TYPES OF FERMENTER Types of Fermenter Aerobic fermenters may be classified depending on how the gas is distributed Stirred Tank Reactor Airlift Loop Reactor Immobilised System Basic ID: 161957
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Slide1
TYPES
TYPES OF
FERMENTERSlide2
Types of Fermenter
Aerobic
fermenters
may be classified depending
on how
the gas is distributed
Stirred Tank Reactor
Airlift
Loop Reactor
Immobilised
SystemSlide3
Basic
Fermenter
Design Criteria
(
i
)
Nature of microbial
cell
(a) Hydrodynamic characteristics
(b) Mass and Heat Transfer
(c) Kinetics
(d) Genotype and Phenotype
(ii
)
Environmental Control and Monitoring of the
process
(a) pH, temperature, dissolved oxygen etc.
(b) Asepsis and
avoiding
contamination
(
iii)Process factors
(a) Effect on other unit operations
(b) Economics
(c) Potential for scale-upSlide4
In such reactors, circulation is caused by the motion of injected gas through a central tube with fluid re-circulating through the head space where excess air and the by-product CO
2
disengage.
The degassed liquid then flows down the annular space outside the draught tube
Advantages
Low shearEasier to maintain sterilityIncreased oxygen solubility Can allow large vesselsDisadvantagesHigh capital costHigh energy costsHard to control conditionsFoaming hinders gas -liquid separation
Air lift reactor
sSlide5
Stirred Tank Reactors
Most commonly used
fermenter
Made from stainless steel
Height to Diameter ratio 2:1 and 6:1
Baffles prevent a large central vortexAlso used to carry coolants in large systemsSlide6
Basic features: stirred tank bioreactor
Agitation system
The function of the agitation system is to
provide good mixing and thus increase mass transfer rates through the bulk liquid and bubble boundary layers.
provide the appropriate shear conditions required for the breaking up of bubbles. The agitation system consists of the agitator and the baffles.
The baffles are used to break the liquid flow to increase turbulence and mixing efficiency.Slide7
Stirred Tank ReactorSlide8
STR - Control systems
An agitator system
An oxygen delivery system
A foam control system
A temperature control system
A pH control system
Sampling ports
A cleaning and sterilizing system.
A sump and dump line for emptying of the reactor. Slide9
Radial flow impellers -
Rushton
turbine
The most commonly used agitator in microbial fermentations
Like all radial flow impellers, the Rushton turbine is designed to provide the high shear conditions required for breaking bubbles and thus increasing the oxygen transfer rate.
Agitator design and operationSlide10
Aeration and Agitation
The transfer of energy, nutrients, substrate and metabolite within the bioreactor must be brought about by a suitable mixing device. The efficiency of any one nutrient may be crucial to the efficiency of the whole fermentation.
For the three phases, the stirring of a bioreactor brings about the following:
Dispersion of air in the nutrient solution
Homogenisation to equalise the temperature and the concentration of nutrients throughout the
fermenterSuspension of microorganisms and solid nutrients
Dispersion of immiscible liquidsSlide11
Sterilization
Sterilizing the feed solution is essential because the media cannot contain foreign microbes because this could severely hinder the growth of the production microbe
Most popular method is heat sterilization of the feed solution Slide12
MODIFICATIONS
(
i
) Important in tank reactor design:
1
. Continuous flow (activated sludge waste treatment)· Suitable when substrate at low conc.· Allows greater control on growth rate\ cell physiology2. Immobilised cells - may be membrane (e.g. hollow fibre reactor), immobilised onto support such as ceramic (
e.g
packed-bed) or in polymers (
e.g
alginate beads)
· Increases rate of reaction
· Microenvironment created protects cells e.g. from shear damage
3. Low energy aeration\ mixing
Air-lift, draft-tubes, loop reactors etc.
· Increase height to diameter ratio. Increased path length of bubble, improves mass transfer
· Results in decreased shear levels, important in
floc
systems.Slide13