MATHEMATICAL MODELING OF CONTINUOUS ETHANOL FERMENTATION IN A TOWER REACTOR WITH RECYCLING OF FLOCCULATING YEAST
S. C. Oliveira, A. E. S. Visconti, H. F. Castro, and R. Giudici
Faculdade de Engenharia Quimica de Lorena
Departamento de Biotechnologia
Rodovia Itajubá-Lorena km 74.5
Caixa Postal 116
CEP 12600-000 - Lorena-SP-Brazil
A tower fermenter with flocculating yeasts has raised great interest because of the high operational stability and productivity presented by this system. A mathematical model for continuous ethanol production in a tower reactor with recycling of flocculating yeast is proposed. The model was developed by incorporating these parameters: continuous-flow stirred-tank reactor model for the hydrodynamic behavior of the reactor, substrate limitation, inhibition phenomena linked both to ethanol and biomass, absence of fermentation in the settler, and no loss of cell viability during the processing. The kinetic parameters were obtained from data of the process in steady state. All experiments were carried out using a flocculating yeast strain, IR-2, isolated from fermented food and identified as Saccharomyces cerevisiae. Cane sugar juice was used as substrate with a sugar concentration of 150 g/L. The medium was supplemented with nutrient salts and yeast extract. Different values of dilution rates were employed (0.14–0.44 h-1), and the temperature was held constant (T = 32oC). The values of the kinetic parameters were consistent with other published data about yeast growth under similar conditions, and model predictions agreed well with experimental data.