Thursday, 15 October 2015

Can Making Seawater Drinkable Quench the World's Thirst?


Seawater Desalination Plants For Filtered Water

Generating fresh drinking water from sea through desalination has always been the best option to the water shortage faced during the year. Oceans tend to cover over 70% of the surface of the earth which contains 97% of its water. However the efforts essential in the achievement of this simple procedure seems to be costly. But now with enhancement in technologies, the cost has been reduced to half with huge desalination plants coming up all around the globe.

The biggest seawater desalination plant ever has just ramped up to full production in Israel’s Sorek plant near Tel Aviv which will make about 624 million litres of filtered water daily, selling around 1,000 litres equal to weekly consumption of Brit for 45p. The Ras al-Khair plant in Saudi Arabia tends to reach full production in December.

Created in the peninsula’s Eastern Province, it would be much bigger, speeding a billion litres a day to Riyadh where the population seems to be on the rise. A connected power plant would be yielding 2.4 million watts of electricity. The desalination plant in the US, San Diego’s Carlsbad, which is the country’s largest, would be in operation from November.

Reverse Osmosis – Utilises Less Energy – New Lease of Life

The old style of extracting drinking water from sea or saline water was to boil it then collect the evaporated water as a pure distillate which tends to utilise lot of energy but works well when combined with industrial plants which can produce heat as a by-product.

The new desalination plant at Saudi Arabia tends to pair with a power plant for this purpose. But in recent years, reverse osmosis, a technology which has been since 1960s utilises less energy has been given a new lease of life. It involves pushing salt water at high pressure via a polymer membrane comprising of holes around a fifth of a nanometre in size.

A nanometre is said to be a billionth of a metre, and the holes which are small enough to block the salt molecule are big enough to enable the water molecule through. Profession Nidal Hilal at Swansea University, editor-in-chief of the journal explains that this membrane tends to strip all the salts and minerals totally from the water and get clean water coming down as infiltrate and the distillation on the other side is saline with high content of salt.

However, these membranes may get clogged easily and lose its performance but with improved technology and pre-treatment techniques, there is a possibility of keeping them working efficiently for a longer period. Sorek’s designers in Israel tend to save energy by utilising double sized pressure vessels.

Dr Jack Gilron, head of Desalination and Water Treatment at Ben Gurion comments that one would need less pressure vessels to generate water which means fewer pipes and less connection. The researchers at Massachusetts Institute of Technology – MIT in US had experimented with semi-permeable membranes which were made from atom thick graphene that need less pressure to function and thus saves energy even though the technology is not yet prepared for mass production.

With regards to forward osmosis, Professor Nick Hankins, chemical engineer at the University of Oxford is of the opinion that it is an alternative option of removing the salt from seawater. A highly concentrated solution is utilised to draw it through instead of pushing the fresh water through the membrane, which efficiently sucks it from the sea water. Thereafter the diluted solutes are removed producing pure water.

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