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$33 million upgrade for sewage treatment plant 
More than $33 million is being spent upgrading Christchurch’s sewage treatment plant. Underneath the city, day in day out, sewage makes its way to the City Council wastewater treatment plant at Bromley. It is a process that is out of sight and out of mind for most people - but not wastewater engineers. They are halfway through an upgrading of the plant that will cost $33.7 million when it is completed in 2006. The treatment of sewage is a large, complex and expensive operation that is vital to the health and wellbeing of the city. Sewage is mostly water and the treatment plant is there to remove all pollutants and produce an effluent that is as near as possible to fresh water for reuse or return to the environment. The slope of the plains and the Port Hills provide the grade on much of the reticulation system to convey the sewage by gravity towards the treatment plant. More than 70 pumping stations pump sewage from low-lying areas, such as those near the Avon and Heathcote Rivers. Major extensions have been undertaken since the Bromley plant was built in 1962. For instance, in 1969 the number of primary sedimentation tanks were increased from three to seven and in 1975 a fourth secondary sedimentation tank was added. Over the years, the plant has been progressively modernised and expanded and in 1986 covers were put over the trickling filters to capture odours that annoyed residents, mostly in the eastern suburbs. Today lesser odours are back because some of the treatment plant is out of action while more improvements are made. These odours are kept to a minimum while the construction continues. More than 140,000 tonnes of sewage is received at Bromley each day. The treatment processes remove nearly 30 tonnes a day of solids that are separately treated. And after three weeks' treatment, followed by dewatering, these solids (like damp soil) are used on farm paddocks or as a soil conditioner for the Burwood landfill. Later it will be spread on Council forests. The liquid effluent is discharged into the Avon-Heathcote Estuary/Ihutai twice a day at high tide. While the effluent does not meet contact recreation standards, much of the estuary does meet this standard most of the time. In fact, the effluent contains nitrogen and phosphorus nutrient that is beneficial to the estuary's biological diversity. The Avon-Heathcote Estuary and the treatment plant's oxidation ponds support more than 20,000 birds of many species. Another bonus is that the treatment plant produces its own power. It is 100 per cent self-sufficient in energy production and continuously sells power to the national grid system. The power is produced from methane gas, which is produced in the treatment of solids. pic - The extension- in- progress of Christchurch’s wastewater treatment plant, at Bromley. |
