UV365 induced elimination of contaminants of emerging concern in the presence of residual nitrite: Roles of reactive nitrogen species

Abstract

The presence of nitrite (NO2−) is inevitable with concentrations of several mg L−1 in some typical water bodies. In this study, UV at wavelength of 365 nm was investigated to degrade contaminants of emerging concern (CECs) in the presence of NO2− at environmentally relevant concentrations (0.1–5.0 mg L−1). Six selected CECs with different structures were efficiently removed because of the generation of reactive nitrogen species (RNS) and hydroxyl radical (HO•) from photolysis of NO2−. Contributions of UV365 photolysis, RNS, and HO• to CEC degradation in UV365/NO2− system were calculated, and RNS were found to be the predominant species that are responsible for CEC degradation. The second major contributor is HO• for the degradation of selected CECs except for the case of sulfadiazine. Impacts of water matrix components (including dissolved oxygen, solution pH, and natural organic matter) on CEC degradation in UV365/NO2− system were evaluated. Furthermore, evolution profiles of CECs and NO2− in UV365/NO2− system were tracked when actual water samples were used as background, and a simultaneous removal of CECs and NO2− was observed. Transformation products of bisphenol A and carbamazepine were proposed according to the results of HPLC/MS and quantum chemistry calculations. Nitration induced by RNS and hydroxylation induced by HO• are main reactions occurred during CEC degradation in UV365/NO2− system. Overall, UV365 is a potential technology to remove CECs and NO2− in aquatic environment when residual NO2− is present. Our present study also provides possibility for the application of sunlight to remediate water co-polluted by CECs and NO2−.