Desalination

Desalination
This article is about removing salt from water. For soil desalination, see Soil salinity control.
Water desalination
Methods

Desalination, desalinization, or desalinisation refers to any of several processes that remove some amount of salt and other minerals from water. More generally, desalination may also refer to the removal of salts and minerals,[1] as in soil desalination.[2]

Water is desalinated in order to convert salt water to fresh water so it is suitable for human consumption or irrigation. Sometimes the process produces table salt as a by-product. Desalination is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused on developing cost-effective ways of providing fresh water for human use in regions where the availability of fresh water is, or is becoming, limited.

Large-scale desalination typically uses extremely large amounts of energy as well as specialized, expensive infrastructure, making it very costly compared to the use of fresh water from rivers or groundwater.[3]

However, along with recycled water this is one of the few non-rainfall dependent water sources particularly relevant to countries like Australia which traditionally have relied on rainfall in dams to provide their drinking water supplies.

The world's largest desalination plant is the Jebel Ali Desalination Plant (Phase 2) in the United Arab Emirates. It is a dual-purpose facility that uses multi-stage flash distillation and is capable of producing 300 million cubic metres of water per year. By comparison the largest desalination plant in the United States is located in Tampa Bay, Florida, and operated by Tampa Bay Water, which began desalinating 34.7 million cubic meters of water per year in December 2007.[4] The Tampa Bay plant runs at around 12% the output of the Jebel Ali Desalination Plants. The largest desalination plant in South Asia is the Minjur Desalination Plant near Chennai in India which produces 100,000 cubic meters of water per day, or 36.5 million cubic meters of water per year.[5][6] According to International Desalination Association 2009, there are 14,451 desalination plants in operation worldwide, producing 59.9 million cubic meters per day (15.8 billion gallons a day), a year on year increase of 12.3%.[7]

Schematic of a multi-stage flash desalinator
A – Steam in
B – Seawater in
C – Potable water out
D – Waste out
E – Steam out
F – Heat exchange
G – Condensation collection
H – Brine heater
Plan of a typical reverse osmosis desalination plant

Contents

Methods

The traditional process used in these operations is vacuum distillation—essentially the boiling of water at less than atmospheric pressure and thus a much lower temperature than normal. This is because the boiling of a liquid occurs when the vapor pressure equals the ambient pressure and vapor pressure increases with temperature. Thus, because of the reduced temperature, energy is saved. A leading distillation method is multi-stage flash distillation accounting for 85% of production worldwide in 2004.[8]

Reverse osmosis desalination plant in Barcelona, Spain

The principal competing processes use membranes to desalinate, principally applying reverse osmosis technology.[9] Membrane processes use semi-permeable membranes and pressure to separate salts from water. Reverse osmosis plant membrane systems typically use less energy than thermal distillation, which has led to a reduction in overall desalination costs over the past decade. Desalination remains energy intensive, however, and future costs will continue to depend on the price of both energy and desalination technology.

Considerations and criticism

Cogeneration

Cogeneration is the process of using excess heat from power production to accomplish another task. For desalination, cogeneration is the production of potable water from seawater or brackish groundwater in an integrated, or "dual-purpose", facility in which a power plant is used as the source of energy for the desalination process. The facility’s energy production may be dedicated entirely to the production of potable water (a stand-alone facility), or excess energy may be produced and incorporated into the energy grid (a true cogeneration facility). There are various forms of cogeneration, and theoretically any form of energy production could be used. However, the majority of current and planned cogeneration desalination plants use either fossil fuels or nuclear power as their source of energy. Most plants are located in the Middle East or North Africa, due to their petroleum resources and subsidies. The advantage of dual-purpose facilities is that they can be more efficient in energy consumption, thus making desalination a more viable option for drinking water in areas of scarce water resources.[10][11]

Shevchenko BN350, a nuclear-heated desalination unit

In a December 26, 2007, opinion column in the The Atlanta Journal-Constitution, Nolan Hertel, a professor of nuclear and radiological engineering at Georgia Tech, wrote, "... nuclear reactors can be used ... to produce large amounts of potable water. The process is already in use in a number of places around the world, from India to Japan and Russia. Eight nuclear reactors coupled to desalination plants are operating in Japan alone ... nuclear desalination plants could be a source of large amounts of potable water transported by pipelines hundreds of miles inland..."[12]

