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Title: COLLOID-FACILITATED TRANSPORT IN VARIABLY SATURATED POROUS MEDIA: NUMERICAL MODELING AND EXPERIMENTAL VERIFICATION.

Author
item HE, C. - U.C. RIVERSIDE, CA
item SIMUNEK, J. - U.C. RIVERSIDE, CA
item PANG, L. - INT ENV SCI, NEW ZEALAND
item Bradford, Scott

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2005
Publication Date: 11/1/2005
Citation: He, C., Simunek, J., Pang, L., Bradford, S.A. 2005. Colloid-facilitated transport in variably saturated porous media: numerical modeling and experimental verification. [CD-ROM] Agronomy Abstracts. SSSA Annual Meeting. Salt Lake City, UT.

Interpretive Summary:

Technical Abstract: Strongly sorbing chemicals (e.g., heavy metals, radionuclides, pharmaceuticals, and/or explosives) in soils are associated predominantly with the solid phase, which is commonly assumed to be stationary. However, recent field- and laboratory-scale observations have shown that, in the presence of mobile colloidal particles (e.g., microbes, humic substances, clays and metal oxides), the colloids could act as pollutant carriers and thus provide a rapid transport pathway for strongly sorbing contaminants. To address this problem, we have developed a one-dimensional numerical model based on the HYDRUS-1D software package that incorporates mechanisms associated with colloid and colloid-facilitated solute transport in variably saturated porous media. This numerical model accounts for both colloid and solute movement due to convection, diffusion, and dispersion in variably saturated soils, as well as for solute movement facilitated by colloid transport. The colloids transport module additionally considers processes of attachment/detachment to/from the solid phase and/or the air-water interface, straining, and/or size exclusion. Various blocking and depth dependent functions can be used to modify the attachment and straining coefficients. The solute transport module uses the concept of two-site sorption to describe nonequilibrium adsorption-desorption reactions to the solid phase. The module further assumes that the contaminant can be sorbed onto surfaces of both deposited and mobile colloids, fully accounting for the dynamics of colloids movement between different phases. The application of the model will be demonstrated using the experimental data from batch and column experiments, conducted to investigate the adsorption of cadmium (Cd) onto Bacillus subtilis spores and Escherichia coli vegetative cells and Cd transport in alluvial gravel aquifer media in the presence of these bacteria. Numerical results simulating bacteria transport, as well as the colloid-facilitated Cd transport will be compared with experimental results.