Continuous ethanol fermentation in a tower reactor with flocculating yeastrecycle: scale-up effects on process performance, kinetic parameters and model predictions

An unsegregated and unstructured model dei eloped for a small-scale process of ethanol production in a tower reactor with cell recycle was applied to describe the experimental data obtained in a large-scale process. The model was developed considering the following points: reactor hydrodynamic behav ior analogous to that of ideal CSTR, substrate limitation, inhibition pheno mena linked both to ethanol and to biomass, absence of fermentation in the settler, and no loss of cell viability. The scale-up criterion consisted in maintaining an identical relation settler volume/fermentor volume on the t wo scales. All large-scale experiments were carried out using a flocculatin g yeast strain IR-2, isolated from fermented food, and identified as Saccha romyces cerevisiae. Sugarcane juice was used as the substrate source with s ugar concentrations of 150 g/l. Different values of dilution rate and recyc le ratio were employed (D = 0.11-0.33 h(-1), alpha = 5.4-18.0) and the temp erature was of 32 degrees C. The kinetic parameters were similar on both sc ales and the model predictions agreed well with the large-scale experimenta l data.