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Microbial-Induced Heterogeneity in the Acoustic Properties of Porous Media
Citation:
Davis, C. A., L. J. Pyrak-Nolte, E. A. Atekwana, D. D. WERKEMA, AND M. E. Haugen. Microbial-Induced Heterogeneity in the Acoustic Properties of Porous Media . GEOPHYSICAL RESEARCH LETTERS. American Geophysical Union, Washington, DC, 36:21405-21410, (2009).
Impact/Purpose:
Bioclogging caused by biofilm development is a phenomenon that can cause significant changes in the physical properties of porous media including porosity and permeability changes that influence fluid flow and transport properties [e.g., Vandevivere and Baveye, 1992; Brovelli et al., 2009] and remediation efforts [e.g., Baveye et al., 1998]. Numerical models and simulations have been developed to qualitatively forecast the change in hydraulic properties of a porous medium from bioclogging [e.g., Brovelli et al., 2009]. Bioclogging processes are dynamic and are influenced by many phenomena including initial heterogeneities in biomass distribution as well as the physical properties of the porous medium [e.g., Brovelli et al., 2009]. A major difficulty inherent with experimental modeling approaches is that in situ quantitative information from direct observation of biological growth and clogging from field data is difficult to obtain at the appropriate spatiotemporal scales needed for model validation [Dupin and McCarty, 2000]. Minimally invasive diagnostic techniques are needed to provide near real-time information of the spatiotemporal distribution of biofilms in porous media for validating predictive models and for monitoring microbial growth in situ.
Description:
Acoustic wave data were acquired over a two-dimensional region of a microbial-stimulated sand column and an unstimulated sand column to assess the spatiotemporal changes in a porous medium caused by microbial growth and biofilm formation. The acoustic signals from the unstimulated sample were relatively uniform over the 2D scan region. The data from the biologically stimulated sample exhibited a high degree of spatial variation in the acoustic amplitude measurements, with some regions of the sample exhibiting an increase in attenuation while other regions exhibited a decrease. Environmental scanning electron microscopy showed apparent differences in the structure/texture of biofilm between regions of increased and decreased acoustic wave amplitude. We conclude from these observations that variations in microbial growth and biofilm structure causes heterogeneity in the elastic properties of porous media. Our results suggest that acoustic measurements may provide a semi-quantitative approach for the validation of bioclogging models and numerical simulations. INDEX TERMS: 5102 Acoustic properties, 0416 Biogeophysics, 0463 Microbe/mineral interactions.