Mahmoodlu Mojtaba G, Pontedeiro Elizabeth M, Pérez Guerrero Jesús S, Raoof Amir, Majid Hassanizadeh S, van Genuchten Martinus Th
Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands; Department of Watershed and Rangeland Management, Gonbad Kavous University, Iran.
Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands; Department of Nuclear Engineering, Federal University of Rio de Janeiro, UFRJ, Rio de Janeiro, Brazil.
J Contam Hydrol. 2017 Jan;196:43-51. doi: 10.1016/j.jconhyd.2016.12.004. Epub 2016 Dec 10.
In this study we performed batch experiments to investigate the dissolution kinetics of trichloroethylene (TCE) and toluene vapors in water at room temperature and atmospheric pressure. The batch systems consisted of a water reservoir and a connected headspace, the latter containing a small glass cylinder filled with pure volatile organic compound (VOC). Results showed that air phase concentrations of both TCE and toluene increased relatively quickly to their maximum values and then became constant. We considered subsequent dissolution into both stirred and unstirred water reservoirs. Results of the stirred experiments showed a quick increase in the VOC concentrations with time up to their solubility limit in water. VOC vapor dissolution was found to be independent of pH. In contrast, salinity had a significant effect on the solubility of TCE and toluene vapors. VOC evaporation and vapor dissolution in the stirred water reservoirs followed first-order rate processes. Observed data could be described well using both simplified analytical solutions, which decoupled the VOC dynamics in the air and water phases, as well as using more complete coupled solutions. However, the estimated evaporation (k) and dissolution (k) rate constants differed by up to 70% between the coupled and uncoupled formulations. We also numerically investigated the effects of fluid withdrawal from the small water reservoir due to sampling. While decoupling the VOC air and water phase mass transfer processes produced unreliable estimates of k, the effects of fluid withdrawal on the estimated rate constants were found to be less important. The unstirred experiments showed a much slower increase in the dissolved VOC concentrations versus time. Molecular diffusion of the VOCs within the aqueous phase became then the limiting factor for mass transfer from air to water. Fluid withdrawal during sampling likely caused some minor convection within the reservoir, which was simulated by increasing the apparent liquid diffusion coefficient.
在本研究中，我们进行了批次实验，以研究三氯乙烯（TCE）和甲苯蒸气在室温和大气压下于水中的溶解动力学。批次系统由一个储水器和一个相连的顶空组成，后者包含一个装有纯挥发性有机化合物（VOC）的小玻璃圆筒。结果表明，TCE和甲苯的气相浓度相对较快地增加至其最大值，然后保持恒定。我们考虑了随后在搅拌和未搅拌的储水器中的溶解情况。搅拌实验的结果表明，VOC浓度随时间迅速增加，直至达到其在水中的溶解度极限。发现VOC蒸气的溶解与pH无关。相比之下，盐度对TCE和甲苯蒸气的溶解度有显著影响。搅拌储水器中VOC的蒸发和蒸气溶解遵循一级速率过程。使用简化的解析解（将VOC在空气和水相中的动力学解耦）以及更完整的耦合解，都能很好地描述观测数据。然而，耦合和非耦合公式之间估计的蒸发（k）和溶解（k）速率常数相差高达70%。我们还通过数值研究了采样导致小储水器中流体抽出的影响。虽然将VOC空气和水相质量传递过程解耦会产生对k的不可靠估计，但发现流体抽出对估计速率常数的影响不太重要。未搅拌实验表明，溶解的VOC浓度随时间的增加要慢得多。此时，VOC在水相中的分子扩散成为从空气向水传质的限制因素。采样期间的流体抽出可能在储水器内引起了一些轻微对流，这通过增加表观液体扩散系数来模拟。
