Determination of the interparticular effective diffusion coefficient for CO2 and O2 in solid state fermentation

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Abstract
A simple experimental diffusion controlled fermentor (DCF), coupled with the use of a mathematical model based on mass balance, is proposed to measure the variation of the gas (CO2 and O2) diffusion coefficients in solid state fermentation. The DCF was packed with an ion‐exchange resin impregnated with a nutritive medium and inoculated with Aspergillus niger. The growth conditions in the DCF were very similar to those found in equipment operated with convective oxygen supply. The diffusion coefficient was shown to be very dependent on the biomass concentration within the solid state fermentor, and attained values of less than 5% of the molecular diffusion in air when the biomass in the fermentor reached 27 mg dry/g dry support.