Department of Civil and Environmental Engineering, Tufts University, 200 College Avenue, Room 113 Anderson Hall, Medford, Massachusetts 02155, United States.
Environ Sci Technol. 2010 Dec 1;44(23):9105-11. doi: 10.1021/es102536f. Epub 2010 Nov 5.
Abiotic and biotic reductive dechlorination with chlorinated ethene dense non-aqueous-phase liquid (DNAPL) source zones can lead to significant fluxes of complete and incomplete transformation products. Accurate assessment of in situ rates of transformation and the potential for product sequestration requires knowledge of the distribution of these products among the solid, aqueous, and organic liquid phases present within the source zone. Here we consider the fluid-fluid partitioning of two of the most common incomplete transformation products, cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC). The distributions of cis-DCE and VC between the aqueous phase and tetrachloroethene (PCE) and trichloroethene (TCE) DNAPLs, respectively, were quantified at 22 °C for the environmentally relevant, dilute range. The results suggest that partition coefficients (concentration basis) for VC and cis-DCE are 70 ± 1 L(aq)/L(TCE DNAPL) and 105 ± 1 L(aq)/L(PCE DNAPL,) respectively. VC partitioning data (in the dilute region) were reasonably approximated using the Raoult's law analogy for liquid-liquid equilibrium. In contrast, data for the partitioning of cis-DCE were well described only when well-parametrized models for the excess Gibbs free energy were employed. In addition, available vapor-liquid and liquid-liquid data were employed with our measurements to assess the temperature dependence of the cis-DCE and VC partition coefficients. Overall, the results suggest that there is a strong thermodynamic driving force for the reversible sequestration of cis-DC and VC within DNAPL source zones. Implications of this partitioning include retardation during transport and underestimation of the transformation rates observed through analysis of aqueous-phase samples.
非生物和生物还原脱氯与氯化碳氢化合物（DNAPL）污染源区可导致完全和不完全转化产物的大量通量。准确评估原位转化速率和产物固定的潜力需要了解这些产物在源区存在的固、水和有机液相中的分布。在这里，我们考虑了两种最常见的不完全转化产物，顺-1,2-二氯乙烯（顺-DCE）和氯乙烯（VC）的流体-流体分配。在 22°C 下，分别定量了顺-DCE 和 VC 分别在水相和四氯乙烯（PCE）和三氯乙烯（TCE）DNAPL 之间的分配。结果表明，VC 和顺-DCE 的分配系数（浓度基础）分别为 70±1 L(aq)/L(TCE-DNAPL)和 105±1 L(aq)/L(PCE-DNAPL)。VC 的分配数据（在稀区）可以通过拉乌尔定律类比合理地近似用于液-液平衡。相比之下，仅当采用适当参数化的超额吉布斯自由能模型来描述顺-DCE 的分配数据时，数据才能得到很好的描述。此外，还利用可用的汽-液和液-液数据与我们的测量结果相结合，评估了顺-DCE 和 VC 分配系数的温度依赖性。总的来说，结果表明，在 DNAPL 源区中，顺-DC 和 VC 的可逆固定具有很强的热力学驱动力。这种分配的影响包括在运输过程中的滞后和通过分析水相样品低估观察到的转化速率。
