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Reverse Osmosis

Osmosis is the movement of a solvent from an area of low solute concentration to one of high solute concentration, provided that pressure and temperatures of both areas are equivalent; in this manner, the two differently-concentrate solutions reach equilibrium. Reverse osmosis, on the other hand, is a method for purifying that solvent by forcing it through a filter that traps the solute on one side, with the purified solvent coming through.

In most, but not all, cases, reverse osmosis requires the use of a semipermeable membrane that allows the solvent to pass but not the solute. These membranes typically lack pores, but have dense polymers laid out in a microscopically-thin layer. When water is being purified, it crosses the membrane through diffusion, but it must be pushed through with at least 5 MPa - 20 MPa (50 bar - 200 bar) of pressure. The pressure applied to the solution being purified must be greater than the osmotic pressure in the solution.

Reverse osmosis is valuable in desalination of ocean water, and has been applied to this end since the 1970s. Carbon filters are also used commonly to purify drinking water.

Web Resources On Reverse Osmosis

How does reverse osmosis work?
What Is Reverse Osmosis?

Book Resources On Reverse Osmosis

Reverse Osmosis and Nanofiltration by American Water Works Association
Reverse Osmosis Technology by Bipin S. Parekh (Ed)

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