Scheffersomyces stipitis biofilm reactor for ethanol production from acid-pretreated/detoxified and glucose- or xylose-enriched rice husk hydrolysate under a continuous process

Ethanol is one of the most important platform chemicals that can be produced in a continuous biofilm reactor. The continuous system can be easily adapted to a biofilm reactor, which is a useful tool for ethanol production by microorganisms. In this study, two different media (the first medium: acid-pretreated/detoxified and glucose-enriched rice husk hydrolysate; the second medium: acid-pretreated/detoxified and xylose-enriched rice husk hydrolysate) were used for ethanol production in a continuous biofilm reactor. Both medium (1.5 L) were supplemented with 1% (w/v) yeast extract and 2% (w/v) peptone. The dilution rate for the first medium was between 0.02 and 0.12 h⁻¹, while for the second medium, it was between 0.01 and 0.05 h⁻¹. When the first medium was used for ethanol fermentation in a continuous system, maximum ethanol productivity of 0.418 g/L/h and maximum biomass productivity of 0.196 g/L/h were yielded at dilution rates of 0.08 and 0.10 h⁻¹, respectively. As for the second medium for ethanol fermentation in a continuous system, their values were 0.083 and 0.079 g/L/h at dilution rates of 0.03 and 0.04 h⁻¹, respectively. Additionally, the yield factors for biomass and ethanol (Y⁰_X/S and Y⁰_P/S) were also found to be 0.642 g X/g S and 0.49 g P/g S for the first medium and 0.254 g X/g S and 0.27 g P/g S for the second medium, respectively. In addition, although cost-effective ethanol production regarding energy cost and recovery time is desired, the use of the non-enriched sterile and enriched non-sterile media in a repeated-batch biofilm reactor caused low fermentation kinetics. Consequently, ethanol production was successfully performed by using Scheffersomyces stipitis in a continuous PCS-biofilm reactor including acid-pretreated/detoxified and glucose- or xylose-enriched rice husk hydrolysate, which gave higher ethanol concentration compared with subsequent ethanol fermentation in a repeated-batch biofilm reactor.