Tomofumi TANNO

Research on analysis of water quality change of combined sewer overflow and the CSO control for pollution load from CSO in Nagaoka City

Shoichi FUJITA Toshiya KOMATSU Shuji HIMENO

The Japanese government decided to improve the combined sewer system as a matter of national policy. Municipalities with CSO problems embarked on full programs for the improvement works. We newly developed an auto sampling system that gathers water at the same time the overflow starts. Several countermeasures for the CSO control are proposed and evaluated through observations and analysis in the city.
Furthermore, we continuously observed the water quality of combined sewer overflow. Therefore, we clarified quantitatively the phenomenon of the first flash and rain water dilution that have not been clear. As a result, it turned out that the pollution load to the river by CSO became more than the amount of a total discharge from the sewage plant in Nagaoka City during the dry weather. As for measures of the CSO control, it has been calculated that a 5000m3 basin and other improvement measures are the most preferable. The techniques are capable of general use and can be applied in many cities in the world.