Additionally, the current trend in dual-purpose facilities is hybrid configurations, in which the permeate from an RO desalination component is mixed with distillate from thermal desalination. Basically, two or more desalination processes are combined along with power production. Such facilities have already been implemented in Saudi Arabia at Jeddah and Yanbu.[13]

A typical aircraft carrier in the U.S. military uses nuclear power to desalinate 400,000 US gallons (1,500,000 l; 330,000 imp gal) of water per day.[14]

Economics

A number of factors determine the capital and operating costs for desalination: capacity and type of facility, location, feed water, labor, energy, financing, and concentrate disposal. Desalination stills now control pressure, temperature and brine concentrations to optimize the water extraction efficiency. Nuclear-powered desalination might be economical on a large scale.[15][16]

While noting that costs are falling, and generally positive about the technology for affluent areas that are proximate to oceans, one study argues that "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 biggest water problems." and "Indeed, one needs to lift the water by 2,000 metres (6,600 ft), or transport it over more than 1,600 kilometres (990 mi) 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, high transport costs would add to the high 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. In many places, the dominant cost is desalination, not transport; the process would therefore be relatively less expensive in places like Beijing, Bangkok, Zaragoza, Phoenix, and, of course, coastal cities like Tripoli."[17] After being desalinated at Jubail, Saudi Arabia, water is pumped 200 miles (320 km) inland through a pipeline to the capital city of Riyadh.[18] For cities on the coast, desalination is being increasingly viewed as an untapped and unlimited water source.

Desalination makes sense only after less expensive options are exhausted, including recycling water and fixing broken infrastructure.[citation needed] Water is reused in Las Vegas NV, Fountain Valley CA, Fairfax VA, El Paso TX and Scottsdale AZ. Compared to desalinated sea water, recycling requires 50% less energy due to the significantly lower salt content and produces new water at 30% less cost to the consumer, without the damage to marine life and ecosystems common to desalination plants.[citation needed]

Israel is now desalinating water at a cost of US$0.53 per cubic meter.[19] Singapore is desalinating water for US$0.49 per cubic meter.[20] Many large coastal cities in developed countries are considering the feasibility of seawater desalination, due to its cost effectiveness compared with other water supply options, which can include mandatory installation of rainwater tanks or stormwater harvesting infrastructure. Studies[citation needed] have shown that the desalination option is more cost-effective than large-scale recycled water for drinking, and more cost-effective in Sydney than the vastly expensive option of mandatory installation of rainwater tanks or stormwater harvesting infrastructure. The city of Perth has been successfully [21] operating a reverse osmosis seawater desalination plant since 2006, and the Western Australian government have announced that a second plant will be built to serve the city's needs. A desalination plant is now operating in Australia's largest city of Sydney,[22] and the Wonthaggi desalination plant under construction in Wonthaggi, Victoria.

The Perth desalination plant is powered partially by renewable energy from the Emu Downs Wind Farm.[23] A wind farm at Bungendore in NSW has been purpose-built to generate enough renewable energy to offset the energy use of the Sydney plant,[24] mitigating concerns about harmful greenhouse gas emissions, a common argument used against seawater desalination due to the energy requirements of the technology. The purchase or production of renewable energy to power desalination plants naturally adds to the capital and/or operating costs of desalination. However, recent experience in Perth and Sydney indicates that the additional cost is acceptable to communities, as a city may then augment its water supply without doing environmental harm to the atmosphere. The Queensland state government also purchased renewable energy certificates on behalf of its Gold Coast plant which will see the plant offset its carbon emissions for the initial 18 to 20 months of operations, bringing its environmental footprint down, in line with the other major plants that will be operating around the same time, in Perth and Sydney.

