Municipal Wastewater and Sludge Treatment
Stephenville, NL
This is the largest subsurface engineered wetland system design providing secondary treatment in Atlantic Canada.
It is located in the Town of Stephenville, on the west coast of the Island of Newfoundland, Canada. The system is located on the Stephenville airport property. A first for Transport Canada, no other sewage treatment systems are allowed on Airports. Subsurface flow ensures that the wetland does not attract waterfowl or other wildlife that could impact the airport operations and has created no issues since its installation.
Mr. Glenn Sharp, P. Eng was the lead engineer on this award winning 20,000 m2 wetland system which serves a population of 7,800. The average flow is 3,500 m3/d, or approx. 1.0 million gallons/day. The wetland system consists of 8 horizontal-flow subsurface wetland beds, 2 verticalflow subsurface wetland beds and 4 sludge treatment cells.
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 engineered 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. Wetland plants mineralize the sludge from the clarifier, producing a compost-like material. Onsite wetland sludge treatment cells provide significant cost savings by eliminating expensive conventional sludge drying and transportation costs or simply the costs for disposal.
The quality of the incoming wastewater fluctuates corresponding to daily and seasonal variations. Daily peaks are typically at midmorning and in the evening. These peaks are recorded as elevated BOD levels entering the clarifier. By the time the effluent has passed through the wetland the BOD has been reduced by 97% to approximately 5-10 mg/l. This is well below Stephenville’s limit of 40 mg/l for ocean discharge. Similar results have been obtained for total suspended solids, phosphorous, and Total & Fecal Coliform.
The wetland system was constructed in 2006 but due to delays in the headworks and collection system the system was not commissioned until 2009, making it now 14 years old. Just a youngster with the expectation it will be working late into its 70’s and possibly even longer, as the oldest systems in Europe with this design are now projecting to operate for over 100 years.
This project, along with others with our similar engineered wetland designs have received numerous environmental excellence awards from such entities as: CME, NRC, FCM, ACWWA, PEGNL, APEGNB, SPAWN, NL Dept. of Env. Our designs are now generating Carbon Offsets, through our broker Carbon Zero funds are now flowing where we expect soon to be able to provide Zero Cost to operate options. For details see our affiliated company www.sharpmgmt.ca .
