Lect Bio React. Dsgn)
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BIOREACTORDESIGNProf Madya Dr. Umi Kalsom Md Shah
Dept. Bioprocess Technology
BTK5301 (Bioreactor System)
22/07/10
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Types of Bioreactor
Major Function:
To provide controlled environment for
growth of microorganism (or mixture)
to obtain desired product.
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Points to be considered in designing and
constructing bioreactor:
1)M
icrobiological and biochemical characteristicsof cell systems.
2) Hydrodynamic characteristics of the bioreactor.
3) Mass and heat characteristics of the bioreactor.
4) Kinetic of cell growth and product formation.
5) Genetic stability characteristics of the cell system.
6) Aseptic equipment design.
7) Control of bioreactor environment (macro and
microenvironments).
8) Implication of bioreactor design on downstream
product separation.
9) Capital and operating costs of the bioreactor.
10) Potential for bioreactorscale up.
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Vary in size and complexity,
test tube (10 ml) tocomputer controlled
fermenters (>100 m3).
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Little or no power used for aeration.Aeration - dependent on transfer of oxygen
through the still surface of the culture.
1. STANDING CULTURES
PoorRate of oxygen transfer- due to small
surface area.
Used in small-scale (oxygen supply is not
critical).
Ex: biochemical tests for identification of
bacteria (test-tubes containing 5-10 mL of
media).
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a. T- Flasks
Small scale culture of animal cells. Incubated
horizontally to increase the surface area for
oxygen transfer.
Surface aeration rate can be increased
using large volume flasks.
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b. Fernback Flasks
Fig. 1 shows a 3 L "Fernback" flaskcontaining 1 L of medium and a 250 mL
Erlenmeyer flask containing 100 mL of
medium. Note how the former has a large
surface area.
Figure 1
Fernback
flask
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Large Pyrex flasks are used for small-
scale production of fermented products.
Ex: Kombucha tea, (a tea brewed bymixture of yeasts and acetic acid
bacteria).
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c. Surface Cultures
Standing culture aeration is not
restricted to the laboratory. In some
countries, where availability of
electricity is unreliable, citric acid is
produced using surface culture
techniques.
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Aspergillus nigermycelia are grown on
surface of liquid media in large shallowtrays. The medium is neither gassed
nor agitated.
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Ex: Aerobic solid substrate
fermentations (biomass is grown
on solid biodegradable substrates
such as water softened bran, rice orbarley, solids continuously or
periodically turned over to improve
aeration and to regulate culture
temperature).
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Ex: 1. Production ofkoji by
Aspergillus oryzae on soya beans,
(part ofsoya sauce process).
2. Mushroom cultivation.
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For small scale cell cultivation
(continuous shaking of culture fluid),
higher oxygen transfer rates.
Shaking breaks liquid surface and
provides greatersurface area for oxygen
transfer.
Increased rates of oxygen transfer are
also achieved by entrainment of oxygen
bubbles at the surface of the liquid.
2. SHAKE FLASKS
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a. Factors Affecting KLa (volumetric
oxygen transfer rate)
Rate of oxygen transferis dependent on:
1. shaking speed,
2. liquid volume,
3. shake flask design
KLa increases with
liquid surface area KLa is higher when
baffles are present
KLa decreases with
liquid volume
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y KLa increase with shaking speed.
y At high shaking speeds, bubbles
become entrained into medium tofurther increase oxygen transfer rate.
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3. MECHANICALLY STIRRED
BIOREACTORS
Most important bioreactorfor industrial
application, (pharmaceutical industry).
y Low capital cost, low operating costs,best understood and flexible.
y Non-sparged mechanically agitated
bioreactors can supply sufficient aerationfor microbial fermentations with liquid
volumes up to 3 L.
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y However, stirring speeds of up to
600 rpm may be required before the
culture is not oxygen limited.
In non-sparged reactors, oxygen istransferred from head-space above
fermenter liquid.
Agitation continually breaks the liquid
surface and increases surface area foroxygen transfer.
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Air-sparged fermenters can have liquid
volumes of greater than 500,000 L
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Airlift fermenters are more expensive
to construct than bubble column
reactors.
An airlift fermenter differs from bubblecolumn bioreactors by the presence of a
draft tube provides better mass and heat
transfer efficiencies and more uniform
shear conditions.
