Editing Desalination (section)

==Experimental techniques==
Other desalination techniques include:

===Waste heat===
Thermally-driven desalination technologies are frequently suggested for use with low-temperature [[waste heat]] sources, as the low temperatures are not useful for [[process heat]] needed in many industrial processes, but ideal for the lower temperatures needed for desalination.<ref name=WarsingerEntropy /> In fact, such pairing with waste heat can even improve electrical process:
[[Diesel generators]] commonly provide electricity in remote areas. About 40–50% of the energy output is low-grade heat that leaves the engine via the exhaust. Connecting a thermal desalination technology such as [[membrane distillation]] system to the diesel engine exhaust repurposes this low-grade heat for desalination. The system actively cools the [[diesel generator]], improving its efficiency and increasing its electricity output. This results in an energy-neutral desalination solution. An example plant was commissioned by Dutch company [[Aquaver]] in March 2014 for [[Gulhi]], Maldives.<ref>[http://www.eip-water.eu/desalination-plant-powered-waste-heat-opens-maldives/ "Desalination plant powered by waste heat opens in Maldives"] ''European Innovation Partnerships (EIP) news''. Retrieved March 18, 2014</ref><ref>[http://www.desalination.com/wdr/50/8/island-finally-gets-its-own-supply/ "Island finally gets its own water supply"] {{webarchive|url=https://web.archive.org/web/20140318193613/http://www.desalination.com/wdr/50/8/island-finally-gets-its-own-supply |date=March 18, 2014 }}, ''Global Water Intelligence'', February 24, 2014. Retrieved March 18, 2014</ref>

===Low-temperature thermal===
Originally stemming from [[ocean thermal energy conversion]] research, [[low-temperature thermal desalination]] (LTTD) takes advantage of water boiling at low pressure, even at [[ambient temperature]]. The system uses pumps to create a low-pressure, low-temperature environment in which water boils at a temperature gradient of {{convert|8|-|10|C-change}} between two volumes of water. Cool ocean water is supplied from depths of up to {{convert|600|m|abbr=on}}. This water is pumped through coils to condense the water vapor. The resulting condensate is purified water. LTTD may take advantage of the temperature gradient available at power plants, where large quantities of warm wastewater are discharged from the plant, reducing the energy input needed to create a temperature gradient.<ref name="isope1">{{cite web|last=Sistla|first=Phanikumar V.S.|title=Low Temperature Thermal DesalinbationPLants|url=http://www.isope.org/publications/proceedings/ISOPE_OMS/OMS%202009/papers/M09-83Sistla.pdf|work=Proceedings of the Eighth (2009) ISOPE Ocean Mining Symposium, Chennai, India, September 20–24, 2009|publisher=International Society of Offshore and Polar Engineers|access-date=June 22, 2010|display-authors=etal|archive-url=https://web.archive.org/web/20111004094556/http://www.isope.org/publications/proceedings/ISOPE_OMS/OMS%202009/papers/M09-83Sistla.pdf|archive-date=October 4, 2011|url-status=dead}}</ref>

Experiments were conducted in the US and Japan to test the approach. In Japan, a spray-flash evaporation system was tested by Saga University.<ref>Haruo Uehara and Tsutomu Nakaoka [http://www.ioes.saga-u.ac.jp/VWF/general-review_e.html Development and Prospective of Ocean Thermal Energy Conversion and Spray Flash Evaporator Desalination] {{webarchive|url=https://web.archive.org/web/20120322075415/http://www.ioes.saga-u.ac.jp/VWF/general-review_e.html |date=March 22, 2012 }}. ioes.saga-u.ac.jp</ref> In Hawaii, the National Energy Laboratory tested an open-cycle OTEC plant with fresh water and power production using a temperature difference of {{Convert|20|C-change}} between surface water and water at a depth of around {{convert|500|m|abbr=on}}. LTTD was studied by India's National Institute of Ocean Technology (NIOT) in 2004. Their first LTTD plant opened in 2005 at Kavaratti in the [[Lakshadweep]] islands. The plant's capacity is {{convert|100000|L|abbr=on}}/day, at a capital cost of INR 50 million (€922,000). The plant uses deep water at a temperature of {{convert|10|to|12|C}}.<ref name=irc>[https://www.indiatimes.com/news/india/indian-scientists-develop-world-s-first-low-temperature-thermal-desalination-plant-357286.html Indian Scientists Develop World's First Low Temperature Thermal Desalination Plant]. Retrieved January 1, 2019.</ref> In 2007, NIOT opened an experimental, floating LTTD plant off the coast of [[Chennai]], with a capacity of {{convert|1000000|L|abbr=on}}/day. A smaller plant was established in 2009 at the North Chennai Thermal Power Station to prove the LTTD application where power plant cooling water is available.<ref name="isope1"/><ref>[http://www.headlinesindia.com/archive_html/18April2007_35210.html Floating plant, India] {{webarchive|url=https://web.archive.org/web/20080827213914/http://www.headlinesindia.com/archive_html/18April2007_35210.html |date=August 27, 2008 }}. Headlinesindia.com (April 18, 2007). Retrieved May 29, 2011.</ref><ref>[https://web.archive.org/web/20071031012249/http://www.hindu.com/2007/04/21/stories/2007042109200400.htm Tamil Nadu / Chennai News : Low temperature thermal desalination plants mooted]. The Hindu (April 21, 2007). Retrieved March 20, 2011.</ref>

