Chen Han, Lin Tao, Yan Xiaoshu, Xu Hang
Ministry of Education Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Hohai University, Nanjing 210098, PR China; College of Environment, Hohai University, Nanjing 210098, PR China.
Ministry of Education Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Hohai University, Nanjing 210098, PR China; College of Environment, Hohai University, Nanjing 210098, PR China.
Sci Total Environ. 2022 Feb 1;806(Pt 2):150612. doi: 10.1016/j.scitotenv.2021.150612. Epub 2021 Sep 28.
The formation of haloacetonitriles (HANs) during chlorination after sulfite/ultraviolet (UV) treatment of bromate (BrO) in the presence of amino acids (AAs) was investigated. During sulfite/UV treatment, the primary species hydrated electrons (e) and hydrogen atom radicals (H) dominated the reduction of BrO to bromide (Br), whereas the sulfite anion radicals (SO) and H degraded AAs to produce the intermediates HN=C(CH)-COOH, CH-CH=NH, and CH-C≡N via α‑hydrogen abstraction and NH-hydrogen abstraction mechanisms. During post-chlorination, Br was converted to HBrO/BrO-, and the HN=C(CH)-COOH, CH-CH=NH, and CH-C≡N groups featured higher bromine utilization factor (BUF) and chlorine utilization factor (CUF) values than AAs, enhancing the formation of dibromoacetonitrile (DBAN) and dichloroacetonitrile (DCAN). The energetic feasibility of the transformation pathway, that is, HN=C(CH)-COOH, CH-CH=NH, and CH-C ≡ N formation via hydrogen abstraction by SO and H and their further conversion to HANs, was proved by density functional theory calculations, which showed stepwise negative Gibbs free energy changes (ΔG < 0). The effects of pH and water matrices (e.g., HCO, Cl, Fe, and natural organic matter) were comprehensively evaluated. Although 72% of BrO was removed by sulfite/UV treatment in the presence of AAs, the cytotoxicity index (CTI) and genotoxicity index (GTI) during post-chlorination increased by 213% and 125%, respectively, due to the formation of 24 CXR-type disinfection by-products (DBPs), especially brominated DBPs. Accordingly, more attention should be given to the formation of brominated DBPs during post-chlorination when using sulfite/UV processes to remove BrO in the presence of AAs. As a solution, using monochloramine instead of chlorine as a disinfectant after the sulfite/UV process could significantly lower the CTI and GTI values by alleviating the formation of brominated DBPs.
研究了在氨基酸（AAs）存在下，亚硫酸盐/紫外线（UV）处理溴酸盐（BrO）后氯化过程中卤代乙腈（HANs）的形成情况。在亚硫酸盐/UV处理过程中，主要物种水合电子（e）和氢原子自由基（H）主导了BrO还原为溴化物（Br）的过程，而亚硫酸根阴离子自由基（SO）和H通过α-氢提取和NH-氢提取机制将AAs降解为中间体HN=C(CH)-COOH、CH-CH=NH和CH-C≡N。在后续氯化过程中，Br转化为HBrO/BrO-，与AAs相比，HN=C(CH)-COOH、CH-CH=NH和CH-C≡N基团具有更高的溴利用因子（BUF）和氯利用因子（CUF）值，促进了二溴乙腈（DBAN）和二氯乙腈（DCAN）的形成。密度泛函理论计算证明了转化途径的能量可行性，即通过SO和H的氢提取形成HN=C(CH)-COOH、CH-CH=NH和CH-C≡N，以及它们进一步转化为HANs，计算结果显示吉布斯自由能变化呈逐步负值（ΔG < 0）。综合评估了pH值和水基质（如HCO、Cl、Fe和天然有机物）的影响。尽管在AAs存在下，亚硫酸盐/UV处理去除了72%的BrO，但由于形成了24种CXR型消毒副产物（DBPs），尤其是溴化DBPs，后续氯化过程中的细胞毒性指数（CTI）和遗传毒性指数（GTI）分别增加了213%和125%。因此，在AAs存在下使用亚硫酸盐/UV工艺去除BrO时，应更加关注后续氯化过程中溴化DBPs的形成。作为一种解决方案，在亚硫酸盐/UV工艺后使用一氯胺代替氯作为消毒剂，可以通过减轻溴化DBPs的形成显著降低CTI和GTI值。
