Desalination: drinking seawater

Removing salt from seawater to combat water scarcity is one solution that is gaining traction. But the technologies involved have serious environmental consequences.

By Bertrand Beauté

It’s called the blue planet for a reason... three-quarters of the Earth’s surface is covered by water, hence the characteristic colour. But 97% of that water contains salt, making it undrinkable and unusable. Fresh water – the remaining 3% – is scattered unequally across the world and is mostly found in the form of ice. As a result, more than four billion people live in regions that experience a drought at least once a year. So, why not transform the planet’s immense reserves of salt water into drinkable water? "Ocean water is a never-ending resource," said  Angel Sanz, director of strategic development at Suez and former head of the International Desalination Association (IDA). "Desalination is a real solution for regions that need water."

The idea is not new. In ancient times, the Greek philosopher Aristotle wrote about fishermen’s first attempts to desalinate water. By heating salt water at a high temperature (more than 100°C), the fishermen created vapour which, when gathered and condensed, became drinkable. This technique, called distillation, was still being used two millennia later when the first desalination plants were built in the 1960s. But it has one major flaw: distillation uses a very large amount of energy, which is why desalination has long been a niche market reserved for Gulf countries with lots of oil.

The discovery of reverse osmosis in the early 1970s gradually changed this trend. The technique separates water and salt by forcing water through semi-permeable membranes that allow water molecules to pass through but not salt. "The desalination industry was restricted for a long time due to the technique’s energy consumption and cost. But the discovery and steady improvement of the membranes used for reverse osmosis made this method more accessible," said Sanz. "The energy consumption required for desalination has fallen by two-thirds over 40 years."


There are more than 20,000 desalination plants around the world, which supply more than 300 million people with drinkable water


As a result, the cost has fallen significantly. Twenty years ago, the price of desalinated water was 2 francs per cubic metre (m3). Today, it is 1 franc, but varies considerably depending on the region and therefore the energy sources used. Comparatively, Swiss tap water, which varies by town, is priced at an average of 1.60 francs per cubic metre.

Improved energy efficiency, coupled with low prices, has caused desalination to become a booming industry. From 2010 to 2020, the volume of water desalinated globally increased nearly 100%, from 60 million cubic metres per day to 115 million cubic metres. In total, there are more than 20,000 desalination plants around the world, which supply more than 300 million people with drinkable water. "Not all of these plants process ocean water," said Sanz. "40% of desalination plants process brackish water, which is water that has considerably less salt than ocean water or wastewater."

This market will continue to grow. According to the latest UN-Water report, published in March 2021, desalination will become "a solution to droughts for coastal communities around the world over the next 15 years." The market, which is currently worth nearly $17.7 billion yearly is expected to reach $32.1 billion in 2027, according to predictions from the firm Research & Markets. Several companies, such as Veolia and Suez (France), Abengoa (Spain), IDE Technologies (Israel), and Xylem (US) share this lucrative space.

"The desalination market has become a service market," said Miguel Angel Sanz of Suez. "Building new plants generates $4 to $5 billion in revenue yearly, and use and maintenance brings in $10 billion yearly." In Israel, for example, nearly 70% of all drinkable water consumed is now processed using this method. This is a godsend for companies in the industry: "The membranes used for reverse osmosis wear out quickly due to the high pressure exerted and corrosion. So they need to be changed regularly," said Xavier Regnard, analyst for investment bank Bryan, Garnier & Co. "It is a cash cow for companies in the industry that sell and operate these plants. It’s a bit like Nespresso: once you buy the machine, you have to keep buying the capsules."


"Half of the world’s desalination capacity is located in the Middle East and North Africa," said Sanz. "But demand is rising sharply in Asia with annual growth of 30%, compared to 15% in the US and 5% in Europe." This is because desalination is no longer used only in desert climates and remote areas. Since 2009, Barcelona has operated a plant that can produce 200,000 cubic meters of potable water per day, and London has had a similar set-up since 2010. In the United States, California and Florida are currently investing hundreds of millions of dollars to build new desalination plants. "The Barcelona plant was designed as a backup in the event of a crisis," said Sanz, who participated in the sale of the plant as a Suez employee. "In normal times, it is not used. But during a drought, the Spanish government can simply push a button and produce enough to supply 1.3 million Catalan residents with water. This is why residents have called it the sixth dam." This plant is only used sparingly, however, because the environmental cost of desalinated water is still very high, compared to water taken from rivers or groundwater tables. "Desalination technology has made progress, but these methods still use a lot of energy," said Regnard, an analyst for investment bank Bryan, Garnier & Co. "Given the current environmental situation, I am not sure that desalination is the right answer. I would rather improve the networks and reduce water consumption."


"Desalination technology still uses a lot of energy"

Xavier Regnard, analyst at Bryan, Garnier & Co.


Australia uses desalination plants heavily, and is taking steps to improve the environmental consequences. For all of the country’s biggest projects, the government now encourages the use of renewable energies. For example, 100% of energy needs for the reverse osmosis plant in Perth are supplied by a wind farm. The same is true in Morocco, which is currently building the largest desalination plant in Africa in Agadir, where energy will be partially supplied by wind turbines.

At the same time, researchers are trying to improve the energy efficiency of desalination plants. Inspired by aquaporins – pores present on the surface of human cells that only let water pass through – an international team was able to reduce the energy needed for desalination by 12%, according to a paper published in Nature Nanotechnology in November 2020. "We are working with several large companies that use our membranes in their plants," said chemist Mihail Barboiu, member of the European Institute of Membranes in Montpellier, which coordinated the research. "But industrialisation takes time."

"In the next 10 years, energy consumption will decrease by 10% to 15% due to innovations such as new, more effective membranes," said Miguel Angel Sanz. "But the most significant impact is the increased size of each plant. The bigger the plant, the more energy it saves, due to economies of scale."

But energy supply isn’t the only pitfall for desalination. In a study published in the journal Science of the Total Environment in 2019, researchers sounded alarm bells about the massive disposal of brine, a substance filled with salt and chemical products that is produced during desalination. Producing one litre of drinkable water results in one litre of brine discharged into the ocean. The researchers believe that this leads to elevated salt levels in oceans, making it difficult or even impossible for marine ecosystems to sustain flora and fauna. Sanz disagrees: "In countries that have used desalination for a long time, we haven’t seen any impact." After four years of studies, the Australian government also stated that desalination did not have a significant impact on marine life. This conclusion is still being disputed by scientists, as many other studies have shown that some species are becoming endangered in places where brine is being discharged.

Furthermore, while 174 countries currently use desalination to meet their water demands, the technique is still primarily used by rich countries, with less than 0.1% of plants located in low-income countries. Sub-Saharan African countries experience droughts often, but desalination technologies are quite rare. In 2015, Ghana was the first West African country to open a plant in Accra. It was built by Spanish company Abengoa and can produce 60,000 cubic metres of water per day. Senegal also built a plant in Dakar with a capacity of 50,000 cubic metres per day, which is expected to open in 2021.