1. Chapter 3: Bioreactor Design

2. Product Requirement
Biological System Identification
Stoichiometry and Medium Design
Heat & Mass Transfer
Constraints
Upstream
Constraints
Kinetics
Plasmid stability
Shear sensitivity
Bioreactor Type Selection
Downstream
Constraints
Mass & Heat Transfer
Rates
Bioreactor System Design
Mixing
Sterilization & Containment
Instrumentation &
Control
Product Separation &
Purification
Supplies

3. Introduction
The performance of a bioreactor depends on many functions:
Biomass concentration, must remain high
Sterile conditions, must be maintained
Effective agitation, so that the distribution of substances and microorganisms in the reactor is uniform
Heat removal
Creation of correct shear conditions.

4. 3 Groups of Bioreactor for Industrial Production
Non-stirred, non-aerated (76%)
Non-stirred, aerated (11%)
Stirred, aerated (13%)
Non-stirred, non-aerated vessels are used for traditional products such as wine, beer and cheese.

5. Stirred Tank Bioreactor
Low capital cost and low operating cost.
For lab experiments, can be up to 20 L.
From glass or stainless steel
Height : Diameter, between 2:1 and 6:1 depending on the amount of heat to be removed
Stirrer may be top or bottom driven
Fitted with baffles to prevent a large central vortex and improve mixing
4 baffles for vessels less than 3 m diameter
6 – 8 baffles for larger vessels
Width of baffle is between T/10 and T/12, T is the tank diameter

6. Foam Production A common phenomenon in microbial fermentation.
Arises from the flow of air through the liquid fermentation medium and the subsequent formation of small bubbles as a consequence of mixing.
If the bubble film is not strong enough, the bubble is easily destroyed and no foam is formed.
This strength is dependent mainly on the surface tension of the liquid.
The surface tension of pure water is N/m which is always higher than the surface tension of fermentation media ( N/m)

7. Foam Production (cont)
Compounds that contributes to lowering the surface tension – protein, protein hydrolysates, oils, fats.
Cell lysis can also brings an increase in protein concentration.
Except for beer production, foam is usually a negative phenomenon.
It can fill the head space of the bioreactor and clog filters – increase in pressure.
Wetting the filters – contamination
Stable foam – can cause oxygen entrapment

8. Solution to Foaming Problem
Mechanical foam breakers
Chemical antifoaming agents

9. Bubble Column A vessel without mechanical agitation
Aeration and mixing are achieved by gas sparging, therefore less energy
For production of Baker’s yeast, beer and vinegar, wastewater treatment
Generally cylindrical vessel with height greater than twice the diameter
No internal structure except sparger
Perforated horizontal plates installed in tall columns to break up and redistribute coalesced bubbles.

10. Advantage of Bubble Column
Low capital cost
Lack of moving parts
Satisfactory heat and mass transfer performance