What is a Fermenter?

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What is a Fermenter?

• Vessel or tank in which whole cells or cell-free
  enzymes transform raw materials into biochemical
  products and/or less undesirable by-products
• Also termed a Bioreactor
• The basic function of a fermenter is to provide a
  suitable environment in which an organism can
  efficiently produce a target product

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• Tower fermenter
• Air Lift fermenter
• Deep jet fermenter
• Bubble column fermenter
• Memebrane Bioreactor
• Packed column fermentor

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Cross section of a fermenter  
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Stirred Tank Reactor
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Cross section of a fermenter for Penicillin
production  
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Air lift reactors

• 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 CO2
  disengage.
• The degassed liquid then flows down the annular
  space outside the draught tube

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A Tubular Tower Fermenter  Alcohol fermentation

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AIR LIFT FERMENTER with Internal loop
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Bubble driven bioreactors
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Airlift reactors

• Advantages
• Low shear
• Easier to maintain sterility
• Increased oxygen solubility (KLa)
• Can allow large vessels
• Disadvantages
• High capital cost
• High energy costs
• Hard to control conditions
• Foaming hinders gas -liquid separation

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Bioreactor configurations
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Bioreactor configurations
Bubble column In bubble-column reactors, aeration
and mixing are achieved by gas sparging this
requires less energy than mechanical stirring.
Bubble columns are applied industrially for
production of bakers yeast, beer and vinegar,
and for treatment of wastewater. A
height-to-diameter ration of 31 is common in
bakers yeast production for other applications,
towers with H/D of 61 have been used. The
advantages are low capital cost, lack of moving
parts, and satisfactory heat and mass transfer
performance. Foaming can be problem. Homogeneous
flow all bubbles rise with the same upward
velocity and there is no back-mixing of the gas
phase. Heterogeneous flow At higher gas
velocity. Bubbles and liquid tend to rise up in
the center of the column while a corresponding
down flow of liquid occurs near the walls.
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Bioreactor configurations
Airlift reactor Airlift reactors are often chosen
for culture of plant and animal cells and
immobilized catalyst because shear level are low.
Gas is sparged into only part of the vessel cross
section called the riser. Gas hold-up and
decreased liquid fluid density cause liquid in
the riser to move upwards. Gas disengages at the
top of the vessel leaving heavier bubble-free
liquid to recirculate through the downcomer.
Airlift reactors configurations are internal-loop
vessels and external-loop vessels. In the
internal-loop vessels, the riser and downcomer
are separated by an internal baffle or draft
tube. Air may be sparged into either the draft
tube or the annulus. In the external-loop
vessels, separated vertical tubes are connected
by short horizontal section at the top and
bottom. Because the riser and downcomer are
further apart in external-loop vessels, gas
disengagement is more effective than in
internal-loop devices. Fewer bubbles are carried
into the downcomer, the density difference
between fluids in the riser and downcomer is
greater, and circulation of liquid in the vessel
is faster. Accordingly, mixing is usually better
in external-loop than internal-loop reactors.
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Bioreactor configurations
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Other bioreactors
Packed bed Used with immobilized or particulate
biocatalysts, for example during the production
of aspartate and fumarate, conversion of
penicillin to 6-aminopenicillanic acid, and
resolution of amino acid isomers. Damaged due to
particle attrition is minimal in packed beds
compared with stirred reactors. Mass transfer
between the liquid medium and solid catalyst is
facilitated at high liquid flow rate through the
bed. To achieve this, packed are often operated
with liquid recycle. The catalyst is prevented
from leaving the columns by screens at the liquid
exit. Aeration is generally accomplished in a
separated vessel because if air is sparged
directly into the bed, bubble coalescence
produces gas pockets and flow channeling or
misdistribution. Packed beds are unsuitable for
processes which produce large quantities of
carbon dioxide or other gases which can become
trapped in the packing.
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Other bioreactors
Fluidized bed To overcome the disadvantages of
packed bed, fluidized bed may be preferred.
Because particles are in constant motion,
channeling and clogging of the bed are avoided
and air can be introduced directly into the
column. Fluidized bed reactors are used in waste
water treatment with sand or similar material
supporting mixed microbial populations, and with
flocculating organisms in brewing and production
of vinegar. Trickle bed Is another variation of
the packed bed. Liquid is sprayed onto top of the
packing and trickles down through the bed in
small rivulets. Air may be introduced at the
base because the liquid phase is not continuous
throughout the column, air and other gases move
with relative ease around the packing.
Trickle-bed reactors are used widely for aerobic
wastewater treatment.
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Other bioreactors
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Airlift bioreactor
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Airlift bioreactor

• The region into which bubbles are sparged is
  called the air-riser. The air-riser may be on the
  inside or the outside of the draft-tube. The
  latter design is preferred for large scale
  fermenters as it provides better heat transfer
  efficiencies.
• The rising bubbles in the air-riser cause the
  liquid to flow in a vertical direction. To
  counteract these upward forces, liquid will flow
  in a downward direction in the down-comer. This
  leads to liquid circulation and thus improved
  mixing efficiencies as compared to bubble
  columns.
• The enhanced liquid circulation also causes
  bubbles to move in a uniform direction at a
  relatively uniform velocity. This bubble flow
  pattern reduces bubble coalescence and thus
  results in higher kLa values as compared to
  bubble column reactors.

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9. Fluidised bed reactors
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Fluidised bed reactors

• Fluidised bed bioreactors are one method of
  maintaining high biomass concentrations and at
  the same time good mass transfer rates in
  continuous cultures.
• Fluidised bed bioreactors are an example of
  reactors in which mixing is assisted by the
  action of a pump. In a fluidised bed reactor,
  cells or enzymes are immobilised in and/or on the
  surface of light particles.
• A pump located at the base of the tank causes the
  immobilised catalysts to move with the fluid. The
  pump pushes the fluid and the particles in a
  vertical direction. The upward force of the pump
  is balanced by the downward movement of the
  particles due to gravity. This results in good
  circulation.

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Fluidised bed reactors

• For aerobic microbial systems, sparging is used
  to improve oxygen transfer rates.
• A draft tube may be used to improve circulation
  and oxygen transfer. Both aerobic and anaerobic
  fluidised bed bioreactors have been developed for
  use in waste treatment.
• Fluidised beds can also be used with microcarrier
  beads used in attached animal cell culture.
• Fluidised-bed microcarrier cultures can be
  operated both in batch and continuous mode. In
  the former the fermentation fluid is recycled in
  a pump-around loop.

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Fluidised bed reactors