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.