Effects of UV-C radiation on the survival of copepods and oocysts: implications for drinking water processing facilities

In southern China, ozonation/biologically active carbon (O3/BAC) filter technology is widely applied in drinking water treatment facilities, but the current processing method often fails to eliminate copepods. Phyllodiaptomus tunguidus and Heliodiaptomus falxus are commonly found in drinking water processing facilities that use O3/BAC technology. This study explored the efficacy and mechanism of 254 nm UV radiation for elimination of copepods and oocysts. Both tested species had a similar profile of mortality after UV-C radiation, and all adults and oocysts were inactivated when a minimal dose of 540 μJ cm−2 was applied. The population survival time was negatively correlated with radiation duration, but positively correlated with water depth. Radiation duration and culture time had a significant effect on mortality (P < 0.01). When the dose reached 1,944 μJ cm−2, copepods displayed muscle breakage and mobility loss and oocysts displayed loose internal structure and arrested embryonic development, and were unable to hatch. UV-C radiation appears to be a low-cost and convenient method to effectively inactivate copepods and their oocysts in drinking water processing facilities without disinfection by-products.