Micropollutant abatement in granular activated carbon (GAC) filters is governed by both sorption and biodegradation processes. Yet a comprehensive understanding of which micropollutants are biodegraded, how much biodegradation contributes to GAC’s performance, and how GAC’s properties affect biodegradation, remains limited. This study addresses these knowledge gaps by combining reactive transport modeling with pilot-scale experiments, investigating the fate of 45 micropollutants in parallel GAC and sand filters operated at contact times of up to 100 min. Tracer tests and modeling showed that GAC’s high intragrain porosity (40%) prolongs solute-biomass contact times by a factor of 1.7 compared to sand. Higher respiration activity in GAC was attributed to prolonged contact times for biodegradation of both micropollutants and other dissolved organics. Significantly enhanced abatement at contact times exceeding 25 min suggested biodegradation for 25 of 45 micropollutants. The formation of biotransformation products further confirmed biodegradation of diclofenac and the highly sorptive compounds venlafaxine and hydrochlorothiazide exclusively in GAC. Overall, these findings demonstrate that (i) GAC enables biodegradation of more micropollutants than sand (24 vs. 16), regardless of sorption affinity; (ii) intragrain porosity prolongs solute-biomass contact times, being relevant for degradable compounds featuring little sorption; and (iii) GAC hosts functionally distinct microbial biomass capable of unique biotransformation compared to sand.

Reducing nitrous oxide (N₂O) emissions from wastewater treatment plants is essential for achieving the sector's net-zero goals by 2050. Yet the complexity of operating full-scale wastewater treatment obscures our understanding of the mechanisms behind N₂O formation and hence, the development of targeted mitigation strategies. Three main pathways are known to contribute to net N₂O emissions, but their relative and absolute importance shifts over time and is controlled by the interplay of multiple parameters. To date, attempts to experimentally disentangle these pathways under conditions representative of full-scale systems have been unsuccessful. This study developed and validated a novel methodology to distinguish major N₂O production pathways. The methodology was implemented over one year of operation in two parallel pilot reactors treating dynamically varying municipal wastewater directly extracted from an actual sewer system, thereby closely replicating full-scale conditions. Online isotope analysis was used to validate pathway separation. Stable isotopes showed that the N₂O production by the hydroxylamine pathway is negligible under all studied conditions. Nitrifier denitrification was successfully isolated from heterotrophic denitrification by controlling the concentration of ammonium, nitrite, and dissolved oxygen and became more active at lower dissolved oxygen concentrations. Lower dissolved oxygen, higher organic carbon availability, and lower pH increased N₂O production by heterotrophic denitrification during aeration. These new insights provide a systematic framework for understanding N₂O dynamics and support the development of mitigation strategies at full-scale.

Pharmaceuticals and their human metabolites are significant sources of micropollutants in the aquatic environments due to incomplete removal during wastewater treatment. While parent compounds have been widely studied, the fate of their metabolites across treatment stages remains poorly understood, despite the fact that most pharmaceuticals are excreted in metabolized forms. Using a combination of full-scale wastewater treatment plant (WWTP) observations, laboratory experiments, and modeling, this study aimed to assess and compare the removal of 290 parent pharmaceuticals and 154 human metabolites across biological and advanced wastewater treatment stages, to evaluate the influence of human metabolic modifications on removal rates. The findings from the field data confirmed that phase II metabolites are often efficiently degraded during biological treatment, and cleaved into corresponding parent compounds or phase I metabolites, with median removals of 84% to 97% in the three WWTPs. In contrast, phase I metabolites show a similar behavior to their parent compounds and are often not more efficiently abated, with median removals ranging between 38% to 53% for parents and phase I metabolites. Advanced treatments, including ozonation with and without granular activated carbon filtration, showed significant median reductions of 79% to 92% for parent pharmaceuticals and 54% to 82% for metabolites, with removal efficiencies correlating with ozone doses. Laboratory biotransformation experiments identified reaction-specific pseudo-first-order rate constants, with carboxylic acids showing increased persistence, potentially as a result of their high oxidation state, which limits further degradation under aerobic conditions. Moreover, the laboratory experiments confirmed that acetylated and glucuronidated phase II metabolites are more efficiently abated during biological treatment, while sulfates are more stable compared to their parent compounds. A mechanistic model using the experimentally determined biotransformation rate constants was established, showing strong agreement with measured data for compounds with high or low biotransformation rates. Predictions for partially degraded compounds showed higher uncertainty, reflecting the complex interactions between biotransformation, sorption and operational parameters. This work provides a detailed assessment of the behavior and fate of pharmaceuticals and especially their metabolites during wastewater treatment, emphasizes the importance of understanding transformation pathways, and offers valuable insights for optimizing removal strategies and minimizing environmental impacts.

