Department Process Engineering

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

Der Reinigungseffekt für Mikroverunreinigungen wird von ARA über periodische Messungen der Leitsubstanzen bestimmt. Für den täglichen Betrieb lassen sich zusätzlich anhand von UV-Messungen sowie anhand der dosierten Mengen an Ozon oder Aktivkohle zeitnahe Aussagen zur Reinigungsleistung machen.

Characterising bioflocculation and settling in activated sludge processes is mandatory to better understand and optimise organic matter removal and capture. Among the few indicators available, Threshold Of Flocculation (TOF) reflects the ability of activated sludge to settle following Stokesian settling mechanisms. In this work, the original method to determine TOF has been improved to gain accuracy and reproducibility. An R-script was proposed for systematic analysis of the experimental curves representing the total suspended solids supernatant concentration as a function of the initial concentration of the total suspended solids. The strength of this new method is to base curve analysis on the settling mechanisms that occur in the experimental setup. Two thresholds are mathematically identified, corresponding to (i) the solid concentration required to induce discrete flocculent settling and (ii) the minimum concentration to form large flocs that interact with each other (TOF). The novel method was successfully applied to different types of sludge (HRAS, CAS, and densified sludge).

Das inDENSE^®-Verfahren wurde auf der ARA Gossau-Grüningen getestet. Nach einem Jahr wurde ein Anteil an granuliertem Schlamm von rund 50% und ein Schlammvolumenindex zwischen 40 und 70 ml/g beobachtet. DNA-Analysen zeigten, dass die bakterielle Gesamtpopulation saisonal konstanter blieb und Nitrit-oxidierende Bakterien im granulierten Schlamm akkumulierten. Durch die verbesserten Absetzeigenschaften können die Kapazität der ARA und die Stickstoffelimination signifikant gesteigert werden.

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

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

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

Das Qualitätsziel einer 80%igen Elimination von Mikroverunreinigungen ist in der Schweiz für ausgewählte ARA auch bei Regenwetterverhältnissen stets einzuhalten. Hohe Niederschläge verursachen hohe Mischwasserzuläufe zur ARA, die in der Menge häufig das Doppelte der Trockenwettermenge übersteigt. Der Schmutzwasseranteil (Abwassermatrix) ist dann um das Vielfache verdünnt. Dieser Umstand verursacht hydraulische Effekte wie verkürzte hydraulische Aufenthaltszeiten in den Behandlungsstufen und führt zu verkürzten Kontakt- und Reaktionszeiten in den Reaktoren. U.a. können Kurzschlussströme entstehen, die die EMV erniedrigen können. Die EMVStufen in der Schweiz sind auf Mischwasserzulauf ausgelegt und es wurden über die letzten Jahre angepasste Betriebsstrategien für die verschiedenen
EMV-Verfahren erarbeitet, so dass in aller Regel das Qualitätsziel erreicht wird. Dennoch bleibt der sichere, wirtschaftliche sowie nachhaltige Betrieb der Anlagen anspruchsvoll mit hohen Herausforderungen.
Aktuelle Untersuchungen der Eawag zum Verhalten höher beladener GAK im Einzelfilter zeigten bei Kontakt mit stark verdünntem Abwasser trotz 20-minütiger Kontaktzeit verringerte Sorptionsleistung bis hin zur Desorption von Einzelsubstanzen. Ob dieser Umstand auch bei einem Parallelbetrieb zu beobachten ist, sollen weiterführende Untersuchungen im Praxisbetrieb von GAK-Filtrationen zeigen. Im Fall der GAK-Filtration der ARA Glarnerland mit langanhaltenden Regennachläufen und Schmelzwasserzulauf wurde eine PAK-Dosierung in die Biologie vorgeschaltet bzw. wird aktuell realisiert, um allenfalls Einbussen durch verdünnte Abwassermatrix abzufangen.

There have been significant advances in the use of biological and physical selectors for the intensification of continuously flowing biological wastewater treatment (WWT) processes. Biological selection allows for the development of large biological aggregates (e.g., mobile biofilm, aerobic granules, and densified biological flocs). Physical selection controls the solids residence times of large biological aggregates and ordinary biological flocs, and is usually accomplished using screens or hydrocyclones. Large biological aggregates can facilitate different biological transformations in a single reactor and enhance liquid and solids separation. Continuous-flow WWT processes incorporating biological and physical selectors offer benefits that can include reduced footprint, lower costs, and improved WWT process performance. Thus, it is expected that both interest in and application of these processes will increase significantly in the future. This review provides a comprehensive summary of biological and physical selectors and their design and operation.

Enteroviruses, which are commonly circulating viruses shed in the stool, are released into the sewage system and only partially removed or inactivated, resulting in the discharge of infectious enteroviruses into the environment. Activated sludge and chlorination remove or inactivate enterovirus genotypes to different extents, and thus have the potential to shape the population that will be discharged. The goal of this study was to evaluate how activated sludge and chlorination treatment shape an enterovirus population at the genotype level, using a population of eight genotypes commonly found in sewage: CVA9, CVB1, CVB2, CVB3, CVB4, CVB5, E25, E30. Our results show that the extent of inactivation varied among genotypes, but also across sludge samples. We find that the effluent of activated sludge systems will be depleted in CVA9, CVB1 and CVB2 while E25 together with CVB3, CVB4 and CVB5 will be prevalent. Furthermore, we found that microbial inactivation was the main mechanism of infectivity loss in the activated sludge, while adsorption to the sludge flocs was not significant. During effluent chlorination, we also observed that CVB5, CVB3 and to a lesser extent E25 were less susceptible to chlorination while E30 was readily inactivated, and activated sludge-derived EPS provided further protection against chlorination. This study contributes to a better understanding of the variability of sewage treatment efficacy against different enteroviruses.

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.

The effects of solvents and heating temperatures on the recovery and degradation of gel-forming EPS (Extracellular Polymeric Substances) extracted from aerobic granular sludge were investigated. Sodium hydroxide has allowed a better EPS solubilization compared to sodium carbonate (711.3 ± 38 and 408.4 ± 4 mg VS /g VS respectively) but the capacity to precipitate gel-forming EPS at acidic pH was higher in sodium carbonate (22% compared to 6% in sodium hydroxide at 80 °C). Increasing the temperature from 20 °C to 80 °C during EPS solubilization has multiplied the amount of solubilized matter by 4 in sodium carbonate and 2.2 in sodium hydroxide. Similar biochemical composition but different molecular weight profiles were observed for the two solubilized EPS extracts, evidencing partial degradation of the polymers in sodium hydroxide. Furthermore, coupling molecular weight analysis and precipitation yield measurement revealed that the lower precipitation of sodium hydroxide solubilized EPS is related to the size reduction due to degradation. Altogether these results help to guide towards a unified protocol for the extraction of gel-forming EPS.

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

The production of volatile fatty acids (VFAs) represents a relevant option to valorize municipal wastewater (MWW). In this context, different capture technologies can be used to recover organic carbon from wastewater in form of solids, while pre-treatment of those solids has the potential to increase VFA production during subsequent fermentation. Our study investigates how VFA composition produced by fermentation is influenced (i) by the choice of the capture technology, as well as (ii) by the use of thermal alkaline pre-treatment (TAP). Therefore, the fermentation of solids originating from a primary settler, a micro-sieve, and a high-rate activated sludge (HRAS) system was investigated in continuous lab-scale fermenters, with and without TAP. Our study demonstrates that the capture technology strongly influences the composition of the produced solids, which in turn drives the complexity of the fermenter's microbial community and ultimately, of the VFA composition. Solids captured with the primary settler or micro-sieve consisted primarily of polysaccharides, and led to the establishment of a microbial community specialized in the degradation of complex carbohydrates. The produced VFA composition was relatively simple, with acetate and propionate accounting for >90% of the VFAs. In contrast, the HRAS system produced biomass-rich solids associated with higher protein contents. The microbial community which then developed in the fermenter was therefore more diversified and capable of converting a wider range of substrates (polysaccharides, proteins, amino acids). Ultimately, the produced VFA composition was more complex, with equal fractions of isoacids and propionate (both ~20%), while acetate remained the dominant acid (~50%). Finally, TAP did not significantly modify the VFA composition while increasing VFA yields on HRAS and sieved material by 35% and 20%, respectively. Overall, we demonstrated that the selection of the technology used to capture organic substrates from MWW governs the composition of the VFA cocktail, ultimately with implications for their further utilization.

