The Christchurch City Council has said the smell from the Christchurch Wastewater Treatment Plant could last for months.

It follows the fire on the 1st of November which damaged two big trickling filters at the wastewater treatment plant.

The council said because they are now unable to use the trickling filters, they have had to make modifications to the wastewater treatment process.

“The wastewater entering the oxidation ponds isn’t as thoroughly treated as it was before the fire – there are more solids and organic material in the ponds – so we are getting more odour issues.”

“During and after the fire, wastewater was flushed through the trickling filters to help put out hot spots and any smouldering areas. At a result, a lot of soot and a much reduced level of dissolved oxygen flowed through into the second half of the treatment process, harming the treatment biomass.” 

In a statement, the council said “unfortunately the smell could last for some time. It could take several months for the biomass to regrow. Until the treatment biomass is healthy again, odours will occur. We have been using water misters to help suppress the smell from the material in the trickling filters. We have also been adding poly aluminium chloride – an odourless powder that dissolves in water – at two key points in the wastewater treatment process. This ‘poly dosing’ settles more of the suspended solids in the wastewater, improving the quality of the wastewater as it progresses through the plant.”

“We are dosing the oxidation ponds with hydrogen peroxide and installing a number of aerators to help increase the oxygen levels in the ponds. The aerators will improve the quality of the wastewater in the ponds and reduce the smell.”

The council said while the smell from the plant may be unpleasant, there is no evidence to suggest that it is harmful. “

Multiple investigations are under way into the cause of the fire.