Seawater desalination is of great interest to MIT (Massachusetts Institute of Technology). Three years ago, one of its research teams suggested using graphene membranes to accelerate reverse osmosis and reduce energy consumption. Today, engineers from the research institute were awarded the top prize in the Desal 2015 competition for their project to develop mobile units powered by solar energy. A promising idea that could provide greater access to desalination in emerging countries.
The use of solar energy in seawater desalination is not a new concept. But the solution developed by the team of researchers at MIT in partnership with the US company Jain Irrigation Systems has the benefit of making complex technology affordable. They have created a small mobile unit capable of supplying a village with drinking water. Its operating cost is significantly reduced through the use of solar energy, which replaces fossil fuels, and the choice of electrodialysis technology. Solar panels recharge the batteries supplying power to an electrodialysis system. This extracts the Na+ and Cl- ions (that make up the salt molecule) by passing them through membranes under the effect of an electric field. The sun’s ultraviolet rays are then used to purify the fresh water. In New Mexico, 8,000 litres were desalinated in 24 hours using this technique.
MIT/Jain Irrigation Systems laureates. Credits: ©Alexander Stephens, Bureau of Reclamation
However, the engineers from MIT are not the only ones working on “solar desalination”. The heat team from the Institute of Technology of Saint-Malo, in partnership with the École polytechnique in Thiès (Senegal) and the Monastir Faculty of Sciences (Tunisia) are also working in this field. To achieve their goals of self-sustainability and make their prototype more economical, the students and professors opted for a low-energy system: the vacuum vapour compression of seawater at 70°C instead of 100°C, followed by condensation to recover the fresh water. Their prototype is currently being tested and could be deployed within small units installed in isolated villages or on boats.