Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2006
Publication Date: 11/1/2006
Citation: Bradford, S.A., Simunek, J., Bettahar, M., Van Genuchten, M.T., Yates, S.R. 2006. Significance of straining in colloid deposition: evidence and implications. Water Resources Research. VOL 42, W12S15 Interpretive Summary: Computer models for predicting the transport and retention of pathogenic microorganisms in soils and aquifers are typically based on filtration theory. This theory assumes that the amount of microbes retained in the soil is controlled by chemical interactions between the microbes and the soil surfaces. Over the past decade considerable research suggests that this theory does not provide an adequate description of microbe retention in many soil systems, because it does not include the potential influence of physical factors such as soil pore size and surface roughness. This work highlights experimental evidence that indicates that these physical factors can play an important role in microbe retention. The implications of microbe straining in soil pores is discussed, and areas for future research are identified.
Technical Abstract: Filtration theory is often used to characterize colloid attachment when deposition is controlled by chemical interactions between colloids and grain surfaces. Over the past decade considerable research suggests that colloid deposition is frequently not consistent with filtration theory predictions under unfavorable attachment conditions. Filtration theory does not include the potential influence of pore structure, grain-grain junctions, and surface roughness on straining deposition. This work highlights recent experimental evidence that indicates that straining can play an important role in colloid deposition, and may explain many of the reported limitations of filtration theory. This conclusion is based upon pore size distribution information, size exclusion, time and concentration dependent deposition behavior, colloid size distribution information, hyperexponential deposition profiles, the dependence of deposition on colloid and porous medium size, batch release rates, micromodel observations, and deposition at textural interfaces. The implications of straining in unsaturated and heterogeneous systems are also discussed, as well as the potential influence of system hydrodynamics. The inability of attachment theory predictions to describe experimental colloid transport data is demonstrated. Specific tests to identify the occurrence and/or absence of straining and attachment are proposed.