Chapter 3:Bioreactor Design

Product Requirement

Biological System Identification

Stoichiometry and Medium Design

Kinetics

Bioreactor Type Selection

Bioreactor System Design

Heat & Mass Transfer Constraints

Plasmid stability

Shear sensitivity

Mass & Heat Transfer Rates

Instrumentation & Control

SuppliesProduct Separation & Purification

Sterilization & Containment

Mixing

Downstream Constraints

Upstream Constraints

Introduction

The performance of a bioreactor depends on many functions:

Biomass concentration, must remain high

Sterile conditions, must be maintainedEffective agitation, so that the

distribution of substances and microorganisms in the reactor is uniform

Heat removalCreation of correct shear conditions.

3 Groups of Bioreactor for Industrial Production

1. Non-stirred, non-aerated (76%)2. Non-stirred, aerated (11%)3. Stirred, aerated (13%)

Non-stirred, non-aerated vessels are used for traditional products such as wine, beer and cheese.

Stirred Tank BioreactorLow capital cost and low operating cost.For lab experiments, can be up to 20 L.From glass or stainless steelHeight : Diameter, between 2:1 and 6:1

depending on the amount of heat to be removedStirrer may be top or bottom drivenFitted with baffles to prevent a large central

vortex and improve mixing4 baffles for vessels less than 3 m diameter6 – 8 baffles for larger vesselsWidth of baffle is between T/10 and T/12, T is the

tank diameter

Foam ProductionA 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 – contaminationStable foam – can cause oxygen

entrapment

Solution to Foaming Problem

Mechanical foam breakersChemical antifoaming agents

Bubble ColumnA vessel without mechanical agitationAeration and mixing are achieved by gas

sparging, therefore less energyFor production of Baker’s yeast, beer and

vinegar, wastewater treatmentGenerally cylindrical vessel with height

greater than twice the diameterNo internal structure except spargerPerforated horizontal plates installed in

tall columns to break up and redistribute coalesced bubbles.

Advantage of Bubble Column

Low capital costLack of moving partsSatisfactory heat and mass

transfer performance