Scale-up of Aerobic bioreactors

Aerobic bioreactors

• Most of the industrial bioprocesses are aerobic

• Oxygen is an important nutrient for microorganism for growth

• The oxygen transfer rate can control the overall rate of the

bioprocess in aerobic bioreactors

Widely used types are

Stirred tank reactor Air lift columnBubble column

• the system physical properties• the biochemical properties • the operational conditions(gas flow rate, stirrer tip speed)• the geometrical parameters of bioreactor (kind and size of

bioreactor, design and number of stirrers, etc.)

The parameters in the first two groups are determined by the nature of the system and can not be altered freely; the last two groups depend on the process parameters and on the device used

Parameters affecting the Oxygen transfer rate

Steps of scale up…

• Find geometric parameters of the larger scale bioreactor– Stirred tank reactor

Vessel diameter, Height, Impeller diameter– Bubble column

Height, Diameter

• Use scale up criteria to determine operational parameters of the larger scale– Stirred tank reactor

Impeller speed, Air flow rate– Bubble column

Air flow rate

Geometric correlations of a stirred tank reactor

For Turbine blade impellers

W

L

H

D

J

E Di

Scale-up criteria

– Constant volumetric mass transfer coefficient(KLa)

– Constant power consumption per unit volume(P/V)

– Constant impeller tip speed(пND)

– Constant Reynolds number(Re)

– Constant dissolved oxygen concentration (CO2)

Scale-up criteria

Percentage of each criteria used in fermentation industry

(Garcia & Gomez, 2009)

Scale-up criteria

(Garcia and Gomez,2009)

Constant tip speed

N1= Impeller speed of small bioreactor

N2= Impeller speed of Large bioreactor

Di1= Impeller diameter of small bioreactor

Di2= Impeller diameter of large bioreactor

N = Impeller speedD = Impeller diameterρL= Density of the liquidμL=Viscosity of the liquid

Constant Reynolds number

Constant Power consumption per unit volume

Ungassed power consumption ,

Np

(Rushton’s equation)

Constant Power consumption per unit volume

Ungassed power consumption ,

Gassed power consumption ,

(Rushton’s equation)

Constant Power consumption per unit volume

Constant volumetric mass transfer coefficient (kLa)•There are large no.of empirical correlations

Ex: empirical correlations to determine Kla for Newtonian fluids in stirred tank reactors

(Garcia and Gomez,2009)