===Thermoionic process===
In October 2009, Saltworks Technologies announced a process that uses solar or other thermal heat to drive an [[ion]]ic current that removes all [[sodium]] and [[chlorine]] ions from the water using ion-exchange membranes.<ref>[http://www.economist.com/sciencetechnology/displayStory.cfm?story_id=14743791 Current thinking], ''The Economist'', October 29, 2009</ref>

===Evaporation and condensation for crops===
The [[Seawater greenhouse]] uses natural evaporation and condensation processes inside a [[greenhouse]] powered by solar energy to grow crops in arid coastal land.

=== Ion concentration polarisation (ICP) ===
In 2022, using a technique that used multiple stages of ion [[Concentration polarization|concentration polarisation]] followed by a single stage of [[electrodialysis]], researchers from [[Massachusetts Institute of Technology|MIT]] manage to create a filterless portable desalination unit, capable of removing both dissolved salts and [[suspended solids]].<ref name="YoonKwonKangBrackHan2022">{{Cite journal |last1=Yoon |first1=Junghyo |last2=Kwon |first2=Hyukjin J. |last3=Kang |first3=SungKu |last4=Brack |first4=Eric |last5=Han |first5=Jongyoon |date=2022-05-17 |title=Portable Seawater Desalination System for Generating Drinkable Water in Remote Locations |url=https://pubs.acs.org/doi/10.1021/acs.est.1c08466 |journal=Environmental Science & Technology |language=en |volume=56 |issue=10 |pages=6733–6743 |doi=10.1021/acs.est.1c08466 |pmid=35420021 |bibcode=2022EnST...56.6733Y |s2cid=248155686 |issn=0013-936X}}</ref> Designed for use by non-experts in remote areas or [[natural disaster]]s, as well as on military operations, the prototype is the size of a suitcase, measuring 42 × 33.5 × 19&nbsp;cm<sup>3</sup> and weighing 9.25&nbsp;kg.<ref name="YoonKwonKangBrackHan2022" /> The process is fully automated, notifying the user when the water is safe to drink, and can be controlled by a single button or smartphone app. As it does not require a high pressure pump the process is highly energy efficient, consuming only 20 watt-hours per liter of drinking water produced, making it capable of being powered by common portable [[solar panel]]s. Using a filterless design at low pressures or replaceable filters significantly reduces maintenance requirements, while the device itself is self cleaning.<ref name="MIT2022">{{Cite web |title=From seawater to drinking water, with the push of a button |url=https://news.mit.edu/2022/portable-desalination-drinking-water-0428 |access-date=2022-08-03 |website=MIT News {{!}} Massachusetts Institute of Technology |date=28 April 2022 |language=en}}</ref> However, the device is limited to producing 0.33 liters of drinking water per minute.<ref name="YoonKwonKangBrackHan2022" /> There are also concerns that fouling will impact the long-term reliability, especially in water with high [[turbidity]]. The researchers are working to increase the efficiency and production rate with the intent to commercialise the product in the future, however a significant limitation is the reliance on expensive materials in the current design.<ref name="MIT2022" />

===Other approaches===

Adsorption-based desalination (AD) relies on the moisture absorption properties of certain materials such as Silica Gel.<ref>{{cite web|title=A Study of Silica Gel Adsorption Desalination System|url=https://digital.library.adelaide.edu.au/dspace/bitstream/2440/82463/8/02whole.pdf|work=Jun Wei WU|access-date=November 3, 2016}}</ref>

