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Water & Wastewater Treatment Plants Processes

Water Treatment Plant Process

The City of Lethbridge gets all of its water from the Oldman River. A river is considered a surface water supply. Lethbridge do​es not use groundwater from wells. Our Water Treatment Plant processes river water into safe, healthy drinking water.

The certified operators at the treatment plant performed about 29,000 water tests as part of their daily routines each year:

  • Daily water tests
  • Bacteria tests performed by the Provincial Public Health Laboratory each week
  • Monthly chemical analysis that includes metals and disinfection by-products
  • At least twice per year, treated water samples are subjected to a scan of 40 organic compounds, including pesticide chemicals, over 40 tests for metals, and other routine analysis

Over 32,000 tests are conducted on our treated water each year

The City of Lethbridge water distribution system consists of approximately 590 km of water main and 6 storage reservoirs with pump stations. The water mains and pump stations deliver water to residences and businesses throughout the city and neighbouring communities. 

The Water Treatment Plant draws our water supply from the Oldman River. The Plant is capable of treating 150 million litres of water per day and uses a multi-step treatment process.​​​​

  1. Oldman River: The water enters the Water Treatment Plant from the Oldman River.
  2. Screening: The water then enters the Water Treatment Plant, passing through screens, which filter the water of larger debris before entering the treatment process. A screen exists to stop large items that get caught in the pump and cannot complete the treatment process. For Example: branches.
  3. Low Lift Pumps: This type of pump is used to lift water from the river into the Water Treatment Plant for the treatment process.
  4. Coagulation: The mixer allows for coagulation to occur, which is the addition of approved water treatment chemicals (Polyaluminum chloride) to convert microscopic particles and other contaminants into larger and heavier particles.
  5. Clarification: Clarifiers are settling tanks; clarifiers use sedimentation, a process that removes the majority of the larger particles from the mixer by settling them in tanks. Activated Carbon is added at this point of the treatment process.
  6. Activated Carbon: is used in the form of powdered activated carbon (PAC). Activated Carbon absorbs organic compounds found in the water and is used as needed to control taste, odour, and colour in the water. The dosage of activated carbon added to the water ranges from 1mg/L to 15mg/L. The concentration of activated carbon remaining in the treated water is not detectable. The use of this chemical is not necessary to produce potable quality water.
  7. Disinfection: Disinfection is the addition of chlorine, which disinfects the water so it is safe for drinking. Chlorine is added after the sedimentation process, before the water moves to the filtration treatment process.
  8. Filtration: Filtration of the "settled" water, from the clarifier, removes most of the remaining particles to thousandths of a millimetre (too small to see).
  9. Ultraviolet Disinfection: Ultraviolet (UV) disinfection of the water with chlorine is a way to protect public health from disease causing organisms that can be found in the river. The risk to public health is reduced further by treatment with UV light. Before the water leaves the treatment plant, we combine the chlorine with ammonia to form chloramine. This reduces the formation of disinfection by-products, and ensures a long-lasting "residual" to protect our water against bacteria or other organisms on its journey to your home tap.

Polyaluminum chloride - is key to the particle removal processes of coagulation and flocculation. It transforms the naturally occurring microscopic particles found in the water into larger particles (a.k.a. floc) that can be settled or filtered from the water. Polyaluminum chloride is more effective in cold water and contains less aluminum than the historically used Aluminum Sulphate (alum). The dosage of polyaluminum chloride added to treat the water ranges from 20mg/L to 120mg/L. The concentration of polyaluminum chloride remaining in the treated water is not detectable. The use of this chemical is necessary to produce potable quality water. Polymers – organic polyelectrolytes – are occasionally used in small amounts to enhance flocculation under extreme conditions, particularly in cold water when the chemical reactions can occur more slowly. The dosage of polymers added to the water is 0.1mg/L to 1.0mg/L. The concentration of polymers remaining in the treated water is not detectable. The use of this chemical is necessary to produce potable quality water.

Chlorine - disinfects the water so that it is safe for drinking purposes. This chemical destroys micro-organisms such as bacteria and viruses in the water which can pose a threat to public health. The dosage of chlorine added to the water is 2mg/L to 4mg/L. The resulting concentration of chloramine in the treated water is 1.8mg/L to 2.2mg/L. The use of this chemical is necessary to produce potable quality water.

The chemicals Ammonium and Fluoride are added after the UV Disinfectant stage, before the water is pumped to the storage reservoirs.

Ammonia (Ammonium Hydroxide) - is used to combine with chlorine to form “Chloramine”. Chloramine maintains its disinfecting properties for a longer time than does free chlorine. This is particularly useful for long distribution mains and large storage reservoirs. The dosage of ammonia added to the water is 0.5mg/L to 1.0mg/L. The resulting concentration of chloramine in the treated water ranges from 1.8mg/L to 2.2mg/L. The use of this chemical is necessary to produce potable quality water.

Fluoride (Hydrofluorosilicic Acid) - is added as a dental health measure to prevent tooth decay. Its application is authorized under City Bylaw # 3236 and has been added to the water in Lethbridge since 1974. The dosage of fluoride added to the water is 0.5mg/L to 0.7mg/L. The resulting concentration of fluoride in the treated water is 0.7mg/L to 0.9mg/L. The use of this chemical is not necessary to produce potable water.

Water Treatment Plant Coagulation, Clarification, and Disinfection

Water Treatment Plant Filtration and Ultraviolet (UV) Disinfection


The Plant site is on the east bank of the river, south of Whoop-Up Drive, and across the river from the University of Lethbridge. We process an average of about 53 million litres of high quality drinking water on a daily basis.

