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United States Department of Agriculture

Agricultural Research Service

Research Project: Protection of Food and Water Supplies from Pathogen Contamination Title: Colloid adhesive parameters for chemical heterogeneous porous media

Authors
item Bradford, Scott
item Torkzaban, Saeed -

Submitted to: Langmuir
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 7, 2012
Publication Date: September 7, 2012
Repository URL: http://www.ars.usda.gov/SP2UserFiles/Place/53102000/pdf_pubs/P2398.pdf
Citation: Bradford, S.A., Torkzaban, S. 2012. Colloid adhesive parameters for chemical heterogeneous porous media. Langmuir. 28:13643-13651.

Interpretive Summary: Transport properties of colloids, such as microorganisms, are affected by small scale variations in charge on the surfaces of the soil and colloids. The objective of this study was to develop a model to predict colloid transport parameters for chemically heterogeneous soil and colloids. Simulation results demonstrated that colloid transport parameters were complex functions that were sensitive to the chemical heterogeneity properties, the colloid size, the solution chemistry, and velocity of flowing water. The findings from this study will be of interest to scientists and engineers concerned with predicting the fate of colloids in the environment.

Technical Abstract: A simple modeling approach was developed to calculate colloid adhesive parameters for chemically heterogeneous porous media. The area of the zone of electrostatic influence between a colloid and solid-water interface (Az) was discretized into a number of equally sized grid cells to capture chemical heterogeneity within this region. These cells were divided into fractions having specific zeta potentials (e.g., negative or positive values). Colloid adhesive parameters such as the mean value of the zeta potential, the minimum and maximum in the interaction energy, the colloid sticking efficiency (a), and the fraction of the solid surface area that contributes to colloid immobilization (Sf) were calculated for all possible charge realizations within Az. The probability of a given charge realization in Az was calculated using a binomial mass distribution. Probability density functions (PDFs) for the colloid adhesive parameters on the heterogeneous surface were subsequently calculated at the representative elementary area (REA) scale for a porous medium. This approach was applied separately to the solid-water interface (SWI) and the colloid, or jointly to both the SWI and colloid. Results show that the PDFs of colloid adhesive parameters at the REA scale were sensitive to the size of the colloid and the heterogeneity, the charge and number of grid cells, and the ionic strength.

Last Modified: 8/30/2014