Analysis of ethanol production from xylose using Pichia stipitis in microaerobic conditions through experimental observations and kinetic modelling

Hydrolysis of biomass (e.g. bagasse) leads to xylose as one of the primary sugars for fermentation to bioethanol, along with glucose. The selection of a suitable microorganism and consequently selection of suitable aeration levels for the selected microorganism plays a significant role in xylose conversion. This work focuses on the kinetics of bioethanol production from xylose using Pichia stipitis with the development of a MATLAB mathematical model (based on the combined Andrews and Levenspiel's model with oxygen limitation and inhibition terms included), considering the effects of substrate, oxygen, biomass and product concentrations on sugar utilisation, growth rate and ethanol formation. Experiments were carried out to validate the kinetic model under anaerobic and microaerobic growth conditions in a batch process. The results showed good correlation with an average R2 of 0.92 for bioethanol production, 0.95 for xylose consumption and 0.83 for biomass growth. Different aeration levels of 0.0, 0.1 and 0.2 vvm and different initial biomass concentrations of 0.3, 1.5 and 3 g L-1 were tested, in which the combination of aeration at 0.1 vvm and a biomass concentration of 3 g L-1 resulted in the highest ethanol yield and productivity of 0.45 g g-1 and 0.75 g L-1 h-1 respectively.