Municipal waste water treatment plant in Montreal, Canada Prepared by Guillaume Fournier

Montreal Second biggest city in Canada (1.6 million inhabitants) Home to one of the biggest waste water treatment plant in North America. Montreal being an island, before 1984, all sewage were going straight in surrounding rivers.

Rivière des prairies waste water treatment plant Situated on the extreme eastern part of the island of Montreal. Cleans 95% of Montreal sewage Took from 1976 to 1998 to construct the sewage system and the plant to it’s final form. Cost: billions $ cad (0.87 billions euros) Average flow of waste water coming in the station: cubic meters/day. When raining, it goes up to cubic meters/day.

Map of the sewage system in Montreal

How does the plant works? Pumping Bar screening Sand removal Settling tanks Sludge processing: storing, homogenisation, conditioning, dewatering, incineration

Pumping First operation within the waste water plant. Can pump 88 cubic meter of waste water per second. 17 pumps for a total power of 2500 to 5150 horsepower depending on the flow of waste water. Gets the water to the surface in channels.

Bar screening The water is pumped to 2 channels. Coagulant is added before the screening. Only the biggest residues are stopped in the screens (2.5cm and more). There are 8 bar screens that are 4.6m in height. Mechanical rakes get the sludge out. What happens to the sludge ? See on next slide!

Sludge from bar screening Transported by conveyor to the dewatering processing. Dewatered by 2 drum presses to reduce the volume and humidity of the sludge. Sludge is sent to landfill. 2 tons and a half of sludge is sent everyday.

Sand removal Sand sedimentation in continual chamber trap. 14 channels of 68 meters X 7 meters X 4 meters. Water is slowed down so the sedimentation takes maximum 10 minutes. Sand is pumped to trucks that goes to landfill. 14 tons of sand is pulled out of the water everyday.

Settling tanks 21 rectangular settling tanks (30X90 meters). Floculant is added at the entrance of the tank (FeCl, Alun) to help sedimentation. Water has to sediment during 2 hours to get a good quality Rakes collect the top layer and bottom layer of sludge and push them into pumps. Water is ready to go back into the river; the sludge is sent to the sludge treatment part.

Sludge processing: storing 4 reservoirs of 5000 cubic meters. Air is pumped constantly into the sludge to keep it easier to process. The gases that go out are processed by sodium hypochlorite before behing released into the atmosphere.

Sludge processing: homogenisation and conditioning Sludge is then processed to 5 tanks with agitators to keep it homogenised It is then conditioned with cationic particules that favorise the separation of solid and liquid particules Solid concentration: 3.5%

Sludge processing: dewatering and incineration 10 filter-press gets the water out of the sludge; gets the sludge to about 32% of solid particules. The sludge is now called a ‘cake’. Cakes are principally processed to the 4 incinerator, total capacity of incineration of 400 tons per day. Ashes are dumped into trucks and transported to the landfill. The heat emitted by the incinerator is used to heat the different buildings of the waste water treatment plant.

Sludge processing: overflow of humid cakes ? 2 silos of 250 tons can process the overflow of humid cakes in case of huge melts of snow or big rains. They can be then processed to 2 other drying unit that can make the cakes up to 92% of solids.

Performance In Canada, there are no regulations of the BOD / COD of treated water. Still, in 2006, the BOD and COD were reduced of 40% in average. Fecal matters reduced by 48%. Respects 100% of all MAMR norms (Quebec Minister of Municipals Affairs)

Impact on the environment Before 1986, more then 500 metric tonnes of dry sludge were thrown directly in the surrounding rivers per day. Nowadays, less then 50 tonnes per day. Before the plant, more then 5.6 tonnes of phosphorus per day were going directly in the rivers. Now it is less then 1.3 tonnes per day. Regeneration of St-Lawrence River and Rivière des Prairies from a completely polluted state to being able to swim in the water without any dangers. PICTURE TIME!

Pumping station

Residues of the mechanical screening

Sand removal

Settling tank

Filter-press

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