16 Mar 2022

Christchurch City Council staff are installing eight aerators at the fire-damaged wastewater treatment plant as part of the mid-term recovery plan to reduce unpleasant smells.

A crane has lifted the 75kw aerators into two clarifier tanks that have been converted into aeration basins.

Infrastructure, Planning and Regulatory Services General Manager Jane Davis says having the aerators pump more oxygen into the wastewater is expected to gradually decrease the odours and improve the wastewater quality before it enters the oxidation ponds.

“We expect to have the aerators functional in the next two-to-three weeks. We’ll undertake some testing to ensure the modifications are working satisfactorily, then bring the plant’s changes online by the end of April,” Ms Davis says.

“It’s likely to take a number of weeks for the biology of the plant to fully adjust to the altered treatment process.”

“It’s important to note that while we expect these works will reduce the smells, odours aren’t likely to reduce to pre-fire levels until a permanent solution has been put in place.”

Once the current clarifier conversion project is completed, staff will finalise continue with the detailed design to provide additional aeration into the oxidation ponds.

In the meantime, Ms Davis says poly aluminium chloride will continue to be added to the wastewater at two key points in the process.

This ‘poly-dosing’ settles more of the suspended solids and reduces the organic loading of the supernatant wastewater - the clear liquid from the top - that now bypasses the trickling filters and goes on to the secondary contact tanks.

The team is also adding hydrogen peroxide – a compound that naturally breaks down into water and oxygen – to the wastewater before it’s discharged into the oxidation ponds.

For more information and updates on the recovery from the wastewater treatment plant fire, visit ccc.govt.nz/wastewaterfire.