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Design and Operation of
Conventional Bioreactor
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Basic functions of a fermentor for microbial or animal cell
cultures:1. The vessel should capable of aseptic operation for number of days
2. Adequate aeration/agitationshould be provided to the microbes
3. Mixingshould not cause any damage to the organism
4. Power consumption should be low
5. System of temp., pHcontrol and sampling facilities should be
provided
6. Vessel should be designed in such that minimal use of labour in
operation, harvesting, cleaning and maintenance
7. Similar geometryto both smaller and larger vessels
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Baffle
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Operation of a Conventional bioreactor
Basically involves 5 steps
1. Sterilization
2. Inoculation and Sampling
3. Aeration
4. Control systems
5. Cleaning
1. Sterilizationi) Batch sterilization ( direct or indirect method)
Bioreactor + medium is sterilized
Injecting steam directly in to the Vessel containing the medium Or
Injecting the pressurized steam in to the coil surrounding the vessel
Whole system is heated to 121oC/20 mins
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DisadvantageTakes longer time (2-3hrs) to reach sterilization temp(121 C)
Once temp reached it should be maintained for another20-60mins,followed by cooling for 1 hour
Alter nutrient solution
Change in color and pH occurs and Destroy vitamins
ii) Continuous sterilization
Bioreactor
Nutrient solution (rapidly heated to 140 C for 30-120sec)
by injecting the steam directly or medium can be sterilized through
Heat exchangers
(Sterilized by Injecting the steam directly)
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2. Inoculation and Sampling
Stock culturelarge volume of inoculum is prepared until the
inoculum has a volume of 5 -10% of the working volume of the
production fermenter .
After inoculationFermenter is regularly sampled to examine culture
contamination and to measure product concentration
Aseptic inoculation and sampling is performed using steam locked
port (T-shaped arrangement of piping with a valve in each arm)
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Fermentor
Feed Tank
Cooling
Tank
2ndHeat exchanger
90-120 C
for 20-30 sec
140 C for 30 -120 Sec
1stHeat exchanger
aaaaaaaaaaaaaaaa
Continuous Sterilization by Heat Exchangers
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Usually small fermenters with Steam locked port is used for
inoculum preparation and linked to the production vessel via piping.
These T arm pipes are always maintained in sterile condition by
passing pressurized steam. During inoculation and sampling, valve
to the steam supply is shut down.
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Fermenter attached with steam locked port
Fermenter
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3.Aeration
Aeration of a fermentation medium has two functions
1. To supply oxygen to the production organism
2. To remove CO2 from the bioreactor
Thus the aeration system is designed to promote exchange of gases
between air and medium.
Oxygen- supplied from air, is compressed by a compressor and stored
in tanks
Then it is passed in to the fermenter through flow meter (regulate flow
rate), then a sterilizing filter
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Usually air supplied at the bottom of the fermenter via sparger -
(hollow plate perforated with small holes)- the air supplied into the
medium as small bubbles
Smaller bubbles have greater surface volume ratio and more efficient
in gas exchange. This gas exchange occurs at the interface betweenthe two bubbles surface
After exchange , air bubbles rise to the surface of the medium,
breaks up and releases the gas they contain ( for this purpose,
fermenters are not filled completely, 20% capacity of vessel left free)
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i) Airlift System of aeration
- Simple aeration system
-These fermenters do not have mechanical agitation systems (motor,
shaft, impeller blades)
- Involves sparging of air in at the base of the bioreactor
- Bubbles rise up producing upward flow of the medium
- Thus the system is called Airlift system.
A tube is placed at the centre of an airlift fermenter to channel
the liquid flow around the system. This tube is called draft tube
- Most suitable for fermentation of animal and plant cell cultures
since the mechanical agitation produces high shearing stress that
may damage the cells.
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-Most widely used for large-scale production of monoclonal
antibodies.
Advantage:It has no moving parts , easy maintenance and
operation
Disadvantage: Aeration capacity is low
Aeration capacityis a measure of the maximum rate at which
oxygen can be dissolved into the medium
For aerobic organism, aeration capacity should be > O2demand( rate at which the growing cultures requires O2)
The aeration capacity of an airlift system is directly
proportional to the air flow rate and internal pressure
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ii) Stirred system of aeration
-Aeration capacity of the medium is enhanced by stirring
-Stirring is done by impellers
-Aeration capacityproportional to the stirrer speed, rate of air flow
and internal pressure.
Small fermenter -one impeller at the base of the shaft
Larger fermenter- several impellers throughout the shaft
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Types of impellers
1. Disc impeller (most common type)
48 radial blades are projected out atthe edge of the disc
2. Turbine impeller
Blades are in curved shape
Turbine stirrer requires 50% less air when compared with
disc stirrer, for same yield
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3. MIG Impeller and INTERMIG Impeller
-Both consist of stirring arms with blades attached at an angle
-They requrie 25% and 40% of less air for the same yeild when
compared with disc-turbine stirrer.
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Uses of stirrers/impellers
-Used to mix bluk fluid and gas phase
-Air dispersion
-Oxygen transfer and heat transfer
-Maintaining uniform environment throughout the vessel
Advantage of stirred system
- produce higher aeration capacity than air lift system
Disadvantage of stirred system
- requires energy for stirring
- more maintenance is required
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Baffles
- are narrow rectangular metal plates, fixed to the internal walls-Usually 4 baffles are fixed in STR
-Increase turbulence and there by increase aeration capacity
-Increase residence time of the bubble
-Increase the energy required for stirring
-Wider baffles increase agitation effect where as narrow baffles
drops sharply
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-In large fermenters (>100 m3), two baffles are used as heat
exchangers
-These baffles are installed in such that a gap should be present
between baffles and fermenter wall
-This allows scouring action around and behind the baffles
- There by minimize the growth on baffles and fermenter wall
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4. Control systems
During fermentations, parameters( temp, pH, DO conc. and nutrient
conc. will vary
To maintain optimal conditions for growth and product formation,
such variables are monitored and controlled
Biosensors - used for online measurement and control of important
parameters in a more accurate manner.
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II) pH
During fermentation, organism grows and they change the pH of themedium
pH of the medium is measured using pH electrode which must be in
direct contact with the medium and fixed in the vessel wall using air
tight seal.
This electrode is linked to a control unit which activates pumps to
pump in acid or alkali as required.
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III)Oxygen tension
Conc. Of dissolved oxygen in the medium is measured using an oxygen
electrode, which is in direct contact with the medium and linked to a
control unitalter the air flow rate or stirrer speed to increase, there by
increase in DO takes place and vice versa
IV) Nutrient Concentration
Nutrient conc. in the medium is limited to prevent wastage or toprevent inhibitory effects of high conc. Of nutrients
Using ion-selective and enzyme selective electrodes, it is possible to
control nutrients like ammonia and glucose
V) F
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V) Foam
Media are rich in proteins which form stable foam during agitation
and aeration
Accumulation of foam takes place in head space.
Foam probe fixed in head space will sense the foam and send the
signal to control unit ,which in turn pump in anti-foam as required
These antifoams lowers the surface tension of the medium and cause
bubbles to collapse
Instead of antifoam , some fermenters are equipped with mechanical
foam braker which is placed at the top of the fermenter
VI Cleaning
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