Willows keep us clean and green

Water is one of the most precious resources we have, and yet the way we dispose of it is hardly what we’d call sustainable.

The UK’s sewage systems collect an estimated 11 billion litres of waste water per day, equivalent to 150 litres per person. In a move which suggests acknowledgement of the lack of sustainability of such a trend, the UK Government aims to cut wastewater production to 130 litres per person per day by 2030. Believe it or not, but willow trees might just serve as a useful naturally-occurring way of cleaning up wastewater, and even offering a source of biofuel.

Weeping willows sweep the waters clean

With their distinctive long branches and knife-like leaves, willows have a close affinity to water. These trees are thirstier than most, characteristically fast-growing and with root systems that are incredibly good at filtering out waste products such as nitrogen which are typically found in waste water. While such contaminants might be enough to make any plant or tree wilt, willows are remarkably adept at tolerating high levels of nitrogen.

Willows are an ideal form of wastewater treatment, as they are known as nitrogen-fixing trees capable of handling agricultural run-off. Imperial College London reports that some of its researchers along with others from the Université de Montréal concluded that 30 million litres of wastewater could be treated per hectare using what they term a ‘bio-refinery’.

…we can use natural biological systems, advanced chemical engineering and green technologies to harness to meet environmental challenges. We’re only at the start of developing such solutions to help improve the environment but I think they are very much within reach.

– Louis Hennequin, Department of Chemical Engineering, Imperial College London

Based on experiments conducted in Quebec, Canada, the team believe that refineries consisting of willow root systems could be arranged in such a way to filter wastewater effectively without need of more artificial or technologically-advanced solutions. Admittedly, the volume of water which could be treated may vary depending on the location, but it suggests water refineries could be looking a great deal greener in the coming years.

Fuel in the willows

Not only are willows proposed as a greener and more efficient way of managing large volumes of wastewater for treatment. Imperial College London reports that these trees could be capable of producing high yields of biofuel in a way that wouldn’t impact food production. Stemming from their rapid growth cycles, willow trees are an ideal candidate for biofuel production, because the cell walls of willow trees are rich in the sugars needed to distil into bio-ethanol.

Willows could be a viable source of biofuel in favour of traditional ones such as rapeseed, corn, soybeans or sugar beet, as it would take the pressure off these crops, especially with regards to demand as food products. In order to harvest enough biofuel, willow plantations could be grown, with some set aside for water filtration purposes, alongside those set aside purely for biomass and biofuel production. Bio-refineries can extract the sugars and other useful organic components from these willows to produce fuel, as well as the chemicals which could be used to create plastics.

Since time immemorial, willows have also been revered for their medicinal powers, owed largely due to the presence of salicylic acid in their cells. This acid is a core ingredient in aspirin, while other chemicals found in the processing of willow biomass have been found to produce chemicals with anti-inflammatory, anti-oxidant, anti-microbial or even anti-cancerous properties. On the face of it, willows tick many boxes, as they can not only give us cleaner water, but power us in the future, as well as heal us.

Main image: The Wanaka Willow, located at the southern end of Lake Wānaka in the Otago region of New Zealand. 

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