending on the element. The lowest detectable mass, based on counting statistics, was 1.4 ag for Pb, which corresponds to a diameter of 6.1 nm of a spherical, metallic NP. The approach can not only be used for NP characterization, but also holds promise for the sensitive determination of trace elements in organic solvents.
Murazzi, M. E., Cherubini, P., Brunner, I., Kägi, R., Saurer, M., Ballikaya, P., … Gessler, A. (2022). Can forest trees take up and transport nanoplastics?. iForest, 15(2), 128-132. doi:10.3832/ifor4021-015, Institutional Repository

Plastic contamination of ecosystems has increased dramatically over the last decades, raising concerns about the negative impacts of plastic particles on aquatic and terrestrial systems. In recent years, the focus of most research has shifted from large fragments (macroplastic) to micro- (<5 mm) and more recently to nano-plastic (<1000 nm) particles as more evidence has come to light about their ubiquity in water, soils, and living systems, and their effects on ecosystem and human health. In this study, we investigate nanoplastic uptake in the roots of seedlings (1-2 years old) of three different tree species and assess their transport to different tissues. Parts of the main roots of silver birch (Betula pendula Roth), sessile oak (Quercus petraea Matt. [Liebl.]), and Norway spruce (Picea abies [L.] Karst.) were immersed for one or four days in a suspension containing 13C-labelled nano-sized polystyrene particles (13C-nPS; 99% 13C, d = 28 ± 8 (1 σ) nm). Carbon stable isotope analysis showed significant 13C enrichment (P < 0.05) in the immersed part of the root after one day of treatment in all three species, and after four days in Q. petraea alone. Signals of significant 13C enrichment were also found in the aboveground tissues of the trees. The stem of B. pendula in particular showed a significant 13C enrichment after one day of treatment (P < 0.01). This indicates that nanoplastic particles can be taken up through tree roots into the tree’s central cylinder, where they are subsequently conveyed through the tree by acropetal transport via the xylem.
Notini, L., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2022). Coexisting goethite promotes Fe(II)-catalyzed transformation of ferrihydrite to goethite. Environmental Science and Technology, 56(17), 12723-12733. doi:10.1021/acs.est.2c03925, Institutional Repository

In redox-affected soil environments, electron transfer between aqueous Fe(II) and solid-phase Fe(III) catalyzes mineral transformation and recrystallization processes. While these processes have been studied extensively as independent systems, the coexistence of iron minerals is common in nature. Yet it remains unclear how coexisting goethite influences ferrihydrite transformation. Here, we reacted ferrihydrite and goethite mixtures with Fe(II) for 24 h. Our results demonstrate that with more goethite initially present in the mixture more ferrihydrite turned into goethite. We further used stable Fe isotopes to label different Fe pools and probed ferrihydrite transformation in the presence of goethite using 57Fe Mössbauer spectroscopy and changes in the isotopic composition of solid and aqueous phases. When ferrihydrite alone underwent Fe(II)-catalyzed transformation, Fe atoms initially in the aqueous phase mostly formed lepidocrocite, while those from ferrihydrite mostly formed goethite. When goethite was initially present, more goethite was formed from atoms initially in the aqueous phase, and nanogoethite formed from atoms initially in ferrihydrite. Our results suggest that coexisting goethite promotes formation of more goethite via Fe(II)-goethite electron transfer and template-directed nucleation and growth. We further hypothesize that electron transfer onto goethite followed by electron hopping onto ferrihydrite is another possible pathway to goethite formation. Our findings demonstrate that mineral transformation is strongly influenced by the composition of soil solid phases.
Philipp, M., Bucheli, T. D., & Kaegi, R. (2022). The use of surrogate standards as a QA/QC tool for routine analysis of microplastics in sewage sludge. Science of the Total Environment, 835, 155485 (9 pp.). doi:10.1016/j.scitotenv.2022.155485, Institutional Repository

The efficient retention of microplastic particles (MP) during wastewater treatment results in their accumulation in the sewage sludge. Thus, sewage sludge represents a key matrix for understanding MP flows between engineered and natural systems. Building on previous reports, we present a sample preparation protocol optimized for digested sewage sludge. The key steps include acid digestion supported by Fenton reagents, enzymatic digestion, and density separation using sodium polytungstate (density of 1.9 gcm−3). We use colored polyethylene (PE) spheres as surrogate standards to assess sample specific recoveries in terms of number and size, based on visible light (vis) microscopy and focal plane array - micro-Fourier transform - infrared (FPA-μ-FT-IR) imaging. The FT-IR spectra of common MP were identical before and after the digestion procedures and morphological changes were observed for polylactide fibers only. Average recovery rates for PE spheres, polypropylene fibers and polyethylene terephthalate fragments extracted from spiked digested sewage sludge and determined using (automated) vis microscopy ranged from 80% to 100%. Similar recovery rates of around 80% were also obtained for PE spheres based on FPA-μ-FT-IR measurements. The median diameters of red and blue PE spheres in dry state and recovered from spiked deionized water and from extracts of spiked digested sewage sludge determined using vis microscopy ranged between 46 μm and 67 μm. These diameters were similar to 54 μm and 61 μm obtained from the FPA-μ-FT-IR measurements of the corresponding deionized water samples and digested sludge extracts and in line with data from the producer (53 μm–63 μm). Using our digestion protocol in combination with surrogate standards, we measured MP number concentrations of around 10,000 #/g in dried, digested sewage sludge, in agreement with recent results from other studies.
Pulido-Reyes, G., Magherini, L., Bianco, C., Sethi, R., von Gunten, U., Kaegi, R., & Mitrano, D. M. (2022). Nanoplastics removal during drinking water treatment: laboratory- and pilot-scale experiments and modeling. Journal of Hazardous Materials, 436, 129011 (13 pp.). doi:10.1016/j.jhazmat.2022.129011, Institutional Repository

Microplastics detected in potable water sources and tap water have led to concerns about the efficacy of current drinking water treatment processes to remove these contaminants. It is hypothesized that drinking water resources contain nanoplastics (NPs), but the detection of NPs is challenging. We, therefore, used palladium (Pd)-labeled NPs to investigate the behavior and removal of NPs during conventional drinking water treatment processes including ozonation, sand and activated carbon filtration. Ozone doses typically applied in drinking water treatment plants (DWTPs) hardly affect the NPs transport in the subsequent filtration systems. Amongst the different filtration media, NPs particles were most efficiently retained when aged (i.e. biofilm coated) sand was used with good agreements between laboratory and pilot scale systems. The removal of NPs through multiple filtration steps in a municipal full-scale DWTP was simulated using the MNMs software code. Removal efficiencies exceeding 3-log units were modeled for a combination of three consecutive filtration steps (rapid sand filtration, activated carbon filtration and slow sand filtration with 0.4-, 0.2- and 3.0-log-removal, respectively). According to the results from the model, the removal of NPs during slow sand filtration dominated the overall NPs removal which is also supported by the laboratory-scale and pilot-scale data. The results from this study can be used to estimate the NPs removal efficiency of typical DWTPs with similar water treatment chains.
Rhein, F., Nirschl, H., & Kaegi, R. (2022). Separation of microplastic particles from sewage sludge extracts using magnetic seeded filtration. Water Research X, 17, 100155 (11 pp.). doi:10.1016/j.wroa.2022.100155, Institutional Repository

Microplastic particles (MP) are efficiently retained in wastewater treatment plants and enriched in sewage sludge. For monitoring MP contents in wastewater systems, sewage sludge is thus well suited, but also requires an isolation of MP from the sludge matrix, as other sewage sludge components may interfere with the MP identification and quantification. Although organic matter in sludge samples can be removed through acid and enzymatic digestion procedures, cellulose - mainly from toilet paper - remains in the digests, due to its high chemical resistivity and similar density to MP. We apply the separation concept of magnetic seeded filtration to isolate MP through selective hetero-agglomeration with magnetic seed particles. MP and cellulose differ in their hydrophobic properties and we investigate to what extent these differences can be exploited to selectively form MP-magnetite hetero-agglomerates in the presence of cellulose. These hetero-agglomerates are subsequently separated using a magnet. Five MP types (Polyethylene terephthalate (PET), polypropylene (PP), low density polyethylene (LDPE), polyvinyl chloride (PVC) and polystyrene (PS)) and cellulose particles were mixed in different combinations with both hydrophilic and hydrophobic (silanized) magnetite particles. PET, PP, LDPE and PS only poorly agglomerated with pristine (hydrophilic) magnetite, but efficiently formed hetero-agglomerates with hydrophobic magnetite and were successfully removed from suspensions (80 - 100 %). PVC agglomerated more efficiently with pristine than with hydrophobic magnetite and cellulose only agglomerated to a limited extent with either hydrophilic or hydrophobic magnetite, resulting in a high process selectivity. Results from experiments conducted at different ionic strengths and with hydrophilic and hydrophobic magnetite suggests that the agglomeration process was dominated by hydrophobic interactions. Enzymatic and oxidative treatment of the MP only marginally affected the separation efficiencies and (treated) MP spiked to sewage sludge extracts were successfully recovered using magnetic seeded filtration.
Schulz, K., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2022). Stabilization of ferrihydrite and lepidocrocite by silicate during Fe(II)-catalyzed mineral transformation: impact on particle morphology and silicate distribution. Environmental Science and Technology, 56(9), 5929-5938. doi:10.1021/acs.est.1c08789, Institutional Repository

Interactions between aqueous ferrous iron (Fe(II)) and secondary Fe oxyhydroxides catalyze mineral recrystallization and/or transformation processes in anoxic soils and sediments, where oxyanions, such as silicate, are abundant. However, the effect and the fate of silicate during Fe mineral recrystallization and transformation are not entirely understood and especially remain unclear for lepidocrocite. In this study, we reacted (Si-)ferrihydrite (Si/Fe = 0, 0.05, and 0.18) and (Si-)lepidocrocite (Si/Fe = 0 and 0.08) with isotopically labeled 57Fe(II) (Fe(II)/Fe(III) = 0.02 and 0.2) at pH 7 for up to 4 weeks. We followed Fe mineral transformations with X-ray diffraction and tracked Fe atom exchange by measuring aqueous and solid phase Fe isotope fractions. Our results show that the extent of ferrihydrite transformation in the presence of Fe(II) was strongly influenced by the solid phase Si/Fe ratio, while increasing the Fe(II)/Fe(III) ratio (from 0.02 to 0.2) had only a minor effect. The presence of silicate increased the thickness of newly formed lepidocrocite crystallites, and elemental distribution maps of Fe(II)-reacted Si-ferrihydrites revealed that much more Si was associated with the remaining ferrihydrite than with the newly formed lepidocrocite. Pure lepidocrocite underwent recrystallization in the low Fe(II) treatment and transformed to magnetite at the high Fe(II)/Fe(III) ratio. Adsorbed silicate inactivated the lepidocrocite surfaces, which strongly reduced Fe atom exchange and inhibited mineral transformation. Collectively, the results of this study demonstrate that Fe(II)-catalyzed Si-ferrihydrite transformation leads to the redistribution of silicate in the solid phase and the formation of thicker lepidocrocite platelets, while lepidocrocite transformation can be completely inhibited by adsorbed silicate. Therefore, silicate is an important factor to include when considering Fe mineral dynamics in soils under reducing conditions.
Schwarzfischer, M., Niechcial, A., Lee, S. S., Sinnet, B., Wawrzyniak, M., Laimbacher, A., … Spalinger, M. R. (2022). Ingested nano- and microsized polystyrene particles surpass the intestinal barrier and accumulate in the body. NanoImpact, 25, 100374 (9 pp.). doi:10.1016/j.impact.2021.100374, Institutional Repository

Plastic pollution is a major global challenge of our times, baring a potential threat for the environment and the human health. The increasing abundance of nanoplastic (NP) and microplastic (MP) particles in the human diet might negatively affect human health since they - particularly in patients suffering from inflammatory bowel disease (IBD) – might surpass the intestinal barrier. To investigate whether ingested plastic particles cross the intestinal epithelium and promote bowel inflammation, mice were supplemented with NP or MP polystyrene (PS) particles for 24 or 12 weeks before inducing acute or chronic dextran sodium sulfate (DSS) colitis with continuous plastic administration. Although ingested PS particles accumulated in the small intestine and organs distant from the gastrointestinal tract, PS ingestion did not affect intestinal health nor did it promote colitis severity. Although the lack of colitis-promoting effects of small PS particles might be a relief for IBD patients, potential accumulative effects of ingested plastic particles on the gastrointestinal health cannot be excluded.
Stetten, L., Hofmann, T., Proux, O., Landrot, G., Kaegi, R., & von der Kammer, F. (2022). Transformation of zinc oxide nanoparticles in freshwater sediments under oxic and anoxic conditions. Environmental Science: Nano, 9(11), 4255-4267. doi:10.1039/d2en00709f, Institutional Repository

The transformation of zinc oxide nanoparticles (ZnO NPs) has been largely investigated in wastewater treatment plants, recognized as important intermediates before the discharge of NPs into the environment. However, considering direct releases of the pristine ZnO NP forms, additional studies on ZnO NP fate in different environmental compartments are encouraged. In this work, we investigated ZnO NP transformation in lacustrine sediments under defined redox conditions. Using X-ray absorption spectroscopy and wet chemical analyses, we followed ZnO NP and Zn2+ fate over a three-month period in sediments incubated under oxic or anoxic sulfide-rich conditions. Under oxic conditions, ZnO NPs were dissolved within a few hours. By contrast, ZnO NP dissolution under anoxic conditions was much slower, with ∼19% of ZnO NPs remaining at the end of the incubation, together with ∼41% of ZnS, ∼15% of Zn adsorbed onto phyllosilicates and ∼27% of Zn-phyllosilicate-like species. The transient formation of Zn–organic complexes under oxic conditions supports that ZnO NP dissolution is driven by organic compounds, followed by Zn adsorption onto phyllosilicates and the subsequent formation of Zn-layered minerals. Under anoxic conditions, ZnO NP dissolution is inhibited by the precipitation of amorphous ZnS and controlled by the progressive growth of ZnS NPs. These results improve the understanding of ZnO NP transformation in slightly alkaline freshwater sediments and highlight the need to assess NP fate under environmentally relevant conditions.
Szakas, S. E., Lancaster, R., Kaegi, R., & Gundlach-Graham, A. (2022). Quantification and classification of engineered, incidental, and natural cerium-containing particles by spICP-TOFMS. Environmental Science: Nano, 9, 1627-1638. doi:10.1039/d1en01039e, Institutional Repository

Cerium containing nanoparticles (Ce-NPs) from geogenic and anthropogenic sources are frequently found in the environment, and the ability to determine the origins of Ce-NPs relies on the presence of other rare earth elements (REEs), such as La. In this study, we develop a scheme to classify individual natural, incidental, and engineered Ce-containing particles using spICP-TOFMS. Well-characterized CeO2 engineered particles (Ce-ENPs), incidental particles (Ce-INPs) from ferrocerium mischmetal, and natural particles (Ce-NNPs) from ground minerals (bastnaesite and parisite) are used as a model particle system. Based on mixtures of these three Ce-NP types, we demonstrate that the measured signals of Ce, La, and Nd in Ce-NNPs follow Poisson statistics and have conserved element ratios. The Ce-INPs we measure have similar Ce : La mass ratios to those of the Ce-NNPs, and Ce : Nd mass ratios can be used to distinguish these two Ce-NP types. Based on this, we develop particle-type-specific detection limits (LD,sp) for the measurement of La and Nd in Ce-NNPs. Our approach establishes LD,sp values with defined confidence intervals to control false-positive particle-type assignments, and allows us to accurately classify engineered, incidental, and natural Ce-NPs down to effective spherical diameters of 32, 35, and 45 nm, respectively. In pure Ce-NNP suspensions, this approach accurately classifies 68% of all detected Ce-NPs with <4% false assignments. For ternary mixtures of Ce-ENPs, INPs, and NNPs, we classify 56% to 76% of all detected Ce-NPs. We demonstrate a linear response with increasing concentrations of Ce-INPs and Ce-ENPs across approximately three orders of magnitude and can classify particles down to ratios of ∼1:50 for anthropogenic : natural Ce-NPs.
Berg, M., Suess, E., Cayo, L., Bouchet, S., Hug, S. J., Kaegi, R., … Buser, A. M. (2021). Quecksilber im Schweizer Abwasser. Konzentrationen, Massenflüsse, Speziierung und Rückhalt. Aqua & Gas, 101(1), 14-20. , Institutional Repository

In einer landesweiten Studie wurde Quecksilber in Abwässern und Klärschlämmen analysiert, jährliche Gesamtmengen des abwasserbürtigen Quecksilbers ermittelt und die Einhaltung der gesetzlichen Vorgaben überprüft. Ebenso wurde die durchschnittliche Fracht pro Einwohner und der Beitrag der Abwasserreinigungsanlagen zur Quecksilberbelastung der Oberflächengewässer ermittelt. Auf nationaler Ebene waren diese Kennzahlen bisher nicht bekannt.
Etique, M., Bouchet, S., Byrne, J. M., Thomasarrigo, L. K., Kaegi, R., & Kretzschmar, R. (2021). Mercury reduction by nanoparticulate vivianite. Environmental Science and Technology, 55(5), 3399-3407. doi:10.1021/acs.est.0c05203, Institutional Repository

Mercury (Hg) is a toxic trace element of global environmental concern which has been increasingly dispersed into the environment since the industrial revolution. In aquatic and terrestrial systems, Hg can be reduced to elemental Hg (Hg0) and escape to the atmosphere or converted to methylmercury (MeHg), a potent neurotoxin that accumulates in food webs. FeII-bearing minerals such as magnetite, green rusts, siderite, and mackinawite are recognized HgII reducers. Another potentially Hg-reducing mineral, which commonly occurs in Fe- and organic/P-rich sediments and soils, is the ferrous iron phosphate mineral vivianite (FeII3(PO4)2·8H2O), but its reaction with HgII has not been studied to date. Here, nanoparticulate vivianite (particle size ∼ 50 nm; FeII content > 98%) was chemically synthesized and characterized by a combination of chemical, spectroscopic, and microscopic analyses. Its ability to reduce HgII was investigated at circumneutral pH under anoxic conditions over a range of FeII/HgII ratios (0.1–1000). For FeII/HgII ratios ≥1, which are representative of natural environments, HgII was very quickly and efficiently reduced to Hg0. The ability of vivianite to reduce HgII was found to be similar to those of carbonate green rust and siderite, two of the most effective Hg-reducing minerals. Our results suggest that vivianite may be involved in abiotic HgII reduction in Fe and organic/P-rich soils and sediments, potentially contributing to Hg evasion while also limiting MeHg formation in these ecosystems.
Kaegi, R., Gogos, A., Voegelin, A., Hug, S. J., Winkel, L. H. E., Buser, A. M., & Berg, M. (2021). Quantification of individual Rare Earth Elements from industrial sources in sewage sludge. Water Research X, 11, 100092 (11 pp.). doi:10.1016/j.wroa.2021.100092, Institutional Repository

Rare Earth Elements (REEs) are used in increasing amounts in technical applications and consumer products. However, to date, the contribution of industrial sources to the loads of individual REEs in wastewater streams have not been quantified. Here, we determine the REE contents in sludge collected from 63 wastewater treatment plants (WWTPs) across Switzerland. To quantify the industrial fraction of individual REEs in the sewage sludge, we develop two complementary approaches, based on REE ratios and REE pattern fitting. Unspecific (background) inputs, with REE patterns similar to the averaged REE pattern of soils collected across Switzerland, dominate the REE budget of most WWTPs. A few WWTPs receive significant REE inputs from specific industrial sources. Based on population equivalents of Switzerland, we estimate a total annual load of 4200 kg Cerium (Ce, 0.5 g Ce year-1 capita-1), with an industrial contribution of 2000 kg year-1. The latter agrees with estimates of probabilistic mass flow models for engineered nanoscale CeO2 particles discharged to the sewer network. About 7 kg year-1 of Samarium (Sm,total for Switzerland: 184 kg year-1 or 0.02 g Sm year-1 capita-1) and 3 kg year-1 of Europium (Eu,total for Switzerland: 44 kg year-1 or 0.005 g Eu year-1 capita-1) are assigned to industrial inputs from single WWTPs. Gadolinium (Gd) is used in the form of a stable complex as contrast agent in magnetic resonance imaging. Assuming 10% removal of Gd during wastewater treatment, we calculate an annual discharge of 90 kg of Gd from one individual WWTP to surface waters. WWTPs with exceptionally high industrial inputs of specific REEs warrant detailed investigations to identify the respective sources and to assess whether REE concentrations in effluents are elevated to the same degree.
Kaegi, R., Fierz, M., & Hattendorf, B. (2021). Quantification of nanoparticles in dispersions using transmission electron microscopy. Microscopy and Microanalysis, 27(3), 557-565. doi:10.1017/S1431927621000398, Institutional Repository

The quantification of the particle size and the number concentration (PNC) of nanoparticles (NPs) is key for the characterization of nanomaterials. Transmission electron microscopy (TEM) is often considered as the gold standard for assessing the size of NPs; however, the TEM sample preparation suitable for estimating the PNC based on deposited NPs is challenging. Here, we use an ultrasonic nebulizer (USN) to transfer NPs from aqueous suspensions into dried aerosols which are deposited on TEM grids in an electrostatic precipitator of an aerosol monitor. The deposition efficiency of the electrostatic precipitator was ≈2%, and the transport efficiency of the USN was ≈7%. Experiments using SiO2NPs (50-200 nm) confirmed an even deposition of the nebulized particles in the center of the TEM grids. PNCs of the SiO2NPs derived from TEM images underestimated the expected PNCs of the suspensions by a factor of up to three, most likely resulting from droplet coagulation and NP aggregation in the USN. Nevertheless, single particles still dominated the PNC. Our approach results in reproducible and even deposition of particles on TEM grids suitable for morphological analysis and allows an estimation of the PNC in the suspensions based on the number of particles detected by TEM.
Kuehr, S., Diehle, N., Kaegi, R., & Schlechtriem, C. (2021). Ingestion of bivalve droppings by benthic invertebrates may lead to the transfer of nanomaterials in the aquatic food chain. Environmental Sciences Europe, 33(1), 35 (16 pp.). doi:10.1186/s12302-021-00473-3, Institutional Repository

Background: Manufactured nanomaterials (MNMs) are released into the environment in increasing quantities. Consequently, MNMs also reach the aquatic environment, where they can interact with different organisms. Previous studies have already shown that filter-feeding bivalves can ingest nanomaterials from the surrounding water leading to higher concentration of the material. Furthermore, they have been shown to be vectors for environmental chemicals and pathogens to other organisms, as their feces/pseudofeces (F/pF) play a crucial role as a food source for other species. We exposed bivalves (Corbicula sp.) to MNMs and performed experiments to investigate the possible transport of MNMs by their feces to the benthic amphipod Hyalella azteca. Silver (Ag) and gold (Au) nanoparticles (NPs) as well as fluorescent polystyrene nanoparticles were used in this study. They allowed the investigation of the metal content of the bivalves’ feces and the amphipods feeding on it, as well as the localization of the fluorescent particles in the body of the animals.
Results: Examination of the feces by fluorescence microscope and determination of the total metal content by inductively coupled plasma mass spectrometry (ICP-MS) showed a high accumulation of the exposed MNMs in the F/pF. The examination of fecal matter, using transmission electron microscopy confirmed the nanoparticulate character of the metals in the examined fecal matter. After exposure of amphipods to the MNMs containing fecal matter, the fluorescent MNMs were localized in the animals gut. The chronic exposure of juvenile amphipods over 21 days to feces enriched with Au MNMs caused significant effects on the growth of the amphipods. The transfer of both metals (Ag and Au) from the fecal matter to the amphipods was confirmed after total metal measurements.
Conclusion: Probably, for the first time, it has been shown that when exposed to MNMs bivalves can transfer these particles to other benthic species. Transfer is via released F/pF upon which the benthic species feed and thus could ingest the particles. The high concentrations of MNMs in the fecal matter raises concerns about the potential accumulation and transfer of the materials and associated ecotoxicological effects in invertebrates such as benthic amphipods.
Kuehr, S., Kaegi, R., Maletzki, D., & Schlechtriem, C. (2021). Testing the bioaccumulation potential of manufactured nanomaterials in the freshwater amphipod Hyalella azteca. Chemosphere, 263, 127961 (15 pp.). doi:10.1016/j.chemosphere.2020.127961, Institutional Repository

Standardized experimental approaches for the quantification of the bioaccumulation potential of nanomaterials in general and in (benthic) invertebrates in particular are currently lacking. We examined the suitability of the benthic freshwater amphipod Hyalella azteca for the examination of the bioaccumulation potential of nanomaterials. A flow-through test system that allows the generation of bioconcentration and biomagnification factors was applied. The feasibility of the system was confirmed in a 2-lab comparison study. By carrying out bioconcentration and biomagnification studies with gold, titanium dioxide and silver nanoparticles as well as dissolved silver (AgNO3) we were able to assess the bioaccumulation potential of different types of nanomaterials and their exposure pathways. For this, the animals were examined for their total metal body burden using inductively coupled mass spectroscopy (ICP-MS) and for the presence of nanoparticulate burdens using single-particle ICP-MS. The role of released ions was highlighted as being very important for the bioavailability and bioaccumulation of metals from nanoparticles for both examined uptake paths examined (bioconcentration and biomagnification). In 2018 a tiered testing strategy for engineered nanomaterials was proposed by Handy et al. that may allow a waiver of bioaccumulation fish studies using inter alia invertebrates. Data gained in studies carried out with invertebrates like the developed Hyalella azteca test may be included in this proposed tiered testing strategy.
Mehrabi, K., Kaegi, R., Günther, D., & Gundlach-Graham, A. (2021). Emerging investigator series: automated single-nanoparticle quantification and classification: a holistic study of particles into and out of wastewater treatment plants in Switzerland. Environmental Science: Nano, 8(5), 1211-1225. doi:10.1039/d0en01066a, Institutional Repository

Single particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS), in combination with online microdroplet calibration, allows for the determination of particle number concentrations (PNCs) and the amount (i.e. mass) of ICP-MS-accessible elements in individual particles. Because sp-ICP-TOFMS analyses of environmental samples produce rich datasets composed of both single-metal nanoparticles (smNPs) and many types of multi-metal NPs (mmNPs), interpretation of these data is well suited to automated analysis schemes. Here, we present a new data analysis approach that includes: 1. automatic particle detection and elemental mass determinations based on online microdroplet calibration, 2. correction of false (randomly occurring) multi-metal associations caused by measurement of coincident but distinct NPs, and 3. unsupervised clustering analysis of mmNPs to identify unique classes of NPs based on their element compositions. To demonstrate the potential of our approach, we analyzed water samples collected from the influent and effluent of five wastewater treatment plants (WWTPs) across Switzerland. We determined elemental masses in individual NPs, as well as PNCs, to estimate the NP removal efficiencies of the individual WWTPs. From WWTP samples collected at two points in time, we found an average of 90% and 94% removal efficiencies of single-metal and multi-metal NPs, respectively. Between 5% to 27% of detected NPs were multi-metal; the most abundant particle types were those rich in Ce-La, Fe-Al, Ti-Zr, and Zn-Cu. Through hierarchical clustering, we identified NP classes conserved across all WWTPs, as well as particle types that are unique to one or a few WWTPs. These uniquely occurring particle types may represent point sources of anthropogenic NPs. We describe the utility of clustering analysis of mmNPs for identifying natural, geogenic NPs, and also for the discovery of new, potentially anthropogenic, NP targets.
Mehrabi, K., Kaegi, R., Günther, D., & Gundlach-Graham, A. (2021). Quantification and clustering of inorganic nanoparticles in wastewater treatment plants across Switzerland. Chimia, 75(7-8), 642-646. doi:10.2533/chimia.2021.642, Institutional Repository

Single particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry (sp-ICP-TOFMS), in combination with online microdroplet calibration, allows the determination of particle number concentrations (PNCs) and the masses of elements in individual particles. Because sp-ICP-TOFMS analyses of environmental samples produce rich datasets composed of both single-metal nanoparticles (smNPs) and many types of multi-metal NPs (mmNPs), interpretation of these data is well suited to automated analysis schemes. Here, we present a data analysis approach that includes automatic particle detection and elemental mass determinations based on online microdroplet calibration, and unsupervised clustering analysis of mmNPs to identify unique classes of NPs based on their element compositions. To demonstrate the potential of our approach, we analyzed wastewater samples collected from the influent and effluent of five wastewater treatment plants (WWTPs) across Switzerland. We determined elemental masses in individual NPs, as well as PNCs, to estimate the NP removal efficiencies of the individual WWTPs. Through hierarchical clustering, we identified NP classes conserved across all WWTPs; the most abundant particle types were those rich in Ce-La, Fe-Al, Ti-Zr, and Zn-Cu. In addition, we found particle types that are unique to one or a few WWTPs, which could indicate point sources of anthropogenic NPs.
Wielinski, J., Gogos, A., Voegelin, A., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Release of gold (Au), silver (Ag) and cerium dioxide (CeO2) nanoparticles from sewage sludge incineration ash. Environmental Science: Nano, 8(11), 3220-3232. doi:10.1039/D1EN00497B, Institutional Repository

Engineered nanoparticles (NPs) that are released into wastewater are retained by wastewater treatment plants (WWTPs) and accumulate in sewage sludge. Increasing shares of sludge are incinerated and landfilled, especially in industrialized countries. It is debated whether certain types of NPs can outlive the incineration process and subsequently be released from sewage sludge ash (SSA) landfills. To investigate the release of different types of NPs from SSA, we spiked gold (Au), silver (Ag) and cerium dioxide (CeO2) NPs to a pilot WWTP increasing the Au, Ag and Ce concentrations to 30, 43 and 389 mg kg-1 (dry matter basis) in the digested sludge. The spiked sludge was incinerated in a pilot fluidized bed reactor resulting in SSA with Au, Ag and Ce concentrations of 61, 103 and 854 mg kg-1. In addition, two sludge samples from a full-scale WWTP with Au concentrations of 5 and 16 mg kg-1 were incinerated, resulting in SSA with 9 mg kg-1 and 30 mg kg-1 Au. The spiked Au-NPs remain largely unaltered during the wastewater treatment and incineration process, whereas Ag-NPs and CeO2-NPs undergo transformation. During simulated landfill leaching in columns flushed with 400 to 500 pore volumes of artificial rainwater, Ag and Ce were retained in the ash, whereas about 17% of the spiked Au was released, mainly in particulate form. Lower fractions of mostly particulate Au were released from the ashes (3 and 9%) of unspiked SSA. In conclusion, unaltered Au-NPs significantly leach from landfilled SSA, whereas the incorporation of Ag-NPs and CeO2-NPs as transformed species into the SSA matrix limits the leaching of (nano)particulate and dissolved Ag and Ce compounds.
Wielinski, J., Voegelin, A., Grobéty, B., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Transformation of TiO2 (nano)particles during sewage sludge incineration. Journal of Hazardous Materials, 411, 124932 (14 pp.). doi:10.1016/j.jhazmat.2020.124932, Institutional Repository

Titanium dioxide (TiO2) (nano)particles are produced in large quantities and their potential impacts on ecosystems warrants investigations into their fate after disposal. TiO2 particles released into wastewater are retained by wastewater treatment plants and accumulate in digested sludge, which is increasingly incinerated in industrialized countries. Therefore, we investigated the changes of the Ti-speciation during incineration of as-received sludge and of sludge spiked with anatase (d=20–50 nm) or rutile (d=200–400 nm) using X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). In the as-received sludge, rutile and anatase were the dominant Ti bearing minerals and both remained unaffected by the anaerobic treatment. During incineration, Ti reacts with hematite to members of the hematite-ilmenite solid solution series (Hem-Ilm). Up to 80% of the Ti spiked as anatase transformed into Hem-Ilm, a distorted 6-fold coordinated Ti (Ti(IV)sulfate) and rutile during incineration. Up to 30% and 60% of rutile transformed into Hem-Ilm and Ti(IV)sulfate represented phases in fly and bottom ash, respectively. Fe and Ti were spatially correlated in ash derived from as-received and anatase spiked sludge, whereas only a thin layer of the spiked rutile reacted with Fe, in line with XAS data. This study highlights the transient nature of nano-Ti species during sewage sludge incineration.
Al-Sid-Cheikh, M., Rowland, S. J., Kaegi, R., Henry, T. B., Cormier, M. A., & Thompson, R. C. (2020). Synthesis of 14C-labelled polystyrene nanoplastics for environmental studies. Communications Materials, 1(1), 97 (8 pp.). doi:10.1038/s43246-020-00097-9, Institutional Repository

Available analytical methods cannot detect nanoplastics at environmentally realistic concentrations in complex matrices such as biological tissues. Here, we describe a one-step polymerization method, allowing direct radiolabeling of a sulfonate end-capped nano-sized polystyrene (nPS; proposed as a model nanoplastic particle representing negatively charged nanoplastics). The method, which produces nanoplastics trackable in simulated environmental settings which have already been used to investigate the behavior of a nanoplastic in vivo in a bivalve mollusc, was developed, optimized and successfully applied to synthesis of 14C-labeled nPS of different sizes. In addition to a description of the method of synthesis, we describe the details for quantification, mass balance and recovery of the labelled particles from complex matrices offered by the radiolabelling approach. The radiolabeling approach described here, coupled to use of a highly sensitive autoradiographic method for monitoring nanoplastic body burden and distributions, may provide a valuable procedure for investigating the environmental pathways followed by negatively charged nanoplastics at low predicted environmental concentrations. Whether the behaviour of the synthetic nPS manufactured here, synthesised using a very common inititator, represents that of manufactured nPS found in the environment, remains to be seen.
Dörner, L., Schmutz, P., Kägi, R., Kovalenko, M. V., & Jeurgens, L. P. H. (2020). Electrophoretic deposition of nanoporous oxide coatings from concentrated CuO nanoparticle dispersions. Langmuir, 36(28), 8075-8085. doi:10.1021/acs.langmuir.0c00720, Institutional Repository

Electrophoretic deposition (EPD) of nanoporous oxide coatings is an interesting research avenue owing to the experimental simplicity and broad scope of applications and materials. In this study, the properties of concentrated (up to 5000 mg/L), nonaqueous CuO nanoparticle (NP) dispersions were tailored to produce micrometer-thick, nanoporous CuO films by EPD. In particular, we performed a systematic investigation of the electrophoretic mobilities and size distributions of dispersed CuO aggregates and developing agglomerates in different organic solvents for concentrations ranging from 50 to 5000 mg/L with and without surfactant addition. Time-resolved dynamic light scattering analyses showed that aggregate mobilities and agglomeration rates decrease with increasing hydrocarbon chain length of the organic solvent (from ethanol to hexanol) and thus with increasing viscosity. The highest electrophoretic mobility was obtained for CuO NP aggregates and agglomerates dispersed in ethanol as a solvent. However, the addition of ≥0.5 wt % acetylacetone as a surfactant is required to stabilize these dispersions for subsequent EPD and at the same time introduce a net attractive (electrostatic) interaction between neighboring agglomerates on the substrate to promote layer formation during the EPD step. The produced micrometer-thick nanoporous CuO coatings can serve as high surface area nanostructured materials or nanoporous scaffolds in catalysis, combustion, propellants, and nanojoining.
Frehland, S., Kaegi, R., Hufenus, R., & Mitrano, D. M. (2020). Long-term assessment of nanoplastic particle and microplastic fiber flux through a pilot wastewater treatment plant using metal-doped plastics. Water Research, 182, 115860 (9 pp.). doi:10.1016/j.watres.2020.115860, Institutional Repository

In recent years, several studies have investigated the flux of particulate plastic through municipal waste water treatment plants (WWTP). Challenges related to time consuming analytical methods have limited the number of sampling points and detection limits have hampered quantification of nanoplastic and microplastic fiber fluxes through WWTPs. By synthesizing nanoplastic particles and microplastic fibers labeled with a rare metal (Pd and In, respectively) which can be measured as a proxy for the plastic itself, we have circumvented major analytical pitfalls associated with (micro)plastic measurements. In this study, we spiked the labeled materials to a pilot WWTP mimicking the activated sludge process (nitrification, de-nitrification and secondary clarification). Using a mass flow model for WWTP sludge, we assessed the behavior of particulate plastic in relation to the removal of organic matter. Triplicate samples were collected from the mixed liquor and from the effluent at least twice weekly over the entire experimental run time of 40 d. Our findings show that in discrete grab samples during steady state conditions, at least 98% of particulate plastics were associated with the biosolids. A positive correlation between total suspended solids (TSS) and plastic concentrations was observed in the sludge as well as in the effluent. Because of the strong association between particulate plastic and TSS, TSS removal is likely a good indicator of plastic removal in a full scale WWTP. Therefore, additional process steps in a full-scale WWTP which further reduce the TSS load will likely retain nanoplastic particles and microplastic fibers effectively and consequently increase the removal rates.
Geitner, N. K., Ogilvie Hendren, C., Cornelis, G., Kaegi, R., Lead, J. R., Lowry, G. V., … Wiesner, M. R. (2020). Harmonizing across environmental nanomaterial testing media for increased comparability of nanomaterial datasets. Environmental Science: Nano, 7(1), 13-36. doi:10.1039/c9en00448c, Institutional Repository

The chemical composition and properties of environmental media determine nanomaterial (NM) transport, fate, biouptake, and organism response. To compare and interpret experimental data, it is essential that sufficient context be provided for describing the physical and chemical characteristics of the setting in which a nanomaterial may be present. While the nanomaterial environmental, health and safety (NanoEHS) field has begun harmonization to allow data comparison and re-use (e.g. using standardized materials, defining a minimum set of required material characterizations), there is limited guidance for standardizing test media. Since most of the NM properties driving environmental behaviour and toxicity are medium-dependent, harmonization of media is critical. A workshop in March 2016 at Duke University identified five categories of test media: aquatic testing media, soil and sediment testing media, biological testing media, engineered systems testing media and product matrix testing media. For each category of test media, a minimum set of medium characteristics to report in all NM tests is recommended. Definitions and detail level of the recommendations for specific standardized media vary across these media categories. This reflects the variation in the maturity of their use as a test medium and associated measurement techniques, variation in utility and relevance of standardizing medium properties, ability to simplify standardizing reporting requirements, and in the availability of established standard reference media. Adoption of these media harmonization recommendations will facilitate the generation of integrated comparable datasets on NM fate and effects. This will in turn allow testing of the predictive utility of functional assay measurements on NMs in relevant media, support investigation of first principles approaches to understand behavioral mechanisms, and support categorization strategies to guide research, commercial development, and policy.
Gogos, A., Wielinski, J., Voegelin, A., von der Kammer, F., & Kaegi, R. (2020). Quantification of anthropogenic and geogenic Ce in sewage sludge based on Ce oxidation state and rare earth element patterns. Water Research X, 9, 100059 (8 pp.). doi:10.1016/j.wroa.2020.100059, Institutional Repository

Emissions of Ce from anthropogenic activities (anthropogenic Ce) into urban wastewater systems and the environment result from its widespread industrial use (abrasives, catalysts, nanotechnology). Because Ce in sewage sludge can also be of geogenic origin, the quantification of anthropogenic Ce in sewage sludge remains elusive. In this study, we evaluated the suitability of Ce oxidation state and rare earth element (REE) patterns for the quantification of anthropogenic Ce fractions in sewage sludge. A diverse set of soil samples served to gain baseline information on geogenic Ce. Geogenic Ce in the soils was characterized by high Ce(III) fractions (≥70%) and their REE patterns were comparable to the REE patterns of the upper continental crust. The sewage sludges contained on average ∼80% Ce(IV) (range 18–108%), pointing to the importance of anthropogenic inputs of Ce(IV). The quantification of the anthropogenic Ce fraction based on Ce oxidation state, however, was associated with considerable uncertainty because geogenic and anthropogenic Ce cannot exclusively be assigned to Ce(III) and Ce(IV), respectively. The REE patterns of most sewage sludges indicated a clear enrichment of Ce compared to heavier REE. Based on the assumption that the industrially used Ce is free of (most) other REE, we estimated the fraction of anthropogenic Ce in the sludges based on individual Ce/REE ratios. For the individual sludges the anthropogenic contributions were very variable (10–100%) but consistent fractions were obtained for individual sludges when calculated based on Ce/Dy (dysprosium), Ce/Er (erbium) and Ce/Eu (europium) ratios. Electron microscopy analysis of sludges dominated by anthropogenic Ce revealed that the Ce was mostly contained in nanoscale particles devoid of elements characteristic of Ce-bearing minerals. Thus, anthropogenic Ce contents derived from REE patterns may be used to validate current mass flow models for engineered CeO2 nanoparticles.
Hagemann, N., Schmidt, H. P., Kägi, R., Böhler, M., Sigmund, G., Maccagnan, A., … Bucheli, T. D. (2020). Wood-based activated biochar to eliminate organic micropollutants from biologically treated wastewater. Science of the Total Environment, 730, 138417 (11 pp.). doi:10.1016/j.scitotenv.2020.138417, Institutional Repository

Implementing advanced wastewater treatment (WWT) to eliminate organic micropollutants (OMPs) is a necessary step to protect vulnerable freshwater ecosystems and water resources. To this end, sorption of OMP by activated carbon (AC) is one viable technology among others. However, conventional AC production based on fossil precursor materials causes environmental pollution, including considerable emissions of greenhouse gases. In this study, we produced activated biochar (AB) from wood and woody residues by physical activation and evaluated their capability to eliminate OMPs in treated wastewater. Activated biochar produced under optimized conditions sorbed 15 model OMPs, of which most were dissociated at circumneutral pH, to the same or higher extent than commercial AC used as a reference. While wood quality played a minor role, the dosage of the activation agent was the main parameter controlling the capacity of ABs to eliminate OMP. Our results highlight the possibility for local production of AB from local wood or woody residues as a strategy to improve WWT avoiding negative side effects of conventional AC production.
Hoffmann, K., Bouchet, S., Christl, I., Kaegi, R., & Kretzschmar, R. (2020). Effect of NOM on copper sulfide nanoparticle growth, stability, and oxidative dissolution. Environmental Science: Nano, 7(4), 1163-1178. doi:10.1039/c9en01448a, Institutional Repository

Metal sulfide nanoparticles have recently been discovered in natural environments subject to fluctuating redox conditions such as wetlands and river floodplains, which are often very rich in natural organic matter (NOM). Strong binding of chalcophile metals like copper by NOM is expected to interfere with sulfide precipitation and is likely to affect the growth of these nanoparticles. We therefore conducted experiments on the formation of copper sulfide nanoparticles (CuxS NPs) in anoxic solutions with varying Cu (50, 500 μmol L-1) and sulfide (100, 1000 μmol L-1) concentrations in the absence and presence of Suwannee River fulvic acid (SRFA, 0, 5, 50 mg C L-1). The size development of the CuxS nanoparticles and their stability were tracked over 4 weeks using transmission electron microscopy (TEM) and size-exclusion chromatography coupled to ICP-MS (SEC-ICP-MS). Additional dissolution experiments were performed in closed containers in the absence and presence of O2 and fulvic acid over several months providing insights into the oxidative dissolution behavior of CuxS. Our results highlight the high colloidal stability of CuxS nanoparticles in anoxic environments irrespective of the NOM concentration. Median particle diameters ranged between a few and a few tens of nanometers with larger particles forming in more concentrated suspensions. At low Cu and S concentrations, fulvic acid restricted particle growth by up to 25% compared to SRFA-free suspensions and metal sulfide clusters even smaller than 1 nm were detected. The CuxS nanoparticles exhibited a remarkable chemical stability against oxidative dissolution and were only dissolved when both fulvic acid and O2 were present.
Hoffmann, K., Christl, I., Kaegi, R., & Kretzschmar, R. (2020). Effects of natural organic matter (NOM), metal-to-sulfide ratio and Mn2+ on cadmium sulfide nanoparticle growth and colloidal stability. Environmental Science: Nano, 7(11), 3385-3404. doi:10.1039/d0en00764a, Institutional Repository

Redox-dynamic environments such as river floodplains and wetlands have been identified as sources of natural metal sulfide nanoparticles (MS NPs). However, little information is available on how their growth and colloidal stability are affected by the concentrations of metals and sulfide in solution, the presence of natural organic matter (NOM), and the possible incorporation of other metal cations such as Fe2+ or Mn2+. Here, we performed experiments on the formation of CdS nanoparticles (CdS NPs) in anoxic solutions with varying Cd (50, 100, 500 μmol L-1) and sulfide (50, 100, 1000 μmol L-1) concentrations in the absence and presence of Suwannee River fulvic acid (SRFA, 0, 5, 50 mg C per L). Additionally, we studied the influence of different metal-to-sulfide ratios and varying Mn2+ (0, 0.1, 0.5, 1 mmol L−1) concentrations on CdS aggregation using dynamic light scattering (DLS), transmission electron microscopy (TEM), and electrophoretic mobility measurements. The incorporation of Mn into the crystal lattice of CdS over 8 weeks was investigated with X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Our results show that after 24 hours, small CdS primary particles with median diameters of a few nanometers (d~TEM = 2-14 nm) formed large aggregates (d~TEM = 167 nm) and that increasing SRFA concentrations progressively constrained the size of these aggregates (down to 19 nm) irrespective of the initial reactant stoichiometry. When NOM was absent or at low concentration, higher metal-to-sulfide ratios (≥1) and Mn2+ concentrations (≥0.5 mmol L-1) led to reduced colloidal stability of the suspensions. We found that in suspensions containing Mn2+, 10-30% of the Cd atoms in the crystal lattice were substituted by Mn during the formation of CdS, which was prevented by NOM.
Mast, J., Verleysen, E., Hodoroaba, V. D., & Kaegi, R. (2020). Characterization of nanomaterials by transmission electron microscopy: measurement procedures. In V. D. Hodoroaba, W. E. S. Unger, & A. G. Shard (Eds.), Micro and nano technologies. Characterization of nanoparticles. Measurement processes for nanoparticles (pp. 29-48). doi:10.1016/B978-0-12-814182-3.00004-3, Institutional Repository
Pulido-Reyes, G., Mitrano, D. M., Kägi, R., & von Gunten, U. (2020). The effect of drinking water ozonation on different types of submicron plastic particles. In M. Cocca, E. Di Pace, M. E. Errico, G. Gentile, A. Montarsolo, R. Mossotti, & M. Avella (Eds.), Springer Water. Proceedings of the 2nd international conference on microplastic pollution in the Mediterranean Sea (pp. 152-157). doi:10.1007/978-3-030-45909-3_24, Institutional Repository

Plastic pollution has increased in line with the increased plastic production over the last 60 years, having reached all environments globally and potentially affecting drinking water supplies [1, 2, 3]. For example, microplastics have recently been detected in both potable water sources and bottled water for consumption [4], leading researchers to question the efficacy of current water treatment practices. [...]
Suess, E., Berg, M., Bouchet, S., Cayo, L., Hug, S. J., Kaegi, R., … Buser, A. M. (2020). Mercury loads and fluxes from wastewater: a nationwide survey in Switzerland. Water Research, 175, 115708 (10 pp.). doi:10.1016/j.watres.2020.115708, Institutional Repository

Mercury (Hg) pollution threatens ecosystems and human health. Wastewater treatment plants (WWTPs) play a key role in limiting Hg discharges from wastewaters to rivers and lakes, but large-scale studies to estimate Hg loads and discharge at national levels are scarce. We assessed the concentration, flux, speciation, and removal of Hg in municipal wastewater throughout Switzerland by investigating 64 WWTPs in a pre-study and a subset of 28 WWTPs in the main study. We also studied the behavior and pathways of Hg along the various treatment steps in a state-of-the-art WWTP. The resulting dataset, representative of industrialized countries, provides an overview of (i) current Hg concentration ranges, (ii) average per capita loads, and (iii) wastewater Hg inputs into surface waters. The results allowed estimation of a total Hg (THg) load in Swiss wastewater of 130 ± 30 kg THg/year (15.7 mg/capita/y), of which 96 ± 4% is retained in sewage sludge. About 4.7 ± 0.5 kg THg/year (0.57 mg/capita/y) is discharged with the treated wastewater into surface waters. This corresponds to only 1.5-3% of the THg load carried by the major Swiss rivers, indicating that >95% of riverine Hg originates from other sources. Extrapolation to the population of Europe would yield a total amount of 11,700 kg THg/year in raw wastewater, with some 480 kg THg/year discharged to surface waters. Monomethyl mercury on average accounted for 0.23% of THg, and its fraction remained constant along the different treatment steps.
Svendsen, C., Walker, L. A., Matzke, M., Lahive, E., Harrison, S., Crossley, A., … Spurgeon, D. J. (2020). Key principles and operational practices for improved nanotechnology environmental exposure assessment. Nature Nanotechnology, 15, 731-742. doi:10.1038/s41565-020-0742-1, Institutional Repository

Nanotechnology is identified as a key enabling technology due to its potential to contribute to economic growth and societal well-being across industrial sectors. Sustainable nanotechnology requires a scientifically based and proportionate risk governance structure to support innovation, including a robust framework for environmental risk assessment (ERA) that ideally builds on methods established for conventional chemicals to ensure alignment and avoid duplication. Exposure assessment developed as a tiered approach is equally beneficial to nano-specific ERA as for other classes of chemicals. Here we present the developing knowledge, practical considerations and key principles need to support exposure assessment for engineered nanomaterials for regulatory and research applications.
ThomasArrigo, L. K., Bouchet, S., Kaegi, R., & Kretzschmar, R. (2020). Organic matter influences transformation products of ferrihydrite exposed to sulfide. Environmental Science: Nano, 7(11), 3405-3418. doi:10.1039/d0en00398k, Institutional Repository

In redox-dynamic environments, sorption to poorly-crystalline, nanometer-sized Fe(III)-(oxyhydr)oxides like ferrihydrite influences the biogeochemical cycling of nutrients and trace elements. Under sulfate-reducing conditions, the reductive dissolution of ferrihydrite leads to the release of associated constituents, which may be re-immobilized via sorption to secondary Fe minerals. To date, studies following the kinetics and transformation pathways of Fe(III)-(oxyhydr)oxides upon exposure to dissolved sulfide (S(-II)) have largely focused on pure Fe minerals. However, in nature, Fe(III)-(oxyhydr)oxides are often found in association with organic matter (OM). Because ferrihydrite-OM associations exhibit characteristics and biogeochemical reactivity differing from those of pure ferrihydrite, in this study, we compared sulfidization kinetics and transformation pathways of a pure ferrihydrite to those of ferrihydrite coprecipitated with contrasting organic ligands; polygalacturonic acid, galacturonic acid, and citric acid (C/Fe molar ratio ~0.55). Incorporating aqueous- and solid-phase S and Fe speciation analyses (via wet chemistry techniques and S and Fe X-ray absorption spectroscopy) in addition to X-ray diffraction and electron microscopy, we studied both rapid (<7 days) and long-term (12 months) mineral transformations as well as the impact of varying S(-II)/Fe molar ratios at neutral pH. Our results showed that at low S(-II)/Fe molar ratios (=0.1), poorly-crystalline Fe sulfide minerals (e.g. mackinawite) did not form in any (co)precipitate. In contrast, at higher S(-II)/Fe molar ratios (=0.5), mackinawite rapidly precipitated, with higher contributions detected in the coprecipitates than in the pure ferrihydrite. Aging of the samples led to further mineral transformations, including divergent pyrite and greigite precipitation, and an overall increase in the crystallinity of secondary mineral phases. Still, the fraction of residual ferrihydrite at 12 months was higher in the OM-containing coprecipitates, with the most ferrihydrite preservation observed in coprecipitates comprising carboxyl-poor ligands (galacturonic acid and citric acid). This suggests that the presence of OM inhibited S(-II)-induced ferrihydrite mineral transformations and that the composition of the associated OM influenced mineral transformation pathways. Collectively, these results suggest that further studies regarding sulfidization pathways should include OM in order to better represent environmental conditions.
Urstoeger, A., Wimmer, A., Kaegi, R., Reiter, S., & Schuster, M. (2020). Looking at silver-based nanoparticles in environmental water samples: repetitive cloud point extraction bridges gaps in electron microscopy for naturally occurring nanoparticles. Environmental Science and Technology, 54(19), 12063-12071. doi:10.1021/acs.est.0c02878, Institutional Repository

The growing use of silver-based nanoparticles (Ag-b-NPs) in everyday products goes hand in hand with their release into the environment, resulting in ng L–1 traces in natural water bodies. In order to assess their fate, possible transformations and ecotoxicology—essential information to proper risk assessment—particle size, shape, and chemical composition have to be determined. Transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDX) is a powerful tool for determining these particle characteristics, but it requires high particle concentrations in order to produce statistically reliable results. In this study, we will present the extraction of Ag-b-NPs at environmentally relevant concentrations down to 5 ng L–1 from artificial as well as environmental water samples via cloud point extraction on a repetitive basis. The combination with an on-grid centrifugation technique ensures an efficient concentration and deposition of the extracted particles onto the TEM grid for subsequent TEM-EDX measurements. Furthermore, electron microscopy investigations were supplemented by single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) measurements. Ag-b-NPs were successfully visualized and characterized at environmentally relevant concentrations of 5 ng L–1 with TEM-EDX and sp-ICP-MS measurements. Their size, shape, and chemical composition were not affected by the sample preparation.
Velimirovic, M., Wagner, S., Monikh, F. A., Uusimäki, T., Kaegi, R., Hofmann, T., & von der Kammer, F. (2020). Accurate quantification of TiO2 nanoparticles in commercial sunscreens using standard materials and orthogonal particle sizing methods for verification. Talanta, 215, 120921 (10 pp.). doi:10.1016/j.talanta.2020.120921, Institutional Repository

The implementation and enforcement of product labeling obligation as required, for example, by the cosmetic product regulation, needs simple and precise validated analytical methods. This also applies to the analysis of nanoparticles in products such as cosmetics. However, the provision of such methods is often hampered by inaccurate sizing due to unwanted nanoparticle changes, interference of matrix components with sizing and interactions between nanoparticles and analytical instrumentation. It is, therefore, necessary to develop appropriate sample preparation methods that preserve NP properties and reduce or remove matrix compounds that interfere with sizing. Further, accurate particle size analysis of samples containing unknown and possibly multiple nanoparticulate constituents is needed. In this study, we evaluated three sample preparation methods to identify and quantify TiO2 nanoparticles in sunscreens. Specifically, we used a combination of ultracentrifugation and hexane washing, thermal destruction of the matrix, and surfactant assisted particle extraction. The method accuracy was assessed by two internal reference samples: pristine TiO2 nanoparticles (NM104) and similar TiO2 nanoparticles dispersed in a sunscreen matrix. The PSDs were determined using an asymmetrical flow field-flow fractionation hyphenated with multi-angle light scattering and inductively coupled plasma-mass spectroscopy. Particle sizing was based on size calibration of the particle retention time in the AF4. Computation of radius of gyration from MALS data was used as an orthogonal particle sizing approach to verify ideal elution and particle size data from the AF4 calibration. Among the three tested sample preparation methods surfactant assisted particle extraction revealed TiO2 nanoparticle recoveries of above 90% and no increase in particle size due to sample preparation was observed. Finally, the sample preparation methods were applied to two commercial sunscreen samples revealing the existence of TiO2-NP < 100 nm. Conclusively, the surfactant assisted particle extraction method can provide valid data for TiO2-NPs in sunscreen and possibly for cosmetic samples of similar matrix.
Wielinski, J. J. (2020). Investigations into the fate of engineered transition metal nano particles during sewage sludge incineration (Doctoral dissertation). doi:10.3929/ethz-b-000473625, Institutional Repository

Engineered nanoparticles (ENP) are applied in consumer products and industrial processes to increase profitability and sustainability through reduced resource consumption, e.g., TiO2-NP in sun screens, ZnO-NP in cosmetics and paints or Ag-NP and CuO-NP as anti-microbial agents. However, critical discussions about unintended, adverse effects of ENP on humans, soil- and aquatic organisms have always accompanied their usage. Therefore, investigations into the fate of ENP after their use phase are necessary to enable a reliable assessment of the risks associated with the use of such novel materials. Previous research efforts showed that after usage, large shares of ENP applied in consumer products are discharged to wastewater and transported to wastewater treatment plants (WWTPs). WWTPs retain > 95% of ENP leading to their accumulation in sewage sludge. In Switzerland, sewage sludge is incinerated preferably in mono-combustion fluidized bed reactors (FBRs) and the resulting ashes are landfilled for resource recovery in the future. To contribute to a better understanding of the fate and behavior of ENP in the urban environment, the following research questions were addressed: (i) how can the kinetics of sewage sludge devolatilization be quantified, (ii) what chemical and physical transformations of ENP occur during the sewage sludge combustion, (iii) what are the possibilities of synchrotron hard X-ray chemical imaging to study transformation products of ENP, and lastly (iv) to what extent are ENP released from sewage sludge ash landfill sites? [...]

