Recycling Rice Straw into Biofuel "Ethanol" by Saccharomyces cerevisiae and Pichia guilliermondii

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This study suggests a new effective chemical pretreatment to hydrolyze rice straw for efficient ethanol production. It introduces a new yeast strain that ferments rice straw hydrolyzate more efficiently than Saccharomyces cerevisiae. The results proved the effectiveness of alkali application before HCl to delignify rice straw and to make it more appropriate for hydrolysis. The application of the hydrolyzing enzymes (cellulase and pectinase) resulted in hydrolysis of pretreated rice straw up to 94.3%. The total sugars released due to pretreatment-enzyme system was about 624 mg g–1 dry mass and the glucose fraction was 198 mg g–1. The results indicated that Pichia guilliermondii is more effective to ferment rice straw hydrolyzate than S. cerevisiae. P. guilliermondii produced larger amounts of bioethanol (7.72 g L–1) than S. cerevisiae (6.13 g L–1)under the same conditions. Our results suggest an appropriate pretreatment system (the cold dilute alkali-acid) and a new effective yeast strain to ferment the rice straw hydrolyzate to produce large amounts of bioethanol.