Air is a critical and indispensable gas for all sorts of fermentation. It is regarded by many engineers as a process fluid. Air itself is needed for all sorts of microbial culture because microorganisms use air for metabolism, for growth and for production of metabolites and biomass.
In many cases specialised air is needed. It may be compressed fermenter air or a form which is oxygen-enriched. Such air is often needed for concentrated sparging and for blanketing fermenters. The desired level of aeration of the broth or fermentation medium is achieved by monitoring dissolved oxygen levels.
Fermented air has to be free of unwanted microorganisms which might be airborne. This would also include viruses which can severely damage a fermentation by preventing growth and development of biomass. Contamination impacts yields and wrecks product quality.
At the other end of the process is the removal of exhaust gases. This also means removal of microorganisms which could contaminate the atmosphere.
Fermenter compressed air and gas is supplied to a fermenter vessel, firstly by passing it through a conditioning unit. It then passes through a series of pre-filters and then a sterile filter usually with a valve in between each unit. The sterile air enters the fermentation vessel.
The exhaust gas is also conditioned by passing through a pre-filter and then a sterile filter.
The pre-filters are usually of 0.22 microns or greater to pick up dust and particulates. The sterile filter will be a minimum 0.22 micron in pore size.
Ingredients or product-containing storage tanks used in the fermentation or the final product areas must also be protected by tank vent filtration so that unnecessary airborne microbial contamination is avoided. It also means that the tank contents are not exposed to the environment.
An old idea but worth knowing about