Biomass evolution in porous media and its effects on permeability under starvation conditions

The purpose of this study was to understand bacteria profile modification a nd its applications in subsurface biological operations such as biobarrier formation, in situ bioremediation, and microbial-enhanced oil recovery. Bio mass accumulation and evolution in porous media were investigated both expe rimentally and theoretically. To study both nutrient-rich and carbon-source -depleted conditions, Leuconostoc mesenteroides was chosen because of its r apid growth rate and exopolymer production rate. Porous micromodels were us ed to study the effects of biomass evolution on the permeability of a porou s medium. Bacterial starvation was initiated by switching the feed from a n utrient solution to a buffer solution in order to examine biofilm stability under nutrient-poor conditions. Four different evolution patterns were ide ntified during the nutrient-rich and nutrient-depleted conditions used in t he micromodel experiments. In phase I, the permeability of the porous micro model decreased as a result of biomass accumulation in pore bodies and pore throats. In phase II, starvation conditions were initiated. The depletion of nutrient in the phase II resulted in slower growth of the biofilm causin g the permeability to reach a minimum as all the remaining nutrients were c onsumed. In phase III, permeability began to increase due to biofilm slough ing caused by shear stress. In phase IV, shear stress remained below the cr itical shear stress for sloughing and the biofilm remained stable for long periods of time during starvation. The critical shear stress for biofilm sl oughing provided an indication of biofilm strength. Shear removal of biofil ms occurred when shear stress exceeded critical shear stress. A network mod el was used to describe the biofilm formation phenomenon and the existence of a critical shear stress. Simulations were in qualitative agreement with the experimental results, and demonstrate the existence of a critical shear stress. (C) 2000 John Wiley & Sons, Inc.