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Deep cleaning at NPDC’s wastewater treatment plant

News Local Featured news
PUBLISHED: 14 JUL 2022

Deep cleaning at NPDC’s wastewater treatment plant

While most of us get to ‘flush and forget’ – keeping the city’s wastewater system ticking is a big job.

The team at NPDC’s New Plymouth Wastewater Treatment Plant recently emptied the impressive-sounding bioreactor basin 2.

The work involved cleaning out the debris from the diffuser grids which inevitably gets into the system and replacing all 2,740 diffusers (which look like upside-down showerheads). Some parts were changed to make the bioreactor system more efficient, restore capacity and reduce energy use.

NPDC Three Waters Manager Mark Hall says the diffusers are a key part of the treatment process as they distribute oxygen through the wastewater. They were installed in 2013 and had worked continuously since then.

Each basin at the treatment plant can hold 9,500 cubic metres of wastewater.

Fast facts:

  • The New Plymouth Wastewater Treatment Plant was built in 1984.
  • On average, NPDC handles 25 million litres of wastewater each day, looking after more than 25,850 properties in the district.
  • Clean treated water is discharged to the Tasman Sea via a 480m ocean outfall, and the water’s quality is one of the cleanest in New Zealand.


NPDC is investing $248 million over the next 10 years to fix the district’s plumbing.