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

The presence of nitrite (NO) is inevitable with concentrations of several mg L 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 NO at environmentally relevant concentrations (0.1-5.0 mg L). 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 NO. Contributions of UV photolysis, RNS, and HO to CEC degradation in UV/NO 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 UV/NO system were evaluated. Furthermore, evolution profiles of CECs and NO in UV/NO system were tracked when actual water samples were used as background, and a simultaneous removal of CECs and NO 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 UV/NO system. Overall, UV is a potential technology to remove CECs and NO in aquatic environment when residual NO is present. Our present study also provides possibility for the application of sunlight to remediate water co-polluted by CECs and NO.