Sleep Brent E, Seepersad David J, Kaiguo M O, Heidorn Christina M, Hrapovic Leila, Morrill Penny L, McMaster Michaye L, Hood Eric D, Lebron Carmen, Lollar Barbara Sherwood, Major David W, Edwards Elizabeth A
Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada, M5S 3E5.
Environ Sci Technol. 2006 Jun 1;40(11):3623-33. doi: 10.1021/es051493g.
A bench-scale study was performed to evaluate the enhancement of tetrachloroethene (PCE) dissolution from a dense nonaqueous phase liquid (DNAPL) source zone due to reductive dechlorination. The study was conducted in a pair of two-dimensional bench-scale aquifer systems using soil and groundwater from Dover Air Force Base, DE. After establishment of PCE source zones in each aquifer system, one was biostimulated (addition of electron donor) while the other was biostimulated and then bioaugmented with the KB1 dechlorinating culture. Biostimulation resulted in the growth of iron-reducing bacteria (Geobacter) in both systems as a result of the high iron content of the Dover soil. After prolonged electron donor addition methanogenesis dominated, but no dechlorination was observed. Following bioaugmentation of one system, dechlorination to ethene was achieved, coincident with growth of introduced Dehalococcoides and other microbes in the vicinity and downgradient of the PCE DNAPL (detected using DGGE and qPCR). Dechlorination was not detected in the nonbioaugmented system over the course of the study, indicating that the native microbial community, although containing a member of the Dehalococcoides group, was not able to dechlorinate PCE. Over 890 days, 65% of the initial emplaced PCE was removed in the bioaugmented, dechlorinating system, in comparison to 39% removal by dissolution from the nondechlorinating system. The maximum total ethenes concentration (3 mM) in the bioaugmented system occurred approximately 100 days after bioaugmentation, indicating that there was at least a 3-fold enhancement of PCE dissolution atthis time. Removal rates decreased substantially beyond this time, particularly during the last 200 days of the study, when the maximum concentrations of total ethenes were only about 0.5 mM. However, PCE removal rates in the dechlorinating system remained more than twice the removal rates of the nondechlorinating system. The reductions in removal rates over time are attributed to both a shrinking DNAPL source area, and reduced flow through the DNAPL source area due to bioclogging and pore blockage from methane gas generation.
开展了一项实验室规模的研究，以评估由于还原脱氯作用，从致密非水相液体（DNAPL）源区中四氯乙烯（PCE）溶解的增强情况。该研究在一对二维实验室规模的含水层系统中进行，使用的是来自特拉华州多佛空军基地的土壤和地下水。在每个含水层系统中建立PCE源区后，一个进行生物刺激（添加电子供体），而另一个先进行生物刺激，然后用KB1脱氯培养物进行生物强化。由于多佛土壤中铁含量高，生物刺激导致两个系统中均出现了铁还原菌（地杆菌属）的生长。长时间添加电子供体后，产甲烷作用占主导，但未观察到脱氯现象。在对一个系统进行生物强化后，实现了向乙烯的脱氯，这与引入的脱卤球菌属及其他微生物在PCE DNAPL附近及下游的生长同时发生（使用变性梯度凝胶电泳和定量聚合酶链反应检测）。在研究过程中，未强化生物的系统中未检测到脱氯现象，这表明本地微生物群落尽管包含脱卤球菌属的一个成员，但无法对PCE进行脱氯。在超过890天的时间里，在进行生物强化的脱氯系统中，65%的初始注入PCE被去除，相比之下，未脱氯系统通过溶解去除了39%。生物强化系统中乙烯总浓度的最大值（3 mM）大约在生物强化后100天出现，这表明此时PCE的溶解至少增强了3倍。在此之后，去除率大幅下降，特别是在研究的最后200天，此时乙烯总浓度的最大值仅约为0.5 mM。然而，脱氯系统中PCE的去除率仍是非脱氯系统去除率的两倍多。去除率随时间的下降归因于DNAPL源区面积的缩小，以及由于生物堵塞和甲烷气体产生导致的孔隙堵塞，流经DNAPL源区的流量减少。
