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Title page for etd-1104110-150418


URN etd-1104110-150418 Statistics This thesis had been viewed 3062 times. Download 1033 times.
Author Jen-wei Chang
Author's Email Address No Public.
Department Bioengineering
Year 2010 Semester 1
Degree Ph.D. Type of Document Doctoral Dissertation
Language English Page Count 139
Title Medium formulation and fermentation strategies for very high gravity ethanol production
Keyword
  • very high gravity
  • medium formulation
  • Ethanol
  • Ethanol
  • medium formulation
  • very high gravity
  • Abstract In this study, we report the development of a fermentation medium designed specifically for very-high-gravity (VHG) ethanol production by Saccharomyces cerevisiae. By keeping amount of yeast pitched at ~107 cells ml-1, corn steep powder (CSP) at 1 % (w/v), and other medium components at low levels, the highest ethanol concentration (158.27±4.29 g l-1, equivalent to 20.06±0.54 %, v/v) was attained in 48h using batch fermentation. Comparatively, the lowest ethanol concentration (138.08±7.63 g l-1, equivalent to 17.50±0.97 %, v/v) was obtained when amount of yeast pitched and CSP was maintained at ~106 cells ml-1 and 5% w/v, respectively. A high-level amount of yeast pitched gives rise to fast glucose consumption rate; however, a high-level CSP retards yeast propagation, resulting in low ethanol production rate in the later stage of fermentation.
    t50, derived from logistic dynamic model, was proposed and implemented to evaluate VHG fermentation subjected to the variation of different culture compositions. t50 is the time required to consume 50% of initial glucose concentration (symbolized as ), or is the time required to produce half of the final ethanol concentration (symbolized as ). A 24 factorial experimental design, including four key ingredients: urea, ammonium sulfate, corn steep powder, and amount of yeast pitched, was planned to attest the applicability of t50 to discriminate the effectiveness of different growth media during VHG fermentation. The analysis of variance shows that t50 could differentiate among different VHG growth media, and be further adopted to cluster 16 datasets into four groups according to corn steep powder and amount of yeast pitched. The t50 difference between two VHG growth media varies 8.34 ~9.12 h, implying that the selection of a proper growth medium for VHG fermentation could drastically reduce fermentation time, thereby increasing the annual ethanol productivity.
    A 22 experimental plan was implemented to investigate the effect of dual free amino nitrogen (FAN) supplementation on the sweet sorghum fermentation under very-high-gravity (VHG) conditions. A rapid initial FAN uptake rate signified insufficient provision of utilizable nitrogen by sorghum mash alone. The ethanol productivity was 3.03 g L-1h-1 (equivalent to 146 g l-1 ethanol in 48 h when FAN was added) as compared to 0.93 g L-1h-1 (equivalent to 144 g l-1 ethanol in 156 h when FAN was not added) by using configuration of simultaneous saccharification and fermentation (SSF). Whereas, the ethanol productivity was 2.18 g L-1h-1 (equivalent to 139 g l-1 ethanol in 64 h when FAN was provided) as compared to 0.68 g L-1h-1 (equivalent to 125 g l-1 ethanol in 185 h when FAN was not provided) by using configuration of separate hydrolysis and fermentation (SHF). Results indicate that SSF configuration with a dual addition of FAN-containing substances is the most efficient fermentation configuration among investigated cases. Such a configuration results in the highest ethanol yield and the shortest fermentation time. The ethanol productivity of this configuration was increased by 60 % as compared to other similar findings reported previously.
    Advisor Committee
  • Kow-Jen Duan - advisor
  • none - co-chair
  • none - co-chair
  • none - co-chair
  • none - co-chair
  • Files indicate access worldwide
    Date of Defense 2010-09-29 Date of Submission 2010-11-05


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