Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr. Denis O'Carroll

2nd Supervisor

Dr. Jason Gerhard

Joint Supervisor

Abstract

Engineered nanoparticles are widely used and will eventually be released to the subsurface environment and contaminate groundwater resources. However, the transport of engineered nanoparticles through soil is currently not well understood and cannot be modelled in any fundamental manner, placing groundwater resources at risk from nanoparticle contamination. This inability to accurately simulate transport is due to a lack of experimental information on nanoparticle interactions in the pore spaces of real soils.

This thesis illuminates the pore-scale processes governing silver nanoparticle transport through soil. In addition, it examines the influence of surface chemistry and grain/pore distributions on those processes. For the first study, a method was developed and validated which employs Synchrotron X-ray Computed Microtomography (SXCMT) to experimentally quantify changing concentrations of silver nanoparticles, both spatially and temporally, within real soil pore spaces during transport. For the second study, the SXCMT imaging method was employed to experimentally investigate the role of pore-scale processes on silver nanoparticle transport through different soils representing different surface chemistries and grain distributions. The experiments found that nanoparticle transport and retention is significantly impacted by small regions of low fluid velocity near grain-grain contacts (termed ‘immobile zones’). For the third study, the experimental SXCMT datasets from the second study were coupled with Computational Fluid Dynamics to estimate the pore-scale nanoparticle mass flux and flow rates. The estimated distributions of mass flux and flow rates suggested that the current approach to modelling nanoparticle retention was incapable of considering mass flow in the centers of soil pores, rendering it unable to accurately predict the rate at which nanoparticles will be retained by soil.

Overall, this thesis presents the first experimental datasets of pore-scale nanoparticle concentrations during transport. These previously unobtainable datasets provided the first direct confirmation of ‘immobile zones’ and their contribution to anomalous nanoparticle transport behaviour. In addition, they provided some of the first evidence as to why current modelling approaches are unable to predict nanoparticle retention rates.

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