零价铁活化过硫酸盐降解地下水三氯乙烯过程的碳氯同位素分馏研究

Application of zerovalent iron-activated persulfate is promising for in-situ remediation of chlorinated aliphatic hydrocarbons (CAHs) in contaminated groundwater. However, a key technical problem to be solved how to accurately quantify the degradation of pollutants in order to evaluate the effectiveness of the in situ remediation method. Environmental isotope method is among the most effectively tools for resolving the issue. A prerequisite and critical parameter for applying this tool in fields is to determine and characterize the isotope fractionation and its impact factors during CAHs degradation in zerovalent iron-activated persulfate. Trichloroethene is typical contaminant in groundwater. Thus, this study investigate the carbon and chlorine isotope fractionation during trichloroethene degradation in zerovalent iron-activated persulfate with isotope analytical techniques. The objectives of this study are (i) to determine the carbon and chlorine isotope enrichment factors as well as the relative change in carbon and chlorine isotope ratios; (ii) to reveal the potential influence of factors for the carbon and chlorine isotope fractionation; (iii) to explore the mechanism for the carbon and chlorine isotope fractionation during trichloroethene degradation in zerovalent iron-activated persulfate. This study has important scientific significance and application value for promoting technologies development of in-situ remediation of organic contaminants in groundwater, which would provide scientific basis and technical parameters for applying isotope analysis to quantify effectiveness of in-situ remediation implemented by zerovalent iron-activated persulfate, and which would enrich and improve database for isotope fractionation associated with processes for in-situ remediation of organic contaminants in groundwater and provide a reference for similar studies.

零价铁活化过硫酸盐原位修复地下水氯代脂肪烃污染极具应用前景，其亟待解决的技术难题是如何准确量化污染物降解效果以评价原位修复方法的有效性。环境同位素方法是解决该难题的一种重要而有效的工具，其应用的前提和关键是表征零价铁活化过硫酸盐降解过程的同位素分馏及其影响因素。本申请拟选取地下水氯代脂肪烃污染的典型物质三氯乙烯（TCE）作为目标污染物，利用碳氯同位素分析技术，开展零价铁活化过硫酸盐降解TCE过程的碳氯同位素分馏研究，确定该降解过程的碳、氯同位素富集系数以及碳氯同位素分馏相关关系，揭示碳、氯同位素分馏的影响因素及影响规律，揭示该降解过程的同位素分馏机理。本研究的开展为应用环境同位素方法定量评价零价铁活化过硫酸盐原位修复效果提供理论依据和技术参数，丰富完善地下水有机污染原位修复过程的同位素分馏数据库并可供类似研究借鉴，对于推动地下水有机污染原位修复技术发展具有重要科学意义和应用价值。

稳定同位素分析为识别有机污染降解过程（或反应机理）和量化原位修复效果提供了一种有力工具，其应用的前提和关键是确定特定反应过程（或降解途径）中目标污染物的同位素分馏大小和变异性。本研究利用同位素分析技术和自由基淬灭技术，表征了零价铁（Fe0）活化过硫酸盐以及特定自由基降解三氯乙烯（TCE）过程的同位素分馏大小及其变异性，揭示了过硫酸盐活化降解TCE过程中同位素分馏的影响因素及作用机理。Fe0活化过硫酸盐反应降解TCE过程产生了显著的同位素分馏，表明稳定同位素分析具备识别降解过程和量化修复效果的应用潜力。受控于降解过程中同时存在多种竞争反应及其各自的相对贡献量，氯离子显著影响Fe0活化过硫酸盐降解TCE过程的同位素分馏。因而利用同位素瑞利分馏原理量化原位修复效果时，根据污染修复场地氯离子含量高低选择适合的同位素富集系数至关重要。Fe0活化过硫酸盐降解TCE过程的同位素分馏未受其它无机阴离子和反应条件影响，这减小了同位素分析量化原位修复效果的不确定性。此外，本研究首次测定了硫酸根自由基（SO4·-）降解TCE过程的富集系数，显著不同于羟基自由基（HO·）降解TCE的富集系数。这表明稳定同位素分析可以用于识别同一反应体系中SO4·-和HO·降解TCE的相对贡献量。本研究丰富了同位素分馏数据库并可供类似研究借鉴，有助于促进同位素分析技术在污染水文地质学中应用。