Scale-up of Bioprocesses
479
Table 11.1. Basic tasks of the bioreactor
Function
Com m ent
Containment
Ensurance of sterility
Introduction of gaseous reactants
Typically oxygen, but also in some cases the
carbon source e.g. methane
Introduction of liquid reactants
Typically the carbon source is a liquid sugar
solution
Removal of gaseous products
Carbon dioxide is the most common gaseous
product to be removed
Control of the physical environment
Temperature and pH normally need to be
controlled. Shear rates may need to be limited
Suspension
Cells and particulate matter need to be
suspended
Dispersion
Mixing of two-phase systems
Table 11.1. A number of different reactor types have been developed to fulfill these tasks. A rich
source of inspiration for the design of novel bioreactors, is the great variety of natural
bioreactors. As examples of these can be mentioned ponds, calf stomachs or termite guts
(Cooney, 1983, Brune 1998).
Most bioreactors fall into one of the following categories; unstirred vessels, stirred vessels,
bubble columns, airlift reactors, membrane reactors, fluidized beds, or packed beds. The reactor
types differ primarily with respect to mode of agitation and aeration. In mechanically agitated
reactors, mixing is obtained via internal stirrers, whereas in pneumatically agitated reactors the
flow is achieved by the aeration only. In loop reactors part o f the liquid is continuously
withdrawn by means of a pump to an external circulation loop. Aeration, substrate addition and
heat transfer may all be placed in the external loop.
stirrer
sparger
a
bed with a
g.
Immobilized
draft
tube
sparger
aeration
Fig. 11.2. Schematic representation of some reactor types, a) stirred tank reactor, b) bubble column, c)
airlift reactor, d) trickle bed reactor, e) loop reactor with external circulation and heat exchanger.
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