Photolysis of Mono- and Dichloramines in UV/Hydrogen Peroxide: Effects on 1,4-Dioxane Removal and Relevance in Water Reuse.

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.