INFLUENCE OF BIOFILM ACCUMULATION ON POROUS-MEDIA HYDRODYNAMICS

Laboratory-scale porous media biofilm reactors were used to evaluate the effect of biofilm accumulation, measured as the average thickness along a 50-mm flow path, on media porosity, permeability, and friction factor. Media tested consisted of 1-mm glass spheres, 0.70-mm sand, 0.54-mm sand, and 0.12-mm glass and sand. Pseudomonas aeruginosa was used as inoculum and 25 mg L-1 glucose substrate was continuously supplied to the reactor. Reactors were operated under constant piezometric head conditions resulting in a flow rate decrease as biofilm developed. The progression of biofilm thickness followed a sigmoidal-shaped curve reaching a maximum thickness after approximately 5 days. Media porosity decreased between 50 and 96% with increased biofilm accumulation while permeability decreased between 92 and 98%. Porous media friction factor increased substantially for all media tested. Observations of permeability in the biofilm-media matrix indicate that a minimum permeability [(3-7) X 10(-8) cm2] persisted after biofilm thickness has reached a maximum value. Such results indicate substantial interaction between mass transport, hydrodynamics, and biofilm accumulation at the fluid-biofilm interface in porous media. Improved understanding of these interactions will lead to industrial and environmental applications in biohydrometallurgy, enhanced oil recovery, and bioremediation of contaminated groundwater and soil.