Kinetics and Modeling of Co-Fermentation Using Saccharomyces Cerevisiae and Pichia Stipitis in Glucose and Xylose Media for Bioethanol Production

Ethanol produced from lignocellulosic biomass resources is a fuel with potential to match the convenient features of petroleum, but reducing substantially the emissions of greenhouse gases in comparison with fossil fuels. Using either pure ethanol or in mixed blends with gasoline, the fuel octane is boosted, tailpipe emissions of CO are reduced, and fuel combustion is improved. A wide variety of lignocellulosic biomass is available in our planet, and its major components, cellulose and hemicellulose can be used to obtain 6- and 5-carbon carbohydrates. To achieve this, biomass must be pre-treated and hydrolyzed. The resulting carbohydrates can be converted to ethanol following several biochemical pathways in which microorganisms play an important role as biocatalysts. This work features the fermentation of mixtures of glucose and xylose as the main components of cellulose and hemicellulose, respectively; to obtain ethanol using two different native yeast strains of Saccharomyces cerevisiae and Pichia stipitis, whose efficiency to ferment glucose and xylose has been demonstrated in previous studies. For P. stipitis, efficiency was also studied in our preliminary screening of xylose-fermenting yeast strains including Pachysolen tannophilus and Candida shehatae . We are focused in determining a series of experimental kinetic parameters, including specific cell mass growth rate, substrate uptake, production formation and yield coefficients to evaluate ethanol production, to mathematically model sugar consumption and ethanol production. Modeling of the fermentation processes through adequate mass balances and biokinetics to match with experimental results for both individual and mixtures fermentations will become a very important tool for the design of efficient biomass fermentation processes.