| Description |
Colloid filtration theory (CFT) fails to predict engineered nanoparticle and pathogen transport in the environment due to the presence of nano- to macroscale physiochemical heterogeneity. In order to improve transport predictions at field-scales, it is necessary to first understand colloid attachment at the pore- to column-scales. The impacts of nanoscale roughness on colloid attachment at the pore-scale were elucidated by contrasting colloid attachment to glass surface with roughness varying three orders of magnitude. Colloid attachment and detachment were examined under favorable and unfavorable (i.e., repulsion absent and present) conditions for colloids ranging in size from 0.02 to 4.4 μm. Roughness closed the gap between favorable and unfavorable conditions observed for smooth glass: from above via hydrodynamic slip, and from below via decreased repulsion for rough surfaces. Particle trajectory simulations incorporating various mechanistic impacts of roughness allowed further clarity on the effects of roughness on delivery and immobilization. The slip length was calibrated to experimentally observed tangential colloid velocities, and it was found to equal the relief between maximum asperities. Contrary to popular theory, the radius of curvature effects of roughness increase or decrease the magnitude of colloid-surface interactions, but cannot reverse them. Charge heterogeneity covaries with roughness, with increased spatial density of large versus small heterodomains. Additionally, multiple interactions with asperities (e.g., attachment iv in concavities) increase colloid adhesion. Pathogen prevalence in two contrasting hydrogeologic settings in Wisconsin was explored by comparing transport of nondecaying colloids in media collected from the Central Sands and Kewaunee County. Column-scale experiments demonstrated several orders of magnitude less retention of virus- to protozoa-sized (0.1 to 4.2 μm) colloids in macropores in till compared to sand. Particle trajectory simulations using representative geometries for granular media and macropores elucidated the roles of impingement, diffusion, and settling as delivery mechanisms to surfaces. Delivery to surfaces in granular media serve as an effective pathogen removal mechanism. |
