Bioprocess Engineering

, Volume 8, Issue 1–2, pp 49–53

Improved scale-up strategies of bioreactors

  • L. -K. Ju
  • G. G. Chase


Effective scale-up is essential for successful bioprocessing. While it is desirable to keep as many operating parameters constant as possible during the scale-up, the number of constant parameters realizable is limited by the degrees of freedom in designing the large-scale operation. Scale-up of aerobic fermentations is often carried out on the basis of a constant oxygen transfer coefficient, kLa, to ensure the same oxygen supply rate to support normal growth and metabolism of the desired high cell populations. In this paper, it is proposed to replace the scale-up criterion of constant kL by a more direct and meaningful criterion of equal oxygen transfer rate at a predetermined value of dissolved oxygen concentration. This can be achieved by using different oxygen partial pressures in the influent gas streams for different scales of operation. One more degree of freedom, i.e., gas-phase oxygen partial pressure, is thus added to the process of scale-up. Accordingly, one more operating factor can be maintained constant during scale-up. It can be used to regulate the power consumption in large-scale fermentors for economical considerations or to describe the fluid mixing more precisely. Examples are given to show that the results of optimization achieved in the bench-scale study can be translated to the production-scale fermentor more successfully with only a small change in the gas-phase oxygen partial pressure employed in the bench-scale operation.

List of Symbols

a m2/m3

Specific gas/liquid interfacial area

CL mole/m3

Dissolved oxygen concentration in bulk liquid phase

C* mole/m3

Equilibrium oxygen concentration at gas/liquid interface

Di m

Impeller diameter

DT m

Bioreactor diameter

HL mole/m3 · atm

Henry's-law constant

kL m/s

Liquid-phase mass transfer coefficient

N 1/s

Impeller agitation speed


Number of impellers

OTR mole/s · m3

Oxygen transfer rate per unit volume of the medium

Pg kW

Power input in aerated fermentation

Po kW

Power input in non-gassed fermentation

pg atm

Gas-phase oxygen partial pressure

Q m3/s

Volumetric gas flow rate


Impeller Reynolds number

TQ Joule

Torque applied to the mixer shaft

V m3

Liquid volume

vs m/s

Superficial gas velocity

μ kg/m · s

Liquid viscosity

ϱ kg/m3

Liquid density


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Copyright information

© Springer-Verlag 1992

Authors and Affiliations

  • L. -K. Ju
    • 1
  • G. G. Chase
    • 1
  1. 1.Department of Chemical EngineeringThe University of AkronAkronUSA

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