Our oceans cover ¾ of our planet but the water is too salty to drink. Fresh water dropping from the skies is only 2.5% of all of the earth’s water. And 70% of that water is either buried in deep aquifers or frozen on high mountain tops. A mere 1% is thus free to be tapped by us all. Have we found a way to invert this?

The world’s population is growing and our freshwater needs double every 20 years[1] but with so much salty water around us, transforming it into drinking water[2] should prove to be the solution mankind has been looking for since the Greeks successfully did so centuries ago.

Traditional thermal salt removing techniques require high temperatures. A major impediment has always been the cost of such operations, especially if they are to be thought of on a scale large enough to supply fresh water to entire cities.

Modern desalinization techniques have been in use since the 1950s, either through distillation or by reverse osmosis, more commonly known as RO.

With distillation, the water is left to evaporate and is then condensed, but as it uses a lot of energy in the process, it is mostly used by countries where fossil energy is readily available and at low cost.

With RO the desalination process relies on membranes permeable to water but capable of retaining the dissolved salt. It also relies on the use of high pressure, thus causing damage to the filtering capacity and resistance of the membrane. The result is a short operating life.

Recent approaches have moved towards the use of chemicals[3] and research carried out on alternative components such as the use of nanotubes and aquaporins, water channels which will allow easier water flow at reduced pressure.[4]


Source: Sunit Parekh-Gaihede, sunitparekh.com and Hydralab, hydralab.com

As an alternative, electricity is being used in de-ionization processes, applying it to seawater, attracting salt ions towards electrodes where they can be absorbed and later released.[5]

On top of this, most of these processes mean that there is concentrated brine left over, and this is pernicious to local ecosystems – with fossil-fuels linked to this technology bringing on more greenhouse gas emissions.

The 13,000 desalinization plants already in production today are barely enough to provide 0.5% of global daily water needs. Faster, simpler methods had to be found.

And now, at last, a low cost desalination system is being developed, able to produce drinking water in off-grid, remote areas to be used by developing countries and disaster areas.

The next generation technology will hardly use any energy and can be used by all with a simple method which will remove salt from seawater quickly and efficiently by creating a small electrical field.

The process called “electrochemically mediated seawater desalination” will eliminate the need for any membranes by separating the salt from the water on a micro-scale.[6]

The idea is to apply a small voltage of only 3.0 volts to a plastic chip filled with seawater, which has two branches as micro-channels.

At the junction of these channels, the electrode neutralises some of the chloride ions in the seawater, raising the local electric field sufficient enough to divert the salts into one channel and the desalinated water – the freshwater – into another.

The technology is there – these micro-channels are the size of human hair today and produce 40 nanolitres of freshwater per minute. Now we have to make them produce many litres of water per day!

A drop from heaven

Image source: University of Texas, Austin

By Silvia Pelham

[1] Estimated by analysts in Goldman Sachs http : // www.alternet.org / story / 105083 / why_big_banks_may_be_trying_to_buy_up_your_public_water_system and the United Nations expect demand to outstrip supply by more than 30 percent come 2040.

[2] Desalizination.

[3] Oasys, an American firm, is using an ammonia and carbon dioxide mixture which, when heated, decomposes into gases, enabling easy removal of salt. They also use low natural thermal energy such as solar heat and geothermal steam. http://oasyswater.com

[4] By Aquaporin, a Danish firm. http://www.aquaporin.dk/

[5] PROINGESA, a Spanish firm is applying capacitive deionization to sewage and water treatment. http:// www.proingesa.es / en / proyectsidi2 / adecar.html.

[6] This method is being further developed in the United States by Okeanos Technologies. http://www.okeanostech.com/