Chapter 3: Bioreactor Design

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

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.

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.

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

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 0.072 N/m which is always higher than the surface tension of fermentation media (0.06-0.065 N/m)

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

Solution to Foaming Problem Mechanical foam breakers Chemical antifoaming agents

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.

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