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Bonnybrook Wastewater Treatment Plant Upgrades and Expansion

Calgary is a big city on a small river, and we continue to grow. This has meant increased amounts of wastewater created and a larger demand on our current wastewater treatment plants.

Bonnybrook Expansion Program

We are investing over $1 Billion in a program of extensive upgrades and expansions to the Bonnybrook Wastewater Treatment Plant, to protect the environment and accommodate our city’s future growth.

This program will:

  • expand the capacity of the plant to treat wastewater, from 950,000 to 1.37 million people and,
  • accommodate population growth until the mid-2030s, and,
  • increase energy efficiency and resiliency.

Aerial view of Bonnybrook Expansion Program during construction

The Bonnybrook Expansion Program covers a large area and it is essential the plant continues to operate and treat wastewater while being upgraded.

Plant D Expansion

The Plant D Expansion is the largest component of the Bonnybrook Expansion Program which will increase the total treatment capacity to approximately 1.4 million citizens. 

Plant D includes a number of key projects, including:

  • installation of three additional secondary treatment bioreactors and six additional secondary clarifiers to provide additional secondary treatment capacity.
  • installation of two new primary clarifiers for additional primary treatment capacity.
  • retrofits and upgrades to the existing solids handling digesters.
  • retrofits and upgrades to the existing ultraviolet (UV) disinfection facility.
  • installation of a new thermal hydrolysis facility for solids handing and the generation of bio-gas for the co-generation facility.
  • installation of new bio-gas handling and storage facilities.
  • construction of a new outfall to the river.
  • installation of a new effluent filtration facility
  • flood projection berm

Plant D Primary Treatment – In Service March 2021

New Primary Clarifiers

The Plant D primary treatment expansion was put into service in March 2021.  This expansion included the construction of two new primary clarifiers, a new primary influent channel, widening of the existing primary effluent channel and upgrades to a number of associated pumping systems throughout the plant.  FRP covers were also installed on existing Primary Sludge Gravity Thickener tanks to aid with odour control.

Plant D Secondary Treatment – In Service October 2021

Phase 1 – In Service October 2021

Phase 2 – Construction started in March 2024

The first phase of the Plant D secondary treatment expansion was put into service in October 2021.  Phase 1 included the construction of two new biological nutrient removal (BNR) reactors, four new secondary clarifiers, two new pumphouses, two new process air headers, a new secondary effluent channel and utilities to tie to the existing infrastructure. 

With this expansion, the installed treatment capacity of the Bonnybrook Waste Water Treatment Plant has been increased by 217,000 Equivalent Population and is now able to treat an additional 94 ML/d average flow and 235 ML/d peak flow.

Stormwater infrastructure upgrades and landscaping were completed in 2022.

The second phase of the Plant D Secondary Treatment expansion includes the construction of a third BNR reactor and two additional secondary clarifiers.  This will increase the capacity of the Bonnybrook Waste Water Treatment Plant by an additional 108,000 Equivalent Population.  

Secondary Treatment Bioreactors

Secondary Treatment Bioreactors

Secondary Treatment Clarifiers

Secondary Treatment Clarifiers

Ultraviolet (UV) Disinfection Facility Upgrade – In Service April 2021

Retrofitted UV Disinfection Facility in operation April 2021

The retrofits and upgrades allow the UV Building to continue to disinfect treated effluent from Bonnybrook. The installed new Ultraviolet (UV) Effluent Disinfection System (Wedeco)is designed for total peak flow capacity of 1,524 ML/d to accommodate growth in north Calgary over the next 25 years. This key project is complete and in-service. 

New Bonnybrook Outfall – In Service March 2021

Aerial view of the Outfall Control Structure looking south

The new outfall was commissioned and put into service in March 2021. It has been upgraded to accommodate increased flows with hydraulic capacity of 1,962 ML/d from the plant. It is located just south of the CN Rail river crossing over the Bow River.

The outfall was extended a further 900 m downstream with two new 700 m long, 3.6m x 3.0m pre-cast concrete effluent box conduits to a new effluent Outfall Control Structure (OCS) to provide further flood resiliency and includes an improved diffusion system (four new 1.8m diameter multi-port, in-bed exfiltration effluent diffusers) in the river to enhance environmental performance. From the OCS, approximately 450 m long emergency outfall spillway was constructed to convey the effluent further south to the Bow River during river flood conditions.

The old plant outfall just north of the Calf Robe Bridge is no longer in use and has been decommissioned.  The old outlets by the Calf Robe Bridge have been concreted over.

