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  • 1
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Fermentation experiments were performed to obtain time-dependent data on broth rheology for three filamentous microorganisms, Streptomyces rimosus, Actinomadura roseorufa and Saccharopolyspora erythraea, cultivated under standard conditions in a mechanically stirred bioreactor. Rheological data were successfully analysed using Mitschka's technique and flow curves of the cultures described by the “power law” model in the range of shear rate between 5 and 100 s–1. Consistency coefficients of the cultures were found to vary continuously with fermentation time while flow behaviour index fell sharply within the first few hours of cultivation and then remained practically unchanged till the end of fermentation. The pH of the biomass was found to have a strong influence on both consistency coefficient and flow behaviour index.
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  • 2
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Measurements of oxygen transfer were made during cultivation of the yeast Saccharomyces cerevisiae in a 90–250 litre working volume concentric tube airlift fermenter. Results demonstrated that the rate of oxygen transfer varies with position in the fermenter, being higher in the riser and top-section than in the downcomer and lowest near the base of the fermenter. The time for liquid circulation was generally smaller than the time constant for oxygen transfer (1/kLa) indicating that the rate of oxygen transfer was slow compared to the rate of liquid movement. Measured dissolved oxygen concentrations therefore did not represent the equilibrium arising from the balance between the rates of oxygen transfer and oxygen depletion. Hence measuredk L a values were not representative of local oxygen transfer conditions but instead were indicators of the rate of mass transfer the liquid flow had encountered prior to reaching the point of measurement. Generally the individual rates of oxygen transfer in the vessel were found to increase with increasing vessel height.
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  • 3
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Hydrodynamic and oxygen transfer comparisons were made between two ring sparger locations, draft tube and annulus, in a concentric pilot scale airlift reactor with a baker's yeast suspension. Sectional hydrodynamic measurements were made and a mobile DOT probe was used to characterise the oxygen transfer performance through the individual sections of the reactor. The hydrodynamic performance of the reactor was improved by using a draft tube ring sparger rather than the annulus ring sparger. This was due to the influence of the ratio of the cross sectional area of the downcomer and riser (A D/AR) in conjunction with the effect of liquid velocity and a parameter,C 0, describing the distribution of the liquid velocity and gas holdup across the riser on the bubble coalescence rates. The mixing performance of the reactor was dominated by the frequency of the passage of the broth through the end sections of the reactor. An optimum liquid height above the draft tube, for liquid mixing was demonstrated, above which no further improvement in mixing occurred. The liquid velocity and degree of gas entrainment showed little dependency on top section size for both sparger configurations. Extreme dissolved oxygen heterogeneity was demonstrated around the vessel with both sparger configurations and was shown to be detrimental to the oxygen uptake rate of the baker's yeast. Dissolved oxygen tensions below 1% air saturation occurred along the length of the riser and then rose in the downcomer. The greater oxygen transfer rate in the downcomer than in the riser was caused by the combined effects of a larger slip velocity in the downcomer which enhancedk La and gas residence time, high downcomer gas holdup, and the change in bubble size distribution between the riser and downcomer. The position of greatest oxygen transfer rate in the downcomer was shown to be affected by the reactor from the influence on downcomer liquid linear velocity.
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  • 4
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pseudomonas putida was grown in a 2.5-l fermentor on a mineral salts medium. Glucose was fed normally over an 18-h period. Gluconate reached about 5 g l-1 in the medium and then fell to zero as it was utilised. The maximum toluene dioxygenase specific activity (2 g g-1 h-1) was obtained over the last 6 h of the fermentation when the pH was fully controlled. In fermentations done at low dissolved O2 tension (DOT) values there was an overall reduction in the cellular enzyme level. When stored at 4°C in phosphate buffer, pH 7.0, harvested bacteria lost half their activity in about 90 h.
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  • 5
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A constitutive blocked mutant (UV4) of Pseudomonas putida was grown in a 2.5-l fermentor on a mineral salts medium. Glucose was fed normally over an 18-h period. Gluconate reached about 5 gl−1 in the medium and then fell to zero as it was utilised. The maximum toluene dioxygenase specific activity (2 g g−1 h−1) was obtained over the last 6 h of the fermentation when the pH was fully controlled. In fermentations done at low dissolved O2 tension (DOT) values there was an overall reduction in the cellular enzyme level. When stored at 4°C in phosphate buffer, pH 7.0, harvested bacteria lost half their activity in about 90 h.
