Principle Microbiology

Filters may be of two types.
(1) Batch Filters (2) Continuous Filters

Batch Filters

PLATE AND FRAME FILTERS
A plate and frame filter is a pressure filter in which the simplest form consists of plates and frames ar ranged alternately. The plates are covered with filter cloths or filter pads. The plates and frames are assembled on a horizontal framework and held together by means of a hand screw or hydraulic tam so that there is no leakage between the plates and frames which form a series of liquid-tight compartments. The slurry is fed to the filter frame through the continuous channel formed by the holes in the corners of the plates and frames. The filtrate passes through the filter cloth or pad, runs down grooves in the filter plates and is then discharged through outlet taps to a channel. Sometimes, if aseptic conditions are required, the outlets may lead directly into a pipe. The solids are retained within the frame and filtration is stopped when the frames are completely filled or when the flow of filtrate becomes uneconomicaly low.
On an industrial scale the plate and frame filter is one of the cheapest filters per unit of filtering space area requires the least floor space, but it is intermittent in operation (a batch process) and there may be considerable wear of filter cloths as a result of frequent dismantling.
This type of filter is most suitable for fermentation broths with a solids content and low resistance to filtration. It is widely used as a ‘polishing’ device in breweries to filter out residual yeast cells. following initial clarification by centrifugation or rotary vacuum filtration.
It may also be used for collecting high value solids that would not justify the use of a continuous filter. Because of high labour costs and the time involved in dismantling, cleaning and reassembly, these filters should not be used when removing large quantities of worthless solids from a broth.