Reverse Osmosis (RO)

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. But what is Reverse Osmosis?

What is the Process Behind 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

Osmosis Illustration with a 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 that 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.

Reverse Osmosis Applications

Reverse osmosis can be used in virtually any application where the presence of the impurities in water will cause problems. Several examples are drinking water, production, process equipment boilers, precise analytical or testing procedures etc. Examples of industries that have a demonstrated need for high quality follow.

  • Electronics – Manufacturers of electronic components require the highest quality water available. Reverse osmosis is frequently used to remove most of the impurities in a water supply prior to its introduction into a polishing ion exchange system. Reverse osmosis extends the life of the ion exchange beds and reduces the total cost of producing large volumes of high purity water.
  • Chemicals – The manufacturer of chemicals requires varying qualities of water, depending on the nature of the chemical production process involved. Reverse osmosis water alone will produce a suitable product water in some cases and it is used as pre-treatment when higher qualities are necessary.
  • Electroplating – Reverse osmosis has been successfully applied in this industry, not only to purify water for use in the plating solution makeup water and drag out baths, but also to concentrate valuable plating metals in the waste stream for recycling in a closed loop operation.
  • Drinking water – Reverse osmosis is used extensively in desalting sea or brackish water for potable use, both of a small and a large scale. The process requires relative low energy and therefore is particularly attractive in this application.

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Frequently Asked Questions – FAQs

How pure is reverse osmosis water?

Reverse Osmosis (RO) is often used to partially clean-up tap water to make it roughly 90 percent to 99 percent pure. This method is called Reverse Osmosis and is usually capable of eliminating 90-99 percent of most pollutants. It’s not perfect but it’s a very cost-effective technology; if used properly, the RO Membrane will last for years.

What is the process of reverse osmosis?

Reverse osmosis (RO) is a water purification process that removes ions, unwanted molecules and larger particles from drinking water using a partially permeable membrane. Reverse osmosis is thus the application of an external pressure to reverse the natural flow of pure solvent.

What are the advantages of reverse osmosis?

One benefit of reverse osmosis is the ability to effectively extract several dissolved substances, and provide a strong degustation of finished water. Another benefit is that RO will not add any other chemicals to your water. The dissolved substances are merely separated from the incoming water.

What contaminants does a reverse osmosis remove?

Reverse osmosis systems will eliminate common chemical contaminants (metal ions, aqueous salts), including sodium, chloride, copper, chromium, and lead; may reduce arsenic, fluoride, radium, sulphate, calcium, magnesium, potassium, nitrate, and phosphorous.

What is the purpose of reverse osmosis?

Reverse osmosis (RO) is a water purification process that removes ions, unwanted molecules and larger particles from drinking water using a partially permeable membrane. As a result, the solute is kept on the membrane’s pressurized side and the pure solvent is allowed to pass to the other side.

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