The paper presents the investigations on first flush phenomenon based on the total suspended solids (TSS) concentration measurement during selected rainfalls at central part of Czestochowa (Poland) and also the hydrodynamic model of the catchment. The model allows to present the conception of first flush management using an improved flow diverter Septurn. Flow diverters used in the separate sewer systems create a hybrid system called “semi-separate” sewage system, which allows to treat the first flush volume in the waste water treatment plant (WWTP). Proposed construction of the flow diverter makes possible to capture significant part of the pollutant load (TSS) and simultaneously to reduce volume discharges to WWTPs during wet weather.
Keywords: first flush, flow diverter, semi-separate sewer system, stormwater