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P7SOIL HYDRAULIC CONDUCTIVITY REDUCTIONS CAUSED BY ULTRAMICRO BACTERIA |
J.C. Ziegler(1), J.P. Turner(1), Y.A. Osman(2), J. Chase(2), and L.A. Bulla(2), (1)Department of Civil and Architectural Engineering, (2)Department of Molecular Biology, University of Wyoming, University Station, Laramie, WY 82071-3354 |
Laboratory hydraulic conductivity tests were conducted on specimens of a silty sand. Without biofilm treatment, the hydraulic conductivity of this soil is in the range of k = 1.5 x 10-6 to 2 x 10-5 cm/sec. Previous studies showed that k could be reduced by two to three orders of magnitude by mixing this soil with a bacterial solution containing full-size cells of the bacterium Beijerinckia indica, followed by permeation with nutrient solution. The observed reductions in k are attributed to the formation of a plugging biofilm and indicate the potential for creating containment barriers using biofilm-treated soil.
In the present study, cells of B. indica were deprived of nutrients for a period of time sufficient to form ultramicrobacteria (UMB). UMB are defined as having a diameter of less than 0.3 (m. The main physical responses to nutrient deprivation are reduction in cell size to form UMB and a decrease in cell adhesion properties. These properties of UMB may offer several advantages for creating containment barriers in situ. The smaller size and reduced adhesion may allow for deeper penetration and less chance of "skin plugging." Specimens of the silty sand were compacted at optimum moisture content, placed in a flexible wall permeameter, and saturated. This was followed by permeation with a solution containing UMB cells of B. indica. The UMB were resuscitated by allowing nutrient solution to permeate through the specimen. Hydraulic conductivity was monitored throughout the test sequence. Results show that the UMB can be resuscitated, a plugging biofilm is formed, and k is reduced to approximately 4 x 5-8 cm/sec. Methods, materials, and testing procedures will be described in detail. Test results, including the effects of the composition of the UMB fluid suspensions and total volume of UMB provided, will be presented and analyzed. Potential applications of UMB to biofilm barrier technology will be discussed. Key words: ultramicrobacteria, biofilm, hydraulic conductivity, soil, containment barriers
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