Development of combined nanofiltration and forward osmosis process for production of ethanol from pretreated rice straw

•NF-FO hybrid process to treat the liquid fraction from hot water-pretreated rice straw.•NF-FO hybrid process generated a ethanol concentration of 25.6 g L−1.•NF-FO hybrid process has the potential for ethanol production from pretreated rice straw.

A membrane process combining nanofiltraion (NF) and forward osmosis (FO) was developed for the sugar concentration with the aim of high bio-ethanol production from the liquid fraction of rice straw. The commercial NF membrane, ESNA3, was more adequate for removal of fermentation inhibitors (such as acetic acid) than the FO membrane, whereas the commercial FO membrane, TFC-ES, was more adequate for concentration of the sugars than the NF membrane. The liquid fraction was subjected to the following process: NF concentration with water addition (NF(+H2O)) → enzymatic hydrolysis → FO concentration. This NF(+H2O)-FO hybrid process generated a total sugar content of 107 g·L−1. Xylose-assimilating S. cerevisiae produced 24 g·L−1 ethanol from the liquid fraction that was diluted 1.5-fold and then concentrated by the NF(+H2O)-FO hybrid process. The NF(+H2O)-FO hybrid process has the potential for optimized ethanol production from pretreated lignocellulosic biomass.