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Wastewater Treatment Plant 

The Wastewater Treatment Plant protects the people, property, and environment downstream from Saskatoon along the South Saskatchewan River. The Plant is designated as a Class 4 treatment facility, the highest level of certification in Canada. The treatment of wastewater is regulated by provincial and national criteria.

Plant History

The Wastewater Treatment Plant in Saskatoon was built in 1971. Since that time, the Plant has had numerous improvements and expansions to meet new environmental laws and serve the growing population of Saskatoon.

The first major expansion of the facility was in 1991 when the Plant was upgraded from a primary treatment facility to an enhanced primary treatment facility. This upgrade included:

  • The addition of chemicals to reduce the levels of biochemical oxygen demand, phosphorus and solids entering the river;
  • two additional Primary Settling Basins;
  • one additional Digester;
  • improved chemical feed equipment;
  • an additional boiler; an expanded laboratory and maintenance facility;
  • and deep storage and drying bed cells at the Biosolids storage site.

In 1996, Secondary Treatment facilities costing $52 million were added. The new Biological Nutrient Removal (BNR) process further reduces the levels of phosphorus, nitrogen, and dissolved organic matter in the effluent discharge to the river. With the BNR process, the addition of chemicals for secondary treatment is no longer necessary. Saskatoon was one of the first cities in Canada to use this process.

An additional pipeline from the Digesters to the Biosolids Handling Facility north of the City was added in 2005.  The Grit and Screen Facility upgrade was completed in November 2008. An Ultraviolet Disinfection facility was completed in November 2009, which eliminated the use of chlorine in the treatment process.  The nutrient recovery facility was added in 2013.

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The Wastewater Treatment Plant Today

 Wastewater Treatment Plant

Grit and Screen Facility
The Grit and Screen Facility is where sewage first enters the plant.   The wastewater first passes through bar screens to remove any material (rags) larger than 12.5 mm in size.  The rags are then washed, shredded and dewatered.  The wastewater then passes through a centrifical grit removal process.  The grit is washed and dewatered.  The rags and grit is then transported to the landfill for proper disposal.  The wastewater then flows by gravity to the Primary Sedimentation Basins.

Primary Sedimentation Basins
This is where suspended solids settle out and floating scum is removed for further treatment. Upon entering the Primary Sedimentation Basins, the velocity of the wastewater is reduced to 0.3 metres per minute, allowing fine particles to settle to the bottom. Settled sludge on the bottom of the basins is continuously scraped into hoppers at the end of tanks. It takes about 4 hours for wastewater to flow through the Primary Sedimentation Basins. Upon completion, the primary effluent is pumped to the Bioreactors and the settled sludge is pumped to the Fermenters or Digesters. The scum from the top of the basins is collected in hoppers and pumped to the Digesters.

Pump Station
The Primary Effluent Pump (PEP) Station pumps primary effluent from the Primary Sedimentation Basins to the Bioreactors.

The Fermenters are where the primary sludge that settled out from the Primary Sedimentation Basins is processed. Fermentation converts the organic material into Volatile Fatty Acids (VFA's). An example of a VFA is acetic acid or vinegar. The VFA's are sent to the Bioreactors and utilized by the nutrient consuming micro-organisms.

The two Bioreactors are where the Biological Nutrient Removal (BNR) process takes place. This natural process greatly reduces the concentration of dissolved organic compounds in the effluent and removes unwanted carbon, phosphorus, and nitrogen from the wastewater without the addition of chemicals. In the Bioreactor, the effluent from the Primary Sedimentation Basins is mixed with micro-organisms and Volatile Fatty Acids (VFA's). The micro-organisms come from the secondary clarifiers (see below), where they have settled out and are then returned to the Bioreactors. The VFA's are created in the Fermenter (see above). The micro-organisms naturally break down excess carbon and nutrients present in the wastewater. The effluent is moved through carefully controlled anaerobic (absence of available oxygen), anoxic (chemically available oxygen only), and aerobic (abundance of free oxygen) zones of the Bioreactors. Each of these areas remove specific organic compounds as the micro-organisms continue to grow and flourish, consuming impurities in the wastewater. After approximately 9 hours in the Bioreactors, the effluent flows to the Secondary Clarifiers.

