Purple guinea grass: Pretreatment and ethanol fermentation

Abstract

Treatment with dilute sulfuric acid (H2SO4) or calcium hydroxide (Ca(OH)2) at 121°C and 103.4 kPa was used to improve the efficiency of the cellulose digestion of purple guinea grass. Cellulase hydrolysis of the dilute H2SO4-pretreated purple guinea grass under optimized conditions (6% (w/v) in 3% (w/v) H2SO4 for 30 min) yielded a slightly higher level of reducing sugars than that from the Ca(OH)2 pretreatment under optimized conditions (6% (w/v) in 4% (w/v) Ca(OH)2 for 5 min). However, the level of glucose released from the Ca(OH)2-pretreated purple guinea grass was slightly higher than that from the dilute H2SO4 pretreatment. Ethanol fermentation, via the separate hydrolysis and fermentation (SHF) process using Saccharomyces cerevisiae, of the Ca(OH)2-pretreated purple guinea grass and then hydrolyzed with commercial cellulase (9PFU/g, dry wt.) for 6 h yielded ethanol at 0.44 g/g glucose (0.21 g/g cellulose) within 48 h, while that from the simultaneous saccharification and fermentation process yielded 14.3% less ethanol at 0.18 g/g cellulose within 96 h (including the 6 h saccharification time). The ethanol yield from the SHF process increased 1.14-fold to 0.497 g/g glucose (0.24 g/g cellulose) when the fermentation was performed in a 5 L fermentor.