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Behind the scenes of Montreal's wastewater treatment plant

Services-Conseils - Visite station d'épuration

We know that wastewater affects the health of rivers and watercourses. So we went to the source, that is to say behind the scenes of the Jean-R.-Marcotte wastewater treatment plant, which treats almost all of Montreal's wastewater! We came away impressed by the workload that it represents and by the ingenuity of the process (which will be significantly improved once the water ozonation step is added) and for my part, I must say the smell that comes from it!

The Jean-R wastewater treatment plant. Marcotte: a huge factory

Every day, the Jean-R.-Marcotte treatment plant treats approximately 5 million cubic meters of wastewater before returning it to the St. Lawrence River. That's half of the wastewater treated in Quebec! It receives all wastewater from Sainte-Anne-de-Bellevue to Riviere-des-Prairies—Pointe-aux-Trembles, where it is located. There is indeed a small wastewater treatment plant on Notre-Dame Island in Montreal, but its size has nothing to do with the Jean-R.-Marcotte station.

Visite de la station d’épuration Jean-R. Marcotte par la Fondation Rivières_Crédit photo : Élisabeth Caron-Sergerie
Visit to the Jean-R wastewater treatment plant. Marcotte by the Fondation Rivières

How is wastewater treated?

We put on our masks, helmets and protective gloves to follow the journey of transforming wastewater into treated water.

1. Passage to the pumping station 

Wastewater arrives at the treatment plant underground. They are therefore brought up to the surface at the pumping station in enormous suction wells, some of which are up to 43 meters deep! There are two for the northern waters of the island, and two others for the southern waters. The water is then sent into huge pipes. Everything works thanks to 17 pumps and 17 motors, as well as an energy center containing generators in the event of a power outage. Indeed, a cessation of operations is inconceivable! 

Station d'Épuration - Canaux - Montréal

2. Chemical treatment

So far, my fine nose and I are doing well. But things get bad near the intake canals, where the water goes after its visit to the pumping station. It must be said that so far, no treatment has taken place. This is about to change: a coagulant is injected, which will reduce phosphates in the water and increase the efficiency of settling, a subsequent step.

3. Screening

Large pieces are removed using screens at the pretreatment center. Large pieces include stools, toilet paper, or items that shouldn't be there, like tampons or wipes. The biggest and weirdest object the station team found in their screens? An orange cone…

Waste that does not belong (wood, plastic, etc.) is sent to rotary presses to remove water, then to a sanitary landfill by truck.


4. Desanding

Head to the sand traps, which look like a swimming pool. (We actually wondered how much we would be willing to take a dip for.) This step is used to remove the sand or gravel from the water, by depositing it at the bottom of the water. And yes: these materials are found in large quantities in wastewater, being used in winter to make our roads less slippery. The sand goes into the sanitary landfill site, while the water receives a physicochemical treatment – a coagulant (ferric chloride) and a coagulant aid (polymer) – just before continuing its path into the ponds. decantation. 

Usine d'épuration de Montréal
Fourteen sand traps receive the wastewater for around ten minutes

5. Decantation

Here, the water sits for a long time, while the suspended matter separates from the rest of the water and settles to the bottom. This separation is made possible thanks to the physico-chemical treatment at the outlet of the sand traps. The material found at the bottom is called “sludge”. This is where the phosphorus is contained, and therefore through this process this contaminant is eradicated. And what's on the surface? Apart from the tampons that we saw twirling on the walkways, pushed by the wind, we call it foam. The sludge and scum go to the sludge treatment building, where the magic continues! 

Salle des gâteaux

6. Sludge dewatering and incineration 

Press filters dehydrate the sludge, which then takes on the beautiful little name “cake” (yum!). The cakes will either be transformed into pellets for agricultural purposes, or be cremated, the ashes of which will be buried.

The largest ozone treatment plant in the world!

Ozonation for better wastewater treatment

Despite all this process, the treated water is not particularly clean: we absolutely would not swim in it, and we would drink it even less! That said, a disinfection step will be added by 2025 which will greatly improve the quality of the effluent water:ozonation. Thus, we will be able to say goodbye to a very large part of the E.coli, viruses and pharmaceuticals! There will still be organic matter that consumes oxygen (we are planning further work to tackle this in the coming years). At the end of this investment of $717 million, the Montreal wastewater treatment plant will become the largest ozone treatment plant in the world! 


An enriching visit to the Montreal wastewater treatment plant

Considering the importance of the resort, our expectations were high. We were pleasantly surprised to see that the employees are able to manage the operation of the interceptors according to the receiving environments during rains in order to limit spills. And to ensure real-time management of a remote-controlled valve system. In other words, everything is done to limit overflows! 

However, this is not enough to eliminate them: the best thing is to reduce them at the source. Natural catchment solutions could be favored more by the City. And what better way to achieve this than green infrastructure, such as parks or rain gardens? At least, theozonation is under intensive construction and this will have a beneficial effect for the river and its users! 

I left this visit to the Montreal wastewater treatment plant with a lot of respect for its employees. Not only for their ability to tolerate the ambient odor, but because they do a very important job, serving of the environment. Far from the spotlight.

You have the power to mitigate the impacts of wastewater on the St. Lawrence River by avoiding using a waste disposal and flushing down the toilet: 
- Hair;
– Tampons, wipes and other sanitary products;
– Leftover cooking oils, sauces, vinaigrettes, in short any food product! You can put them in a container in the freezer, then in the compost;
– Orange cones!

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