Reassessment of the estimation of dissolved oxygen concentration profile and K(L)a in solid-state fermentation

Oxygen mass transfer in aerobic microbial growth systems is often a limitin g factor for optimal growth and productivity. Oxygen mass transfer has been widely studied in submerged fermentations but has attracted as yet little attention for solid state fermentations. The parallel to submerged fermenta tion has led to the incorrect interpretation and use of the overall oxygen mass transfer coefficient (K(L)a) to assess the ability of a particular fer mentation system to supply the oxygen to microorganisms. The use of K(L)a, as traditionally defined, should be used with caution in solid substrate fe rmentation systems because there is no convection on the liquid side of the medium, and oxygen is consumed in the biofilm. Hence, K(L)a must be redefi ned for solid state fermentation. In this payer, the use of oxygen mass tra nsfer coefficients in solid state fermentations is clarified. Published lit erature data were analysed with a simple pseudo-steady-state model and used to discuss the influence of the biofilm thickness, the dissolved oxygen di ffusion coefficient, the convective gas mass transfer coefficient, and the gas flow rate on the oxygen mass transfer coefficient in solid state fermen tations. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.