Auf den Kläranlagen Furt/Bülach und Glarnerland des Abwasserverbandes Glarnerland (AVG, Bilten) wurden zwischen 2014 und 2019 umfangreiche Untersuchungen zur Elimination von Mikroverunreinigungen mittels granulierter Aktivkohle (GAK) durchgeführt. Ziel war es, unter Schweizer Praxisbedingungen die Machbarkeit, Effizienz und Wirtschaftlichkeit des Verfahrens zu evaluieren. Fazit beider Forschungsprojekte ist, dass sich die GAK-Filtration zur Spurenstoffelimination gemäss Schweizer Gesetzgebung eignet. Das Verfahren ist technisch und wirtschaftlich realisierbar und hat sich als praxistauglich erwiesen.

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.

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 (H_reactor), 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.

Zukünftig werden auf der ARA Muri dank einer neuen Reinigungsstufe Mikroverunreinigungen aus dem Abwasser entfernt. Die GAK-Filtration bietet viele Vorteile und wird nicht nur verfahrenstechnisch, sondern auch ästhetisch optimal in die bestehenden Strukturen der ARA Muri eingebunden. Zur sicheren Umsetzung wurden in einer Pilotierung wichtige Fragen beantwortet, insbesondere wie die Filterzellen möglichst ideal mit einer Parallelschaltung für eine maximale Beladung zu verschalten sind.

Phototrophic biofilms, also known as periphyton, are microbial freshwater communities that drive crucial ecological processes in streams and lakes. Gaining a deep mechanistic understanding of the biological processes occurring in natural periphyton remains challenging due to the high complexity and variability of such communities. To address this challenge, we rationally developed a workflow to construct a synthetic community by co-culturing 26 phototrophic species (i.e., diatoms, green algae, and cyanobacteria) that were inoculated in a successional sequence to create a periphytic biofilm on glass slides. We show that this community is diverse, stable, and highly reproducible in terms of microbial composition, function, and 3D spatial structure of the biofilm. We also demonstrate the ability to monitor microbial dynamics at the single species level during periphyton development and how their abundances are impacted by stressors such as increased temperature and a herbicide, singly and in combination. Overall, such a synthetic periphyton, grown under controlled conditions, can be used as a model system for theory testing through targeted manipulation.

Particulate organic substrate (X_B) 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 X_B 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 X_B is converted into soluble organic substrate (S_B) and volatile fatty acids (S_VFA) 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 X_B was hydrolysed and 11% of influent X_B was then used for internal carbon-storage during 90 min anaerobic plug-flow feeding. The major fraction of influent X_B (80%) leaked into the aerobic SBR phase, where X_B was then hydrolysed and oxidised aerobically by ordinary heterotrophic organisms (OHOs). Under aerobic fully-mixed conditions, the flocs successfully competed for X_B with the granules. Aerobic X_B 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 X_B under anaerobic conditions and to reduce the leakage of X_B to aerobic conditions. The introduction of a 60 min anaerobic idle phase after a 60 min plug-flow feeding phase almost doubled the anaerobic X_B 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 X_B was still utilised by OHOs during the aerobic SBR phase.

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.

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.

This worked assessed the potential of alginate-like exopolymers (ALE) hydrogels recovered from aerobic granular sludge (AGS) in removing compounds commonly present in municipal wastewater. Batch sorption experiments were performed with ALE hydrogels at different operating conditions. Results showed that ALE hydrogels can only remove phosphate, at removal efficiencies of up to 90.8% and practical loadings of 1.22 ± 0.07 mg PO₄^3--P/g TS_ALE. Phosphate removal was observed even in the presence of competing ions. Moreover, neutral to acidic pH values strongly impaired the phosphate removal (28.9 ± 0.8% at pH = 6.00), while basic pH at around 8.50 was the most favourable (up to 90.8% at pH = 8.67). However, ALE hydrogels contributed to the increase in COD, total nitrogen and total phosphorus in the bulk liquid, what suggests that ALE need to be further tailored. Therefore, this study demonstrates that ALE represent a relevant approach for the recovery of phosphates from municipal wastewater.

Biofouling layer (i.e., biofilm) is an inevitable presence for the membrane filtration processes. In this study, we elucidated biofouling formation from the perspective of affecting the attachment of bacteria for the first time, whereby the role of initial available biopolymers was revealed. Results demonstrated that the presence of initial available biopolymers increased the abundance of the genus Caulobacter, which was capable of mineralizing biopolymers; whereas, for the typically oligotrophic species of Polynucleobacter, it exhibited low abundance. Greater concentrations of polysaccharides and proteins were accumulated in the biofouling layer, when provided with initial biopolymers, and the biofilm structure was more heterogeneous with larger pore size and higher thickness. Thereby, the corresponding filtration system exhibited greater permeability and better removal performance of organics. Collectively, the initial available biopolymers altered the attachment conditions for the bacteria, which subsequently impacted the bacterial community, and in turn biofilm composition, physical structure and filtration performance.

Implementing advanced wastewater treatment (WWT) to eliminate organic micropollutants (OMPs) is a necessary step to protect vulnerable freshwater ecosystems and water resources. To this end, sorption of OMP by activated carbon (AC) is one viable technology among others. However, conventional AC production based on fossil precursor materials causes environmental pollution, including considerable emissions of greenhouse gases. In this study, we produced activated biochar (AB) from wood and woody residues by physical activation and evaluated their capability to eliminate OMPs in treated wastewater. Activated biochar produced under optimized conditions sorbed 15 model OMPs, of which most were dissociated at circumneutral pH, to the same or higher extent than commercial AC used as a reference. While wood quality played a minor role, the dosage of the activation agent was the main parameter controlling the capacity of ABs to eliminate OMP. Our results highlight the possibility for local production of AB from local wood or woody residues as a strategy to improve WWT avoiding negative side effects of conventional AC production.

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

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.

Particulate substrate (X_B) is the major organic substrate fraction in most municipal wastewaters. However, the impact of X_B on aerobic granular sludge (AGS) systems is not fully understood. This study evaluated the physical retention of X_B 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 X_B retention in AGS SBR were evaluated. X_B mass-balancing and magnetic resonance imaging (MRI) were applied. During the anaerobic plug-flow feeding, most X_B was retained in the first few cm of the settled sludge bed within the interstitial voids, where X_B settled and accumulated ultimately resulting in the formation of a filter-cake. Sedimentation and surface filtration were thus the dominant X_B retention mechanisms during plug-flow conditions, indicating that contact and attachment of X_B to the biomass was limited. X_B retention was variable and influenced by the X_B influent concentration, sludge bed composition and upflow feeding velocity (v_ww). X_B retention increased with larger X_B influent concentrations and lower v_ww, which demonstrated the importance of sedimentation on X_B retention during plug-flow conditions. Hence, large fractions of influent X_B likely re-suspended during aerobic fully-mixed conditions, where X_B then preferentially and rapidly attached to the flocs. During fully-mixed conditions, increasing floc fractions, longer mixing times and larger X_B concentrations increased X_B retention. Elevated X_B retention was observed after short mixing times < 60 min when flocs were present, and the contribution of flocs towards X_B 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 X_B during aerobic fully-mixed conditions of AGS SBR. Therefore, a complete wash-out of flocs is not desirable in AGS systems treating municipal wastewater.

Auf der Kläranlage Glarnerland wurde im Rahmen des Forschungsprojektes «Pilotversuche zur erweiterten Abwasserbehandlung mit granulierter Aktivkohle (GAK) und kombiniert mit Teilozonung (O3/GAK)» die Machbarkeit und Effizienz der genannten Verfahrenstechniken zur Spurenstoffelimination untersucht. Im weiteren Verlauf der Untersuchungen wurde zudem auch die Option der Dosierung von Pulveraktivkohle (PAK) in die biologische Stufe, welche mit dem S::Select®-Verfahren betrieben wird, als Vorstufe zur GAK erprobt.

Ziel der Pilotierung war die Erarbeitung von Entscheidungsgrundlagen zur Auswahl eines optimalen Verfahrens oder einer Verfahrenskombination für die angestrebte Realisierung der Spurenstoffelimination beim Abwasserverband Glarnerland. Zudem sollten Langzeiterfahrungen zum Betrieb von GAK-Filtrationen bezüglich Effizienz, Betrieb und vor allem Standzeiten (erreichte Bettvolumina) von verschiedenen GAK-Typen bei unterschiedlichen Kontaktzeiten bei einem Abwasser mit hohem gelöstem organischen Kohlenstoff (DOC) gesammelt werden.

Die Pilotanlage Vorozonung/GAK-Filtration ging Ende Januar 2017 auf der ARA Glarnerland in Betrieb und wurde im August 2019 ausser Betrieb gesetzt. Es wurden vier verschiedene GAK-Produkte untersucht (CSC «HC HK 1000», CarboTech «Pool W1-3», Jacobi «Aquasorb 5010», CabotNorit «GAC 1020 EN»). Parallel wurden alle GAK-Kolonnen (ausser Jacobi «Aquasorb 5010») während der gesamten Betriebsdauer mit einer Vorozonung bei einer spezifischen Ozondosis von rund 0.2 gO3/gDOC betrieben. [...]
 

