| dc.description.abstract | Sugar beet pulp (SBP), the residue remaining after sucrose extraction, is
currently sold as an animal feed. Humans cannot digest the cellulose in the pulp
unlike ruminant animals. The pulp is primarily comprised of cellulose,
hemicellulose, and pectin which can be hydrolyzed with commercial enzymes into
fermentable sugars such as, glucose, arabinose, galacturonic acid, xylose, and
galactose. These sugars can be fermented to produce ethanol. This research
tested the variation of several enzymes, enzyme loading rates, solids loading
rates, and fermenting organisms to increase ethanol yields from sugar beet pulp.
Several commercial enzymes (cellulases, hemicellulases, pectinases, and
proteases) were tested to determine impact on SBP hydrolysis. Two commercial
enzyme preparations (Viscozyme and Pectinex) were compared. Viscozyme
produced the highest sugar yields because of increased cellulose hydrolysis, while
Pectinex showed less cellulase activity. All enzyme treatments resulted in similar
hemicellulose and pectin hydrolysis. Pretreatment with proteases reduced sugar
yields from hydrolysis by 10-30% compared to hydrolysis without pretreatment.
Escherichia coli K011, a genetically modified organism (GMO), and
Saccharomyces cerevisiae were used to ferment SBP hydrolyzate to increase
ethanol yields (g EtOH/g SBP) and concentrations (g/L). In the "Parallel"
fermentation, pectinase was used to solubilize pectin and hemicellulose. After
separation, the liquid stream was fermented with E. coli K011 and the high-cellulose solid fraction was fermented using S. cerevisiae and additional cellulase
enzymes (Celluclast and Novozyme 188). The "Parallel" method initially produced
under 0.15 g EtOH/g SBP but was improved with pH regulation to yield 0.23 g
EtOH/g SBP. The separation method limited ethanol production.
The ethanol yields from three additional fermentation methods ("E. coli
K011 Only", "Serial", and "Reverse Serial") were compared. The "E. coli K011
Only" method was the baseline fermentation for comparison of the remaining three
fermentation methods. SBP was hydrolyzed with pectinase, cellulase, and
cellobiase before fermentation with E. coli K011 to yield 0.192 g ethanol/ g SBP.
The total hydrolysis of the SBP limited ethanol production. The "Serial"
fermentation began by solubilizing pectin and hemicellulose with pectinases. All of
the flask contents were fermented with E. coli K011. The remaining cellulose-rich
SBP was then hydrolyzed with cellulases and fermented by S. cerevisiae. Initial
ethanol yields were under 0.15 g EtOH/g SBP but improved to 0.238 g EtOH/g
SBP. Acetic acid concentrations limited ethanol production by S. cerevisiae. The
"Reverse Serial" simultaneous saccharification and fermentation (SSF) started with
pectinases, cellulases, cellobiases, and S. cerevisiae. Remaining arabinose and
galacturonic acid were fermented with E. coli K011 to produce a peak ethanol
yield of 0.299 g EtOH/g SBP.
The methods approached and exceeded published results (0.277 g EtOH/g
SBP) (Doran and Foster, 2000) to successfully increase ethanol yields. Ethanol
concentrations were limited by high SBP moisture content and low solids loading
rates. | en_US |
