ERT314
BIOREACTOR SYSTEM
CHAPTER 3: TYPES OF BIOREACTOR
Internal-loop airlift
External-loop airlift
 Constrain: homogenous flow only occurs at low gas flow rates and
when bubbles leaving the sparger are evenly distributed.
 Can operate at higher gas flow rate, provide better mixing than bubble column
Internal-loop
airlift
Riser
and
downcomer
are
separated by internal baffle or draft
tube; air may be sparged into either
draft tube (figure a) or annulus (fig. b)
Gas hold up and decreased liquid
density cause the liquid in the riser to
move upwards.
Gas disengaged at the top of the
vessel, leaving the heavier bubblefree liquid to recirculate through the
downcomer.
Liquid circulates in airlift reactors as
a result of density difference between
riser and downcomer.
(a)
(b)
External loop airlift
 Separate vertical tubes are connected by
short horizontal section at the top and bottom.
Compared to internal-loop,
 Because the riser and downcomer are further
apart, gas disengagement are more effective.
 Fewer bubbles are carried into the
downcomer, the density difference between
fluids in riser and downcomer is greater,
therefore circulation of liquid in the vessel is
faster.
 Mixing is better
or
 Unsuitable for processes which
produce large quantities of gases which
can be trapped in the packing
 Used commercially with immobilised
cell and enzyme for production of
aspartate and fumarate, conversion of
penisilin to 6-aminopenicillanic
Fluidised Bed Bioreactor
At lower fluid velocities, the solids remain in place
as the fluid passes through the voids in the material.
This is known as a packed bed reactor.
As the fluid velocity is increased, the reactor will
reach a stage where the force of the fluid on the solids
is enough to balance the weight of the solid material.
This stage is known as incipient fluidization and occurs
at this minimum fluidization velocity.
Once this minimum velocity is surpassed, the
contents of the reactor bed begin to expand and swirl
around much like an agitated tank or boiling pot of
water. The reactor is now a fluidized bed.
Because particles are in constant motion, channelling
and clogging of bed are avoided. Air can be introduced
directly.
Application: waste treatment with sand or similar
material supporting microbial populations, brewing and
production of vinegar.
Membrane bioreactor
Comparison between conventional activated sludge (top) with membrane
bioreactor (bottom)
 Low availability of water content reduces the possibility of contamination.
Rotating drum/rotary drum
bioreactor
Fig. 3. Rotating drum bioreactor. (1) Air-inlet, (2) rotating joint, (3) coupling,
(4) air nozzles, (5) air line, (6) rollers, (7) rotating drum, (8) solid medium,
(9) rim.
Source: A. Durand (2003). Bioreactor designs for solid state fermentation.
Biochemical Engineering Journal. Vol 13:113-125
Rotating drum/rotary drum
bioreactor
Lab scale rotary drum bioreactor
Pilot solid state
bioreactor
at 150-180°C
Equipped with lighted vertical sight-glass for inspecting
the content of reactor
continue…
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Industrial fermenter are designed for insitu steam
sterilization
Use sterile air to maintain pressure and discourage
entry of air-borne contaminant.
Filters– prevent passage of microb.
- fitted to exhaust gas lines;
- this serves to contain the culture inside &
insures against contamination if pressure
drops
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