Full Length Research Paper

Ethanol production from Sorghum bicolor using both separate and simultaneous saccharification and fermentation in batch and fed batch systems

Sajid Mehmood^1,3, Muhammad Gulfraz^1*, Nosheen Fatima Rana¹, Asif Ahmad¹, Brigitte Kiær Ahring², Nasir Minhas¹ and Muhammad Faheem Malik³

¹Department of Biochemistry, PMAS Arid Agriculture University Rawalpindi, Murree Road, Rawalpindi 46300 Pakistan.

²Bioscience and Technology (BST), Biocentrum –DTU, Technical University of Denmark, 2800 Lyngby, Denmark.

³University of Gujrat, Hafiz Hayat Campus, Gujrat, Pakistan.

*Corresponding author. E-mail: gulfrazsatti@uaar.edu.pk. Tel.: +92519062268.

Accepted 20 March, 2009

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 using Saccharomyces 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.