13. The dynamic gas out method provides the determination of

the kLa value during a fermentation even at different phases of

the process.

14. Make sure the nitrogen tank is sufficiently full.

15. In the dynamic method for evaluation of kLa, oxygen probe

must has fast response time for accuracy. Response time con-

stant is corresponding to a time when the probe reaches 63% of

its final value when it undergoes a step change according to

concentration. Theoretically, the probe response time is much

smaller than the mass transfer response time: 1/kLa. But in

practice this situation would be change. For approaching the

theory, various method in literature has been improved for

calculation of the kLa for this reason. It is really important

criteria that the response time constant must be smaller than

1/kLa (see ref. 9).

16. The electrode of the DO concentrations in the bioreactor must

be applied in sterile conditions as well as fast response. Also,

this electrode should be able to measure the concentration

instantly. Generally, the electrodes which have these specific

properties are preferred.

17. The level of DO concentration does not fall to Ccrit level for

keeping the constant the volumetric oxygen uptake rate. So,

the oxygen uptake rate of the cells does not change with the

oxygen level.

18. In the determination of volumetric mass transfer coefficient of

biological broth according to this protocol, the dynamic

method is actually corresponding to method of “gas out–gas

in” due to non-aeration and reaeration steps, respectively. The

gas out step must be carried out in a short time.

19. Multiplicity of C value increases the determination of kLa

accuracy. Ensure to record C values in every 5–120 s depending

on the microorganism.

20. In the re-aeration step, a specific limitation could occur. In a

short period, aeration could not catch steady-state. If the gas

residence time is close to time constant of oxygen mass transfer

coefficient, this situation can cause inaccuracy.

References

1. Po¨pel HJ (1983) Aeration and gas transfer.

Delft University of Technology, Delft, The

Netherlands, p 168

2. Bailey JE, Ollis DF 2nd (1986) Biochemical

engineering fundamentals. McGraw-Hill Inter-

national Editions, New York

3. Cengel YA, Ghajar AJ 5th (1997) Heat and

mass transfer: fundamentals & applications.

McGraw-Hill

International

Editions,

New York

4. Treybal R 3rd (1981) Mass transfer operations.

McGraw-Hill

International

Editions,

New York

5. Tu¨rker M 1st (2005) Biyoreaksiyon Mu¨hendi-

slig˘i/Biyolojik Proseslerin Kinetig˘i ve Model-

lenmesi, Su Vakfı Yayınları

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Aysegul Inam et al.