Title

Laboratory-Scale Investigation of the Effect of Microbial Growth on the Geoelectrical Properties of Porous Media

Abstract

We investigated the effect of microbial growth and biofilm formation on low-frequency complex conductivity in porous media. Understanding the direct contribution of microbial growth to the low-frequency electrical response of porous media will lead to the development of models necessary for the interpretation of geoelectrical data from near-surface microbial-active geologic media (e.g. bioremediation). The objectives of this study were to determine (1) the direct effect of microbial growth and biofilm formation, and (2) the relative magnitude of the effect of microbial growth and biofilm formation on low-frequency complex conductivity of porous media. Silica sand packed columns (one control and one experimental set) were constructed in triplicate, treated with nutrient broth and diesel fuel, and microbial growth was stimulated in the experimental columns by the addition of a mixed bacteria culture. Low frequency (0.1-1000 Hz) electrical measurements, and geochemical analyses (i.e. pH, fluid conductivity) were made twice a week for the 60 day duration of the experiment. Sand was periodically sampled from the columns for microbial analysis (extraction of microbial cells from sand grains for direct microbial counting) and environmental scanning electron microscope (ESEM) imaging of grain surface characteristics. The experimental (biostimulated) columns showed a peak in the imaginary conductivity measurements on day 23 (maximum ∼8 × 10-6 S/m) which corresponded with a peak in the microbial cell concentrations (∼7 × 104 cells/mL), followed by a sharp decrease in both the imaginary conductivity and microbial concentrations. The real conductivity showed a general, relatively small increase (>0.04 S/m) between day 0 and 34 for both the control and experimental columns, before decreasing slightly (∼0.01 S/m). The close correspondence of the peaks in the imaginary conductivity and microbial cell concentrations in the experimental column suggest that microbial growth in porous media effects the imaginary (interfacial) conductivity to a greater degree than the real (electrolytic) conductivity, which did not appear to show a relationship with the microbial cell concentrations. We conclude from this study that low-frequency electrical measurements (imaginary conductivity) may aid in investigations aimed at assessing the rate of microbial growth and biofilm formation in porous media.

Meeting Name

19th Symposium on the Application of Geophysics to Engineering and Environmental Problems (2006: Apr. 2-6, Seattle, WA)

Department(s)

Geosciences and Geological and Petroleum Engineering

Second Department

Biological Sciences

Keywords and Phrases

Biofilm Formation; Complex Conductivity; Conductivity Measurements; Electrical Measurement; Electrical Response; Environmental Scanning Electron Microscopes; Fluid Conductivity; Geochemical Analysis; Geoelectrical; Geoelectrical Properties; Geologic Media; Grain Surface; Laboratory Scale; Low Frequency; Media Effects; Microbial Analysis; Microbial Cells; Microbial Concentrations; Microbial Growth; Mixed Bacteria; Near-surface; Sand Grains; Sand-packed Columns; Analytical Geochemistry; Biofilms; Bioremediation; Cell Culture; Cells; Diesel Fuels; Geophysics; Scanning Electron Microscopy; Porous Materials

International Standard Book Number (ISBN)

9781622760657

International Standard Serial Number (ISSN)

1554-8015

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2006 Environmental and Engineering Geophysical Society (EEGS), All rights reserved.

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