Cambridge WWTP Covered Anaerobic Lagoon

Waipa District Council
Pattle Delamore Partners Ltd

Project Scope

A portion of the Cambridge Waste Water Treatment Plant is currently being used by the National Institute for Water & Atmosphere (NIWA) as a large scale demonstration for the treatment of waste water.  NIWA required additional Carbon Dioxide to be injected into their trial ponds in order to enhance the algae growth and this carbon dioxide can be provided by collecting the biogas generated within the anaerobic lagoon and piping it to the site of the NIWA denitrification project.

By covering the existing anaerobic Lagoon, Waipa District Council aimed to achieve the following outcomes:

  • capture the gasses coming off the lagoon
  • removal of rain water from the covered pond
  • feed biogases to the NIWA ponds
  • assess the actual volumes of biogases being captured
  • blow biogases down gas transfer pipework
  • flare off surplus biogases
  • adjust the anaerobic lagoon outlet level to draw off from a different zone of the lagoon
  • allow future desludging of the anaerobic lagoon once the cover is in place

This contract included the supply and installation of a flexible polyethylene cover and associated rain water management and civil works for the existing anaerobic lagoon.

A biogas collection system was also installed beneath the cover together with an accompanying gas flaring system.  An additional standalone blower was installed and connected to an existing gas pipeline to transfer a portion of the biogas to the NIWA trial location.

The existing lagoon overflow pipes were replaced to improve capacity and mitigate air ingress under the cover.