The  desalination of sea water plant stops working due to which of the following reasons?

The pressure applied on the saline water was less than osmotic pressure.

The correct answer is option 1. The pressure applied on the saline water was less than osmotic pressure.

Let us delve into the details of how reverse osmosis works and why the applied pressure being less than the osmotic pressure can stop the desalination process.

Reverse Osmosis Process

Reverse Osmosis (RO) is a water purification process that uses a semi-permeable membrane to remove contaminants from water. The process involves:

Osmosis: Naturally, water moves through a semi-permeable membrane from an area of lower solute concentration (dilute solution) to an area of higher solute concentration (concentrated solution) to equalize solute concentrations on both sides of the membrane. This movement is driven by osmotic pressure, which is the pressure needed to prevent this natural flow.

Reverse Osmosis: In reverse osmosis, we apply external pressure to overcome the osmotic pressure. This pressure forces water from the concentrated side (high salinity) through the semi-permeable membrane to the dilute side (low salinity), leaving the salts and impurities behind. This results in purified water on one side and a concentrated brine on the other.

Key Concepts

Osmotic Pressure: This is the pressure required to prevent the flow of water through the membrane from a dilute solution to a concentrated solution. It depends on the concentration of the solute in the solution. Higher salinity increases osmotic pressure.

Applied Pressure: This is the external pressure applied to the saline water to force it through the membrane against the natural osmotic pressure. For reverse osmosis to work, the applied pressure must be greater than the osmotic pressure.

Why Applied Pressure Must Exceed Osmotic Pressure

If Applied Pressure is Less Than Osmotic Pressure:

Scenario: The natural osmotic pressure will drive water in the direction opposite to what is desired in reverse osmosis. Water will move from the dilute side to the concentrated side, attempting to equalize the solute concentrations.

Result: The water will not pass through the membrane to the dilute side. As a result, the desalination process fails because the water isn't effectively separated from the salts and contaminants.

If Applied Pressure Equals or Exceeds Osmotic Pressure:

Scenario: The external pressure applied to the saline water is sufficient to overcome the osmotic pressure.

Result: Water is forced through the membrane from the concentrated side to the dilute side, leaving behind the salts and impurities. This is the desired operation for desalination, resulting in purified water.

Importance of Proper Pressure Management

Efficiency: Ensuring the applied pressure is greater than the osmotic pressure is crucial for efficient desalination. If the applied pressure is not sufficient, the system cannot effectively remove salts and contaminants, leading to failure in producing clean water.

System Design: Desalination plants are designed to handle the osmotic pressure of the saline water they process. They use high-pressure pumps and other mechanisms to ensure that the applied pressure consistently exceeds the osmotic pressure for effective desalination.

Conclusion

In summary, for a desalination plant using reverse osmosis to function correctly, the applied pressure must be greater than the osmotic pressure of the saline water. If the applied pressure is less than the osmotic pressure, the natural osmotic flow will counteract the process, preventing effective water purification and causing the desalination plant to stop working.