Biomediated Permeability Reduction of Saturated Sands: Fid-Bau Portal

Biomediated Permeability Reduction of Saturated Sands

DeJong, J. T

AbstractNew, alternative in situ ground improvement techniques are necessary to address increased performance demands and growing environmental concerns of traditional grouting methods. To date, the controlled use of microbiological processes has demonstrated promise in the ability of microbes and their activity to address this need. A particular form of biological improvement is the use of biofilms, an organic accumulation of cells and extracellular polymeric substances (EPS), in saturated soils. By adhering and accumulating on particle surfaces, biofilms can cause clogging of the pore volume and induce significant reductions in permeability. The void-filling nature of biofilms allows for possible field applications to control groundwater, heal leaks, and prevent internal erosion in structures such as earth dams and levees. This laboratory study investigated the growth characteristics and robustness of biofilm-treated sands. Experimental results indicate that biofilms are capable of reducing permeability of saturated sands by 100-fold or more after only two to three weeks of nutrient treatment. These improvements can be maintained indefinitely with continued nutrient treatments, after which a gradual return to initial conditions occurs. Permeability reductions were shown to remain stable in a variety of adverse conditions including two months of starvation, reverse flow, and fluctuating hydraulic gradients. Further tests indicated that biofilm growth in this study was highly heterogeneous, with the majority of clogging occurring near the inlet face. The results of this study show strong potential for the use of biofilms to reduce permeability, but future studies are required to improve uniformity as the process is scaled to field applications.