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 H 2O2 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 NO 3- concentration of 10 mgL-1 NO 3--N, the concentration of NO2- produced was above 0.1 mgL-1 NO2--N, the Germany drinking water standard. When 25 mgL-1 H2O 2 was added, the NO2- level was decreased below the standard.
- Low-pressure UV lamp