Reverse
Osmosis
Reverse osmosis is a separation process
that uses pressure to force a solvent through a membrane
that retains the solute on one side and allows the pure
solvent to pass to the other side, meaning it allows
the passage of solvent but not of solute. In reverse
osmosis, the idea is to use the membrane to act like
an extremely fine filter to create drinkable water from
salty water.
The membranes used for reverse osmosis
have a dense barrier layer in the polymer matrix where
most separation occurs. In most cases the membrane is
designed to allow only water to pass through this dense
layer while preventing the passage of solutes (such
as salt ions). This process requires that a high pressure
be exerted on the high concentration side of the membrane,
usually 30-250 psi for fresh and brackish water, and
600-1000 psi for seawater.
Reverse osmosis (RO) is used to reduce
dissolved solids from feed waters. Municipalities and
industrial facilities are able to use RO permeate as
a consistently pure drinking water supply and to transform
drinking water to high purity water for industrial use
at microelectronics, food and beverage, power, pharmaceutical
facilities, and can be used for removing bacteria, pyrogens,
and organic contaminants.
RO systems are also now extensively used
by marine aquarium enthusiasts, as the domestic water
supply contains substances that are extremely toxic
to most species of saltwater fish. In the production
of bottled mineral water, the water passes through a
RO water processor to remove pollutants and microorganisms,
including the smallest microbe known, archaeobacteria.
In the United States, house hold drinking
water purification systems, including a reverse osmosis
step, are commonly used for improving water for drinking
and cooking.
