Wastewater treatment plant fire extinguished

The fire that destroyed part of the Christchurch Wastewater Treatment Plant in Bromley has finally been extinguished.

The odour from the burnt filter material and the disruption to the wastewater treatment process are expected to steadily reduce over the coming weeks following the fire that destroyed two trickling filters and parts of an air extraction system.

Christchurch City Council head of three waters and waste Helen Beaumont said on Friday all surface hotspots from the November 1 blaze appear to be out, but water misters will continue to be used to suppress any smell.

"There was a significant odour increase as a result of the fire and subsequent breakdown of parts of the treatment process," Beaumont said.  

"In response, the council’s wastewater team has made changes to the operation of the plant to compensate for the loss of the trickling filters, improve the quality of the wastewater passing into the ponds and to reduce the potential for odours.

"We’ve increased aeration in the secondary contact tanks by 200 per cent to partially undertake the work done previously by the trickling filters. We have also increased the capacity and contact time in these tanks to maximise effectiveness."

Poly aluminium chloride is also being added to the wastewater at two key points in the process.

"This ‘poly-dosing’ settles more of the suspended solids and reduces the organic loading of the supernatant wastewater - the clear liquid from the top - that now bypasses the trickling filters and goes on to the secondary contact tanks."

Beaumont said some of the biosolids, a by-product of wastewater treatment, which have been affected by the fire, had been diverted to landfill due to traces of plastic and fibreglass being present.

She said the team is also adding hydrogen peroxide - which naturally breaks down into water and oxygen - to the wastewater before it is discharged into the oxidation ponds.

The first of a number of surface aerators are scheduled to be installed in the ponds from next week, which will hopefully remove the need to keep using hydrogen peroxide.

"All of these measures have made a significant difference to the unusually high level of odour coming from the wastewater plant in the days following the fire," Beaumont said.

"We’re confident the smells coming from the site will continue to decrease."

Beaumont says the fire investigation is continuing and a full damage assessment will not be able to happen until the material within the trickling filters, which is several metres deep, has been removed.

ECan chairwoman Jenny Hughey: Air quality on par with a winter’s night after Bromley fire
Many of you will be aware of the recent fire at the wastewater treatment plant in Bromley. Some of you may even have been directly impacted by it - the smoke coming from the plant was certainly hard to miss.

While it’s a relief that no one was killed or injured, the smoke was unpleasant for many residents, particularly during the early stages of the fire.

One of the roles of the Canterbury Regional Council (Environment Canterbury) is to measure air quality. This includes measuring particulates of a particular size in the air.

On the evening of the fire, our air quality team set up a temporary air monitoring station near the location of the wastewater treatment plant to detect particulates that are small enough to be inhaled.

We compared the data from this temporary station with current and historical data collected from our permanent air monitoring stations around the city.

Although the wind changed direction several times throughout the night, our readings from late in the evening suggest that the amount of smoke was the equivalent of what we would find on an average winter night.

Another role we play in air quality is assessing the intensity and source of odours.

Air can carry all manner of unpleasant smells, with some being a real nuisance for those living or working near the source. Pinpointing the source of an odour or assessing its level of offensiveness is not always easy, however.

The best way to manage odour problems is to make sure that activities that may generate particular smells do not take place near residential areas, and that measures to mitigate the odour are put in place where appropriate.

Since the fire at the Bromley wastewater treatment plant, we have received some complaints about odour via our Smelt-It app, or directly to customer services.

Only a small number of these could be clearly identified as coming from the plant, however. This is partly because of odours that are known to come from other sources in this area at times.

Of course, the damage to the treatment plant will mean that some residents in the area will experience some odour from the plant now and again.

Residents can rest assured, however, that the Christchurch City Council is working hard to make interim changes to the plant’s operations for treating the wastewater to try to minimise any odour.