In December 2007, the South Australian government announced that it would build a seawater desalination plant for the city of Adelaide, Australia, located at Port Stanvac. The desalination plant is to be funded by raising water rates to achieve full cost recovery.[25][26] An online, unscientific poll showed that nearly 60% of votes cast were in favor of raising water rates to pay for desalination.[27]

A January 17, 2008, article in the Wall Street Journal states, "In November, Connecticut-based Poseidon Resources Corp. won a key regulatory approval to build the US$300 million water-desalination plant in Carlsbad, north of San Diego. The facility would produce 50,000,000 US gallons (190,000,000 l; 42,000,000 imp gal) of drinking water per day, enough to supply about 100,000 homes ... Improved technology has cut the cost of desalination in half in the past decade, making it more competitive ... Poseidon plans to sell the water for about US $950 per acre-foot [1,200 cubic metres (42,000 cu ft)]. That compares with an average US$700 an acre-foot [1200 m³] that local agencies now pay for water." [28] $1,000 per acre-foot works out to $3.06 for 1,000 gallons, or $.81 for 1 cubic meter, which is the unit of water measurement that residential water users are accustomed to being billed in.[29]

While this regulatory hurdle was met, Poseidon Resources is not able to break ground until the final approval of a mitigation project for the damage done to marine life through the intake pipe, as is required by California law. Poseidon Resources has made progress in Carlsbad, CA, despite its unsuccessful attempt to complete construction of Tampa Bay Desal, a desalination plant in Tampa Bay, FL, in 2001. The Board of Directors of Tampa Bay Water were forced to buy Tampa Bay Desal from Poseidon Resources in 2001 to prevent a third failure of the project. Tampa Bay Water faced five years of engineering problems and operation at 20% capacity due to marine life and growth captured and stuck to reverse osmosis filters prior to fully utilizing this facility in 2007.[30]

According to a May 9, 2008, article in Forbes, a San Leandro, California, company called Energy Recovery Inc. has been desalinating water for US $0.46 per cubic meter.[31]

According to a June 5, 2008, article in the Globe and Mail, a Jordanian-born chemical engineering doctoral student at the University of Ottawa, named Mohammed Rasool Qtaisha, has invented a new desalination technology that is alleged to be between 600% and 700% more water output per square meter of membrane than current technology. According to the article, General Electric is looking into similar technology, and the U.S. National Science Foundation announced a grant to the University of Michigan to study it as well. Because the patents were still being worked out, the article was very vague about the details of this alleged technology.[32]

While desalinating 1,000 US gallons (3,800 l; 830 imp gal) of water can cost as much as $3, the same amount of bottled water costs $7,945.[33]

Environmental

Intake

One of the main environmental considerations of ocean water desalination plants is the impact of the open ocean water intakes[citation needed], especially when co-located with power plants. Many proposed ocean desalination plants' initial plans relied on these intakes despite perpetuating ongoing impacts on marine life[citation needed]. In the United States, due to a recent court ruling under the Clean Water Act, these intakes are no longer viable without reducing mortality, by 90%, of the life in the ocean; the plankton, fish eggs and fish larvae.[34] There are alternatives, including beach wells that eliminate this concern, but require more energy and higher costs while limiting output.[35] Other environmental concerns include air pollution and greenhouse gas emissions from the power plants.

Outflow

To limit the environmental impact of returning the brine to the ocean, it can be diluted with another stream of water entering the ocean, such as the outfall of a waste water treatment plant or power plant. While seawater power plant cooling water outfalls are not freshwater like waste water treatment plant outfalls, the salinity of the brine will still be reduced. If the power plant is medium- to large-sized and the desalination plant is not enormous, the flow of the power plant's cooling water is likely to be at least several times larger than that of the desalination plant. Another method to reduce the increase in salinity is to spread the brine via a diffuser to mix in a mixing zone so that there is only a slight increase in salinity. For example, once the pipeline containing the brine reaches the sea floor, it can split off into many branches, each one releasing the brine gradually along its length through small holes. This method can be used in combination with the joining of the brine with power plant or waste water plant outfalls.

There are methods of desalination, particularly in combination with open pond evaporation (solar desalination), that do not discharge brine back into the ocean at all.