Künstlich produzierte Nanopartikel (NP) werden in Konsumgütern und industriellen Prozessen zur Steigerung von Effizienz und Nachhaltigkeit durch reduzierten Ressourceneinsatz verwendet, z.B. TiO2-NP in Sonnencreme, ZnO-NP in Kosmetika und Farbe oder Ag-NP und CuO-NP zu antimikrobiellen Zwecken. Allerdings ist stets vor ungewollten, nachteiligen Effekten solcher NP gegenüber Menschen, sowie Boden- und Wasserorganismen gewarnt worden. Daher sind Studien über die Transformation und den Verbleib von NP nach ihrer Nutzungsphase notwendig um die oben genannten Risiken der Nutzung solcher neuartigen Materialen zuverlässig abschätzen zu können. Vorangegangene Studien haben gezeigt, dass ein grosser Teil der NP in Konsumgütern in Abwasserkanäle entlassen wird und in Abwasserreinigungsanlangen (ARAs) gelangt. ARAs halten über 95% der einkommenden NP zurück, welche folglich im Faulschlamm aufkonzentriert werden. In der Schweiz wird Faulschlamm vorzugsweise in speziell dafür errichteten Wirbelbettreaktoren verbrannt und die anfallende Asche wird von Asche aus anderen Brennstoffen getrennt deponiert um daraus in der Zukunft Ressourcen rückzugewinnen.
Um ein besseres Verständnis des Verhaltens von NP in städtischen Abwassersystemen und insbesondere während der Klärschlammverbrennung zu gewinnen, wurden die folgenden Forschungsfragen adressiert: (i)Wie lässt sich die Verbrennungskinetik von Klärschlamm quantifizieren, (ii) welche physikalischen und chemischen Transformationsprozesse unterlaufen NP während der Klärschlammverbrennung, (iii) wie können Transformationsprodukte von NP mithilfe synchrotronbasierter, chemische Bildgebung identifiziert werden und (iv) wie gross ist das Freisetzungspotential von NP aus Klärschlammaschedeponien? [...]
Wielinski, J., Marafatto, F. F., Gogos, A., Scheidegger, A., Voegelin, A., Müller, C. R., … Kaegi, R. (2020). Synchrotron hard X-ray chemical imaging of trace element speciation in heterogeneous samples: development of criteria for uncertainty analysis. Journal of Analytical Atomic Spectrometry, 35, 567-579. doi:10.1039/C9JA00394K, Institutional Repository

Synchrotron hard X-ray spectroscopy with focussing optics allows recording X-ray fluorescence (XRF) maps at energies around element specific X-ray absorption edges. Stacking multiple XRF maps along the energy axis yields chemical images that contain spatially resolved information on the speciation of the absorber in the sample matrix at the micrometre scale. Short dwell times needed to keep measurement time and radiation-induced sample changes within acceptable limits result in spectral noise that affects the uncertainty in data analysis. In this study, we develop a model to quantify the uncertainty associated with the processing of XRF image stacks using Bayesian inference. To demonstrate the potential of our approach, the model is applied to stacks of XRF maps collected around the copper (Cu) K-edge (pixel size: 3 × 3 μm2, map sizes: 500 × 500 μm2). The investigated samples include digested sewage sludge spiked with either CuO nanoparticles (NP) or dissolved CuSO4 and their corresponding ashes obtained through incineration. The chemical imaging data reveal differences in species distribution between sludge spiked with CuO NP or dissolved Cu. These differences disappear during the incineration process and the resulting ashes exhibit almost identical Cu species distribution. The uncertainty analysis approach developed in this study can be used for data interpretation, but can also be used for the planning of chemical imaging experiments at synchrotron beamlines.
Wigger, H., Kägi, R., Wiesner, M., & Nowack, B. (2020). Exposure and possible risks of engineered nanomaterials in the environment - current knowledge and directions for the future. Reviews of Geophysics, 58(4), e2020RG000710 (25 pp.). doi:10.1029/2020RG000710, Institutional Repository

The consequences that engineered nanomaterials (ENMs) may cause in the environment have been under investigation for more than 15 years. Hundreds of millions of euros/dollars have been invested into safety issues of ENMs, and much progress has been made in the understanding of their fate and effects in the environment. After an initial phase of "observing the effects," research has shifted toward elucidating the mechanisms of fate and ecotoxicological effects. This also included a stronger focus on exposure issues and the development of analytical methods and computational models to predict exposure. First environmental risk assessments for ENM were performed, and much progress has been achieved on the way to nanospecific and material‐specific assessments. The release of ENM from products and their transformation in technical and natural compartments profoundly affect the form in which the ENMs are present in the environment. A crucial aspect in all areas is if there are truly nanospecific issues of the novel‐added functionalities of ENM that are different from dissolved metals, larger particles, or natural particles. This review outlines progress in understanding the environmental dimensions of ENMs and areas that merit further investigation: To what extent are ENMs different from their natural counterparts and how "long" do we need to track them in natural and technical systems? A major challenge will be in developing methods for studying particle‐mediated processes and their effects on ecosystems and organisms in a more general sense, going beyond just ENM, for example, to natural nanoparticles, microplastics, and extracellular vesicles.
Xu, J., Avellan, A., Li, H., Clark, E. A., Henkelman, G., Kaegi, R., & Lowry, G. V. (2020). Iron and sulfur precursors affect crystalline structure, speciation, and reactivity of sulfidized nanoscale zerovalent iron. Environmental Science and Technology, 54(20), 13294-13303. doi:10.1021/acs.est.0c03879, Institutional Repository

The reactivity of sulfidized nanoscale zerovalent iron (SNZVI) is affected by the amount and species of sulfur in the materials. Here, we assess the impact of the Fe (Fe2+ and Fe3+) and S (S2O42-, S2-, and S62-) precursors used to synthesize both NZVI and SNZVI on the resulting physicochemical properties and reactivity and selectivity with water and trichloroethene (TCE). X-ray diffraction indicated that the Fe precursors altered the crystalline structure of both NZVI and SNZVI. The materials made from the Fe3+ precursor had an expanded lattice in the Fe0 body-centered-cubic (BCC) structure and lower electron-transfer resistance, providing higher reactivity with water (∼2-3 fold) and TCE (∼5-13 fold) than those made from an Fe2+ precursor. The choice of the S precursor controlled the S speciation in the SNZVI particles, as indicated by X-ray absorption spectroscopy. Iron disulfide (FeS2) was the main S species of SNZVI made from S2O42-, whereas iron sulfide (FeS) was the main S species of SNZVI made from S2-/S62-. The former SNZVI was more hydrophobic, reactive with, and selective for TCE compared to the latter SNZVI. These results suggest that the Fe and S precursors can be used to select the conditions of the synthesis process and provide selected physicochemical properties (e.g., S speciation, hydrophobicity, and crystalline structure), reactivity, and selectivity of the SNZVI materials.
Xu, J., Avellan, A., Li, H., Liu, X., Noël, V., Lou, Z., … Lowry, G. V. (2020). Sulfur loading and speciation control the hydrophobicity, electron transfer, reactivity, and selectivity of sulfidized nanoscale zerovalent iron. Advanced Materials, 32(17), 1906010 (10 pp.). doi:10.1002/adma.201906910, Institutional Repository

Sulfidized nanoscale zerovalent iron (SNZVI) is a promising material for groundwater remediation. However, the relationships between sulfur content and speciation and the properties of SNZVI materials are unknown, preventing rational design. Here, the effects of sulfur on the crystalline structure, hydrophobicity, sulfur speciation, corrosion potential, and electron transfer resistance are determined. Sulfur incorporation extended the nano-Fe0 BCC lattice parameter, reduced the Fe local vacancies, and lowered the resistance to electron transfer. Impacts of the main sulfur species (FeS and FeS2) on hydrophobicity (water contact angles) are consistent with density functional theory calculations for these FeSx phases. These properties well explain the reactivity and selectivity of SNZVI during the reductive dechlorination of trichloroethylene (TCE), a hydrophobic groundwater contaminant. Controlling the amount and speciation of sulfur in the SNZVI made it highly reactive (up to 0.41 L m-2 d-1) and selective for TCE degradation over water (up to 240 moles TCE per mole H2O), with an electron efficiency of up to 70%, and these values are 54-fold, 98-fold, and 160-fold higher than for NZVI, respectively. These findings can guide the rational design of robust SNZVI with properties tailored for specific application scenarios.
Zeumer, R., Hermsen, L., Kaegi, R., Kühr, S., Knopf, B., & Schlechtriem, C. (2020). Bioavailability of silver from wastewater and planktonic food borne silver nanoparticles in the rainbow trout Oncorhynchus mykiss. Science of the Total Environment, 706, 135695 (12 pp.). doi:10.1016/j.scitotenv.2019.135695, Institutional Repository

Silver nanoparticles (AgNPs) are present in a wide field of applications and consumer products and are likely to be released into the environment, mainly via urban and industrial sewage due to their extensive use. Even though AgNPs are mostly retained within the sludge of wastewater treatment plants (WWTPs), a small amount of mainly sulfidized particles still enters the aquatic environment, where they can be taken up by various aquatic organisms and transferred along the food chain. In this study, uptake and bioavailability of Ag from AgNPs following aqueous and dietary exposure were investigated in the rainbow trout Oncorhynchus mykiss. AgNPs in the effluent of model WWTPs and in tap water were used to perform aqueous exposure studies. No significant Ag uptake into the gills and carcass of the analyzed fish could be found for wastewater-borne AgNPs. However, when added to tap water at a concentration of 12.4 μg L-1, a maximum total Ag tissue concentrations of around 100 μg kg-1 and 50 μg kg-1 in gills and carcass were measured, respectively. For the dietary exposure studies, freshwater zooplankton was exposed to AgNPs, and used for the preparation of food pellets with a total Ag concentration of 121.5 μg kg-1. During the feeding study with rainbow trout significant total Ag concentrations up to 34.3 μg kg-1 could be found in the digestive tract. However, only a limited transfer of Ag through the intestinal walls into the carcass could be detected. AgNPs in plankton and WWTP effluent were characterized by transmission electron microscopy (TEM) in combination with energy dispersive X-ray spectroscopy (EDX) and found to be sulfidized. This transformation most presumably has led to their limited bioavailability for fish. The results emphasize the importance of realistic test conditions for the risk assessment of AgNPs by the use of environmental matrices.
Aeppli, M., Vranic, S., Kaegi, R., Kretzschmar, R., Brown, A. R., Voegelin, A., … Sander, M. (2019). Decreases in iron oxide reducibility during microbial reductive dissolution and transformation of ferrihydrite. Environmental Science and Technology, 53(15), 8736-8746. doi:10.1021/acs.est.9b01299, Institutional Repository

Ferrous iron formed during microbial ferric iron reduction induces phase transformations of poorly crystalline into more crystalline and thermodynamically more stable iron (oxyhydr)oxides. Yet, characterizing the resulting decreases in the reactivity of the remaining oxide ferric iron toward reduction (i.e., its reducibility) has been challenging. Here, we used the reduction of six-line ferrihydrite by Shewanella oneidensis MR-1 as a model system to demonstrate that mediated electrochemical reduction (MER) allows directly following decreases in oxide ferric iron reducibility during the transformation of ferrihydrite into goethite and magnetite which we characterized by X-ray diffraction analysis and transmission electron microscopy imaging. Ferrihydrite was fully reducible in MER at both pHMER of 5.0 and 7.5. Decreases in iron oxide reducibility associated with ferrihydrite transformation into magnetite were accessible at both pHMER because the formed magnetite was not reducible under either of these conditions. Conversely, decreases in iron oxide reducibility associated with goethite formation were apparent only at the highest tested pHMER of 7.5 and thus the thermodynamically least favorable conditions for iron oxide reductive dissolution. The unique capability to adjust the thermodynamic boundary conditions in MER to the specific reducibilities of individual iron (oxyhydr)oxides makes this electrochemical approach broadly applicable for studying changes in iron oxide reducibility in heterogeneous environmental samples such as soils and sediments.
Aeppli, M., Kaegi, R., Kretzschmar, R., Voegelin, A., Hofstetter, T. B., & Sander, M. (2019). Electrochemical analysis of changes in iron oxide reducibility during abiotic ferrihydrite transformation into goethite and magnetite. Environmental Science and Technology, 53(7), 3568-3578. doi:10.1021/acs.est.8b07190, Institutional Repository

Electron transfer to ferric iron in (oxyhydr-)oxides (hereafter iron oxides) is a critical step in many processes that are central to the biogeochemical cycling of elements and to pollutant dynamics. Understanding these processes requires analytical approaches that allow for characterizing the reactivity of iron oxides toward reduction under controlled thermodynamic boundary conditions. Here, we used mediated electrochemical reduction (MER) to follow changes in iron oxide reduction extents and rates during abiotic ferrous iron-induced transformation of six-line ferrihydrite. Transformation experiments (10 mM ferrihydrite-FeIII) were conducted over a range of solution conditions (pHtrans = 6.50 to 7.50 at 5 mM Fe2+ and for pHtrans = 7.00 also at 1 mM Fe2+) that resulted in the transformation of ferrihydrite into thermodynamically more stable goethite or magnetite. The changes in iron oxide mineralogy during the transformations were quantified using X-ray diffraction analysis. MER measurements on iron oxide suspension aliquots collected during the transformations were performed over a range of pHMER at constant applied reduction potential. The extents and rates of iron oxide reduction in MER decreased with decreasing reaction driving force resulting from both increasing pHMER and increasing transformation of ferrihydrite into thermodynamically more stable iron oxides. We show that the decreases in iron oxide reduction extents and rates during ferrihydrite transformations can be linked to the concurrent changes in iron oxide mineralogy.
Bakshi, M., Liné, C., Bedolla, D. E., Stein, R. J., Kaegi, R., Sarret, G., … Larue, C. (2019). Assessing the impacts of sewage sludge amendment containing nano-TiO2 on tomato plants: a life cycle study. Journal of Hazardous Materials, 369, 191-198. doi:10.1016/j.jhazmat.2019.02.036, Institutional Repository

Increasing evidence indicates the presence of engineered nanoparticles (ENPs) in sewage sludge derived from wastewater treatment. Land application of sewage sludge is, therefore, considered as an important pathway for ENP transfer to the environment. The aim of this work was to understand the effects of sewage sludge containing nano-TiO2 on plants (tomato) when used as an amendment in agricultural soil. We assessed developmental parameters for the entire plant life cycle along with metabolic and bio-macromolecule changes and titanium accumulation in plants. The results suggest that the sewage sludge amendment containing nano-TiO2 increased plant growth (142% leaf biomass, 102% fruit yield), without causing changes in biochemical responses, except for a 43% decrease in leaf tannin concentration. Changes in elemental concentrations (mainly Fe, B, P, Na, and Mn) of plant stem, leaves and, to a lesser extent fruits were observed. Fourier-transformed infrared analysis showed maximum changes in plant leaves (decrease in tannins and lignins and increase in carbohydrates) but no change in fruits. No significant Ti enrichment was detected in tomato fruits. In conclusion, we evidenced no acute toxicity to plants and no major implication for food safety after one plant life cycle exposure.
Dörner, L., Cancellieri, C., Rheingans, B., Walter, M., Kägi, R., Schmutz, P., … Jeurgens, L. P. H. (2019). Cost-effective sol-gel synthesis of porous CuO nanoparticle aggregates with tunable specific surface area. Scientific Reports, 9, 11758 (15 pp.). doi:10.1038/s41598-019-48020-8, Institutional Repository

CuO nanoparticles (NPs) are applied in various key technologies, such as catalysis, energy conversion, printable electronics and nanojoining. In this study, an economic, green and easy-scalable sol-gel synthesis method was adopted to produce submicron-sized nanoporous CuO NP aggregates with a specific surface area > 18 m²/g. To this end, a copper-carbonate containing precursor was precipitated from a mixed solution of copper acetate and ammonia carbonate and subsequently calcinated at T ≥ 250 °C. The thus obtained CuO nanopowder is composed of weakly-bounded agglomerates, which are constituted of aggregated CuO NPs with a tunable size in the range of 100–140 nm. The CuO aggregates, in turn, are composed of equi-axed primary crystallites with a tunable crystallite size in the range of 20–40 nm. The size and shape of the primary CuO crystallites, as well as the nanoporosity of their fused CuO aggregates, can be tuned by controlled variation of the degree of supersaturation of the solution via the pH and the carbonate concentration. The synthesized submicron-sized CuO aggregates can be more easily and safely processed in the form of a solution, dispersion or paste than individual NPs, while still offering the same enhanced reactivity due to their nanoporous architecture.
Gogos, A., Wielinski, J., Voegelin, A., Emerich, H., & Kaegi, R. (2019). Transformation of cerium dioxide nanoparticles during sewage sludge incineration. Environmental Science: Nano, 6, 1765-1776. doi:10.1039/C9EN00281B, Institutional Repository

Production volumes of cerium dioxide nanoparticles (CeO2 NP) are predicted to increase in the near future, which will result in increasing amounts of CeO2 NP discharged into wastewater systems and their accumulation in the sewage sludge. At the same time, thermal treatments of sewage sludge, especially incineration, are gaining in importance. Therefore, knowledge on the physical–chemical transformations of CeO2 NP during wastewater treatment and sludge incineration is critical for assessing possible (eco-) toxicological effects related to the increased use of CeO2 NP. We, thus, incinerated unspiked municipal sewage sludge as well as sludge spiked with CeO2 of different particle sizes (4 nm (CeO2-s1), 26 nm (CeO2-s2) and >16 μm (CeO2-s3)) in a pilot fluidized bed reactor to investigate the (size dependent) transformation of CeO2 under conditions mimicking full-scale incineration facilities. We used Ce K- and LIII-edge X-ray absorption spectroscopy (XAS) complemented by analytical electron microscopy to assess the changes in Ce speciation and to characterize the morphology of the pristine and the transformed Ce-(nano)particles. After one week of incubation in digested sludge under anaerobic conditions, CeO2-s1 already showed partial reduction (≈40%) to a Ce(III)-phase. Cerium dioxide of larger particle size (CeO2-s2 and -s3) was less reactive and did not show any detectable reduction within the same reaction time. Incineration of the sludge in general led to a further reduction of Ce, irrespective of whether the Ce was spiked (CeO2-s1, CeO2-s2, CeO2-s3) or already present in the sludge. Reduction during incineration was nearly complete for CeO2-s1 but much less pronounced for CeO2-s2 and -s3. Ce(IV) in larger (primary-) particle sizes thus was more resistant to reduction during anaerobic digestion and incineration. In addition, elemental distribution maps of the CeO2-s1 fly ash revealed elevated Ce signal intensities evenly distributed over areas of several 100 nm. The complementary results obtained from spectroscopic and microscopic analyses indicate that incineration led to the reductive decomposition of the initial CeO2-s1 NP and the sequestration of Ce(III) into a mineralogical phase with probably allanite-like local Ce(III) coordination. Our results, thus, highlight the importance of particle size and the surrounding matrix both affecting the transformation of CeO2 during sewage sludge incineration.
Hagemann, N., Bucheli, T. D., Schmidt, H. P., Kägi, R., Böhler, M., & McArdell, C. S. (2019). Aktivkohle - Made in Switzerland!. Aqua & Gas, 99(1), 32-38. , Institutional Repository

Die Elimination von Mikroverunreinigungen in der Abwasserreinigung mit Aktivkohle oder Ozon ist eine wichtige Massnahme zum vorbeugenden Schutz der Gewässer und der Trinkwasserressourcen der Schweiz. Während der Einsatz von Ozon mit einem hohen Energieverbrauch einhergeht, führt der Einsatz von Aktivkohle andernorts zu negativen Umweltauswirkungen, da die Aktivkohle zum Teil aus fossilen Ausgangsstoffen wie Stein- oder Braunkohle hergestellt und zudem über weite Strecken transportiert wird. Aktivkohlen mit sehr guten Eliminationsleistungen könnten aber auch in der Schweiz aus einheimischen erneuerbaren Roh- und Reststoffen hergestellt werden.
Hoppe, M., Schlich, K., Wielinski, J., Köser, J., Rückamp, D., Kaegi, R., & Hund-Rinke, K. (2019). Long-term outdoor lysimeter study with cerium dioxide nanomaterial. NanoImpact, 14, 100170 (9 pp.). doi:10.1016/j.impact.2019.100170, Institutional Repository

Fate and impact of cerium dioxide nanomaterials (CeO2 NM) in soil remains uncertain. Most of the recent environmental studies used high doses of CeO2 NM in short-term laboratory experiments and stated soil as large sink for NM. Recent studies covering the life cycle of plants found evidence for particle uptake in crop plants, and triggered concern about NM entering the food chain. Here, we present a 25 months outdoor lysimeter study that investigates the translocation, biological impact, and transformation of CeO2 NM in soils cultivated with different crops (wheat (Triticum aestivum L.), canola (Brassica napus L.), and barley (Hordeum vulgare L.)). Low doses of CeO2 NM (NM-212, 10 and 50 mg CeO2 NM kg−1 soil) were applied to a Cambisol by sewage sludge or artificial rainwater. To simulate ploughing, the CeO2 NM was mixed into the first 20 cm of the lysimeter soil. Three weeks after the NM application by sewage sludge and five days after the latest NM application by artificial rainwater wheat seeds were sown.
We found no vertical Ce translocation to deeper soil layers as well as negligible release of Ce into percolating water, confirming that soil is a sink for CeO2 NM. Furthermore, no inhibition of the NM sensitive ammonium oxidizing bacteria (AOB) was observed which implies a low bioavailability of CeO2 NM in soil. The detected Ce root uptake for canola (Ce < 35.7 mg kg−1) and barley (Ce < 61.8 mg kg−1) indicates that physico-chemical conditions in the rhizosphere or the aging of the NM in soil can remobilize the applied CeO2 NM to some extent. One can speculate that the obtained reduction of Ce4+ to Ce3+ (≈ 50% after 25 months) was coupled to different conditions (ionic strength, pH, water content, soil organic matter content) in the rhizosphere and necessary for the root accumulation of Ce.
Due to negligible mobility in the soil-water interface, as well as non-toxicity to AOB, the environmental risk of the tested CeO2 NM appears to be low, compared to other highly mobile emergent pollutants. Nonetheless, further long-term investigations need to focus on the speciation and localization of NM in plants to clarify uptake and impact of NM to crops.
Salas, P., Odzak, N., Echegoyen, Y., Kägi, R., Sancho, M. C., & Navarro, E. (2019). The role of size and protein shells in the toxicity to algal photosynthesis induced by ionic silver delivered from silver nanoparticles. Science of the Total Environment, 692, 233-239. doi:10.1016/j.scitotenv.2019.07.237, Institutional Repository

Because of their biocide properties, silver nanoparticles (AgNPs) are present in numerous consumer products. The biocidal properties of AgNPs are due to both the interactions between AgNP and cell membranes and the release of dissolved silver (Ag+). Recent studies emphasized the role of different nanoparticle coatings in complexing and storing Ag+. In this study, the availability of dissolved silver in the presence of algae was assessed for three AgNPs with different silver contents (59%, 34% and 7% of total Ag), silver core sizes and casein shell thicknesses. The impact of ionic silver on the photosynthetic yield of Chlamydomonas reinhardtii was used as a proxy to estimate the amount of ionic silver toxically active during in vivo assays. The results showed that cysteine, a strong silver ligand, mitigated the toxicity of AgNPs in all cases, demonstrating the key role of Ag+ in this toxicity. The results showed that the AgNPs presenting an intermediate level of silver (34%) were 10 times more effective in terms of total mass (EC50 ten times smaller) than those presenting more (59%) or less (7%) silver. The higher toxicity was due to the higher release of Ag+ under biotic conditions due to the high surface/mass ratio of the nanoparticle silver core. Protein shells played a minor role in altering the availability of Ag+, probably acting as intermediate reservoirs. This study highlighted the utility of a very sensitive biological endpoint (i.e., algal photosynthesis) for the optimization of ionic silver delivery by nanomaterials.
Surette, M. C., Nason, J. A., & Kaegi, R. (2019). The influence of surface coating functionality on the aging of nanoparticles in wastewater. Environmental Science: Nano, 6(8), 2470-2483. doi:10.1039/C9EN00376B, Institutional Repository

Efforts to predict the environmental fate of engineered nanomaterials (ENMs) are frequently based on the physiochemical properties and behavior of the ENMs in their pristine, “as-produced” state. However, it is well-established that ENMs can be physically, biologically, and chemically transformed, resulting in altered physiochemical properties and behavior. Wastewater treatment plants (WWTPs) represent an important stage in an ENM's life-cycle where they can be transformed. To better understand the properties of ENMs discharged from WWTPs into surface waters, we investigated how the transformation processes of aggregation and corona formation are influenced by the surface coating applied to ENMs during their manufacture. Using 40 nm gold nanoparticles coated with polyethylene glycol, lipoic acid, or branched polyethylenimine as model ENMs, batch experiments were performed to investigate aggregation and corona formation during the primary clarification and activated sludge treatment stages. A tangential flow filtration system was used to evaluate if the initial transformations were altered as the aquatic chemistry of the background matrix was changed, mimicking the varying conditions ENMs would experience during transport through a WWTP. Using a combination of corroborative techniques including dynamic light scattering, phase analysis light scattering, ultraviolet-visible light spectroscopy, and transmission electron microscopy, we find that the model ENMs aggregated in each wastewater matrix, regardless of the initial surface coating. Differences in the UV-vis spectra indicate that the nature of the corona acquired by the ENMs differed as a function of the surface coating of the pristine ENMs. In addition, initial ENM transformations during exposure to the influent wastewater persisted even as the background matrix changed. These results support the finding that ENMs discharged from WWTPs will not resemble their pristine analogs. Furthermore, the corona acquired by ENMs in WWTPs may vary in relation to their pristine properties and be dictated by conditions during early stage exposures.
ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2019). Ferrihydrite growth and transformation in the presence of ferrous iron and model organic ligands. Environmental Science and Technology, 53(23), 13636-13647. doi:10.1021/acs.est.9b03952, Institutional Repository

Ferrihydrite (Fh) is a poorly crystalline Fe(III)-oxyhydroxide found in abundance in soils and sediments. With a high specific surface area and sorption capacity at circumneutral pH, ferrihydrite is an important player in the biogeochemical cycling of nutrients and trace elements in redox-dynamic environments. Under reducing conditions, exposure to Fe(II) induces mineral transformations in ferrihydrite; the extent and trajectory of which may be greatly influenced by organic matter (OM). However, natural OM is heterogeneous and comprises a range of molecular weights (MWs) and varied functional group compositions. To date, the impact that the chemical composition of the associated OM has on Fe(II)-catalyzed mineral transformations is not clear. To address this knowledge gap, we coprecipitated ferrihydrite with model organic ligands selected to cover a range of MWs (25 000–50 000 vs <200 Da) as well as carboxyl content (polygalacturonic acid (PGA) > citric acid (CA) > galacturonic acid (GA)). Coprecipitates (C:Fe ≈ 0.6) were reacted with 1 mM 57Fe(II) for 1 week at pH 7, with time-resolved solid-phase analysis (via X-ray diffraction, X-ray absorption spectroscopy, and electron microscopy) revealing that all ligands inhibited Fe(II)-catalyzed ferrihydrite mineral transformations and the formation of crystalline secondary mineral phases compared to a pure ferrihydrite. For carboxyl-rich coprecipitates (Fh-PGA and Fh-CA), mineral transformations were less inhibited than in the carboxyl poor Fh-GA, and a crystalline lepidocrocite "shell" was formed surrounding the residual ferrihydrite core. However, Fe isotope analysis revealed that all coprecipitates underwent near complete atom exchange. Collectively, our results highlight that ferrihydrite is indeed an active mineral phase in redox-dynamic environments, but that its stability under reducing conditions, and thus capacity for nutrient and trace element retention, depends on the chemical characteristic of the associated OM, specifically OM-induced changes in the particle surface charge and the distribution of organic functional groups.
Uusimaeki, T., Wagner, T., Lipinski, H. G., & Kaegi, R. (2019). AutoEM: a software for automated acquisition and analysis of nanoparticles. Journal of Nanoparticle Research, 21(6), 122 (11 pp.). doi:10.1007/s11051-019-4555-9, Institutional Repository

The era of research on (engineered) nanomaterials (NM) has been thriving for more than a decade and has delivered many beneficial applications, but also raised concerns about potential negative impacts on human health and ecosystems. The precautionary principle, hence, calls for a regulation of certain types of NM, which in consequence requires their unambiguous identification. Most of the currently available definitions of NM rely on an evaluation of the size of the constituent particles and therefore methods have to be developed to measure this parameter. Transmission electron microscopy (TEM) is one of the most promising techniques, as its resolving power well covers the nanosize range. However, limited automation of TEM analyses and possible user bias are major drawbacks of the technique and currently put severe constraints on its broader applications in nanometrology.
Therefore, the goal of this study was to develop a software code, referred to as AutoEM, to automatically acquire TEM images, measure particle sizes and extract the respective particle size distributions (PSD) of (nano)-materials. The AutoEM software also incorporates methods for elemental analyses of individual particles using electron energy loss and energy dispersive X-ray spectroscopy (EELS/EDX) allowing the extraction of element-specific PSDs. Additionally automated acquisition of energy-filtered images (EFTEM) is implemented in the AutoEM software, which can be used, e.g., to derive thickness maps and, thus, to evaluate the thickness of individual (plate-like) particles.
Verleysen, E., Wagner, T., Lipinski, H. G., Kägi, R., Koeber, R., Boix-Sanfeliu, A., … Mast, J. (2019). Evaluation of a TEM based approach for size measurement of particulate (nano)materials. Materials, 12(14), 2274 (20 pp.). doi:10.3390/ma12142274, Institutional Repository

An approach for the size measurement of particulate (nano)materials by transmission electron microscopy was evaluated. The approach combines standard operating procedures for specimen preparation, imaging, and image analysis, and it was evaluated on a series of certified reference materials and representative test materials with varying physical properties, including particle size, shape, and agglomeration state. The measurement of the median value of the minimal external particle diameter distribution was intra-laboratory validated. The validation study included an assessment of the limit of detection, working range, selectivity, precision, trueness, robustness, and ruggedness. An uncertainty that was associated to intermediate precision in the range of 1–7% and an expanded measurement uncertainty in the range of 7–20% were obtained, depending on the material and image analysis mode. No bias was observed when assessing the trueness of the approach on the certified reference materials ERM-FD100 and ERM-FD304. The image analysis method was validated in an inter-laboratory study by 19 laboratories, which resulted in a within-laboratory precision in the range of 2–8% and a between-laboratory precision of between 2% and 14%. The automation and standardization of the proposed approach significantly improves labour and cost efficiency for the accurate and precise size measurement of the particulate materials. The approach is shown to be implementable in many other electron microscopy laboratories.
Voegelin, A., Senn, A. C., Kaegi, R., & Hug, S. J. (2019). Reductive dissolution of As(V)-bearing Fe(III)-precipitates formed by Fe(II) oxidation in aqueous solutions. Geochemical Transactions, 20(2) (13 pp.). doi:10.1186/s12932-019-0062-2, Institutional Repository

Iron(III)-precipitates formed by the oxidation of dissolved Fe(II) are important sorbents for major and trace elements in aquatic and terrestrial systems. Their reductive dissolution in turn may result in the release of associated elements. We examined the reductive dissolution kinetics of an environmentally relevant set of Fe(II)-derived arsenate-containing Fe(III)-precipitates whose structure as function of phosphate (P) and silicate (Si) content varied between poorly-crystalline lepidocrocite, amorphous Fe(III)-phosphate, and Si-containing ferrihydrite. The experiments were performed with 0.2–0.5 mM precipitate-Fe(III) using 10 mM Na-ascorbate as reductant, 5 mM bipyridine as Fe(II)-complexing ligand, and 10 mM MOPS/5 mM NaOH as pH 7.0 buffer. Times required for the dissolution of half of the precipitate (t50%) ranged from 1.5 to 39 h; spanning a factor 25 range. At loadings up to ~ 0.2 P/Fe (molar ratio), phosphate decreased the t50% of Si-free precipitates, probably by reducing the crystallinity of lepidocrocite. The reductive dissolution of Fe(III)-phosphates formed at higher P/Fe ratios was again slower, possibly due to P-inhibited ascorbate binding to precipitate-Fe(III). The slowest reductive dissolution was observed for P-free Si-ferrihydrite with ~ 0.1 Si/Fe, suggesting that silicate binding and polymerization may reduce surface accessibility. The inhibiting effect of Si was reduced by phosphate. Dried-resuspended precipitates dissolved 1.0 to 1.8-times more slowly than precipitates that were kept wet after synthesis, most probably because drying enhanced nanoparticle aggregation. Variations in the reductive dissolution kinetics of Fe(II) oxidation products as reported from this study should be taken into account when addressing the impact of such precipitates on the environmental cycling of co-transformed nutrients and contaminants.
Wielinski, J., Gogos, A., Voegelin, A., Müller, C., Morgenroth, E., & Kaegi, R. (2019). Transformation of nanoscale and ionic Cu and Zn during the incineration of digested sewage sludge (biosolids). Environmental Science and Technology, 53(20), 11704-11713. doi:10.1021/acs.est.9b01983, Institutional Repository

Engineered nanoparticles (NP) discharged to sewers are efficiently retained by wastewater treatment plants and accumulate in the sewage sludge, which is commonly digested. The resulting biosolids are either used as fertilizer or incinerated. In this study, we address the transformation of Cu and Zn during sewage sludge incineration and evaluate whether the form of Cu or Zn (nanoparticulate versus dissolved) added to the digested sewage sludge affects the fate of the metals during incineration. We spiked CuO-NP, dissolved CuSO4, ZnO-NP, or dissolved ZnSO4 into anaerobically digested sewage sludge to reach Cu and Zn concentrations of ≈2500 and ≈3700 mg/kg and maintained the sludge under mesophilic, anaerobic conditions for 24 h. Subsequently, the sludge was incinerated in a pilot fluidized bed reactor. The speciation of Cu and Zn in the sludge, derived from X-ray absorption spectroscopy measurements, was dominated by sulfidic species, with >90% of Cu and >60% of Zn coordinated to reduced sulfur groups. In the ash, both Cu (>60%) and Zn (≈100%) were coordinated to oxygen. The chemical speciation of Cu and Zn in the ashes was independent of whether they were spiked in the dissolved or nanoparticulate form and closely matched the speciation of Cu and Zn observed in ashes from full-scale incinerators.
Xu, J., Wang, Y., Weng, C., Bai, W., Jiao, Y., Kaegi, R., & Lowry, G. V. (2019). Reactivity, selectivity, and long-term performance of sulfidized nanoscale zerovalent iron with different properties. Environmental Science and Technology, 53(10), 5936-5945. doi:10.1021/acs.est.9b00511, Institutional Repository

Sulfidized nanoscale zerovalent iron (SNZVI) has desirable properties for in situ groundwater remediation. However, there is limited understanding of how the sulfidation type and particle properties affect the reactivity and selectivity of SNZVI toward groundwater contaminants, or how reactivity changes as the particles age. Here, SNZVI synthesized by either a one-step (SNZVI-1) or two-step (SNZVI-2) process were characterized, and the reactivity of both fresh and aged (1d to 60 d) nanoparticles was assessed. The measured S/Fe ratio was 5.4 ± 0.5 mol % for SNZVI-1 and 0.8 ± 0.1 mol % for SNZVI-2. XPS analysis indicates S2-, S22-, and Sn2- species on the surface of both SNZVI-1 and SNZVI-2, while S22- is the dominant species inside of the SNZVI nanoparticles. SNZVI-1 particles were hydrophobic (contact angle = 103 ± 3°), while the other materials were hydrophilic (contact angles were 18 ± 2° and 36 ± 3° for NZVI and SNZVI-2, respectively). SNZVI-1, with greater S content and hydrophobicity, was less reactive with water than either NZVI or SNZVI-2 over a 60 d period, resulting in less H2 evolution. It also had the highest reactivity with TCE and the lowest reactivity with nitrate, consistent with its higher hydrophobicity. In contrast, both NZVI and SNZVI-2 were reactive with both TCE and nitrate. Both types of SNZVI remained more reactive after aging in water over 60 d than NZVI. These data suggest that the properties of the SNZVI made from a one-step synthesis procedure may provide better reactivity, selectivity, and longevity than that made from a two-step process.
Zheng, Y., Mutzner, L., Ort, C., Kaegi, R., & Gottschalk, F. (2019). Modelling engineered nanomaterials in wet-weather discharges. NanoImpact, 16, 100188 (8 pp.). doi:10.1016/j.impact.2019.100188, Institutional Repository

The impacts of the unintended release of engineered nanomaterials (ENMs) and the resulting exposure to the ecosystems are still poorly understood and intensively debated. In current mass flow models, a global transfer coefficient is used to account for ENMs discharged from sewer systems to surface waters during rain events.
However, different types of sewer systems and specific ENM applications likely require a more elaborate approach to quantify ENM loads entering surface waters during rain events. Therefore, we evaluated the impact of distinguishing between different application areas of ENMs (indoor/outdoor) and different types of sewer systems (combined/separate) on the loads of selected ENMs passing through wastewater systems and reaching the surface water. We applied a dynamic mass flow analysis to eight substances (TiO2, ZnO, Ag, SiO2, FeOx, CuO, CeO2 and carbon black) for six different sewer system configurations. To estimate the runoff from streets and facades, we used a hydrological model developed for dissolved substances. For areas with separate sewer systems only and ENMs predominantly used in and released from outdoor applications (e.g. CuO, carbon black), up to ~80% of the annual loads entering the sewer systems never reach a sewage treatment plant. Those ENMs are directly discharged to surface waters via stormwater outlets. For combined sewer systems and ENMs mainly applied indoors (e.g. Ag, ZnO), the percentage of ENM bypassing sewage treatment plants remains below 2%. Although the model is setup for Switzerland and other geographical areas will show for example different rain characteristics, the relative importance of the different release pathways will broadly remain the same and the results should, therefore, be transferrable to other countries.
Giese, B., Klaessig, F., Park, B., Kaegi, R., Steinfeldt, M., Wigger, H., … Gottschalk, F. (2018). Risks, release and concentrations of engineered nanomaterial in the environment. Scientific Reports, 8(1), 1565 (8 pp.). doi:10.1038/s41598-018-19275-4, Institutional Repository

For frequently used engineered nanomaterials (ENMs) CeO2-, SiO2-, and Ag, past, current, and future use and environmental release are investigated. Considering an extended period (1950 to 2050), we assess ENMs released through commercial activity as well as found in natural and technical settings. Temporal dynamics, including shifts in release due to ENM product application, stock (delayed use), and subsequent end-of-life product treatment were taken into account. We distinguish predicted concentrations originating in ENM use phase and those originating from end-of-life release. Furthermore, we compare Ag- and CeO2-ENM predictions with existing measurements. The correlations and limitations of the model, and the analytic validity of our approach are discussed in the context of massive use of assumptive model data and high uncertainty on the colloidal material captured by the measurements. Predictions for freshwater CeO2-ENMs range from 1 pg/l (2017) to a few hundred ng/l (2050). Relative to CeO2, the SiO2-ENMs estimates are approximately 1,000 times higher, and those for Ag-ENMs 10 times lower. For most environmental compartments, ENM pose relatively low risk; however, organisms residing near ENM 'point sources' (e.g., production plant outfalls and waste treatment plants), which are not considered in the present work, may be at increased risk.
Gogos, A., Voegelin, A., & Kaegi, R. (2018). Influence of organic compounds on the sulfidation of copper oxide nanoparticles. Environmental Science: Nano, 5(11), 2560-2569. doi:10.1039/C8EN00523K, Institutional Repository

Dissolved organic matter (DOM) influences the colloidal properties of engineered nanomaterials (ENMs) and impacts their transport and transformation in the environment. Sulfidation affects the fate and the ecological effects of released chalcophile ENMs. For copper oxide nanoparticles (CuO-NPs), the sulfidation and its kinetics have been described. However, the influence of DOM on this reaction has not been investigated yet. In wastewater systems, having high bisulfide contents, the DOM mainly consists of proteins, polysaccharides and humic substances. We therefore investigated the influence of the organic compounds bovine serum albumin (BSA, model protein), alginate (ALG, model polysaccharide), and polyacrylic acid (PAA, natural organic matter analogue) as well as that of natural humic acid (HA) and filtered wastewater (FW) on the sulfidation of CuO-NPs. Experiments were conducted in solutions buffered to pH 8.0 at concentrations of 1.3 mM CuO and ∼3.2 mM HS−. Increasing amounts of organic compounds were added to reach concentrations of 10–1000 mg L−1. Reacted CuO-NPs were collected at selected time points and characterized using Cu K-edge X-ray absorption spectroscopy and analytical electron microscopy. The sulfidation of the CuO-NPs was complete after 3 h in all experiments, except in the presence of 1000 mg L−1 BSA where ∼30% of CuO remained untransformed. Complete sulfidation of the CuO-NPs as observed in experiments conducted in FW suggests quantitative sulfidation of CuO-NPs in real wastewater. Without organic compounds, initially formed amorphous CuxS transformed into covellite over time. The presence of BSA, HA, ALG, and FW (but not PAA) hampered this transformation resulting in higher fractions of CuxS after sulfidation. Different amounts of CuxS with sizes of 10 kDa up to 10 nm formed during sulfidation depending on the type of organic compound. The properties of the CuxS-NPs formed by CuO-NP sulfidation must be considered when assessing their environmental impact.
Gondikas, A., Von Der Kammer, F., Kaegi, R., Borovinskaya, O., Neubauer, E., Navratilova, J., … Hofmann, T. (2018). Where is the nano? Analytical approaches for the detection and quantification of TiO2 engineered nanoparticles in surface waters. Environmental Science: Nano, 5(2), 313-326. doi:10.1039/c7en00952f, Institutional Repository

Detecting and quantifying engineered nanoparticles (ENPs) in complex environmental matrices requires the distinction between natural nanoparticles (NNPs) and ENPs. The distinction of NNPs and ENPs for regulatory purposes calls for cost-efficient methods, but is hampered by similarities in intrinsic properties, such as particle composition, size, density, surface chemistry, etc. Titanium dioxide (TiO2) ENPs, for instance, are produced in very large quantities but Ti also commonly occurs naturally in nano-scale minerals. In this work, we focus on utilizing particle size and composition to identify ENPs in a system with a significant background concentration of the target metal. We have followed independent approaches involving both conventional and state-of-the-art analytical techniques to detect and quantify TiO2 ENPs released into surface waters from sunscreen products and to distinguish them from Ti-bearing NNPs. To achieve this, we applied single particle inductively coupled plasma mass spectrometry with single-element (spICPMS) and multi-element detection (time-of-flight) spICP-TOFMS, together with transmission electron microscopy (TEM), automated scanning electron microscopy (autoSEM), and bulk elemental analyses. A background concentration of Ti-bearing NPs (approximately 5 × 103 particles per ml), possibly of natural origin, was consistently observed outside the bathing season. This concentration increased by up to 40% during the bathing season. Multi-element analysis of individual particles using spICP-TOFMS revealed that Al, Fe, Mn, and Pb are often present in natural Ti-bearing NPs, but no specific multi-element signatures were detected for ENPs. Our data suggests that TiO2 ENPs enter the lake water during bathing activities, eventually agglomerating and sedimenting. We found adhesion of the TiO2 ENPs to the air-water interface for short time periods, depending on wind conditions. This study demonstrates that the use of spICP-TOFMS and spICPMS in combination with other conventional analytical techniques offers significant advantages for discriminating between NNPs and ENPs. The quantitative data produced in this work can be used as input for modeling studies or as a benchmark for analysis protocols and model validations.
Hagemann, N., Spokas, K., Schmidt, H. P., Kägi, R., Böhler, M. A., & Bucheli, T. D. (2018). Activated carbon, biochar and charcoal: linkages and synergies across pyrogenic carbon's ABCs. Water, 10(2), 182 (19 pp.). doi:10.3390/w10020182, Institutional Repository

Biochar and activated carbon, both carbonaceous pyrogenic materials, are important products for environmental technology and intensively studied for a multitude of purposes. A strict distinction between these materials is not always possible, and also a generally accepted terminology is lacking. However, research on both materials is increasingly overlapping: sorption and remediation are the domain of activated carbon, which nowadays is also addressed by studies on biochar. Thus, awareness of both fields of research and knowledge about the distinction of biochar and activated carbon is necessary for designing novel research on pyrogenic carbonaceous materials. Here, we describe the dividing ranges and common grounds of biochar, activated carbon and other pyrogenic carbonaceous materials such as charcoal based on their history, definition and production technologies. This review also summarizes thermochemical conversions and non-thermal pre- and post-treatments that are used to produce biochar and activated carbon. Our overview shows that biochar research should take advantage of the numerous techniques of activation and modification to tailor biochars for their intended applications.
Kampe, S., Kaegi, R., Schlich, K., Wasmuth, C., Hollert, H., & Schlechtriem, C. (2018). Silver nanoparticles in sewage sludge: bioavailability of sulfidized silver to the terrestrial isopod Porcellio scaber. Environmental Toxicology and Chemistry, 37(6), 1606-1613. doi:10.1002/etc.4102, Institutional Repository

Silver nanoparticles (AgNPs) are efficiently converted during the wastewater‐treatment process into sparingly soluble Ag sulfides (Ag2S). In several countries, sewage sludge is used as a fertilizer in agriculture. The bioavailability of sulfidized Ag to the terrestrial isopod Porcellio scaber was investigated. Sewage sludge containing transformed AgNPs was obtained from a laboratory‐scale sewage‐treatment plant operated according to Organisation for Economic Co‐operation and Development (OECD) guideline 303a. The results of transmission electron microscopy with energy dispersive X‐ray of sludge samples suggest that AgNPs were completely transformed to Ag2S. Adult isopods were exposed to OECD 207 soil substrate amended with the AgNP spiked sludge for 14 d (uptake phase) followed by an elimination phase in unspiked soil of equal duration. Most of the Ag measured in P. scaber at the end of the uptake phase was found in the hindgut (71%), indicating that only a minor part of the estimated Ag content was actually assimilated by the isopods with 16.3 and 12.7% found in the carcass and hepatopancreas, respectively. As a result of this, the Ag content of the animals dropped following transition to unspiked sludge within 2 d to one‐third of the previously measured Ag concentration and remained stable at this level until the end of the elimination period. The present study shows that Ag2S in sewage sludge is bioavailable to the terrestrial isopod P. scaber.
Neidhardt, H., Winkel, L. H. E., Kaegi, R., Stengel, C., Trang, P. T. K., Lan, V. M., … Berg, M. (2018). Insights into arsenic retention dynamics of Pleistocene aquifer sediments by in situ sorption experiments. Water Research, 129, 123-132. doi:10.1016/j.watres.2017.11.018, Institutional Repository

The migration of arsenic (As) enriched groundwater into Pleistocene aquifers as a consequence of extensive groundwater abstraction represents an increasing threat to the precious water resources in Asian delta regions. Pleistocene aquifer sediments are typically rich in FeIII-(hydr)oxides and are capable to adsorb high amounts of As. This results in a pronounced accumulation of As in Pleistocene aquifers, where high As groundwater infiltrates from adjacent Holocene aquifers. However, As retention by Pleistocene aquifers over long-term time scales remains largely unknown. We studied As sorption in situ by placing natural Pleistocene sediments and pure mineral phases directly inside groundwater monitoring wells at a study site near Hanoi (Vietnam). This in situ exposure allows for constant flushing of the samples with unaltered groundwater and the establishment of undisturbed sorption equilibria similar to those in local aquifer sediments, which is not readily attainable in traditional laboratory sorption experiments. The groundwaters in our experimental wells were characterized by different As concentrations (0.01–6.63 μmol/L) and redox states, reaching from suboxic to anoxic conditions (Eh of +159 to −4 mV). Results show that adsorption is the dominant As retention mechanism, independent from the respective groundwater chemistry (i.e. concentrations of dissolved P, HCO3− and Si). Whilst most of the As sorbed within the first week, sorption further increased slowly but consistently by 6–189%, respectively, within six months. Hence, the As sorption behavior of Pleistocene aquifer sediments should be determined over longer periods to avoid an underestimation of the As sorption capacity. Accompanying desorption experiments revealed that about 51% of the sorbed As was remobilized within six months when exposed to low As groundwater. We therefore conclude that a considerable proportion of the As accumulated in the aquifer sediments is prone to remobilization once the As concentrations in migrating groundwater decline. Remobilization of As should be considered in local water management plans to avoid contamination of precious groundwater resources with this As legacy.
Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Larue, C., de Nolf, W., Reyes-Herrera, J., … Sarret, G. (2018). Searching for relevant criteria to distinguish natural vs. anthropogenic TiO2 nanoparticles in soils. Environmental Science: Nano, 5(12), 2853-2863. doi:10.1039/c8en00386f, Institutional Repository

Nanosized TiO2 is one of the most produced nanomaterials. Agricultural soils are a major compartment of accumulation of TiO2-NPs after release from consumer products into the sewer system, due to the use of sewage sludge as a soil amendment. TiO2 is naturally present in soils, and distinguishing between anthropogenic and natural TiO2 in soils is thus important to assess the risks associated with the increased use of nano-TiO2. Methods to distinguish these materials in complex matrices such as soils are currently lacking. The purpose of this study was, therefore, to search for characteristic physical and chemical properties of natural and engineered nano-TiO2, based on a combination of bulk, micro and nanofocused X-ray fluorescence and X-ray absorption spectroscopy, transmission electron microscopy, X-ray diffraction and chemical analyses. Digested sewage sludge, agricultural soil and sludge-amended soil were studied by these techniques. The particle size distribution was not a relevant criterion since the sludge and the sludge-amended soil contained a variety of nanometer- and micrometer sized Ti-containing particles. Both the sludge and the soil contained a mixture of rutile and anatase, with a minor proportion of amorphous TiO2. In the sludge, there was no trend relating particle size and Ti mineralogy. The morphology of the TiO2 particles proved to be different in the two matrices, with smooth faceted particles in the sludge and rough irregular ones in the soil. In addition, natural TiO2 particles were included in micro and macroaggregates of the soil and formed intricate assemblages with minerals and organic compounds. In the sludge, TiO2 formed homo and heteroaggregates of simpler structure, richer in organic matter. Thus, the study of the morphology of TiO2 particles and their status in unperturbed mineral-organic assemblages may provide some insights into their origin. The observed differences may attenuate over time, due to the incorporation of the sludge material within the soil structure.
Senn, A. C., Hug, S. J., Kaegi, R., Hering, J. G., & Voegelin, A. (2018). Arsenate co-precipitation with Fe(II) oxidation products and retention or release during precipitate aging. Water Research, 131, 334-345. doi:10.1016/j.watres.2017.12.038, Institutional Repository

The co-precipitation of arsenate (As(V)) with Fe(III)-precipitates is of great importance in water treatment and critically affects the fate of As in environmental systems. We studied the effects of dissolved phosphate (P; 0-1 mM), silicate (Si; 0 or 0.5 mM) and Ca (0, 0.5 and 4 mM) on the sequestration of 7 μM As(V) by Fe(III)-precipitates formed by the oxidation of 0.5 mM Fe(II) in aerated bicarbonate-buffered solutions with an initial pH of 7.0 as well as the retention or release of As(V) after precipitate aging for 30 d at 40 °C. Dissolved As(V) concentrations in fresh precipitate suspensions greatly varied as a function of the initial dissolved P/Fe ratio ((P/Fe)init) and the concentrations of Ca and Si. Limited As(V) removal was observed at (P/Fe)init that exceeded the critical ratio (P/Fe)crit above which exclusively (Ca-)Fe(III)-phosphate forms. Effective As(V) removal was observed at (P/Fe)init < (P/Fe)crit, where initial formation of (Ca-)Fe(III)-phosphate is followed by the formation of Si-ferrihydrite in Si-containing electrolytes and of poorly-crystalline lepidocrocite and hydrous ferric oxide in the Si-free electrolytes. The retention of As(V) and P by fresh Fe(III)-precipitates was most effective in systems containing both Ca and Si. In the Si- and Ca-free electrolytes at (P/Fe)init of ~0.2–0.6, the rapid onset of precipitate aging with conversion of Fe(III)-phosphate to ferrihydrite resulted in a substantial remobilization of As(V) (up to 55% of initially precipitated As(V)). Ca reduced As remobilization during aging by stabilizing Ca-Fe(III)-phosphate and promoting Ca-phosphate formation, and Si by stabilizing Si-ferrihydrite against transformation. Consequently, also after aging, the lowest dissolved As(V) and P fractions were observed in precipitate suspensions containing both Ca and Si.
Thalmann, B., Kägi, R., & von Gunten, U. (2018). Metalle in der Ozonung. Verhalten von ausgewählten Metallen: Oxidation von Metallsulfiden und Metallkomplexen. Aqua & Gas, 98(4), 68-77. , Institutional Repository

Metallsulfide (CuS, ZnS, CdS) werden während der Ozonbehandlung von geklärtem Abwasser nahezu vollständig in Metallionen und Sulfat umgewandelt. Auch organische Komplexbildner, wie EDTA oder NTA, werden durch die Ozonung teilweise zerstört. Dies führt zu einer Freisetzung der entsprechenden Metallionen. Toxische Effekte, hervorgerufen durch erhöhte Konzentrationen von Metallionen, wurden jedoch nur für sehr hohe Kupferkonzentrationen, die dem Abwasser als Kupfersulfide zugegeben worden waren, beobachtet und sind deshalb im «normalen» Abwasser nicht zu erwarten.
Thalmann, B., von Gunten, U., & Kaegi, R. (2018). Ozonation of municipal wastewater effluent containing metal sulfides and metal complexes: kinetics and mechanisms. Water Research, 134, 170-180. doi:10.1016/j.watres.2018.01.042, Institutional Repository

Ozonation can be applied to mitigate the discharge of organic micropollutants from municipal wastewater treatment plants (WWTPs) to the aquatic environment. The toxicity of metals also present in WWTP effluents strongly depends on their speciation. Therefore, knowledge on the change of the metal speciation during ozonation of a WWTP effluent is essential to assess possible negative impacts. The kinetics and the stoichiometries of the reactions of ozone with three metal sulfides (ZnS, CuS and CdS) and metal-ethylenediaminetetraacetate (EDTA)/nitriloriacetic acid (NTA) complexes of Cu(II), Cd(II), Ni(II), Zn(II), Mg(II) and Pb(II) were investigated. With a stoichiometric factor of 2.6–3.9 moles of ozone per mole of sulfide and apparent second-order rate constants at pH 8 > 104 M−1 s−1, a complete oxidation of the sulfides and a concomitant release of the respective metals is expected during ozonation of a WWTP effluent for enhanced micropollutant abatement. The apparent second-order rate constants at pH 8 for the reactions of metal-EDTA complexes with ozone ranged from 42 M−1s−1 to 2.0 × 104 M−1s−1 and increased in the order Cd(II) < Cu(II) < Mg(II) < Ni(II) < Zn(II). Approximately 40% of Cd(II)-EDTA spiked to a WWTP effluent was oxidized at typical specific ozone doses of 0.5–0.7 gO3/gDOC. For the other metal-EDTA complexes a significantly higher fraction was oxidized. The bioavailable fraction determined by the diffusive-gradient thin films (DGT) method in the WWTP effluent increased during ozonation, due to the oxidative release of the metal ions. Algal toxicity (chlamynomodas reinhardtii) tests with CuS/CdS spiked WWTP effluent revealed a high tolerance toward Cu and Cd in the respective media. A toxic response was only observed at Cu concentrations above 10 μM, which is above typical WWTP effluent concentrations. Biological post-treatment after ozonation generally reduced the bioavailability of the metals, which resulted in a lower toxicity. Therefore, the biological post-treatment serves as an additional barrier to protect the downstream ecology of receiving waters.
Ulmer, P., Kaegi, R., & Müntener, O. (2018). Experimentally derived intermediate to silica-rich arc magmas by fractional and equilibrium crystallization at 1·0 GPa: an evaluation of phase relationships, compositions, liquid lines of descent and oxygen fugacity. Journal of Petrology, 59(1), 11-58. doi:10.1093/petrology/egy017, Institutional Repository

Differentiation of hydrous primary, mantle-derived magmas is a fundamental process to generate evolved intermediate to SiO2-rich compositions forming the bulk of the continental and island arc crust. This study focuses on the results of equilibrium and fractional crystallization experiments at 1·0 GPa using two different primary magmas representing deep (90 km) and shallow (35 km) mantle extraction depths. Experiments on a hydrous high-Mg basalt were conducted at graphite-saturated and more oxidized conditions (NNO to NNO + 2, where NNO is nickel–nickel oxide buffer) to exploit the influence of fO2 on phase assemblages and the evolution of derivative liquids. The liquid line of descent (LLD) was simulated from liquidus to near-solidus conditions ranging from 1330°C to 720°C. H2O contents varied from about 2·0 to more than 10 wt %. The LLD covers the entire compositional range from high-Mg basalt to high-silica rhyolite and evolves from metaluminous to peraluminous compositions at 56–60 wt % SiO2 under oxidizing conditions. The observed crystallization sequences and the LLD reveal contrasting behavior depending on oxidation state, H2O content and equilibrium versus fractional crystallization. Equilibrium crystallization of high-Mg basalt under reducing conditions is initially dominated by olivine fractionation followed by Cr-rich spinel, clinopyroxene (cpx), and orthopyroxene (opx). Finally, between 1060 and 1000°C, amphibole formed by a peritectic reaction consuming cpx + olivine and forming amphibole + opx, resulting in 16% silica-undersaturated trachy-basaltic liquid. Equilibrium crystallization of the same composition under oxidizing conditions is characterized by strongly enhanced olivine and cpx fractionation and suppression of opx only occurring as a result of the peritectic amphibole-forming reaction at and below 1040°C. The liquid at 980°C is a peraluminous, alkali-poor, high-Al andesite representing ∼15% residual liquid. Fractional crystallization of the high-Mg basalt under oxidizing conditions evolves through fractionation of early olivine joined by cpx at 1200°C, followed by opx and hercynitic spinel (1140–1080°C) and amphibole at 1050°C coexisting with cpx (and spinel) to 980°C. At 950°C both garnet and plagioclase (plag) join amphibole as liquidus phases. This paragenesis (plus ilmenite and apatite) persists to 750°C with 16% residual liquid relative to the initial basaltic composition. Liquids evolve continuously from basalt to rhyolite, crossing the metaluminous–peraluminous boundary at about 60 wt % SiO2. Fractional crystallization of the basaltic andesite starting material differs at high temperature, where opx and cpx are the liquidus phases (1200–1080°C), followed by amphibole at the expense of opx. Below 950°C the phase assemblage is identical except at the lowest temperature (720°C), where quartz saturates in a high-silica rhyolitic liquid representing 20% of the initial basaltic andesite. Liquid compositions of the two starting compositions converge below 950°C, with the exception of K2O, which behaves incompatibly along the liquid line of descent. The H2O-undersaturated fractional crystallization experiments on the high-Mg basaltic composition under relatively reducing conditions evolve towards tholeiitic or alkalic compositions owing to early plagioclase (at 1140°C) and abundant opx (at 1110°C) crystallization followed by garnet–cpx–plag–ilmenite at 1080°C. Closed-system equilibrium crystallization under relatively oxidized conditions is characterized by significant expansion of the olivine stability field (>250°C, 1280–1000°C) relative to more reducing conditions, causing depletion of the liquid in ferrous iron and increase of ferric iron. The resulting fO2 of the coexisting basaltic liquids increases by more than 3 log units from about NNO + 2 to NNO + 5·5 over the temperature range >1200–1040°C, potentially offering an explanation for the more oxidized character of hydrous arc magmas as opposed to low-H2O tholeiitic magmas.
Vriens, B., Voegelin, A., Hug, S., Kaegi, R., Berg, M., & Winkel, L. (2018). Spurenelemente in Schweizer Abwasser. Aktuelle Konzentrationen und Frachten. Aqua & Gas, 98(1), 40-46. , Institutional Repository

In einem landesweiten Screening wurden in 64 Schweizer Kläranlagen die aktuellen Konzentrationsbereiche und Frachten von Spurenelementen erfasst. Anhand dieser Werte wurde die Einhaltung der gesetzlichen Vorgaben überprüft sowie die gegenwärtigen durchschnittlichen Pro-Kopf-Elementfrachten und der ökonomische Wert der Elementfrachten berechnet. Bisher waren für viele Spurenelemente diese Kennzahlen nicht bekannt.
Wielinski, J., Müller, C., Voegelin, A., Morgenroth, E., & Kaegi, R. (2018). Combustion of sewage sludge: kinetics and speciation of the combustible. Energy and Fuels, 32(10), 10656-10667. doi:10.1021/acs.energyfuels.8b02106, Institutional Repository

Combustion of sewage sludge has become a viable route for sewage sludge management especially as the agricultural use of sewage sludge has become increasingly difficult due to more stringent requirements regarding the quality of sewage sludge. Combustion of digested sewage sludge in dedicated monocombustion facilities is advantageous, as it substantially reduces the volume of the sludge and still allows for a recovery of phosphorus from the sewage sludge ash at a later stage. Despite increasing amounts of sewage sludge being combusted, knowledge on the respective combustion kinetics is still fragmentary. The goal of this study was, therefore, to identify the major combustion reactions of sewage sludge, assess their Arrhenius parameters (activation energy and pre-exponential factor), and assign suitable reference compounds to the individual reactions. For that purpose, experiments were conducted using a thermogravimetric analyzer (TGA). With matrix inversion, we identified 10 individual reactions. Despite the apparent kinetic compensation most likely caused by insufficient precision of the TGA temperature setting, we were able to relate the major reactions of sewage sludge combustion to the combustion of individual reference compounds. In addition to cellulose and lignin, which dominated the weight loss with 35% and 20%, respectively, hemicellulose, xylan, alginate, and calcite were identified. The dominant fraction of cellulose is consistent with recent studies identifying cellulose mainly originating from toilet paper as a major organic constituent in wastewater. As the identified model compounds explain more than 80% of the total weight loss observed, our approach allows a rough speciation of the combustibles of sewage sludge based on TGA experiments.
Auvinen, H., Kaegi, R., Rousseau, D. P. L., & Du Laing, G. (2017). Fate of Silver Nanoparticles in Constructed Wetlands - a Microcosm Study. Water, Air, and Soil Pollution, 228(3) (11 pp.). doi:10.1007/s11270-017-3285-9, Institutional Repository

