Evaluating the effectiveness of point-of-use UVC LED disinfection of activated carbon block filter effluent among private well users

Abstract

Point of use (POU) water treatment systems are a cost-effective method for providing safe drinking water in the absence of a central water treatment system, such as in homes relying on private wells and low-resource areas where funds for large scale treatment systems are unavailable. Activated carbon block (ACB) filters are a popular method for removing chemical contaminants but have little benefit in controlling microbial contaminants from private well water. This research investigates the effectiveness of a multibarrier approach to POU treatment for private wells by adding a UV disinfection step for treating ACB effluent. An ACB filter followed by an in-line POU Light Emitting Diode (LED) UV disinfection device was installed in 17 homes using well water in North Carolina. Influent and effluent samples were collected monthly for 5 months (Oct 2019-Feb 2020). Total coliforms, heterotrophic plate count (HPC) and male-specific coliphages were measured on paired influent and effluent samples. Mean UV influent (effluent) concentrations were 40 (1.7) MPN per 100 mL, 944 (1172) CFU per 1 mL, and 5.7 (6.8) PFU per 100 mL for coliforms, HPC, and coliphages, respectively. A statistically significant decrease was found in the UV effluent samples for coliforms (Wilcoxon signed rank test, p = 0.029) but not for heterotrophic bacteria or male-specific coliphages. Heterotrophic bacteria exhibited a shift in the microbial community with the species richness decreasing in the UV effluent. Overall, the POU UVC LED device did not achieve health protective levels of disinfection in this study, potentially due to UV-resistant species, viral aggregation, measurement challenges, lamp fouling, and/or other water quality factors. Private well users, policymakers, and/or public health agencies considering UVC LED technology for microbial control in private well water should validate performance in their local context and continue to promote other good well stewardship behaviors to ensure microbiologically safe water.