The wellbeing of our residents is our top priority and we continue to focus on work that will improve the quality of life for everyone who has been living with a horrible odour since the fire on 1 November 2021.

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We’re working as fast as we can to implement new methods for treating wastewater and appoint contractors to remove the rotting material from inside the treatment plant.

We know that many of you have been living with a stench since the fire on 1 November 2021.

We apologise for the horrible smells from our wastewater treatment plant. We continue to prioritise work that will reduce the odour and we appreciate your patience as we do everything we can to improve the situation.

Below you can find an overview of the project, timeline, frequently asked questions and past newsletters. This page will be updated regularly to keep you informed.

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 the oxidation ponds and the material inside the trickling filters after it rains.

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.

An independent air quality specialist has assessed the composition of the stench coming from the plant. The results confirm hydrogen sulphide and methyl mercaptan – commonly associated with poorly running wastewater plants – gases that smell bad at very low levels.

The gases are present at concentrations below those considered toxic, however, we know the ongoing stench is affecting people’s wellbeing.

We'll continue to work with Environment Canterbury and the Medical Officer of Health to monitor and report on the odours.

Read the report and analysis [PDF, 1.3 MB] of the 5 May testing.

Read the report [PDF, 210 KB] of the 12 May testing.

Southern Demolition and Salvage Ltd started work on site on Thursday 12 May. They're working six days a week, 12 hours per day, to remove the rotting material from the fire-damaged tricking filters at the Christchurch Wastewater Treatment Plant.

Work is expected to be completed within four months. This means by early September one of the main sources of stench from the plant will have been eliminated.

Read more on Newsline(external link).

The smell

Treatment plant 
The smell is coming from two sources – the trickling filters where the fire occurred and the oxidation ponds. We’re working to have both issues resolved by the coming summer.

Oxidation ponds
The fire severely damaged the trickling filters so we lost a critical part of our wastewater treatment process. As a result, poorer quality effluent is being discharged into the oxidation ponds, so the ponds began to smell. If you remember Bromley in the 1960s and 70s, that smell would be very familiar.

Immediately after the fire, we began adding hydrogen peroxide to the wastewater flowing into the oxidation ponds to maximise the oxygen saturation in the water and minimise the potential smells.

Churning additional oxygen into the wastewater is key to improving the quality of the effluent being discharged to the oxidation ponds. We have sourced aerators from different parts of the world to do this and have converted two of the plant’s four clarifiers into aeration basins using this equipment.

The equipment arrived in the country in late February, was assembled and then lifted into the basins in mid-March. The aerators were turned on in early April(external link). It will take between four and six weeks for the aeration basins to adjust and stabilise to the new treatment process. We expect the odours coming from the ponds will continue to reduce over this period.

The trickling filters

During the 1 November 2021 fire, the roofs on the trickling filters were destroyed. Immediately after the fire, the burnt plastic media housed inside the round concrete trickling filters gave off an acrid smell.

That smell largely went away but over time the material inside the filters has started to putrefy. When it rains the filter media gets wet and the organic matter trapped within the media putrefies, releasing a pungent odour until it dries.

Removing the filters
We had to carry out an extensive investigation into the fire and the damage it caused and work through an insurance claim, all of which has taken time. Other parties involved have also been carrying out their own investigations.

We needed to fully understand the damage to inform our remedial options, but our insurer has now agreed that the filter media needs to be removed regardless of whether the end result is a repair or a rebuild.

Demolishing the filters
We may end up having to demolish the filters. However, the material inside the filters is classed as a hazardous material and the concrete structures are huge – each is about three storeys high and 55 metres wide. We need to make sure that whatever we end up doing is safe for nearby residents, our contractors and the environment.

The material inside the trickling filters
The bulk of the material is a mix of plastic and biomass, which was used to help treat the sewage being processed through the plant. Some of the biomass within the tricking filters is rotting and that is causing the stench.

Removing the material from inside the trickling filters

Southern Demolition and Salvage Ltd started work on site on Thursday 12 May. They're working six days a week, 12 hours per day, to remove the rotting material from the fire-damaged tricking filters at the Christchurch Wastewater Treatment Plant. Work is expected to be completed within four months. This means by early September one of the main sources of stench from the plant will have been eliminated.

It’s a complex task as the trickling filters have 8 metre-high concrete walls and there are about 26,000 cubic metres – about the volume of 10 Olympic swimming pools – of material to remove.

The material will be loaded into sealed bins and transported to the Kate Valley landfill where it will be treated as hazardous waste.

Unfortunately, there are days when the smell could get worse as material deep inside the trickling filters gets exposed to the elements and starts rotting.

We know this is the last thing that residents want to hear, but at least we now have clear timeframes around when the removal work should be completed. By springtime, the stench from the plant should be much less of an issue.

