MACROTRANSPORT OF A BIOLOGICALLY REACTING SOLUTE THROUGH POROUS-MEDIA

A physically based model is developed to study the transport of a solu te utilized by microorganisms forming a biofilm coating on sail grains in a porous medium. A wavy-walled channel is used as a geometrical mo del of a porous medium and a biofilm is attached to the channel wall. Within the biofilm the solute is consumed according to a first-order v olumetric rate. A numerical study is performed to obtain the dependenc e of the macrotransport coefficients on the Peclet number and Damkohle r number. It is found that in some cases of practical importance the p ore fluid is not well mixed, and mass transport limitations can contro l macroreaction rates. For diffusion-limited cases (large Damkohler nu mbers) increased solvent velocity can enhance the macroreaction rate b y a factor of almost 3. Mean solute and mean solvent velocities are, i n general, not equal, and mean solute velocities can exceed mean solve nt velocities by 60% at high Damkohler numbers. These results agree qu alitatively with those of a previous numerical study by Edwards et al. [1993]. The results also suggest that due to the spatially variable p ore geometry, the biomass nearest the pore throat is more effective at consuming the solute than biomass in the pore chamber. A comparison i s made between mass transfer correlations and the results determined f or the macroreaction rate coefficient, We find that over a limited ran ge of Peclet numbers a macroscale Sherwood number follows the Pe(1/3) behavior determined from experimental mass transfer correlations and p redicted by boundary layer theory.