Potential of cellulases from Thai isolated fungi for ethanol production from bagasse

Abstract

Sugarcane bagasse is one of the most promising agricultural by-products for conversion to biofuels. Here, ethanol fermentation from bagasse has been achieved using an integrated process combining mechanical pretreatment, enzymatic hydrolysis and fermentation. Pretreatment by ball milling for 2 h was sufficient for nearly complete cellulose structural transformation to an accessible amorphous form. The pretreated cellulosic residues were hydrolyzed by a crude enzyme preparation from Penicillium chrysogenum BCC 4504 containing cellulase activity combined with Aspergillus flavus BCC 7179 preparation containing complementary β-glucosidase activity. Saccharification yields of 84.0% and 70.4% for glucose and xylose, respectively, were obtained after hydrolysis at 45oC, pH 5 for 72 h, which were significantly greater than those obtained with a commercial enzyme mixture containing Acremonium cellulase and Optimash BG. A high conversion yield of undetoxified pretreated bagasse (5%, w/v) hydrolysate to ethanol was attained on separate hydrolysis and fermentation process using Pichia stipitis BCC 15191, at pH 5.5, 30oC for 96 h resulting in an ethanol concentration of 10.7 g/L, corresponding to a conversion yield of 0.36 g ethanol/g available fermentable sugars. Comparable ethanol conversion efficiency was obtained by a simultaneous saccharification and fermentation process which led to production of 10.1 g/L ethanol after 72 h fermentation under the same conditions. This study thus demonstrated the potential use of a simple integrated process with minimal environmental impact with the use of promising alternative on-site enzymes and yeast for the production of ethanol from this potent lignocellulosic biomass.