Wastewater Treatment Plant odour control

  • Project typeImprovement work
  • Project value$7.5 million
  • Project scheduleApril 2024 to September 2025
  • Contractor nameUnited Civil
Whangarei's Wastewater Treatment Plant with water at the top of a wastewater tank in the foreground reflecting the sky and other tanks between it and hills in the background.

We are putting an odour-control system in place at our Wastewater Treatment Plant on Kioreroa Road.

The project includes covering and ventilating five components to address odour complaints and prepare for increased commercial activity near the facility.

It includes installing odour-control covers and treatment systems (bio filters) for the:

  • inlet works (where the untreated sewage comes in for treating)
  • screenings bin (where the lumps go)
  • sludge thickener tanks (that reduce the water in the sludge prior to disposal)
  • sludge holding tanks
  • snail bin*.

The new odour-control system will significantly reduce odour emissions. It is designed with longevity and safety in mind to align with the plant's operational requirements.

The entire system, including its hazardous area classifications, ensures a safer and more compliant operational environment.

The treatment plant will remain operational throughout this long-term project, which requires a number of complex tasks.

What's a snail bin?

The water treatment plant has three large trickling filters - large round bins filled with granite rock. The wastewater trickles over the rocks and the algae growing on them.

The algae take massive amounts of nutrients out of the wastewater and clean it up. It’s a very robust and natural process, accelerated by engineering technology.

The algae attract small snails (about 3 millimetres long), which just love the environment in the trickling filter – it is wet and full of food. The snails grow there by the billions.

Every now and then a few snails are swept out with the wastewater and are filtered out before the water goes to further cleaning.

Those “few snails” however, add up to two to three cubic metres per week. We put them in our snail bin and empty it every week.

However, this is long enough for it to develop one of the worst smells in the wastewater treatment plant.


79 Kioreroa Road, Whangārei 0110  View Map

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