Due to its energy consumption, desalinating sea water is generally more costly than fresh water from surface water or groundwater.

 

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Desalination

Desalination is a process that removes mineral components from saline water. More generally, desalination is the removal of salts and minerals from a substance. One example is soil desalination. This is important for agriculture. It is possible to desalinate saltwater, especially sea water, to produce water for human consumption or imigation. The by-product of the desalination process is brine. Many seagoing ships and submarines use desalination. Modem interest in desalination mostly focuses on cost-effective provision of fresh water for human use. Along with recycled wastewater, it is one of the few water resources independent of rainfall,

Barcelona, Spain

Due to its energy consumption, desalinating sea water is generally more costly than fresh water from surface water or groundwater, water recycling and water conservation, however, these alternatives are not always available and depletion of reserves is a critical problem worldwide H Desalination processes are using either thermal methods (in the case of distillation) or membrane based methods (eg. in the case of reverse osmosis)

An estimate in 2018 found that "18,426 desalination plants are in operation in over 150 countries. They produce 87 million cubic meters of clean water each day and supply over 300 million people. The energy intensity has improved. It is now about 3 kWh/m³ (in 2018), down by a factor of 10 from 20-30 kWh/m² in 1970, Nevertheless, desalination represented about 25% of the energy consumed by the water sector in 2016.

History

Ancient Greek philosopher Aristotle observed in his work Meteorology that "salt water, when it turns into vapour, becomes sweet and the vapour does not form salt water again when it condenses", and that a fine wax vessel would hold potable water after being submerged long enough in seawater, having acted as a membrane to filter the salt.

At the same time the desalination of seawater was recorded in China. Both the Classic of Mountains and Water Seas in the Period of the Warring States and the Theory of the Same Year in the Eastern Han Dynasty mentioned that people found that the bamboo mats used for steaming rice would form a thin outer layer after long use. The as-formed thin film had adsorption and ion exchange functions, which could adsorb salt.

Numerous examples of experimentation in desalination appeared throughout Antiquity and the Middle Ages, but desalination became feasible on a large scale only in the modern era.  A good example of this experimentation comes from Leonardo da Vinci (Florence, 1452), who realized that distilled water could be made cheaply in large quantities by adapting a still to a cookstove.  During the Middle Ages elsewhere in Central Europe, work continued on distillation refinements, although not necessarily directed towards desalination, 

The first major land-based desalination plant may have been installed under emergency conditions on an island off the coast of Tunisia in 1560.It is believed that a garrison of 700 Spanish soldiers was besieged by the Turkish army and that, during the siege, the captain in charge fabricated a still capable of producing 40 barrels of fresh water per day, though details of the device have not been reported. 

Before the Industrial Revolution, desalination was primarily of concern to oceangoing ships, which otherwise needed to keep on board supplies of fresh water. Sir Richard Hawkins (1562-1622), who made extensive travels in the South Seas, reported that he had been able to supply his men with fresh water by means of shipboard distillation.  Additionally, during the early 1600s, several prominent figures of the era such as Francis Bacon and Walter Raleigh published reports on desalination. These reports and others,  set the climate for the first patent dispute concerning desalination apparatus. The two first patents regarding water desalination were approved in 1675 and 1683 (patents No. 184/199 and No. 226,120l published by William Walcot and Robert Fitzgerald (and others), respectively). Nevertheless, neither of the two inventions entered service as a consequence of scale-up difficulties. [14] No significant improvements to the basic seawater distillation process were made during the 150 years from the mid-1600s until 1800.

When the frigate Protector was sold to Denmark in the 1780s (as the ship Hussaren) its still was studied and recorded in great detail. 1211 In the United States, Thomas Jefferson catalogued heat based methods going back to the 1500s, and formulated practical advice that was publicized to U.S. ships on the reverse side of sailing clearance permits. 

Beginning about 1800, things started changing as a consequence of the appearance of the steam engine and the so-called age of steam,  Knowledge of the thermodynamics of steam processes  and the need for a pure water source for its use in boilers generated a positive effect regarding distilling systems. Additionally, the spread of European colonialism induced a need for freshwater in remote parts of the world, thus creating the appropriate climate for water desalination. 

In parallel with the development and improvement of systems using steam (multiple-effect evaporators), these type of devices quickly demonstrated their desalination potential. In 1852, Alphonse René le Mire de Normandy was issued a British patent for a vertical tube seawater distilling unit that, thanks to its simplicity of design and ease of construction, gained popularity for shipboard use.  Land-based units did not significantly appear until the latter half of the nineteenth century. In the 1860s, the US Army purchased three Normandy evaporators, each rated at 7000 gallons/day and installed them on the islands of Key West and Dry Tortugas,  Another land-based plant was installed at Suakin during the 1880s that provided freshwater to the British troops there. It consisted of six-effect distillers with a capacity of 350 tons/day. 

After World War II, many technologies were developed or improved such as Multi Effect Flash desalination (MEF) and Multi Stage Flash desalination (MSF). Another notable technology is freeze-thaw desalination, 1281 Freeze-thaw desalination, (cryo-desalination or FD), excludes dissolved minerals from saline water through crystallization. 

