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Colloid Transport in Environmental Granular Porous Media

Abstract:

Colloids are nano- to micro-sized particles (biological and nonbiological) suspended in water. They are important as contaminants (e.g. pathogens), or carriers of contaminants (e.g. dissolved organic matter or clays) in water, as well as in a multitude of other contexts ranging from subsurface cleanup of hazardous waste (e.g. nano zero valent iron) to drug delivery in biological systems. The above contexts all involve colloid transport in porous media, wherein a complex set of physical and chemical interactions act on colloids. These interactions originate at the nanoscale and propagate to the field scale, leading to complex transport behaviors that are difficult to predict even following several decades of research on this topic. In this article, we provide a conceptual description of these interactions and impacts. The physical transport processes governing colloid transport are reviewed, culminating in predictions of pore-scale transport behavior that are upscaled to predictions of transport at the field scale. A major impediment to prediction has been the complexity of interactions when colloids and collectors (porous media grains) are both negatively charged, leading to repulsion between them. We review strategies to recognize the nanoscale heterogeneity that allows colloid attachment despite overall repulsion, as well as the influence of nonspherical shape on their transport.