Department Process Engineering

Process Engineering

The research focus of the Process Engineering Department (ENG) ranges from current and future wastewater and drinking water treatment problems, as well as water pollution control and resource reuse. Our long-term goal is to develop sustainable concepts of the water and nutrient cycle in residential areas.

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News

A fairer assessment of wastewater treatment in mountain huts

The alternative method of assessing the cleaning performance of small wastewater treatment plants for mountain huts using potassium as a tracer is currently being validated by measurements at Chamanna Cluozza and other mountain huts (Photo: Adobe Stock).
February 12, 2025 –

The conditions in mountain huts often make it difficult and impractical to meet the requirements for wastewater treatment. A new approach to assessing cleaning performance could change that.

The conditions in mountain huts often make it difficult and impractical to meet the requirements for wastewater treatment. A new approach to assessing cleaning performance could change that.
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2024 Otto-Jaag Water Protection Prize for Valentin Faust

ETH Rector Günther Dissertori presents Valentin Faust with the 2024 Otto-Jaag Water Protection Prize (Photo: ETH, Alessandro Della Bella).
November 18, 2024 –

During ETH Day on 16 November 2024, environmental engineer Valentin Faust was awarded the Otto-Jaag Water Protection Prize for his doctoral thesis. His work provides important insights about the production of fertiliser from human...

During ETH Day on 16 November 2024, environmental engineer Valentin Faust was awarded the Otto-Jaag Water Protection Prize for his doctoral thesis. His work provides important insights about the production of fertiliser from human urine.
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Dry summers: reusing treated wastewater could help

The use of treated municipal wastewater to irrigate agricultural land has been permitted in some of Switzerland’s neighbouring countries since 2023 (Photo: Adobe Stock).
October 17, 2024 –

With climate change, hot and dry summers are becoming more frequent, causing water shortages in some regions of Switzerland. Reusing treated wastewater could help to solve this problem. This has been demonstrated by an Eawag team...

With climate change, hot and dry summers are becoming more frequent, causing water shortages in some regions of Switzerland. Reusing treated wastewater could help to solve this problem. This has been demonstrated by an Eawag team on behalf of the FOEN and some cantons. The researchers also explain what still needs to be done to put the option into practice.
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Water Hub: new movie!

Publications

Appiah-Twum, H., Van Winckel, T., Santolin, J., De Paepe, J., Hellweg, S., Larsen, T. A., … Spiller, M. (2025). Environmental impact of integrating decentralized urine treatment in the urban wastewater management system: a comparative life cycle assessment. Water Research, 282, 123630 (14 pp.). doi:10.1016/j.watres.2025.123630, Institutional Repository

As municipal wastewater treatment regulations become more stringent, integrating source-separated urine treatment into centralized urban wastewater management offers a ‘hybrid’ solution. However, it is not clear how the environmental impacts of such hybrid systems compare to highly efficient centralized wastewater treatment plants (WWTPs) with low N2O emissions and electricity use. In this study, a consequential life cycle assessment was used to compare the environmental impact of three urine separation hybrid wastewater treatment systems – which combine decentralized urine treatment with a highly efficient central WWTP– to a centralized WWTP treating mixed wastewater (baseline). The studied urine treatment systems include partial nitrification & distillation, struvite precipitation & stripping/scrubbing, and partial nitritation/anammox. Additionally, the environmental impact of urine pre-treatment by calcium hydroxide and electrochemical alkalinization methods on the partial nitrification & distillation system was evaluated. The results show that all hybrid scenarios have a lower environmental impact in the freshwater ecotoxicity, marine toxicity, freshwater eutrophication, and marine eutrophication categories compared to the baseline. However, all hybrid scenarios resulted in higher impacts on global warming compared to the baseline, with direct N2O emissions being a key variable. Additionally, it was identified that urine alkalinization increased the environmental impact of the treatment system in 7 out of the 10 impact categories. A Pareto frontier analysis was developed to guide decision makers on where hybrid solutions could be used as a strategy to reduce the global warming impacts of conventional WWTPs. Using N2O-N emission factors of 75 WWTPs, 87 % of centralized WWTPs had a lower global warming impact compared to partial nitrification & distillation, and 91 % compared to partial nitritation/anammox hybrid solutions. However, at electricity demands of 1 kWh/PE/day and 1.5 kWh/PE/day at the central WWTP, both hybrid solutions showed lower global warming impact than all the studied WWTPs. The study highlights the potential of hybrid wastewater treatment solutions as a strategy to reduce global warming impacts in WWTPs with high N2O emissions and electricity use as well as a means to reduce marine eutrophication (i.e. nitrogen pollution).
Britschgi, L., Wei, S., Proesl, A., Morgenroth, E., & Derlon, N. (2025). The critical role of flocs in nitrification in full-scale aerobic granular sludge-based WWTP. Water Research, 274, 123021 (13 pp.). doi:10.1016/j.watres.2024.123021, Institutional Repository

