Verification of the Disinfection Effect of LED Near-UV Irradiation Unit on Household Johkasou Treated Water

Abstract

 Chlorine disinfection is commonly used in household Johkasou because the equipment is simple, and the disinfecting effect is maintained for a long time due to residual chlorine. However, it is necessary to consider new disinfection methods to improve maintenance and management efficiency. In recent years, with the development of LEDs capable of emitting near-ultraviolet (near－UV) rays, it has become possible to introduce UV disinfection, which was previously only possible at medium-sized Johkasou or larger sewage treatment plants, into the small Johkasou of ordinary households. In small Johkasou, the water quality and flow rate are likely to fluctuate over time depending on the lifestyle of each household, which is predicted to affect the UV disinfection efficiency. Research on this issue has yet to be conducted. In this study, an LED near－UV disinfection unit was installed in an actual household Johkasou, and the effects of water quality and flow rate on UV disinfection efficiency were examined. The results showed that UV disinfection can sufficiently inactivate coliform bacteria and Escherichia coli in advanced treatment type Johkasou (target water quality, BOD: 10 mg･L－¹ or less, SS: 10 mg･L－¹ or less). However, it was confirmed that decreased UV irradiation time due to increased flow rate reduces the UV disinfection efficiency. Therefore, UV disinfection units are considered more effective when combined with higher-functioning flow equalization.