Factors Affecting Kla

FACTORS AFFECTING THE VALUES OF

VOLUMETRIC MASS TRANSFER COEFFICIENTS (kLa) IN FERMENTATION SYSTEMS

FACTORS AFFECTING THE VALUES OF MASS TRANSFER COEFFICIENTS IN FERMENTATION SYSTEMS •Various operating parameters and physico-chemical properties of fermentation broth affects mass transfer rate, which in turn show effect on kLa.

Factors affecting the value of kLa are: 1. Bubble size

8.Pressure

2.Gas Hold-up 9. Antifoaming agents

3.Gas Velocity 10. Presence of cells 4.Type of gas sparger

11. Surface active solutes 5.Type of agitation 6. Power input to agitator

7.Temperature

1.Bubble size

•Bubble size has great effect on kLa as the gas is sparged discretely into the fermentation broth in the form of small bubbles. •Small bubbles have high interfacial area. No.of bubbles

Bubble volume (mm3)

Bubble Diameter (mm)

Surface Area (mm2)

Increase in area (%)

1

4.19

2

12.57

-

2

2X2.1

1.59

2X7.91

26.0

3

3X1.4

1.39

3X6.0

44.2

Effect of bubble size on interfacial area and various other parameters Bubble Dia

a

kL

Bubble rise velocity

Gas Holdup

Internal recirculation

Bubble rigidity

Big

Small

High

High

Less

Yes

No

Small

High

Small

Low

High

No

Yes

2. Gas Hold-up

Gas Hold-up is the volume fraction of the gas held up in the total volume comprising the liquid and the held-up gas together. e= VG/(VG+VL) = VG/V Higher values of e indicates higher amount of gas held up in the system. Smaller bubbles (dB