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Montreal aims to minimize overflows during Marcotte wastewater project

Don Wall
Montreal aims to minimize overflows during Marcotte wastewater project
CITY OF MONTREAL - Pomerleau will be installing an ozone disinfection system at Montreal’s huge J.-R.-Marcotte wastewater treatment plant.

Montreal, which was the last major city in North America to begin treating its wastewater, will boost its reputation with the launch of $360 million in wastewater treatment upgrades including work to install an ozone wastewater disinfection process at its J.-R.-Marcotte wastewater treatment plant.

Pomerleau was awarded a contract of $93.2-million last March to kick off the ozone project.

Work will get underway in phases with various shutdowns required. The plant will remain operational at all times, but its treatment capacity will have to be reduced for two periods of six months, the first from the first day of this November to April 30, 2023.

The team is hoping to minimize wastewater overflows during the period of capacity slowdown, with overflows to waterways anticipated only during major rain or snowmelt events.

City of Montreal spokesperson Hugo Bourgoin said project co-ordination looks to be the main difficulty. Luck will be part of the equation.

“The main challenge related to the realization of this project is to co-ordinate the work in the portion of the channels while keeping the mission of the wastewater treatment plant in operation throughout the duration,” said Bourgoin. “To achieve this, each of the two channels of the station will have to be isolated and emptied to carry out the work to install new siphons.”

The second channel will be closed from November 2023 to April 2024.

A McGill University water advocacy website chronicled Montreal’s record on treatment of wastewater. The Marcotte plant currently only carries out primary treatment of sewage, removing solids and some nutrients but leaving behind bacteria, viruses, pharmaceuticals, heavy metals and other contaminants. In 2004, the Sierra Club gave Montreal’s water treatment system a grade of F-minus.

Ozonation uses ozone, an oxidizer, to disinfect water, the McGill advocates explained.

It is believed to effectively destroy bacteria and viruses in wastewater and reduce the amount of pharmaceuticals and industrial chemicals left in the water.

The City of Montreal said ozone disinfection of water leaving the Marcotte plant will reduce nearly 100 per cent of viruses and bacteria and 75 per cent to 85 per cent of pharmaceutical residues.

The plant, the largest of its kind in North America, treats 45 per cent the province’s domestic water supply.

“This project has been awaited for years by environmental groups and by all those concerned about the health of the wildlife of the St. Lawrence,” stated Maja Vodanovic, head of water on the City of Montreal’s executive committee.

The two critical periods of closure were chosen to minimize the possible effect of overflows on the aquatic ecology with regard to the environment, recreational activities and various works of infrastructure, the city said.

“It is also important to emphasize that the water that will be discharged will be greatly diluted especially if it will occur in times of heavy rain,” said Bourgoin.

The city has stated that a reoccurrence of 2015’s “Flushgate,” when eight billion litres of untreated sewage were dumped into the river during repairs to a sewer main, would not be possible.

A real-time control system at the station will make it possible to prioritize the sites of overflows to the places where the impacts will be least felt.

The first phase of the work consists of ensuring that the discharge channels of the station are watertight to ensure efficient contact of ozone with wastewater.

To allow the station to continue to operate during the work on the main channel, a temporary bypass channel will be built.

Besides the ozonation unit, other components include an oxygen production unit and an electrical substation that is already built for the disinfection project.

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