Colloid Retention in Porous Media of Various Porosities: Predictions by the Hemispheres-in-Cell Model

Abstract

The hemispheres-in-cell model for colloid transport and deposition in simple granular filtration media preserves the utilities provided in the Happel sphere-in-cell but also incorporates features (e.g., grain-to-grain contact) that are shown to drive colloid deposition from experiments and simulations when colloid-surface repulsion exists (Ma, H.; Pedel, J.; Fife, P.; Johnson, W. P. Environ. Sci. Technol., 2009, in press). The capability of the hemispheres-in-cell model to predict colloid deposition in the absence of repulsive energy barriers for different particle sizes and fluid flow velocities was previously examined (Ma, H.; Pedel, J.; Fife, P.; Johnson, W. P. Environ. Sci. Technol., 2009, in press). In this article, we examine the influence of porosity on colloid deposition in terms of theoretical (simulated) collector efficiencies from the hemispheres-in-cell model, as well as existing models, to examine whether expected trends in porosity are similar among the different models. The need for experimentally determined collector efficiencies for porosities outside the range of 0.33-0.42 is highlighted. We demonstrate agreement between existing experimental results and our model predictions, indicating that the hemispheres-in-cell model can potentially serve as a new model geometry to develop a predictive theory of colloid filtration in the presence of energy barriers, a condition that is typical in environmental contexts.