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 temporary ventilation system has been installed.
- A permanent ventilation system will be installed in the future.
2. Primary settlement tanks
The majority of odour is coming from the primary settlement tanks. We're taking many actions to address this odour including:
- Reducing the number of tanks in service to move sewage through the system more quickly.
- Manual daily scum removal.
- Covering chambers with surface disturbance including the primary bypass and secondary return chambers.
- Investigating an odour containment spray system.
- Investigating improving the automatic water spray scum removal system.
- Ruled out using specialist scum removal machinery as it would be ineffective.
3. Temporary secondary treatment
- A consultant is reviewing the design guidelines and will provide operational and troubleshooting advice.
- They're also reviewing the system and looking for opportunities to optimise performance.
4. Odour control system
- The system has been rewired so both fans can be used at the same time.
- Engaging a contractor to renew the remaining bed media.
5. Oxidation ponds
- All 16 aerators are once again in service following repairs to a vertical shaft aerator and disc aerator.
- As we move into winter, and temperatures cool down, the biology of the ponds changes. In previous years this has resulted in a short-term increase in odour coming from the ponds.
- This year our team is trialling a new way of operating the ponds during this period to reduce odour.
- During this period wastewater is being diverted past the ponds located close to residential properties. Skipping these ponds entirely will reduce the impact on neighbouring residents and wastewater will also spend less time in the ponds overall.
- We'll be monitoring the ponds closely to see if these changes are effective in reducing odour while ensuring we don’t exceed our ocean discharge limits.
6. Digesters
- A project is in the final stages to upsize the pipework, aiming to reduce the emergency release of biogas.
- We’re doing more proactive maintenance, which reduces the amount of biogas being released.
7. Sludge dryer
- An extensive maintenance overhaul of the sludge dryer will be carried out to reduce wet biosolid accumulation on site.
Wind trends in Bromley
Information about wind directions in Bromley and how they differ over the seasons.