Abstract:
The profile of the inner-tubing gas pressure for a tubular membrane aeration system
was quantified. The correlations among the overall volumetric oxygen transfer coefficient
(k[subscript L]a), the inner-tubing pressure, the tubing tightness, and the gas throughput are
experimentally analyzed. A mathematical model was developed to describe the
underlying phenomena. The results established the base for comparison with other
aeration techniques.
A novel method employing in situ laser imaging technology to monitor bubbles and
cells, and analyze bubble size distributions in a micro-sparged bioreactor was developed.
The effects of bioreactor operations on bubble size distributions were determined with
following results:
1) Spargers with larger pores produced larger bubbles in most cases
2) Higher sparging rates resulted in bubble size increases up to 10%
3) Pluronic F68 shrank bubbles up to 30%. When the concentration of Pluronic F68
exceeded 1 g/L, no additional impact was observed.
4) Emulsion silicone antifoam up to 25 ppm had no impact on bubbles
5) Cell density (up to 22x10⁶ cells/mL) or culture age has no effect on bubble sizes
In multiple 1 5-L long-term high-density cultures of animal cells, the correlations
between sparging rate and cell damage for using 0.5 μm and 15 μm-pore spargers were
quantified. At cell density of 2x10⁷ cells/mL, sparging above 0.025 vvm using the 0.5-μm
sparger was detrimental to cells, while 0.054 vvm was detrimental for the 15-μm sparger.
A model was developed to predict the rate of cell death resulted from cell-bubble
interactions for high-density industrial animal cell cultures.
The effect of high superficial velocity of sparging gas on cells at the sparger surface
proved insignificant.
A new dissolved CO₂ sensor proved to be reliable for long-term use in industrial
perfusion cell cultures. A novel method for the control of dissolved CO₂ while
simultaneously maintaining DO₂ and pH setpoints was developed. The continuous
control of dissolved CO₂, DO₂ and pH is achieved by simultaneously adjusting the total
sparging rate as well as the ratio of O₂, N₂ and CO₂ gas contents. This control strategy
enables optimization of dissolved CO₂ in industrial culture processes and allows for
improved cell growth and protein production.
