Reverse Osmosis Systems (RO)

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Reverse osmosis (RO) is a membrane separation process in which feed water flows along the membrane surface under pressure. Purified water permeates the membrane and is collected, while the concentrated water, containing dissolved and undissolved material that does not flow through the membrane, is discharged to the drain.

The key requirements of Reverse Osmosis (RO) process are a membrane and water under a pressure. Other requirements include pre-filtration to remove suspended impurities and carbon to remove chlorine (damages the membrane).

Most membranes remove 90-99+ % of the dissolved impurities depending on the impurity and the composition of water.

Reverse osmosis systems (RO Systems) remove salts, microorganisms and many high molecular weight organics. System capacity depends on the water temperature, total dissolved solids in feed water, operating pressure and the overall recovery of the system.

Osmosis can be defined as the spontaneous passage of a liquid from a dilute to a more concentrated solution across an ideal semipermeable membrane which allows the passage of the solvent (water) but not the dissolved solids (solutes). (See Fig. 1.) The transfer of the water from one side of the membrane to the other continues until the head or pressure (P) is large enough to prevent any net transfer of the solvent (water) to the more concentrated solution. At equilibrium, the quantity of water passing in either direction is equal, and the pressure (P) is then defined as the osmotic pressure of the solution having that particular concentration of dissolved solids.

If a piston is placed on the more-concentrated solution side of a semipermeable membrane (see Fig. 2) and a pressure, P, is applied to the solution, the following conditions can be realized: (1) P is less than the osmotic pressure of the solution and the solvent still flows spontaneously toward the more concentrated solution; (2) P equals the osmotic pressure of the solution and solvent flows at the same rate in both directions, i.e., no net change in water levels; (3) P is greater than the osmotic pressure of the solution and solvent flows from the more concentrated solution to the "pure" solvent side of the membrane. Condition (3) shown in Fig. II-2, represents the phenomenon of reverse osmosis.


Envirotech specializes in the supply of reverse osmosis systems for desalination, industrial water reuse, electronics manufacturers, potable water supplies and for food and beverage industries. Our packaged RO units can supply from several cubic meters per day to several hundred cubic meters per day.