Wastewater collection and treatment

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COVID-19 status

In summary:

  • Ottawa’s wastewater (treated and untreated) is not considered a risk for transmission of COVID-19 to people in our community.
  • COVID-19 does not survive wastewater treatment and will not be spread to the public or workers through treated water released to the Ottawa River.
  • The COVID-19 virus does not remain viable in Ottawa’s biosolids, and can be safely applied to local farmland. Additional facts about COVID-19 in relation to land application of biosolids in Ontario is available from the Water Environment Association of Ontario.

Although the COVID-19 virus can remain viable in untreated wastewater for up to two (2) weeks, depending on environmental conditions such as air and water temperature, COVID-19 researchers consider the risk of transmission to humans from untreated wastewater in properly maintained and operated wastewater systems to be very low. The virus that causes COVID-19 is not a very robust virus and the amount that remains viable and able to cause disease in wastewater drops very quickly over time.

The World Health Organization states that wastewater systems have not been identified as an infectious source of the COVID-19 virus. The COVID-19 virus, like any other pathogenic microorganism that enters the wastewater stream, is not thought to pose risks to the public or workers. The concept of wastewater removal through sewage systems and processing at wastewater treatment facilities is to safely deal with whichever pathogens that have entered the sewage stream. Accordingly, existing occupational health and safety precautions for wastewater workers are considered sufficient.

The Wastewater COVID-19 Surveillance study in Ottawa is detecting RNA (genetic material) from the COVID-19 virus in wastewater samples. The study is measuring how frequently COVID-19 virus genetic material is found, but not if it is intact or infectious. This study is helping us track the intensity of COVID-19 cases in our community and should not be interpreted as a risk to the public.

Ottawa’s biosolids program continues to safely operate during the COVID-19 pandemic.  No health risks to workers or the pubic associated with this service have been identified.  Biosolids are available to farmers for application on farmland provided they follow Ontario’s Nutrient Management Act and Ottawa's Biosolids Best Management Practices that ensure all applications are reviewed and are protective of public health and the environment. Biosolids management is an important aspect of our wastewater treatment process, and will continue in compliance with all municipal, provincial and federal legislation and requirements.

Wastewater treatment

Wastewater is water that has been used and discharged by homes, businesses and industrial sources. It is 99.9 percent water by weight, with a very small portion (0.1 percent) of dissolved and suspended solids.

Before it is returned to the Ottawa River, Wastewater is thoroughly treated at the Robert O. Pickard Environmental Centre (ROPEC) to ensure it is safe for the public’s health and the environment. ROPEC collects wastewater from more than 90% of Ottawa's population. For a detailed description of this treatment process, download our wastewater treatment brochure: Let's Explore Wastewater Treatment.

Treatment process

1. Preliminary:

  • Coarse screening/pumping: Wastewater flows to the plant through enormous pipes buried deep in the ground. Once the wastewater arrives at the treatment plant, any object bigger than a shoe gets screened out.
  • Fine screening: Screens will catch smaller objects like sticks and rags.
  • Grit removal: Degrit tanks separate pebbles, grit and sand from the other solids that can be further treated.

2. Primary:

  • Removal of settled solids (sludge) and floatable material (scum).

3. Secondary:

  • Naturally occurring bacteria remove dissolved and suspended organic pollutants. Removal of phosphorus takes place by adding a solution of iron to the wastewater. Iron captures the phosphorus, creating a solid that can sink and be separated from the water. 

4. Disinfection:

  • Before it is finally returned to the Ottawa River, the treated water is first disinfected using sodium hypochlorite, year round.

Process control

Protecting the health of the Ottawa River is an important part of treating wastewater. Processing of wastewater or sewage is monitored 24/7. Sensors throughout the plant allow staff to monitor the treatment process and notify them of any problems. The monitoring and testing program ensures quality targets are met and potential process problems are identified early.

Generating electricity at the Robert O. Pickard Environmental Centre (ROPEC)

As wastewater is treated and processed, methane and carbon dioxide are produced. In 1998 a process was added to convert these gases into electricity and heat through a process called cogeneration. Cogeneration produces 5 megawatts of heat and electricity which provides 50% of ROPEC's energy needs on an annual basis. The cogeneration facility produces enough electricity for approximately 1,500 homes.


