On 1 November 2021, a large fire destroyed both of the trickling filters at the Christchurch wastewater treatment plant in Bromley.
The trickling filters are a critical piece of the sewerage treatment process and the damage to them made the treatment process considerably less effective.
As a consequence, Christchurch residents, particularly those downwind during the predominantly easterly winds, have experienced a significant increase in unpleasant odours.
These smells initially came from the burnt trickling filters, but are now coming from areas of the Christchurch Wastewater Treatment Plant and oxidation ponds.
Despite our best efforts, the change to the treatment process without the trickling filters means there is an increase in solids and biological material entering the oxidation ponds, contributing to the stench.
Work to address odour
The interactive map below shows what we’ve got planned or underway to address odour at the Wastewater Treatment Plant. We’ll keep this map up-to-date as our work changes.
Select a hot spot to see a description of what work is being done to address odour at different parts of the plant.
- Green: Good treatment stage process performance, the probability of odour is low.
- Orange: Average treatment stage process performance, the probability of odour is possible.
- Red: Poor treatment stage process performance, the probability of odour is high.
1. Inlet screen room
A project is underway to install a new ventilation system which complies with the hydrogen sulphide safe working limits. It's estimated this work will be complete in early 2025.
2. Primary settlement tanks
We're preparing a tender for a project to improve the automatic water spray scum removal system. Funding for this project was confirmed through the Long-Term Plan 2024-2034.
3. Temporary secondary treatment
We carried out a review the operating parameters of the temporary activated sludge plant.
We're now in the first phase of trialing new operating parameters and are preparing to move to phase two of the trial.
4. Oxidation ponds
The oxidation ponds have now transitioned into winter mode, with the algae having died off for the winter.
The flow regime which was in place to mitigate odours from the ponds during the summer–to-winter transition has now been removed, and flow is again passing through all the ponds.
15 of 16 aerators are currently in service. Our contractor is working on reinstating the remaining aerator and it should be back in service in the next couple of days.
5. Digesters
A project is planned to upsize the pipework, aiming to reduce the emergency release of biogas.
This is expected to be complete by the end of 2026.
6. Sludge dryer
We're preparing a tender for a project to carry out an extensive maintenance overhaul of the sludge dryer to reduce wet biosolid accumulation on site.
Funding for this project was confirmed through the Long-Term Plan 2024-2034.
Wind trends in Bromley
Information about wind directions in Bromley and how they differ over the seasons.