Abteilung Verfahrenstechnik

Brauchwasser-Wiederverwendung

Wir entwickeln Technologien zur Aufbereitung von Grauwasser oder Abwasser für die Wiederverwendung von Brauchwasser. Unser Schwerpunkt liegt auf der Entwicklung robuster Technologien, die im Gebäude- oder Gerätemaßstab eingesetzt werden können. Bei der Aufbereitungstechnologie wird häufig eine biologische Behandlung in Kombination mit einer Ultrafiltration als erster Schritt eingesetzt. Die anschließende Behandlung umfasst eine weitere biologische Behandlung (z. B. mit biologischer Aktivkohle) oder Desinfektion (z. B. Chlordosierung, Elektrolyse zur Chlorerzeugung, UV).

Ein weiterer Schwerpunkt ist die Online-Überwachung der Systemleistung mit einfachen Sensoren wie der Messung des Oxidations-Reduktions-Potenzials (ORP).

Neben der Entwicklung von Technologien arbeiten wir auch an der Schnittstelle zwischen Technologie und Nutzerwahrnehmung. Wir tragen zur Entwicklung geeigneter Richtlinien und Implementierungsrahmen bei.

Kontakt

Prof. Dr. Eberhard Morgenroth Tel. +41 58 765 5539 E-Mail senden
GDM ist eine einfache, wartungsfreie Technologie für die Trinkwasserversorgung ohne Elektrizität und Chemie.

GDM Gravity-Driven Membrane technologie
Chancen und Risiken der Wasserwiederverwendung von gereinigtem Abwasser in der Schweiz

Wasserwiederverwendung

Publikationen

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.
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.
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). 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.
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. [...]
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.
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.
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.
Gauthier, J., Boulain, H., van Vugt, J. J. F. A., Baudry, L., Persyn, E., Aury, J. M., … Drezen, J. M. (2021). Chromosomal scale assembly of parasitic wasp genome reveals symbiotic virus colonization. Communications Biology, 4(1), 104 (15 pp.). doi:10.1038/s42003-020-01623-8, Institutional Repository

Endogenous viruses form an important proportion of eukaryote genomes and a source of novel functions. How large DNA viruses integrated into a genome evolve when they confer a benefit to their host, however, remains unknown. Bracoviruses are essential for the parasitism success of parasitoid wasps, into whose genomes they integrated ~103 million years ago. Here we show, from the assembly of a parasitoid wasp genome at a chromosomal scale, that bracovirus genes colonized all ten chromosomes of Cotesia congregata. Most form clusters of genes involved in particle production or parasitism success. Genomic comparison with another wasp, Microplitis demolitor, revealed that these clusters were already established ~53 mya and thus belong to remarkably stable genomic structures, the architectures of which are evolutionary constrained. Transcriptomic analyses highlight temporal synchronization of viral gene expression without resulting in immune gene induction, suggesting that no conflicts remain between ancient symbiotic partners when benefits to them converge.
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.
Dennis, A. B., Ballesteros, G. I., Robin, S., Schrader, L., Bast, J., Berghöfer, J., … Gadau, J. (2020). Functional insights from the GC-poor genomes of two aphid parasitoids, Aphidius ervi and Lysiphlebus fabarum. BMC Genomics, 21(1), 376 (27 pp.). doi:10.1186/s12864-020-6764-0, Institutional Repository

