Lime pretreatment, enzymatic saccharification and fermentation of rice hulls to ethanol

Rice hulls used in this study contained 35.6 +/- 0.1% cellulose and 12.0 +/- 0.7% hemicellulose. The maximum yield of monomeric sugars from rice hulls (15.0%, w/v) by lime pretreatment (100 mg g(-1) hulls, 121 degrees C, 1h) and enzymatic saccharification (45 degrees C, pH 5.0, 72h) using a cocktail of three commercial enzyme preparations (cellulase, beta-glucosidase and hemicellulase) at the dose level of 0.15 ml of each enzyme preparation g(-1) hulls was 154 +/- 1 mg g(-1) (32% yield). The lime pretreatment did not generate any detectable furfural and hydroxymethyl furfural in the hydrolyzate. The concentration of ethanol from lime-pretreated enzyme-saccharified rice hull (138 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 degrees C in 19 h was 9.8 +/- 0.5 gl(-1) with a yield of 0.49 g g(-1) available sugars. The ethanol concentration was 11.0 +/- 1.0 gl(-1) in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 degrees C in 53 h. Published by Elsevier Ltd.