In distillation saltwater is heated in one container to make the water evaporate, leaving the salt behind. The desalinated vapor is then condensed to form water in a separate container. Although long known, distillation has found limited application in water supply because of the fuel costs involved in converting saltwater to vapor. Representative of the early attempts in this direction were the solar distillation methods employed (c.49 B.C.) by the legions of Julius Caesar for using water from the Mediterranean. Modern technological advances led to the development of more efficient distillation units using solar energy; however, since these units have small capacities, their utility is restricted.
Distillation plants having high capacities and using combustible fuels employ various devices to conserve heat. In the most common system a vacuum is applied to reduce the boiling point of the water, or a spray or thin film of water is exposed to high heat, causing flash evaporation; the water is flashed repeatedly, yielding fresh distilled water. This multistage flash distillation method is used in more than 2,000 desalination plants, including one in Saudi Arabia that produces 250 million gallons of freshwater per day.
Another method of desalination is by electrodialysis. When salt dissolves in water, it splits up into charged particles called ions. Placed in a container with a negative electrode at one end and a positive electrode at the other, the ions are filtered by the membranes as they are attracted toward the electrodes; they become trapped between semipermeable membranes, leaving outside the membranes a supply of desalinated water that can be tapped. The first large installation using this process began operating in South Africa in 1958, but its electrical demands make it impractical except where such energy is abundant.
By far the most promising approach is the reverse osmosis process, in which pressure is applied to saltwater to force it through a special membrane. Only pure water passes, leaving concentrated seawater behind. Where multistage flash distillation costs about $4 per 1,000 gallons, reverse osmosis costs about half that amount. This process is used by a plant in the Tampa Bay area, Florida, that produces 25 million gallons of drinking water a day. Another type uses an empty hollow sphere of semipermeable material that is lowered into the sea. The water flowing into the sphere is fresh, since the salt is excluded by the membrane that covers the entire sphere and is its guard.
One final approach is under development in Hawaii, where different layers of seawater display a large temperature differential. Here an Ocean Thermal Energy Conversion plant is being built which will use steam produced by the flash method to produce energy, then condense the steam into freshwater. Three such plants could produce a hundred megawatts of power, as well as supply 30% of Hawaii's water needs.
For emergency use, i.e., in lifeboats, various systems are available in addition to solar or fuel-heated distillation devices. One device made of flexible plastic is worn around the waist of the user to employ body heat for evaporation.
Qatar is a peninsula in the east of Arabia, bordering the Persian Gulf and Saudi Arabia, in a strategic location near major petroleum deposits. Qatar occupies 11,437 square kilometers on a peninsula that extends approximately 160 kilometers north into the Persian Gulf from the Arabian Peninsula. Varying in width between fifty-five and ninety kilometers, the land is mainly flat (the highest point is 103 meters) and rocky. Notable features include coastal salt pans, elevated limestone formations (the Dukhan anticline) along the west coast under which lies the Dukhan oil field, and massive sand dunes surrounding Khawr al Udayd, an inlet of the gulf in the southeast known to local English speakers as the Inland Sea. Of the islands belonging to Qatar, Halul is the most important. Lying about ninety kilometers east of Doha, it serves as a storage area and loading terminal for oil from the surrounding offshore fields. Hawar and the adjacent islands immediately off the west coast are the subject of a territorial dispute between Qatar and Bahrain.
The capital, Doha, is located on the central east coast on a sweeping (if shallow) harbor. Other ports include Umm Said, Al Khawr, and Al Wakrah. Only Doha and Umm Said are capable of handling commercial shipping, although a large port and a terminal for loading natural gas are planned at Ras Laffan, north of Al Khawr. Coral reefs and shallow coastal waters make navigation difficult in areas where channels have not been dredged.
Qatar shares its land border with the United Arab Emirates (UAE), with which in 1993 it continued to have a dispute in the Khawr al Udayd area. The boundary with Saudi Arabia was settled in 1965 but never demarcated. Qatar's northwest coast is fewer than thirty kilometers from Bahrain.
Doha is the capital of the country and the major administrative, commercial, and population center. In 1993 it was linked to other towns and development sites by a system of about 1,000 kilometers of paved roads. Doha's international airport has an approximately 4,500-meter main runway, capable of receiving all kinds of aircraft.
The long summer (May through September) is characterized by intense heat and alternating dryness and humidity, with temperatures exceeding 55° C. Temperatures are moderate from November through May, although winter temperatures may fall to 17° C, which is relatively cool for the latitude. Rainfall is negligible, averaging 100 millimeters per year, confined to the winter months, and falling in brief, sometimes heavy storms that often flood the small ravines and the usually dry wadis. Sudden, violent dust storms occasionally descend on the peninsula, blotting out the sun, causing wind damage, and momentarily disrupting transport and other services.
The scarcity of rainfall and the limited underground water, most of which has such a high mineral content that it is unsuitable for drinking or irrigation, restricted the population and the extent of agricultural and industrial development the country could support until desalination projects began. Although water continues to be provided from underground sources, most is obtained by desalination of seawater.
total: 11,437 km²
land: 11,437 km²
water: 0 km²
total: 60 km
border countries: Saudi Arabia 60 km
Coastline: 563 km
contiguous zone: 24 nautical miles (44 km)
exclusive economic zone: as determined by bilateral agreements, or the median line
territorial sea: 12 nautical miles (22 km)
lowest point: Persian Gulf 0 m
highest point: Qurayn Abu al Bawl 103 m
arable land: 1%
permanent crops: 0%
permanent pastures: 5%
forests and woodland: 0%
other: 94% (1993 est.)
Irrigated land: 80 km² (1993 est.)
Environment - current issues: limited natural fresh water resources are increasing dependence on large-scale desalination facilities
Environment - international agreements:
party to: Biodiversity, Climate Change, Desertification, Hazardous Wastes, Law of the Sea, Ozone Layer Protection
signed, but not ratified: none of the selected agreements
WIPO PUBLISHES PATENT OF BABCOCK BORSIG STEINMULLER FOR "SYSTEM AND METHOD FOR THE DESALINATION OF SEA WATER" (EMIRATI, KUWAITI INVENTORS)
Mar 20, 2012; GENEVA, March 18 -- Publication No. WO/2012/028607 was published on March 8. Title of the invention: "SYSTEM AND METHOD FOR THE...
WIPO ASSIGNS PATENT TO ECOPETROL FOR "SYSTEM FOR THE DEHYDRATION AND DESALINATION OF HYDROCARBONS" (COLOMBIAN INVENTORS)
Jun 30, 2011; GENEVA, June 30 -- Publication No. WO/2011/077198 was published on June 30. Title of the invention: "SYSTEM FOR THE DEHYDRATION...
WIPO ASSIGNS PATENT TO IDROPAN DELL'ORTO DEPURATORI FOR "ASSEMBLY FOR THE DESALINATION OF WATER FOR A WATER SUPPLY SYSTEM" (ITALIAN INVENTOR)
Oct 10, 2011; GENEVA, Oct. 10 -- Publication No. WO/2011/121436 was published on Oct. 6. Title of the invention: "ASSEMBLY FOR THE DESALINATION...
WIPO ASSIGNS PATENT OF S.TRA.TE.G.I.E. FOR "APPARATUS FOR INDEPENDENT INSTANT PRODUCTION OF FRESHWATER FROM DESALINATION OF SEAWATER ABOARD SEAFARING CRAFT" (ITALIAN INVENTORS)
Nov 24, 2011; GENEVA, Nov. 22 -- Publication No. WO/2011/141944 was published on Nov. 17. Title of the invention: "APPARATUS FOR INDEPENDENT...