Bioethanol production using lignocellulosic materials and thermophilic microbial hydrolysis

Cellulose is the most abundant renewable material in nature, which is converted to simple sugar, glucose, by cellulase enzymes. Cellulase enzymes are one of the most important industrial enzymes that are widely used in the production of biofuels. This study aimed to use wheat straw as a carbon source for Saccharomyces cerevisiae yeast cells to produce bioethanol. Physical grinding and phosphoric acid plus hydrogen peroxide chemical pretreatment methods were carried out for the removal of lignin and hemicellulose from the structure of wheat straw and obtaining a cellulose-rich material. Thermophilic filamentous fungi were isolated from cow manure, and two isolates were selected based on the levels of endoglucanase, exoglucanase, and total cellulase activities and identified based on DNA sequences of internal transcribed spacer regions. Hydrolysates were obtained from enzymatic hydrolysis of pretreatment wheat straw by thermophilic cellulase enzymes. Fermentation of Saccharomyces cerevisiae yeast cells was performed in hydrolysates for bioethanol production. Aspergillus fumigatus isolate indicated 147.11, 515.9, and 453.78 U/mg wheat straw for exoglucanase, endoglucanase, and total cellulase activities, respectively. These activities were, respectively, measured as 380.35, 730.24, and 372.76 U/mg wheat straw for Rhizomucor pusillus isolate. Pretreatment procedures functioned efficiently and increased the cellulose part of wheat straw up to 88.91%. Hydrolysates of pretreated wheat straw (obtained from Aspergillus fumigatus and Rhizomucor pusillus cellulase activities) resulted in 21.88 and 24.02 g/L (4.05 and 5.31%) bioethanol by Saccharomyces cerevisiae yeast fermentation, respectively. It seems that utilizing thermophilic cellulase enzymes and wheat straw is a promising economic process for bioethanol production.