Optimization of enzymatic hydrolysis and ethanol fermentation from AFEX-treated rice straw.
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.
Zhong
Cheng
C
Key Laboratory of Systems Bioengineering of State Education Ministry, School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, People's Republic of China. chzhong.tju@gmail.com
Lau
Ming W
MW
Balan
Venkatesh
V
Dale
Bruce E
BE
Yuan
Ying-Jin
YJ
D001709:Biotechnology / Q000379:methods*; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D005936:Glucans / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D012275:Oryza / Q000378:metabolism*; D018547:Plant Stems / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*
D005936:Glucans; D000431:Ethanol; D006026:Glycoside Hydrolases