Efficient ethanol production from rice straw through cellulose restructuring and high solids loading fermentation by Mucor indicus

Abstract

The production of high concentrations of ethanol from N-methylmorpholine N-oxide- (NMMO) and phosphoric acid-pretreated rice straw was investigated at high solid loadings (solid-state) using filamentous fungus Mucor indicus. The impacts of most influential factors on ethanol production by simultaneous saccharification and fermentation (SSF), i.e., enzyme loadings (2.5, 5, 10, and 20 FPU/g substrate), solids loadings (15, 20, and 30% w/w), and SSF time (72 and 120 h), were assessed. The highest glucose concentrations were 106.5 and 94.1 g/L gained from 72-h hydrolysis of the straw pretreated with NMMO and phosphoric acid at 15% (w/w) solids loadings, respectively. The highest ethanol concentrations were 63.4 and 69.0 g/L, achieved by 30% solids loading from 72-h SSF of the straw pretreated with NMMO and phosphoric acid at 20 and 10 FPU celluloses per g substrate, respectively. A prolonged SSF process at enzyme loadings less than 5 FPU/g straw could not improve ethanol concentration from NMMO-pretreated straw, while ethanol concentrations above 40 g/L (61.0 and 59.9 g/L) were achieved through 120-h fermentation of the straw pretreated with phosphoric acid at 30% solid loading. The highest ethanol yields were 73.7 and 100% of the theoretical yield gained from the straw pretreated with phosphoric acid and NMMO, respectively, at the lowest solids loading (15%) and the highest enzyme loading (20 FPU/g substrate). © 2022