Assessing Mixing Effectiveness in a Bioreactor

EXPERIMENT 3

ASSESSING MIXING EFFECTIVENESS IN A BIOREACTOR

1.0 OBJECTIVES

1.1  To relate the mixing speed with absorption efficiency.

1.2  To study the types of impellers and their mixing patterns.

1.3  To study the importance of mixing in a fermentation process.

2.0 COURSE OUTCOME

CO3: Ability to design a stirred tank bioreactor according to the specific application through group discussion, experiment and oral presentation.

3.0 INTRODUCTION

In fermentation process, mixing is one of the important operations in order to get a good yield. Mixing process is needed in a stirred tank bioreactor to provide the cells access to all substrates, including oxygen in aerobic culture. Besides that, heat to or from the broth has to be transferred by mixing the broth rapidly to get the desired temperature for the culture. Mixing in the bioreactor is achieved by using mechanical agitation using impeller. Good macromixing (bulk circulation) and micromixing (near the molecule scale) is important to provide rapid mixing.

4.0 MATERIALS AND EQUIPMENTS

4.1 2 liter Microbial bioreactor

4.2 Distilled water

4.3 Dye

4.4 Activated carbon

4.5 Four types of impellers

4.6 Plastic beads

EFFECT OF MIXING SPEED ON DYE REMOVAL

5.0 PROCEDURES

5.1  Fill in the bioreactor with 1L distilled water and add 200 mg of dye according to the following table.

5.2 Set the stirrer to 150 rpm for 5 minutes to produce homogenous dye solution.

5.3 After 5 minutes, stop stirring. Add 1 g of activated carbon into the bioreactor.

5.4 Adjust the stirrer to 50 rpm.

5.5. After 10 minutes, take sample of the dye solution and record the absorbance at 665 nm.

5.6 Repeat the above steps 5.1 – 5.5 using a new stirrer speed (100 rpm increment).

EFFECT OF IMPELLER TYPES ON MIXING PATTERNS

6.0 PROCEDURES

6.1  Fill in a tank with 2 L of clean water.

6.2  Place the plastic beads into the water.

6.3  Install one impeller of your interest to the stirrer holder.

6.4  Ensure that the impeller is placed in the middle of the tank with sufficient space below.

6.5  Turn on the impeller at 100 rpm and observe the mixing pattern made by the beads.

6.6  Repeat the above steps using other impellers.

7.0  RESULTS AND DISCUSSION

7.1 Plot a graph of dye absorbance versus time.

7.2 Discuss the result of dye removal based on mixing speed.

7.3 Draw the mixing pattern observed from different types of impellers and discuss their mixing effectiveness.

8.0  CONCLUSION

8.1 Based on the experimental procedure done and the result taken, draw some conclusions to this experiment.

9.0  QUESTIONS

9.1  Explain the importance of mixing in fermentation process.

9.2  List the types of impellers and their applications in fermentation process.

9.3  Describe ‘vortex’ and its implication in mixing effectiveness.