A team led by University of South Australia researchers has pioneered a new soil remediation technique that is significantly faster, simpler, safer, and more cost-effective than currently available methods for potentially solving soil pollution.
A recent report by the UN’s Food and Agriculture Organization identifies soil pollution as a significant threat to the global production of safe and sufficient food. They noted that removing pollutants from the soil is currently “a technically complex and costly undertaking, [with costs] ranging from tens of thousands to hundreds of millions of USD per year”.
A UniSA-led team, including Associate Professor Haolan Xu and Dr Gary Owens, has developed a new remediation technique that uses a super-efficient 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 a greatly 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,” said Owens.
“This means plants can be used to extract contaminants from soil. However, the process is very slow, often taking multiple growing seasons. This is particularly the case in heavily contaminated situations. That is where 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 much faster and without any of the problems caused by toxicity.”
Soil pollution is a global problem
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 and pollutants from the soil into the biomimetic plant body.
“The solar evaporator used in this system is a variation of technology we are developing for many purposes, including desalination and wastewater purification,” said 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.
“It is a fascinating adaptation of solar evaporation techniques, with huge potential for addressing a growing global problem.”
The evaporator and the contaminant-capture component are made from cheap, abundantly available materials with extremely long operational lives. The system requires very little maintenance, with minimal setup and running costs.
“Installing this system is about as easy as driving some stakes into the ground,” said Xu. “Unlike some existing soil washing techniques, it doesn’t disturb or destroy the soil composition.
“Also, the water 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.”
New technique a simple process for solving soil pollution
Further adding value to the technique, Dr 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 repeatedly,” he said.
The remediation technique has been successfully tested on various 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.
“By adjusting the properties of the adsorption material, we could use this to remove antibiotics or PFAS from the soil and to reduce soil salinity,” said Xu.
“As it is so simple and adaptable, this could be a complete game changer – a paradigm shift – for soil remediation,” said Owens.
“And that could have a massive impact on millions worldwide.”
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