There are several methods. Each has advantages and disadvantages but all are useful.

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Technologies

Desalination is an artificial process by which saline water (generally sea water) is converted to fresh water. The most common desalination processes are distillation and reverse osmosis

There are several methods. Each has advantages and disadvantages but all are useful. The methods can be divided into membrane-based (eg, reverse osmosis) and thermal-based (e.g multistage flash distillation) methods. The traditional process of desalination is distillation (le. boiling and re-condensation of seawater to leave salt and impurities behind)

There are currently two technologies with a large majority of the world's desalination capacity, multi stage flash distillation and reverse comosis,

Distillation

Solar distillation

Solar distillation mimics the natural water cycle, in which the sun heats sea water enough for evaporation to occur. After evaporation, the water vapor is condensed onto a cool surface, There are two types of solar desalination. The first type uses photovoltaic cells to convert solar energy to electrical energy to power desalination. The second type converts solar energy to heat, and is known as solar thermal powered desalination.

Natural evaporation

Water can evaporate through several other physical effects besides solar irradiation, These effects have been included in a multidisciplinary desalination methodology. in the IBTS Greenhouse. The IBTS is an industrial desalination (power plant on one side and a greenhouse operating with the natural water cycle (scaled down 1:10) on the other side. The various processes of evaporation and condensation are hosted in low-tech utilities, partly underground and the architectural shape of the building itself. This integrated biotectural system is most suitable for large scale desert greening as it has a km footprint for the water distillation and the same for landscape transformation in desert greening, respectively the regeneration of natural fresh water cycles.

Vacuum distillation

In vacuum distillation atmospheric pressure is reduced, thus lowering the temperature required to evaporate the water. Liquids boil when the vapor pressure equals the ambient pressure and vapor pressure increases with temperature.

Effectively, liquids boll at a lower

Water desalination

Methods

Distillation

Multi-stage flash distillation (MSF)

Multiple-effect distillation (MED)

Vapor-compression (VC)

lon exchange

Membrane processes

lectrodialysis reversal (EDR)

Reverse osmosis (RO)

Nanofiltration (NF)

Membrane distillation (MD)

Forward osmosis (FO)

Freezing desalination

Geothermal desalination

Solar desalination

Solar humidification-dehumidification (HDH)

Multiple-effect humidification (MEH)

Seawater greenhouse

Methane hydrate crystallization

High grade water recycling

Wave-powered desalination

temperature, when the ambient atmospheric pressure is less than usual atmospheric pressure. Thus, because of the reduced pressure, low-temperature "waste" heat from electrical power generation or industrial processes con be employed.

Multi-stage flash distillation

Water is evaporated and separated from sea water through multi-stage flash distillation, which in a series of flash evaporations, Each subsequent flash process uses energy released from the condensation of the water vapor from the previous step.

Multiple-effect distillation

Multiple-effect distillation (MED) works through a series of steps called "effects Incoming water is sprayed onto pipes which are then heated to generate steam. The steam is then used to heat the next batch of incoming sea water. To increase efficiency, the steam used to heat the sea water can be taken from nearby power plants. Although this method is the most thermodynamically efficient among methods powered by heat, a few limitations exist such as a max temperature and max number of effects

Vapor-compression distillation

Vapor-compression evaporation involves using either a mechanical compressor or a jet stream to compress the vapor present above the liquid. The compressed vapor is then used to provide the heat needed for the evaporation of the rest of the sea water. Since this system only requires powet, it is more cost effective if kept at a small scale

Membrane distillation

Membrane distillation uses a temperature difference across a membrane to evaporate vapor from a brine solution and condense pure water on the colder side, The design of the membrane can have a significant effect on efficiency and durability. A study found that a membrane created via co-axial electrospinning of PVDF-HFP and silica aerogel was able to filter 99.99% of salt after continuous 30-day usage.

Osmosis

Reverse osmosis

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The leading process for desalination in terms of installed capacity and yearly growth is reverse osmosis (RO) The RO membrane processes use semipermeable membranes and applied pressure (on the membrane feed side) to preferentially induce water permeation through the membrane while rejecting salts. Reverse osmosis plant membrane systems typically use less energy than thermal desalination processes. Energy cost in desalination processes varies considerably depending on water salinity, plant size and process type. At present the cost of seawater desalination, for example, is higher than traditional water sources, but it is expected that costs will continue to decrease with technology improvements that include, but are not limited to, improved efficiency reduction in plant footprint, improvements to plant operation and optimization, more effective feed pretreatment, and lower cost energy sources,

Reverse osmosis uses a thin-film composite membrane, which comprises an ultra-thin, aromatic polyamide thin-film. This polyamide film gives the membrane its transport properties, whereas the remainder of the thin-film composite membrane provides mechanical support. The polyamide film is a dense, void-free polymer with a high surface area, allowing for its high water permeability. A 2021 study found that the water permeability is primarily governed by the internal nanoscale mass distribution of the polyamide active layer ha

The reverse osmosis process requires maintenance. Various factors interfere with efficiency, ionic contamination (calcium, magnesium etc.); dissolved organic carbon (DOC); bacteria; viruses colloids and insoluble particulates, biofouling and scaling. In extreme cases, the RO membranes are destroyed. To mitigate damage, various pretreatment stages are introduced. Anti-scaling inhibitors include acids and other agents such as the organic polymers polyacrylamide and polymateic acid, phosphonates and polyphosphates. Inhibitors for fouling are biocides (as oxidants against bacteria and viruses), such as chlorine, ozone, sodium or calcium hypochlorite. At regular intervais, depending on the membrane contamination, fluctuating seawater conditiona; or when prompted by monitoring processes, the membranes need to be cleaned, known as emergency or shock-flushing. Flushing is done with inhibitors in a fresh water solution and the system must go offline. This procedure is environmentally risky, since contaminated water is diverted into the ocean without treatment. Sensitive marine habitats can be irreversibly damaged

Off-grid solar powered desalination units use solar energy to fill a buffer tank on a hill with seawater. The reverse osmosis process receives its pressurized seawater feed in non-sunlight hours by gravity, resulting in sustainable drinking water production without the need for fossil fuels, an electricity grid or batteries Osmosis) Nano-tubes are also used for the same function (le., Reverse

Deep sea reverse osmosis (DSRO) installs equipment on the seabed to force water through RO membranes using the ocear's naturally occurring water pressure. A 2021 study suggested DSRO could improve energy efficiency compared to standard RO by up to 50%. The concept of DSRO has long been known, but has only recently become feasible due to technological advances from the deep sea oil and gas industry, drawing early-stage investments in DSRO startups,

Forward osmosis

Forward samosis uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for this separation is an osmotic pressure gradient, such as a "draw" solution of high concentration.