High Productivity Ethanol Fermentation of Glucose & Xylose Using Membrane Assisted Continuous Cell Recycle

Abstract

Rapid and high-yield conversion of xylose to ethanol remains a significant bottleneck in the cost-effective production of ethanol using mixed sugars derived from lignocellulosic biomass (LBM). The present study attempts to circumvent this by separate continuous fermentation of glucose and xylose using high cell densities of a Saccharomyces cerevisiae mutant (ICT-1) and a Scheffersomyces stipitis mutant (M1CD), respectively, with the help of external microfiltration membrane-assisted cell recycling. Different cell densities and aeration rates for xylose fermentation were studied to optimize continuous fermentation. Consistent high ethanol yields and productivities of 0.46 g/g and 5.19 g/L/h with glucose, and 0.38 g/g and 1.62 g/L/h with xylose were achieved in simple media. This provided an average ethanol yield of 0.44 g/g on combined sugars and an average productivity of 3.4 g/L/h, which is higher than typical molasses-based batch ethanol fermentation. The study thus highlights the potential of a high cell density recycling strategy as an effective approach for separate ethanol fermentation of LBM-derived sugars.