Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, 510275, PR China.
Shenzhen Environmental Science and New Energy Technology Engineering Laboratory, Tsinghua-Berkeley Shenzhen Institute, Shenzhen, 518055, PR China.
Water Res. 2021 Apr 15;194:116914. doi: 10.1016/j.watres.2021.116914. Epub 2021 Feb 8.
The UV/monochloramine (UV/NHCl) process is an emerging advanced oxidation process (AOP) to remove organic contaminants in water treatment with radicals including hydroxyl radicals (HO), reactive chlorine species (RCS) and reactive nitrogen species (RNS). This study investigated the formation of nitro(so) and chlorinated products and toxicity alteration during the UV/NHCl treatment of phenol. RNS and/or RCS induced the formation of nitro(so), chlorinated and polymeric compounds during phenol transformation by UV/NHCl. These compounds dramatically increased the cytotoxicity to Chinese hamster ovary cells after 20 min UV/NHCl treatment, which was 10 times higher than that after 24 h chloramination. The increase of cytotoxicity in UV/NHCl was primarily attributable to 4-nitrosophenol, and the cytotoxicity followed the order of 4-nitrosophenol >> 4-nitrophenol > 2,4,6-trichlorophenol > 2,4-dichlorophenol > phenol. 4-Nitrosophenol was significantly generated by the combination of NO and phenoxy radical, where the maximum conversion rates of phenol to 4-nitrosophenol increased from 4.9% to 62.4% when pH increased from 5 to 10. The highest conversion rate was at pH 10 because the NO concentration increased with increasing pH from 5 to 10 in UV/NHCl, as verified by the electron paramagnetic resonance (EPR) analysis. Nitrophenols were also detected at much lower concentrations than 4-nitrosophenol, which were mainly formed by the oxidation of 4-nitrosophenol and the combination of NO with phenoxy radicals. RCS was responsible for the formation of chlorinated products mainly through Cl addition and the reactions of Cl/Cl with phenoxy radicals. Also, RCS and RNS significantly enhanced the formation of carbonaceous (i.e., chloroform and chloral hydrate) and nitrogenous disinfection byproducts (i.e., chloropicrin and dichloroacetonitrile) in UV/NHCl. This study indicates that the UV/NHCl treatment significantly increased toxicity and validates the roles of RNS and RCS in producing toxic nitro(so) and chlorinated products.
UV/ 单氯胺（UV/NHCl）工艺是一种新兴的高级氧化工艺（AOP），可通过羟基自由基（HO）、活性氯物种（RCS）和活性氮物种（RNS）等自由基去除水处理中的有机污染物。本研究考察了酚在 UV/NHCl 处理过程中形成的亚硝（砜）和氯化产物及其毒性变化。在 UV/NHCl 作用下，RNS 和/或 RCS 诱导亚硝（砜）、氯化和聚合化合物的形成，从而导致酚的转化。与 24 小时氯化消毒相比，经过 20 分钟 UV/NHCl 处理后，这些化合物使中国仓鼠卵巢细胞的细胞毒性显著增加了 10 倍。UV/NHCl 中细胞毒性的增加主要归因于 4-亚硝基苯酚，细胞毒性的顺序为 4-亚硝基苯酚>4-硝基苯酚>2,4,6-三氯苯酚>2,4-二氯苯酚>苯酚。4-亚硝基苯酚是由 NO 和苯氧基自由基结合产生的，当 pH 值从 5 增加到 10 时，苯酚转化为 4-亚硝基苯酚的最大转化率从 4.9%增加到 62.4%。在 pH 10 时，转化率最高，因为在 UV/NHCl 中，NO 浓度随 pH 值从 5 增加到 10 而增加，这一点通过电子顺磁共振（EPR）分析得到了验证。硝基苯酚的浓度也远低于 4-亚硝基苯酚，主要通过 4-亚硝基苯酚的氧化和 NO 与苯氧基自由基的结合形成。RCS 主要通过 Cl 加成和 Cl/Cl 与苯氧基自由基的反应形成氯化产物。此外，RCS 和 RNS 显著促进了 UV/NHCl 中碳质（即三氯甲烷和水合氯醛）和含氮消毒副产物（即氯仿和二氯乙腈）的形成。本研究表明，UV/NHCl 处理显著增加了毒性，并证实了 RNS 和 RCS 在产生有毒亚硝（砜）和氯化产物中的作用。
