Christchurch Wastewater Treatment Plant situation

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.

Click on the hot spots to see a description of what work is being done to address odour at different parts of the plant. 

 

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

  • A vertical shaft aerator and disc aerator went unexpectedly out of service over the weekend. The vertical shaft aerator went down following damage and needs to be replaced with one of our critical spares that the contractor keeps available for instances like this. 
  • The disc aerator has minor damage and needs to be removed, inspected and repaired.
  • Both aerators are expected to be back in service on Friday 5 April.
  • At this stage, the loss of two aerators isn’t having an effect on the oxidation ponds. Fourteen aerators remain in service and forecast wind conditions are good for dispersing any additional odour in the short term. We’ll provide ongoing updates on this.
  • We have a plan to minimise the odour from the ponds, which could occur during the summer-to-winter transition. This is being put in place over the next two weeks.  

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.

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