Ozone disinfection: Construction at the Jean-R.-Marcotte water treatment station

Last updated May 27, 2022
Reading time: 2 min

Soon, it will be possible to eliminate almost all viruses, bacteria and pharmaceutical products from wastewater treated at the Jean-R.-Marcotte treatment station. Learn more about the largest ozonation unit in the world that is being built.

All about the work site

Work at the Jean-R.-Marcotte is being done so that wastewater can be treated by ozonation, a procedure that consists of injecting ozone at the end of the treatment process.

Ozonation is a very advantageous solution from an environmental perspective. A number of elements must be implemented to use this technology. Work will be completed in several steps in order for ozonation to be implemented in 2025.


Phase 1: April 2022 to December 2024

  • April to November 2022 - Work on the bypass duct
  • November 2022 to April 2023 - Work on duct 1
  • November 2023 to April 2024 - Work on duct 2

Phase 1: Construction in evacuation channels

The first phase of construction consists of hermetically sealing the station’s evacuation channels to make sure the ozone’s contact with wastewater is safe, efficient and effective. 

A temporary bypass channel will be built so that the station can continue operating through the main channel during construction. 

Future phases will include buildings and structures to complete the project.

Wastewater treatment during construction

The treatment capacity of this station will be reduced during two six-month periods between November 2022 and April 2023 as well as between November 2023 and April 2024. On sunny days, the station can process wastewater normally. However, runoff is inevitable during heavy rains or when snow melts. The station’s treatment capacity will be reduced during two six-month periods between November 2022 and April 2023 as well as between November 2023 and April 2024.

To measure runoff and control its impact, we conducted a study using statistics from the past 10 years. The study estimates that the volume of water that could be discharged into the St. Lawrence would be six times weaker per hour than during the construction that took place in 2015. Moreover, the runoff would mainly be composed of rainwater and mixed with a portion of wastewater. 

As well, the treatment station has an integrated control system to prioritize runoff sites. When flooding occurs, water will be directed to the areas of the river that are the least likely to affect human and aquatic health.

The Jean-R.-Marcotte station

The Jean-R.-Marcotte treatment station is the third largest in the world. 

It treats 45 per cent of Québec’s wastewater, which represents an average of 2.3 cubic metres per day  —  more than an Olympic stadium each day. 

It operates 24 hours a day and 350 employees keep it running smoothly.

Presentation project letter