School of Earth and Environmental Science, Queens College, City University of New York, Flushing, NY 11367, USA.
School of Earth and Environmental Science, Queens College, City University of New York, Flushing, NY 11367, USA.
J Contam Hydrol. 2018 Jan;208:68-78. doi: 10.1016/j.jconhyd.2017.10.006. Epub 2017 Nov 14.
In a field study, aqueous cyclodextrin (CD) was investigated for its ability to extract chlorinated volatile organic compounds (cVOC), such as trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), and dichloroethene (DCE) through in-situ flushing of a sandy aquifer. After cessation of aquifer flushing, a plume of CD was left. Changes in CD, cVOC, and inorganic terminal electron acceptors (TEAs) (DO, nitrate, sulfate, iron) were monitored in four rounds of wellwater sampling (20, 210, 342, and 425days after cessation of active pumping). Post-CD flushing VOC levels rebounded (850% for TCE, 190% for TCA, and 53% for DCE) between the first two sampling rounds, apparently due to rate-limited desorption from aquifer media and dissolution from remaining NAPL. However, substantial reduction in the mass of TCE (6.3 to 0.11mol: 98%) and TCA (2.8 to 0.73mol: 74%) in groundwater was observed between 210 and 425days. DCE should primarily be produced from the degradation of TCE and is expected to subsequently degrade to chloroethene. Since DCE levels decreased only slightly (0.23 to 0.17mol: 26%), its degradation rate should be similar to that produced from the decaying TCE. Cyclodextrin was monitored starting from day 210. The mass of residual CD (as measured by Total Organic Carbon) decreased from 150mol (day 210) to 66 (day 425) (56% decrease). The naturally anaerobic zone within the aquifer where residual CD mass decreased coincided with a loss of other major potential TEAs: nitrate (97% loss), sulfate (31%) and iron (31%). In other studies, TCE and 1,1,1-TCA have been found to be more energetically favorable TEAs than sulfate and iron and their degradation via reductive dechlorination has been found to be enhanced by the fermentation of carbohydrates. Such processes can explain these observations, but more investigation is needed to evaluate whether residual levels of CD can facilitate the anaerobic degradation of chlorinated VOCs.
在一项实地研究中，研究了环糊精（CD）在原位冲洗砂质含水层时提取氯化挥发性有机化合物（cVOC）的能力，例如三氯乙烯（TCE）、1,1,1-三氯乙烷（TCA）和二氯乙烯（DCE）。含水层冲洗停止后，留下了一股 CD 溶液。在停止主动抽水后，进行了四轮井水采样（停止后 20、210、342 和 425 天），监测 CD、cVOC 和无机末端电子受体（TEA）（DO、硝酸盐、硫酸盐、铁）的变化。在第一轮和第二轮采样之间，CD 冲洗后的 VOC 水平反弹（TCE 为 850%，TCA 为 190%，DCE 为 53%），显然是由于含水层介质中速率限制解吸和剩余 NAPL 的溶解。然而，在 210 天至 425 天之间，地下水 TCE（6.3 至 0.11mol：98%）和 TCA（2.8 至 0.73mol：74%）的质量大幅减少。DCE 主要应源自 TCE 的降解，预计随后会降解为氯代乙烯。由于 DCE 水平仅略有下降（0.23 至 0.17mol：26%），其降解速率应与从衰减的 TCE 产生的降解速率相似。从第 210 天开始监测环糊精。残留 CD 的质量（以总有机碳计）从 150mol（第 210 天）减少到 66（第 425 天）（减少 56%）。在含水层中残留 CD 质量减少的自然厌氧区与其他主要潜在 TEA 硝酸盐（97%损失）、硫酸盐（31%）和铁（31%）的损失同时发生。在其他研究中，已发现 TCE 和 1,1,1-TCA 比硫酸盐和铁更有利于 TEA，并且通过还原脱氯降解它们的过程已发现通过碳水化合物的发酵得到增强。这些过程可以解释这些观察结果，但需要进一步研究以评估残留 CD 水平是否可以促进氯化 VOC 的厌氧降解。
