Enhanced Formation of Brominated and Nitrogenous Disinfection Byproducts in Drinking Water Disinfection with Chlorocyanurates

Disinfection of drinking water provides essential protection against microbial pathogens. However, disinfectants react with organic matter and other constituents in water to form disinfection byproducts (DBPs), which are of concern for human health. Chlorocyanurates are chlorine-based disinfectants that have been used for drinking water in point-of-use and emergency contexts. Little is known about chlorocyanurate DBP formation beyond the potential to form lower regulated trihalomethanes and haloacetic acids compared to chlorine. In this study, regulated and unregulated DBP formation was evaluated for multiple chlorocyanurate formulations to understand the effect of the chlorine-to-cyanuric acid ratio on DBP mixture composition and calculated toxicity by comparison to conventional chlorine. Chlorocyanurates produced lower regulated DBPs by ∼10-50% compared to chlorine but promoted bromine incorporation in most DBP classes by 50-200% and produced higher calculated toxicity than chlorine under most conditions. Enhanced dichloroacetonitrile formation by chlorocyanurates was partly attributed to trichloramine formation from the degradation of chlorocyanurates by hypochlorite. Thus, chlorocyanurates may promote multiple DBP toxicity drivers. Water quality and operational considerations are identified to minimize DBP toxicity while using chlorocyanurate disinfectants, which remain an important option for drinking water disinfection in low-resource settings.