Background: Parasitoid wasps have fascinating life cycles and play an important role in trophic networks, yet little is known about their genome content and function. Parasitoids that infect aphids are an important group with the potential for biological control. Their success depends on adapting to develop inside aphids and overcoming both host aphid defenses and their protective endosymbionts.
Results: We present the de novo genome assemblies, detailed annotation, and comparative analysis of two closely related parasitoid wasps that target pest aphids: Aphidius ervi and Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae). The genomes are small (139 and 141 Mbp) and the most AT-rich reported thus far for any arthropod (GC content: 25.8 and 23.8%). This nucleotide bias is accompanied by skewed codon usage and is stronger in genes with adult-biased expression. AT-richness may be the consequence of reduced genome size, a near absence of DNA methylation, and energy efficiency. We identify missing desaturase genes, whose absence may underlie mimicry in the cuticular hydrocarbon profile of L. fabarum. We highlight key gene groups including those underlying venom composition, chemosensory perception, and sex determination, as well as potential losses in immune pathway genes.
Conclusions: These findings are of fundamental interest for insect evolution and biological control applications. They provide a strong foundation for further functional studies into coevolution between parasitoids and their hosts. Both genomes are available at https://bipaa.genouest.org.
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.
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.
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.
Jacquin, C., Monnot, M., Hamza, R., Kouadio, Y., Zaviska, F., Merle, T., … Héran, M. (2018). Link between dissolved organic matter transformation and process performance in a membrane bioreactor for urinary nitrogen stabilization. Environmental Science: Water Research and Technology, 4(6), 806-819. doi:10.1039/c8ew00029h, Institutional Repository

A lab-scale membrane bioreactor was fed with fresh urine collected from source separation public toilets to perform full nitrification, urinary nitrogen stabilization and effluent sanitation. After acclimation, a nitrogen loading rate (NLR) of 1.2 kg TN per m3 d−1 was reached with an average nitrification rate of 98.3%. Dissolved organic matter (DOM) transformation was studied within the MBR to identify biomass activity indicators that could be used for process optimization. By combining three-dimensional excitation emission fluorescence (3DEEM) and liquid chromatography coupled with organic carbon detection, nitrogen detection and UV detection (LC-OCD-OND-UVD), it was possible to investigate the transformation and fate of urine DOM during biological reactions and membrane separation. Results show that urine is mainly composed of low molecular weight molecules (<1000 Da) easily consumed by the active biomass. This consumption came with the production of soluble microbial products (SMP): biopolymers and humic substances. Significant correlations were observed between 3DEEM indicators and the NLR values. Biopolymers were mainly retained by the membrane and tended to accumulate in the reactor, which was of major interest since they were identified as DOM consumed by the active biomass in case of system instabilities. Humic substances were slightly retained by the membrane and mostly implied in irreversible fouling. This original approach allowed highlighting the quick active biomass acclimation under challenging conditions of high strength ammonia solutions such as urine.
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.
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.
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.
Schmidt, T. C., Morgenroth, E., Schirmer, M., Effenberger, M., & Haderlein, S. B. (2002). Use and occurrence of fuel oxygenates in Europe. In A. F. Diaz & D. L. Drogos (Eds.), ACS symposium series: Vol. 799. Oxygenates in gasoline. Environmental aspects (pp. 58-79). doi:10.1021/bk-2002-0799.ch005, Institutional Repository

In contrast to the US, fuel oxygenates are generally used as octane enhancers in Europe rather than to increase the oxygen level in gasoline for a cleaner combustion. To achieve the high average octane ratings of European gasolines (95 RON), currently more than 2.5 Mt/a of fuel oxygenates, mainly methyl tert-butyl ether (MTBE) are used. Stimulated by the public discussion in the US, there is a growing awareness of groundwater pollution related to the use of MTBE as a gasoline component. Although the number of leakage and spill sites in Europe is supposedly lower than in the US due to earlier implementation of strict storage facility regulations, contamination of groundwater with MTBE is significant. Owing to the lack of a uniform European standard, however, the situation may vary considerably in different European countries. Recent survey studies in northern and central Europe on groundwater pollution by MTBE revealed background concentrations of up to 3 μg/L, and concentrations at point sources of up to 500 mg/L. For southern and eastern European countries there is no data available to us on regulations or MTBE levels in the environment. Due to growing concern regarding groundwater pollution by MTBE, alternative octane enhancers are put forward in some European countries. While the dialkyl ethers tert-amyl methyl ether (TAME) and ethyl tert-butyl ether (ETBE) are already in use, the introduction of ethanol is being discussed.
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.