Framework for Enhanced Stormwater Management by Optimization of Sewer Pumping Stations

Control and reduction of pollution from stormwater overflow is a major concern to be addressed by municipalities in order to improve the quality of the receiving water bodies and the environment in general. In the European context, these actions are driven by the Water Directive 2000/60/CE. In this regard, assessment studies of the potential load from sewer networks recognize the need for adaptation and upgrade of existing networks with waterworks and management measures. In many cases this is done by building first-flush detention tanks that, however, present consistent practical and economical burdens. In this work, simple rules to manage existing pumping stations in combined sewer systems are proposed as a way to apply management rules that mitigate pollution load. Such rules can be easily implemented in real cases with minimal cost of activation and no need of additional infrastructures. The procedure is based on the previous knowledge of the precipitation forcing and of a quantity/quality model of the sewer network. The steps adopted are (1) use of a (long-term, high-resolution) sequence of rainfall events to compute a wide spectrum of flow conditions (hydrographs and pollutographs) to the pumping stations; (2) definitions of a pumping rule to apply to the whole sequence of events to filter the incoming flow toward the wastewater treatment plant, so to compute outflows; and (3) efficiency assessment of the pumping rule by cumulative frequency analysis of water volume, pollutant mass, and pollutant mean concentration. Rule optimization can be performed by iterating points (2) and (3). An example is proposed to show how two simple parameters (a discharge threshold on the inflow and a maximum pumping time) can control the management of water and pollutant fluxes. Numerical results show that a proper optimization allows one to reduce the pumped volumes (thus reducing energy requirements and increasing the treatment plant efficiency) without significant changes to the overall pollutant mass outflow. The new pumping rules can be implemented on real stations with minimal and economically sustainable interventions.