==== Forward osmosis ====
One process was commercialized by Modern Water PLC using [[forward osmosis]], with a number of plants reported to be in operation.<ref>{{cite journal|title=FO plant completes 1-year of operation|url=http://www.modernwater.co.uk/files/files/WDR%20-%2044.pdf|archive-url=https://web.archive.org/web/20241222200124/http://www.modernwater.co.uk/files/files/WDR%20-%2044.pdf|url-status=dead|archive-date=December 22, 2024|access-date=May 28, 2011|journal=Water Desalination Report|date=November 15, 2010|pages=2–3}}</ref><ref>{{cite news|title=Modern Water taps demand in Middle East|url=http://www.modernwater.co.uk/files/files/demand_mdeast_n.pdf|access-date=May 28, 2011|newspaper=The Independent|date=November 23, 2009}}{{Dead link|date=November 2019 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite book|chapter-url=https://www.osmotic-engineering.com/wp-content/uploads/2019/08/PER11-198.pdf|chapter=Forward Osmosis Desalination: A Commercial Reality|author1=Thompson N.A. |author2=Nicoll P.G. |date=September 2011|publisher=International Desalination Association|title= Proceedings of the IDA World Congress|location=Perth, Western Australia}}</ref>

==== Hydrogel based desalination ====
[[File:TOC new.png|thumb|upright=1.25|Scheme of the desalination machine: the desalination box of volume <math>V_{box}</math> contains a gel of volume <math>V_{gel}</math> which is separated by a sieve from the outer solution volume <math>V_{out} = V_{box} - V_{gel}</math>.  The box is connected to two big tanks with high and low salinity by two taps which can be opened and closed as desired.  The chain of buckets expresses the fresh water consumption followed by refilling the low-salinity reservoir by salt water.<ref name="RudBorisovKosovan2018">{{cite journal|title=Thermodynamic model for a reversible desalination cycle using weak polyelectrolyte hydrogels|journal=Desalination|volume=442|page=32|doi=10.1016/j.desal.2018.05.002 |ref=Rud2018|year=2018|last1=Rud|first1=Oleg|last2=Borisov|first2=Oleg|last3=Košovan|first3=Peter|bibcode=2018Desal.442...32R |s2cid=103725391}}</ref>]]
The idea of the method is in the fact that when the hydrogel is put into contact with aqueous salt solution, it swells absorbing a solution with the ion composition different from the original one. This solution can be easily squeezed out from the gel by means of sieve or microfiltration membrane. The compression of the gel in closed system lead to change in salt concentration, whereas the compression in open system, while the gel is exchanging ions with bulk, lead to the change in the number of ions. The consequence of the compression and swelling in open and closed system conditions mimics the reverse Carnot Cycle of refrigerator machine. The only difference is that instead of heat this cycle transfers salt ions from the bulk of low salinity to a bulk of high salinity. Similarly to the Carnot cycle this cycle is fully reversible, so can in principle work with an ideal thermodynamic efficiency. Because the method is free from the use of osmotic membranes it can compete with reverse osmosis method. In addition, unlike the reverse osmosis, the approach is not sensitive to the quality of feed water and its seasonal changes, and allows the production of water of any desired concentration.<ref name="RudBorisovKosovan2018"/>

==== Small-scale solar ====
The United States, France and the United Arab Emirates are working to develop practical [[solar desalination]].<ref>[http://cleantechnica.com/2015/01/25/uae-france-announce-partnership-jointly-fund-renewable-energy-projects/ UAE & France Announce Partnership To Jointly Fund Renewable Energy Projects], Clean Technica, January 25, 2015</ref> AquaDania's WaterStillar has been installed at Dahab, Egypt, and in Playa del Carmen, Mexico. In this approach, a [[solar thermal collector]] measuring two square metres can distill from 40 to 60 litres per day from any local water source – five times more than conventional stills. It eliminates the need for plastic [[Polyethylene terephthalate|PET]] bottles or energy-consuming water transport.<ref>[http://www.barrymansfield.com/pdf/Tapping%20A%20Market%20CNBC%20European%20Business.pdf Tapping the Market], CNBC European Business, October 1, 2008</ref> In Central California, a startup company WaterFX is developing a solar-powered method of desalination that can enable the use of local water, including runoff water that can be treated and used again. Salty groundwater in the region would be treated to become freshwater, and in areas near the ocean, seawater could be treated.<ref>{{cite web|last1=Peters|first1=Adele|title=Can This Solar Desalination Startup Solve California Water Woes?|url=http://www.fastcoexist.com/3026234/can-this-solar-desalination-startup-solve-california-water-woes|work=Fast Company|access-date=February 24, 2015|date=2014-02-10}}</ref>

