Wastewater Treatment

The Riverhead Wastewater Treatment Facility is a conventional primary treatment plant that treats wastewater from the City of St. John’s, the City of Mount Pearl and the Town of Paradise. This service area has a total population of approximately 135,000 people. It produces approximately 135 million litres of wastewater on an average day.

Riverhead's treatment removes:

30 to 40% of organic material
50 to 80% of the suspended solids
up to 99.5 per cent of all fecal coliform

The removed material adds up to approximately 30 tonnes of solid waste that is no longer deposited in St. John's Harbour.

Flushing inappropriate materials down your toilet causes costly repairs and maintenance. Protect your wastewater system: learn what not to flush.

An aerial view of the Riverhead Wastewater Facility on Southside Road in St. John's

Riverhead Wastewater Treatment Facility

Understanding the Process

The process to treat wastewater is an interesting one:

Wastewater Path

Wastewater travels through the sanitary sewer and combined sewer pipelines to the treatment facility.

Wastewater flows into the treatment plant through a mechanical screen and into a pump station. There, submersible pumps lift the screened wastewater up to the grit tank inlet channel. Then, wastewater flows by gravity into three aerated grit tanks. There sand, silt, gravel and other inorganic material are settled out while organic material is kept in suspension.

The screened and de-gritted wastewater flows over weirs at the end of each grit tank to the grit tank effluent channel. It then flows through the primary influent channels to three primary clarifiers. The primary clarification process removes over 50% of the suspended solids. Organics settle to the tank floor to form a sludge blanket. The clarified wastewater flows over weirs at the end of the primary clarifiers and into the primary effluent channel.

The final stage of treatment is chlorination and dechlorination. The wastewater flows from the clarifiers to the chlorine contact tank influent channel. Chlorine is injected through a diffuser and mixed with the effluent. Sodium bisulphite is added at the effluent weir at the end of the contact tank to dechlorinate the final effluent before discharge to St. John's Harbour.

Solids Path

Material removed by the mechanical screens in the shallow and deep pump stations is conveyed to a disposal bin by screw conveyers. These solids are washed, compacted and deposited in a solid waste container for disposal. Grit that settles to the bottom of the grit tanks is mixed with water to form a grit slurry and pumped to grit classifiers in the deep pump station. The grit classifiers clean and dewater the grit and deposit it in a solid waste container for disposal.

The sludge that settles out in the primary clarifiers forms a sludge blanket on the tank floor that is collected and directed to our anaerobic digesters for further stabilization and treatment. Anaerobic digesters heat and mix the solids. This reduces the volatile organic solids content while producing methane gas for use in the facility's hot water boilers. The stabilized sludge is pumped from the digesters to centrifuges and dewatered for disposal.