How to Desalinate Seawater

Desalination is now regularly considered as an instrument in many regions’ water planning processes for meeting future water needs. As populations increase and sources of quality fresh drinking water decline, many communities are considering using desalination processes to supply fresh water where other sources and treatment procedures are not economical or environmentally responsible.

In many cases, water from the ocean needs to be treated and/or filtered prior to desalination processes. Thermal desalination processes typically use heat to evaporate the water, leaving dissolved components.

Most desalination technologies use one of two methods, heat distillation and membrane filtration. Distillation is the most straightforward of thermal desalination processes, and energy efficiency has been significantly improved in this simpler process (Water Research Foundation, 2006). Thermal is a more old-school approach: before the 1980s, 84% of water desalinated went through thermal.

Both thermal and membrane desalination processes create a flow of brinewater, which has high concentrations of salts and other minerals or chemicals, which are removed in the desalination process, or added to help pre-treat saline feedwater. Seawater desalination is a process that removes salts and other components in order to create clean water.

Desalination is done by boiling the seawater and collecting the steam (thermal) or pushing it through special filters (membrane). The most common process of desalination is called reverse osmosis, which works by pushing seawater over a membrane under high pressure to remove minerals.

All desalination methods create a concentrated waste product consisting of salts found in the seawater and chemicals used in the process. Desalination plants draw their saltwater directly from the ocean, and the water that is transported from its source to the plant may kill or damage fish and other smaller marine organisms. Today, desalination plants are used to turn seawater into drinking water for ships and many dry regions around the world, as well as treating water from other areas that are polluted with both natural and non-natural contaminants.

Despite the economic and environmental obstacles, desalination is becoming more and more attractive as we exhaust our supply of water from other sources. Much more needs to be done to make better use of the water we have, but with a growing global population and diminishing water supplies, the economic tide could turn soon in favor of desalination. The United Nations projects that by 2025, fourteen percent of Earths land area will depend on desalination for its water needs.

The biggest users of desalinated water are the Middle East, primarily Saudi Arabia, Kuwait, UAE, Qatar, and Bahrain, where around 70% of global capacity is used; and North Africa, primarily Libya and Algeria, where around 6% of global capacity is used. Among industrialized countries, the US is one of the largest users of desalinated water, particularly in California and parts of Florida.

According to the International Desalination Association, as of June 2015, there were 18,426 desalination plants operating around the world, producing 86.8 million m3/d, providing water to 300 million people. It is difficult to pin down a precise dollar amount for desalination: that number fluctuates widely from place to place, depending on the costs of labor and energy, the cost of land, the terms of the financing deal, or even the salt content of the water.

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Kwaong Noi

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