State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, China.
State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, China.
Water Res. 2023 Nov 1;246:120673. doi: 10.1016/j.watres.2023.120673. Epub 2023 Sep 26.
The oxidation kinetics of Mn(II) by free chlorine is relatively low under near-neutral pH conditions which limits the Mn removal efficiency in drinking water treatment. Therefore, this study investigated the oxidation efficiency of Mn(II) by the UV-enhanced chlorination (UV/chlorine) system and identified the responsible reactive radical species. The results show that the oxidation kinetic of Mn(II) was greatly enhanced by the UV/chlorine system under near-neutral pH or even acidic conditions. The pseudo-first-order reaction rate of Mn(II) at pH 8.0 (within the first 20 min) increased from 2.60 × 10 s to 3.41 × 10 s. Based on the scavenging experiments and the steady-state kinetic modeling, ClO and ClO, whose steady-state concentration (∼10 M and ∼10 M, respectively at pH 8.0) was at least 4 orders of magnitude higher than that of HO and Cl, were recognized as the dominant reactive species contributing to the oxidation of Mn(II). Kinetic model calculations indicate that the contribution of ClO to the oxidation of Mn(II) was consistently maintained above 70 %, and ClO also played an important role in the oxidation of Mn(II) especially under acidic and alkaline conditions. In addition, the background components of HCO and Cl had negligible influence on the oxidation efficiency because they barely changed the concentration of the ClO and ClO. This study first demonstrates the important role of ClO in the oxidation of Mn(II) in the UV/chlorine system, and the possible role of ClO in the degradation of some organic pollutants needs to be carefully evaluated in the future.
在近中性 pH 条件下，自由氯对 Mn(II)的氧化动力学相对较低，这限制了饮用水处理中 Mn 的去除效率。因此，本研究考察了 UV 增强氯化（UV/氯气）系统对 Mn(II)的氧化效率，并确定了起作用的活性自由基种类。结果表明，在近中性 pH 条件下，甚至在酸性条件下，UV/氯气系统极大地增强了 Mn(II)的氧化动力学。在 pH 8.0 时（在前 20 分钟内），Mn(II)的假一级反应速率从 2.60×10 s增加到 3.41×10 s。基于猝灭实验和稳态动力学模型，ClO 和 ClO ，其在 pH 8.0 时的稳态浓度（分别约为 10 M 和 10 M）至少比 HO 和 Cl 高 4 个数量级，被认为是导致 Mn(II)氧化的主要活性物质。动力学模型计算表明，ClO 对 Mn(II)氧化的贡献一直保持在 70%以上，ClO 在 Mn(II)氧化中也起着重要作用，尤其是在酸性和碱性条件下。此外，HCO 和 Cl 的背景成分对氧化效率的影响可以忽略不计，因为它们几乎不改变 ClO 和 ClO 的浓度。本研究首次证明了在 UV/氯气系统中，ClO 在 Mn(II)氧化中的重要作用，而在未来需要仔细评估 ClO 在一些有机污染物降解中的可能作用。
