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Title: Critical role of surface roughness on colloid retention and release in porous media

item TORKZABAN, SAEED - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item Bradford, Scott

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2015
Publication Date: 10/19/2015
Citation: Torkzaban, S., Bradford, S.A. 2015. Critical role of surface roughness on colloid retention and release in porous media. Water Research. 88:274-284. doi: 10.1016/j.watres.2015.10.022.

Interpretive Summary: Roughness occurs on all natural surfaces. This study examined the importance of surface roughness on colloid (such as pathogenic microbes, nanoparticles, and clay) interactions, retention and release in sand. Results demonstrate that roughness produced weak interactions of colloids with soil particles that allowed them to be retained only on a small portion of the solid surface that was associated with roughness that was greater than or equal to the colloid size. This information will be of use to scientists and engineers concerned with predicting colloid interactions, retention, and release in natural environments and engineering applications.

Technical Abstract: A thorough understanding of colloid transport in porous media is of great importance in many environmental and industrial applications. Extended-DLVO theory was employed to investigate the influence of nanoscale surface roughness (NSR) on the magnitudes of the secondary (F2min) and primary energy (F1min) minima, the height of energy barrier against F1min attachment ('Fa), and the height of the energy barrier against detachment from the F1min ('Fd). This information was used to explain colloid (0.5 and 2 µm) attachment and detachment processes in column and batch experiments under different solution ionic strength (IS) and pH conditions. Results demonstrated that the density and height of NSR significantly influenced the interaction energy parameters that affect colloid attachment and detachment. In particular, values of 'Fa and 'Fd significantly decreased in the presence of NSR. Colloid attachment in the F1min was predicted at some localized locations on the solid surface, even for the larger 2 µm colloid under low IS conditions. However, NSR yielded a much weaker F1min compared with that of smooth surfaces. Detachment of colloids from a F1min increased with decreasing IS and increasing pH due to the impact of NSR on the values of 'Fd. The results suggest that changes in chemical conditions would cause the disappearance of the 'Fd for only a fraction of the attached colloids in the F1min. Pronounced differences in the amount of colloid retention in batch and column studies indicate that colloids interacting in weak F1min were efficiently removed by hydrodynamic forces in batch systems, whereas microscopic roughness hampered hydrodynamic removal in column studies by altering the lever arms associated with applied hydrodynamic and resisting adhesive torques.