Repeated-batch fermentation of Scheffersomyces stipitis in biofilm reactor for ethanol production from the detoxified and glucose- or xylose-enriched rice husk hydrolysate and its kinetic modeling

Abstract

• Ethanol production from detoxified and glucose- or xylose-enriched RHH in biofilm reactor. • Maximum Y P/S from glucose- and xylose-enriched RHH were 35.01 and 23.5%, respectively. • Kinetic modeling of culture-tube ethanol fermentation made to select the PCS material. • Kinetic modeling of ethanol fermentation in repeated-batch biofilm reactor of S. stipitis. The present study aims to determine the best biofilm support material (BSM) via culture tube fermentation, produce ethanol from the detoxified and glucose- or xylose-enriched rice husk hydrolysate (RHH) by using Scheffersomyces stipitis (ATCC 58784) in the biofilm reactor, and model kinetically the ethanol fermentation performed in culture-tubes and the biofilm reactor. The activated charcoal was employed to detoxify the acid-pretreated RHH. As a result of the culture-tube fermentation performed in both glucose- and xylose-based media, a BSM that includes polypropylene (50%), soybean hulls (35%), soybean flours (5%), yeast extract (5%), bovine albumin (5%), and some minerals (w/w) was chosen. With this BSM, ethanol yield (Y P/S ) and production (P) were 38.83% and 3.61 g/L for glucose-based medium and 33.06% and 3.80 g/L for xylose-based medium. Ethanol fermentations were performed at 30 °C temperature, medium pH 6.2, and 150 rpm agitation rate without aeration. Based on the results of the fermentation in the repeated-batch biofilm reactor established with the selected BSM, maximum Y P/S and P were 35.01% and 2.57 g/L when glucose was used as the sole carbon source (Medium A). Regarding the fermentation in which the RHH was used, Y P/S and P were 23.50% and 1.98 g/L when 75% RHH (1.125-L) and 25% glucose (0.375-L) were used as carbon sources, respectively (Medium D). When the RHH (50%, 0.75-L) was supplemented with xylose (50%, 0.75-L), Y P/S and P were 22.65% and 1.96 g/L, respectively (Medium E). Additionally, modeling results demonstrated that ethanol production was growth-dependent since α ≠ 0 and β≌0 and sugars were utilized for ethanol production and microbial growth because γ≫m. Consequently, the RHH is a promising carbon source to produce ethanol in the repeated-batch biofilm reactor. Also, the biofilm reactor constructed was operated for 648 h without contamination. Therefore, the biofilm reactor system can be used for long-term production of value-added products using microorganisms.