Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biosystems Engineering

Committee Chair/Advisor

Drapcho, Caye M

Committee Member

Toler , Joe E

Committee Member

Tzeng , Jeremy

Committee Member

Walker , Terry H


ABSTRACT Thermotoga neapolitana can use different sources of carbon and nitrogen for growth and produces biological hydrogen. Sources of carbon (glucose, sucrose, xylose, xylan, cellulose, cellobiose, starch, corn starch, beet bulp pellet, and rice flour) and nitrogen (yeast extract, fish meal, cottonseed meal, canola meal, linseed meal, and soybean meal) were compared. In the carbon studies, glucose, sucrose, rice flour, and xylan produced similar levels of hydrogen. In the nitrogen studies, Trypticase combined with alternative nitrogen sources can efficiently increases the yield of hydrogen produced by Thermotoga neapolitana. Yeast extract with trypticase as the dual nitrogen sources produced significantly increased concentration of hydrogen than the other combinations tested. Soybean meal and canola meal were second choices as alternative nitrogen sources. Sucrose and rice flour were promising carbon sources to replace glucose, and soybean meals was a promising nitrogen source to replace yeast extract for Thermotoga neapolitana. Thermotoga neapolitana can utilize rice flour as sole carbon source, and soybean meal as one of nitrogen sources to produce hydrogen. Uniform design was used as experimental design to optimize the fermentation medium. The optimized medium was composed of 9 g/L rice flour, 4.5 g/L soybean meal, and 4.5 g/L trypticase. The hydrogen concentration for this optimized medium was 0.07083±0.006198 g H2/L medium or 35.42±3.10 mmol H2/L medium. The increased hydrogen concentration from control medium to optimized medium was 21.6%. Thermotoga neapolitana ferments glucose as carbon source to produce acetate, carbon dioxide, and hydrogen as major products. The exponential phase of the bacterial growth was between 2hrs and 10hrs of incubation time. The maximum cell mass concentration was reached after 10hrs of incubation. The stationary phase lasted for 10hrs, and the death phase began at 20hrs. The pH of broth decreased during the bacterium growth, which may inhibit hydrogen production. The maximum hydrogen partial pressure in this study was 45 kPa at 77°C, and hydrogen partial pressure might inhibit the hydrogen production in this batch fermentation, an estimate of the critical hydrogen partial pressure of 38kPa was calculated for the batch fermentation of Thermotoga neapolitana at 77°C. The maximum specific growth rate ( ) of Thermotoga neapolitana with glucose as carbon source was 0.94hr-1 at 77°C. The Monod half saturation constant (KS) was 0.57 g/L, the observed biomass yield from substrate was 0.25 g/g glucose or 44.59 g/mol glucose, the observed hydrogen yield from substrate was 0.028 g/glucose or 2.50 mol H2 /mol glucose, and the observed hydrogen yield from biomass was 0.114 g/g dry weight. When glucose concentration was 5.0 g/L, the doubling time was 0.84hr or 49mins.



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