==== Passarell ====
The Passarell process uses reduced atmospheric pressure rather than heat to drive evaporative desalination. The pure water vapor generated by distillation is then compressed and condensed using an advanced compressor. The compression process improves distillation efficiency by creating the reduced pressure in the evaporation chamber. The compressor [[centrifuge]]s the pure water vapor after it is drawn through a demister (removing residual impurities) causing it to compress against tubes in the collection chamber. The compression of the vapor increases its temperature. The heat is transferred to the input water falling in the tubes, vaporizing the water in the tubes. Water vapor condenses on the outside of the tubes as product water. By combining several physical processes, Passarell enables most of the system's energy to be recycled through its evaporation, demisting, vapor compression, condensation, and water movement processes.<ref>[http://www.waterdesalination.com/theory.htm The "Passarell" Process]. Waterdesalination.com (November 16, 2004). Retrieved May 14, 2012.</ref>

==== Geothermal ====
Geothermal energy can drive desalination. In most locations, [[geothermal desalination]] beats using scarce groundwater or surface water, environmentally and economically.{{Citation needed|date=January 2012}}

==== Nanotechnology ====
[[Nanotube membrane]]s of higher permeability than current generation of membranes may lead to eventual reduction in the footprint of RO desalination plants. It has also been suggested that the use of such membranes will lead to reduction in the energy needed for desalination.<ref name="LLNL">{{cite press release
 |title       = Nanotube membranes offer possibility of cheaper desalination
 |publisher   = [[Lawrence Livermore National Laboratory]] Public Affairs
 |date        = May 18, 2006
 |url         = http://www.llnl.gov/pao/news/news_releases/2006/NR-06-05-06.html
 |access-date  = September 7, 2007
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20061001091253/http://www.llnl.gov/pao/news/news_releases/2006/NR-06-05-06.html
 |archive-date = October 1, 2006
 |df          = mdy-all
}}</ref>

Hermetic, sulphonated [[Nanotechnology|nano]]-composite membranes have shown to be capable of removing various contaminants<!-- The previous statement claimed that "almost all contaminants are removed..."  This is not a proper statement. The statement should focus on what was actually shown and proven.  --> to the parts per billion level, <!-- This statement is vague and not helpful. The specific process needs to be mentioned or the statement should be removed. -->and have little or no susceptibility to high salt concentration levels.<ref>{{cite web|last=Cao|first=Liwei|url=https://patents.google.com/patent/US8222346/en?oq=Dais+Analytic+desalination |title=Patent US8222346 – Block copolymers and method for making same |access-date=July 9, 2013}}</ref><ref>{{cite web|last=Wnek|first=Gary|url=https://patents.google.com/patent/US6383391/en?oq=Dais+Analytic+desalination |title=Patent US6383391 – Water-and ion-conducting membranes and uses thereof |access-date=July 9, 2013}}</ref><ref>{{cite news|last=Cao|first=Liwei|url=http://www.prnewswire.com/news-releases/dais-analytic-corporation-announces-product-sale-to-asia-functional-waste-water-treatment-pilot-and-key-infrastructure-appointments-210236821.html |title= Dais Analytic Corporation Announces Product Sale to Asia, Functional Waste Water Treatment Pilot, and Key Infrastructure Appointments |agency=PR Newswire |date=June 5, 2013 |access-date=July 9, 2013}}</ref>

==== Biomimesis ====
[[Biomimetic]] [[Biological membrane|membranes]] are another approach.<ref>{{cite web |url= http://www.sandia.gov/water/desal/research-dev/membrane-tech.html |title=Sandia National Labs: Desalination and Water Purification: Research and Development |publisher=sandia.gov |year=2007 |access-date=July 9, 2013}}</ref>

