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.
The 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 larger than 12.5 mm in size. This material is then washed, shredded and dewatered. The wastewater then passes through a centrifical grit removal process. The grit is washed and dewatered. The material 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.
Fermenters
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.
Bioreactor
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.
What is Biological Nutrient Removal (BNR)?
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.
Digester
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, or biogas, 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.
Biogas and Biosolids
What is Biogas?
Biogas is a by-product created during the digestion of solids removed in the wastewater treatment process. Digestion of the solids occur in three digesters. These biogases are composed of approximately 65 percent methane, 35 percent carbon dioxide and trace amounts of hydrogen sulphide. At the Saskatoon Wastewater Treatment Plant the biogas is captured and used as a fuel for the boilers to heat the many buildings and the digesters on site.
By using the energy from biogas, the Wastewater Treatment Plant saves approximately $300,000 a year in heating costs and reduces greenhouse gas emissions.
There are several wastewater treatment plants in North America that are using the biogas produced in their treatment process to generate electricity by powering small turbines. The use of biogas for electrical generation is being investigated at the Saskatoon Wastewater Treatment Plant as part of the City of Saskatoon's ongoing environmental commitment.
What happens to the Biosolids?
After 20 days in the digesters (the final stage of the treatment process for solids), the biosolids, as they are now called, are pumped twelve kilometres north of Saskatoon via two pipelines. The biosolids are then stored in asphalt-lined storage cells. Each spring and fall these cells are pumped out, and the biosolids are spread on nearby farmer's fields by a process called liquid injection.
Biosolids and Agriculture
The treatment process at the Wastewater Treatment Plant removes the dangerous pathogens in the solids. The biosolids that are left over are an excellent soil conditioner and fertilizer. Using digested sludge as a soil conditioner adds nutrients back into the soil as well as aiding in moisture retention.
Liquid Injection
The solids are removed from the deep storage cells by first mixing the sludge, and then pumping it through a pipeline and injecting it directly into the land. The sludge is injected at a depth of 0 - 10 centimeters depending on soil conditions and the density of the biosolids.
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.
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.
Treatment Process
Every time you flush the toilet, take a shower or wash the dishes, you send wastewater down the drain to an underground network of pipes. These pipes, through a series of pumping lift stations, carry the wastewater to the Wastewater Treatment Plant located on Whiteswan Drive. The raw sewage that arrives at the Plant goes through an extensive treatment process to ensure that when it re-enters the South Saskatchewan River, it is safe for people living downstream and for the environment.
Step One
The first step for the raw sewage when it reaches the Wastewater Treatment Plant is the removal of heavy particles from the liquid. This happens in the Grit and Screen Building. Here, the sewage passes through a screen system to remove any material greater that 12.5 mm in size. The wastewater then passes through a centrifical grit removal system. The materials are removed and transported to the landfill.
Step Two
The wastewater then travels to the Primary Sedimentation Basins where its speed is reduced. This allows fine particles to settle. The settling process divides the materials into settled material at the bottom of the basins, called sludge, and wastewater.
The sludge is moved to hoppers at the ends of the tanks by scrapers and is sent to the Fermenters (large, closed tanks with mixing mechanisms), or to the Digesters. At the Fermenters, Volatile Fatty Acids (VFAs) are created through fermentation (a biological process that breaks down organic matter). These VFAs are then used in the next stage of treatment. Small amounts of fermenter sludge is periodically wasted to the Digesters to ensure the continued success of the fermentation process.
As the wastewater leaves these basins, any floating grease or scum is skimmed from its surface and sent to the Digesters. The wastewater, now called primary effluent, is pumped to the Bioreactors.
Step Three
The bioreactors are a state-of-the-art Biological Nutrient Removal (BNR) facility. The wastewater is treated by using micro-organisms instead of traditional chemical methods to break down the unsettled particles and nutrients. The micro-organisms do this by using the nutrients in the wastewater as a food source. VFAs created by the fermenters are used in this process by some of the micro-organisms. The process of BNR is environmentally friendly and helps ensure a cleaner, more natural final product.
Step Four
After nine hours in the Bioreactors, the effluent flows by gravity to the Secondary Clarifiers. Here the micro-organisms in the wastewater settle to the bottom and are returned to the Bioreactors.
