Trichloroethylene (TCE) is a solvent that widely contaminates groundwater. Neutral pH has been shown to optimize TCE reductive dehalogenase activity in cell extracts and cell suspensions. Anaerobic bacteria from TCE-contaminated subsurface sediment might also show maximum dechlorinating activity when the pH is neutralized in the sediment.; Encapsulated phosphate buffers were investigated as a method for controlling pH in situ where neutral pH might improve dechlorination of TCE. These capsules (1 mm average diameter), which are coated with a pH-sensitive polymer (Eudragit™ S100), release KH2PO4 into sediment pore water when pH levels rise above 7.0. These capsules were tested in sediment microcosms and sand and sediment flow-through columns. The sediment was obtained from a contaminated groundwater aquifer at the Department of Energy's Savannah River Site (SRS).; The initial test of capsule release occurred in denitrifying sediment microcosms. pH levels above 8.0 were measured in microcosms to which no capsules had been added while the pH in bottles containing capsules remained within 0.2 pH units of 7.0. Two more tests to characterize the capsules were performed in sand columns specially designed to house the capsules. Near complete conversion of 80 mg N/L of nitrate and 152 mg/L of ethanol per day resulted in a mean pH increase from 6.2 to 8.2 in the column without capsules. The column containing the capsules maintained the target pH of 7.0 ± 0.2 for four weeks. The encapsulated phosphate buffer was effective at neutralizing a 1.5-unit pH change in saturated sediment microcosms and sand columns. This study demonstrates the potential for this technology to mediate pH changes in situ.; The pH in microcosms containing sediment from SRS was adjusted to different set points in order to determine whether 7.0 is the optimum pH level for reductive dechlorination of TCE in sediment. Statistically, maximum vinyl chloride production occurred at a pH of 4 (p 0.0001). The results implied that a pH of 7 would not necessarily optimize TCE dechlorination in sediment. Though pH appeared to have affect TCE dechlorination, the low production of metabolites indicated that in situ pH control would not be efficacious for promoting reductive dechlorination at SRS.
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机译:三氯乙烯(TCE)是一种广泛污染地下水的溶剂。已显示中性pH可优化细胞提取物和细胞悬浮液中的TCE还原性脱卤素酶活性。当中和pH值的中性沉淀物中的TCE污染的地下沉淀物中的厌氧细菌也可能显示最大的脱氯活性。研究了封装的磷酸盐缓冲液作为原位控制pH的方法,其中中性pH可以改善TCE的脱氯性。这些胶囊(平均直径1毫米)涂有对pH敏感的聚合物(Eudragit™S100),当pH值达到一定水平时,它们会将KH 2 sub> PO 4 sub>释放到沉积物孔隙水中升至7.0以上。这些胶囊在沉积物微观世界以及沙子和沉积物流过柱中进行了测试。沉积物是从能源部萨凡纳河站点(SRS)受污染的地下水含水层中获得的。胶囊释放的最初测试发生在反硝化沉积物的微观世界中。在未添加胶囊的微观世界中测量了高于8.0的pH值,而装有胶囊的瓶子中的pH保持在7.0的0.2 pH单位内。在专门设计用于容纳胶囊的沙柱中进行了另外两项表征胶囊的测试。每天没有胶囊的色谱柱几乎完全转化为80 mg N / L的硝酸盐和152 mg / L的乙醇,导致平均pH从6.2增加到8.2。装有胶囊的柱子将目标pH值保持在7.0±0.2的水平达四个星期。包封的磷酸盐缓冲液可有效中和饱和沉积物微观世界和沙柱中的1.5个单位的pH值变化。这项研究证明了这项技术在介导pH原位改变中的潜力。将包含来自SRS的沉积物的微观世界中的pH值调整到不同的设定点,以确定7.0是否为沉积物中TCE还原脱氯的最佳pH值。从统计学上讲,最大的氯乙烯产量在pH为4时发生(p <0.0001)。结果表明,pH 7不一定会优化沉积物中TCE的脱氯。尽管pH似乎影响了TCE的脱氯,但代谢产物的低产量表明原位 italic> pH控制对于促进SRS的还原性脱氯是无效的。
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