Weltweit stehen Kommunen vor der Aufgabe, Wassersysteme mittelfristig an neue Gegebenheiten anzupassen und sie resilienter gegen unvorhersehbare Ereignisse zu machen. Digitale Lösungen für das Abwasser- und Wassermanagement werden dafür immer bedeutsamer.

Cities worldwide are facing several challenges connected to urbanization and climate change. Several cities have identified the implementation of nature-based solutions (NBS) as an option to mitigate several challenges at once. However, can two different aims be reached with NBS in the same location? This question has not yet been addressed. This paper discusses the spatial compatibility of NBS implementation strategies to tackle (1) urban heat island (UHI) effects and (2) water pollution at the same location. The evaluation is based on a spatial analysis of Berlin. We found a positive correlation of high UHI and median high stormwater pollution loads for zinc, total suspended solids, Polycyclic Aromatic Hydrocarbons and Terbutryn. Out of more than 14,000 building/street sections analyzed, 2270 showed spatial matching of high UHI and high stormwater pollution loads. In the majority of building/street sections, stormwater pollution was high for three out of the four parameters. We conclude that the compatibility of NBS implementation for both challenges depends both on the implementation strategies for NBS and on the specific NBS measures. Our spatial analysis can be used for further planning processes for NBS implementation.

Thermal hydrolysis (TH) increases the anaerobic biodegradability of waste activated sludge (WAS), but also refractory organic and nutrient return load to a wastewater treatment plant (WWTP). This could lead to an increase in effluent chemical oxygen demand (COD) of the WWTP. The aim of this study was to investigate the trade-off between increase in biogas production through TH and anaerobic digestion and increase in refractory COD in dewatered sludge liquors at different temperatures of TH in lab-scale. WAS was thermally hydrolyzed in temperature range of 130e170 C for 30 min to determine its biomethane potential (BMP). After BMP test, sludge was dewatered and sludge liquor was aerated in Zahn-Wellens test to determine its non-biodegradable soluble COD known as refractory soluble COD (sCODref). With increasing temperature in the range of 130e170 C, BMP of WAS increased by 17e27%, while sCODref increased by 3.9e8.4%. Dewaterability was also enhanced through relative increase in cake solids by 12 e30%. A conversion factor was defined through mass balance to relate sCODref to volatile solids of raw WAS. Based on the conversion factor, expected increase in effluent CODs of six WWTPs in Berlin were predicted to be in the range of 2e15 mg/L after implementation of TH at different temperatures. It was concluded that with a slight decrease in temperature, formation of sCODref could be significantly reduced, while still benefiting from a substantial increase in biogas production and dewaterability improvement.

Organische Spurenstoffe wie Rückstände von Arzneimitteln oder Kosmetika können auf Wasserlebewesen bereits in geringen Konzentrationen negative Auswirkungen haben [1]. In der Schweiz werden bis 2040 ausgewählte Abwasserreinigungsanlagen (ARA) mit Reinigungsstufen zur Spurenstoffelimination ausgerüstet. Heute sind bereits auf zehn Kläranlagen die neuen Reinigungsstufen in Betrieb. Für diesen ARA-Ausbau eignen sich Verfahren mit Ozon, Pulverkohle (PAK) oder granulierter Aktivkohle (GAK) [2]. Die Belastung der Gewässer durch organische Spurenstoffe geht dadurch deutlich zurück, was zu einer Verbesserung der Wasserqualität führt [1, 3]. Der Nutzen dieser Reinigungsstufen ist somit unbestritten. Deren Betrieb benötigt aber zusätzliche Betriebsmittel, was wiederum Treibhausgasemissionen und andere Umweltauswirkungen verursacht. ARA tragen nur im tiefen Prozentbereich zu den gesamten Schweizer Treibhausgasemissionen bei, und die Spurenstoffelimination ist lediglich eine von mehreren Reinigungsstufen. Dennoch sollten die mit dem Betrieb dieser zusätzlichen Reinigungsstufen verbundenen Auswirkungen auf die Umwelt möglichst gering ausfallen. Der vorliegende Artikel verdeutlicht, welche Faktoren stark zum CO2-Fussabdruck der verschiedenen Verfahren auf Schweizer Kläranlagen beitragen. Dieses Wissen kann bei der Planung und hauptsächlich bei der Betriebsoptimierung von Reinigungsstufen zur Spurenstoffelimination unterstützen. Viele CO2-sparende Massnahmen führen auch dazu, dass die Kosten für Betriebsmittel und Strom sinken. Klimafreundlicher Gewässerschutz kann sich also auch aus wirtschaftlicher Sicht lohnen.

