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.
Research Article|September 01 2009
Nitrite formation during low pressure ultraviolet lamp irradiation of nitrate
Water Sci Technol (2009) 60 (6): 1393-1400.
Ning Lu, Nai-Yun Gao, Yang Deng, Qing-Song Li; Nitrite formation during low pressure ultraviolet lamp irradiation of nitrate. Water Sci Technol 1 September 2009; 60 (6): 1393–1400. doi: https://doi.org/10.2166/wst.2009.475
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