Digesters Upgrades Phase 1 – In Service May 2021

Digester Upgrades Phase 1 is complete and was in-service as of May 2021. The four anaerobic mesophilic digesters were retrofitted with new hydraulic sludge mixing systems. Two new digester pump houses were constructed to house six sludge mixing pumps and a new low pressure biogas header was installed.

Construction of Digester Upgrades Phase 2 for two additional anaerobic digesters started in February 2021 and is scheduled for completion in summer 2024.

Bio-gas Handling and Storage Facility – In Service January 2021

New Low Pressure Gas Holder in operation January 2021

The installation of new 2,000 m3 low pressure gas holder is complete and in service. 

The new storage facility will assist in the operation of the new Cogeneration Facility at Bonnybrook.

Flood Protection

A flood protection berm is being constructed to protect the Bonnybrook Wastewater Treatment Plant from potential future flooding.  The 700 m long East portion of the flood protection berm was completed in Fall 2021 and construction of the South berm was completed in 2022. 

As part of the Flood Protection project, a new extension to the regional pathway was opened December 22, 2021.  This extension is on the west bank of the Bow River between the Bonnybrook Bridge and the Graves Bridge (near Glenmore Trail). A North portion of the flood protection berm remains to be constructed.  Completion of this work is in progress. 

Waste Gas Burners

Construction of a new waste gas burner facility is currently underway.  This project includes the construction of three new enclosed waste gas burners and the removal of the two existing candlestick flares.  The project also includes the construction of a new building for associated equipment, piping, electrical and instrumentation and controls necessary for the operation of the new waste gas burners.  The waste gas burners are used to burn any excess biogas not being used to generate electricity.  The new waste gas burners are scheduled to be in-service in summer 2024.

Upcoming projects as part of the Plant D Expansion:

Effluent Filtration Facility

Thermal Hydrolysis Facility

Video credit: Multivista

Brief History

The Bonnybrook Wastewater Treatment Plant is the largest of Calgary's three wastewater treatment plants.

Originally built in the 1930s, Bonnybrook has undergone significant modifications and upgrades over time to increase its treatment capacity to meet the needs of a growing city. Bonnybrook serves the communities north of Glenmore Trail in the city, as well as Cochrane, Airdrie and the Elbow Valley.

Related Documents

Program timeline

Construction commenced in 2014 and continues into 2026.

Here are some of the key milestones achieved to date:

  • Summer 2016 – Construction start on the Plant D Expansion Digester upgrades.
  • Fall 2016 – Construction start on the flood protection berm.
  • Fall 2017 – completion of the Dewatering facility.
  • Fall 2018 – completion of Phase One of the electrical upgrades.
  • Spring 2018
    • Construction start of Plant D Expansion Secondary Treatment Phase 1.
    • Construction start of the  Ultraviolet Disinfection Facility Upgrade.
  • Summer 2018 – construction start of new Bonnybrook Outfall.
  • Winter 2018 – completion of the Plant B and C upgrades
    • 6 new secondary clarifiers. 
    • Replacement of mechanical equipment in existing clarifiers.
    • Replacement of sludge pumps and pipework.
    • Upgrades to the existing Dissolved Air Flocculation (DAF) facility. 
  • Summer 2019 – Construction start of the Plant D Expansion Primary Treatment, new biogas storage facility, and cogeneration facility expansion.
  • Winter 2020 – The City of Calgary continues to work along the west side of the Bow River bank, building a new Bonnybrook outfall and emergency bypass channel.
  • October 2021 update – The Plant D Expansion Primary Treatment, Secondary Treatment Phase 1, UV Disinfection Facility Upgrade, Biogas Storage Facility, Digester Upgrades Phase 1 and new Bonnybrook Outfall are all in-service.  With this new and upgraded infrastructure in place, the Bonnybrook WWTP capacity has been increased by 20% to service the population growth in the North Catchment.  
  • May 2024 update – Construction has commenced on Plant D Expansion Secondary Treatment Phase 2.

Additional updates

A number of other projects that support the expansion program and the general reliability and efficiency of the plant:

  • modernization and expansion of the air blower facilities on site. The use of air is a vital component of the treatment process and improves energy efficiency and reliability.
  • replacement of old boilers in heating plant with high capacity, energy efficient ones.
  • a new fats, oils and grease facility that increases our capacity to receive these waste products and the efficiency of treatment.
  • a new treated effluent water facility. This facility takes treated wastewater and circulates it around the plant to support the treatment process. It also pumps treated wastewater to the ENMAX Shepard Energy Centre for use as cooling water.


Please call or submit a 311 Service Request. For media inquiries please call 403-828-2954

This information has no legal status and cannot be used as an official interpretation of the various bylaws, codes and regulations currently in effect. The City of Calgary accepts no responsibility to persons relying solely on this information. Web pages are updated periodically. ​