Lu Ning, Gao Nai-Yun, Deng Yang, Li Qing-Song
State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China.
Water Sci Technol. 2009;60(6):1393-400. doi: 10.2166/wst.2009.475.
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.
在紫外线（UV）消毒过程中，原水中存在的硝酸盐（NO3-）可能会转化为亚硝酸盐（NO2-），而亚硝酸盐会引发严重的人类疾病。在本研究中，在253.9nm的低压紫外线（LPUV）灯照射下，研究了不同实验条件下NO3-向NO2-的转化。研究的实验变量包括初始NO3-浓度、溶液pH值（6.2 - 9.5）和过氧化氢（H2O2）剂量（0 - 25mg L(-1)）。此外，还测定了二氧化钛（TiO2）的影响。结果表明，在高初始NO3-浓度和高pH值下，NO2-的生成会增加，但通过引入H2O2或光催化剂TiO2会在不同程度上受到抑制。pH值对NO2-生成的影响可能是由于氢离子对几种中间体如过氧亚硝酸盐（ONOO-）、N2O3和N2O4稳定性的影响。而H2O2和TiO2的抑制作用归因于产生了额外的羟基自由基（OH），其清除了NO2-。在pH值为9.5且初始NO3-浓度为10mg L(-1) NO3--N时，产生的NO2-浓度高于0.1mg L(-1) NO2--N，这超过了德国饮用水标准。当添加25mg L(-1) H2O2时，NO2-水平降至标准以下。
