Solar evaporator provides cheap soil remediation solution

Researchers from the University of South Australia have pioneered a solar-based soil remediation technique that is said to be faster, simpler, safer and more cost-effective than currently available methods, with a recent report from the Food and Agriculture Organization of the United Nations noting that removing pollutants from soil is currently “a technically complex and costly undertaking [with costs] ranging from tens of thousands to hundreds of millions of USD per year”.

Explaining the concept behind the system, which is described in the Chemical Engineering Journal, team member Dr Gary Owens said, “Plants naturally draw mineral components out of the soil when they move water from their roots into their stems, leaves and flowers, where those mineral components are trapped.

“This means plants can be used to extract contaminants from soil, but the process is very, very slow, often taking multiple growing seasons, particularly in heavily contaminated situations, where the soil toxicity means the plants struggle to grow and often die.

“We have created a system that mimics this process — a form of biomimetic plant — but one that does so at a much faster rate and without any of the problems caused by toxicity.”

Worldwide, more than 10 million sites are considered soil-polluted, with more than half contaminated by heavy metals such as cadmium and lead, or metalloids such as arsenic. The new system can remove such contaminants in as little as two weeks by using a super-efficient solar evaporation surface to rapidly draw water from the soil through a sponge-like filter that traps contaminants.

“The solar evaporator used in this system is a variation of technology we are developing for many purposes, including desalination and wastewater purification,” said team member Associate Professor Haolan Xu.

“We are achieving world-leading evaporation rates with this technology in many other areas, and as far as we know, this is the first time this approach has been applied to soil remediation.”

Both the evaporator and the contaminant-capture component are made from cheap, abundantly available materials with extremely long operational lives, and the system requires very little maintenance, with minimal setup and running costs. According to Xu, “Installing this system is about as easy as driving some stakes into the ground and unlike some existing soil-washing techniques, it doesn’t disturb or destroy the soil composition.

“Also, the water that is added to the soil could be captured from the evaporator and recycled, meaning this could operate as a closed system, with almost no running costs.”

In addition, Owens said it is a relatively simple process to remove the captured contaminants from the biomimetic plant body. “This means those materials can be harvested for reuse, and the adsorption material, which has a very high saturation point, can be reused over and over again,” he said.

The remediation technique has so far been successfully tested on a range of heavy metals including lead, chromium, cadmium and zinc. The research team believes it will also prove a viable approach to removing other major soil contaminants, with Xu saying the properties of the adsorption material could be adjusted to remove antibiotics or PFAS from soil, and to reduce soil salinity.

“As it is so simple and adaptable, this really could be a complete game changer — a paradigm shift — for soil remediation,” Owens added.

Image credit: iStock.com/Chet_W

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