Electrokinetic-enhanced migration of solutes for improved bioremediation in heterogeneous granular porous media

Contaminated land is a global problem. Where it presents an unacceptable risk to receptors such as human health or ecosystems, remediation actions must be taken. Current remediation technologies can be ineffective due to mass transfer limitations. A typical scenario where these limitations control remediation efficacy is a physically heterogeneous aquifer where hydraulic conductivity (K) varies spatially. Under these conditions remediation is limited by solute migration across K boundaries. This thesis couples two remediation technologies, in situ bioremediation and electrokinetics (EK), to overcome the mass transfer limitations presented by physically heterogeneous settings. Bioremediation is the transformation of contaminants into less harmful substances by microorganisms; and EK is the application of a direct current to initiate certain transport processes independent of K. Where bioremediation is limited due to the influence of physical heterogeneity, EK transport processes could be applied to initiate an additional flux of solutes across K boundaries. This thesis investigates the influence of physical heterogeneity on EK migration of an amendment designed to enhance bioremediation. The research presented in this thesis advances the current state of knowledge for EK-BIO applications both at the fundamental level and field-scale using laboratory and desk based studies respectively. Laboratory apparatus was designed and built to accommodate physical heterogeneity, electrokinetic transport of solutes and contaminant biodegradation. Broadly, two types of EK experiment were conducted. Firstly, EK amendment migration under abiotic conditions on different arrangements of physical heterogeneity. Secondly, experiments in the same laboratory setup that introduced contaminant and microbial variables. From these experiments a conceptual framework is developed that describes the influence of physical heterogeneity on the EK transport of an amendment. It relates the spatial change in material properties associated with physical heterogeneity with aspects of EK application, such as the voltage gradient, and observes the implications for amendment transport. For example a layered contrast in material type generated a non-uniform electric field when direct current was applied, this led to non-uniform EK transport of the amendment relative to homogeneous settings. When contaminant and microbial variables were introduced to the experimental setup a greater understanding of EK-BIO applications to physically heterogeneous settings was gained. These experiments highlight and discuss the technical issues applying EK to enhance bioremediation by amendment addition versus contaminant removal by EK induced pore fluid movement. Desk based studies included a review of EK-BIO literature and a sustainability assessment that considered EK-BIO at the field scale. The review summarises the practical aspects of the technology in applications to natural environments. It notes that numerous limitations exist to EK-BIO applications in these settings but that there are many different implementation methods that can mitigate these effects. The sustainability assessment compares EK-BIO with conventional remediation technologies against specific criteria for a complex site contaminated with BTEX and MTBE. EK-BIO compares well to other technologies however characteristics of the site will determine the potential sustainability benefits of applying EK.