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 completed in April 2025.
2. Primary settlement tanks
A review of operational practices has resulted in a recorded reduction in odour generation from the primary tanks. This will continue to be monitored
3. Temporary secondary treatment
We carried out a review the operating parameters of the temporary activated sludge plant. The optimisation trial has been completed, and the operating parameters have now been implemented. This has resulted in a recorded reduction in odour generation from the secondary treatment process. This will continue to be monitored.
4. Oxidation ponds
The oxidation ponds have now transitioned into summer mode, and our site staff are actively monitoring them to ensure optimal performance.
Site staff are working closely with our contractor to ensure the aerators remain fully operational.
5. Digesters
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.
6. Sludge dryer
A project to do an extensive maintenance overhaul of the sludge dryer is in the process of being scoped and specifications prepared. It is not possible at this time to confirm the revised project delivery date.