Regular articleImproving bioethanol production by Scheffersomyces stipitis using retentostat extractive fermentation at high xylose concentration

- An innovative process with simultaneous ethanol fermentation and extraction was developed.
- High cell density of Scheffersomyces stipitis was achieved using retentostat extractive process.
- Bioconversion of concentrated xylose feed streams was evaluated.
- Ethanol levels were kept low inside the reactor avoiding inhibition.
- Ethanol removal was an efficient strategy to increase xylose consumption and ethanol productivity.

The improvement of yields and productivity for second-generation ethanol (2G) production as well as a better understanding of industrial yeasts and processes are required. Nevertheless, a process to produce 2G ethanol efficiently from lignocellulosic C5-sugars has not yet been proposed. Scheffersomyces stipitis presents good fermentation performance, promising to be a potential biocatalyst for converting C5-sugars to ethanol. In order to evaluate yeast performance, experiments were carried out in a retentostatic extractive vacuum system (REV) with total cell retention, controlled substrate feeding (at different xylose concentrations 100-200 g L−1) and simultaneous ethanol production and extraction. During REV at 100 g L−1, it was possible to achieve an efficient ethanol production. The optimum dilution rate was 0.025 h−1. To avoid stress effects to the yeast metabolism, the ethanol was continuously extracted. Low ethanol concentrations were kept inside the fermenter (25-35 g L‐1), resulting in higher yields and productivity when compared with batch, fed-batch and continuous cultures.