Contenido

Se pueden utilizar los siguientes métodos:[5]​.

Thermal processes

This method evaporates seawater by applying a heat source and then condenses it. Repeat the operation several times, in some cases adding elements to the process that help capture any substance present in the impure water that you want to extract. The heat source is applied in each of the phases.[5]​.

This method is similar to the previous one, but the primary heat source is applied only to the first stage. For the next stage, the heat from the steam generated in the previous stage is used.

It is an energy recovery process where energy is added to low pressure vapor (usually water vapor) by compressing it. The result is a smaller volume of steam at a higher temperature and pressure, which can be used to do useful work. Typically, compressed steam can be used to heat the mother liquor to produce low pressure steam.

This method uses a closed space exposed to sunlight inside which the water evaporates and then condenses upon contact with the colder surface that separates it from the outside. The drops are carried down a slope until they gather at the edge of space. Its production is 1-4 l/day/m².[5]​.

Desalination with nuclear reactors.

Nuclear reactors can also be used in desalination processes, either in dual configurations producing electricity and process heat, or dedicated solely to supplying thermal energy. This technology is considered a low-carbon option for freshwater production in water-limited regions.[6]​.

Membrane technologies

Electrodialysis was first proposed in 1890 by Maigrot and Sabates, who built the first device for syrup desalination. This device used carbon as an electrode and permanganate paper as a membrane.[7]​.

The electrodialysis process used for desalination consists of passing salt water through charged membranes that trap the ions dissolved in the salt water with the aim of extracting and producing fresh water.[8]​.

In summary, when a direct electrical current is applied, the membranes selectively allow only sodium ions (Na+) or chloride ions (Cl-) to pass through. This causes the ions to move and become more concentrated as they are retained in these membranes, thus obtaining fresh water. The efficiency of this process depends on several factors, such as the intensity of the current and the permeability of the membranes used. On the other hand, the cost of the process depends on the concentration of salt in the water, since the more ions that need to be removed and depending on their electrochemical properties, the more electrical energy is required.[9]​.

In 1954, the first electrodialysis desalination plant was built for the Aramco company (Saudi Arabia). Starting this year, many other desalination plants were built that operate using this technology.[7]​.

Reverse Osmosis (RO) is a process in which fresh water is obtained from salt water. Natural osmosis is a phenomenon that consists of, if there is a semipermeable membrane separating two solutions with the same solvent, the solvent passes through it, but not the dissolved salts, from the side where the concentration of salts is lowest to the highest, until on both sides of the membrane the solutions have the same concentration. This process is carried out without external energy input, and is generated by what is called osmotic pressure.

Reverse osmosis consists of passing the solvent (in this case water) through the semipermeable membrane from the side where the most concentrated solution is (sea water, with dissolved salts), to the opposite side, without the salts passing through. In this case, energy is required, in the form of pressure, which will be slightly higher than the osmotic pressure that would make the low concentration solvent pass to the high concentration side. The pressure necessary to achieve reverse osmosis depends on the amount of dissolved salts and the degree of desalination that is desired. An increase in entropy results from the use of energy in the process.

The sea is a virtually unlimited source of salt water. A reverse osmosis plant needs to process a volume of seawater up to three times greater than the total amount of desalinated water that will be obtained in the end. Therefore, the design of the wells or collection system must consider this factor for their capacity.

The use of a graphene sheet with 1.8 nm pores to replace membranes in the reverse osmosis process for water desalination is in the research phase (TRL2). According to current research, much higher efficiencies would be obtained than with current membranes, and there would be lower energy requirements. In the current state, the drawback is the cost of graphene membranes, but it is expected that in the future these costs can be reduced.[10]​.

