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Small-scale commercial water purifying facilities and industrial-scale desalination plants commonly use multiple stages in the purification process to produce drinkable water. 

Reverse osmosis (also known as RO) is a key stage in removing salt and mineral impurities from the water. 

Continue reading to understand how reverse osmosis works, the components of the reverse osmosis system, and its applications.

How Does Reverse Osmosis Work?

Reverse osmosis is an active method of purifying water. As the name implies, it is the opposite of the passive process of osmosis. 

Graphic showing osmosis vs. reverse osmosis
Osmosis vs. reverse osmosis

In reverse osmosis, the solvent passes through a semipermeable membrane from a high concentration of solution to low concentration of solution with the application of pressure. 

This process allows solutes, such as salts and minerals, to be left behind on the other side of the membrane. This process purifies the solvent.

Key Takeaways

  • Reverse osmosis is a way of purifying water by forcing it through a semipermeable membrane

  • The water (solvent) that’s being purified flows from high concentration of solution to low concentration, leaving behind dissolved solutes like salts

  • Small-scale commercial water facilities and large-scale desalination plants use reverse osmosis

The Basic Principles of Reverse Osmosis

The basic principles of reverse osmosis involve the use of pressure to force water into a semipermeable membrane. 

The filtration membrane does not allow molecules bigger than water molecules to pass through. This leaves behind salts, minerals, and other dissolved impurities. 

As a result, the water that passes through the membrane is cleaner than the water fed into the system.

What Is The Reverse Osmosis Process?

Below is a diagram of a basic water purification system with a reverse osmosis component. 

As you can see, there are different stages of water purification. 

Graphic showing the reverse osmosis process

The water passes through pre-filters that remove sediments, chlorine taste, and odour. It is in the next stage that reverse osmosis occurs, and then the water passes through a post-carbon tube and is ready to be dispensed.

Key Components of a Reverse Osmosis System

Reverse osmosis systems may slightly vary in design and complexity, but there are few key components that allow the system to function. If one of these is absent, the system will fail. 

The main component of the system is the reverse osmosis membrane, which is housed in a pressure resistant tube. This is where the solutes or molecular/ionic impurities are separated from the water. 

The second most important component is the system’s pump that powers the flow of water and provides the necessary pressure. 

Finally, the third most important component is the storage tank where the filtered water is stored. 

ReAgent's water plant
ReAgent’s water purification system

What Are the Benefits of Reverse Osmosis?

Reverse osmosis helps ensure safe drinking water. The process is especially very useful in areas where the water source is dirty, such as an open well. 

Industrial-scale desalination plants that primarily use reverse osmosis are crucial to the economy and survival of nations that rely on seawater as their source of water.

Compared to other methods of purifying water, reverse osmosis is highly efficient in eliminating inorganic contaminants such as salts and minerals. It is excellent in removing the following harmful substances from water:

  • Sodium
  • Sulphate
  • Calcium
  • Mercury
  • Lead
  • Arsenic
  • Fluoride
  • Chloride

RO is an energy-efficient process. Considering that the system is mainly powered by an electric water pump, the heat produced is minimal and the electricity use is proportional to the amount of filtered water produced. Consequently, it is also cost-effective.

Another benefit is that the process can provide clean water on demand. This is especially true for systems designed for household use. 

For example, after a hurricane or flooding, sources of drinking water can be contaminated. You can use a reverse osmosis system by simply connecting it to your household tap.

Purification of Water

A reverse osmosis system can be used on either a small-scale or large-scale purification of water. It makes water safe to drink, and can also make water suitable for clinical purposes, such as diagnostic laboratory tests.

Removal of Contaminants

The removal of contaminants from water, particularly salts and minerals, can be accomplished in an efficient and cost-effective manner using the reverse osmosis system.

What Are The Disadvantages Of Reverse Osmosis?

The biggest disadvantage of water that has undergone reverse osmosis is the taste. Most of the minerals and ions in treated water are removed by the process. This gives water a “flat”, unpalatable taste. 

The water itself may not be very suitable for long-term drinking and large amounts of consumption because it may actually cause dehydration as the electrolytes in your cells become diluted.

Reverse Osmosis vs. Distillation

In reverse osmosis, impurities are removed through pressurised filtration. In the distillation process, impurities are removed through water evaporation, and then water condensation in a separate container.

A graphic showing the distillation process
The distillation process

Reverse Osmosis vs. Deionisation

In reverse osmosis, dissolved minerals and ions are prevented from passing through a membrane while allowing water to pass through. 

Meanwhile, in the deionisation process, ions are removed through the use of charged resin beds that attract them.

Conclusion

Reverse osmosis cannot passively occur. It requires an energy input to create water pressure that pushes the water through a semipermeable membrane. Compared to other means of water purification, reverse osmosis can be more efficient and cost-effective.

About the author

Homar Murillo

Science Writer

Homar has a Masters degree in Environmental Science & Biochemistry and five years’ experience as a chemistry teacher. His extensive experience has made him a top science and manufacturing writer for ReAgent since 2020. He is a father of three beautiful children and is currently obsessed with the youngest, baby Barbara.

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