School of Earth Science and Engineering, Hohai University, Nanjing 210098 China.
School of Earth Science and Engineering, Hohai University, Nanjing 210098 China.
Ecotoxicol Environ Saf. 2022 Jun 15;238:113566. doi: 10.1016/j.ecoenv.2022.113566. Epub 2022 Apr 28.
Understanding solute transport through macroscopic interfaces is essential to understand the effects of geological heterogeneity on contaminant transport in porous media. Studies of solute transport in compartmental porous media have noted the asymmetry of breakthroughs (BTCs) in solute movement across material interfaces, indicating the presence of discontinuous concentration that makes solute transport directionally dependent. Transition interfaces are more common in nature than sharp interfaces. To understand solute transport across transition interfaces, well-controlled laboratory experiments were performed. A numerical model was also built to understand mass accumulation and concentration discontinuity through transition as well as sharp interfaces. We conclude that directionally dependent asymmetry of BTCs was found with both sharp and transition interfaces. The asymmetry of BTCs was more pronounced at a transition interface than at a sharp interface. The mobile and immobile (MIM) model can better capture the directionally dependent transport of solutes through a sharp/transition interface than the advection-dispersion equation (ADE). The mobile water partition coefficient (β) and mass transfer coefficient (ω) in MIM were lager in the direction from fine sand to coarse sand (F-C). The time difference between tracer replace and tracer input is greater in the presence of an interface, especially transition interfaces. Even at small Reynolds numbers (1 × 10 to 0.116), solute transport across a discontinuous interface under reversible flow directions is most likely dominated by convective dispersion rather than an assumed diffusion process.
理解宏观界面处的溶质运移对于理解地质非均质性对多孔介质中污染物运移的影响至关重要。在分隔多孔介质中溶质运移的研究中，人们注意到溶质穿过物质界面运移的穿透曲线（BTC）存在不对称性，这表明存在不连续的浓度分布，使得溶质运移具有方向性。在自然界中，过渡界面比尖锐界面更为常见。为了理解溶质穿过过渡界面的运移，我们进行了精心控制的实验室实验。还建立了一个数值模型，以了解通过过渡和尖锐界面的质量积累和浓度不连续性。我们得出的结论是，无论是尖锐界面还是过渡界面，BTC 的方向性不对称都很明显。在过渡界面上，BTC 的不对称性比尖锐界面上更为明显。与对流弥散方程（ADE）相比，MIM 模型（Mobile and Immobile Model）能够更好地捕捉溶质通过尖锐/过渡界面的方向依赖性运移。在 MIM 中，细砂到粗砂（F-C）方向上的可动水分配系数（β）和质量传递系数（ω）更大。存在界面时，特别是过渡界面时，示踪剂替代和示踪剂输入之间的时间差更大。即使在较小的雷诺数（1×10 到 0.116）下，可逆流方向下穿过不连续界面的溶质运移很可能主要由对流弥散作用主导，而不是假设的扩散过程。