Aerobic granular sludge (AGS) is usually considered to be a biofilm system consisting of granules only, although practical experience suggests that flocs and granules of various sizes co-exist. This study thus focused on understanding the contribution of flocs and granules of various sizes to nitrification in a full-scale AGS-based wastewater treatment plant (WWTP) operated as a sequencing batch reactor (SBR). The size distribution in terms of total suspended solids (TSS) and the distribution of the nitrifying communities and activities were monitored over 14 months. Our results indicate that AGS is a hybrid system in which flocs (<0.25 mm) play a critical role in nitrification. AGS consisted of 36 % flocs and 50 % large granules (>2 mm) at a TSS concentration of 4.7 ± 0.7 gTSS L-1. The growth of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in large granules was limited due to the high mass transfer limitation in biofilm and the high solids retention time (SRT) of flocs, where favorable conditions for the growth of nitrifiers were maintained during the warm season. The specific activities of the small aggregates (<1 mm) were 5 to 15 times higher than those of large granules. As a result, flocs contributed >50 % to nitrification during the warm season, whereas granules >1 mm contributed <20 %. Such predominance of flocs in nitrification became problematic in the cold season when the minimum SRT of NOB increased to values similar to the floc SRT, resulting in 79 % loss of the NOB. Consequently, NOB activities dropped, and elevated effluent nitrite concentrations of several mgN L-1 were monitored. We suggest operating AGS systems similarly to hybrid systems in order to promote the enrichment of NOB in the granules by controlling the floc SRT at low values smaller than the minimum SRT of NOB throughout the year.
Crosset-Perrotin, G., Moraz, A., Portela, R., Alcolea-Rodriguez, V., Burrueco-Subirà, D., Smith, C., … Fairbrother, D. H. (2025). Production, labeling, and applications of micro- and nanoplastic reference and test materials. Environmental Science: Nano. doi:10.1039/d4en00767k, Institutional Repository

Challenges inherent to the extraction of micro- and nanoplastics (MNPs) from the environment, combined with the limited range of commercially available MNPs, have prompted an increasing number of researchers to generate in-house reference and test MNPs. The first part of this review provides a comprehensive overview of existing MNP production methods, including top-down and bottom-up fabrication techniques. Strengths and weaknesses of different methods are compared and contrasted, and the potential for optimization and control over MNP properties is discussed. Methods to label and to artificially weather MNPs before, during, or after production, as well as appropriate dispersion protocols for introducing MNPs into different media, are also covered. The second part of this review focuses on how reference and test MNPs have been implemented in different types of studies, categorized as toxicity, uptake, fate, and monitoring. Given the wide range of properties needed to fully define MNPs, we propose a set of essential properties that need to be characterized depending on the study type. Looking forward, we suggest future needs, not only in the creation of reference MNPs, but also in experimental protocols that would help to better understand the behavior and impacts of MNPs. Overall, this review aims to provide the necessary information to guide researchers in decision-making regarding which reference MNPs are most appropriate to answer their specific research questions and to serve as a framework that will contribute to obtaining reliable, benchmarked data urgently needed to develop consensus on the fate and risk posed by MNPs.
Farine, C., Lüthi, C., Niwagaba, C. B., Morgenroth, E., & Narayan, A. S. (2025). Interlinkages and indicators: novel assessment of water, sanitation and solid waste services in schools in two Ugandan towns. Frontiers in Water, 7, 1544779 (11 pp.). doi:10.3389/frwa.2025.1544779, Institutional Repository

The status of Water, Sanitation, and Hygiene (WASH) in schools in sub-Saharan Africa remains dire. Only 46% have access to basic water services, 44% to basic sanitation services, and 26% to basic hygienic services. Although integrating these services with other water and waste streams could benefit service provision, a systematic methodology for such integration does not exist yet. This research approaches a first step–a methodology for an integrated assessment of water, sanitation, and solid waste management (SWM) services in schools. In addition, a modified version of the Joint Monitoring Program’s WASH service ladder for schools is provided for a detailed understanding of the service levels. A total of 16 schools from two small towns in Uganda are taken as case studies to identify the current service levels, interlinkages between the sectors as well as their enabling environment. Using surveys, stakeholder interviews, observations, and water quality measurements, the results show several cross-contamination pathways leading to exposure of pupils to pathogens. Finance and policies are major inhibitors of positive interlinkages and limited skills and capacities amplify negative interlinkages. The results emphasize the need for a shift toward further integrated planning of the water and waste services in schools and other institutions.

Events

24.06.​2025,
9.00 am
Lausanne
Elimination poussée de l'azote des eaux usées municipales

Cours d’approfondissement PEAK-VSA V60/25

04.12.​2025,
9.00 am
Eawag Dübendorf
Emissionen von Reifenpartikeln und Auswirkungen auf die Umwelt

PEAK-Basiskurs B36/25

Research Projects

Is a space research program, aiming to develop a bioregenerative life support system for long-term space missions and space habitations for example on Mars.

Melissa «Micro Ecological Life Support System Alternative»
NEST building
Sustainable urban water and wastewater management applied and implemented in the modular NEST building.

WaterHub at NEST
Modelling of aerobic granular sludge (AGS) reactors

Eawag Aerobic Granular Sludge (AGS) Model
Many WWTPs are reaching their maximum treatment and clarification capacities, and solutions must be found to upgrade those existing plants.

Micro-sieving of municipal wastewater
Opportunities and risks of reusing treated wastewater in Switzerland

Water Reuse Switzerland
The Swiss Federal Council set the ambitious goal to reach net-zero greenhouse gas emissions by 2050.

SCENE - Reducing N2O emissions from wastewater treatment
Dynamic of greenhouse gas emissions in nutrient removing wastewater treatment plants

N2O - Dynamic of greenhouse gas emissions
Systematic investigation of hybrid model approaches for the prediction of nitrous oxide emissions in biological wastewater treatment

MAD4WW

More Research Projects