What is desalination and why does it matter?
It’s common knowledge that the majority of water on Earth isn’t drinkable thanks to salt and other minerals in the seas and oceans.
In fact, drinking water from the ocean will actually dehydrate you if you consume too much of it.
But it is possible to harvest all of this salty water and increase the 2.5% of the Earth’s drinkable reserves.
How? Through a process called desalination.
Desalination refers to the means of removing salt and other minerals in sea water in order to create potable water. It turns the once undrinkable substance into a consumable and usable substance for humans. While it is a process that is destined to help with the planet’s supply of drinking water, it does require a lot of energy to operate.
How does desalination work?
There are several methods of desalination which are used the world over. The majority of these methods use heat to extract minerals – think of a pot of boiling water, but on a much larger scale. While the water boils and turns into vapour, it leaves behind nearly all of the elements that don’t belong in H2O.
For example, the vacuum distillation lowers the point of atmospheric pressure, which lowers the boiling point of water. This lessens the amount of energy required for the process. Again, it is similar to that of the boiling pot.
Another method is that of the multi-stage flash distillation. It utilises a series of super quick and hot evaporations to remove the salt and minerals. Though the vacuum and multi-stage flash methods have slightly different mechanics, they do yield similar results.
The most common form of desalination is reverse osmosis, which forces the minerals to be removed from the water. Before the actual process begins, the sea water requires a few steps of filtration because it is taken directly from the ocean. First, the water is cleaned by passing through a multi-media filter, which comprises of layered granular materials, such as gravel. It is then passed through a cartridge filter, which removes more impurities.
The water is then shot through a membrane, which only allows water through, but not salt and other minerals. A portion of the salted water is used to power the machine, while the rest is pumped back to the ocean to an area where it won’t damage the local ecology. The cleaner water is then put through a process where calcium carbonate (CaC03) is added in order to change the taste and bring up the PH levels. This water is then pumped into the local water supply for human consumption.
The cons of desalination
Though the desalinisation process may sound easy, especially the variants that require the boiling of water, it does come with its own drawbacks. The desalination plants are expensive to build and require constant maintenance, especially the membranes. This means that a plant may be to shut off for some time while the membranes are cleaned or replaced.
There are also health risks to humans. Researchers have found a possible link between iodine deficiency and those that consume desalination water.
Desalination is a requirement
Drinkable sources of water are often susceptible to droughts, natural disasters, and climate change. However, oceans are a source of water that is almost immovable in our current climates, which makes them an ideal source of fresh water. As much as dams are used to collect and store fresh water for consumption, they are not foolproof solutions.
In May 2016, representatives from the Western Cape and Kwa-Zulu Natal announced that both provinces would receive desalination plants in the coming months, which is in addition to other plants around the country. Though cost and technology had hindered projects in the past, it was said that the advancements in water purification means the plants are now more viable than ever.
In the central parts of the Western Cape, more specifically Cape Town, there has yet to exist a desalination plant. This has proved to be a misstep on the city’s part as the recent droughts in the province has taken a great toll on its residents and industries. It was announced in June by the mayor of the city, Patricia de Lille, that residents could be drinking purified sea water by August.
While the government looks into a new desalination plant, startups in the private sector are trying to take the water crisis challenge head on. Stellenbosch University’s LaunchLab held a pitching competition to find the four best startups for the challenge, with one idea looking to minimise the evaporation of water from dams.
The need for desalination plants grows with each passing season. If humans want to continue to have drinkable water, they will need to adapt and refine the technology to clean it.