Pollutant Load Discharged from Johkasou Systems and its Impact on Water Quality of River and Lake

Data on the water quality of about 500 effluent samples collected from septic tank (johkasou) systems being used at individual residences in Gunma prefecture were examined to determine the treatment performance of each system. The pollutant loads discharged from the johkasou systems were calculated using the water quality data. In addition, more effective means of wastewater management in an unsewered area where most of town's wastewater was mainly treated by tandoku-shori johkasou systems were discussed on the basis of the calculated pollutant load factor. The results of the water quality analysis showed that the treatment performance of the advanced gappei-shori johkasou (type 1-3) system was the highest of all the johkasou systems. Changing the tandoku-shori johkasou system to the type 1-3 system is recommended to prevent the eutrophication of a lake in the unsewered area.