An experimental study of mass diffusion and reaction rate in an anaerobic biofilm

An experimental reactor consisting of two chambers, separated by a porous ceramic immobilization matrix, was constructed to measure the effective diffusivity of different compounds and the consumption rates of acetate in developing biofilms. In initial experiments, effective diffusivities for acetate, propionate, isopropanol, and lithium salt through the ceramic immobilization matrix in the absence of biofilm were determined to be 40% to 50% less than in water at infinite dilution. The effective diffusivity of the lithium salt was similar to that of acetate. The effective diffusivity of the lithium salt through biofilms of thickness in the range of 200 to 1200 microm was essentially constant with a value of approximately 7% of that in water at infinite dilution. Acetate consumption in the biofilm was linearly proportional to biofilm thickness up to a biofilm depth of 800 microm. Deviation from linearity appeared in biofilm thicknesses greater than 800 microm. Results of these experiments support previous reports that immobilized cell reactors have significantly higher bioconversion rates than suspended cell systems.