How wastewater gets to the treatment plant
How wastewater gets to the treatment plant
Compared to other New Zealand cities Christchurch is much flatter, and due to its unique environmental feature 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 the sewer facts and figures.
In Christchurch, sewage (which is almost all water) is carried through a network of underground pipes and pumps to the 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.
Odour management
It is important that sewage gets to the Treatment Plant as soon as possible to avoid odour generation from decaying sewage. The length of time wastewater takes will depend on the distance from the treatment plant (1-24 hours maximum). Christchurch has a particular problem with this as it has one of the flattest sewage 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 wastes along.
Soil filters are used in some locations to treat odours from the piping system.
How you can assist
Domestic users are by far the biggest generators of wastewater due to the wide variety of uses of water in the home. Of the main sources of water use in the home, the kitchen, bathroom, and toilet are the heaviest users of water - with toilet flushing consuming the most water. See how much water we use.
Householders can help to ensure the wastewater system runs efficiently by checking that house roof downpipes are not being fed into gully traps but rather into a stormwater drain. Proper installation will ensure that your stormwater will not get into the sewer to cause overflows during times of heavy rain. This will avoid raw sewage waste seeping into rivers and spilling onto streets and private property.
Reporting any overflows seen also helps make our service delivery more efficient.
Another way you can help the system work more effectively is avoiding installing waste disposal units or 'waste grinders' where possible, as these put an extra load on the sewerage system in terms of the volume of matter requiring decomposition. It is better to compost kitchen wastes if you can. Make sure you don't let excess fats go down the drain, as these are a common cause of blockages.
Industrial responsibility
Industry can also assist via adoption of cleaner production methods of waste minimisation plus onsite treatment of by-products where warranted. Such measures have the potential for significant environmental benefit as many firms use large amounts of certain chemicals in their manufacturing process and the resultant by-products are then introduced into the sewer system. See Trade Waste.
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 out from the wastewater), extra sedimentation tanks and dewatering plant (to dry reclaimed biosolids) the Christchurch Treatment Plant is well equipped to offer its services to adjacent communities as the total loading of small communities just outside of Christchurch is less than 2% 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.
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