Wang Wen-Long, Lee Min-Yong, Du Ye, Zhou Tian-Hui, Yang Zheng-Wei, Wu Qian-Yuan, Hu Hong-Ying
Key Laboratory of Microorganism Application and Risk Control of Shenzhen, Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Institute of Environment and Ecology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, PR China.
Department of Environmental Resources Research, National Institute of Environmental Research, Seogu, Incheon 22689, Republic of Korea.
Environ Int. 2021 Dec;157:106793. doi: 10.1016/j.envint.2021.106793. Epub 2021 Jul 28.
Pre-ozonation can reduce the formation of disinfection byproducts (DBPs) and related adverse effects during subsequent chlorination, but the change of each molecular weight (MW) fraction during each step of combined pre-ozonation and post-chlorination has not been well illustrated. In this study, it was investigated in terms of electron-donating-moieties (EDMs) and UVA for a representative natural organic matter from Suwanee river (SRNOM). Pre-ozonation suppressed the post-chlorination of SRNOM through oxidation of almost all EDMs (>85%) and UVA (>90%) in high MW fractions (HMW, >3.2 kDa) and moderate EDMs (43%) and UVA (72%) in medium MW fractions (MMW, 1.0-3.2 kDa). Furthermore, pre-ozonation led to comparable abatements of EDMs and UVA for HMW fractions, but lower abatement of EDMs than UVA for MMW fractions. However, when t-BuOH was used as an OH-quencher, pre-ozonation led to a few instances in which there were higher abatements of EDMs than UVA for the MMW fraction. These findings suggested that the HMW fraction dominantly underwent ring-cleavage of phenols via O- or OH-oxidation. Differently, the MMW fraction underwent ring-cleavage of phenols and quinones-formation via O-oxidation, but occasionally underwent hydroxylation and hydro-phenol formation via OH-oxidation. Because of forehand elimination of reactive moieties (e.g. EDMs), pre-ozonation obviously inhibited the formation of representative DBPs (67%-84% inhibition), total organic chloride (51% inhibition) and cytotoxicity (31% inhibition), but may have promoted the formation of carbonyl-DBPs (trichloroacetone and chloral hydrate). When compared with UVA, EDMs would better for surrogate of DBPs formation. EDM abatement surrogated the formation of total organic chlorine (TOCl) and cytotoxicity following a two-stage phase, possibly because the speciation of DBPs and transformation products varied with the abatement of EDMs.
预臭氧化可减少后续氯化过程中消毒副产物（DBPs）的形成及相关不利影响，但预臭氧化和后氯化各步骤中各分子量（MW）组分的变化尚未得到充分阐明。在本研究中，针对来自苏万尼河的代表性天然有机物（SRNOM），从供电子基团（EDMs）和紫外光A（UVA）方面进行了研究。预臭氧化通过氧化高分子量组分（HMW，>3.2 kDa）中几乎所有的供电子基团（>85%）和紫外光A（>90%）以及中等分子量组分（MMW，1.0 - 3.2 kDa）中43%的供电子基团和72%的紫外光A，抑制了SRNOM的后氯化。此外，预臭氧化对HMW组分的供电子基团和紫外光A的去除程度相当，但对MMW组分的供电子基团的去除程度低于紫外光A。然而，当使用叔丁醇作为羟基自由基猝灭剂时，预臭氧化导致在某些情况下MMW组分中供电子基团的去除程度高于紫外光A。这些发现表明，HMW组分主要通过O - 或OH - 氧化使酚类发生开环反应。不同的是，MMW组分通过O - 氧化使酚类发生开环反应并形成醌类，但偶尔也会通过OH - 氧化发生羟基化和形成氢酚。由于预先消除了活性基团（如供电子基团），预臭氧化明显抑制了代表性消毒副产物的形成（抑制率为67% - 84%）、总有机氯化物（抑制率为51%）和细胞毒性（抑制率为31%），但可能促进了羰基消毒副产物（三氯丙酮和水合氯醛）的形成。与紫外光A相比，供电子基团更适合作为消毒副产物形成的替代指标。供电子基团的去除在两阶段过程中替代了总有机氯（TOCl）的形成和细胞毒性，这可能是因为消毒副产物和转化产物的形态随供电子基团的去除而变化。
