Around 35% of the world’s population (2 billion people) may not have sufficient drinking water to satisfy their daily needs by 2025. That seems crazy when water covers over 70% of the surface of our planet. About 97% of all the water on Earth is in oceans, which is unfortunately undrinkable. Of the remaining 3%, 2% of it is frozen in ice caps and glaciers. That leaves only 1% for the global population of 7.8 billion people (8.1 billion by 2025) to drink. Knowing that it doesn’t seem so crazy that so many people thirst, does it?
The obvious solution is to make seawater drinkable. However, that’s easier said than done. Desalination, as it is called, is a complicated procedure. The problem is that salt particles tend to crystallize within the various components of water desalination devices. The crystallized salt clogs these technologies, causing a reduction in performance over time and limiting such devices’ durability. However, to solve this problem would ensure the constant production of freshwater. So, that’s what a team of engineers from Politecnico di Torino, in collaboration with MIT, have been work on.
After two years of studying the mechanisms underlying the transport of salt particles in desalination devices, the team realized there was an inconsistency between experimental observations and classical theoretical models of salt transport. They found that the difference is due to the Marangoni effect. They then developed a prototype solar desalination device that can spontaneously remove accumulated salt. Their invention could be the answer to providing drinking water to billions of people sustainably.
First author Matteo Morciano, a researcher at the Energy Department of the Politecnico di Torino, explained:
The Marangoni effect is a phenomenon also present in nature, which can be observed in everyday life: In an aqueous solution, liquid molecules interact with each other through intermolecular bonds that generate forces called ‘cohesion forces.’ Two solutions with different concentrations will have different cohesion forces. The presence of this concentration variation, and therefore of cohesion forces causes the liquid to flow away from regions of low concentration, generating a re-mixing process. This effect is responsible for the ‘tears’ of wine that are observed on the walls of the glass when shaken.
The Marangoni effect, due to a change in concentration in the liquid, can therefore be engineered and exploited to increase the re-mixing of solutions with different concentrations. In our desalination device (where the treated solutions are based on seawater at different concentrations), this phenomenon allows us to avoid the accumulation of salt in the evaporators, ensuring constant and lasting distilled water productivity and safeguarding the components subject to deterioration. Our strategy was, therefore, to design a device capable of taking full advantage of this effect, achieving a further step towards future commercial applications of the device.
Their current prototype can filter 15 liters of water per 1 square meter area daily. The results of this research could be beneficial to the development of new desalination devices that guarantee stable and long-lasting performance. The team is now making a new prototype that is more versatile and able to be industrialized.