Generally, a large tank or pond is used that is filled by gravity at sea level, after coarse filtering. The water from the pond is transported by feed pumps to the desalination system. A supplement of chemical products arrives at the inlet of the feed pumps by means of metering pumps. This is how the water is prepared to pass four types of filters that retain particles larger than four microns. The main step in water production is the separation of H O from the mixture of salts and minerals present in sea water. This step is carried out in the reverse osmosis stage, ensuring that the salts do not cross the membranes of the RO modules. Previously, it must be ensured that the diatom and microalgae particles do not reach the membranes and for this there are three previous sand filtration steps before the last microfiltration step using synthetic fiber cartridges. Filtration success also depends on the proper introduction of coagulants. Depending on the filtration quality, the membrane change cycle is generated between 2 and 5 years. Chemical dispersants introduced before microfiltration prevent the precipitation of minerals within the membranes.

Since all aspects of the process are automated, the operators' job is supervision and maintenance.

The rejected brine is 55% of the raw water (although it depends on the desalination technology used). While 45% of the water obtained leaves at atmospheric pressure, a regulated backpressure must be ensured in the rejection flow. This reject flow always contains something like 55% (100% - % gain) of the pressure energy provided by the pumps and it is highly desirable to recover this energy for higher performance. Some of the recovered energy can return to the same desalination and recovery cycle more than once.

While the plant is in production mode, the outlet pressure is controlled by a regulating valve. 'Pressure Exchanger' converters are used and with them in the pressure exchange up to 95% of the energy of the rejection flow can be recovered directly by means of pumping using positive displacement. This energy recovery pump increases the flow of more raw water to the entrance of the membranes. The plant uses 'Pressure Exchanger' units near each set of reverse osmosis element tubes.

The osmosis water or the permeate from the reverse osmosis modules must be conditioned to meet certain high quality characteristics, since the water produced has an acidic pH and a low carbonate content, which makes it a highly corrosive product. This requires its preparation before distribution and consumption. The pH is adjusted with calcium carbonate to a value of 7.7. Additionally, if required by municipal regulations for the use of drinking water, sodium fluoride and hypochlorite are also added.

Spain is the fifth country in the number of desalination plants in the world with a total of 900 plants that have a capacity of 1.45 million cubic meters per day.[11]​.

Due to their function, desalination plants must be installed near a water source, specifically, the sea. They are dedicated to desalinating seawater, at a distance of between a few tens of meters to 3 kilometers. The further away it is from the coast, the greater the pressure necessary to capture the water and, therefore, the energy consumption will be higher, which will make the entire process more expensive.

The first desalination plant in Spain was built in 1965 in Lanzarote with evaporation technology, through solar energy, which is hardly used today, and which has been replaced by reverse osmosis. This project was initiated by a private body to improve the status of the island and promote tourism. The plant was capable of producing about 2000 cubic meters of water per day. However, the plant consumed more than 50 kWh of electricity per cubic meter of water produced, which means that it was too expensive and that is why its technology was replaced. The success of the project was such that it led to the replication of similar initiatives in other regions, such as Fuerteventura, Gran Canaria and the city of Ceuta.[12]​.

In Las Palmas de Gran Canaria, the first desalination plant in Spain was built with the reverse osmosis method in 1971. It is currently managed by Emalsa. Among the most recently built, the El Prat de Llobregat plant stands out in the highly populated metropolitan region of Barcelona, ​​affected by intermittent droughts and with relatively contaminated surface waters in the Llobregat basin.

Como toda actividad humana, la desalinización de agua de mar no está exenta de impactos ambientales. No obstante, con la evolución de las tecnologías que la hacen posible y de sus procesos, se ha hecho cada vez más sostenible en términos energéticos y de descarga de residuos.[13]​[14]​ Los retos medioambientales en los diseños de las plantas desalinizadoras se pueden recoger en los siguientes puntos:[15]​.

The discharge of concentrated brine makes life difficult for marine ecosystems. Marine life is also influenced by the intake of seawater for the desalination plant. Cuando se extrae una gran cantidad de agua del mar, los organismos marinos y las algas son absorbidos por la toma, lo que provoca una perturbación en el ecosistema.

