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The conversion of biomass to ethanol and microbial biomass protein
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The conversion of lignocellulosic biomass to two value-added products, microbial biomass protein (MBP) and ethanol, was studied. Bagasse (BAG) was hydrolyzed by Phanarochaete chtysosporium. Excess sugars were utilized by a diazotrophic bacteria, Azotobacter vinelandii resulting in 15% crude protein (CP, dry substrate basis) for AFEX-treated BAG, a 300% increase over untreated, Pchrysosporium inoculated, BAG (5% CP). AFEX-treated BAG was also hydrolyzed by commercial enzymes followed by A. vine/andii fermentation resulting in 20% CP (dry substrate basis), a 2000% increase over untreated BAG (1 % CP). Fermentations with high solids ratios and no agitation provided the most economically attractive MBP production method. Essential amino acid profiles of the final products satisfied FAO/WHO requirements except for lysine. Ethanol fermentations were conducted with (AFEX-treated and untreated) switchgrass (SWG), coastal bermudagrass (CBG), and BAG. Hydrolysis was conducted with commercial enzymes, and a crude enzymes lysate from cultures of three microorganisms. A genetically-engineered Klebsiella oxytoca fermented sugars to ethanol. Glucose was rapidly fermented to ethanol. Xylose utilization was slower and incomplete with greater inefficiencies at higher sugar concentrations. For commercial enzymes hydrolysis and Koxytoca fermentation, based on experimental yields, about 220 L ethanol could be produced per ton AFEX treated SWG, versus 90 L ethanol per ton untreated SWG. Protein extraction did not hinder ethanol fermentation. About 250 L, 205 L, and 1 08 L ethanol could be produced per ton protein-extracted (AFEX) CBG, non-extracted (AFEX) CBG and untreated CBG respectively. Ethanol yields from BAG corresponded to production of 222 L ethanol per ton BAG. With crude enzymes hydrolysis and Koxytoca fermentation, experimental yields could lead to ethanol production of 240 L, 207 L and 153 L per ton of SWG, CBG and BAG respectively. Crude enzymes activity was 11.4 IU/ml corresponding to an enzyme loading of 11.4 IU/g substrate compared to 5 IU/g substrate for commercial enzymes. Crude enzymes compared favorably with commercial enzymes in terms of reducing sugars and ethanol yields. The research provided a sound basis for future work in biomass conversion systems to fuel and feed. The efficacy of AFEX-treatment on lignocellulosic materials was amply demonstrated.
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Reshamwala, Sultan (1994). The conversion of biomass to ethanol and microbial biomass protein. Master's thesis, Texas A&M University. Available electronically from
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