Timeline to replace the trickling filters
It’s likely to be years before we’re able to fully rebuild or replace the trickling filters.

The fire

The cause of the fire
Investigations are ongoing into the cause and origin of the fire.  Due to the complexity of the investigation, and the fact other parties are involved, we are not in a position to share any further information at this stage.

We have been in constant communication with our insurer since the fire. The wastewater treatment plant was fully insured. Our insurer has accepted our claim but a settlement has not yet been reached. Investigations are still determining whether the trickling filters are a rebuild or a repair.


Running the wastewater treatment plant without the trickling filters
We have modified the plant so that we can bypass the trickling filters.

As mentioned earlier, we have converted two of the plant’s four clarifiers into aeration basins. Once wastewater passes through these new aeration basins, submersible pumps will push the wastewater through to the remaining two clarifier tanks.

The new system is close to being fully commissioned. The new aeration basins will not fully compensate for the treatment work that was previously undertaken by the trickling filters. However, they will greatly improve the quality of the wastewater being discharged into the oxidation ponds and the overall biological health of the ponds.

We will be closely monitoring the water quality in the ponds to assess the effectiveness of the aeration basins. If we need to, we will install more aerators in the oxidation ponds to further improve the water quality.

Work began on-site on 12 May, with site establishment and ramp construction occurring over the first four weeks.

The material from the trickling filters will be removed between weeks four and 17, with work expected to be finished by early September 2022.

Floor pad, pipe removal and back-filling of the two trickling filters will take place from weeks 14 to 27, with the entire project completed by December 2022.

Here is a timeline to remove the material from inside the trickling filters.

Timeline of key events and decisions

1 November 2021

Emergency Services respond to a fire at the Wastewater Treatment Plant in Bromley. Both of the trickling roof filters collapse.

The damage can't be assessed properly until the fire is completely out.

4 November 2021

The Council installs a sprinkler system to get rid of hot spots and help reduce the smell.

The Council also begins working on an adaptive management plan to figure out the best possible outcome for the discharge of wastewater from the plant.

26 November 2021

The fire is officially completely extinguished by the fire service.

The Council identifies the need to remove the two trickling filters. Both filters store 13,000 cubic metres of material.

The Council starts using misters and poly aluminium chloride - an odourless powder that dissolves in water - to help suppress the smell.  Poly dosing also settles more of the suspended solids in the wastewater, improving the water quality as it progresses through the plants.

Hydrogen peroxide - a  compound that naturally breaks down into water and oxygen – starts to be added to the wastewater before it’s discharged into the oxidation ponds.

6 December 2021

The Council completes a successful trial to remove a section of the fire-damaged media from the plant.

This means that the Council can begin assessing the stability of the structures.

17 December 2021

Council staff plan to convert two of the plant’s four clarifier tanks (or secondary contact) into aeration tanks.

Installing four aerators in each of the two tanks will help decrease the bad smells and improve the quality of the wastewater being discharged.

The Council anticipates that it will be years before the trickling filters can be replaced or rebuilt.

14 February 2022

Aeration components begin to arrive and we're able to implement our interim plan to minimise odours from the fire-damaged plant.

16 March 2022

Eight aerators are installed in two of the plant’s four clarifiers.

6 April 2022

The aerators installed in March are turned on.

At about the same time, increased odours from the trickling filters are detected after wet weather. It's determined that the acute stench is caused by the material inside the trickling filters rotting and drying out.

12 April 2022

The Council decides to fast-track the appointment of a contractor to remove the burnt filter material from the Bromley Wastewater Treatment Plant.

3 May 2022

Independent testing to better understand the odours from around the fire-damaged Christchurch Wastewater Treatment Plant detects small amounts of hydrogen sulphide and methyl mercaptan.

May 2022

Filter media removal work starts

September 2022

Filter media removal expected to be completed.

17 May 2022: Christchurch City Council is responding to calls from residents living close to the fire-damaged wastewater treatment plant for help to deal with the impacts of the stench.

Mayor Lianne Dalziel and Councillors received a briefing today from Council staff on discussions they have had with partner agencies on what help can be provided to the affected community as quickly as possible.

“Residents living near the plant are bearing the brunt of the stench. They have told us their power bills have gone up because they are using dehumidifiers and fans all the time because they cannot leave their windows open,’’ says Mayor Dalziel.

Read more on Newsline(external link)

We know the stench has been awful for those of you living nearby.

18 May 2022: We haven't received any interest in the free wellbeing workshops we had offered to the community, and have decided to cancel them at this time. However, should the need arise and the community wish for them to be held, we'll be more than happy to facilitate them in the future.

If you're concerned about your health, we recommend you see your GP or health provider.

If the situation is impacting your mental health, you can call or text 1737 at any time and talk to a trained counsellor for free.


Past newsletters