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Title: An explanation for differences in the process of colloid adsorption in batch and column studies

Author
item TREUMANN, SVANTJE - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item TORKZABAN, SAEED - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item Bradford, Scott
item VISALAKSHAN, RAHUL - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item PAGE, DECLAN - Commonwealth Scientific And Industrial Research Organisation (CSIRO)

Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2014
Publication Date: 6/20/2014
Citation: Treumann, S., Torkzaban, S., Bradford, S.A., Visalakshan, R.M., Page, D. 2014. An explanation for differences in the process of colloid adsorption in batch and column studies. Journal of Contaminant Hydrology. 164:219-229.

Interpretive Summary: The retention of pathogenic bacteria and viruses in soils has traditionally been studies in batch or column studies, but results from these two approaches are generally not consistent. The objective of this study was to systematically investigate differences in microbial retention in batch and column experiments, using four sizes of latex microspheres as surrogates for microorganisms. The rate of colloid retention and the fraction of the solid surface area that contributes to colloid retention were different in batch and column experiments due to differences in the hydrodynamics, and the role of surface roughness and pore structure on colloid retention in column systems. These results provided insight on the proper mathematical model to describe microbial transport and retention in soils, and demonstrated limitations of the conventional approach to determine microbial interactions in soils. This information will be of interest to scientists and engineers concerned with assessing risks of pathogen contamination in soils and groundwater.

Technical Abstract: It is essential to understand the mechanisms that control virus and bacteria removal in the subsurface environment to assess the risk of groundwater contamination with fecal microorganisms. This study was conducted to explicitly provide a critical and systematic comparison between batch and column experiments. The aim was to investigate the underlying factors causing the commonly observed discrepancies in colloid adsorption process in column and batch systems. We examined the colloid adsorption process of four different sizes of carboxylate-modified latex (CML) microspheres, as surrogate for viruses and bacteria, on quartz sand in batch and column experiments over a wide range of solution ionic strengths. Our results show that adsorption of colloids in batch systems should consider irreversible attachment and blocking process because the attachment/detachment model was found to be inadequate in describing the batch results. Conversely, an irreversible attachment-blocking model was found to accurately describe the results of both batch and column experiments. The rate of retention was found to depend highly on colloid size, solution IS and the fraction of the sand surface area favorable for attachment. The rate of retention and the fraction of the surface area favorable for colloid attachment were different in batch and column experiments due to differences in the hydrodynamics, and the role of surface roughness and pore structure on colloid retention. Results from column and batch experiments were generally not comparable, especially for larger colloids (greater than or equal to 0.5 µm). Predictions based on classical DLVO theory were found to inadequately describe interaction energies between colloids and sand surfaces.