Today’s Solutions: May 31, 2023

Water scarcity is one of the most challenging problems humanity faces. Water is floating in the air all around us and in our oceans, but despite having so much water on Earth, only a tiny fraction of it is actually drinkable — while the rest of it is either too salty, contaminated, or difficult to access.

To address this, a team of scientists at Caltech has developed a new system that can tap into two different sources to produce fresh drinking water — by purifying contaminated water during the day and collecting fog droplets during the night.

The key component of the technology involves a hydrogel membrane whose surface is etched with a particular pattern, containing an array of tiny hydrophilic structures modeled after the spines of cacti.

“Cacti are uniquely adapted to survive dry climates,” says Ye Shi, co-author of the study. “In our case, these spines, which we call ‘micro-trees,’ attract microscopic droplets of water that are suspended in the air, allowing them to slide down the base of the spine and coalesce with other droplets into relatively heavy drops that eventually converge into a reservoir of water that can be utilized.”

As explained by New Atlas, by placing a membrane of this hydrogel in a box, you virtually create a device that can collect pure drinking water. During the day, it absorbs heat from sunlight, which heats contaminated water underneath the membrane creating steam that’s then collected on a transparent cover and runs into a reservoir. At night, you can remove this cover to expose the membrane to fog from the outside.

In experiments, samples of the material ranging between 55 and 125 cm2(8.5 and 19.4 in2) generated about 125 ml (4.2 oz) of water from evaporation and about 35 ml (1.2 oz) from fog overnight. While that may not sound like much, the team says that the eventual daily yield could be up to 34 L (9 gallons) per m2 (10.8 ft2) of the material.

Original study: Nature Communications — All-day fresh water harvesting by microstructured hydrogel membranes

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