Council not yet able to assess damage after wastewater treatment plant blaze
Tuesday, 2 November 2021
Engineers are scrambling to figure out the best way to keep adequately processing Christchurch’s wastewater after losing use of two large filters in an extensive fire.
The large blaze began just after 3pm on Monday and destroyed the roofs of two buildings that are part of the Bromley wastewater treatment plant, owned by the city council.
Each building housed a trickling filter, one part of the complex wastewater treatment process.
The fire was put out early on Tuesday, and investigators are now combing the wreckage to determine how it started.
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Council engineers have not yet been able to assess the damage, but hope to get inside on Wednesday.
The two filters at the centre of the blaze are now being bypassed, and council engineers are working to find the best method for optimising and treating wastewater before it reaches the ocean outfall.
“That's where it enters the environment, so it’s about optimising everything before that point of discharge,” council water boss Helen Beaumont told Stuff.
Beaumont was uncertain about the current quality of the wastewater being discharged, but hoped to have more details about the plan to optimise effluent “in a few days”.
The two damaged filters were a “significant” part of the treatment process, she said.
Beaumont said the rest of the Bromley plant was back operating and people did not need to worry about not being able to flush toilets.
Residents were evacuated and health officials issued a public health warning when the fire broke out. On Tuesday officials warned the “strong smell” may linger for some time.
Contractors were refurbishing the roof of one of the filter buildings, and had been doing so for a number of weeks, when the fire broke out.
At its peak almost 50 firefighters fought the flames, which sent a huge plume of black smoke across the city.
Beaumont said the smoke was caused by the material of the destroyed roofs – plastic reinforced with fibreglass.
She said firefighters reported the roof of one filter building had collapsed and burnt away completely, while the second building’s roof had fallen in, though its centre remained intact.
She was not yet sure if the buildings would have to be demolished.
“Certainly the roof structure is completely destroyed and the rotating arms within the trickling filters will be severely damaged, and I doubt we can repair those,” Beaumont said.
The big question for the council was whether the filter’s large concrete enclosure was structurally compromised, she said.
Beaumont said it was not possible to say how long, or how much it would cost, to replace the trickling filters until a full damage assessment could be undertaken.
Trickling filters are part of the wastewater treatment process. Water from sedimentation tanks is pumped up to the top of the filters where it is evenly spread over the surface of the filters.
“They are a large and important part … so we will have to do a bit of work to optimise other parts of that [treatment] process to ensure that we get a good quality effluent,” Beaumont said.
The council has employed an independent investigator to work with Fire and Emergency NZ and WorkSafe to establish what happened.
Beaumont did not wish to comment on who, if anyone, was at fault for the blaze.
Professor Mark Milke, from the University of Canterbury’s civil and natural resources engineering department, said more of the wastewater would likely now go through aerated tanks at the Bromley plant.
He said the tanks and the trickling filters essentially do a similar job, but in a different way.
Milke said with the loss of the trickling filters, there were fewer backup systems for the plant to rely on.
“So if something else goes wrong, then they are going to start getting some issues,” he said.