Ethanol can be used as a complete fuel or as an octane enhancer, and has the advantages of being renewable and environmentally friendly. Ethanol produced by a fermentation process, generally referred to as bioethanol, is considered to be a partial solution to the worldwide energy crisis. Traditionally, industrial bioethanol fermentation involves two major steps: starch hydrolysis and fermentation. Since the key microorganism, Saccharomyces cerevisiae, lacks amylolytic activity and is unable to directly utilize starch for proliferation and fermentation, it requires intensive amount of energy and pure starch hydrolyzing enzymes to gelatinize, liquefy and dextrinize the raw starch before fermentation. It has been suggested that genetically engineered yeast which expresses amylolytic enzymes could potentially perform simultaneous starch hydrolysis and fermentation. This improvement could greatly reduce the capital and energy costs in current bioethanol producing plants and make bioethanol production more economical. In this project, a novel yeast strain of Saccharomyces cerevisiae was genetically engineered in such a way that barley alpha-amylase was constitutively expressed and immobilized on the yeast cell surface. This particular alpha-amylase was selected based on its superior kinetic properties and its pH optimum which is compatible with the pH of yeast culture media. The cDNA encoding barley Ñ-amylase, with a secretion signal sequence, was fused to the cDNA encoding the C-terminal half of a cell wall anchoring protein, alpha-agglutinin. The fusion gene was cloned downstream of a constitutive promoter ADH1 in a yeast episomal plasmid pAMY. The pAMY harbouring yeast showed detectable amylolytic activity in a starch plate assay. In addition, alpha-amylase activity was detected only in the cell pellet fraction and not in the culture supernatant. In batch fermentation studies using soluble wheat starch as sole carbon source, even though pAMY harbouring yeast was able to hydrolyse soluble starch under fermentation conditions, no ethanol was produced. This was probably due to insufficient alpha-amylase activity which resulted from the enzyme being anchored on the cell wall by alpha-agglutinin. Further research using alternative cell surface anchoring system might be able to produce yeast with industrial applications.

Ethanol can be used as a complete fuel or as an octane enhancer, and has the advantages of being renewable and environmentally friendly. Ethanol produced by a fermentation process, generally referred to as bioethanol, is considered to be a partial solution to the worldwide energy crisis. Traditionally, industrial bioethanol fermentation involves two major steps: starch hydrolysis and fermentation. Since the key microorganism, Saccharomyces cerevisiae, lacks amylolytic activity and is unable to directly utilize starch for proliferation and fermentation, it requires intensive amount of energy and pure starch hydrolyzing enzymes to gelatinize, liquefy and dextrinize the raw starch before fermentation. It has been suggested that genetically engineered yeast which expresses amylolytic enzymes could potentially perform simultaneous starch hydrolysis and fermentation. This improvement could greatly reduce the capital and energy costs in current bioethanol producing plants and make bioethanol production more economical. In this project, a novel yeast strain of Saccharomyces cerevisiae was genetically engineered in such a way that barley alpha-amylase was constitutively expressed and immobilized on the yeast cell surface. This particular alpha-amylase was selected based on its superior kinetic properties and its pH optimum which is compatible with the pH of yeast culture media. The cDNA encoding barley Ñ-amylase, with a secretion signal sequence, was fused to the cDNA encoding the C-terminal half of a cell wall anchoring protein, alpha-agglutinin. The fusion gene was cloned downstream of a constitutive promoter ADH1 in a yeast episomal plasmid pAMY. The pAMY harbouring yeast showed detectable amylolytic activity in a starch plate assay. In addition, alpha-amylase activity was detected only in the cell pellet fraction and not in the culture supernatant. In batch fermentation studies using soluble wheat starch as sole carbon source, even though pAMY harbouring yeast was able to hydrolyse soluble starch under fermentation conditions, no ethanol was produced. This was probably due to insufficient alpha-amylase activity which resulted from the enzyme being anchored on the cell wall by alpha-agglutinin. Further research using alternative cell surface anchoring system might be able to produce yeast with industrial applications.

