Thermally-driven desalination technologies are frequently suggested for use with low-temperature waste heat sources .

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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 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. 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 Guihi, Maldives4444

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 8-10 °C (14-18 "F) between two volumes of water Cool ocean water is supplied from depths of up to 600 m (2,000 ft). 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,

Experiments were conducted in the US and Japan to test the approach, in Japan, a spray-flash evaporation system was tested by Saga University in Hawail, the National Energy Laboratory tested an open-cycle OTEC plant with fresh water and power production using a temperature difference of 20 °C (36 'F) between surface water and water at a depth of around 500 m (1,600 ft) LTTD was studied by India's National Institute of Ocean Technology (NICT) in 2004. Their first LTTD plant opened in 2005 at Kavaratti in the Lakshadweep islands. The plant's capacity is 100.000 L (22.000 imp galt 26,000 US gal)/day, at a capital cost of INR 50 million (€922,000). The plant uses deep water at a temperature of 10 to 12 °C (50 10 54 "F). In 2007, NIOT opened an experimental, floating LTTD plant off the coast of Chennai, with a capacity of 1,000,000 L (220,000 imp gal: 260,000 US gal)/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

Thermolonic process

In October 2009, Saltworks Technologies announced a process that uses solar or other thermal heat to drive an ionic current that removes all sodium and chlorine ions from the water using ion exchange membranes .

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

lon concentration polarisation (ICP)

In 2022, using a technique that used multiple stages of ion concentration polarisation followed single stage of electrodialysis, researchers from MIT manage to create a filterless portable desalination unit, capable of removing both dissolved salts and suspended solids Designed for use by non-experts in remote areas or natural disasters, as well as on military operations, the prototype is the size of a suitcase, measuring 42 x 33.5 x 19 cm³ and weighing 9.25 kg. 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 panels. Using a filterless design at low pressures or replaceable filters significantly reduces maintenance requirements, while the device Itself is self cleaning However, the device is limited to producing 0.33 liters of drinking water per minute. 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 20

Other approaches

Adsorption-based desalination (AD) relies on the moisture absorption properties of certain materials such as Silica Gel

Forward osmosis

One process was commercialized by Modern Water PLC using forward osmosis, with a number of plants reported to be in operation .

Hydrogel based desalination.

salinity

desalination flow of tons

Scherme of the desalination machine the desalination box of volume contains a pet of solume V which is separated by a sive from the VoVhee Vat The bo solution to two big tanks with high and low salinity by twe taps which can be opened and closed as tested. The chain of buckets expresses the fresh water consumption towed by efling the low sality reservoir by saft water

The idea of the method is in the fact that when the hydrogel is put into contact with aqueous sa 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 sæve 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 Camot 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,

Small-scale solar

The United States, France and the United Arab Emirates are working to develop practical solar desalination 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 PET bottles or energy-consuming water transport 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,

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 centrifuges 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

Geothermal

Geothermal energy can drive desalination. In most locations, geothermal desalination beats using scarce groundwater or surface water, environmentally and economically.

Nanotechnology

Nanotube membranes 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

Hermetic, sulphonated nano-composite membranes have shown to be capable of removing various contaminants to the parts per billion level, and have little or no susceptiblity to high salt concentration levels

Blomimesis

Biomimetic membranes are another approach,

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. As of 2012 a demonstration plant was operating in Singapore, Researchers at the University of Texas at Austin and the University of Marburg are developing more efficient methods of electrochemically mediated seawater desalination, Des

Electrokinetic shocks

A process employing electrokinetic shock waves can be used to accomplish membraneless desalination at ambient temperature and pressure. In this process, anions and cations in salt water are exchanged for carbonate anioris 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 of this method is on par with electrodialysin and reverse osmosis

Temperature swing solvent extraction

Temperature Swing Solvent Extraction (TISSE) 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 70 °C (158 °F), which may not require active heating in a study, TSSE removed up to 98.4 percent of the salt in brine. A solvent whose solubility vanes 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.

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 m³/day. The system operates with no external power, and is constructed of recycled plastic bottles .