Nano-enabled materials are produced at growing volumes which increases the likelihood of nanoparticles being released into the environment. Constructed wetlands (CWs) are likely to receive wastewater containing nanoparticles leaching from products during usage. Therefore, we investigate the retention of silver nanoparticles (Ag-NPs) in microcosms simulating CWs treating domestic wastewater. The effects of aeration and organic matter content on the Ag-NP removal efficiencies are studied in particular. CWs remove most of the Ag (80-90%) and the largest fraction of Ag is found in/on the biofilm. Detailed electron microscopy analyses suggest that Ag-NPs are transformed into Ag2S in all microcosm experiments. The good correlation between total suspended solids (TSS) and the Ag concentration measured in the effluent indicates that Ag-NPs are bound to the solids in the effluent. Aeration of the microcosms does not affect the release of Ag-NPs from the systems but increasing organic matter leads to increased amounts of Ag passing the CWs, correlating with the increased release of TSS from the CWs. These results suggest that Ag-NPs are retained with the (suspended) solids in CWs and that the removal efficiency of TSS is an important factor determining the discharge of Ag-NPs from CWs.
Gogos, A., Thalmann, B., Voegelin, A., & Kaegi, R. (2017). Sulfidation kinetics of copper oxide nanoparticles. Environmental Science: Nano, 4(8), 1733-1741. doi:10.1039/C7EN00309A, Institutional Repository

Sulfidation of copper oxide nanoparticles (CuO NPs) in urban wastewater systems is expected to influence their impact on the environment. However, the kinetics of this reaction has not been studied to date and the reaction mechanism remains largely unexplored. We therefore investigated the sulfidation kinetics of CuO NPs reacted with bisulfide (HS−) at concentrations relevant to wastewater systems. Pristine CuO NPs (50 nm, 7.7 μM) were reacted with HS− (26.4–105.6 μM) in oxic solutions buffered to pH 8.0. The reaction progress was monitored using silver nitrate to quench the reaction and selectively dissolve the copper sulfides (Cux) and zincon to spectrophotometrically quantify the released Cu2+. In addition, the reaction products were characterized at selected time points using analytical electron microscopy and X-ray absorption spectroscopy (XAS). The sulfidation rate of the CuO NPs was best described by a pseudo first order rate law and the corresponding half-life times ranged between 1 and 6 minutes. XAS results showed that crystalline CuO NPs rapidly transformed into amorphous CuxS and gradually into crystalline CuS (covellite). The comparable size of pristine and transformed primary particles, the similar morphology of their aggregates, and the initial formation of CuO–CuxS core–shell structures revealed by analytical electron microscopy suggest that the initial sulfidation occurred via a direct conversion reaction mechanism. Our findings suggest that CuO NPs released from various sources into wastewater will rapidly transform into amorphous CuxS and eventually recrystallize into covellite.
Kaegi, R., Englert, A., Gondikas, A., Sinnet, B., von der Kammer, F., & Burkhardt, M. (2017). Release of TiO2 – (nano) particles from construction and demolition landfills. NanoImpact, 8, 73-79. doi:10.1016/j.impact.2017.07.004, Institutional Repository

A large fraction of engineered nanomaterials (ENM) will be deposited in landfills and it is assumed that ENM are securely locked in landfill sites and cannot leach into the environment (e.g. surface waters). However, experimental evidence supporting this assumption is lacking, as current production volumes of ENM are still too small and/or analytical techniques not sensitive enough to allow for the detection and quantification of ENM in landfill leachates. TiO2 particles are currently used in large quantities, for example in construction materials such as paints and renders as white pigments and their sizes extend into the nano-size range. We, therefore, selected TiO2 particles as a surrogate to assess the potential release of ENM from construction and demolition (C & D) landfill sites. We collected leachate samples from a landfill over one year and used complementary analytical techniques, including inductively coupled plasma (ICP) – optical emission spectroscopy (OES), automated scanning electron microscopy (auto SEM), transmission electron microscopy (TEM) and single particle ICP - mass spectrometry (spICPMS) to quantify TiO2 particles in landfill leachates. Total elemental Ti contents were mostly around a few tens of μg L− 1 and were strongly correlated with total suspended solids. Based on the volumetric discharge of the landfill leachate water from the landfill, we estimate a total amount of ~ 0.5 kg of TiO2 particles that are released annually from the landfill. Ti concentrations derived from ICP-OES measurements were in good agreement with quantifications based on TiO2 particles detected by auto SEM analyses. spICPMS measurements indicated a number concentration of Ti-containing particles in the order of 105 mL− 1 and TEM analyses dominantly revealed nanoscale TiO2 particles with a spherical shape typically observed for TiO2 particles used as white pigments. In addition, angular TiO2 particles with a well-defined crystal habitus were detected, suggesting that also natural TiO2 particles of comparable sizes are present in the landfill leachates. The results from this study indicate that (nanoscale) TiO2 particles are released from C & D landfill sites (~ 5 g/year). Although the amount of TiO2 particles released from C & D landfill sites may still be rather low, these particles may serve as proxy for assessing the future release of ENM from C & D landfill sites, which may become relevant as an increasing use of ENM is predicted for construction materials in general.
Kraas, M., Schlich, K., Knopf, B., Wege, F., Kägi, R., Terytze, K., & Hund-Rinke, K. (2017). Long-term effects of sulfidized silver nanoparticles in sewage sludge on soil microflora. Environmental Toxicology and Chemistry, 36(12), 3305-3313. doi:10.1002/etc.3904, Institutional Repository

The use of silver nanoparticles (AgNPs) in consumer products such as textiles leads to their discharge into wastewater and consequently to a transfer of the AgNPs to soil ecosystems via biosolids used as fertilizer. In urban wastewater systems (e.g., sewer,wastewater treatment plant [WWTP], anaerobic digesters) AgNPs are efficiently converted into sparingly soluble silver sulfides (Ag2S), mitigating the toxicity of the AgNPs. However, long-termstudies on the bioavailability and effects of sulfidized AgNPs on soilmicroorganisms are lacking. Thus we investigated the bioavailability and long-term effects of AgNPs (spiked in a laboratory WWTP) on soil microorganisms. Before mixing the biosolids into soil, the sludges were either anaerobically digested or directly dewatered. The effects on the ammonium oxidation process were investigated over 140 d. Transmission electron microscopy (TEM) suggested an almost complete sulfidation of the AgNPs analyzed in all biosolid samples and in soil, with Ag2S predominantly detected in long-term incubation experiments. However, despite the sulfidation of the AgNPs, soil ammonium oxidation was significantly inhibited, and the degree of inhibition was independent of the sludge treatment. The results revealed that AgNPs sulfidized under environmentally relevant conditions were still bioavailable to soil microorganisms. Consequently, Ag2S may exhibit toxic effects over the long term rather than the short term.
Praetorius, A., Gundlach-Graham, A., Goldberg, E., Fabienke, W., Navratilova, J., Gondikas, A., … von der Kammer, F. (2017). Single-particle multi-element fingerprinting (spMEF) using inductively-coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) to identify engineered nanoparticles against the elevated natural background in soils. Environmental Science: Nano, 4(2), 307-314. doi:10.1039/c6en00455e, Institutional Repository

The discrimination of engineered nanoparticles (ENPs) from the natural geogenic background is one of the preeminent challenges for assessing their potential implications. At low ENP concentrations, most conventional analytical techniques are not able to take advantage of inherent differences (e.g. in terms of composition, isotopic signatures, element ratios, structure, shape or surface characteristics) between ENPs and naturally occurring nanoscale particles (NNPs) of similar composition. Here, we present a groundbreaking approach to overcome these limitations and enable the discrimination of man-made ENPs from NNPs through simultaneous detection of multiple elements on an individual particle level. This new analytical approach is accessible by an inductively-coupled plasma time-of-flight mass spectrometer (ICP-TOFMS) operated in single-particle mode. Machine learning is employed to classify ENPs and NNPs based on their unique elemental fingerprints and quantify their concentrations. We demonstrate the applicability of this single-particle multi-element fingerprinting (spMEF) method by distinguishing engineered cerium oxide nanoparticles (CeO2 ENPs) from natural Ce-containing nanoparticles (Ce-NNPs) in soils at environmentally relevant ENP concentrations, orders of magnitude below the natural background.
Senn, A. C., Kaegi, R., Hug, S. J., Hering, J. G., Mangold, S., & Voegelin, A. (2017). Effect of aging on the structure and phosphate retention of Fe(III)-precipitates formed by Fe(II) oxidation in water. Geochimica et Cosmochimica Acta, 202, 341-360. doi:10.1016/j.gca.2016.12.033, Institutional Repository

Iron(III)-precipitates formed by Fe(II) oxidation in aqueous solutions affect the cycling and impact of Fe and other co-precipitated elements in environmental systems. Fresh Fe(III)-precipitates are metastable and their transformation into more stable phases during aging may result in the release of initially co-precipitated ions. Phosphate, silicate, Mg and Ca play key roles in determining the structure and composition of fresh Fe(III)-precipitates. Here we examine how these ions affect the structure and phosphate retention of Fe(III)-precipitates formed by oxidation of 0.5 mM dissolved Fe(II) at pH 7.0 after aging for 30 days at 40 °C.
Iron K-edge X-ray absorption spectroscopy (XAS) shows that aged precipitates consist of the same structural units as fresh precipitates: Amorphous Fe(III)- or Ca-Fe(III)-phosphate, ferrihydrite, and poorly crystalline lepidocrocite. Mg, Ca, and dissolved phosphate stabilize (Ca-)Fe(III)-phosphate against transformation into ferrihydrite. Silicate further attenuates (Ca-)Fe(III)-phosphate transformation. The crystallinity of lepidocrocite formed in phosphate- and silicate-free solutions slightly increases during aging. The transformation of Fe(III)- and Ca-Fe(III)-phosphate into ferrihydrite and ongoing ferrihydrite crystallization during aging result in the release of co-precipitated phosphate. Dissolved Ca on the other hand limits phosphate concentrations to values consistent with solubility control by octacalciumphosphate. Owing to the combined effects of Ca and silicate, phosphate is most effectively retained by Fe(III)-precipitates formed and aged in Ca- and silicate-containing solutions. The results from this study contribute to an improved understanding of the formation and transformation of Fe(III)-precipitates and emphasize that the complexity of Fe(III)-precipitate dynamics in the presence of multiple interfering solutes must be considered when addressing their impact on major and trace elements in environmental systems.
Vriens, B., Voegelin, A., Hug, S. J., Kaegi, R., Winkel, L. H. E., Buser, A. M., & Berg, M. (2017). Quantification of element fluxes in wastewaters: a nationwide survey in Switzerland. Environmental Science and Technology, 51(19), 10943-10953. doi:10.1021/acs.est.7b01731, Institutional Repository

The number and quantities of trace elements used in industry, (high-tech) consumer products, and medicine are rapidly increasing, but the resulting emissions and waste streams are largely unknown. We assessed the concentrations of 69 elements in digested sewage sludge and effluent samples from 64 municipal wastewater treatment plants as well as in major rivers in Switzerland. This data set, representative of an entire industrialized country, presents a reference point for current element concentrations, average per-capita fluxes, loads discharged to surface waters, and economic waste-stream values. The spatial distribution of many individual elements could be attributed either to predominant geogenic or to anthropogenic inputs. Per-capita element fluxes ranged from <10 μg day−1 (e.g., Au, In, and Lu) to >1 mg day−1 (e.g., Zn, Sc, Y, Nb, and Gd) and >1 g day−1 (e.g., for P, Fe, and S). Effluent loads of some elements contributed significantly to riverine budgets (e.g., 24% for Zn, 50% for P, and 83% for Gd), indicating large anthropogenic inputs via the wastewater stream. At various locations, precious metal concentrations in sludge were similar to those in profitable mining ores, with total flux values of up to 6.8 USD per capita per year or 15 USD per metric ton of dry sludge.
Kaegi, R. (2016). Separation and analysis of nanoparticles (NP) in aqueous environmental samples. In B. Xing, C. D. Vecitis, & N. Senesi (Eds.), Wiley-IUPAC series in biophysico-chemical processes in environmental systems. Engineered nanoparticles and the environment. Biophysicochemical processes and toxicity (pp. 53-74). doi:10.1002/9781119275855.ch4, Institutional Repository

Engineered nanoparticles (NP) are defined as intentionally manufactured particles with at least one dimension between 1 and 100 nm. Colloids are roughly defined as particles with a diameter between 1 nm and 1 μm (Buffle and Leeuwen, 1992). Engineered NP, thus, represent a small subgroup of colloids. It has been suggested to distinguish between natural NP, incidental NP, and engineered NP (Christian et al. 2008; Farre et al. 2009; Hassellöv and Kaegi 2009). Several trace metals of geogenic origin are bound to colloids, such as clay minerals, or even form eigencolloids (e.g., metal hydroxides and metal sulfides). As these colloids often occur in the nanoscale range (Lead and Wilkinson 2006), they are classified as natural NP. In addition to being in the nanoscale range (1-100 nm), incidental NP are the by-products of human activities. For example, they are emitted from internal combustion engines (e.g., diesel soot) or coal-fired power plants (e.g., fly ash). Engineered NP, such as carbon nanotubes (CNT) or titanium dioxide (TiO2)-NP, can have the same elemental composition as natural or incidental NP, but they are synthesized on purpose with additional functionalities. To assess the effects of human activities on the environment, incidental and engineered NP have to be separated from natural NP and, even more specifically, to assess the impact of engineered NP on the environment, particles of this specific subgroup have to be distinguished from the other two NP types at each stage of their life cycle (Wiesner et al. 2009). Therefore, it is necessary to develop methods that allow a quantitative detection of engineered NP in complex matrices of different environmental compartments. [...]
Meier, C., Voegelin, A., Pradas Del Real, A., Sarret, G., Mueller, C. R., & Kaegi, R. (2016). Transformation of silver nanoparticles in sewage sludge during incineration. Environmental Science and Technology, 50(7), 3503-3510. doi:10.1021/acs.est.5b04804, Institutional Repository

Silver nanoparticles (Ag-NP) discharged into the municipal sewer system largely accumulate in the sewage sludge. Incineration and agricultural use are currently the most important strategies for sewage sludge management. Thus, the behavior of Ag-NP during sewage sludge incineration is essential for a comprehensive life cycle analysis and a more complete understanding of the fate of Ag-NP in the (urban) environment. To address the transformation of Ag-NP during sewage sludge incineration, we spiked metallic Ag0-NP to a pilot wastewater treatment plant and digested the sludge anaerobically. The sludge was then incinerated on a bench-scale fluidized bed reactor in a series of experiments under variable conditions. Complementary results from X-ray absorption spectroscopy (XAS) and electron microscopy–energy dispersive X-ray (EM–EDX) analysis revealed that Ag0-NP transformed into Ag2S-NP during the wastewater treatment, in agreement with previous studies. On the basis of a principal component analysis and subsequent target testing of the XAS spectra, Ag0 was identified as a major Ag component in the ashes, and Ag2S was clearly absent. The reformation of Ag0-NP was confirmed by EM–EDX. The fraction of Ag0 of the total Ag in the ashes was quantified by linear combination fitting (LCF) of XAS spectra, and values as high as 0.8 were found for sewage sludge incinerated at 800 °C in a synthetic flue gas atmosphere. Low LCF totals (72% to 94%) indicated that at least one relevant reference spectrum was missing in the LCF analysis. The presence of spherical Ag-NP with a diameter of <50 nm extending into the sub-nm range was revealed by electron microscopy analyses. The rapid formation of Ag0-NP from Ag2S during sewage sludge incineration, as demonstrated in this study, needs to be considered in the life cycle assessment of engineered Ag-NP.
Petersen, E. J., Flores-Cervantes, D. X., Bucheli, T. D., Elliott, L. C. C., Fagan, J. A., Gogos, A., … Winchester, M. R. (2016). Quantification of carbon nanotubes in environmental matrices: current capabilities, case studies, and future prospects. Environmental Science and Technology, 50(9), 4587-4605. doi:10.1021/acs.est.5b05647, Institutional Repository

Carbon nanotubes (CNTs) have numerous exciting potential applications and some that have reached commercialization. As such, quantitative measurements of CNTs in key environmental matrices (water, soil, sediment, and biological tissues) are needed to address concerns about their potential environmental and human health risks and to inform application development. However, standard methods for CNT quantification are not yet available. We systematically and critically review each component of the current methods for CNT quantification including CNT extraction approaches, potential biases, limits of detection, and potential for standardization. This review reveals that many of the techniques with the lowest detection limits require uncommon equipment or expertise, and thus, they are not frequently accessible. Additionally, changes to the CNTs (e.g., agglomeration) after environmental release and matrix effects can cause biases for many of the techniques, and biasing factors vary among the techniques. Five case studies are provided to illustrate how to use this information to inform responses to real-world scenarios such as monitoring potential CNT discharge into a river or ecotoxicity testing by a testing laboratory. Overall, substantial progress has been made in improving CNT quantification during the past ten years, but additional work is needed for standardization, development of extraction techniques from complex matrices, and multimethod comparisons of standard samples to reveal the comparability of techniques.
Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Sinnet, B., Magnin, V., Findling, N., … Sarret, G. (2016). Fate of Ag-NPs in sewage sludge after application on agricultural soils. Environmental Science and Technology, 50(4), 1759-1768. doi:10.1021/acs.est.5b04550, Institutional Repository

The objective of this work was to investigate the fate of silver nanoparticles (Ag-NPs) in a sludge-amended soil cultivated with monocot (Wheat) and dicot (Rape) crop species. A pot experiment was performed with sludges produced in a pilot wastewater treatment plant containing realistic Ag concentrations (18 and 400 mg kg–1, 14 mg kg–1 for the control). Investigations focused on the highest dose treatment. X-ray absorption spectroscopy (XAS) showed that Ag2S was the main species in the sludge and amended soil before and after plant culture. The second most abundant species was an organic and/or amorphous Ag—S phase whose proportion slightly varied (from 24% to 36%) depending on the conditions. Micro and nano X-ray fluorescence (XRF) showed that Ag was preferentially associated with S-rich particles, including organic fragments, of the sludge and amended soils. Ag was distributed as heteroaggregates with soil components (size ranging from ≤0.5 to 1–3 μm) and as diffused zones likely corresponding to sorbed/complexed Ag species. Nano-XRF evidenced the presence of mixed metallic sulfides. Ag was weakly exchangeable and labile. However, micronutrient mobilization by plant roots and organic matter turnover may induce Ag species interconversion eventually leading to Ag release on longer time scales. Together, these data provide valuable information for risk assessment of sewage sludge application on agricultural soils.
Thalmann, B., Voegelin, A., Morgenroth, E., & Kaegi, R. (2016). Effect of humic acid on the kinetics of silver nanoparticle sulfidation. Environmental Science: Nano, 3(1), 203-212. doi:10.1039/c5en00209e, Institutional Repository

The sulfidation of metallic silver nanoparticles (AgNP) observed in urban wastewater systems and in natural waters reduces their toxicity by several orders of magnitude. However, the reaction rate of this transformation is only poorly understood and the influence of humic acid (HA) on AgNP sulfidation has not been studied to date. We therefore investigate the sulfidation kinetics of AgNP reacted with bisulfide (HS−) in the absence and presence of HA and evaluate different kinetic models to describe the observed reaction kinetics. Citrate-stabilized AgNP of different sizes (20–200 nm) were reacted with an excess of HS− in the absence of HA as well as at HA concentrations ranging from 50 to 1000 mg L−1. The extent of AgNP sulfidation after the selected reaction times was determined by X-ray absorption spectroscopy (XAS). The overall sulfidation rate increased with decreasing AgNP size and increasing HA concentration. The sulfidation rate of the AgNP was best described by a diffusion-limited solid state reaction model (parabolic rate law). The corresponding half-lives of the AgNP ranged from minutes to hours. The increase of the sulfidation rate with increasing HA concentration may be explained by the adsorption of HA onto the AgNP surface facilitating the access of HS− to the particle surface. The results from analytical transmission electron microscopy suggest that the AgNP were sulfidized asymmetrically in the absence of HA. In the presence of HA, the initially formed concentric core–shell Ag0–Ag2S structures developed into hollow Ag2S nanoparticles with increasing reaction time, possibly via the Kirkendall effect.
Vriens, B., Berg, M., Hug, S., Kägi, R., Voegelin, A., & Winkel, L. (2016). Ermittlung der Konzentrationsbereiche von Spurenelementen in Abwasserreinigungsanlagen. Zusammenfassender Schlussbericht. Dübendorf: Eawag. , Institutional Repository
Burkhardt, M., Dietschweiler, C., Schmidt, S., Englert, A., Hemmann, J., Sinnet, B., & Kägi, R. (2015). Titandioxid. Leitsubstanz für Nanopartikel im Deponiesickerwasser. Aqua & Gas, 95(12), 40-47. , Institutional Repository

Nanopartikel können auf Deponien und von dort mit dem Sickerwasser in Vorfluter gelangen. Als Leitsubstanz für Nanopartikel wurde das Weisspigment Titandioxid in Wasserproben der lnertstoffdeponien Bruni und Schwanental untersucht. Vorgestellt werden insbesondere die Herausforderungen an die analytischen Methoden zur Erfassung von Nanopartikeln in Wasserproben und die ermittelten Massenflüsse.
Fedotova, N., Kaegi, R., Koch, J., & Günther, D. (2015). Influence of dispersion agents on particle size and concentration determined by laser-induced breakdown detection. Spectrochimica Acta B: Atomic Spectroscopy, 103-104(1), 92-98. doi:10.1016/j.sab.2014.12.002, Institutional Repository

Laser-induced breakdown detection (LIBD) is a very promising analytical technique to determine the size and the concentration of nanoparticles (NPs) in aqueous suspensions. The measurement principle is based on the formation of individual plasma events selectively produced when a pulsed, focused laser beam hits a NP. The breakdown probability (BDP) is defined as the ratio of the number of plasma events detected to the total number of laser pulses applied. Energy curves are established by recording the BDP as a function of the laser energy which is increased in a stepwise manner. The size and the concentration of NPs in aqueous suspensions can be extracted from recorded energy curves. Although several studies have already documented the potential of the LIBD technique to detect NPs at trace concentrations in aqueous suspensions, the effect of dissolved matrix constituents (e.g. dispersion agents, which are frequently used to stabilize NPs in suspension) on the LIBD signal has not been addressed, yet.
We therefore recorded energy curves of ultrahigh purity (UHP) water and NP suspensions both spiked with different dispersion agents at different concentrations. An increasing shift of the energy curves towards lower energies was observed with increasing concentrations of dispersion agents. The LIBD-derived size of the NPs was less affected by the presence of dispersion agents than the LIBD-derived particle number concentrations, which deviated by up to 300% from the expected values. The effects on the calculated concentrations were most pronounced at low (2 · 107 particles mL− 1) NP concentrations and at higher NP concentrations (3 · 108 particles mL− 1), the effect of the dispersion agents on the energy curves became negligible. These results show that dissolved matrix constituents substantially affect LIBD measurements, especially at low NP concentrations.
Hofacker, A. F., Behrens, S., Voegelin, A., Kaegi, R., Lösekann-Behrens, T., Kappler, A., & Kretzschmar, R. (2015). Clostridium species as metallic copper-forming bacteria in soil under reducing conditions. Geomicrobiology Journal, 32(2), 130-139. doi:10.1080/01490451.2014.933287, Institutional Repository

Recent studies have reported the formation of Cu0 nanoparticles (CuNP) by suspended bacteria in pore water of periodically flooded soils, but the bacteria have not yet been identified. The aim of this study was to identify the CuNP-forming bacteria and to determine the location of CuNP formation relative to the bacterial cell surface. Electron microscopy revealed that the bacteria were rod-shaped spore formers and suggested that CuNP were formed in the periplasm. Combined results from denaturing gradient gel electrophoresis, 16S rRNA gene clone libraries, and classic microbiological cultivation techniques provided strong evidence for a Clostridium sp. strain as the CuNP-forming bacteria. Clostridia are well-adapted to frequent flooding and drying due to their ability to form spores and may play an important role in Cu cycling and metallic Cu formation in redox-dynamic environments.
Kaegi, R., Voegelin, A., Sinnet, B., Zuleeg, S., Siegrist, H., & Burkhardt, M. (2015). Transformation of AgCl nanoparticles in a sewer system - a field study. Science of the Total Environment, 535, 20-27. doi:10.1016/j.scitotenv.2014.12.075, Institutional Repository

Silver nanoparticles (Ag-NP) are increasingly used in consumer products and their release during the use phase may negatively affect aquatic ecosystems. Research efforts, so far, have mainly addressed the application and use of metallic Ag(0)-NP. However, as shown by recent studies on the release of Ag from textiles, other forms of Ag, especially silver chloride (AgCl), are released in much larger quantities than metallic Ag(0). In this field study, we report the release of AgCl-NP from a point source (industrial laundry that applied AgCl-NP during a piloting phase over a period of several months to protect textiles from bacterial regrowth) to the public sewer system and investigate the transformation of Ag during its transport in the sewer system and in the municipal wastewater treatment plant (WWTP). During the study period, the laundry discharged ~85 g of Ag per day, which dominated the Ag loads in the sewer system from the respective catchment (72–95%) and the Ag in the digested WWTP sludge (67%). Combined results from electron microscopy and X-ray absorption spectroscopy revealed that the Ag discharged from the laundry to the sewer consisted of about one third AgCl and two thirds Ag2S, both forms primarily occurring as nanoparticles with diameters < 100 nm. During the 800 m transport in the sewer channel to the nearby WWTP, corresponding to a travel time of ~30 min, the remaining AgCl was transformed into nanoparticulate Ag2S. Ag2S-NP also dominated the Ag speciation in the digested sludge. In line with results from earlier studies, the very low Ag concentrations measured in the effluent of the WWTP (< 0.5 μg L− 1) confirmed the very high removal efficiency of Ag from the wastewater stream (> 95%).
Müller, P., Mielke, J., Hodoroaba, V. D., Kägi, R., & Ryner, M. (2015). Assessment of different electron microscopy techniques for particle size quantification of potential nanomaterials. Microscopy and Microanalysis, 21(S3), 2403-2404. doi:10.1017/S1431927615012799, Institutional Repository
Senn, A. C., Kaegi, R., Hug, S. J., Hering, J. G., Mangold, S., & Voegelin, A. (2015). Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in water at near-neutral pH: interdependent effects of phosphate, silicate and Ca. Geochimica et Cosmochimica Acta, 162, 220-246. doi:10.1016/j.gca.2015.04.032, Institutional Repository

We studied the interdependent effects of phosphate, silicate and Ca on the formation of Fe(III)-precipitates by oxidation of 0.5 mM Fe(II) in near-neutral bicarbonate-buffered aqueous solutions at concentrations relevant for natural water resources. Complementary results obtained by a suite of analytical techniques including X-ray absorption spectroscopy and transmission electron microscopy showed that the ratio of initially dissolved phosphate over Fe(II) ((P/Fe)init) had a major impact on precipitate formation. At (P/Fe)init above a critical ratio ((P/Fe)crit) of ∼0.5 in 8 mM NaHCO3 and ∼0.8 in 4 mM Ca(HCO3)2 electrolyte, Fe(II) oxidation led to exclusive formation of amorphous basic Fe(III)-phosphate or Ca–Fe(III)-phosphate ((Ca-)Fe(III)-phosphate) with maximum precipitate P/Fe ratios ((P/Fe)ppt) of ∼0.7 in Na and ∼1.1 in Ca electrolyte. Enhanced phosphate uptake in the presence of Ca was due to phosphate-Ca interactions coupled to Fe precipitation, mainly formation of mitridatite-like Ca–Fe(III)-phosphate polymers and Ca-phosphate polymers. At (P/Fe)init < (P/Fe)crit, in the absence of silicate, (Ca-)Fe(III)-phosphate precipitation was followed by the formation of poorly crystalline lepidocrocite and concomitant transformation of the (Ca-)Fe(III)-phosphate into a phosphate-rich ferrihydrite-type precipitate with a (P/Fe)ppt of ∼0.25. In the presence of 0.5 mM silicate, initially formed (Ca-)Fe(III)-phosphate nanoparticles became coated with silicate-rich ferrihydrite during continuing Fe(II) oxidation and only limited transformation of the (Ca-)Fe(III)-phosphate occurred. The results from this study indicate the complexity of Fe(III)-precipitate formation in the presence of interfering solutes and its consequences for precipitate structure and phosphate sequestration. The findings provide a solid basis for further studies of the reactivity of different Fe(III)-precipitate types and for the systematic assessment of their impact on Fe, phosphate and trace elements dynamics in natural and engineered systems.
Thalmann, B., Voegelin, A., von Gunten, U., Behra, R., Morgenroth, E., & Kaegi, R. (2015). Effect of ozone treatment on nano-sized silver sulfide in wastewater effluent. Environmental Science and Technology, 49(18), 10911-10919. doi:10.1021/acs.est.5b02194, Institutional Repository

Silver nanoparticles used in consumer products are likely to be released into municipal wastewater. Transformation reactions, most importantly sulfidation, lead to the formation of nanoscale silver sulfide (nano-Ag2S) particles. In wastewater treatment plants (WWTP), ozonation can enhance the effluent quality by eliminating organic micropollutants. The effect of ozonation on the fate of nano-Ag2S, however, is currently unknown. In this study, we investigate the interaction of ozone with nano-Ag2S and evaluate the effect of ozonation on the short-term toxicity of WWTP effluent spiked with nano-Ag2S. The oxidation of nano-Ag2S by ozone resulted in a stoichiometric factor (number of moles of ozone required to oxidize one mole of sulfide to sulfate) of 2.91, which is comparable to the results obtained for the reaction of bisulfide (HS–) with ozone. The second-order rate constant for the reaction of nano-Ag2S with ozone (k = 3.1 × 104 M–1 s–1) is comparable to the rate constant of fast-reacting micropollutants. Analysis of the ozonation products of nano-Ag2S by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) revealed that ozonation dominantly led to the formation of silver chloride in WWTP effluent. After ozonation of the Ag2S-spiked effluent, the short-term toxicity for the green algae Chlamydomonas reinhardtii increased and reached EC50 values comparable to Ag+. This study thus reveals that ozone treatment of WWTP effluent results in the oxidation of Ag2S and, hence, an increase of the Ag toxicity in the effluent, which may become relevant at elevated Ag concentrations.
Thalmann, B. A. D. (2015). Transformations of silver nanoparticles in urban wastewater and water systems (Doctoral dissertation). doi:10.3929/ethz-a-010579189, Institutional Repository

Metallic silver nanoparticles (AgNP) are increasingly applied in consumer products from which they are probably released to the urban wastewater and water system. Due to the antimicrobial activity of AgNP, they are of high ecotoxicological concern and an engineered nanomaterial of priority for environmental risk assessment. Transformations of AgNP can have large efects on their toxicity toward aquatic organism. Most importantly, the sulidation of AgNP is known to reduce the toxicity of Ag by several orders of magnitude. Thus, a proper understanding of the sulidation of AgNP in the urban wastewater and water system is crucial for in-depth environmental risk assessments. Furthermore, the ozonation of the eluent of wastewater treatment plant (WWTP) to mitigate micropollutants is likely to further change the Ag speciation. he irst objective of this thesis was to understand the sulidation kinetics of AgNP with bisulide (HS-) and metal sulides. The second objective was to study the impact of ozone treatment on sulidized AgNP. [...]

Silber Nanopartikel (AgNP) werden vermehrt in Konsumgütern angewandt, von welchen die Partikel durch den Gebrauch in das urbane Abwasser und Wasser ausgewaschen werden können. Aufgrund ihrer antimikrobieller Wirkung stellen sie ein potentielles Risiko für die Umwelt dar, welches abgeschätzt werden sollte. Durch Umwandlung in der Umwelt ändert sich die Speziierung der AgNP was die Toxizität gegenüber aquatischen Organismen und Planzen beeinlusst. Die Reaktion von AgNP mit Suliden, genannt Sulidierung, zum Beispiel reduziert die Ag Toxizität um mehrere Grössenordnungen. Deshalb ist es für eine Risikoeinschätzung der AgNP in der Umwelt wichtig die Sulidierung im urbanen Abwasser und Wasser zu verstehen. Im Abwasser ist die dominante Sulid Quelle Bisulid (HS-), welches in erhöhten Konzentrationen zu inden ist. Für das Oberlächengewässer hingegen ist die Sulidierung mit Metallsuliden wahrscheinlicher, da sie persistenter gegen die Oxidation mit Sauerstof sind. Das erste Ziel dieser Dissertation war deshalb die Sulidierung von AgNP mit HS- und Metallsuliden zu verstehen. [...]
Duester, L., Burkhardt, M., Gutleb, A. C., Kaegi, R., Macken, A., Meermann, B., & von der Kammer, F. (2014). Toward a comprehensive and realistic risk evaluation of engineered nanomaterials in the urban water system. Frontiers in Chemistry, 2, 39 (6 pp.). doi:10.3389/fchem.2014.00039, Institutional Repository

The European COoperation in Science and Technology (COST) Action ES1205 on the transfer of Engineered Nano materials from wastewater Treatment and stormwatEr to Rivers (ENTER) aims to create and to maintain a trans European network among scientists. This perspective article delivers a brief overview on the status quo at the beginning of the project by addressing the following aspects on engineered nano materials (ENMs) in the urban systems: (1) ENMs that need to be considered on a European level; (2) uncertainties on production-volume estimations; (3) fate of selected ENMs during waste water transport and treatment; (4) analytical strategies for ENM analysis; (5) ecotoxicity of ENMs, and (6) future needs. These six step stones deliver the derivation of the position of the ES1205 network at the beginning of the projects runtime, by defining six fundamental aspects that should be considered in future discussions on risk evaluation of ENMs in urban water systems.
Gogos, A., Kaegi, R., Zenobi, R., & Bucheli, T. D. (2014). Capabilities of asymmetric flow field-flow fractionation coupled to multi-angle light scattering to detect carbon nanotubes in soot and soil. Environmental Science: Nano, 1(6), 584-594. doi:10.1039/c4en00070f, Institutional Repository

Analytical detection and quantification of multi-walled carbon nanotubes (MWCNTs) in complex matrices such as soils is very challenging. In an initial approach to this task, we identify MWCNTs by making use of their different (e.g., rod-like) shape compared to other (native) soil particles and in particular soot, which is ubiquitously present in soils. A shape factor ρ, determined using asymmetric flow field-flow fractionation coupled to multi-angle light scattering (aF4-MALS), was used to discriminate MWCNTs of different aspect ratios, as well as mixtures of soot and MWCNTs, in pure suspensions. MALS results were additionally confirmed using automated electron microscopy image analysis. We then analyzed different soil types which consistently showed ρ-values that differed from pure MWCNTs. To test the performance of the method for MWCNT detection in such complex matrices, we conducted standard additions of a MWCNT as well as soot to an agricultural soil. Extracts from these MWCNT-spiked soils showed increased ρ-values compared to soot-spiked or native soil. The method detection limit for the MWCNT was 1.6 to 4.0 mg g−1 soil and lies within the range of commonly used black carbon quantification methods, but is much higher than any currently predicted environmental concentration. Additionally, the method is currently limited by a relatively narrow dynamic range of ρ. Despite these limitations, our results suggest that aF4-MALS provides specific shape information that may be linked to an actual MWCNT presence in soils. Further method improvement potential is outlined along different steps of the workflow.
Grass, R. N., Schälchli, J., Paunescu, D., Soellner, J. O. B., Kaegi, R., & Stark, W. J. (2014). Tracking trace amounts of submicrometer silica particles in wastewaters and activated sludge using silica-encapsulated DNA barcodes. Environmental Science and Technology Letters, 1(12), 484-489. doi:10.1021/ez5003506, Institutional Repository

Although silica particles are among the widest utilized engineered nanoparticles, the measurement of silica particles at low exposure concentrations is impeded by the high background concentrations of silicates in the environment. To circumvent this analytical limitation, we describe a new method for tracing submicrometer silica particles in water by the usage of silica particles fully encapsulating unique DNA codes. Because DNA can be detected at extremely low concentrations by quantitative polymerase chain reaction (PCR), the encapsulation of DNA in silica allows an indirect measure of the concentration of silica particles down to the sub-parts per billion range (micrograms per liter). To provide insight into the capability of this novel technology, we utilized DNA-loaded submicrometer silica particles to follow the fate of silica particles in the analytically most demanding biological stages of wastewater treatment solutions (activated sludge). At various initial particle concentrations ranging from 10 ppb (10 µg/L) to 10 ppm (10 mg/L) and under both aerobic and anoxic conditions, we are able to show that >97% of the particles were removed from the wastewater by incorporation into sludge biomass.
Kroll, A., Behra, R., Kaegi, R., & Sigg, L. (2014). Extracellular polymeric substances (EPS) of freshwater biofilms stabilize and modify CeO2 and Ag nanoparticles. PLoS One, 9(10), e110709 (16 pp.). doi:10.1371/journal.pone.0110709, Institutional Repository

Streams are potential receiving compartments for engineered nanoparticles (NP). In streams, NP may remain dispersed or settle to the benthic compartment. Both dispersed and settling NP can accumulate in benthic biofilms called periphyton that are essential to stream ecosystems. Periphytic organisms excrete extracellular polymeric substances (EPS) that interact with any material reaching the biofilms. To understand the interaction of NP with periphyton it is therefore crucial to study the interaction of NP with EPS. We investigated the influence of EPS on the physicochemical properties of selected NP (CeO2, Ag) under controlled conditions at pH 6, 7.6, 8.6 and light or dark exposure. We extracted EPS from five different periphyton communities, characterized the extracts, and exposed CeO2 and carbonate-stabilized Ag NP (0.5 and 5 mg/L, both 25 nm primary particle size) and AgNO3 to EPS (10 mg/L) over two weeks. We measured NP size distribution, shape, primary particle size, surface plasmon resonance, and dissolution. All EPS extracts were composed of biopolymers, building blocks of humic substances, low molecular weight (Mr) acids, and small amphiphilic or neutral compounds in varying concentrations. CeO2 NP were stabilized by EPS independent of pH and light/dark while dissolution increased over time in the dark at pH 6. EPS induced a size increase in Ag NP in the light with decreasing pH and the formation of metallic Ag NP from AgNO3 at the same conditions via EPS-enhanced photoreduction. NP transformation and formation were slower in the extract with the lowest biopolymer and low Mr acid concentrations. Periphytic EPS in combination with naturally varying pH and light/dark conditions influence the properties of the Ag and CeO2 NP tested and thus the exposure conditions within biofilms. Our results indicate that periphytic organisms may be exposed to a constantly changing mixture of engineered and naturally formed Ag NP and Ag+.
Neidhardt, H., Berg, M., Stengel, C., Winkel, L. H. E., Kaegi, R., Trang, P. T. K., … Viet, P. H. (2014). Arsenic adsorption on iron mineral phases under reducing conditions: results from an in-situ field experiment. In M. I. Litter, H. B. Nicolli, M. Meichtry, N. Quici, J. Bundschuh, P. Bhattacharya, & R. Naidu (Eds.), One century of the discovery of Arsenicosis in Latin America (1914-2014) (pp. 83-84). London: CRC Press. , Institutional Repository

Intrusion of As-rich groundwater into previously As-free aquifers due to extensive groundwater extraction is an increasing cause of concern, especially in Southeast Asia. We studied in-situ As adsorption processes by exposing synthetic Fe-mineral coated sand, as well as original sediment material, to high As groundwater under reducing conditions. Samples were placed in three monitoring wells located in a well-investigated study area (Van Phuc, Vietnam). The amount of adsorbed As reflected an As adsorption potential in the following order: hematite sand > ferrihydrite sand > original Pleistocene sand > goethite sand, and increased proportionally to the concentration of dissolved As in the respective groundwater. Results further indicate transformation of the exposed Fe-minerals, which is presumably controlled by biogeochemical processes. This alteration is expected to cause pronounced changes in the As adsorption potential of the Fe-minerals over time, which is subject to ongoing research.
Thalmann, B., Voegelin, A., Sinnet, B., Morgenroth, E., & Kaegi, R. (2014). Sulfidation kinetics of silver nanoparticles reacted with metal sulfides. Environmental Science and Technology, 48(9), 4885-4892. doi:10.1021/es5003378, Institutional Repository

Recent studies have documented that the sulfidation of silver nanoparticles (Ag-NP), possibly released to the environment from consumer products, occurs in anoxic zones of urban wastewater systems and that sulfidized Ag-NP exhibit dramatically reduced toxic effects. However, whether Ag-NP sulfidation also occurs under oxic conditions in the absence of bisulfide has not been addressed, yet. In this study we, therefore, investigated whether metal sulfides that are more resistant toward oxidation than free sulfide, could enable the sulfidation of Ag-NP under oxic conditions.
We reacted citrate-stabilized Ag-NP of different sizes (10–100 nm) with freshly precipitated and crystalline CuS and ZnS in oxygenated aqueous suspensions at pH 7.5. The extent of Ag-NP sulfidation was derived from the increase in dissolved Cu2+ or Zn2+ over time and linked with results from X-ray absorption spectroscopy (XAS) analysis of selected samples. The sulfidation of Ag-NP followed pseudo first-order kinetics, with rate coefficients increasing with decreasing Ag-NP diameter and increasing metal sulfide concentration and depending on the type (CuS and ZnS) and crystallinity of the reacting metal sulfide. Results from analytical electron microscopy revealed the formation of complex sulfidation patterns that seemed to follow preexisting subgrain boundaries in the pristine Ag-NP. The kinetics of Ag-NP sulfidation observed in this study in combination with reported ZnS and CuS concentrations and predicted Ag-NP concentrations in wastewater and urban surface waters indicate that even under oxic conditions and in the absence of free sulfide, Ag-NP can be transformed into Ag2S within a few hours to days by reaction with metal sulfides.
Voegelin, A., Kaegi, R., Berg, M., Nitzsche, K. S., Kappler, A., Lan, V. M., … Steininger, R. (2014). Solid-phase characterisation of an effective household sand filter for As, Fe and Mn removal from groundwater in Vietnam. Environmental Chemistry, 11(5), 566-578. doi:10.1071/EN14011, Institutional Repository

Household sand filters are widely used in Vietnam to remove As, Fe and Mn from anoxic groundwater used as a drinking water resource. To expand the mechanistic knowledge of the filter functioning, we investigated the bulk and micrometre-scale distribution of Fe, As, P and Mn and the speciation of Fe, Mn and As in a sand filter after 8 years of operation using bulk and micro-focussed X-ray fluorescence spectrometry (XRF) and X-ray absorption spectroscopy (XAS) and scanning electron microscopy coupled with energy dispersive X-ray detection (SEM-EDX). Effective oxygenation of the anoxic groundwater enables the oxidative removal of Fe, As and Mn in the filter sand. Our results show that Fe is retained in the filter as a 2-line ferrihydrite-like FeIII-precipitate that coats sand grains, and that As accumulates dominantly as pentavalent arsenate. The very close spatial correlation of accumulated As and P with Fe throughout the filter sand and down to the micrometre-scale and the effective Fe, P and As retention at an estimated average water residence time of only 30 min suggest that their uptake is governed by a combination of fast sorption reactions, surface-catalysed FeII oxidation and mediated AsIII co-oxidation. In contrast, Mn is retained in separate MnIV/III-(oxyhydr)oxide coatings and concretions, probably as a result of coupled surface-catalysed and microbial MnII oxidation. Silicate sorbed to the ferrihydrite-like FeIII-coatings inhibits their crystallisation and associated remobilisation of P and As. The periodic drainage and aeration of the filter favours the oxidation of any residual FeII and AsIII and the formation of dense Fe precipitates and may thereby contribute to effective filter operation over several years.
Wenk, C. B., Kaegi, R., & Hug, S. J. (2014). Factors affecting arsenic and uranium removal with zero-valent iron: laboratory tests with Kanchan-type iron nail filter columns with different groundwaters. Environmental Chemistry, 11(5), 547-557. doi:10.1071/EN14020, Institutional Repository

Zero-valent iron (ZVI)-based filters are able to remove arsenic and other pollutants from drinking water, but their performance depends on the form of ZVI, filter design, water composition and operating conditions. Kanchan filters use an upper bucket with ZVI in the form of commercial iron nails, followed by a sand filter, to remove arsenic and pathogens. We evaluated factors that influence the removal of arsenic and uranium with laboratory columns containing iron nails with six different synthetic groundwaters with 500 μg L–1 AsIII, 50 μg L–1 U, 2 mg L–1 B, and with 0 and 2 mg L–1 P (added as o-phosphate), 0.25 and 2.5 mM Ca, 3.2 and 8.3 mM HCO3–, at pH 7.0 and 8.4 over 30 days. During the first 10 days, As removal was 65–95 % and strongly depended on the water composition. As removal at pH 7.0 was better than at pH 8.4 and high P combined with low Ca decreased As removal. From 10–30 days, As removal decreased to 45–60 % with all columns. Phosphate, in combination with low Ca concentrations lowered As removal, but had a slightly positive effect in combination with high Ca concentrations. U removal was only 10–70 %, but showed similar trends. The drop in performance over time can be explained by decreasing release of iron to solution due to formation of layers of FeIII phases and calcite covering the iron surface. Mobile corrosion products contained ferrihydrite, Si-containing hydrous ferric oxides, and amorphous Fe–Si–P phases. Comparisons with another type of ZVI filter (SONO-filter) were used to evaluate filter design parameters. Higher ZVI surface areas and longer contact times should lead to satisfactory As removal with Kanchan-type filters.
Yang, Y., Doudrick, K., Bi, X., Hristovski, K., Herckes, P., Westerhoff, P., & Kaegi, R. (2014). Characterization of food-grade titanium dioxide: the presence of nanosized particles. Environmental Science and Technology, 48(11), 6391-6400. doi:10.1021/es500436x, Institutional Repository

Titanium dioxide (TiO2) is widely used in food products, which will eventually enter wastewater treatment plants and terrestrial or aquatic environments, yet little is known about the fraction of this TiO2 that is nanoscale, or the physical and chemical properties of TiO2 that influence its human and environmental fate or toxicity. Instead of analyzing TiO2 properties in complex food or environmental samples, we procured samples of food-grade TiO2 obtained from global food suppliers and then, using spectroscopic and other analytical techniques, quantified several parameters (elemental composition, crystal structure, size, and surface composition) that are reported to influence environmental fate and toxicity. Another sample of nano-TiO2 that is generally sold for catalytic applications (P25) and widely used in toxicity studies, was analyzed for comparison. Food-grade and P25 TiO2 are engineered products, frequently synthesized from purified titanium precursors, and not milled from bulk scale minerals. Nanosized materials were present in all of the food-grade TiO2 samples, and transmission electron microscopy showed that samples 1–5 contained 35, 23, 21, 17, and 19% of nanosized primary particles (<100 nm in diameter) by number, respectively (all primary P25 particles were <100 nm in diameter). Both types of TiO2 aggregated in water with an average hydrodynamic diameter of >100 nm. Food-grade samples contained phosphorus (P), with concentrations ranging from 0.5 to 1.8 mg of P/g of TiO2. The phosphorus content of P25 was below inductively coupled plasma mass spectrometry detection limits. Presumably because of a P-based coating detected by X-ray photoelectron spectroscopy, the ζ potential of the food-grade TiO2 suspension in deionized water ranged from −10 to −45 mV around pH 7, and the iso-electric point for food-grade TiO2 (2 (Si content of 0.026–0.062% and Al content of 0.0006–0.810%) was also different from the case for P25 and would influence the environmental fate of TiO2. X-ray diffraction analysis confirmed the presence of anatase and/or rutile in the food-grade materials, and although the presence of amorphous TiO2 could not be ruled out, it is unlikely on the basis of Raman analysis. The food-grade TiO2 was solar photoactive. Cationic dyes adsorbed more readily to food-grade TiO2 than P25, indicating very different potentials for interaction with organics in the environment. This research shows that food-grade TiO2 contains engineered nanomaterials with properties quite different from those of P25, which has previously been used in many ecotoxicity studies, and because food-grade TiO2 is more likely than P25 to enter the environment (i.e., potentially higher exposure levels), there is a need to design environmental (and human) fate and toxicity studies comparing food-grade to catalytic TiO2.
Hofacker, A. F., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2013). Mercury mobilization in a flooded soil by incorporation into metallic copper and metal sulfide nanoparticles. Environmental Science and Technology, 47(14), 7739-7746. doi:10.1021/es4010976, Institutional Repository

Mercury is a highly toxic priority pollutant that can be released from wetlands as a result of biogeochemical redox processes. To investigate the temperature-dependent release of colloidal and dissolved Hg induced by flooding of a contaminated riparian soil, we performed laboratory microcosm experiments at 5, 14, and 23 °C. Our results demonstrate substantial colloidal Hg mobilization concomitant with Cu prior to the main period of sulfate reduction. For Cu, we previously showed that this mobilization was due to biomineralization of metallic Cu nanoparticles associated with suspended bacteria. X-ray absorption spectroscopy at the Hg LIII-edge showed that colloidal Hg corresponded to Hg substituting for Cu in the metallic Cu nanoparticles. Over the course of microbial sulfate reduction, colloidal Hg concentrations decreased but continued to dominate total Hg in the pore water for up to 5 weeks of flooding at all temperatures. Transmission electron microscopy (TEM) suggested that Hg became associated with Cu-rich mixed metal sulfide nanoparticles. The formation of Hg-containing metallic Cu and metal sulfide nanoparticles in contaminated riparian soils may influence the availability of Hg for methylation or volatilization processes and has substantial potential to drive Hg release into adjacent water bodies.
Hofacker, A. F., Voegelin, A., Kaegi, R., Weber, F. A., & Kretzschmar, R. (2013). Temperature-dependent formation of metallic copper and metal sulfide nanoparticles during flooding of a contaminated soil. Geochimica et Cosmochimica Acta, 103, 316-332. doi:10.1016/j.gca.2012.10.053, Institutional Repository

Riparian floodplains in temperate regions are affected by pronounced seasonal variations in soil and water temperature. This affects the rates and interplay of microbial and abiotic geochemical processes that control the fate of metals in contaminated floodplain soils, including potential release into surface and groundwater during periodic flooding. Here, we investigated how temperature affects chalcophile trace metal contaminants (Cu, Cd, Pb) upon flooding of a riparian soil contaminated by past mining activities. In soil microcosms incubated at 23, 14, and 5 °C, the reductive dissolution of Mn(III,IV) and Fe(III) (oxyhydr)oxides and the release of dissolved Mn2+ and Fe2+ were significantly slower and less intense at the lower temperatures, which was reflected in a decrease of trace metal mobilization via the dissolution of metal oxide sorbents and cation competition for sorption sites. The onset of sulfate reduction was significantly delayed at lower temperatures and the apparent rate of sulfate reduction was decreased, especially at 5 °C. This resulted in elevated high dissolved Cu, Cd, and Pb concentrations over weeks of flooding at 5 °C, whereas colloidal metal sulfide formation dominated Cu, Cd, and Pb pore water dynamics at higher temperatures of 14 and 23 °C due to fast sulfate reduction. Cu K-edge X-ray absorption fine structure spectroscopy revealed metallic Cu(0) as the main colloidal Cu species prior to sulfate reduction at all three temperatures. Analytical electron microscopy showed that Cu(0) particles were associated with suspended bacteria, suggesting biomineralization of Cu(0). Upon onset of sulfate reduction, metallic Cu particles were transformed into CuxS with incorporation of smaller amounts of Cd and Pb. Concomitantly, freely dispersed mixed Cu–Cd–Pb sulfide nanoparticles precipitated in the pore water. Other metals with higher metal sulfide solubility products did not react with the limited amounts of biogenic sulfide. The median size of the mixed metal sulfide nanoparticles increased from 21 nm at 23 °C to 70 nm at 5 °C. During ∼30 days of soil flooding at 23 and 14 °C, Cu speciation in the soil matrix changed from Cu(II) bound to soil organic matter in the oxic soil to 66% CuxS, with intermittent formation of about 14% metallic Cu(0). In contrast, at 5 °C, sulfate reduction and formation of Cu(0) were strongly retarded. After ∼30 days of flooding at 23 and 14 °C, nearly all Cd and about 25% of total Pb in the soil, were precipitated in mixed metal sulfides. Our results demonstrate that temperature controls trace metal dynamics during soil flooding via its influence on microbial reduction of terminal electron acceptors. Even at low temperatures, soil flooding may trigger the release of chalcophile metals from contaminated floodplain soils by sorbent reduction, competitive sorption, and formation of nanoparticulate metal-bearing colloids.
Kaegi, R., Voegelin, A., Ort, C., Sinnet, B., Thalmann, B., Krismer, J., … Mueller, E. (2013). Fate and transformation of silver nanoparticles in urban wastewater systems. Water Research, 47(12), 3866-3877. doi:10.1016/j.watres.2012.11.060, Institutional Repository

Discharge of silver nanoparticles (Ag-NP) from textiles and cosmetics, todays major application areas for metallic Ag-NP, into wastewater is inevitable. Transformation and removal processes in sewers and wastewater treatment plants (WWTP) will determine the impact of Ag-NP on aquatic and terrestrial environments, via the effluents of the WWTP and via the use of digested sludge as fertilizer. We thus conducted experiments addressing the behavior of Ag-NP in sewers and in WWTP.
We spiked Ag-NP to a 5 km long main trunk sewer and collected 40 wastewater samples after 500 m, 2400 m and 5000 m each according to the expected travel times of the Ag-NP. Excellent mass closure of the Ag derived by multiplying the measured Ag concentrations times the volumetric flow rates indicate an efficient transport of the Ag-NP without substantial losses to the sewer biofilm. Ag-NP reacted with raw wastewater in batch experiments were sulfidized to roughly 15% after 5 h reaction time as revealed by X-ray absorption spectroscopy (XAS). However, acid volatile sulfide (AVS) concentrations were substantially higher in the sewer channel (100 μM) compared to the batch experiments (3 μM; still sufficient to sulfidize spiked 2 μM Ag) possibly resulting in a higher degree of sulfidation in the sewer channel. We further investigated the removal efficiency of 10 nm and 100 nm Ag- and gold (Au)-NP coated with citrate or polyvinylpyrrolidone in activated sludge batch experiments. We obtained very high removal efficiencies (∼99%) irrespective of size and coating for Ag- and Au-NP, the latter confirming that the particle type was of minor importance with respect to the degree of NP removal. We observed a strong size dependence of the sulfidation kinetics. We conclude that Ag-NP discharged to the wastewater stream will become sulfidized to various degrees in the sewer system and are efficiently transported to the WWTP. The sulfidation of the Ag-NP will continue in the WWTP, but primarily depending on the size the Ag-NP, may not be complete. Very high removal efficiencies in the WWTP will divert most of the Ag-NP mass flow to the digester and only a small fraction of the Ag will be released to surface waters.
Neumann, A., Kaegi, R., Voegelin, A., Hussam, A., Munir, A. K. M., & Hug, S. J. (2013). Arsenic removal with composite iron matrix filters in Bangladesh: a field and laboratory study. Environmental Science and Technology, 47(9), 4544-4554. doi:10.1021/es305176x, Institutional Repository

The main arsenic mitigation measures in Bangladesh, well-switching and deep tube wells, have reduced As exposure, but water treatment is important where As-free water is not available. Zero-valent iron (ZVI) based SONO household filters, developed in Bangladesh, remove As by corrosion of locally available inexpensive surplus iron and sand filtration in two buckets. We investigated As removal in SONO filters in the field and laboratory, covering a range of typical groundwater concentrations (in mg/L) of As (0.14–0.96), Fe (0–17), P (0–4.4), Ca (45–162), and Mn (0–2.8). Depending on influent Fe(II) concentrations, 20–80% As was removed in the top sand layer, but As removal to safe levels occurred in the ZVI-layer of the first bucket. Residual As, Fe, and Mn were removed after re-aeration in the sand of the second bucket. New and over 8-year-old filters removed As to <50 μg/L and mostly to <10 μg/L and Mn to <0.2 mg/L. Vertical concentration profiles revealed formation of Fe(II) by corrosion of Fe(0) with O2 and incorporation of As into forming amorphous Fe phases in the composite iron matrix (CIM) of newer filters and predominantly magnetite in older filters. As mass balances indicated that users filtered less than reported volumes of water, pointing to the need for more educational efforts. All tested SONO filters provided safe drinking water without replacement for up to over 8 years of use.
Schwyzer, I., Kaegi, R., Sigg, L., & Nowack, B. (2013). Colloidal stability of suspended and agglomerate structures of settled carbon nanotubes in different aqueous matrices. Water Research, 47(12), 3910-3920. doi:10.1016/j.watres.2013.01.057, Institutional Repository

Carbon nanotubes (CNTs) are often processed in suspended form and therefore a release of CNT-suspensions into the aquatic environment is plausible. In this study, the behaviour of two physico-chemically very different CNT types in the presence of varying, environmentally relevant calcium-containing media was investigated, including the long-term colloidal stability and the sedimentary structures of settled CNTs. Calcium induced CNT flocculation, however, the stability of the CNTs in the medium did not monotonously decrease with increasing calcium concentration. At intermediate calcium concentrations (0.5–1.5 mM Ca) pre-dispersed CNTs were stabilized in humic acid medium to similar, temporarily even to higher degree than in the absence of calcium. Between pH 5 and 8 only at the highest pH an influence on CNT stability was observed by either promoting flocculation or stabilisation depending on the CNT type. Humic acid stabilized CNTs much better than fulvic acid. Generally, the colloidal stability of the long, thick CNTs with higher surface oxygen content was less affected by the media composition.
An investigation of the settled CNT material using analytical electron microscopy revealed the presence of spheroidal, bundle-like and net like CNT-agglomerate structures. Calcium possibly acted as bridging agent linking CNTs in a network like manner, temporarily increasing the CNT concentrations stabilized in the supernatants due to the low density of these structures. With increasing settling time the CNTs formed a fluffy sediment layer at the bottom of the reaction vessels. Bundle-like CNT agglomerates were also observed within that layer of settled CNTs, possibly caused by calcium neutralizing the surface charges. Furthermore, the CNT suspensions contained spheroidal CNT agglomerates, most likely residues from the original dry powder that were not disaggregated. The analysis of settled CNT material is a novelty and illustrates CNT agglomerate structures possibly accumulating in the sediments of aquatic systems subsequent to CNT emissions.
Voegelin, A., Senn, A. C., Kaegi, R., Hug, S. J., & Mangold, S. (2013). Dynamic Fe-precipitate formation induced by Fe(II) oxidation in aerated phosphate-containing water. Geochimica et Cosmochimica Acta, 117, 216-231. doi:10.1016/j.gca.2013.04.022, Institutional Repository

We studied the effect of phosphate on the precipitation of Fe during the oxidation of 1 mM Fe(II) in aerated 8 mM NaHCO3–CO2 buffered aqueous solutions at near-neutral pH. The structure and morphology of the precipitates were analyzed by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe K-edge, and transmission electron microscopy (TEM). Up to an initial dissolved P/Fe ratio of ∼0.55, most phosphate was incorporated into the fresh Fe(III)-precipitates. At dissolved P/Fe ratios from 0.55 to 1.91, the precipitate P/Fe ratios only exhibited a minor increase from 0.56 to 0.72. XRD patterns and Fe EXAFS spectra indicated a shift in precipitate type from mostly poorly-crystalline lepidocrocite in the absence of phosphate to amorphous Fe(III)–phosphate (mostly monomeric and oligomeric Fe(III) coordinated with phosphate) at dissolved P/Fe ratios >0.55. A time-resolved oxidation experiment at an initial dissolved P/Fe ratio of 0.29 revealed that amorphous Fe(III)–phosphate formed during Fe(II) oxidation until phosphate was nearly depleted from solution. During continuing Fe(II) oxidation, about half of the newly formed Fe(III) contributed to the polymerization of Fe–phosphate into phosphate-rich hydrous ferric oxide with a maximum P/Fe ratio of 0.25 (HFO-P; edge-sharing linkage of Fe(III) octahedra) and about half precipitated as poorly-crystalline lepidocrocite in the phosphate-depleted solution. At initial P/Fe ratios <0.2, initially formed Fe(III)–phosphate was fully transformed into HFO-P during continuing Fe(II) oxidation. The dynamic interactions between phosphate and Fe described in this study impact the structure of fresh Fe(III)-precipitates at redox transitions in environmental and technical systems. The modulating effects of other dissolved species such as silicate and Ca on Fe precipitate formation and implications for co-transformed trace elements require further study.
Bonalumi, M. (2012). Effect of pumped-storage operations on temperature, turbidity and sedimentation in reservoirs and possible mitigation measures (Doctoral dissertation). doi:10.3929/ethz-a-007586451, Institutional Repository

Temperature, suspended-particle distribution and sedimentation were surveyed and modeled in two pumped-storage hydropower plants, both located in Switzerland.
One of them, the Grimselsee-Oberaarsee plant, consists of two reservoirs connected with a pumped-storage scheme since more than 30 years. Due to different glacier coverage of the catchment, the two reservoirs exhibit different particle concentration and sedimentation. Our investigation performed between 2007 and 2009 shows that the originally clearer reservoir (Oberaarsee) has become colder, more turbid and subject to higher sedimentation, while pumped-storage operations have decreased these parameters in the formerly more turbid reservoir (Grimselsee). However, pumped-storage operations show no direct effect on particles, as particlesize changes due to the turbulent shear stress occurring in the penstocks could not be determined. [...]

