Addressing odours from the Wastewater Treatment Plant

We know the recent odour from the Christchurch Wastewater Treatment Plant is frustrating. The update below provides more detailed information on what’s been causing the odour and the steps we’re taking to address it.

Our staff are doing all they can to tweak operations at the plant when unexpected odours arise. Operating the plant in its damaged state is an ongoing challenge and we’re doing the best we can to solve problems as quickly as possible.

Our recent monitoring has shown that the odour is coming from the primary settlement tanks at the Christchurch Wastewater Treatment Plant. The tanks are one of the key processes for treating sewage as it comes into the plant. There are seven tanks, which hold incoming sewage allowing the sludge in the sewage to settle to the bottom of the tanks. The sludge then goes to the plant’s sludge digesters for treatment.

The primary settlement tanks have under-performed over the summer and have been identified as one of the main contributors of odour. We are taking measures to improve the performance of the tanks by reducing the number in service. By doing this we’re reducing the amount of time sewage is held in the tanks, which reduces the odour being emitted by them.

At the same time, we’re having conversations with suppliers of odour suppression equipment to assess whether that would help tackle any odours that arise from the tanks.

An external odour-specialist consultant is now half-way through their intensive odour monitoring survey of the plant, and site staff are using this information to make real-time operational decisions on site to try and reduce the odour.

At the temporary activated sludge plant we’re trialling the addition of another aeration lane. The trial will help us understand if increasing the amount of aeration in this phase of the process makes a difference to the performance of the temporary plant. We’ll be closely monitoring this over the course of the next month to assess any benefits.

The oxidations ponds continue to operate well. Pond #1 now has 15 of the 16 aerators back in service. One of the vertical shaft aerators is being removed and taken to the workshop for servicing, with an anticipated return date of mid-to-late-March. Staggering maintenance of the aerators is important as it improves the resilience of the plant and reduces the chance of multiple aerators being out of service at any one time. 

Hydrogen sulphide monitor results

The graph for this week shows that H2S is being detected in the Shortland Street area, and this occurs at times when the wind is coming from the treatment plant itself rather than the direction of the ponds. 

Our staff are doing all they can to reduce the odour as quickly as possible and are making changes to processes at the plant.

Currently there are no readings for the dog shelter as that meter is being used at another site.

Detections at the South New Brighton School are likely to be from sea lettuce in the estuary. We are continuing with monitoring in this area to investigate this.

Where to get help

If you need health support, we have information available on our website. This includes information on Pegasus Health's Partnership Community Workers and contact numbers for Healthline and counselling services.

Stay updated

We want everyone to be able to stay updated on our response and recovery from the treatment plant fire, and we regularly post new information and reports on ccc.govt.nz/wastewaterfire 

You're welcome to send this update to your networks. If you know someone in the community who doesn’t have email or internet access, please print this newsletter off and pass it to them.

If you know of anyone who would like to receive this e-newsletter they can subscribe online. 

If you have any questions, or would like further information on the project, please call us on 03 941 8999 or 0800 800 169 or email wastewater@ccc.govt.nz  

Thanks for your patience and understanding. We’ll be in touch again soon.