The Robert O. Pickard Environmental Center meets all provincial guidelines for wastewater effluent as defined by the Ontario's Ministry of the Environment, Conservation and Parks (MECP).

Actual volume of wastewater treated at the Robert O. Pickard Environmental Centre

  Capacity (millions of litres/day) Actual (2019)
Average 545 436
Peak 1,362.5 1,392

Ottawa’s wastewater treatment plant

About the Robert O. Pickard Environmental Centre (ROPEC)

  • Provides secondary level treatment (physical and biological) of domestic, commercial and industrial wastewater - returning treated water to the Ottawa River.
  • Situated on 67 hectares of land adjacent to the Canotek Business Park in Ottawa East. 28.4 hectares remains available for future growth.
An aerial view of the Robert O. Pickard Environmental Centre.


  • Originally built in 1962, providing primary level treatment, and called the Green’s Creek Pollution Control Centre.
  • Expansions in 1971 and 1975 to provide needed capacity for the growing City.
  • Major expansion and rehabilitation from 1988 to 1993 increasing treatment capacity, improving biosolids processing, and adding odour control. Level of treatment improved from primary treatment to include biological secondary treatment.
  • Renamed for Robert O. Pickard, retired Commissioner of Works in the former Regional Municipality of Ottawa-Carleton.
  • Mr. Pickard helped initiate an expansion and upgrade of the centre to provide Ottawa with improved wastewater treatment capacities.
  • Addition of dechlorination process in 2013 to remove chlorine prior to discharge of treated water to the Ottawa River.

Wastewater collection system

Ottawa's wastewater collection system gathers wastewater from homes, businesses and industrial sites, transporting it through a network of sewers, pumping stations and forcemains to trunk sewers. The wastewater then flows to the Robert O. Pickard Environmental Centre for treatment.

Ottawa’s wastewater collection system covers 2,796 square kilometres and extends from West-Carleton to Cumberland. It includes:

  • 2,846 km of sanitary sewers
  • 108 km of combined sewers
  • 71 wastewater pumping stations
  • More than 92,000 manholes
  • Approximately 234,000 service connections
  • Sewer pipes ranging in size from 20 cm to three metres in diameter

In the rural areas, a variety of collection methods are used:

  • Richmond, Munster Hamlet and Carp are connected to the municipal trunk system.
  • Elsewhere individual septic systems are used and the sludge from septic tanks is transported to the Robert O. Pickard Centre for treatment.

Sewer odours

Who do I call if there is a strong sewer smell coming from outside my home?

Call 3-1-1.

What to do if there is a strong sewer smell coming from the basement?

To prevent smells from the sewer entering your home, the plumbing in your basement has a "trap" installed that creates a barrier when filled with water. The trap is under the floor in the basement and is the first place to look if you have odours in your home.

  • Sometimes in older homes the water in the trap leaks or evaporates and the barrier is broken. To reintroduce the barrier, pour a few cups of water in the basement floor drain.
  • In newer homes, the trap in your home is kept full through a discharge from the trap seal primer valve. If this odour occurs in newer homes, check to see if the primer valve is operating properly or call a plumber.

If the smell persists after a few hours or if the smell is from a sewer back-up, please contact 3-1-1.

What to do if there is an offensive odour coming from one of my sinks?

Often residents may experience an offensive odour while near a sink or after filling a glass. If you think the odour is from the glass of water, take the glass to another room. If you no longer detect the odour from the glass, it may be the sink that is the source of the odour. Often a small amount of commercial drain cleaner will remove any material collected in the trap of the sink that is creating the odour.

Combined sewer overflows (CSOs)

What is a combined sewer overflow (CSO)?

The City of Ottawa has three types of sewers: wastewater, stormwater, and combined. 