Eight cecally fistulated geldings were used in a randomized 4 x 4 Latin square design to observe the effect varying levels of dietary starch had on cecal environment. The 4 treatment rations contained 2 g starch/kg BW (Diet 2), 4 g/kg BW (Diet 4), 6 g/kg BW (Diet 6), or 8 g/kg BW (Diet 8). The rations were comprised of a commercial pelleted feed to meet 2 g starch/kg BW in each treatment, with ground corn used to fulfill the remaining starch requirements in each diet. Soybean meal was added to ensure diets were iso-nitrogenous, and cottonseed hulls were used to equalize dry matter intake. A 21 day adaptation period was allowed before cecal contents were sampled. Samples were drawn 4 hours after the morning meal and were immediately tested for pH. Samples were used to count total anaerobic bacteria and lactic acid bacteria, as well as determine methane activity, ammonia activity, volatile fatty acids, and in vitro dry matter digestibility (IVDMD). Stoichiometric calculations were performed to give an indirect measure of fermented hexose, methane, and carbon dioxide. Diet did not influence dry matter intake (DMI), however it did have an effect on starch intake (P < 0.0001) and caused a linear increase in starch consumption as the amount of offered starch increased (P < 0.0001). Diet did not influence the pH of the cecum (P > 0.05), although a tendency for a linear decrease (P < 0.06) in pH from 6.92 ? 6.58 occurred when dietary starch increased. Total anaerobic bacteria and lactic acid bacteria were unaffected by treatment diets (P > 0.05). Propionate production was affected by dietary treatment (P < 0.05), causing a quadratic increase (P = 0.04) from 8.26 to 14.13 mM as starch in the diets increased. Diet did not affect the production of acetate, butyrate, or ammonia (P > 0.05). Results found that stoichiometric calculations and IVDMD values were not affected by diet (P > 0.05). These results show that starch intake influenced the production of fermentative by-products, which caused decreases in pH, although there was no observed increase in the bacterial populations of the cecum.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 55-61).

Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Rachel Chen; Committee Member: Dr. Athanassios Sambanis; Committee Member: Dr. Sankar Nair. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (MTech (Electrical Engineering))--Peninsula Technikon, 2002. / Word processed copy. Summary in English. Includes bibliographical references (leaves 147-155). Also available online.

published_or_final_version / Zoology / Master / Master of Philosophy

published_or_final_version / Zoology / Master / Master of Philosophy

No description available.

The success of enhanced biological phosphorus removal depends on the constant availability of volatile fatty acids (VFAs). To reduce costs of purchasing external carbon, waste streams would be a preferred source for nutrient removal. VFAs were shown to vary in the incoming sewage and fermentate from primary sludge (PS). Another available source of organic to generate VFAs is waste activated sludge (WAS). The effect of solids retention time and biomass concentration, as well as the effect of temperature and requirement for mixing on generation of VFA from the fermentation of WAS were investigated. It was found that VFA yields from sludge fermentation increased with SRT. At the longest SRT of 10 days improved biomass degradation resulted in the highest soluble to total COD ratio and the highest VFA yield. WAS fermentation was found highly temperature-dependent. The overall VFA–COD concentration in the non-mixed reactors was much lower than the mixed reactors. The study of fermentation of PS, WAS and a mixture of WAS and PS demonstrated that PS fermentation predictably generated a significantly higher amount of soluble COD than WAS. Co-fermentation of WAS with PS enhanced soluble COD production and increased the release of phosphate and ammonium. Fermentation of combined PS and WAS sludge generated a concentration of phosphate high enough to allow phosphorus recovery as struvite The effect of using glycerol as an external carbon source in biological phosphorus removal was investigated. Using glycerol directly resulted in the failure of the process which maintained enhanced biological phosphorus removal. When glycerol was co-fermented with waste activated sludge, significant VFA production was observed. By 2 | P a g e supplying the system with the VFA-enriched supernatant of the fermentate, biological phosphorus removal was enhanced. It was concluded that, if glycerol was to be used as external carbon source for biological phosphorous removal, the effective approach was to ferment glycerol with waste activated sludge. According to the cost analysis, the economic benefit of WAS fermentation can be demonstrated in three ways: 1) cost saving in external carbon addition; 2) cost saving in sludge handling; 3) revenue from phosphorus. At current condition, the value of the recovered P product is insignificant relative to the cost of chemicals that required for recovery and capital cost of the facilities. However, P recovery becomes important when the sustainability take into account.