The Office of Saline Water was created in the United States Department of the Interior in 1955 in accordance with the Saline Water Conversion Act of 1952, This act was motivated by a water shortage in California and inland western United States. The Department of the Interior allocated resources including research grants, expert personnel, patent data, and land for experiments to further advancements, 

The results of these efforts included the construction of over 200 electrodialysis and distillation plants globally, reverse osmosis (RO) research, and international cooperation (for example, the First International Water Desalination Symposium and Exposition in 1965).  The Office of Saline Water merged into the Office of Water Resources Research i 1974.

The first industrial desalination plant in the United States opened in Freeport, Texas in 1961 after a decade of regional drought. 

By the late 1960s and the early 1970s, RO started to show promising results to replace tradition thermal desalination units. Research took place at state universities in California, at the Dow Chemical Company and DuPont, 1931 Many studies focus on ways to optimize desalination systems.  The first commercial RO plant, the Coalinga desalination plant, was inaugurated in California in 1965 for brackish water, 136) Dr. Sidney Loeb, in conjunction with staff at UCLA, designed a large pilot plant to gather data on RO, but was successful enough to provide freshwater to the residents of Coalinga. This was a milestone in desalination technology, as it proved the feasibility of RO and its advantages compared to existing technologies (efficiency, no phase change required, ambient temperature operation, scalability, and ease of standardization), A few years later, in 1975, the first sea water reverse osmosis desalination plant came into operation.

As of 2000, more than 2000 plants were operated. The largest are in Saudi Arabia, Israel, and the UAE; and the biggest plant with a volume of 1,401,000 m3/d is in Saudi Arabia (Ras Al Khair) 

This decade also saw progress in integrating renewable energy sources, such as solar and wind power, into desalination systems. Though initially in early stages, these efforts paved the way for more environmentally sustainable desalination practices. 

The 2010s and 2020s marked the emergence of next-generation membranes, including graphene-based membranes, aquaporin-inspired biomimetic membranes, ceramic membranes, and nanocomposites. These materials significantly improved water permeability, selectivity, and fouling resistance. 

As of 2021 22,000 plants were in operation 3l In 2024 the Catalan government installed a floating offshore plant near the port of Barcelona and purchased 12 mobile desalination units for the northern region of the Costa Brava to combat the severe drought. 

In 2012, cost averaged $0.75 per cubic meter. By 2022, that had declined (before inflation) to $0.41. Desalinated supplies are growing at a 10%+ compound rate, doubling in abundance every seven years, 

Between 2024 and 2025, Spain has recently announced a €340 million investment to build Africa's largest desalination plant in Casablanca, demonstrating the growing importance of large-scale desalination infrastructure.

Applications

External audio

"Making the Deserts Bloom: Harnessing nature to deliver us from drought" (https://www.sciencehistory.org/distillations/podcast/ma)

king-the-deserts-bloom), Distillations

Podcast and transcript, Episode 239, March 19, 2019, Science History Institute

Schematic of a multistage flash desalinator

A-steam in B-seawater in C-potable water out D-brine out (waste) E-condensate out Fheat exchange G-condensation collection (desalinated water)

H-brine heater

The pressure vessel acts as a countercurrent heat exchanger.

A vacuum pump lowers the pressure in the vessel to facilitate the evaporation of the heated seawater (brine) which enters the vessel from the right side (darker shades indicate lower temperature). The steam condenses on the pipes on top of the vessel in which the fresh sea water moves from the left to the right.

There are now about 21,000 desalination plants in operation around the globe. The biggest ones are in the United Arab Emirates, Saudi Arabia, and Israel. The world's largest desalination plant is located in Saudi Arabia (Ras Al-Khair Power and Desalination Plant) with a capacity of 1,401,000 cubic meters per day.

Desalination is currently expensive compared to most alternative sources of water, and only a very small fraction of total human use is satisfied by desalination.  It is usually only economically practical for high-valued uses (such as household and industrial uses) in arid areas. However, there is growth in desalination for agricultural use and highly populated areas such as Singapore or California,  The most extensive use is in the Persian Gulf.

While noting costs are falling, and generally positive about the technology for affluent areas in proximity to oceans, a 2005 study argued, "Desalinated water may be a solution for some water-stress regions, but not for places that are poor, deep in the interior of a continent, or at high elevation. Unfortunately, that includes some of the places with the biggest water problems.", and, "Indeed, one needs to lift the water by 2000 m, or transport it over more than 1600 km to get transport costs equal to the desalination costs. 

Thus, it may be more economical to transport fresh water from somewhere else than to desalinate it. In places far from the sea, like New Delhi, or in high places, like Mexico City, transport costs could match desalination costs. Desalinated water is also expensive in places that are both somewhat far from the sea and somewhat high, such as Riyadh and Harare. By contrast in other locations transport costs are much less, such as Beijing, Bangkok, Zaragoza, Phoenix, and, of course, coastal cities like Tripoli,  After desalination at Jubail, Saudi Arabia, water is pumped 320 km inland to Riyadh, 1521 For coastal cities, desalination is increasingly viewed as a competitive choice.

In 2023, Israel was using desalination to replenish the Sea of Galilee's water supply. 

Not everyone is convinced that desalination is or will be economically viable or environmentally sustainable for the foreseeable future. Debbie Cook wrote in 2011 that desalination plants can be energy intensive and costly. Therefore, water-stressed regions might do better to focus on conservation or other water supply solutions than invest in desalination plants.