A vast network of 1600km of gravity sewage pipes, 24,000 manholes and 91 pumping stations continuously convey wastewater to the Christchurch Wastewater Treatment Plant for processing (see diagram).
Compared to other New Zealand cities, Christchurch is much flatter and, due to its unique environmental features, has its own particular reticulation challenges. Less pumping is needed over hills, but more pumping is required on the plains as the ground is often too uniform for gravity alone to naturally move the wastewater load along. For more information, see sewer facts and figures.
In Christchurch, sewage (which is almost all water) is carried through a network of underground pipes and pumps to the Christchurch Wastewater Treatment Plant. Over 80 pumping stations pump the sewage from low areas around the city, particularly near the Avon and Heathcote Rivers. Five terminal pumping stations then pump all the flow to the treatment plant.
It is important that sewage gets to the treatment plant as soon as possible to avoid odour generated from its decay. The length of time wastewater takes will depend on the distance from the treatment plant (one to 24 hours maximum).Christchurch has a particular problem with this as it has one of the flattest sewerage systems in the world. Where the volume of wastewater is not sufficient to cause a rapid flow, it is sometimes necessary to flush extra water down line through the pipes to move waste along.
Soil filters are used in some locations to treat odours from the piping system.
Cross boundary collection and treatment
Wastewater from outside the city boundaries - from Prebbleton, Lincoln, Springston, and Tai Tapu - is also accepted for treatment.
With mechanical upgrades and new equipment including additional digesters (to break down solids separated from the wastewater), extra sedimentation tanks and dewatering plant (to dry reclaimed biosolids), the Christchurch Wastewater Treatment Plant is well equipped to offer its services to adjacent communities. The total loading of small communities just outside of Christchurch is less than two per cent of the treatment plant's total capacity.
Going the other way, Christchurch has a consent to apply solid products from the treatment plant in forests in Selwyn District as a fertiliser and soil conditioner. See Biosolids for more information.
