Desalting refers to a water treatment process that removes salts from water. It is also called desalination or desalinization. Desalting can be done in a number of ways, but the result is always the same: drinking water is produced from brackish (somewhat salty) water or seawater. Desalting technologies can be used for a number of applications, but the purpose of this report is to discuss the use of desalting to produce drinking water from saline water for domestic or municipal purposes. Throughout history, people have continually tried to treat salty water so that it could be used for drinking and agriculture. Of all the globe’s water, 94 percent is salt water from the oceans and 6 percent is fresh. Of the latter, about 27 percent is in glaciers and 72 percent is underground.
While this salt water is important for transportation and fisheries, it is too salty to sustain human life or farming. Desalting techniques have increased the range of water resources available for use by a community. Until recently, only water with a dissolved solid (salt) content generally below about 1,000 milligrams per liter (mg/L) was considered acceptable for a community water supply. This limitation sometimes restricted the size and location of communities around the world and often led to hardship for many who could not afford to live near a ready supply of fresh water. The application of desalting technologies over the past 50 years has changed this in many places. Villages, cities, and industries have now developed or grown in many of the arid and water-short areas of the world where sea or brackish waters are available and have been treated with desalting techniques.
This change has been very noticeable in parts of the arid Middle East, North Africa, and some of the islands of the Caribbean, where the lack of fresh water severely limited development. Now, modern cities and major industries have developed in some of those areas thanks to the availability of fresh water produced by desalting brackish water and seawater.
About half of the world ’s desalted water is produced with heat to distill fresh water from seawater. The distillation process mimics the natural water cycle in that salt
water is heated, producing water vapor that is in turn condensed to form fresh water. In a laboratory or industrial plant, water is heated to the boiling point to produce the maximum amount of water vapor. The process that accounts for the most desalting capacity for seawater is multi-stage flash distillation, commonly referred to as the Multi-Stage Flash process or MSF.
In the MSF process, seawater is heated in a vessel called the brine heater. This is generally done by condensing steam on a bank of tubes that carry seawater, which passes through the vessel or brine-heater. This heated seawater then flows into another vessel, called a stage; where the ambient pressure is lower, causing the water to immediately boil. The sudden introduction of the heated water into the...