Information about the November 2021 Christchurch Wastewater Treatment Plant fire.
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.
The installation of a new ventilation system was completed in April 2025, improving air quality in the building to meet safe working standards for hydrogen sulphide levels.
A review of operational practices has resulted in a recorded reduction in odour generation from the primary tanks. This will continue to be monitored
Our secondary treatment is operated as per our optimised plan. The performance of the process and odour generation is monitored.
Essential maintenance work on the clarifiers is planned for early 2026.
Our ponds are currently operating in summer mode, with natural processes like algae growth helping to keep them healthy.
Pond 1 already has surface aerators to manage loading and reduce odour. We are planning to install three more aerators on Pond 2 in early 2026.
We are currently trialling four different supplier’s products to assess if they can help reduce odour.
A project to upsize the pipework to reduce the emergency release of biogas is currently under review. It is not possible at this time to confirm the revised project delivery date.
An extensive maintenance overhaul of the biosolids dryer is 50% complete. The target date for full completion is June 2026.