Pollutant characteristics and first flush effect of runoff in combined sewer system

The discharges of combined sewer overflows into the receiving waters will influence the quality of the receiving waters. Several parameters, such as the type and area of the catchment, the characteristics of the rain, can influence the pollutant characteristic and first flush effect of runoff in combined sewer system. The different type catchment in representative combined sewer system, Mingtong river basin, was selected to study the pollutant characteristic and first flush effect of runoff. It was found that the concentration of pollutants was substantially higher during the initial period of stormwater runoff than lasted period. The characteristic and speciation of different pollutants was quite different. The dissolved N is the main speciation of N pollutant, and the particulate P is the main speciation of P pollutant. The event mean concentrations(EMC) is the highest in the beginning of the rainy season, lowest in the middle of the rainy season, and middle in the end of the rainy season. The magnitude of the EMC is characterized in the order of residential areaurban integrated areaintegrated areaurban and suburb combined area. The precipitation rainfall is the key factor that control the first flush effect, the magnitude of the first flush is grater for high precipitation.