How to keep 12.8 tonnes of microplastics out of Montréal’s water

An analysis by Polytechnique Montréal reveals the efficiency of citizen science—and filters on washing machines

February 8, 2023

Montréal – If every washing machine in Montréal were fitted with a special filter, nearly 13 tonnes of microplastics could be diverted from the city’s wastewater network each year. That was the conclusion of a team of Polytechnique Montréal researchers on Wednesday as they announced the results of a citizen science study.

The accumulation of microplastics in waterways can be damaging to both ecosystems and human health. These tiny particles pose a huge problem. They are easily ingestible by marine species, and extremely difficult to remove from water.

The primary reason for this crisis is the fact that our clothes are made of synthetic materials and that we wash them over and over again. During machine washing, polluting fibres are released from the textiles and carried away in the water effluent. In other words, with every load of washing, local waterways become a little more polluted.

What if microplastics could “come out in the wash?”

With the St. Lawrence River among the waterways with the highest concentration of microplastics in the world, the Groupe de recommandations et d’actions pour un meilleur environnement (Recommendation and Actions Group for a Better Environment, better known by its French acronym GRAME) undertook to answer that question as part of the project Pour un fleuve plus propre (“For a cleaner river”). The organization tasked a multidisciplinary team at Polytechnique with analyzing the composition of residue trapped by filters installed on individual washing machines. With support from RECYC-QUÉBEC and Mitacs, as part of the Mitacs Accelerate program, they sought out the expertise of the water engineering and chemical engineering teams led by Dominique Claveau-Mallet and Abdellah Ajji, respectively Assistant Professor in the Department of Civil, Geological and Mining Engineering and Full Professor in the Department of Chemical Engineering.

“With scientific talent mobilized worldwide toward the study of microplastics in waterways, every day we fine-tune our knowledge of the situation,” explains Professor Claveau-Mallet, who led the project at Polytechnique. “The findings are cause for concern. Our research project was therefore prompted by a sense of urgency. The goal was to concretely evaluate a possible solution.”

Citizen contribution

The experiment got under way in June 2021 and extended over a six-month period, in real-world conditions, i.e., people’s daily loads of laundry. Some 30 households took part in the citizen science exercise. They installed the filters themselves, then collected lint containing microfibres after each load and recorded information about the washing conditions.

“Our goal when we initiated the project was to develop a better understanding of the problem, but more importantly, a better definition of the solutions,” says Catherine Houbart, Executive Director of GRAME. “We believe it is vital that community concerns and needs be considered as part of future decisions regarding the preservation of our environment. That’s why it was important to involve the population in all phases of the project.”

Notes Yvonne Bourque, one of the participants in the citizen science project: “The research team could easily have chosen to conduct the experiment in a controlled environment, with washing machines running continuously in a lab, but they went with a participatory approach, which is really commendable. That choice is obviously a plus in terms of authenticity, but above all it helps in establishing constructive dialogue between the scientific and citizen communities, and in consolidating the trust relationship between them.”

One plastic bottle per household

Before the capturability of plastic microfibres could be quantified, a materials characterization step was necessary. “To be sure that the plastic microfibres would not be altered during the chemical treatments, we experimented with various lint digestion protocols,” explains Mohammed Abourich, an Environmental Engineering graduate at Polytechnique Montréal who authored a Master’s report on the project. “The method we decided on ensured that the integrity of the fibres was preserved, which allowed us to clearly identify the nature of the contaminants present and their respective proportions. In particular, the sample analysis revealed that plastics could account for up to 32% of the mass of the lint. Armed with that data, we took out our calculators.”

The result of the team’s preliminary calculation: by installing a filter like the one tested during the study, the average Montréal household could keep up to 16 grams of plastics per year from entering the wastewater stream. That’s the equivalent of one 500 mL plastic bottle. “Extrapolating to the scale of the city of Montréal, that’s 12.8 tonnes of plastic that could potentially be diverted,” Mr. Abourich concludes.

One challenge, multiple solutions

While the results are impressive, the lead researcher, Professor Claveau-Mallet, won’t go as far as to boast about the approach as a miracle cure for the proliferation of unwanted effluent in our waterways: “Our takeaway is that, while not a panacea, the filters offer significant retention potential. And unlike other technological solutions, it would be possible to roll out this method on a large scale over the short to medium term,” she says.

“One avenue that could be considered is for washer manufacturers to build in the filtersat the design stage. More broadly, however, it’s obvious that the fashion industry must rethink its production methods. And society as a whole needs to make a shift toward more responsible consumption,” Professor Claveau-Mallet concludes.

Next steps already announced

The NSERC Alliance and Mitacs Accelerate programs have jointly awarded a four-year, $480,000 subsidy to Professor Claveau-Mallet as lead researcher in a project to develop a detection method and purification strategies for tackling microplastics in municipal wastewater collection and treatment systems. The project will be conducted in collaboration with the firm Claro Inc. and the cities of Repentigny, Longueuil and Laval.

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About Polytechnique Montréal

Established in 1873, Polytechnique Montréal is one of Canada’s largest engineering education and research universities, and is located on the Université de Montréal campus – North America’s largest Francophone university campus. With nearly 57,000 graduates and over 120 academic programs, Polytechnique has trained 22% of the Ordre des ingénieurs du Québec (OIQ)’s current membership. Polytechnique Montréal is also distinguished by its more than 300 talented professors and 10,000 students. Its overall annual budget is $300 million, including $100 million reserved exclusively for research.

Audrey Rondeau, Communications Advisor, Polytechnique Montréal / 514 690-3553

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