Temperatura, particelle in sospensione e sedimentazione sono state oggetto di studio in due diversi sistemi di pompaggio/turbinaggio, entrambi situati in Svizzera.
Il primo, Grimselsee-Oberaarsee, consiste in due laghi artificiali connessi ormai da più di 30 anni. A causa della presenza dei ghiacciai, che variano da un bacino imbrifero all’altro, la concentrazione di particelle e la sedimentazione risulta essere differente nei due laghi. Le nostre campagne di studio (periodo 2007-2009) mostrano infatti che, causa pompaggio/turbinaggio il lago inizialmente più limpido (Oberaarsee) si è intorbidito, raffreddato ed è aumentata la sedimentazione mentre che nel lago originariamente più torbido (Grimselsee) i parametri appena elencati sono diminuti. L’effetto delle pompe/turbine resta confinato ai due laghi artificiali, anche perché una analisi del diametro delle particelle prima e dopo il passaggio attraverso le macchine idrauliche (origine di sforzi turbulenti di taglio) non ha evidenziato variazioni. [...]
Hagendorfer, H., Kaegi, R., Parlinska, M., Sinnet, B., Ludwig, C., & Ulrich, A. (2012). Characterization of silver nanoparticle products using asymmetric flow field flow fractionation with a multidetector approach - a comparison to transmission electron microscopy and batch dynamic light scattering. Analytical Chemistry, 84(6), 2678-2685. doi:10.1021/ac202641d, Institutional Repository

Due to the already prevalent and increasing use of silver-nanoparticle (Ag-NP) products and the raised concerns in particular for the aquatic environment, analytical techniques for the characterization of such products are of need. However, because Ag-NP products are of different compositions and polydispersities, analysis especially of the size distribution is challenging. In this work, an asymmetric flow field flow fractionation (A4F) multidetector system (UV/vis, light scattering, inductively coupled plasma mass spectrometry - ICPMS), in combination with a method to distinguish and quantify the particle and dissolved Ag fractions (ICPMS after ultracentrifugation), for the characterization of Ag-NP products with different degrees of polydispersities is presented. For validation and to outline benefits and limitations, results obtained from batch dynamic light scattering (batch-DLS) and transmission electron microscopy (TEM) were compared. With the developed method a comprehensive understanding in terms of dissolved Ag and Ag-NP concentration as well as an element selective, mass- and number particle size distribution (PSD) was obtained. In relation to batch-DLS, the reliability of the data was improved significantly. In comparison to TEM, faster measurement times and the ability to determine the samples directly in dispersions are clearly advantageous. The proposed setup shows potential for a rapid- and reliable characterization method of virtually any polydisperse metallic NP dispersion, many of them available on the market already.
Mertens, J., Rose, J., Kägi, R., Chaurand, P., Plötze, M., Wehrli, B., & Furrer, G. (2012). Adsorption of arsenic on polyaluminum granulate. Environmental Science and Technology, 46(13), 7310-7317. doi:10.1021/es204508t, Institutional Repository

The kinetics and efficiencies of arsenite and arsenate removal from water were evaluated using polyaluminum granulates (PAG) with high content of aluminum nanoclusters. PAG was characterized to be meso- and macroporous, with a specific surface area of 35 ± 1 m2 g–1. Adsorption experiments were conducted at pH 7.5 in deionized water and synthetic water with composition of As-contaminated groundwater in the Pannonian Basin. As(III) and As(V) sorption was best described by the Freundlich and Langmuir isotherm, respectively, with a maximum As(V) uptake capacity of 200 μmol g–1 in synthetic water. While As(III) removal reached equilibrium within 40 h, As(V) was removed almost entirely within 20 h. Micro X-ray fluorescence and electron microscopy revealed that As(III) was distributed uniformly within the grain, whereas As(V) diffused up to 81 μm into PAG. The results imply that As(V) is adsorbed 3 times faster while being transported 105 times slower than As(III) in Al hydroxide materials.
Schwyzer, I., Kaegi, R., Sigg, L., Smajda, R., Magrez, A., & Nowack, B. (2012). Long-term colloidal stability of 10 carbon nanotube types in the absence/presence of humic acid and calcium. Environmental Pollution, 169(1), 64-73. doi:10.1016/j.envpol.2012.05.004, Institutional Repository

The colloidal stabilities of ten carbon nanotubes (CNTs) having varying physico-chemical properties were compared in long-term experiments. The presence of Suwannee River Humic Acid (SRHA) increased the fraction of CNTs in the supernatants (4–88% for the various CNT types) after addition in pre-dispersed form and 20 days of shaking and 5 days of settling. These suspensions were monomodal, containing individually suspended CNTs with highly negative surface charges. Calcium (2 mM) removed most of the CNT types from the supernatant, due to CNT-agglomerate formation initiated by reduction in surface charge. The amount of SRHA adsorbed to the different CNT types did not correlate (r2 < 0.1) with the percentage of CNTs remaining in suspension. Multiple linear regression analysis revealed that the oxygen content and the diameter of the CNTs significantly influenced the percentage of stabilized CNTs, resulting in an increased fraction of functionalized and large-diameter CNTs that remained in suspension.
Sternitzke, V., Kaegi, R., Audinot, J. N., Lewin, E., Hering, J. G., & Johnson, C. A. (2012). Uptake of fluoride from aqueous solution on nano-sized hydroxyapatite: examination of a fluoridated surface layer. Environmental Science and Technology, 46(2), 802-809. doi:10.1021/es202750t, Institutional Repository

Hydroxyapatite (Ca10(PO4)6(OH)2, HAP), both as a synthetic material and as a constituent of bone char, can serve as an effective and relatively inexpensive filter material for fluoride (F–) removal from drinking water in low-income countries. Fluoride uptake on HAP can occur through different mechanisms, which are, in principle, influenced by solution composition. Suspensions of HAP (2 g L–1) were equilibrated under controlled pH conditions (pH 6.5, 7.3, 9.5) at 25 °C for 28 d after the addition of different F– concentrations (0.5–7.0 mM). The reacted HAP solids were examined with Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Nano Secondary Ion Mass Spectroscopy (NanoSIMS). Fluoride uptake on HAP was dependent on pH, with the highest capacity at pH 6.5; the lowest uptake was found at pH 9.5. Under all experimental conditions, the thermodynamically stable mineral phase was fluorapatite, (Ca10(PO4)6F2, FAP). Fluoride uptake capacity was quantified on the basis of FTIR and XPS analysis, which was consistent with F– uptake from solution. The results of XPS and NanoSIMS analyses indicate that a fluoridated surface layer with a thickness of several nanometers is formed on nanosized HAP.
Bonalumi, M., Anselmetti, F. S., Kaegi, R., & Wüest, A. (2011). Particle dynamics in high-Alpine proglacial reservoirs modified by pumped-storage operation. Water Resources Research, 47(9), 1-15. doi:10.1029/2010WR010262, Institutional Repository

Temperature and suspended particle distribution were surveyed and modeled in two high-Alpine reservoirs in Switzerland, connected by pumped-storage operations for ∼30 years. Due to different glacier coverage of the catchments, the two reservoirs exhibit different particle concentrations and temperatures. After ice-breakup, the lower reservoir with a higher glacier cover in its catchment experiences a higher particle input becoming more turbid than the upper reservoir, which in contrast becomes warmer and thermally more stratified. The pumped-storage operations, which replace the basin volumes annually at least 6 (larger lower basin) to 10 (smaller upper basin) times, modify the physical characteristics of the two reservoirs. This is especially so in winter, when they are ice-covered, without riverine input and at low water level. Our reservoir investigations between 2007 and 2009 and the subsequent particle-balance model show that the upper and lower basins have become more and less turbid, respectively. Pumped-storage operations modify the stratification and particle distribution in both reservoirs and therefore alter the particle outflow and sedimentation. However, on the basis of particle concentrations and reservoir volumes, it is evident that the annually integrated particle release to downstream (∼40% of total) and to overall sedimentation (∼60%) have hardly changed. The budget model was useful in the prediction of particle distribution and sedimentation dynamics in the pumped-storage system. It implies that this approach can be useful for further employment during planning stages of power plants in order to modify and mitigate downstream particle loads in reservoir operations.
Bukowiecki, N., Zieger, P., Weingartner, E., Jurányi, Z., Gysel, M., Neininger, B., … Baltensperger, U. (2011). Ground-based and airborne in-situ measurements of the Eyjafjallajökull volcanic aerosol plume in Switzerland in spring 2010. Atmospheric Chemistry and Physics, 11(19), 10011-10030. doi:10.5194/acp-11-10011-2011, Institutional Repository

The volcanic aerosol plume resulting from the Eyjafjallajökull eruption in Iceland in April and May 2010 was detected in clear layers above Switzerland during two periods (17–19 April 2010 and 16–19 May 2010). In-situ measurements of the airborne volcanic plume were performed both within ground-based monitoring networks and with a research aircraft up to an altitude of 6000 m a.s.l. The wide range of aerosol and gas phase parameters studied at the high altitude research station Jungfraujoch (3580 m a.s.l.) allowed for an in-depth characterization of the detected volcanic aerosol. Both the data from the Jungfraujoch and the aircraft vertical profiles showed a consistent volcanic ash mode in the aerosol volume size distribution with a mean optical diameter around 3 ± 0.3 μm. These particles were found to have an average chemical composition very similar to the trachyandesite-like composition of rock samples collected near the volcano. Furthermore, chemical processing of volcanic sulfur dioxide into sulfate clearly contributed to the accumulation mode of the aerosol at the Jungfraujoch. The combination of these in-situ data and plume dispersion modeling results showed that a significant portion of the first volcanic aerosol plume reaching Switzerland on 17 April 2010 did not reach the Jungfraujoch directly, but was first dispersed and diluted in the planetary boundary layer. The maximum PM10 mass concentrations at the Jungfraujoch reached 30 μg m−3 and 70 μg m−3 (for 10-min mean values) during the April and May episode, respectively. Even low-altitude monitoring stations registered up to 45 μg m−3 of volcanic ash related PM10 (Basel, Northwestern Switzerland, 18/19 April 2010). The flights with the research aircraft on 17 April 2010 showed one order of magnitude higher number concentrations over the northern Swiss plateau compared to the Jungfraujoch, and a mass concentration of 320 (200–520) μg m−3 on 18 May 2010 over the northwestern Swiss plateau. The presented data significantly contributed to the time-critical assessment of the local ash layer properties during the initial eruption phase. Furthermore, dispersion models benefited from the detailed information on the volcanic aerosol size distribution and its chemical composition.
Hagendorfer, H., Kaegi, R., Traber, J., Mertens, S. F. L., Scherrers, R., Ludwig, C., & Ulrich, A. (2011). Application of an asymmetric flow field flow fractionation multi-detector approach for metallic engineered nanoparticle characterization - prospects and limitations demonstrated on Au nanoparticles. Analytica Chimica Acta, 706(2), 367-378. doi:10.1016/j.aca.2011.08.014, Institutional Repository

In this work we discuss about the method development, applicability and limitations of an asymmetric flow field flow fractionation (A4F) system in combination with a multi-detector setup consisting of UV/vis, light scattering, and inductively coupled plasma mass spectrometry (ICPMS). The overall aim was to obtain a size dependent-, element specific-, and quantitative method appropriate for the characterization of metallic engineered nanoparticle (ENP) dispersions. Thus, systematic investigations of crucial method parameters were performed by employing well characterized Au nanoparticles (Au-NPs) as a defined model system.
For good separation performance, the A4F flow-, membrane-, and carrier conditions were optimized. To obtain reliable size information, the use of laser light scattering based detectors was evaluated, where an online dynamic light scattering (DLS) detector showed good results for the investigated Au-NP up to a size of 80 nm in hydrodynamic diameter. To adapt large sensitivity differences of the various detectors, as well as to guarantee long term stability and minimum contamination of the mass spectrometer a split-flow concept for coupling ICPMS was evaluated. To test for reliable quantification, the ICPMS signal response of ionic Au standards was compared to that of Au-NP. Using proper stabilization with surfactants, no difference for concentrations of 1–50 μg Au L−1 in the size range from 5 to 80 nm for citrate stabilized dispersions was observed. However, studies using different A4F channel membranes showed unspecific particle–membrane interaction resulting in retention time shifts and unspecific loss of nanoparticles, depending on the Au-NP system as well as membrane batch and type. Thus, reliable quantification and discrimination of ionic and particular species was performed using ICPMS in combination with ultracentrifugation instead of direct quantification with the A4F multi-detector setup.
Figures of merit were obtained, by comparing the results from the multi detector approach outlined above, with results from batch-DLS and transmission electron microscopy (TEM). Furthermore, validation performed with certified NIST Au-NP showed excellent agreement. The developed methods show potential for characterization of other commonly used and important metallic engineered nanoparticles.
Kaegi, R., Voegelin, A., Sinnet, B., Zuleeg, S., Hagendorfer, H., Burkhardt, M., & Siegrist, H. (2011). Behavior of metallic silver nanoparticles in a pilot wastewater treatment plant. Environmental Science and Technology, 45(9), 3902-3908. doi:10.1021/es1041892, Institutional Repository

We investigated the behavior of metallic silver nanoparticles (Ag-NP) in a pilot wastewater treatment plant (WWTP) fed with municipal wastewater. The treatment plant consisted of a nonaerated and an aerated tank and a secondary clarifier. The average hydraulic retention time including the secondary clarifier was 1 day and the sludge age was 14 days. Ag-NP were spiked into the nonaerated tank and samples were collected from the aerated tank and from the effluent. Ag concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) were in good agreement with predictions based on mass balance considerations. Transmission electron microscopy (TEM) analyses confirmed that nanoscale Ag particles were sorbed to wastewater biosolids, both in the sludge and in the effluent. Freely dispersed nanoscale Ag particles were only observed in the effluent during the initial pulse spike. X-ray absorption spectroscopy (XAS) measurements indicated that most Ag in the sludge and in the effluent was present as Ag2S. Results from batch experiments suggested that Ag-NP transformation to Ag2S occured in the nonaerated tank within less than 2 h. Physical and chemical transformations of Ag-NP in WWTPs control the fate, the transport and also the toxicity and the bioavailability of Ag-NP and therefore must be considered in future risk assessments.
Lorenz, C., Hagendorfer, H., von Goetz, N., Kaegi, R., Gehrig, R., Ulrich, A., … Hungerbühler, K. (2011). Nanosized aerosols from consumer sprays: experimental analysis and exposure modeling for four commercial products. Journal of Nanoparticle Research, 13, 3377-3391. doi:10.1007/s11051-011-0256-8, Institutional Repository

Consumer spray products are already on the market in the cosmetics and household sector, which suggest by their label that they contain engineered nanoparticles (ENP). Sprays are considered critical for human health, because the lungs represent a major route for the uptake of ENP into the human body. To contribute to the exposure assessment of ENP in consumer spray products, we analyzed ENP in four commercially available sprays: one antiperspirant, two shoe impregnation sprays, and one plant-strengthening agent. The spray dispersions were analyzed by inductively coupled plasma mass spectrometry (ICPMS) and (scanning-) transmission electron microscopy ((S)TEM). Aerosols were generated by using the original vessels, and analyzed by scanning mobility particle sizer (SMPS) and (S)TEM. On the basis of SMPS results, the nanosized aerosol depositing in the respiratory tract was modeled for female and male consumers. The derived exposure levels reflect a single spray application. We identified ENP in the dispersions of two products (shoe impregnation and plant spray). Nanosized aerosols were observed in three products that contained propellant gas. The aerosol number concentration increased linearly with the sprayed amount, with the highest concentration resulting from the antiperspirant. Modeled aerosol exposure levels were in the range of 1010 nanosized aerosol components per person and application event for the antiperspirant and the impregnation sprays, with the largest fraction of nanosized aerosol depositing in the alveolar region. Negligible exposure from the application of the plant spray (pump spray) was observed.
Schwyzer, I. I. (2011). Colloidal stability of carbon nanotubes in aqueous media of environmental relevance (Doctoral dissertation). doi:10.3929/ethz-a-007317859, Institutional Repository

Carbon nanotubes (CNTs) are engineered nanoparticles with unique physical and chemical properties making them promising for a broad range of industrial applications. Large scale synthesis and wide spread use of CNTs has increased the likelihood of the unintended release of CNTs into the environment. Environmental exposure of CNTs can occur during their whole life-cycle - production, use and disposal of CNTs, and CNTcontaining products. CNTs may reach the aquatic environment through waste water, runoff from contaminated areas, and aerosol-deposition. Knowledge about the partitioning of CNTs between the water column and the sediment is required to assess the potential impact of CNTs on the ecosystem. Depending on where (sediment or solution) and in which form (single CNTs or CNT agglomerates) CNTs are present in the aquatic environment, different organisms (benthic or pelagic) can be exposed and varying degrees of bioavailability would be expected, respectively. [...]

Kohlenstoffnanoröhrchen (CNTs) sind synthetisch hergestellte Nanopartikel mit einzigartigen physikalischen und chemischen Eigenschaften, was sie für vielfältigste Anwendungen attraktiv macht. CNT Synthese und Anwendung in grossem Stil birgt das Risiko, dass CNTs ungewollt in die Umwelt gelangen. Eine Freisetzung in die Umwelt ist dabei während des gesamten Lebenszyklus der CNTs möglich, d.h. während der Produktion, der Nutzung und der Entsorgung von CNTs und Produkten, die diese enthalten. Die aquatische Umwelt kann über Abwasser, über Abschwemmung von kontaminierten Stellen und über Aerosol-Deposition betroffen sein. Um potenzielle Risiken der CNTs auf das Ökosystem abschätzen zu können, ist es relevant zu wissen, ob der Verbleib der CNTs mehrheitlich im Sediment oder in der Wassersäule zu erwarten ist. Je nach dem wo (Sediment oder Wassersäule) und in welcher Form die CNTs (einzeln oder als Agglomerate) vorliegen, werden andere Organismen exponiert sein (benthische oder pelagische) und wird die Bioverfügbarkeit der Partikel variieren. [...]
Schwyzer, I., Kaegi, R., Sigg, L., Magrez, A., & Nowack, B. (2011). Influence of the initial state of carbon nanotubes on their colloidal stability under natural conditions. Environmental Pollution, 159(6), 1641-1648. doi:10.1016/j.envpol.2011.02.044, Institutional Repository

The colloidal stability of dry and suspended carbon nanotubes (CNTs) in the presence of amphiphilic compounds (i.e. natural organic matter or surfactants) at environmentally realistic concentrations was investigated over several days. The suspensions were analyzed for CNT concentration (UV–vis spectroscopy), particle size (nanoparticle tracking analysis), and CNT length and dispersion quality (TEM). When added in dry form, around 1% of the added CNTs remained suspended. Pre-dispersion in organic solvent or anionic detergent stabilized up to 65% of the added CNTs after 20 days of mild shaking and 5 days of settling. The initial state of the CNTs (dry vs. suspended) and the medium composition hence are critical determinants for the partitioning of CNTs between sediment and the water column. TEM analysis revealed that single suspended CNTs were present in all suspensions and that shaking and settling resulted in a fractionation of the CNTs with shorter CNTs remaining predominantly in suspension.
Burkhardt, M., Zuleeg, S., Kägi, R., Sinnet, B., Eugster, J., Boller, M., & Siegrist, H. (2010). Verhalten von Nanosilber in Kläranlagen und dessen Einfluss auf die Nitrifikationsleistung in Belebtschlamm. Fate of nanosilver in wastewater treatment plants and their impact on nitrification activity in sewage sludge. Umweltwissenschaften und Schadstoff-Forschung, 22(5), 529-540. doi:10.1007/s12302-010-0153-2, Institutional Repository

Background, aim and scope The application of nanosilver is increasing. Knowledge on the fate and behavior of nanosilver in wastewater and wastewater treatment plants is scarce. Studies under real world conditions are completely lacking. We studied (1) the impact of nanosilver on the nitrification of sewage sludge, (2) quantified the mass flow of nanosilver in a pilot-plant, and (3) verified the mass balance in a full-scale municipal wastewater treatment plant where nanosilver is introduced to the municipal plant by an indirect discharger.
Materials and Methods The addition of four different nanosilver additives on ammonia oxidation in activated sludge has been studied in batch-reactors at two concentrations (1, 100 mg/L Ag) with two exposure times (2 h, 6 days). The pilot-plant treating 70 population equivalents of domestic wastewater is operated with a 12 day sludge age. Nanosilver was applied to the activated sludge tank within two sludge ages. The silver concentrations were measured in sludge and effluent samples during dosing and the following two sludge ages. The adsorption and speciation of silver particles has been analyzed using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Influent, effluent and sludge were sampled on a full-scale plant (60 000 equivalent inhabitants) and analyzed for silver.
Results Silver nitrate, metallic nanosilver, nano-scaled silver chloride and microcomposite silver did not show any effect on ammonia oxidation after the addition of 1 mg/L Ag to the activated sludge (corresponding to 250 mg Ag per kg solids). In contrast, 100 mg/L Ag inhibited the nitrification process by 100 % after the addition of silver nitrate and 20–30 % after addition of colloidal polymer-coated nanosilver. A complete mass balance of the pilot-plant, a steady-state system with known fluxes, demonstrates significant enrichment of silver in the sewage sludge (96 %) after the addition of silver chloride to the plant and small losses of silver into the secondary effluent (4 %). The mass fluxes are similar to metallic colloidal nanosilver investigated under the same conditions. The mass balance has been consistently confirmed by the full-scale study in a municipal wastewater treatment plant. The silver fluxes correspond to the fluxes of the suspended solids in sludge and effluent. Overall, it is estimated that from public wastewater treatment plants about 4–40 mg/a Ag per inhabitant equivalent are discharged annually to the receiving water. The analysis by SEM-EDX demonstrates adsorption and incorporation of nanosilver on biological flocs. This method yields first insight into complex building and transformation of silver associated with sulfide after adding metallic nanosilver and silver chloride to wastewater.
Discussion Silver ions released from nanosilver react immediately with large amounts of chloride present in wastewater to form silver chloride. Silver ions may react with organic ligands or sulfide groups additionally. Consequently, even silver nitrate added with 1 mg/L Ag (250 mg Ag/kg TS) to activated sludge did not inhibit nitrification activity. Very high amounts of nanosilver, i. e. 100 mg/L Ag, overburdened the system and equilibrium condition between silver ion release and ligands was not reached. The mass balance reflects the excellent attachment of nanosilver to activated sludge and biological flocs. Therefore, the main elimination process of nanosilver is attachment to the activated sludge. The elimination of nanosilver is high compared to organic and inorganic micro pollutants omnipresent in wastewater. Any further reduction of suspended solids in the effluent water will reduce the silver load.
Conclusions Generally, in wastewater nanosilver occurs bonded to activated sludge flocs and therefore the elimination of nanosilver is efficient under operation conditions typical for wastewater treatment plants. The major fraction of nanosilver is removed from the system by the excess sludge withdrawal. Nonetheless, the efficiency may be further improved by a tertiary filtration step. All analyses of influent, effluent and sludge confirmed that silver exists as silver sulfide. Due to a negligible water solubility of this silver species, silver ions are not subsequently released.
Recommendations and perspectives Nanosilver research should be driven to the identification of transformation processes in real environmental matrices and the influence of coatings on the adsorption behavior. There is no need for action to take special measures for nanosilver removal in the area of municipal wastewater treatment plants compared to ubiquitous hazardous organic pollutants may present in wastewater. Nevertheless, source control measures following the precautionary principle should be performed.
Glaus, R., Kaegi, R., Krumeich, F., & Günther, D. (2010). Phenomenological studies on structure and elemental composition of nanosecond and femtosecond laser-generated aerosols with implications on laser ablation inductively coupled plasma mass spectrometry. Spectrochimica Acta B: Atomic Spectroscopy, 65(9–10), 812-822. doi:10.1016/j.sab.2010.07.005, Institutional Repository

In laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), the properties of laser-generated aerosols, such as size and composition, are crucial for matrix-independent quantification. In this study, the aerosol particle morphology and elemental composition generated by two state-of-the-art laser systems (ArF excimer nanosecond-UV laser and Ti:sapphire femtosecond-IR laser) were investigated by electron microscopic techniques. Electrostatic sampling of the aerosols directly onto transmission electron microscopy (TEM) grids allowed us to study the morphology and elemental composition of the aerosols using TEM and TEM–EDX (energy dispersive X-ray spectroscopy) analyses, respectively. The results of the electron microscopic studies were finally compared to the LA-ICPMS signals of the main matrix components. The investigations were carried out for non-conducting materials (glass and zircon), metallic samples (steel and brass) and semiconductors (sulfides). The studies confirm that ns-LA-generated aerosols dominantly consist of nanoparticle agglomerates while conducting samples additionally contain larger spherical particles (diameter typically 50 to 500 nm). In contrast to ns-laser ablation, fs-LA-generated aerosols consist of a mixture of spherical particles and nanoparticle agglomerates for all investigated samples. Surprisingly, the differences in elemental composition between nanoparticle agglomerates and spherical particles produced with fs-LA were much more pronounced than in the case of ns-LA, especially for zircon (Si/Zr fractionation) and brass (Cu/Zn fractionation). These observations indicate different ablation and particle formation mechanisms for ns- and fs-LA. The particle growth mechanism for ns-LA is most likely a gas-to-particle conversion followed by agglomeration and additional hydrodynamic sputtering for conducting samples. On the other hand, phase explosion is assumed to be responsible for the mixture of large spherical particles and nanoparticle agglomerates as found for fs-LA-generated aerosols. Based on these mechanisms, the overall temporal elemental fractionation effects in ns-LA-ICPMS seem to occur mainly during the ablation. This effect was not observed for fs-LA-ICPMS despite the element separation into different particle fractions, which, on the other hand, could induce severe ICP-induced fractionation.
Hagendorfer, H., Lorenz, C., Kaegi, R., Sinnet, B., Gehrig, R., Goetz, N. V., … Ulrich, A. (2010). Size-fractionated characterization and quantification of nanoparticle release rates from a consumer spray product containing engineered nanoparticles. Journal of Nanoparticle Research, 12(7), 2481-2494. doi:10.1007/s11051-009-9816-6, Institutional Repository

This study describes methods developed for reliable quantification of size- and element-specific release of engineered nanoparticles (ENP) from consumer spray products. A modified glove box setup was designed to allow controlled spray experiments in a particle-minimized environment. Time dependence of the particle size distribution in a size range of 10–500 nm and ENP release rates were studied using a scanning mobility particle sizer (SMPS). In parallel, the aerosol was transferred to a size-calibrated electrostatic TEM sampler. The deposited particles were investigated using electron microscopy techniques in combination with image processing software. This approach enables the chemical and morphological characterization as well as quantification of released nanoparticles from a spray product. The differentiation of solid ENP from the released nano-sized droplets was achieved by applying a thermo-desorbing unit. After optimization, the setup was applied to investigate different spray situations using both pump and gas propellant spray dispensers for a commercially available water-based nano-silver spray. The pump spray situation showed no measurable nanoparticle release, whereas in the case of the gas spray, a significant release was observed. From the results it can be assumed that the homogeneously distributed ENP from the original dispersion grow in size and change morphology during and after the spray process but still exist as nanometer particles of size <100 nm. Furthermore, it seems that the release of ENP correlates with the generated aerosol droplet size distribution produced by the spray vessel type used. This is the first study presenting results concerning the release of ENP from spray products.
Kaegi, R., Voegelin, A., Folini, D., & Hug, S. (2010). Effect of phosphate, silicate, and Ca on the morphology, structure and elemental composition of Fe(III)-precipitates formed in aerated Fe(II) and As(III) containing water. Geochimica et Cosmochimica Acta, 74(20), 5798-5816. doi:10.1016/j.gca.2010.07.017, Institutional Repository

We investigated Fe(III)-precipitates formed from Fe(II) oxidation in water at pH 7 as a function of dissolved Fe(II), As(III), phosphate, and silicate in the absence and presence of Ca. We used transmission electron microscopy (TEM), including selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) to characterize the morphology, structure and elemental composition of the precipitates. Results from our companion X-ray absorption spectroscopy (XAS) study suggested that the oxidation of Fe(II) leads to the sequential formation of distinct polymeric units in the following order: Fe(III)–phosphate oligomers in the presence of phosphate, silicate-rich hydrous ferric oxide (HFO-Si) at high Si/Fe (>0.5) or 2-line ferrihydrite (2L-Fh) at lower Si/Fe (0.1–0.5), and lepidocrocite (Lp) in the absence of phosphate at low Si/Fe (<0.1). Results from this study show that the size of the polymeric units increased along the same sequence and that the aggregation of these polymeric units resulted in spherical particles with characteristic surface textures changing from smooth to coarse. The diameter of the spherical particles increased from 15 to 380 nm as the molar ratio (P + Si + As)/Fe(II) in the starting solution decreased and larger spherical particles precipitated from Ca-containing than from Ca-free solutions. These trends suggested that the size of the spherical particles was controlled by the charge of the polymeric units. Spherical particles coagulated into flocs whose size was larger in the presence than in the absence of Ca. Further observations pointed to the importance of Fe(II) oxidation and polymerization versus polymer aggregation and floc formation kinetics in controlling the spatial arrangement of the different polymeric units within Fe(III)-precipitates. The resulting structural and compositional heterogeneity of short-range-ordered Fe(III)-precipitates likely affects their colloidal stability and their chemical reactivity and needs to be considered when addressing the fate of co-transformed trace elements such as arsenic.
Kaegi, R., Sinnet, B., Zuleeg, S., Hagendorfer, H., Mueller, E., Vonbank, R., … Burkhardt, M. (2010). Release of silver nanoparticles from outdoor facades. Environmental Pollution, 158(9), 2900-2905. doi:10.1016/j.envpol.2010.06.009, Institutional Repository

In this study we investigate the release of metallic silver nanoparticles (Ag-NP) from paints used for outdoor applications. A facade panel mounted on a model house was exposed to ambient weather conditions over a period of one year. The runoff volume of individual rain events was determined and the silver and titanium concentrations of 36 out of 65 runoff events were measured. Selected samples were prepared for electron microscopic analysis. A strong leaching of the Ag-NP was observed during the initial runoff events with a maximum concentration of 145 μ Ag/l. After a period of one year, more than 30% of the Ag-NP were released to the environment. Particles were mostly <15 nm and are released as composite colloids attached to the organic binders of the paint. Microscopic results indicate that the Ag-NP are likely transformed to considerably less toxic forms such as Ag2S.
Latkoczy, C., Kägi, R., Fierz, M., Ritzmann, M., Günther, D., & Boller, M. (2010). Development of a mobile fast-screening laser-induced breakdown detection (LIBD) system for field-based measurements of nanometre sized particles in aqueous solutions. Journal of Environmental Monitoring, 12(7), 1422-1429. doi:10.1039/c002020f, Institutional Repository

Laser-induced breakdown detection (LIBD) is a promising method to detect trace amounts of nanoparticles (NP, <100 nm) in aqueous suspensions. Based on available systems, we developed a mobile LIBD, designed for on-site and on-line measurements. We used the energy ratio of every laser pulse before and after passing the laser beam through the aqueous sample as a new method to detect laser-induced plasma events. The particle size and the particle number density are derived from recorded energy curves. Our LIBD is operated with a Nd:YAG laser at 100 Hz significantly reducing the measurement times compared to other LIBD systems operated at 20 Hz and increasing the capabilities for monitoring purposes. Long-term experiments on water samples revealed losses of NP up to 75% in 15 mL and 35% in 5 L sample containers after 3 months. The size of the particles remained constant (5 L) or slightly decreased (15 mL) indicating significant adsorption of NP to the walls of the sampling containers. Furthermore, we monitored the NP content of water after different purification steps at a drinking water plant (Maennedorf, Lake Zurich, Switzerland). Activated carbon filtration resulted in an increase of the particle size from ∼20 nm to ∼75 nm possibly caused by the release of organic fragments derived from the biology within the activated carbon tank. After the final ultrafiltration step the particle size was around 10 nm in agreement with the nominal cutoff of 100 kDa of the membrane. The results underline the strength of a fast-screening LIBD to detect relative changes in NP size and concentration.
Leisinger, S. M., Lothenbach, B., Saout, G. L., Kägi, R., Wehrli, B., & Johnson, C. A. (2010). Solid solutions between CrO4- and SO4-ettringite Ca6(Al(OH)6)2[(CrO4)x(SO4)1-x]3*26 H2O. Environmental Science and Technology, 44(23), 8983-8988. doi:10.1021/es100554v, Institutional Repository

Chromate is a toxic contaminant of potential concern, as it is quite soluble in the alkaline pH range and could be released to the environment. In cementitous systems, CrO42− is thought to be incorporated as a solid solution with SO42− in ettringite. The formation of a solid solution (SS) could lower the soluble CrO42− concentrations.
Ettringite containing SO42− or CrO42− and mixtures thereof have been synthesized. The resulting solids and their solubility after an equilibration time of 3 months have been characterized. For CrO4-ettringite at 25 °C, a solubility product log KS0 of −40.2 ± 0.4 was calculated: log KCrO4−ettringite = 6log{Ca2+} + 2log{Al(OH)4−} + 3log{CrO42−} + 4log{OH−} + 26log{H2O}. X-ray diffraction and the analysis of the solution indicated the formation of a regular solid solution between SO4- and CrO4-ettringite with a miscibility gap between 0.4 ≤ XCrO4 ≤ 0.6. The miscibility gap of the SO4- and CrO4-ettringite solid solution could be reproduced with a dimensionless Guggenheim fitting parameter (a0) of 2.03.
The presence of a solid solution between SO4- and CrO4-ettringite results in a stabilization of the solids compared to the pure ettringites and thus in an increased uptake of CrO42− in cementitious systems.
Leisinger, S., Lothenbach, B., Lesaout, G., Kägi, R., Wehrli, B., & Johnson, C. A. (2010). Sulphate and chromate-AFt solid solutions; characterization and thermodynamic modeling (p. (4 pp.). Presented at the International RILEM symposium on concrete modelling – CONMOD'10. Lausanne, Switzerland. , Institutional Repository

The aim of the research project is to determine the processes controlling the solubility of chromate in cementitious matrices in order to be able to predict porewater concentrations from solid-phase composition. In the absence of thermodynamic data concerning possible CrO4 limiting phases we are at present not in a position to predict solubility of CrO42- in cementitious systems. In a first step solid solutions of CrO4- and SO4-AFt have been prepared, characterized and thermodynamic stability ranges were determined. Solubility calculations of the solid solution series were carried out using the geochemical modelling code GEMS (Gibbs Energy Minimization Selektor). Solubility data are presented in a Lippmann diagram.
Mikutta, C., Frommer, J., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2010). Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation. Geochimica et Cosmochimica Acta, 74(19), 5574-5592. doi:10.1016/j.gca.2010.06.024, Institutional Repository

In oxic environments contaminated with arsenate (As(V)), small polyhydroxycarboxylates such as citrate may impact the structure of precipitating ferrihydrite (Fh) and thus the surface speciation of As(V). In this study, ‘2-line’ Fh was precipitated from ferric nitrate solutions that were neutralized to pH 6.5 in the presence of increasing citrate concentrations and in the absence or presence of As(V). The initial citrate/Fe and As/Fe ratios were 0–50 mol% and 5 mol%, respectively. The reaction products, enriched with up to 0.32 mol citrate per mole Fe, were characterized by X-ray diffraction, transmission electron microscopy, and Fe and As K-edge X-ray absorption spectroscopy. Citrate decreased the particle size of Fh by impairing the polymerization of Fe(O,OH)6 octahedra via edge and corner linkages. In the presence of citrate and As(V), coordination numbers of Fe decreased by up to 28% relative to pure Fh. Citrate significantly reduced the static disorder of Fe–O bonds, implying a decreased octahedral distortion in Fh. Mean bond distances in Fh were not affected by citrate and remained constant within error at 1.98 Å for Fe–O, 3.03 Å for Fe–Fe1, and 3.45 Å for Fe–Fe2. Likewise, citrate had no effect on the As–Fe (3.31 Å) bond distance in As(V) coprecipitated with Fh. The As K-edge EXAFS data comply with the formation of (i) only monodentate binuclear (2C) As(V) surface complexes and (ii) combinations of 2C, monodentate mononuclear (1V), and outersphere As(V) surface complexes. Our results suggest that increasing citrate concentrations led to a decreasing 1V/2C ratio and/or that citrate increasingly impaired the formation of outersphere As(V) complexes. Moreover, citrate stabilized colloidal suspensions of Fh (pH 4.3–6.6, I 0.45 M) and reduced Fh formation at the expense of soluble Fe(III)-citrate complexes. At initial citrate/Fe ratios 25 mol%, between 8% and 41% of total Fe was bound in Fe(III)-citrate complexes after Fh formation. Polynuclear Fe(III)-citrate species were found to bind As(V) via surface complexes indistinguishable by EXAFS from those of As(V) adsorbed to or coprecipitated with Fh. Our study implies that low molecular weight polyhydroxycarboxylates may enhance the mobility of As(V) in aqueous systems of high ionic strength (e.g., neutralizing acid mine drainage) by colloidal stabilization of suspended Fh particles and the formation of ternary As(V) complexes.
Voegelin, A., Kaegi, R., Frommer, J., Vantelon, D., & Hug, S. J. (2010). Effect of phosphate, silicate, and Ca on Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water studied by X-ray absorption spectroscopy. Geochimica et Cosmochimica Acta, 74(1), 164-186. doi:10.1016/j.gca.2009.09.020, Institutional Repository

We studied the local coordination and structure of Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water (buffered to pH 7 by 8 mM bicarbonate) using synchrotron-based X-ray absorption spectroscopy (XAS) at the K-edges of Fe, P, Ca, and As. Dissolved phosphate, silicate, and Ca at different ratios relative to each other and to Fe affect the forming Fe(III)-phases in a complex manner. The high affinity of phosphate for Fe(III) results in the predominant precipitation of Fe(III)-phosphate as long as dissolved phosphate is present, with Fe(III) polymerization limited to small oligomers. In Ca-containing solution, Ca uptake by Fe(III)–Ca-phosphate involves the linkage and coagulation of negatively charged Fe(III)-phosphate oligomers via Ca–O–P bonds. In the absence of phosphate, dissolved silicate at Si/Fe ratios above ~0.5 results in the formation of hydrous ferric oxide (HFO) with mainly edge-sharing Fe–Fe linkage. At lower Si/Fe ratios of ~0.5–0.1, mainly 2-line ferrihydrite (2L-Fh) with both edge- and corner-sharing Fe–Fe linkage forms. Only in the absence of phosphate at low Si/Fe ratio, lepidocrocite (Lp) forms. In solutions containing sufficient Fe(II), aeration results in the sequential precipitation of Fe(III)-(Ca-)phosphate, HFO or 2L-Fh (depending on solution Si/Fe), and finally Lp. The amount and oxidation state of As co-precipitated with Fe(III) are controlled by the co-oxidation of As(III) with Fe(II), which increases with initial Fe/As ratio, and the competitive uptake of phosphate, As(V) and less strongly sorbing silicate and As(III). This study demonstrates that the diversity and sequence of short-range-ordered Fe(III)-precipitates forming by Fe(II) oxidation in near-neutral natural waters depend on water chemistry. Because differences in the colloidal stability and biogeochemical reactivity of these phases will affect the fate of associated major and trace elements, the different Fe(III)-precipitates and their specific biogeochemical properties must be taken into account when addressing nutrient and contaminant dynamics at redox boundaries in natural and engineered systems.
Behra, R., Kägi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Effects of engineered nanoparticles. Eawag News [engl. ed.], 67, 22-24. , Institutional Repository

As nanoparticles are already widely used, it was only too likely that they would ultimately find their way into the environment. This has now been demonstrated for the first time by Eawag studies - which also show how engineered nanoparticles can exert toxic effects on aquatic organisms.
Behra, R., Kaegi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Les nanoparticules synthétiques et leurs effets. Eawag News [éd. fr.], 67, 22-24. , Institutional Repository

Les nanoparticules sont déjà employées dans un grand nombre de domaines. Il semble donc hautement probable qu’elles se retrouvent tôt ou tard dans l’environnement. Des études de l’Eawag ont démontré pour la première fois la réalité de ce phénomène et ­montrent d’autre part de quelle manière les nanoparticules synthétiques peuvent perturber les organismes aquatiques.
Behra, R., Kaegi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Synthetische Nanopartikel und ihre Wirkung. Eawag News [dtsch. Ausg.], 67, 22-24. , Institutional Repository

Nanopartikel werden heute bereits breit eingesetzt. Da ist es nur wahrscheinlich, dass sie früher oder später auch in der Umwelt landen. Studien der Eawag wiesen dies nun erstmals nach und zeigen darüber hinaus, auf welche Weise sich synthetische Nanopartikel negativ auf Gewässerorganismen auswirken können.
Burkhardt, M., Zuleeg, S., Etter, B., Marti, T., Landert, J., Eugster, J., … Vonmont, H. (2009). Nanosilber in Fassadenbeschichtungen. Auswaschung im Vergleich mit Titandioxid und organischen Bioziden. Dübendorf: Eawag; Empa. , Institutional Repository

Die Anwendung von Nanopartikeln, die antimikrobiell wirksam sind, unterliegt der Zulassung durch die Biozidprodukteverordnung. Dies gilt insbesondere für Nanosilber, da die freigesetzten Silberionen ökotoxisch hoch wirksam sind. Derzeit ist unklar, ob Nanopartikel in Fassaden dauerhaft eingebettet sind und welche Belastung sich mit einer möglichen Auswaschung verbindet.
Zur Klärung der Fragen wurde die Auswaschung von Nanosilber und Titandioxid aus Fassaden unter standardisierten Versuchsbedingungen sowie unter natürlichem Witterungseinfluss untersucht. Berücksichtigt wurde eine Aussenfarbe mit Nanosilber. Im Weisspigment Titandioxid mit einem mittleren Grösse von 200-400 nm liegen weniger als 0.1% der Masse in Nanogrösse (<100 nm) vor. Dieser geringe Massenanteil entspricht aber rund 10% der gesamten Partikelanzahl. Daher wurde auch Titandioxid untersucht und als Leitsubstanz für die Auswaschung von Nanopartikeln in Farben und Putzen herangezogen. [...]
Hassellöv, M., & Kaegi, R. (2009). Analysis and characterization of manufactured nanoparticles in aquatic environments. In J. R. Lead & E. Smith (Eds.), Environmental and human health impacts of nanotechnology (pp. 211-266). doi:10.1002/9781444307504.ch6, Institutional Repository

This chapter aims to discuss the minimum set of key properties that describe nanoparticles (NPs) in aquatic environments, and to review suitable analysis and characterization methods. Special focus is on characterization of manufactured NPs and associated nanoscale processes (Gilbert and Banfield, 2005). Manufactured NPs have recently raised concerns because of their potential effects on human health and the environment (Colvin, 2003; Donaldson et al., 2004; Handy et al., 2008; Nel et al., 2006; Oberdorster et al., 2005). Therefore, the analytical demands related to both exposure and effect assessment are discussed. Atmospheric NPs and airborne exposure are not covered in this chapter, but within Chapters 5 and 8, and also reviewed elsewhere (Burleson et al., 2004; Maynard, 2000); Powers et al., 2007). One aim has been to bring together concepts and knowledge from analytical chemistry, (e.g. quantitative determination of chemical composition in nanoparticle ensembles, such as size fractions or on a single NP), the mature field of particle size analysis (mainly developed for micron particles) (Barth and Flippen, 1995), environmental colloid science (Wilkinson and Lead, 2007) and the young field of nanometrology (Graham, 2007).
Kaegi, R., Wenk, C., & Hug, S. (2009). Elimination de l'arsenic par le fer colloïdal. Eawag News [éd. fr.], 66, 13-15. , Institutional Repository

Face à une contamination de l’eau potable par l’arsenic, la filtration est un bon moyen de lutte. Les systèmes employés sont basés sur la capacité des colloïdes de fer à piéger l’arsenic. Mais selon la composition chimique de l’eau, le fonctionnement des filtres est plus ou moins efficace. L’Eawag a recherché les causes potentielles de perturbation et étudié les possibilités d’optimisation technique des filtres.
Kaegi, R. (2009). Les nanoparticules dans l'eau potable. Eawag News [éd. fr.], 66, 7-9. , Institutional Repository

De plus en plus de produits du quotidien renferment des nanoparticules synthétiques. Nos connaissances sur leur émission et leur comportement dans l’environnement sont cependant encore très limitées. En outre, on ignore aussi très largement quelles sont les quantités de nanoparticules naturellement présentes, notamment dans l’eau potable. Nous avons tenté de dresser un état des lieux.
Kaegi, R., & Sinnet, B. (2009). Nanoparticles in drinking water. Eawag News [engl. ed.], 66, 7-9. , Institutional Repository

Synthetic nanoparticles are increasingly being used in everyday products, but little is known about environmental releases of these materials. Our knowledge of how many natural nanoparticles occur in drinking water is also inadequate. An initial assessment is presented here.
Kägi, R., Wenk, C., & Hug, S. (2009). Arsenentfernung mittels Eisenkolloiden. Eawag News [dtsch. Ausg.], 66, 13-15. , Institutional Repository

Ist Trinkwasser mit Arsen belastet, können Filtersysteme Abhilfe schaffen. Darin bindet das Arsen an Eisenkolloide. Doch je nach Wasserzusammensetzung funktionieren die Filter nicht optimal. Die Eawag erforschte nun, woran das liegt und wie zukünftige Filter konstruiert sein müssen.
Kägi, R., Wenk, C., & Hug, S. (2009). Arsenic removal using iron colloids. Eawag News [engl. ed.], 66, 13-15. , Institutional Repository

Drinking water contaminated with arsenic can be treated using filters in which arsenic is adsorbed onto iron colloids. However, the performance of these systems may not be optimal, depending on the composition of the water. Eawag has now investigated the processes involved - and how the design of future filters could be optimized.
Kägi, R., & Sinnet, B. (2009). Nanopartikel im Trinkwasser. Eawag News [dtsch. Ausg.], 66, 7-9. , Institutional Repository

Immer mehr Produkte in unserem Alltag enthalten synthetische Nanopartikel. Noch aber ist wenig über ihren Eintrag in die Umwelt bekannt. Genauso wenig weiss man, wie viele natürliche Nanopartikel überhaupt im Trinkwasser vorkommen. Eine erste Bestandsaufnahme.
Vernooij, M. G. C., Mohr, M., Tzvetkov, G., Zelenay, V., Huthwelker, T., Kaegi, R., … Grobéty, B. (2009). On source identification and alteration of single diesel and wood smoke soot particles in the atmosphere; an X-Ray microspectroscopy study. Environmental Science and Technology, 43(14), 5339-5344. doi:10.1021/es800773h, Institutional Repository

Diesel and wood combustion are major sources of carbonaceous particles in the atmosphere. It is very hard to distinguish between the two sources by looking at soot particle morphology, but clear differences in the chemical structure of single particles are revealed by C(1s) NEXAFS (near edge X-ray absorption fine structure) microspectroscopy. Soot from diesel combustion has a dominant spectral signature at ~285 eV from aromatic π-bonds, whereas soot from wood combustion has the strongest signature at ~287 eV from phenolic carbon bonds. To investigate if it is possible to use these signatures for source apportionment purposes, we collected atmospheric samples with either diesel or wood combustion as a dominant particle source. No spectra obtained from the atmospheric particles completely matched the emission spectra. Especially particles from the wood dominated location underwent large modifications; the phenolic spectral signature at ~287 eV is greatly suppressed and surpassed by the peak attributed to the aromatic carbon groups at ~285 eV. Comparison with spectra from diesel soot samples experimentally aged with ozone show that very fast modification of the carbon structure of soot particles occurs as soon as they enter the atmosphere. Source attribution of single soot particles with microspectroscopy is thus hardly possible, but NEXAFS remains a powerful tool to study aging effects.
Weber, F. A., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2009). Contaminant mobilization by metallic copper and metal sulphide colloids in flooded soil. Nature Geoscience, 2, 267-271. doi:10.1038/NGEO476, Institutional Repository

Colloids, such as submicrometre mineral particles or bacterial cells, can act as carriers enhancing the mobility of poorly soluble contaminants in subsurface environments1,2. In sulphate-reducing soils and sediments, metal sulphide precipitation has been proposed3-6 to generate contaminant-bearing sulphide colloids, which could transport contaminants traditionally thought to be immobilized by metal sulphide formation7. However, direct evidence for such a process is lacking. Here, we report the composition and morphology of pore-water colloids formed in contaminated floodplain soil when flooded with synthetic river water over a four-week period. We show that, on flooding, bacteria dispersed in the pore water mobilize copper by inducing biomineralization of metallic copper(0). We suggest that copper(0) crystals form by disproportionation of copper(I), which is released by copper-stressed bacteria to maintain copper homeostasis8,9. Sulphate reduction, which started on the fourth day of flooding, resulted in the mobilization of cadmium and lead, which were partitioned to copper-rich sulphide colloids showing two types of morphology: bacterium-associated 50–150-nm-diameter hollow particles formed through copper(0) transformation, and dispersed <50 nm nanoparticles, probably formed through homogeneous precipitation. The slow deposition of both types of sulphide colloid ensured elevated contaminant concentrations in the pore water for weeks. Our findings imply that colloid formation can enhance contaminant release from periodically sulphate-reducing soils and sediments, potentially polluting surface- and groundwaters.
Zuleeg, S., Burkhardt, M., Boller, M., Kägi, R., Sinnet, B., Eugster, J., & Siegrist, H. (2009). Charakterisierung und Bilanzierung von Silber im Abwasser einer Wäscherei. Dübendorf: Eawag: Das Wasserforschungs-Institut des ETH-Bereichs. , Institutional Repository

Die Anwendung von Silber zur Textilveredelung wurde in einer industriellen Wäscherei bilanziert und der Eintrag in das Abwasser erfasst. Der Silbereinsatz erfolgt in Form von Silberchlorid. Quantifiziert wurden die Einsatzmenge, das Vorkommen über einzelne Schritte im Waschvorgang und die Abflusskonzentrationen. Dabei kamen chemische und mikroskopische Methoden zur Analyse des Silbers zum Einsatz.
Zunächst wurde eine Wasserbilanz über die einzelnen Prozessschritte der Wäscherei erarbeitet. Auf dieser Basis wurde die im Ablauf der Wäscherei zu erwartende Silbermenge abgeschätzt. Die Wäschereibilanz und der Eintrag in Richtung einer Abwasserreinigungsanlage (ARA) wurden mit gezielten Probenahmen und chemischer Analytik verifiziert. Die Konzentrationen von Silber im Abwasser der Wäscherei liegen im Bereich von 500-800 μg/L bei einem täglichen Abwasservolumen von ca. 150 m3 am Tag. Dies entspricht einer Tagesfracht von 75-120 g Silber, die regelmässig werktags der ARA zugeleitet werden. [...]
Zuleeg, S., Burkhardt, M., Boller, M., Kägi, R., Sinnet, B., Eugster, J., & Siegrist, H. (2009). Charakterisierung und Bilanzierung von Silberpartikeln in Abwasserreinigungsanlagen. Dübendorf: Eawag: Das Wasserforschungs-Institut des ETH-Bereichs. , Institutional Repository

In der vorliegenden Studie wurden der Verbleib und das Verhalten von Silberpartikeln in Belebtschlamm und in Abwasserreinigungsanlagen (ARA) untersucht. Das Projekt besteht aus drei Teilprojekten:
(1) Hemmung der Nitrifikation im Belebtschlamm durch verschiedene Silberformen
(2) Bilanzierung von Silber in einer Pilot-ARA
(3) Vorkommen von Silber in einer realen ARA.
In den Laborversuchen wurden marktübliche Silberadditive eingesetzt, die in der Industrie - vornehmlich im textilen Bereich - zur Anwendung kommen. [...]
von Gunten, U., Egli, T., Hammes, F., Helbing, J., Kaegi, R., & Pronk, W. (2009). Wave21. Drinking water for the 21st century. Final report. Schriftenreihe der Eawag: Vol. 20. Retrieved from http://www.lib4ri.ch/institutional-bibliography/eawag/schriftenreihe-der-eawag.html, Institutional Repository
Burkhardt, M., Kägi, R., Sinnet, B., Zuleeg, S., Simmler, H., Vonbank, R., … Boller, M. (2008). Biozide - Suche nach Alternativen. Nanopartikel in Fassadenbeschichtungen. Coviss, 4, 14-17. , Institutional Repository

Gegen Algen und Pilze auf Fassaden werden in der Regel Biozide eingesetzt. Ob Nanosilber und photoaktives Nanotitandioxid unproblematische Alternativen oder Ergänzungen zu Bioziden darstellen, ist unklar. Die Eawag und Empa, zwei Forschungsinstitute des ETH-Bereichs, untersuchen erstmals die Auswaschung aus Fassadenanstrichen im Labor und unter Feldbedingungen. Damit werden wesentliche Grundlagen zur Dauerhaftigkeit und Risikobewertung erarbeitet.
Jermann, D., Pronk, W., Kägi, R., Halbeisen, M., & Boller, M. (2008). Influence of interactions between NOM and particles on UF fouling mechanisms. Water Research, 42(14), 3870-3878. doi:10.1016/j.watres.2008.05.013, Institutional Repository

This study focused on the mechanistic effects of molecular interactions between inorganic particles (kaolinite) and the two main NOM fouling fractions of polysaccharides (alginate) and humics (humic acids) in ultrafiltration. Fouling effects were studied during the dead-end filtration of individual and mixed compounds as well as during the subsequent filtration of individual compounds. SEM analyses were performed to further study the fouling-layer structure. A significant synergistic effect was observed during combined particle–NOM fouling, which was considerably greater than the sum of particle and organic fouling alone. Synergistic fouling could be explained by NOM–particle interactions in the feed solution and during the fouling process. Kaolinite alone formed a fouling layer of particle aggregates, whereas humic acid adsorption onto kaolinite resulted in a fouling layer of stabilized colloids of humic acid and kaolinite. In the case of alginate, simultaneous pore-blocking and cake-layer formation of NOM and kaolinite dominated the fouling. In both cases, incorporation of the organics in the kaolinite fouling layer resulted in a fouling cake of significantly reduced porosity compared to individual particle filtration. Irreversible fouling by NOM could not be prevented by kaolinite. SEM images showed patches of the particle-fouling layer remaining on the membrane surface after backwashing, which can be linked to particle–membrane associations by NOM bridging.
Kaegi, R., Wagner, T., Hetzer, B., Sinnet, B., Tzvetkov, G., & Boller, M. (2008). Size, number and chemical composition of nanosized particles in drinking water determined by analytical microscopy and LIBD. Water Research, 42(10–11), 2778-2786. doi:10.1016/j.watres.2008.02.009, Institutional Repository

In this paper we comprehensively characterized particles in drinking water originating from a lake water source. We focused on particles smaller than a few hundred nm. Several analytical techniques were applied to obtain information on number concentration, size distribution, morphology and chemical composition of the particles. Morphological information was obtained by atomic force microscopy (AFM) analysis. Two types of particles, spherical aggregates up to a few tens of nm and elongated fibers were identified. Similar structures were also observed in transmission electron microscope (TEM) images. A size distribution of the particles was obtained by applying image analysis (IA) tools on the TEM images. IA results showed an exponential increase of the particle number concentration down to 40 nm, which is the lower detection limit of our setup. The total number of particles down to 10 nm and the average particle diameter were determined with the laser-induced breakdown detection (LIBD) method. The results were in good agreement with the TEM-IA data and showed a total number concentration of roughly 108 particles/mL in the purified water. The carbon of the particles was investigated with scanning transmission X-ray microscopy (STXM), which revealed that most particles were organic matter; the C-1s spectra were typical for dissolved organic matter.
The methods were applied to characterize the particles from two different drinking waters treated with different methods (conventional vs. ultrafiltration (cut-off 100 kDa)). The results showed that the particle number density following ultrafiltration was lower by a factor of 5–10, compared to conventional treatment. However, the average particle diameter in the finished water of both treatment trains was roughly the same.
Kaegi, R., Ulrich, A., Sinnet, B., Vonbank, R., Wichser, A., Zuleeg, S., … Boller, M. (2008). Synthetic TiO2 nanoparticle emission from exterior facades into the aquatic environment. Environmental Pollution, 156(2), 233-239. doi:10.1016/j.envpol.2008.08.004, Institutional Repository

We present direct evidence of the release of synthetic nanoparticles from urban applications into the aquatic environment. We investigated TiO2 particles as these particles are used in large quantities in exterior paints as whitening pigments and are to some extent also present in the nano-size range.
TiO2 particles were traced from exterior facade paints to the discharge into surface waters. We used a centrifugation based sample preparation which recovers TiO2 particles between roughly 20 and 300 nm. Analytical electron microscopy revealed that TiO2 particles are detached from new and aged facade paints by natural weather conditions and are then transported by facade runoff and are discharged into natural, receiving waters. Microscopic investigations are confirmed by bulk chemical analysis. By combining results from microscopic investigations with bulk chemical analysis we calculated the number densities of synthetic TiO2 particles in the runoff.
Navarro, E., Piccapietra, F., Wagner, B., Marconi, F., Kaegi, R., Odzak, N., … Behra, R. (2008). Toxicity of silver nanoparticles to Chlamydomonas reinhardtii. Environmental Science and Technology, 42(23), 8959-8964. doi:10.1021/es801785m, Institutional Repository

Silver nanoparticles (AgNP) are likely to enter the aquatic environment because of their multiple uses. We have examined the short-term toxicity of AgNP and ionic silver (Ag+) to photosynthesis in Chlamydomonas reinhardtii using fluorometry. AgNP ranged in size from 10 to 200 nm with most particles around 25 nm. As determined by DGT (diffusive gradients in thin films), by ion-selective electrode, and by centrifugal ultrafiltration, about 1% of the AgNP was present as Ag+ ions. Based on total Ag concentration, toxicity was 18 times higher for AgNO3 than for AgNP (in terms of EC50). However, when compared as a function of the Ag+ concentration, toxicity of AgNP appeared to be much higher than that of AgNO3. The ionic Ag+ measured in the AgNP suspensions could not fully explain the observed toxicity. Cysteine, a strong Ag+ ligand, abolished the inhibitory effects on photosynthesis of both AgNP and Ag+. Together, the results indicate that the interaction of these particles with algae influences the toxicity of AgNP, which is mediated by Ag+. Particles contributed to the toxicity as a source of Ag+ which is formed in presence of algae.
Burkhardt, M., Kägi, R., Simmler, H., Ulrich, A., & Boller, M. (2007). Nanopartikel auf Fassaden erforschen. Thema Umwelt, 2, 12-13. , Institutional Repository

Nanosilber und Nanotitandioxid haben das Potenzial, problematische Biozide zur Bekämpfung von Algen und Pilzen auf Fassaden zu ergänzen oder zu ersetzen. Allerdings ist bis heute völlig unklar, ob und in welchem Umfang diese Nanopartikel die Umwelt und die menschliche Gesundheit beeinträchtigen können. Um die Chancen und Risiken dieser Technologie abwägen und mit den heute üblichen Bioziden vergleichen zu können, haben Eawag und Empa, zwei Forschungsinstitute des ETH-Bereichs, ein Forschungsprojekt lanciert.
Fierz, M., Kaegi, R., & Burtscher, H. (2007). Theoretical and experimental evaluation of a portable electrostatic TEM sampler. Aerosol Science and Technology, 41(5), 520-528. doi:10.1080/02786820701253327, Institutional Repository

In this study, we present the design, calibration, and performance evaluation of a portable TEM sampler to collect ultrafine particles on TEM grids. The sampler is based on electrostatic deposition. We performed calibration experiments with monodisperse model particles of different size, morphology, and chemistry to evaluate the efficiency of the device. Additionally, we modeled the performance of the TEM sampler using finite element calculations to calculate the sampling efficiency as function of particle size. We find a good agreement between the model calculations and calibration experiments, but with a systematic deviation of about 30%. We present further experiments with polydisperse particles and derive particle size distributions and absolute number concentrations from TEM images. The shape of the size distribution is very similar to the corresponding SMPS measurements, while the total number concentration has a larger uncertainty. Thanks to the compact design of the sampler, it can be used to collect ultrafine particles even in remote or hostile environments, where no electric power is available.
Lorenzo, R., Kaegi, R., Gehrig, R., Scherrer, L., Grobéty, B., & Burtscher, H. (2007). A thermophoretic precipitator for the representative collection of atmospheric ultrafine particles for microscopic analysis. Aerosol Science and Technology, 41(10), 934-943. doi:10.1080/02786820701581834, Institutional Repository

In this article, the potential of a thermophoretic sampling device to derive quantitative particle size distributions and number concentrations of aerosols based on microscopic single particle analysis is explored. For that purpose a plate-to-plate thermophoretic precipitator to collect ultrafine atmospheric particles for TEM (transmission electron microscopy) analysis has been calibrated and characterized. The representativeness of the samples has been verified in a series of experiments. Results show that, for particles with diameters of 15 nm to 300 nm, the precipitator's collection efficiency is independent of size, shape, and composition of the particles. Hence, its samples accurately represent the original aerosol. A numerical model of thermophoretic deposition within the device has been developed and tailored to the specifications of the precipitator. The model has been used to derive the particle number density and size distribution of several calibration aerosols using the TEM analysis of the samples taken with the thermophoretic precipitator as input parameters. The results agree very well with the on-line measurements of the calibration aerosols. This work demonstrates that our thermophoretic sampling device can be used to derive quantitative particle size distributions and number concentrations of ultrafine particles based on microscopic single particle analysis.
Yang, T., Holzer, L., Kägi, R., Winnefeld, F., & Keller, B. (2007). In situ nanomanipulators as a tool to separate individual tobermorite crystals for AFM studies. Ultramicroscopy, 107(10–11), 1068-1077. doi:10.1016/j.ultramic.2007.02.042, Institutional Repository

Atomic force microscopy (AFM) studies of cementitious materials are limited, mainly due to the lack of appropriate sample preparation techniques. In porous autoclaved aerated concrete (AAC), calcium silicate hydrate (C–S–H) is produced in its crystalline form, tobermorite. The crystals are lath-like with a length of several micrometers. In this work, we demonstrate the application of nanomanipulators to separate an individual tobermorite crystal from the bulk AAC for subsequent AFM investigations. The nanomanipulators are operated directly in an environmental scanning electron microscope (ESEM). We studied the interaction between moisture and the tobermorite surface under controlled relative humidity (RH). The results of topography and adhesion force measurements with AFM suggest that the surface of tobermorite is hydrophobic, which contrasts the macroscopic material properties (e.g. moisture transport in capillary pores).
Kaegi, R., & Gasser, P. (2006). Application of the focused ion beam technique in aerosol science: detailed investigation of selected, airborne particles. Journal of Microscopy, 224(2), 140-145. doi:10.1111/j.1365-2818.2006.01669.x, Institutional Repository

The focused ion beam technique was used to fabricate transmission electron microscope lamellas of selected, micrometre-sized airborne particles. Particles were sampled from ambient air on Nuclepore polycarbonate filters and analysed with an environmental scanning electron microscope. A large number of particles between 0.6 and 10 μm in diameter (projected optical equivalent diameter) were detected and analysed using computer-controlled scanning electron microscopy. From the resulting dataset, where the chemistry, morphology and position of each individual particle are stored, two particles were selected for a more detailed investigation. For that purpose, the particle-loaded filter was transferred from the environmental scanning electron microscope to the focused ion beam, where lamellas of the selected particles were fabricated. The definition of a custom coordinate system enabled the relocation of the particles after the transfer. The lamellas were finally analysed with an analytical transmission electron microscope. Internal structure and elemental distribution maps of the interior of the particles provided additional information about the particles, which helped to assign the particles to their sources. The combination of computer-controlled scanning electron microscopy, focused ion beam and transmission electron microscopy offers new possibilities for characterizing airborne particles in great detail, eventually enabling a detailed source apportionment of specific particles. The particle of interest can be selected from a large dataset (e.g. based on chemistry and/or morphology) and then investigated in more detail in the transmission electron microscope.
Mavrocordatos, D., Kaegi, R., & Schmatloch, V. (2002). Fractal analysis of wood combustion aggregates by contact mode atomic force microscopy. Atmospheric Environment, 36(36-37), 5653-5660. doi:10.1016/S1352-2310(02)00702-1, Institutional Repository

Atomic force microscopy (AFM) is a powerful tool for the characterization of nanoparticles allowing to obtain fundamental parameters of morphology such as the size of individual particles, the number of particles per aggregate, the size distribution and finally the AFM allows one to determine the volume. All these parameters are accessible for the native aspect of the particles while AFM works under ambient temperature and pressure. We present here the analysis of wood combustion particles and their morphological parameters. Using our results for the 3D values, we were able to calculate the fractal dimension (Df) of the aggregates. As the Df is characteristic to the aggregation regime that particles undergo, we determined that wood particle aggregates follow a diffusion limited aggregation regime (Df=1.95). In parallel, in-situ analysis of the hydration effect has been studied in water at pH 7 and shows that the morphology is significantly influenced by the hydration. The composition observed by analytical electron microscopy (AEM) and atomic emission spectrometry (AES) enabled us to correlate the in-situ measurements by AFM with the hydration behavior of these particles and the fractal dimension.

