Process

Reverse Osmosis Process Principle

November 18, 2020

Today we will talk about the Process which is almost at everyone’s house. It is our daily need. We are talking about Reverse Osmosis also known as RO system. Today in whole world everyone is using RO purifier for water purification. We are also using the RO system in the industry to purifier different solutions. Before talking about the RO in detail let’s understand different terminologies.

Semi Permeable Membrane:

It is a selective barrier that allows some molecules to pass through it while stops others.

Osmosis:

It is a process where a less concentrated solution passes through a semi-permeable membrane to a more concentrated solution.

Reverse Osmosis:

It is an exact opposite process than Osmosis where more solvent from the more concentrated solution will pass to dilute solution through a semi-permeable membrane.

Osmotic pressure:

It is a pressure that stops the flow of dilute solution to concentrated solution through a semi-permeable membrane.

To purify the water we need to remove salts and ions from concentrated water. For that, we need a particular setup which is shown in the figure at top.

Here, we are using a membrane to separate solvent and solutes. On one side we are putting pure solvent and on another side, we are putting a concentrated solution. Naturally, the pure solvent will flow towards the concentrated solution to equalize the concentration on both sides. If we apply pressure on a concentrated solution higher than its osmotic pressure then the pure solvent will flow in the opposite direction which is from the concentrated solution to pure solvent by leaving ions, salts, and other impurities on the same side because it can’t pass through the membrane.

Membrane selection is very crucial in the RO purifier. Let’s understand it with an example. Many porous membranes are available to purify water. Cellulose acetate is a very efficient membrane for water purification. The membrane of cellulose acetate with 40% acetyl removes 95-98% of salts at 50-90 atm pressure but the only drawback is water flux is very low. To increase salt rejection efficiency we can increase acetyl content but it will reduce water flux drastically. Then the new membrane is discovered which is asymmetric cellulose acetate of thickness 1 micrometer.

Advantages of Reverse Osmosis Process:

It has a very compact design so we can fit it anywhere.
It removes not only salts but also removes minerals, bacteria, viruses, and metal particles.
The life of the membrane is more than 1.5 years.
Parts are replaceable and easily available.
It is efficient at atmospheric temperature only.

Disadvantages of Reverse Osmosis Process:

It removes all the minerals so it will cause bone problems if we drink RO water for a long time.
It also removes beneficial minerals.
It rejects a high quantity of wastewater.
Need to replace filter after periodic time.

Reference:- waterontop, fda.gov, byjus