Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, 510275, China.
Water Res. 2018 Aug 1;139:220-227. doi: 10.1016/j.watres.2018.04.013. Epub 2018 Apr 6.
The Co(II)/peroxymonosulfate (Co(II)/PMS) process, producing sulfate radicals (SO), effectively removes organic pollutants in water, while producing a significant amount of bromate (BrO) in the presence of bromide (Br). This paper investigates the ammonia (NH) addition, chlorine-ammonia (Cl-NH) and ammonia-chlorine (NH-Cl) pretreatment strategies in controlling BrO formation in 20 min in the Co(II)/PMS process at pH 4.0. The addition of NH retarded the BrO formation, but only at a reduction level of about 9.5% for NH concentration of 50 μM, and was mainly attributed to the protonation of NH at pH 4 (99.99% as NH, did not react with HOBr). Both the Cl-NH and NH-Cl pretreatment strategies at HOCl and NH dosages of 15 and 50 μM, respectively, reduced 95% or more of the overall BrO formation and retarded the BrO formation, with the NH-Cl pretreatment strategy outperforming Cl-NH. The reduction of the BrO formation was mainly attributed to the formation of monochloramine (NHCl) in both pretreatment strategies. NHCl effectively outcompetes SO to react with HOBr and forms NHBrCl, with the apparent reaction rate constant between NHCl and HOBr more than 100 times faster than that between SO and HOBr. However, the oxidation/degradation of NHBrCl in the Co(II)/PMS process reforms HOBr, and, although less in quantity, is oxidized to BrO at higher Co(II) and Br concentrations. Thus, the NH-Cl and Cl-NH pretreatment strategies inhibit the BrO formation more significantly at lower Co(II) and Br concentrations. In all cases, the generation of SO in 20 min was not affected by the implementation of the three BrO pretreatment strategies.
钴（II）/过一硫酸盐（Co（II）/PMS）过程产生硫酸根自由基（SO），可有效去除水中的有机污染物，但在存在溴化物（Br）的情况下会产生大量的溴酸盐（BrO）。本文研究了在 pH 值为 4.0 的 Co（II）/PMS 体系中，20 分钟内添加氨（NH）、氯氨（Cl-NH）和氨氯（NH-Cl）预处理策略对控制 BrO 形成的影响。添加 NH 会抑制 BrO 的形成，但仅在 NH 浓度为 50 μM 时降低约 9.5%，这主要归因于 pH 值为 4 时 NH 的质子化（99.99%为 NH，不会与 HOBr 反应）。HOCl 和 NH 的剂量分别为 15 和 50 μM 时，Cl-NH 和 NH-Cl 预处理策略均能将总 BrO 形成量减少 95%以上，且 NH-Cl 预处理策略的效果优于 Cl-NH。BrO 形成的减少主要归因于两种预处理策略中均形成一氯胺（NHCl）。NHCl 有效地与 HOBr 竞争反应，形成 NHBrCl，NHCl 与 HOBr 的表观反应速率常数比 SO 与 HOBr 的反应速率常数快 100 多倍。然而，在 Co（II）/PMS 体系中，NHBrCl 的氧化/降解会重新形成 HOBr，虽然数量较少，但在较高的 Co（II）和 Br 浓度下会被氧化为 BrO。因此，在较低的 Co（II）和 Br 浓度下，NH-Cl 和 Cl-NH 预处理策略更显著地抑制了 BrO 的形成。在所有情况下，三种 BrO 预处理策略的实施并未影响 20 分钟内 SO 的生成。
