Desalination: the process that removes excess salt and other minerals from water.

Water is desalinated in order to convert salt water to fresh water so it is suitable for human consumption or irrigation. Sometimes the process produces table salt as a by-product. The main interest in using this process is focused on developing cost-effective ways of providing fresh water for human use in regions where the availability of fresh water is, or is becoming, limited.

Large-scale desalination uses extremely large amounts of energy as well as specialized, expensive infrastructure, making it very costly compared to the use of fresh water from rivers or groundwater.

The world's largest desalination plant is the Jebel Ali Desalination Plant in the United Arab Emirates. It is a dual-purpose facility that uses multi-stage flash distillation and is capable of producing 300 million cubic metres of water per year.

Methods:

1. The traditional process used in these operations is vacuum distillation—essentially the boiling of water at less than atmospheric pressure and thusa much lower temperature than normal. Thus, because of the reduced temperature, energy is saved.

2. The principal competing processes use membranes to desalinate, principally applying reverse osmosis technology. Membrane processes use semi-permeable membranes and pressure to separate salts from water. Reverse osmosis plant membrane systems typically use less energy than thermal distillation, which has led to a reduction in overall desalination costs over the past decade.

3 Multi-stage flash distillation (MSF) is a water desalination process that distills sea water by flashing a portion of the water into steam in multiple stages of what are essentially counter-current heat exchangers. Multi-stage flash distillation plants produce over 85 percent of all desalinated water in the world.

Anne Sewell

4:13 pm November 19