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Document Type

Thesis - University Access Only

Award Date

2013

Degree Name

Master of Science (MS)

Department

Biology and Microbiology

First Advisor

William R. Gibbons

Abstract

Challenges associated with pretreatment, densification and storage of corn stover (CS), switchgrass (SG) and prairie cordgrass (PCG) were addressed as part of a cellulose-to-ethanol process. It is most cost-effective to transport densified cellulosic materials; however this can be cost prohibitive. AFEX pretreatment coupled with an innovative densification method allowed reduced costs per unit. Five conditions were examined: untreated (control), AFEX pretreated, pretreated/densified, pretreated/stored, and pretreated/densified/stored. Two enzyme doses of cellulase and β-glucosidase were employed, using a separate hydrolysis and fermentation (SHF) system. The high dose utilized 15 filter paper units (FPU)/g glucan of cellulase and 64 cellobiase units (CBU)/ml β-glucosidase. The low dose rate used one-third of each dose. An industrial fuel ethanol strain of Saccharomyces cerevisiae was utilized. Samples were tested for pH, yeast viability, and carbohydrate, organic acid and ethanol concentration using high performance liquid chromatography (HPLC). Pretreatment provided significant improvement in hydrolysis and fermentation yields, increasing glucose and ethanol yields by an average of 16% to 58% and 13% to 43%, respectively, over all substrates. The low enzyme dosage resulted in consistently lower and more variable glucose and ethanol yields compared to the high dosage.. Glucose yields averaged 49% versus 70%, while ethanol yields averaged 32% versus 56%, respectively. Thus the low dose would not be suitable for commercial application. Concerning densification into PAKS, results were substrate specific. Sugar and ethanol yields from PCG and SG were negatively impacted by densification. Glucose yields dropped from 62% to 53%, and ethanol yields fell from 46% to 38% in non-densified substrates versus PAKS. Glucose yields from CS improved following densification, rising from 62% to 65% while ethanol yield improved from 44% to 52%, respectively. Storage did not adversely affect conversion efficiency and may be beneficial. Glucose yields for AFEX and PAKS increased following storage from 59% to 68%, 50% to 54% and 62% to 64% for CS, SG and PCG, respectively. PCG ethanol production was contrary to other substrates with fresh substrates yielding 46% and stored averaging 34%. CS ethanol yield increased from 45% to 51% and SG yield remained the same at 44%.

Library of Congress Subject Headings

Corn stover
Switchgrass
Spartina
Energy crops
Ethanol as fuel
Biomass conversion

Description

Includes bibliographical references (pages 122-137)

Format

application/pdf

Number of Pages

155

Publisher

South Dakota State University

Rights

In Copyright - Educational Use Permitted
http://rightsstatements.org/vocab/InC-EDU/1.0/

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