Influence of mold growth on the pressure drop in aerated solid state fermentors

The measurement of pressure drop(Δ P ) across an aerated fermentation bed is proposed as alternative on‐line sensor for the qualitative and, in some cases, quantitative, macroscopic changes in a static solid state fermentor. An increase in the Δ P is correlated with the evolution of the different phases of Aspergillus niger growth: germination, vegetative growth, limitation, and sporulation, we observed in the microscope. For the case where the support is not modified during the fermentation and the water content remains constant, i.e., a synthetic resin (Amberlite IRA‐900), the gas phase permeability of the bed is directly related to the biomass content. For example, the permeability of the bed is reduced to 5% of the initial value when biomass attains 21 mg dry biomass/g dry support. Biomass was appropriately predicted from the Δ P measurements in an independent test. Experiments with different initial sucrose solution concentrations showed that biomass could not be produced beyond a certain level (21.5 mg dry biomass/g dry support) which suggests steric limitations. For the case of wheat bran and cane bagasse, the increase in Δ P was related qualitatively to the evolution in the growth and the morphology of the mold . © 1993 Wiley & Sons, Inc.