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Title: Colloid release and clogging in porous media: Effects of solution ionic strength and flow velocity

Author
item TORKZABAN, SAEED - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item Bradford, Scott
item VANDERZALM, JOANNE L. - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item PATTERSON, BRADLEY - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item HARRIS, BRETT - Curtin University
item PROMMER, HENNING - Commonwealth Scientific And Industrial Research Organisation (CSIRO)

Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2015
Publication Date: 6/19/2015
Citation: Torkzaban, S., Bradford, S.A., Vanderzalm, J., Patterson, B.M., Harris, B., Prommer, H. 2015. Colloid release and clogging in porous media: Effects of solution ionic strength and flow velocity. Journal of Contaminant Hydrology. 181: 161-171.doi: 10.1016/j.jconhyd.2015.06.005.

Interpretive Summary: Managed Aquifer Recharge (MAR) is an increasingly important way to store, recover, and treat drinking and irrigation water supplies. However, MAR performance is strongly influenced by mobilization of clay particles that can drastically decrease the aquifer permeability due to clogging. Experiments and simulations were conducted to study clay mobilization and clogging on aquifer samples under representative MAR conditions. Decreases in the solution ionic strength were found to mobilize clays and clog the cores, whereas increases in water velocity or a flow interruption diminished clogging and improved the core permeability. These results will be of interest to scientists, engineers, and government officials concerned with MAR performance.

Technical Abstract: The release and retention of in-situ colloids in aquifers play an important role in the sustainable operation of managed aquifer recharge (MAR) schemes. The processes of colloid release, retention, and associated permeability changes in consolidated aquifer sediments were studied by displacing native groundwater with reverse osmosis-treated (RO) water at various flow velocities. Significant amounts of colloid release occurred when: (i) the native groundwater was displaced by RO-water with a low ionic strength (IS), and (ii) the flow velocity was increased in a stepwise manner. The amount of colloid release and associated permeability reduction upon RO-water injection depended on the initial clay content of the core. The concentration of released colloids was relatively low and the permeability reduction was negligible for the core sample with a low clay content of about 1.3%. In contrast, core samples with about 6 and 7.5% clay content exhibited: (i) close to two orders of magnitude increase in effluent colloid concentration and (ii) more than 65% permeability reduction. Incremental improvement in the core permeability was achieved when the flow velocity increased, whereas a short flow interruption provided a considerable increase in the core permeability. This dependence of colloid release and permeability changes on flow velocity and colloid concentration was consistent with colloid retention and release at pore constrictions due to the mechanism of hydrodynamic bridging. A mathematical model was formulated to describe the processes of colloid release, transport, retention at pore constrictions, and subsequent permeability changes. Our experimental and modeling results indicated that only a small fraction of the in-situ colloids was released for any given change in the IS or flow velocity. Comparison of the fitted and experimentally measured effluent colloid concentrations and associated changes in the core permeability showed good agreement, indicating that the essential physics were accurately captured by the model.