Concentrated brine is not only concentrated in salt, but also contains chemicals such as pre- and post-treatment anti-scaling agents. Furthermore, the brine discharged from thermal distillation plants exits at a relatively high temperature which means thermal pollution that influences marine life in such a way that only some marine plants or animals can withstand the high temperature near the outlet of thermal distillation plants.

High energy consumption is considered the most influential factor inhibiting the growth of seawater desalination. Currently, most desalination processes are powered by energy obtained from fossil fuels which results in gas emissions that pollute the environment. In the case of solar-based desalination processes, it is considered a promising method to alleviate the environmental impact of water desalination and also provide a sustainable source of drinking water.

Many methods are currently used for brine removal. The brine can be discharged to the sea or river, to solar ponds or injected into deep saline aquifers. Discharging into the sea or ocean is the least expensive method. When brine is discharged into the sea, it tends to sink to the bottom. Typically, the brine discharge is diluted with seawater to reduce its salinity before being discharged into the sea. The brine is discharged into deep seawater that normally has a strong current. This reduces the harmful effects of brine on marine life. Brine discharges to a solar pond or injection into a deep saline aquifer is a more expensive method. These solar ponds and saline aquifers are often located far from the desalination plant, requiring a long pipeline for transportation. This method has drawbacks because it can increase salt in the soil and increases groundwater salinity if linear under the solar pond is not used. Using a solar pond for brine disposal carries the risk of contaminating groundwater.

The desalination process has a long history, which began with the first human attempts to drink sea water, which faced multiple difficulties. It is not clear when our ancestors became frustrated with not being able to drink seawater and thought about purifying it. However, some of the oldest references to the process of desalinating water are found in the Bible.[16]​.

The history of desalination goes back millennia. The Ancient Greek philosopher Aristotle (384-322 BC) already described in his work Metrology[17]​ that "salt water, when converted into steam, becomes sweet and the steam does not form salt water again when it condenses" laying the foundations for thermal desalination. In this same work he also described that "a thin wax vessel will contain drinking water after being submerged for a sufficient time in seawater, this having acted as a filter for the salt" thus laying the foundations for membrane-based desalination. Based on Aristotle's observations, in the 17th century Leonardo da Vinci proposed adapting an alembic to a wood-burning stove to "produce large quantities of drinking water from seawater at a very low cost".[18]

In China, the classic text "Classic of Mountains and Seas in the Warring States Period" (475-221 BC), which is a compilation of mythology and geography, suggests that bamboo mats used to steam rice could form a thin outer layer which possessed adsorption and ion exchange capabilities and could therefore adsorb salt.[16]

Later, Alexander of Aphrodisias (193-217), commenting on Aristotle's book Meteorology, described for the first time a distillation process that made it possible to obtain fresh water from salt water. This method consisted of suspending large sponges in the mouth of a bronze vessel inside which seawater was boiling. The evaporated water was collected in these sponges and when it condensed, it was discovered that it was fresh water.[16]​.

In the century the first patents for thermal desalination devices appeared. William Walcot") proposed a patent in 1675[19]​ on "the art of converting corrupt water into something useful for use and sea water into fresh and fresh water in large quantities by very cheap and simple methods." A few years later, in 1683,[20] Robert Fitzgerald (nephew of Robert Boyle) patented a similar invention that caused litigation between the two: "a way of converting salt or brackish water into fresh water, suitable for drinking, boiling, washing or other ordinary use by means of a certain device or devices not previously used in our domains." Neither of the two patents were ever used due to technical problems in their large-scale extension.[21]​ In 1717, the French doctor Paul Gauthier introduced a new desalination technique that used the alembic.[22]​.

The first invention with large-scale application dates back to 1852, when Alphonse René Le Mire de Normandy" filed a patent on "the production of fresh water from sea water".[23] Thanks to the recent popularization of steam-powered ships, De Normandy's invention was a commercial success that led him to sell more than two thousand of his inventions and found a company to produce them.[23] De Normandy's device can also be considered the first to be used successfully on land on a large scale. In 1861, three of its desalination devices were used by the United States Union Army for months in Key West (Florida) where they provided them with more than 1000 L of drinking water per day. of seawater per day in an area of 4,757 square meters.[22]​.

