School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou, 510275, China.
Guangzhou Municipal Engineering Design & Research Institute, Guangzhou, 510060, China.
Water Res. 2019 Apr 1;152:226-233. doi: 10.1016/j.watres.2018.12.065. Epub 2019 Jan 14.
The presence of ammonium (NH) in drinking water treatment results in inhibition of disinfection efficiency and formation of nitrogenous disinfection by-products. Our previous study found monochloramine (NHCl) photolysis under 254 nm UV irradiation can be effective for removal of NH; however, the mechanisms of NH degradation in this process were unknown. The kinetics and fundamental radical chemistry responsible for NH removal in the UV/NHCl process were investigated in this study. The results showed that the pseudo first-order rate constant for NH degradation in the UV/NHCl process ranged between 3.6 × 10 to 1.8 × 10 s. Solution pH affected radical conversion and a higher NH degradation efficiency was achieved under acidic conditions. The effects of chloride were limited; however, the presence of either bicarbonate or natural organic matter scavenged radicals and inhibited NH removal. NHCl photolysis generated an aminyl radical (NH) and a chlorine radical (Cl) that further transformed to a chlorine dimer (Cl) and a hydroxyl radical (HO). The second-order rate constants for Cl and Cl reacting with NH were estimated as 2.59 × 10 Ms and 3.45 × 10 Ms at pH 3.9, respectively. Cl, Cl, and HO contributed 95.2%, 3.5%, and 1.3% to NH removal, respectively, at the condition of 3 mM NHCl and pH 7.5. Major products included nitrite and nitrate, possibly accompanied by nitrogen-containing gases. This investigation provides insight into the photochemistry of NH degradation in the UV/NHCl process and offers an alternative method for drinking water production.
饮用水处理中氨（NH）的存在会抑制消毒效率并形成含氮消毒副产物。我们之前的研究发现，254nmUV 照射下的一氯胺（NHCl）光解可以有效地去除 NH；然而，该过程中 NH 降解的机制尚不清楚。本研究考察了 UV/NHCl 过程中 NH 去除的动力学和基本自由基化学。结果表明，UV/NHCl 过程中 NH 降解的假一级速率常数在 3.6×10 到 1.8×10 s 之间。溶液 pH 影响自由基转化，在酸性条件下可实现更高的 NH 降解效率。氯离子的影响有限；然而，碳酸氢根或天然有机物的存在会消耗自由基并抑制 NH 的去除。NHCl 光解生成氨自由基（NH）和氯自由基（Cl），进一步转化为氯二聚体（Cl）和羟基自由基（HO）。在 pH 3.9 时，Cl 和 Cl 与 NH 的二级反应速率常数分别估计为 2.59×10 和 3.45×10 Ms。在 3mMNHCl 和 pH7.5 的条件下，Cl、Cl 和 HO 对 NH 去除的贡献率分别为 95.2%、3.5%和 1.3%。主要产物包括亚硝酸盐和硝酸盐，可能伴有含氮气体。本研究深入了解了 UV/NHCl 过程中 NH 降解的光化学，并为饮用水生产提供了一种替代方法。