The influence of wastewater (WW) composition and the bioaggregates types (floccular vs. aerobic granular sludge - AGS) on the content, physical-chemical, hydrogel and rheological properties of Alginate-Like Exopolymers (ALE) was studied. Results showed that ALE are a complex mixture of proteins, humic acids and polysaccharides. Overall, rather similar ALE content and composition was observed for the different types of sludge. Only the AGS fed with acetate and propionate yielded significantly larger amount of ALE (261 ± 33 mg VS_ALE/g VS_sludge, +49%) and of uronic sugars in ALE (254 ± 32 mg_{glucuronic acid}/g VS_ALE, +62%) than bioaggregates fed with no/very little volatile fatty acids. Mannuronic acids are involved in the cohesion of the hydrogels. ALE hydrogels elasticity changed significantly with the type/origin of the bioaggregates. ALE hydrogels elasticity from AGS was always higher than from flocs when fed with real WW. Hence, different types of sludge impact the properties of the recovered ALE.

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

Alginate-like exopolymers (ALE) are present in the extracellular polymeric substances (EPS) of biological sludge such as aerobic granular sludge (AGS). The recovery of ALE from excess sludge produced by wastewater treatment plants (WWTP) is a relevant approach for the recovery of valuable products of industrial interest. However, little is known about dynamics of ALE content in sludge and associated factors. Thus, this study aimed at assessing the dynamics of EPS and ALE in terms of content, some chemical properties and influencing environmental factors along granulation in a sequencing batch reactor treating municipal wastewater. Results indicated that the EPS content was not correlated with the development of AGS, while the ALE content was higher, more stable and steadily increased after granulation achievement. Overall, 236 ± 27 mg VS_ALE/g VS_sludge was recovered from AGS and 187 ± 94 mg VS_ALE/g VS_sludge from flocs. However, the lower ALE content in flocs may be compensated by the higher sludge production rate in activated sludge systems. Principal component analysis (PCA) revealed that ALE content positively correlates with the nutrient and organic substrate conversion, and with the fraction of large AGS. Microbial analyses indicated that a stable microbial community composition was associated with a higher and more stable ALE content. ALE recovered from both flocs and AGS was endowed with hydrogel property, and no clear difference in their elemental composition and functional groups was observed. Therefore, our study provides insights about quantitative and qualitative aspects of ALE which are helpful for the improvement of waste biological sludge valorization.

Die vorliegende Anleitung soll interessierte Fachkreise und Akteure im Themengebiet zur Durchführung von Schüttelversuchen zur Bestimmung der Reinigungsleistung von Pulveraktivkohle (PAK) zur Entfernung von Mikroverunreinigungen aus kommunalem Abwasser befähigen. Die Anwendungen von PAK zur Spurenstoffelimination werden zukünftig auf Kläranlagen zunehmen, so dass sich diese Anleitung an Kläranlagenbetreiber und andere Dienstleister richtet, die einen Bedarf zur Evaluation geeigneter Aktivkohlen als auch zur Überprüfung von Produktlieferungen haben. Die vorgestellte Verfahrensweise ist durch gut ausgebildetes Klärwerkspersonal in einem gängigen Kläranlagenlabor der Eigenüberwachung der Abwasserreinigungsanlage durchführbar.
Das Dokument gibt konkrete Hinweise zur gezielten Vorgehensweise bei PAK-Auswahl, Probenahme von Abwasser, Vorbereitung und Durchführung der Versuche sowie zur Analytik und Bewertung der Ergebnisse. Es zeigt auf, welche Fragestellungen durch derartige Versuche beantwortet werden können. Das Dokument widerspiegelt die bisherigen Erfahrungen, welche an der Eawag gemacht wurden und gibt Hinweise zur Vorgehensweise ab, wobei auch auf andere Methoden und Erfahrungen hingewiesen wird. Das Dokument ist unter verschiedenen Fachleuten abgestimmt worden. Hinweise auf andere Erfahrungen oder zur Verbesserung der Vorgehensweise sowie Neuerungen im Themengebiet sind von den Autoren sehr erwünscht und richten sich bitte an die Verfasser bzw. an den VSA.

Die ARA Sihltal wird heute ohne Vorklärung betrieben, soll jedoch aufgrund der zukünftigen Bevölkerungsentwicklung und zur energetischen Optimierung mit einer Vorklärung erweitert werden. Wegen der sehr engen Platzverhältnisse kann eine maschinelle Vorklärung (Trommelsieb) einfacher realisiert werden als eine konventionelle Vorklärung. Die Pilotversuche bestätigen, dass das Trommelsieb aus betrieblicher Sicht und bezüglich Abscheideleistung eine gleichwertige Vorklärung bietet.

Die Elimination von Mikroverunreinigungen in der Abwasserreinigung mit Aktivkohle oder Ozon ist eine wichtige Massnahme zum vorbeugenden Schutz der Gewässer und der Trinkwasserressourcen der Schweiz. Während der Einsatz von Ozon mit einem hohen Energieverbrauch einhergeht, führt der Einsatz von Aktivkohle andernorts zu negativen Umweltauswirkungen, da die Aktivkohle zum Teil aus fossilen Ausgangsstoffen wie Stein- oder Braunkohle hergestellt und zudem über weite Strecken transportiert wird. Aktivkohlen mit sehr guten Eliminationsleistungen könnten aber auch in der Schweiz aus einheimischen erneuerbaren Roh- und Reststoffen hergestellt werden.

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.

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.

Im vorliegenden Bericht wird die Möglichkeit zur Widerverwertung von in der Trinkwasseraufbereitung genutzter Pulveraktivkohle betrachtet. Dazu werden die zur Wiederverwertung notwendigen, förderlichen oder auch hinderlichen Rahmenbedingungen aufgezeigt und diskutiert.
Der Bericht zeigt auf, dass die Wiederverwertung von in der Trinkwasseraufbereitung genutzter Aktivkohle unter bestimmten Rahmenbedingungen für Trinkwasserproduzent und Wiederverwerter (bspw. Abwasserreinigungsanlage) sinnvoll und ökonomisch attraktiv sein kann.
Basierend auf der geführten Diskussion wird den Trinkwasserproduzenten eine Entscheidungsmatrix an die Hand gegeben mit deren Hilfe die Sinnhaftigkeit einer PAK Wiederverwertung bewertet werden kann.
Am Beispiel der Trinkwasseraufbereitungsanlage Muttenz wird ein aktuelles Projekt zur Wiederverwertung von Pulveraktivkohle gezeigt und die bereits getroffenen Massnahmen beschrieben. An Hand der Entscheidungsmatrix und zur besseren Einordnung für den Leser wurde die Situation der TWA Muttenz bewertet.

Fünf bis zehn Gramm Pulveraktivkohle weisen die Oberfläche eines Fussballfeldes auf. Das faszinierende schwarze Pulver kann vielerorts eingesetzt werden, zum Beispiel auf Abwasserreinigungsanlagen, um Mikroverunreinigungen aus dem Abwasser zu eliminieren – und dies immer häufiger. Auf dem Markt sind zahlreiche PAK-Sorten verfügbar, die zwar äusserlich nicht zu unterscheiden sind, aber dennoch unterschiedliche Eigenschaften aufweisen. Dieser Artikel soll Betreiber und Ingenieure bei der Entscheidung unterstützen, welche Pulveraktivkohle für ihr Abwasser optimal ist und wie sie die Qualität neuer Lieferungen überprüfen können.

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.

Microbial biofilms can be both cause and cure to a range of emerging societal problems including antimicrobial tolerance, water sanitation, water scarcity and pollution. The identities of extracellular polymeric substances (EPS) responsible for the establishment and function of biofilms are poorly understood. The lack of information on the chemical and physical identities of EPS limits the potential to rationally engineer biofilm processes, and impedes progress within the water and wastewater sector towards a circular economy and resource recovery. Here, a multidisciplinary roadmap for addressing this EPS identity crisis is proposed. This involves improved EPS extraction and characterization methodologies, cross-referencing between model biofilms and full-scale biofilm systems, and functional description of isolated EPS with in situ techniques (e.g. microscopy) coupled with genomics, proteomics and glycomics. The current extraction and spectrophotometric characterization methods, often based on the principle not to compromise the integrity of the microbial cells, should be critically assessed, and more comprehensive methods for recovery and characterization of EPS need to be developed.

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

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.
 

