Investigation of Colloid Transport under Unsaturated Steady Flow Conditions Using a Geocentrifuge

地下胶体可以增强强吸附污染物的运动，这种现象被称为胶体促进污染物传输。在有流动的地下胶体存在的情况下，污染物可能比没有胶体的情况下移动得更快、更远，从而绕过土壤和沉积物的过滤和缓冲能力。因此，命运和传输模型忽略了胶体促进的传输，因此往往低估了污染物的移动。对污染物去向和迁移的长期预测以及风险评估依赖于对地下过程的准确描述，在强吸附污染物的情况下，需要考虑将可移动胶体作为潜在的污染物载体。这项研究的总体目标是阐明控制胶体在非饱和多孔介质中的去向和迁移的相关机制，重点是土壤和沉积物。其具体目标是：(1)改进实验测量技术，以量化非饱和流动条件下的胶体传输；(2)描述含水率与流速对非饱和多孔介质中胶体动员和传输的重要性；以及(3)通过纳入相关胶体传输过程的数学公式，修改现有的胶体传输程序(Hydrus-1D)。地心离心机的使用为研究多孔介质中的胶体传输提供了全新的实验机会。通过改变实验装置的加速度，可以独立控制多孔介质的含水率和水力流量。因此，可以阐明这些因素的作用和相互作用，以获得对胶体运输和动员的机械理解。也可以用低导水率的材料进行试验，可以缩短试验时间。我将设计一种用于地心离心机的新型实验系统，并将进行一系列非饱和流动下的胶体输运实验。此外，我将使用一种新的建模方法来验证和推广实验测量和结果。非饱和流动和运输代码(Hydrus-1D)将被修改为包括可变加速度(高于重力)，以适应地心离心机系统。修改后的Hydrus代码将用于外推测量，并将测量结果调整回正常重力。

Subsurface colloids can enhance the movement of strongly sorbing contaminants, a phenomenon called colloid-facilitated contaminant transport. In the presence of mobile subsurface colloids, contaminants may move faster and farther than in the absence of colloids, thereby bypassing the filter and buffer capacity of soils and sediments. Fate and transport models neglecting colloid-facilitated transport therefore often underpredict contaminant movement. Long-term predictions of contaminant fate and transport as well as risk assessment rely on an accurate representation of subsurface processes, and in the case of strongly sorbing contaminants, need to consider mobile colloids as potential contaminant carriers. The overall goal of this research project is to elucidate the relevant mechanisms controlling colloid fate and transport in unsaturated porous media, with emphasis on soils and sediments. The specific objectives are to (1) improve experimental measurement techniques to quantify colloid transport under unsaturated flow conditions; (2) delineate the importance of water content vs flow rate on colloid mobilization and transport in unsaturated porous media; and (3) modify an existing colloid transport code (Hydrus-1D) by incorporating mathematical formulations of the relevant colloid transport processes. The use of a geocentrifuge offers completely new experimental opportunities to study colloid transport in porous media. By changing the acceleration of the experimental setup the water content and the hydraulic flow rate of the porous media can be controlled independently. Therefore, the role and the interplay of these factors can be elucidated to obtain a mechanistic understanding of colloid transport and mobilization. Experiments can also be conducted with materials of low hydraulic conductivity, and the experimental time can be shortened. I will design a novel experimental system for use in a geocentrifuge, and will conduct a series of colloid transport experiments under unsaturated flow. Additionally, I will validate and generalize the experimental measurements and results by using a new modelling approach. An unsaturated flow and transport code (Hydrus-1D) will be modified to include variable accelerations (higher than gravity) to accommodate the geocentrifuge system. The modified Hydrus code will be used to extrapolate and scale measurements back to normal gravity.