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This artificial mangrove desalinates extremely salty water

Desalination may be about to revolutionise the way the world’s cities manage their water supplies – but not in the way you might expect.

A water-purifying mechanism dubbed the ‘mangrove device’ by its Yale University inventors can desalinate water with a salt concentration nearly 10-fold that of seawater.

The device, developed in the lab of environmental engineer Professor Menachem Elimelech, mimics the mangrove’s ability to generate negative pressure, the process of reverse osmosis in its root system and evaporation in its leaves.

While most desalination technologies use pumps to create extremely high pressure as a means of separation, the mangrove device uses evaporation to ‘passively’ arrive at the same result.

In simulating the mangrove’s natural process of desalinating water using the negative tension generated by the evaporative capillary forces in its leaves, the researchers found mangrove trees follow basic principles of physics.

Elimelech said the team solved some long-standing mysteries about tree hydraulics and the way in which mangrove leaves both soak up and evaporate water.

“We were just curious about how nature does some things, and it’s such an amazing thing that we were able to describe it with physics,” he said.

“We showed that the tree follows physical principles, and that we can mimic them in a microfluidic device.” 

Soaking up stormwater

The US researchers’ work also promises to lead to the creation of smaller devices, which could play an important role in water sensitive urban design.

Jongho Lee, who co-authored an article on the device that appeared in the latest issue of Science Advances, said it has the potential to be used for flood reduction by incorporating it into ‘sponge cities’.

These are metropolises with buildings designed to absorb and catch rainwater and reuse it, helping to reduce flooding and make cities more sustainable.

“Buildings could be designed to work as mangrove trees,” Lee said.

“Their outside walls would work as leaves and the foundations would act as roots filtering out contaminants.”

In such a city, “the buildings themselves would soak up excess groundwater and evaporate the water from their walls and roofs”.

The idea will almost certainly create interest if storms and storm surges continue to increase in frequency as a result of climate change, the researchers say.

But, as they also point out in their research, as mangrove forests disappear in alarming numbers, synthetic mangroves can’t replicate all the benefits of real mangroves. 

“Mangrove-inspired city design is promising for protecting people from the most extreme effects of storm surges and flooding, but in many places, the best way to do that will be leaving old-fashioned, living mangrove forests intact to do what they do best,” they said.

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