A fed-batch culture is a semi-batch operation in which the nutrients necessary for
cell growth and product formation are fed either intermittently or continuously via
one or more feed streams during the course of an otherwise batch operation. The
culture broth is harvested usually only at the end of the operational period, either
fully or partially (the remainder serving as the inoculum for the next repeated run).
This process may be repeated (repeated fed-batch) a number of times if the cells are
fully viable and productive. Thus, there are one or more feed streams but no effluent
during the course of operation. Sources of carbon, nitrogen, phosphates, nutrients,
precursors, or inducers are fed either intermittently or continuously into the culture
by manipulating the feed rates during the run. The products are harvested only at
the end of the run. Therefore, the culture volume increases during the course of
operation until the volume is full. Thereafter, a batch mode of operation is used
to attain the final results. Thus, the fed-batch culture is a dynamic operation. By
manipulating the feed rates, the concentrations of limiting nutrients in the culture
can be manipulated either to remain at a constant level or to follow a predetermined
optimal profile until the culture volume reaches the maximum, and then a batch
mode is used to provide a final touch. In so doing, the concentration of the desired
product or the yield of product at the end of the run is maximized. This type of
operation was first called a fed-batch culture or fed-batch fermentation.
1,2 It is also
known as Zulaufverfahren in German or ryukaho2 (a flow addition method) in
Japanese. Obviously, this type of operation is a semi-batch reactor operation that is
used for chemical and biochemical reactions. In environmental engineering dealing
with toxic waste, this type of operation is known as a fill and draw operation or as
a sequencing batch reactor. In biomedical engineering, the breathing process in and
out of the lung is known as stick and balloon, as the volume of the lung increases as
we inhale and decreases as we exhale, which is a form of fed-batch process.