Researchers at the ETH Zurich have developed a novel method for capturing and decanting H2O from fog

ETH researchers have developed an innovative system that collects and purifies water extracted from fog (Photo: ETH Zurich/Adobe Stock/Montage)

In some areas of the world that are naturally foggy and far from water sources, such as the interior of Peru, Bolivia, Chile and Morocco, it is not uncommon for people to hang nets outdoors to catch small droplets of water that form the haze.

The problem of this technique is that thewater collected from fog in this way it can incorporate many of the polluting substances present in the atmosphere: the consequence is that in some areas, despite hundreds of liters being collected per day, the water extracted from the fog is not clean enough to be drunk or used in cooking.

The researchers of Federal Polytechnic of Zurich have therefore developed a method that allows the production of clean, even drinkable water, starting from the fog-catching net technique: the new system combines a single technology the collection and the water purification caught in the nets.

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Fog capture nets: an ancient but renewed technology

The first systems for capture water droplets from fog they date back to the pre-Columbian age: the first known method for collecting water from the mist using condensation consisted of placing containers under the branches of some trees. The first traces of this collection system date back to the years of the Inca Empire.

In 1969, the technology had already evolved into 100 square meter networks capable of supplying water to an entire military base: it took place in South Africa, and the network system allowed the production of approximately 11 liters of water per day.

Today the projects of water collection via networks (metallic, bamboo or other materials) are widespread throughout the world, and contribute significantly to meeting the water needs of cities and settlements that do not have access to water sources of another type.

In countries like Peru, Bolivia and Chile it is not uncommon for people to hang nets to catch water droplets, and the same happens in the hinterland of Morocco and other hot countries: in home or more structured format, the technology is well known and appreciated almost everywhere.

Using one fog-catching net measuring just a few square metres, up to hundreds of liters of water can be collected per day, which can be used for washing and, when conditions allow, for cooking.

The problem with this system, in fact, is that the water collected is not always clean enough to be considered drinkable.

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The purification of water captured by the milky meteor

A key disadvantage of this method water collection è the impact of air pollution on water quality: dangerous substances dispersed in the environment also end up in droplets trapped by nets.

In many of the world's major cities, the air is so polluted that water collects from the fog it's not clean enough to be drunk or used for cooking without first being treated. The study by the researchers of Federal Polytechnic of Zurich was created precisely to respond to this critical issue.

Thanks to a particular coating based on polymers and titanium dioxide, the fog-catching network developed by researchers at the Swiss university manages to simultaneously collect and purify water.

La technology di water purification is based on chemistry: titanium dioxide, the researchers explain, acts as chemical catalyst by breaking down the molecules of various organic pollutants present in the water, which thus become harmless.

"Our system not only collects the fog but also treats the collected water", explains Ritwick Ghosh, "which means it can be used in areas with air pollution, such as densely populated urban centres”. The scientist, who comes from the Max Planck Institute for Polymer Research in Mainz, conducted this project during an extended stay at ETH Zurich.

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"The heart of our project”, we read in thearticle published in Nature, “it is a wire mesh covered with anatase titanium dioxide nanoparticles embedded in a polymer matrix".

In other words, the system developed by researchers at Zurich Polytechnic consists of a narrow mesh lattice of metal wire, coated with a mixture of specially selected polymers and titanium dioxide, a mineral pigment widely used for making cosmetics.

"Once activated by sunlight, the photoactive titanium dioxide layer decomposes organic molecules such as diesel, even in the absence of sunlight”, explain the researchers: the only one energy required from this ingenious system is one small and regular dose of UV rays.

In outdoor tests, the study reads, the device shows “a water treatment efficiency greater than 85 percent”: the one proposed by ETH scientists is therefore a very efficient solution, which could allow entire communities to tackle the problem of water scarcity without having to resort to combustion or other energy sources.

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Passive water purification: the solution does not require energy

The new system forextraction of water from fog it was tested in the laboratory and in a small pilot plant in Zurich. The researchers were able to collect the 8 percent of the water in the artificially created fog and of break down 94 percent of organic compounds that had been added, including diesel and the chemical bisphenol A, which are known to be dangerous to health.

In addition to collecting drinking water from fog, this system could also be used profitably for recover the water used in cooling towers. "In the United States, where I live, we use a large amount of fresh water to cool power plants", explains Thomas Schutzius, then head of the ETH project and now a professor at the University of California, Berkeley.

As the professor explains, “it would make sense to capture some of this water before it escapes and make sure it is pure in case you want to return it to the environment”. Previous research by Ghosh, first author of the study, had focused precisely on water recovery from cooling towers.

This new technology, however, opens up much broader possibilities: once installed, this system requires no maintenance or energy. Thanks to a property known as catalytic memory, half an hour of sunlight is enough to activate the titanium oxide for 24 hours, which remains active even in the dark.

The new system, therefore, presents itself as an economic and rational solution not only for address drinking water scarcity in rural areas and cities around the world, but also for expand potential of collecting water from fog, an underestimated basin that could also involve large industry.

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Collecting and purifying water extracted from fog: the new system based on polymers and titanium dioxide (Photo: Envato)