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Bioreactors - A bioreactor is a device in which a substrate of low value is utilized by living cells or enzymes to generate a product of higher value. Bioreactors are extensively used for food processing, fermentation, waste treatment, etc. On the basis of the agent used, bioreactors are grouped into two broad classes:

(i) those based on living cells and,
(ii) those employing enzymes.

But in terms of process requirements, they are of the following types:
(i) aerobic,
(ii) anaerobic,
(iii) solid state, and
(iv) immobilized cell bioreactors.

All bioreactors deal with heterogeneous systems having two or more phases, e.g., liquid, gas, solid. Therefore, optimal conditions for fermentation necessitate efficient transfer of mass, heat and momentum from one phase to the other.
A bioreactor should provide for the following:
(i) agitation (for mixing of cells and medium),
(ii) aeration (aerobic fermenters; for O2 supply),
(iii) regulation of factors like temperature, pH, pressure, aeration, nutrient feeding, liquid level, etc.,
(iv) sterilization and maintenance of sterility, and

(v) withdrawal of cells/medium (for continuous fermenters). Modem fermenters are usually integrated with computers for efficient process monitoring, data acquisition, etc.

The size of fermenters ranges from 1-21 laboratory fermenters to 500,000 1 or, occasionally, even more; fermenters of upto 1.2 million litres have been used. Generally, 20-25% of fermenter volume is left unfilled with medium as "head space" to allow for splashing, foaming and aeration. The fermenter design varies greatly depending on the type of fermentation for which it is used.

 
 

 

 
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