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 bubble- free 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

 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 or

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:

Rotating drum/rotary drum bioreactor Lab scale rotary drum bioreactor

Pilot solid state bioreactor

Equipped with lighted vertical sight-glass for inspecting the content of reactor at °C

continue…  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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