What is Reverse Osmosis Process?

The ocean contains about 96.5% of all the water on the planet Earth. However, the water found in the oceans contains salts, making it unfit for human use. This is where reverse osmosis technology offers a way to achieve the desalination of seawater.

What is Reverse Osmosis?

But what is Reverse Osmosis? It is a process wherein a pressure greater than the osmotic pressure is added on the solution side of the semipermeable membrane (abbreviated to SPM) to cause the pure solvent to pass through the semipermeable membrane and gather in a separate area.

Osmosis

To understand what is reverse osmosis, it is important to first understand what osmosis is. Osmosis is the movement of the molecules of the solvent from an area where the concentration of the solute is low, through a semipermeable membrane, to an area where the concentration of solute is high.

The process of osmosis can be halted by applying some amount of pressure at the solution side of the semipermeable membrane. This minimum pressure required to halt the process of osmosis is called osmotic pressure.

Osmotic pressure can also be used to measure the tendency of solvents to pass through the SPM to the region of higher solute concentration via osmosis. An illustration of the process of osmosis is given below.
Osmosis Illustration with semipermeable membrane

Process of Reverse Osmosis

Now that the process of osmosis is understood, the question – What is Reverse Osmosis? can be answered in a simple and clear manner. As discussed above, Osmotic pressure is the minimum pressure which must be applied to stop the flow of the solvent through the semipermeable membrane.

Now, when a pressure greater than the osmotic pressure is applied on the solution side ( the side where the concentration of solute is high), the solvent particles on the solution side pass through the semipermeable membrane to the area where the concentration of solute is low. This reversed flow of the solvent through the SPM is called reverse osmosis.

An illustration of the process of reverse osmosis is shown below. Note that the pressure applied on the solution side must be higher than the osmotic pressure for the reverse osmosis process to proceed.

Reverse Osmosis Process- Illustration

What is Reverse Osmosis? (Illustration)

It can be observed from the illustration given above that the process of reverse osmosis and osmosis are entirely dependent on whether the pressure applied is greater than the osmotic pressure.

Osmotic pressure is a colligative property and it is reliant on the solution concentration. The reverse osmosis process is very important in the purification of water. Many water purifiers used today include reverse osmosis as one of the steps in the purification process.

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