  • Wastewater sewers: Collect wastewater from homes, businesses and industries, and transport the wastewater through a network of sewers, pumping stations and forcemains to main or trunk sewers, and direct it to the Robert O. Pickard Environmental Centre for treatment. 
  • Stormwater sewers: Carry rainfall and other surface water run-off directly to the nearest creek, stream or river, generally without treatment.
  • Combined sewers: Collect and transport both sanitary wastewater and stormwater runoff in a single pipe. This type of collection system was typically installed from 1880 to 1960 and is still in operation in older areas of most Canadian cities.

During dry weather, wastewater is collected and carried from a combined sewer to the City's wastewater treatment plant. During heavy rainstorms or snowmelts, the combined sewer may not be able to handle the high volume of stormwater runoff entering the system. Most of the wastewater is transported to treatment plants via the wastewater pipe, but to prevent flooding and sewer backups, some of the rain and wastewater mixture is diverted as overflow into the river.

The practice of discharging overflows during the normal operation of combined sewer systems is accepted by the Ministry of the Environment, Conservation and Parks (MECP). In Ottawa, these events are monitored and reported to the MECP and downstream users such as water purification plants and special interest groups.

What is the City doing to prevent overflows?

The City of Ottawa has implemented the following plan to mitigate the impact of combined sewer overflows into the Ottawa River:

  • The Combined Sewage Storage Tunnel (CSST) is the most significant infrastructure project that the City has undertaken to mitigate the impact of CSOs into the Ottawa River.
  • Real time controls to ensure maximum capture of overflows before they occur
    • Real time controls permit the remote activation and control of overflow equipment combined with continuous monitoring of pipe flow data to maximize the capture and treatment of wastewater flow from combined sewer systems
  • Ongoing sewer separation projects
  • Review of the effectiveness of the current sewer separation program, in comparison to other projects
  • Development and implementation of a Wet Weather Infrastructure Management Plan
  • Installation of devices to remove floatable material from wastewater and prevent it from reaching the river in the event an overflow occurs

The City has been working for many years to separate remaining combined sewers. The value of the work completed to date is estimated at $750 million. With the current funding framework, it is expected the planned separation work will be completed in approximately 25 years.

The City has made the following improvement to existing systems:

  • Water level, flow monitoring and alarm devices installed in major combined sewer overflows and monitored daily to alert staff if an overflow occurs
  • Strengthened protocols to provide prompt notification to the MECP Spills Action Centre and Council in the event of an overflow
  • Construction upgrades are in process for the overflow sites that were the major contributors to the total volume of sewage released during combined sewer overflows
  • Improved regulator inspection and maintenance are improved and now scheduled monthly, weekly after each rain and within 24 hours of receiving an alarm

Sewer overflow sites

There are 13 locations in Ottawa where sewer overflows may enter the river:

Map of Ottawa combined sewer overflow outfall locations
  1. Ladouceur CSO Outfall
  2. Merton CSO Outfall
  3. Booth-Wellington Regulator Overflow
  4. CSST-Kent Overflow
  5. Rideau Canal Regulator Overflow
  6. Keefer Regulator Overflow
  7. Dufferin CSO Outfall
  8. Hemlock CSO Outfall
  9. Sandridge Storage Tank Overflow
  10. Alvin Heights CSO Outfall and RCAF CSO Outfall
  11. RCAF West CSO Outfall
  12. Springhurst CSO Outfall
  13. Clegg CSO Outfall

Combined sewer overflows are generally diverted to flow into the Ottawa River.

The three combined sewer overflow sites that contribute the largest volumes of CSOs are:

  • Rideau Regulator Overflow
  • Booth Regulator Overflow
  • Keefer Regulator Overflow

Overflow activity (January 1, 2020 to date)

PLEASE NOTE: The volume indicated in the chart below (CSO) denotes the volume of combined overflow mixture which is comprised of storm water and wastewater. The majority of overflows occur during heavy rain and snowfall/melting periods. The chart below indicates the date, cause, and volume of each overflow event.