Marc Böhler

Brander, A., Wunderlin, P., Gulde, R., & Böhler, M. (2024). MV-Stufen Stabil Betreiben. Hilfreiche Betriebsparameter. Aqua & Gas, 104(1), 54-61. , Institutional Repository

Der Reinigungseffekt für Mikroverunreinigungen wird von ARA über periodische Messungen der Leitsubstanzen bestimmt. Für den täglichen Betrieb lassen sich zusätzlich anhand von UV-Messungen sowie anhand der dosierten Mengen an Ozon oder Aktivkohle zeitnahe Aussagen zur Reinigungsleistung machen.
Böhler, M. A., Carl, F., Zhu, M., McArdell, C. S., Frömelt, A., & Joss, A. (2023). Spurenstoffelimination bei stark verdünnter Abwassermatrix – Erfahrungen, Kenntnisstand und Herausforderungen. In M. Wessling & T. Wintgens (Eds.), 15. Aachener Tagung Wassertechnologie. Verfahren der Abwasserbehandlung und Wasseraufbereitung (pp. 14-23). Aachen: RWTH Aachen University. , Institutional Repository

Das Qualitätsziel einer 80%igen Elimination von Mikroverunreinigungen ist in der Schweiz für ausgewählte ARA auch bei Regenwetterverhältnissen stets einzuhalten. Hohe Niederschläge verursachen hohe Mischwasserzuläufe zur ARA, die in der Menge häufig das Doppelte der Trockenwettermenge übersteigt. Der Schmutzwasseranteil (Abwassermatrix) ist dann um das Vielfache verdünnt. Dieser Umstand verursacht hydraulische Effekte wie verkürzte hydraulische Aufenthaltszeiten in den Behandlungsstufen und führt zu verkürzten Kontakt- und Reaktionszeiten in den Reaktoren. U.a. können Kurzschlussströme entstehen, die die EMV erniedrigen können. Die EMVStufen in der Schweiz sind auf Mischwasserzulauf ausgelegt und es wurden über die letzten Jahre angepasste Betriebsstrategien für die verschiedenen
EMV-Verfahren erarbeitet, so dass in aller Regel das Qualitätsziel erreicht wird. Dennoch bleibt der sichere, wirtschaftliche sowie nachhaltige Betrieb der Anlagen anspruchsvoll mit hohen Herausforderungen.
Aktuelle Untersuchungen der Eawag zum Verhalten höher beladener GAK im Einzelfilter zeigten bei Kontakt mit stark verdünntem Abwasser trotz 20-minütiger Kontaktzeit verringerte Sorptionsleistung bis hin zur Desorption von Einzelsubstanzen. Ob dieser Umstand auch bei einem Parallelbetrieb zu beobachten ist, sollen weiterführende Untersuchungen im Praxisbetrieb von GAK-Filtrationen zeigen. Im Fall der GAK-Filtration der ARA Glarnerland mit langanhaltenden Regennachläufen und Schmelzwasserzulauf wurde eine PAK-Dosierung in die Biologie vorgeschaltet bzw. wird aktuell realisiert, um allenfalls Einbussen durch verdünnte Abwassermatrix abzufangen.
Böhler, M. A., Joss, A., & McArdell, C. S. (2022). GAK-Filter für die Spurenstoffentfernung. Erfahrungen und Betriebsergebnisse der Pilotstudien ARA Furt/Bülach und Glarnerland. Aqua & Gas, 102(1), 48-54. , Institutional Repository

Auf den Kläranlagen Furt/Bülach und Glarnerland des Abwasserverbandes Glarnerland (AVG, Bilten) wurden zwischen 2014 und 2019 umfangreiche Untersuchungen zur Elimination von Mikroverunreinigungen mittels granulierter Aktivkohle (GAK) durchgeführt. Ziel war es, unter Schweizer Praxisbedingungen die Machbarkeit, Effizienz und Wirtschaftlichkeit des Verfahrens zu evaluieren. Fazit beider Forschungsprojekte ist, dass sich die GAK-Filtration zur Spurenstoffelimination gemäss Schweizer Gesetzgebung eignet. Das Verfahren ist technisch und wirtschaftlich realisierbar und hat sich als praxistauglich erwiesen.
Kessler, M., Löwenberg, J., Böhler, M., & Strebel, P. (2022). Neue Reinigungsstufe für die ARA Muri. Aqua & Gas, 102(12), 74-79. , Institutional Repository

Zukünftig werden auf der ARA Muri dank einer neuen Reinigungsstufe Mikroverunreinigungen aus dem Abwasser entfernt. Die GAK-Filtration bietet viele Vorteile und wird nicht nur verfahrenstechnisch, sondern auch ästhetisch optimal in die bestehenden Strukturen der ARA Muri eingebunden. Zur sicheren Umsetzung wurden in einer Pilotierung wichtige Fragen beantwortet, insbesondere wie die Filterzellen möglichst ideal mit einer Parallelschaltung für eine maximale Beladung zu verschalten sind.
Brander, A., Böhler, M., McArdell, C., & Joss, A. (2021). Hinweise zur Planung und Auslegung von diskontinuierlich gespülten GAK-Filtern zur Elimination organischer Spurenstoffe aus kommunalem Abwasser unter besonderer Berücksichtigung der Anforderungen und Erfahrungen in der Schweiz (p. (6 pp.). Presented at the 14. Aachener Tagung Wassertechnologie. Verfahren der Wasseraufbereitung und Abwasserbehandlung. Aachen, Deutschland. , Institutional Repository
Böhler, M. A., Hagemann, N., Bucheli, T., Brander, A., & McArdell, C. S. (2021). Erneuerbare Aktivkohlen für die Spurenstoffelimination aus kommunalem Abwasser - Performance und Potenzial biogener Ausgangsstoffe (p. (8 pp.). Presented at the 14. Aachener Tagung Wassertechnologie. Verfahren der Wasseraufbereitung und Abwasserbehandlung. Aachen, Deutschland. , Institutional Repository
Böhler, M. A., McArdell, C. S., Oltramare, C., Hernandez, A., Büeler, A., & Siegrist, H. (2021). PAK-Dosierung in die biologische Stufe mit S::Select®-Verfahren zur erweiterten Abwasser-behandlung auf der ARA Glarnerland. In 14. Aachener Tagung Wassertechnologie. Verfahren der Wasseraufbereitung und Abwasserbehandlung (p. (10 pp.). Aachen: RWTH Aachen. , Institutional Repository
Böhler, M., Hernandez, A., McArdell, C. S., Siegrist, H., Joss, A., & Baggenstos, M. (2020). Elimination von Spurenstoffen durch granulierte Aktivkohle-Filtration (GAK). Grosstechnische Untersuchungen auf der ARA Furt, Bülach. Schlussbericht. Dübendorf: Eawag. , Institutional Repository
Böhler, M., Joss, A., McArdell, C., & Meier, A. (2020). Hinweise zur Planung und Auslegung von diskontinuierlich gespülten GAK-Filtern zur Elimination organischer Spurenstoffe aus kommunalem Abwasser. Konsenspapier zum Ergebnis des Workshops vom 9.12.2019 an der Eawag. Dübendorf: Eawag; VSA. , Institutional Repository
Böhler, M., Joss, A., McArdell, C., & Meier, A. (2020). Notice explicative pour la planification et le dimensionnement de filtres à charbon actif en grains (CAG) rétrolavés discontinuellement pour l'élimination des composés traces organiques dans les eaux usées communales. Document de synthèse suite au workshop du 9.12.2019 à l'Eawag. Dübendorf: Eawag; VSA. , Institutional Repository
Hagemann, N., Schmidt, H. P., Kägi, R., Böhler, M., Sigmund, G., Maccagnan, A., … Bucheli, T. D. (2020). Wood-based activated biochar to eliminate organic micropollutants from biologically treated wastewater. Science of the Total Environment, 730, 138417 (11 pp.). doi:10.1016/j.scitotenv.2020.138417, Institutional Repository

Implementing advanced wastewater treatment (WWT) to eliminate organic micropollutants (OMPs) is a necessary step to protect vulnerable freshwater ecosystems and water resources. To this end, sorption of OMP by activated carbon (AC) is one viable technology among others. However, conventional AC production based on fossil precursor materials causes environmental pollution, including considerable emissions of greenhouse gases. In this study, we produced activated biochar (AB) from wood and woody residues by physical activation and evaluated their capability to eliminate OMPs in treated wastewater. Activated biochar produced under optimized conditions sorbed 15 model OMPs, of which most were dissociated at circumneutral pH, to the same or higher extent than commercial AC used as a reference. While wood quality played a minor role, the dosage of the activation agent was the main parameter controlling the capacity of ABs to eliminate OMP. Our results highlight the possibility for local production of AB from local wood or woody residues as a strategy to improve WWT avoiding negative side effects of conventional AC production.
Köpping, I., McArdell, C. S., Borowska, E., Böhler, M. A., & Udert, K. M. (2020). Removal of pharmaceuticals from nitrified urine by adsorption on granular activated carbon. Water Research X, 9, 100057 (10 pp.). doi:10.1016/j.wroa.2020.100057, Institutional Repository

Nitrification and distillation of urine allow for the recovery of all nutrients in a highly concentrated fertilizer solution. However, pharmaceuticals excreted with urine are only partially removed during these two process steps. For a sustainable and safe application, more extensive removal of pharmaceuticals is necessary. To enhance the pharmaceutical removal, which is already occurring during urine storage, nitrification and distillation, an adsorption column with granular activated carbon (GAC) can be included in the treatment train. We executed a pilot-scale study to investigate the adsorption of eleven indicator pharmaceuticals on GAC. During 74 days, we treated roughly 1000 L of pre-filtered and nitrified urine spiked with pharmaceuticals in two flow-through GAC columns filled with different grain sizes. We compared the performance of these columns by calculating the number of treated bed volumes until breakthrough and carbon usage rates. The eleven spiked pharmaceuticals were candesartan, carbamazepine, clarithromycin, diclofenac, emtricitabine, hydrochlorothiazide, irbesartan, metoprolol, N4-acetylsulfamethoxazole, sulfamethoxazole and trimethoprim. At the shortest empty bed contact time (EBCT) of 25 min, immediate breakthrough was observed in both columns shortly after the start of the experiments. Strong competition by natural organic material (NOM) could have caused the low pharmaceutical removal at the EBCT of 25 min. At EBCTs of 70, 92 and 115 min, more than 660 bed volumes could be treated until breakthrough in the column with fine GAC. The earliest breakthrough was observed for candesartan and clarithromycin. On coarse GAC, only half the number of bed volumes could be treated until breakthrough compared to fine GAC. The probable reason for the later breakthrough with fine GAC is the smaller intraparticle diffusive path length. DOC and UV absorbance measurements at 265 nm indicated that both parameters can be used as indicators for the breakthrough of pharmaceuticals. In contrast to pharmaceuticals and DOC, the nutrient compounds ammonium, nitrate, phosphate, potassium and sulfate were not removed significantly. A comparison with literature values suggests that the amount of GAC needed to remove pharmaceuticals from human excreta could be reduced by nearly two orders of magnitude, if urine were treated on site instead of being discharged and treated in a centralized wastewater treatment plant.
McArdell, C. S., Böhler, M., Hernandez, A., Oltramare, C., Büeler, A., & Siegrist, H. (2020). Pilotversuche zur erweiterten Abwasser-behandlung mit granulierter Aktivkohle (GAK) und kombiniert mit Teilozonung (O3/GAK) auf der ARA Glarnerland (AVG). Ergänzende Untersuchungen zur PAK-Dosierung in die biologische Stufe mit S::Select®-Verfahren in Kombination mit nachfolgender GAK. Schlussbericht. Dübendorf: Eawag. , Institutional Repository

Auf der Kläranlage Glarnerland wurde im Rahmen des Forschungsprojektes «Pilotversuche zur erweiterten Abwasserbehandlung mit granulierter Aktivkohle (GAK) und kombiniert mit Teilozonung (O3/GAK)» die Machbarkeit und Effizienz der genannten Verfahrenstechniken zur Spurenstoffelimination untersucht. Im weiteren Verlauf der Untersuchungen wurde zudem auch die Option der Dosierung von Pulveraktivkohle (PAK) in die biologische Stufe, welche mit dem S::Select®-Verfahren betrieben wird, als Vorstufe zur GAK erprobt.

Ziel der Pilotierung war die Erarbeitung von Entscheidungsgrundlagen zur Auswahl eines optimalen Verfahrens oder einer Verfahrenskombination für die angestrebte Realisierung der Spurenstoffelimination beim Abwasserverband Glarnerland. Zudem sollten Langzeiterfahrungen zum Betrieb von GAK-Filtrationen bezüglich Effizienz, Betrieb und vor allem Standzeiten (erreichte Bettvolumina) von verschiedenen GAK-Typen bei unterschiedlichen Kontaktzeiten bei einem Abwasser mit hohem gelöstem organischen Kohlenstoff (DOC) gesammelt werden.

Die Pilotanlage Vorozonung/GAK-Filtration ging Ende Januar 2017 auf der ARA Glarnerland in Betrieb und wurde im August 2019 ausser Betrieb gesetzt. Es wurden vier verschiedene GAK-Produkte untersucht (CSC «HC HK 1000», CarboTech «Pool W1-3», Jacobi «Aquasorb 5010», CabotNorit «GAC 1020 EN»). Parallel wurden alle GAK-Kolonnen (ausser Jacobi «Aquasorb 5010») während der gesamten Betriebsdauer mit einer Vorozonung bei einer spezifischen Ozondosis von rund 0.2 gO3/gDOC betrieben. [...]
 
Böhler, M. A., Remy, C., Löwenberg, J., Hagemann, N., Hernandez, A., Joss, A., & McArdell, C. S. (2019). Kann die Kohle nachhaltig sein? – Einsatz von Aktivkohle zur Elimination von Spurenstoffen aus kommunalem Abwasser. In M. Wessling & J. Pinnekamp (Eds.), 13. Aachener Tagung Wassertechnologie. Verfahren der Wasseraufbereitung und Abwasserbehandlung (pp. 51-62). Aachen: RWTH Aachen. , Institutional Repository
Böhler, M. (2019). Laborversuche zur Bestimmung der Reinigungsleistung von Pulveraktivkohle zur Entfernung von Mikroverunreinigungen auf Kläranlagen. Anleitung. Dübendorf: Eawag. , Institutional Repository

Die vorliegende Anleitung soll interessierte Fachkreise und Akteure im Themengebiet zur Durchführung von Schüttelversuchen zur Bestimmung der Reinigungsleistung von Pulveraktivkohle (PAK) zur Entfernung von Mikroverunreinigungen aus kommunalem Abwasser befähigen. Die Anwendungen von PAK zur Spurenstoffelimination werden zukünftig auf Kläranlagen zunehmen, so dass sich diese Anleitung an Kläranlagenbetreiber und andere Dienstleister richtet, die einen Bedarf zur Evaluation geeigneter Aktivkohlen als auch zur Überprüfung von Produktlieferungen haben. Die vorgestellte Verfahrensweise ist durch gut ausgebildetes Klärwerkspersonal in einem gängigen Kläranlagenlabor der Eigenüberwachung der Abwasserreinigungsanlage durchführbar.
Das Dokument gibt konkrete Hinweise zur gezielten Vorgehensweise bei PAK-Auswahl, Probenahme von Abwasser, Vorbereitung und Durchführung der Versuche sowie zur Analytik und Bewertung der Ergebnisse. Es zeigt auf, welche Fragestellungen durch derartige Versuche beantwortet werden können. Das Dokument widerspiegelt die bisherigen Erfahrungen, welche an der Eawag gemacht wurden und gibt Hinweise zur Vorgehensweise ab, wobei auch auf andere Methoden und Erfahrungen hingewiesen wird. Das Dokument ist unter verschiedenen Fachleuten abgestimmt worden. Hinweise auf andere Erfahrungen oder zur Verbesserung der Vorgehensweise sowie Neuerungen im Themengebiet sind von den Autoren sehr erwünscht und richten sich bitte an die Verfasser bzw. an den VSA.
Hagemann, N., Bucheli, T. D., Schmidt, H. P., Kägi, R., Böhler, M., & McArdell, C. S. (2019). Aktivkohle - Made in Switzerland!. Aqua & Gas, 99(1), 32-38. , Institutional Repository

Die Elimination von Mikroverunreinigungen in der Abwasserreinigung mit Aktivkohle oder Ozon ist eine wichtige Massnahme zum vorbeugenden Schutz der Gewässer und der Trinkwasserressourcen der Schweiz. Während der Einsatz von Ozon mit einem hohen Energieverbrauch einhergeht, führt der Einsatz von Aktivkohle andernorts zu negativen Umweltauswirkungen, da die Aktivkohle zum Teil aus fossilen Ausgangsstoffen wie Stein- oder Braunkohle hergestellt und zudem über weite Strecken transportiert wird. Aktivkohlen mit sehr guten Eliminationsleistungen könnten aber auch in der Schweiz aus einheimischen erneuerbaren Roh- und Reststoffen hergestellt werden.
Löwenberg, J., Böhler, M., Stegmann, W., & Meier, A. (2019). Wiederverwertung von Pulveraktivkohle aus der Trinkwasseraufbereitung zur Umsetzung der Spurenstoffelimination auf kommunalen Kläranlagen. Projektbericht. Pratteln: CSD Envirotec. , Institutional Repository

Im vorliegenden Bericht wird die Möglichkeit zur Widerverwertung von in der Trinkwasseraufbereitung genutzter Pulveraktivkohle betrachtet. Dazu werden die zur Wiederverwertung notwendigen, förderlichen oder auch hinderlichen Rahmenbedingungen aufgezeigt und diskutiert.
Der Bericht zeigt auf, dass die Wiederverwertung von in der Trinkwasseraufbereitung genutzter Aktivkohle unter bestimmten Rahmenbedingungen für Trinkwasserproduzent und Wiederverwerter (bspw. Abwasserreinigungsanlage) sinnvoll und ökonomisch attraktiv sein kann.
Basierend auf der geführten Diskussion wird den Trinkwasserproduzenten eine Entscheidungsmatrix an die Hand gegeben mit deren Hilfe die Sinnhaftigkeit einer PAK Wiederverwertung bewertet werden kann.
Am Beispiel der Trinkwasseraufbereitungsanlage Muttenz wird ein aktuelles Projekt zur Wiederverwertung von Pulveraktivkohle gezeigt und die bereits getroffenen Massnahmen beschrieben. An Hand der Entscheidungsmatrix und zur besseren Einordnung für den Leser wurde die Situation der TWA Muttenz bewertet.
Meier, A., & Böhler, M. (2019). Pulveraktivkohle - Welche passt? Wahl, Beschaffung und Qualitätssicherung von Pak zur Elimination von Mikroverunreinigungen. Aqua & Gas, 99(1), 22-31. , Institutional Repository

Fünf bis zehn Gramm Pulveraktivkohle weisen die Oberfläche eines Fussballfeldes auf. Das faszinierende schwarze Pulver kann vielerorts eingesetzt werden, zum Beispiel auf Abwasserreinigungsanlagen, um Mikroverunreinigungen aus dem Abwasser zu eliminieren – und dies immer häufiger. Auf dem Markt sind zahlreiche PAK-Sorten verfügbar, die zwar äusserlich nicht zu unterscheiden sind, aber dennoch unterschiedliche Eigenschaften aufweisen. Dieser Artikel soll Betreiber und Ingenieure bei der Entscheidung unterstützen, welche Pulveraktivkohle für ihr Abwasser optimal ist und wie sie die Qualität neuer Lieferungen überprüfen können.
Siegrist, H., Joss, A., Boehler, M., McArdell, C. S., & Ternes, T. (2019). Organic micropollutant control. In G. Mannina, G. Ekama, H. Ødegaard, & G. Olsson (Eds.), Advances in wastewater treatment (pp. 231-260). doi:10.2166/9781780409719_0231, Institutional Repository

About 100,000 chemical substances have economic uses, of which 4,600 substances are produced annually in quantities exceeding 1,000 tons in the OECD member states. During production and disposal, as well as after regular use, a significant portion of these substances will unavoidably enter the aquatic environment, where they can have ecotoxicological effects, such as fish feminization. Organic compounds are increasingly being detected in water bodies and in sewage sludge in low concentration ranges (μg/L and ng/L), being referred to as organic micropollutants. T he removal of micropollutants by conventional municipal wastewater treatment is incomplete and a multitude of compounds are only slightly abated. To significantly reduce eco-toxicological effects of micropollutants in receiving waters and water resources, additional treatment steps (e.g. ozonation or activated carbon adsorption) are required in combination with measures taken at the source. Ozonation requires complete nitrification and it might not be suitable for wastewater with high industrial wastewater fractions and high bromide concentrations due to the production of bromate and increased oxidation by-products. Powdered activated carbon (PAC) addition is already broadly applied. PAC can be recycled to the activated sludge treatment to improve micropollutant removal and therefore reduce PAC consumption. Recently granular activated carbon (GAC) filters are increasingly investigated and built in full scale for micropollutant and dissolved organic carbon (DOC) removal. Additional measures in wastewater treatment should be based on careful micropollutant mass flux studies to identify critical catchment areas so that relevant hot spots can be addressed.
Bourgin, M., Beck, B., Boehler, M., Borowska, E., Fleiner, J., Salhi, E., … McArdell, C. S. (2018). Evaluation of a full-scale wastewater treatment plant upgraded with ozonation and biological post-treatments: abatement of micropollutants, formation of transformation products and oxidation by-products. Water Research, 129, 486-498. doi:10.1016/j.watres.2017.10.036, Institutional Repository

To protect the ecosystem and drinking water resources in Switzerland and in the countries of the downstream catchments, a new Swiss water protection act entered into force in 2016 aiming to reduce the discharge of micropollutants from wastewater treatment plants (WWTPs). As a consequence, selected WWTPs must be upgraded by an advanced treatment for micropollutant abatement with suitable and economic options such as (powdered) activated carbon treatment or ozonation. WWTP Neugut (105′000 people equivalent) was the first WWTP in Switzerland to implement a long-term full-scale ozonation. Differing specific ozone doses in the range of 0.35–0.97 g O3/g DOC were applied to determine the adequate ozone dose to fulfill the requirements of the Swiss water protection act. Based on this assessment, a specific ozone dose of 0.55 g O3/g DOC is recommended at this plant to ensure an average abatement of the twelve selected indicator substances by ≥80% over the whole treatment. A monitoring of 550 substances confirmed that this dose was very efficient to abate a broad range of micropollutants by >79% on average. After ozonation, an additional biological post-treatment is required to eliminate possible negative ecotoxicological effects generated during ozonation caused by biodegradable ozonation transformation products (OTPs) and oxidation by-products (OBPs). Three biological treatments (sand filtration, moving bed, fixed bed) and granular activated carbon (GAC, fresh and pre-loaded) filtration were evaluated as post-treatments after ozonation. In parallel, a fresh GAC filter directly connected to the effluent of the secondary clarifier was assessed. Among the three purely biological post-treatments, the sand filtration performed best in terms of removal of dissolved organic carbon (DOC), assimilable organic carbon (AOC) and total suspended solids (TSS). The fresh activated carbon filtration ensured a significant additional micropollutants abatement after ozonation due to sorption. The relative abatement of the indicator substances ranged between 20 and 89% after 27′000 bed volumes (BV) and was still substantial at 50′000 BV. In an identical GAC filter running in parallel and being fed with the effluent of the secondary clarifier, the elimination was less efficient. Seven primary OTPs (chlorothiazide and six N-oxides) formed during ozonation could be quantified thanks to available reference standards. Their concentration decreased with increasing specific ozone doses with the concomitant formation of other OTPs. The seven OTPs were found to be stable compounds and were not abated in the biological post-treatments. They were sorbed in the fresh GAC filter, but less efficiently than the corresponding parent compounds. Two OBPs, bromate (BrO3−) and N-nitrosodimethylamine (NDMA), were formed during ozonation but did not exceeded 5 μg/L for bromate and 30 ng/L for NDMA at the recommended specific ozone dose of 0.55 g O3/g DOC. NDMA was well abated in all post-treatments (minimum 41% during fixed bed filtration, maximum 83% during fresh GAC filtration), while bromate was very stable as expected.
Böhler, M. A., & Seyfried, A. (2018). Versuchsergebnisse zur Membranstrippung auf der Kläranlage Altenrhein und Auswirkungen einer Teilstrombehandlung auf die Emissionen der Abwasserreinigung (pp. 1-21). Presented at the 10. Aachener Tagung zur Behandlung der Stickstoffrückbelastung aus der Schlammentwässerung. Leverkursen, Germany. , Institutional Repository

Die Rückgewinnung von Nährstoffen aus Abwasser wird in der Zukunft aus Gründen der Nachhaltigkeit und zunehmend auch aus Gründen der Wirtschaftlichkeit mehr an Bedeutung gewinnen. Ein derzeit von der Eawag mit verschiedenen Partnern evaluiertes chemisch/physikalisches Verfahren der N-Rückgewinnung über eine Membranstrippung (sogenannte Membrankontaktoren) ist auf einer Kläranlagen in der Westschweiz seit Mitte 2016 erfolgreich im Einsatz. Weitere volltechnische Realisierungen solcher Anlagen stehen in Deutschland und der Schweiz in der Planung oder kurz vor der volltechnischen Umsetzung.
Der Beitrag gibt einen Überblick über den derzeitigen Wissensstand zur Technologie wie die Verfahrensführung, Vorbehandlung, spezifische Verbräuche (Energie, Betriebsstoffe) und Kosten. Neben Ergebnissen aus diversen Pilotversuchen, welche die Eawag mit ihren Partnern durchgeführt hat, wird auch über das EU-Projekt "POWERSTEP" (http://powerstep.eu/case-studies/cs6-altenrhein-switzerland) und über weitere volltechnische Umsetzungen berichtet.
Hagemann, N., Spokas, K., Schmidt, H. P., Kägi, R., Böhler, M. A., & Bucheli, T. D. (2018). Activated carbon, biochar and charcoal: linkages and synergies across pyrogenic carbon's ABCs. Water, 10(2), 182 (19 pp.). doi:10.3390/w10020182, Institutional Repository

Biochar and activated carbon, both carbonaceous pyrogenic materials, are important products for environmental technology and intensively studied for a multitude of purposes. A strict distinction between these materials is not always possible, and also a generally accepted terminology is lacking. However, research on both materials is increasingly overlapping: sorption and remediation are the domain of activated carbon, which nowadays is also addressed by studies on biochar. Thus, awareness of both fields of research and knowledge about the distinction of biochar and activated carbon is necessary for designing novel research on pyrogenic carbonaceous materials. Here, we describe the dividing ranges and common grounds of biochar, activated carbon and other pyrogenic carbonaceous materials such as charcoal based on their history, definition and production technologies. This review also summarizes thermochemical conversions and non-thermal pre- and post-treatments that are used to produce biochar and activated carbon. Our overview shows that biochar research should take advantage of the numerous techniques of activation and modification to tailor biochars for their intended applications.
Benstoem, F., Nahrstedt, A., Boehler, M., Knopp, G., Montag, D., Siegrist, H., & Pinnekamp, J. (2017). Performance of granular activated carbon to remove micropollutants from municipal wastewater - a meta-analysis of pilot- and large-scale studies. Chemosphere, 185, 105-118. doi:10.1016/j.chemosphere.2017.06.118, Institutional Repository

For reducing organic micropollutants (MP) in municipal wastewater effluents, granular activated carbon (GAC) has been tested in various studies. We did systematic literature research and found 44 studies dealing with the adsorption of MPs (carbamazepine, diclofenac, sulfamethoxazole) from municipal wastewater on GAC in pilot- and large-scale plants. Within our meta-analysis we plot the bed volumes (BV [m3 water/m3 GAC]) until the breakthrough criterion of MP-BV20% was reached, dependent on potential relevant parameters (empty bed contact time EBCT, influent DOC DOC0 and manufacturing method). Moreover, we performed statistical tests (ANOVAs) to check the results for significance. Single adsorbers operating time differs i.e. by 2500% until breakthrough of diclofenac-BV20% was reached (800-20,000 BV). There was still elimination of the “very well/well” adsorbable MPs such as carbamazepine and diclofenac even when the equilibrium of DOC had already been reached. No strong statistical significance of EBCT and DOC0 on MP-BV20% could be found due to lack of data and the high heterogeneity of the studies using GAC of different qualities. In further studies, adsorbers should be operated[20,000 BV for exact calculation of breakthrough curves, and the following parameters should be recorded: selected MPs; DOC0; UVA254; EBCT; product name, manufacturing method and raw material of GAC; suspended solids (TSS); backwash interval; backwash program and pressure drop within adsorber. Based on our investigations we generally recommend using reactivated GAC to reduce the environmental impact and to carry out tests on pilot scale to collect reliable data for process design.
Bitterwolf, S., Böhler, M., Siegrist, H., & Joss, A. (2017). Elimination von Spurenstoffen durch granulierte Aktivkohle (GAK) Filtration: Grosstechnische Untersuchungen auf der ARA Furt-Bülach. Zwischenbericht. Dübendorf: Eawag. , Institutional Repository
Böhler, M., Fleiner, J., Siegrist, H., McArdell, C. S., Teichler, R., Bourgin, M., … Blunschi, M. (2017). Biologische Nachbehandlung von kommunalem Abwasser nach Ozonung – ReTREAT. Schlussbericht. Dübendorf: Eawag. , Institutional Repository

Der vorliegende Bericht fasst die Ergebnisse des Forschungsprojektes "Biologische Nachbehandlung von kommunalem Abwasser nach Ozonung", kurz "ReTREAT", zusammen. Das Projekt wurde durch das Bundesamtes für Umwelt (BAFU) im Rahmen der Umwelttechnologieförderung (UTF) finanziert. Zudem wurde das Projekt durch hohe Eigen- und Cash-Leistungen der Industriepartner finanziell und technisch unterstützt.
Ziel des Projektes war es Untersuchungen zur Leistungsfähigkeit und Effizienz verschiedener Verfahren der biologischen Nachbehandlung zur Reduktion der ökotoxikologischen Wirkung und zur Reduktion von Transformationsprodukten von ozonten, kommunalem Abwassers durchzuführen.
Böhler, M., Fleiner, J., McArdell, C. S., Teichler, R., Siegrist, H., Kienle, C., … Wunderlin, P. (2017). Projekt ReTREAT. Untersuchungen zu Verfahren für die biologische Nachbehandlung nach Ozonung. Aqua & Gas, 97(5), 54-63. , Institutional Repository

Im Rahmen des Projekts ReTREAT wurden verschiedene Verfahren auf deren Eignung als biologische Nachbehandlung nach einer Ozonung getestet. Der Fokus lag dabei – neben allgemeinen Reinigungseffekten – insbesondere auf dem Abbau von labilen Reaktionsprodukten sowie deren ökotoxikologischen Wirkungen.
Böhler, M. (2017). Überblick und Erfahrungen mit der membranbasierten Ammoniak-Strippung (p. (14 pp.). Presented at the 10. DWA Klärschlammtage. Würzburg, Germany. , Institutional Repository

Die Rückgewinnung von Nährstoffen aus Abwasser wird in der Zukunft aus Gründen der Nachhaltigkeit und zunehmend auch aus Gründen der Wirtschaftlichkeit mehr an Bedeutung gewinnen. Ein derzeit von der Eawag mit verschiedenen Partnern evaluiertes chemisch/physikalisches Verfahren der N-Rückgewinnung über eine Membranstrippung (sogenannte Membrankontaktoren) ist auf einer Kläranlagen in der Westschweiz seit Mitte 2016 erfolgreich im Einsatz. Weitere volltechnische Realisierungen solcher Anlagen stehen in Deutschland und der Schweiz in der Planung oder kurz vor der volltechnischen Umsetzung.
Der Beitrag gibt einen Überblick über den derzeitigen Wissensstand zur Technologie wie die Verfahrensführung, Vorbehandlung, spezifische Verbräuche (Energie, Betriebsstoffe) und Kosten. Neben Ergebnissen aus diversen Pilotversuchen, welche die Eawag mit ihren Partnern durchgeführt hat, wird auch über das EU-Projekt "POWERSTEP" (http://powerstep.eu/case-studies/cs6-altenrhein-switzerland) und über weitere volltechnische Umsetzungen berichtet.
Böhler, M., Fleiner, J., Siegrist, H., Seyfried, A., & Egli, C. (2017). Überblick und Erfahrungen mit der membranbasierten Ammoniak-Strippung – Rückgewinnung von Stickstoff aus Abwässern der Schlammbehandlung. Presented at the 12. Aachener Tagung Wassertechnologien. Aachen, Germany. , Institutional Repository

Die Rückgewinnung von Nährstoffen aus Abwasser wird in der Zukunft aus Gründen der Nachhaltigkeit und zunehmend auch aus Gründen der Wirtschaftlichkeit mehr an Bedeutung gewinnen. Ein derzeit von der Eawag mit verschiedenen Partnern evaluiertes chemisch/physikalisches Verfahren der N-Rückgewinnung über eine Membranstrippung (sogenannte Membrankontaktoren) ist auf einer Kläranlagen in der Westschweiz seit Mitte 2016 erfolgreich im Einsatz. Weitere volltechnische Realisierungen solcher Anlagen stehen in Deutschland und der Schweiz in der Planung oder kurz vor der volltechnischen Umsetzung. Der Beitrag gibt einen Überblick über den derzeitigen Wissensstand zur Technologie
Benstörm, F., Nahrstedt, A., Böhler, M., Knopp, G., Montag, D., Siegrist, H., & Pinnekamp, J. (2016). Granulierte Aktivkohle – Ein Review halb- und großtechnischer Untersuchungen. In J. Pinnekamp & V. Kölling (Eds.), Gewässerschutz, Wasser, Abwasser: Vol. 239. 49. Essener Tagung für Wasser und Abfallwirtschaft. "Wasserwirtschaft 4.0" (p. 52 (17 pp.). Aachen, Germany: RWTH Aachen, Institut für Siedlungswasserwirtschaft. , Institutional Repository
Bitterwolf, S. (2016). Volltechnische Untersuchungen zur Elimination von Mikroverunreinigungen aus kommunalem Abwasser mittels Ozon und granulierter Aktivkohle auf der ARA Furt, Bülach (CH) (Master thesis). 93 p. , Institutional Repository
Böhler, M., Fleiner, J., McArdell, C. S., Kienle, C., Schachtler, M., & Siegrist, H. (2016). Biologische Nachbehandlung von kommunalem Abwasser nach Ozonung - ReTREAT. In J. Pinnekamp & V. Kölling (Eds.), Gewässerschutz, Wasser, Abwasser: Vol. 239. 49. Essener Tagung für Wasser und Abfallwirtschaft. "Wasserwirtschaft 4.0" (p. (13 pp.). Aachen, Germany: RWTH Aachen, Institut für Siedlungswasserwirtschaft. , Institutional Repository
Krampe, J., & Böhler, M. (2016). Ein Projekt mit Leuchtturm-Charakter. Gas- und Wasserfach: Wasser, Abwasser, 157(1), 28-31. , Institutional Repository

Stickstoffelimination im Seitenstrom – damit beschäftigen sich aktuell zwei Fallstudien im Rahmen von PowerStep: Prof. Dr.-Ing. Jörg Krampe (Vorstand des Forschungsbereiches Wassergütewirtschaft des Instituts für Wassergüte, Ressourcenmanagement und Abfallwirtschaft der Technischen Universität Wien) arbeitet dazu an der Case Study 5 in Zusammenarbeit mit dem Abwasserverband Wörgl-Kirchbichl an der Kläranlage Kirchbichl in Österreich (100 000 EW); Auf der Kläranlage Altenrhein in der Schweiz (120 000 EW) ist Marc Böhler (Eidgenössische Anstalt für Wasserversorgung, Abwasserreinigung und Gewässerschutz, Eawag) zusammen mit dem Abwasserverband Altenrhein für die Case Study 6 verantwortlich. Im Interview mit gwf-Wasser | Abwasser sprechen Prof. Dr.-Ing. Jörg Krampe und Marc Böhler über ihre Hintergründe, Aussichten und Ziele.
Löwenberg, J., Zenker, A., Krahnstöver, T., Boehler, M., Baggenstos, M., Koch, G., & Wintgens, T. (2016). Upgrade of deep bed filtration with activated carbon dosage for compact micropollutant removal from wastewater in technical scale. Water Research, 94, 246-256. doi:10.1016/j.watres.2016.02.033, Institutional Repository

The removal of micropollutants from drinking and wastewater by powdered activated carbon (PAC) adsorption has received considerable attention in research over the past decade with various separation options having been investigated. With Switzerland as the first country in the world having adopted a new legislation, which forces about 100 wastewater treatment plants to be upgraded for the removal of organic micropollutants from municipal wastewater, the topic has reached practical relevance.
In this study, the process combination of powdered activated carbon (PAC) adsorption and deep bed filtration (DBF) for advanced municipal wastewater treatment was investigated over an extended period exceeding one year of operation in technical scale. The study aimed to determine optimum process conditions to achieve sufficient micropollutant removal in agreement with the new Swiss Water Ordinance under most economic process design.
It was shown that the addition of PAC and Fe3+ as combined coagulation and flocculation agent improved effluent water quality with respect to dissolved organic pollutants as well as total suspended solids (TSS), turbidity and PO4–P concentration in comparison to a DBF operated without the addition of PAC and Fe3+. Sufficient micropollutant (MP) removal of around 80% was achieved at PAC dosages of 10 mg/L revealing that PAC retained in the filter bed maintained considerable adsorption capacity. In the investigated process combination the contact reactor serves for adsorption as well as for flocculation and allowed for small hydraulic retention times of minimum 10 min while maintaining sufficient MP removal. The flocculation of two different PAC types was shown to be fully concluded after 10–15 min, which determined the flocculation reactor size while both PAC types proved suitable for the application in combination with DBF and showed no significant differences in MP removal. Finally, the capping of PAC dosage during rain water periods, which resulted in lower dosage concentrations, was efficient in limiting PAC consumption during these events without suffering from negative effects on process performance or effluent quality.
Boehler, M. A., Heisele, A., Seyfried, A., Grömping, M., & Siegrist, H. (2015). (NH4)2SO4 recovery from liquid side streams. Environmental Science and Pollution Research, 22(10), 7295-7305. doi:10.1007/s11356-014-3392-8, Institutional Repository

Two methods of recovering nitrogen from liquid side streams are presented in this paper. The first method was demonstrated at an ammonia stripping plant treating 5–7 m3/h sludge water at the wastewater treatment plant (WWTP) Kloten-Opfikon (CH). In addition to the usual stripping and scrubbing columns, a third column had been added in order strip CO2, thus reducing the NaOH-demand of the subsequent ammonia stripping. At first, just the stripping plant was put into operation and optimized without any pre-treatment of the supernatant. Next, the CO2-stripper column was activated and optimized by gas measurements to minimize free ammonia losses, heat losses, and energy consumption. Key operational aspects of the plant were evaluated. Finally, up to 1.4 m3/h source-separated urine was successfully fed into the stripping facility. The second ammonia removal method using hydrophobic hollow fiber membranes was tested in two small pilot systems by different manufacturers in 2012 and 2013 at WWTP Neugut. In this technology, free ammonia gas in the sludge liquid diffuses at pH >9.3 from the sludge liquid through the air-filled pores of the microporous hydrophobic membrane into concentrated sulfuric acid flowing through the hollow fibers, forming ammonium sulfate. The small pore size and the hydrophobic nature of the membrane prevent the liquid phase from entering into the pores due to the surface tension effect. Practical experience regarding operational parameters like wastewater flow rate, pH, temperature, ammonia concentration, fouling and precipitations processes, optimal flow schemes, and process configurations was collected.
Luning, L., van Dijk, L., Boehler, M. A., Siegrist, H. R., & Heisele, A. (2015). Results from pilot- tests for ammonia–stripping by membrane-modules (p. 5 (14 pp.). Presented at the 9. Aachener Tagung zur Behandlung der Stickstoffrückbelastung aus der Schlammentwässerung. Leipzig, Germany. , Institutional Repository

The increase of the world population and the increasing demand for agricultural products will result in a further application of fertilizer providing the required convertible nitrogen and phosporus. Due to improved sanitation and sewerage, the amounts of these components in waste water will also increase. However, the production of nitrogen fertilizer via the Haber-Bosch process and the elimination of the nitrogen from municipal waste water streams by denitrification are cost and energy intensive. The latter also produces nitrous oxide (N2O), a very strong greenhouse gas. Furthermore phosphorus, an essential fertilizer for high performance agriculture and high quality phosphorus resources, will run out in the near future.

In this context, technologies for nutrient separation and recovery out of waste water streams and sludge liquids will get more and more attention in the coming future.
Wittmer, A., Heisele, A., McArdell, C. S., Böhler, M., Longree, P., & Siegrist, H. (2015). Decreased UV absorbance as an indicator of micropollutant removal efficiency in wastewater treated with ozone. Water Science and Technology, 71(7), 980-985. doi:10.2166/wst.2015.053, Institutional Repository

Ozone transforms various organic compounds that absorb light within the UV and visible spectra. UV absorbance can therefore be used to detect the transformation of chemicals during ozonation. In wastewater, decolourisation can be observed after ozonation. This study investigates the correlation of the UV absorbance difference between the ozonation inlet and outlet and the removal efficiency of micropollutants in wastewater. The absorbance at 254 and 366 nm was measured at the ozonation inlet and outlet, as was the concentration of 24 representative micropollutants and the dissolved organic carbon (DOC). The results clearly showed that the relative decrease of absorbance (ΔAbs) is positively correlated with the relative removal efficiency of micropollutants. We therefore suggest that UV absorbance can be used as a feedback control parameter to achieve optimal ozone dosage in wastewater treatment plants and to gain a fast insight into the process efficiency and stability of the ozonation.
Boehler, M., Bolzonella, D., Braguglia, C. M., Gallipoli, A., Gianico, A., Levantesi, C., … Mininni, G. (2013). Innovative treatment solutions for sewage sludge recovery on a FP7 project routes. Environmental Engineering and Management Journal, 12(S11), 11-14. , Institutional Repository

ROUTES is addressed to assess new routes in wastewater and sludge treatment focusing on three main objectives:
1. optimization of the sludge quality for agricultural use with the goal to produce a clean and full stabilized sludge through intensive stabilization processes with attention to a broad spectrum of parameters including micropollutants, pathogens and their indicators.
2. minimization of the sludge to be disposed by innovative technical solutions based on different approaches, either on the water or sludge treatment lines;
3. recovery of valuable resources before sludge disposal by producing a liquid fertilizer [(NH4)2SO4], biopolymers or optimizing methane production by anaerobic treatments.
Technical and economic assessment of the investigated techniques on laboratory and pilot scale were carried out in a typical benchmarking study. The whole set of data is then provided to the partner involved in environmental assessment where different impact categories are considered (global warming potential, acidification potential, eutrophication potential and photochemical ozone creation potential).
Böhler, M., Morgenroth, E., Siegrist, H., Haueter, R., Rensch, D., Sterkele, B., … Beurer, I. (2013). Machbarkeits‐ und Vergleichsstudie zur Umstellung der chemischen Phosphorelimination mittels Eisen‐ auf Aluminium‐Produkte auf kommunalen Abwasserreinigungsanlagen. Dübendorf: Eawag. , Institutional Repository

Stand und (Mehr-) Kosten der Fällung im Kanton Zürich

Alle Kläranlagen des Kanton Zürichs betreiben eine chemische Phosphor-Fällung. Zeitweise werden auch sogenannte Kombi-Produkte bestehend aus Eisen und Aluminium zur Bekämpfung schlechter Absetzeigenschaften angewendet. Eine reine Aluminium-Fällung wird auf keiner Kläranlage im Kanton vorgenommen, so dass hier keine Langzeiterfahrungen zum Einsatz von reinen Aluminium-Produkten vorliegen.

Die derzeitigen Kosten für Fällmittel (Basis AWEL-Daten-Erhebung B5) auf den Kläranlagen des Kantons sind sehr unterschiedlich. In Abhängigkeit der Verfahrenswahl, des verwendeten Fällmittel-Produkte und der geforderten Einleitwerte ergeben sich derzeit reale Kosten in einer Spannweite von 4 bis 15 Sfr. je Kilogramm Phosphor, welches über eine Fällung eliminiert wird. Hohe Kosten entstehen insbesondere bei Verwendung von Kombi-Produkten und für kleine Kläranlagen. Die günstigste Variante und zugleich mengenmässig der bedeutendste Anteil stellt die Verwendung von Grünsalz (Fe(II) dar, welches von 5 Kläranlagen, darunter den zwei grössten des Kantons eingesetzt werden.

