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Small drinking water systems account for about 90% of United States systems and serve about 53 million people; that’s one fifth of the U.S. population.  Given their size and lack of resources, these small systems face more of a struggle to meet regulations, and rely heavily on disinfection, particularly by chlorine.  However, using chlorine risks the formation of harmful disinfection byproducts (DBPs) and chlorine-resistant pathogens.  There is therefore an interest in ultraviolet disinfection, which can reduce such formation, as while as degrade certain contaminants chlorine cannot.  UV disinfection, though, is associated with increased workloads in terms of training, operation and maintenance, and higher doses require more energy.  Furthermore, UV still must be coupled with chlorine in order to provide a distribution system residual, and the broader environmental impacts of such technologies, especially in the context of small water systems (< 10,000 people), are not well established. 

Considering the thus clearly complicated trade-offs between chlorine disinfection and ultraviolet disinfection, and the need for small drinking water system stakeholders to make appropriate decisions about disinfection technologies, CU Boulder’s Prof. Sherri Cook and PhD student Christopher Jones, with help from Prof. Karl Linden and MS student Elizabeth Shilling, have performed a comprehensive and quantitative study comparing the environmental impacts of chlorine and UV primary disinfection in the context of small water systems.  The goal of their study, which employs life cycle assessment (LCA) methodology, is to provide the information needed for small water systems to make the design and operational disinfection decisions that will minimize environmental impacts without comprising public health.  Three representative water quality and regulatory scenarios were evaluated: 1) a typical scenario representing the use of filtration and a chlorine residual; 2) a chlorine residual exemption scenario; and 3) a filtration exemption scenario.  Overall, they found that, from an LCA perspective, using UV instead of chlorine was best in only a few cases (i.e. high pumping pressure but filtration not required), while, in all other cases, chlorine was environmentally preferred (though the comparison was affected by contact zone materials and energy sources).