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.

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

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.

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.

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

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

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