During periods of heavy rainfall storm sewage volumes can exceed the capacity of combined sewer systems and overflow to surface water bodies. Combined sewer overflows (CSO) cause significant impacts on the water quality and their identification is crucial to plan CSO control programs or to fulfil legal requirements. This paper proposes and demonstrates six different methods to identify the occurrence of CSO based on information on the sewer system alone (methods 1 and 2), in combination with rain data (methods 3 and 4) or in combination with water quality data of the receiving surface water (methods 5 and 6). The methods provide different information on CSO, from occurrence to pollution load and impacts in receiving surface water. The methods introduced have all been applied to the Berlin urban water system. Based on these experiences they are compared considering the effort needed for their application, the required data and the obtained output. It is concluded that certainty of CSO identification can be increased by combining some of the presented methods.

In the city of Berlin regular combined sewer overflows (CSO) lead to acute stress of aquatic organisms in the receiving River Spree and its side channels. Of most concern are oxygen depressions, following the inflow of degradable organic matter via ~180 CSO outlets, along a river stretch of 16 km. For the assessment of the severity of these oxygen depressions, an existing impact-based approach suggested by Lammersen (1997) was combined with information on the local fish fauna. Application of this locally adapted assessment method to seven years of oxygen measurements at a CSO hotspot in the river yielded an annual average of 14 periods with suboptimal conditions for which adverse effects on the fish fauna are expected and 20 periods with critical conditions for which acute fish kills are possible. Further investigation on rain and sewer management data proved that such critical conditions only occurred as a direct result of CSO events, whereas suboptimal conditions are also possible at dry weather and may last up to 32 days (Riechel et al. 2010).

Rural watersheds often face diffuse pollution problems due to agricultural activities. In the Ic watershed in Brittany (France), nitrate concentrations in rivers frequently exceed the EUthreshold of 50 mg-NO3 L-1, despite various actions to reduce the impact from agriculture. As a result, other solutions are considered, such as mitigation systems that can prevent transfer of agricultural pollutants from cropland to the streams. Constructed wetlands have been shown to fit this aim, because they can reach significant N removal for water residence times above ~12 hours, can be implemented decentrally within rural watersheds, while meeting cost and policy requirements. However, constructed wetlands require space, which is particularly scarce and costly in intensively used agricultural watersheds. As a consequence, it was decided to test a more area-effective solution in three pilot systems. On the one hand land-use itself was optimized (i) at site 1 by placing two wetlands with same inflow and dimension on an area of minor agricultural value adjacent to a stream (one surface and one subsurface-flow, both 20 x 10 meters) and (ii) at site 2 by building an elongated infiltration wetland (45 x 2 meters) directly in an existing drainage ditch, thus preventing any use of agricultural surface. In both cases farmers agreed to the placement of the wetlands free of charge. On the other hand it was attempted to raise the areal removal efficiency, with a focus on denitrification, since nitrate is of most concern with inflow concentrations to the sites ranging between 30 and 66 mg-NO3 L-1. This increase in denitrification is attempted (a) by increasing the range of anoxic zones within the wetlands and (b) by adding carbon sources. For (a) one wetland at each site is filled with gravel with bottom outlets to enforce underground passage. Moreover saturation level within the infiltration wetlands and thus hydraulic retention time, can be controlled at drain outlets. For (b) organically rich soil is added to both wetlands at site 1 and carbon sources are mixed with the gravel at site 2. The three wetlands have been constructed in 2010 and are currently monitored for flow and water quality at inlets, as well as at surface and subsurface outlets. The monitoring will allow the calculation of substance mass balances for the entire rain season, expected from December 2010 to May 2011.

During its passage through the City of Berlin (Germany), the quality of the River Spree is strongly influenced by combined sewer overflows (CSO), which lead to critical oxygen concentrations (DO) every year and to occasional larger fish kills. A continuous integrated monitoring concept, using state-of-the-art online sensors, was planned and started in spring 2010. It combines (i) continuous measurements of the quality and flow rates of 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. The first monitoring results show that continuous water quality measurements in CSO outlets and at downstream river stations are possible at high accuracy, even for comparably complex parameters such as chemical oygen demand (COD). Analysis of measured data confirms the significance of CSO discharges on receiving waters and underlines the value of continuous measurements in describing the local dynamics of the CSO and their impacts on water bodies.

