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

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

 

2015

2016

2017

2018

2019

Annual volume                m3

25,341,627

22,869,117

22,814,067

25,646,213

26,055,499

Daily average                  m3/day

69,384

62,554

62,531

70,352

71,047

Anionic polymer             tonnes

0.7

0.7

0.7

0.6

0.7

Cationic polymer            tonnes

10.9

13.4

13.5

13.5

12.3

Ferric sulfate                   tonnes

398.5

452.7

427.5

406.6

447.7

Lime                                tonnes

118.9

113.3

108.67

187.2

161.2

Power consumption         MW

5,137

5,063

5,139

6,105

6,332

Diesel Generators            hours

187

177

225

145

 

Biosolids (Wet)               tonnes

11,449

11,311

11,128

11,183

11,188

Biosolids (Dry)                tonnes

3,229

3,169

3,082

3,154

3,105

Solids                               %

28.2

28.0

27.7

28.2

27.8

Precipitation                    mm

1352

995

1052

1360

1,334

Cost / m3                          $

$0.20

$0.21

$0.19

$0.19

 

           

 

Approximately 11,635 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 Southeast Regional Service Commission's (ECO 360) 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 2019, 11,311 tonnes of biosolids were shipped from the WWTF to the Composting Facility.

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 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 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: 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, Biochemical Oxygen Demand (BOD), floatable debris and grease through physical and chemicals processes. There are 4 new Primary Clarifiers that were commissioned in 2019. Once the full biological process is commissioned, the new Primary Clarifiers will continue to provide solids settling ahead of the Bioreactor and be able to provide chemically enhanced primary treatment during periods of extreme high flows. 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 and even higher with the use of chemical coagulants.

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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