Fig. 1

Schematic flow for ethanol fermentation from hydrothermally pretreated rice straw. Hydrothermal pretreatment of rice straw gives the solid and liquid fractions. The supernatant obtained after centrifugation of the liquid fraction, which contains oligomeric and monomeric sugars, was concentrated by nanofiltration (NF), followed by two rounds of dilution and NF concentration, to remove low molecular weight (MW) (<150 Da) fermentation inhibitors. Then, oligomeric sugars in the NF concentrate were enzymatically hydrolyzed to monomeric sugars, and the resulting black precipitate was recovered. Finally, the fraction with monomeric sugars was permeated through an ultrafiltration (UF) membrane to remove high MW (≥150,000 Da) fermentation inhibitors. This UF permeate and solid fraction can be fermented by Saccharomyces cerevisiae for ethanol production [14]