Advanced oxidation processes (AOPs) relying on the generation of highly reactive radicals are effective for the abatement of refractory contaminants during water treatment. Inorganic nitrogen is widely present in aquatic environments, which results in the formation of reactive nitrogen species (RNS) and alters the transformation pathways of contaminants in AOPs. The roles of RNS in the transformation of phenol by UV/NH2Cl, UV/peroxydisulfate/NO2− (UV/PDS/NO2−) and UV/H2O2/NO2− were investigated. RNS (e.g., *NO and *NO2) were significantly generated in UV/NH2Cl, UV/PDS/NO2− and UV/H2O2/NO2−, in which the formation of *NO in UV/NH2Cl was directly demonstrated by electron paramagnetic resonance (EPR). The involvement of RNS results in the significant formation of highly toxic nitro(so) compounds. Nitro(so)phenols and chloropicrin were obviously formed during the degradation of phenol by UV/NH2Cl. Also, the formation of nitrophenols was strongly enhanced in UV/PDS/NO2−, which yield (47.5%) was significantly higher than that in UV/H2O2/NO2− (5.3%). This was due to that SO4*− and HO* reacts with phenol mainly through electron transfer and addition to generate phenoxy radicals and phenol-HO-adduct radicals, respectively. Phenoxy radicals react quickly with *NO2 to produce nitrophenols, while phenol-HO-adduct radicals were converted to hydroxyphenols via the reaction with O2. The formation of nitro(so) compounds significantly increased the cytotoxicity and mutagenicity, indicating that the involvement of RNS in water treatment by AOPs deserves valid concern.

Roles of reactive nitrogen species in the transformation of phenol during advanced oxidation processes

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