Growing demands and increasing scarcity of fresh water resources necessitate potable water reuse, which has been implemented with the aid of UV-based advanced oxidation processes (UV/AOPs) that remove potentially hazardous trace organic contaminants from reclaimed water. During the potable reuse treatment process, chloramines are added to prevent membrane fouling that are carried over to the UV/AOP, where hydrogen peroxide (H₂O₂) is commonly added. However, the impact of chloramines on the photolysis of H₂O₂ and the overall performance of the UV/AOP remains unknown. This study investigated the impacts of the photochemistry of monochloramine (NH₂Cl) and dichloramine (NHCl₂) associated with the photolysis of H₂O₂ on the degradation of 1,4-dioxane (1,4-D), a trace organic contaminant ubiquitous in recycled water. Results indicated that NH₂Cl and NHCl₂ alone functioned as oxidants upon UV photolysis, which produced HO^• and Cl₂^•- as the two primary oxidative radicals. The speciation of chloramines did not have a significant impact on the degradation kinetics. The inclusion of monochloramine in UV/H₂O₂ greatly decreased 1,4-D removal efficiency. HO^• was the major radical in the mixed H₂O₂/chloramine system. Results from this study suggest that recognizing the existence of chloramines in UV/H₂O₂ systems is important for predicting UV/AOP performance in the treatment train of potable reuse.

Mariano Romano

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