A Novel Equation for Predicting Attachment Efficiency of Colloid Deposition Under Unfavorable Chemical Conditions.

This study proposes a novel model for predicting attachment efficiency of colloid deposition in porous media under unfavorable conditions by taking into account the coupled effects of diffusion process and hydrodynamic forces on colloid attachment efficiency. The Maxwell approach was used to quantify effects of diffusion process on attachment efficiency by coupling primary- and secondary-minimum deposition and the influence of hydrodynamic drag on attachment efficiency is quantitatively determined via comparing adhesive and hydrodynamic torques that act on the colloids at primary and secondary minima. Main findings include (i) the attachment efficiency does not change with increase in flow velocity until it reaches a critical point at which the attachment efficiency begins to decrease as flow velocity further increases; (ii) the attachment efficiencies predicted by the new model are in good agreement with experimental observations. Our study suggests that the effects of fluid drag on colloids of environmental concern (e.g., viruses and bacteria) deposited in the vicinity of grain surfaces must be considered in transport models for accurate predictions of their travel time in the subsurface environments.