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What are Fermentors?
Fermentors, also known as bioreactors, are sterilised and enclosed vessels that are used for the growth of microorganisms under optimal conditions. The microorganisms can be grown in large quantities to produce metabolites for commercial uses. Fermentors are equipped with special components for heating, mixing, and aeration. Its volume can be as big as 500,000 litres for an industrial scale, or as small as 1 litre for laboratory uses.
Different Types of Fermentors
Continuous Stirred-Tank Fermentor
The continuous stirred-tank reactor (CSTR) is composed of a vessel with pipes, pumps, valves, agitator, motor, shaft, and impeller(s). The shaft is situated at the bottom of the tank, and the number of impellers depends on the size of the bioreactor.
In this type of fermentor, a structure called sparger is found that keeps adding air to the culture medium. It is a ring-like structure with many holes. The sparger, along with the impellers, distribute gas in the entire vessel. The impellers break down the bubbles into smaller ones that are homogeneously distributed in the bioreactor.
Airlift Fermentor
The airlift bioreactors contain a baffle or a draft tube in the middle through which air is pumped into the vessel. There are two types of airlift fermentors:
- Internal loop airlift bioreactor: It has a single central draft tube that provides inner circulation channels.
- External loop airlift bioreactor: It contains external loops that separate the liquids flowing into independent channels.
Packed Bed Fermentor
In a packed bed fermentor, a hollow tube or pipe is packed with a biocatalyst. The bed is immobile in nature. The culture medium flows through the biocatalyst, which produces the metabolites continuously in the broth. These bioreactors are easy to operate but are often blocked due to poor oxygen circulation.
Read: Types of Fermentation
Fluidised Bed Fermentor
In this type of reactor, a solid granular bed that is usually made up of a biocatalyst is present. The fluid, that is, liquid or gas, is passed through the solid bed at high speeds, such that the suspended solid behaves like a fluid. This type of fermentor is used for microbial flocs, immobilised cells, and enzymes.
Membrane Fermentor
Membrane bioreactors work in conjugation with ultrafiltration and microfiltration. This type of fermentor is used for the biological treatment of wastewater. There are two types of membrane bioreactors:
- Submerged membrane bioreactor: In this type of fermentor, the membrane is found inside the vessel submerged in the wastewater.
- Side-stream membrane bioreactor: In this type of fermentor, the membrane is found outside the reactor and filtration by the membrane is an additional step in the whole process.
Bubble Column Fermentor
A bubble column fermentor is equipped with a cylindrical column that is filled with liquid, and gas is inserted into it from the bottom. It is vertically arranged, such that the introduction of gas from the bottom creates a turbulent stream and allows optimum gas exchange. The sparger mixes the contents of the vessel. The liquid flows either in a parallel direction or in a counter-current direction.
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Also Read:
- Types of Fermentation: Definition, Process, and Advantages
- Alcoholic Fermentation – Definition, Location and Equation
- Difference between Batch and Continuous Fermentation
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