Dissertation/Thesis Abstract

Geophysical monitoring of subsurface microbial processes
by Williams, Kenneth Hurst, Ph.D., University of California, Berkeley, 2008, 164; 3332055
Abstract (Summary)

Microorganisms alter their physical and chemical environments, and changes in mineralogy and fluid chemistry are especially magnified during bioremediation. The ability to resolve the onset, location, and persistence of these changes may significantly improve implementation of bioremediation. The focus of this dissertation is the development of geophysical monitoring approaches sensitive to variations in electrical polarization, electrochemical gradients, and elastic moduli resulting from stimulated microbial activity. The geophysical monitoring approaches were tested in laboratory column experiments using sulfate and iron reducing microorganisms and validated during biostimulation experiments in a uranium-contaminated aquifer near Rifle, Colorado.

Laboratory experiments confirmed that changes in induced polarization (IP), self-potential (SP), and acoustic wave signatures accompanied alterations in sediment and pore fluid characteristics resulting from stimulation of sulfate reducing bacteria. Precipitation of zinc and iron sulfides within pores altered interfacial conduction processes and the ability of the sediments to dissipate acoustic energy, impacting the IP and acoustic signals, respectively. Increases in dissolve sulfide created electrochemical potential differences between electrodes, yielding SP anomalies exceeding 600 mV. The generation of SP anomalies in the absence of an inert conductor was attributed to galvanic effects at the electrode surfaces. The combination of methods proved sensitive to spatiotemporal changes in active biomass and the accumulation of metal sulfide precipitates.

Validation of the SP and IP monitoring methods was accomplished during field biostimulation experiments. Voltages exceeding 800 mV were measured between subsurface electrodes and a surface-based reference. The onset and persistence of the SP anomalies correlated with both the accumulation of dissolved sulfide and the removal of uranium from groundwater, suggesting a means for monitoring the stability of favorable redox conditions over large distances.

Spatiotemporal variations in the IP phase response correlated with changes in groundwater geochemistry reflecting stimulated iron and sulfate reduction and sulfide mineral precipitation. The accumulation of both mineral precipitates and electroactive ions altered the ability of pore fluids to conduct electrical charge, accounting for the IP phase response. Differences in the high and low frequency phase response during periods of iron and sulfate reduction suggest an ability to discriminate between the two processes.

Indexing (document details)
Advisor: Banfield, Jillian F.
School: University of California, Berkeley
School Location: United States -- California
Source: DAI-B 69/09, Dissertation Abstracts International
Subjects: Geophysics, Biogeochemistry, Environmental science
Keywords: Bioremediation, Geophysical monitoring, Induced polarization, Self-potential
Publication Number: 3332055
ISBN: 978-0-549-84078-7
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