The system in the STR is not at a steady-state in the course of

re-oxygenation. In this step, the rate of DO concentration change is

equal to oxygen transfer rate from gas into liquid. If the rate of DO

concentration change with time is equal to zero and final DO

concentration as steady value is equal to CL (C^∗¼ CL), an expres-

sion could be obtained [9].

1.3

The Steady-State

Method

Steady-state methods are based on a chemical or biochemical reac-

tion that occurs in the liquid, which acts as an oxygen absorber.

Steady-state method is based on the oxygen flow rate and the

difference between the input O2 concentration and the output O2

concentration. This approach allows the kLa to change over time

with a reduction in oxygen concentration. In other words, this

method uses the global oxygen balance in the reactor’s gas phase.

Some notable errors may occur due to the small difference in O2

concentration between the inlet and outlet gas streams [9, 10].

kLa, is a measure of the use of oxygen in gas–liquid systems. kLa

value is very important in the synthesis of products and biomass,

since metabolically obtaining energy is related to oxygen produced

by ventilation systems. There are many variables that are effective in

kLa value, also known as aeration efficiency. These parameters are

mainly; turbulence in the ventilation pool, i.e., mixing, air pressure,

air flow rate, temperature, properties of the fluid (density, viscosity,

etc.) and the availability of foaming inhibitors [11].

2

Materials

The bioreactor type is chosen as stirred tank reactor with two

baffles for this protocol. The capacity of the STR is 3 L with a

working volume of 2 L (see Note 1).

2.1

Bioreactor

1. Sparger: Orifice type.

2. Impeller: 6-blade Rushton turbine.

3. Air pump: Use with silicone pipes.

4. Dissolved oxygen probe: Polarographic type.

5. Temperature detector.

6. Sampling port.

7. Control unit of bioreactor: Follow the temperature, dissolved

oxygen concentration, aeration (gas flow rate), and agitation

(stirrer speed).

8. Nitrogen tank: Use and arrange with pressure regulator.

2.2

Microorganism

Get the stock culture of Escherichia coli as a model organism for

aerobic production in bioreactor (see Note 2).

Volumetric Mass Transfer Coefficient Measurement

19