| Summary: | 博士 === 國立成功大學 === 化學工程學系碩博士班 === 97 === In this dissertation, mixed and pure culture (i.e., Klebsiella sp. HE1) were immobilized to produce various biofuels, such as hydrogen, ethanol, 1,3-propanediol and 2,3-butanediol. A series of cell immobilization approaches were used to entrap mixed microflora for hydrogen production. We found that the cells immobilized with a composite matrix of AC + CH + TiO2 (Activated carbon + Chitosan + Titanium oxide) displayed a good H2 production rate of 21.3 mmol l-1 h-1and a hydrogen yield 5.1 mol H2/mol sucrose. The results from this work suggest the potential of using the immobilized-cell systems for continuous H2 production in practice. We also found that immobilized-cell system was suitable for batch and continuous H2 production giving a high stability and efficiency. The cells entrapped with novel composite polymeric matrix (PMMA/collagen/activated carbon) displayed good mechanical strength and H2-producing activity. Batch tests were conducted to explore favorable conditions for H2 production with the PMMA immobilized cells. Under optimal conditions, continuous H2 fermentation was conducted at a hydraulic retention time (HRT) of 4-8 h, giving the best H2-producing rate of 1.8 l h-1 l-1 (over 7 fold of the best batch result) at a HRT of 6 h and a H2 yield of 2.0 mol H2/mol sucrose. The outcome of this work suggests the potential of using this immobilized-cell system for continuous H2 production in practice.
Using a continuously stirred tank bioreactor (CSTR), production of the two biofuels (hydrogen and ethanol) was dependent on the sugar substrate used and also varied with the HRT shifting operation. It is of great interest to observe that sequential HRT decreasing and increasing had significant impact on the biofuels producing performance. The HRT shifting operation appeared to influence the abundance and composition of bacterial population in the culture, and also governed the organic loading rate, which is normally a critical factor affecting the fermentation kinetics. In contrast, energy generation from glucose substrate seemed to be more efficient during a HRT-increasing process.
For the feasible bioreactor systems for simultaneous production of H2 and ethanol as biofuels, fluidized bed reactors (FBR) were able to produce H2 and ethanol at a significant higher rate than packed bed reactors (PBR) due to better mass transfer efficiency in FBR. In PBR (packed bed bioreactor), glucose gave the best performance in terms of production rate and yield of the two biofuels, displayed a good EtOH production rate 378 mmol l-1 h-1and EtOH yield 0.65 mol EtOH /mol substrate. This difference in substrate preference could be due to variations in bacterial population structure resulting from different bioreactor configuration.
Finally, a Klebsiella sp. HE1 strain isolated from sewage sludge, using an indigenous Klebsiella sp. HE1 strain for simultaneous production of H2, ethanol, 1,3-propanediol and 2,3-butanediol as biofuels or industrially applicable biochemical products. The H2-producing HE1 strain successfully isolated from aerobic and anaerobic sludge exhibitied the ability to produce hydrogen gas, 1,3-propanediol, 2,3-butanediol, ethanol from glycerol and sucrose substrate. This study shows the efficiency of producing 7.0 mmol l-1 h-1 of 1,3-propanediol with a yield of 0.37 mol 1,3-propanediol/mol glycerol and of producing 7.1 mmol l-1 h-1 of 2,3-butanediol with a yield of 0.59 mol 2,3-butanediol /mol sucrose. Using Klebsiella sp. to convert abundant and low-cost glycerol generated during the production of biodiesel into higher value products (1,3-propanediol or 2,3-butanediol etc.) represents a promising route to achieve economic viability in the biofuels industry.
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