Municipal wastewater treatment plants are important contributors to the discharge of micropollutants to the aquatic environment. Therefore, in Switzerland it has been decided to treat the water at these point sources to reduce the discharge of micropollutants from municipal wastewater effluents. A team of scientists at Eawag has evaluated treatment options, which need to be readily available, easily applicable, and cheap. Based on a rigorous assessment, activated carbon-based processes and ozonation were selected. In this paper the focus is on ozonation, and the different aspects of its application are discussed, including kinetics and mechanisms for ozone reactions with micropollutants and matrix components, formation, and fate of transformation products in biological post-filtration and toxicological aspects. Finally, upgrading of ozonation is described including outreach of this approach to other countries.

Nitrit ist eine ökotoxikologisch problematische Substanz und führt auf Kläranlagen ausserdem zur Bildung von klimaschädlichem Lachgas. In der hier vorgestellten Studie werden verschiedene Online-Sensoren verglichen und deren Messunsicherheit in Ablauf und Belebtschlamm erfasst.

Nitrit ist eine ökotoxikologisch problematische Substanz und führt auf Kläranlagen zur Bildung von klimaschädlichem Lachgas. Auf nitrifizierenden Belebtschlammanlagen kann Nitrit saisonal akkumulieren und erhöhte Ablaufwerte treten auf. Hier diskutieren wir die Häufigkeit von Überschreitungen des Nitrit-Richtwerts auf Schweizer ARA und schlagen Gegenmassnahmen vor.

Micropollutants removal efficiency strongly vary across different aerobic wastewater treatment plants, resulting in their frequent detection in surface and ground waters. Seasonal temperature variation is a major factor influencing plant performance, but it is still unclear how prolonged periods of temperature change impact microbiome and micropollutant biotransformation. This work investigates the effect of long-term temperature variation on the microbial dynamics in an activated sludge system, and the impact on micropollutant biotransformation. Sequencing batch reactors were used as model system and 4–40 °C temperature range was studied. 16S rRNA amplicon sequencing showed that temperature drives microbial structure (gDNA) and activity (RNA), rather than time, and this was stronger below 15 °C and above 25 °C. The microbial community was richest and more diverse at 20 °C, while rarer and more specific taxa became predominant over time, at more extreme temperatures. This suggested that less abundant taxa might be responsible for maintaining the biotransformation capability in the activated sludge at extreme temperatures. Micropollutant biotransformation rates mostly deviated from the classic Arrhenius model below 15 °C and above 25 °C, indicating that prolonged exposure to temperature changes leads to temperature-induced taxonomic shifts, resulting in the emerging of different sets of biotransformation pathways over different temperature ranges.

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.

Lachgas ist neben Kohlendioxid und Methan eines der potentesten Treibhausgase und hauptverantwortlich für den Abbau der stratosphärischen Ozonschicht. Auf Schweizer Abwasserreinigungsanlagen (ARA) ist die Faulwasserbehandlung, die hauptsächlich mit dem ein- oder zweistufigen anaeroben Ammonium-Oxidation-Verfahren (Anammox) durchgeführt wird, eine mögliche Quelle für Lachgas. Messungen zeigen, dass die Lachgasemissionen im klimarelevanten Bereich liegen und Reduktionsmassnahmen zu empfehlen sind.