==== Electrochemical ====
In 2008, Siemens Water Technologies announced technology that applied electric fields to desalinate one cubic meter of water while using only a purported 1.5 kWh of energy. If accurate, this process would consume one-half the energy of other processes.<ref>[http://news.asiaone.com/News/AsiaOne%2BNews/Singapore/Story/A1Story20080623-72473.html Team wins $4m grant for breakthrough technology in seawater desalination] {{webarchive|url=https://web.archive.org/web/20090414025925/http://news.asiaone.com/News/AsiaOne%2BNews/Singapore/Story/A1Story20080623-72473.html |date=April 14, 2009 }}, The Straits Times, June 23, 2008</ref> As of 2012 a demonstration plant was operating in Singapore.<ref>{{cite web|url=http://www.mining.com/new-desalination-process-uses-50-less-energy-78254/|title=New desalination process uses 50% less energy {{!}} MINING.com|date=2012-09-06|website=MINING.com|language=en-US|access-date=2016-06-11}}</ref> Researchers at the University of Texas at Austin and the University of Marburg are developing more efficient methods of electrochemically mediated seawater desalination.<ref>{{cite web|url=https://www.sciencedaily.com/releases/2013/06/130627125525.htm|title=Chemists Work to Desalinate the Ocean for Drinking Water, One Nanoliter at a Time|work=Science Daily|date=June 27, 2013|access-date=June 29, 2013}}</ref>

==== Electrokinetic shocks ====
A process employing electrokinetic shock waves can be used to accomplish membraneless desalination at ambient temperature and pressure.<ref>{{cite journal |url=http://microfluidics.stanford.edu/Publications/ITP/Shkolnikov%202012%20Desalination%20and%20hydrogen,%20chlorine,%20and%20sodium%20hydroxide%20production%20via%20electrophoretic%20ion%20exchange%20and%20precipitation.pdf |title=Desalination and hydrogen, chlorine, and sodium hydroxide production via electrophoretic ion exchange and precipitation |volume=14 |issue=32 |pages=11534–45 |first1=Viktor |last1=Shkolnikov |journal=Physical Chemistry Chemical Physics |date=April 5, 2012 |access-date=July 9, 2013 |doi=10.1039/c2cp42121f |pmid=22806549 |last2=Bahga |first2=Supreet S. |last3=Santiago |first3=Juan G. |bibcode=2012PCCP...1411534S |archive-date=December 8, 2021 |archive-url=https://web.archive.org/web/20211208155008/http://microfluidics.stanford.edu/Publications/ITP/Shkolnikov%202012%20Desalination%20and%20hydrogen,%20chlorine,%20and%20sodium%20hydroxide%20production%20via%20electrophoretic%20ion%20exchange%20and%20precipitation.pdf |url-status=dead }}</ref> In this process, anions and cations in salt water are exchanged for carbonate anions and calcium cations, respectively using electrokinetic shockwaves. Calcium and carbonate ions react to form [[calcium carbonate]], which precipitates, leaving fresh water. The theoretical [[Energy efficiency (physics)|energy efficiency]] of this method is on par with [[electrodialysis]] and [[reverse osmosis]].

==== Temperature swing solvent extraction ====
Temperature Swing Solvent Extraction (TSSE) uses a solvent instead of a membrane or  high temperatures.

[[Solvent extraction]] is a common technique in [[chemical engineering]]. It can be activated by low-grade heat (less than {{Convert|70|C||abbr=}}, which may not require active heating. In a study, TSSE removed up to 98.4 percent of the salt in brine.<ref>{{Cite web|url=https://www.cnet.com/news/scientists-discover-game-changing-way-to-remove-salt-from-water/|title=Scientists discover a game-changing way to remove salt from water|first=Claire|last=Reilly|website=CNET}}</ref> A solvent whose solubility varies with temperature is added to saltwater. At room temperature the solvent draws water molecules away from the salt. The water-laden solvent is then heated, causing the solvent to release the now salt-free water.<ref>{{Cite web|url=https://singularityhub.com/2019/06/18/inching-towards-abundant-water-new-progress-in-desalination-tech/|title=Inching Towards Abundant Water: New Progress in Desalination Tech|last=Ramirez|first=Vanessa Bates|date=2019-06-18|website=Singularity Hub|language=en-US|access-date=2019-06-19}}</ref>

It can desalinate extremely salty brine up to seven times as salty as the ocean. For comparison, the current methods can only handle brine twice as salty.

==== Wave energy ====
A small-scale offshore system uses wave energy to desalinate 30–50 m<sup>3</sup>/day. The system operates with no external power, and is constructed of recycled plastic bottles.<ref>{{Cite web |last=Blain |first=Loz |date=2022-11-21 |title=Wave-powered buoys vastly reduce the ecological cost of desalination |url=https://newatlas.com/good-thinking/oneka-wave-power-desalination/ |access-date=2022-11-25 |website=New Atlas |language=en-US}}</ref>