The present study aims to explore the relationship between rainfall variables and water quality/quantity characteristics of combined sewer overflows (CSO), by the use of multivariate statistical methods and online measurements at a principal CSO outlet in Berlin (Germany). Canonical correlation results showed that the maximum and average rainfall intensities are the most influential variables to describe CSO water quantity and pollutant loads whereas the duration of the rainfall event and the rain depth seem to be the most influential variables to describe CSO pollutant concentrations. The analysis of Partial Least Squares (PLS) regression models confirms the findings of the canonical correlation and highlights three main influences of rainfall on CSO characteristics: (i) CSO water quantity characteristics are mainly influenced by the maximal rainfall intensities, (ii) CSO pollutants concentrations were found to be mostly associated with duration of the rainfall and (iii) pollutants loads seemed to be principally influenced by dry weather duration before the rainfall event. The prediction quality of PLS models is rather low (R² < 0.6) but results can be useful to explore qualitatively the influence of rainfall on CSO characteristics.

The presented work studies the influence of the sampling strategy on the quality of locally calibrated UV-VIS probe measurements in combined sewer overflows (CSO) and the receiving river. Results indicate that UV-VIS spectrometers are not able to provide reliable measurements of water quality in urban stormwater without being calibrated to local conditions with laboratory analyses of water samples. The use of the global calibration (supplied by the manufacturer) led to errors of at least 30% and 45% for CSO load and river concentration of chemical oxygen demand (COD), respectively. Even with reliable local calibration, COD loads contained significant uncertainties close to 20%. Uncertainties in COD load and concentration decrease below 30% if more than 15-20 samples (i.e. 3-4 stormwater events) are sampled for local calibration. The effort and associated sampling costs to gain more than 15-20 samples are much less effective, since load and concentration uncertainties remain relatively stable with an increasing number of samples used for the calibration. The presented analysis aims at supporting practitioners in the planning, operation and calibration of UV-VIS spectrometer probes.

The present study aims at demonstrating the possibilities of on-line sensors for describing CSO emissions and river impacts. A continuous integrated monitoring, using state-of-the-art on-line sensors, was started in Berlin in 2010. It combines (i) continuous measurements of water quality and flow rates of combined sewer overflows (CSO) at one main CSO outlet and (ii) continuous measurements of water quality parameters at four sites within the urban stretch of the receiving river. UV-VIS probes provide continuous measurements of parameters such as chemical oxygen demand (COD) with relatively low uncertainties (10-30%). However, experience shows that on-line UV-VIS probes are not able to provide accurate measurements of water quality without being calibrated to local conditions. Several methodologies to analyze on-line CSO and river measurements are presented and illustrated with an exemplary event. Results show that reliable information such as the CSO load, the proportion of wastewater in CSO, the contribution of wastewater to CSO load, the first flush effect and the intensity of river impacts can be gained at high precision and temporal resolution. Given the broad range of high quality information from CSO impacts in the river to the characterization of CSO emissions, the study suggests the use of continuous integrated monitoring programs to support decisions on CSO management.

A continuous monitoring, using UV-VIS spectrometers, was carried out in Berlin from 2010 to 2012. It combined (i) continuous measurements of the quality and flow rates of combined sewer overflows (CSO) at one main CSO outlet downstream of the overflow structure and (ii) continuous measurements of water quality parameters at five sites within the urban stretch of the receiving River Spree. Locally, the collection of data aims at (i) characterizing CSO emissions, (ii) assessing the local dynamics and intensity of CSO impacts on the river and (iii) calibrating sewer and river water quality models being part of a planning tool for future CSO management in Berlin (Riechel et al., 2011). UV-VIS spectrometers are in-situ probes, which measure absorbance spectra ranging from UV to visual wavelengths. Concentrations, such as chemical oxygen demand (COD), are calculated from these spectra. Due to the varying composition of waste and river water a local calibration is required to enhance the measurement quality. According to Gamerith et al. (2011), manufacturer global calibration can lead to systematic error up to 50% for COD measurements.

Das vorgestellte modellbasierte Werkzeug bildet Mischwasserüberläufe aus dem Berliner Mischkanalsystem und deren kurzfriste Auswirkungen im Gewässer ab. Es soll für die Maßnahmenplanung und die Berechnung von Zukunftsszenarien verwendet werden. Das Werkzeug zeigt eine gute Übereinstimmung mit Messungen bezüglich des Verlaufes der Sauerstoffkonzentration im Gewässer und des Auftretens kritischer Bedingungen für die Fischfauna. Eine Szenarienuntersuchung für ein Extremjahr zeigt, dass durch die bis zum Jahr 2020 geplante Stauraumvergrößerung die Häufigkeit fischkritischer Bedingungen im Gewässer bereits um ein Drittel reduziert werden kann. Eine Reduktion um ein zusätzliches Drittel wäre durch weitergehende Maßnahmen im Bereich der Entsiegelung möglich. Die verbleibenden fischkritischen Bedingungen sind das Ergebnis von sehr starken Regenereignissen und können kaum verhindert werden. Eine durch Klimaveränderung erhöhte oder reduzierte Regenintensität im Sommer hätte starken Einfluss auf das Auftreten fischkritischer Bedingungen; die erwartete Temperaturerhöhung würde hingegen hauptsächlich die Sauerstoffsituation bei Trockenwetter verschlechtern.

Das vorgestellte modellbasierte Werkzeug bildet Mischwasserüberläufe aus dem Berliner Mischkanalsystem und deren kurzfristige Auswirkungen im Gewässer ab. Es soll für die Massnahmenplanung und die Berechnung von Zukunftsszenarien verwendet werden. Das Werkzeug zeigt eine gute Übereinstimmung mit Messungen bezüglich des Verlaufes der Sauerstoffkonzentration im Gewässer und des Auftretens kritischer Bedingungen für die Fischfauna.

In order to efficiently tackle odour problems from sewers which are connected with resident’s complaints and health risks, reliable online odour monitoring is necessary. Multi-gas sensor systems (electronic noses), which display a broad range of odorants, may substitute common online odour monitoring devices in the future. Four electronic noses with different configurations were tested over a period of 8 months at a sewer research plant of Berliner Wasserbetriebe. The objective was to analyse the applicability of four electronic noses for sewer odour management. 11 evaluation criteria were defined to evaluate the E-noses measurement behaviour, stability and their general practicability and handling. Generally it can be mentioned that the results are promising and the E-noses show good potentials. The E-noses which showed good results in predicting the odour concentration at the site have lack of some practical features. Whereas the systems which provide more possibilities (e.g. remote control, direct odour display) and have more complex gas preparation or measurements modes (like thermal desorption) showed lower capabilities to measure the actual odour at the site.