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

UVA photolysis of nitrite (NO) 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 under environmentally relevant conditions. The results demonstrated that more than 3 log inactivation of K-12, , and sp. BM1-1 was achieved by UVA photolysis of 2.0 mg-N L of NO in synthetic drinking water and real surface water. The inactivation was mainly attributed to the reactive species generated from UVA photolysis of NO rather than UVA irradiation or NO oxidation alone. The inactivation was predominantly contributed by the reactive nitrogen species (NO and ONOO/HOONO) instead of the reactive oxygen species (HO or O). A kinetic model to simulate the reactive species generation from UVA photolysis of NO 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., DO - labeling with Raman spectroscopy) were used to demonstrate that the inactivation by the UVA/NO 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.