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Acoustic Wave Monitoring of Biofilm Development in Porous Media
Citation:
Davis, C. A., L. J. Pyrak-Nolte, E. A. Atekwana, AND D. D. WERKEMA. Acoustic Wave Monitoring of Biofilm Development in Porous Media. Presented at American Geophysical Union Spring Joint Assembly Meeting, Toronto, QC, CANADA, May 24 - 27, 2009.
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Presentation
Description:
Biofilm development in porous media can result in significant changes to the hydrogeological properties of subsurface systems with implications for fluid flow and contaminant transport. As such, a number of numerical models and simulations have been developed in an attempt to qualitatively forecast the affect of bioclogging on hydraulic properties. Limitations exist, however, with the application of these models as bioclogging processes are dynamic and quantitative information from the direct observation of biological growth and clogging is often unavailable. Here, we report on the results of a laboratory column experiment in which a minimally invasive acoustic wave imaging technique was used for the spatiotemporal characterization of biofilm development in porous media. Biofilm development was stimulated in silica sand-packed columns using a Pseudomonas aeruginosa PAO1 bacteria culture and acoustic (compressional) wave data were collected over a two-dimensional region for 29 days. In addition, complex conductivity, fluid conductivity, and pH measurements were collected to assess the progress of the stimulated microbial growth. The results from the biologically stimulated sample (nutrients and bacteria inocula) exhibited a high degree of spatial variation in the acoustic amplitude measurements. Portions of the biostimulated sample exhibited an increase in attenuation (up to 73%), while other portions showed a decrease in attenuation (~45%). The acoustic signals measured for the unstimulated sample (nutrients only), however, were relatively uniform over the 2D scan region. Environmental scanning electron microscope (ESEM) imaging of sand from the biostimulated column collected upon termination of the experiment verified the presence of biofilms on sand surfaces. ESEM imaging also revealed apparent qualitative differences in the structure and/or thickness of biofilm material between areas of variable acoustic wave amplitude. We infer from these observations that enhanced microbial growth and the presence of biofilms in the sand columns had a variable affect on the spatiotemporal elastic properties of porous media. Our results suggest that acoustic measurements may provide diagnostic semi-quantitative data for the validation of bioclogging models and numerical simulations.