Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA.
Chemical Advanced Resolution Methods Laboratory, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA; Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA.
Water Res. 2018 May 15;135:22-30. doi: 10.1016/j.watres.2018.02.015. Epub 2018 Feb 8.
Considering the increasing identification of trace organic contaminants in natural aquatic environments, the removal of trace organic contaminants from water or wastewater discharge is an urgent task. Ultraviolet (UV) and UV-based advanced oxidation processes (AOPs), such as UV/hydrogen peroxide (UV/HO), UV/free chlorine and UV/persulfate, are attractive and promising approaches for the removal of these contaminants due to the high reactivity of active radical species produced in these UV-AOPs with a wide variety of organic contaminants. However, the removal efficiency of trace contaminants is greatly affected by the presence of background dissolved organic matter (DOM). In this study, we use ultrahigh resolution mass spectrometry to evaluate the transformation of a standard Suwanee River fulvic acid DOM isolate in UV photolysis and UV-AOPs. The use of probe compounds allows for the determination of the steady-state concentrations of active radical species in each UV-AOP. The changes in the H/C and O/C elemental ratios, double bond equivalents, and the low-molecular-weight transformation product concentrations of organic acids reveal that different DOM transformation patterns are induced by each UV-AOP. By comparison with the known reactivities of each radical species with specific organic compounds, we mechanistically and systematically elucidate the molecular-level DOM transformation pathways induced by hydroxyl, chlorine, and sulfate radicals in UV-AOPs. We find that there is a distinct transformation in the aliphatic components of DOM due to HO• in UV/HO and UV/free chlorine. Cl• induced transformation of olefinic species is also observed in the UV/free chlorine system. Transformation of aromatic and olefinic moieties by SO are the predominant pathways in the UV/persulfate system.
考虑到在自然水生环境中痕量有机污染物的日益增多，去除水中或废水中的痕量有机污染物是一项紧迫的任务。由于这些 UV-AOPs 中产生的活性自由基物种具有很高的反应活性，能够与各种有机污染物发生反应，因此紫外线 (UV) 和基于 UV 的高级氧化工艺 (AOPs)，如 UV/过氧化氢 (UV/HO)、UV/自由氯和 UV/过硫酸盐，是去除这些污染物的有吸引力和有前途的方法。然而，痕量污染物的去除效率受到背景溶解有机物 (DOM) 的存在的极大影响。在这项研究中，我们使用超高分辨率质谱来评估标准苏瓦尼河富里酸 DOM 分离物在 UV 光解和 UV-AOP 中的转化。探针化合物的使用允许确定每种 UV-AOP 中活性自由基物种的稳态浓度。有机酸酸的 H/C 和 O/C 元素比、双键当量和低分子量转化产物浓度的变化表明，每种 UV-AOP 都会引起不同的 DOM 转化模式。通过与每种自由基与特定有机化合物的已知反应性进行比较，我们从机制上和系统上阐明了 UV-AOP 中羟基、氯和硫酸根自由基诱导的 DOM 转化途径。我们发现，由于 HO•在 UV/HO 和 UV/自由氯中，DOM 的脂肪族成分发生了明显的转化。在 UV/自由氯体系中也观察到 Cl•诱导的烯烃物种的转化。在 UV/过硫酸盐体系中，SO 诱导的芳香族和烯烃部分的转化是主要途径。
