3lecture types 2
TRANSCRIPT
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BIOREACTORBIOREACTOR
TYPES -II
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Airlift bioreactor
An air-lift reactor is divided into three regions:the air-riser, down-comerand disengagement
zone. The region into which bubbles are sparged is
called the air-riser. The air-riser may be on theinside or the outside of the draft-tube. The latter
design is preferred for large scale fermenters as itprovides better heat transfer efficiencies.
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Airlift bioreactor
The rising bubbles in the air-riser cause the liquidto flow in a vertical direction. To counteract theseupward forces, liquid will flow in a downwarddirection in the down-comer. This leads to liquidcirculation and thus improved mixing efficienciesas compared to bubble columns.
The enhanced liquid circulation also causesbubbles to move in a uniform direction at arelatively uniform velocity. This bubble flow
pattern reduces bubble coalescence and thusresults in higher kLa values as compared tobubble column reactors.
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Immobilized Cell
Reactors
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Fixed bed reactors
In fixed bed fermenters, the cells are
immobilized by absorption on or
entrapment in solid, non-moving solid
surfaces.
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In one type of fixed bed fermenter, the
cells are immobilized on the surfaces of
immobile solid particles such as
>plastic blocks
>concrete blocks
>wood shavings or
>fibrous material such as plastic or glass
wool.
*In other types of fixed-bed fermenters, the
cells are immobilized in solidified gels
such as agar or carrageenin.
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**Industrial applications of fixed
bed reactors includewaste water treatment
production of enzymes andamino acids
steroid transformations
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Cellrecyclesystems
In a fermenter with cell recycle the cellsare separated from the effluent and then
recycled back to the fermenter; thusminimizing cell removal from thefermenter
Cell recycle is used in activated sludgesystems. A portion of the cells areseparated in a settling tank and returned tothe activated sludge fermenter.
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Packed and Trickle bed
Bioreactors Packed bed reactors often suffer from
problems caused by poor mass transferrates and clogging. Despite this they areused commercially with enzymatically
catalysts and with slowly or non-growingcells.
Trickle bed reactors are a class of packedbed reactors in which the medium flows(or trickles) over the solid particles. Inthese reactors, the particles are notimmersed in the liquid. They are used
widely in aerobic treatment of sewage.
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Fluidized bed reactors
Fluidized bed bioreactors are an example
of reactors in which mixing is assisted by
the action of a pump. In a fluidized bed
reactor, cells or enzymes are immobilized
in and/or on the surface of light particles.
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Aerationand Agitationin
Animal Cell Bioreactors
Animal cells fragilecan be easilydamaged
In mammalian cell culture the objectives ofmaximizing oxygen transfer must bebalanced by the need to maintain cellintegrity. Fortunately, mammalian cellgrowth rates are considerably slower thanthose of most aerobic microorganisms andoxygen transfer requirements are therefore
also proportionately lower.
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Methodsofminimizingcell damage
Bubblefreeoxygenation - External
oxygenation
A more commonly used and effective
method of bubble free oxygenation is to
use a separate oxygenation chamber: Themediumisoxygenated inaseparateunit
whichcaneither beastirred tankreactorora
staticmixer. Theoxygenated medium is
pumped intothe bioreactorwhiletheoxygen
depleted medium ispumped backintothe
oxygenationunit
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Thesameprinciplecan beused
withimmobilized cellculturessuchasfluidized bed and fibre
bed reactors.
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