Auf Grundlage einer Preisanfrage der grössten Fällmittel-Lieferanten des Kantons wurde eine Kostenabschätzung der Mehrkosten bei Umstellung auf ein reines Aluminium-Produkt vorgenommen. Im Vergleich zu Fe(II)-Produkten bzw. Fe(III)-Produkten ergibt sich ein um rund 2.4 respektive um 1.3-fach höherer Einkaufspreis für das Fällmittel. Auf Basis einer Phosphor-Massenbilanz wurden in Abhängigkeit der derzeit verwendeten Fällmittelmengen (Beta-Wert 1.9 mol/mol) eine Abschätzung der Mehrkosten für die Fällmittelbeschaffung der Kläranlagen berechnet. [...]
Morales, N., Boehler, M. A., Buettner, S., Liebi, C., & Siegrist, H. (2013). Recovery of N and P from urine by struvite precipitation followed by combined stripping with digester sludge liquid at full scale. Water, 5(3), 1262-1278. doi:10.3390/w5031262, Institutional Repository

A novel ammonia stripping method, including a CO2 pre-stripper was used to treat a mix of supernatant liquor from an anaerobic digester and urine in order to recycle nitrogen as ammonium sulfate at full-scale in the WWTP Kloten/Opfikon. Waste streams were not generated, since the ammonia was recovered as a marketable nitrogen fertilizer, turning a waste product into a valuable product. The efficiency of this system was increased by means of the addition of pre-treated urine collected separately at EAWAG building. The separation step was performed by the use of water free urinals and urine diversion flush toilets. An increase of 10% in the liquid flux with the addition of the urine translated into a 40% increase of the ammonia concentration in the inlet of the stripping unit. The achievement of these percentages generated a proportional increase in the fertilizer production. The urine pre-treatment was carried out by adding magnesium to produce a precipitate of struvite. The first experiments with the combined treatment showed the feasibility of the combination of the separation and pre-treatment steps.
Boehler, M., Zwickenpflug, B., Hollender, J., Ternes, T., Joss, A., & Siegrist, H. (2012). Removal of micropollutants in municipal wastewater treatment plants by powder-activated carbon. Water Science and Technology, 66(10), 2115-2121. doi:10.2166/wst.2012.353, Institutional Repository

Micropollutants (MP) are only partly removed from municipal wastewater by nutrient removal plants and are seen increasingly as a threat to aquatic ecosystems and to the safety of drinking water resources. The addition of powder activated carbon (PAC) is a promising technology to complement municipal nutrient removal plants in order to achieve a significant reduction of MPs and ecotoxicity in receiving waters. This paper presents the salient outcomes of pilot- and full-scale applications of PAC addition in different flow schemes for micropollutant removal in municipal wastewater treatment plants (WWTPs). The sorption efficiency of PAC is reduced with increasing dissolved organic carbon (DOC). Adequate treatment of secondary effluent with 5–10 g DOC m−3 requires 10–20 g PAC m−3 of effluent. Counter-current use of PAC by recycling waste PAC from post-treatment in a contact tank with an additional clarifier to the biology tank improved the overall MP removal by 10 to 50% compared with effluent PAC application alone. A dosage of 15 g PAC m−3 to a full-scale flocculation sand filtration system and recycling the backwash water to the biology tank showed similar MP elimination. Due to an adequate mixing regime and the addition of adapted flocculants, a good retention of the fine fraction of the PAC in the deep-bed filter were observed (1–3 g TSS m−3; TSS: total suspended solids). With double use of PAC, only half of the PAC was required to reach MP removal efficiencies similar to the direct single dosage of PAC to the biology tank. Overall, the application of PAC in WWTPs seems to be an adequate and feasible technology for efficient MP elimination (>80%) from wastewater comparable with post ozonation.
Böhler, M., Büttner, S., Liebi, C., & Siegrist, H. (2012). Dünger aus Abwasser. Ammoniakstrippung mittels Luft zur Behandlung von Faulwasser und Urin auf der Kläranlage Kloten/Opfikon. Aqua & Gas, 92(1), 26-31. , Institutional Repository

Auf der Kläranlage Kloten/Opfikon wurde erstmals in der Schweiz das Verfahren der Luftstrippung zur Stickstoffrückgewinnung aus Faulwasser volltechnisch umgesetzt. Das Verfahren beinhaltet neben der Ammoniakstrippung eine Faulwasservorbehandlung in Form eines CO2-Strippers, welche eine 50%ige Reduktion des Laugenbedarfs erlaubt und eine deutliche Effizienzsteigerung des nachhaltigen Verfahrens erbringt. Die Idee der vorgängigen CO2-Strippung zur pH-Wert-Anhebung wurde von der Eawag entwickelt und ist grosstechnisch einzigartig.
Böhler, M., Wittmer, A., Heisele, A., Wohlhausser, A., Salhi, L., von Gunten, U., … Beck, B. (2012). Ergänzende Untersuchungen zur Elimination von Mikroverunreinigungen auf der Ara Neugut. Dübendorf: Eawag. , Institutional Repository

Die vorliegende Berichterstattung gibt Auskunft über weitergehende Untersuchungen und Abklärungen in Zusammenhang mit der Elimination von Mikroverunreinigungen auf der ARA Neugut.
Im Kontext mit einer notwendigen biologischen Nachbehandlung von ozontem Abwasser wurde in 2012 eine Abwasserfiltration mit granulierter Aktivkohle in den Versuchseinrichtungen der Eawag betrieben. Neben dem Beladungsverhalten bezüglich DOC und Mikroverunreinigungen wurde auch die Praxistauglichkeit einer derartigen Filtration evaluiert, nämlich in wieweit auf Basis der vorhandenen Infrastrukturen bestehender Sandfiltrationen eine derartige GAK-Filtration möglich ist. [...]
Böhler, M. A., & Liebi, C. (2012). Reduzierter NaOH-Verbrauch bei der Ammoniak-Strippung durch den Einsatz einer vorgeschalteten CO2-Strippung – Betriebserfahrungen auf der ARA Klothen-Opfikon (p. 6 (18 pp.). Presented at the 8. Aachener Tagung zur Stickstoffrückbelastung. Heidelberg, Germany. , Institutional Repository

Die Rückgewinnung von Nährstoffen aus Abwasser wird in der Zukunft aus Gründen der Nachhaltigkeit und zunehmend auch aus wirtschaftlichen Gründen mehr an Bedeutung gewinnen. Die Luft- und Dampfstrippung sind bis heute die einzigen volltechnischen Verfahren mit dem Stickstoff aus Prozessabwässern rückgewonnen werden kann, da in den biologischen Verfahren der Stickstoff durch Denitrifikation in die Atmosphäre verloren geht. Ein von der Eawag mit Partnern derzeit ebenfalls evaluiertes drittes Verfahren der N-Rückgewinnung über eine Membranstrippung steht bisher erst kurz vor einer volltechnischen Realisierung, sodass mit dieser Technologie noch keine Praxiserfahrungen und Daten zur Verfügung stehen.
Auf der Kläranlage Kloten/Opfikon wurde zum ersten mal in der Schweiz das Verfahren der Luftstrippung zur Stickstoffrückgewinnung aus Faulwasser volltechnisch umgesetzt. Das Verfahren beinhaltet neben der Ammoniakstrippung zudem eine Faulwasservorbehandlung in Form eines CO2-Strippers, welche eine 50%-tige Reduktion des Laugebedarfs erlaubt und eine deutliche Effizienzsteigerung des nachhaltigen Verfahrens erbringt. Die Idee der vorgängigen CO2-Strippung zur pH-Wert-Anhebung wurde von der Eawag entwickelt und ist grosstechnisch einzigartig. Das Produkt des Verfahrens ist ein in der Landwirtschaft nachgefragter Flüssigdünger, der nun von der Kläranlage vermarktet wird. Das vorliegende Manuskript berichtet über die Erfahrungen beider Inbetriebnahme und über die Betriebsresultate nach nun mehr als 1-jährigem Betrieb.
Im Rahmen einer Kostenstudie wurden zudem verschiedene Behandlungsverfahren gegenübergestellt. Hier zeigt sich, das vor der Wahl eines geeigneten Verfahrens die individuellen Rahmenbedingungen auf der Kläranlage abgeklärt sein sollten, bevor ein Entscheid für ein Verfahren getroffen werden kann. Die spezifischen baulichen, verfahrenstechnischen und betrieblichen Bedingungen der betrachteten Kläranlagen können grossen Einfluss auf die Ergebnisse des Variantenstudiums haben.
Im vorgestellten Variantenvergleich zeigt sich, dass heute die Stickstoffrückgewinnung via Luftstrippung oder Membranstrippung bezüglich der Jahreskosten unwesentlich höher ausfällt, als das kostengünstige Nitritations/Anammox-Verfahren, bei dem der Stickstoff verloren geht. Zudem konnte aufgezeigt werden, dass die Mehrinvestitionskosten für eine vorgängige CO2-Strippung durch geringere Betriebskosten - bedingt durch die Laugeneinsparung - kompensiert werden können.
Kobler, B., Le Goaziou, Y., Rigault, M., Sauvignet, P., Böhler, M., Brocker, S., … Rettby, R. (2012). Untersuchungen zur Elimination von Mikroverunreinigungen aus kommunalem Abwasser mittels PAK in einem Actiflo®Carb und durch Ozon auf der ARA Schönau, Cham (GVRZ). Nidau: Alpha Umwelttechnik AG. , Institutional Repository
Böhler, M., Zwickenpflug, B., Dorusch, F., Hollender, J., Siegrist, H., Ternes, T., & Fink, G. (2011). Aktivkohledosierung (p. (11 pp.). Presented at the VSA-Fortbildungskurs: Mikroverunreinigungen und Aspekte zu Energie und Stickstoff. Emmetten, Schweiz. , Institutional Repository
Böhler, M., Zwickenpflug, B., Grassi, M., Behl, M., Neuenschwander, S., Siegrist, H., … Wullschläger, W. (2011). Aktivkohledosierung in den Zulauf zur Sandfiltration Kläranlage Kloten/Opfikon. Dübendorf: Eawag. , Institutional Repository

Nach einer verfahrenstechnischen Optimierung zur direkten Dosierung von Aktivkohle vor der Filtration in einer halbtechnischen Pilotanlage der Eawag konnte in einer zweiten grosstechnischen Anwendung auf der Kläranlage Kloten/Opfikon eine effiziente und hinreichende Spurenstoffelimination über 9 Wochen vollzogen werden.
Zentral in dieser Verfahrensvariante ist die weitestgehende Abtrennung der dosierten Pulveraktivkohle vom gereinigten Abwasser. In der Dosierzeit konnte die feine PAK effizient im Filtermedium zurückgehalten werden. Im Vergleich zur Referenzstrasse erhöhten sich die AFS-Ablaufwerte um rd. 1 - 2 mgAFS/L, lagen jedoch durchgehend deutlich unter dem geforderten Grenzwert von 5 mgAFS/l. [...]
Böhler, M., Zwickenpflug, B., Grassi, M., Behl, M., Hollender, J., Ternes, T., … Siegrist, H. (2011). Micropollutant removal by powder activated carbon addition to sand filtration (pp. 1-3). Presented at the 8th IWA leading edge conference on water and wastewater technologies. Amsterdam, The Netherlands. , Institutional Repository
Böhler, M., & Siegrist, H. (2011). Pak-Dosierung in den Zulauf zur Flockungs-Sandfiltration Kläranlage Kloten/Opfikon - Grosstechnische Umsetzung im Rahmen ergänzender Untersuchungen zum Micropoll-Projekt (pp. 1-18). Presented at the Seminar „Weitergehende Abwasserreinigung". Hennef: DWA. , Institutional Repository
Abegglen, C., Böhler, M., Hollender, J., Zimmermann, S., Zwickenpflug, B., von Gunten, U., … Thonney, D. (2010). Mikroverunreinigungen in Kläranlagen. Technische Verfahren zur Elimination von organischen Spurenstoffen. GWA Gas, Wasser, Abwasser, 90(7), 587-594. , Institutional Repository

Micropollutants in Wastewater Treatment Plants. Technologies to Eliminate Organic Trace Contaminants. Today’s mechanical-biological treatment plants only inadequately remove organic micropollutants. Advanced technologies are necessary such as ozonation or adsorption on powdered active carbon (PAC) in order to increase removal capacity. These two techniques are being evaluated in various tests on the laboratory level, but also on a large scale. Both ozonation and PA C adsorption are suitable for reducing the emission of organic trace elements from settlement drainage systems into the various bodies of water. This article presents the current knowledge of both technologies for application in municipal wastewater treatment systems.
Abegglen, C., Böhler, M., & Siegrist, H. (2010). Mikroverunreinigungen reduzieren. Tec21, 36, 20 (8 pp.). doi:10.5169/seals-130709, Institutional Repository
Ante, S., Böhler, M., Ellerhorst, S., Fink, G., Knacker, T., Joss, A., … Zwickenpflug, B. (2010). NEPTUNE. New sustainable concepts and processes for optimization and upgrading municipal wastewater and sludge treatment. A specific targeted research project under the thematic priority 'Global change and ecosystems'. Work packages 1 and 3. Deliverable 1.1 and 3.3 · Fate and occurrence of micropollutants, microorganisms and viruses and strategies to minimize their release in plant effluent. sine loco: Eawag. , Institutional Repository

Analytical methods, compound occurrence and transformation products
The palette of analytical methods available for analyzing micropollutants in wastewater covers a wide variety of compounds: 152 compounds belonging to 16 different classes were applied within this project. Of relevance due to their occurrence and toxic potency are the new methods developed for biocides, UV-filters, benzothiazoles and antivirals: the majority persist wastewater treatment and many are found in surface waters at concentrations justifying more attention within the micropollutant discussion.
A major break through of the project is the development of methods for systematic transformation product identification. These are applicable for biological degradation as well as for chemical oxidative treatment. [...]
Böhler, M., Zwickenpflug, B., Dorusch, F., Hollender, J., Siegrist, H., Fink, G., … Ellerhorst, S. (2010). Vergleichende Untersuchungen verschiedener Anwendungen von Pulveraktivkohle zur Elimination von Spurenstoffen aus kommunalem Abwasser. In J. Pinnekamp (Ed.), GWA - Gewässerschutz, Wasser & Abwasser: Vol. 220. 43. Essener Tagung für Wasser- und Abfallwirtschaft „Perspektiven und Risiken“ (p. 16 pp.). Aachen: Gesellschaft zur Förderung des Instituts für Siedlungswasserwirtschaft an der RWTH Aachen e.V. , Institutional Repository
Morgan-Sagastume, F., Karlsson, A., Werker, A., De Gussem, K., Roels, J., Weemaes, M., … Petrova, S. (2010). NEPTUNE. New sustainable concepts and processes for optimization and upgrading municipal wastewater and sludge treatment. A specific targeted research project under the thematic priority 'Global change and ecosystems'. Work package 5 · Dissemination. Deliverable 5.4 · Catalogue with criteria for evaluating technologies. sine loco: Eawag. , Institutional Repository
Zwickenpflug, B., Böhler, M., Sterkele, B., Joss, A., Siegrist, H., Traber, J., … Fink, G. (2010). Einsatz von Pulveraktivkohle zur Elimination von Mikroverunreinigungen aus kommunalem Abwasser. Dübendorf: Eawag. , Institutional Repository

Der vorliegende Abschlussbericht des Micropoll-Teilprojektes zur Elimination von Spurenstoffen aus kommunalem Abwasser mittels Pulveraktivkohle (PAK) fasst die zentralen Ergebnisse der Pilotierungen und Einzelversuche aller Projektphasen der letzten drei Jahren zusammen.
Hauptziel des Projektes war es durch den Betrieb von halbtechnischen Pilotanlagen und zielgerichteten Einzeluntersuchungen weitere Klärung und Erfahrungen zum Einsatz von Aktivkohle zur Spurenstoffelimination in der kommunalen Abwasserbehandlung zu liefern. Während der ersten Projektphase wurden im Wesentlichen Grundlagen evaluiert (1. - 2. Zwischenbericht), während in den Versuchsphasen zwei und drei empirische und praxisorientierte Untersuchungen vorgenommen wurden. [...]
Abegglen, C., Joss, A., Boehler, M., Buetzer, S., & Siegrist, H. (2009). Reducing the natural color of membrane bioreactor permeate with activated carbon or ozone. Water Science and Technology, 60(1), 155-165. doi:10.2166/wst.2009.331, Institutional Repository

The suitability of two membrane bioreactors for on-site wastewater treatment and reuse in Switzerland was investigated. The treated wastewater was used for toilet flushing and gardening, with water recycling rates of 30% (single family house) and almost 100% (toilets in a cable car station) respectively. Due to the recycling, an increase in a natural yellowish-brown color was observed, leading to double flushing of the toilets, higher cleaning requirements and increased permeate production. Color removal with ozone, powdered (PAC) and granulated (GAC) activated carbon was assessed in laboratory and field experiments. PAC was added directly into the MBR, whereas ozonation and GAC were applied to the permeate. The dosage of ozone or activated carbon depended on the recycling rate and color intensity. If color removal is necessary, PAC is the option best suited to small treatment plants, with a requirement of 30–50 g m-3 for 30% and 100 g m-3 for 100% water recycling.
Böhler, M., & Siegrist, H. (2009). Optimierung der chemischen Phosphorfällung - Leistungsgrenzen und betriebliche Auswirkungen (p. (33 pp.). Presented at the 82. Siedlungswasserwirtschaftliches Kolloquium. Stuttgart, Deutschland. , Institutional Repository

Die chemische Fällung des gelösten Phosphors des Abwassers ist ein effizienter und zentraler Prozess in der Abwasserbehandlung zur Erreichung weitergehender Ziele in der Nährstoffelimination und ist heute etablierter Verfahrensbestandteil auf den meisten Abwasserreinigungsanlagen in Europa.

Da Phosphor ein essentieller Nährstoff ist und durch Phosphor die Eutrophierung von Gewässern gesteuert wird, wurde in der Schweiz neben dem Phosphorverbot in Waschmitteln intensiv an einer Optimierung der konventionellen Fällung geforscht und neue Technologien entwickelt. Hierzu gehören die Technologie der Zwei-Punkt-Fällung und die der kostenintensiveren und betrieblich aufwendigeren Flockungsfiltration.

Ziel ist es punktförmige Phosphoremissionen durch Kläranlagen in Fliessgewässern in Seeeinzugsgebieten und den Seen selbst zu minimieren. Dieses Ziel äussert sich in einer Gesetzgebung mit im EU-Vergleich sehr tiefen Grenzwerten. Gemäss Gewässerschutzverordnung der Schweiz von 1998 haben alle Kläranlagen im Einzugsgebiet der Seen und Kläranlagen ab 10.000 EW unterhalb der Seen eine Ablaufkonzentration bezüglich Gesamt-P von 0.8 gPtot/m3 einzuhalten. Es ist insgesamt eine Elimination von 80% der Gesamt-P-Rohabwasserfracht zu erreichen. Diese Auflage kann kantonal verschärft werden, so dass in der Praxis alle Kläranlagen im direkten Einzugsgebiet der Seen verschärfte Auflagen haben (z. Bsp. der Zürichsee mit 0.2 gPtot/m3 oder der Bodensee mit der Bodenseerichtlinie geltend für alle Anrainer mit 0.3 gPtot/m3).

Das vorliegende Manuskript führt in die allgemeinen Grundlagen und Technik der Phosphorelimination mittels konventioneller Fälltechnik ein. Hierbei wird im besonderen Masse auf die Dimensionierung und Auslegung der Zwei-Punkt-Fällung eingegangen, da diese eine für viele Kläranlagen der Schweiz geeignete Technologie ist, die seit vielen Jahren bestehenden Zielvorgaben zu erfüllen.

Ein Überblick über die langjährige Praxis mittels Fallbeispielen der chemischen Phosphat-Elimination in der Schweiz zeigt auf, dass die oben genannten Einleitwerte sowohl mit einer Intensivierung der konventionellen Fällung durch erhöhte Fällmittelgaben als auch mit einer Fällmittel sparenden Zwei-Punkt-Fällung im Vergleich zur Flockungsfiltration gut erreicht werden können.
Joss, A., Böhler, M., Wedi, D., & Siegrist, H. (2009). Proposing a method for online permeability monitoring in membrane bioreactors. Water Science and Technology, 60(2), 497-506. doi:10.2166/wst.2009.370, Institutional Repository

Reliable and efficient operation of membrane bioreactors (MBR) for centralized municipal wastewater treatment strongly depends on a good monitoring of the membrane permeability, a value often used to quantify the transmissibility (i.e. the inverse of the flow resistance) of the membrane. By directly or indirectly evaluating this parameter the operator normally plans on the necessity and effectivity of maintenance activities. To allow the operator monitoring the membrane performance closely, the present paper proposes a method for online permeability based on the measurements of permeate flow, transmembrane pressure and water temperature. The theoretical background of the method is discussed and a data set of 250 days of continuous pilot operation of a municipal MBR equipped with three different standard membrane modules is used for testing. The method is numerically simple enough to allow being implemented on any programmable logical controller.
Böhler, M., & Siegrist, H. (2008). "Möglichkeiten zur Optimierung der chemischen Phosphorfällung an hessischen Kläranlagen". Dübendorf: Eawag. , Institutional Repository

Das vorliegende Gutachten beschreibt die technischen Möglichkeiten und das Potential zur weiteren Reduktion der Phosphoremissionen durch chemische Fällung auf Kläranlagen im Bundesland Hessen. In der Betrachtung stehen nur Kläranlagen, welche bereits eine Phosphorelimination betreiben. Zudem werden neben den Effekten dieser erhöhten chemischen Elimination auch die zu erwartenden Kosten für den Kläranlagenbetrieb abgeschätzt.

Für die Berechnung des Potenzials wurde für eine Beispielrechnung als maximale Gesamt-Phosphorkonzentration 0.5 gPtot/m3 im Ablauf der Kläranlagen angesetzt. Dieses Qualitätsziel beinhaltet im Mittel einen Orthophosphatgehalt von 0.15 gPO4-P/l. Die weiteren Anteile im genannten Qualitätsziel ergeben sich aus dem nicht fällbaren gelösten Anteil (0.05 bis 0.1 g/m3) und aus dem partikulär gebundenen Anteil im Feststoffabtrieb der Kläranlagen (etwa 0.25 gP/m3). Da die zuletzt genannten Fraktionen aufgrund der spezifischen Randbedingungen des Einzugsgebietes bzw. der Kläranlage selbst schwanken können, kann anteilig die Orthophosphatkonzentration bei gleichzeitiger Einhaltung des gewählten Qualitätszieles ebenfalls variieren.

Die für die Berechnungen zu Grunde gelegten Ausgangsdaten entstammen zum einen aus der Datenbank des Landes Hessen. Zu anderen basieren diese auf den allgemein anerkannten Regeln der Technik oder auf Erfahrungswerten durch die langjährige Anwendung der vorgestellten Technologien.

Das den Berechnungen zur Abschätzung der zusätzlichen Fällmittelmengen und der anfallenden Fällschlammmengen zu Grunde gelegte molare Verhältnis vom einzusetzenden Fällmittel zum zu fällenden Phosphat wurde durch Gewichtung der Frachten, welche aus dem Mittel der Zu- und Ablaufkonzentrationen der Gesamtkläranlagen resultiert, ermittelt. Anschliessend wurden die entsprechenden Mengen für jede einzelne Kläranlage errechnet. Die Bemessung erfolgt über den gelösten Anteil der Phosphorfrachten und basiert auf der Bemessungsgrundlage nach Siegrist und Boller.
Boehler, M., & Siegrist, H. (2007). Potential of activated sludge ozonation. Water Science and Technology, 55(12), 181-187. doi:10.2166/wst.2007.407, Institutional Repository

The disposal of sewage sludge and the agricultural use of stabilised sludge are decreasing due to more stringent regulations in Europe. An increasing fraction of sewage sludge must,therefore be dewatered, dried, incinerated and the ashes disposed of in landfills. These processes are cost-intensive and also lead to the loss of the valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Partial ozonation of the return sludge of an activated sludge system significantly reduces excess sludge production, improves the settling properties of the sludge and reduces bulking and scumming. The solubilised COD will also improve denitrification if the treated sludge is recycled to the anoxic zone. However, ozonation partly kills nitrifiers and could therefore lead to a decrease of the effective solid retention time of the nitrifier, thus reducing the safety of the nitrification. This paper discusses the effect of ozonation on sludge reduction, the operating stability of nitrification, the improvement of denitrification and also presents an energy and cost evaluation.
Boehler, M., Joss, A., Buetzer, S., Holzapfel, M., Mooser, H., & Siegrist, H. (2007). Treatment of toilet wastewater for reuse in a membrane bioreactor. Water Science and Technology, 56(5), 63-70. doi:10.2166/wst.2007.557, Institutional Repository

Toilet wastewater is treated and reused on site at Europe's highest membrane bioreactor (MBR), located in a cable car mountain station in the ski resort of Zermatt. Negative impacts on the sensitive mountain environment are minimised by reusing close to 100% of the treated wastewater for toilet flushing. Besides 100% nitrogen removal, 80% of phosphorus was also eliminated. This paper presents operational results, optimisations of sludge management, decoloration and long-term maintenance of biomass in the very low-loaded summer season. From a global view the experiences and results of the project are of great importance, proposing a solution to a problem existing 100-fold in the Alps as well as in and regions all over the world: reducing water consumption for sanitation by reuse.
Boehler, M., & Siegrist, H. (2006). Potential of activated sludge disintegration. Water Science and Technology, 53(12), 207-216. doi:10.2166/wst.2006.423, Institutional Repository

The disposal of sewage sludge and the agricultural use of stabilized sludge are decreasing due to more stringent regulations in Europe. An increasing fraction of sewage sludge must therefore be dewatered, dried, incinerated and the ashes disposed of in landfills. These processes are cost-intensive and also lead to the loss of the valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Disintegration of biological sludge by mechanical, thermal and physical methods could significantly reduce excess sludge production, improve the settling properties of the sludge and reduce bulking and scumming. The solubilized COD could also improve denitrification if the treated sludge is recycled to the anoxic zone. However, disintegration partly inhibits and kills nitrifiers and could therefore shorten their effective solid retention time, thus reducing the safety of the nitrification. This paper discusses the potential of disintegration on sludge reduction, the operating stability of nitrification, the improvement of denitrification and also presents an energy and cost evaluation.
Kolisch, G., Boehler, M., Arancibia, F. C., Pinnow, D., & Krauss, W. (2005). A new approach to improve sludge dewatering using a semi-continous hydraulic press system. Water Science and Technology, 52(10-11), 211-218. doi:10.2166/wst.2005.0696, Institutional Repository

In future, it will be necessary to incinerate an increasing proportion of the sludge produced by public wastewater treatment. In this context, equipment for more effective dewatering of sewage sludge is required. A hydraulic press system (Bucher HP) which has been used to date in the food industry could represent an alternative to the sludge dewatering systems currently used. The basic suitability of this press system was demonstrated in comprehensive industrial-scale trials at the Glarnerland STP (Switzerland). Dry solids contents of up to 43% were measured in the pressed sludge. Currently, the optimization of individual process parameters is being investigated in a pilot plant at the Schwelm STP operated by Wupperverband (Germany).
Böhler, M., Siegrist, H., & Müller, J. (2004). Energie- und Stoffbilanzen in der Schlammbehandlung, Effekt der Schlammdesintegration. In Abwasserreinigung der Zukunft (pp. 1-22). Schweiz: Verband Schweizer Abwasser- und Gewässerschutzfachleute. , Institutional Repository

Energie- und Stoffbilanzen in der Schlammbehandlung sind ein effizientes Werkzeug zur Beurteilung betrieblicher und wirtschaftlicher Aspekte sowohl in der Praxis aber auch im Bereich der Planung neuer Behandlungsanlagen. Insbesondere vor dem Hintergrund, dass in grossen Abwasserreinigungsanlagen heute die Betriebskosten für die Schlamm-behandlung und -entsorgung rd. 30 bis 40% der gesamten Betriebskosten ausmachen können und ein hoher baulicher wie maschineller Aufwand nötig ist, um die Infrastruktur bereitzustellen (Lindtner, 2004), wird eine detaillierte Betrachtung bedeutend.
Im Mittelpunkt der Betrachtung steht das Verfahren der anaeroben Stabilisierung, welche vielfach als zweistufige, mesophile Schlammfaulung auf den Schweizer Abwasserreinigungsanlagen realisiert ist. Neben den wesentlichen Grundlagen zur Einführung in die Thematik werden praktische Beispiele mit Übungen für Massen- und Energieflüsse in der Schlammbehandlung vorgestellt. Die Effekte der Desintegration auf die Energie- und Stoffflüsse in der Schlammbehandlung werden aufgezeigt.
Böhler, M., & Siegrist, H. (2004). Partial ozonation of activated sludge to reduce excess sludge, improve denitrification and control scumming and bulking. Water Science and Technology, 49(10), 41-49. doi:10.2166/wst.2004.0604, Institutional Repository

Disposal of sewage sludge is forbidden and agricultural use of stabilized sludge will be banned in 2005 in Switzerland. The sludge has to be dewatered, dried, incinerated and the ashes disposed in landfills. These processes are cost intensive and lead also to the loss of valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Partial ozonation of the return sludge of an activated sludge system reduces significantly excess sludge production, improves settling properties of the sludge and reduces bulking and scumming. The solubilized COD will also improve denitrification if the treated sludge is recycled to the anoxic zone. But ozonation will partly inhibit and kill nitrifiers and might therefore lead to a decrease of the effective solid retention time of the nitrifier, which reduces the safety of the nitrification. This paper discusses the effect of ozonation on sludge reduction, the operation stability of nitrification, improvement of denitrification and gives also an energy and cost evaluation.
Böhler, M., & Siegrist, H. (2004). Schlammdesintegration mit Ozon, Ultraschall und Enzymen in der Belebung. In Abwasserreinigung der Zukunft (pp. 1-22). Schweiz: Verband Schweizer Abwasser- und Gewässerschutzfachleute. , Institutional Repository

Die biologische Abwasserreinigung kommunaler und gewerblicher Abwässer wird heute vorwiegend durch das Belebungsverfahren vollzogen. Der im Rahmen dieses Prozesses anfallende Überschussschlamm wird in aufwendigen Verfahren entwässert, getrocknet, verbrannt und deponiert, die landwirtschaftliche Nutzung entfällt in Zukunft. Ab 2005 wird gemäss neuen gesetzlichen Auflagen nur noch der Entsorgungspfad der Verbrennung in der Schweiz zur Verfügung stehen (BUWAL, 2001, BLW, 2003), welcher als kostenintensivster anzusehen ist. Vor diesem Hintergrund gewinnt die Verfügbarkeit von zweckdienlichen Informationen über Möglichkeiten der Reduktion bei Entstehung und Entsorgung grosse Bedeutung.
Untersuchungen haben ergeben, dass durch eine gezielte Desintegration von Belebtschlamm und bei Rückführung dieses Schlammes in die Biologie eine Reduktion der Mengen erreicht werden kann. Neben der Schlammminimierung können auch andere positive Einflüsse auf die Nährstoffelimination und den gesamten Betrieb der ARA selbst beobachtet werden.
Zur Desintegration von Klärschlamm stehen unterschiedliche Technologien zur Verfügung. Aktuelle grosstechnische Praxisuntersuchungen auf Kläranlagen und Detailuntersuchungen im Labormassstab haben gezeigt, dass zur Desintegration von Belebtschlamm besonders die Desintegration durch Ozonierung (Yasui et al., 1994, Ried et al., 2002, Böhler und Siegrist, 2003), bzw. die Behandlung mit Ultraschall (Diehm et al., 2004, Eder und Günther, 2003, AVT, 2003) geeignet sind.
Der vorliegende Beitrag verschafft einen Überblick über die Effekte dieser Verfahren bei Einsatz in der Belebung. Im Vordergrund stehen die Auswirkungen auf die Nährstoffelimination, wobei auch eine Betrachtung der betrieblichen Aspekte erfolgt. Neben dem Schwerpunkt der Ozonierung und der Ultraschallbehandlung von Belebtschlamm wird die Möglichkeit der Desintegration mittels Enzymen vorgestellt. Ein aktuelles Fallbeispiel für den Einsatz von Enzymen in der Klärschlammfaulung auf einer Schweizer Kläranlage zeigt die Wirkungen einer biochemischen Desintegration auf.
Rieger, L., Böhler, M., Thomann, M., Gujer, W., & Siegrist, H. (2004). Qualitatskontrolle von Online-Messgeräten. In H. Kroiss (Ed.), Wiener Mitteilungen: Vol. 187. Datengewinnung, -verwaltung und -nutzung in der Wassergütewirtschaft: ÖWAV-Seminar - Wien 2004, TU Wien, 03. - 04. März 2004 (pp. 279-294). Wien: Technische Universität. , Institutional Repository

Nicht kontrollierte Online-Messtechnik auf Kläranlagen birgt die Gefahr nicht entdeckter systematischer Fehler, die zu Fehlentscheidungen oder gar schwerwiegenden Sicherheitsproblemen führen können. Es wird ein Ansatz vorgestellt, der es dem zuständigen Personal ermöglicht, die eingesetzten Messgeräte zu kontrollieren, ,,Ausser-Kontrolle-Situationen" zu erkennen und geeignete Massnahmen zu ergreifen. Werden keine systematischen Fehler identifiziert, sollte die Genauigkeit der Messkette bestimmt werden. Hierzu wird ein Konzept vorgeschlagen, das die Messung im Betrieb charakterisiert und so die benötigten Informationen z.B. für die optimale Parametrisierung eines Reglers bereitstellt.

Zur Kontrolle von Online-Messgeräten sollte in regelmässigen Abständen eine Überprüfung mit Labormethoden erfolgen. Eine statistische und grafische Auswertung gibt eine klare Übersicht über den Verlauf der Kontroll-Messungen und ermöglicht ein schnelles Reagieren auf Fehlmessungen. Eine signifikante Abweichung vom kalibrierten Grundzustand wird als Indikator für das Auftreten eines extremen Ausreissers oder einer systematischen Änderung der Messbedingungen interpretiert. Das zweistufige Konzept unterscheidet Warnmeldungen und Alarmmeldungen. Warnmeldungen werden aufgrund erster Hinweise auf Fehlmessungen angezeigt und sollen verstärkte Kontrollen bzw. Wartungsaktionen veranlassen. Alarmmeldungen basieren auf strengeren Kriterien und bestätigen eine vermutete Ausser-Kontrolle-Situation
Boehler, M., Pinnow, D., Krauss, W., Brauchli, H., & Siegrist, H. (2003). An innovative application for an established technology to improve sludge dewatering. In Conference Proceedings of New Zealand Water and Waste Association (NZWWA) annual conference (p. (8 pp.). Auckland: NZWWA. , Institutional Repository

This paper presents the results of full-scale waste water treatment plant (WWTP) sludge dewatering trials using a Bucher de-juicing press model HP2500 (Boehler et al., 2003). Besides digested sludge from the WWTP at Glarnerland sludge from five other WWTP's was also dewatered. The investigations show that with hydraulic system tested dry solids (DS) contents of 32-41% (with a throughput of approximately 5 m3 h-1) could be reached. With extended cycle / batch time DS contents of up to 43.5% could be achieved. Dewatering trials with raw sludge (not putrefied) from two different WWTP's resulted in DS content of 35% and 41%. The dosage of coagulant aids, particle size distribution and volatile suspended solids (VSS) have a significant influence on the dewatering results. An economic efficiency calculation is presented with direct comparison to a centrifuge used at the WWTP. Return of investment is expected to be achieved within 3 years.
Böhler, M., Siegrist, H., Pinnow, D., Müller, D., Krauss, W., & Brauchli, H. (2003). Neue Presstechnologie zur verbesserten Klärschlammentwässerung. Schlussbericht zu den Unteruchungen auf der ARA Glarnerland (AVG). Dübendorf: Eawag. , Institutional Repository

Der vorliegende Schlussbericht fasst die Ergebnisse der Untersuchungen auf der ARA Glarnerland zur Entwässerung von Klärschlamm mittels einer Fruchtpresse zusammen. Er ersetzt den Zwischenbericht von Ende 2002.
Neben der Dokumentation der Praxisuntersuchungen werden die wesentlichen Grundlagen zur Einführung in die Thematik und zur besseren Einordnung der Ergebnisse genannt. Die Entwässerungsversuche auf der ARA Glarnerland des Abwasserverbandes Glarnerland mit einer HP2500 Fruchtpresse der Firma Bucher Guyer AG bzw. der Bucher Foodtech haben gezeigt, dass mit dem für die maschinelle Klärschlammentwässerung neuen System eine Schlammentwässerung vorteilhaft ist.
In einer ersten Phase des Projektes wurden Pressparameter ermittelt, welche einen sicheren und stabilen Prozess der Entwässerung gewährleisten. In einer weiteren Phase wurden Optimierungen bezüglich des Betriebes und des Systems selbst (Drainagesystem) vorgenommen. [...]

This final report presents the results of full-scale waste water treatment plant (WWTP) sludge dewatering trials using a Bucher de-juicing press model HP2500. Besides digested sludge from the WWTP at Glarnerland, Sludge from five other WWTP’s was also dewatered. The investigations show that with hydraulic system tested dry solids (DS) contents of 32-41% (with a throughput of approximately 5 m3 h-1) could be reached. With extended cycle / batch time DS contents of up to 43.5% could be achieved. Dewatering trials with raw sludge (not putrefied) from two different WWTP’s resulted in DS content of 35% and 41%. The dosage of coagulant aids, particle size distribution and volatile suspended solids (VSS) have a significant influence on the dewatering results. An economic efficiency calculation is presented with direct comparison to a centrifuge used at the WWTP. Return of investment is expected to be achieved within 3 years.
Fux, C., Böhler, M., Huber, P., Egli, K., van der Meer, J. R., & Siegrist, H. (2003). Faulwasserbehandlung. Separate anaerobe Ammoniumoxidation (Anammox). GWA Gas, Wasser, Abwasser, 83(11), 787-797. , Institutional Repository

Overall nitrogen elimination in wastewater treatment plants can be improved by separate treatment of the ammonium rich sludge digester effluents. In this report special attention is paid to anaerobic ammonium oxidation. In a first aerobic reactor about 50 % of the ammonium is oxidized to nitrite (partial nitritation), and this is subsequently reduced anaerobically to nitrogen gas using the remaining ammonium as an electron donor (anammox). This sustainable as well as costeffective reactor combination was tested over months at pilot scale resulting in 85–90 % nitrogen removal without addition of any external carbon source.
Rieger, L., Alex, J., Winkler, S., Boehler, M., Thomann, M., & Siegrist, H. (2003). Progress in sensor technology - progress in process control? Part I: Sensor property investigation and classification. Water Science and Technology, 47(2), 103-112. doi:10.2166/wst.2003.0096, Institutional Repository

To ensure correctly operating control systems, the measurement and control equipment in WWTPs must be mutually consistent. The dynamic simulation of activated sludge systems could offer a suitable tool for designing and optimising control strategies. Ideal or simplified sensor models represent a limiting factor for comparability with field applications. More realistic sensor models are therefore required. Two groups of sensor models are proposed on the basis of field and laboratory tests: one for specific sensors and another for a classification of sensor types to be used with the COST simulation benchmark environment. This should lead to a more realistic test environment and allow control engineers to define the requirements of the measuring equipment as a function of the selected control strategy.
Fux, C., Boehler, M., Huber, P., Brunner, I., & Siegrist, H. (2002). Biological treatment of ammonium-rich wastewater by partial nitritation and subsequent anaerobic ammonium oxidation (anammox) in a pilot plant. Journal of Biotechnology, 99(3), 295-306. doi:10.1016/S0168-1656(02)00220-1, Institutional Repository

In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the nitrogen load is recirculated to the main stream with the return liquors from dewatering. Separate treatment of this ammonium-rich digester supernatant would significantly reduce the nitrogen load of the activated sludge system. Some years ago, a novel biological process was discovered in which ammonium is converted to nitrogen gas under anoxic conditions with nitrite as the electron acceptor (anaerobic ammonium oxidation, anammox). Compared to conventional nitrification and denitrification, the aeration and carbon-source demand is reduced by over 50 and 100%, respectively. The combination of partial nitritation to produce nitrite in a first step and subsequent anaerobic ammonium oxidation in a second reactor was successfully tested on a pilot scale (3.6 m3) for over half a year. This report focuses on the feasibility of nitrogen removal from digester effluents from two different wastewater treatment plants (WWTPs) with the combined partial nitritation/anammox process. Nitritation was performed in a continuously stirred tank reactor (V=2.0 m3) without sludge retention. Some 58% of the ammonium in the supernatant was converted to nitrite. At 30 °C the maximum dilution rate Dx was 0.85 d-1, resulting in nitrite production of 0.35 kg NO2-N mreactor -3 d-1. The nitrate production was marginal. The anaerobic ammonium oxidation was carried out in a sequencing batch reactor (SBR, V=1.6 m3) with a nitrogen elimination rate of 2.4 kg N mreactor -3 d-1 during the nitrite-containing periods of the SBR cycle. Over 90% of the inlet nitrogen load to the anammox reactor was removed and the sludge production was negligible. The nitritation efficiency of the first reactor limited the overall maximum rate of nitrogen elimination.
Fux, C., Böhler, M., Huber, P., & Siegrist, H. (2001). Stickstoffelimination durch anaerobe Ammoniumoxidation (Anammox). In Forschungs- und Entwicklungsinstitut für Industrie- und Siedlungswasserwirtschaft sowie Abfallwirtschaft (Ed.), Stuttgarter Berichte zur Siedlungswasserwirtschaft: Vol. 166. Der Stickstoff im Wasser/Abwasser (pp. 35-50). München: Oldenbourg Verlag. , Institutional Repository

Zur Oxidation von Ammonium sind bis anhin nur aerobe Systeme in Betracht gezogen worden. Vor einigen Jahren liess sich in einem denitrifizierenden Fliessbett-Reaktor beobachten, dass Ammonium bei ammoniumreichen Abwässern auch unter anoxischen Bedingungen oxidiert wird (Mulder et al., 1995). Anderseits konnte man bei belüfteten Tauchtropfkörpern, wo wenig bis kein organischer Kohlenstoff im Abwasser vorhanden war, eine beträchtliche Ammoniumelimination feststellen (Hippen et al., 1997, Siegrist et al., 1998). Aufgrund dieser Beobachtungen musste angenommen werden, dass auch noch andere biologische Prozesse als die konventionelle Nitrifikation und Denitrifikation zur Stickstoffelimination beitragen.

Nico Derlon

Bou-Sarkis, A., Paul, E., Bessiere, Y., Derlon, N., & Girbal-Neuhauser, E. (2024). Impact of biochemical properties on the gelation of EPS extracted from aerobic granules. Journal of Environmental Chemical Engineering, 12(5), 113648 (10 pp.). doi:10.1016/j.jece.2024.113648, Institutional Repository

Extracellular Polymeric Substances (EPS) extracted from aerobic granular sludge are a promising source of gel-forming biopolymers. Gaining insights on the charge distribution of these polymers was performed through a fractionation using anionic chromatography. A gelling factor (GF) based on the apparent gel volume and the reactivity of polymers to calcium was attributed to each eluted fraction. The GF values of the eluted anionic EPS correlated with their negative charge. A GF of 0.04 ± 0.03 is measured for molecules eluted at NaCl 0.25 M and a GF of 0.32 ± 0.02 for the molecules eluted at NaCl 0.75 M. However, upon reaching a very high negative charge (elution at NaCl 1 M), the gelation capacity decreases. The size distribution of gelling molecules was analyzed by Size Exclusion Chromatography. High Molecular Weight (MW) molecules are predominantly involved in gelation (between 65 % and 100 % of the high molecular weight fraction from each sample) while low MW molecules participation is relatively limited (lower than 40 % of the low molecular weight fraction from each sample). Moreover, infra-red spectroscopy analysis of the molecules before and after calcium addition showed that mostly proteins and polysaccharides contribute to the hydrogel formation. Colorimetric methods showed that around 60 % of the uronic acids present in the samples could form hydrogels whereas proteins’ participation varied between 0 % and 100 % depending on the fraction. Thus, modulating EPS extraction and purification methods to ensure the preservation of their molecular weight and the selection of appropriate negative charge could be a strategy for EPS valorization.
Fau, Z., Damien, T., Azais, A., Derlon, N., Chazarenc, F., & Gillot, S. (2024). Towards a standardised analysis of experimental Threshold Of Flocculation (TOF) curves. Water Science and Technology, 90(7), 2103-2113. doi:10.2166/wst.2024.308, Institutional Repository

Characterising bioflocculation and settling in activated sludge processes is mandatory to better understand and optimise organic matter removal and capture. Among the few indicators available, Threshold Of Flocculation (TOF) reflects the ability of activated sludge to settle following Stokesian settling mechanisms. In this work, the original method to determine TOF has been improved to gain accuracy and reproducibility. An R-script was proposed for systematic analysis of the experimental curves representing the total suspended solids supernatant concentration as a function of the initial concentration of the total suspended solids. The strength of this new method is to base curve analysis on the settling mechanisms that occur in the experimental setup. Two thresholds are mathematically identified, corresponding to (i) the solid concentration required to induce discrete flocculent settling and (ii) the minimum concentration to form large flocs that interact with each other (TOF). The novel method was successfully applied to different types of sludge (HRAS, CAS, and densified sludge).
Fumasoli, A., Probst, M., Wett, B., Derlon, N., Wenger, R., & Rérolle, M. (2024). Indense - Verfahren für Granulierten Schlamm. Erfahrungen und Erkenntnisse aus einem ein jährigen Pilotenversuch auf der ARA Gossau-Grüningen. Aqua & Gas, 104(1), 32-39. , Institutional Repository

Das inDENSE®-Verfahren wurde auf der ARA Gossau-Grüningen getestet. Nach einem Jahr wurde ein Anteil an granuliertem Schlamm von rund 50% und ein Schlammvolumenindex zwischen 40 und 70 ml/g beobachtet. DNA-Analysen zeigten, dass die bakterielle Gesamtpopulation saisonal konstanter blieb und Nitrit-oxidierende Bakterien im granulierten Schlamm akkumulierten. Durch die verbesserten Absetzeigenschaften können die Kapazität der ARA und die Stickstoffelimination signifikant gesteigert werden.
Pechaud, Y., Derlon, N., Queinnec, I., Bessiere, Y., & Paul, E. (2024). Modelling biofilm development: the importance of considering the link between EPS distribution, detachment mechanisms and physical properties. Water Research, 250, 120985 (16 pp.). doi:10.1016/j.watres.2023.120985, Institutional Repository

In industry, treatments against biofilms need to be optimized and, in the wastewater treatment field, biofilm composition needs to be controlled. Therefore, describing the biochemical and physical structures of biofilms is now required to better understand the influence of operating parameters and treatment on biofilms. The present study aims to investigate how growth conditions influence EPS composition, biofilm physical properties and volume detachment using a 1D biofilm model. Two types of EPS are considered in the present model, proteins and polysaccharides. The main hypotheses are that: (i) the production of polysaccharides occurs mainly under strong nutrient limitation(s) while the production of proteins is coupled to both the substrate uptake rate and the lysis process; (ii) the local biofilm porosity depends on the local biofilm composition. Both volume and surface detachment occur in biofilms and volume detachment extent depends on the biofilm local cohesion and thus on the local composition of biofilms for a given shear stress.
The model is based on experimental trends and aims to represent these observations on the basis of biochemical and physical processes. Four case studies covering a wide range of contrasting growth conditions such as different COD/N ratios, applied SOLR and shear stresses are investigated. The model predicts how the biochemical and physical biofilm structures change as a result of contrasting growth conditions. More precisely simulation results are in good agreement with the main experimental observations reported in the literature, such as: (i) a strong nitrogen limitation of growth induces an important accumulation of polysaccharides leading to a more porous and homogenous biofilm, (ii) a high applied surface organic loading load allows to obtain a high biofilm thickness, (iii) a strong shear stress applied during the biofilm growth leads to a reduction of the biofilm thickness and to a consolidation of the biofilm structure. Overall, this model represents a relevant decision tool for the selection of appropriate enzymatic treatments in the context of negative biofilm control. From our results, it appears that protease based treatments should be more appropriate for biofilms developed under low COD/N ratios (about 20 gCOD/gN) whereas both glucosidases and proteases based treatments should be more appropriate for biofilms developed under high COD/N ratio (about 70 gCOD/gN). In addition, the model could be useful for other applications such as resource recovery in biofilms or granules, and help to better understand biological membrane fouling.
Bou-Sarkis, A., Paul, E., Girbal-Neuhauser, E., Derlon, N., & Bessiere, Y. (2023). Detection of gel-forming polymers via calcium crosslinking, applied to the screening of extracellular polymeric substances extracted from biological aggregates. Gels, 9(2), 157 (14 pp.). doi:10.3390/gels9020157, Institutional Repository

The valorization of biological aggregates through the extraction of hydrogel-forming polymers can enhance the economics and sustainability of various processes in which bacteria are involved in organic waste transformation, such as wastewater treatment. Achieving these goals requires the development of a method capable of detecting the presence of gel-forming polymers in complex mixtures containing biopolymers that are most often unknown and uncharacterized. A miniaturized screening method capable of detecting gelation via ionic crosslinking using only 1 to 3 mg of the tested samples (commercial molecules or extracellular polymeric substances, EPSs) is proposed. The method consists of calculating a percentage of reactivity (%R) through UV-vis spectra and determining the percentage of gel volume (%Vg) formed after the addition of calcium. Both factors were combined to give a gelling factor (GF), and the test was applied to pure commercial molecules (BSA, DNA, alginate (ALV), and a mixture of them), allowing the classification of the following solutions according to their gel-forming capacity: GF(ALV) > GF(ALV+DNA) > GF(BSA+ALV+DNA) > GF(BSA+ALV) > GF(DNA) > GF(BSA+DNA) > GF(BSA). As a relevant tool for screening hydrogel-forming solutions, the method was applied to the EPS extracted from aerobic granular sludge. The EPS (0.5% w/v) had a GF of 0.16 ± 0.03, equivalent to approximately half of the GF of ALV (0.38 ± 0.02 at 0.5% w/v). The developed test pushes the limits of the existing gel-detection techniques because it allows for quicker, less consuming, and more informative gelation detection through the use of simple methods that do not require sophisticated equipment.
Brison, A., Rossi, P., & Derlon, N. (2023). Single CSTR can be as effective as an SBR in selecting PHA-storing biomass from municipal wastewater-derived feedstock. Water Research X, 18, 100165 (13 pp.). doi:10.1016/j.wroa.2023.100165, Institutional Repository

A key step for the production of polyhydroxyalkanoates (PHAs) from organic waste streams is the selection of a biomass with a high PHA-storage capacity (selection-step), which is usually performed in sequencing batch reactors (SBR). A major advancement would be to perform such selection in continuous reactors to facilitate the full-scale implementation of PHA production from municipal wastewater (MWW)-derived feedstock. The present study therefore investigates to what extent a simple continuous-flow stirred-tank reactor (CSTR) represents a relevant alternative to anSBR. To this end, we operated two selection reactors (CSTR vs. SBR) on filtered primary sludge fermentate while performing a detailed analysis of the microbial communities, and monitoring PHA-storage over long-term (∼150 days) and during accumulation batches. Our study demonstrates that a simple CSTR is as effective as an SBR in selecting biomass with high PHA-storage capacity (up to 0.65 gPHA gVSS−1) while being 50% more efficient in terms of substrate to biomass conversion yields. We also show that such selection can occur on VFA-rich feedstock containing nitrogen (N) and phosphorus (P) in excess, whereas previously, selection of PHA-storing organisms in a single CSTR has only been studied under P limitation. We further found that microbial competition was mostly affected by nutrient availability (N and P) rather than by the reactor operation mode (CSTR vs. SBR). Similar microbial communities therefore developed in both selection reactors, while microbial communities were very different depending on N availability. Rhodobacteraceae gen. were most abundant when growth conditions were stable and N-limited, whereas dynamic N- (and P-) excess conditions favoured the selection of the known PHA-storer Comamonas, and led to the highest observed PHA-storage capacity. Overall, we demonstrate that biomass with high storage capacity can be selected in a simple CSTR on a wider range of feedstock than just P-limited ones.
Daigger, G. T., Kuo, J., Derlon, N., Houweling, D., Jimenez, J. A., Johnson, B. R., … Boltz, J. P. (2023). Biological and physical selectors for mobile biofilms, aerobic granules, and densified-biological flocs in continuously flowing wastewater treatment processes: a state-of-the-art review. Water Research, 242, 120245 (13 pp.). doi:10.1016/j.watres.2023.120245, Institutional Repository

There have been significant advances in the use of biological and physical selectors for the intensification of continuously flowing biological wastewater treatment (WWT) processes. Biological selection allows for the development of large biological aggregates (e.g., mobile biofilm, aerobic granules, and densified biological flocs). Physical selection controls the solids residence times of large biological aggregates and ordinary biological flocs, and is usually accomplished using screens or hydrocyclones. Large biological aggregates can facilitate different biological transformations in a single reactor and enhance liquid and solids separation. Continuous-flow WWT processes incorporating biological and physical selectors offer benefits that can include reduced footprint, lower costs, and improved WWT process performance. Thus, it is expected that both interest in and application of these processes will increase significantly in the future. This review provides a comprehensive summary of biological and physical selectors and their design and operation.
Derlon, N., & Villez, K. (2023). Editorial: water resource recovery modelling 2021 (WRRmod2021 conference). Water Science and Technology, 87(12), III-IV. doi:10.2166/wst.2023.175, Institutional Repository
Larivé, O., Torii, S., Derlon, N., & Kohn, T. (2023). Selective elimination of enterovirus genotypes by activated sludge and chlorination. Environmental Science: Water Research and Technology, 9(6), 1620-1633. doi:10.1039/d3ew00050h, Institutional Repository

Enteroviruses, which are commonly circulating viruses shed in the stool, are released into the sewage system and only partially removed or inactivated, resulting in the discharge of infectious enteroviruses into the environment. Activated sludge and chlorination remove or inactivate enterovirus genotypes to different extents, and thus have the potential to shape the population that will be discharged. The goal of this study was to evaluate how activated sludge and chlorination treatment shape an enterovirus population at the genotype level, using a population of eight genotypes commonly found in sewage: CVA9, CVB1, CVB2, CVB3, CVB4, CVB5, E25, E30. Our results show that the extent of inactivation varied among genotypes, but also across sludge samples. We find that the effluent of activated sludge systems will be depleted in CVA9, CVB1 and CVB2 while E25 together with CVB3, CVB4 and CVB5 will be prevalent. Furthermore, we found that microbial inactivation was the main mechanism of infectivity loss in the activated sludge, while adsorption to the sludge flocs was not significant. During effluent chlorination, we also observed that CVB5, CVB3 and to a lesser extent E25 were less susceptible to chlorination while E30 was readily inactivated, and activated sludge-derived EPS provided further protection against chlorination. This study contributes to a better understanding of the variability of sewage treatment efficacy against different enteroviruses.
Stoffel, D., Derlon, N., Traber, J., Staaks, C., Heijnen, M., Morgenroth, E., & Jacquin, C. (2023). Gravity-driven membrane filtration with compact second-life modules daily backwashed: an alternative to conventional ultrafiltration for centralized facilities. Water Research X, 18, 100178 (12 pp.). doi:10.1016/j.wroa.2023.100178, Institutional Repository

Gravity-driven membrane (GDM) filtration is a strategic alternative to conventional ultrafiltration (UF) for the resilient production of drinking water via ultrafiltration when resources become scarce, given the low dependency on energy and chemicals, and longer membrane lifetime. Implementation at large scale requires the use of compact and low-cost membrane modules with high biopolymer removal capacity. We therefore evaluated (1) to what extent stable flux can be obtained with compact membrane modules, i.e., inside-out hollow fiber membranes, and frequent gravity-driven backwash, (2) whether we can reduce membrane expenses by effectively utilizing second-life UF modules, i.e., modules that have been discarded by treatment plant operators because they are no longer under warranty, (3) if biopolymer removal could be maintained when applying a frequent backwash and with second-life modules and (4) which GDM filtration scenarios are economically viable compared to conventional UF, when considering the influence of new or second-life modules, membrane lifetime, stable flux value and energy pricing. Our findings showed that it was possible to maintain stable fluxes around 10 L/m2/h with both new and second-life modules for 142 days, but a daily gravity-driven backwash was necessary and sufficient to compensate the continuous flux drop observed with compact modules. In addition, the backwash did not affect the biopolymer removal. Costs calculations revealed two significant findings: (1) using second-life modules made GDM filtration membrane investment less expensive than conventional UF, despite the higher module requirements for GDM filtration and (2) overall costs of GDM filtration with a gravity-driven backwash were unaffected by energy prices rise, while conventional UF costs rose significantly. The later increased the number of economically viable GDM filtration scenarios, including scenarios with new modules. In summary, we proposed an approach that could make GDM filtration in centralized facilities feasible and increase the range of UF operating conditions to better adapt to increasing environmental and societal constraints.
Bou-Sarkis, A., Pagliaccia, B., Ric, A., Derlon, N., Paul, E., Bessiere, Y., & Girbal-Neuhauser, E. (2022). Effects of alkaline solvents and heating temperatures on the solubilization and degradation of gel-forming Extracellular Polymeric Substances (EPS) extracted from aerobic granular sludge. Biochemical Engineering Journal, 185, 108500 (9 pp.). doi:10.1016/j.bej.2022.108500, Institutional Repository

The effects of solvents and heating temperatures on the recovery and degradation of gel-forming EPS (Extracellular Polymeric Substances) extracted from aerobic granular sludge were investigated. Sodium hydroxide has allowed a better EPS solubilization compared to sodium carbonate (711.3 ± 38 and 408.4 ± 4 mg VS /g VS respectively) but the capacity to precipitate gel-forming EPS at acidic pH was higher in sodium carbonate (22% compared to 6% in sodium hydroxide at 80 °C). Increasing the temperature from 20 °C to 80 °C during EPS solubilization has multiplied the amount of solubilized matter by 4 in sodium carbonate and 2.2 in sodium hydroxide. Similar biochemical composition but different molecular weight profiles were observed for the two solubilized EPS extracts, evidencing partial degradation of the polymers in sodium hydroxide. Furthermore, coupling molecular weight analysis and precipitation yield measurement revealed that the lower precipitation of sodium hydroxide solubilized EPS is related to the size reduction due to degradation. Altogether these results help to guide towards a unified protocol for the extraction of gel-forming EPS.
Brison, A., Rossi, P., & Derlon, N. (2022). Influent carbon to phosphorus ratio drives the selection of PHA-storing organisms in a single CSTR. Water Research X, 16, 100150 (11 pp.). doi:10.1016/j.wroa.2022.100150, Institutional Repository

Enriching a biomass with a high fraction of polyhydroxyalkanoate-storing organisms (PHA-storers) represents an essential step in the production of PHAs (bioplastics) from municipal wastewater using mixed microbial cultures. A major challenge is however to create selective growth conditions that are favourable to PHA-storers. Our study thus investigates to what extent the influent COD to phosphorus (COD:P) ratio can be used as a tool for the robust selection of PHA-storers in a single continuous-flow stirred-tank reactor (CSTR). Therefore, we operated five CSTRs in parallel, fed with synthetic wastewater (50% acetate - 50% propionate) with different COD:P ratios (200−1000 gCOD gP−1), and performed a detailed analysis of the microbial communities over long-term (30−70 solid retention times). Our study demonstrates that efficient and robust selection of PHA-storers can be achieved in a single CSTR at high influent COD:P ratios. The selective advantage for PHA-storers increases with the influent COD:P ratio, but only if growth conditions remain limited by both C-substrate and P. In contrast, selection performance deteriorates when COD:P ratios are too high and growth conditions are limited by P only. At an optimal COD:P ratio of 800 gCOD gP−1, a stable microbial community consisting of >90% PHA-storers and dominated by Pannonibacter sp. was selected in the long-term. Finally, our results suggest that high COD:P ratios provide a selective advantage to microorganisms with low cellular P requirements, explaining why different PHA-storers (i.e., Xanthobacter sp. vs. Pannonibacter sp.) were selected depending on the influent COD:P ratio (i.e., 200 vs. 800 gCOD gP−1). Overall, our results provide relevant insights for the development of a new approach for selecting PHA-storers, based on the use of a single CSTR and control of the influent COD:P ratio.
Brison, A., Rossi, P., Gelb, A., & Derlon, N. (2022). The capture technology matters: composition of municipal wastewater solids drives complexity of microbial community structure and volatile fatty acid profile during anaerobic fermentation. Science of the Total Environment, 815, 152762 (13 pp.). doi:10.1016/j.scitotenv.2021.152762, Institutional Repository

The production of volatile fatty acids (VFAs) represents a relevant option to valorize municipal wastewater (MWW). In this context, different capture technologies can be used to recover organic carbon from wastewater in form of solids, while pre-treatment of those solids has the potential to increase VFA production during subsequent fermentation. Our study investigates how VFA composition produced by fermentation is influenced (i) by the choice of the capture technology, as well as (ii) by the use of thermal alkaline pre-treatment (TAP). Therefore, the fermentation of solids originating from a primary settler, a micro-sieve, and a high-rate activated sludge (HRAS) system was investigated in continuous lab-scale fermenters, with and without TAP. Our study demonstrates that the capture technology strongly influences the composition of the produced solids, which in turn drives the complexity of the fermenter's microbial community and ultimately, of the VFA composition. Solids captured with the primary settler or micro-sieve consisted primarily of polysaccharides, and led to the establishment of a microbial community specialized in the degradation of complex carbohydrates. The produced VFA composition was relatively simple, with acetate and propionate accounting for >90% of the VFAs. In contrast, the HRAS system produced biomass-rich solids associated with higher protein contents. The microbial community which then developed in the fermenter was therefore more diversified and capable of converting a wider range of substrates (polysaccharides, proteins, amino acids). Ultimately, the produced VFA composition was more complex, with equal fractions of isoacids and propionate (both ~20%), while acetate remained the dominant acid (~50%). Finally, TAP did not significantly modify the VFA composition while increasing VFA yields on HRAS and sieved material by 35% and 20%, respectively. Overall, we demonstrated that the selection of the technology used to capture organic substrates from MWW governs the composition of the VFA cocktail, ultimately with implications for their further utilization.
Derlon, N., Desmond, P., Rühs, P. A., & Morgenroth, E. (2022). Cross flow frequency determines the physical structure and cohesion of membrane biofilms developed during gravity-driven membrane ultrafiltration of river water: implication for hydraulic resistance. Journal of Membrane Science, 643, 120079 (10 pp.). doi:10.1016/j.memsci.2021.120079, Institutional Repository

We evaluated how intermittent shear influences the physical structure, material properties and hydraulic resistance of membrane biofilms developed during gravity-driven ultrafiltration of river water, with the ultimate goal of increasing the filtration performances. Our results indicate intermittent shear helps slowing-down the flux decline but does not help to increase the level of stabilisation of the permeate flux. After several weeks, the biofilms exposed to different shear regimes were indeed characterised by similar hydraulic resistance. But the characteristic time to achieve a stable flux increased from 7 d to 25d when increasing the shear frequency. Also, most of the hydraulic resistance (up to 95%) was governed by the base layer that remained attached after erosion tests. With increasing exposure to shear conditions, the biofilms became more cohesive and more elastic, thus resisting better to cross flow conditions. Overall, our results demonstrate that engineering membrane biofilms with a desired permeability is not feasible using intermittent shear due to significant adaptability of the biofilms to their hydraulic environment.
Derlon, N., Garcia Villodres, M., Kovács, R., Brison, A., Layer, M., Takács, I., & Morgenroth, E. (2022). Modelling of aerobic granular sludge reactors: the importance of hydrodynamic regimes, selective sludge removal and gradients. Water Science and Technology, 86(3), 410-431. doi:10.2166/wst.2022.220, Institutional Repository

Hydraulic selection is a key feature of aerobic granular sludge (AGS) systems but existing aerobic granular sludge (AGS) models neglect those mechanisms: gradients over reactor height (Hreactor), selective removal of slow settling sludge, etc. This study aimed at evaluating to what extent integration of those additional processes into AGS models is needed, i.e., at demonstrating that model predictions (biomass inventory, microbial activities and effluent quality) are affected by such additional model complexity. We therefore developed a new AGS model that includes key features of full-scale AGS systems: fill-draw operation, selective sludge removal, distinct settling models for flocs/granules. We then compared predictions of our model to those of a fully mixed AGS model. Our results demonstrate that hydraulic selection can be predicted with an assembly of four continuous stirred tank reactors in series together with a correction code for plug-flow. Concentration gradients over the reactor height during settling/plug-flow feeding strongly impact the predictions of aerobic granular sludge models in terms of microbial selection, microbial activities and ultimately effluent quality. Hydraulic selection is a key to predict selection of storing microorganisms (phosphorus-accumulating organisms (PAO) and glycogen-accumulating organisms (GAO)) and in turn effluent quality in terms of total phosphorus, and for predicting effluent solid concentration and dynamic during plug-flow feeding.
Lamprecht, O., Wagner, B., Derlon, N., & Tlili, A. (2022). Synthetic periphyton as a model system to understand species dynamics in complex microbial freshwater communities. npj Biofilms and Microbiomes, 8, 61 (14 pp.). doi:10.1038/s41522-022-00322-y, Institutional Repository