  • CSO: Combined Sewer Overflow
  • SSO: Sanitary Sewer Overflow
Date Event Cause Volume (m3)
01-11-2020 CSO Rain 58,520 m3
03-03-2020 CSO Rain 870 m³
03-20-2020 CSO Rain 23,990 m3
03-29-2020 CSO Rain 26,300 m³
05-15-2020 CSO Rain 4,940 m³
05-29-2020 CSO Rain 11,450 m³
05-30-2020 CSO Rain 80 m³
06-28-2020 CSO Rain 20 m³
07-17-2020 CSO Rain 2,110 m³
07-19-2020 CSO Rain 30,830 m³
07-29-2020 CSO Rain 150 m³
07-30-2020 CSO Rain 1,200 m³
08-02-2020 CSO Rain 44,980 m³
08-04-2020 CSO Rain 12,540 m³
08-11-2020 CSO Rain 590 m³
08-16-2020 CSO Rain 39,550 m³
08-23-2020 CSO Rain 11,920 m³
08-29-2020 CSO Rain 34,900 m³
09-02-2020 CSO Rain 3,780 m³
09-13-2020 CSO Rain 200 m³
09-29-2020 CSO Rain 680 m³
10-07-2020 CSO Rain 6,440 m³
10-21-2020 CSO Rain 3,680 m³
12-24-2020 CSO Rain 24,300 m³
03-26-2021 CSO Rain 55,730 m³
08-29-2021 CSO Rain 680 m³
09-06-2021 CSO Rain 10 m³
09-15-2021 CSO Rain 1660 m³
10-16-2021 CSO Rain 61,870 m³
11-16-2021 SSO Faulty Instrumentation 310 m³
05-16-2022 CSO Rain 12,450 m³
05-21-2022 CSO Rain 910 m³
05-27-2022 CSO Rain 20  m³
06-01-2022 SSO Rain 17.68 m³
07-24-2022 CSO Rain 17.44 m³
08-09-2022 CSO Rain 31,370 m³
04-05-2023 CSO Rain 28,230 m³
04-30-2023  CSO Rain 52,280 m³
06-24-2023 CSO Rain 34.74 m³
06-26-2023 CSO Rain 67,310 m³
07-01-2023 CSO Rain 190.3 m³
07-13-2023 CSO Rain 10 m3
07-18-2023 CSO Rain 130 m3
07-28-2023 CSO Rain 160 m3
08-03-2023 CSO Rain 20 m3
08-10-2023 CSO Rain 315,840 m3
09-18-2023 CSO Rain 20 m3

Historical overflow activity (CSOs only)

CSO activity during the Annual Reporting Period (April 15 to November 15).

Year Number of Events Volume Precipitation (mm)
2019 26 810,000 m3 635 mm
2018 58 536,000 m3 524 mm
2017 79 1,611,000 m3 923 mm
2016 85 413,000 m3 495 mm
2015 80 180,000 m3 332 mm
2014 101 552,000 m3 640 mm
2013 179 213,000 m3 581 mm
2012 142 237,000 m3 523 mm
2011 161 230,000 m3 533 mm
2010 322 673,000 m3 646 mm
2009 384 851,000 m3 649 mm
2008 325 877,000 m3 600 mm
2007 253 730,000 m3 555 mm
2006 271 1,090,000 m3 796 mm

Bypasses and Overflows

The Robert O. Pickard Environmental Centre (ROPEC) is designed to divert wastewater flow in emergency situations. There are two types of diversions:

  • Bypass: The wastewater receives partial treatment. Solid materials are removed from the wastewater and harmful bacterial are reduced before it is released to the river.
  • Overflow: The wastewater receives the lowest level of treatment. Harmful bacteria are reduced before it is released to the river.

The practice of bypassing and overflowing is accepted by the Ministry of the Environment, Conservation and Parks (MECP) during an emergency or if written permission is given by the MECP. In Ottawa, these events are monitored and reported to the MECP and downstream users such as water purification plants.

Bypass Activity (August 24, 2018 to date)

Date Event Cause Volume (m3)
May 21, 2023 No wastewater diverted, but treatment level of the wastewater was reduced and equivalent to a bypass. Power outage due to Derecho. 633,000
April 5, 2023 No wastewater diverted, but treatment level of the wastewater was reduced and equivalent to a bypass. Power outage due to ice storm. 1,303,000

Overflow Activity (August 24, 2018 to date)

There have been no overflow events.