Water Education - Water Quality

Can you make seawater drinkable? Page 2

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Some examples of U.S. cities currently using, or planning to use desalination include: Tampa Bay Water has constructed a 25-million-gallon-per-day desalination facility in Apollo Beach in Hillsborough County, FL. El Paso Water Utilities and Fort Bliss officials collaborated to build the country's largest inland desalination plant. As of 2021, the largest desalination plant in the United States belongs to The Claude "Bud" Lewis Carlsbad Desalination Plant with 50 million gallons a day as freshwater production rate. The plant draws brackish water from an underground aquifer that provides about 40 percent of El Paso's municipal water supply. The Groundwater Recovery Enhancement and Treatment (GREAT) program in Oxnard, CA blends desalted groundwater with high-quality water the city buys from a neighboring water district.

There are a number of ways to forestall this, however. One of those ways - desalination - is already being used across the country to stretch water supplies, clean up polluted water and provide protection for aquifers. The technique is ancient, dating back to the 4th century B.C. when, according to the National Water Supply Improvement Association, Greek sailors used simple evaporation to desalinate seawater. The technology, however, is far more modern. Desalination - separating saline water into fresh water and water containing the concentrated salts - is accomplished in two main ways: through distillation or the use of membranes. Nearly 60 percent of the world's desalted water is produced via the first method by heating salty water to produce water vapor that is then condensed to form freshwater. The second process uses membranes to separate the salts from the water.

In reverse osmosis (RO) facilities, water is forced through bundles of membranes under pressure, leaving behind impurities. In electrodialysis reversal (EDR) plants, an electrical current transfers ions through membranes, resulting in desalted water and concentrates. Worldwide, desalting plants have the capacity to produce 3.5 billion gallons of water a day, nearly enough to provide 15 gallons a day for every American. Some nations, such as Saudi Arabia and Malta, desalt ocean water to produce freshwater for public and industrial consumption. In the United States, most desalting plants treat brackish water, a process that costs one-third to one-fourth as much as the treatment involved in desalting ocean water. The product water is used for direct supply, reserves or groundwater recharge.

According to the American Desalting Association (ADA), other uses include irrigation, wastewater treatment and water purification. Hospitals, resorts, manufacturing plants, oil rigs, and pleasure boats also employ desalination technology. During the Persian Gulf War, the Army had mobile desalination units that could produce 3,000 gallons per hour of potable water from brackish pools. In a 1988 report, the Congressional Office of Technology Assessment suggested desalination could find application in treating contaminated groundwater, be it runoff from mines, agriculture, landfills, or storage tanks. Of desalting in general, the report noted, "Desalination should be included as a viable option in any evaluation of water-supply alternatives."

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