Desalination through Heating

One form of extractive industry which is nearly always located close to the oceans (or to brackish lakes) is that of desalination - the extraction of freshwater from salt-water. Although an energy intensive process when using heating, desalination is a critical industry in countries which are short of fresh water. Typically extraction is through a process of distillation, requiring the water to be heated. In about 25% of plants a membrane process is operated by which water is filtered through a semipermeable membrane, leaving the salts behind.

By the end of the 20th century an estimated 8 million cubic metres (8 million tonnes) of fresh water were being extracted daily in several thousand desalination plants. The majority of these (75%) were in the Middle East, however a further 10% were in the US and 5% each in Europe and Africa.

The waste product from desalination is concentrated brine, which may, in some cases also be at elevated temperatures. While this is inimical to most marine life, it can be relatively rapidly diluted, so that pollution from desalination plants is generally localised, and can be sufficiently well managed as to be negligible. The intense energy consumption of the production process is, of course, a contributor to greenhouse gas emissions.