Die Rückgewinnung von Nährstoffen aus Abwasser wird in der Zukunft aus Gründen der Nachhaltigkeit und zunehmend auch aus Gründen der Wirtschaftlichkeit mehr an Bedeutung gewinnen. Ein derzeit von der Eawag mit verschiedenen Partnern evaluiertes chemisch/physikalisches Verfahren der N-Rückgewinnung über eine Membranstrippung (sogenannte Membrankontaktoren) ist auf einer Kläranlagen in der Westschweiz seit Mitte 2016 erfolgreich im Einsatz. Weitere volltechnische Realisierungen solcher Anlagen stehen in Deutschland und der Schweiz in der Planung oder kurz vor der volltechnischen Umsetzung.
Der Beitrag gibt einen Überblick über den derzeitigen Wissensstand zur Technologie wie die Verfahrensführung, Vorbehandlung, spezifische Verbräuche (Energie, Betriebsstoffe) und Kosten. Neben Ergebnissen aus diversen Pilotversuchen, welche die Eawag mit ihren Partnern durchgeführt hat, wird auch über das EU-Projekt "POWERSTEP" (http://powerstep.eu/case-studies/cs6-altenrhein-switzerland) und über weitere volltechnische Umsetzungen berichtet.

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.

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.

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.

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.

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.

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.

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.

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.

Biochar and activated carbon, both carbonaceous pyrogenic materials, are important products for environmental technology and intensively studied for a multitude of purposes. A strict distinction between these materials is not always possible, and also a generally accepted terminology is lacking. However, research on both materials is increasingly overlapping: sorption and remediation are the domain of activated carbon, which nowadays is also addressed by studies on biochar. Thus, awareness of both fields of research and knowledge about the distinction of biochar and activated carbon is necessary for designing novel research on pyrogenic carbonaceous materials. Here, we describe the dividing ranges and common grounds of biochar, activated carbon and other pyrogenic carbonaceous materials such as charcoal based on their history, definition and production technologies. This review also summarizes thermochemical conversions and non-thermal pre- and post-treatments that are used to produce biochar and activated carbon. Our overview shows that biochar research should take advantage of the numerous techniques of activation and modification to tailor biochars for their intended applications.

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.

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

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, X_carrier 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 X_carrier and associated biofilms, and evaluates the impact that X_carrier 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.

Der vorliegende Bericht fasst die Ergebnisse des Forschungsprojektes "Biologische Nachbehandlung von kommunalem Abwasser nach Ozonung", kurz "ReTREAT", zusammen. Das Projekt wurde durch das Bundesamtes für Umwelt (BAFU) im Rahmen der Umwelttechnologieförderung (UTF) finanziert. Zudem wurde das Projekt durch hohe Eigen- und Cash-Leistungen der Industriepartner finanziell und technisch unterstützt.
Ziel des Projektes war es Untersuchungen zur Leistungsfähigkeit und Effizienz verschiedener Verfahren der biologischen Nachbehandlung zur Reduktion der ökotoxikologischen Wirkung und zur Reduktion von Transformationsprodukten von ozonten, kommunalem Abwassers durchzuführen.

Im Rahmen des Projekts ReTREAT wurden verschiedene Verfahren auf deren Eignung als biologische Nachbehandlung nach einer Ozonung getestet. Der Fokus lag dabei – neben allgemeinen Reinigungseffekten – insbesondere auf dem Abbau von labilen Reaktionsprodukten sowie deren ökotoxikologischen Wirkungen.

Die Rückgewinnung von Nährstoffen aus Abwasser wird in der Zukunft aus Gründen der Nachhaltigkeit und zunehmend auch aus Gründen der Wirtschaftlichkeit mehr an Bedeutung gewinnen. Ein derzeit von der Eawag mit verschiedenen Partnern evaluiertes chemisch/physikalisches Verfahren der N-Rückgewinnung über eine Membranstrippung (sogenannte Membrankontaktoren) ist auf einer Kläranlagen in der Westschweiz seit Mitte 2016 erfolgreich im Einsatz. Weitere volltechnische Realisierungen solcher Anlagen stehen in Deutschland und der Schweiz in der Planung oder kurz vor der volltechnischen Umsetzung.
Der Beitrag gibt einen Überblick über den derzeitigen Wissensstand zur Technologie wie die Verfahrensführung, Vorbehandlung, spezifische Verbräuche (Energie, Betriebsstoffe) und Kosten. Neben Ergebnissen aus diversen Pilotversuchen, welche die Eawag mit ihren Partnern durchgeführt hat, wird auch über das EU-Projekt "POWERSTEP" (http://powerstep.eu/case-studies/cs6-altenrhein-switzerland) und über weitere volltechnische Umsetzungen berichtet.

Die Rückgewinnung von Nährstoffen aus Abwasser wird in der Zukunft aus Gründen der Nachhaltigkeit und zunehmend auch aus Gründen der Wirtschaftlichkeit mehr an Bedeutung gewinnen. Ein derzeit von der Eawag mit verschiedenen Partnern evaluiertes chemisch/physikalisches Verfahren der N-Rückgewinnung über eine Membranstrippung (sogenannte Membrankontaktoren) ist auf einer Kläranlagen in der Westschweiz seit Mitte 2016 erfolgreich im Einsatz. Weitere volltechnische Realisierungen solcher Anlagen stehen in Deutschland und der Schweiz in der Planung oder kurz vor der volltechnischen Umsetzung. Der Beitrag gibt einen Überblick über den derzeitigen Wissensstand zur Technologie

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.

To this day, obtaining reliable characterization of sludge settling properties remains a challenging and time-consuming task. Without such assessments however, optimal design and operation of secondary settling tanks is challenging and conservative approaches will remain necessary. With this study, we show that automated sludge blanket height registration and zone settling velocity estimation is possible thanks to analysis of images taken during batch settling experiments. The experimental setup is particularly interesting for practical applications as it consists of off-the-shelf components only, no moving parts are required, and the software is released publicly. Furthermore, the proposed multivariate shape constrained spline model for image analysis appears to be a promising method for reliable sludge blanket height profile registration.

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.

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 (V_WW) 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 g_TSS⁻¹ was observed either at very low (1 m h⁻¹) or at high V_WW (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 V_WW 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 V_WW 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 (V_WW 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.

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.

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.

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 (X_U) (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.

Traditionally, chemical and physical methods have been used to control biofouling on membranes by inactivating and removing the biofouling layer. Alternatively, the permeability can be increased using biological methods while accepting the presence of the biofouling layer. We have investigated two different types of metazoans for this purpose, the oligochaete Aelosoma hemprichi and the nematode Plectus aquatilis. The addition of these grazing metazoans in biofilm-controlled membrane systems resulted in a flux increase of 50% in presence of the oligochaetes (Aelosoma hemprichi), and a flux increase of 119–164% in presence of the nematodes (Plectus aquatilis) in comparison to the control system operated without metazoans. The change in flux resulted from (1) a change in the biofilm structure, from a homogeneous, cake-like biofilm to a more heterogeneous, porous structure and (2) a significant reduction in the thickness of the basal layer. Pyrosequencing data showed that due to the addition of the predators, also the community composition of the biofilm in terms of protists and bacteria was strongly affected. The results have implications for a range of membrane processes, including ultrafiltration for potable water production, membrane bioreactors and reverse osmosis.

Stickstoffelimination im Seitenstrom – damit beschäftigen sich aktuell zwei Fallstudien im Rahmen von PowerStep: Prof. Dr.-Ing. Jörg Krampe (Vorstand des Forschungsbereiches Wassergütewirtschaft des Instituts für Wassergüte, Ressourcenmanagement und Abfallwirtschaft der Technischen Universität Wien) arbeitet dazu an der Case Study 5 in Zusammenarbeit mit dem Abwasserverband Wörgl-Kirchbichl an der Kläranlage Kirchbichl in Österreich (100 000 EW); Auf der Kläranlage Altenrhein in der Schweiz (120 000 EW) ist Marc Böhler (Eidgenössische Anstalt für Wasserversorgung, Abwasserreinigung und Gewässerschutz, Eawag) zusammen mit dem Abwasserverband Altenrhein für die Case Study 6 verantwortlich. Im Interview mit gwf-Wasser | Abwasser sprechen Prof. Dr.-Ing. Jörg Krampe und Marc Böhler über ihre Hintergründe, Aussichten und Ziele.

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

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.

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 g_COD.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 g_O2.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.

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.

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

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.

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). [...]

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.

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.

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.

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 mg_O2l^-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 mg_O2l^-1 and completely taken up and intracellular stored acetate of 100 mg_CODl^-1. An average SND efficiency of 26.4±13.6 % was reached therefore.
Denitrification rates of 1.22±0.16 mg_N∙g_VSS^-1∙h^-1 (Case 1) and 0.89±0.05 mg_N∙g_VSS^-1∙h^-1 (Case 2) were observed.
The fraction of large granules (d>0.63 mm) of only 10 % by weight (g_VSS) 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.

