INACTIVATION EFFECT OF UV-LED ON INDICATOR BACTERIA IN JOHKASOU EFFLUENT WATER

Abstract

 Chlorine inactivation is commonly used in Johkasou, however, its human health risk and environmental impact are concerned. In recent years, small UV-LED with low voltage has been developed, then it is expected to be an alternative way for inactivation in Johkasou. In this research, effects of UV-LED inactivation on three indicator bacteria; coliforms, E.coli, and enterococci in the effluent from Johkasou were examined. Although the removal rates of all three indicator bacteria increased with the increase in UV irradiation time, enterococci showed higher resistance to UV. Since a positive correlation between Abs 280 nm and BOD concentration in the effluent water was observed, it would be important to reduce BOD concentration before the inactivation tank for improving UV irradiation efficiency. The inverse relation between water depth of the inactivation tank and removal rates of indicator bacteria suggests that the use of a shallow inactivation tank would be effective to increase coefficient WF.