Rainfall runoff models are frequently used for design processes for urban infrastructure. The most sensitive input for these models is precipitation data. Therefore, it is crucial to account for temporal and spatial variability of rainfall events as accurately as possible to avoid misleading simulation results. This paper aims to show the significant errors that can occur by using rainfall measurement resolutions in urban environments that are too coarse. We analyzed the spatial variability of rainfall events from two years with the validated data of 22 rain gauges spread out over an urban catchment of 125 km². By looking at the interstation correlation of the rain gauges for different classes of rainfall intensities, we found that rainfall events with low and intermediate intensities show a good interstation correlation. However, the correlation drops significantly for heavy rainfall events suggesting higher spatial variability for more intense rainstorms. Further, we analyzed the possible deviation from the spatial rainfall interpolation that uses all available rain gauges when reducing the number of rain gauges to interpolate the spatial rainfall for 24 chosen events. With these analyses we found that reducing the available information by half results in deviations of up to 25% for events with return periods shorter than one year and 45% for events with longer return periods. Assuming uniformly distributed rainfall over the entire catchment resulted in deviations of up to 75% and 125%, respectively. These findings are supported by the work of past research projects and underline the necessity of a high spatial measurement density in order to account for spatial variability of intense rainstorms.

The aim of this work is to investigate how open data can play a beneficial role in the regulation of combined sewer overflows (CSOs). The investigation consists of a review and critical discussion of historic CSO design, alongside more recent developments of regulations and emerging experiences of monitoring CSOs and different levels of data openness. The study focuses on practice in 10 European countries/regions. The novelty of this work comes from its review of historical development of design guidelines and regulations, shifts in the aims of these regulations, practicalities around implementation and testing of compliance, alongside the openness and availability of data. The main conclusions are that increasingly complex regulation goes hand in hand with limited compliance checking and opaque decision-making, whereas opening up relatively simplistic performance data has generated public and political discussion about urban drainage systems and the potential costs of improvements in water quality of the impacted surface water bodies. Making CSO data open does, however, need to be done with due care. Collaboration with trusted citizen groups, ensuring the data are correct, easy to access, and understand, as well as avoiding a blame culture are all of key importance.

Toxic pollutants in wastewater can negatively affect biological processes in WWTPs, leading to operational failures and environmental harm if undetected. This study refines the ISO 8192 method for enhanced toxicity detection in WWTPs, meeting the critical need for rapid and reliable monitoring. The novelty of this study lies in the optimization and identification of sensitive boundary conditions (e.g., temperature stability, consistent mixing speed, and immediate aeration), which are crucial for ensuring the accuracy and reproducibility of the method. The optimization results indicate that sludge prepared via settling yields EC₅₀ values comparable with those achieved with sludge prepared via centrifugation. For total oxygen consumption inhibition, the EC₅₀ values were 9.22 ± 0.21 mg/L (centrifuged) and 9.42 ± 0.16 mg/L (settled), with nitrification inhibition values of 1.92 ± 1.24 mg/L and 2.17 ± 1.5 mg/L, respectively. The verification results obtained using samples from the Graz and Trofaiach WWTPs demonstrate EC₅₀ values of 12.38 ± 2.05 mg/L and 12.25 ± 0.62 mg/L (total oxygen consumption inhibition), 23.31 ± 4.62 mg/L and 19.32 ± 0.29 mg/L (heterotrophic inhibition), and 1.54 ± 0.94 mg/L and 3.48 ± 2.65 mg/L (nitrification inhibition), which are all within the accepted ranges of validity of the method. The optimized ISO 8192 method provides a robust and efficient tool for WWTPs, enabling rapid responses to toxicity events and supporting regulatory compliance. These refinements enhance the practicality and reliability of the method.

This dataset compiles continuous hydraulic and water quality observations from the combined sewer overflow structure at the outlet of the Graz-West R05 catchment in Austria, covering the period from 2008 to 2011. It integrates high-resolution in-sewer measurements of flow rate, water level, flow velocity and water quality parametres (COD, TSS, temperature), complemented by laboratory analyses of discrete grab samples. Water quality parametres were monitored using an in situ UV/VIS spectrometer installed on a floating pontoon. Additional locally calibrated COD values derived from laboratory measurements are included. The in-sewer data were acquired at 1 or 3 min intervals depending on flow conditions. Flow rates, water levels and overflow discharges were monitored using radar and ultrasonic sensors. Three nearby tipping-bucket rain gauges provided time-stamped precipitation increments, enabling the detailed reconstruction of wet-weather dynamics. A hydrodynamic SWMM model of the catchment, including geospatial information and dry-weather calibration, is included to support modelling applications. This combination of long-term measurements and a calibrated hydrodynamic model supports the development, testing and validation of process-based, statistical or data-driven approaches for simulating combined sewer system behaviour and pollutant dynamics.

Zusammenfassung: Niederschlagswasser- und Mischwassereinleitungen können für einige Spurenstoffe aus dem urbanen Bereich der dominierende Eintragspfad in die Gewässer sein. Im Rahmen eines österreichischen Forschungsprojekts wurden an einer Niederschlagswasserkanaleinleitungsstelle in ein Gewässer sowie an einem Mischwasserüberlauf zwei mengenproportionale Jahresmischproben generiert, um die daraus resultierenden ein- bzw. abgeleiteten Jahresschmutzfrachten an Spurenstoffen zum einen messtechnisch zu bestimmen und zum anderen nach einer detaillierten Analyse der Oberflächenbeschaffenheiten in den Einzugsgebieten und entsprechenden Stoffflussanalysen theoretisch ermittelbaren Stofffrachtpotenzialen aus der Literatur gegenüberzustellen. Die dafür gewählte Probenahmestrategie, die dabei gesammelten Erfahrungen bei der Probenahme und die erzielten Ergebnisse aus den Beprobungen werden im Beitrag beschrieben und diskutiert.

Industrial and municipal wastewater may contain substances that inhibit biological processes in wastewater treatment plants (WWTPs), posing risks to operational stability and environmental protection. The aim of this study is to evaluate the practical suitability of the ISO 8192:2007 respiration inhibition test for assessing the toxicity of wastewater. Nitrified activated sludge from a municipal WWTP was used to analyze wastewater from three industrial companies, wastewater from several discharge locations at a hospital, and WWTP influent. Oxygen consumption and inhibition were determined at sample-specific dilution levels and the reference substance 3,5-dichlorophenol. Two samples from the dental department of the hospital showed toxic effects on activated sludge respiration (inhibition > 50%), while no toxic effects were observed in the remaining samples. Several samples exhibited stimulatory effects (inhibition < 0%), indicating the presence of readily biodegradable organic matter. However, inhibitory effects (0–50% inhibition) were detected in individual wastewater samples at higher concentrations. This demonstrates that the method can detect toxicological changes in wastewater and is suitable for routine monitoring and early warning in WWTPs.