Engineered nitrogen (N) removal processes in water treatment plants and N-transformation reactions in polluted environments represent prominent sources of the potent greenhouse gas, nitrous oxide (N₂O). The relevance of microbial and abiotic formation pathways can be assessed by using ¹⁵N tracer techniques. While ¹⁵N-N₂O analysis with optical analyzers is straightforward, the quantification of atom % ¹⁵N of inorganic N compounds, such as ammonium (NH₄⁺), nitrite (NO₂^-), and nitrate (NO₃^-), requires discrete sample analyses that are time-consuming and labor-intensive. In this study, we developed an automated sample preparation unit, coupled to a membrane inlet quadrupole mass spectrometer, for the online, quasi-simultaneous analysis of atom % ¹⁵N in NH₄⁺, NO₂^-, and NO₃^-. This technique was designed and validated for ¹⁵N-spiking applications at moderate (100-200 μmol L^-1, 1 atom % ¹⁵N) to high (2-3 mmol L^-1, 33 atom % ¹⁵N) dissolved inorganic N concentrations typically encountered in sewer systems or contaminated watersheds. The high potential of the developed system, in combination with ¹⁵N-N₂O analysis by Fourier-transform infrared spectroscopy, to constrain N transformations and sources of N₂O was demonstrated in a feasibility study, where nitrifier denitrification was identified as the primary N₂O formation pathway during the partial NH₄⁺ oxidation to NO₂^- in a lab-scale sequencing batch reactor.

Bei der anaeroben Ammonium-Oxidation, kurz Anammox, werden Ammonium und Nitrit im Faulwasser zu Stickstoffgas umgewandelt. Das Verfahren ist auch auf einigen Schweizer ARA im Einsatz. Da aber nicht alle Anlagen die Sollleistung erfüllten, wurde das Anammox-Verfahren untersucht und weiterentwickelt. Mit dem Wechsel von der ein- zur zweistufigen Verfahrensführung wurde nicht nur eine höhere Betriebsstabilität bei der biologischen Entstickung von Rückläufen aus der Schlammentwässerung, sondern teils auch höhere Leistungen erreicht.

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

Ein zeitnahes Biomonitoring mit Nanopore-Sequenzierung gewährt neue Einblicke in die biologischen Prozesse einer Abwasserreinigungsanlage (ARA). Im Rahmen des Projekts «MicROcensus» wurde an verschiedenen ARA die Einsatzfähigkeit solcher Mikrobiom-Analysen als Diagnoseinstrument evaluiert. So unterstützen Momentaufnahmemessungen die Ursachenfindung von Prozessinstabilitäten oder Begleitphänomenen. Während wöchentliche Analysen des Mikrobioms – bei Bekanntsein der jahreszeitlichen Dynamiken - als Frühwarnsystem dienen und praxisrelevante Daten für den ARA-Betrieb liefern können.

Um den biologischen Abbau einer Abwasserprobe zu untersuchen und die refraktäre organische Fracht zu quantifizieren, werden Abbautests eingesetzt. Die Charakterisierung der Abwasserströme führt zu Entscheidungen bezüglich Entsorgung und allfälliger benötigter Vorbehandlungen. Der gängige Zahn-Wellens-Test wurde optimiert, um einen zeiteffizienteren Abbautest zu entwickeln: den alternativen inhärenten Abbautest (AIA-Test).

Die ARA Hofen hat den Infrawatt Innovationspreis 2021 für die Ertüchtigung ihrer Biologiebecken mit dem Konzept der dynamischen Regelung erhalten. Die Leistung der ARA konnte dadurch signifikant erhöht werden, bei stark vermindertem Energieverbrauch und gleichzeitig sehr geringen Lachgasemissionen.

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.

Effluents of wastewater treatment plants can impact microbial communities in the receiving streams. However, little is known about the role of microorganisms in wastewater as opposed to other wastewater constituents, such as nutrients and micropollutants. We aimed therefore at determining the impact of wastewater microorganisms on the microbial diversity and function of periphyton, key microbial communities in streams. We used a flow-through channel system to grow periphyton upon exposure to a mixture of stream water and unfiltered or ultra-filtered wastewater. Impacts were assessed on periphyton biomass, activities and tolerance to micropollutants, as well as on microbial diversity. Our results showed that wastewater microorganisms colonized periphyton and modified its community composition, resulting for instance in an increased abundance of Chloroflexi and a decreased abundance of diatoms and green algae. This led to shifts towards heterotrophy, as suggested by the changes in nutrient stoichiometry and the increased mineralization potential of carbon substrates. An increased tolerance towards micropollutants was only found for periphyton exposed to unfiltered wastewater but not to ultra-filtered wastewater, suggesting that wastewater microorganisms were responsible for this increased tolerance. Overall, our results highlight the need to consider the role of wastewater microorganisms when studying potential impacts of wastewater on the receiving water body.

