The City of Montréal operates seven water treatment plants that serve a total of approximately two million people. One of the plants, the Atwater Water Plant, is among the largest plants in Canada. Housed within several heritage buildings that were constructed between 1912 and 1918, the plant treats approximately 1,500 ML/d of water drawn from the St. Lawrence River and is the most important facility in the city’s treatment network. In 2011, four of the plant’s filtration galleries were converted to an ozone contact basin but the system failed to start up due to a pressure problem discovered during testing. Testing also revealed a problem with hydraulic flow and the potential for ozone gas to escape from the basin into the rest of the plant. The CIMA+ design team analyzed three categories of solutions—hydraulic changes upstream of the contact chambers to reduce water-level fluctuation, modifications to the contact basins, and the addition of ozone destructor equipment—with inputs from physical, digital and hydraulic modelling.
Following the analysis, the team completed a multidisciplinary preliminary study to evaluate the hydraulics, layout and constructability of a new balance chamber upstream of the four ozone contact basins. This chamber will optimize hydraulic flow, thereby reducing pressure losses caused by the start-up of the raw-water pumps. To validate the design, all dimensions, levels and behaviour of the structures under transient conditions were modelled in 3D.
A first among water treatment plants in Québec
The balance chamber is the first of its kind in Québec plants, and the 3D modelling of the layout of the modified treatment train , which required cloud-based computing, was the first instance of this type of testing using StarCCM.
Maintaining an uninterrupted supply of water throughout the improvements
The Atwater Filtration Plant is a critical component of Montréal’s water treatment system, including as a backup supply of drinking water in the event of an incident at another plant. In order to maintain the production of drinking water at all times during the improvements at the plant, the pumped water discharge pipes can be diverted into an abandoned canal, enabling the ozone basins to be bypassed if required.