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The scale-up effects on kinetic parameters and on predictions of a yeast recycle continuous ethanol fermentation model incorporating loss of cell viability were evaluated. The average level of cell viability estimated for large scale was similar to that estimated for small scale, although with a major standard deviation. The values of specific rate of cell viability loss were equal for the two scales. These results were due to the utilization of the same aeration rate for both scales, one of the main factors for cell-viability maintenance. The kinetic parameters were not significantly affected by the scale-up of the fermentation process. Major differences were observed for the maximum specific growth rate and for maximum ethanol concentrations for which, growth and ethanol production are totally inhibited. The scale-up did not result in lack of fit of the mathematical model to the experimental data.

The concept of loss of cell viability was introduced into a model previously developed for a continuous alcoholic fermentation process in a tower reactor with recycling of flocculating yeasts. The two models take into account substrate limitation and inhibition phenomena linked to ethanol and biomass. The kinetic parameters were estimated from steady-state data of several sugar concentrations in feeding stream and constant dilution rate, recycle ratio and temperature. Some parameters of the modified model (maximum specific rates) were significantly different from those estimated with the original model while others (inhibition parameters) remained practically unchanged. Both models provided similar predictions and were equally suitable for modelling of the process.

An unsegregated and unstructured model developed 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 behavior analogous to that of ideal CSTR, substrate limitation, inhibition phenomena 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 two scales. All large-scale experiments were carried out using a flocculating yeast strain IR-2, isolated from fermented food, and identified as Saccharomyces cerevisiae. Sugarcane juice was used as the substrate source with sugar concentrations of 150 g/l. Different values of dilution rate and recycle ratio were employed (D = 0.11–0.33 h−1, α = 5.4–18.0) and the temperature was of 32 °C. The kinetic parameters were similar on both scales and the model predictions agreed well with the large-scale experimental data.