Montreal researchers using willow tree chemistry to treat wastewater

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Stock photo of a willow tree. Credit: gluuker, AdobeStock.

Researchers at the Université de Montréal are experimenting with using the roots of willow trees in plantations to filter untreated wastewater.

Results of the project were recently published in the journal Science of the Total Environment to show how the process could essentially create a “biorefinery” that could treat more than 30 million litres of primary wastewater per hectare each year. The roots of the willow tree filter out nitrogen, the concentration of which is high in wastewater, tripling the biomass produced.

This biomass can then be collected to make renewable lignocellulosic biofuels, researchers found.

“We are still learning how these trees can tolerate and process such high volumes of wastewater, but the complex phytochemical toolkit of willows gives us valuable clues,” said Eszter Sas, lead author of the study and doctoral student, in a statement from Université de Montréal.

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Researchers planted six small plots of willow trees on a piece of land in Quebec. Three of those plots were left un-irrigated, while the other three were irrigated with municipal wastewater effluent at a rate of 29.5 million litres per hectare per year. After three years, three trees were randomly selected from each plot, harvested and analyzed.

The irrigated trees contained three times the above-ground biomass and higher amounts of salicylic acid. They also contained a series of “green” chemicals with important antioxidant, anti-cancer, anti-inflammatory and antimicrobial properties – all enriched by the filtration of wastewater by the roots of willows.

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Graphic illustration of willow tree wastewater treatment. Source: “Science of the Total Environment

As part of their research, Sas and a British-Canadian team of plant scientists, biochemists and chemical engineers from Université de Montréal and Imperial College London, also used advanced metabolomic profiling technology to uncover the new extractable “green” chemicals produced by the trees.

Sas said her team is “only scratching the surface” of the natural chemical complexity of willow trees, which could be harnessed to tackle environmental issues.

“It is astonishing to note all the mysteries which still conceal the vegetable chemistry. Even the willows, which have been growing for thousands of years, have something to teach us,” Sas said.

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