Kinetic models for batch and continuous ethanol fermentation from sweet sorghum juice by yeast immobilized on sweet sorghum stalks

• This is the first report of kinetic models for fuel ethanol fermentation by adsorbed immobilized yeast.
• Unpeeled sweet sorghum stalks were used as carriers for yeast cell immobilization.
• Batch models were applicable at a wide range of initial sugar (130–225 g/L).
• In batch models, data for biomass, sugar and ethanol could be fitted with R2 > 0.90.
• Continuous models could describe changes of sugar and ethanol with R2 > 0.93.

Kinetic models for batch and continuous ethanol fermentation from sweet sorghum juice by Saccharomyces cerevisiae NP 01 immobilized on unpeeled sweet sorghum stalk pieces were developed. The models accounted for substrate limitation, substrate inhibition, ethanol inhibition and cell death. Batch ethanol fermentations were done from juice containing various initial sugar concentrations (120–280 g/L). The estimated values of the maximum specific growth rate (μmax) and Monod constant (Ks) were found to be 0.313 h−1 and 47.51 g/L, respectively, using a Lineweaver–Burk plot. These data were used to develop models for batch and continuous ethanol fermentation. For the batch fermentation, it was found that the models could be used to satisfactorily fit the experimental data for initial sugar concentrations ranging from 130 to 225 g/L. However, for the continuous fermentation, only the data for substrate consumption and ethanol production were well fitted by the developed models.

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