Geophysical characterization of subsurface biofuel contamination and biodegradation
Creators: name: Personna, Yves Robert
Publisher: name: No Publisher Supplied
Year: 2013

description: In the last two decades, the production of ethanol (EtOH), one of the most common biofuels in the USA, has substantially increased due to regulations aiming at reducing air pollution and providing a supplement to petroleum. Scenarios of large spills of EtOH during production, transportation and at storage facilities are likely. Accidental release of EtOH and its persistence in the subsurface pose threats to human health and the environment, including the deterioration of municipal water supplies. Thus, there is a need to develop adequate monitoring tools to help with the remediation efforts of subsurface EtOH contamination. Ethanol presence, interaction and biodegradation could substantially alter the electrical properties of geologic materials, thereby potentially leading to distinctive geophysical responses. This dissertation demonstrates the potential application of non-invasive and cost effective complex resistivity (CR) technique for the characterization of biofuel contamination and biodegradation in the subsurface. The first research topic examined the electrical geophysical signatures arising from groundwater contamination by EtOH. Conductivity measurements were performed at the laboratory scale on EtOH-water mixtures (0 to 0.97 v/v EtOH) and EtOH-salt solution mixtures (0 to 0.99 v/v EtOH) with and without a sand matrix. A mixing model was used to simulate electrical conductivity as a function of EtOH concentration in the mixture. It was found that increasing EtOH concentration resulted in a decrease in measured conductivity magnitude ( ), which reflected changes in relative strength of the types of interactions occurring in EtOH-water mixtures. The second research topic explored the electrical properties associated with EtOH-clay interactions using CR measurements on laboratory columns of varying ethanol (EtOH) concentration (0% to 30% v/v) in a sand-clay (bentonite) matrix. A Debye Decomposition approach was applied to fit the CR data. Overall, the results showed a significant suppression (P ≤ 0.001) of the clay driven polarization with increasing EtOH concentration. The suppression effects are associated with alterations in the electrical double layer (EDL) at the clay-fluid interface due to strong EtOH adsorption on clay and complex intermolecular EtOH-water interactions. The persistent EtOH adsorption on clay also indicated strong hysteresis effects in the electrical response. The third research topic investigated changes in electrical properties during EtOH biodegradation processes in sand matrix using CR measurements in conjunction with geochemical data analysis on microbial stimulated (inoculation of bacterial cells) and control (without bacteria inoculation) columns. A Debye Decomposition approach was applied to fit the CR data. Overall, the results showed a clear distinction between the bio-stimulated and control columns in terms of real ( ) and imaginary ( ) conductivity, phase ( ) and apparent formation factor (Fapp). Temporal geochemical changes and high resolution scanning electron microscopy imaging corroborated the CR findings, thus indicating the sensitivity of CR measurements to EtOH biodegradation processes.