Difference Between Osmosis and Reverse Osmosis

The key difference between osmosis and reverse osmosis is that osmosis is a natural process in which water molecules pass along the concentration gradient while reverse osmosis is a procedure of water purification process that passes water molecules against the concentration gradient across a semi-permeable membrane.

The concept of osmosis is significant as it helps to maintain the osmotic pressure inside both animal and plant cells. Hence, osmosis is the net movement of water from one side of a semi-permeable membrane to the other side due to the difference in the solute concentration between the two sides. This diffusion of water is through a selectively semi-permeable membrane allows passage of water but stops passage of other molecules that are either large or are ions. Moreover, there is another related concept of osmosis called reverse osmosis that employs in water purification process in order to make water pure. This article will explain the difference between osmosis and reverse osmosis in detail.

CONTENTS

1. Overview and Key Difference
2. What is Osmosis
3. What is Reverse Osmosis
4. Similarities Between Osmosis and Reverse Osmosis
5. Side by Side Comparison – Osmosis vs Reverse Osmosis in Tabular Form
6. Summary

What is Osmosis?

Osmosis is a natural phenomenon taking place regularly in all living beings. It refers to the movement of water molecules from a higher water potential area to lower water potential area through a semi-permeable membrane. Since osmosis occurs along the concentration gradient, it does not use energy. Hence, it is a passive process.

Osmosis is the primary process that facilitates the water movements of cells via the cell membrane in both plant and animal cells. Since the cell membrane is a selectively permeable membrane, it allows selected molecules to pass through it. Therefore, only via osmosis, water molecules and solvent molecules transport in and out the cell in order to balance the solute concentration inside and the outside the cell.

What is Reverse Osmosis?

Reverse osmosis is a process applied in desalination of water or purification of water. As the name implies, it is the process of osmosis in the reverse direction. A pressure that is greater than the natural osmotic pressure is applied to water and pushes water to pass through a semi-permeable membrane against the concentration gradient. Consequently, water molecules move through a reverse osmosis membrane from low water potential to higher water potential. Other molecules such as dissolved salts, organics, bacteria and pyrogens will not pass through the membrane. Hence, reverse osmosis facilitates the filtering of water in water purification processes.  Unlike osmosis, reverse osmosis needs an energy input for the application of pressure on water.

Reverse osmosis is a useful process in water purification especially in the desalination of water. It provides several advantages in water purification. Compared to other water purifying procedures, it is a cost-effective procedure. Furthermore, reverse osmosis can filter out almost all the particles including ions and heavy metals. Most importantly, it is capable of eliminating radioactive particles from water samples. Therefore, since this process prevents entering of microorganisms, dissolved salts and other harmful substances to pass through the membrane, it provides safe drinking water for the public, which does not affect the health negatively.

Another advantage of reverse osmosis is that the chemical use is very less in reverse osmosis. Hence, it does not cause health problems. Other than in water purification, principal of reverse osmosis is applied in refrigeration, brewing of water, sterilization applications on hospitals, in clinical analysis, etc.

What are the Similarities Between Osmosis and Reverse Osmosis?

• Osmosis and reverse osmosis occur via a semi permeable membrane.
• In both processes, mainly water molecules move across the membrane.
• Also, both processes do not allow solute particles to cross the membrane.
• Furthermore, the osmotic pressure affects both processes.

What is the Difference Between Osmosis and Reverse Osmosis?

Both osmosis and reverse osmosis are phenomena that refer to the movements of water molecules across a semi-permeable membrane. However, osmosis occurs along the concentration gradient passively while the reverse osmosis occurs against the concentration gradient actively with the consumption of energy. Thus, this is the key difference between osmosis and reverse osmosis. Furthermore, in osmosis, natural osmotic pressure affects the process while in the reverse osmosis, a pressure greater than the natural osmotic pressure is applied in order to pass water molecules against the concentration gradient. Therefore, this is also a significant difference between osmosis and reverse osmosis.

Furthermore, one other difference between osmosis and reverse osmosis is that, unlike osmosis, reverse osmosis requires energy to supply pressure. The below infographic provides more information on the difference between osmosis and reverse osmosis.

Summary – Osmosis vs Reverse Osmosis

Both osmosis and reverse osmosis are essential processes. Osmosis is a naturally occurring process in cells. It describes the movements of water across the cell membrane along the concentration gradient. Reverse osmosis is an osmosis related process. Many industrial processes including water purification employ this process. However, reverse osmosis occurs in the opposite direction of the osmosis against the concentration gradient. Hence, this is the key difference between osmosis and reverse osmosis.

Reference:

1.“What Is Reverse Osmosis?” Puretec Industrial Water | What Is Reverse Osmosis?. Available here

Image Courtesy:

1.”Osmosis diagram”By KDS4444 – Own work, (CC0) via Commons Wikimedia  
2.”A 1000 liter reverse osmosis plant for commercial use”By Vishalsh521 – Own work, (CC BY-SA 3.0) via Commons Wikimedia