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SEA WATER DESALINATION

DESALINATION – AN OVERVIEW

ESALINATION – AN OVERVIEW

Desalination (also called “desalinization” and “desalting”) is the process of removing dissolved salts from water, thus producing fresh water from seawater or brackish water. Desalting technologies can be used for many applications. The most prevalent use is to produce potable water from saline water for domestic or municipal purposes, but use of desalination and desalination technologies for industrial applications is growing, especially in the oil & gas industry.

Of the world’s water, 97.5 percent is salt water from its oceans. Only 2.5 percent is fresh water. Of that 2.5 percent, approximately 69 percent is frozen in glaciers and ice caps, leaving less than 30 percent in fresh groundwater (swamps account for another 1 percent). (Source: United Nations)

 A Naturally Occurring Process

Desalting is actually a natural, continual process and an essential part of the water cycle. Rainwater falls to the ground and eventually flows to the sea, moving over and through the earth, dissolving minerals and other materials along the way, and becoming increasingly salty. As water evaporates through the sun’s energy, it leaves the salts behind, and the resulting water vapor forms clouds that produce rain, thus continuing the cycle.

 The Quest for Water

People have been desalinating water for centuries. One of the first mentions was by Aristotle, who wrote of seawater distillation in 320 BC. Different techniques were used during the ages: Rome’s Pliny the Elder described seawater distillation with condensation on fleece in 70 AD, Greece’s Alexander of Aphrodisias described seawater distillation with condensation on sponges 130 years later, French explorer Jean De Lery reported the successful distillation of seawater during a voyage to Brazil in 1565, and James Cook desalinated seawater during his circumnavigation of the world.

 Developments in Desalination Technology

Through the mid-1900s, the most commonly used techniques involved evaporation and distillation. The development of desalination processes took a major step forward in the 1940s during World War II, when military establishments operating in arid areas needed a way to supply their troops with potable water. By the late 1960s, commercial desalting units producing up to 8,000 cubic meters per day (m3/d) – approximately 2 million U.S. gallons per day – were beginning to be installed in various parts of the world. Most of these installations used thermal (distillation) processes.

In the post-war years, however, scientists began studying osmotic processes to desalinate water. The first reported use of the term “reverse osmosis” – now a popular desalination technology – appeared in the US Department of Interior’s Office of Saline Water Commission 1955 annual report. Development continued, and in the 1970s, commercial membrane processes, such as reverse osmosis (RO) and electrodialysis (ED), began to be used more extensively. Since ED could desalt brackish water more economically than distillation, more interest was focused on using desalination as a way to provide water for municipalities with limited fresh water supplies and the availability of brackish water sources.

By the 1980s, desalination technology became a fully commercial enterprise and by the 1990s, the use of desalination technologies for municipal water supplies was commonplace. The major desalination processes employ membrane and thermal technologies. At present, reverse osmosis (RO) accounts for approximately 60 percent of installed capacity.

 Reducing Energy Consumption and Addressing Environmental Concerns

Today, developments in desalination technologies are specifically aimed at reducing energy consumption and cost, as well as minimizing environmental impacts. Advancements include such new and emerging technologies as forward osmosis, low temperature distillation, membrane distillation, pressure retarded osmosis, biomimetic and graphene membranes. Hybrid plants (especially those using MED) and reverse osmosis are gaining wider use in the Middle East, which has traditionally been home to facilities using more energy-intensive thermal technologies such as MSF.

There is also a push to utilize renewable energy to power desalination plants; for example, Saudi Arabia has made a major investment in solar energy for desalination. In addition, Masdar has organized a program to pilot and help commercialize new energy saving technologies for desalination.

The desalination industry is also paying a great deal of attention to environmental considerations. Environmental safeguards have become increasingly important in siting and permitting of new plants. Monitoring programs are being more widely utilized. Lower energy consumption reduces also a plant’s carbon footprint, and in addition, new technologies are being used successfully to lessen disruptions to marine life during the intake and outfall processes. Studies such as IDA’s Blue Paper on Desalination and the Gulf have raised awareness of steps to leverage best practices and mitigate potential environmental effects of desalination.

While energy consumption has been significantly reduced in the past two decades, IDA’s Energy Task Force has specifically challenged the desalination industry to achieve a further reduction of 20% in energy requirements for seawater desalination by 2015.