Cellulosic ethanol production from green solvent-pretreated rice straw

Cellulosic ethanol production from green solvent (GS) -pretreated rice straw and the effects of green solvents on cellulase enzyme cellic ctec2 and cellobiose-fermenting yeast strain Clavispora NRRL Y-50464 was comprehensively investigated. Using choline chloride/glycerol (CC-GLY) treated rice straw, maximum reducing sugars of 226.7 g/L was obtained with a saccharification efficiency of 87.1% at 20% solids loading and 12 FPU cellic ctec2. An ethanol production of 36.7 g/L was observed from 8% of glucose within 36 h with a conversion efficiency of 90.1%. Incubation of cellulase in green solvents (CC-GLY, choline chloride/1,2-propane diol (CC-PD), choline chloride/ethylene glycol (CC-EG)) at high concentrations (up to 30%, v/v) had no inhibitory effect on cellic ctec2. Moreover, CC-GLY and CC-PD at 10% (v/v) did not affect the growth rate, sugar consumption and ethanol production from Clavispora NRRL Y-50464, while 10% (v/v) CC-EG repressed and delayed the cell growth of the microbe. While, strain Y-50464 was highly sensitive in other green reagents that were evaluated in this study. The green solvent-pretreatment efficiently removed lignin from the ricestraw and improved fermentation efficiency significantly. Green solvents with pH<3.0 inhibited of cellic ctec2 enzyme activity and growth of Clavispora strain NRRL Y-50464. When pH of the green reagents was neutralized or adjusted to pH 5.0, normal enzyme activity and cell growth was observed. Moreover, with selective green reagents i.e. CC-GLY, CC-PD, and CC-EG, cellulosic ethanol production can be accomplished using cellic ctec2 and strain NRRL Y-50464.