土壤类型及组分对热活化过硫酸盐氧化降解土壤中挥发性氯代烃的影响

Effects of Soil Types and Composition on Oxidative Degradation of Volatile Chlorinated Hydrocarbons by Thermally Activated Persulfate

为了探究高级氧化技术对土壤中有机氯代烃的氧化降解作用,为ISCO(in situ chemical oxidation)技术体系提供重要的理论依据和数据支撑,考察了热活化过硫酸盐(persulfate,PS)氧化降解不同类型土壤(砂类土壤、黏土类土壤)中挥发性氯代烃污染物(三氯乙烯(TCE)、三氯乙烷(TCA)、顺式-1,2-二氯乙烯(cis-1,2-DCE)、1,2-二氯乙烷(1,2-DCA))的效能;同时,通过硫酸盐与土壤相互作用过程研究,探究了不同土壤介质中有机质和无机组分在过硫酸盐消耗中所占比例。结果表明:在50℃时,热活化过硫酸盐可有效降解土壤中1,2-DCA、cis-1,2-DCE、TCA和TCE,砂类土壤介质中4种氯代烃降解效果依次为25%、89%、5%和61%,黏土类土壤介质中4种氯代烃降解效果依次为35%、86%、8%和63%;4种氯代烃的降解效果从高到低顺序依次为cis-1,2-DCE、TCE、1,2-DCA、TCA,砂类土壤中的氯代烃总体降解效果优于黏土类土壤中氯代烃的降解效果。另外,土壤中过硫酸盐氧化降解氯代烃反应研究发现,砂类和黏土类土壤介质组分中有机质消耗率分别为81.3%和72.6%,铁元素消耗率分别为80.5%和38.6%,表明土壤介质组分与过硫酸盐发生了氧化还原反应,从而导致过硫酸盐自身的大量消耗。由此可知,土壤介质中的有机质、铁元素等矿物质均参与过硫酸盐的消耗过程,且土壤有机质、铁元素与氯代烃之间在消耗过硫酸盐反应上存在竞争关系,土壤组分过多地消耗了过硫酸盐,导致了氯代烃的氧化降解效率较低。因此,针对实际有机氯代烃污染场地,采用过硫酸盐氧化技术进行修复时,过硫酸盐的实际投加量要远高于化学计量值,需充分考虑到土壤组分对过硫酸盐自身的消耗作用。

This study focused on the thermally activated persulfate oxidation of the volatile chlorinated hydrocarbon （TCE, TCA, cis-1,2-DCE and 1,2-DCA） in the different soil media,sandy soil and clayey soil, and the interaction between persulfate and the two soil media in oxidation reaction was investigated to determine the contribution of organic and inorganic matter to the persulfate consumption in the soil system, which would provide an important theoretical basis and empirical guide for a successful design of ISCO technology in soil remediation. The results showed good degradation rates of 1,2-DCA, cis-1,2-DCE, TCA, and TCE by thermally activated persulfate oxidation in the both soil systems at 50℃. The degradation rates of the four chlorinated hydrocarbons in sandy soil were 25%, 89%, 5%, and 61% respectively; while the rates in clayey soil were 35%, 86%, 8%, and 63% respectively. The rates followed the order of cis-1,2-DCE〉TCE〉1,2-DCA〉TCA. The rates in sandy soil were higher than those in clayey soil. In addition, the organic matter in sandy soil and clayey soil was reduced up to 81.3% and 72.6% respectively, and the iron content in sandy soil and clayey soil was reduced up to 80.5% and 38.6% respectively. This further indicated that a redox reaction occurred between persulfate and the soil composition, leading to a large amount of persulfate consumption. Herein, organic matter, iron and other inorganic matter in the soil media were involved in the persulfate consumption, and there was a competitive relationship among organic, iron and the four chlorinated hydrocarbons for the consumption of persulfate. Thus, too much persulfate was consumed by the soil component, resulting in a relatively low degradation rate of the four chlorinated hydrocarbons. Therefore, during the actual implementation, the dosage of persulfate should be much higher than the stoichiometric amount in the on-site remediation for the chlorinated hydrocarbons contaminated field sites by the thermally activated persulfate.