Abstract
BackgroundEfficient cofermentation of glucose and xylose is necessary for economically feasible bioethanol production from lignocellulosic biomass. Here, we demonstrate pretreatment of sugarcane bagasse (SCB) with green liquor (GL) combined with ethanol (GL–Ethanol) by adding different GL amounts. The common Saccharomyces cerevisiae (CSC) and thermophilic S. cerevisiae (TSC) strains were used and different yeast cell mass ratios (CSC to TSC) were compared. The simultaneous saccharification and cofermentation (SSF/SSCF) process was performed by 5–20% (w/v) dry substrate (DS) solid loadings to determine optimal conditions for the co-consumption of glucose and xylose.ResultsCompared to previous studies that tested fermentation of glucose using only the CSC, we obtained higher ethanol yield and concentration (92.80% and 23.22 g/L) with 1.5 mL GL/g-DS GL–Ethanol-pretreated SCB at 5% (w/v) solid loading and a CSC-to-TSC yeast cell mass ratio of 1:2 (w/w). Using 10% (w/v) solid loading under the same conditions, the ethanol concentration increased to 42.53 g/L but the ethanol yield decreased to 84.99%. In addition, an increase in the solid loading up to a certain point led to an increase in the ethanol concentration from 1.5 mL GL/g-DS-pretreated SCB. The highest ethanol concentration (68.24 g/L) was obtained with 15% (w/v) solid loading, using a CSC-to-TSC yeast cell mass ratio of 1:3 (w/w).ConclusionsGL–Ethanol pretreatment is a promising pretreatment method for improving both glucan and xylan conversion efficiencies of SCB. There was a competitive relationship between the two yeast strains, and the glucose and xylose utilization ability of the TSC was better than that of the CSC. Ethanol concentration was obviously increased at high solid loading, but the yield decreased as a result of an increase in the viscosity and inhibitor levels in the fermentation system. Finally, the SSCF of GL–Ethanol-pretreated SCB with mixed S. cerevisiae strains increased ethanol concentration and was an effective conversion process for ethanol production at high solid loading.
Highlights
Efficient cofermentation of glucose and xylose is necessary for economically feasible bioethanol production from lignocellulosic biomass
In this paper, sugarcane bagasse (SCB) was subjected to green liquor (GL)–Ethanol pretreatment
This study showed that GL–Ethanol pretreatment is a promising pretreatment method for improving the ethanol production in the SSCF process, due to both better glucan and xylan conversion efficiencies of SCB as well as the higher lignin removal rate
Summary
Efficient cofermentation of glucose and xylose is necessary for economically feasible bioethanol production from lignocellulosic biomass. Ho et al [11] made a breakthrough by creating super-stable genetically engineered glucose–xylose-cofermenting Saccharomyces yeasts that contain multiple copies of the same three xylose-metabolizing genes stably integrated in the yeast chromosome, which made it possible to move the biomass-to-ethanol technology by the continuous cofermentation of glucose and xylose much closer to commercialization. One significant challenge is to achieve efficient and simultaneous uptake of pentose and hexose sugars in the fermentation process [12] Another limitation of cellulosic ethanol production is the difficulty of using a high solid loading in simultaneous saccharification and cofermentation (SSF/SSCF), which restricts the final ethanol concentration [13]
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