Curtin Water Quality Research Centre, Department of Chemistry, Curtin University, GPO Box U1987, 6845 Perth, Western Australia, Australia; School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea.
Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland; School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale Lausanne (EPFL), CH-1015 Lausanne, Switzerland; ETH Zurich, Swiss Federal Institute of Technology, Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environment Systems (D-USYS), Universitätstrasse 16, CH-8092 Zürich.
Water Res. 2020 Dec 15;187:116418. doi: 10.1016/j.watres.2020.116418. Epub 2020 Sep 19.
Pre-oxidation is often used before disinfection with chlorine to decrease the reactivity of the water matrix and mitigate the formation of regulated disinfection byproducts (DBPs). This study provides insights on the impact of oxidative pre-treatment with chlorine dioxide (ClO), ozone (O), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Natural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV) and the electron donating capacity (EDC). Changes in NOM reactivity and abatement of DBP precursors are also assessed. The impact of pre-oxidants (based on molar concentration) on UV abatement ranked in the order O > Mn(VII) > Fe(VI)/ClO, while the efficiency of pre-oxidation on EDC abatement followed the order Mn(VII) > ClO > Fe(VI) > O and two phases were observed. At low specific ClO, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV compared to the EDC was observed (~ 8% EDC abatement per 1% UV abatement). This suggests the oxidation of phenolic-type moieties to quinone-type moieties which absorb UV and don't contribute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar abatement of EDC and UV (~ 0.9-1.2% EDC abatement per 1% UV abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O abated the relative UV more effectively, due to a more efficient cleavage of aromatic rings. For a pre-oxidation with Mn(VII), ClO and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide (AOX) formation were obtained. In contrast, O pre-treatment led to a lower chlorine demand and AOX formation for equivalent EDC abatement. For all oxidants trihalomethane formation was poorly correlated with both EDC and UV The EDC abatement was found to be a pre-oxidant-independent surrogate for haloacetonitrile formation. These results emphasize the benefits of combining EDC and UV measurement to understand and monitor oxidant-induced changes of NOM and assessing DBP formation.
预氧化通常在使用氯消毒之前进行，以降低水基质的反应性，并减轻规定的消毒副产物（DBP）的形成。本研究提供了关于使用二氧化氯（ClO）、臭氧（O）、高铁酸盐（Fe（VI））和高锰酸盐（Mn（VII））进行氧化预处理对苏万尼河天然有机物（SRNOM）特性的影响的见解，这些特性由 254nm 处的紫外吸光度（UV）和电子供体容量（EDC）来表征。还评估了 NOM 反应性的变化和 DBP 前体的去除。预氧化剂（基于摩尔浓度）对 UV 去除的影响顺序为 O > Mn（VII）> Fe（VI）/ClO，而对 EDC 去除的预氧化效率顺序为 Mn（VII）> ClO > Fe（VI）> O，并观察到两个阶段。在低浓度的特定 ClO、Fe（VI）和 Mn（VII）剂量下，对应于 < 50% EDC 去除的情况下，与 EDC 相比，UV 的相对去除率有限（~ 1% UV 去除率对应 8% EDC 去除率）。这表明酚类基团氧化为醌类基团，这些基团吸收 UV 光但不贡献于 EDC。在更高的氧化剂剂量（> 50% EDC 去除）下，EDC 和 UV 的去除率相似（~ 1% UV 去除率对应 0.9-1.2% EDC 去除率），这表明芳环的断裂。与其他氧化剂相比，O 更有效地去除相对 UV，这是由于芳环的更有效断裂。对于 Mn（VII）、ClO 和 Fe（VI）的预氧化，在 EDC 去除率与氯需求或可吸附有机卤素（AOX）形成之间获得了类似的相关性。相比之下，O 预处理导致在相当的 EDC 去除率下，氯需求和 AOX 形成较低。对于所有氧化剂，三卤甲烷的形成与 EDC 和 UV 的相关性都很差。EDC 的去除被发现是卤代乙腈形成的预氧化剂无关替代物。这些结果强调了结合 EDC 和 UV 测量以了解和监测 NOM 中氧化剂诱导的变化并评估 DBP 形成的好处。
