Principle Microbiology

(1) String discharge :- Fungal mycelia produce a fibrous filter cake which can easily be separated from the drum by string discharge.
Long lengths of string 1.5 cm apart are threaded over the drum and round two rollers.
The cake is lifted free from the upper part of the drum when the vacuum pressure is released and carried to the small rollers where it falls free.

(2) Scraper dircharge :- Yeast cells can be collected on a filter drum with a knife blade for scraper disc.
The filter cake which builds up on the drum is removed by an accurately positioned knife blade.
Because the knife is close to the drum, there may be gradual wearing of the filter cloth on the drum.

(3) Scraper discharge with precoating of the drum :- The filter cloth on the drum can be blocked by bacterial cells or mycelia of actinomycetes.
This problem is overcome by precoating the drum with a layer of filter-aid 2-10 cm thick.
The cake which builds up on the drum during operation is cut away by the knife blade.
Which mechanically advances towards the drum at a controlled slow rate.
Alternatively, the blade may be operated manually when there is an indication of ‘blinding’ which may be apparent from a reduction in the filtration rate.
In either case the cake is removed together with a very thin layer of precoat.