The formation and application of aerobic granules for the treatment of real wastewaters still remains challenging. The high fraction of particulate organic matter (X_S) present in real wastewaters can affect the granulation process. The present study aims at understanding to what extent the presence of X_S 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 X_S. Two reactors fed with synthetic wastewaters were operated in absence (R1) or presence (R2) of starch as proxy for X_S. Different operating conditions were evaluated. Our results indicated that the presence of X_S 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 X_S 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 X_S, the selection pressure should be significantly reduced.

Ozone transforms various organic compounds that absorb light within the UV and visible spectra. UV absorbance can therefore be used to detect the transformation of chemicals during ozonation. In wastewater, decolourisation can be observed after ozonation. This study investigates the correlation of the UV absorbance difference between the ozonation inlet and outlet and the removal efficiency of micropollutants in wastewater. The absorbance at 254 and 366 nm was measured at the ozonation inlet and outlet, as was the concentration of 24 representative micropollutants and the dissolved organic carbon (DOC). The results clearly showed that the relative decrease of absorbance (ΔAbs) is positively correlated with the relative removal efficiency of micropollutants. We therefore suggest that UV absorbance can be used as a feedback control parameter to achieve optimal ozone dosage in wastewater treatment plants and to gain a fast insight into the process efficiency and stability of the ozonation.

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.

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 d_0.5 = 3.6 μm) or larger (kaolin with diatomaceous earth 50/50%, d_0.5 = 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.

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.

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.

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.

Wastewater pH affects the transfer of H₂S from liquid to gas and hence impacts on the extent of odour and corrosion. Sewage pH may change significantly in sewer networks due to, for example, the fermentation of organic compounds, particularly when the hydraulic retention time is long, the discharge of trade wastes that are organic-rich or with extreme pH, and the intentional addition of alkali to raise the sewage pH. Such a variation of pH is expected to affect sulfate reduction by sewer biofilms. In this work, experimental studies were carried out to reveal the detailed effects of pH on sulfidogenesis by anaerobic sewer biofilms developed in a laboratory sewer reactor fed with real sewage, and the potential causes for the inhibitory effects observed under both high and low pH conditions. The data clearly showed that the sewer biofilm had the highest sulfate reduction rate at around neutral pH (6.5–7.5), and the activity decreased when pH was higher or lower. The data also suggested that the inhibiting effect at a higher pH is likely due to the inhibitory effects of free ammonia, while at a lower pH it is more likely due to the pH itself. An inhibition model formulated based on the above hypotheses was able to adequately describe the measured sulfide production rates under different pH levels and different free ammonia concentrations, as well as data previously reported in literature. The calibrated model was used to simulate sulfide production in a sewer network receiving alkali dosage. The model adequately predicted sulfide production in the network, which could not be achieved with a model not considering the pH effect.

ROUTES is addressed to assess new routes in wastewater and sludge treatment focusing on three main objectives:
1. optimization of the sludge quality for agricultural use with the goal to produce a clean and full stabilized sludge through intensive stabilization processes with attention to a broad spectrum of parameters including micropollutants, pathogens and their indicators.
2. minimization of the sludge to be disposed by innovative technical solutions based on different approaches, either on the water or sludge treatment lines;
3. recovery of valuable resources before sludge disposal by producing a liquid fertilizer [(NH₄)₂SO₄], biopolymers or optimizing methane production by anaerobic treatments.
Technical and economic assessment of the investigated techniques on laboratory and pilot scale were carried out in a typical benchmarking study. The whole set of data is then provided to the partner involved in environmental assessment where different impact categories are considered (global warming potential, acidification potential, eutrophication potential and photochemical ozone creation potential).

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. [...]

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.

This study aims at evaluating the mechanisms of biofilm detachment with regard of the physical properties of the biofilm. Biofilms were developed in Couette–Taylor reactor under controlled hydrodynamic conditions and under different environmental growth conditions. Five different conditions were tested and lead to the formation of two aerobic heterotrophic biofilms (aeHB1 and aeHB2), a mixed autotrophic and heterotrophic biofilm (MAHB) and two anoxic heterotrophic biofilms (anHB1 and anHB2). Biofilm detachment was evaluated by monitoring the size of the detached particles (using light-scattering) as well as the biofilm physical properties (using CCD camera and image analysis). Results indicate that volume erosion of large biofilm particles with size ranging from 50 to 500 μm dominated the biomass loss for all biofilms. Surface erosion of small particles with size lower than 20 μm dominates biofilm detachment in number. The extent of the volume detachment events was governed by the size of the biofilm surface heterogeneities (i.e., the absolute biofilm roughness) but never impacted more than 80% of the mean biofilm thickness due to the highly cohesive basal layer. Anoxic biofilms were smoother and thinner than aerobic biofilms and thus associated with the detachment of smaller particles. Our results contradict the simplifying assumption of surface detachment that is considered in many biofilm models and suggest that discrete volume events should be considered.

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 (k_d) 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 k_d 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.

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.

A novel ammonia stripping method, including a CO₂ pre-stripper was used to treat a mix of supernatant liquor from an anaerobic digester and urine in order to recycle nitrogen as ammonium sulfate at full-scale in the WWTP Kloten/Opfikon. Waste streams were not generated, since the ammonia was recovered as a marketable nitrogen fertilizer, turning a waste product into a valuable product. The efficiency of this system was increased by means of the addition of pre-treated urine collected separately at EAWAG building. The separation step was performed by the use of water free urinals and urine diversion flush toilets. An increase of 10% in the liquid flux with the addition of the urine translated into a 40% increase of the ammonia concentration in the inlet of the stripping unit. The achievement of these percentages generated a proportional increase in the fertilizer production. The urine pre-treatment was carried out by adding magnesium to produce a precipitate of struvite. The first experiments with the combined treatment showed the feasibility of the combination of the separation and pre-treatment steps.

Micropollutants (MP) are only partly removed from municipal wastewater by nutrient removal plants and are seen increasingly as a threat to aquatic ecosystems and to the safety of drinking water resources. The addition of powder activated carbon (PAC) is a promising technology to complement municipal nutrient removal plants in order to achieve a significant reduction of MPs and ecotoxicity in receiving waters. This paper presents the salient outcomes of pilot- and full-scale applications of PAC addition in different flow schemes for micropollutant removal in municipal wastewater treatment plants (WWTPs). The sorption efficiency of PAC is reduced with increasing dissolved organic carbon (DOC). Adequate treatment of secondary effluent with 5–10 g DOC m⁻³ requires 10–20 g PAC m⁻³ of effluent. Counter-current use of PAC by recycling waste PAC from post-treatment in a contact tank with an additional clarifier to the biology tank improved the overall MP removal by 10 to 50% compared with effluent PAC application alone. A dosage of 15 g PAC m⁻³ to a full-scale flocculation sand filtration system and recycling the backwash water to the biology tank showed similar MP elimination. Due to an adequate mixing regime and the addition of adapted flocculants, a good retention of the fine fraction of the PAC in the deep-bed filter were observed (1–3 g TSS m⁻³; TSS: total suspended solids). With double use of PAC, only half of the PAC was required to reach MP removal efficiencies similar to the direct single dosage of PAC to the biology tank. Overall, the application of PAC in WWTPs seems to be an adequate and feasible technology for efficient MP elimination (>80%) from wastewater comparable with post ozonation.

Auf der Kläranlage Kloten/Opfikon wurde erstmals in der Schweiz das Verfahren der Luftstrippung zur Stickstoffrückgewinnung aus Faulwasser volltechnisch umgesetzt. Das Verfahren beinhaltet neben der Ammoniakstrippung eine Faulwasservorbehandlung in Form eines CO2-Strippers, welche eine 50%ige Reduktion des Laugenbedarfs erlaubt und eine deutliche Effizienzsteigerung des nachhaltigen Verfahrens erbringt. Die Idee der vorgängigen CO2-Strippung zur pH-Wert-Anhebung wurde von der Eawag entwickelt und ist grosstechnisch einzigartig.

Die vorliegende Berichterstattung gibt Auskunft über weitergehende Untersuchungen und Abklärungen in Zusammenhang mit der Elimination von Mikroverunreinigungen auf der ARA Neugut.
Im Kontext mit einer notwendigen biologischen Nachbehandlung von ozontem Abwasser wurde in 2012 eine Abwasserfiltration mit granulierter Aktivkohle in den Versuchseinrichtungen der Eawag betrieben. Neben dem Beladungsverhalten bezüglich DOC und Mikroverunreinigungen wurde auch die Praxistauglichkeit einer derartigen Filtration evaluiert, nämlich in wieweit auf Basis der vorhandenen Infrastrukturen bestehender Sandfiltrationen eine derartige GAK-Filtration möglich ist. [...]

