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Theoretical Principles of Reverse Osmosis Historical Background and Scientific

The natural osmosis or direct is known, as we have seen, since antiquity, and consists in the dissolution of a solvent (usually water) and a solute consisting of one or more chemicals (salts ) in solution.

If we put to one side of a membrane and pure water across water with mineral salts, pure water will pass to the side of water with salt until balance pressures, gauge the height difference between the two levels is what is known as osmotic pressure solution.

Someone who does not know the phenomenon of osmosis and casually observed this phenomenon in an experimental team, the first thing you will notice is that the way that contradicts common sense occurs because the osmotic flow occurs precisely in the opposite direction to that expected by comparison with hydrodynamic systems.


If we have a system of communicating vessels separated by a porous barrier will be able to make a prediction of the direction of flow of fluid between the vessels. Elapse in the direction of the vessel with the highest level to lowest vessel to reach equilibrium. Similar would happen with a system that we put together two different levels of heat, the heat flow would be more at least until the balance .

But if that same experience changes in one cup water water with sugar, ie for a solution, something amazing happens, even though the water level alone is less than that of other glass will flow from the water only made the sugar water, reaching a difference levels that will stop the flow. That difference is the level that will measure the osmotic pressure .

This is the natural phenomenon of osmosis . The theory allowed to consider what would happen if you increase the pressure side with salt water ( brackish), since if the reverse occurred, ie clean water passing salt to the other side (in the contained in the A to B) we would have a system to remove salt-laden water of the same or for concentrating a solute that we specify.



So if we apply an external pressure greater than its natural osmotic pressure , the concentrated solution flowing solvent and a concentration of solutes (salts), and therefore able to reduce the a water salinity.

The osmotic pressure to be overcome depends on the type of solute and its concentration, as we shall see, but we can say that the range of pressures be between 5 and 60 bar 5 and 60 Kg/cm2   lbf/in2 71 and 851.

The phenomenon contrary to the natural osmosis is what is known as REVERSE OSMOSIS .

This system can perform separation processes and / or concentration. Applied to water, allows the separation of 95% of dissolved salts, thereby reducing we salinity of brackish and sea .