To gain better understanding of the impact of combined sewer overflows (CSO) on the chemical and ecological status of lowland rivers and to evaluate the effect of CSO control measures a planning instrument for impact-based CSO management is being developed in Berlin, Germany. After completion the model-based planning instrument will be used by the Berlin water and wastewater utility and the water authority for scenario analysis of CSO management strategies. To adapt the planning instrument to their respective needs and to guarantee an efficient transfer of the results a specific project structure was established. Through direct participation in project management, technical and scientific work as well as demonstration the end-users can influence the development and provide technical input on local issues. First project results show the relevance of CSO impacts compared to the background condition of the Berlin river system and the need for additional measurements to provide data for model adaptation, calibration and validation.

The Berliner Wasserbetriebe are the largest water supply and wastewater disposal company in Germany. They are challenged to tackle various kinds of odour problems emerging from the sewer network. The continuous extension of sewer networks and a decrease in water consumption (in Berlin: ~ 20 % in the last 16 years, according to the statistical office BB, 2009) have led to elevated odour emissions arising from sewer systems. Together with growing public concern over odours from water treatment works, this has led to increasing numbers of odour complaints in urban catchments (Stuetz and Frechen, 2001; ATV-DVWK-M 154, 2003; Barjenbruch, 2003). Different odour abatement technologies are widely-used but often response only after consumer complaints and do not consider adequate identification of odour problems beforehand. An operational, together with a scientific approach is necessary in order to apply effective measures or combinations thereof. In Berlin annually almost 3 Mio € are spent by BWB to reduce odour emissions from the Berlin sewer system (BWB, 2006). Applied measures vary from dosing of nitrate or iron hydroxide sludge, flushing, or compensation by means of bio-filters or masking. The quantification of odour by means of continuous odour monitoring solutions such as electronic noses can contribute to minder economic and operational risks in odour management. The paper presents the research project ODOCO-ARTNOSE, dealing with the evaluation of electronic noses for the online application in sewer systems. The KompetenzZentrum Wasser Berlin (research centre) in cooperation with the Berlin water utilities Berliner Wasserbetriebe and Veolia Water will carry out bench tests with selected, commercially available chemosensor arrays to identify advanced applications of electronic noses in odour management in sewer networks. Objectives of the project are to analytically assess the online-ability of electronic noses by means of a multi-criteria methodology and to specify future odour control services based on the application of e-noses in sewer networks. The potential of electronic noses will be evaluated as tool to fulfil certain needs, namely (i) support for planning/designing of odour preventive measures and abatement strategies, (ii) support for real-time odour control and (iii) data acquisition tool to supervise and document (industrial) dischargers, document the effect of abatement measures and document legal compliance. Tests are possible to be carried out in the frame of a sewer research plant or within the sewer system of Berlin. A large-scale research plant was developed by Berliner Wasserbetriebe for investigating different odour and corrosion strategies. The plant consists of 2 independent gravity lines and is fed by combined wastewater from Berlin, pumped directly from the sewer. Various milieu conditions can be generated. The paper places current challenges within the city of Berlin into perspective and displays examples of odour abatement strategies of Berliner Wasserbetriebe. Expected outcomes and correlated benefits of the project will be presented. The methodological approach relies on a transparent selection of chemosensor array systems, on bench tests following a sophisticated measurement program and the evaluation of the electronic noses by clear defined criteria.

The present study examines the contribution of combined sewer overflows (CSO) to loads and concentrations of trace contaminants in receiving surface water. A simple method to assess the ratio of CSO to wastewater treatment plant (WWTP) effluents was applied to the urban River Spree in Berlin, Germany. The assessment indicated that annual loads are dominated by CSO for substances with removal in WWTP above w95%. Moreover, it showed that substances with high removal in WWTP can lead to concentration peaks in the river during CSO events. The calculated results could be verified based on eight years of monitoring data from the River Spree, collected between 2000 and 2007. Substances that are well removed in WWTP such as NTA (nitrilotriacetic acid) were found to occur in significantly increased concentration during CSO, while the concentration of substances that are poorly removable in WWTP such as EDTA (ethylenediaminetetraacetic acid) decreased in CSO-influenced samples due to dilution effects. The overall results indicate the potential importance of the CSO pathway of well-removable sewage-based trace contaminants to rivers. In particular, high concentrations during CSO events may be relevant for aquatic organisms. Given the results, it is suggested to include well-removable, sewage-based trace contaminants, a substance group often neglected in the past, in future studies on urban rivers in case of combined sewer systems. The presented methodology is suggested for a first assessment, since it is based solely on urban drainage data, which is available in most cities.

