Mathematical modeling for ethanol fermentation from molasses by Saccharomyces cerevisiae M30

Abstract

A mathematical model is developed to explain the process dynamics of ethanol production by flocculating yeast, Saccharomyces cerevisiae M30. Molasses, the main feedstock for ethanol production in Thailand, is used as the substrate source for all experiments. Firstly, the experiments are carried out by the batch fermentation in shaking flasks with the initial sugar concentration ranging from 3 to 25%w/v and incubate at 33℃. Subsequently, the optimal initial sugar concentration growth and production is found to be 22%w/v. At the optimal initial sugar concentration (22%w/v), the fermentation is performed with operating temperature ranging from 30 to 42℃. The mathematical model is developed from Monod kinetic model. It consists of three main factors; initial substrate concentration, substrate and ethanol concentration, and operating temperature, and counts with death rate and cell maintenance for biomass equation. Polynomial equation is used to describe the relationship between initial substrate concentration and kinetic parameters. Then, exponential relationships between operating temperature and kinetic parameters such as both maximum specific growth rate and production rate and maximum production concentrations are determined. The parameters of model are converged by using least-square method. The results reveal a good agreement between the simulation and the experiment data. The optimum conditions of ethanol batch fermentation by using molasses as substrate are at 22%w/v initial reducing sugar and 33.c of operating temperature. The results can be further used to improve the ethanol fermentation process performance.