The concentrated seawater has the potential to harm ecosystems, especially marine environments in regions with low turbidity and high evaporation that already have elevated salinity. Examples of such locations are the Persian Gulf, the Red Sea and, in particular, coral lagoons of atolls and other tropical islands around the world[citation needed].

The UAE, Qatar, Bahrain, Saudi Arabia, Kuwait and Iran have 120 desalination plants between them. These plants flush nearly 24 tons of chlorine, 65 tons of algae-harming antiscalants used to descale pipes, and around 300 kg of copper into the Persian Gulf every day. [36]

Because the brine is denser than the surrounding sea water due to the higher solute concentration, discharge into water bodies means that the ecosystems on the bed of the water body are most at risk because the brine sinks and remains there long enough to damage the ecosystems. Careful re-introduction can minimize this problem. For example, for the desalination plant and ocean outlet structures to be built in Sydney from late 2007, the water authority states that the ocean outlets will be placed in locations at the seabed that will maximize the dispersal of the concentrated seawater, such that it will be indistinguishable from normal seawater between 50 and 75 metres (160 and 246 ft) from the outlet points. Sydney is fortunate to have typical oceanographic conditions off the coast that allow for such rapid dilution of the concentrated byproduct, thereby minimizing harm to the environment.

In Perth, Australia, in 2007, the Kwinana Desalination Plant was opened. The water is sucked in from the ocean at only 0.1 metres per second (0.33 ft/s), which is slow enough to let fish escape. The plant provides nearly 140,000 cubic metres (4,900,000 cu ft) of clean water per day.[37] This is the same at Queensland's Gold Coast Desalination Plant and Sydney's Desalination Plant.

Desalination compared to other water supply options

Increased water conservation and water use efficiency remain the most cost-effective priorities in areas of the world where there is a large potential to improve the efficiency of water use practices.[38] While comparing ocean water desalination to waste water reclamation for drinking water shows desalination as the first option, using reclamation for irrigation and industrial use provides multiple benefits.[39] Urban runoff and storm water capture also provide benefits in treating, restoring and recharging groundwater.[40] A proposed alternative to desalinization in the state of California and other areas in the American Southwest is the commercial importation of bulk water either by very large crude carriers converted to water carriers, or via pipelines. The idea is politically unpopular in Canada, where governments have been scrambling to impose trade barriers to bulk water exports as a result of a claim filed in 1999 under Chapter 11 of the North American Free Trade Agreement (NAFTA) by Sun Belt Water Inc. a company established in 1990 in Santa Barbara, California, to address pressing local needs due to a severe drought in that area. Sun Belt maintains a web site where documents relating to their dispute are posted online.[41]

Experimental techniques and other developments

In the past, many novel desalination techniques have been researched with varying degrees of success.

One such process which has recently been commercialised by Modern Water plc is a forward osmosis based process for desalinated water, with a number of plants reported in operation.[42][43][44]

Other techniques have also attracted research funding. For example, to offset the energy requirements of desalination, the U.S. government is working to develop practical solar desalination.

As an example of newer theoretical approaches for desalination, focusing specifically on maximizing energy efficiency and cost effectiveness, the Passarell Process may be considered.[45]

Other approaches involve the use of geothermal energy. From an environmental and economic point of view, in most locations geothermal desalination can be preferable to using fossil groundwater or surface water for human needs, as in many regions the available surface and groundwater resources already have long been under severe stress.

Recent research in the U.S. indicates that nanotube membranes may prove to be extremely effective for water filtration and may produce a viable water desalination process that would require substantially less energy than reverse osmosis.[46]

Another method being looked into for water desalination is the use of biomimetic membranes [47]

On June 23, 2008, it was reported that Siemens Water Technologies had developed a new technology, based on applying electric field on seawater, that desalinates one cubic meter of water while using only 1.5 kWh of energy, which, according to the report, is one half the energy that other processes use.[48]

Fresh water can also be produced by freezing seawater, as happens naturally in the polar regions, and is known as freeze-thaw desalination.

