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​The Rossdale Water Treatment Plant has been in operation in Edmonton since 1903. The current plant was built in 1947 and expanded in 1956.

Infrastructure

  • Maximum capacity: 280 ML/d
  • Rossdale reservoirs hold 100 ML
  • UV disinfection

Process

The water treatment process includes coagulation, flocculation, and filtration and uses free chlorine, chloramine, and UV light for disinfection.

Intakes

The intake structures for the water treatment plant are located in the deepest part of the North Saskatchewan River, near the lowlift pump station. They are situated below the water surface so oil and floating debris pass over them.

Screens

Screens are located just before the lowlift pumps to strain out debris which may enter the intake pipe. The screens are designed with small holes which keep out fish, sticks, and leaves. The screens are rotated and periodically cleaned using back-wash water to return debris to the river.

Lowlift Pumps

The lowlift pumps get their name because they pump at a high volume but at “low” pressure. The lowlift pump are approximately 1,000 horsepower and pump at a rate of 20 – 200 millions of litres per day (MLD).

Chemical Injection

Alum and powdered activated carbon are the first chemicals added to the water. These chemicals are added by feed pumps which are adjustable to supply the correct dosages.

Rapid Mix

When the chemicals are added, it is necessary to mix them thoroughly with the water. High intensity mixing is done at the lowlift pump station or mixing chamber.

Flocculation

Following rapid mix, polymer is added and the water is then slowly mixed to encourage the formation of floc. Floc (large jelly-like particles) results from the attraction of dirt particles to the chemicals alum and polymer. The floc later settles out of the water by gravity.

Sedimentation

After the floc is formed, it is then allowed to settle to the bottom of a clarifying basin. This is the process of sedimentation. Once the dirt-laden floc settles to the bottom of the basin, sludge is removed and the clear water is decanted from the surface.

Disinfection

Free chlorine (0.8 % Sodium Hypochlorite) is added after clarification to kill harmful bacteria and other microbes. After filtration, the water passes through ultraviolet (UV) disinfection that renders the microorganisms harmless. Ammonia is then added and combines with chlorine to form a long-lasting disinfectant called monochloramine.

Filtration

The water is filtered by allowing it to slowly flow down through a layer of anthracite coal (about 50 cm) and a layer of sand (about 30 cm). The filters are regularly cleaned by pumping air and water back up through the sand and anthracite coal to dislodge any accumulated particles.

On-site Reservoirs

After filtration, the water goes into on-site reservoirs where it is stored until required. The reservoirs provide additional time for disinfection and also allows the treatment plant to handle variations in water demand throughout the day.

Highlift Pumps

Highlift pumps get their name because they are required to pump water at “high” pressure. These pumps are each 2,000 to 4,000 horsepower and pump 90 – 200 MLD at a pressure of about 150 pounds per square inch (psi).

Expansions and upgrades

  • 1947: Plant #1 was constructed
  • 1956: Plant #2 opened; designed for 250,000 people
  • 1981-89: Plant was refurbished
  • 2003: UV disinfection operational