HR: 13:40h
AN: H12H-01    [PDF]
TI: Effect of Hydrocarbon Biodegradation on the Low-Frequency Electrical Properties of Unconsolidated Sediments
AU: * Abdel Aal, G Z
EM: gagv4@umr.edu
AF: University of Missouri-Rolla, Geology and Geophysics Dept. 125 McNutt Hall, Rolla, MO 65401 United States
AU: Atekwana, E A
EM: atekwana@umr.edu
AF: University of Missouri-Rolla, Geology and Geophysics Dept. 125 McNutt Hall, Rolla, MO 65401 United States
AU: Slater, L D
EM: lslater@andromeda.rutgers.edu
AF: Rutgers University, Department of Earth and Environmental Sciences, Rutgers, NJ 07102 United States
AU: Atekwana, E A
EM: eliota@umr.edu
AF: University of Missouri-Rolla, Geology and Geophysics Dept. 125 McNutt Hall, Rolla, MO 65401 United States
AB: A laboratory sand column experiment was conducted to investigate the effect of biodegradation of diesel on low-frequency electrical measurements over a period of 36 weeks. Uniform fine to medium grained sands were used in the columns with the following experimental treatments: nutrients; nutrients + diesel; nutrients + diesel + bacteria. The first two columns were kept sterile by adding 200 mg/l mercury chloride, whereas the third column was kept active. Spectral electrical measurements were conducted in the frequency range 0.1 to 1000 Hz biweekly for the first twenty weeks and monthly for the duration of the experiment. Evidence of biodegradation in the active column was determined by monitoring the changes in concentration of terminal electron acceptors (e.g., nitrate and sulfate) and total benzene, toluene, ethylbenzene and xylene (BTEX). After 36 weeks, we observed in general that the active column exhibited major changes in electrical and geochemical parameters compared to sterile columns. The active column showed about 100 and 120 percent increase in the magnitude of the real and imaginary conductivities, respectively. No significant increases in the real and imaginary conductivity were observed in the sterile columns. We note that, (a) the relative increase in the real conductivity exceeded the relative increase in the fluid conductivity, and (b) the relative increase in the imaginary conductivity (polarization) exceeded the relative increase in the real conductivity. The active column further showed 70 to 90 percent depletion in nitrate, sulfate and BTEX concentrations. Moreover, magnesium and calcium concentrations increased within the active column to about 120 to160 percent (respectively) compared to the sterile column. The major biogeochemical changes associated with the active column are an indication of active microbial degradation of diesel. Moreover, the increase in calcium and magnesium ion concentrations in the active column, concurrent with a decrease in pH is indicative of mineral weathering accompanying the degradation process. Based on the geochemical analyses and the electrical parameters, we argue that microbial alteration of surface chemistry (increase of surface charge density and ionic mobility) at the mineral-fluid interface, coupled with increases in the electrical conductivity of the electrolyte, explain our observations in the active column. We conclude from this study that low-frequency electrical measurements have the potential to monitor the biogeochemical and physical changes of hydrocarbon contaminated soils undergoing biodegradation.
DE: 1615 Biogeochemical processes (4805)
DE: 3914 Electrical properties
DE: 4803 Bacteria
DE: 4815 Ecosystems, structure and dynamics
DE: 4854 Physicochemical properties
SC: Hydrology [H]
MN: 2003 Fall Meeting