Chloramines Hydrolysis-Induced Advanced Oxidation Processes: Mechanism Investigation and Applications for Potable Reuse
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Chloramines Hydrolysis-Induced Advanced Oxidation Processes: Mechanism Investigation and Applications for Potable Reuse

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Abstract

Water reuse has been proposed and implemented as a promising solution to address the water scarcity issue. Water reuse treatment typically contains monochloramine (NH2Cl) and dichloramine (NHCl2). Chloramines bypass the RO membrane and photolyze as photo-oxidants in the ultraviolet light-based advanced oxidation processes (UV/AOP). Small and neutral contaminants easily diffuse through membrane-based treatments, and UV/AOP oxidizes organic micropollutants. However, the treatment requires high energy consumption. The goal of this dissertation is to study the mechanistic insights of chloramine hydrolysis and its potential implications for rapid trace organic removal in water reuse scenarios. First, the formation and the subsequent hydrolysis of NHCl2 were investigated in the mixed system of HOCl and NH2Cl. It was observed that the highest 1,4-D removal was at pH 6 with the HOCl-to-NH2Cl molar ratio of 1. These conditions favored the formation and the hydrolytic decay of NHCl2. It was also found that the crucial intermediate, peroxynitrite (ONOO-), was experimentally measured in the mixed system of HOCl/NH2Cl. Further, it was determined that 60-70% of 1,4-D removal was due to the generated HO• in the mixed HOCl and NH2Cl system. Second, the mechanisms that govern the rapid hydrolytic decay of NHCl2 for HO• generation were uncovered. Also, the oxidative capacity of the NHCl2-initiated system was examined in water reuse-related conditions. It was determined that the highest HO• exposure was at pH 8.4 with the NH2Cl-to-NHCl2 molar ratio of 1 in the NHCl2-initiated system. It was validated that the decay of NHCl2 and the intermediate ONOO- decided the eventual HO• exposure. It was also demonstrated that the NHCl2-initiated oxidative system is comparable to the newly proposed UV/AOPs. Third, the NHCl2 hydrolysis system could be exploited for organic contaminant removal when the pH is alkaline with UV irradiation. This process was shown to produce HO•, demonstrating that ONOO- was generated during the process. Lastly, the oxidative capacity of the UV/ONOO- at alkaline pHs was confirmed to be comparable to other existing UV/AOPs. The outcomes of the aforementioned projects allow water reuse facilities to design better treatment processes and optimize the operational parameters for potential implications of the novel techniques.

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This item is under embargo until January 26, 2025.