AIR FILTERS IN FERMENTATION

The success of pure culture aerobic fermentation depend on the continuous supply of sterilized air to the broth. This is usually achieved by putting a filter in the air line prior to the air entry into the fermentor.

The principle of microbial exclusion by filters could either be by:
1 the membrane filter which prevents particles exceeding the pore size of the filters to enter the fermentation broth. Membrane filters are often called as absolute filters. Absolute filters are those in which the pores are smaller than the microorganisms to be removed. Thus, absolute filters are 100% efficient in removing microorganisms.
2 cartridge filters which prevent the entry of microorganisms by electrostatic adhesion of the particles to the filter media. The filter media are made up of fibrous materials such as cotton, glass, slag or steel wool. The pores in fibrous filters are larger than the particles which are to be removed in the range of 0.5 to l5µm. Removal of microorganisms is not absolute as there is always a possibility for the microorganisms to pass through the filter irrespective of the filter depth. However, fermentation industries prefer using the fibrous filters due to fermentation industries are using fibrous filters due to their cheaper costs and lower pressure drop


The filters used in the fermentor face a lot of torture and stress in carrying out its effective filtration duties because:

1 The filters are subjected to repeated sterilization at high temperature and pressure
2 The amount of air which they have to filter is simply awesome. If air is supplied at the rate of 1vvm, just imagine for a large fermentor operating over 5 days??!! And this fermentor is used in hundreds of fermentation runs! Wow!!

One of the most common mistakes made by many who use fermentors is their lack of interest to examine or follow the schedule life expectancies of fermentor components. They would not bother to check until the fermentation process is contaminated ( That is if they still realize that they are suffering from contamination!)

Filters need to be physically examined for wear and tears and especially for microbial growth. It is not surprising to see microbial growth occurring in the filters especially when filters are wet and not sterilized after a particular run. Spores easily thrive in poor sterilizing actions

The filters must always be used with the proper side maintained . Always use the same side each time. You can ensure this by marking the filter casing with a permanent marker pen

Make sure during autoclaving, filters do not get accidentally wetted by positioning the filter casing especially if it lies below the broth line of the fermentor

Ensure during autoclaving the line to the filters are properly clipped

Wet filters are bad as they will cause partial blockage of the airflow resulting in secondary problems which affect the fermentation process

The air used in the fermentor should be supplied by oil free pumps and compressors