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  • 6
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Limitations in mass and momentum transfer coupled with high hydrostatic pressures create significant spatial variations in dissolved gas concentrations in large fermenters. Microorganisms are subjected to fluctuating environmental conditions as they pass through the zones in a stirred vessel or along a closed loop fermenter. A 7-litre fermenter was modified to simulate the dissolved gas and hydrostatic pressure gradients in large vessels. The effect of cycling dissolved oxygen tension (DOT) on penicillin production by Penicillium chrysogenum P1 was investigated. The fermentation was affected by evironmental conditions such as medium composition, pH, size of inoculum, stirrer speed and DOT. Inoculum size below 10% (v/v) and stirrer speeds above 850 rpm caused significant reductions in specific prenicillin production rates (qpen). qpen values were measured at different constant DOT levels. Below 30% air saturation qpen decreased sharply and no production was observed at 10%. Penicillin synthesis was impaired irreversibly below 10% DOT. The same profile was observed at higher stirrer speeds and air flow rates indicating that the effect was a physiological one. Oxygen uptake of the culture was affected significantly below 7% DOT, demonstrating that the critical DOT values for penicillin production and oxygen uptake are two distinct parameters. Carrying out the fermentation at one atmosphere over pressure was found to have no effect. When the dissolved oxygen concentration of the culture medium was cycled around the critical DOT for penicillin production, a considerable decrease in the specific penicillin production rate was observed. The effect was reversible but not transient, indicating a shift in cell metabolism. These results demonstrate the unfavourable effect of fluctuating environmental conditions on culture performance in stirred tanks. They suggest that these effects should be accounted for during strain selection, process development and scale up stages of an industrial process if the productivities in small scale vessels are to be obtained.
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  • 7
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Penicillium chrysogenum spores have been immobilized by adsorption on two grades of wet or dry diatomaceous earth particles, Chromosorb-W and Celite R-633. Almost 90% of the spores were adsorbed within 2 h and those remaining in suspension were removed by washing to minimise the growth of free mycelia. After germination the immobilized biomass was almost independent of the spore loading on the particles and whether or not the spore suspension was added to wet or dry particles. The free biomass obtained was less than 5% of the immobilized biomass.
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  • 8
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The use of free and immobilised Arthrobacter simplex (NCIB 8929) for steroid Δ1-dehydrogenation in two-liquid-phase, stirred-tank reactors has been compared. Product formation is related to the logarithm of the water-octanol partition coefficient (log P) of the organic solvent employed, but the relationship is different for the two forms of the biocatalyst. No reaction was seen with either biocatalyst in media containing solvents of log P≤2.5. For free bacteria, product formation rose linearly with log P thereafter to a maximum at a value of 9.8. With immobilised bacteria, product formation reached a maximum with a solvent of log P=4.0 and remained constant with solvents of higher log P value. Consequently extended reactor operation was possible with immobilised bacteria, and the production of high quality (〉 95% purity) steroid product was demonstrated.
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  • 9
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The antibiotic, difficidin, and its hydroxylated derivative, oxydifficidin, were synthesised by cultures of Bacillus subtilis grown on a complex medium in batch culture at dissolved oxygen tensions (DOT) of 15, 20 and 40% air saturation. During part of the growth phase the DOT was cycled about the control value and the effect on growth and antibiotic production observed. In fermentations with cycling at 15 and 20% DOT the growth yields were lower than for the fermentations done at constant DOT throughout. There appears to be a complex interaction between growth rate and difficidin production rate which led to a reduced specific production rate at 15% DOT as a result of cycling.
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  • 10
    ISSN: 1432-0797
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The influence of mechanical forces resulting from the rotation of (multiple) turbine impellers on the morphology and penicillin production of Penicillium chrysogenum Panlabs P-1 was investigated in batch fermentations using semi-defined media. Experiments were carried out at three different scales of fermentation, 5 dm3,100 dm3 and 1000 dm3 working volume, with the impeller tip speed ranging from 2.5 to 6.3 m/s. Throughout all fermentations, the dissolved oxygen concentration never fell below the critical value for maximum penicillin production. Morphological measurements using image analysis showed that the mean main hyphal length and mean hyphal growth unit increased during the rapid growth period and then decreased to a relatively constant value dependent on the agitation intensity. The specific rate of penicillin production (q pen)and the average main hyphal length during the linear penicillin production phase were lower at high agitation speed, which promoted more rapid mycelial fragmentation and a higher branching frequency. Comparison of the results from the three scales showed that impeller tip speed is a poor scale up parameter whereas a term based on mycelial circulation through the zone of high energy dissipation fitted the data well.
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