Preparation Stages for Filtration

A number of preparation steps alluded to earlier assist in achieving optimtmi filterability. The major ones are briefly described below. 

Where particles of a colloidal nature are encountered in liquor clarification, a precoat and or filter aid are often required to prevent deposited particles from being carried 

A precoat serves only as a protective covering over the filter medium to prevent the particles from reaching the pores, while the filter aid added to the influent assists in particle separation and cake formation. Filter aids serve as obstructions, intervening between the particles to prevent their compacting, and producing, under the pressure velocity impact, a more or less impervious layer on the filter medium, or if a precoat is used, on it. 

In some instances, precoats are used, not because of danger to filter cloth clogging, but to permit the use of a coarser filter medium such as metallic cloths. This can extend operating life or improve corrosion resistance. 

Temperature has a direct impact on viscosity, which in turn affects the flowrate. It is an important factor in filtration, since lower viscosity leads to liquor penetration into smaller voids and in shorter times. Occasionally, temperature plays a role in altering the particle form or composition, and this in turn affects the clarification rate. 

---