The sea to drink

Blue gold is becoming increasingly scarce, and to satisfy our water needs, we have to look to the open sea... Desalinating seawater to make fresh water is now a global challenge. Researchers at theEuropean Membrane Institute have just taken a major step forward.

Artificial water channels inserted in a polyamide membrane © Mihail Barboiu, European Membrane Institute (CNRS/ENSC Montpellier/Université de Montpellier)

According to the UN, by 2030 the planet will be suffering from a 40% shortage of drinking water, while its population continues to grow. But where do we go to find water when the water tables that supply our bodies are no longer sufficient to cover our needs? The answer: the sea. " Today, 20% of the water we use is desalinated seawater ", explains Mihail Barboiu of theEuropean Membrane Institute (IEM). But with our freshwater resources dwindling, in 50 years' time 60-70% of our water will have to come from the sea. A real challenge to which the researcher has just made a significant contribution.

Reverse osmosis

Separating salt from water is no mean feat. " The ions that make them up are the same size, so we can't simply filter them out. To get around this problem, the researchers use reverse osmosis: " We pass the water through a special membrane that retains the salt," explains Mihail Barboiu. But here again, the solution is not obvious. " When a permeable membrane separates two solutions withdifferent salt concentrations, the water naturally circulates through the membrane until the concentrations on either side balance out - this is called osmosis ", explains the specialist.

Once there is as much salt in both solutions, osmotic equilibrium is reached. " To keep the water flowing after this point, we need to apply pressure to force the flow - this is reverse osmosis. An effective technique, but one that requires a lot of energy to generate the pressure. " Reducing the amount of energy required is a realchallenge to improve seawater desalination capacities ".

Permeability and selectivity

This is where researchers at theIEM researchers have come up with a new kind of membrane that allows water to pass through more easily, while retaining salt effectively. Their recipe? A polyamide membrane into which we have inserted artificial water channels". These channels are synthetic compounds that form pores permeable to water molecules, while rejecting ions. " The result is a membrane with greater permeability and good selectivity ," explains Mihail Barboiu. More permeable, it lets water through more easily, and the amount of energy required to force the flow is therefore lower. Challenge met.

An innovation that has already proved its worth, with figures to back it up. " It is three times more permeable than current membranes, without losing selectivity," explains Mihail Barboiu. As a result, these super-membranes allow 75% more water to flow through them than current industrial membranes. " They reduce the amount of energy needed to desalinate seawater by 12%, which is a considerable improvement," says the researcher. It also means that the same amount of energy can be used to produce more fresh water. Already patented, this work was published in Nature Nanotechnology on November 9.