There are two main types of filter media — a solid sieve which traps the solid particles, with or without the aid of filter paper, and a bed of granular material which retains the solid particles as it passes. The first type allows the solid particles, i.e. the residue, to be collected intact; the second type does not permit this. Also, when the solid particles are very fine, it is often cheaper and easier to discard the contaminated granules than to clean the solid sieve.
Filter media can be cleaned by rinsing with solvents or detergents. Alternatively, in engineering applications, such as swimming pool water treatment plants, they may be cleaned by backwashing.
Examples of the first type include filter paper used with a Buchner, Hirsch, filter funnel or other similar funnel. A sintered-glass funnel is often used in chemistry laboratories because it is able to trap very fine particles, while permitting the particles to be removed by a spatula.
Examples of the second type include filters at municipal and swimming pool water treatment plants, where the granular material is sand. In the laboratory, Celite or diatomaceous earth is packed in a Pasteur pipette (microscale) or loaded on top of a sintered-glass funnel to serve as the filter bed.
