Design of Fermentation Processes
Table 9.1. Advantages and disadvantages of different modes of operation of the stirred tank reactor.
Mode of operation
Can be used for different
High labor cost:
Skilled labor is
reactions every day.
Can be properly sterilized.
Little risk of infection or strain
Much idle time:
of inoculum, cleaning after the
Complete conversion of substrate
emptying and cleaning.
Works all the time:
low labor cost,
good utilization of reactor.
due to the
autocatalytic nature of microbial
reactions, the productivity can be
When the production of the desired
compound is catabolite repressed,
continuous production or fed-batch
Automation may be very appealing.
Constant product quality.
Combines the advantages of batch
and continuous operation.
Excellent for control and
optimization of a given production
continuous production for months fails
Infection, e.g., a short
interruption of the
continuous feed sterilization.
Spontaneous mutation of the
microorganism to a non-
can rarely be used for
other productions without substantial
process equipment must be designed for
low volumetric rate, continuous
operation-unless holding tanks are used.
Some of the disadvantages of both
batch and continuous operation-but
advantages far outweigh the
disadvantages, and fed-batch is used to
produce both biomass (baker’s yeast),
industrial enzymes and antibiotics.
Substrates from the gas phase are transferred to the liquid phase by spargers or through high
efficiency nozzles. Coalescence of gas bubbles is minimized by forcing the gas- liquid dispersion
through static mixers or by redispersion in the vicinity of the mechanical mixers as further
discussed in Chapter 10. The numerous patents describing the placement of mechanical mixers,
of air lift reactors, and reactors with forced flow through static mixers or with rapid recirculation
of liquid, injection of gas in the high- pressure recirculation loop and dispersion of the gas liquid