The first modern desalination plant was built in 1961 by the Dow Chemical Company in Freeport (Texas), Texas. The plant was based on a multi-effect distillation system with 17 energetically integrated effects (stages) with a single point of heat input. The production capacity was 3800 m/day (1 MGD) of drinking water from nearby seawater. The presence of the desalination plant in Freeport "Freeport (Texas)") considerably increased the security of access to water for the local population and industry.[24]​.

The first desalination plant based on the reverse osmosis process was built in 1965 in Coalinga, California. It was a pilot plant with the capacity to produce 19 m/day of drinking water from the brackish water available in the local wells (salinity 2500 mg/L) and used primitive cellulose acetate membranes designed by Sidney Loeb at the University of California at Los Angeles (UCLA).[26] The objective of the pilot plant was to check if it was possible to avoid the consumption of fresh water transported by train or truck from other places. localities.[27]​ The primitive desalination available at the time was finally discarded due to its high cost and a canal "Canal (engineering)") was built to transport fresh water continuously to the city.[27]​.

The last major milestone in the history of desalination is the construction of the first seawater desalination plant based on reverse osmosis technology. The plant was built in Jeddah (Saudi Arabia) in 1976 and used water from the Red Sea (salinity 40,000 mg/L) to produce 12,000 m/day of drinking water.[28] The semipermeable membranes used in the plant were much more sophisticated than those used in Coalinga and were based on a composite material made up of a thin layer of spirally wound polyamide very similar to those used today in day. Its membranes allowed it to work between 60 and 70 bar "Bar (pressure unit)") of pressure (depending on the degree of fouling#Fouling "Membrane (object)")) with an average recovery of 30% in drinking water.[28]​.

Contenido

Se pueden utilizar los siguientes métodos:[5]​.

Thermal processes

This method evaporates seawater by applying a heat source and then condenses it. Repeat the operation several times, in some cases adding elements to the process that help capture any substance present in the impure water that you want to extract. The heat source is applied in each of the phases.[5]​.

This method is similar to the previous one, but the primary heat source is applied only to the first stage. For the next stage, the heat from the steam generated in the previous stage is used.

It is an energy recovery process where energy is added to low pressure vapor (usually water vapor) by compressing it. The result is a smaller volume of steam at a higher temperature and pressure, which can be used to do useful work. Typically, compressed steam can be used to heat the mother liquor to produce low pressure steam.

This method uses a closed space exposed to sunlight inside which the water evaporates and then condenses upon contact with the colder surface that separates it from the outside. The drops are carried down a slope until they gather at the edge of space. Its production is 1-4 l/day/m².[5]​.

Desalination with nuclear reactors.

Nuclear reactors can also be used in desalination processes, either in dual configurations producing electricity and process heat, or dedicated solely to supplying thermal energy. This technology is considered a low-carbon option for freshwater production in water-limited regions.[6]​.

Membrane technologies

Electrodialysis was first proposed in 1890 by Maigrot and Sabates, who built the first device for syrup desalination. This device used carbon as an electrode and permanganate paper as a membrane.[7]​.

The electrodialysis process used for desalination consists of passing salt water through charged membranes that trap the ions dissolved in the salt water with the aim of extracting and producing fresh water.[8]​.

In summary, when a direct electrical current is applied, the membranes selectively allow only sodium ions (Na+) or chloride ions (Cl-) to pass through. This causes the ions to move and become more concentrated as they are retained in these membranes, thus obtaining fresh water. The efficiency of this process depends on several factors, such as the intensity of the current and the permeability of the membranes used. On the other hand, the cost of the process depends on the concentration of salt in the water, since the more ions that need to be removed and depending on their electrochemical properties, the more electrical energy is required.[9]​.