According to MSNBC, a report by Lux Research estimated that the worldwide desalinated water supply will triple between 2008 and 2020.[49]

Desalination through evaporation and condensation for crops growth

The Seawater Greenhouse uses evaporation and condensation natural processes inside a greenhouse powered by solar energy to enable the growth of crops in coastal arid land.

Low-temperature thermal desalination

Low-temperature thermal desalination (LTTD) takes advantage of the fact that water boils at low pressures, even as low as ambient temperature. The system uses vacuum pumps to create a low pressure, low-temperature environment in which water boils at a temperature gradient of 8 to 10 °C between two volumes of water. Cooling water is supplied from sea depths of as much as 600 metres (2,000 ft). This cold water is pumped through coils to condense the evaporated water vapor. The resulting condensate is purified water. The LTTD process may also take advantage of the temperature gradient available at power plants, where large quantities of warm waste water are discharged from the plant, reducing the energy input needed to create a temperature gradient.[50]

The principle of LTTD is known for a long time, originally stemming from ocean thermal energy conversion research. Some experiments were conducted in U.S. and Japan to test the low-temperature driven desalination technology. In Japan, a spray flash evaporation system was tested by Saga University.[51] In US, at Hawaii Islands, the National Energy Laboratory tested an open-cycle OTEC plant with fresh water and power production using a temperature of 20 °C between surface water and water at a depth of around 500 m. LTTD was studied by India's National Institute of Ocean Technology (NIOT) from 2004. Their first LTTD plant was opened in 2005 at Kavaratti in the Lakshadweep islands. The plant's capacity is 100,000 litres (22,000 imp gal; 26,000 US gal)/day, at a capital cost of INR 50 million (€922,000). The plant uses deep water at a temperature of 7 to 15 °C (45 to 59 °F).[52] In 2007, NIOT opened an experimental floating LTTD plant off the coast of Chennai with a capacity of 1,000,000 litres (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.[50][53][54]

Thermo-ionic process

In October 2009, Saltworks Technologies, a Canadian firm, announced a process that uses solar or other thermal heat to drive an ionic current that empties all the sodium and chlorine ions from the water.[55]

Existing facilities and facilities under construction

Aruba

The island of Aruba has a large (world’s largest at the time of its inauguration) desalination plant with the total installed capacity of 42,000 metric tons (11.1 million gallons or 42 × 103 m3) per day.[56]

Australia

A combination of increased water usage and lower rainfall/drought in Australia has caused State governments to build a number of desalination plants, including the recently commissioned Kurnell Desalination Plant serving the Sydney area. While desalination has been adopted by state governments to secure water supply, it is highly energy intensive (~$140 energy demand/ML) and has a high carbon footprint due to continued reliance on Australia's coal-based energy generation.

A Seawater Greenhouse has been built in Port Augusta in 2010 [57] [58][59]

Bahrain

  • The Al Hidd Desalination Plant on Muharraq island treats seawater through a multistage flash process, and produces 30 million US gallons (110,000 m3) per day. This project was completed in 2000. The Al Hidd distillate forwarding station, comprises a 410 million litres distillate water storage in 45 million litres steel tanks. A 135 million litres/day forwarding pumping station sends flows to the Hidd blending station, Muharraq blending station, Hoora blending station, Sanabis blending station and Seef blending station and which has an option for gravity supply for low flows to blending pumps and pumps which forward to Janusan, Budiya and Saar.[60]
  • When completed in three phases, the Durrat Al Bahrain sea water reverse osmosis (SWRO) desalination plant will have a capacity of 36,000 cubic meters of potable water per day which will serve the irrigation needs of the entire Durrat Al Bahrain development.[61] The Bahrain-based utility company, Energy Central Co (ECC) will provide the plant a 25-year design, build and operate contract.[62]

China

China operates the Beijiang Desalination Plant in Tianjin, a combination desalination and coal-fired power plant designed to alleviate Tianjin's critical water shortage. Though the facility has the capacity to produce 200,000 cubic meters of potable water per day, it has never operated at more than one quarter capacity due to difficulties with local utility companies and an inadequate local infrastructure.[63]