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2. Airlift Bioreactors - draft tube
y The main functions ofdraft tube:
1. Increase mixing through the reactor
2. The draft tube enhances axial
mixing throughout the whole reactor
3. Reduce bubble coalescence.
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Due to circulatory effect, draft tube induces in
the reactor. Circulation occurs in one
direction and hence the bubbles also travel inone direction.
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5. AIRLIFT BIOREACTOR
a. Air-riser and Down-comerThree regions: air-riser, down-comerand
disengagement zone.
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y Air-riser: region into which
bubbles are sparged (inside or outside ofdraft-tube).
y The rising bubbles in the air-riser
cause the liquid to flow in a vertical
direction. To counteract these upwardforces, liquid will flow in a downward
direction in the down-comer.
y
This leads to liquid circulation and thusimproved mixing efficiencies as
compared to bubble columns.
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y Enhanced liquid circulation causes
bubbles to move in a uniform direction at arelatively uniform velocity.
y This bubble flow pattern reduces
bubble coalescence and thus results in higherKLa values as compared to bubble column
reactors.
y Disengagement zone: add volume tothe reactor, reduce foaming minimize
recirculation of bubbles through the down
comer.
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6. FIXED BED REACTORS
y Cells are immobilized by
absorption on or entrapment in solid,non-moving solid surfaces(e.g: plastic
blocks, concrete blocks, wood shavings or
fibrous material such as plastic or glass
wool)..
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y The liquid feed is either pumpedthrough or allowed to trickle over the
surface of the solids where the immobilized
cells convert the substrates into products.
y
Once steady state has been reached there
will be a continuous cell loss from the solid
surfaces.
y
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Used in waste treatment and asbiological filters in small aquarium
water recycling systems.
y In other types of fixed-bed
fermenters, the cells are immobilizedin solidified gels such as agaror
carragenan.
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y Cells are trapped inside pores of gels
(better cell retention and a large effective
surface area for cell entrapment).
y
Increase surface area for cell
immobilization: hollow fibres and pleated
membranes as immobilization surfaces.
y
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Industrial applications: waste watertreatment, production of enzymes and
amino acids, steroid transformations
y Advantages: non-growing
cells can be used. Cells enzymatically
act on substrates in the feed. The
cells can be eitherinactivated ornot
fed nutrients required for growth.
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7. PACKED BED BIOREACTOR
y Rate of mass transfer between cells
and medium depends on flow rate and on
thickness of biomass film on or near the
surface of the solid particles.
y Problems: poor mass transfer rates
and clogging.
y Used commercially with
enzymatically catalysts and with slowly or
non-growing cells.
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8. TRICKLE FLOW BIOREACTORS
y
Class of packed bed reactors, inwhich medium flows (or trickles) over the
solid particles. Particles are not immersed in
the liquid.
y Used in aerobic treatment of
sewage. Oxygen transfer is enhanced by
ensuring cells are covered by only a very thin
layer of liquid, thus reducing the distanceover which the dissolved oxygen must diffuse
to reach the cells.
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y
Because stirring is not used,considerable capital and energy
costs are saved. However, oxygen
transfer rates per unit volume are
low compared with sparged stirredtank systems.
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9. FLUIDIZED BED BIOREACTORS
y
Maintaining high biomassconcentrations, good mass transfer rates
in continuous cultures.
y Mixing is assisted by the action of a
pump.y
cells or enzymes are immobilized in and/or
on the surface of light particles.
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y A pump located at base of tank
causes the immobilized catalysts to move
with the fluid. The pump pushes fluid and
particles in a vertical direction.
y Upward force of the pump is
balanced by the downward movement ofthe particles due to gravity.
y This results in good circulation. For
aerobic microbial systems, sparging is used
to improve oxygen transfer rates.y
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y Fluidized-bed microcarrier cultures
can be operated both in batch andcontinuous mode.
Use of small particles increases the
surface area for cell immobilization andmass transfer. Because the particles are
small and light, they can be easily made
to flow with the liquid (ie. fluidized).
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y Fluidization of particles leads to the
surface of particles being continuously
turned over (increases mass transfer rate).y
y Used in wastewater treatment.
Aquarium scale fluidized bioreactors for
biological nitrification are readily available.
2 Category: 2 phase system (not
aerated) and 3 phase system (aerated
by sparging).
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Used for animal cell culture. Animal
cells are trapped in gels or on the
surface of special particles known as
"microcarriers". Ex: perfusion culture
technology used for animal cell
culture.
6.10 INDUSTRIAL BIOREACTORS
y Worlds largest fermenter (fromChemical and Engineering News), 200 ft high
and 25 ft diameter.
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