Biotransformation is the most important process removing manmade chemicals from the environment, yet mechanisms governing this essential ecosystem function are underexplored. To understand these mechanisms, we conducted experiments in flow-through systems, by colonizing stream biofilms under different conditions of mixing river water with treated (and ultrafiltered) wastewater. We performed biotransformation experiments with those biofilms, using a set of 75 micropollutants, and could disentangle potential mechanisms determining the biotransformation potential of stream biofilms. We showed that the increased biotransformation potential downstream of wastewater treatment plants that we observed for specific micropollutants contained in household wastewaters (downstream effect) is caused by microorganisms released with the treated effluent, rather than by the in-stream exposure to those micropollutants. Complementary data from 16S rRNA amplicon-sequencing revealed 146 amplicon sequence variants (ASVs) that followed the observed biotransformation patterns. Our results align with findings for community tolerance, and provide clear experimental evidence that microorganisms released with treated wastewater integrate into downstream biofilms and impact crucial ecosystem functions.

Neue Leistungsanforderungen an Abwasserreinigungsanlagen hinsichtlich Ablaufqualität, Energieeffizienz und Treibhausgasemission werden immer bedeutender. Um dabei Zielkonflikte zu vermeiden, ist bei der Optimierung die genaue Überwachung der Prozesse erforderlich. So ist die Messung von Gaskonzentrationen in der Abluft aus biologischen Reinigungsstufen ein nützliches Werkzeug, um verschiedene Zielsetzungen einer ARA hochaufgelöst und wartungsarm zu überwachen.

Lachgas (N₂O) ist ein starkes Treibhausgas und die wichtigste ozonzerstörende Substanz in der Stratosphäre. Auf Abwasserreinigungsanlagen wird N₂O während des biologischen Stickstoffabbaus gebildet, der somit die grösste Treibhausgasquelle während des Reinigungsprozesses darstellt. Reduktionsmassnahmen sind deshalb von grosser Bedeutung und gemäss neuen Erkenntnissen durch eine Optimierung der Nitrifikation und Denitrifikation auch erreichbar.

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

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

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

Ozonation of secondary-treated wastewater for the abatement of micropollutants requires a reliable control of ozone doses. Changes in the UV absorbance of dissolved organic matter (DOM) during ozonation allow to estimate micropollutant abatement on-line and were therefore identified as feed-back control parameter. In this study, the suitability of the electron-donating capacity (EDC) as an additional surrogate parameter which is independent of optical DOM properties was evaluated during full-scale ozonation. For this purpose, a recently developed EDC analyzer was enhanced to enable continuous on-line EDC and UV absorbance measurements. During a multi-week monitoring campaign at the wastewater treatment plant of Zurich, Switzerland, specific ozone doses were varied from 0.13 to 0.91 mg_O3⋅mg_DOC^-1 and selected micropollutants with different ozone reactivities were analyzed by LC-MS in conjunction with bromate analysis by IC-MS. In agreement with previous laboratory studies, the relative residual UV absorbance and EDC both decreased exponentially as a function of the specific ozone dose and, in comparison to the residual UV absorbance, residual EDC values showed a more pronounced decrease at low specific ozone doses ≤0.34 mg_O3⋅mg_DOC^-1. Logistic regression models allowed to estimate relative residual micropollutant concentrations in the ozonation effluent using either the residual UV absorbance or EDC as explanatory variable. Averaging those models along the explanatory variables allowed to estimate target values in relative residual UV absorbances and EDC for specific micropollutant abatement targets. In addition, both parameters allowed to identify conditions with elevated conversions of bromide to bromate. Taken together, these findings show that the integration of relative residual EDC values as a second control parameter can improve existing absorbance-based ozonation control systems to meet micropollutant abatement targets, particularly for treatment systems where low ozone doses are applied.

