Sewage is waste from all sinks, toilets, laundries, kitchens and bathrooms. This waste flows through a sewerage network of underground pipes and pumping stations to one of three treatment plants throughout the city.
Sewerage network quick facts
- 1,022km of pipes
- 62 pump stations
- 3 treatment plants
- 1 dewatering plant
- 24 million litres of sewage per year
- 58 years average age of network pipes
- $580 million replacement value
Sewerage treament plants
There are two sewage treatment plants in Wellington - Moa Point and the Western Treatment Plant (Karori) - and a sludge treatment plant at the Southern Landfill.
The Council also has a 27.6% share in the Porirua Treatment Plant which treats sewage from Wellington's northern suburbs.
The Council contracts United Water International to operate Wellington's three treatment plants.
The Moa Point Treatment Plant was granted new consents on 11 May 2009. These consents will continue for 25 years (expire 11 May 2034).
The Western Treatment Plant was granted new consents on 28 July 2010. These consents will continue for 25 years (expire 28 July 2035).
The Sludge Treatment Plant was granted new consents on 7 May 2012. These consents will continue for 12 years (expire 14 June 2024). The consents allow the following:
- to discharge contaminants to air from the sludge dewatering plant
- to discharge contaminants to air from the disposal of sludge to landfill
- to discharge dewatered waste to land at the landfill.
Waste treatment process
At the Moa Point Treatment Plant, sewage travels through a series of screens, tanks, bioreactors, clarifiers and ultraviolet treatments before being discharged as liquid into Cook Strait.
- Non-organic - large, non-organic materials such as toilet paper are first removed using screens. This rubbish is washed and compressed and sent to the Southern Landfill for disposal.
- Solid sewage (sludge) - as sewage travels through sedimentation tanks, the majority of solids are removed. This sludge is taken to the Southern Landfill Sludge Treatment Plant where it is de-watered (water removed from solids).
- Effluent - a series of tanks and bioreactors use a combination of sedimentation and bacteria to decompose almost 70% of carbonaceous material. Remaining liquid effluent is exposed to ultraviolet light to destroy any harmful bacteria. The treated liquid is finally discharged, through a long outfall, 1.8km into Cook Strait.