Die Rückgewinnung von Nährstoffen aus Abwasser wird in der Zukunft aus Gründen der Nachhaltigkeit und zunehmend auch aus wirtschaftlichen Gründen mehr an Bedeutung gewinnen. Die Luft- und Dampfstrippung sind bis heute die einzigen volltechnischen Verfahren mit dem Stickstoff aus Prozessabwässern rückgewonnen werden kann, da in den biologischen Verfahren der Stickstoff durch Denitrifikation in die Atmosphäre verloren geht. Ein von der Eawag mit Partnern derzeit ebenfalls evaluiertes drittes Verfahren der N-Rückgewinnung über eine Membranstrippung steht bisher erst kurz vor einer volltechnischen Realisierung, sodass mit dieser Technologie noch keine Praxiserfahrungen und Daten zur Verfügung stehen.
Auf der Kläranlage Kloten/Opfikon wurde zum ersten mal in der Schweiz das Verfahren der Luftstrippung zur Stickstoffrückgewinnung aus Faulwasser volltechnisch umgesetzt. Das Verfahren beinhaltet neben der Ammoniakstrippung zudem eine Faulwasservorbehandlung in Form eines CO₂-Strippers, welche eine 50%-tige Reduktion des Laugebedarfs erlaubt und eine deutliche Effizienzsteigerung des nachhaltigen Verfahrens erbringt. Die Idee der vorgängigen CO₂-Strippung zur pH-Wert-Anhebung wurde von der Eawag entwickelt und ist grosstechnisch einzigartig. Das Produkt des Verfahrens ist ein in der Landwirtschaft nachgefragter Flüssigdünger, der nun von der Kläranlage vermarktet wird. Das vorliegende Manuskript berichtet über die Erfahrungen beider Inbetriebnahme und über die Betriebsresultate nach nun mehr als 1-jährigem Betrieb.
Im Rahmen einer Kostenstudie wurden zudem verschiedene Behandlungsverfahren gegenübergestellt. Hier zeigt sich, das vor der Wahl eines geeigneten Verfahrens die individuellen Rahmenbedingungen auf der Kläranlage abgeklärt sein sollten, bevor ein Entscheid für ein Verfahren getroffen werden kann. Die spezifischen baulichen, verfahrenstechnischen und betrieblichen Bedingungen der betrachteten Kläranlagen können grossen Einfluss auf die Ergebnisse des Variantenstudiums haben.
Im vorgestellten Variantenvergleich zeigt sich, dass heute die Stickstoffrückgewinnung via Luftstrippung oder Membranstrippung bezüglich der Jahreskosten unwesentlich höher ausfällt, als das kostengünstige Nitritations/Anammox-Verfahren, bei dem der Stickstoff verloren geht. Zudem konnte aufgezeigt werden, dass die Mehrinvestitionskosten für eine vorgängige CO₂-Strippung durch geringere Betriebskosten - bedingt durch die Laugeneinsparung - kompensiert werden können.

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.

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.

Nach einer verfahrenstechnischen Optimierung zur direkten Dosierung von Aktivkohle vor der Filtration in einer halbtechnischen Pilotanlage der Eawag konnte in einer zweiten grosstechnischen Anwendung auf der Kläranlage Kloten/Opfikon eine effiziente und hinreichende Spurenstoffelimination über 9 Wochen vollzogen werden.
Zentral in dieser Verfahrensvariante ist die weitestgehende Abtrennung der dosierten Pulveraktivkohle vom gereinigten Abwasser. In der Dosierzeit konnte die feine PAK effizient im Filtermedium zurückgehalten werden. Im Vergleich zur Referenzstrasse erhöhten sich die AFS-Ablaufwerte um rd. 1 - 2 mgAFS/L, lagen jedoch durchgehend deutlich unter dem geforderten Grenzwert von 5 mgAFS/l. [...]

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.

Micropollutants in Wastewater Treatment Plants. Technologies to Eliminate Organic Trace Contaminants. Today’s mechanical-biological treatment plants only inadequately remove organic micropollutants. Advanced technologies are necessary such as ozonation or adsorption on powdered active carbon (PAC) in order to increase removal capacity. These two techniques are being evaluated in various tests on the laboratory level, but also on a large scale. Both ozonation and PA C adsorption are suitable for reducing the emission of organic trace elements from settlement drainage systems into the various bodies of water. This article presents the current knowledge of both technologies for application in municipal wastewater treatment systems.

Analytical methods, compound occurrence and transformation products
The palette of analytical methods available for analyzing micropollutants in wastewater covers a wide variety of compounds: 152 compounds belonging to 16 different classes were applied within this project. Of relevance due to their occurrence and toxic potency are the new methods developed for biocides, UV-filters, benzothiazoles and antivirals: the majority persist wastewater treatment and many are found in surface waters at concentrations justifying more attention within the micropollutant discussion.
A major break through of the project is the development of methods for systematic transformation product identification. These are applicable for biological degradation as well as for chemical oxidative treatment. [...]

Der vorliegende Abschlussbericht des Micropoll-Teilprojektes zur Elimination von Spurenstoffen aus kommunalem Abwasser mittels Pulveraktivkohle (PAK) fasst die zentralen Ergebnisse der Pilotierungen und Einzelversuche aller Projektphasen der letzten drei Jahren zusammen.
Hauptziel des Projektes war es durch den Betrieb von halbtechnischen Pilotanlagen und zielgerichteten Einzeluntersuchungen weitere Klärung und Erfahrungen zum Einsatz von Aktivkohle zur Spurenstoffelimination in der kommunalen Abwasserbehandlung zu liefern. Während der ersten Projektphase wurden im Wesentlichen Grundlagen evaluiert (1. - 2. Zwischenbericht), während in den Versuchsphasen zwei und drei empirische und praxisorientierte Untersuchungen vorgenommen wurden. [...]

The suitability of two membrane bioreactors for on-site wastewater treatment and reuse in Switzerland was investigated. The treated wastewater was used for toilet flushing and gardening, with water recycling rates of 30% (single family house) and almost 100% (toilets in a cable car station) respectively. Due to the recycling, an increase in a natural yellowish-brown color was observed, leading to double flushing of the toilets, higher cleaning requirements and increased permeate production. Color removal with ozone, powdered (PAC) and granulated (GAC) activated carbon was assessed in laboratory and field experiments. PAC was added directly into the MBR, whereas ozonation and GAC were applied to the permeate. The dosage of ozone or activated carbon depended on the recycling rate and color intensity. If color removal is necessary, PAC is the option best suited to small treatment plants, with a requirement of 30–50 g m^-3 for 30% and 100 g m^-3 for 100% water recycling.

Die chemische Fällung des gelösten Phosphors des Abwassers ist ein effizienter und zentraler Prozess in der Abwasserbehandlung zur Erreichung weitergehender Ziele in der Nährstoffelimination und ist heute etablierter Verfahrensbestandteil auf den meisten Abwasserreinigungsanlagen in Europa.

Da Phosphor ein essentieller Nährstoff ist und durch Phosphor die Eutrophierung von Gewässern gesteuert wird, wurde in der Schweiz neben dem Phosphorverbot in Waschmitteln intensiv an einer Optimierung der konventionellen Fällung geforscht und neue Technologien entwickelt. Hierzu gehören die Technologie der Zwei-Punkt-Fällung und die der kostenintensiveren und betrieblich aufwendigeren Flockungsfiltration.

Ziel ist es punktförmige Phosphoremissionen durch Kläranlagen in Fliessgewässern in Seeeinzugsgebieten und den Seen selbst zu minimieren. Dieses Ziel äussert sich in einer Gesetzgebung mit im EU-Vergleich sehr tiefen Grenzwerten. Gemäss Gewässerschutzverordnung der Schweiz von 1998 haben alle Kläranlagen im Einzugsgebiet der Seen und Kläranlagen ab 10.000 EW unterhalb der Seen eine Ablaufkonzentration bezüglich Gesamt-P von 0.8 gP_tot/m³ einzuhalten. Es ist insgesamt eine Elimination von 80% der Gesamt-P-Rohabwasserfracht zu erreichen. Diese Auflage kann kantonal verschärft werden, so dass in der Praxis alle Kläranlagen im direkten Einzugsgebiet der Seen verschärfte Auflagen haben (z. Bsp. der Zürichsee mit 0.2 gP_tot/m³ oder der Bodensee mit der Bodenseerichtlinie geltend für alle Anrainer mit 0.3 gP_tot/m³).

