Wastewater treatment blaze extinguished after burning for 19 days
Friday, 19 November 2021
A large fire that broke out at Christchurch's wastewater treatment plant and caused significant damage has been extinguished after burning for 19 days.
A plume of thick black smoke blew across much of the city after the roofs of two buildings housing filters collapsed during the blaze on November 1, leading to a public health warning.
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.
Christchurch City Council, which owns the plant, said on Friday all surface hotspots from blaze now appear to have been put out, but water misters will continue to be used to suppress any smell.
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**
Odours from the burnt filter material and the disruption to the wastewater treatment process are expected to steadily reduce over the coming weeks.
The roofs were made of plastic, reinforced with fibreglass.
“There was a significant odour increase as a result of the fire and subsequent breakdown of parts of the treatment process,” the council’s head of three waters Helen Beaumont said.
“We’re confident the smells coming from the site will continue to decrease.”
The wastewater team subsequently made changes to the plant to compensate for the loss of trickling filters to improve the quality of the wastewater passing into the ponds and to reduce the potential for odours, she said.
Other measures included increasing aeration of the plant’s secondary tanks, adding poly aluminium chloride to the wastewater, diverting by-products of the wastewater to landfill, and adding hydrogen peroxide to the wastewater.
Poly aluminium chloride is a water treatment chemical that helps with coagulation.
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 their surface.
The fire investigation continues, and a full damage assessment will not happen until the material within the trickling filters, which is several metres deep, is removed.
Despite the damage, the wider wastewater plant in Bromley is still running. Residents do not need to change any habits, such as flushing toilets.
The council has employed an independent investigator to work with WorkSafe and Fire and Emergency NZ.
The cause of the fire remains unknown.