The maximum daily production in 2017 was 133.2 million litres, on July 18th.

Wastewater Treatment Plant Process

The water we use in our houses and businesses goes to the Wastewater Treatment Plant. This water is cleaned and discharged back to the Oldman River. The sludge from the process is used for fertilizer.

Several steps are required to treat our wastewater, which has the capacity to treat 80 million litres of wastewater a day (MLD) average flow and a peak of 160 MLD.

The City collects all the wastewater that comes out of homes, schools, and businesses . The wastewater flows through the sanitary  piping system by gravity and  pumps to our Wastewater Treatment Plant.


1.       Headworks: Screen and Grit Removal

When wastewater reaches a treatment plant, it passes through screens that remove larger materials such as plastic bags, toys, sticks, and golf balls. The wastewater then travels into grit cyclone separators where the heavier material settles to the bottom and is taken to the Waste and Recycling Center. This water, known as Primary Influent, flows by gravity to the Primary Clarifiers.

2.       Primary Clarifiers

These are open-air tanks used for settling and skimming. The water stays in these tanks for about two hours. After that, more material settles at the bottom. This sludge and top skimming waste (scum) are pumped to the digesters for anaerobic (without oxygen) decomposition. The overflow from these tanks (primary effluent) goes to the secondary process for further treatment.

The treatment process is then separated into two parts:

  • Liquid treatment processing: Bioreactors (BVioP), Secondary Clarifiers, Ultraviolet Disinfection (U.V.), final Effluent
  • Sludge treatment processing: Digesters, Sludge as Fertilizer, Methane Gas

3.       Bioreactors: Step BioP: Liquid Treatment Processing

Biological treatment processes are systems that use microorganisms to degrade organic contaminants from wastewater. The incoming secondary influent stream is split and fed stepwise to each anaerobic zone. The mixed liquor exiting the first three aerobic zones is directed to the anoxic zone of the next step in the process. Denitrified mixed liquor from the end of the anoxic zones is recycled to the corresponding anaerobic zone. After a long retention time, the mixed liquor flows to the secondary clarifiers.

4.       Secondary Clarifiers: Liquid Treatment Processing

In the secondary clarifiers, which are large, open-air tanks, the mixed liquor is retained for a few hours. During this period, the activated sludge settles by gravity and the clear secondary effluent overflows the clarifiers' weirs and flows to the ultraviolet-light disinfection facility. Most of the settled activated sludge is returned to the bioreactors to repopulate it with micro-organisms. Excess activated sludge is pumped to the gravity belt thickener to remove most of the water and is then sent to the anaerobic digesters.

5.       Ultraviolet Disinfection (U.V.): Liquid Treatment Processing

Effluent from the secondary clarifiers flows to the ultraviolet disinfection facility. The ultraviolet light disrupts the micro-organisms, making them incapable of reproduction and they can no longer cause disease. Ultraviolet-light disinfection, unlike chlorine, adds no harmful chemicals to the plant's final effluent.

6.       Final Effluent: Liquid Treatment Processing

Final effluent flows from the ultraviolet-light disinfection facility and is discharged into the river. The final effluent consistently meets the stringent effluent standards set by Alberta Environmental Protection. The effluent is clear, colorless, , and very low in organic solids, suspended solids, phosphorus, ammonia nitrogen and pathogenic (disease-causing) micro-organisms.

7.       Digesters: Sludge Treatment Processing

In the covered anaerobic digesters, the combined primary and activated sludges are digested for approximately 30 days by anaerobic bacteria (bacteria that grow only in the absence of oxygen). The naturally-occurring bacteria break down complex organic materials into simple and stable substances such as water, methane, and carbon dioxide. The digested sludge becomes less odorous and many disease causing organisms are destroyed. This biological sludge treatment process, or anaerobic digestion, is enhanced by constant mixing, using compressed digester gas, and heating to maintain digester temperature at 35 degrees Centigrade, the ideal temperature for anaerobic bacteria growth. Anaerobic digestion produces digester gas, which consists of approximately 65 per-cent methane and 35 per-cent carbon dioxide.

8.       Sludge as Fertilizer: Sludge Treatment Processing

The digested sludge is applied to agricultural land as a means of disposal. Each year 6000 dry tonnes (or 90,000 cubic meters)  is hauled from the city to farms as far as 30km away. The digested sludge is rich in nutrients which help improve crop yield. The amount of sludge that can be used on an individual field is carefully regulated according to provincial regulations. Excess supernatant (water) is returned to the start of the wastewater treatment process.

9.       Methane Gas: Sludge Treatment Processing

The methane gas from the anaerobic digesters is used as fuel by the plant’s co-generation facility.  The generators convert methane to heat and electricity for use at the plant. This significantly reduces the plants energy costs.

The Wastewater Treatment Plant recycles water all around the Treatment Plant through our E-water system (effluent water).  Treated water is pumped back into the Treatment Plant to use for washing, rinsing and cleaning applications. This helps reduce the amount of potable water consumed at the Wastewater Treatment Plant on a daily basis.

The City’s Wastewater Treatment Plant and Utility is funded by revenue from residential and commercial wastewater rates. Our wastewater collection system consists of 575 km of sewer and 19 lift stations.  The sewers and lift stations convey wastewater from residences and businesses in all areas of the City to the Wastewater Treatment Plant. The treatment plant removes contaminants from the wastewater and discharges clean, disinfected effluent into the Oldman River south of Peenaquim Park.

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