Das vorliegende Manuskript führt in die allgemeinen Grundlagen und Technik der Phosphorelimination mittels konventioneller Fälltechnik ein. Hierbei wird im besonderen Masse auf die Dimensionierung und Auslegung der Zwei-Punkt-Fällung eingegangen, da diese eine für viele Kläranlagen der Schweiz geeignete Technologie ist, die seit vielen Jahren bestehenden Zielvorgaben zu erfüllen.

Ein Überblick über die langjährige Praxis mittels Fallbeispielen der chemischen Phosphat-Elimination in der Schweiz zeigt auf, dass die oben genannten Einleitwerte sowohl mit einer Intensivierung der konventionellen Fällung durch erhöhte Fällmittelgaben als auch mit einer Fällmittel sparenden Zwei-Punkt-Fällung im Vergleich zur Flockungsfiltration gut erreicht werden können.

Reliable and efficient operation of membrane bioreactors (MBR) for centralized municipal wastewater treatment strongly depends on a good monitoring of the membrane permeability, a value often used to quantify the transmissibility (i.e. the inverse of the flow resistance) of the membrane. By directly or indirectly evaluating this parameter the operator normally plans on the necessity and effectivity of maintenance activities. To allow the operator monitoring the membrane performance closely, the present paper proposes a method for online permeability based on the measurements of permeate flow, transmembrane pressure and water temperature. The theoretical background of the method is discussed and a data set of 250 days of continuous pilot operation of a municipal MBR equipped with three different standard membrane modules is used for testing. The method is numerically simple enough to allow being implemented on any programmable logical controller.

Das vorliegende Gutachten beschreibt die technischen Möglichkeiten und das Potential zur weiteren Reduktion der Phosphoremissionen durch chemische Fällung auf Kläranlagen im Bundesland Hessen. In der Betrachtung stehen nur Kläranlagen, welche bereits eine Phosphorelimination betreiben. Zudem werden neben den Effekten dieser erhöhten chemischen Elimination auch die zu erwartenden Kosten für den Kläranlagenbetrieb abgeschätzt.

Für die Berechnung des Potenzials wurde für eine Beispielrechnung als maximale Gesamt-Phosphorkonzentration 0.5 gP_tot/m³ im Ablauf der Kläranlagen angesetzt. Dieses Qualitätsziel beinhaltet im Mittel einen Orthophosphatgehalt von 0.15 gPO4-P/l. Die weiteren Anteile im genannten Qualitätsziel ergeben sich aus dem nicht fällbaren gelösten Anteil (0.05 bis 0.1 g/m³) und aus dem partikulär gebundenen Anteil im Feststoffabtrieb der Kläranlagen (etwa 0.25 gP/m³). Da die zuletzt genannten Fraktionen aufgrund der spezifischen Randbedingungen des Einzugsgebietes bzw. der Kläranlage selbst schwanken können, kann anteilig die Orthophosphatkonzentration bei gleichzeitiger Einhaltung des gewählten Qualitätszieles ebenfalls variieren.

Die für die Berechnungen zu Grunde gelegten Ausgangsdaten entstammen zum einen aus der Datenbank des Landes Hessen. Zu anderen basieren diese auf den allgemein anerkannten Regeln der Technik oder auf Erfahrungswerten durch die langjährige Anwendung der vorgestellten Technologien.

Das den Berechnungen zur Abschätzung der zusätzlichen Fällmittelmengen und der anfallenden Fällschlammmengen zu Grunde gelegte molare Verhältnis vom einzusetzenden Fällmittel zum zu fällenden Phosphat wurde durch Gewichtung der Frachten, welche aus dem Mittel der Zu- und Ablaufkonzentrationen der Gesamtkläranlagen resultiert, ermittelt. Anschliessend wurden die entsprechenden Mengen für jede einzelne Kläranlage errechnet. Die Bemessung erfolgt über den gelösten Anteil der Phosphorfrachten und basiert auf der Bemessungsgrundlage nach Siegrist und Boller.

The disposal of sewage sludge and the agricultural use of stabilised sludge are decreasing due to more stringent regulations in Europe. An increasing fraction of sewage sludge must,therefore be dewatered, dried, incinerated and the ashes disposed of in landfills. These processes are cost-intensive and also lead to the loss of the valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Partial ozonation of the return sludge of an activated sludge system significantly reduces excess sludge production, improves the settling properties of the sludge and reduces bulking and scumming. The solubilised COD will also improve denitrification if the treated sludge is recycled to the anoxic zone. However, ozonation partly kills nitrifiers and could therefore lead to a decrease of the effective solid retention time of the nitrifier, thus reducing the safety of the nitrification. This paper discusses the effect of ozonation on sludge reduction, the operating stability of nitrification, the improvement of denitrification and also presents an energy and cost evaluation.

Toilet wastewater is treated and reused on site at Europe's highest membrane bioreactor (MBR), located in a cable car mountain station in the ski resort of Zermatt. Negative impacts on the sensitive mountain environment are minimised by reusing close to 100% of the treated wastewater for toilet flushing. Besides 100% nitrogen removal, 80% of phosphorus was also eliminated. This paper presents operational results, optimisations of sludge management, decoloration and long-term maintenance of biomass in the very low-loaded summer season. From a global view the experiences and results of the project are of great importance, proposing a solution to a problem existing 100-fold in the Alps as well as in and regions all over the world: reducing water consumption for sanitation by reuse.

The disposal of sewage sludge and the agricultural use of stabilized sludge are decreasing due to more stringent regulations in Europe. An increasing fraction of sewage sludge must therefore be dewatered, dried, incinerated and the ashes disposed of in landfills. These processes are cost-intensive and also lead to the loss of the valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Disintegration of biological sludge by mechanical, thermal and physical methods could significantly reduce excess sludge production, improve the settling properties of the sludge and reduce bulking and scumming. The solubilized COD could also improve denitrification if the treated sludge is recycled to the anoxic zone. However, disintegration partly inhibits and kills nitrifiers and could therefore shorten their effective solid retention time, thus reducing the safety of the nitrification. This paper discusses the potential of disintegration on sludge reduction, the operating stability of nitrification, the improvement of denitrification and also presents an energy and cost evaluation.

In future, it will be necessary to incinerate an increasing proportion of the sludge produced by public wastewater treatment. In this context, equipment for more effective dewatering of sewage sludge is required. A hydraulic press system (Bucher HP) which has been used to date in the food industry could represent an alternative to the sludge dewatering systems currently used. The basic suitability of this press system was demonstrated in comprehensive industrial-scale trials at the Glarnerland STP (Switzerland). Dry solids contents of up to 43% were measured in the pressed sludge. Currently, the optimization of individual process parameters is being investigated in a pilot plant at the Schwelm STP operated by Wupperverband (Germany).

Energie- und Stoffbilanzen in der Schlammbehandlung sind ein effizientes Werkzeug zur Beurteilung betrieblicher und wirtschaftlicher Aspekte sowohl in der Praxis aber auch im Bereich der Planung neuer Behandlungsanlagen. Insbesondere vor dem Hintergrund, dass in grossen Abwasserreinigungsanlagen heute die Betriebskosten für die Schlamm-behandlung und -entsorgung rd. 30 bis 40% der gesamten Betriebskosten ausmachen können und ein hoher baulicher wie maschineller Aufwand nötig ist, um die Infrastruktur bereitzustellen (Lindtner, 2004), wird eine detaillierte Betrachtung bedeutend.
Im Mittelpunkt der Betrachtung steht das Verfahren der anaeroben Stabilisierung, welche vielfach als zweistufige, mesophile Schlammfaulung auf den Schweizer Abwasserreinigungsanlagen realisiert ist. Neben den wesentlichen Grundlagen zur Einführung in die Thematik werden praktische Beispiele mit Übungen für Massen- und Energieflüsse in der Schlammbehandlung vorgestellt. Die Effekte der Desintegration auf die Energie- und Stoffflüsse in der Schlammbehandlung werden aufgezeigt.

Disposal of sewage sludge is forbidden and agricultural use of stabilized sludge will be banned in 2005 in Switzerland. The sludge has to be dewatered, dried, incinerated and the ashes disposed in landfills. These processes are cost intensive and lead also to the loss of valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Partial ozonation of the return sludge of an activated sludge system reduces significantly excess sludge production, improves settling properties of the sludge and reduces bulking and scumming. The solubilized COD will also improve denitrification if the treated sludge is recycled to the anoxic zone. But ozonation will partly inhibit and kill nitrifiers and might therefore lead to a decrease of the effective solid retention time of the nitrifier, which reduces the safety of the nitrification. This paper discusses the effect of ozonation on sludge reduction, the operation stability of nitrification, improvement of denitrification and gives also an energy and cost evaluation.

