Assessment of ultraviolet disinfection for unfiltered water supplies

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Ultraviolet (UV) disinfection of drinking water is an effective and increasingly popular method to inactivate chlorine-resistant pathogens of public health concern. In Canada, UV treats over 21% of all drinking water, and recent surveys of treatment facilities identify this technology as a top choice for increasing disinfection effectiveness. Since particulates and other material in natural waters can interfere with the disinfection process by blocking or reflecting light, it is recommended that UV be applied after filtration. However, filtration is not practiced universally, and several unfiltered water supplies utilize UV for disinfection. There are gaps in knowledge regarding UV effectiveness for unfiltered waters, and performance must be well understood under a range of conditions for the protection of public health. The proposed work aims to address knowledge gaps by quantifying relationships between a wide range of unfiltered water quality conditions and UV effectiveness. Two full-scale treatment facilities that apply UV to unfiltered waters will be used as models and to provide representative samples. Disinfection achieved will be identified through standardized microorganism bioassays after exposure to collimated UV light. Using experimental data, the adequacy of current monitoring and operational practices will be considered. This work will also look at ways to improve the accuracy of UV monitoring protocols to ensure that disinfection can be achieved even with challenging source water conditions. Project outcomes will include new data to advance industry best practices in UV disinfection of unfiltered water supplies at Canadian facilities.