Filtration is a method of separating solid impurities from liquid by allowing the liquid to pass through a filter, which usually consists in a porous material such as cotton wool, cloth, paper, glass wool or asbestos. The filter traps solid particles, and the size of its pores or holes determines which particles pass through. Water flows through the material at a low speed.
The filter permits water to pass while retaining most solid matter. The process of filtration is typically done repeatedly to ensure that unwanted particles are removed from the water. The method of filtering water through a granular bed is called slow sand filtration. This is the oldest filtration method, but it is still commonly used in municipal water treatment plants today.
In modern filtration systems, a multimedia filter is used. The filter’s primary constituent material is carbon, which forms a solid block unlike the loosely structured sand filters. Aside from solid carbon, the water filter also includes other media substances. It cleans water through chemical and physical processes. Chemically, the multimedia filter performs adsorption, in which the carbon’s atomic charge causes the particles to abandon their bond with the water and attach chemically to the filter. Physically, the filter blocks unwanted particles through its molecular structures that are bigger than water. In organic chemistry laboratories, suction filtration and gravity filtration are widely used.