Peter M. Kilonzo

The effects of non-Newtonian fermentation broth viscosity and small bubble segregation on oxygen mass transfer in gas-lift bioreactors: a critical review

Abstract This review paper deals with the effects of non-Newtonian fermentation broth viscosities on gas–liquid mixing and oxygen mass transfer characteristics to provide knowledge for the design and development of gas-lift bioreactors, which can operate satisfactorily with high viscosity fermentation broths. The effect of small bubble segregation is also examined.

Effects of surface treatment and process parameters on immobilization of recombinant yeast cells by adsorption to fibrous matrices.

The effects of surface properties of Saccharomyces cerevisiae strains 468/pGAC9 and 468 on adhesion to polyethyleneimine (PEI) and/glutaraldehyde (GA) pre-treated cotton (CT), polyester (PE), polyester+cotton (PECT), nylon (NL), polyurethane foam (PUF), and cellulose re-enforced polyurethane (CPU) fibers were investigated. Process parameters (circulation velocity, pH, ionic strength, media composition and surfactants) were also examined. 80%, 90%, and 35% of the cells were adsorbed onto unmodified CT, PUF, and PE, respectively. PEI-GA pre-treated CT and alkali treated PE yielded 25% and 60% cell adhesion, respectively. Adsorption rate (K(a)) ranged from 0.06 to 0.17 for CT and 0.06-0.16 for PE at varied pH. Adhesion increased by 15% in the presence of ethanol, low pH and ionic strength, and decreased by 23% in the presence of yeast extract and glucose. Shear flow and 1% Triton X-100 detached 62% and 36% nonviable cells from PE and CT, respectively, suggesting that cell immobilization in fibrous-bed bioreactors can be controlled to optimize cell density for long-term stability.

Airlift-driven fibrous-bed bioreactor for continuous production of glucoamylase using immobilized recombinant yeast cells.

Continuous production of a fungal glucoamylase by immobilized recombinant Saccharomyces cerevisiae strain C468 containing plasmid pGAC9. Yeast cells were immobilized on hydrophilic cotton cloth in an inverse internal loop airlift-driven bioreactor. Free-cell culture in the airlift and stirred tank bioreactors confirmed the plasmid instability of the recombinant yeast. Enhanced glucoamylase productivity and plasmid stability were observed both in the free and immobilized cell cultures in the airlift bioreactor system. The glucoamylase level of the free-cell culture in the airlift bioreactor was approximately 20% higher than that in the in stirred tank bioreactor due to high cell density (cell dry weight/volume of bioreactor) and fraction of the plasmid-carrying cells. A potentially high glucoamylase activity of 161U/L and a corresponding volumetric productivity of 3.5U/Lh were achieved when a cell density of approximately 85g/L (or 12.3g/g fiber) was attained in the fibrous-bed immobilized cell bioreactor system. The stable glucoamylase production was achieved after five generations, at which time a fraction of approximately 62% of the plasmid-carrying cells was realized in the immobilized cell system. Plasmid stability was increased for the immobilized cells during continuous culture at the operating dilution rate. The volumetric and specific productivities and fraction of plasmid-carrying cells in the immobilized cell system were higher than in the free-cell counterpart, however. This was in part due to the high viability (approximately 80%) in the immobilized cell system and the selective immobilization of the plasmid-carrying cells in the fibrous bed, and perhaps increased plasmid copy number.

Production of Ethanol Using Immobilised Cell Bioreactor Systems

Crude oil and its derivatives are the sources of the vast proportion of fuels used today. However, the 1973 oil embargo and accompanying increases in oil prices, along with the prospective of fossil fuels exhaustion in the near future [1-3] triggered an extensive interest in search for alternative sources of liquid fuels. Amongst these alternatives is the production of ethanol by fermentation process using renewable plant products. The production of industrial ethanol by fermentation started in the 19 century and used as an automotive fuel in the late 1930s. The production, however, declined in the late 1940s as a result of competition with ethanol produced chemically by direct hydration of cheap oil-based ethylene. Because of the increasing environmental concerns in recent years regarding greenhouse gas emission (1996, Habitat II Agenda), interest is again turning to fermentation ethanol as a motor fuel. The use of biomass derived ethanol as a gasoline substitute or supplement has been implemented with a great zeal in Brazil and in the U.S. In 2002, production in Brazil reached about 7.0 billion gallons (BG) and 2.2 BG in the U.S [4]. According to the U.S. gasohol program, fuel ethanol production is expected to reach 2.3 BG in 2004 increasing to 5.0 BG in 2012. To boost this program, the U.S administration is providing market, loan and tax credits for ethanol made from renewable sources. The cost of fermentation ethanol is, however, higher than gasoline. Ethanol’s wholesale price in the U.S. is about US

Bioethanol production from starchy biomass by direct fermentation using Saccharomyces diastaticus in batch free and immobilized cell systems.

1.10/gal. This compared with an average price of about 70¢/gal for gasoline at the refinery [4]. However, as a gasoline additive, ethanol in the U.S. obtains an excise tax reduction that amounts to 5.3¢/gallon for winter gasoline that contains 10% ethanol. This is equivalent to a subsidy of 53¢/gal of ethanol. The selection of a suitable and cheap raw material is therefore central to the economics of any new ethanol plant. Furthermore, since ethanol is a low cost, high volume product, the economic success of such a product depends very much on the capital and operating costs.

Surface Modifications for Controlled and Optimized Cell Immobilizationby Adsorption: Applications in Fibrous Bed Bioreactors ContainingRecombinant Cells

Direct ethanol fermentation of soluble starch or dextrin with the amylolytic yeast Saccharomyces diastaticus was investigated in batch free and immobilized cells systems. In batch fermentations, the cells fermented high dextrin concentrations more efficiently. More than 92 g/l of ethanol was produced from 240 g/l of dextrin, at a conversion efficiency of 90%. The conversion efficiency decreased to 60% but a higher final ethanol concentration of 147 g/l was attained with a medium containing 500 g/l of dextrin. S. diastaticus in an immobilized cell bioreactor produced 83 g/l of ethanol from 240 g/l of dextrin, corresponding to an ethanol volumetric productivity of 9.1 g/l/h.

Effects of geometrical design on hydrodynamic and mass transfer characteristics of a rectangular-column airlift bioreactor

The effects of surface properties of S. cerevisiae strains 468/pGAC9 and 468 on adhesion to polyethylenimine (PEI) and/glutaraldehyde (GA) pretreated cotton (CT), polyester (PE), polyester + cotton (PECT), nylon (NL), polyurethane foam (PUF), and cellulose re-enforced polyurethane (CPU) fibers were investigated. Process parameters (circulation velocity, pH, ionic strength, media composition and surfactants) were also examined. 80, 90, and 35% of the cells were adsorbed onto unmodified CT, PUF and PE, respectively. PEI-GA pre-treated CT and alkali treated PE yielded 25% and 60% cell adhesion, respectively. Adsorption rate (Ka) ranged from 0.06 to 0.17 for CT and 0.06 to 0.16 for PE at varied pH. Adhesion increased by 15% in the presence of ethanol, low pH and ionic strength, and decreased by 23% in the presence of yeast extract and glucose. Shear flow and 1% Triton X-100 detached 62 and 36% nonviable cells from PE and CT, respectively, suggesting that cell immobilization in fibrousbed bioreactors can be controlled to optimize cell density for long-term stability.