Water covers 70% of the earth’s surface, but only 3% is freshwater. The majority is saline and ocean-based, that we can’t drink. 

Most of this freshwater is frozen, leaving only half a percent of the unfrozen water accessible for our needs. 

This limited supply of fresh water and increased global water consumption make finding clean, drinkable water challenging. This is where Desalination comes in. 

What is Desalination? It’s a process of removing salt from seawater, which has the potential to generate billions of potable water to help meet our needs. 

In the areas of severe freshwater scarcity, desalination can be a good choice. As of 2024, there are over 16,000 desalination plants in 177 countries, generating an estimated 95 million m3/day of fresh water.

Below, we’ve discussed the whole desalination process, its workings, methods, and advantages and disadvantages in detail. Let’s have a look.

How Does Desalination Work?

To solve the water crisis, it’s essential to understand how desalination works. The process includes separating salt molecules from water molecules. Every desalination method comes with a different approach.

Desalination uses two types of water: seawater and brackish water. Seawater is taken from the surface of the sea. Brackish water, which is less salty than seawater, is commonly found in aquifers.

Some methods of desalination also help remove hardness of water, making it suitable for various industrial and agricultural uses.

They are useful in providing drinkable water. Each method has its own advantages and disadvantages. The most common desalination methods are distillation and reverse osmosis. The methods can be further divided into membrane-based and thermal-based methods as shown in the image below.

Methods Of Desalination

The methods of desalination are as follows:

Thermal-based Desalination Technology

Thermal desalination involves heating salty water. The condensed steam is collected to produce pure water. The process removes dissolved salts and other impurities. Due to the high costs, thermal technology is rarely used for brackish water desalination.

They are further divided into four three groups that are as follows:

1)- Multi-Stage Flash Distillation (MSF):

 The multi-stage flash distillation process involves distillation through several multi-stage chambers. In this process, the water is heated under high pressure and led into the first chamber, where pressure is released. Generally, only a tiny percentage of feed water is converted into vapor and condensed.

2)-Multi-Effect Distillation (MED):

The multi-effect distillation process uses the principles of evaporation and condensation at reduced ambient pressure. Here, the water boils at a lower temperature as pressure decreases.

The water vapor from the initial vessel is used to heat the second vessel. The process is repeated multiple times, using the steam from the previous stage to evaporate more seawater. This method is efficient and requires less energy. The more vessels are the higher the performance ratio. Several MED plants are found overseas in the Caribbean and the Middle East.

3)- Vapor Compression Distillation (VCD):

 The vapor compression is combined with other processes, such as MED. The process comes from the compression of vapor rather than the direct exchange of heat from steam produced in the boiler. The compressed vapor then supplies the necessary heat to evaporate the remaining seawater.  The VC units are small. They are used in hotels, resorts, and industry.

4)- Wave-powered Distillation:

It does not use any electricity in the manufacturing process. It involves a series of paddles that are moved forward and backward by the waves, and the resulting energy is harnessed to filter seawater.

Membrane-based Desalination Technology

Membrane Desalination is the process where a semipermeable membrane removes salt and minerals from salty water. The six types of membrane desalination are as follows:

1)- Reverse Osmosis (RO):

Reverse Osmosis is one of the most popular desalination methods. An RO system uses pressure to force saline water through a membrane, rejecting salts, chlorine, dirt, and other dissolved materials. The seawater requires higher pressure as compared to brackish water in this process.

2)- Electrodialysis:

Electrodialysis is a voltage-driven membrane process introduced in the 1960s, about 10 years before reverse osmosis. It uses a pressure-driven pump to push water through a semipermeable membrane. It is used to treat wastewater, seawater, and brackish water.

Electrodialysis uses a selective membrane that only allows positive or negative ions to pass through. The process is more expensive to install than RO as it is more resistant to membrane deterioration.

3)- Membrane Distillation:

Membrane distillation uses a temperature difference to evaporate vapor from a brine solution. This separates pure water vapor from contaminants. It produces purified water on one side and a concentrated solution on the other. 

4)- Nanofiltration:

Nanofiltration is primarily used for drinking water. It allows beneficial minerals to pass through the membrane, which RO cannot. It also helps to separate molecules according to their size.

Nanofiltration helps the removal of dissolved salts and minerals, sugars, bacterial and viral pathogens, biological matter, metal ions, latex and oil emulsions, carbon, proteins or enzymes.

5)- Forward Osmosis:

Forward osmosis is a natural process where water moves naturally through a semi-permeable membrane. It goes from low solute to high solute concentration areas. This happens because of osmotic pressure differences. It is used for water purification and desalination. 

6)- Ultrafiltration:

In some areas, pretreating seawater is very difficult, so ultrafiltration is used. This process helps separate microscopic solids from soluble compounds using pressure and ultrafine membrane media. Using ultrafiltration technologies for desalination is essential for treating municipal or industrial wastewater.

Other Processes

1)- Freeze Desalination:

The process of freeze desalination is based on water phase change from liquid to solid. As ice crystals form, salt and other impurities are excluded from their structure. Residual salt is washed from the crystals, recovering product water. The process is more efficient than the thermal process because the energy needed to freeze water is one-seventh of what is required to boil water.

Benefits Of Desalination Of Water

The main benefits of desalination of water are as follows:

• Helps with habitat protection.
• Plants are safely located.
• Provides people with potable water ( clean & fresh drinking water)
• Provides water to the agricultural industry.
• Water quality is safe; it does not harm any living being.
• Helps to preserve current freshwater supplies.
• Unlimited ocean water as a source.

Advantages and Disadvantages of Desalination

There are certain advantages and disadvantages of desalination that are as follows:

Desalination Plants Across The World

Desalination plants are widespread worldwide, especially in regions with limited access to fresh water or facing water scarcity. These desalination plants provide clean water for drinking, agriculture, and industrial purposes.

The Rabigh 3 desalination project is one of the world’s largest desalination plants. Located in the Kingdom of Saudi Arabia, it was awarded to ACWA Power. With a 600,000 m3/day capacity, 600 million liters of water would be produced daily. Saudi is one of the largest awarded RO desalination plants.

The different desalination plants across the world are as follows:

• Ras AI Khair, Saudi Arabia\
• Jubail Water and Power Company (JWAP)
• Sorek-2, Israel
• Taweelah, UAE
• Shuaibah 3, Saudi Arabia

Facts About Desalination Plants

• Asia will become the most significant growth market for desalination globally by 2030. Total capacity is projected to nearly double over the next decade.
• Singapore and India also rely heavily on desalination, including extensive facilities like the Tuaspring Destination Plant in Singapore and the Chennai plant in India.
• Expanding desalination capacity is necessary for supporting industrialization and economic growth.

Conclusion

As water demand escalates with climate risks and population growth, major desalination plants offer a reliable means of expanding supply without burdening our ecosystems. While intensive energy consumption requires careful management, improving technologies and sustainable integration make desalination a long-term investment for water security.

Responsible planning today can prepare societies for increasing uncertainty and help environmentalists maintain sustainability for the future. With careful consideration of local people, desalination can serve diverse water management portfolios, guaranteeing stable supplies even during severe drought.

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