EVALUATION OF TORTUOSITY FACTORS AND EFFECTIVE DIFFUSIVITIES IN BIOFILMS

A cylindrical model (CM) and a random porous cluster model (RPCM) have been developed in this paper to evaluate tortuosities, tortuosity factors, and effective diffusivities within biofilms, based on measurable biofilm properties. The tortuosity factor and the ratio of effective diffusivities to diffusivities in bulk solution (D-e/D-b) of the biofilm can be evaluated from biofilm porosity data by employing the CM presented in this paper. Both tortuosities and effective diffusivities depend on the densities and porosities of biofilms. For biofilms with porosities of 0.84-0.93 in the top layers and 0.58-0.67 in the bottom layer, it was found that tortuosity factors increase from 1.15 to approximately 1.6, while ratios of D-e/D-b decrease from 68-81% in the top layer to 38-45% in the bottom layer, based on the CM. The spatial distributions of biofilm properties affect the effectiveness factor profiles directly. Using incorrect ratios of D-e/D-b would result in false modeling results.