Wastewater treatment is the process of taking raw wastewater, and converting it through a variety of treatments into a final effluent that is without the solids and as many of the harmful characteristics of the original wastewater as possible.

There are a variety of different treatments used and available around the world and New Zealand, as there are in the wastewater treatment plants in Christchurch and Banks Peninsula.

They are all quite different in the way they treat but follow the general treatment practice of preliminary, primary, secondary and tertiary treatment. Biosolids are produced as a result of the treatment process and these are all taken to the Christchurch Wastewater Treatment Plant.

The treatment process

  • Preliminary, removal of floating material, heavy settleable, and large suspended solids, using structures like sreens, grit Chambers and flow equalization.
  • Primary, the removal of organic solids using sedimentation like primary sedimentation tanks.
  • Secondary, aerobic, or anaerobic biological decomposition of organic matter using such things as intermittent sand filters, trickling filters, aeration tanks, imhoff tanks.
  • Tertiary, removal of the remaining organic matter and killing pathogenic bacteria, using maturation pond disinfection, Ultra Violet (UV) light disinfection, and chlorination.

Most of the treatment plants that the council operate discharge to the ocean and harbours, but there are a couple that discharge to land. The treatment plants are often having improvements added or being upgraded to improve the final effluent quality and minimise the environmental effects.

The treatment plants are monitored by the council and by the Regional Council (ECAN) to make sure that they meet the environmental measures set under their consents to discharge.

There is a plan for the removal of the treatment plants of the Lyttelton Harbour and pumping the wastewater from the communities serviced by the existing plants to the Christchurch Wastewater Treatment Plant.