Remediating soil and water with plants

08.16.2022

She has just been awarded the 2022 European Inventor Award. Claude Grison, director of the ChimEco laboratory, has developed phytoremediation methods for decontaminating soil and water, using plants. Better still, the metals recovered serve as “green” catalysts to synthesise drugs or cosmetics. CNRS News takes a closer look at her technique based on the floating primrose-willow, an invasive exotic plant that proliferates in southern France.

Originally from South America and introduced to the Montpellier (southern France) botanic gardens in the nineteenth century, the primrose-willow acclimated so well to our regions that it invaded the canals of the Rhône River – and all of the wetlands of southern France. With the help of a specialised company, Grison and her team harvest approximately ten tons of the plant per year.

Cyril Frésillon / ChimEco / CNRS Photothèque

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This photograph clearly features the root system of the primrose-willow, which proliferates in canals and rivers. This system allows the plant to naturally absorb large quantities of the metallic elements present in water, and to store them using a physiochemical phenomenon known as biosorption.

Cyril Frésillon / ChimEco / CNRS Photothèque

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Grison examining the day's harvest. The massive extraction of primrose-willow helps control harmful proliferation. By covering the water's surface, it forces other aquatic plants into the shadows, ultimately causing their disappearance and threatening biodiversity.

Cyril Frésillon / ChimEco / CNRS Photothèque

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Back at the laboratory. After several days of drying, BioInspir technician Serge de Lussy grinds the primrose-willow into a powder of fine particles. The entire plant will be used in various processes in green chemistry, which is more environmentally friendly, and is based in particular on less polluting synthesis methods and solvents.

Cyril Frésillon / ChimEco / CNRS Photothèque

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For instance, here the ChimEco engineer Armelle Garcia is filling a filtration column with the invaluable primrose-willow powder. The goal is to produce a plant-based biosorption filter that uses the plant's natural properties to retain metals and other pollutants.

Cyril Frésillon / ChimEco / CNRS Photothèque

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The filter, which is totally bio-sourced, is then installed by Grison's team near the Orbiel, a polluted river in the Aude department (southwestern France). The captured water passes through filtration columns, and the primrose-willow powder absorbs various metals such as zinc, arsenic, and iron.

Claude Grison / ChimEco CNRS

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After being used, the filters packed with metals are taken back to the laboratory. This device (a microwave plasma atomic emission spectroscope) can measure the quantities absorbed. However, under no circumstances must the filters themselves become waste headed for already saturated containment sites. Grison is set on finding another use for them.

Cyril Frésillon / ChimEco / CNRS Photothèque

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That is the main innovation, as the plant-based filters are then transformed into “ecocatalysts”. They are “eco(logical)” since they do not come from mining activities with a major environmental footprint. They are “catalysts” because they accelerate the chemical reactions required to synthesise new molecules, which is precisely what this ChimEco researcher is doing thanks to a microwave reactor.

Cyril Frésillon / ChimEco / CNRS Photothèque

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As a result, the primrose-willow no longer invades wetlands and now serves as a plant-based filter to clean up contaminated water. Furthermore, these filters are being recycled as ecocatalysts for the perfume and medical industries. A hat-trick! BioInspir, the start-up founded by Grison, also produces the first solvents that are 100% bio-sourced and fully biodegradable.

Cyril Frésillon / ChimEco / CNRS Photothèque

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