Modelling Saint Malo WWTP & Development of a Decision Support Tool for the Management of the Combined System Sewer-WWTP

The regulation drawn from the French law on water of 1992 imposes on communities to treat their wastewater, except in case of exceptional rainy events. The seaside towns have also to respect the directive of 1975 concerning the quality of bathing water. Anjou Recherche launched in April 2001 an integrated study on the modelling of the sewage system of Saint Malo (Brittany, France), i.e. sewer network, wastewater treatment plant (WWTP) and receiving water. This study is embedded in a global project, with the overall aim to limit the impact of direct discharges towards the sea, and thus, preserve the quality of bathing water of the city. The method applied consists of obtaining a model for each part of the sewage system based on dedicated software. In a second step, these models are associated in a decision support tool especially made for operational use. The different models have been built, calibrated and validated using several data sets. A first version of the decision support tool has been completed and installed on site beginning of 2005. Currently, only the sewer network model is included in this version. Next developments will aim at integrating the WWTP model, before to consider its extension to the receiving water part.