School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Transport and Retention of Colloids in Saturated and Unsaturated Porous Media

By

Christopher Scott Gray

Advisor:

Dr. Susan E. Burns (CEE)

Committee Members:

Dr. Chloe Arson (CEE), Dr. J. David Frost (CEE), Dr. Paul W. Mayne (CEE), Dr. Christian Huber (EAS)

Date & Time: January 8, 2016 8:00am

Location: Sustainable Education Building, 122

ABSTRACT

The transport of colloidal particles in subsurface geological deposits plays an important role in many natural processes, from geochemical cycling of elements in aquifers to the transport of highly mobile bacteria and viruses. Colloids are of importance in geotechnical systems, where engineers are typically concerned with controlling the hydraulic conductivity of filters, such as in dam cores or landfill liners, or improving soil stiffness by utilizing microbial induced precipitation. Colloids are of particular importance to geoenvironmental engineers, as these highly mobile particles can act as vectors for immobile contaminants, effectively bypassing groundwater treatment systems. The transport of colloids themselves may be of concern such as in the case of pathogenic biocolloids and toxic nanoparticles.

This study explores the transport and retention of colloids in saturated and unsaturated silica sand, iron oxide coated sand, and natural zeolite, all of which are common components in permeable reactive barriers. Column flow cell studies demonstrate that colloid mobility is significantly affected by porewater chemistry and theoretical DLVO calculations elucidate differing colloid retention mechanisms in the three geomaterials. Results reveal that colloid transport in geomaterials is reduced in steady-state unsaturated flow, with zeolite significantly enhancing colloid retention. Studies exploring the mobilization of colloids from reactive geomaterials by a downward propagating drying front indicate that reactive geomaterials can enhance colloid retention.

This work also investigates the role of colloid shape on transport and retention in saturated and unsaturated silica sand using spherical and ellipsoidal colloids. Theoretical DLVO interaction potential energies calculated using surface element integration reveal that colloid shape affects interaction with the soil surface, while column studies demonstrate colloid shape affects transport, retention, and mobilization in saturated and unsaturated sand.