Phototrophic biofilms, also known as periphyton, are microbial freshwater communities that drive crucial ecological processes in streams and lakes. Gaining a deep mechanistic understanding of the biological processes occurring in natural periphyton remains challenging due to the high complexity and variability of such communities. To address this challenge, we rationally developed a workflow to construct a synthetic community by co-culturing 26 phototrophic species (i.e., diatoms, green algae, and cyanobacteria) that were inoculated in a successional sequence to create a periphytic biofilm on glass slides. We show that this community is diverse, stable, and highly reproducible in terms of microbial composition, function, and 3D spatial structure of the biofilm. We also demonstrate the ability to monitor microbial dynamics at the single species level during periphyton development and how their abundances are impacted by stressors such as increased temperature and a herbicide, singly and in combination. Overall, such a synthetic periphyton, grown under controlled conditions, can be used as a model system for theory testing through targeted manipulation.
Layer, M., Brison, A., Garcia Villodres, M., Stähle, M., Házi, F., Takács, I., … Derlon, N. (2022). Microbial conversion pathways of particulate organic substrate conversion of aerobic granular sludge systems: limited anaerobic conversion and the essential role of flocs. Environmental Science: Water Research and Technology, 8(6), 1236-1251. doi:10.1039/D1EW00841B, Institutional Repository

Particulate organic substrate (XB) represents the major fraction of organic substrate in low-strength municipal wastewater (MWW) but its hydrolysis, conversion and utilisation in aerobic granular sludge (AGS) are not well understood. We systematically analysed through modelling the microbial conversion pathways of XB in AGS systems operated as sequencing batch reactors and treating municipal wastewater. Based on our current understanding of AGS systems, we developed an AGS model in Sumo® to better understand (1) during which phases of the SBR cycle (anaerobic plug-flow feeding or aerobic fully-mixed conditions), (2) by what biomass fraction (granules or flocs) and (3) via which microbial processes XB is converted into soluble organic substrate (SB) and volatile fatty acids (SVFA) and further utilised. The validity of all our results was evaluated by assessing the sensitivity of findings on the biomass distribution (floc fraction) (SCENARIO #1), SBR cycle (SCENARIO #2), and biofilm properties (SCENARIO #3). Our results indicate that only 20% of influent XB was hydrolysed and 11% of influent XB was then used for internal carbon-storage during 90 min anaerobic plug-flow feeding. The major fraction of influent XB (80%) leaked into the aerobic SBR phase, where XB was then hydrolysed and oxidised aerobically by ordinary heterotrophic organisms (OHOs). Under aerobic fully-mixed conditions, the flocs successfully competed for XB with the granules. Aerobic XB hydrolysis and its further utilisation by OHOs occurred mainly in flocs despite their minor biomass fraction (13% of total suspended solids), preventing excessive OHO growth on granules and demonstrating that flocs are beneficial for AGS systems treating MWW. Also, the model allowed us to better understand that the SBR sequence can be optimised to make better use of XB under anaerobic conditions and to reduce the leakage of XB to aerobic conditions. The introduction of a 60 min anaerobic idle phase after a 60 min plug-flow feeding phase almost doubled the anaerobic XB hydrolysis and internal carbon-storage by phosphorus and glycogen accumulating organisms (PAOs and GAOs), respectively, compared to 90 min plug-flow feeding. Nonetheless, most influent XB was still utilised by OHOs during the aerobic SBR phase.
Morgenroth, E., & Derlon, N. (2022). Entwicklung der biologischen Abwasserreinigung: Belebtschlamm vs Biofilmsysteme. In T. Wintgens & J. Pinnekamp (Eds.), Gewässerschutz, Wasser, Abwasser. 55. Essener Tagung für Wasserwirtschaft. Wasserwirtschaft im Klimawandel (p. 31 (12 pp.). Aachen: Gesellschaft zur Förderung des Instituts für Siedlungswasserwirtschaft an der RWTH Aachen. , Institutional Repository
Stoffel, D., Rigo, E., Derlon, N., Staaks, C., Heijnen, M., Morgenroth, E., & Jacquin, C. (2022). Low maintenance gravity-driven membrane filtration using hollow fibers: effect of reducing space for biofilm growth and control strategies on permeate flux. Science of the Total Environment, 811, 152307 (13 pp.). doi:10.1016/j.scitotenv.2021.152307, Institutional Repository

The implementation of centralized drinking water treatment systems necessitates lower operational costs and improved biopolymer removal during ultrafiltration (UF), which can be afforded by gravity-driven membrane (GDM) filtration. However, prior to implementing GDM filtration in centralized systems, biofilm growth in compacted membrane configurations, such as inside-out hollow fiber (HF), and its impact on permeate flux need to be investigated. To this end, we operated modules with distinct limits on available space for biofilm growth: (1) outside-in 1.5 mm 7-capillary HF (non-limited), (2) inside-out 1.5 mm 7-capillary HF (limited), and (3) inside-out 0.9 mm 7-capillary HF (very limited). Here, we observed that the lower the space available for biofilm growth, the lower the permeate flux. To improve GDM performance with inside-out HF, we applied daily shear stress to the biofilm surface with forward flush (FF) or combined relaxation and forward flush (R+FF). We showed that applying shear stress to the biofilm surface was insufficient for controlling flux loss due to low available space for biofilm growth. At the experimental endpoint, we backwashed with a stepwise transmembrane pressure (TMP) increase or a single TMP on all inside-out HF modules, which removed the biofilm from its base. Afterwards, higher fluxes were yielded. We also showed that all modules exhibited a gradual increase in biopolymer removal followed by stabilization between 70 and 90%. Additionally, control of biofilm growth with surface shear stress did not affect biopolymer removal. In summary, the implementation of inside-out HF with GDM filtration is challenged by low available space for biofilm growth, but may be remedied with a regular backwash to remove biofilm from its base. We showed that a wider range of GDM applications are available; making GDM potentially compatible with implementation in centralized systems, if space limitation is taken into consideration for operation optimization.
Benstöm, F., Meda, A., Baumann, P., Derlon, N., Lackner, S., Layer, M., … Wichern, M. (2021). Aerobe Verfahren mit granuliertem Schlamm zur Abwasserbehandlung - Arbeitsbericht der DWA­Arbeitsgruppe KA­6.3. "Biofilmverfahren"*) - Teil 1. KA: Korrespondenz Abwasser Abfall, 68(4), 281-288. , Institutional Repository

Unter bestimmten Prozessbedingungen entsteht in der konventionellen Abwasserreinigung aus flockenförmigem Belebtschlamm (FloS) aerober granulierter Schlamm (AGS), der in der Regel ohne Zugabe von Aufwuchskörpern gebildet wird. Prinzipiell können mit AGS die gleichen Reinigungsleistungen wie mit FloS erzielt werden. Im Vergleich zu konventionellen Anlagen ohne AGS können jedoch vergleichsweise höhere Biomassenkonzentrationen und kürzere Absetzzeiten des Schlamms erreicht und damit potenziell Reaktorvolumina eingespart werden. Somit können Verfahren mit AGS eine interessante Alternative zu etablierten Verfahren sein. Der vorliegende Arbeitsbericht erläutert die derzeit verfügbaren AGS-Verfahrensvarianten (diskontinuierlich und kontinuierlich), diskutiert erstmalig typische Verfahrenskennwerte und gibt Hinweise zu planerischen Aspekten und noch offenen Fragen.
Moraes Schambeck, C., Ribeiro da Costa, R. H., & Derlon, N. (2021). Phosphate removal from municipal wastewater by alginate-like exopolymers hydrogels recovered from aerobic granular sludge. Bioresource Technology, 333, 125167 (10 pp.). doi:10.1016/j.biortech.2021.125167, Institutional Repository

This worked assessed the potential of alginate-like exopolymers (ALE) hydrogels recovered from aerobic granular sludge (AGS) in removing compounds commonly present in municipal wastewater. Batch sorption experiments were performed with ALE hydrogels at different operating conditions. Results showed that ALE hydrogels can only remove phosphate, at removal efficiencies of up to 90.8% and practical loadings of 1.22 ± 0.07 mg PO43--P/g TSALE. Phosphate removal was observed even in the presence of competing ions. Moreover, neutral to acidic pH values strongly impaired the phosphate removal (28.9 ± 0.8% at pH = 6.00), while basic pH at around 8.50 was the most favourable (up to 90.8% at pH = 8.67). However, ALE hydrogels contributed to the increase in COD, total nitrogen and total phosphorus in the bulk liquid, what suggests that ALE need to be further tailored. Therefore, this study demonstrates that ALE represent a relevant approach for the recovery of phosphates from municipal wastewater.
Zhang, L., Graham, N., Derlon, N., Tang, Y., Siddique, M. S., Xu, L., & Yu, W. (2021). Biofouling by ultra-low pressure filtration of surface water: the paramount role of initial available biopolymers. Journal of Membrane Science, 640, 119740 (9 pp.). doi:10.1016/j.memsci.2021.119740, Institutional Repository

Biofouling layer (i.e., biofilm) is an inevitable presence for the membrane filtration processes. In this study, we elucidated biofouling formation from the perspective of affecting the attachment of bacteria for the first time, whereby the role of initial available biopolymers was revealed. Results demonstrated that the presence of initial available biopolymers increased the abundance of the genus Caulobacter, which was capable of mineralizing biopolymers; whereas, for the typically oligotrophic species of Polynucleobacter, it exhibited low abundance. Greater concentrations of polysaccharides and proteins were accumulated in the biofouling layer, when provided with initial biopolymers, and the biofilm structure was more heterogeneous with larger pore size and higher thickness. Thereby, the corresponding filtration system exhibited greater permeability and better removal performance of organics. Collectively, the initial available biopolymers altered the attachment conditions for the bacteria, which subsequently impacted the bacterial community, and in turn biofilm composition, physical structure and filtration performance.
Layer, M., Garcia Villodres, M., Hernandez, A., Reynaert, E., Morgenroth, E., & Derlon, N. (2020). Limited simultaneous nitrification-denitrification (SND) in aerobic granular sludge systems treating municipal wastewater: mechanisms and practical implications. Water Research X, 7, 100048 (13 pp.). doi:10.1016/j.wroa.2020.100048, Institutional Repository

Simultaneous nitrification-denitrification (SND) is, in theory, a key advantage of aerobic granular sludge systems over conventional activated sludge systems. But practical experience and literature suggests that SND and thus total nitrogen removal are limited during treatment of municipal wastewater using AGS systems. This study thus aims at quantifying the extent and understanding the mechanisms of SND during treatment of municipal wastewater with aerobic granular sludge (AGS) systems. Experiments (long-term and batch-tests) as well as mathematical modelling were performed. Our experimental results demonstrate that SND is significantly limited during treatment of low-strength municipal wastewater with AGS systems (14-39%), while almost full SND is observed when treating synthetic influent containing only diffusible substrate (90%). Our simulations demonstrate that the main mechanisms behind limited SND are (1) the dynamics of anoxic zone formation inside the granule, (2) the diffusibility and availability of electron-donors in those zones and (3) the aeration mode. The development of anoxic zones is driven by the utilisation of oxygen in the upper layers of the granule leading to transport limitations of oxygen inside the granule; this effect is closely linked to granule size and wastewater composition. Development of anoxic zones during the aerobic phase is limited for small granules at constant aeration at bulk dissolved oxygen (DO) concentration of 2 mgO2 L-1, and anoxic zones only develop during a brief period of the aerated phase for large granules. Modelling results further indicate that a large fraction of electron-donors are actually utilised in aerobic rather than anoxic redox zones - in the bulk or at the granule surface. Thus, full SND cannot be achieved with AGS treating low strength municipal wastewater if a constant DO is maintained during the aeration phase. Optimised aeration strategies are therefore required. 2-step and alternating aeration are tested successfully using mathematical modelling and increase TN removal to 40-79%, without compromising nitrification, and by shifting electron-donor utilisation towards anoxic redox conditions.
Layer, M., Bock, K., Ranzinger, F., Horn, H., Morgenroth, E., & Derlon, N. (2020). Particulate substrate retention in plug-flow and fully-mixed conditions during operation of aerobic granular sludge systems. Water Research X, 9, 100075 (11 pp.). doi:10.1016/j.wroa.2020.100075, Institutional Repository

Particulate substrate (XB) is the major organic substrate fraction in most municipal wastewaters. However, the impact of XB on aerobic granular sludge (AGS) systems is not fully understood. This study evaluated the physical retention of XB in AGS sequencing batch reactor (SBR) during anaerobic plug-flow and then aerobic fully-mixed conditions. The influence of different sludge types and operational variables on the extent and mechanisms of XB retention in AGS SBR were evaluated. XB mass-balancing and magnetic resonance imaging (MRI) were applied. During the anaerobic plug-flow feeding, most XB was retained in the first few cm of the settled sludge bed within the interstitial voids, where XB settled and accumulated ultimately resulting in the formation of a filter-cake. Sedimentation and surface filtration were thus the dominant XB retention mechanisms during plug-flow conditions, indicating that contact and attachment of XB to the biomass was limited. XB retention was variable and influenced by the XB influent concentration, sludge bed composition and upflow feeding velocity (vww). XB retention increased with larger XB influent concentrations and lower vww, which demonstrated the importance of sedimentation on XB retention during plug-flow conditions. Hence, large fractions of influent XB likely re-suspended during aerobic fully-mixed conditions, where XB then preferentially and rapidly attached to the flocs. During fully-mixed conditions, increasing floc fractions, longer mixing times and larger XB concentrations increased XB retention. Elevated XB retention was observed after short mixing times < 60 min when flocs were present, and the contribution of flocs towards XB retention was even more pronounced for short mixing times < 5 min. Overall, our results suggest that flocs occupy an environmental niche that results from the availability of XB during aerobic fully-mixed conditions of AGS SBR. Therefore, a complete wash-out of flocs is not desirable in AGS systems treating municipal wastewater.
Moraes Schambeck, C., Girbal-Neuhauser, E., Böni, L., Fischer, P., Bessière, Y., Paul, E., … Derlon, N. (2020). Chemical and physical properties of alginate-like exopolymers of aerobic granules and flocs produced from different wastewaters. Bioresource Technology, 312, 123632 (11 pp.). doi:10.1016/j.biortech.2020.123632, Institutional Repository

The influence of wastewater (WW) composition and the bioaggregates types (floccular vs. aerobic granular sludge - AGS) on the content, physical-chemical, hydrogel and rheological properties of Alginate-Like Exopolymers (ALE) was studied. Results showed that ALE are a complex mixture of proteins, humic acids and polysaccharides. Overall, rather similar ALE content and composition was observed for the different types of sludge. Only the AGS fed with acetate and propionate yielded significantly larger amount of ALE (261 ± 33 mg VSALE/g VSsludge, +49%) and of uronic sugars in ALE (254 ± 32 mgglucuronic acid/g VSALE, +62%) than bioaggregates fed with no/very little volatile fatty acids. Mannuronic acids are involved in the cohesion of the hydrogels. ALE hydrogels elasticity changed significantly with the type/origin of the bioaggregates. ALE hydrogels elasticity from AGS was always higher than from flocs when fed with real WW. Hence, different types of sludge impact the properties of the recovered ALE.
Ranzinger, F., Matern, M., Layer, M., Guthausen, G., Wagner, M., Derlon, N., & Horn, H. (2020). Transport and retention of artificial and real wastewater particles inside a bed of settled aerobic granular sludge assessed applying magnetic resonance imaging. Water Research X, 7, 100050 (9 pp.). doi:10.1016/j.wroa.2020.100050, Institutional Repository

The removal or degradation of particulate organic matter is a crucial part in biological wastewater treatment. This is even more valid with respect to aerobic granular sludge and the impact of particulate organic matter on the formation and stability of the entire granulation process. Before the organic part of the particulate matter can be hydrolyzed and finally degraded by the microorganism, the particles have to be transported towards and retained within the granulated biomass. The understanding of these processes is currently very limited. Thus, the present study aimed at visualizing the transport of particulate organic matter into and through an aerobic granular sludge bed. Magnetic Resonance Imaging (MRI) was successfully applied to resolve the different fractions of a granular sludge bed over time and space. Quantification and merging of 3D data sets allowed for a clear determination of the particle distribution within the granular sludge bed. Dextran coated super paramagnetic iron oxide nanoparticles (SPIONs, dp = 38±10 nm) served as model particles for colloidal particles. Microcrystalline cellulose particles (dp = 1-20 μm) tagged with paramagnetic iron oxide were applied as a reference for toilet paper, which is a major fraction of particulate matter in domestic wastewater. The results were supplemented by the use of real wastewater particles with a size fraction between 28 and 100 μm. Colloidal SPIONs distributed evenly over the granular sludge bed penetrating the granules up to 300 μm. Rinsing the granular sludge bed proved their immobilization. Microcrystalline cellulose and real wastewater particles in the micrometer range accumulated in the void space between settled granules. An almost full retention of the wastewater particles was observed within the first 20 mm of the granular sludge bed. Moreover, the formation of particle layers indicates that most of the micrometer-sized particles are not attached to the biomass and remain mobile. Consequently, these particles are released into the bulk phase when the granulated sludge bed is resuspended.
Schambeck, C. M., Magnus, B. S., de Souza, L. C. R., Leite, W. R. M., Derlon, N., Bittencourt Guimarães, L., & Ribeiro da Costa, R. H. (2020). Biopolymers recovery: dynamics and characterization of alginate-like exopolymers in an aerobic granular sludge system treating municipal wastewater without sludge inoculum. Journal of Environmental Management, 263, 110394 (11 pp.). doi:10.1016/j.jenvman.2020.110394, Institutional Repository

Alginate-like exopolymers (ALE) are present in the extracellular polymeric substances (EPS) of biological sludge such as aerobic granular sludge (AGS). The recovery of ALE from excess sludge produced by wastewater treatment plants (WWTP) is a relevant approach for the recovery of valuable products of industrial interest. However, little is known about dynamics of ALE content in sludge and associated factors. Thus, this study aimed at assessing the dynamics of EPS and ALE in terms of content, some chemical properties and influencing environmental factors along granulation in a sequencing batch reactor treating municipal wastewater. Results indicated that the EPS content was not correlated with the development of AGS, while the ALE content was higher, more stable and steadily increased after granulation achievement. Overall, 236 ± 27 mg VSALE/g VSsludge was recovered from AGS and 187 ± 94 mg VSALE/g VSsludge from flocs. However, the lower ALE content in flocs may be compensated by the higher sludge production rate in activated sludge systems. Principal component analysis (PCA) revealed that ALE content positively correlates with the nutrient and organic substrate conversion, and with the fraction of large AGS. Microbial analyses indicated that a stable microbial community composition was associated with a higher and more stable ALE content. ALE recovered from both flocs and AGS was endowed with hydrogel property, and no clear difference in their elemental composition and functional groups was observed. Therefore, our study provides insights about quantitative and qualitative aspects of ALE which are helpful for the improvement of waste biological sludge valorization.
Fumasoli, A., Bützer, S., Kraft, T., Derlon, N., Lüdin, K., Behl, M., & Maissen, B. (2019). Trommelsieb als Vorklärbecken-Ersatz. Erkenntnisse aus einem Pilotversuch auf der ARA Sihltal. Aqua & Gas, 99(10), 76-82. , Institutional Repository

Die ARA Sihltal wird heute ohne Vorklärung betrieben, soll jedoch aufgrund der zukünftigen Bevölkerungsentwicklung und zur energetischen Optimierung mit einer Vorklärung erweitert werden. Wegen der sehr engen Platzverhältnisse kann eine maschinelle Vorklärung (Trommelsieb) einfacher realisiert werden als eine konventionelle Vorklärung. Die Pilotversuche bestätigen, dass das Trommelsieb aus betrieblicher Sicht und bezüglich Abscheideleistung eine gleichwertige Vorklärung bietet.
Jafari, M., Derlon, N., Desmond, P., van Loosdrecht, M. C. M., Morgenroth, E., & Picioreanu, C. (2019). Biofilm compressibility in ultrafiltration: a relation between biofilm morphology, mechanics and hydraulic resistance. Water Research, 157, 335-345. doi:10.1016/j.watres.2019.03.073, Institutional Repository

Poroelastic fluid-structure interaction models were coupled to experimental data to determine the effects of biofilm spatial distribution of mechanical and hydraulic properties on the biofilm hydraulic resistance and compressibility in membrane filtration processes. Biofilms were cultivated on ultrafiltration membranes for 20 and 30 days under high (0.28 bar) and low (0.06 bar) transmembrane pressure (TMP), in dead-end filtration mode. Subsequently, biofilms were subjected to a compression/relaxation cycles by step-wise TMP changes. Structural deformation of biofilms during compression was observed in-situ using optical coherence tomography.
Experimental results show that the observed increase in the biofilm hydraulic resistance during compression is not necessarily accompanied by a detectable biofilm thickness reduction. A dual-layer biofilm model with a dense base and porous top layer could explain these observed results. Because porosity controls indirectly the mechanical response of biofilms under compression, results could be described without assuming a gradient in mechanical properties within the biofilm. The biofilm surface roughness did not significantly influence the water flux in this study. However, the fraction of biofilm base layer directly exposed to bulk liquid could be a good indicator in the determination of water flux. The main implications of this study for the design and operation of low-pressure membrane systems (e.g., MF and UF with fouling layer being the main filtration resistance) lays in the selection of favorable operational TMP and biofilm morphology.
Layer, M., Adler, A., Reynaert, E., Hernandez, A., Pagni, M., Morgenroth, E., … Derlon, N. (2019). Organic substrate diffusibility governs microbial community composition, nutrient removal performance and kinetics of granulation of aerobic granular sludge. Water Research X, 4, 100033 (16 pp.). doi:10.1016/j.wroa.2019.100033, Institutional Repository

Basic understanding of formation of aerobic granular sludge (AGS) has mainly been derived from lab-scale systems with simple influents containing only highly diffusible volatile fatty acids (VFA) as organic substrate. This study compares start-up of AGS systems fed by different synthetic and municipal wastewaters (WW), characterised by increasing complexity in terms of non-diffusible organic substrate. Four AGS reactors were started with the same inoculum activated sludge and operated for one year. The development of AGS, settling characteristics, nutrient and substrate removal performance as well as microbial community composition were monitored. Our results indicate that the higher the content of diffusible organic substrate in the WW, the faster the formation of AGS. The presence of non-diffusible organic substrate in the influent WW led to the formation of small granules and to the presence of 20–40% (% of total suspended solids) of flocs in the AGS. When AGS was fed with complex influent WW, the classical phosphorus and glycogen accumulating organisms (PAO, GAO) were outcompeted by their fermentative equivalents. Substrate and nutrient removal was observed in all reactors, despite the difference in physical and settling properties of the AGS, but the levels of P and N removal depended on the influent carbon composition. Mechanistically, our results indicate that increased levels of non-diffusible organic substrate in the influent lower the potential for microbial growth deep inside the granules. Additionally, non-diffusible organic substrates give a competitive advantage to the main opponents of AGS formation – ordinary heterotrophic organisms (OHO). Both of these mechanisms are suspected to limit AGS formation. The presented study has relevant implications for both practice and research. Start-up duration of AGS systems treating high complexity WW were one order of magnitude higher than a typical lab-scale system treating VFA-rich synthetic WW, and biomass as flocs persisted as a significant fraction. Finally, the complex synthetic influent WW – composed of VFA, soluble fermentable and particulate substrate - tested here seems to be a more adequate surrogate of real municipal WW for laboratory studies than 100%-VFA WW.
Pronk, W., Ding, A., Morgenroth, E., Derlon, N., Desmond, P., Burkhardt, M., … Fane, A. G. (2019). Gravity-driven membrane filtration for water and wastewater treatment: a review. Water Research, 149, 553-565. doi:10.1016/j.watres.2018.11.062, Institutional Repository

Gravity-driven membrane (GDM) filtration has been investigated for almost 10 years. The technology is characterized not only by relatively lower transmembrane pressures which can be achieved by gravity (extremely low energy consumption), but also by the phenomenon of flux stabilization: A biofilm is allowed to form on the membrane and a stabilization of flux occurs which is related to biological processes within the biofilm layer on the membrane. This enables stable operation during a year or longer without any cleaning or flushing. Initially, the technology was developed mainly for household drinking water treatment, but in the meantime, the research and application has expanded to the treatment of greywater, rainwater, and wastewater as well as the pretreatment of seawater for desalination. This review covers the field from the rather fundamental research on biofilm morphology and microbial community analysis to the impact of feedwater composition, process parameters and organic removal performance. Not only household applications, but also for community-scale treatment and full-scale applications are discussed. In addition, the application potential is highlighted in comparison to conventional ultrafiltration. Finally, an overall assessment is illustrated and the research and development needs are identified.
Seviour, T., Derlon, N., Simonsen Dueholm, M., Flemming, H. C., Girbal-Neuhauser, E., Horn, H., … Lin, Y. (2019). Extracellular polymeric substances of biofilms: suffering from an identity crisis. Water Research, 151, 1-7. doi:10.1016/j.watres.2018.11.020, Institutional Repository

Microbial biofilms can be both cause and cure to a range of emerging societal problems including antimicrobial tolerance, water sanitation, water scarcity and pollution. The identities of extracellular polymeric substances (EPS) responsible for the establishment and function of biofilms are poorly understood. The lack of information on the chemical and physical identities of EPS limits the potential to rationally engineer biofilm processes, and impedes progress within the water and wastewater sector towards a circular economy and resource recovery. Here, a multidisciplinary roadmap for addressing this EPS identity crisis is proposed. This involves improved EPS extraction and characterization methodologies, cross-referencing between model biofilms and full-scale biofilm systems, and functional description of isolated EPS with in situ techniques (e.g. microscopy) coupled with genomics, proteomics and glycomics. The current extraction and spectrophotometric characterization methods, often based on the principle not to compromise the integrity of the microbial cells, should be critically assessed, and more comprehensive methods for recovery and characterization of EPS need to be developed.
Silva, M. O. D., Desmond, P., Derlon, N., Morgenroth, E., & Pernthaler, J. (2019). Source community and assembly processes affect the efficiency of microbial microcystin degradation on drinking water filtration membranes. Frontiers in Microbiology, 10, 843 (15 pp.). doi:10.3389/fmicb.2019.00843, Institutional Repository

Microbial biofilms in gravity-driven membrane (GDM) filtration systems can efficiently degrade the cyanotoxin microcystin (MC), but it is unclear if this function depends on the presence of MC-producing cyanobacteria in the source water habitat. We assessed the removal of MC from added Microcystis aeruginosa biomass in GDMs fed with water from a lake with regular blooms of toxic cyanobacteria (ExpL) or from a stream without such background (ExpS). While initial MC removal was exclusively due to abiotic processes, significantly higher biological MC removal was observed in ExpL. By contrast, there was no difference in MC degradation capacity between lake and stream bacteria in separately conducted liquid enrichments on pure MC. Co-occurrence network analysis revealed a pronounced modularity of the biofilm communities, with a clear hierarchic distinction according to feed water origin and treatment type. Genotypes in the network modules associated with ExpS had significantly more links to each other, indicating that these biofilms had assembled from a more coherent source community. In turn, signals for stochastic community assembly were stronger in ExpL biofilms. We propose that the less “tightly knit” ExpL biofilm assemblages allowed for the better establishment of facultatively MC degrading bacteria, and thus for higher overall functional efficiency.
 
Carrel, M., Morales, V. L., Beltran, M. A., Derlon, N., Kaufmann, R., Morgenroth, E., & Holzner, M. (2018). Biofilms in 3D porous media: delineating the influence of the pore network geometry, flow and mass transfer on biofilm development. Water Research, 134, 280-291. doi:10.1016/j.watres.2018.01.059, Institutional Repository

This study investigates the functional correspondence between porescale hydrodynamics, mass transfer, pore structure and biofilm morphology during progressive biofilm colonization of a porous medium. Hydrodynamics and the structure of both the porous medium and the biofilm are experimentally measured with 3D particle tracking velocimetry and micro X-ray Computed Tomography, respectively. The analysis focuses on data obtained in a clean porous medium after 36 h of biofilm growth. Registration of the particle tracking and X-ray data sets allows to delineate the interplay between porous medium geometry, hydrodynamic and mass transfer processes on the morphology of the developing biofilm. A local analysis revealed wide distributions of wall shear stresses and concentration boundary layer thicknesses. The spatial distribution of the biofilm patches uncovered that the wall shear stresses controlled the biofilm development. Neither external nor internal mass transfer limitations were noticeable in the considered system, consistent with the excess supply of nutrient and electron acceptors. The wall shear stress remained constant in the vicinity of the biofilm but increased substantially elsewhere.
Carrel, M., Morales, V. L., Dentz, M., Derlon, N., Morgenroth, E., & Holzner, M. (2018). Pore-scale hydrodynamics in a progressively bioclogged three-dimensional porous medium: 3-D particle tracking experiments and stochastic transport modeling. Water Resources Research, 54(3), 2183-2198. doi:10.1002/2017WR021726, Institutional Repository

Biofilms are ubiquitous bacterial communities that grow in various porous media including soils, trickling, and sand filters. In these environments, they play a central role in services ranging from degradation of pollutants to water purification. Biofilms dynamically change the pore structure of the medium through selective clogging of pores, a process known as bioclogging. This affects how solutes are transported and spread through the porous matrix, but the temporal changes to transport behavior during bioclogging are not well understood. To address this uncertainty, we experimentally study the hydrodynamic changes of a transparent 3-D porous medium as it experiences progressive bioclogging. Statistical analyses of the system's hydrodynamics at four time points of bioclogging (0, 24, 36, and 48 h in the exponential growth phase) reveal exponential increases in both average and variance of the flow velocity, as well as its correlation length. Measurements for spreading, as mean-squared displacements, are found to be non-Fickian and more intensely superdiffusive with progressive bioclogging, indicating the formation of preferential flow pathways and stagnation zones. A gamma distribution describes well the Lagrangian velocity distributions and provides parameters that quantify changes to the flow, which evolves from a parallel pore arrangement under unclogged conditions, toward a more serial arrangement with increasing clogging. Exponentially evolving hydrodynamic metrics agree with an exponential bacterial growth phase and are used to parameterize a correlated continuous time random walk model with a stochastic velocity relaxation. The model accurately reproduces transport observations and can be used to resolve transport behavior at intermediate time points within the exponential growth phase considered.
Derlon, N., Layer, M., Morgenroth, E., Adler, A., Gelb, A., & Holliger, C. (2018). Boues granulaires aérobies. État de l'art de la recherche actuelle et future. Aqua & Gas, 98(1), 14-19. , Institutional Repository

Les boues granulaires aérobies offrent plusieurs avantages pour le traitement biologique des eaux usées municipales par rapport au procédé à boues activées conventionnels. Cependant, malgré un nombre croissant d’applications industrielles et municipales, notre recul sur les boues granulaires aérobies reste limité. L’EPFL et l’Eawag ont évalué au cours des dernières années les mécanismes, performances et limites des systèmes de boues granulaires aérobies. Dans cet article, nous résumons notre compréhension des facteurs influençant les propriétés des boues granulaires aérobies et fournissons une appréciation globale de cette nouvelle technologie.
Derlon, N., Pronk, W., & Morgenroth, E. (2018). Membranes d'ultrafiltration. La présence de biofilms: un avantage pour stabiliser le flux et augmenter la qualité du perméat. Aqua & Gas, 98(5), 30-35. , Institutional Repository

L’utilisation de systèmes composites combinant une couche biologique (le biofilm) supportée par une barrière physique (la membrane) a de multiples avantages pour le traitement des eaux (production d’eau potable, recyclage des eaux grises). Cet article présente comment tirer profit de la microbiologie des biofilms afin d’améliorer la qualité du perméat et faire fonctionner des systèmes membranaires à flux constant pendant plusieurs années, et ce sans maintenance.
Desmond, P., Best, J. P., Morgenroth, E., & Derlon, N. (2018). Linking composition of extracellular polymeric substances (EPS) to the physical structure and hydraulic resistance of membrane biofilms. Water Research, 132, 211-221. doi:10.1016/j.watres.2017.12.058, Institutional Repository

The effect of extracellular polymeric substances (EPS) on the meso-scale physical structure and hydraulic resistance of membrane biofilms during gravity driven membrane (GDM) filtration was investigated. Biofilms were developed on the surface of ultrafiltration membranes during dead-end filtration at ultra-low pressure (70 mbar). Biofilm EPS composition (total protein, polysaccharide and eDNA) was manipulated by growing biofilms under contrasting nutrient conditions. Nutrient conditions consisted of (i) a nutrient enriched condition with a nutrient ratio of 100:30:10 (C: N: P), (ii) a phosphorus limitation (C: N: P ratio: 100:30:0), and (iii) a nitrogen limitation (C: N: P ratio: 100:0:10). The structure of the biofilm was characterised at meso-scale using Optical Coherence Tomography (OCT). Biofilm composition was analysed with respect to total organic carbon, total cellular mass and extracellular concentrations of proteins, polysaccharides, and eDNA. 2D-confocal Raman mapping was used to characterise the functional group composition and micro-scale distribution of the biofilms EPS. Our study reveals that the composition of the EPS matrix can determine the meso-scale physical structure of membrane biofilms and in turn its hydraulic resistance. Biofilms grown under P limiting conditions were characterised by dense and homogeneous physical structures with high concentrations of polysaccharides and eDNA. Biofilm grown under nutrient enriched or N limiting conditions were characterised by heterogeneous physical structures with lower concentrations of polysaccharides and eDNA. For P limiting biofilms, 2D-confocal Raman microscopy revealed a homogeneous spatial distribution of anionic functional groups in homogeneous biofilm structures with higher polysaccharide and eDNA concentrations. This study links EPS composition, physical structure and hydraulic resistance of membrane biofilms, with practical relevance for the hydraulic performances of GDM ultrafiltration.
Desmond, P. (2018). Linking hydraulic resistance to the physical structure of membrane biofilms (Doctoral dissertation). doi:10.3929/ethz-b-000296862, Institutional Repository

Gravity driven membrane (GDM) ultrafiltration is a continuous dead-end filtration process for potable and non-potable water production. GDM operates on the principle of tolerating biofilm development on the membranes surface for the benefit of minimum membrane maintenance, stable flux production, and improved permeate quality. The biological activity afforded by the tolerated biofilm allows degradation of foulants that would otherwise accumulate on the surface of the membrane, decreasing permeate flux. However, membrane biofilms are not without problems. The presence of a biofilm increases the hydraulic resistance, which exceeds the intrinsic resistance of the membrane, leading to low yet stable permeate flux. The purpose of the presented thesis is to evaluate what structural feature of the biofilm can exert a resistance to hydraulic passage and how hydraulic resistance is influenced by the biofilms mechanical response to changes in process operation (e.g., transmembrane pressure (TMP), cross-flow). Towards this goal, the approach taken to determine the link between hydraulic resistance and the biofilms structural and mechanical characteristics shall examine: (a) how different biofilm physical structures affect hydraulic resistance; (b) how compression affect physical structure and related hydraulic resistance; (c) how hydraulic resistance changes over the biofilms depth. A key advancement of the current study is evaluating the link between biofilm physical structure and resulting hydraulic resistance using in-situ and non-invasive methods for chemical, structural and mechanical characterization, using 2D confocal Raman microscopy and optical coherence tomography, respectively.

Results of the presented thesis indicate that the formation of GDM biofilms is influenced by the nutrient availability (carbon, nitrogen, and phosphorus), which determined composition and micro-scale spatial distribution of extracellular polymeric substances (EPS). High concentrations of anionic polymers, homogeneously distributed in space, led to the formation of thin dense homogenous physical structures which had a higher hydraulic resistance. Low concentration of anionic polymers, heterogeneously distributed in space, led to the formation of thick heterogeneous physical structures with a low hydraulic resistance. Taken together, it is demonstrated that thicker heterogeneous structures imposed less hydraulic resistance than thin dense homogeneous structure, indicating density rather than thickness is the structural determinant of a biofilms hydraulic resistance.

The hydraulic resistance of membrane biofilms is also linked to their structural response to perpendicular and parallel flow. With increasing perpendicular flow, heterogeneous biofilms became irreversibly compressed, while homogeneous biofilms were reversibly compressed. Irreversible compression results from the reduction of the biofilm roughness and porosity and led to an irreversible increase in hydraulic resistance. With increasing hydraulic shear stress (flow parallel to the membrane), we demonstrated stratification in the physical structure, cohesion and hydraulic resistance of GDM biofilms. Detachment of a thick surface layer roughness had limited impact on hydraulic resistance due to retention of a cohesive base layer with a high hydraulic resistance.

The presented thesis provides a fundamental understanding of how hydraulic resistance is linked to a biofilms composition, physical structure and mechanical strength. Our evaluation of biofilm physical structure and hydraulic resistance in GDM systems has demonstrated that heterogeneous physical structures exert limited hydraulic resistance and have a low mechanical strength. Greater hydraulic resistance is exerted by thin dense base layer at the surface of the membrane. We suggest GDM membrane operators (a) maintain constant transmembrane pressure to avoided compaction of heterogeneous structure, (b) avoid hydraulic shear due to limited effect on resistance due to retention of thin and dense cohesive base layer and (c) focus on efforts to decrease the hydraulic resistance by increasing structural heterogeneity "in-place" by way of predation and/or nutrient enrichment.
Desmond, P., Morgenroth, E., & Derlon, N. (2018). Physical structure determines compression of membrane biofilms during Gravity Driven Membrane (GDM) ultrafiltration. Water Research, 143, 539-549. doi:10.1016/j.watres.2018.07.008, Institutional Repository

Increasing transmembrane pressure (TMP) can compress and increase the hydraulic resistance of membrane biofilms. The purpose of the present study is to evaluate how compression of membrane biofilms occurs and how structural rearrangement can affect hydraulic resistance. Biofilms with heterogeneous and homogeneous physical structures were grown in membrane fouling simulators (MFS) in dead-end mode for 20 days with either (i) a nutrient enriched condition with a nutrient ratio of 100:30:10 (C: N: P), (ii) a phosphorus limitation (C: N: P ratio: 100:30:0), or (iii) river water (C: N: P ratio: ca. 100:10:1). The structural and hydraulic response of membrane biofilms to (a) changes in transmembrane pressures (0.06-0.1-0.5-0.1-0.06 bar) and (b) changes in permeate flux (10-15-20-15-10 L/m2/h) were investigated. Optical coherence tomography (OCT) was used to monitor biofilm structural response, and OCT images were processed to quantify changes in the mean biofilm thickness and relative roughness. Nutrient enriched and river water biofilms had heterogeneous physical structures with greater surface roughness (Ra' > 0.2) than homogeneous P limiting biofilms (Ra' < 0.2). Compression of biofilms with rough heterogeneous structures (Ra' > 0.2) was irreversible, indicated by irreversible decrease in surface roughness, partial relaxation in mean biofilm thickness and irreversible increase in hydraulic resistance. Compression of homogeneous biofilm (Ra' < 0.2) was on the other hand reversible, indicated by full relaxation of the biofilms structure and restoration of initial hydraulic resistance. Hydraulic response (i.e., change in the specific biofilm resistance) did not correspond with the change in physical structure of heterogeneous biofilms. The presented study provides a fundamental understanding of how biofilm physical structure can affect the biofilm's response to a change in TMP, with practical relevance for the operation of GDM filtration systems.
Desmond, P., Böni, L., Fischer, P., Morgenroth, E., & Derlon, N. (2018). Stratification in the physical structure and cohesion of membrane biofilms – implications for hydraulic resistance. Journal of Membrane Science, 564, 897-904. doi:10.1016/j.memsci.2018.07.088, Institutional Repository

This study aimed at evaluating stratification of hydraulic resistance over the depth of membrane biofilms developed during gravity driven membrane (GDM) ultrafiltration. Biofilms were grown in membrane fouling simulators (MFS) for 25 days under 3 contrasting influent conditions: nutrient enriched, phosphorus limiting, and river water influent. Shear rheology was used to determine the biofilms material characteristics (e.g., elasticity, yield stress). Optical coherence tomography (OCT) was used to determine the response of the biofilms physical structure (e.g., thickness) to increased hydraulic shear stress from 0 up to 2.6 Pa. Stratification was observed in nutrient enriched and river water biofilms and which partially detached by erosion of their rough top layer under low shear conditions. A cohesive base layer remained attached to the membrane surface under high shear conditions, indicating stratification in cohesion over the biofilms depth. Erosion of the top layer only resulted in a slight decrease in the biofilm hydraulic resistance indicating that the very cohesive and thin base layer also represent significant hydraulic resistance. Conversely, P limiting biofilms had uniform structural and mechanical characteristics, detaching by sloughing and peeling at low and high shear stress respectively. Biofilms formed under phosphorus limiting conditions had equal elasticity, yet a lower yield stress compared to nutrient enriched and river water biofilms respectively and were more susceptible to detachment. The scientific implication of the presented work demonstrates that biofilm detachment is influenced by both the structural (surface heterogeneity) and material characteristics (e.g., yield stress), with practical relevance for hydraulic resistance during GDM filtration.
Jafari, M., Desmond, P., van Loosdrecht, M. C. M., Derlon, N., Morgenroth, E., & Picioreanu, C. (2018). Effect of biofilm structural deformation on hydraulic resistance during ultrafiltration: A numerical and experimental study. Water Research, 145, 375-387. doi:10.1016/j.watres.2018.08.036, Institutional Repository

Biofilm formation in membrane systems negatively impacts the filtration system performances. This study evaluated how biofilm compression driven by permeate flow increases the hydraulic resistance and leads to reduction in permeate flux. We analysed the effect of biofilm compression on hydraulic resistance and permeate flux through computational models supported by experimental data. Biofilms with homogeneous surface structure were subjected to step-wise changes in flux and transmembrane pressure during compression and relaxation tests. Biofilm thickness under applied forces was measured non-invasively in-situ using optical coherence tomography (OCT). A numerical model of poroelasticity, which couples water flow through the biofilm with biofilm mechanics, was developed to correlate the structural deformation with biofilm hydraulics (permeability and resistance). The computational model enabled extracting mechanical and hydrological parameters corresponding to the experimental data. Homogeneous biofilms under elevated compression forces experienced a significant reduction in thickness while only a slight increase in resistance was observed. This shows that hydraulic resistance of homogeneous biofilms was affected more by permeability decrease due to pore closure than by a decrease in thickness. Both viscoelastic and elastoplastic models could describe well the permanent biofilm deformation. However, for biofilms under study, a simpler elastic model could also be used due to the small irreversible deformations. The elastic moduli fitting the measured data were in agreement with other reported values for biofilm under compression. Biofilm stiffening under larger flow-driven compression forces was observed and described numerically by correlating inversely the elastic modulus with biofilm porosity. The importance of this newly developed method lies in estimation of accurate biofilm mechanical parameters to be used in numerical models for both membrane filtration system and biofouling cleaning strategies. Such model can ultimately be used to identify optimal operating conditions for membrane system subjected to biofouling.
Boltz, J. P., Johnson, B. R., Takács, I., Daigger, G. T., Morgenroth, E., Brockmann, D., … Derlon, N. (2017). Biofilm carrier migration model describes reactor performance. Water Science and Technology, 75(12), 2818-2828. doi:10.2166/wst.2017.160, Institutional Repository

The accuracy of a biofilm reactor model depends on the extent to which physical system conditions (particularly bulk-liquid hydrodynamics and their influence on biofilm dynamics) deviate from the ideal conditions upon which the model is based. It follows that an improved capacity to model a biofilm reactor does not necessarily rely on an improved biofilm model, but does rely on an improved mathematical description of the biofilm reactor and its components. Existing biofilm reactor models typically include a one-dimensional biofilm model, a process (biokinetic and stoichiometric) model, and a continuous flow stirred tank reactor (CFSTR) mass balance that [when organizing CFSTRs in series] creates a pseudo two-dimensional (2-D) model of bulk-liquid hydrodynamics approaching plug flow. In such a biofilm reactor model, the user-defined biofilm area is specified for each CFSTR; thereby, Xcarrier does not exit the boundaries of the CFSTR to which they are assigned or exchange boundaries with other CFSTRs in the series. The error introduced by this pseudo 2-D biofilm reactor modeling approach may adversely affect model results and limit model-user capacity to accurately calibrate a model. This paper presents a new sub-model that describes the migration of Xcarrier and associated biofilms, and evaluates the impact that Xcarrier migration and axial dispersion has on simulated system performance. Relevance of the new biofilm reactor model to engineering situations is discussed by applying it to known biofilm reactor types and operational conditions.
Carrel, M., Beltran, M. A., Morales, V. L., Derlon, N., Morgenroth, E., Kaufmann, R., & Holzner, M. (2017). Biofilm imaging in porous media by laboratory X-ray tomography: combining a non-destructive contrast agent with propagation-based phase-contrast imaging tools. PLoS One, 12(7), e0180374 (18 pp.). doi:10.1371/journal.pone.0180374, Institutional Repository

X-ray tomography is a powerful tool giving access to the morphology of biofilms, in 3D porous media, at the mesoscale. Due to the high water content of biofilms, the attenuation coefficient of biofilms and water are very close, hindering the distinction between biofilms and water without the use of contrast agents. Until now, the use of contrast agents such as barium sulfate, silver-coated micro-particles or 1-chloronaphtalene added to the liquid phase allowed imaging the biofilm 3D morphology. However, these contrast agents are not passive and potentially interact with the biofilm when injected into the sample. Here, we use a natural inorganic compound, namely iron sulfate, as a contrast agent progressively bounded in dilute or colloidal form into the EPS matrix during biofilm growth. By combining a very long source-to-detector distance on a X-ray laboratory source with a Lorentzian filter implemented prior to tomographic reconstruction, we substantially increase the contrast between the biofilm and the surrounding liquid, which allows revealing the 3D biofilm morphology. A comparison of this new method with the method proposed by Davit et al (Davit et al., 2011), which uses barium sulfate as a contrast agent to mark the liquid phase was performed. Quantitative evaluations between the methods revealed substantial differences for the volumetric fractions obtained from both methods. Namely, contrast agent—biofilm interactions (e.g. biofilm detachment) occurring during barium sulfate injection caused a reduction of the biofilm volumetric fraction of more than 50% and displacement of biofilm patches elsewhere in the column. Two key advantages of the newly proposed method are that passive addition of iron sulfate maintains the integrity of the biofilm prior to imaging, and that the biofilm itself is marked by the contrast agent, rather than the liquid phase as in other available methods. The iron sulfate method presented can be applied to understand biofilm development and bioclogging mechanisms in porous materials and the obtained biofilm morphology could be an ideal basis for 3D numerical calculations of hydrodynamic conditions to investigate biofilm-flow coupling.
Derlon, N., Thürlimann, C., Dürrenmatt, D., & Villez, K. (2017). Batch settling curve registration via image data modeling. Water Research, 114, 327-337. doi:10.1016/j.watres.2017.01.049, Institutional Repository

To this day, obtaining reliable characterization of sludge settling properties remains a challenging and time-consuming task. Without such assessments however, optimal design and operation of secondary settling tanks is challenging and conservative approaches will remain necessary. With this study, we show that automated sludge blanket height registration and zone settling velocity estimation is possible thanks to analysis of images taken during batch settling experiments. The experimental setup is particularly interesting for practical applications as it consists of off-the-shelf components only, no moving parts are required, and the software is released publicly. Furthermore, the proposed multivariate shape constrained spline model for image analysis appears to be a promising method for reliable sludge blanket height profile registration.
Cunningham, M. (2016). Particulate substrate (Xs) retention mechanisms during feeding of an aerobic granular sludge (AGS) system (Master thesis). 35 p. , Institutional Repository

Aerobic granular sludge (AGS) has been proposed as a lower cost alternative to activated sludge in municipal wastewater treatment. AGS has a settling velocity up to twenty times greater than activated sludge (Rocktaschel, 2013). Granules have multiple redox zones which potentially allows for carbon, nitrogen, and phosphorous removal to occur in a single reactor (Giesen et al., 2013). These benefits reduce AGS reactor tank volume, equipment and aeration requirements—resulting in cost savings. However, growing AGS with wastewater and other feed waters with high particulate substrate (Xs) results in undesirable fluffy less dense granules and floc growth (de Kreuk et al., 2010).
A proposed solution is maximizing Xs attachment, hydrolysis and consumption during the anaerobic plug flow feeding phase of a sequencing batch reactor (SBR) cycle (de Kreuk et al., 2010). This thesis aims to better understand how biomass composition (ratio of granules to flocs), Xs size, and feeding velocity influence Xs retention. The secondary objective is to compare Xs retention by flocs and granules under fully mixed conditions.
A column test was developed to compare cellulose and wastewater Xs attachment to granules, flocs and granular sludge under plug flow conditions. A feed velocity of 1.4 m/h resulted in greater Xs retention compared to 3 and 5 m/h by all types of biomass; the outlier scenario is wastewater fed at 3 m/h, which could be attributed to Xs wastewater concentration in those tests. Granules performed better than flocs, which was surprising given that in granular media filtration a smaller media diameter leads to better particle retention (Yao et al., 1971; Darby et al., 1990). Abrupt changes to the biomass bed structure through channel formation or fractioning into multiple segments is proposed as an explanation. Furthermore, channeling and fractioning affected the distribution of retained Xs in the bed. The hydrolysis rate is a function of biomass and Xs concentration; therefore, the distribution of retained Xs in the bed is an important topic for potential future research (Morgenroth et al., 2002).
The jar tests also further emphasize the importance of maximizing Xs retention and consumption by granules during the anaerobic phase. Flocs performed better than granules at capturing Xs in fully mixed conditions. This indicates that flocs are likely to survive on Xs that is available in the supernatant, or was retained by the bed of granules but becomes available during the aerobic cycle because it was not fully consumed.
Overall, this thesis provides a first step into understanding the fate of Xs in AGS systems treating municipal wastewater. This topic involves physical (Xs retention) and biological (Xs hydrolysis and degradation) processes. Previous research on granular media filtration and contact stabilization is helpful for developing experimental procedures. Continued research into this topic can help maximize the economic benefits of AGS for wastewater treatment by improving granule morphology and limiting floc growth.
Derlon, N., Wagner, J., Ribeiro da Costa, R. H., & Morgenroth, E. (2016). Formation of aerobic granules for the treatment of real and low-strength municipal wastewater using a sequencing batch reactor operated at constant volume. Water Research, 105, 341-350. doi:10.1016/j.watres.2016.09.007, Institutional Repository

This study aimed at evaluating the formation of aerobic granular sludge (AGS) for the treatment of real and low-strength municipal wastewater using a column sequencing batch reactor (SBR) operated in fill-draw mode (constant volume). The focus was on understanding how the wastewater upflow velocity (VWW) applied during the anaerobic feeding influenced the sludge properties and in turn the substrate conversion. Two different strategies were tested: (1) washing-out the flocs by imposing high wastewater upflow velocities (between 5.9 and 16 m h−1) during the anaerobic feeding (Approach #1) and (2) selective utilization of organic carbon during the anaerobic feeding (1 m h−1) combined with a selective sludge withdrawal (Approach #2). A column SBR of 190 L was operated in constant volume during 1500 days and fed with real and low-strength municipal wastewater. The formation of AGS with SVI30 of around 80 mL gTSS−1 was observed either at very low (1 m h−1) or at high VWW (16 m h−1). At 16 m h−1 the AGS was mainly composed of large and round granules (d > 0.63 mm) with a fluffy surface, while at 1 m h−1 the sludge was dominated by small granules (0.25 < d < 0.63 mm). The AGS contained a significant fraction of flocs during the whole operational period. A considerable and continuous washout of biomass occurred at VWW higher than 5.9 m h−1 (Approach #1) due to the lower settling velocity of the AGS fed with municipal wastewater. The low sludge retention observed at VWW higher than 5.9 m h−1 deteriorated the substrate conversion and in turn the effluent quality. High solid concentrations (and thus solid retention time) were maintained during Approach #2 (VWW of 1 m h−1), which resulted in an excellent effluent quality. The study demonstrated that the formation of AGS is possible during the treatment of real and low-strength municipal wastewater in a SBR operated at constant volume. Low wastewater upflow velocities should be applied during the anaerobic feeding phase in order to ensure enough biomass retention and efficient substrate removal.
Derlon, N., Grütter, A., Brandenberger, F., Sutter, A., Kuhlicke, U., Neu, T. R., & Morgenroth, E. (2016). The composition and compression of biofilms developed on ultrafiltration membranes determine hydraulic biofilm resistance. Water Research, 102, 63-72. doi:10.1016/j.watres.2016.06.019, Institutional Repository

This study aimed at identifying how to improve the level of permeate flux stabilisation during gravity-driven membrane filtration without control of biofilm formation. The focus was therefore on understanding (i) how the different fractions of the biofilms (inorganics particles, bacterial cells, EPS matrix) influence its hydraulic resistance and (ii) how the compression of biofilms impacts its hydraulic resistance, i.e., can water head be increased to increase the level of permeate flux stabilisation. Biofilms were developed on ultrafiltration membranes at 88 and 284 cm water heads with dead-end filtration for around 50 days. A larger water head resulted in a smaller biofilm permeability (150 and 50 L m−2 h−1 bar−1 for biofilms grown at 88 cm and 284 cm water head, respectively). Biofilms were mainly composed of EPS (>90% in volume). The comparison of the hydraulic resistances of biofilms to model fouling layers indicated that most of the hydraulic resistance is due to the EPS matrix. The compressibility of the biofilm was also evaluated by subjecting the biofilms to short-term (few minutes) and long-term variations of transmembrane pressures (TMP). A sudden change of TMP resulted in an instantaneous and reversible change of biofilm hydraulic resistance. A long-term change of TMP induced a slow change in the biofilm hydraulic resistance. Our results demonstrate that the response of biofilms to a TMP change has two components: an immediate variation of resistance (due to compression/relaxation) and a long-term response (linked to biofilm adaptation/growth). Our results provide relevant information about the relationship between the operating conditions in terms of TMP, the biofilm structure and composition and the resulting biofilm hydraulic resistance. These findings have practical implications for a broad range of membrane systems.
Ding, A., Liang, H., Li, G., Derlon, N., Szivak, I., Morgenroth, E., & Pronk, W. (2016). Impact of aeration shear stress on permeate flux and fouling layer properties in a low pressure membrane bioreactor for the treatment of grey water. Journal of Membrane Science, 510, 382-390. doi:10.1016/j.memsci.2016.03.025, Institutional Repository

Two different aeration regimes were studied in a low pressure gravity driven membrane bioreactor without any flushing or (back-) washing. In one reactor, the aeration was positioned below the membrane module, thus exposing the membranes to aeration shear stress. A second reactor was operated at low shear stress by placing the aerator in a different compartment. Flux stabilization at 2.0 L/(m2 h) occurred in the reactor with low shear stress while no flux stabilization was observed in the reactor with aeration shear stress, resulting in a flux of 0.5 L/(m2 h) after 120 days. The thickness of the bio-fouling layer in the reactor with aeration shear was smaller (129 vs. 344 µm), which implies that shear stress resulted in a thinner, denser and less permeable bio-fouling layer. The results can be explained by differences in (1) the morphology of the bio-fouling layer and (2) the EPS contents (proteins and polysaccharides) in the bio-fouling layer. The low-shear system provides a suitable solution for decentralized grey water treatment, or other conditions where maintenance and energy consumption should be minimized. Furthermore, the results can contribute to decrease the energy consumption in MBR systems.
Habermacher, J., Benetti, A. D., Derlon, N., & Morgenroth, E. (2016). Degradation of the unbiodegradable particulate fraction (XU) from different activated sludges during batch digestion tests at ambient temperature. Water Research, 98, 206-214. doi:10.1016/j.watres.2016.04.005, Institutional Repository

One strategy for the management of excess sludge in small wastewater treatment plants (WWTPs) consists in minimizing the excess sludge production by operating the WWTP at very long solids retention times (SRTs > 30 days). A number of recent studies have suggested that sludge minimization at very long SRT results from the degradation of the unbiodegradable particulate fraction (XU) (influent unbiodegradable compounds and endogenous decay products). But the biodegradability of the unbiodegradable particulate fraction has only been evaluated during batch digestion test performed at ambient temperature with sludge fed with synthetic wastewaters. It is not clear to what extent observations made for sludge fed with synthetic influents can be transposed to sludge fed with real influent. The current study thus focused on evaluating the biodegradability of the unbiodegradable particulate fraction for sludge fed with real wastewater. Batch digestion tests (400 days, ambient temperature) were conducted with three different sludges fed with either synthetic or real influents and exposed to aerobic or intermittent aeration conditions. Our results indicate that volatile suspended solids (VSS) decreased even after complete decay of the active biomass (i.e., after 30 days of aerobic batch digestion) indicating that the unbiodegradable particulate fraction is biodegradable. However, very low degradation rates of the unbiodegradable particulate fraction were monitored after day 30 of digestion (0.7-1.7·10-3 d-1). These values were in the lower range of previously published values for synthetic wastewaters (1-7.5·10-3 d-1). The low values determined in our study indicate that the rate could decrease over time or that sludge composition influences the degradability of the unbiodegradable particulate fraction. But our results also demonstrate that extracellular polymeric substances (EPS) have a minor impact on the biodegradability of the unbiodegradable particulate fraction. Overall bound EPS were indeed biodegradable under all conditions and thus did not accumulate in the unbiodegradable particulate fraction. Different bound EPS pools (e.g., cation bound EPS) were associated with specific degradation behaviors. Besides improved mechanistic understanding of sludge degradation processes, our results have implications for the development of decentralized wastewater treatment technologies with on-site reduction of excess sludge.
Klein, T., Zihlmann, D., Derlon, N., Isaacson, C., Szivak, I., Weissbrodt, D. G., & Pronk, W. (2016). Biological control of biofilms on membranes by metazoans. Water Research, 88, 20-29. doi:10.1016/j.watres.2015.09.050, Institutional Repository

Traditionally, chemical and physical methods have been used to control biofouling on membranes by inactivating and removing the biofouling layer. Alternatively, the permeability can be increased using biological methods while accepting the presence of the biofouling layer. We have investigated two different types of metazoans for this purpose, the oligochaete Aelosoma hemprichi and the nematode Plectus aquatilis. The addition of these grazing metazoans in biofilm-controlled membrane systems resulted in a flux increase of 50% in presence of the oligochaetes (Aelosoma hemprichi), and a flux increase of 119–164% in presence of the nematodes (Plectus aquatilis) in comparison to the control system operated without metazoans. The change in flux resulted from (1) a change in the biofilm structure, from a homogeneous, cake-like biofilm to a more heterogeneous, porous structure and (2) a significant reduction in the thickness of the basal layer. Pyrosequencing data showed that due to the addition of the predators, also the community composition of the biofilm in terms of protists and bacteria was strongly affected. The results have implications for a range of membrane processes, including ultrafiltration for potable water production, membrane bioreactors and reverse osmosis.
Meili, N. (2016). Improvement of permeate quality after gravity-driven membrane filtration (Master thesis). 42 p. , Institutional Repository

Removal of bacteria and reduction of the assimilable organic carbon (AOC) are two of the main goals in drinking water treatment. In a gravity‐driven membrane (GDM) system the bacteria are retained by an ultrafiltration membrane while the biofilm on top of the membrane reduces the AOC concentration. But with the ageing of the biofilm, the AOC concentration in the permeate increases and the drinking water quality deteriorates (Derlon et al., 2014).
In this thesis, the influence of multiple GDMs in series on the permeate quality is investigated. An experiment with five GDMs in series, fed with a 5 mg C L‐1 acetate feed, is conducted. The permeate after each GDM was analyzed for its acetate concentration, total organic carbon (TOC) concentration and total cell count (TCC). The biofilm on each GDM was analyzed for its TOC, TCC and adenosine triphosphate (ATP) content as well as its biofilm resistance. The mean biofilm thickness was measured with optical coherence tomography.
The results of the experiment showed a decrease of TCC in the permeate at the time of sampling, as well as after three days of incubation at 30 °C, over the number of GDMs. The TOC, TCC and ATP in the biofilm decreased over the number of GDMs. So did the biofilm resistance and the mean biofilm thickness. These results indicate a decrease of AOC over the number of GDMs.
No flux stabilization over the five GDMs in series was observed. The flux varied between 3 L m‐2 h‐1 and 4 L m‐2 h‐1. This flux is higher than expected and can be explained by the low biofilm resistance of the GDM 2 to 5. Biofilm 1 displays by far the highest biofilm resistance to flux.
Overall, multiple GDMs in series result in a decrease of TCC in the permeate and therefore in an increase of the permeate quality. The flux obtained was higher than expected. Hence, multiple GDMs in series should be further investigated for drinking water treatment.
Niadiodava, H. (2016). Mechanisms governing simultaneous nitrification-denitrification in aerobic granular sludge (Master thesis). 28 p. , Institutional Repository

Aerobic granular sludge (AGS) is a new technology for biological treatment of wastewater. Simultaneous removal of organic matter, nitrogen and phosphorus is possible in an AGS reactor due to the large physical size of granules and their heterogeneous structure. While sufficient removal efficiencies of C and P have been achieved, N removal from municipal wastewaters using AGS still remains a challenge.
To address this knowledge gap, a model was developed in SUMO software to assess the mechanisms driving simultaneous nitrification and denitrification (SND) in a granular sludge reactor. Nitrification and denitrification can be accomplished in a single reactor due to coexistence of aerobic and anoxic zone in granules. Therefore, the objective of this master’s thesis is to evaluate the influence of oxygen concentration and anoxic volume in the granules on SND performance. Another objective is to evaluate the contribution of phosphorous accumulating organisms (PAO) on SND as PAOs are mainly responsible for the denitrification in AGS.
The granular sequenced batch reactor (SBR) module in SUMO was used to simulate mass transport and conversion processes occurring in the reactor. A low-strength influent with particulate organic carbon, which is typical for the municipal wastewater, was used in the study. A total COD concentration was 420 gCOD.m-3. The model included growth and decay of nitrifiers, ordinary heterotrophs and PAO. Three case studies were analyzed with low, intermediate and high granulation. The simulations were performed under different airflow resulting in different dissolved oxygen concentration in the bulk.
The highest SND of 96% was achieved for the simulation with intermediate granulation and oxygen concentration in the bulk reaching 1.2 gO2.m-3. Complete nitrification occurred in this simulation. The fraction of anoxic volume in the granule reached 100% and remained high during most of the aerobic period, which is significantly higher than the anoxic volume in cases with low or high granulation. In case with intermediate granulation, high PHA concentrations are found in anoxic layers of the granule. Therefore, there is a sufficient amount of organic carbon for denitrification by PAOs. In cases with low and high granulation, most of the PHA was concentrated in the aerobic layers and was not available for denitrification by PAOs.
To conclude, this study shows that aerobic granular sludge can be an effective technology for treatment of municipal wastewater, achieving high nitrification and SND efficiencies. However, special consideration shall be paid to oxygen concentration, anoxic volume in the granule and organic carbon availability in the anoxic zone.
Shen, Y., Huang, C., Monroy, G. L., Janjaroen, D., Derlon, N., Lin, J., … Nguyen, T. H. (2016). Response of simulated drinking water biofilm mechanical and structural properties to long-term disinfectant exposure. Environmental Science and Technology, 50(4), 1779-1787. doi:10.1021/acs.est.5b04653, Institutional Repository

Mechanical and structural properties of biofilms influence the accumulation and release of pathogens in drinking water distribution systems (DWDS). Thus, understanding how long-term residual disinfectants exposure affects biofilm mechanical and structural properties is a necessary aspect for pathogen risk assessment and control. In this study, elastic modulus and structure of groundwater biofilms was monitored by atomic force microscopy (AFM) and optical coherence tomography (OCT) during three months of exposure to monochloramine or free chlorine. After the first month of disinfectant exposure, the mean stiffness of monochloramine- or free-chlorine-treated biofilms was 4 to 9 times higher than those before treatment. Meanwhile, the biofilm thickness decreased from 120 ± 8 μm to 93 ± 6–107 ± 11 μm. The increased surface stiffness and decreased biofilm thickness within the first month of disinfectant exposure was presumably due to the consumption of biomass. However, by the second to third month during disinfectant exposure, the biofilm mean stiffness showed a 2- to 4-fold decrease, and the biofilm thickness increased to 110 ± 7–129 ± 8 μm, suggesting that the biofilms adapted to disinfectant exposure. After three months of the disinfectant exposure process, the disinfected biofilms showed 2–5 times higher mean stiffness (as determined by AFM) and 6–13-fold higher ratios of protein over polysaccharide, as determined by differential staining and confocal laser scanning microscopy (CLSM), than the nondisinfected groundwater biofilms. However, the disinfected biofilms and nondisinfected biofilms showed statistically similar thicknesses (t test, p > 0.05), suggesting that long-term disinfection may not significantly remove net biomass. This study showed how biofilm mechanical and structural properties vary in response to a complex DWDS environment, which will contribute to further research on the risk assessment and control of biofilm-associated-pathogens in DWDS.
Chomiak, A., Traber, J., Morgenroth, E., & Derlon, N. (2015). Biofilm increases permeate quality by organic carbon degradation in low pressure ultrafiltration. Water Research, 85, 512-520. doi:10.1016/j.watres.2015.08.009, Institutional Repository

We investigated the influence of biofouling of ultrafiltration membranes on the removal of organic model foulants and ultimately on the quality of permeate. Gravity Driven Membrane ultrafiltration (GDM) membrane systems were operated with modified river water during five weeks without control of the biofilm formation. Three GDM systems were studied: two systems with biofilms exposed to (A) variable or (B) constant load of organic foulants, and (C) one system operated without biofilm and exposed to constant foulant loading. Biodegradable dextran or non-biodegradable polystyrene sulfonate model foulants were tested. Substrate biodegradability was confirmed by Size Exclusion Chromatography (SEC) and by degradation batch tests (D). The GDM systems (A) and (B) were fed with pre-filtered river water supplemented with dextran (Dex) of 1, 150 or 2000 kDa, or polystyrene sulfonate (PSS) of 1 or 80 kDa at concentrations of 2–3.5 mgC L−1. In exp. (C) the feed water consisted of deionized water with 25 mgC L−1 of either PSS 1, 80 kDa or Dex 2000 kDa.
The biofilm formation on UF membrane surfaces controlled the foulant permeation and thus the permeate quality. Biofilms exposed to continuous foulant loading (exp. B) degraded low molecular weight (LMW) biodegradable foulants (1 kDa Dex), which improved the permeate quality. For high molecular weight (HMW) substrates (150, 2000 kDa Dex), the improvement of the permeate quality was observed after 7 days of biofilm formation, and resulted from the foulant hydrolysis followed by degradation. For non-biodegradable foulants, an improvement of 20% of the retention was observed for the polystyrene (1, 80 kDa PSS) due to the presence of biofilms on membrane surfaces. For variable foulant loading (exp. A) the biofilms hydrolysed the large biodegradable foulants but did not degraded them fully, which resulted a deterioration of the permeate quality (except for the LMW dextran (1 kDa) that was fully degraded). Overall, the “biofilm + membrane” composite retained a larger amount of biodegradable foulant than the membrane alone, due to the activity of the biofilm. However, this resulted in an increased biofilm accumulation and reduced flux. In presence of the biofilm, the highest fluxes were observed for control (no foulant) and for small non-biodegradable foulants (PSS 1 kDa). Low fluxes were observed for the accumulating on membrane surface or degradable foulants (exp. B). But, the lowest fluxes were observed in absence of the biofilm (exp. C) due to physical accumulation of the foulants (PSS 80 kDa and Dextran 2000 kDa). Overall our study demonstrates that the presence of biofilms on membrane surfaces has some benefits: (i) biofilm helps to increase the permeate quality and (ii) biofilms protect the membrane from further fouling. Permeate flux stabilizes in the case of biofilm-membrane composite, while it continuously declines in the case of the membrane only.
Chomiak, A. (2015). Influence of inorganic and organic matter in gravity driven membrane ultrafilatration (Doctoral dissertation). doi:10.3929/ethz-a-010453952, Institutional Repository

The main advantage of membrane filtration processes is efficiency of separation, which allows to reach very high quality treated water. However, main disadvantages are cost of the treatment (electricity, chemicals) and membrane fouling, which can severely reduce the efficiency of the filtration process. Biofouling and biofilm formation is a major type of fouling due to biological deposition and activity on any membrane type surface. Biofilms on membranes significantly reduce permeation rates, and as such are removed and controlled by using chemical treatments (Flemming 2002). [...]

