Water Filters

Water Filters

A filter is a device which removes impurities from water by means of a fine physical barrier and/or chemical processes. Filters are used to cleanse water for irrigation, drinking water, aquariums, and swimming pools. Water Filters can be bought at stores to filter drinking water. Two major brands are PUR and Brita. These water filters remove things that are harmful to your health, things that can increase the chance of getting cancer, and things that taste or smell bad. The phyiscs of filters is based on sieving, ion exchanges and other processes.

Reverse Osmosis

In simple terms, reverse osmosis is the process of pushing a solution through a filter that traps the solute from one side and allows the obtainment of the pure solvent from the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute.

The membranes used for reverse osmosis have no pores, the separation takes place in a dense polymer layer of only microscopic thickness. Usually only water can cross the membrane. The water goes into solution in the polymer of which the membrane is manufactured, and crosses it by diffusion. High pressure is necessary, usually 5 MPa - 20 MPa (50 bar - 200 bar).

This process is best known for its use in desalination - removing the salt from sea water to get fresh water - since the early 1970s.

The term reverse osmosis refers to osmosis, the natural movement of solvent from a compartment of low solute concentration through a membrane to a compartment of high solute concentration if no external pressure is applied.

Desalination

Other than desalination, reverse osmosis is a more economical unit opearation for concentrating food liquids i.e. fruit juices. Researches are done on concentration of orange juice and tomato juice. Its advantages including a low operating cost and not involving heat processes, which makes it suitable for heat-labile substances like protein and enzymes.