Our wastewater system includes eight treatment plants, connected to our homes and businesses by pipes, manholes and pumping stations.
Pipes and pump stations convey wastewater (sewage) from homes and businesses to eight treatment plants, one in Christchurch and seven on Banks Peninsula.
The City of Christchurch was built on low, flat, water-logged land and with no sewage system and cesspits for the wastewater. In its early days Christchurch was particularly beset with the problem of water-borne diseases such as dysentery and typhoid. In 1874 it had the highest death rate of any centre in New Zealand.
With this as a background, in 1875 the Christchurch Drainage Board was formed and construction on Christchurch’s first pump station and first piped network was started in the late 1870s.
The original Number One Pump Station on the corner of Tuam St and Mathesons Rd is still standing (minus its smoke stack) and is a privately owned demolition sale yard.
Now a vast network of 2,679 kilometres of public wastewater pipes, 30,817 manholes and 239 pumping, lift and vacuum stations continuously convey wastewater to the Christchurch Wastewater Treatment Plant for treatment and disposal.
Compared to other New Zealand cities, Christchurch is much flatter and, due to its unique environmental features, has its own particular wastewater network challenges. Pumping is required on the plains as the ground is often too flat for gravity alone to naturally move the wastewater load along. For more information on the Christchurch wastewater system, see facts and figures.
It is important that wastewater 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 wastewater systems in the world. Where the volume of wastewater is not sufficient to cause a rapid flow, or where the pipe grades are too flat, it is sometimes necessary to flush extra water down line through the pipes to move wastewater along.
Bark biofilters are used in 33 locations to treat odours from the wastewater network.
The Christchurch Wastewater Treatment Plant at Bromley treats the wastewater from all of urban Christchurch (as well as Tai Tapu). The average daily flow is 185,000,000 litres per day. The highly treated wastewater is discharged through a 1.8 metre diameter pipe which has its outlet 3 kilometres into the Pacific Ocean off South New Brighton.
The Akaroa Harbour treatment plants have to cope with the wastewater from large numbers of tourists so the type and amount of wastewater that arrives at the treatment plants can change quite dramatically from winter to summer and even from weekday to weekend or on busy public holidays. This can cause variations in the treatment process.
The standard of the treated wastewater is monitored by the Council and Environment Canterbury to meet the resource consent conditions.
Many of the treatment plants will have upgrades or changes in the near future, including the Akaroa wastewater scheme, the Lyttelton Harbour wastewater scheme and the Wainui wastewater scheme.