ESTIMATION OF MICROBIAL LOAD DISCHARGED FROM A SEWAGE TREATMENT PLANT TO RECEIVING WATERS

Abstract

 The occurrences of primary treatment discharge from sewage treatment plants (STPs) including CSOs and SSOs have been frequently reported in recent years. However, it is still unclear how much pathogen are discharged along with primary treatment discharge into receiving waters. Therefore, this research was aiming at understanding of the pathogen load discharged from a STP which receives sewage from separate sewers with partially-combined sewer drainage areas. This STP facitates biological treatment as well as high-speed coagulation sedimentation treatment. Concentrations of Escherichia coli (E. coli) and F-phage in wastewater were measured before and after chlorination tank, and at high-speed coagulation sedimentation treatment facility, both in rainy and fine weather. Based on the concentrations and statistical model, the annual loads of E. coli and F-phage discharged from each facility were estimated. As a result, primary treatment discharge in rainy day occupied almost half of both E. coli and F-phage loads from the biological treatment facility, which was followed by biological treatment effluent in rainy whether without primary treatment discharge, and the load in the fine weather. The high-speed coagulation sedimentation facility of E. coli was about 1% of the total load from the STP, while that of F-phage was about half of the total load. This is the first study to incestigate the load of microbials discharged from the STP, and demonstrate the impact of the primary treatment discharge in rainy day.