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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/de-mineralizing
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 "desiccates" 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 (you
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Page last
updated February 27, 2003 |
