Enzymatic saccharification and fermentation of alkaline peroxide pretreated rice hulls to ethanol

Rice hulls used in this study contained 35.62 ± 0.12% cellulose and 11.96 ± 0.73% hemicellulose. Alkaline H2O2 pretreatment and enzymatic saccharification methods were evaluated for conversion of rice hull cellulose and hemicellulose to simple sugars. The yield of sugars from diluted alkaline peroxide pretreated (7.50% H2O2, v/v; pH 11.5; 35 °C; 24 h) rice hulls (15.0%, w/v) after enzymatic saccharification (45 °C, pH 5.0, 72 h) by three commercial enzyme preparations (cellulase, β-glucosidase, and xylanase) using 0.12 ml of each enzyme preparation per g hulls was 428 ± 12 mg/g (90% yield). During the pretreatment, no measurable furfural and hydroxymethyl furfural were produced. The almost complete conversion (96%) of rice hulls to sugars was achieved by saccharifying the liquid and solid fractions separately after alkaline peroxide pretreatment. The concentration of ethanol from alkaline peroxide pretreated, enzyme saccharified rice hull (39 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 °C in 24 h was 8.2 ± 0.2 g/l with a yield of 0.49 g/g available sugars (0.21 g/g hulls). The ethanol concentration was 8.0 ± 0.2 g/l with a yield of 0.20 g/g hulls in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 °C in 48 h.