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What Is
Reverse Osmosis?
Reverse Osmosis, simply expressed, is a specific process which
employs the use of semi permeable membranes for the desalting/demineralizing of water.
Nature applies semi permeable membranes in many ways from the
osmosis phenomenon occurring in plants to the the various
functions in the human body. These membranes are selective in
purpose such as the lungs which separate gases from gases to the
digestive tract which separates liquids from liquids. Membrane
processes, in the generic sense, are quite broad and little
agreement exists on the actual physics involved associated with
the transport of materials through these membrane walls.
The phenomenon of osmosis was discovered in 1748 and is
described as the transport of a fluid, the solvent (such as
water), through a semi permeable membrane to a solution of higher
concentration, the solute. However, it has been only since the
late 1950's that scientists have been able to develop synthetic
membranes which can duplicate some of what nature does so well.
Out of the research has evolved the specific process known as
REVERSE OSMOSIS where the natural occurring phenomenon is
reversed by applying pressure to the fluid on the solute side of
the semi permeable membrane. The Reverse Osmosis process is also
used in systems producing high quality water for a vast range of
users; the medical community, pharmaceutical industry, electronic
manufacturers, and power utilities, to mention a few.
A well know example of OSMOSIS is illustrated in the drinking
of sea water. Salt water is consumed which increases the salt
concentrate of the fluids surrounding the body cells. Water
"transports" across the cell walls by osmosis, trying
to dilute the salt water. In doing so, the cells dehydrate and
the cell actually "dessicates" or dies from lack of
water.
Osmosis is described as the transport of a fluid (water) or
solvent in which a solute (salt) is dissolved across a semi permeable membrane from the side of lower concentration
(milligrams per liter) to the side of higher concentration. Each
and every solution has its own inherent characteristic
"osmotic pressure" dependent on the concentration of
salts in the solution. The application of a pressure higher than
the osmotic pressure applied to the opposite side forces the
solvent in the opposite direction across the membrane, i.e., from
the side of higher concentration to the side of lesser
concentration. This is called "REVERSE OSMOSIS".
The theories of water transport through membranes are many,
with little organized agreement amongst the researchers. It is
generally accepted that porosity of the membrane is very tight
with holes (if you want to call them that) of 5 to 20 angstroms
(.00000002 inches in diameter). The membranes are several mils
thick with most consisting of an asymmetric layer (active
membrane) with the balance a more porous substrate, spongy in
nature that serves as the support for the asymmetric portion.
For more information on Reverse Osmosis click here-
Water Quality
Association - What Is....Reverse Osmosis (pdf document).
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