Secondary Clarifiers
The Secondary Clarifiers are where any remaining solids along with the micro-organisms from the Bioreactors settle to the bottom and the clear effluent flows out the top of the basins. Of the settled micro-organisms, about 90% are returned to the Bioreactors to be used again in the BNR process and 10% are sent to the DAF Thickener and then to the Digesters for further solids treatment. The clarified final effluent flows from the Secondary Clarifiers to the Ultraviolet Disinfection Facility before being released to the river.

Ultraviolet Disinfection System
The wastewater passes around high output UV lamps, where the light is absorbed by and disrupts the molecular structure of DNA molecules in the micro-organisms. This renders the cells unable to replicate before they die. The disinfection stage takes seconds, with the final effluent then passing over a weir through an outlet channel and into the river.

DAF Thickener
The Dissolved Air Flotation (DAF) Thickener is where air is introduced to the waste solids from the Secondary Clarifiers and the Bioreactors. This causes the solids to collect at the surface much thicker than when they were introduced. The thickened solids are then scraped from the surface of the DAF Thickener and pumped to the Digesters.

Three large Digesters are where solids from the Primary Sedimentation Basin, Fermenters and DAF Thickener are further broken down by micro-organisms into gases and biosolids.  The tanks are routinely mixed and maintained at a temperature of 35ºC. The Digesters are also completely sealed in an oxygen-free atmosphere. These carefully monitored conditions help the bacteria break down the sludge into methane, CO2, and stabilized digested sludge over a period of twenty days. One of the by-products from the process, methane gas, is recycled as fuel for the boilers that heat the plant and the Digesters. After twenty days, the digested sludge is pumped through a 200mm diameter pipeline 12 kilometres north of Saskatoon into gravity settling ponds where it is thickened and stored. Twice a year, in the summer and fall, the Biosolids are pumped out and spread on farmland using a technique called Liquid Injection.

WASSTRIP and Nutrient Recovery Facility
The nutrient recovery facility is a side stage process which produces a high grade slow release granular fertilizer.  The settled micro-organisms from the secondary clarifiers are intercepted prior to them entering the DAF (Dissolved Air Flotation) Thickener.  They are held in a WASSTRIP  reactor; an anaerobic (no Oxygen available) environment for approximately 20 hours.  This allows them to release some of their stored Phosphorus and Magnesium into the solution.  In the DAF Thickener, the water removed from the thickening process is now rich in nutrients. The water is blended with Ammonia rich supernatant from the sludge settling ponds prior to being introduced into the Ostara Pearl Reactor.  The reactor is a fluidized bed upflow reactor where the soluable nutrients form together to produce a mineral called Struvite (Magnesium Ammonium Phosphate).  This mineral is a highly valuable fertilizer used in greenhouse and turf industries.  This process reduces the overall nutrient load of the treatment plant, which increases reliability, capacity, and the final effluent quality.

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Control Room
The Control Room is where Plant Operators monitor all aspects of the wastewater treatment process and lift station operation 24 hours a day, 365 days a year. Numerous electronic controls, monitoring devices, and computers are used to continuously ensure the proper operation of the plant and quality of effluent being discharged to the South Saskatchewan River.

Utility Building
The Utility Building contains additional low pressure boilers, associated heating equipment, airblowers for the bioreactors, standby generators, and an equipment storage area.

Heating Building
The Heating Building is where maintenance on plant equipment is performed and tools are stored. The Heating Building also houses low pressure boilers, heat exchangers, pumps and other equipment required to maintain the process.


Wastewater Treatment Plant            Yes      975-2541  Yes  Public 
Service Name: Wastewater Treatment Plant
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