Cyprus

There are also desalination plants in Cyprus, like the one near the town of Larnaca.[64] This is called the Dhekelia Desalination Plant, which utilises the reverse osmosis system.[65]

Gibraltar

The fresh water supply in Gibraltar is supplied by a number of reverse osmosis and multi-stage flash desalination plants.[66] There is also a demonstration forward osmosis desalination plant operational.[67]

Israel

The Hadera seawater reverse osmosis (SWRO) desalination plant in Israel is the largest of its kind in the world.[68][69] The project was developed as a Build-Operate-Transfer (BOT) by a consortium of three international companies: Veolia water, IDE Technologies and Elran.[70]

Existing Israeli water desalination facilities[71]
Location Opened Capacity
(mln m3/year)		 Cost of water
(per m3)		 Notes
Ashkelon August 2005 120 (as of 2010) NIS 2.60 [72]
Palmachim May 2007 45 NIS 2.90 [73]
Hadera December 2009 127 NIS 2.60 [74]
Israeli water desalination facilities under construction
Location Opening Capacity
(mln m3/year)		 Cost of water
(per m3)		 Notes
Ashdod 2012 100 (expansion up to 150 possible) NIS 2.40 [75][76]
Soreq 2013 150 (expansion up to 300 approved) NIS 2.01 – 2.19 [77]

Maldives

Maldives is a small island nation and some of the islands of Maldives depend on desalination as a source of water.

Oman

A pilot Seawater Greenhouse was built in 2004 near Muscat, Oman. In collaboration with Sultan Qaboos University, providing an opportunity to develop a sustainable horticultural sector on the Batinah coast.[78]

Saudi Arabia

The Saline Water Conversion Corporation of Saudi Arabia provides 50% of the municipal water in the Kingdom, operates a number of desalination plants, and has contracted $1892 million [79] to a Japanese-South Korean consortium to build one capable of producing a billion litres a day, opening at the end of 2013. They currently operate approximately 14 plants in the Kingdom;[80] one example at Shoaiba cost $1060 million and produces 450 million litres a day.

Spain

Lanzarote, Canary Islands

Lanzarote is the easternmost of the autonomous Canary Islands. It is of volcanic origin and has only very limited natural water supplies. A commercial desalination plant was installed in 1964 as a private initiative. This served the whole island and started off the tourism industry. In 1974 the venture was injected with investments from local and municipal governments and a larger infrastructure was put in place. In 1989 INALSA[81] was formed as the Lanzarote Island Waters Consortium. The plant has been inspected by foreign visitors from places with interest in desalination.

Tenerife, Canary Islands

A prototype Seawater Greenhouse was constructed in Tenerife in 1992.[82]

El Prat del Llobregat, Catalonia

El Prat, near Barcelona, has a desalination plant completed in 2009 and meant to provide water to the Barcelona metropolitan area, specially during the periodic severe droughs that put the drinking water provision under serious stress.

United Arab Emirates (Abu Dhabi)

  • Taweelah A1 Power and Desalination Plant has an output 385,000,000 litres (85,000,000 imp gal; 102,000,000 US gal) per day of clean water.
  • Umm Al Nar Desalination Plant has an output of 394,000,000 litres (87,000,000 imp gal; 104,000,000 US gal) per day of clean water.
  • Fujairah F2 is to be completed by July 2010 will have a water production capacity of 492,000,000 litres (108,000,000 imp gal; 130,000,000 US gal) per day.[83]
  • A Seawater Greenhouse was constructed on Al-Aryam Island, Abu Dhabi, United Arab Emirates in 2000.

United Kingdom

Jersey Desalination Plant

Jersey Water commissioned the first desalination plant in the British Isles in 1970. The plant was built in an abandoned quarry close to the sea at La Rosière, Corbiere, at the south-west corner of the Island. Sea water was pumped into a deep pond (quarry pool) within the old quarry before being abstracted for desalination.

The original desalination plant used a multi-stage flash (MSF) distillation process, whereby the sea water was boiled under vacuum, evaporated and condensed into a fresh water distillate.

