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Title: Resolving the coupled effects of hydrodynamics and DLVO forces on colloid attachment in porous media

item Bradford, Scott

Submitted to: Langmuir
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2007
Publication Date: 8/18/2007
Citation: Torkzaban, S., Bradford, S.A., Walker, S.L. 2007. Resolving the coupled effects of hydrodynamics and DLVO forces on colloid attachment in porous media. Langmuir. Vol 23:9652-9660

Interpretive Summary: Retention of microorganism and other colloid particles in soils depends on chemical reactions between the colloids and the soil particles. The currently accepted theory has not considered the forces that are associated with flowing water on colloid retention. A computer model was used to study the influence of both chemical forces and forces due to flowing water on colloid retention on a single soil grain. Results demonstrate that colloid retention is highly sensitive to both of these forces, and will depend on the size and shape of the soil grain and colloid. This information will be useful to help develop improved theories to accurately predict microorganism transport and fate in soils.

Technical Abstract: Transport of colloidal particles in porous media is governed by the rate at which the colloids strike and stick to collector surfaces. Classic filtration theory has considered the influence of system hydrodynamics on determining the rate that colloids strike collector surfaces, but has neglected the influence of hydrodynamic forces in the calculation of the collision efficiency. Computational simulations based on the sphere-in-cell model were conducted that considered the influence of hydrodynamic and DLVO forces on colloid attachment to collectors of various shape and size. Our analysis indicated that hydrodynamic and DLVO forces and collector shape and size significantly influenced the colloid collision efficiency. Colloid attachment was only possible on regions of the collector where the torque from hydrodynamic shear acting on colloids adjacent to collector surfaces was less than the adhesive (DLVO) torque that resists detachment. The fraction of the collector surface area on which attachment was possible increased with solution ionic strength, collector size and decreasing flow velocity. Simulations demonstrated that quantitative evaluation of colloid transport through porous media will require nontraditional approaches which account for hydrodynamic and DLVO forces as well as collector shape and size.