Estimation of substrate effective diffusivities in anaerobic bioparticles

A simple and rapid method to estimate effective diffusivities (D-e) of subs trates in bioparticles containing anaerobic sludge is proposed. The method is based on substrate mass balances under unsteady-state conditions utilizi ng data obtained from 'finite-bath' assays performed in an incubator shaker . The experiments were carried out under conditions of negligible liquid-ph ase mass transfer resistance and absence of biochemical reactions. The firs t condition was obtained by the application of high agitation speeds. The b iomass was inactivated with ethanol solution 50% (v/v) to reach the second condition. Values of the effective diffusivity (D-e) of glucose, sucrose an d acetate were obtained from the temporal variation of substrate concentrat ion in the bulk liquid in assays utilizing alginate gel and polyurethane fo am bioparticles. Additionally, the specific methanogenic activity technique was used to evaluate the effectiveness of the method proposed for biomass inactivation. The method used to estimate the substrate diffusivity coeffic ient was found to provide suitable values of D-e for substrates at very low concentrations. Values of D-e for glucose, sucrose and acetate in alginate gel bioparticles were estimated as 0.58 x 10(-5), 1.06 x 10(-5) and 1.49 x 10(-5) cm(2) s(-1), respectively. The value of D-e for glucose in polyuret hane foam particles was found to correspond to the value of glucose diffusi on in water at infinite dilution. The method applied for cell inactivation was found to be adequate for intraparticle mass transfer experiments, makin g the temporary sludge inactivity long enough to avoid interference due to biochemical reactions.