Removal work to start at wastewater treatment plant

The tricky process of removing the material housed within the two trickling filters damaged in the fire at the Christchurch Wastewater Treatment Plant will begin in early December.

The two trickling filters – the large round concrete structures at the plant – each house about 12,000 cubic metres of material that needs to be removed before a full damage assessment can be completed.

“We will be removing a small amount material in early December as a trial run of the proposed removal methodology,’’ says Christchurch City Council’s Infrastructure, Planning and Regulatory Services General Manager Jane Davis.

“The outcomes of this will help determine the best approach for removing the material and the likely timeframes for doing this work.’’

The loss of the trickling filters at the treatment plant has forced changes to the wastewater treatment process.

However, testing to date shows only a slight change in the quality of the effluent leaving the plant and it still operating within the conditions of its consent to discharge wastewater into Pegasus Bay.

“Unfortunately with the trickling filters out of action, there is an unpleasant smell coming from the plant. We want to reassure residents that we are doing everything we can to reduce the odour. However, we also need to be honest about the fact that this could remain an issue for some time,’’ Ms Davis says.

To help suppress the smell, water misters are being used and poly aluminium chloride – an odourless powder that dissolves in water – is being added at two key points in the wastewater treatment process.

This “poly dosing”’ settles more of the suspended solids in the wastewater, improving the water quality as it progress through the plants.

The first of a number of aerators is also scheduled to be installed in the oxidation ponds shortly. It’s hoped these aerators will replace the need to add hydrogen peroxide – a compound that naturally breaks down into water and oxygen – to the wastewater before it is discharged into the oxidation ponds.

“Until the full damage assessment is completed, it is not possible to say how long it will take, or how much it will cost, to replace the trickling filters,’’ Ms Davis says.