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

The currently applied approaches to estimate direct greenhouse gas (GHG) emissions of nitrous oxide (N₂O) and methane (CH₄) from wastewater treatment (sector 5D) in the national greenhouse gas inventories of Switzerland are based on the IPCC guidelines (IPCC 2006). A review of the Swiss application of guidelines showed that the guidelines are only partly representative for Switzerland (Eawag 2018). Hence, an extended study was performed including extensive monitoring campaigns on Swiss wastewater treatment plants (WWTPs), analysis of existing data sets and literature reviews. The present document summarizes the study and suggests an improved methodology for an assessment of the GHG emissions of sector 5D.
N₂O emission are drastically underestimated with the current methodology. Additionally, source allocation of emissions is not representative. Hence, we suggest a new methodology based on 17 (14 Swiss and 3 from literature) long-term monitoring campaigns on full-scale WWTPs and an analysis of nitrogen flows in Swiss WWTPs. The decreasing N₂O emissions since 1990 link to improvements of nitrogen removal rates on WWTPs. Further reductions are expected in the coming decades because of further planned improvements of nitrogen removal on Swiss WWTPs. Major uncertainties within the new methodology can be linked to the emission factor of WWTPs with carbon removal only. The occurrence of such plants decreased substantially between 1990 and 2020.
CH₄ emissions are overestimated with the current methodology. Additionally, source allocation of emissions is not representative. Hence, we propose a new methodology based on monitoring campaigns and a literature review. Emissions increased moderately since 1990 along with an increase in population.

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

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

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

Lachgasemissionen (N₂O) tragen substantiell zu bedeutenden, globalen Umweltproblemen bei: dem Klimawandel und der stratosphärischen Zerstörung von Ozon. Kläranlagen (ARAs) sind relevante N₂O Punktquellen und verursachen einen relevanten Teil der anthropogenen Emissionen. Gegenwärtig werden die N₂O Emissionen aus ARAs in den meisten Treibhausgasinventaren jedoch unterschätzt, da die Emissionsprozesse in den üblicherweise verwendeten IPCC Richtlinien unzureichend abgebildet werden. Die Hauptgründe dafür sind eine limitierte Verfügbarkeit an repräsentativen Langzeitdaten und ein fehlendes Verständnis der N₂O Bildung während der biologischen Stickstoffelimination auf ARAs. Insbesondere die Ursachen für die saisonale Variabilität der Emission sind unbekannt. Die hohe Variabilität im Jahresverlauf unterstreicht die Notwendigkeit von Langzeitmess-kampagnen als Grundlage für eine repräsentative Schätzung der Emissionsfaktoren. Deshalb hatte die vorliegende Doktorarbeit folgende Zielsetzung: (i) Entwicklung und Anwendung einer Methode zur langfristigen Emissions-überwachung und zur Abschätzung repräsentativer Emissionsfaktoren (EFs), (ii) Erarbeitung eine Methode für eine realistischere Abschätzung der landesweiten N₂O Emissionen ARAs sowie (iii) Charakterisierung von ursächlichen Faktoren für die saisonale Variabilität, um schließlich Maßnahmen zur Emissionsminderung vorzuschlagen. [...]

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

Anaerobic ammonium oxidation (anammox) plays an important role in aquatic systems as a sink of bioavailable nitrogen (N), and in engineered processes by removing ammonium from wastewater. The isotope effects anammox imparts in the N isotope signatures (¹⁵N/¹⁴N) of ammonium, nitrite, and nitrate can be used to estimate its role in environmental settings, to describe physiological and ecological variations in the anammox process, and possibly to optimize anammox-based wastewater treatment. We measured the stable N-isotope composition of ammonium, nitrite, and nitrate in wastewater cultivations of anammox bacteria. We find that the N isotope enrichment factor ¹⁵ε for the reduction of nitrite to N₂ is consistent across all experimental conditions (13.5‰ ± 3.7‰), suggesting it reflects the composition of the anammox bacteria community. Values of ¹⁵ε for the oxidation of nitrite to nitrate (inverse isotope effect, - 16 to - 43‰) and for the reduction of ammonium to N₂ (normal isotope effect, 19-32‰) are more variable, and likely controlled by experimental conditions. We argue that the variations in the isotope effects can be tied to the metabolism and physiology of anammox bacteria, and that the broad range of isotope effects observed for anammox introduces complications for analyzing N-isotope mass balances in natural systems.

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