Wastewater Treatment

wastewater treatment plantEach year we treat seven to eight million cubic metres of wastewater at the New Plymouth Wastewater Treatment Plant. That is the equivalent of four billion two-litre milk bottles. 


New Plymouth Wastewater Treatment Plant

The New Plymouth Wastewater Treatment Plant was built in 1984 and is located in the eastern area of New Plymouth.

The plant takes raw sewage and trade wastes from New Plymouth City, Bell Block, Inglewood, Waitara and Oakura. It uses a biological treatment process known as activated sludge aeration to produce a high quality effluent. The clean effluent is discharged to the Tasman Sea via a 480m ocean outfall.

The quality of the water leaving the plant is one of the cleanest in New Zealand and well within the New Zealand standard for safe swimming and seafood gathering.


How does the wastewater process work?

  1. The sewerage pipe network conveys your discharged wastewater to the treatment plant or a pump station.
  2. Pump stations at Te Henui, Glen Avon, Waitara and Bell Block pump waste water to the plant.
  3. The waste passes through milliscreens, which are rotating drum screens with 3mm wide openings that remove plastic and other solids from the wastewater.
  4. The wastewater then passes through a grit trap basin where steady stirring causes grit to swirl to the centre and bottom of the basin. This grit is periodically removed, washed and removed for land disposal.
  5. The wastewater then passes into two aeration basins where micro-organisms, collectively called “activated sludge” feed on the organic waste in the waste water. Pathogens (disease-causing organisms) and contaminants from the wastewater stick to the activated sludge ready for removal. Each basin has six large aerators which keep the basin contents mixed and provide the oxygen necessary for the activated sludge organisms to live, feed and multiply.
  6. Three clarifiers separate the activated sludge from the water. The clusters of activated sludge settle to the bottom of the clarifiers and are drawn off to return to the sludge pump station. Most of the sludge is returned to the aeration basins to maintain the biological levels, while surplus is diverted to the sludge de-watering plant and undergoes three stages of thickening followed by thermal drying to turn them into a biosolids fertiliser called  Bioboost.
  7. The clarified water receives a small dose of sodium hypochlorite prior to the chlorine contact tank to kill any remaining pathogens.
  8. The clean water is then piped to the marine outfall located 1km north of the plant, which diffuses the discharged water with sea water as it is released into the open sea.

  Diagram showing the Wastewater Treatment Plant's processes



Bioboost is an organic, slow-release, granular fertiliser suitable for general garden use - both residential and commercial.

It is produced from heat-dried biosolids at New Plymouth’s Wastewater Treatment Plant.

Visit the Bioboost website to find out how it is made, how to use it and where to buy it from.

For technical issues or enquiries please contact David Tong from Bioboost Ltd on 027 445 8218 or contact us on 06-759 6060.