By 1997 the MSF plant had reached the end of its operational life and it was decided to replace this important standby water resource with a modern plant using the Reverse Osmosis (RO) process, giving a number of significant operational benefits.

On Friday 9th July 1999, General Sir Michael Wilkes KCB CBE, Her Majesty’s Lieutenant Governor of Jersey, officially opened the new RO desalination plant at La Rosière.

Beckton Desalination Plant

The first large scale water desalination plant in the United Kingdom, the Thames Water Desalination Plant,[84] has been built in Beckton, east London for Thames Water by Acciona Agua

United States

El Paso (Texas) Desalination Plant

Brackish groundwater has been treated at the El Paso plant since around 2004. Producing 27,500,000 US gallons (104,000,000 l; 22,900,000 imp gal) of fresh water daily (about 25% of total freshwater deliveries) by reverse osmosis, it is a crucial contribution to water supplies in this water-stressed city.[85]

Tampa Bay Water Desalination Project

The Tampa Bay Water Desalination project was originally a private venture led by Poseidon Resources. This project was delayed by the bankruptcy of Poseidon Resources' successive partners in the venture, Stone & Webster, then Covanta (formerly Ogden) and its principal subcontractor Hydranautics. Poseidon's relationship with Stone & Webster through S & W Water LLC ended in June 2000 when Stone & Webster declared bankruptcy and Poseidon Resources purchased Stone & Webster's stake in S & W Water LLC. Poseidon Resources partnered with Covanta and Hydranautics in 2001, changing the consortium name to Tampa Bay Desal. Through the inability of Covanta to complete construction bonding of the project, the Tampa Bay Water agency was forced to purchase the project from Poseidon on May 15, 2002, and underwrite the project financing under its own credit rating. Tampa Bay Water then contracted with Covanta Tampa Construction, which produced a project that did not meet required performance tests. Covanta Tampa Construction's parent company filed bankruptcy in October 2003 to prevent losing the contract with Tampa Bay Water. Then, Covanta Tampa Construction filed bankruptcy prior to performing renovations that would have satisfied contractual agreements. This resulted in nearly six months of litigation between Covanta Tampa Construction and Tampa Bay Water. In 2004, Tampa Bay Water hired a renovation team, American Water/Acciona Aqua, to bring the plant to its original, anticipated design. The plant was deemed fully operational in 2007[30] and is designed to run at a maximum capacity of 25 million US gallons (95,000 m3) per day.[86] Nevertheless, the plant continues to be set with problems limiting it to producing only about half that amount (14 million US gallons (53,000 m3) per day in 2009.[87]

Yuma Desalting Plant (Arizona)

The Yuma Desalting Plant was constructed under authority of the Colorado River Basin Salinity Control Act of 1974 to treat saline agricultural return flows from the Wellton-Mohawk Irrigation and Drainage District. The treated water is intended for inclusion in water deliveries to Mexico thereby preserving the like amount of water in Lake Mead. Construction of the plant was completed in 1992 and it has operated on two occasions since then. The plant has been maintained, but largely not operated due to surplus and then normal water supply conditions on the Colorado River.[88] An agreement was reached in April 2010 between the Southern Nevada Water Authority, the Metropolitan Water District of Southern California, the Central Arizona Project and the U.S. Bureau of Reclamation to underwrite the cost of running the plant in a year long pilot project.[89]

Trinidad and Tobago

The Republic of Trinidad and Tobago is using desalination to free up more of the island's water supply for drinking purposes. The desalination facility, opened in March 2003, is considered to be the first of its kind. It is the largest desalination facility in the Americas and will process 28,800,000 US gallons (109,000,000 l; 24,000,000 imp gal) of water a day and sell water at the price of $2.67 per 1,000 US gallons (3,800 l; 830 imp gal).[90] This facility will be located at Trinidad's Point Lisas Industrial Estate, a park of more than 12 companies in various manufacturing and processing functions and will allow for easy access to water for both factories and residents in the country.[91]

