In countries such as Peru, Bolivia, Chile, Morocco, or Oman, people living in foggy areas often hang up nets to catch droplets of water, which trickle down the mesh and are collected to provide water for for drinking, cooking, or washing. By using a fog net with an area of only a few square meters, as much as several hundred liters of water can be harvested daily.
Although this method can be a blessing for foggy regions with little rain or spring water, a major drawback is atmospheric pollution, since dangerous pollutants also end up in the droplets of water. In many of the world’s large cities, pollution is so prevalent that any water harvested from fog is not clean enough to be used untreated for drinking or cooking.
Now, a team of scientists led by ETH Zurich has developed a revolutionary method that collects water from fog while simultaneously purifying it. To achieve this, the experts devised a close-mesh lattice of metal wire coated with a mixture of specially selected polymers and titanium dioxide.
While the polymers ensure that water droplets collect efficiently on the mesh and then trickle down as fast as possible into a container before being taken away by the wind, the titanium dioxide acts as a chemical catalyst, breaking down the molecules of many organic pollutants contained in the droplets and 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 centers,” said lead author Ritwick Ghosh, a scientist at the Max Planck Institute for Polymer Research.
Once installed, this groundbreaking technology requires little to no maintenance and no energy besides from a small but regular dose of UV to regenerate the catalyst. Due to a property known as photocatalytic memory, half an hour of sunlight is sufficient to reactivate the titanium oxide for another 24 hours. Since periods of sunlight are often rare in foggy areas, this is a very useful quality.
The experts tested the new fog collector in the lab and in a small pilot plant in Zurich, and were able to collect eight percent of the water in artificially created fog and break down 94 percent of the organic compounds which had been added to it (including extremely fine diesel droplets and bisphenol A, a hormonally active chemical).
Besides harvesting drinking water from fog, this novel technology could also be employed to recover water used in the 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 senior author Thomas Schutzius, a professor of Mechanical Engineering at the University of California, Berkeley who conducted the study while leading the Laboratory for Multiphase Thermofluidics and Surface Nanoengineering at ETH Zurich.
“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.”
In future research, the scientists hope to further refine these methods in order to make greater use of fog and steam as a previously underutilized source of water that could alleviate the needs of millions of people living in areas afflicted by water scarcity.
The study is published in the journal Nature Sustainability.
Using fog as a water source is an idea that has been employed in various regions of the world, especially in areas where freshwater is scarce.
Fog collection involves using large pieces of mesh or netting (fog collectors) to capture water droplets present in the fog. As the fog passes through these nets, the tiny droplets of water get trapped and merge to form larger droplets. These droplets then run down into a collection system, such as a gutter, and from there into storage tanks.
Fog collection a sustainable and passive method, requiring minimal energy or resources. It can be implemented in areas where other water sources are scarce or polluted.
The yield can be unpredictable and varies depending on the intensity and frequency of the fog. It may not be sufficient as a primary water source for large communities but can be a supplemental source.
In areas like the Atacama Desert in Chile, one of the driest places on earth, fog collection has been used to provide water for local communities.
When it comes to agriculture, fog collection can be used to provide supplemental irrigation. In reforestation efforts, the collected water can assist in supporting young plants until they’re established.