Alkaline Pretreatment of Coastal Bermudagrass for Bioethanol Production

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Title: Alkaline Pretreatment of Coastal Bermudagrass for Bioethanol Production
Author: Wang, Ziyu
Advisors: Ratna R. Sharma, Committee Member
Steven W. Peretti, Committee Member
Jay J. Cheng, Committee Chair
Abstract: Sodium hydroxide and lime pretreatments of coastal bermudagrass for enhanced reducing sugars recovery were investigated in this study. In the study of sodium hydroxide pretreatment, coastal bermudagrass was pretreated with 0.5% to 3% (w/v) NaOH solutions for 15 min to 90 min at 121°C. For lime pretreatment, a variety of temperatures (room temperature to 121°C) at a range of residence times with different lime loadings (0.02 to 0.20 g/g dry biomass) were examined. Sodium hydroxide pretreatment at 121°C was more effective than lime pretreatment with regard to lignin removal with an average difference of 55%. After enzymatic hydrolysis with excessive cellulases and cellobiase, the best total reducing sugars yield for lime pretreatment was 78% of the theoretical maximum which is comparable to 77% for NaOH pretreatment at 121°C. The optimal conditions for NaOH pretreatment at 121°C are 15 min and 0.75% NaOH under which glucan and xylan conversion rates were approximately 91% and 65% respectively. As for lime pretreatment, the best condition is 100°C for 15 min with a lime loading of 0.1 g/g dry biomass under which 87% of glucan and 68% of xylan were converted to glucose and xylose respectively. The coastal bermudagrass pretreated under the recommended conditions with NaOH and lime was hydrolyzated with different enzyme loadings (cellulases: 0 to 40 FPU (FPU, filter paper unit, expressed as µmol of glucose produced per minute with filter paper as a substrate) /g dry biomass; cellobiase: 0 to 70 CBU (CBU, cellobiase unit, expressed as µmol of cellobiose that is converted into glucose per minute with cellobiose as a substrate)/g dry biomass). A cellulases loading of 20 FPU/g was required to improve sugar recovery for lime-pretreated biomass, while 15 FPU/g was sufficient for enhanced sugar yield for NaOH-pretreated biomass. The optimal cellobiase loading was found to be 10 CBU/g for the two types of pretreated biomass. The supplementation of xylanase during hydrolysis was not beneficial to higher sugar recovery for both pretreatment methods. More than 99% of glucose in the hydrolyzate was utilized by the yeast strain for ethanol production with 95% of the theoretical maximum yield for the hydrolyzate and 83% of the theoretical yield for the raw biomass. There was no significant difference in ethanol yield between NaOH and lime-pretreated coastal bermudagrass.
Date: 2009-03-19
Degree: MS
Discipline: Biological and Agricultural Engineering

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