Sedimentation Tanks (primary tanks)

Main pumping station

The Main Pumping Station located on the plant site at Outhouse Point (property having been granted initially to a Mr. Robert Outhouse) is the heart of the collector sewer system, a point of collection for all lines and continuous pumping to the Wastewater Treatment Facility (WWTF).The cylindrical structure extends 30 m below grade and 9 m above ground, much like a 10-storey building underground.

Wastewater Treatment Facility (WWTF)

The Septage Receiving Building has specialized equipment that receives regional (50km radius from the WWTF) septic tank waste (2020 - 12,130,000 litres), grinds it and removes the heavy solids before flowing into the fine screens.  The pre-treatment building houses screening equipment, grit tanks, and grit handling equipment. Primary clarifiers allow for solids to settle.  The Blower Building provides oxygen to the Bioreactor to reduce CBOD5.  Four 39 m in diameter secondary clarifiers are used to allow more solids to settle.  The dewatering building houses dewatering centrifuges, screw conveyors, lime silos and polymer equipment all of which transform the wastewater by-products (sludge) extracted from wastewater at the bottom of the primary and secondary clarifiers into an important feedstock for the Composting Facility, namely biosolids.

The original WWTF was commissioned in 1994 with a capacity of 115,000,000 litres per day.  The upgraded WWTF is capable of processing flows ranging from a daily average of 90,000,000 to 143,000,000 (storm flow) litres per day.

Wastewater Operations

The five-year historical operational data can be seen in the below table:







Annual volume                m3






Daily average                  m3/day






Anionic polymer             tonnes






Cationic polymer            tonnes






Ferric sulfate                   tonnes






Lime                                tonnes






Power consumption         MWh






Biosolids (Wet)               tonnes






Biosolids (Dry)                tonnes






Solids                               %






Precipitation                    mm






Cost / m3                          $








In 2020, approximately 12,130,000 litres of septage and grey water collected from rural communities surrounding Greater Moncton (50-km radius) were also treated at the WWTF. Inorganic solids such as sand and gravel particles and screenings are removed in preliminary treatment through the screening and grit removal process and transported to the Southeast Regional Service Commission's (Eco360) waste management facility for disposal.

Chemically assisted primary treatment uses chemical coagulants to increase capture of settleable solids.  Sludge is dewatered by centrifuge to increase dryness.  Lime is then added to produce lime-stabilized biosolids.  In 2020, 11,047 tonnes of biosolids were shipped from the WWTF to the Composting Facility.

Wastewater treatment process 

The GMWC operates a secondary four-step feed Biological Nutrient Removal treatment plant located at 355 Hillsborough Rd in Riverview. Wastewater from Moncton, Dieppe and Riverview arrive at the wet well reservoirs of the pumping station from where it is pumped to initiate preliminary treatment (screening and grit removal).


The GMWC Pumping Station facility serves to lift wastewater from the underground tunnels and sewers to the preliminary treatment building. This station is cylindrical in shape and is divided into two halves a dry well and a wet well. In the dry well, motors, pumps, electrical control, etc. are located. The wet well is further divided into two halves of 1,800m3 volume and 27 m depth, these two wet wells are interconnected through gates. Pumping is carried out by 4 centrifugal pumps with a capacity of 1,020 L/s.

Preliminary treatment 

The wastewater pumped from the Pumping Station enters the inlet chamber located ahead of the fine screen channels to initiate preliminary treatment. From this point wastewater flows by gravity to downstream unit processes. GMWC Preliminary Treatment consist of the following physical processes:

  1. Screening: Two mechanically cleaned fine screens (6mm spacing) and an emergency bar screen (bar spacing of 11 mm) remove large debris like rocks, sticks, rags, paper products and plastics. Screenings are discharged into screw conveyors and then conveyed to disposal bins. For final disposal, screenings are transported to a sanitary landfill. Screening removes large debris which may otherwise interfere with downstream operation of pumps, valves, diffusers, etc.

  2. Grit Removal: Four Aerated Grit chamber are located downstream from the fine screens to remove grit. Inert material like sand, gravel, cinders and other generally non putrescible materials having a settling velocity greater than most organic material are known as grit.

At the chambers air is injected perpendicular to the wastewater flow creating a spiral roll velocity pattern, allowing grit to be washed off from the stream. Settled grit is removed from the chambers and pumped to the degritting cyclones. Centrifugal forces further separate grit from the liquid at the cyclones, liquid stream is returned back to the process. The grit stream leaving cyclones is sent to a grit classifier for further rinsing and draining of the material prior to disposal.

Primary treatment 

GMWC Primary treatment removes suspended organic solids through a biological secondary treatment process. There are 4 new Primary Clarifiers that were commissioned in 2019. The combined volume of the four Primary Clarifiers is 13 million litres or equivalent to five Olympic size swimming pools. They are capable of processing flows ranging from 90 to 143 million litres per day.  Wastewater enters the primary clarifiers from the grit tanks and the suspended organic solids settle to the bottom of the clarifiers where they are pumped for dewatering or recycled back to the Bioreactor to maintain healthy and hungry bacteria levels.  The wastewater flows into the Bioreactor.

Floating scum, on the surface of the primary clarifiers, is directed to a scum box that is used to collect the grease and floatables which are removed using a vacuum truck and disposed of at an approved disposal facility.  

Biological Nutrient Removal

The Bioreactor has anoxic, anaerobic and aerobic sections that serve to remove nutrients (ammonia and phosphorous) and reduce carbonaceous biochemical oxygen demand (CBOD5) increasing the amount of oxygen in the effluent.  Bacteria eat a lot of the organic solids before the wastewater flows to the secondary clarifiers.

Secondary Clarifiers

Wastewater flow is split into four 39 metre diameter secondary clarifiers that are used to provide additional solids settling helping to remove more solids from the effluent in order to meet the Federal Effluent Regulations.  The wastewater is carried to the center column of each tank through underground piping.  Outlet ports located in the top section of each column are used to diffuse the flow entering the Clarifier.

Rotating rake arms equipped with deflector blades are continuously scraping the settled sludge across the bottom of the tank to a central sludge thickening well and sludge hopper.

Clarified wastewater (effluent) is then discharged to the Petitcodiac River.  Sludge is pumped using progressing cavity pumps to the solids handling facility.

Floating scum, on the surface of the secondary clarifiers, is directed outward to a scum baffle using skimmer arms.  A scum box is used to collect the grease and floatables which then flow by gravity to a scum hopper.  Scum is pumped from the hopper back to an outlet located at the base of the center column using centrifugal pumps located in the Primary Galleries.

Dewatering Building 

The Dewatering Building houses dewatering centrifuges, screw conveyors, sludge storage tanks, mixing tanks for primary and secondary sludge, rotary drum thickeners, lime silos and polymer equipment all of which transforms the wastewater by-products (biosolids) extracted from wastewater into an important feedstock for the Composting Facility.

Sludge is dewatered by centrifuges to increase dryness.  Lime is then added to produce lime-stabilized biosolids.  In 2020, 11,047 tonnes of biosolids were shipped from the WWTF to the Composting Facility.