Access to clean water is problematic, particularly within dry regions such as in areas of Peru, Bolivia, and Chile, although there is a significant amount of fog in the mountainous areas of the country.
In such countries, it’s pretty usual for folks residing in foggy locations to hang up nets to capture water droplets. These droplets gradually seep through the mesh and are gathered to provide water for various purposes like drinking, cooking, and washing.
Surprisingly, even with just a few square meters of fog net, as much as several hundred liters of water can be harvested every day. This can be a blessing for regions with little rain but where fog is a common occurrence.
However, atmospheric pollution can contaminate the water harvested from fog, making it unsafe for drinking and cooking.
Now, ETH Zurich researchers have developed a water treatment method that collects water from fog and simultaneously purifies it.
The method uses a close-mesh lattice of metal wire coated with certain polymers as well as titanium dioxide. The polymers ensure that water droplets collect efficiently on the mesh and then trickle down as quickly as possible into a container.
Meanwhile, the titanium oxide acts as a chemical catalyst, breaking down the organic pollutant molecules contained in the droplets when exposed to UV in sunlight. Just 30 minutes of sunlight exposure was enough to reactivate the titanium oxide for a further 24 hours. This is a very useful quality since periods of sunlight are often rare in areas prone to fog.
The technology requires no energy apart from a small but regular dose of UV to regenerate the catalyst. In addition, it needs little or no maintenance once installed.
During outdoor tests, using a rationally engineered wire mesh coating that was pre-activated with UV light, researchers were able to collect about 8% of the water from the fog. They also demonstrated exceptional organic pollutant reduction values of 85% and 94% when the UV index was low and high, respectively.
This coating also passively treats water contaminants such as diesel or bisphenol A, underpinning the possibility of using such a concept in a real-world environment against a range of pollutants.
“Our system not only harvests fog but also treats the harvested water, meaning it can be used in areas with atmospheric pollution, such as densely populated urban centers,” Ritwick Ghosh, a scientist at the Max Planck Institute for Polymer Research in Mainz, explains in the press release.
Journal reference:
- Ritwick Ghosh, Adrien Baut, Giorgio Belleri, Michael Kappl, Hans-Jürgen Butt, and Thomas M. Schutzius. Photocatalytically reactive surfaces for simultaneous water harvesting and treatment. Nature Sustainability, 2023; DOI: 10.1038/s41893-023-01159-9