Everything you always wanted to know about desalination

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Fresh water being unequally distributed around the globe, it is a scarce resource in some regions. Fresh water demand for human consumption, agriculture and industry has also largely increased over the past years and is expected to continue to grow.

Desalination is an alternative solution to increase the available water resources.

HOW MUCH WATER COMES FROM DESALINATION?

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According to the International Desalination Association, in 2017, the total worldwide installed desalination capacity represents 92.5 million m3/day. Roughly 60% of desalination is devoted to human consumption. It is estimated that some 300 million people rely on this process for their daily water usage.

Kuwait for instance has an average rainfall of 110mm per year and produces almost 100% of its fresh water use through desalination.

IS DESALINATED WATER DRINKABLE ?

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Thermal desalination processes produce distilled water, which is quite pure. Whereas seawater contains some 40 kilos of salt per ton, distilled water has only a few grams of salt per ton. In this sense it does not comply with WHO recommendations. However having a glass of it would not be a problem for most of us. The problem is preservation of such water since it will acidify, become corrosive and can easily be contaminated.

Therefore water desalinated for human consumption is mineralised and chlorinated before dispatch.

FOR HOW LONG HAS SEAWATER BEEN DESALINATED ?

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The sun has done it forever ... by evaporation to provide rain. Steam powered ships were first equipped with evaporators for the production of boilers make-up water (1900). Desalination units were first used on board ships and were then widely developed with the growth of OPEC countries (1970). The capacity of the plants has grown drastically over that period, from a few hundreds cubic meters per day in the 1960's to hundreds of thousands cubic meters per day for the largest desalination plants nowadays.

Desalination is used for industrial, human consumption or agricultural purposes. Petroleum or chemical industries always need large quantities of pure water for boilers or process requirements. Wherever local supply cannot meet their own requirements they will go to desalination to free themselves from local constraints. This particular industrial use represents one third of the world wide installed capacity. 60% of desalination is devoted to human consumption: thus a reliable water resource is created and enables sustainable development of a population in a region.

Agricultural use is mainly a second hand use: in many Middle East countries, desalinated water is first devoted to human consumption, then after treatment it is re-used in irrigation.

A few percent of desalination capacity is for military, navy, tourism uses ...etc...

Coming soon ... more questions and answers on desalination

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