The effect of combined sewer overflow (CSO) control measures should be validated during operation based on monitoring of CSO activity and subsequent comparison with (legal) requirements. However, most CSO monitoring programs have been started only recently and therefore no long-term data is available for reliable efficiency control. A method is proposed that focuses on rainfall data for evaluating the effectiveness of CSO control measures. It is applicable if a sufficient time-series of rainfall data and a limited set of data on CSO discharges are available. The method is demonstrated for four catchments of the Berlin combined sewer system. The analysis of the 2000-2007 data shows the effect of CSO control measures, such as activation of in-pipe storage capacities within the Berlin system. The catchment, where measures are fully implemented shows less than 40 % of the CSO activity of those catchments, where measures have not yet or not yet completely been realised.

The Berliner Wasserbetriebe are the largest water supply and wastewater disposal company in Germany. They are challenged to tackle various kinds of odour problems emerging from the sewer network. The continuous extension of sewer networks and a decrease in water consumption (in Berlin: ~ 20 % in the last 16 years, according to the statistical office BB, 2009) have led to elevated odour emissions arising from sewer systems. Together with growing public concern over odours from water treatment works, this has led to increasing numbers of odour complaints in urban catchments (Stuetz and Frechen, 2001; ATV-DVWK-M 154, 2003; Barjenbruch, 2003). Different odour abatement technologies are widely-used but often response only after consumer complaints and do not consider adequate identification of odour problems beforehand. An operational, together with a scientific approach is necessary in order to apply effective measures or combinations thereof. In Berlin annually almost 3 Mio € are spent by BWB to reduce odour emissions from the Berlin sewer system (BWB, 2006). Applied measures vary from dosing of nitrate or iron hydroxide sludge, flushing, or compensation by means of bio-filters or masking. The quantification of odour by means of continuous odour monitoring solutions such as electronic noses can contribute to minder economic and operational risks in odour management. The paper presents the research project ODOCO-ARTNOSE, dealing with the evaluation of electronic noses for the online application in sewer systems. The KompetenzZentrum Wasser Berlin (research centre) in cooperation with the Berlin water utilities Berliner Wasserbetriebe and Veolia Water will carry out bench tests with selected, commercially available chemosensor arrays to identify advanced applications of electronic noses in odour management in sewer networks. Objectives of the project are to analytically assess the online-ability of electronic noses by means of a multi-criteria methodology and to specify future odour control services based on the application of e-noses in sewer networks. The potential of electronic noses will be evaluated as tool to fulfil certain needs, namely (i) support for planning/designing of odour preventive measures and abatement strategies, (ii) support for real-time odour control and (iii) data acquisition tool to supervise and document (industrial) dischargers, document the effect of abatement measures and document legal compliance. Tests are possible to be carried out in the frame of a sewer research plant or within the sewer system of Berlin. A large-scale research plant was developed by Berliner Wasserbetriebe for investigating different odour and corrosion strategies. The plant consists of 2 independent gravity lines and is fed by combined wastewater from Berlin, pumped directly from the sewer. Various milieu conditions can be generated. The paper places current challenges within the city of Berlin into perspective and displays examples of odour abatement strategies of Berliner Wasserbetriebe. Expected outcomes and correlated benefits of the project will be presented. The methodological approach relies on a transparent selection of chemosensor array systems, on bench tests following a sophisticated measurement program and the evaluation of the electronic noses by clear defined criteria.

The quality of the River Spree during its passage through the city of Berlin is mainly influenced by the discharge of treated effluent from waste water treatment plants and by combined sewer overflows (CSO). CSO are discharged diffusely and during short periods of time leading to acute impacts like oxygen depletion and locally increased ammonia concentration in the river. They are dominant stress factors to Berlin’s lowland River Spree and its biocenosis. In order to improve the water quality of the River Spree, measures limiting the emissions of CSO are envisaged such as utilization of in-pipe storage capacities, implementation of weirs for real-time control, construction of additional stormwater tanks. In order to build an efficient and immission oriented strategy with the different available solutions and to be able to cope with future challenges the Berlin Centre of Competence for Water (KWB), Berliner Wasserbetriebe, Veolia Water and the Berlin Senate of Environment are conducting two projects, the EU project PREPARED and the MIA-CSO project. An impact-based CSO management instrument is being developed with the aim to evaluate measures of CSO control. It consists in (i) a river water quality/ecosystem model that will be used to simulate water quality processes in the receiving water and (ii) a methodology to identify critical water quality situations occurring in the Spree River. For model adaptation, calibration and validation an integrated monitoring is conducted. The monitoring consists in (i) continuously measuring the quality and flow of CSO discharges at one representative network location and (ii) in parallel, continuously monitoring water quality parameters at 5 sites within the impacted stretch of the Spree River. The concept of the integrated monitoring, i.e. definition of monitoring sites as well as monitoring strategy and design will be presented during the M3 Workshop.