In 1954, the first electrodialysis desalination plant was built for the Aramco company (Saudi Arabia). Starting this year, many other desalination plants were built that operate using this technology.[7]​.

Reverse Osmosis (RO) is a process in which fresh water is obtained from salt water. Natural osmosis is a phenomenon that consists of, if there is a semipermeable membrane separating two solutions with the same solvent, the solvent passes through it, but not the dissolved salts, from the side where the concentration of salts is lowest to the highest, until on both sides of the membrane the solutions have the same concentration. This process is carried out without external energy input, and is generated by what is called osmotic pressure.

Reverse osmosis consists of passing the solvent (in this case water) through the semipermeable membrane from the side where the most concentrated solution is (sea water, with dissolved salts), to the opposite side, without the salts passing through. In this case, energy is required, in the form of pressure, which will be slightly higher than the osmotic pressure that would make the low concentration solvent pass to the high concentration side. The pressure necessary to achieve reverse osmosis depends on the amount of dissolved salts and the degree of desalination that is desired. An increase in entropy results from the use of energy in the process.

The sea is a virtually unlimited source of salt water. A reverse osmosis plant needs to process a volume of seawater up to three times greater than the total amount of desalinated water that will be obtained in the end. Therefore, the design of the wells or collection system must consider this factor for their capacity.

The use of a graphene sheet with 1.8 nm pores to replace membranes in the reverse osmosis process for water desalination is in the research phase (TRL2). According to current research, much higher efficiencies would be obtained than with current membranes, and there would be lower energy requirements. In the current state, the drawback is the cost of graphene membranes, but it is expected that in the future these costs can be reduced.[10]​.

Generally, a large tank or pond is used that is filled by gravity at sea level, after coarse filtering. The water from the pond is transported by feed pumps to the desalination system. A supplement of chemical products arrives at the inlet of the feed pumps by means of metering pumps. This is how the water is prepared to pass four types of filters that retain particles larger than four microns. The main step in water production is the separation of H O from the mixture of salts and minerals present in sea water. This step is carried out in the reverse osmosis stage, ensuring that the salts do not cross the membranes of the RO modules. Previously, it must be ensured that the diatom and microalgae particles do not reach the membranes and for this there are three previous sand filtration steps before the last microfiltration step using synthetic fiber cartridges. Filtration success also depends on the proper introduction of coagulants. Depending on the filtration quality, the membrane change cycle is generated between 2 and 5 years. Chemical dispersants introduced before microfiltration prevent the precipitation of minerals within the membranes.

Since all aspects of the process are automated, the operators' job is supervision and maintenance.

The rejected brine is 55% of the raw water (although it depends on the desalination technology used). While 45% of the water obtained leaves at atmospheric pressure, a regulated backpressure must be ensured in the rejection flow. This reject flow always contains something like 55% (100% - % gain) of the pressure energy provided by the pumps and it is highly desirable to recover this energy for higher performance. Some of the recovered energy can return to the same desalination and recovery cycle more than once.

While the plant is in production mode, the outlet pressure is controlled by a regulating valve. 'Pressure Exchanger' converters are used and with them in the pressure exchange up to 95% of the energy of the rejection flow can be recovered directly by means of pumping using positive displacement. This energy recovery pump increases the flow of more raw water to the entrance of the membranes. The plant uses 'Pressure Exchanger' units near each set of reverse osmosis element tubes.

The osmosis water or the permeate from the reverse osmosis modules must be conditioned to meet certain high quality characteristics, since the water produced has an acidic pH and a low carbonate content, which makes it a highly corrosive product. This requires its preparation before distribution and consumption. The pH is adjusted with calcium carbonate to a value of 7.7. Additionally, if required by municipal regulations for the use of drinking water, sodium fluoride and hypochlorite are also added.

Spain is the fifth country in the number of desalination plants in the world with a total of 900 plants that have a capacity of 1.45 million cubic meters per day.[11]​.

