Abstract

The objective of this work was to find the best combination of different experimental conditions during pre-treatment, enzymatic saccharification, detoxification of inhibitors and fermentation of Sorghum bicolor straw for ethanol production. The optimization of pre-treatment using different concentrations of dilute sulfuric acid, various temperatures and residence times was achieved at 121°C, 1% acid concentration, 60 min residence time and enzyme saccharification using cellulase (celluclast 1.5 L) and β-glucosidase (Novozyme 188) at 50°C and pH 4.8 for 48 h. Different surfactants were used in order to increase the monomeric sugar during enzymatic hydrolysis and it has been observed that the addition of these surfactants contributed significantly in cellulosic conversion but no effect was shown on hemicellulosic hydrolysis. Fermentability of hydrolyzate was tested usingSaccharomyces cerevisiae Ethanol Red^TM and it was observed that simultaneous saccharification and fermentation (SSF) with both batch and fed batch resulted in better ethanol yield as compared to separate hydrolysis and fermentation (SHF). Detoxification of furan during SHF facilitated reduction in fermentation time from 96 to 48 h. 98.5% theoretical yield was achieved in SHF with detoxification experiment attaining an ethanol concentration and yield of 23.01 gL^-1 and 0.115 gg^-1 DM respectively. During the SSF batch and fed batch fermentation, the maximum yields of ethanol per gram of dry matter were 0.1257 and 0.1332 g respectively.

Key words: Sorghum bicolor, ethanol, separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), furfural and hydroxymethyl furfural, surfactant, batch and fed batch fermentation.