UVA photolysis of nitrite (NO2-) occurs in a number of natural and engineered aquatic systems. This study reports for the first time that pathogenic microorganisms can be effectively inactivated during the coexposure of UVA irradiation and NO2- under environmentally relevant conditions. The results demonstrated that more than 3 log inactivation of Escherichia coli K-12, Staphylococcus aureus, and Spingopyxis sp. BM1-1 was achieved by UVA photolysis of 2.0 mg-N L-1 of NO2- in synthetic drinking water and real surface water. The inactivation was mainly attributed to the reactive species generated from UVA photolysis of NO2- rather than UVA irradiation or NO2- oxidation alone. The inactivation was predominantly contributed by the reactive nitrogen species (NO2• and ONOO-/HOONO) instead of the reactive oxygen species (HO• or O2•-). A kinetic model to simulate the reactive species generation from UVA photolysis of NO2- was established, validated, and used to predict the contributions of different reactive species to the inactivation under various environmental conditions. Several advanced tools (e.g., D2O - labeling with Raman spectroscopy) were used to demonstrate that the inactivation by the UVA/NO2- treatment was attributed to the DNA destruction by the reactive nitrogen species, which completely suppressed the viable but nonculturable (VBNC) states and the reactivation of bacteria. This study highlights a novel process for the inactivation of pathogenic microorganisms in water and emphasizes the critical role of reactive nitrogen species in water disinfection and purification.
Keywords: UVA; dark repair; disinfection; nitrite; reactive nitrogen species.