title: Nitrite formation during low pressure ultraviolet lamp irradiation of nitrate.
abstract: During ultraviolet light (UV) disinfection, nitrate (NO3-) present in raw water may transform to nitrite (NO2-) that can cause serious human diseases. In this study, the formation of NO2- from NO3- was studied at different experimental conditions under the irradiation of a low-pressure ultraviolet (LPUV) lamp at 253.9 nm. The investigated experimental variables included initial NO3- concentration, solution pH (6.2-9.5), and hydrogen peroxide (H2O2) dose (0-25 mg L(-1)). Moreover, the effect of titanium dioxide (TiO2) was determined. Results showed that the formation of NO2- was enhanced at a high initial NO3- concentration and a high pH, but was inhibited, to some different degrees, by introduction of H2O2 or photocatalyst TiO2. The effect of pH on NO2- formation was probably due to the impact of hydrogen ion on the stability of several intermediates such as peroxynitrite (ONOO-), N2O3, and N2O4. And the inhibiting effects of H2O2 and TiO2 were attributable to production of additional hydroxyl radical (OH) that scavenged NO2-. At pH 9.5 and an initial NO3- concentration of 10 mg L(-1) NO3--N, the concentration of NO2- produced was above 0.1 mg L(-1) NO2--N, the Germany drinking water standard. When 25 mg L(-1) H2O2 was added, the NO2- level was decreased below the standard.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Lu
authors.forename: Nai-Yun
authors.initials: NY
authors.lastname: Gao
authors.forename: Yang
authors.initials: Y
authors.lastname: Deng
authors.forename: Qing-Song
authors.initials: QS
authors.lastname: Li
mesh_terms: D002384:Catalysis; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008029:Lighting; D009573:Nitrites / Q000737:chemistry*; D010782:Photolysis; D011312:Pressure; D014025:Titanium / Q000737:chemistry; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D009573:Nitrites; D014867:Water; C009495:titanium dioxide; D006861:Hydrogen Peroxide; D014025:Titanium