A specially coated metal mesh has harvested water from foggy air while simultaneously removing pollutants.

Designed to harvest drinking water in largely dry areas with heavy atmospheric pollution, the mesh and its solar-powered water treatment method were developed by researchers at ETH Zurich in Switzerland.

In regions with little rain or spring water, such as areas in Peru, Bolivia and Chile, some people in foggy areas hang up nets to catch droplets of water. These droplets trickle down the mesh and are collected for drinking, cooking and washing.

One crucial drawback with this method is atmospheric pollution, as hazardous substances also end up in the droplets of water. In many of the world’s major cities, the air is so polluted that any water harvested from fog is not clean enough to be used without treatment, either for drinking or for cooking.

To tackle the issue, the ETH team developed a close-mesh lattice of metal wire, coated with a mixture of specially selected polymers and titanium dioxide. The polymers ensure that droplets of water collect efficiently on the mesh and then trickle down as quickly as possible into a container, before they can be blown off by the wind. The titanium dioxide acts as a chemical catalyst, breaking down the molecules of many of the organic pollutants contained in the droplets, rendering them harmless.

“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 centres,” researcher Ritwick Ghosh said.

The technology needs little or no maintenance after installation, an ETH announcement said.

No energy is required to use it, apart from a small but regular dose of ultraviolet (UV) light to regenerate the catalyst. This can be provided by half an hour of sunlight, which reactivates the titanium oxide for 24 hours, thanks to a property known as photocatalytic memory. With periods of sunlight often rare in areas prone to fog, this is a “very useful” quality, the researchers said.

The new fog collector was tested in the laboratory and in a small pilot plant in Zurich. Researchers were able to collect 8% of the water from artificially created fog and break down 94% of the organic compounds that had been added to it, including extremely fine diesel droplets and the chemical bisphenol A, a hormonally active agent.

The technology could also be used to recover water used in power station cooling towers. “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 researcher Thomas Schutzius. “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.”

Ghosh now aims to advance the technology and explore commercial application. He hopes to make greater use of fog and steam, helping tackle water scarcity.

Extracted from IMechE website, read more here

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