What's being done about the foul odour at the fire-damaged wastewater plant?

Christchurch City Council staff are putting a number of measures in place in a bid to reduce the foul odour wafting from the fire-damaged Christchurch wastewater treatment plant.

The fire on November 1 last year destroyed two trickling filters at the Bromley plant, and led to nearby residents being evacuated and a public health warning over the smoke.

Since then, unpleasant smells have been wafting across parts of the city, especially to the west of the plant during the easterly wind.

The Christchurch wastewater treatment plant. Photo: Newsline
The Christchurch wastewater treatment plant. Photo: Newsline
Council head of three waters Helen Beaumont said the on-site team has been implementing measures to reduce the odour.

They are adding polymer dosing to the primary sedimentation tanks to reduce the organic loading on the oxidation ponds, she said.

"Polymer dosing helps to ensure that we divert between 65 and 70 per cent of solids to the digesters, which eases the pressure on ponds," Beaumont said.

"Dissolved oxygen level is one of the fastest indicators of pond health and we’re monitoring these levels daily and adjusting the wastewater flow paths to make sure the effluent is spread out across the ponds.

"This improves water quality, reduces the odour and minimises the sludge rising to the surface.

"When surface sludge appears on the ponds, we use a boat to quickly break it up," Beaumont said.

The city council has also borrowed two aerators to use on the oxidation ponds, which are being serviced and are planned to be installed later this month.

"These will help to aerate the ponds and prevent surface sludge, which in turn will reduce the odour," said Beaumont.

In the meantime, the damage assessment of the two trickling filters that were at the centre of the fire is still being done.

Beaumont said until this assessment is completed, it’s not known if the concrete housing can be repaired and the trickling filter media replaced.

She said if the concrete housing is badly damaged, the council will look at options for rebuilding the trickling filters alongside alternative technology.

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