Hydraulic conductivity of compacted soil treated with biofilm

A laboratory study was conducted to evaluate the feasibility of creating low-permeability waste containment barriers using soil treated with bacteria to produce a plugging biofilm. The effects of exopolysaccharide-producing bacteria on the hydraulic conductivity (k) of a compacted silty sand were determined;Values of k for this soil without bacterial treatment ranged from 10(-5) and 10(-6) cm/s, depending on molding moisture content. Soil specimens were molded with a bacterial and nutrient solution, compacted at optimum moisture content, permeated with nutrient solution, and tested for k using a flexible-wall permeameter. Significant reductions in k were observed, and most specimens reached a stable final k of 10(-8) cm/s. The durability of the biofilm was tested by permeation with saline, acidic, and basic solutions, and by subjecting specimens to wet-dry conditions. In most cases these chemical and physical challenges had little or no effect on the reduced k. Results of these tests demonstrate that biofilm treatment may be a feasible technology for creating waste containment barriers in soil.