Deposition and re-entrainment dynamics of microbes and non-biological colloids during non-perturbed transport in porous media in the presence of an energy barrier to deposition

This paper examines the non-perturbed deposition and re-entrainment dynamics of biological and non-biological colloids in porous media in the presence of an energy barrier to deposition at the grain surface. Deposition and re-entrainment rate coefficients were determined from numerical simulation of breakthrough-elution behavior and the profiles of retained colloids. We present composite trends from original and previously published data for biological and non-biological colloids which demonstrate that hydrodynamic drag mitigates deposition and drives re-entrainment of both biological and non-biological colloids in the presence of an energy barrier under nonperturbed conditions. Original data is presented for two sizes of colloids (1.1 and 5.7 mu m microspheres) under a variety of ionic strength and fluid velocity conditions to examine the torque balance governing re-entrainment of colloids attached to the grain surfaces. The analysis indicates that in the presence of an energy barrier to deposition, hydrodynamic drag may influence deposition and re-entrainment of colloids associated directly with the grain surface via primary energy minima. However, the hydrodynamic field would also be expected to influence deposition and re-entrainment of colloids associated with the surface via secondary energy minima. Hence, the observed influences of fluid velocity are consistent with colloid association via either mechanism. These results call for the development of colloid transport theories that explicitly account for the influence of the hydrodynamic field at the grain surface. (C) 2006 Elsevier Ltd. All rights reserved.