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