Combined Sewer Overflows Into The Crati River (Cosenza, Italy)

摘要

Combined Sewer Overflows (CSOs) have been for long time present in the technical literature. A short review of recent contributions is given in the paper. Regulations for reducing CSO impact in the U.S., EU and in Italy are then considered. Different means of controlling CSOs are discussed and among them retention storage is considered as the most frequent. Observations from an experimental catchment in Cosenza, Italy, drained by a combined sewer system with overflow facility, are then presented. They include 28 CSO events, for which the complete hydrographs were registered, obtaining the overflows hydrographs. Six more events were observed for quality data, and TSS, BOD and COD were measured; a regression equation between TSS, BOD and COD was found. Pollutant rates were represented against stormwater volumes, and first foul flush seems to be present only in one of the six events. As EU regulations demand complete storage and treatment of combined sewer overflows, different retention volumes of an off-line tank were analysed, provided that a discharge from 3 to 4 times the dry weather discharge is continuously treated by the treatment plant during storms. Values of the order of 150-200 m~3/ha should reduce the final spill into receiving waters to a few events per year.