Montreal finally ready to go ahead with ozonation plant to treat waste water

Ozonating will help eliminate the viruses, bacteria and pharmaceutical residue that get flushed into the St. Lawrence River. But one engineer involved in the project's earlier phases says ozonation is putting "the cart before the horse."

City says it’s worked out kinks in 10-year-old plan and is ready to build

Sylvain Ouellet, the city councillor responsible for water, has been overseeing the ozonation plant project. (Verity Stevenson/CBC)

The City of Montreal says it's finally ready to move onto the next step of its waste-water treatment project: building the actual plant. 

Former mayor Gérald Tremblay first announced the city would disinfect its waste water using ozone gas in 2008. 

Ozonation helps eliminate the viruses, bacteria and pharmaceutical residue that get flushed into the St. Lawrence River every day.

Unlike most North American cities, Montreal doesn't disinfect its waste water. It only removes solids and some particulates with the use for chemical coagulants. 

The ozonation plant, once completed, is expected to be the largest of its kind in the world, but so far it's hit snag after snag, and some scientists warn it won't be enough to meet new environmental standards that go into effect in 2030.

It was supposed to be up and running by 2018, until engineers discovered a serious design flaw two years ago that has only recently been resolved. 

The problem was with the design of the canals that carry the water to the river, which could have allowed some of the ozone to escape into the air. 

The canals will have to be reconfigured to fix the problem. 

Holes have been dug next to Montreal's Jean-R. Marcotte wastewater treatment plant, where the new ozonation plant will be built. (Verity Stevenson/CBC)

Now that a solution has been found, the city says it will launch a call for tenders within the next year.  The plant could be ready in 2023. 

Sylvain Ouellet, the city councillor responsible for water, says most of the technology needed to make the ozone gas and inject it into the water has already been built and paid for. 

The total cost of the project is now estimated at $500 million — up from the $400 million the city said it would cost last year. 

"The initial estimations, you know, lots of times, it's far from the end," Ouellet said, pointing to the project's initial $210 million price tag. 

The latest increase, Ouellet said, is due to the technical issue that's now been resolved.

The machines that will produce the ozone gas at the new plant are being built in the United States. (Submitted by the City of Montreal)

The plant will be built next to the Jean-R. Marcotte waste-water treatment plant in the Rivière-des-Prairies–Pointe-aux-Trembles borough. The treatment plant is the city's only waste-water system, processing up to 7.6 million cubic metres of water a day, the equivalent of the volume of three Olympic Stadiums.

Large holes have already been dug next to the canals carrying the water to the river, where the plant will be built. The city will also have to build oxygen-generators because pure oxygen is needed to make ozone. 

More costly improvements ahead

Inside Jean-R. Marcotte, engineers have built a miniature version of the ozonation plant scientists will use to test the technology. 

"For the fish and also for the people who swim or boat on the St. Lawrence River, it will be a huge [improvement] for the environment," Ouellet said. 

"It will be the biggest step forward since the opening of this station."

Montreal's new ozonation plant will look something like this once it's completed in about four years. (City of Montreal)

But the treatment won't be enough for Montreal's waste water to meet upcoming federal and provincial standards, taking effect in 2030. 

The biological treatment needed to meet that standard could cost the city up to $1.5 billion. Ouellet said the city is conducting a feasibility study but dismissed the idea it would be needed anytime soon. 

City 'putting cart before the horse,' says expert

But Ronald Gehr, an engineering professor at McGill University specializing in waste-water management, believes the biological treatment is what the city should have prioritized over ozonation. 

"To only later build a biological treatment plant is really putting the cart before the horse, in terms of time," Gehr said. 

That treatment, Gehr said, would eliminate a lot of organic material that is bad for the river and simplify the ozonation process and allow the city to meet the new environmental standards.

Ouellet says the city is moving ahead with ozonation because it determined it to be the most efficient way to disinfect the water.


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