Reactive Nitrogen Species Mediated Inactivation of Pathogenic Microorganisms during UVA Photolysis of Nitrite at Surface Water Levels.

UVA photolysis of nitrite (NO 2 - ) 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 NO 2 - 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 NO 2 - in synthetic drinking water and real surface water. The inactivation was mainly attributed to the reactive species generated from UVA photolysis of NO 2 - rather than UVA irradiation or NO 2 - oxidation alone. The inactivation was predominantly contributed by the reactive nitrogen species (NO 2 • and ONOO - /HOONO) instead of the reactive oxygen species (HO • or O 2 •- ). A kinetic model to simulate the reactive species generation from UVA photolysis of NO 2 - 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., D 2 O - labeling with Raman spectroscopy) were used to demonstrate that the inactivation by the UVA/NO 2 - 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.