Montreal, known as the last major city in North America to implement wastewater treatment, is taking significant steps to enhance its reputation by investing $360 million in wastewater treatment upgrades. These upgrades include the installation of an ozone wastewater disinfection process at the J.-R.-Marcotte wastewater treatment plant.

Last March, Pomerleau secured a $93.2-million contract to initiate the ozone project, which will be implemented in phases with intermittent shutdowns. While the plant will remain operational throughout the process, its treatment capacity will be temporarily reduced for two six-month periods. The first period is scheduled from November 1st, of this year to April 30, 2023.

During the period of reduced treatment capacity, the team aims to minimize wastewater overflows, anticipating that overflows into waterways will occur primarily during significant rain or snowmelt events. Their goal is to mitigate such overflows as much as possible.

According to City of Montreal spokesperson Hugo Bourgoin, project coordination is expected to be the primary challenge. The success of the project will also depend on luck. Bourgoin stated that the main difficulty lies in coordinating the work within the channels while ensuring the continuous operation of the wastewater treatment plant. To accomplish this, each of the two channels of the station will need to be isolated and emptied for the installation of new siphons.

The second channel is scheduled to be closed from November 2023 until April 2024.

Montreal’s wastewater treatment system was given a grade of F-minus by the Sierra Club in 2004, according to a water advocacy website from McGill University. Currently, the Marcotte plant only performs primary treatment of sewage, which removes solids and some nutrients but fails to eliminate bacteria, viruses, pharmaceuticals, heavy metals, and other contaminants.

According to McGill advocates, ozonation is a water disinfection method that utilizes ozone, an oxidizer. It is believed to be effective in eliminating bacteria and viruses present in wastewater, as well as reducing the concentration of pharmaceuticals and industrial chemicals in the water.

According to the City of Montreal, implementing ozone disinfection at the Marcotte plant will result in the removal of nearly 100% of viruses and bacteria, as well as a reduction of 75% to 85% in pharmaceutical residues from the treated water. As the largest plant of its kind in North America, it plays a crucial role in treating 45% of the province’s domestic water supply.

Maja Vodanovic, head of water on the City of Montreal’s executive committee, expressed that this long-awaited project has been highly anticipated by environmental groups and individuals who care about the well-being of the St. Lawrence wildlife. The selection of the two crucial closure periods aims to minimize potential overflows’ impact on the environment, recreational activities, and infrastructure projects, according to the city’s statement.

Bourgoin emphasized that the discharged water will be significantly diluted, particularly during periods of heavy rain. The city has reassured that a repeat of the “Flushgate” incident in 2015, where eight billion liters of untreated sewage were released into the river during sewer main repairs, will not be possible.

The implementation of a real-time control system at the station will enable the prioritization of overflow sites to minimize their impact. The initial phase of the project focuses on ensuring the water tightness of the discharge channels, facilitating effective ozone contact with wastewater. To maintain the station’s operations during the main channel work, a temporary bypass channel will be constructed.

In addition to the ozonation unit, the system comprises an oxygen production unit and an existing electrical substation specifically constructed for the disinfection project.