Due to their function, desalination plants must be installed near a water source, specifically, the sea. They are dedicated to desalinating seawater, at a distance of between a few tens of meters to 3 kilometers. The further away it is from the coast, the greater the pressure necessary to capture the water and, therefore, the energy consumption will be higher, which will make the entire process more expensive.

The first desalination plant in Spain was built in 1965 in Lanzarote with evaporation technology, through solar energy, which is hardly used today, and which has been replaced by reverse osmosis. This project was initiated by a private body to improve the status of the island and promote tourism. The plant was capable of producing about 2000 cubic meters of water per day. However, the plant consumed more than 50 kWh of electricity per cubic meter of water produced, which means that it was too expensive and that is why its technology was replaced. The success of the project was such that it led to the replication of similar initiatives in other regions, such as Fuerteventura, Gran Canaria and the city of Ceuta.[12]​.

In Las Palmas de Gran Canaria, the first desalination plant in Spain was built with the reverse osmosis method in 1971. It is currently managed by Emalsa. Among the most recently built, the El Prat de Llobregat plant stands out in the highly populated metropolitan region of Barcelona, ​​affected by intermittent droughts and with relatively contaminated surface waters in the Llobregat basin.

Como toda actividad humana, la desalinización de agua de mar no está exenta de impactos ambientales. No obstante, con la evolución de las tecnologías que la hacen posible y de sus procesos, se ha hecho cada vez más sostenible en términos energéticos y de descarga de residuos.[13]​[14]​ Los retos medioambientales en los diseños de las plantas desalinizadoras se pueden recoger en los siguientes puntos:[15]​.

The discharge of concentrated brine makes life difficult for marine ecosystems. Marine life is also influenced by the intake of seawater for the desalination plant. Cuando se extrae una gran cantidad de agua del mar, los organismos marinos y las algas son absorbidos por la toma, lo que provoca una perturbación en el ecosistema.

Concentrated brine is not only concentrated in salt, but also contains chemicals such as pre- and post-treatment anti-scaling agents. Furthermore, the brine discharged from thermal distillation plants exits at a relatively high temperature which means thermal pollution that influences marine life in such a way that only some marine plants or animals can withstand the high temperature near the outlet of thermal distillation plants.

High energy consumption is considered the most influential factor inhibiting the growth of seawater desalination. Currently, most desalination processes are powered by energy obtained from fossil fuels which results in gas emissions that pollute the environment. In the case of solar-based desalination processes, it is considered a promising method to alleviate the environmental impact of water desalination and also provide a sustainable source of drinking water.

Many methods are currently used for brine removal. The brine can be discharged to the sea or river, to solar ponds or injected into deep saline aquifers. Discharging into the sea or ocean is the least expensive method. When brine is discharged into the sea, it tends to sink to the bottom. Typically, the brine discharge is diluted with seawater to reduce its salinity before being discharged into the sea. The brine is discharged into deep seawater that normally has a strong current. This reduces the harmful effects of brine on marine life. Brine discharges to a solar pond or injection into a deep saline aquifer is a more expensive method. These solar ponds and saline aquifers are often located far from the desalination plant, requiring a long pipeline for transportation. This method has drawbacks because it can increase salt in the soil and increases groundwater salinity if linear under the solar pond is not used. Using a solar pond for brine disposal carries the risk of contaminating groundwater.

The desalination process has a long history, which began with the first human attempts to drink sea water, which faced multiple difficulties. It is not clear when our ancestors became frustrated with not being able to drink seawater and thought about purifying it. However, some of the oldest references to the process of desalinating water are found in the Bible.[16]​.

