Your wastewater treatment plant fire questions answered

Activated sludge reactor

We're replacing the fire-damaged trickling filters with an activated sludge reactor. Once it's up-and-running it will fix long-standing odour issues impacting local residents.

One of the benefits of a conventional activated sludge reactor does not require separate odour treatment because it produces no odour.   

The odour from interim operations 

We know how distressing the fire and subsequent stench have been for the community – that’s why settling the insurance claim as quickly as possible has been a top priority.  

The Council has a number of projects underway to improve interim operations and will continue weekly monitoring of hydrogen sulphide levels in the area around the plant. 

Keeping the plant running in its damaged state is challenging and there will always be an element of unpredictability, but our team is experienced and quick to respond to whatever is thrown at them. 

The smell originally came from two sources – the now-emptied trickling filters where the fire occurred and the oxidation ponds. 

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 was 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.

Churning additional oxygen into the wastewater is key to improving the quality of the water within the oxidation ponds. In May 2023 we completed the installation of the 16 aerators to provide this oxygen.

We've also installed the temporary activated sludge plate that provides the wastewater to the ponds.

Air-quality testing

Since April 2022, we’ve taken weekly samples from multiple sites, both at the plant and in the neighbourhood.  We also added extra sample locations based on the wind direction. 

 This work clearly identified reduced sulphur compounds (RSC) as the main cause of the odours. RSC are a complex group of substances that have a strong odour, even in low amounts. The monitoring found extremely odorous compounds, such as methyl mercaptan and hydrogen sulphide, present in varying concentrations, depending on the weather and wind direction.  

We installed hydrogen sulphide meters for deployment around the Wastewater Treatment Plant site and across the neighbouring residential areas. Now that we have these meters in place we will have a much better understanding of the different types and levels of odours that people are being exposed to over time.

We continue to publish the hydrogen sulphide results weekly on this website.

The fire 

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. 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. 

New solution approved 

The Council has decided to demolish the trickling filters and instead build a conventional activated sludge reactor.  As part of the long-term plan, we will upgrade our solids treatment processes to create a more resilient and sustainable wastewater operation that can adapt to future demands and challenges. 

How it works

In a conventional activated sludge reactor, wastewater enters an aerated tank where microorganisms flourish and oxidize organic matter. This treatment method efficiently removes organic pollutants and achieves regulatory compliance without needing additional treatment, which is required through the trickling filter process.

The fire-damaged trickling filters are more than 50 years old, and this technology is no longer the best solution for treating wastewater. They’re less adaptable to changes and don’t provide as many opportunities to improve environmental outcomes in the future. 

Timeline and cost 

Design work is underway and it’s expected to take up to three years to complete the design and construction of the new activated sludge reactors. The current estimated cost is $140 million, which will likely be refined following a detailed design. Funding is included in the Long Term Plan so there will be no impact on rates. 

We're well underway with the design of the activated sludge reactor and will look to engage a contractor to assist with further design so we can start construction as soon as possible. The estimated timeframe for design and construction is up to three years.  

Benefits 

Activated sludge reactors are a common and well-known treatment process worldwide and in New Zealand.

Replacing the trickling filters with an activated sludge reactor will give the Council the opportunity to significantly reduce greenhouse gas emissions. Additionally, activated sludge reactors have a smaller footprint that can be upsized in future to accommodate the needs of our growing population. 

One of the benefits of a conventional activated sludge reactor is that it doesn't require separate odour treatment because it produces no odour.

Returning to a fully operational treatment plant will have significant environmental benefits and will have a positive impact on the oxidation ponds.

The greenhouse gas emissions from an activated sludge treatment plant could be significantly reduced because of the high degree of process control that would be available to minimise the formation of nitrous oxide (N2O) in the treatment process.     

Because an activated sludge reactor can be expanded for growth and adjusted to improve environmental outcomes it also provides more resilience.  

Keeping things going while we build the sludge reactor

Until the new activated sludge plant is up and running we have modified the plant so that we can bypass the trickling filters. We can build the activated sludge reactor without disrupting current operations.

In the meantime, we’re working hard to keep the damaged plant operating with minimal odour and will keep the community updated on progress.  

How the temporary wastewater treatment plant operates 

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 now 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 are closely monitoring the water quality in the ponds to assess the effectiveness of the aeration basins.  We have installed 16 aerators on oxidation pond 1, to improve the water quality.

This temporary system is based on what we could swiftly implement. It maximises our ability to treat wastewater while using some of the existing infrastructure at the plant to deliver the best possible chance of success using proven technology.

However, it is a highly lean, temporary system that's doing the job of a $100m trickling filter treatment process. It's operating near its operational limit. 

Pegasus Health community workers

Pegasus Health's Partnership Community Workers (PCWs) are a team of health navigators providing people with free access to health and wellbeing support.  

The PCWs supporting Bromley and Eastern suburb residents with their health concerns are linked to General Practice Teams in the local area.

 PCWs can help residents near the wastewater treatment plant to:

• Enrol with a GP and help them attend health appointments.
• Assist with any difficulties that arise in getting the health support residents need.
• Provide information about health and social services available in the community.
• Provide cultural support and links with interpreter services.

 For further information about the PCW service please contact Pegasus Health on 03 379 1739 from 9am to 5pm on weekdays.

Where to get help

• Pegasus Health(external link)(external link) has a team of partnership community workers in the area who can support people to access health and wellbeing support free of charge. If you have difficulty accessing a family doctor or healthcare provider, phone Pegasus Health on 03 379 1739 from 9am to 5pm on weekdays.
• Your family doctor or healthcare provider can provide support for any health or well-being concerns you have.
• Healthline(external link)(external link) provides free health advice and information – phone 0800 611 116 at all times.
• 1737(external link)(external link) provides free counselling support for Kiwis – phone 1737 at all times.

The insurance settlement 

The insurance settlement is for $85 million. The difference between the settlement and the cost to build the activated sludge reactor has been allowed for the Council’s Long-Term Plan. 

Immediately following the fire, we made a claim under the insurance policy, which entitles the Council to the costs to fix damage caused by the fire, and also some of the costs to operate the wastewater treatment plant while we fix the damage. 

The Council and the insurer had to go through a process to determine the exact extent of the damage and agree upon a methodology, design and associated cost for repair.  

At the same time, we did work to assess the long-term future of the plant. The Council considered other permanent options for secondary wastewater treatment, including an activated sludge reactor. 

Based on the work carried out to assess the damage and design a repair, Council has been able to negotiate a settlement with our insurer which gives us the ability to implement the best permanent solution.