Light-Transmission Visualization of Colloid Transport at the Meso Scale under Heterogeneous Conditions

胶体是地下普遍存在的营养物和污染物运输媒介。除了两相模型的预测之外，移动胶体已被证明可以促进对其表面具有高亲和力的污染物的运输。此外，负责污染物降解的微生物的迁移也是一个胶体运输过程。因此，了解胶体运输过程对于预测土壤污染物的迁移和分解以及设计和实施生物修复系统至关重要。环境中的非均质性是普遍存在的，发生在结构转变、毛细条纹以及湿润和排水前沿，并对胶体运输产生深远影响。本研究的目的是观察中尺度非均质性对变饱和多孔介质中胶体运动的影响。胶体输运的实验室实验主要是在柱中进行的，其中数据收集仅限于流出物突破和实验后破坏性取样，这无法观察到空间和时间变化对胶体输运过程的影响。在这项工作中使用和进一步发展的光传输系统对阐明由中尺度非均匀性引起的输运动力学具有很大的希望。这种可视化技术非常适合于观察饱和转变和物理非均质性对胶体输运的影响。探索的非均质性将包括在毛细条纹处发现的含水量变化，垂直于流动路径的不同介质等级分层的结构变化，以及模拟降水驱动的入渗事件的流动状态变化。粒径和胶体浓度的影响将在每个制度下进行探讨。

Selker 0610076Colloids are ubiquitous agents of nutrient and contaminant transport in the subsurface. Beyond what is predicted by two-phase models, mobile colloids have been shown to facilitate the transport of contaminants having a high affinity for their surfaces. Additionally, the migration of microorganisms responsible for contaminant degradation is also a colloidal transport process. Understanding colloid transport processes is therefore essential for predicting the migration and breakdown of soil-borne contaminants, and for the design and implementation of bioremediation systems. Heterogeneity in the environment is ubiquitous, occurring at textural transitions, the capillary fringe, and at wetting and draining fronts, and has profound impact on colloidal transport. The objective of this study is to observe the effects of meso-scale heterogeneity on the movement of colloids in variably-saturated porous media. Laboratory experiments on colloid transport have been conducted largely in columns where data collection has been limited to effluent break through and post-experimental destructive sampling, which has not allowed observation of the effects of spatial and temporal variability upon colloidal transport processes. The light-transmission system which will be used and further advanced in this work holds great promise for elucidation of transport dynamics resulting from meso-scale heterogeneity. This visualization technique is well-suited to observing the effects of saturation transitions and physical heterogeneities on colloidal transport. Heterogeneities explored will include the water content variation found at the capillary fringe, textural variation as layering of different media grades perpendicular to flow paths, and variation of the flow regime to mimic precipitation-driven infiltration events. The impact of particle size and colloid concentration will be explored within each regime.