What is Desalination?

Desalination is a word that can often be said off-hand, however many people are unsure exactly what it is. Desalination is the process of changing saline water (salt water) into fresh water, so it can be used for drinking, growing crops, washing and more.

In many countries, there simply isn’t enough freshwater for the population, and with little rainfall and desert areas, this scarcity of water can be critical for many people. In fact, the need for fresh, drinkable water is likely to become as important as the need for energy and oil resources in the future.

Seawater is saline, meaning that it has high levels (concentrations) of salts that have been dissolved. When salt water is desalinated, the salt, bacteria and pollution are all removed, meaning it can be converted into fresh water.

Many civilisations would use this process onboard ships, allowing them to convert sea water into water that they could drink.

It’s important to understand that desalination isn’t just a matter of modern science changing the water, and it actually occurs naturally. Once water has been desalinated, it’s actually usually more pure than normal drinking water.

There are two main types of desalination that you should be aware of, in order to understand how the process works.

The first is Reverse Osmosis desalination, which uses osmosis in order to remove impurities and salt from the water, transferring it through a series of membranes. Thermal desalination involves the use of heat, and is often environmentally friendly since it uses waste heat from refineries or power plants to condense and evaporate the water in order to purify it. The most advanced type of desalination plant will actually pretreat the water which allows the plants to operate more efficiently.

Reverse osmosis desalination is the most common technique for desalination around the world, and was developed way back in the 1950s. This involves many different processes and different factors for those selecting the best solution for each situation, including the quality of the water to begin with, how pure the water needs to be when produced, energy requirements, pretreatment, and more.

Another good thing about reverse osmosis desalination, is many different ions and molecules can be removed, which makes it suitable for industrial uses. The water moves from an area that has a low solute concentration, passing through a membrane and into an area that has a high solute concentration. This  movement reduces the system’s energy, generating osmotic pressure.

This means that saline is pressurised against one of the membranes surfaces, and clean water is released from the other side.

Thermal desalination is about mimicking the way that water naturally desalinates- evaporating fro the ocean, gathering up in the atmosphere and then condensation as rain. Heat is vital here, meaning refineries and power plants will often be involved so that this heat can be used.

As more countries around the world demand fresh water, and global warming is changing the world, we can expect desalination to be increasingly important in the future.