Exp 5 Measurement

Lab manual

Experiment 5 KLa measurementObjectives1. To determine KLa of a fermentation system by dynamic gassing out techniques depends upon the monitoring of the increase in dissolve oxygen in agitation and aeration range. 2. To monitor the increase in dissolved oxygen over an adequate range, it is necessary to fast decrease the O2 level to a low value. Two methods can be employed to achieve this lowering of the dissolved oxygen concentration; non-fermentative and fermentative.

3. To study the effect of medium viscosity on KLa value.

Apparatus Bioreactor including pO2 probe.StopwatchChemicals

NaCl

Antifoam

Distilled water

Calibration of dissolved oxygen electrodeBefore calibration the pO2 must be polarized. The polarization must be repeated any time the electrode is disconnected from the amplifier for more than 10 min, but may require less time then. The calibration of pO2-electrode includes zero and slope calibration. The zero is the electrodes current, when no oxygen is present in the culture medium meanwhile the slope is usually the pO2 after saturation of the medium with air at the maximum air supply intended for the process. The calibration of the pO2 electrode involved several steps;

1. Temperature in the culture vessel is adjusted at the operating temperature.2. For "zero" calibration, it could be measured the pO2 of the culture medium before starting the air supply. The medium will be degassed almost completely due to the heat impact during sterilization and thus should not contain dissolved oxygen. Alternatively, we can supply an oxygen-free gas (such as nitrogen of 99.98 purity) to the culture medium to displace the dissolved oxygen until a constant pO2 near 0" can be read at the measurement and control system.3. For slope adjustment, the air supply is activated and the stirring speed is adjusted at the operating value. The medium should be optimally gassed (max. flow rate intended for the process) and mixed. At a stable display of the measured value we can calibrate this as 100 pO2".4. After calibration, the gas supply rate required for the start up of the intended fermentation process can be adjusted on the rotameter of the control unit. Note that the rotameter is calibrated according to standard conditions (temperature 20C, with air at 2 barabs). If it is important to maintain precise operating air flow-rates for further calculations, this makes it necessary to recalculate the indicated flowrate with a correction factor.The calibration of the p02 -electrode is made in the culture vessel after autoclaving and

under the conditions of fermentation.Non-fermentative method

In this technique, the oxygen concentration of the solution is lowered by gassing the liquid out with nitrogen gas, so that the solution is "scrubbed" free of oxygen. Aeration is then initiated at a constant sir flow rate and the increase in dissolved oxygen tension (DOT) is monitored using dissolved oxygen electrode. The profile of DOT during deaeration and aeration is shown in Figure 1. Increase in DOT during aeration can be expressed by Eq. 1;

dCL/dt = KLa (CE-CL)-Qd (1)

(1)

Mass balance for the system;

Rate of change in O2 conc. = Rate of O2 in - Rate of O2 out - Rate of usage Qd

Figure 1: Dynamic gassing out for the determination of KLa values. Aeration was terminated at point A and recommenced at point B.

Since microorganism is not present in the solution, Qd = 0. Eq. 1 becomes

dCL/dt=KLa (CE-CL)

(2)

Can be rewritten as,

dCL/dt = -KLa.CL + KLa.CE

Experimental procedures

1. Set the agitation speed of 500 rpm and 1.0L/min. Purge the nitrogen gas until reach 0% DO. Determine K L a of stirred tank reactor at different air flow rate (0.5, 1.0, 1.5, 2.0 and 2.5 L/min). For this experiment, set the agitation speed at 500 rpm.

2. Determine the effect of increasing agitation speed (200, 400, 600, 800 and 1000 rpm) on K L of a 2 L stirred tank fermenter. For this experiment, set the air flow rate at 1 L/min.

3. In experiment 1 and 2, the fermenter is filled with 1.5 L of distilled water.

4. Investigate the effect of salt (NaCI) and antifoam addition to distilled water on K L a. In this experiment, add 1.5 g of NaCI to 1.5 L distilled water in a fermenter. Determined the K L at a 500 rpm and air flow rate of 1 L/min. Then, add 5 mL of antifoam in a salt solution and determine KLa at the same agitation speed and air flow rate.

Presentation of Results and Discussion1. Plot a graph to show the effect of air flow rate and agitation speed on KLa. Also discuss the effect of the addition of salt and antifoam on KLa.

2. Compare the KLa value determined using different rpm and air flow rate.

3. Discuss the possible cause of error in determination of KLa by using this dynamic gassing out technique.

Results

Non fermentative method

Agitation speed:

rpm

Air flow rate:

L/min

Volume liquid:

L

Note: CE = 100% saturation

time (s)CL (% saturation)CL/tCL(average)Ln(CE CL)

0

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Agitation speed:

rpm

Air flow rate:

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Volume liquid:

L


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Agitation speed:

rpm

Air flow rate:

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Volume liquid:

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Agitation speed:

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Air flow rate:

L/min

Volume liquid:

L


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Agitation speed:

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Air flow rate:

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Volume liquid:

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Agitation speed:

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Air flow rate:

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Volume liquid:

L


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Agitation speed:

rpmAir flow rate:

L/min

Volume liquid:

L



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Agitation speed:

rpm

Air flow rate:

L/min

Volume liquid:

L


0

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Air flow rate:

L/minVolume liquid:

L


Agitation speed:

rpm

Air flow rate:

L/min

Volume liquid:

L


0

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Effect of salt and antifoam addition on KLa

Agitation speed:

rpm

Air flow rate:

L/min

Volume liquid:

L

Agitation speed : _____________ rpm

Air flow rate:

L/min

Volume liquid:

L



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Effect of airflow rate on KLa (500 rpm)

Airflow rate (L/min)KLa (h-1)

0.5

1.0

1.5

2.0

2.5

Effect of agitation speed on KLa (air flow rate = 1 L/min)

Agitation speed (rpm)KLa(h-1)

200

400

600

800

1000

Effect of salt and antifoam addition on KLa.

(Agitation = 500 rpm; Airflow rate = 1 L/min)SubstanceKLa (h-1)

Salt

Antifoam

PAGE CBB 20203 Fermentation TechnologyPage 13

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Exp 5 Measurement