Christchurch Wastewater Treatment Plant update

Thursday 20 November 

Contractor appointed for Activated Sludge Reactor 

A render of the Activated Sludge Reactor

The main construction contract for the Christchurch Wastewater Treatment Plant's Activated Sludge Reactor has now been awarded to HEB Construction, marking a major milestone for the upgrade.

We’re working closely with the contractor to get the site established as soon as possible, with construction expected to start early in the new year. 

This work follows the demolition of the fire-damaged trickling filters earlier this year, clearing the way for the new reactor. Construction is expected to take about three years, with commissioning targeted for 2028.

Once the new facility is operational, it will provide a long-term solution to the odour issues experienced since the fire, while also reducing greenhouse gas emissions and increasing capacity to support our growing population.

We know the fire and its aftermath have had a significant impact on the community, and we appreciate how challenging this period has been. While it has taken time to get to this point, we can now move from planning into delivery, and that’s great news for the plant and the wider community.

Clarifier repair work planned 

Alongside this work, we’re continuing preparation work for a project focused on repairing the clarifiers, which play a vital role in separating solids from treated wastewater before it flows to the oxidation ponds.

The cutoff wall trial continues. This will allow us to isolate the clarifier tanks - a key preparatory step for critical repair works scheduled to begin in March. If the trial is successful, the walls will be installed towards the end of this year, streamlining the upcoming repairs and reducing the impact on normal operations.  

Community meeting planned for December 

A community meeting is planned for December, where Council staff will be on hand to answer questions about the Activated Sludge Reactor project, the upcoming clarifier work, and ongoing operations at the treatment plant. This will be an opportunity for residents to learn more about the upgrades and share feedback.

Once a date is confirmed we'll share the information through a range of channels, including this newsletter, our website and a letterbox drop to surrounding residents. 

Midge control measures trialed 

To prepare for the upcoming midge season, the team recently conducted a dredging trial. The test involved towing the midge dredge, which uses chains to disturb the pond’s sludge layer. This disruption helps break the midge lifecycle by displacing or burying larvae.

The trial was timed to ensure conditions were optimal for minimising odour risk. Aerial images captured during the process show the dredge in action, with sludge rising to the surface where it was disturbed. These images also highlight a key concern – some sludge remained on the surface rather than resettling, reinforcing the potential for odour generation.

Odour monitors were in place throughout the trial, and data from the following 24 hours was analysed. Results confirmed that dredging can influence odour levels – an impact likely to be greater when pond health is poor.

Overall, the trial validates the cautious approach we’ve taken in previous summers while confirming that dredging could be a viable option under the right conditions.

Dredging test in action 

Sludge rising to the surface 

Hydrogen sulphide (H2S) monitoring 

The latest graph from our hydrogen sulphide monitors shows the biological health of the ponds is still fragile. Intermittent low levels of odour are being detected at community monitoring sites. 

Stay updated

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire 

You're welcome to send this update to your networks. If you know someone in the community who doesn’t have email or internet access, please print this newsletter off and pass it to them.

If you know of anyone who would like to receive this e-newsletter they can subscribe online. 

If you have any questions, or would like further information on the project, please call us on 03 941 8999 or 0800 800 169 or email wastewater@ccc.govt.nz  

Thanks for your patience and understanding. We’ll be in touch again soon.