Nitrogen and phosphorus budgets were compiled for the littoral (29 km2) and pelagic (329 km2) of ancient, deep, clear, and hard water Lake Ohrid (Albania and North Macedonia), to assess the importance of the littoral in nutrient retention. P originates mainly from domestic point sources (73%), for N this is karst seepage (50%). Total littoral loads are estimated at 1700 kg P and 23,200 kg N km-2 (area of littoral) yr-1; net littoral retention is 31% ± 13% for P and 40% ± 16% for N, largely in the dense charophyte belt. P retention is mainly due to detritus burial, but also due to coprecipitation; N retention is due to both detritus burial and denitrification. A Monte Carlo plausibility analysis balanced the budget by increasing nonconnected domestic household inputs (from 20% to 27% of external load), and decreasing pelagic sediment P burial by 27% and littoral denitrification by 25%. Scenario projections for 2100 corresponding to SRES A2 and B1 were linked to an AQUASIM lake ecosystem model. Under B1, the changes were small compared to the present. A2, however, led to a major reduction in precipitation, an increase in evapotranspiration, a reduction in river outflow (to ~20%), a doubling in P-loading, a drop in lake level of ~1.5 m, and a decline in the extent of the charophyte belt. Areal loading of the littoral would increase accordingly, but water transparency would not decline much. Also, the littoral vegetation will witness a shift in species composition, and an increase in filamentous Cladophora cover.

Combined sewer overflows (CSOs) are of major environmental concern for impacted surface waterbodies. In the last decades, major storm events have become increasingly regular in some areas, and meteorological scenarios predict a further rise in their frequency. Consequently, control and treatment of CSOs with respect to best practice examples, innovative treatment solutions, and management of sewer systems are an inevitable necessity. As a result, the number of publications concerning quality, quantity, and type of treatments has recently increased. This review therefore aims to provide a critical overview on the effects, control, and treatment of CSOs in terms of impact on the environment and public health, strict measures addressed by regulations, and the various treatment alternatives including natural and compact treatments. Drawing together the previous studies, an innovative treatment and control guideline are also proposed for the better management practices.

Wie können unsere Kommunen die Möglichkeiten, die Regenwasserbewirtschaftung und neuartige Wasserinfrastrukturen als auch blau-grüne Infrastrukturen bieten, gut in ihre Planungsprozesse integrieren? Wie können die Leistungen der einzelnen Maßnahmen schnell, einfach und gut im Rahmen von Planungsworkshops mit Fachakteuren und Laien kommuniziert und genutzt werden? Hierzu wurden im Forschungsprojekt netWORKS 4 sogenannte Infokarten zu 20 Infrastrukturbausteinen als partizipatives Planungstool entwickelt und in verschiedenen Workshops erprobt. Sie sind nun als frei verfügbares Tool kostenlos zugänglich.

Sustainable urban drainage systems (SUDS) can significantly reduce runoff from urban areas. However, their potential to mitigate acute river impacts of combined sewer overflows (CSO) is largely unknown. To close this gap, a novel coupled model approach was deployed that simulates the effect of realistic SUDS strategies, developed for an established city quarter, on acute oxygen depressions in the receiving river. Results show that for an average rainfall year the SUDS strategies reduce total runoff by 28% - 39% and peak runoff by 31% - 48%. Resulting relative reduction in total CSO volume ranges from 45% - 58%, exceeding annual runoff reduction from SUDS by a factor of 1.5. Negative impacts in the form of fish-critical dissolved oxygen (DO) conditions in the receiving river (<2 mg DO/L) can be completely prevented with the SUDS strategies for an average rainfall year. The realistic SUDS strategies were compared with a simpler simulation approach which consists in globally downscaling runoff from all impervious areas. It indicates that such a simple approach does not completely account for the positive effect of SUDS, underestimating CSO volumes for specific rain events by up to 13%. Accordingly, global downscaling is only recommended for preliminary planning purposes.

Technical municipal water infrastructure, urban green areas and urban water bodies can be brought together in an optimized manner to deliver sustainable management of rainwater and domestic wastewater. Moreover, this approach allows urban areas to be designed in a way that leverages ecosystem services that reduce thermal load and thus contributes to a better quality of life despite climate change. To this end, suitable moduls from green and blue infrastructure have been rated in terms of their potential and explained using examples. By defly coupling these elements, their respective strengths can be pooled to unlock synergies. Integrated planning processes that may adopt different approaches help to weaken the impacts of climate change and allow the development of the different infrastructures to be more closely interlinked.