Thermal Stability in Bioreactors Understanding Temperature Control in Bioreactor Systems

Author / Editor: Scott Pratt / Dr. Jörg Kempf

Microbiologists, biochemists, and chemical engineers need to cultivate organisms in a highly controlled manner. As such, bioreactors have become integral to the pharmaceutical, food, and chemical industries. In order to successfully fulfill experimental requirements, suitable conditions and parameters must be provided, which include accurate temperature control, i.e., heating and cooling.

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Bioreactors are crucial for the development of many new processes that will replace traditional chemical based products.
Bioreactors are crucial for the development of many new processes that will replace traditional chemical based products.
(Picture: Thermo Fisher Scientific)

The environmental conditions of a bioreactor, including gas flow rates, temperature, pH, dissolved oxygen levels and agitation rate all need to be closely monitored and controlled. As a vessel in which chemical processes involving organisms or biochemically active substances are carried out, bioreactors can be used for a variety of different purposes. This process is ideal for a number of application areas, with the ability to effectively grow and culture microorganisms. These include bacteria and yeast, which are used in the biotechnological production of pharmaceuticals, antibodies and vaccines, or for the bioconversion of organic waste. However, in order for such bioactivity to occur at an optimal rate, it is vital that internal conditions are highly controlled.

As one of the key variables, temperature must be tightly regulated to ensure that reliable and consistent data is obtained. This is due to the fact that a single batch can require tight temperature control and rapid ramping across a broad temperature range. Even single temperature batches can require both heating and cooling to maintain a stable and accurate temperature throughout based on the type of reaction.

The Bioreactor

A bioreactor can be classed as batch, continuous or fed-batch. In a batch bioreactor, all of the required reagents and catalysts are introduced into a closed system, whereas in a continuous system, perpetual feeding is used to maintain a steady state. As a hybrid of the batch and continuous methods, a fed-batch bioreactor is initiated as a batch, but reagent is added once the initial substrate has been consumed. As the most commonly used type of reactor, batch bioreactors are typically made from glass or stainless steel, which must be sterilized before use. Sterile culture medium is subsequently added to the bioreactor and temperatures are stabilized before inoculation with cultured cells. If combined with a filtration process, membrane fouling can have a negative impact on the overall sterility and efficiency of the bioreactor, especially the heat exchangers which are needed to keep the reaction at a consistent temperature. Biological fermentation is a highly exothermic reaction, so in most cases bioreactors need a source of refrigeration, in the form of an external jacket and/or chiller.