Mechanism, kinetics and DBP formation of UV/NH2Cl process on contaminant removal in aqueous solution: A review

UV-based advanced oxidation processes (AOPs) have been widely applied in water and wastewater treatments. Very recently, the combination of UV and monochloramine (NH2Cl) for contaminant removal attracts increasing attention. In this review, the generation mechanism of reactive species (mainly including Cl., HO. and reactive nitrogen species (RNS)) during UV/NH2Cl process was introduced and elucidated in detail. The various contaminant degradation generally followed the pseudo-first order kinetics (kobs). The kobs was affected by a series of influencing factors (i.e., pH, NH2Cl concentration, co-existing substances, etc.). Especially, compared with other UV-based AOPs, UV/NH2Cl treatment was usually less sensitive to the water matrix in real waters. The degradation mechanisms of various contaminant by UV/NH2Cl treatment generally incorporated three parts, including reactive species, reactive sites and reactions. Herein, very recently, RNS was demonstrated to play a vital role on contaminant decomposition. Moreover, UV/NH2Cl had a high risk of the formation of severely toxic iodo-disinfection byproducts (DBPs) and nitrogen-containing DBPs, though the yield of common DBPs herein was generally less than that in other UV-based AOPs. Finally, knowledge gaps and research needs of UV/NH2Cl were proposed as a reference for future research.