Modelling CWs for CSO treatment – reasonable balancing between detailed description and practicable handling

Simulation models are an important tool in planning urban drainage systems, so enhanced treatment devices need to be implemented in the computing procedures. In combined sewer systems an enhanced treatment of combined sewer overflow (CSO) is required when augmented water quality requirements are demanded or conventional CSO treatment does not meet environmental quality standards. Constructed wetlands (CWs) have become the most common method to provide enhanced treatment of CSO in Germany. D. Meyer*, U. Dittmer** and T. G. Schmitt* * Institute of Urban Water Management, Technical University of Kaiserslautern, PaulEhrlich-Strasse, 14-316, D-67663 Kaiserslautern, Germany ([email protected]) ** Institute of Sanitary Engineering, Water Quality and Solid Waste Management, University of Stuttgart, Bandtaele 2, D-70569 Stuttgart, Germany, (E-mail: [email protected]) Balancing between detailed description and practicable handling in modelling CWs for CSO treatment, also known as retention soil filters (RSFs), depends on modelling aims. To calculate average emissions of these CWs simple approaches like a RSF module in long-term pollution-load model KOSMO are adequate (Kaufmann & Schmitt, 2005). To describe and investigate operational conditions complex biokinetic reaction models like CW2D (Langergraber & Šimůnek, 2005) can be used, but they are not applicable as optimization tools in practical use. To optimise operation and design the model RSF_Sim has been developed. Within the model a reasonable balance between detailed description and practicable handling has to be found. First versions of the new model are able to describe basic processes appropriately. Simulation results for single events show a good match of hydraulic conditions and effluent concentration curves (Meyer et al., 2008). Long-term simulation runs show proper results calculating average emissions, but also indicate needs of more detailed descriptions within the black box under varying operational conditions. Within the paper requirements, methods and prospects of modeling RSFs for practical use are given and discussed.