Reverse Osmosis (RO) , Process, Reverse, Experiment, Advantages, Disadvantages, Questions (For CBSE, ICSE, IAS, NET, NRA 2022)

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The ocean contains about 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.

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 a Semipermeable Membrane

Osmosis Illustration with a semipermeable membrane

Process of Reverse Osmosis

  • 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.
  • 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.

What is Reverse Osmosis?

  • Reverse osmosis is a membrane treatment process primarily used to separate dissolved solutes from water. Reverse osmosis is most commonly known for its use in drinking water purification particularly with regard to removing salt and other effluent materials from water molecules.
  • Reverse osmosis which is also commonly referred to as RO is a type of filtration method used for the removal of molecules and ions from a certain solution.

Reverse Osmosis Principle

  • To break down the process further, due to the presence of membrane, large molecules of the solute are not able to cross through it and they remain on the pressurized side. The pure solvent, on the other hand, is allowed to pass through the membrane.
  • When this happens the molecules of the solute start becoming concentrated on one side while the other side of the membrane becomes dilute. Furthermore, the levels of solutions also change to some degree.
  • In essence, reverse osmosis takes place when the solvent passes through the membrane against the concentration gradient. It basically moves from a lower to a higher concentration.

Experiment

The reverse osmosis process is explained below with the help of an experiment.

How Does Reverse Osmosis Work?

  • An easy experiment can be conducted taking some freshwater and a concentrated aqueous solution. The solutions should be kept on opposite sides with a semipermeable membrane placed in between to separate the two solutions.
  • Pressure should be applied on the side with the concentrated solution. Now this will result in water molecules moving through the membrane to the freshwater side. This basically sums up the process of reverse osmosis.
Reverse Osmosis Process

Reverse Osmosis Process

Benefits of Reverse Osmosis

Below we have discussed some of the benefits of reverse osmosis –

  • This process can be used to effectively remove many types of dissolved and suspended chemical particles as well as biological entities (like bacteria) from the water
  • This technique has a wide application in treating liquid wastes or discharge
  • It is used in purifying water to prevent diseases
  • It helps in the desalinating seawater
  • It is beneficial in the medical field.

Advantages of Reverse Osmosis

  • Reverse Osmosis has several advantages including the following:
  • Bacteria, viruses and pyrogen materials are rejected by the intact membrane. In this respect RO water approaches distilled water in quality.
  • Available units are relatively compact and require little space. They are well suited to home dialysis.
  • In average use, the membrane has a life of a little more than one to two years before replacement is necessary.
  • Periodic complete sterilization of the RO system with formalin or other sterilant is practical.

Disadvantages of Reverse Osmosis

The disadvantages of RO systems include the following;

  • Cellulose acetate membranes have limited pH tolerance. They degrade at temperatures greater than . They are vulnerable to bacteria. They eventually hydrolyze.
  • Polyamide membranes are intolerant of temperature greater than . They have poor tolerance for free chlorine.
  • Thin-film composites are intolerant of chlorine. High flux polysulfones require softening or deionization of feed water to function properly.

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