Reverse Osmosis System - How Does Reverse Osmosis Work

Reverse osmosis is one of the most important methods used in water purification systems. It is an easy and efficient method for purifying water. The RO systems have many commercial benefits, that make them a great success in the industrial field. The osmosis process forms the base of reverse osmosis.

Osmosis is the process of the movement of any liquid from an area of low concentration to an area of higher concentration of that solution, through a permeable or semi-permeable membrane. No external force is applied to bring about the process of osmosis. It is split into two types - forward osmosis and reverse osmosis.

• Solution: The solute and solvent together form the solution.
• Solute: It is the substance that is dissolved in the solution.
• Solvent: It is the liquid in which the solute is dissolved.
• Forward osmosis is the process in which a permeable or semipermeable membrane is used for separating the water from a solution, containing many dissolved solutes as impurities, by the use of osmotic pressure.
• Reverse osmosis, as the name suggests, is the opposite of the forward osmosis process. In this process, the solvent is separated from the solute by passing it through a semipermeable membrane, while applying hydraulic pressure to the solution.

Working of Reverse Osmosis (RO)

In reverse osmosis, the solvent is made to move from the area of high solute concentration to the area of low solute concentration, by the application of external pressure. Generally, any solution that has less amount of solute, flows freely as compared to the solution containing a high amount of solute. It is because high amount of solute saturates the solution and causes it to become stagnant by reducing its potential. When separated by a semipermeable membrane, the solution containing less of solute will flow to the side of the solution containing more solute. This is known as the osmotic effect. In forward osmosis, the solute and solvent are separated by allowing the solvent to flow under the osmotic pressure influence whereas, this influence is suppressed in the reverse osmosis process. The solvent present on the side with higher solute concentration is forced to pass through the membrane to the side with lower solute concentration. The external pressure that has to be applied for the execution of this process, is higher than the osmotic pressure.

The permeable or semipermeable membrane, used in the reverse osmosis process, plays a very important role. It should be designed such that it allows only the solvent i.e. liquid molecules to pass through. Two types of membranes can be used :

• CTA membrane (Cellulose Triacetate): It is specially useful in the removal of chlorine from water. Hence, it is used widely in commercial water filters to purify tap water.
• TFC membrane (Thin Film Composite): It is highly resistant to bacteria and has to be used in combination with carbon filters, if the water to be purified is chlorinated.

Advantages of Reverse Osmosis

• Bacteria, viruses, metals, salts, etc. can be removed efficiently by the RO process.
• Reverse osmosis improves the taste of water by removing the excess salts like potassium and sodium from it.
• One of the main advantages of reverse osmosis is, that it eliminates the traces of chlorine from tap water.

Disadvantages of Reverse Osmosis

• Large amount of water is wasted during purification.
• It is considered to be more expensive as compared to other methods like UV filtration, etc.
• It is a slow process
• It removes the useful minerals from water.
• It cannot block pesticides, herbicides, chlorine and other harmful elements hence, a carbon filter also has to be used in the system.
Benefits of Reverse Osmosis (RO) Systems
• RO system requires very less energy for its working.
• It requires a very low maintenance.
• The RO system uses an automated technique called cross-flow to clean its clogged membrane.
• RO system, when used in water filters, eliminates 98% of the impurities from tap water.
• The water produced by RO technology, when supplied to a gas turbine, improves operating efficiency and increases output by more than 10%.
• RO systems are cost-effective and their price is continually decreasing.
• RO systems do not make use of harmful chemicals, hence are used in many power plants.
Many modern-day water filters use reverse osmosis technique, in combination with other techniques, to generate drinking water in its purest form. RO systems have numerous benefits and therefore, the disadvantages can be overlooked without evoking any major risks.