Die Membranfiltration ist attraktiv für die Trinkwasseraufbereitung, da sie Partikel sicher zurückhalten kann. Nachteile der Membranfiltration sind die hohen Kosten, verursacht durch den Energie‐ und Chemikalienverbrauch, sowie das sogenannte Fouling, welches die Effizienz der Filtration stark beeinträchtigen kann. Eine wichtige Form des Foulings ist das Biofouling bzw. Biofilmwachstum. Biofilme können die Permeabilität der Membran stark beeinträchtigen und werden in der Regel durch regelmässige, chemische Reinigung entfernt (Flemming 2002). [...]
Habermacher, J., Benetti, A. D., Derlon, N., & Morgenroth, E. (2015). The effect of different aeration conditions in activated sludge – side-stream system on sludge production, sludge degradation rates, active biomass and extracellular polymeric substances. Water Research, 85, 46-56. doi:10.1016/j.watres.2015.08.002, Institutional Repository

On-site minimization of excess sludge production is a relevant strategy for the operation of small-scale and decentralized wastewater treatment plants. In the study, we evaluated the potential of activated sludge systems equipped with side-stream reactors (SSRs). This study especially focused on how the sequential exposure of sludge to different aeration conditions in the side-stream reactors influences the overall degradation of sludge and of its specific fractions (active biomass, extracellular polymeric substances (EPS), EPS proteins, EPS carbohydrates). We found that increasing the solid retention time from 25 to 40 and 80 days enhanced sludge degradation for all aeration conditions tested in the side-stream reactor. Also, the highest specific degradation rate and in turn the lowest sludge production were achieved when maintaining aerobic conditions in the side-stream reactors. The different sludge fractions in terms of active biomass (quantified based on adenosine tri-phosphate (ATP) measurements), EPS proteins and EPS carbohydrates were quantified before and after passage through the SSR. The relative amounts of active biomass and EPS to volatile suspended solids (VSS) did not changed when exposed to different aeration conditions in the SSRs, which indicates that long SRT and starvation in the SSRs did not promote the degradation of a specific sludge fraction. Overall, our study helps to better understand mechanisms of enhanced sludge degradation in systems operated at long SRTs.
Morgenroth, E., Derlon, N., Pronk, W., & Larsen, T. A. (2015). Von der Grundlagenforschung zur Anwendung: Trinkwasseraufbereitung und Sanitärversorgung (p. (14 pp.). Presented at the 48. Essener Tagung für Wasser- und Abfallwirtschaft "Forschung trifft Praxis". Aachen, Germany. , Institutional Repository
Ravndal, K. T., Künzle, R., Derlon, N., & Morgenroth, E. (2015). On-site treatment of used wash-water using biologically activated membrane bioreactors operated at different solids retention times. Journal of Water Sanitation and Hygiene for Development, 5(4), 544-552. doi:10.2166/washdev.2015.174, Institutional Repository

Biologically activated membrane bioreactors (BAMBis) were operated at suspended solids retention times (SRT) of 7 and 102 days and at full solids retention. The effect of these different approaches of operation on substrate and nutrient conversion, and on permeate flux was investigated. Variations in organic loads and aeration intensities were also studied. Permeate flux stabilized during long-term operation independently of suspended SRT. Removal of organic substrate was independent of solids concentrations and remained stable over the long term. Microorganisms colonizing the surface of particles were found as the main mechanism responsible for degradation of organic substrate in the particulate form. BAMBi appeared to be a robust technology, adapted to on-site treatment of used wash-water, as it can be operated without control of suspended SRT. Thus BAMBis can be operated for long periods without any control of biofouling and sludge formation, leading to low maintenance needs. When BAMBis were operated at low aeration, the formation of anoxic zones led to combined nitrification and denitrification and thus significant nitrogen removal.
Shen, Y., Monroy, G. L., Derlon, N., Janjaroen, D., Huang, C., Morgenroth, E., … Nguyen, T. H. (2015). Role of biofilm roughness and hydrodynamic conditions in legionella pneumophila adhesion to and detachment from simulated drinking water biofilms. Environmental Science and Technology, 49(7), 4274-4282. doi:10.1021/es505842v, Institutional Repository

Biofilms in drinking water distribution systems (DWDS) could exacerbate the persistence and associated risks of pathogenic Legionella pneumophila (L. pneumophila), thus raising human health concerns. However, mechanisms controlling adhesion and subsequent detachment of L. pneumophila associated with biofilms remain unclear. We determined the connection between L. pneumophila adhesion and subsequent detachment with biofilm physical structure characterization using optical coherence tomography (OCT) imaging technique. Analysis of the OCT images of multispecies biofilms grown under low nutrient condition up to 34 weeks revealed the lack of biofilm deformation even when these biofilms were exposed to flow velocity of 0.7 m/s, typical flow for DWDS. L. pneumophila adhesion on these biofilm under low flow velocity (0.007 m/s) positively correlated with biofilm roughness due to enlarged biofilm surface area and local flow conditions created by roughness asperities. The preadhered L. pneumophila on selected rough and smooth biofilms were found to detach when these biofilms were subjected to higher flow velocity. At the flow velocity of 0.1 and 0.3 m/s, the ratio of detached cell from the smooth biofilm surface was from 1.3 to 1.4 times higher than that from the rough biofilm surface, presumably because of the low shear stress zones near roughness asperities. This study determined that physical structure and local hydrodynamics control L. pneumophila adhesion to and detachment from simulated drinking water biofilm, thus it is the first step toward reducing the risk of L. pneumophila exposure and subsequent infections.
Trottmann, C. (2015). Simultaneous nitrification and denitrification with aerobic granules in municipal wastewater (Master thesis). 31 p. , Institutional Repository

This study aims at the question why SND is only working with very low efficiency for granules fed with municipal wastewaster. Therefore three hypotheses were set up: (i) Absence of anoxic zone within the aerobic granules due to deep penetration of oxygen, (ii) low availability of electron donor (carbon source) for denitrification and (iii) low denitrification rate as fraction of large granules is too small.
Experiments with batch reactors were performed, with aerobic granular sludge (40-60 % granules) from a column sequencing batch reactor fed with municipal wastewater, to verify the hypotheses.
To analyze the influence of a carbon source a distinction of two cases was done. In Case 1 the granules were fed with extra added acetate in a first anaerobic phase. Phosphate,- and glycogenaccumulating bacteria (PAOs and GAOs) stored this acetate intracellular as polyhydroxyalkanoates (PHA) before the aerobic phase started. For Case 2 only particular carbon stored in the matrix of the granules, as extracellular polymeric substances (EPS), was available.
Beside that the oxygen concentration was varied between 0.5-2.2 mgO2l-1 and separate tests with extra added nitrate were done to evaluate the denitrification rate.
For Case 1 the intracellular stored acetate (PHA) caused a stable simultaneous nitrification and denitrification process whereas for Case 2 unstable situations sometimes caused no denitrifaciton at all. The oxygen concentration was found to be a very important and sensitive parameter.
It has a direct impact to the anoxic volume in the granules due to its mass transport limitation by diffusion which is limiting the penetration depth (causing an aerobic surface were nitrification is performed and an anoxic core with denitrifying bacteria).
Highest SND ratios were found in Case 1 at an oxygen concentration level of 0.5-1.0 mgO2l-1 and completely taken up and intracellular stored acetate of 100 mgCODl-1. An average SND efficiency of 26.4±13.6 % was reached therefore.
Denitrification rates of 1.22±0.16 mgN∙gVSS-1∙h-1 (Case 1) and 0.89±0.05 mgN∙gVSS-1∙h-1 (Case 2) were observed.
The fraction of large granules (d>0.63 mm) of only 10 % by weight (gVSS) was relatively low. Therefore it is affirmed that denitrification is low due to this, but not that the denitrification rate is lower than for smaller granules.
Wagner, J., Weissbrodt, D. G., Manguin, V., Ribeiro da Costa, R. H., Morgenroth, E., & Derlon, N. (2015). Effect of particulate organic substrate on aerobic granulation and operating conditions of sequencing batch reactors. Water Research, 85, 158-166. doi:10.1016/j.watres.2015.08.030, Institutional Repository

The formation and application of aerobic granules for the treatment of real wastewaters still remains challenging. The high fraction of particulate organic matter (XS) present in real wastewaters can affect the granulation process. The present study aims at understanding to what extent the presence of XS affects the granule formation and the quality of the treated effluent. A second objective was to evaluate how the operating conditions of an aerobic granular sludge (AGS) reactor must be adapted to overcome the effects of the presence of XS. Two reactors fed with synthetic wastewaters were operated in absence (R1) or presence (R2) of starch as proxy for XS. Different operating conditions were evaluated. Our results indicated that the presence of XS in the wastewater reduces the kinetic of granule formation. After 52 d of operation, the fraction of granules reached only 21% in R2, while in R1 this fraction was of 54%. The granules grown in presence of XS had irregular and filamentous outgrowths in the surface, which affected the settleability of the biomass and therefore the quality of the effluent. An extension of the anaerobic phase in R2 led to the formation of more compact granules with a better settling ability. A high fraction of granules was obtained in both reactors after an increase of the selection pressure for fast-settling biomass, but the quality of the effluent remained low. Operating the reactors in a simultaneous fill-and-draw mode at a low selection pressure for fast-settling biomass showed to be beneficial for substrate removal efficiency and for suppressing filamentous overgrowth. Average removal efficiencies for total COD, soluble COD, ammonium, and phosphate were 87 ± 4%, 95 ± 1%, 92 ± 10%, and 87 ± 12% for R1, and 72 ± 12%, 86 ± 5%, 71 ± 12%, and 77 ± 11% for R2, respectively. Overall our study demonstrates that the operating conditions of AGS reactors must be adapted according to the wastewater composition. When treating effluents that contain XS, the selection pressure should be significantly reduced.
Chomiak, A., Mimoso, J., Koetzsch, S., Sinnet, B., Pronk, W., Derlon, N., & Morgenroth, E. (2014). Biofilm formation and permeate quality improvement in Gravity Driven Membrane ultrafiltration. Water Science and Technology: Water Supply, 14(2), 274-282. doi:10.2166/ws.2013.197, Institutional Repository

The effects of biofilm development on ultrafiltration membranes with regards to permeate stability and permeation rates were investigated using Gravity-Driven Membrane (GDM) filtration. The first part of the study aimed at evaluating the influence of the biofilm on permeate flux quality and quantity with regards to Assimilable Organic Carbon (AOC) degradation. In addition, two types of biological pre-treatments were evaluated: slow sand filtration and packed bed bio-reactor, compared to a control (no treatment). Biofilm formation helped to decrease the AOC content of permeate water, compared to the influent. Both pre-treatments additionally reduced AOC level in permeate and thus increased its biological stability, however none of the systems were able to guarantee microbiologically stable water. Removal of AOC before the GDM filtration reduced the biofilm growth potential, which in turn influenced its physical structure and enhanced the permeation rates. Influence of inorganic particle removal by pre-sedimentation and its effect on the biofilm structure was also studied. Pre-sedimentation of particle populations selected fine and homogenous particle fractions, which lead to the formation of a homogenous biofilm structure characterized by an increased hydraulic resistance. This was clearly visible between horizontally and vertically installed membranes where the latter ones had a significantly reduced flux despite lower deposited particle mass. Presence of larger, heterogeneous particle fractions counterbalanced the negative effects of the fine particles, which overall resulted in enhanced permeation rates.
Chomiak, A., Sinnet, B., Derlon, N., & Morgenroth, E. (2014). Inorganic particles increase biofilm heterogeneity and enhance permeate flux. Water Research, 64, 177-186. doi:10.1016/j.watres.2014.06.045, Institutional Repository

This study investigated the influence of inorganic particles on the hydraulic resistance of biofilm grown on membrane surface during low-pressure dead-end ultrafiltration. Gravity-driven ultrafiltration membrane systems were operated during several weeks without any flushing or cleaning. Smaller (kaolin d0.5 = 3.6 μm) or larger (kaolin with diatomaceous earth 50/50%, d0.5 = 18.1 μm) particles were added to pre-filtered creek water or to unfiltered creek water. It was demonstrated in both experiments that presence of finer particles in the feed water (kaolin) induced formation of compact and homogeneous biofilm structure. On the other hand presence of the larger particles (diatomite) helped to counterbalance the effect of fine particles due to the formation of more heterogeneous and permeable biofilm structure. The hydraulic resistance of biofilms formed with fine particles was significantly higher than the resistance of biofilm formed in (1) absence of any inorganic particles or (2) in presence of the mixed particle population. The membrane orientation (vertical or horizontal) determined which particles were accumulating at the membrane surface, with structural differences shown by Scanning Electron Microscopy (SEM). For vertical membranes, the larger particles were selectively removed due to sedimentation and did not contribute to the biofilm development. Thus the selection of smaller particles due to vertical membrane configuration negatively affected the biofilm structure and permeation rates, and such selective accumulation of fine particles should be avoided.
Derlon, N., Mimoso, J., Klein, T., Koetzsch, S., & Morgenroth, E. (2014). Presence of biofilms on ultrafiltration membrane surfaces increases the quality of permeate produced during ultra-low pressure gravity-driven membrane filtration. Water Research, 60, 164-173. doi:10.1016/j.watres.2014.04.045, Institutional Repository

This study evaluates the effect of the presence of biofilms on membrane surfaces on the quality of permeate produced during Gravity-driven membrane ultrafiltration. GDM ultrafiltration is applied to the decentralized production of drinking water. A second objective was to evaluate to what extent permeate quality is enhanced by pre-treating feed-water (using a packed bed biofilm reactor or a slow sand filter). The influence of the ageing of the biofilm on the permeate quality was evaluated and compared to the effect of virgin membranes. Permeate quality was evaluated in terms of Assimilable Organic Carbon (AOC) content and dissolved organic carbon fractions (e.g. biopolymers). Our results indicate that virgin ultrafiltration membrane remove a small fraction of the AOC and biopolymers (rejection <10%). The presence of a young and thin biofilm on the surface of the ultrafiltration membranes increases the permeate quality due to the degradation of AOC (>80%). However, over long-term the hydrolysis of the organic matter that accumulated on membrane surfaces increases the AOC content of the permeate, thus deteriorating the permeate quality. Pre-treatment of the feed-water help to control the biofilm accumulation and thus to limit the deterioration of the permeate quality. Permeate flux stabilised at average values of 7.5–8.9 L m−2 h−1. But the presence of pre-treatment helped to increase permeate flux (+12 and 19%, with the packed bed biofilm reactor and with the slow sand filter, respectively). Overall our study demonstrates that tolerating the presence of biofilm on membrane surface has a beneficial effect on the quality of permeate even if its quantity is decreased.
Kohler, E., Villiger, J., Posch, T., Derlon, N., Shabarova, T., Morgenroth, E., … Blom, J. F. (2014). Biodegradation of microcystins during gravity-driven membrane (GDM) ultrafiltration. PLoS One, 9(11), e111794 (9 pp.). doi:10.1371/journal.pone.0111794, Institutional Repository

Gravity-driven membrane (GDM) ultrafiltration systems require little maintenance: they operate without electricity at ultra-low pressure in dead-end mode and without control of the biofilm formation. These systems are already in use for water purification in some regions of the world where adequate treatment and distribution of drinking water is not readily available. However, many water bodies worldwide exhibit harmful blooms of cyanobacteria that severely lower the water quality due to the production of toxic microcystins (MCs). We studied the performance of a GDM system during an artificial Microcystis aeruginosa bloom in lake water and its simulated collapse (i.e., the massive release of microcystins) over a period of 21 days. Presence of live or destroyed cyanobacterial cells in the feed water decreased the permeate flux in the Microcystis treatments considerably. At the same time, the microbial biofilms on the filter membranes could successfully reduce the amount of microcystins in the filtrate below the critical threshold concentration of 1 µg L−1 MC for human consumption in three out of four replicates after 15 days. We found pronounced differences in the composition of bacterial communities of the biofilms on the filter membranes. Bacterial genera that could be related to microcystin degradation substantially enriched in the biofilms amended with microcystin-containing cyanobacteria. In addition to bacteria previously characterized as microcystin degraders, members of other bacterial clades potentially involved in MC degradation could be identified.
Martin, K. J., Bolster, D., Derlon, N., Morgenroth, E., & Nerenberg, R. (2014). Effect of fouling layer spatial distribution on permeate flux: a theoretical and experimental study. Journal of Membrane Science, 471, 130-137. doi:10.1016/j.memsci.2014.07.045, Institutional Repository

Fouling layers developing on membrane filters can display significant spatial heterogeneity (roughness), yet the effect of fouling layer spatial distribution on hydraulic resistance has not been studied systematically. We used simple flux models, based on Darcy's law, to assess the impact of spatial distribution on resistance and permeate flux. Our results show that, for a given mean fouling layer thickness, greater spatial heterogeneity could increase fluxes by over an order of magnitude. The degree of error depended on the membrane resistance, fouling layer permeability, and the characteristics of the spatial distribution. We developed 1-dimensional and 2-dimensional flow models, both considering spatial heterogeneity, to improve the accuracy of the conventional model. The proposed models were validated with experimental data from a gravity driven membrane filter with a fouling layer having a high degree of spatial heterogeneity. Accounting for spatial heterogeneity significantly improved the prediction of permeate flux.
Sharma, K., Derlon, N., Hu, S., & Yuan, Z. (2014). Modeling the pH effect on sulfidogenesis in anaerobic sewer biofilm. Water Research, 49(1), 175-185. doi:10.1016/j.watres.2013.11.019, Institutional Repository

Wastewater pH affects the transfer of H2S from liquid to gas and hence impacts on the extent of odour and corrosion. Sewage pH may change significantly in sewer networks due to, for example, the fermentation of organic compounds, particularly when the hydraulic retention time is long, the discharge of trade wastes that are organic-rich or with extreme pH, and the intentional addition of alkali to raise the sewage pH. Such a variation of pH is expected to affect sulfate reduction by sewer biofilms. In this work, experimental studies were carried out to reveal the detailed effects of pH on sulfidogenesis by anaerobic sewer biofilms developed in a laboratory sewer reactor fed with real sewage, and the potential causes for the inhibitory effects observed under both high and low pH conditions. The data clearly showed that the sewer biofilm had the highest sulfate reduction rate at around neutral pH (6.5–7.5), and the activity decreased when pH was higher or lower. The data also suggested that the inhibiting effect at a higher pH is likely due to the inhibitory effects of free ammonia, while at a lower pH it is more likely due to the pH itself. An inhibition model formulated based on the above hypotheses was able to adequately describe the measured sulfide production rates under different pH levels and different free ammonia concentrations, as well as data previously reported in literature. The calibrated model was used to simulate sulfide production in a sewer network receiving alkali dosage. The model adequately predicted sulfide production in the network, which could not be achieved with a model not considering the pH effect.
Derlon, N., Koch, N., Eugster, B., Posch, T., Pernthaler, J., Pronk, W., & Morgenroth, E. (2013). Activity of metazoa governs biofilm structure formation and enhances permeate flux during Gravity-Driven Membrane (GDM) filtration. Water Research, 47(6), 2085-2095. doi:10.1016/j.watres.2013.01.033, Institutional Repository

The impact of different feed waters in terms of eukaryotic populations and organic carbon content on the biofilm structure formation and permeate flux during Gravity-Driven Membrane (GDM) filtration was investigated in this study. GDM filtration was performed at ultra-low pressure (65 mbar) in dead-end mode without control of the biofilm formation. Different feed waters were tested (River water, pre-treated river water, lake water, and tap water) and varied with regard to their organic substrate content and their predator community. River water was manipulated either by chemically inhibiting all eukaryotes or by filtering out macrozoobenthos (metazoan organisms). The structure of the biofilm was characterized at the meso- and micro-scale using Optical Coherence Tomography (OCT) and Confocal Laser Scanning Microscopy (CLSM), respectively. Based on Total Organic Carbon (TOC) measurements, the river waters provided the highest potential for bacterial growth whereas tap water had the lowest. An increasing content in soluble and particulate organic substrate resulted in increasing biofilm accumulation on membrane surface. However, enhanced biofilm accumulation did not result in lower flux values and permeate flux was mainly influenced by the structure of the biofilm. Metazoan organisms (in particular nematodes and oligochaetes) built-up protective habitats, which resulted in the formation of open and spatially heterogeneous biofilms composed of biomass patches. In the absence of predation by metazoan organisms, a flat and compact biofilm developed. It is concluded that the activity of metazoan organisms in natural river water and its impact on biofilm structure balances the detrimental effect of a high biofilm accumulation, thus allowing for a broader application of GDM filtration. Finally, our results suggest that for surface waters with high particulate organic carbon (POC) content, the use of worms is suitable to enhance POC removal before ultrafiltration units.
Derlon, N., Coufort-Saudejaud, C., Queinnec, I., & Paul, E. (2013). Growth limiting conditions and denitrification govern extent and frequency of volume detachment of biofilms. Chemical Engineering Journal, 218, 368-375. doi:10.1016/j.cej.2012.11.061, Institutional Repository

This study aims at evaluating the mechanisms of biofilm detachment with regard of the physical properties of the biofilm. Biofilms were developed in Couette–Taylor reactor under controlled hydrodynamic conditions and under different environmental growth conditions. Five different conditions were tested and lead to the formation of two aerobic heterotrophic biofilms (aeHB1 and aeHB2), a mixed autotrophic and heterotrophic biofilm (MAHB) and two anoxic heterotrophic biofilms (anHB1 and anHB2). Biofilm detachment was evaluated by monitoring the size of the detached particles (using light-scattering) as well as the biofilm physical properties (using CCD camera and image analysis). Results indicate that volume erosion of large biofilm particles with size ranging from 50 to 500 μm dominated the biomass loss for all biofilms. Surface erosion of small particles with size lower than 20 μm dominates biofilm detachment in number. The extent of the volume detachment events was governed by the size of the biofilm surface heterogeneities (i.e., the absolute biofilm roughness) but never impacted more than 80% of the mean biofilm thickness due to the highly cohesive basal layer. Anoxic biofilms were smoother and thinner than aerobic biofilms and thus associated with the detachment of smaller particles. Our results contradict the simplifying assumption of surface detachment that is considered in many biofilm models and suggest that discrete volume events should be considered.
Janjaroen, D., Ling, F., Monroy, G., Derlon, N., Morgenroth, E., Boppart, S. A., … Nguyen, T. H. (2013). Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces. Water Research, 47(7), 2531-2542. doi:10.1016/j.watres.2013.02.032, Institutional Repository

Mechanisms of Escherichia coli attachment on biofilms grown on PVC coupons were investigated. Biofilms were grown in CDC reactors using groundwater as feed solution over a period up to 27 weeks. Biofilm physical structure was characterized at the micro- and meso-scales using Scanning Electron Microscopy (SEM) and Optical Coherence Tomography (OCT), respectively. Microbial community diversity was analyzed with Terminal Restricted Fragment Length Polymorphism (T-RFLP). Both physical structure and microbial community diversity of the biofilms were shown to be changing from 2 weeks to 14 weeks, and became relatively stable after 16 weeks. A parallel plate flow chamber coupled with an inverted fluorescent microscope was also used to monitor the attachment of fluorescent microspheres and E. coli on clean PVC surfaces and biofilms grown on PVC surfaces for different ages. Two mechanisms of E. coli attachment were identified. The adhesion rate coefficients (kd) of E. coli on nascent PVC surfaces and 2-week biofilms increased with ionic strength. However, after biofilms grew for 8 weeks, the adhesion was found to be independent of solution chemistry. Instead, a positive correlation between kd and biofilm roughness as determined by OCT was obtained, indicating that the physical structure of biofilms could play an important role in facilitating the adhesion of E. coli cells.
Martin, K. J., Derlon, N., Morgenroth, E., & Nerenberg, R. (2013). Fouling layer surface heterogeneity improves permeate flux. In 86th Annual Water Environment Federation Technical Exhibition and Conference, WEFTEC 2013: Vol. 1. 86th annual water environment federation technical exhibition and conference (WEFTEC 2013) (pp. 621-629). doi:10.2175/193864713813668079, Institutional Repository

In this research, we used modeling to assess the impact of irregular fouling-layer surface morphology (i.e., roughness) on permeate fluxes. Two membrane filtration models, each based on Darcy's Law, were used to predict fluxes for fouling layers with varying degrees of surface irregularity. One of the models considered the arithmetic mean thickness of the fouling layer, while the other accounted for the actual, irregular surface morphology assuming one-dimensional permeate flow. Surface morphology and permeate-flux data from an ultra-low pressure gravity-driven membrane filter were used to test the models. The models that accounted for the surface morphology were more accurate, especially for highly irregular surface morphologies. These models were also able to correctly predict greater permeate fluxes exhibited by highly irregular surface morphologies despite their having greater mean thicknesses. Our results show that models based on the mean thickness may not accurately characterize the effect of the fouling layer on fluxes. Future research should consider the surface morphology of the fouling layer when devising fouling mitigation strategies.
Derlon, N., Peter-Varbanets, M., Scheidegger, A., Pronk, W., & Morgenroth, E. (2012). Predation influences the structure of biofilm developed on ultrafiltration membranes. Water Research, 46(10), 3323-3333. doi:10.1016/j.watres.2012.03.031, Institutional Repository

This study investigates the impact of predation by eukaryotes on the development of specific biofilm structures in gravity-driven dead-end ultrafiltration systems. Filtration systems were operated under ultra-low pressure conditions (65 mbar) without the control of biofilm formation. Three different levels of predation were evaluated: (1) inhibition of eukaryotic organisms, (2) addition of cultured protozoa (Tetrahymena pyriformis), and (3) no modification of microbial community as a control. The system performance was evaluated based on permeate flux and structures of the biofilm. It was found that predation had a significant influence on both the total amount and also the structure of the biofilm. An open and heterogeneous structure developed in systems with predation whereas a flat, compact, and thick structure that homogeneously covered the membrane surface developed in absence of predation. Permeate flux was correlated with the structure of the biofilm with increased fluxes for smaller membrane coverage. Permeate fluxes in the presence or absence of the predators was 10 and 5 L m−2 h−1, respectively. It was concluded that eukaryotic predation is a key factor influencing the performance of gravity-driven ultrafiltration systems.
Menniti, A., Rieger, L., Boltz, J. P., Johnson, B., Daigger, G., Habermacher, J., … Morgenroth, E. (2012). Critical review on the degradability of endogenous decay products. In Vol. 12. 85th annual water environment federation technical exhibition and conference (WEFTEC 2012) (pp. 7406-7408). Virginia, USA: Water Environment Federation (WEF). , Institutional Repository

Sludge disposal is one of the main cost factors in wastewater treatment. Endogenous processes produce inert materials (endogenous decay products) which contribute a large fraction of the sludge produced in activated sludge treatment. There is evidence that endogenous decay products are degradable under certain conditions. However, a serious knowledge gap exists for the detailed understanding of endogenous processes and specific treatment options influencing the degradability of endogenous decay products. Before models can be applied to describe sludge reduction through degradation of endogenous decay products, we must first understand the endogenous processes producing them and the conditions influencing their degradability. This paper provides a review of the key literature on the degradability of endogenous decay products and summarizes the primary
mechanistic hypotheses based on these observations. These hypotheses are evaluated based on performance of three proposed model structures to predict the sludge production performance of a CannibalTM system.
Joss, A., Derlon, N., Cyprien, C., Burger, S., Szivak, I., Traber, J., … Morgenroth, E. (2011). Combined nitritation–anammox: advances in understanding process stability. Environmental Science and Technology, 45(22), 9735-9742. doi:10.1021/es202181v, Institutional Repository

Efficient nitrogen removal from wastewater containing high concentrations of ammonium but little organic substrate has recently been demonstrated by several full-scale applications of the combined nitritation–anammox process. While the process efficiency is in most cases very good, process instabilities have been observed to result in temporary process failures. In the current study, conditions resulting in instability and strategies to regain efficient operation were evaluated. First, data from full-scale operation is presented, showing a sudden partial loss of activity followed by recovery within less than 1 month. Results from laboratory-scale experiments indicate that these dynamics observed in full scale can be caused by partial inhibition of the ammonia oxidizing bacteria (AOB), while anammox inhibition is a secondary effect due to temporarily reduced O2 depletion. Complete anammox inhibition is observed at 0.2 mg O2·L–1, resulting in NO2– accumulation. However, this inhibition of anammox is reversible within minutes after O2 depletion. Thus, variable AOB activity was identified as the key to reactor stability. With appropriate interpretation of the online NH4+ signal, accumulation of NO2– can be detected indirectly and used to signal an imbalance of O2 supply and AOB activity (no suitable online NO2– electrode is currently available). Second, increased abundance of nitrite-oxidizing bacteria (NOB; competing with anammox for NO2–) is known as another cause of instability. Based on a comparison of parallel full-scale reactors, it is suggested that an infrequent and short-term increased O2 supply (e.g., for maintenance of aerators) that exceeds prompt depletion of oxygen by AOB may have caused increased NOB abundance. The volumetric air supply as a proxy for O2 supply thus needs to be linked to AOB activity. Further, NOB can be washed out of the system during regular operation if the system is operated at a sludge age in the range of 45 days and by controlling the air supply according to the NO3– concentration in the treated effluent. Early detection of growing NOB abundance while the population is still low can help guide process operation and it is suggested that molecular methods of quantifying NOB abundance should be tested.

Céline Jacquin

Hu, Y., Morgenroth, E., & Jacquin, C. (2025). Online monitoring of greywater reuse system using excitation-emission matrix (EEM) and K-PARAFACs. Water Research, 268, 122604 (13 pp.). doi:10.1016/j.watres.2024.122604, Institutional Repository

A currently increasing interest in water reuse is met with the concern about water quality. Excitation-emission matrix (EEM) measurements, which are widely implemented in laboratory analysis, emerge as a promising tool for characterizing both microbial and chemical water qualities in the online monitoring of water reuse systems. However, the robustness of EEM measurements has been rarely validated in actual online monitoring campaigns where predictions are made for new samples independent of those used to establish EEM analysis models, including the popular parallel factor analysis (PARAFAC). In this study, two strategies of conducting PARAFAC were examined for the online monitoring of a greywater reuse system using two EEM datasets from two monitoring periods for model establishment and model testing respectively. With the first strategy that is commonly used in laboratory analyses, an entire EEM datasets from one period was used to establish one PARAFAC model, and the maximum fluorescence intensity (Fmax) of a PARAFAC component was used to predict total cell count (TCC) in another period. However, under the disturbance of dissolved organic matter (DOM) fluorescence in the background, Fmax gave unreliable predictions in model testing. To address this problem, a second and novel strategy was proposed using an EEM clustering and PARAFAC component shift mining technique. This unsupervised algorithm, named K-PARAFACs, automatically groups EEMs into K clusters and on each cluster establishes a cluster-specific PARAFAC model with distinct component shapes. With this method, multiple PARAFAC models were established on one EEM dataset, with each model representing samples with certain TCC ranges and DOM compositions. In model testing, these cluster-specific PARAFAC models served as EEM classifiers. A new sample was not characterized by Fmax but by the cluster-specific model that best fitted the EEM signal of the sample with the least numerical error. The proposed strategy demonstrates its robustness by successfully predicting the TCC trend in test datasets. Our findings suggest that K-PARAFACs is a promising tool that enables robust qualitative monitoring of water reuse systems with background DOM variability.
Endres, L. S., Jacquin, C., González-Lemos, S., Rodríguez-Rodríguez, L., Sliwinski, J., Kaushal, N., … Stoll, H. M. (2024). Climatic and cave settings influence on drip water fluorescent organic matter with implications for fluorescent laminations in stalagmites. Quaternary Research, 118, 41-61. doi:10.1017/qua.2023.41, Institutional Repository

Speleothem fluorescence can provide insights into past vegetation dynamics and stalagmite chronology. However, its origin and especially the formation of fluorescent laminations in stalagmites are poorly understood. We conducted a year-long monthly monitoring of drip water fluorescence in La Vallina Cave (northern Iberian Peninsula) and compared the results to drip water chemistry and active speleothems from the same sites. Drip waters were analyzed using fluorescence spectroscopy and parallel factor analysis (PARAFAC). The resulting five-component model indicates contributions from vegetation, microbial activity, and bedrock. Intra-site fluorescence variability is mainly influenced by changes in overlying vegetation, water reservoir time, and respiration rates. Contrary to prevailing views, we find no systematic increase in drip water fluorescence during rainy conditions across drip sites and seasonal variations in drip water fluorescence are absent at a location where present-day speleothem layers form. Our findings challenge the notion of a higher abundance of humic-like fluorescence during the rainy season as the primary cause for layer formation and suggest additional controls on drip water fluorescence, such as bedrock interaction and microbial reprocessing. We also propose that growth rate may control the dilation of the fluorescence signal in stalagmites, indicating other potential mechanisms for fluorescent layer formation.
Maghsoodi, M., Jacquin, C., Teychené, B., Lesage, G., & Snow, S. D. (2023). Delineating the effects of molecular and colloidal interactions of dissolved organic matter on titania photocatalysis. Langmuir, 39(10), 3752-3761. doi:10.1021/acs.langmuir.2c03487, Institutional Repository

In the face of significant challenges to practical applications of photocatalysis for water treatment, recent reports revealed a potential route to overcome a problem posed by dissolved organic matter (DOM). These studies showed that inhibition of photocatalytic processes by DOM is driven largely by competition for active surface sites on TiO2 or other catalysts, and controlling the type of DOM present in solution could significantly mitigate DOM fouling. Whether or not control of solution parameters could achieve the same preventative action is not known. Here, a series of DOM isolates, including humic acid (HA) and transphilic (TPI), hydrophobic (HPO), or colloidal fractions of organic matter from a membrane bioreactor mixed liquor supernatant, were tested for inhibitory activity under a range of pH values (3, 5, 7, and 9) and ionic compositions (NaCl, CaCl2, and Al2(SO4)3 with ionic strengths (IS) ranging from 0 to 3 M). The resulting TiO2-DOM agglomerates were monitored for size and ζ-potential. Inhibitory profiles were generated using para-chlorobenzoic acid (pCBA) as probe with varying concentrations of inhibitory DOM for each solution condition to discern the extent of surface-phase quenching of radicals. Manipulation of pH clearly impacted inhibition, and the effect varied by DOM type; for example, interference occurred at all pHs for HA, at neutral or basic pHs for TPI, and only at pH 7 for HPO. Particle sizes did not correlate with inhibitory action of DOM. Increases in ionic strength induced growth of TiO2 and TiO2-DOM agglomerates, but again, particle sizes did not correlate to inhibition by DOM. The changes to IS, regardless of ion type, were not affected by the presence of TPI or HPO. Since particle stability did not correlate directly with photocatalytic activity, we suggest that surface-based quenching reactions arise from site-specific adsorption rather than generalized particle destabilization and aggregation.
Stoffel, D., Derlon, N., Traber, J., Staaks, C., Heijnen, M., Morgenroth, E., & Jacquin, C. (2023). Gravity-driven membrane filtration with compact second-life modules daily backwashed: an alternative to conventional ultrafiltration for centralized facilities. Water Research X, 18, 100178 (12 pp.). doi:10.1016/j.wroa.2023.100178, Institutional Repository

Gravity-driven membrane (GDM) filtration is a strategic alternative to conventional ultrafiltration (UF) for the resilient production of drinking water via ultrafiltration when resources become scarce, given the low dependency on energy and chemicals, and longer membrane lifetime. Implementation at large scale requires the use of compact and low-cost membrane modules with high biopolymer removal capacity. We therefore evaluated (1) to what extent stable flux can be obtained with compact membrane modules, i.e., inside-out hollow fiber membranes, and frequent gravity-driven backwash, (2) whether we can reduce membrane expenses by effectively utilizing second-life UF modules, i.e., modules that have been discarded by treatment plant operators because they are no longer under warranty, (3) if biopolymer removal could be maintained when applying a frequent backwash and with second-life modules and (4) which GDM filtration scenarios are economically viable compared to conventional UF, when considering the influence of new or second-life modules, membrane lifetime, stable flux value and energy pricing. Our findings showed that it was possible to maintain stable fluxes around 10 L/m2/h with both new and second-life modules for 142 days, but a daily gravity-driven backwash was necessary and sufficient to compensate the continuous flux drop observed with compact modules. In addition, the backwash did not affect the biopolymer removal. Costs calculations revealed two significant findings: (1) using second-life modules made GDM filtration membrane investment less expensive than conventional UF, despite the higher module requirements for GDM filtration and (2) overall costs of GDM filtration with a gravity-driven backwash were unaffected by energy prices rise, while conventional UF costs rose significantly. The later increased the number of economically viable GDM filtration scenarios, including scenarios with new modules. In summary, we proposed an approach that could make GDM filtration in centralized facilities feasible and increase the range of UF operating conditions to better adapt to increasing environmental and societal constraints.
Stoffel, D., Rigo, E., Derlon, N., Staaks, C., Heijnen, M., Morgenroth, E., & Jacquin, C. (2022). Low maintenance gravity-driven membrane filtration using hollow fibers: effect of reducing space for biofilm growth and control strategies on permeate flux. Science of the Total Environment, 811, 152307 (13 pp.). doi:10.1016/j.scitotenv.2021.152307, Institutional Repository

The implementation of centralized drinking water treatment systems necessitates lower operational costs and improved biopolymer removal during ultrafiltration (UF), which can be afforded by gravity-driven membrane (GDM) filtration. However, prior to implementing GDM filtration in centralized systems, biofilm growth in compacted membrane configurations, such as inside-out hollow fiber (HF), and its impact on permeate flux need to be investigated. To this end, we operated modules with distinct limits on available space for biofilm growth: (1) outside-in 1.5 mm 7-capillary HF (non-limited), (2) inside-out 1.5 mm 7-capillary HF (limited), and (3) inside-out 0.9 mm 7-capillary HF (very limited). Here, we observed that the lower the space available for biofilm growth, the lower the permeate flux. To improve GDM performance with inside-out HF, we applied daily shear stress to the biofilm surface with forward flush (FF) or combined relaxation and forward flush (R+FF). We showed that applying shear stress to the biofilm surface was insufficient for controlling flux loss due to low available space for biofilm growth. At the experimental endpoint, we backwashed with a stepwise transmembrane pressure (TMP) increase or a single TMP on all inside-out HF modules, which removed the biofilm from its base. Afterwards, higher fluxes were yielded. We also showed that all modules exhibited a gradual increase in biopolymer removal followed by stabilization between 70 and 90%. Additionally, control of biofilm growth with surface shear stress did not affect biopolymer removal. In summary, the implementation of inside-out HF with GDM filtration is challenged by low available space for biofilm growth, but may be remedied with a regular backwash to remove biofilm from its base. We showed that a wider range of GDM applications are available; making GDM potentially compatible with implementation in centralized systems, if space limitation is taken into consideration for operation optimization.
Domagała, K., Jacquin, C., Borlaf, M., Sinnet, B., Julian, T., Kata, D., & Graule, T. (2020). Efficiency and stability evaluation of Cu2O/MWCNTs filters for virus removal from water. Water Research, 179, 115879 (10 pp.). doi:10.1016/j.watres.2020.115879, Institutional Repository

Both multi-walled carbon nanotubes (MWCNTs) and metal or metal oxides have demonstrated virus removal efficacy in drinking water applications. In this study, MWCNTs were coated with copper(I) oxide (Cu2O) using three distinct synthesis procedures (copper ion attachment, copper hydroxide precipitation, and [Cu(NH3)4]2+ complex attachment) and virus removal efficacy (using MS2 bacteriophages) was evaluated. All synthesis procedures resulted in the presence of adsorbed, nanosized Cu2O particles on the MWCNTs, shown using X-ray diffraction. Further, transmission electron microscopy confirmed uniform copper(I) oxide distribution along the MWCNTs for all three materials. Virus removal efficacy was assessed for all three synthesised composites both before and after material conditioning (filtering for at least 24 h/280 mL/h), and accounting for additional MS2 inactivation in the permeate due to continued copper inactivation from dissolved/desorbed copper in permeate (time-control). Material conditioning influenced virus removal, with the first litres of water containing higher concentrations of copper than the sixth litres of water, suggesting excess or non-bonded copper species dissolve from filters. Higher copper dissolution was observed for water at pH 5 than at pH 7, which decreased with time. Copper dissolution most likely caused an associated decrease in copper adsorbed to MWCNTs in the filters, which may explain the observed lower MS2 removal efficacy after conditioning. Additionally, the time-control study (immediately after filtration as compared to 2 h after filtration) highlighted continued MS2 inactivation in the permeate over time. The obtained results indicate that the synthesis procedure influences virus removal efficacy for MWCNTs coated with copper oxides and that virus removal is likely due to not only virus electrostatic adsorption to the coated MWCNTs, but also through antiviral properties of copper which continues to act in the permeate. In conclusion, it is highly important to revise the methods of testing filter materials for virus removal, as well as procedure for virus concentration evaluation.
Jacquin, C., Yu, D., Sander, M., Domagala, K. W., Traber, J., Morgenroth, E., & Julian, T. R. (2020). Competitive co-adsorption of bacteriophage MS2 and natural organic matter onto multiwalled carbon nanotubes. Water Research X, 9, 100058 (12 pp.). doi:10.1016/j.wroa.2020.100058, Institutional Repository

A leading challenge in drinking water treatment is to remove small-sized viruses from the water in a simple and efficient manner. Multi-walled carbon nanotubes (MWCNT) are new generation adsorbents with previously demonstrated potential as filter media to improve virus removal. This study therefore aimed to evaluate the field applicability of MWCNT-filters for virus removal in water containing natural organic matter (NOM) as co-solute to viruses, using batch equilibrium experiments. Contrary to previous studies, our results showed with MS2 bacteriophages single-solute systems that the affinity of MWCNT for MS2 was low, since after 3 h of equilibration only 4 log10 reduction value (LRV) of MS2 (20 mL at an initial concentration of 106 PFU MS2/mL) were reached. Single solute experiments with Suwannee river NOM (SRNOM) performed with environmentally-relevant concentrations showed MWCNT surface saturation at initial SRNOM concentrations between 10 and 15 mgC/L, for water pH between 5.2 and 8.7. These results suggested that at NOM:virus ratios found in natural waters, the NOM would competitively suppress virus adsorption onto MWCNT, even at low NOM concentrations. We confirmed this expectation with SRNOM-MS2 co-solute experiments, which showed an exponential decrease of the MS2 LRV by MWCNT with an increase in the initial SRNOM concentration. More interestingly, we showed that pre-equilibrating MWCNT with a SRNOM solution at a concentration as low as 0.4 mgC/L resulted in a LRV decrease of 3 for MS2, due to the formation of a negatively charged SRNOM adlayer on the MWCNT surface. Complementary batch experiments with natural NOM-containing waters and competition experiments with SRNOM in the presence of CaCl2 confirmed that the presence of NOM in waters challenges virus removal by MWCNT-filters, irrespective of the concentration and type of NOM and also in the presence of Ca2+. We therefore conclude that MWCNT-filters produced with commercially available pristine MWCNT cannot be considered as a viable technology for drinking water virus removal.

Andreas Frömelt

Böhler, M. A., Carl, F., Zhu, M., McArdell, C. S., Frömelt, A., & Joss, A. (2023). Spurenstoffelimination bei stark verdünnter Abwassermatrix – Erfahrungen, Kenntnisstand und Herausforderungen. In M. Wessling & T. Wintgens (Eds.), 15. Aachener Tagung Wassertechnologie. Verfahren der Abwasserbehandlung und Wasseraufbereitung (pp. 14-23). Aachen: RWTH Aachen University. , Institutional Repository

Das Qualitätsziel einer 80%igen Elimination von Mikroverunreinigungen ist in der Schweiz für ausgewählte ARA auch bei Regenwetterverhältnissen stets einzuhalten. Hohe Niederschläge verursachen hohe Mischwasserzuläufe zur ARA, die in der Menge häufig das Doppelte der Trockenwettermenge übersteigt. Der Schmutzwasseranteil (Abwassermatrix) ist dann um das Vielfache verdünnt. Dieser Umstand verursacht hydraulische Effekte wie verkürzte hydraulische Aufenthaltszeiten in den Behandlungsstufen und führt zu verkürzten Kontakt- und Reaktionszeiten in den Reaktoren. U.a. können Kurzschlussströme entstehen, die die EMV erniedrigen können. Die EMVStufen in der Schweiz sind auf Mischwasserzulauf ausgelegt und es wurden über die letzten Jahre angepasste Betriebsstrategien für die verschiedenen
EMV-Verfahren erarbeitet, so dass in aller Regel das Qualitätsziel erreicht wird. Dennoch bleibt der sichere, wirtschaftliche sowie nachhaltige Betrieb der Anlagen anspruchsvoll mit hohen Herausforderungen.
Aktuelle Untersuchungen der Eawag zum Verhalten höher beladener GAK im Einzelfilter zeigten bei Kontakt mit stark verdünntem Abwasser trotz 20-minütiger Kontaktzeit verringerte Sorptionsleistung bis hin zur Desorption von Einzelsubstanzen. Ob dieser Umstand auch bei einem Parallelbetrieb zu beobachten ist, sollen weiterführende Untersuchungen im Praxisbetrieb von GAK-Filtrationen zeigen. Im Fall der GAK-Filtration der ARA Glarnerland mit langanhaltenden Regennachläufen und Schmelzwasserzulauf wurde eine PAK-Dosierung in die Biologie vorgeschaltet bzw. wird aktuell realisiert, um allenfalls Einbussen durch verdünnte Abwassermatrix abzufangen.
Wiprächtiger, M., Haupt, M., Froemelt, A., Klotz, M., Beretta, C., Osterwalder, D., … Hellweg, S. (2023). Combining industrial ecology tools to assess potential greenhouse gas reductions of a circular economy. Method development and application to Switzerland. Journal of Industrial Ecology, 27(1), 254-271. doi:10.1111/jiec.13364, Institutional Repository

Industrial ecology (IE) methodologies, such as input/output or material flow analysis and life cycle assessment (LCA), are often used for the environmental evaluation of circular economy strategies. Up to now, an approach that utilizes these methods in a systematic, integrated framework for a holistic assessment of a geographic region's sustainable circular economy potential has been lacking. The approach developed in this study (IE4CE approach) combines IE methodologies to determine the environmental impact mitigation potential of circular economy strategies for a defined geographic region. The approach foresees five steps. First, input/output analysis helps identify sectors with high environmental impacts. Second, a refined analysis is conducted using material flow and LCA. In step 3, circular strategies are used for scenario design and evaluated in step 4. In step 5, the assessment results are compiled and compared across sectors. The approach was applied to a case study of Switzerland, analyzing 8 sectors and more than 30 scenarios in depth. Carbon capture and storage (CCS) from waste incineration, biogas and cement production, food waste prevention in households, hospitality and production, and the increased recycling of plastics had the highest mitigation potential. Most of the scenarios do not influence each other. One exception is the CCS scenarios: waste avoidance scenarios decrease the reduction potential of CCS. A combination of scenarios from different sectors, including their impact on the CCS scenario potential, led to an environmental impact mitigation potential of 11.9 Mt CO2-eq for 2050, which equals 14% of Switzerland's current consumption-based impacts.
Donati, F., Dente, S. M. R., Li, C., Vilaysouk, X., Froemelt, A., Nishant, R., … Hashimoto, S. (2022). The future of artificial intelligence in the context of industrial ecology. Journal of Industrial Ecology, 26(4), 1175-1181. doi:10.1111/jiec.13313, Institutional Repository

Artificial intelligence (AI) applications and digital technologies (DTs) are increasingly present in the daily lives of citizens, in cities and in industries. These developments generate large amounts of data and enhance analytical capabilities that could benefit the industrial ecology (IE) community and sustainability research in general. With this communication, we would like to address some of the opportunities, challenges, and next steps that could be undertaken by the industrial ecology community in this realm. This article is an adapted summary of the discussion held by experts in industrial ecology, AI, and sustainability during the 2021 Industrial Ecology Day conference session titled "The Future of Artificial Intelligence in the Context of Industrial Ecology." In brief, building on previous studies and communications, we advise the industrial ecology community to: (1) create internal committees and working groups to monitor and coordinate AI applications within and outside the community; (2) promote and ensure transdisciplinary efforts; (3) determine optimal infrastructure and governance of AI for IE to minimize undesired effects; and (4) act on effective representation and on reduction of digital divides.
Kim, A., Mutel, C. L., Froemelt, A., & Hellweg, S. (2022). Global sensitivity analysis of background life cycle inventories. Environmental Science and Technology, 56(9), 5874-5885. doi:10.1021/acs.est.1c07438, Institutional Repository

In recent years many Life Cycle Assessment (LCA) studies have been conducted to quantify the environmental performance of products and services. Some of these studies propagated numerical uncertainties in underlying data to LCA results, and several applied Global Sensitivity Analysis (GSA) to some parts of the LCA model to determine its main uncertainty drivers. However, only a few studies have tackled the GSA of complete LCA models due to the high computational cost of such analysis and the lack of appropriate methods for very high-dimensional models. This study proposes a new GSA protocol suitable for large LCA problems that, unlike existing approaches, does not make assumptions on model linearity and complexity and includes extensive validation of GSA results. We illustrate the benefits of our protocol by comparing it with an existing method in terms of filtering of noninfluential and ranking of influential uncertainty drivers and include an application example of Swiss household food consumption. We note that our protocol obtains more accurate GSA results, which leads to better understanding of LCA models, and less data collection efforts to achieve more robust estimation of environmental impacts. Implementations supporting this work are available as free and open source Python packages.
Schneider, M. Y., Quaghebeur, W., Borzooei, S., Froemelt, A., Li, F., Saagi, R., … Torfs, E. (2022). Hybrid modelling of water resource recovery facilities: status and opportunities. Water Science and Technology, 85(9), 2503-2524. doi:10.2166/wst.2022.115, Institutional Repository

Mathematical modelling is an indispensable tool to support water resource recovery facility (WRRF) operators and engineers with the ambition of creating a truly circular economy and assuring a sustainable future. Despite the successful application of mechanistic models in the water sector, they show some important limitations and do not fully profit from the increasing digitalisation of systems and processes. Recent advances in data-driven methods have provided options for harnessing the power of Industry 4.0, but they are often limited by the lack of interpretability and extrapolation capabilities. Hybrid modelling (HM) combines these two modelling paradigms and aims to leverage both the rapidly increasing volumes of data collected, as well as the continued pursuit of greater process understanding. Despite the potential of HM in a sector that is undergoing a significant digital and cultural transformation, the application of hybrid models remains vague. This article presents an overview of HM methodologies applied to WRRFs and aims to stimulate the wider adoption and development of HM. We also highlight challenges and research needs for HM design and architecture, good modelling practice, data assurance, and software compatibility. HM is a paradigm for WRRF modelling to transition towards a more resource-efficient, resilient, and sustainable future.
Frömelt, A. (2007). Marketing compost in Nepal. Field testing of Sandec’s compost marketing handbook. Dübendorf: Eawag. , Institutional Repository

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