Even with today's various sewage-treatment technologies, a great deal of municipal wastewater is still released back into waterways either partially or completely untreated. According to a new study, however, plots of willow trees could be used to clean it up – while also producing useful materials.
Willows are known for being very tolerant of contaminants that they take up through their roots, including the excessive amounts of nitrogen found in raw sewage. Given this fact, scientists from Canada's Université de Montréal and Britain's Imperial College London decided to try using the trees to filter such substances out of wastewater.
To that end, the researchers planted six 10 x 10-meter (32.8-ft) plots of willow trees on a piece of land in the province of Quebec. Three of those plots were left unirrigated, while the other three were irrigated with municipal wastewater effluent at a rate of 29.5 million liters (about 7.8 million US gal) per hectare (2.5 acres), per year. After three years, three trees were randomly selected from each plot, harvested and analyzed.
First of all, it was found that the irrigated trees had three times the above-ground biomass as their control group counterparts. This material could conceivably be processed into eco-friendly biofuels.
Additionally, they contained greater amounts of salicylic acid (which is the natural form of what we know as aspirin), along with various other useful chemicals previously not seen in willow trees. Among other things, these compounds are known to possess "significant antioxidant, anticancer, anti-inflammatory and antimicrobial properties."
U de M's Prof. Frédéric Pitre, who supervised the study, tells us that all of the wastewater was taken up by the trees – this means that none was left over to run off into the environment. That said, he does add that willow-based wastewater treatment isn't effective in the winter months, when the trees are dormant. Nonetheless, the system does still show a great deal of promise.
"It’s amazing how much novel plant chemistry there is still to be discovered, even in willow trees, which have been around for thousands of years," says U de M PhD student Eszter Sas, lead author of a paper on the research. "It seems likely that we’re still only scratching the surface of these trees’ natural chemical complexity, which could be harnessed to tackle environmental problems."
The paper was recently published in the journal Science of the Total Environment.
Source: Université de Montréal
