Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China.
Hainan Provincial Department of Ecological Environment, Haikou 570203, China.
Water Res. 2021 Oct 1;204:117569. doi: 10.1016/j.watres.2021.117569. Epub 2021 Aug 19.
The UV/monochloramine (UV/NHCl) process has attracted increasing attention in water treatment, in which hydroxyl radicals (HO), reactive chlorine species (RCS) and reactive nitrogen species (RNS) are produced. This study investigated the effects of water matrices including halides, natural organic matter (NOM), alkalinity and pH, on the degradation kinetic of a variety of micropollutants and radical chemistry in the UV/NHCl process. The presence of chloride blunted HO and Cl impacts, but enhanced Cl effect on micropollutants reactive toward Cl. The presence of 30 μM bromide led to an 82% decrease in the specific pseudo-first-order rate constants (k') by HO (k'), and significantly diminished RCS efficacy. Reactive bromine species (RBS) were formed in the presence of bromide, while the contribution could not compensate for the decrease of HO and RCS due to their lower reactivity toward micropollutants. Iodide rapidly transformed to HOI via reacting with NHCl, which resulted in a 59% decrease of k' and 12% ∼ 100% decreases of k' by reactive halogen species (RHS) and RNS (k') for most micropollutants. Nevertheless, k' of phenolic compounds, such as paracetamol, bisphenol A and salbutamol, increased in the presence of iodide by 78%, 360% and 130%, respectively, due to the roles of HOI and reactive iodine species (RIS). Bicarbonate decreased the contributions of HO and RCS, but enhanced that of CO for micropollutants reactive toward CO. The presence of 1 mg/L NOM scavenged over half the amount of HO, and also consumed RCS and RNS, resulting in significantly decreased removal of micropollutants. High pH value witnessed enhanced degradation for those micropollutants reactive toward RCS and RNS through deprotonation. The degradation of most micropollutants was inhibited in real drinking water and in the coexistence of halides. This study provides a better understanding of radical chemistry in the UV/NHCl process under a practical water treatment condition.
UV/一氯胺（UV/NHCl）工艺在水处理中受到越来越多的关注，其中会产生羟基自由基（HO）、活性氯物种（RCS）和活性氮物种（RNS）。本研究考察了水基质（包括卤化物、天然有机物（NOM）、碱度和 pH 值）对各种微污染物降解动力学和 UV/NHCl 工艺中自由基化学的影响。氯化物的存在削弱了 HO 和 Cl 的影响，但增强了 Cl 对亲 Cl 微污染物的作用。存在 30 μM 溴化物会使 HO（k'）的特定假一级速率常数（k'）降低 82%，并显著降低 RCS 功效。在溴化物存在的情况下形成了活性溴物种（RBS），但由于其对微污染物的反应性较低，其贡献无法弥补 HO 和 RCS 的减少。碘化物通过与 NHCl 反应迅速转化为 HOI，导致 k'降低 59%，大多数微污染物的 RHS 和 RNS（k'）的 k'降低 12%~100%。然而，由于 HOI 和活性碘物种（RIS）的作用，酚类化合物（如对乙酰氨基酚、双酚 A 和沙丁胺醇）的 k'分别增加了 78%、360%和 130%。碳酸氢盐降低了 HO 和 RCS 的贡献，但增强了 CO 对亲 CO 微污染物的作用。存在 1 mg/L NOM 时，HO 的量被消耗了一半以上，同时也消耗了 RCS 和 RNS，导致微污染物的去除率显著降低。高 pH 值通过去质子化增强了对 RCS 和 RNS 反应性的那些微污染物的降解。在实际饮用水和卤化物共存的情况下，大多数微污染物的降解受到抑制。本研究为在实际水处理条件下更好地理解 UV/NHCl 工艺中的自由基化学提供了依据。
