ABOUT FILTER

The primary purpose of using a filter is to remove impurities from fluids or air. It is a device which usually contains a membrane or layer which is designed in such a manner so that it obstructs the impurities from passing through. The membrane or layers used in the filter are semi-permeable barriers placed perpendicular to the liquid or air-flow. In laboratories the commonly used material for membrane is the filter paper.

Filtration is the process of filtering. It is done by passing the mixture through the filter. The liquid obtained after filtration is known as the filtrate, while the solid left behind in the filter is called the residue, retentate or filtrand. The methods of filtration are various; however, all of the methods endeavor separation of substances. The substance which is to be passed through a filter has to be necessarily a fluid, i.e. a liquid or gas. The methods are different dependent upon whether the material to be filtered is in the fluid phase or not.

Filter is classified in two types - surface filter and depth filter. A surface filter consists of a solid sieve with or without a filter paper which impedes the solid substances from passing through. Examples of surface filter are B¨ąchner funnel, Belt press, Rotary vacuum-drum filter, Crossflow filters. A depth filter on the other hand consists of a bed of granular material which hinders the passage of the solid particles. The former allows the residue to be collected intact while the latter does not.

Filtration systems are used in various industries. To name a few, they are used in Chemical & Petrochemical Processing, Pharmaceutical, Cosmetic and Biotechnology Processing, Water Treatment, Purification & Reclamation, Food, Beverage & Fermentation, etc. The scope and purpose of the filtration systems vary in accordance to the substance which is to be filtered. Oil filtration systems are usually used in automobiles and hydraulic machinery. Air filtration systems are used majorly to clean polluted air in automobiles, buildings as well as aircrafts. Water filtration systems are majorly used to purify water for drinking or other purposes. Filtration systems are also used for waste management.

Filtration is a majorly used process. For example, a coffee filter is used to separate the coffee from the grounds, HEPA filters present in air-conditioning remove particles from air, belt filters separate precious metals in mining, B¨ąchner funnels along with filter papers used in chemical laboratories.