Impacts of Conventional UV254/AOP and Novel UV222/AOP on Disinfection Byproduct Formation in Water Reuse

Abstract During advanced water treatment, UV advanced oxidation processes (UV/AOP) are followed by postchlorination to achieve additional disinfection credits and provide a disinfectant residual in the distribution system. The impact of conventional UV/AOP using 254 nm low-pressure UV lamps (UV254) on disinfection byproduct (DBP) formation has been extensively studied but remains largely unknown for UV/AOP using 222 nm krypton chloride excimer (UV222) lamps, an emerging UV technology. In this study, the concentration of 52 DBPs formed during uniform formation condition (UFC) chlorination was measured following both UV254 and UV222 AOP, in synthetic water and effluent from a carbon-based potable reuse treatment train. Both UV254 and UV222 increased UFC formation of trihalomethanes, haloacetic acids, and haloacetaldehydes, while only UV222 consistently increased halonitromethane (HNM) formation. UV222 treatment led to a 4.7–72-fold increase in HNM formation, increasing from 0.55–0.69 μg/L to 2.6–49.7 μg/L. However, when considering cytotoxicity, UV222 did not have a consistent effect, as calculated cytotoxicity in these waters was driven mostly by haloacetonitriles (HANs), which are not impacted by UV treatment. This study extends previous findings about UV222-driven HNM formation to a water reuse context and highlights the need to mitigate HNM formation during UV222 treatment for potable reuse.