THE EFFECT OF COMBINED SEWER SEWAGE TREATMENT PLANT DISCHARGE DURING RAINY EVENTS ON THE SANITARY MICROORGANISMS OF KATSURA RIVER WATER

Public concerns have recently emerged due to sanitary microorganisms in combined sewer overflows (CSO) during rainy events. The purpose of this study was to investigate the influence of primary treatment discharge from a combined sewer sewage treatment plant (STP) on sanitary microorganisms in receiving Katsura River. To this end, we investigated the presence of sanitary microorganisms in STP discharge and river water during rainy events. In addition, increase in the load of sanitary microorganisms during rainy events was examined based on our previous study during non-rainfall conditions. It was found that primary treatment discharge during rainy events significantly increased in the microbial load of STP discharge and the receiving water. However, the increasing load of the river reach between upstream and downstream points could not be explained by the increase in the STP discharge alone.