Damage to wastewater treatment plant still to be assessed

The city council has engaged an independent investigator to look into the cause of yesterday's Christchurch wastewater treatment plant fire - but says the extent of the damage won't be fully known until the fire in the trickling filters has been completely extinguished.

A Fire and Emergency NZ spokesman said the fire had been extinguished at about noon today. The blaze started on Monday afternoon on the roof of Trickling Filter No2 and then spread across to Trickling Filter No1. It caused thick black smoke to spread across much of the city, leading to the Canterbury DHB issuing a public health warning.

• Investigation into cause of wastewater plant fire
• Fire at Christchurch wastewater plant

Nearly 50 firefighters were working on the fire at its peak yesterday afternoon.

The blaze was brought under control about 6pm but firefighters were still on scene dampening down hotspots in Trickling Filter No2.

Christchurch City Council head of three waters and waste Helen Beaumont said the trickling filters are circular concrete structures filled with plastic media that support the micro-organisms for biological processing of the sewage.

The sewage is introduced into the filter via rotating arms, which spray the sewage across the top of the filter media. Air is forced in through the media to maintain aerobic condition and support biochemical oxidation of the sewage, releasing carbon dioxide and water.

Beaumont said, despite the damage to the trickling filters, the wastewater treatment plant can still accept the full sewage flow from the city.

That is because the trickling filters are only one stage of the treatment process.

"We have contingency plans in place for the wastewater plant and can bring back-up systems into service," Beaumont said.

"Staff are working on ways to optimise the efficiency of the functioning treatment processes so that we can compensate for bypassing the trickling filters."

Beaumont said the contractors were working on the roof completing a refurbishment project when the fire started, but the cause of the blaze is still under investigation.

"We have engaged an independent investigator and are working with both Fire and Emergency New Zealand and Worksafe to establish what happened."

Beaumont says until a full damage assessment is undertaken, it is not possible to say how long, or how much it will cost, to replace the trickling filters.

"This work will be undertaken as soon as it is safe to do.’’