Mechanical milling and membrane separation for increased ethanol production during simultaneous saccharification and co-fermentation of rice straw by xylose-fermenting Saccharomyces cerevisiae

Abstract

Mechanical milling and membrane separation were applied to simultaneous saccharification and co-fermentation from hydrothermally pretreated rice straw. Mechanical milling with minimized 4 cycles enabled 37.5±3.4gL−1 and 45.3±4.4gL−1 of ethanol production after 48h by xylose-fermenting Saccharomyces cerevisiae from solid fractions (200 and 250gL−1) of pretreated rice straw with 5 filter paper unitg-biomass−1 cellulase (respectively, 77.3±7.1% and 74.7±7.3% of theoretical ethanol yield). Use of a membrane-based process including nanofiltration and ultrafiltration increased the sugar concentrations in the liquid fraction of pretreated rice straw and addition of this liquid fraction to 250gL−1 solid fraction increased ethanol production to 52.0±0.4gL−1 (73.8±0.6% of theoretical ethanol yield). Mechanical milling was effective in increasing enzymatic hydrolysis of the solid fraction and membrane separation steps increased the ethanol titer during co-fermentation, leading to a proposal for combining these processes for ethanol production from whole rice straw.