Kinetics of ethanol production by baker's yeast in an integrated process of fermentation and microfiltration

The productivity of a fermentation is proportional to the biomass concentration. The productivity can therefore be increased by retention of the cells in the fermentor. In this study microfiltration was used for cell retention in a fermentation of glucose to ethanol by baker's yeast. Compared to a system without cell retention the productivity could be increased 12-fold to 55 kg/m³ h at a biomass concentration of 135 kg/m³. Maximal ethanol concentrations of 76 kg/m³ were obtained at conditions of growth. At zero growth conditions in the integrated system the ethanol concentration could be increased to about 115 kg/m³, and could be produced for at least 10 hours. The fermentation results in the integrated system could be described reasonably well with a mathematical model based on a different linear inhibition kinetics for growth and substrate consumption.