Pollution Origins and Characteristics of Combined Sewer Overflows from Urban Area

Combined sewer overflows (CSOs) have been considered as a major cause of water quality deterioration of natural water-courses in the vicinity of the heavily urbanized areas. The factors defining the magnitude and occurrence of CSOs are site-specific. It is important to know exact properties of pollutants contained in CSOs to address water quality impacts that are caused by CSOs inputs to the receiving waters. This should be accompanied with an integrated analysis, evaluation programs, thus allowing us to devise an appropriate technology to alleviate the impacts. Pollutant concentrations measured during the storm events are generally higher, especially than those of dry weather conditions except for T-N parameter much highere at the initial phase of CSOs. Based on the rough estimation by the proposed pollutant mass balance, it is found that a main part of wet weather pollutional loads originated from the resuspension of sewer bottom sediments. The dimensionless L(V) curves for determining whether first flush phenomenon occurred or not are well described the pollutant flushing. These results showed that a given fraction of volume contained a load of SS higher than COD, T-P, T-N in the initial phase of wet weather runoff.