Council's 'medium-term solution' for stink from fire-ravaged wastewater plant

Friday, 17 December 2021

The roof on each of these two filters collapsed in the November 1 fire.

Two existing tanks at Christchurch's wastewater treatment plant will be modified to create what the city council describes as a “medium-term solution” for the unpleasant smell.

A large fire destroyed two trickling filters at the Bromley wastewater plant on November 1.

The filters played a crucial role in the wastewater process and unpleasant smells have been wafting across parts of the city since the fire.

Christchurch City Council head of three waters and waste Helen Beaumont said aerators would be installed in two tanks currently used at a different stage of the treatment process.

Christchurch City Council has released drone footage of the fire damage to two filter buildings at the Bromley wastewater treatment plant.

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Drone footage of the damaged trickling filters, a few days after the blaze.

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Aerators could pump more oxygen into the wastewater, which would help decrease unpleasant smells and improve the wastewater quality before it reaches the oxidation ponds, she said.

Christchurch City Council head of three waters and waste Helen Beaumont says the modifications to the wastewater plant will likely stay in place for two to four years.

“This work-around should provide most of the treatment capacity that we’ve lost.”

Four aerators would be installed in each of the two tanks, lifted by cranes. The council would need another 600-kilowatt power supply to power the new aerators too.

The work was expected to be completed by March 2022, Beaumont said. The modifications were expected to stay in place for two to four years.

It is not clear how much the modification would cost as a detailed design of the changes was still ongoing.

Smoke from the November 1 fire at the Bromley wastewater treatment plant fire.

Beaumont said converting the existing tanks was considerably less costly than building new tanks with aerators.

A tank with an aerator works by injecting air bubbles into the bottom. The air allows slime solids to form larger solids. The larger solids are then taken to another stage of treatment, where they become biosolids and biogas.

The wastewater that does not solidify in these two processes flows out to the oxidation ponds.

Beaumont said the new aerators would be a “medium-term solution” while a more permanent solution for repairing or rebuilding the destroyed trickling filters was looked at.

A full damage assessment of the structures housing the filters has begun.

The council would also install more aeration pumps at the oxidation ponds to help address the smell.

Three of these pumps had already been sourced and one was already operating. All three have been loaned by other councils.

Beaumont said the council needed another 10 pumps – and it intended to find new ones to replace those on loan.

She said it could take until September 2022 to find and install the necessary pumps.

Wastewater entering the oxidation ponds since the fire had not been as thoroughly treated as normal.

More solids and organic material was entering the ponds, leading to the smell.

The council was already adding hydrogen peroxide and poly aluminium chloride to the wastewater in a bid to improve its quality.

Previous monitoring had shown the quality of water being pumped into the ocean continued to meet consent conditions.

People living west of the plant are most affected by the smell, because of the prevailing easterly wind.

On still days or when there is a slight breeze, those living on the Southshore spit also experience the unpleasant smell.