Liang Chenju, Wang Zih-Sin, Mohanty Nihar
Department of Environmental Engineering, National Chung Hsing University, 250 Kuo-Kuang Rd., Taichung City 402, Taiwan.
Sci Total Environ. 2006 Nov 1;370(2-3):271-7. doi: 10.1016/j.scitotenv.2006.08.028. Epub 2006 Oct 2.
Application of in situ chemical oxidation (ISCO) involves application of oxidants to contaminants such as trichloroethylene (TCE) in soil or groundwater in place. Successful application of ISCO at a hazardous waste site requires understanding the scavenging reactions that could take place at the site to better optimize the oxidation of target contaminants and identification of site conditions where ISCO using persulfate may not be applicable. Additionally, estimation of the oxidant dose at a site would need identification of groundwater constituents such as alkalinity and chlorides that may scavenge radicals and therefore use up the oxidant that is targeted for the contaminant(s). The objective of this study was to investigate the influence of various levels of chloride and carbonates on persulfate oxidation of TCE at 20 degrees C under controlled conditions in a laboratory. Based on the results of the laboratory experiments, both chloride and alkalinity were shown to have scavenging effects on the rate of oxidation of TCE. It was found that at a neutral pH, persulfate oxidation of TCE was not affected by the presence of bicarbonate/carbonate concentrations within the range of 0-9.20 mM. However, the TCE degradation rate was seen to reduce with an increase in the level of carbonate species and at elevated pHs. TCE degradation in the presence of chlorides revealed no effect on the degradation rate especially at chloride levels below 0.2 M. However, at chloride levels greater than 0.2 M, TCE degradation rate was seen to reduce with an increase in the chloride ion concentration. Prior to application of persulfate as an oxidant, a site should be screened for the presence of scavengers to evaluate the potential of meeting target cleanup goals within a desirable timeframe at the site.
原位化学氧化（ISCO）技术的应用是指将氧化剂应用于土壤或地下水中的污染物，如三氯乙烯（TCE）。在危险废物场地成功应用ISCO技术需要了解场地可能发生的清除反应，以便更好地优化目标污染物的氧化过程，并确定不适用于过硫酸盐ISCO技术的场地条件。此外，估算场地的氧化剂剂量需要识别地下水中的成分，如碱度和氯化物，这些成分可能会清除自由基，从而消耗用于处理污染物的氧化剂。本研究的目的是在实验室可控条件下，研究20℃时不同水平的氯化物和碳酸盐对TCE过硫酸盐氧化的影响。基于实验室实验结果，氯化物和碱度均对TCE的氧化速率有清除作用。研究发现，在中性pH值下，0-9.20 mM范围内的碳酸氢盐/碳酸盐浓度对TCE的过硫酸盐氧化没有影响。然而，随着碳酸盐种类水平的增加和pH值的升高，TCE降解速率会降低。在氯化物存在下的TCE降解表明，尤其是在氯化物水平低于0.2 M时，对降解速率没有影响。然而，当氯化物水平大于0.2 M时，TCE降解速率会随着氯离子浓度的增加而降低。在将过硫酸盐用作氧化剂之前，应对场地进行清除剂筛查，以评估在理想时间范围内实现场地目标清理目标的可能性。
