Inhibitory Effects of UV-LED Irradiation and Period in Darkness on Photoreactivation of Coliforms in Johkasou Treated Water

抄録

With the recent development of ultraviolet light emitting diodes (UV-LEDs), it is now possible to apply UV disinfection, previously used only for medium-to-large sized sewage treatment plants, to Johkasou wastewater, a household wastewater treatment system. However, it is known that coliforms that have been inactivated by UV irradiation regain their activity after of sunlight irradiation, etc. Therefore, in small Johkasou, where discharge channels are often open, photorecovery may occur immediately after UV disinfection. However, no studies have been conducted to investigate photorecovery by sunlight after UV disinfection of wastewater from small Johkasou. In this study, the relationship between the photorecovery of coliforms and the dose of sunlight after UV-LED irradiation of effluent in Johkasou was investigated. As a result, we identified the amount of sunlight that will maximize photoreactivation effect. We also clarified the suppressing effect of an excessive amount of sunlight on the photoreactivation phenomenon. Additionally, since it was confirmed that the photoreactivation effect was suppressed by a certain period of darkness following UV-LED irradiation, it was considered that the photoreactivation effect can also be suppressed by allowing wastewater to reside in darkness for the currently estimated residence time in a disinfection tank.