Saccharification and detoxification of Na2CO3 pretreated rice straw with on-site manufactured enzymes secreted by Aspergillus fumigatus to enhance bioethanol yield

Enzyme production as well as rice straw saccharification and fermentation were integrated to produce bioethanol in this study. Submerged fermentation of Na2CO3 pretreated rice straw to produce a complex enzyme for saccharification by Aspergillus fumigatus was performed. The major component of rice straw, that is cellulose, hemicellulose and lignin was almost completely degraded in 24 h. Using whole pretreated rice straw slurry as the substrate, the maximum concentrations of reducing sugar and ethanol were obtained with values of 63.6 g/L and 30.9 g/L, respectively, in a total hydrolysis and fermentation time at a substrate concentration of 8% (based on the original amount of rice straw). Fed-batch fermentation was employed for enzymolysis and fermentation of rice straw residue. Under a 32% total substrate concentration, 108.6 g/L ethanol was obtained in a total enzymolysis and fermentation time of 40 h. The results from different fermentation methods showed that the laccase produced by A. fumigatus in situ could effectively promote the enzymatic hydrolysis and fermentation through detoxifying the phenols produced during pretreatment and by the enzymatic hydrolysis processes.