Stephenville Wastewater Treatment Facility

The Abydoz Engineered Wetland in Stephenville, Newfoundland was commissioned in 2009-2010. It is the largest subsurface engineered wetland system providing secondary treatment in Canada. Located on the Stephenville airport property, the subsurface flow ensures that the wetland does not attract water fowl or other wildlife that could impact the airport operations.


  • Population: 7,800 P.E. (Population Equivalent)
  • Average Flow: 4,555 m3/day
  • Wetland Treatment Area: 20,000 m2

Inlet Concentration:

  • 95 mg/L BOD
  • 110 mg/L TSS

Outlet Concentration:(Ocean Discharge)

  • 40 mg/L BOD
  • 60 mg/L TSS

Process Description

Effluent from the town passes through a spiral screen to remove plastics and non-biodegradable items. Then the flow enters a primary clarifier to settle out suspended solids. From the clarifier the flow is split eight ways and proceeds through the horizontal-flow wetland beds where biological reduction takes place. The flow is then recombined and passes through two vertical beds with final discharge to the ocean.

Sludge treatment cells are located on the other side of the airport. The wetland sludge cells dewater and mineralize the sludge removed in the clarifier, producing a compost-like material. On site sludge treatment cells provide significant cost savings by eliminating expensive sludge transportation and disposal costs.

Actual Treatment Results: (average over first year operation)

  • BOD: 78 mg/L reduced to 11.6 mg/L (87% Reduction)
  • TSS: 177 mg/L reduced to 11.8 mg/L (92% Reduction)

Total Project Cost:

  • $10 Million (approximately)

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