History of Continuous Fermentation
Many systems in nature have input and output
flows and operate over long time periods; in this sense they are continuous
bioprocesses if active microorganisms are present. Bioprocesses for
useful products probably were rarely continuous because contamination is likely
when there are no precautions against entry of foreign organisms. Until the
discoveries of Louis Pasteur, it was not appreciated that microorganisms were
the causes of disease and spoilage. Ways of keeping feed streams to a bioprocess uncontaminated
were not developed. Until the times of Semmelweiss, surgeons did not even
wash their hands before moving to the next patient. Supperation and puss
while recovering from an incision were considered normal.
In very early times, waste treatment was
continuous. However, the main processes were dumping wastes on land or into
natural waters. Biological waste treatment in channels or vessels is roughly
100 years old and is predominantly continuous because the wastes keep coming.
The concept of continuous culture dates
from the 19th Century when a continuous process for the conversion of waste
beers and wines to vinegar was developed. In this reactor, natural acetic acid
bacterial populations were immobilized on wood shavings. Beer or wine was added
through the top of the reactor and allowed to trickle through the shavings.
Vinegar was collected at an outlet located at the base of the reactor.
The acetic acid discourages
contamination at conditions where the acetobacter thrive.
The chemostat invented in the early 1940's
marked the advent of serious continuous fermentation. The use of continuous
stirred tank reactor to extend duration of culture of microbes was developed in
the 1950s by Novick and Szilard and
Monod. The realization
that a CSTR could be used to maintain microbial growth at a steady state value,
that could be varied from any growth rate up to the maximum µmax,
was an important advance; it broke the traditional thinking at the time that
stable microbial growth was only possible at the maximum rate, corresponding to
the minimum doubling time found in batch cultures. Subsequently, the use of a
well-mixed continuous reactor to study microbial physiology led to important
advances in understanding the cell cycle, metabolic regulation and microbial
product formation.
Go with the flow
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