WC141 MarApr 2025 - Magazine - Page 16
“By having the gases go through that oven, we basically
decompose all the ozone to oxygen so that we don’t have
any ozone emitted to the atmosphere.”
Overview of building structure evolution on Lot 3.
for treating such large volumes of wastewater, and extremely
costly to maintain. Instead, chemists on staff determined that
ozonation, a process where ozone gas is generated from oxygen
and then deployed on-site to disinfect the plant’s outflow, could
disinfect the bacteria, viruses and other microorganisms. “To
me, they were visionaries at the time because they had to fight
the Ministry of Environment in Québec to have this technology
chosen over the UV lamps,” Paoloni said.
More recent evidence has shown that ozone also destroys a
considerable percentage of synthetic contaminants found in
industrial wastes, pesticides, and household pharmaceutical
and personal care products. In 2008, following an extensive
cost-benefit analysis that included anticipated maintenance and
capital expenditures, the City formally settled on ozonation and
approached the provincial and federal governments to share in
the funding. In 2011, the three levels of government announced
an agreement, but it took more than a decade to get shovels in
the ground. Designers initially wanted to go live by 2018 but
soon realized that receiving canals would need considerable
reconfiguration, so they briefly paused the project.
In 2020, with plans refreshed, the City issued tenders but
landed just a single bid that proved complicated, procedurally
fraught and didn’t meet the project’s full needs, so the City
divided the project into nine separate lots and retendered. “By
doing that, we were able to increase the market interest and
competition for the project bids by permitting more construction firms in the province of Québec, which were smaller but
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WATER C AN ADA • M ARCH/APRIL 2025
did not have the financial means, to bid on
the whole project,” Paoloni said.
With work now well underway and full
start-up anticipated by 2028, the Jean-R.Marcotte plant will have 10 ozone generators able to generate up to 57 metric tonnes
of ozone daily. Paoloni said that capacity
stands to make it the world’s largest ozonation plant for disinfecting municipal wastewater, second only to the ozone system for
the Eastern Treatment Plant in Melbourne,
Australia.
Thus far, Montréal crews have fully modified the plant’s waterway infrastructure
(Lot 1), built the foundations and underground networks (Lot 2), and constructed
buildings to house the ozonation and
related equipment (Lot 3).
During construction, the plant has,
by necessity, remained online, with the
ozonation facility effectively added on
and crews working on existing wastewater
canals that were feeding active wells. “It
was very challenging,” Paoloni said. To facilitate construction,
crews modified one canal at a time, diverted wastewater from
one to the other during heavy rainfalls, and reduced the plant’s
peak treatment capacity to 5.2 million cubic metres daily
during two six-month periods, from November through April
in consecutive years, when leisure activity on the St. Lawrence
is relatively low.
With Lots 1 to 3 completed, the focus is now on the
equipment the buildings will house. The City recently issued
contracts for the ozonation system itself, with Lots 4 and 5
including ventilation, electrical instrumentation, and mechanical piping for the buildings that will house the cooling systems
and ozone generators.
Also on tap, as Lot 6, is a destructor building that will
house equipment that will destroy all residual ozone found
in the injection vapour space of the sealing chambers. “Rates
at the plant can vary from 15 to 40 cubic metres per second
during the day,” Paoloni said. “And if we have big rainfalls, it
can go up to 80 or 85. The beauty of our equipment is that
we can prorate it and modulate it to our needs.” This is where
the destructors fit in. “It’s basically a blower that sucks all the
gases out of the vapour space where it’s injected, and goes
through an oven,” Paoloni said, describing an electric-powered
oven that heats a trench to 350 degrees Celsius. “By having
the gases go through that oven, we basically decompose all the
ozone to oxygen so that we don’t have any ozone emitted to
the atmosphere.”
Lot 7 appears anticlimactic compared with the plant’s
WAT E R C A N A D A . N E T
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