Inspection to factor in odour

Christchurch’s council is trying to figure out how to inspect its firedamaged wastewater filters without making odour problems worse for residents.

On November 1, trickling filters at the Bromley wastewater plant were burned in a fire which spread thick, black smoke across the city.

The blaze led to residents being evacuated, and a public health warning, as both filter roofs collapsed.

Jane Davis, the city council’s manager of infrastructure, planning and regulatory services, said it would remove a small amount of material from the filters in early December as a trial.

‘‘The outcome of this will help determine the best approach to removing the material and the likely timelines,’’ Davis said.

Council’s approach would need to ‘‘consider the wider impact on the community’’ as removing the material could make odours worse, she said.

‘‘The trickling filters have been inspected from the air and externally, but we will be unable to do a full inspection of the interior of the structures until the filtering material has been removed.’’

The council has received a few formal complaints about the smell. It has also been made aware of community concern through social media and complaints through Environment Canterbury’s ‘‘Smelt It’’ app.

‘‘Unfortunately, the fire has removed an important step in our wastewater treatment process. As a result we are getting increased odour from the plant and this is likely to continue,’’ Davis said.

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.

Bacterial slime grown inside the filters consumes the nutrients in the wastewater. As more flow is pumped into the filters, the slime is washed off as a floating solid.