It is passage of gases or liquids via a screen like materials with pores size small enough to retain mos. Generally, filtration decontaminate heat sensitive liquids or gases like beverages,intravenous solution, bacteriological media, serum etc. Filtration removes mos rather than destroying them. Effectiveness of filter proportional to size of the pores. However, other factors like electric charge of filter, charge of organisms & nature of fluids can influence the efficacy of filtration.


  1. Inorganic Filter: It consists of pad of procleain or ground glass mounted in filter flask. It is used in sterilization of serum during media preparation.  Eg: Seitz Filter  
  2. Organic Filter: It consists of organic molecules or filter that attracts the organic component of mos. It has large pores. Breke field filter which uses a substance called diatomaceous earth. It is used in swimming pool.  

3. Membrane Filter: It consists of pores of uniform or specific predetermines size. The pores size ranges from 0.01 to 10 micrometer( 0.45 micrometer is the most commonly used to recure common bacteria  but not virus) They are composed of inert cellulose acetate or poly carbonate. This filters are used in lab & industries for sterilization of fluids. In Microbiology lab, it is used for isolation, enumeration & identification of bacteria from water sample.

4) High Efficacy Particulate Air: It is used to filter air & remove mos. It can remove 99% of all air particles including mos diameter than 0.3 micrometer. HEPA filter are used with laminar flow to produce dust & bacterial free air.Similarly, they are used to treat air entering surgical units, pharmaceutical  fillings rooms.


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