Optimization of enzymatic hydrolysis and ethanol fermentation from AFEX-treated rice straw

• Published in: Applied microbiology and biotechnology 2009-09, Vol.84 (4), p.667-676
• Main Authors: Zhong, Cheng, Lau, Ming W, Balan, Venkatesh, Dale, Bruce E, Yuan, Ying-Jin
• Format: Article
• Language: English
• Subjects: Agricultural pollution; Alternative energy sources; Ammonia; Biodiesel fuels; Biofuel production; Biological and medical sciences; Biomass; Biorefineries; Biotechnological Products and Process Engineering; Biotechnology; Biotechnology - methods; Cellulase; Cellulose; Chemical engineering; Conversion; Crop residues; Detoxification; Energy; Enzymes; Ethanol; Ethanol - metabolism; Fermentation; Fundamental and applied biological sciences. Psychology; Glucans - metabolism; Glucose; Glycoside Hydrolases - metabolism; Hydrolysis; Industrial applications and implications. Economical aspects; Laboratories; Life Sciences; Lignin; Lignocellulose; Methods. Procedures. Technologies; Microbial engineering. Fermentation and microbial culture technology; Microbial Genetics and Genomics; Microbiology; Moisture content; Optimization; Oryza - metabolism; Oryza sativa; Plant Stems - metabolism; Refineries; Renewable resources; Rice; Rice straw; Saccharomyces cerevisiae; Saccharomyces cerevisiae - metabolism; Studies; Sugar; Yeast
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-009-2001-0

An abundant agricultural residue, rice straw (RS) was pretreated using ammonia fiber expansion (AFEX) process with less than 3% sugar loss. Along with commercial cellulase (Spezyme® CP) at 15 filter paper unit/g of glucan, the addition of Multifect® Xylanase at 2.67 mg protein/g glucan and Multifect® Pectinase at 3.65 mg protein/g glucan was optimized to greatly increase sugar conversion of AFEX-treated RS. During enzymatic hydrolysis even at 6% glucan loading (equivalent to 17.8% solid loading), about 80.6% of glucan and 89.6% of xylan conversions (including monomeric and oligomeric sugars) were achieved. However, oligomeric glucose and xylose accounted for 12.3% of the total glucose and 37.0% of the total xylose, respectively. Comparison among the three ethanologenic strains revealed Saccharomyces cerevisiae 424A(LNH-ST) to be a promising candidate for RS hydrolysate with maximum ethanol metabolic yield of 95.3% and ethanol volumetric productivity of 0.26 g/L/h. The final concentration of ethanol at 37.0 g/L was obtained by S. cerevisiae 424A(LNH-ST) even with low cell density inoculum. A biorefinery combining AFEX pretreatment with S. cerevisiae 424A(LNH-ST) in separate hydrolysis and fermentation could achieve 175.6 g EtOH/kg untreated rice straw at low initial cell density (0.28 g dw/L) without washing pretreated biomass, detoxification, or nutrient supplementation.