Remediation of Trichloroethylene and Monochlorobenzene-Contaminated Aquifers Using the ORC-GAC-Fe0-CaCO3 System:Volatilization, Precipitation,and Porosity Losses

LIN Qi; V. PLAGENTZ; D. SCHAFER; A. DAHMKE

摘要

The objectives of this study were to illustrate the reaction processes, to identify and quantify the precipitates formed, and to estimate the porosity losses in order to eliminate drawbacks during remediating monochlorobenzene (MCB) and trichloroethylene (TCE)-contaminated aquifers using the ORC-GAC-Fe0-CaCO3 system. The system consisted of four columns (112 cm long and 10 cm in diameter) with oxygen-releasing compound (ORC), granular activated carbon (GAC),zero-valent iron (Fe0), and calcite used sequentially as the reactive media. The concentrations of MCB in the GAC column effluent and TCE in the Fe0 column effluent were below the detection limit. However, the concentrations of MCB and TCE in the final calcite column exceeded the maximum contaminant level (MCL) under the Safe Drinking Water Act of the US Environmental Protection Agency (US EPA) that protects human health and environment. These results suggested that partitioning of MCB and TCE into the gas phase could occur, and also that transportation of volatile organic pollutants in the gas phase was important. Three main precipitates formed in the ORC-GAC-Fe0-CaCO3 system:CaCO3 in the ORC column along with Fe(OH)2 and FeCO3 in the Fe0 column. The total porosity losses caused by mineral precipitation corresponded to about 0.24% porosity in the ORC column, and 1% in the Fe0 column. The most important cause of porosity losses was anaerobic corrosion of iron. The porosity losses caused by gas because of the production and entrapment of oxygen in the ORC column and hydrogen in the Fe0 column should not be ignored. Volatilization, precipitation and porosity losses were considered to be the main drawbacks of the ORC-GAC-Fe0-CaCO3 system in remediating the MCB and TCE-contaminated aquifers. Thus, measurements such as using a suitable oxygen-releasing compound, weakening the increase in pH using a buffer material such as soil, stimulating biodegradation rates and minimizing the plugging caused by the relatively high dissolved oxygen levels should be taken to eliminate the drawbacks and to improve the efficiency of the ORC-GAC-Fe0-CaCO3 system.

机译：这项研究的目的是阐明反应过程，鉴定和量化形成的沉淀物，并估算孔隙度损失，以消除使用ORC-GAC修复被一氯苯（MCB）和三氯乙烯（TCE）污染的含水层时的缺点。 -Fe0-CaCO3系统。该系统由四根色谱柱（长112厘米，直径10厘米）组成，它们依次使用氧气释放化合物（ORC），颗粒状活性炭（GAC），零价铁（Fe0）和方解石。 GAC柱流出物中的MCB浓度和Fe0柱流出物中的TCE浓度低于检测极限。但是，最终方解石柱中MCB和TCE的浓度超过了保护人类健康和环境的美国环境保护署（US EPA）安全饮用水法规定的最大污染物水平（MCL）。这些结果表明，可能发生MCB和TCE进入气相的分配，而且气相中挥发性有机污染物的运输也很重要。在ORC-GAC-Fe0-CaCO3系统中形成了三个主要的沉淀物：ORC柱中的CaCO3以及Fe0柱中的Fe（OH）2和FeCO3。矿物沉淀引起的总孔隙度损失在ORC柱中约为0.24％，在Fe0柱中约为1％。孔隙率损失的最重要原因是铁的厌氧腐蚀。不应忽略由于ORC柱中氧气的产生和截留以及Fe0柱中的氢气导致的由气体引起的孔隙率损失。挥发，沉淀和孔隙度损失被认为是ORC-GAC-Fe0-CaCO3系统在修复受MCB和TCE污染的含水层时的主要缺点。因此，应采取一些措施，例如使用合适的释氧化合物，使用诸如土壤的缓冲材料弱化pH值的增加，刺激生物降解速率并最大程度地减少由相对较高的溶解氧水平引起的堵塞，以消除这些缺点并提高ORC-GAC-Fe0-CaCO3系统的效率。

Remediation of Trichloroethylene and Monochlorobenzene-Contaminated Aquifers Using the ORC-GAC-Fe0-CaCO3 System:Volatilization, Precipitation,and Porosity Losses

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