Filtration

Filtration, process of separating a suspended solid, such as a precipitate, from the liquid in which it is already suspended by straining it through a porous medium that can be penetrated easily by liquids. Filtration is a basic manufacturing process in the chemical-manufacturing industry and is also employed for such diverse purposes as the brewing of coffee, the clarification of sugar syrup, and the treatment of sewage. The liquid to be filtered is called the suspension; the liquid passed by the filter is called the filtrate; and the solid material remaining on the filter is known as the residue.

Four general types of filtering media are employed in filtration processes: granular filters such as sand or crushed charcoal; felted sheet such as paper, or woven filters such as cloth and wire mesh; rigid, porous filters such as those formed when brick or clay is fired at a low temperature; and filters composed of semi-permeable, or penetrable, membranes such as animal membranes. Filters of the last-named type are employed for the separation of dispersed solids by dialysis.