Comparison of Halide Impacts on the Efficiency of Contaminant Degradation by Sulfate and Hydroxyl Radical-Based Advanced Oxidation Processes (AOPs)

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• 作者：Yi Yang ; Joseph J. Pignatello ; Jun Ma ; William A. Mitch
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：February 18, 2014
• 年：2014
• 卷：48
• 期：4
• 页码：2344-2351
• 全文大小：412K
• ISSN：1520-5851

文摘

The effect of halides on organic contaminant destruction efficiency was compared for UV/H₂O₂ and UV/S₂O₈^{2鈥?/sup> AOP treatments of saline waters; benzoic acid, 3-cyclohexene-1-carboxylic acid, and cyclohexanecarboxylic acid were used as models for aromatic, alkene, and alkane constituents of naphthenic acids in oil-field waters. In model freshwater, contaminant degradation was higher by UV/S₂O₈2鈥?/sup> because of the higher quantum efficiency for S₂O₈2鈥?/sup> than H₂O₂ photolysis. The conversion of 鈥?/sup>OH and SO₄鈥⑩€?/sup> radicals to less reactive halogen radicals in the presence of seawater halides reduced the degradation efficiency of benzoic acid and cyclohexanecarboxylic acid. The UV/S₂O₈2鈥?/sup> AOP was more affected by Cl鈥?/sup> than the UV/H₂O₂ AOP because oxidation of Cl鈥?/sup> is more favorable by SO₄鈥⑩€?/sup> than 鈥?/sup>OH at pH 7. Degradation of 3-cyclohexene-1-carboxylic acid, was not affected by halides, likely because of the high reactivity of halogen radicals with alkenes. Despite its relatively low concentration in saline waters compared to Cl鈥?/sup>, Br鈥?/sup> was particularly important. Br鈥?/sup> promoted halogen radical formation for both AOPs resulting in ClBr鈥⑩€?/sup>, Br₂鈥⑩€?/sup>, and CO₃鈥⑩€?/sup> concentrations orders of magnitude higher than 鈥?/sup>OH and SO₄鈥⑩€?/sup> concentrations and reducing differences in halide impacts between the two AOPs. Kinetic modeling of the UV/H₂O₂ AOP indicated a synergism between Br鈥?/sup> and Cl鈥?/sup>, with Br鈥?/sup> scavenging of 鈥?/sup>OH leading to BrOH鈥⑩€?/sup>, and further reactions of Cl鈥?/sup> with this and other brominated radicals promoting halogen radical concentrations. In contaminant mixtures, the conversion of 鈥?/sup>OH and SO₄鈥⑩€?/sup> radicals to more selective CO₃鈥⑩€?/sup> and halogen radicals favored attack on highly reactive reaction centers represented by the alkene group of 3-cyclohexene-1-carboxylic acid and the aromatic group of the model compound, 2,4-dihydroxybenzoic acid, at the expense of less reactive reaction centers such as aromatic rings and alkane groups represented in benzoic acid and cyclohexanecarboxylic acid. This effect was more pronounced for the UV/S₂O₈2鈥?/sup> AOP.}