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ARS Home » Research » Publications at this Location » Publication #315570
Title: Langmuirian blocking of irreversible colloid retention: analytical solution, moments, and setback distance

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

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2015
Publication Date: 9/16/2015
Citation: Leij, F.J., Bradford, S.A., Wang, Y., Sciortino, A. 2015. Langmuirian blocking of irreversible colloid retention: analytical solution, moments, and setback distance. Journal of Environmental Quality. 44:1473-1482. doi: 10.2134/jeq2015.03.0147.

Interpretive Summary: Enhanced transport of colloids such as pathogenic microorganisms occurs in soils as available retention sites fill over time (e.g., blocking). Mathematical expressions were developed to study the influence of blocking on colloid transport, and setback distances and arrival times to protect water resources from contamination. Larger setback distances were needed for small retention rates and capacities, and larger colloid concentrations, whereas the opposite conditions produced a delay in colloid arrival. This information will be of interest to scientists and engineers concerned with assessing the risk of colloid contamination in groundwater environments.

Technical Abstract: Soil and aquifer materials have a finite capacity for colloid 20 retention. Blocking of the limited number of available retention sites further decreases the rate of retention over time and enhances risks (e.g., pathogens or colloid associated contaminants) or benefits (e.g., remediation by microorganisms or nanoparticles) of colloid migration. Our objective was to employ a straightforward procedure, based on variable transformation and Laplace transform, to solve the problem of advective colloid transport with irreversible retention and Langmuirian blocking for a pulse-type condition. Formulas for the mean breakthrough time and retardation factor were obtained using zero- and first-order time moments of the breakthrough curves. Equations for the time and position (setback distance) for a particular colloid concentration were obtained from this information. E. coli D21g breakthrough curves and retention profiles in fine sand at four ionic strengths were well described by the model when parameters were optimized. Illustrative simulations demonstrated that blocking becomes more important for smaller retention capacity (Sm), and for larger retention rate coefficient (k), input concentration (Co), and pulse duration. Blocking tended to delay colloid arrival time at a particular location relative to a conservative tracer, and produced larger setback distances for smaller k and Sm/Co.