Abstract
Performances of disinfection process were investigated at small domestic wastewater treatment plants (Johkasou) which have an important role for excreta/wastewater treatment in individual houses. As disinfection apparatuses were well maintained by owner or qualified contractor, residual chlorine in effluent was detected in most cases even when wastewater from bathtub was discharged. Disinfection efficiency, however, was not perfect, because there were many cases which residual chlorine and coliform/fecal coliform group were detected together in effluent. It became clear that the concentrations of ammonia nitrogen and nitrite nitrogen in treated water should be at least lower than 10 mg/l to pass the effluent standard of coliform group, 3000 number/ml, with using the current disinfection method.
