Seabirds use reverse osmosis to desalinate seawater. They possess a membrane in their throats which allows water molecules to get through and stops the salt. This enables them to drink fresh, unsalted water, and they spit out the salty waste.

Reverse Osmosis and Humans

Humans worked out how to copy this process around 40 years ago for the same reason - to desalinate seawater.

Schematic diagram of a Reverse Osmosis Desalination Plant

Reverse osmosis is a complicated process which uses a membrane under pressure to separate relatively pure water (or other solvent) from a less pure solution. When two aqueous solutions of different concentrations are separated by a semi-permeable membrane, water passes through the membrane in the direction of the more concentrated solution as a result of osmotic pressure. If enough counter pressure is applied to the concentrated solution to overcome the osmotic pressure, the flow of water will be reversed.

Water molecules can form hydrogen bonds in the reverse osmosis membrane and fit into the membrane matrix. The water molecules that enter the membrane by hydrogen bonding can be pushed through under pressure. Most organic substances with a molecular weight over 100 are sieved out, i.e., oils, pyrogens and particulates including bacteria and viruses.

Salt ions, on the other hand, are rejected by a mechanism related to the valence of the ion. Ions are repelled by dielectric interactions; ions with higher charges are repelled to a greater distance from the membrane surface. The nominal rejection ratio of common ionic salts is 85 - 98%.

Membrane

The majority of the commercially manufactured Reverse O smosis (RO) membranes are usually made from cellulose acetate, polysulfonate, and polyamide. The membrane consists of a skin about 0.25 microns and a support layer about 100 microns. The skin is the active barrier and primarily allows water to pass through.

Quality of Reverse Osmosis Product Water

The amount of dissolved solids in water produced by reverse osmosis is approximately a constant percentage of those in the feed water. For example, when the feed water contains 300 ppm total dissolved solids (TDS), the product water may have 15 to 30 ppm (95% and 90% rejection ratio respectively). A RO system design is based on a certain range of feed water TDS, the percentage of rejection and percentage of recovery desired. For a given system, the higher the percentage of recovery or the lower the percentage of rejection, the poorer the quality of product water becomes (click HERE to view Reverse Osmosis Electrolysis Demonstation).

For more information on the Freshly Squeezed Water Reverse Osmosis System, click here or see our full range of water systems here.

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Remember...

Freshly Squeezed Water offers superb Reverse Osmosis Filtration Systems with a number of different financial options to make our system affordable for all. You can find more information on our Reverse Osmosis Water systems throughout this site.