2023-08-23 09:30:08
The scarcity of fresh water and the increase in the world’s population are causing an imbalance between the demand for water and the quantity available. To deal with this, many countries, particularly in the Gulf, are turning to the desalination of seawater, although the current processes are expensive and energy-intensive. Researchers at the Beckman Institute for Advanced Science and Technology (US) are working on a desalination technique using electrodialysis that would save 90% energy. The work in progress gives hope of great progress in the years to come.
The United Nations estimates that in 2025, two-thirds of the world’s population will be affected by water stress issues. This industry, which is booming on all continents, represents a huge challenge for the climate, because while current techniques consume a lot of energy, most of the countries that use these processes are those with a very CO2-intensive electricity mix.[1]…
What is wrong with current desalination techniques?
As we have just said, current desalination techniques are very energy intensive. An IFRI report concerning the Geopolitics of seawater desalination even gives detailed figures of consumption per m³ of desalinated water.
Desalination methods are grouped into two families. On the one hand, there are thermal methods, which represent 25% of the plants installed worldwide, and on the other, membrane methods.
Energy consumption of the different seawater desalination methods (in kWh/m³ of desalinated water)
With this table, we can therefore see that thermal methods are much more energy-intensive than membrane methods.
Electrodialysis: an effective method, but still too costly in terms of energy
Electrodialysis is an electrochemical separation process. This uses direct current to move ions through selective ion exchange membranes.
Electrodialysis eliminates salts and organic matter from wastewater and thus produces drinking water.
Although this membrane process is much more energy efficient than thermal processes, it nevertheless remains energy-intensive and also expensive in terms of maintenance.
Indeed, if we look at the process in detail, we realize that the energy cost comes largely from the separation of the water molecule into two components: a positively charged proton and a negatively charged hydroxide.
Furthermore, the membranes used for the separation require frequent replacement and are also expensive.
A new approach to electrodialysis
The team of researchers from the Beckman Institute for Advanced Science and Technology proposes a new approach to electrodialysis, with two significant improvements.
On the one hand, to save energy, they streamlined the salt separation process by using a redox reaction and the addition of a soluble copolymer.
On the other hand, researchers have replaced conventional ion exchange membranes with nanofiltration membranes, which are more robust and less expensive.[2].
From a chemical point of view, this method is quite different from classical electrodialysis.
Instead of splitting water molecules into positively and negatively charged parts to extract the salt, the redox reaction changes the charge of the entire water molecule all at once.
This achieves the same degree of salt separation, consuming at least ten times less energy than with traditional techniques. Indeed, according to the calculations available in the appendix of the study, with this method, the energy consumption (in theory) necessary for desalination would be between 0.13 and 0.25 kWh/m³.
A purification method successfully tested on wastewater
Although this technique is intended for the desalination of seawater, it has so far been successfully tested on water from a treatment plant, on samples of several liters.
The researchers plan to extend this process soon to salt and brackish water sources, including groundwater and rivers, and they are confident for the future.
In a Press releaseXiao Su, Assistant Professor of Chemical and Biomolecular Engineering at the University of Illinois Urbana-Champaign and corresponding author of this study, said: “We have the right polymer, the right membrane and the right conditions. The science is there, so the next step is to pave the way for the deployment of these devices for water treatment in the real world. I think now is the time to do it and I can’t wait to see it happen. »
[1] Saudi Arabia, China, Kuwait, etc.
[2] More details are available in the study published in the journal ACS Energy Letters.
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#economical #energyefficient #seawater #desalination #method
