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A simple, non-energetic device gathers and purifies misty water.

A silver wire mesh collects droplets of water in front of a gray background.

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In certain parts of the globe, there are communities that do not have convenient access to safe and clean drinking water. This can be attributed to their distant locations, inadequate or damaged infrastructure, or fluctuations in climate. As a result, people in these areas often resort to alternative means of obtaining fresh water, such as collecting rain, dew, vapor, and fog. However, this water can be contaminated and pose risks to health if used.

A new advancement in the collection of fog water has been made, where a polymer coating on a metal mesh is able to both collect and purify contaminated water. Scientists conducted experiments and found that the coated mesh was more effective than current fog harvesters and was also able to purify the water by 91%, producing almost completely clean water without the need for power.

Lead researcher Ritwick Ghosh from the Max Planck Institute for Polymer Research in Mainz, Germany, stated that they do not recommend directly drinking the purified water as they were unable to achieve 100% purification. However, the water can still be used for daily activities such as watering plants or in the washroom.

Out of Thin Air

In areas with limited access to freshwater, different methods can be used to gather water from the air. Examples include using rain barrels to collect rain, utilizing radiative cooling surfaces to condense dew, and using meshes to gather fog. These types of passive devices are particularly beneficial in regions without access to electricity.

Fog-harvested water is frequently polluted due to its ability to capture air pollution within its droplets.

Fog harvesting systems have proven to be highly successful in arid, mountainous regions with little precipitation, such as Chile’s Atacama Desert and the Namib Desert on the southwest coast of Africa. In countries like Chile, Eritrea, Ethiopia, Guatemala, Morocco, and Nepal, where fog harvesters have been installed, they are able to capture thousands of liters of water per day.

However, it cannot be guaranteed that this water is safe for use. Fog droplets have a tendency to capture air pollution, making fog-harvested water susceptible to contamination, especially in areas near sources of pollution like power plants and industrial areas.

Harvest and Clean, Simultaneously

Ghosh’s experiment was inspired by a series of poor air quality incidents around the Indian capital that some dubbed “the Great Smog of Delhi.” With so much smog in the air, the polluting aerosols were being trapped in fog droplets. Fog harvesters around Delhi were collecting the polluted water, which spurred Ghosh and his team to think of ways to passively rid this water of contaminants.

Ghosh and his team experimented with different methods to purify fog water from pollutants using a chemical technique known as photocatalysis. This process involves certain metal oxides becoming chemically reactive when exposed to specific light wavelengths, which enables them to decompose other molecules.

In laboratory experiments, the mesh coated with polymer collected 8% of the fog and removed 91% of organic pollutants within 66 minutes. The video was recorded at a speed of 24⨯. Credit goes to Ritwick Ghosh from ETH Zurich.

2) semiconductor

The scientists applied a thin layer of titanium dioxide semiconductor (TiO2) onto a finely woven metal mesh in their experiments.22

The TiO2 polymer is activated by sunlight. 2

The reaction between the organic pollutants in fog was able to release fresh water into a collector.

Their experiments in both laboratory and natural settings showed that the mesh with polymer coating collected water equally or more effectively than previous uncoated meshes, with an 8% higher collection efficiency. Additionally, the coated mesh successfully purified the water of organic pollutants without the coating breaking off into the collected water. The harvester was able to cleanse the water of up to 91% of organic contaminants, and also process it for diesel and bisphenol A (BPA) in just over an hour.

Furthermore, according to Ghosh, the titanium dioxide is activated by sunlight, eliminating the need for energy. He also noted that the effect persists even after the sunlight has disappeared. The coating on the mesh remains active and able to purify water, even in overcast conditions that are common in foggy regions. This study was published in Nature Sustainability in August.

Providing services in regions with heavy fog and air pollution.

The scientists have introduced a revolutionary fog collector that can capture solar energy on sunny days and use it for purifying water during fog collection. Zuankai Wang, head researcher of the nature-inspired engineering lab at Hong Kong Polytechnic University, stated that both the collection and removal of organic contaminants are as good or better than current technologies. Wang, who was not part of the study, praised the design for its efficiency.

I think that the fog collector is extremely valuable, especially in areas with frequent fog and heavy air pollution.

Wang stated that the fog harvester has significant significance, especially in areas with frequent fog and heavy air pollution. This invention has the capability to provide clean water for nearby communities by simultaneously collecting fog and removing contaminants. In light of the current and worsening air pollution, it is challenging to ensure the purity of fog.

Ghosh stated that upcoming experiments are focused on reducing the duration of fog collection and purification by experimenting with alternative photocatalysts. This is in efforts to enhance the effectiveness of purification and extend the duration of the photocatalytic charge. Additionally, they plan to expand the scale of experimentation to larger sections of mesh in order to gauge the performance of the device in more realistic conditions.

Before and after images of coated wire mesh collecting contaminated water during laboratory tests.Before and after images of coated wire mesh collecting contaminated water during laboratory tests.

In laboratory experiments, scientists exposed a coated mesh to a mist of polluted water vapor. The mesh gathered the contaminated water and began to cleanse it. Credit: Ritwick Ghosh, ETH Zurich.

Wang is anticipating future versions of the device to utilize a stronger photocatalyst in order to enhance the purification process. However, he expressed that the current technology is just a minor advancement in device improvement, but a major breakthrough in its practical use.

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

This article is part of our ENGAGE resource, which provides science news for teachers to use in their lessons. Check out all the ENGAGE articles and let other educators know how you incorporated this article into a classroom activity by commenting below.

Reference: Cartier, K.M.S. (2023), A Simple, Non-Energy Method for Collecting and Purifying Fog Water, Eos, 104, Published on September 28, 2023.

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