Page 291 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Reverse Osmosis
The process of reverse osmosis can remove different types of dissolved and suspended chemical species as well
as biological ones’ alike bacteria from water. This process is useful in both industrial processes and the production
of potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure
solvent is passed to the other side. In particular, this membrane does not allow large molecules or ions through
the holes. Though it allows smaller components of the solution, for instance, solvent molecules like water H2O to
pass through it freely.
In normal osmosis, the solvent naturally moves from an area of low solute concentration through a membrane, to
an area of high solute concentration. Basically, it goes from high water potential to low water potential. The driving
force for the movement of the solvent is because of the reduction in the Gibbs free energy of the system when
the difference in solvent concentration on either side of a membrane is reduced.
By reducing it generates osmotic pressure due to the solvent moving into the more concentrated solution. By
applying an external pressure to reverse the natural flow of solvent is actually reverse osmosis. The process is
similar to other membrane technology applications ever in use.
Reverse Osmosis Principle:
Reverse osmosis works by reversing the accurate principle of osmosis. The salt solution is subjected to pressure
against the semi-permeable membrane. Remember that the applied pressure is greater than the osmotic pres-
sure. Thereby, the molecules move easily from a highly concentrated solution to a less concentrated solution.

Reverse osmosis differs from filtration as if the mechanism of fluid flow is by osmosis across a membrane. The
removal process in membrane filtration is straining, or size exclusion. Here, the holes are approximately 0.01 mi-
crometres or larger. Thus, the process of osmosis can theoretically get perfect efficiency regardless of parameters
such as the solution’s pressure and solution’s concentration.
Drinking Water Purification by Reverse Osmosis:
Reverse osmosis is most commonly in use in drinking water purification from seawater, removing the salt and
other sewage materials from the water molecules.
Generally, household drinking water purification systems, including a process of reverse osmosis. It is commonly
in use for improving water for drinking and cooking.
Such systems typically include a number of steps as follows:
A sediment filter traps particles such as rust and calcium carbonate.
Optionally, it has a second sediment filter with smaller pores.
It contains an activated carbon filter to trap organic chemicals and chlorine, this will attack and degrade some
types of thin-film composite membrane.

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CITS : E & H - Electronics Mechanic - Lesson 160 - 179