ABSTRACT
Precoat filtration depends upon the flow of liquid through cake and factors influencing this rate of movement. A thin layer of filter aid is built up on filter septum by recirculating filter aid slurry. This slurry is composed of water and filter aids, but may also contain cellulose fiber to give stability to precoat cake (mainly when the septum is wire mesh stainless steel cloth). The major advantages of using a precoat are the following: to protect the filter cloth, to give immediate clarity when filtering, and to improve cake removal and cake washing. The grade of filter aid selected will offer the appropriate performance with respect to clarity and flow characteristics. Particles as small as 0.2 µm can be removed by precoat filtration. When a soluble contaminant is present, it must be precipitated prior to filtration; and, where colloidal matter or dispersed particles are present, precoat filtration alone may not be adequate to reduce the turbidity to desired level.
