New system captures fog and turns it into clean water

ETH Zurich

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Researchers from ETH Zurich have developed a system that captures fog in the atmosphere and simultaneously removes contaminants while running using solar power.

The harvesting and water treatment system consists of a metal wire mesh with a solar-light-activated reactive coating that captures the fog. The droplets of water then trickle down into a container below. The mesh is coated with a mixture of specially selected polymers and titanium dioxide, which acts as a chemical catalyst and breaks down the molecules of the pollutants into harmless particles.

“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,” said Ritwick Ghosh, co-author of the paper and a scientist at the Max Planck Institute for Polymer Research.

The system is energy-efficient as it needs little or no maintenance. Very little energy is required through a regular small UV dose to regenerate the catalyst. Half an hour of sunlight is enough to reactivate the titanium oxide for 24 hours, claim the researchers in the press release.

This characteristic is essential for areas that don’t receive enough sunlight.

The researchers tested the fog collected in their labs and a small plant in Zurich. This is a red flag in the study as it limits our understanding of how their newly developed system would perform in the real-world atmosphere.

As per the press release, researchers collected 8 percent of the water from the artificially created lab fog and broke down 94 percent of the organic compounds like diesel droplets and bisphenol A, which had been added.

“In the cooling towers, steam escapes up into the atmosphere. In the United States, where I live, we use a great deal of fresh water to cool power plants,” said Thomas Schutzius, another co-author of the paper and a professor at the University of California, Berkeley.

“It would make sense to capture some of this water before it escapes and ensure that it is pure in case you want to return it back to the environment,” he added.

Through their study, the researchers want to address the global challenge of water scarcity. Even though we have enough freshwater sources, their latest system could further develop water harvesting systems.

The study was published in the peer-reviewed scientific journal Nature Sustainability.

Study abstract:

Atmospheric water harvesting provides decentralized and sustainable supplies of freshwater in areas away from natural water resources. However, an important challenge is that water sources such as fog are subject to contamination from airborne pollutants, especially near population centers. Here we demonstrate a rationally designed system that can capture fog at high efficiency while simultaneously degrading organic pollutants. At the heart of our design is a wire mesh coated with anatase titanium dioxide nanoparticles embedded in a polymer matrix. Once activated by sunlight, the photoactive titanium dioxide layer decomposes organic molecules such as diesel, even in the absence of sunlight; moreover, the wettability of the mesh surface is engineered to enhance water extraction. In outdoor tests, the device can maintain a good fog harvesting performance as well as a water treatment efficiency of >85%. The continuous production of water with passive purification demonstrated in our study provides an energy-free solution to address water scarcity.