Desalination plants represent the future of securing a sustainable source of water in regions facing water scarcity.

Desalination, the technique of converting saltwater into fresh water, is a crucial concept, so important that even young students are taught its significance.

This knowledge is vital because excessive consumption of saltwater can have serious health consequences, as the high salt content can overwhelm the body, causing dehydration and possible organ damage.

As the availability of global freshwater resources decreases, desalination plants are taking on a more critical role, converting the vast waters of the ocean into accessible drinking water. By extracting salt from seawater, these plants help meet the growing global demand for clean water. Let’s take a closer look at how these essential systems function.

How Desalination Works

Water covers about 70% of our planet's surface, yet a staggering 97% of it is too salty for consumption. This is where desalination steps in to provide a solution, turning seawater into potable water, as highlighted by NatGeo.

While there are various techniques to separate salt from water, approximately 90% of desalination processes rely on two main methods: reverse osmosis and multistage flash distillation. Let’s explore how each of these methods works in detail.

Reverse Osmosis

As previously discussed, consuming salt water can negatively impact our health by disrupting the natural balance of our cells. Inside our cells, there's a process called osmosis that seeks to equalize the salt concentration both inside and outside the cell. Reverse osmosis applies this concept to water purification.

This process involves a unique membrane, resembling an extremely fine filter, which permits only water to pass through, blocking the salt. Strong pumps are used to force the salt water through this membrane, ensuring that only pure water emerges on the other side, leaving the salt behind. This technique is how reverse osmosis desalination plants turn salty water into fresh, drinkable water.

Multistage Flash

In contrast to reverse osmosis, which filters out salt and other impurities using a semipermeable membrane, the multistage flash method employs heat and pressure changes to transform salt water into fresh water.

The term 'flash' describes the rapid evaporation caused by a sudden drop in pressure, and this process is repeated over multiple stages, which is how it got its name.

In each phase of the conversion process, saltwater is subjected to steam heat and reduced pressure. This causes a portion of the water to rapidly evaporate, or 'flash,' into water vapor, which is essentially fresh water. The remaining salty solution is known as 'brine.'

Similar to reverse osmosis, this technique usually doesn't require additional chemicals or softeners [source: Organization of American States]. However, despite the promise of desalination, large-scale plants currently supply only a small fraction of the world's daily freshwater needs.

Desalination Plants Around the World

As of 2022, there are over 20,000 desalination plants in operation globally, producing more than 95 million cubic meters of water each day. The Middle East remains a key center for desalination, driven by water scarcity issues and advancements in the technology.

The Sorek Desalination Plant in Israel, which began operations in 2013, was once among the largest seawater reverse osmosis (SWRO) desalination plants in the world. However, with the rapid growth of desalination technology, even larger plants have been constructed in various regions worldwide.

While desalination technology has improved over time, people have different opinions about it. For instance, in Israel, concerns have been raised about the taste and possible health effects of desalinated water.

Studies, including those from Saudi Arabia, confirm that properly executed desalination processes yield water that is safe to drink and of similar quality to bottled water. Additionally, using desalinated tap water has an environmental edge over bottled water by reducing plastic waste.

Portable desalination technology has also progressed in recent years. A variety of portable devices now exist for emergency situations, hiking, or personal use. These tools can turn salty or contaminated water into potable water, providing vital solutions in areas with scarce freshwater resources.

Salt and Beyond

You might think desalination is all about removing salt from seawater, but the process goes further. Desalination also eliminates organic and biological contaminants, ultimately producing high-quality drinking water that doesn't carry harmful diseases like diarrhea.

This is crucial because nearly 4 million people die annually "due to inadequate water supply, sanitation, and hygiene," as reported by the United Nations.

Lewis Carlsbad Desalination Facility

The Claude "Bud" Lewis Carlsbad Desalination Facility, situated in Carlsbad, California, holds the title of the largest seawater desalination plant in the Western Hemisphere.

Inaugurated in December 2015, the plant uses reverse osmosis technology to transform seawater from the Pacific Ocean into drinkable water. With a daily production of around 50 million gallons of potable water, it supplies about 10 percent of San Diego County's water needs.

This seawater desalination plant was constructed in response to frequent droughts and the need for a dependable, drought-resistant water source. The project incorporates an energy recovery system to minimize energy consumption and features environmental measures to safeguard marine life.

While desalination presents a potential solution to water scarcity, it also raises concerns regarding energy use and environmental effects, especially the disposal of brine byproduct. Nevertheless, the Carlsbad plant serves as a model for other regions exploring desalination as a means to combat water shortages.

Future of Desalination

As the global number of desalination plants continues to rise, so too does the need for innovative technologies to power these facilities. At present, large-scale desalination operations demand considerable energy to run and often require extensive maintenance due to the frequent fouling of components such as membranes [source: Schirber].

Cost is another significant concern: Over the past fifty years, both public and private investments in desalination technology development have exceeded one billion dollars globally. Despite the advancements made, the notion that desalination could completely eliminate water scarcity remains far from achievable.

This is because the costs involved in planning, constructing, and managing desalination plants are still prohibitively high.

On average, the cost of converting one acre-foot — about 325,000 gallons — of seawater into fresh water ranges from $2,000 to $3,000, requiring a significant amount of energy [source: ABC News]. When comparing reverse osmosis to multistage flash desalination, reverse osmosis is the more energy-efficient method.

With reverse osmosis, only one-third of the seawater is needed to produce the same amount of fresh water as with multistage flash. This results in lower energy consumption and reduced costs for pumping seawater to the plant and disposing of the brine.

The Brine Issue

Unfortunately, both desalination methods — like all desalination technologies — produce brine. This byproduct, which contains high salt concentrations, poses a serious threat to aquatic ecosystems when it is released back into natural water bodies.

Brine, due to its high density, tends to sink to the seabed, creating a layer that restricts oxygen flow. This can lead to oxygen-deprived zones that negatively affect marine life, particularly organisms in benthic habitats [source: University of Texas at Austin].

Researchers are investigating various ways to reduce the environmental consequences of brine produced by desalination. Advanced techniques such as electrodialysis and forward osmosis are being explored to enhance water recovery rates, thus minimizing brine production.

Other approaches include mixing brine with treated wastewater before releasing it, which lowers its salinity. The cultivation of halophyte plants — a type of marine vegetation that thrives in salty environments — is another possible solution.

Portable Desalination Devices

A portable desalination unit presents an innovative solution for converting saline water into drinkable water, particularly vital in remote or disaster-stricken areas. In 2022, MIT researchers created a compact, suitcase-sized model that operates with remarkable energy efficiency, powered by an affordable solar panel.

This device differs from traditional ones by eliminating the need for filters. Instead, it uses electrical power for water purification, greatly reducing maintenance requirements.

These innovations make portable desalination devices indispensable for places such as isolated islands, ships on long journeys, refugees affected by natural disasters, or military personnel stationed in remote outposts.

“This represents the culmination of a decade-long journey for my team and me. We spent years studying the physics of individual desalination methods, but integrating those advances into a compact system and proving its effectiveness in the ocean was incredibly meaningful and rewarding,” says senior author Jongyoon Han, a professor of electrical engineering and computer science, biological engineering, and a member of the Research Laboratory of Electronics (RLE).

In addition to government support in both the U.S. and internationally, private investors are increasingly turning their attention to improving desalination technologies. One thing is clear: Enhancing desalination could transform water-scarce regions for the better.