Wastewater treatment

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 pre-treatment building houses screening equipment, grit tanks, grit handling equipment, chemical storage and feeding equipment. Three 39 m in diameter settling tanks are used for the chemically enhanced primary treatment. 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 into an important feedstock for the Composting Facility, namely biosolids.

The actual WWTF was commissioned in 1994 with a capacity of 115,000 m3 per day, or 25 million gallons per day. The plant was laid out to facilitate expansion to biological treatment in the future.

Wastewater operations

In 2013, the WWTF processed more than 23.8 million m³ of wastewater or an average of 65,257 m³ per day. At this flow rate, one 8 m in diameter above-ground pool would be filled every 90 seconds.

The existing enhanced primary treatment is designed to remove primary suspended solids. In 2013, the removal rate was measured at 70.4%. Biological oxygen demand (BOD) is a measure of organic biodegradable matter which is partially removed (approximately 40-45%) with the current process. The planned plant upgrades to biological treatment would bring these removal rates to more than 95%.

Approximately 2.8 million 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 SE Recycle (formerly Westmorland-Albert Solid Waste Corporation) 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 2013, 10,376 tonnes of biosolids were shipped from the WWTF to the Composting Facility.

Chemical consumption:

  • Primary treatment chemicals: 49,906 kg
  • Dewatering polymers: 12,919 kg
  • Hydrated lime for biosolids treatment: 133,585 kg

Total GMWC power consumption for 2013 was 5,846 MW hours – or an average of 16,020 KW hours per day, the equivalent to approximately 350 homes. More than 90% of this consumption was for the WWTF alone.

Wastewater treatment process

The GMWC operates a chemically assisted primary 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) followed by primary treatment (settling).

Pumping

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 bar 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 bar screens (bar spacing of 19 mm) remove large debris like rocks, sticks, rags, paper products and plastics. Screenings are discharge 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: Two Aerated Grit chamber are located downstream bar 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, Biochemical Oxygen Demand (BOD), floatable debris and grease through physical and chemicals processes.

Coagulation

A chemical product called a chemical coagulant is added to the wastewater upstream clarifiers to enhance solids removal. The chemical coagulant destabilizes the negatively charged particles to reduce the forces that keep the particles apart. This allows their agglomeration to form settleable flocs.

Flocculation

The chemical product used to aid the flocculation process (the formation of flocs) is called a flocculant. A synthetic organic anionic polymer is used in addition to chemical coagulants, to bring smaller particles together thereby increasing their size and further enhancing clarification.

Settling

Wastewater flow is split into three sedimentation circular tanks (primary tanks). 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.

Scum removal

Floating scum, on the surface of the 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.

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