Bioreactors Flashcards
What are the characteristics of Batch reactors?
➢ Changing conditions, transient growth rate, high initial substrate concentration, and different phases of growth.
➢ More common
What are the characteristics of Chemostat reactors?
➢ Steady-state, constant low concentration of substrate, constant growth rate that can be set by setting the dilution rate.
➢ More efficient
Which type of reactor is more common?
Batch.
What factors influence the choice of continuous versus batch production?
➢ Productivity
➢ Flexibility
➢ Control
➢ Genetic stability
➢ Operability
➢ Economics
➢ Regulatory
In reactor choices, how is PRODUCTIVITY defined?
➢ Rate of product per time per volume.
➢ Chemostat is better for growth-associated products.
➢ Wasted time in the batch process.
In reactor choices, how is FLEXIBILITY defined?
➢ Ability to make more than one product with the same reactor.
➢ Batch is better.
In reactor choices, how is CONTROL defined?
➢ Maintaining the same conditions for all of the products produced.
➢ In theory, Chemostat is better, steady state.
In reactor choices, how is GENETIC STABILITY defined?
➢ Maintaining the organism with the desired characteristics.
➢ Chemostat selects for fast-growing mutants that may not have the desired characteristics.
In reactor choices, how is OPERABILITY defined?
➢ Maintaining a sterile system
➢ Batch is better.
In reactor choices, how is REGULATORY defined?
➢ Validation of the process.
➢ Initially, many process batch, too expensive to re-validate after clinical trials.
Reasons for batch popularity
➢ Equations were for cell mass.
➢ Selective pressure of a chemostat is detrimental to engineered
organisms.
➢ It is more mechanically reliable.
➢ Batch system is more flexible.
Specialized Reactors under Chemostat
➢ Chemostat with Recycle
➢ Multistage Chemostat
➢ Fed-batch
➢ Perfusion
Can we operate a chemostat with a dilution rate greater than maximum growth rate?
No. The cell growth cannot keep up with how fast the cels are removed from the reactor, and after some time the cells would wash out of the reactor.
What conditions would we want to operate a chemostat with a dilution rate greater than the maximum growth rate?
We want a high dilution rate when we have a high volume of feed with a low concentration of substrate. Waste water treatment has these characteristics.
Steps for Multistage Chemostat
➢ First chemostat is fed with a non-inducing growth substrate, allowing the recombinant strain to be produced
➢ The effluent from the first chemostat feeds a second chemostat that is fed inducer, and the product is produced.
These are added continually to the second chemostat not allowing take-over by a fast-growing mutant
New recombinant cells
They gain some advantages of a CSTR and retain some disadvantages of batch
Fed-batch reactors
What happens in fed-batch operation?
○ Reduces substrate inhibition or catabolic repression, allows for high conversion, and the extension of stationary phase.
○ Semi-batch nature usually leads to higher operations cost and batch variability.
These are started as batch cultures and grown to an initial cell concentration X, after which fed-batch operation begins
Fed-batch cultures
Perfusion culture:
➢ Usually done in animal cell culture.
➢ Constant medium flow.
➢ Cell retention.
➢ Selective removal of dead cells.
➢ Removal of cell debris, inhibitory by products.
➢ High medium use, costs raw materials and sterilization
Immobilized cell systems:
➢ High cell concentrations.
➢ Cell reuse.
➢ Eliminates cell washout at high dilution rates.
➢ High volumetric productivities.
➢ May provide favorable microenvironment.
➢ Genetic stability.
➢ Protection from shear damage.
Major limitation for immobilized cell systems include:
Mass transfer (diffusional) resistances.
Diffusional Limitations:
➢ Analysis similar to immobilized enzymes.
➢ Damkohler Number
➢ Effectiveness Factor
➢ Thiele Modulus
Advantage over immobilized systems:
Whole cells provide cofactors, reducing power, energy that many enzymatic reactions require
Types of immobilization:
➢ Active Immobilization
➢ Passive Immobilization
Active immobilization is:
➢ similar to enzyme mobilization
➢ entrapment and binding
It is the most widely used method of cell immobilization.
Physical entrapment
Various matrices/ Porous polymers in physical entrapment:
○ Agar
○ Alginate
○ Carrageenan
○ Polyacrylamide
○ Chitosan
○ Gelatin
○ Colagen
Physical entrapment also includes:
➢ Porous Metal Screens
➢ Polyurethane
➢ Silica Gel
➢ Polystyrene
➢ Cellulose Triacetate
➢ Polymer beads are also typically used.
➢ Encapsulation
➢ Macroscopic membrane-based reactors (hollow fiber)
Methods of preparing polymer beads
● Gelation of Polymers
● Precipitation of Polymers
● Ton Exchange Gelation
● Polycondensation
● Polymerization
Physical adsorption is:
➢ There is direct contact between nutrients and support materials.
➢ High cell loadings.
➢ Selection of suitable support materials is highly based on adsorption capacity and strength of binding.
Disadvantage of physical adsorption
porous support materials causes intraparticle pore diffusion
(at high cell densities) and hard to control microenvironmental conditions
This is widely used for enzymes but not for cells
Covalent binding
In general, good support materials should be:
➢ rigid and chemically inert
➢ bind cells firmly
➢ high loading capacity
This includes biofilm (multilayer growth on solid surfaces)
Passive immobilization
Biological films include:
➢ Multilayer growth of cells on solid support surfaces.
➢ Support materials can be biologically active or inert.
➢ Common in wastewater treatment and mold fermentations.
Immobilized bioreactors include:
➢ Packed-column
➢ Fluidized-bed
➢ Airlift
Packed-columns are:
➢ similar to plug flow reactor
➢ can be a recycle chamber
Feed flows through a column packed with immobilized cells.
How does a fluidized-bed function:
Feed flows up through a bed of immobilized cells, fluidizing the immobilized cell particles
How do airlifts work?
Air bubbles suspend the immobilized cell particles in a reactor.
Solid fermentations include:
➢ Low moisture levels or water activities.
➢ Agricultural products or foods.
➢ Smaller reactor volume.
➢ Low contamination due to low moisture.
➢ Easy product separation.
➢ Energy efficiency.
➢ Differentiated microbiological structures