The history of desalination goes back millennia. The Ancient Greek philosopher Aristotle (384-322 BC) already described in his work Metrology[17]​ that "salt water, when converted into steam, becomes sweet and the steam does not form salt water again when it condenses" laying the foundations for thermal desalination. In this same work he also described that "a thin wax vessel will contain drinking water after being submerged for a sufficient time in seawater, this having acted as a filter for the salt" thus laying the foundations for membrane-based desalination. Based on Aristotle's observations, in the 17th century Leonardo da Vinci proposed adapting an alembic to a wood-burning stove to "produce large quantities of drinking water from seawater at a very low cost".[18]

In China, the classic text "Classic of Mountains and Seas in the Warring States Period" (475-221 BC), which is a compilation of mythology and geography, suggests that bamboo mats used to steam rice could form a thin outer layer which possessed adsorption and ion exchange capabilities and could therefore adsorb salt.[16]

Later, Alexander of Aphrodisias (193-217), commenting on Aristotle's book Meteorology, described for the first time a distillation process that made it possible to obtain fresh water from salt water. This method consisted of suspending large sponges in the mouth of a bronze vessel inside which seawater was boiling. The evaporated water was collected in these sponges and when it condensed, it was discovered that it was fresh water.[16]​.

In the century the first patents for thermal desalination devices appeared. William Walcot") proposed a patent in 1675[19]​ on "the art of converting corrupt water into something useful for use and sea water into fresh and fresh water in large quantities by very cheap and simple methods." A few years later, in 1683,[20] Robert Fitzgerald (nephew of Robert Boyle) patented a similar invention that caused litigation between the two: "a way of converting salt or brackish water into fresh water, suitable for drinking, boiling, washing or other ordinary use by means of a certain device or devices not previously used in our domains." Neither of the two patents were ever used due to technical problems in their large-scale extension.[21]​ In 1717, the French doctor Paul Gauthier introduced a new desalination technique that used the alembic.[22]​.

The first invention with large-scale application dates back to 1852, when Alphonse René Le Mire de Normandy" filed a patent on "the production of fresh water from sea water".[23] Thanks to the recent popularization of steam-powered ships, De Normandy's invention was a commercial success that led him to sell more than two thousand of his inventions and found a company to produce them.[23] De Normandy's device can also be considered the first to be used successfully on land on a large scale. In 1861, three of its desalination devices were used by the United States Union Army for months in Key West (Florida) where they provided them with more than 1000 L of drinking water per day. of seawater per day in an area of 4,757 square meters.[22]​.

The first modern desalination plant was built in 1961 by the Dow Chemical Company in Freeport (Texas), Texas. The plant was based on a multi-effect distillation system with 17 energetically integrated effects (stages) with a single point of heat input. The production capacity was 3800 m/day (1 MGD) of drinking water from nearby seawater. The presence of the desalination plant in Freeport "Freeport (Texas)") considerably increased the security of access to water for the local population and industry.[24]​.

The first desalination plant based on the reverse osmosis process was built in 1965 in Coalinga, California. It was a pilot plant with the capacity to produce 19 m/day of drinking water from the brackish water available in the local wells (salinity 2500 mg/L) and used primitive cellulose acetate membranes designed by Sidney Loeb at the University of California at Los Angeles (UCLA).[26] The objective of the pilot plant was to check if it was possible to avoid the consumption of fresh water transported by train or truck from other places. localities.[27]​ The primitive desalination available at the time was finally discarded due to its high cost and a canal "Canal (engineering)") was built to transport fresh water continuously to the city.[27]​.

The last major milestone in the history of desalination is the construction of the first seawater desalination plant based on reverse osmosis technology. The plant was built in Jeddah (Saudi Arabia) in 1976 and used water from the Red Sea (salinity 40,000 mg/L) to produce 12,000 m/day of drinking water.[28] The semipermeable membranes used in the plant were much more sophisticated than those used in Coalinga and were based on a composite material made up of a thin layer of spirally wound polyamide very similar to those used today in day. Its membranes allowed it to work between 60 and 70 bar "Bar (pressure unit)") of pressure (depending on the degree of fouling#Fouling "Membrane (object)")) with an average recovery of 30% in drinking water.[28]​.