Flow and pollutant measurements in a combined sewer system to operate a wastewater treatment plant and its storage tank during storm events

Urban storm drainage is considered using an integrated approach taking into account all parts of the sewer system: pipes, storage tanks, overflows, treatment plant and receiving waters. This paper presents an experimental research in Boran-sur-Oise (France) where continuous measurements are carried out in the combined sewer system (catchment area 61 ha), in the storage tank (245 m³) and in the treatment plant (3000 p.e.). One of the objectives is a comprehensive knowledge of effects of storm events on treatment plant process and efficiency. Catchment, sewer system, storage tank, treatment plant and measurements are described. Results for an autumn rainfall are given as an example. Many impacts on the treatment plant are observed. Despite the load increase compared with dry weather periods, especially for TSS and ammonia, the plant efficiency remains satisfactory. Short-term and long-term impacts are distinguished. New rules for storage tank operation are proposed to avoid hydraulic plant overloading and to use the stormwater solids-settling properties. These rules will be tested in the future to verify their compatibility with receiving water quality requirements. Measurements in upstream sewer system could also be used in the future to operate stormwater treatment systems during storm events.