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Published 16/12/2020

Work begins on upgrading the Porirua wastewater treatment plant

Work has begun to upgrade the Porirua Wastewater Treatment Plant, with the installation of new ultra-violet (UV) disinfection equipment that will increase the volume of wastewater that can be disinfected.

Porirua Mayor Anita Baker says this is a critical first step in increasing the capacity of the plant by 2023, to stop overflows of partially treated wastewater from the plant to the sea during heavy rain.

“This is the first part of a multi-million upgrade that will be completed by 2023.”

Wellington Water Chief Advisor Wastewater Steve Hutchison says ultraviolet (UV) light disinfection is the final stage in treating wastewater.

“It destroys remaining bacteria and viruses down to safe levels before the fully treated liquid is discharged to the sea,” says Mr Hutchinson.

Currently the Porirua wastewater treatment plant can treat a peak of 1,000 litres per second.  In heavy rain the amount of wastewater delivered by the network can reach up to 1,300 litres per second, and so some partially treated wastewater is discharged off Rukutane Point, as happened during an extreme rainfall event at the end of November.

Steve Hutchison says by 2023 the peak capacity of the plant will be 1,500 litres per second.

“This will mean the plant will be better able to treat all incoming wastewater, even after heavy rain. Combined with network upgrades it will also be able to handle a growing population over coming decades,” he says.

Mr Hutchison says Porirua City Council and Wellington Water have a range of work under way to address wider network issues, including:

  • Identifying and repairing cross-connections where stormwater gets into the wastewater (sewage) pipes overloading their capacity
  • Setting up regional drainage inspection crews to investigate faults on public and private drainage
  • Plans for a city centre wastewater storage tank, enabling better management of peak flows to the wastewater treatment plant and reducing the frequency of overflows to the environment
  • Longer term programme of wastewater pipe and pump station renewals and upgrades across the network.

 At the Wastewater Treatment Plant, the UV upgrade works will happen over the summer. Most of the activity will be inside the plant boundary, apart from traffic to and from the site.

Meanwhile the council’s application to Greater Wellington Regional Council for a consent to continue operating the wastewater treatment plant for the next 20 years is expected to be notified for public submissions between March and June 2021. For more on the consent application see here.



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