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The first step in treating wastewater is screening, where large items like wood, rags, and plastics are removed from the water.

There are two fine screens with 6 mm holes, each placed in a 2-meter-wide channel. These catch the debris, which is then washed, compacted, and sent to a disposal bin.

A third channel has a manual coarse screen for backup, and a fourth channel with an overflow weir is used only in emergencies to bypass the main screens.

The second step in preliminary treatment is grit removal. In this stage, heavier materials like sand and gravel settle to the bottom, while lighter organic matter stays in the water and moves on to the next step.

This system includes two vortex grit tanks, each with a paddle mixer and a slurry pump. The settled grit is pumped into two grit classifiers, which remove the water from the slurry and send the dry grit to disposal bins.

Right after the grit tanks, a chemical called ferric chloride is added to the wastewater. This helps remove phosphorus and suspended solids more effectively.

The system includes two storage tanks and two feed pumps that add the chemical based on the flow of the water.

After screening, grit removal, and chemical addition, the wastewater flows into a channel that splits into two parshall flumes, which measure the flow.

From there, the flow is divided into a main channel that feeds four identical primary clarifiers. Air is added to the incoming channel using centrifugal blowers to prevent solids from settling too early.

The primary treatment system includes four primary clarifiers. In these tanks, heavier organic materials settle to the bottom by gravity, forming a sludge blanket.

Collector flights move the sludge to a hopper at the end of each tank. At the same time, surface skimmers remove floating scum and grease near the surface.

Both the settled sludge and the removed scum are then pumped to digestion facilities for further treatment.

After primary treatment, wastewater is pumped through the Primary Effluent Pumping Station (PEPS) to the Biological Aerated Filter (BAF).

An alkalinity solution is added after pumping to help maintain proper pH for treatment. The BAF has six filter cells filled with two types of media—polystyrene beads and plastic disks—that support microorganisms and help filter solids.

Air is added to help these microorganisms grow. They remove organic matter, ammonia, and phosphorus from the water as it moves upward through the filters.

The biological filters need regular backwashing to clean off excess biomass. The backwash water is stored temporarily in two tanks.

The facility can either add this backwash water back to the primary inlet or send it to two gravity thickeners. Alum is added to help solids settle in the thickeners.

The settled solids are pumped to a sludge thickening facility, which uses holding tanks, rotating drum thickeners, and a polymer system to concentrate the solids before sending them to the primary digester.

The clear liquid from this process is returned to the primary inlet channel.

After the BAF, the water flows through a parshall flume to measure the flow before entering the chlorine contact tanks.

A chlorine gas system adds chlorine for disinfection. It includes two sets of chlorinators that dose the water to ensure the water is properly disinfected.

Two chlorine contact tanks provide enough time for the chlorine to work before the water moves on.

Before the treated water is released into Lake Ontario, chlorine is removed using a dechlorination system with calcium thiosulphate.

The system includes one storage tank and two metering pumps that add the chemical right after the final flow meter in the outfall chamber.

After dechlorination, the treated water is released into Lake Ontario through two outfall pipes, one 1500 mm and one 900 mm in diameter.

At the end of each pipe, 17 diffusers spread the water 25 meters offshore and 16 meters below the surface.

Raw sludge, grease, scum, and thickened backwash residuals are pumped to the primary digester throughout the day.

The digestion facility has two anaerobic digesters with shared gas systems, a sludge holding tank, pumps, and a heat exchanger.

The digesters mix sludge and gas to break down waste, producing methane-rich gas and biosolids.

The methane gas fuels the boiler, which provides heat for digestion and the facility’s buildings.

The biosolids are dewatered and, when conditions allow, used as fertilizer and soil conditioner on farms.

Liquid biosolids are pumped into centrifuges where polymer is added to help solids stick together.

The centrifuge separates solids (called cake) from liquid (called centrate).

The cake, about 24% solids, is stored, while the centrate is returned to the start of treatment.