Step Five
The clear effluent from the Secondary Clarifiers flows through the UV Disinfection system. Finally the treated effluent flows over a weir and into the South Saskatchewan River.
Step Six
The sludge and/or scum removed from the Primary Sedimentation Basins, Fermenters, Bioreactors and Secondary Clarifiers will remain in the Digester at 35 degrees Celsius for approximately 20 days. Because there is no oxygen present in the Digesters, it is an anaerobic process and the bacteria produce methane and carbon dioxide as they break down the sludge. The methane is used as a fuel for the boilers in the Heating Building that heat the Wastewater Treatment Plant.
Step Seven
Stabilized sludge, the end product from the digestion process, is pumped 12 kilometres north of the Plant and is stored in deep ponds. Twice a year the sludge is pumped out and applied to farmers' fields by a process called liquid injection. The sludge is an excellent soil conditioner adding nutrients and moisture.
The treatment plant also implemented the first full scale nutrient recovery facility in Canada. It produces a high-grade granular fertilizer product from the sludge effluent.
Highly trained Plant operators in the control room closely monitor all aspects of the Wastewater Treatment Plant, twenty-four hours a day, seven days a week. The on-site laboratory continuously tests the processes to ensure that the effluent going back into the river meets or exceeds environmental criteria.
Discharge Quality
Through a Permit to Operate, Saskatchewan Environment regulates the levels of discharges from the plant because of the potential impact to the river. Monthly effluent quality reports are provided to both Saskatchewan Environment and Environment Canada.
In order to ensure that the process is working properly, technologists take over 7500 samples per year. The laboratory performs a variety of analytical tests, which are based on Standard Methods for the Examination of Water and Wastewater, along with the recommended quality control and quality assurance tests.
By keeping abreast of new technology and trends in the wastewater industry, the City of Saskatoon's Wastewater Treatment Plant will continue to provide an essential service for the citizens of Saskatoon and to protect the environment upon which we all depend
Frequently Asked Questions
Why is there an odour from the Wastewater Treatment Plant and why is it worse some times of the year?
Odours from the Plant are produced as organic matter in the wastewater is broken down by micro-organisms. Odours may be worse at some times of year when cleaning or maintenance is being performed in certain areas of the Plant. There is also a greater potential for odours in the late summer. Not only is the wastewater temperature warmest during this time of year, but days of calm, humid weather can cause odours to accumulate in low areas near the Plant.
Are all of the micro-organisms removed before the final effluent is released to the river?
Prior to the final effluent being released to the river, the treated water flows through the UV Disinfection system where UV light is added to deactive harmful micro-organisms and disease-causing bacteria which may still be present.
What is UV disinfection and why is it used?
Ultraviolet (UV) light is used as an alternative to chlorine to disinfect wastewater from disease-causing bacteria, viruses, and protozoa. As UV light passes through the effluent, disease-causing bacteria are deactivated, thus eliminating the risk of disease. UV also has the advantage of being able to deactivate Giardia and Cryptosporidium, which can be present in wastewater and are a public health concern.
What is Bio-aerosol monitoring?
Bio-aerosol monitoring is carried out at different locations around the Wastewater Treatment Plant. The results of the monitoring tell workers the concentrations of biological particles and micro-organisms present in the air. This information helps the City ensure a safe working environment for its employees.
What is Liquid Injection?
Liquid Injection is the process used to “inject” digested biosolids into agricultural fields as a nutrient-rich soil conditioner and fertilizer. The injection process forces the biosolids directly into the soil.
Is Liquid Injection safe for acreages surrounding the farms using this method of fertilization?
To ensure the safety of biosolids for agricultural use, testing is performed by specially trained laboratory staff. Subsequent monitoring of soil and groundwater is performed in areas around where biosolids have been applied to ensure there are no negative impacts. All applicable Provincial and Federal regulations for the safe application of biosolids on land are followed.
What is the flame burning at the Wastewater Treatment Plant?
Methane and carbon dioxide gases are produced as solids are broken down in the Digesters. Some of the gas is used to fuel boilers that heat the Wastewater Treatment Plant. Excess gas is burned off in a flare stack resulting in a flame that can sometimes be seen at the Plant.
How much does it cost to treat the sewage?
About 53 cents per cubic metre.