(356a) Targeted Groundwater Remediation Using Engineered Colloids

Over half of the US population relies on groundwater for its drinking water supply. However, porous groundwater aquifers are often subject to contamination by non-aqueous phase liquids (NAPLs), such as chlorinated solvents, that are discharged by industrial processes and improper waste disposal. These NAPLs are immiscible with water; thus, capillary forces keep them trapped in aquifer pores and render NAPL removal challenging. To address this problem, colloidal particles have been explored to enhance NAPL removal from groundwater aquifers due to their potential to localize at NAPL-water interfaces, which would enable them to chemically degrade NAPLs in situ. However, these particles often aggregate and deposit onto the solid surfaces surrounding aquifer pores, which strongly hinders their ability to reach NAPLs, thus limiting the efficacy of this approach.

In this PhD project, I address these challenges by studying the multi-scale interactions between immiscible fluids, colloidal particles, and a solid porous medium. Using confocal microscopy, we first identify the fundamental mechanisms of particle deposition and erosion in porous media at various injection conditions. Furthermore, we find that we can harness these naturally occurring deposition and erosion processes to promote immiscible fluid mobilization, in the absence of surface activity or chemical reactivity. To further unravel the underlying physics of this process and understand the complex interplay between colloidal interactions, hydrodynamics, and capillarity, we next look at single-pore phenomena that arise between dense multi-particle aggregates and immiscible fluid droplets as they flow. As immiscible fluid interfaces pass over deposited particles, we observe that they strongly adsorb to it, and show that this surprising behavior arises due to the influence of capillary forces exerted by the fluid interface as it impinges on the particles, forcing them to overcome the electrostatic energy barrier to adsorption. Thus, the surface coverage of the interface by particles increases with time as the fluid droplet traverses the channel. Eventually, the interface becomes saturated with adsorbed particles, defining a finite “carrying capacity” of these immiscible fluid interfaces. In addition to altering the resultant deposition pattern and the immiscible fluid interface’s rheology, we explore the ability of this dynamic capillarity-induced erosion to alter immiscible fluid pathways using a pore network model, which reveals that certain regimes of deposition and erosion can generate vastly different immiscible fluid displacement patterns than what is predicted by standard invasion percolation theory.

Armed with a rich knowledge of how immiscible fluids and colloidal particles interact in porous media, we finally fabricate reactive, organic-inorganic colloidal particles whose surface properties can be tuned using a variety of molecular and process parameters. We begin to explore how these particles stably spread through aquifer pore spaces, which may allow control over targeting contaminants for in situ degradation. Taken together, this research addresses an urgent threat to our water security.

Research Interests: bio-inspired materials, biodegradable polymers, biofuels, carbon capture & storage, colloids, flow through porous media, fluid mechanics, nanomaterials & nanotechnology, network modeling, porous media characterization, porous media fabrication, porous media modeling, sustainability, water remediation