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Title: Analytic solutions for colloid transport with time- or depth-dependent retention in porous media

Author
item LEIJ, FEIKE - California State University
item Bradford, Scott
item SCIORTINO, ANTONELLA - California State University

Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2016
Publication Date: 11/1/2016
Citation: Leij, F.J., Bradford, S.A., Sciortino, A. 2016. Analytic solutions for colloid transport with time- or depth-dependent retention in porous media. Journal of Contaminant Hydrology. 195:40-51. doi: 10.1016/j.jconhyd.2016.10.006.

Interpretive Summary: An ability to simulate the transport of colloids such as pathogenic microorganisms and nanoparticles is needed to protect soil and water resources from contamination. A new model was developed to simulate colloid transport in soils and aquifers that exhibits time- or depth-dependent retention. Simulations results provided valuable insights on causes for many observed complexities associated with colloid transport and retention. 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: Elucidating and quantifying the transport of industrial nanoparticles (e.g. silver, carbon nanotubes, and graphene oxide) and other colloid-size particles such as viruses and bacteria is important to safeguard and manage the quality of the subsurface environment. Analytic solutions were derived for aqueous and solid phase colloid concentrations in a porous medium where colloids were subject to advective transport and reversible time and/or depth-dependent retention. Time-dependent blocking and ripening retention were described using a Langmuir-type equation with a rate coefficient that respectively decreased and increased linearly with the retained concentration. Depth-dependent retention was described using a rate coefficient that is a power-law function of distance. The stream tube modeling concept was employed to extend these analytic solutions to transport scenarios with two different partitioning processes (i.e., two types of retention sites). The sensitivity of concentrations was illustrated for the various time- and/or depth-dependent retention model parameters. The developed analytical models were subsequently used to describe breakthrough curves and, in some cases, retention profiles from several published column studies that employed nanoparticle or pathogenic microorganisms. Simulations results provided valuable insights on causes for many observed complexities associated with colloid transport and retention, including: increasing or decreasing effluent concentrations with continued colloid application, a delay in breakthrough, low concentration tailing, and retention profiles that are hyper-exponential, exponential, linear, or non-monotonic with distance.