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.
diagram of a Reverse Osmosis Desalination Plant
Reverse osmosis is now used in medicine and industry
as a means of purifying or separating water and other solvents
from other components. In recent years, it has been used increasingly
for making pure water for dialysis in hospitals and for producing
Water for Injection.
Reverse Osmosis: A Scientific Explanation
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%.
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
Quality of Reverse Osmosis Product
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. The video below shows a Reverse
Osmosis Electrolysis Demonstation.
1. Gregor, H.P.,
and Gregor, C.D., "Synthetic Membrane Technology," Scientific
American, July, 1978.
2. Sourirajan, S., Reverse Osmosis, Logos Press, London; Academic Press, New
York, N.Y., 1970.
3. Karger, Barry L. et al. An Introduction to Separation Science. New York: Wiley,
4. Londale, H. and Podall, T., Ed. Reverse Osmosis Membrane Research. New York:
Plenum Press, 1972.
5. Elias, S., "Membrane Processing," Food Engineering. Oct. 1979.
6. Lacey, R. E., "Membrane Separation Process," Chem. Eng., Sept. 1972.
7. Datta, R. et al. "Concentration of Antibiotics by Reverse Osmosis," Biotechnology
and Bioengineering XIX, 1419-1429, 1977.
8. Favero, M. S., Peterson, N. J., et al. "Gram-Negative Water Bacteria
in Hemodialysis Systems," Health Laboratory Science, Vol. 12. No. 4. 1975.
9. Klumb, G. H., "Reverse Osmosis - A Process in the Purification of Water
for Parenteral Administration," Bulletin of the Parenteral Drug Association,
Vol. 29. No. 5. 1975.
10. Frith, C. F., Dawson, F. W. and Sampson, R. L., "Water for Injection
USP XIX By Reverse Osmosis," Bulletin of the Parenteral Drug Association,
Vol. 30, No. 2, 1976.
11. Hoag, Selwyn B. and William F. Albern. "Reverse Osmosis: The Economical
Production of Quality Water," Plumbing Engineer, May-June, 1977.
12. Juberg, Donald L. "Application of Reverse Osmosis for the Generation
of Water for Injection," Bulletin of the Parenteral Drug Association 31:
70-78, March-April, 1977.
13. Belfort, G., Rotem, Y., and Katzenelson, E., "Virus Concentration Using
Hollow Fiber Membranes," Water Research, Vol. 9, 1975.
14. Osol, Arthur, Ed. Remington's Pharmaceutical Sciences, 16th Edition, Easton,
Penn: Mack, 1980.
15. Peterson, N. J., et al. Quarterly Reports, April-June, 1976, July-Sept. 1977.
HHS, PHS, CDC, Phoenix, Lab. Div., Phoenix, Arizona.
The information in this section is based on
Technical Guide of the Food and Drug Administration
(FDA) in the USA.
End of Article
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
What Is Reverse Osmosis and How Does It Work?
An examination of the process of reverse osmosis by Freshly