Between two fields, we often see ditches. They carry agricultural runoff to rivers and rivers. Despite all efforts to reduce unnecessary inputs, this water may contain contaminants, such as pesticides.
A researcher from the École de technologie supérieure (ETS) has just designed a filter that could decontaminate this agricultural water before it reaches the waterways.
“We would place the filter at the end of the ditch, before it flows into a watercourse”, explains Mathieu Lapointe, who described the principle of his filter in April in the magazine Nature. “The filter contains molecules that attract contaminants, especially pesticides and phosphorus. It would suffice to wash the filter medium once or twice a year. We are in the process of seeing how to wash it, for example at what pH. »
PHOTO PROVIDED BY MATHIEU LAPOINTE
Mathieu Lapointe with his prototype. On the left, the contaminated water, in the center, the filtration media and, on the right, the purified water.
Mr. Lapointe tested his idea in the laboratory with agricultural water collected on the banks of the Yamaska. He also designed a prototype that will be tested later this summer, in collaboration with the Union des producteurs agricole (UPA).
“Relevant” innovation
“Mr. Lapointe’s innovation is very relevant and very promising for the agricultural and municipal worlds,” explains Julien Pagé, vice-president of the Fédération de l’UPA de la Montérégie. “Ideally, the inputs stay in the field. Agriculture is expensive, so we want to get the right doses. But there can be soil leaching when there is runoff water. We don’t have much control over heavy rain. »
PHOTO ALAIN ROBERGE, THE PRESS
A stream flows into the Yamaska River after crossing agricultural fields in the region.
Recently, a tightening of the regulations on agricultural runoff was considered by the CAQ government, then was postponed for four years.
The type of agricultural runoff treatment was not specified. But everyone knows that a treatment that will eliminate these under-the-radar molecules, like pesticides, will be needed soon. So the actors in the agricultural and municipal sectors are preparing.
Mathieu Lapointe, researcher at the École de technologie supérieure
One of the current obstacles, according to Mr. Lapointe, is that there are very few laboratories actually capable of detecting pesticides in water, and that they are mainly located in universities.
The challenge of treating water in Saint-Hyacinthe
Mr. Lapointe also works with the Saint-Hyacinthe drinking water treatment plant, which takes its water from the Yamaska. “It’s a plant that already has to treat water where there is a lot of agricultural pollution. They are aware of the problem of molecules that are, for the moment, under the radar, for example pesticides and other agricultural contaminants. »
PHOTO ALAIN ROBERGE, THE PRESS
Researcher Mathieu Lapointe testing his technology near the Yamaska
A visit to the Saint-Hyacinthe plant reveals the challenge of agricultural pollution. “Taking water from the St. Lawrence, for example, as a source of drinking water does not require a lot of effort,” says Alexandre Lamoureux, director of engineering at Saint-Hyacinthe. “In Saint-Hyacinthe, we have specific challenges. The Yamaska, where we have our water intake, has a lot of turbidity, even before agricultural pollution. »
Turbidity is a measure of water clarity. The Yamaska has an average ranging from 8 to 15, with peaks over 300. The St. Lawrence River has an average turbidity of 3 to 5 and peaks between 10 and 15.
The Montérégie plant is one of the few in Quebec to combine activated carbon, ozone and ultraviolet (UV) treatments, according to Mr. Lapointe. “Saint-Hyacinthe also has several injection points for coal, ozone and chlorine, for more flexibility. In the golf bag of water treatment, Saint-Hyacinthe probably has all the clubs. »
High levels of pesticides in the Yamaska
In 2019, a study by the University of Montreal published in the journal Environmental Pollution had reported high levels of certain pesticides in the Yamaska and other rivers in agricultural regions of Quebec.
Saint-Hyacinthe’s assistant director general, Charles Laliberté, specifies that pesticides “are a subject of major concern to the population”. In addition to weekly sampling to ensure the quality of the water, Saint-Hyacinthe conducts more in-depth analyzes four times a year to detect pesticides in particular. The results are still substandard.
“We probably eliminate some of the pesticides by ozonation,” says François Tremblay, plant supervisor. We are one of the pioneer cities. »
The capacity of the Saint-Hyacinthe plant was tripled in 1989 and “upgrading”, including UV treatment, took place in 2018-2019. More recently, gaseous chlorine has been replaced by liquid chlorine, because of the risk of leakage.
Learn more
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- 1647 nanograms per liter
- Quantity of glyphosate, a herbicide, in Yamaska in July 2017, near the St. Lawrence
SOURCE : Environmental Pollution
- 800 nanograms per liter
- Aquatic life protection threshold for glyphosate, according to the Canadian Council of Ministers of the Environment
SOURCE : Environmental Pollution