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Introduction to Drinking Water Through Reverse Osmosis
The reverse osmosis process was developed in the late 1950's and is the latest major technology in water purification. It is considered to be one of the great discoveries of our century.
The real claim to fame for the reverse osmosis process is its ability to remove a very wide spectrum of impurities from water, using no chemicals and very little energy.
With the exception of distillation, reverse osmosis is the only known process which can remove all the following classifications of impurities:
• Particulate matter • Colloidal matter • Dissolved mineral salts • Organic molecules • Bacteria • Viruses • Pyrogen
What is Reverse Osmosis?
In the reverse osmosis process, water is forced by pressure against a very special plastic material called semi permeable membrane (which looks a little like thick Saran Wrap). The unique properties of this membrane allow water molecules to pass through while the dissolved mineral salts or total dissolved solids (TDS) and virtually all particulate matter, even viruses, are left behind.
The dissolved impurities (TDS), such as the mineral salts, are actually repelled from the surface of the membrane. The rejection of other classes of impurities such as sediment, bacteria, and organics is achieved through a mechanical straining action. To appreciate the fineness of this "strainer", note that its pores are on the order of about .00000001 inches, or one one-hundred-millionth of an inch!
In practice, if we continued to apply pressure to separate our pure water molecules though the membrane, the dissolved impurities would become so concentrated they would come out of the solution and "foul" the membrane surface. Therefore, a mechanism must be provided for continuously carrying away the impurities left behind at the membrane surface. This is the so-called "reject" water that must be sacrificed to make pure or "product" water. The percentage of pure or "product" water separated out of the total water used (product plus reject) is known as the "recovery". The degree of recovery, in addition to how well impurities are "rejected", is governed by the factors relating to the chemistry of the particular water being purified and the type of equipment used. |
