Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou, 510006, China; Southern Marine Science and Engineering Guangdong Laboratory, Guangzhou, 511458, China; State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090, China.
Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou, 510006, China; Southern Marine Science and Engineering Guangdong Laboratory, Guangzhou, 511458, China; State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090, China.
Water Res. 2020 Jun 1;176:115725. doi: 10.1016/j.watres.2020.115725. Epub 2020 Mar 16.
Sulfate radical-based advanced oxidation processes (SR-AOPs) show a good prospect for effective elimination of organic contaminants in water due to the powerful oxidation capability and good adaptability of sulfate radical (SO). However, great concerns have been raised on occurrence of the carcinogenic byproduct bromate (BrO) in SR-AOPs. The present article aims to provide a critical review on BrO formation during bromine (Br)-containing water oxidation by various SR-AOPs. Potential reaction mechanisms are elaborated, mainly involving the sequential oxidation of bromide (Br) by SO to Br-containing radicals (e.g., bromine atom (Br•)) and then to hypobromous acid/hypobromite (HOBr/OBr), which acts as the requisite intermediate for BrO formation. Some key influencing factors on BrO formation are discussed. Particularly, dissolved organic matter (DOM) as a component ubiquitously present in aquatic environments shows a significant suppression effect on BrO formation, primarily attributed to the reduction of Br• by DOM to Br. The reaction of Br• with DOM can hardly produce organic brominated byproducts, while their formation is mainly due to the bromination of HOBr/OBr generated through nonradical pathways such as the direct reaction of Br with oxidants (e.g., peroxymonosulfate (PMS)) or other reactive species derived from catalytic activators (e.g., Co(III) in the Co(II)/PMS process). The debromination of brominated pollutants during their oxidation by SO results in the release of Br, which, however, is not further transformed to BrO until coexisting organic matters are mineralized nearly completely. Furthermore, possible strategies for control of BrO formation in SR-AOPs as well as the future research needs are proposed.
基于硫酸盐自由基的高级氧化工艺 (SR-AOPs) 由于硫酸根自由基 (SO) 的强大氧化能力和良好的适应性，在有效去除水中有机污染物方面显示出良好的前景。然而，人们对 SR-AOPs 中致癌副产物溴酸盐 (BrO) 的产生表示了极大的关注。本文旨在对各种 SR-AOPs 中含溴水氧化过程中 BrO 形成的情况进行批判性评价。阐述了潜在的反应机制，主要涉及 SO 对溴化物 (Br) 的连续氧化，生成含溴自由基（如溴原子 (Br•)），然后生成次溴酸/次溴酸盐 (HOBr/OBr)，这是 BrO 形成的必要中间体。讨论了影响 BrO 形成的一些关键因素。特别是，作为水生环境中普遍存在的组成部分的溶解有机物 (DOM) 对 BrO 形成表现出显著的抑制作用，这主要归因于 DOM 还原 Br•为 Br。Br•与 DOM 的反应几乎不会产生有机溴化副产物，而其形成主要归因于 HOBr/OBr 的溴化，HOBr/OBr 是通过非自由基途径生成的，例如 Br 与氧化剂（例如过一硫酸盐 (PMS)) 或其他源自催化活性剂（例如 Co(II)/PMS 工艺中的 Co(III)）的反应性物种的直接反应。SO 氧化溴化污染物时的脱溴作用导致 Br 的释放，但只有当共存有机物几乎完全矿化时，Br 才会进一步转化为 BrO。此外，还提出了在 SR-AOPs 中控制 BrO 形成的可能策略以及未来的研究需求。