Die biologische Abwasserreinigung kommunaler und gewerblicher Abwässer wird heute vorwiegend durch das Belebungsverfahren vollzogen. Der im Rahmen dieses Prozesses anfallende Überschussschlamm wird in aufwendigen Verfahren entwässert, getrocknet, verbrannt und deponiert, die landwirtschaftliche Nutzung entfällt in Zukunft. Ab 2005 wird gemäss neuen gesetzlichen Auflagen nur noch der Entsorgungspfad der Verbrennung in der Schweiz zur Verfügung stehen (BUWAL, 2001, BLW, 2003), welcher als kostenintensivster anzusehen ist. Vor diesem Hintergrund gewinnt die Verfügbarkeit von zweckdienlichen Informationen über Möglichkeiten der Reduktion bei Entstehung und Entsorgung grosse Bedeutung.
Untersuchungen haben ergeben, dass durch eine gezielte Desintegration von Belebtschlamm und bei Rückführung dieses Schlammes in die Biologie eine Reduktion der Mengen erreicht werden kann. Neben der Schlammminimierung können auch andere positive Einflüsse auf die Nährstoffelimination und den gesamten Betrieb der ARA selbst beobachtet werden.
Zur Desintegration von Klärschlamm stehen unterschiedliche Technologien zur Verfügung. Aktuelle grosstechnische Praxisuntersuchungen auf Kläranlagen und Detailuntersuchungen im Labormassstab haben gezeigt, dass zur Desintegration von Belebtschlamm besonders die Desintegration durch Ozonierung (Yasui et al., 1994, Ried et al., 2002, Böhler und Siegrist, 2003), bzw. die Behandlung mit Ultraschall (Diehm et al., 2004, Eder und Günther, 2003, AVT, 2003) geeignet sind.
Der vorliegende Beitrag verschafft einen Überblick über die Effekte dieser Verfahren bei Einsatz in der Belebung. Im Vordergrund stehen die Auswirkungen auf die Nährstoffelimination, wobei auch eine Betrachtung der betrieblichen Aspekte erfolgt. Neben dem Schwerpunkt der Ozonierung und der Ultraschallbehandlung von Belebtschlamm wird die Möglichkeit der Desintegration mittels Enzymen vorgestellt. Ein aktuelles Fallbeispiel für den Einsatz von Enzymen in der Klärschlammfaulung auf einer Schweizer Kläranlage zeigt die Wirkungen einer biochemischen Desintegration auf.

Nicht kontrollierte Online-Messtechnik auf Kläranlagen birgt die Gefahr nicht entdeckter systematischer Fehler, die zu Fehlentscheidungen oder gar schwerwiegenden Sicherheitsproblemen führen können. Es wird ein Ansatz vorgestellt, der es dem zuständigen Personal ermöglicht, die eingesetzten Messgeräte zu kontrollieren, ,,Ausser-Kontrolle-Situationen" zu erkennen und geeignete Massnahmen zu ergreifen. Werden keine systematischen Fehler identifiziert, sollte die Genauigkeit der Messkette bestimmt werden. Hierzu wird ein Konzept vorgeschlagen, das die Messung im Betrieb charakterisiert und so die benötigten Informationen z.B. für die optimale Parametrisierung eines Reglers bereitstellt.

Zur Kontrolle von Online-Messgeräten sollte in regelmässigen Abständen eine Überprüfung mit Labormethoden erfolgen. Eine statistische und grafische Auswertung gibt eine klare Übersicht über den Verlauf der Kontroll-Messungen und ermöglicht ein schnelles Reagieren auf Fehlmessungen. Eine signifikante Abweichung vom kalibrierten Grundzustand wird als Indikator für das Auftreten eines extremen Ausreissers oder einer systematischen Änderung der Messbedingungen interpretiert. Das zweistufige Konzept unterscheidet Warnmeldungen und Alarmmeldungen. Warnmeldungen werden aufgrund erster Hinweise auf Fehlmessungen angezeigt und sollen verstärkte Kontrollen bzw. Wartungsaktionen veranlassen. Alarmmeldungen basieren auf strengeren Kriterien und bestätigen eine vermutete Ausser-Kontrolle-Situation

This paper presents the results of full-scale waste water treatment plant (WWTP) sludge dewatering trials using a Bucher de-juicing press model HP2500 (Boehler et al., 2003). Besides digested sludge from the WWTP at Glarnerland sludge from five other WWTP's was also dewatered. The investigations show that with hydraulic system tested dry solids (DS) contents of 32-41% (with a throughput of approximately 5 m³ h^-1) could be reached. With extended cycle / batch time DS contents of up to 43.5% could be achieved. Dewatering trials with raw sludge (not putrefied) from two different WWTP's resulted in DS content of 35% and 41%. The dosage of coagulant aids, particle size distribution and volatile suspended solids (VSS) have a significant influence on the dewatering results. An economic efficiency calculation is presented with direct comparison to a centrifuge used at the WWTP. Return of investment is expected to be achieved within 3 years.

Der vorliegende Schlussbericht fasst die Ergebnisse der Untersuchungen auf der ARA Glarnerland zur Entwässerung von Klärschlamm mittels einer Fruchtpresse zusammen. Er ersetzt den Zwischenbericht von Ende 2002.
Neben der Dokumentation der Praxisuntersuchungen werden die wesentlichen Grundlagen zur Einführung in die Thematik und zur besseren Einordnung der Ergebnisse genannt. Die Entwässerungsversuche auf der ARA Glarnerland des Abwasserverbandes Glarnerland mit einer HP2500 Fruchtpresse der Firma Bucher Guyer AG bzw. der Bucher Foodtech haben gezeigt, dass mit dem für die maschinelle Klärschlammentwässerung neuen System eine Schlammentwässerung vorteilhaft ist.
In einer ersten Phase des Projektes wurden Pressparameter ermittelt, welche einen sicheren und stabilen Prozess der Entwässerung gewährleisten. In einer weiteren Phase wurden Optimierungen bezüglich des Betriebes und des Systems selbst (Drainagesystem) vorgenommen. [...]

This final report presents the results of full-scale waste water treatment plant (WWTP) sludge dewatering trials using a Bucher de-juicing press model HP2500. Besides digested sludge from the WWTP at Glarnerland, Sludge from five other WWTP’s was also dewatered. The investigations show that with hydraulic system tested dry solids (DS) contents of 32-41% (with a throughput of approximately 5 m3 h-1) could be reached. With extended cycle / batch time DS contents of up to 43.5% could be achieved. Dewatering trials with raw sludge (not putrefied) from two different WWTP’s resulted in DS content of 35% and 41%. The dosage of coagulant aids, particle size distribution and volatile suspended solids (VSS) have a significant influence on the dewatering results. An economic efficiency calculation is presented with direct comparison to a centrifuge used at the WWTP. Return of investment is expected to be achieved within 3 years.

Overall nitrogen elimination in wastewater treatment plants can be improved by separate treatment of the ammonium rich sludge digester effluents. In this report special attention is paid to anaerobic ammonium oxidation. In a first aerobic reactor about 50 % of the ammonium is oxidized to nitrite (partial nitritation), and this is subsequently reduced anaerobically to nitrogen gas using the remaining ammonium as an electron donor (anammox). This sustainable as well as costeffective reactor combination was tested over months at pilot scale resulting in 85–90 % nitrogen removal without addition of any external carbon source.

To ensure correctly operating control systems, the measurement and control equipment in WWTPs must be mutually consistent. The dynamic simulation of activated sludge systems could offer a suitable tool for designing and optimising control strategies. Ideal or simplified sensor models represent a limiting factor for comparability with field applications. More realistic sensor models are therefore required. Two groups of sensor models are proposed on the basis of field and laboratory tests: one for specific sensors and another for a classification of sensor types to be used with the COST simulation benchmark environment. This should lead to a more realistic test environment and allow control engineers to define the requirements of the measuring equipment as a function of the selected control strategy.

Zur Oxidation von Ammonium sind bis anhin nur aerobe Systeme in Betracht gezogen worden. Vor einigen Jahren liess sich in einem denitrifizierenden Fliessbett-Reaktor beobachten, dass Ammonium bei ammoniumreichen Abwässern auch unter anoxischen Bedingungen oxidiert wird (Mulder et al., 1995). Anderseits konnte man bei belüfteten Tauchtropfkörpern, wo wenig bis kein organischer Kohlenstoff im Abwasser vorhanden war, eine beträchtliche Ammoniumelimination feststellen (Hippen et al., 1997, Siegrist et al., 1998). Aufgrund dieser Beobachtungen musste angenommen werden, dass auch noch andere biologische Prozesse als die konventionelle Nitrifikation und Denitrifikation zur Stickstoffelimination beitragen.