Chemostat

File:Chemostat.png

A chemostat. A flow of nutrient enters the chemostat. The growth of bacteria consumes some of the nutrient. In the outflow bacteria are harvested (most likely not all of the nutrient is consumed so some exits the reactor as well.)

A chemostat (from Chemical environment is static) is a device used in microbiology for growing and harvesting microbes. It consists of two primary parts: a nutrient reservoir and a growth chamber. The most important feature of a chemostat is that all fermentation parameters; growth chamber volume, dissolved oxygen, nutrient concentrations, pH, cell density, etc, remain constant throughout the experiment.

Some sources of concern are:

1. Foaming results in overflow with the volume of liquid not exactly constant
2. Some very fragile cells are ruptured when caught between the magnetic stirring bar and the glass of the vessel. Suspending the stirring bar usually corrects this fault.
3. Changing pumping rate by turning the pump on and off over short time periods may not work because cells respond to sudden changes by altering their rates. Very short intervals of on/off are alright.
4. Bacteria travel upstream quite easily. They will reach the reservoir of sterile medium quickly unless the liquid path is interrupted by an air break in which the medium falls in drops through air.

The chemostat is typically used to gather steady state data about an organism in order to generate a mathematical model relating to its metabolic processes.

Chemostats are frequently used in the industrial manufacture of ethanol. In this case, several chemostats are used in series, each maintained at decreasing sugar concentrations.

See also

• Biochemical engineering
• Continuous stirred-tank reactor (CSTR)

References

1. http://www.midgard.liu.se/~b00perst/chemostat.pdf
2. http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Contin/chemosta.htm
3. A final thesis including mathematical models of the chemostat and other bioreactors

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