Dirt-cheap solution to soil pollution problem

A recent report by the United Nation’s (UN) Food and Agriculture Organisation identified soil pollution as a major threat to the global production of safe and sufficient food. It noted that removing pollutants from soil is “a technically complex and costly undertaking, ranging from tens of thousands to hundreds of millions USD per year”.

A University of South Australia (UniSA) team including Associate Professor Haolan Xu and Dr Gary Owens developed a remediation technique that uses a solar evaporation surface to draw water from the soil through a sponge-like filter that traps contaminants, mimicking the process of transpiration that occurs in natural plants, but at an accelerated rate.

“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,” Owens said. “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.”

Globally, over 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 is designed to remove such contaminants in as little as two weeks.

“The solar evaporator used in this system is a variation of technology we are developing for many purposes, including desalination and wastewater purification,” Xu said. “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. It is a very exciting adaptation of solar evaporation techniques, with huge potential for addressing a growing global problem.”

Both the evaporator and the contaminant-capture component are made from low-cost, abundantly available materials, and the system requires little maintenance, with minimal set-up and running costs.

“Installing this system is about as easy as driving some stakes into the ground,” Xu said. “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.”

Owens says removing the captured contaminants from the biomimetic plant body is a relatively simple process.

“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 been successfully tested on a range of heavy metals including lead, chromium, cadmium and zinc, and the research team believes it may prove a viable approach to removing other major contaminants.

“By adjusting the properties of the adsorption material, we could use this to remove antibiotics or PFAS from soil, and to reduce soil salinity,” Xu said.

“As it is so simple and adaptable, this really could be a complete game changer — a paradigm shift — for soil remediation,” Owens said. “And that could have a massive impact on millions of people around the world.”

Image credit: iStock.com/Ivan-balvan