In nature

Giant Petrel with brine emitting tube nostril

Seabirds distill sea water, by using Countercurrent exchange in a gland with a Rete mirabile. The gland secretes highly concentrated brine stored near the nostrils above the beak. The bird then "sneezes" the brine out to the sea. As freshwater is not available in their environment, seabirds like pelicans, petrels, albatrosses, gulls and terns possess this gland which allows the birds to drink the salty water from their environment while they are hundreds miles away from land.[92][93]

Mangrove leaf with salt crystals

Mangroves are trees which grow in sea water. Mangroves are able to secrete the salt by trapping it into parts of the root, which are then eaten by animals (usually crabs). Additional salt removal is done by storing it in leaves which then fall off. Some types of mangrove have glands on the leaf, which work in a similar way to the seabird desalination gland. Salt is extracted to the leaf exterior as small crystals, which then fall off the leaf.[94]

Willow trees and Reeds are known to uptake salt and other contaminants, effectively desalinating the water. This is used in artificial constructed wetlands, for treating sewage[95]

Rain and Dew are the outcome of large scale desalination through evaporation, in what is known as the water cycle. Fresh water floats above sea water, so during storms or in lakes where there is undersea volcanic activity causing the water to boil and then condensate, large bodies of freshwater can be found at the sea or lake surface, covering the more salty seawater below. Freshwater on the surface of seawater is common at estuaries.[96]

See also

References

  1. ^ "Desalination" (definition), The American Heritage Science Dictionary, Houghton Mifflin Company, via dictionary.com. Retrieved on 2007-08-19.
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  • desalination — [dē sā΄lə nə zā′shən, dēsal΄əzā′shəndē sal΄ə nā′shən] n. 〚 DE + SALIN(E) + ATION〛 the removal of salt, esp. from sea water to make it drinkable: also desalinization [dē sā΄lə nə …   Universalium

  • desalination — de‧sal‧i‧na‧tion [diːˌsælˈneɪʆn] noun [uncountable] when salt is removed from sea water so that the water can be used in homes and factories, and on farm crops: • Water desalination is still an expensive prospect. • the world s largest seawater …   Financial and business terms

  • desalination — n. same as {desalinization}. Syn: desalinization, desalinisation. [WordNet 1.5] …   The Collaborative International Dictionary of English

  • desalination — 1958, from DE (Cf. de ) + salination (see SALT (Cf. salt)). As a verb, desalt is recorded from 1909 …   Etymology dictionary

  • desalination — [dē sā΄lə nə zā′shən, dēsal΄əzā′shəndē sal΄ə nā′shən] n. [ DE + SALIN(E) + ATION] the removal of salt, esp. from sea water to make it drinkable: also desalinization [dē sā΄lə nə zā′shən, dēsal΄əzā′shən] desalinate [dē′sal′ə nāt΄] vt. desalinated …   English World dictionary

  • Desalination — Fließbild einer dreistufigen Entspannungsverdampfungsanlage zur Meerwasserentsalzung Als Meerwasserentsalzung bezeichnet man die Gewinnung von Trinkwasser oder Betriebswasser aus Meerwasser durch die Verringerung des Salzgehaltes. Die Entsalzung… …   Deutsch Wikipedia

  • desalination — de|sal|i|na|tion [ ,disælı neıʃn ] noun uncount the process of removing salt from ocean water so that the water can be used. A desalination plant is a place where this process takes place …   Usage of the words and phrases in modern English

  • desalination — [[t]di͟ːsælɪne͟ɪʃ(ə)n[/t]] N UNCOUNT Desalination is the process of removing salt from sea water so that it can be used for drinking, or for watering crops …   English dictionary

  • desalination — UK [ˌdiːsælɪˈneɪʃ(ə)n] / US [ˌdɪsælɪˈneɪʃ(ə)n] noun [uncountable] the process of removing salt from sea water so that the water can be used. A desalination plant is a place where this process takes place …   English dictionary

  • desalination — gėlinimas statusas T sritis chemija apibrėžtis Vandenyje ištirpusių druskų kiekio mažinimas. atitikmenys: angl. demineralization; desalination; desaltation; desalting; freshening; water freshening rus. опреснение …   Chemijos terminų aiškinamasis žodynas

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