Assessment of substrate load and process pH for bioethanol production - Development of a kinetic model

In the present work, four levels of initial substrate concentration (2%, 4%, 7%, and 10% w/v glucose), and six pH values (4.0, 4.5, 5.0, 5.5, 6.0, and 6.5) at 2% substrate load were used to assess their impact on bioethanol production from Saccharomyces cerevisiae, in order to develop a kinetic model. A synthetic medium, containing glucose as the only carbon and energy source was used as the fermentation substrate. An innovative kinetic model was developed to fit the obtained data since several bioethanol production inhibition models reported in literature failed to sufficiently describe the experimental results. To this end, the logistic model was used to express the inhibition of biomass growth and the Monod model to describe the limitation of growth due to substrate depletion. In addition, S-max was imported as the parameter that affects the yield of ethanol production rate to biomass growth rate (Y-e/x), as a function of substrate concentration. Two more parameters were used to describe substrate (glucose) consumption for maintenance purposes (K-cm) and simultaneous bioethanol production (Y-cm) during the biomass stationary phase, where bioethanol is still being produced. The proposed model showed a high coefficient of correlation, R-2 = 0.9694. Both the yeast growth and bioethanol production were not substantially affected by the pH, within the range of pH values tested in this study.