Christchurch City Council has announced the completion of a project aimed at minimising odours coming from the city’s wastewater treatment plant oxidation ponds.

The project involved the installation of 16 aerators, including 11 vertical shaft aerators and five disc aerators.

The aerators churn more than 300kg of oxygen into the pond wastewater every hour, which improves the biological health of the pond.

Operations Manager, Adam Twose, said that although some localised, temporary odours had been expected as the aerators initially disturbed the sludge build-up at the bottom of the pond, the smells had been much less than anticipated.

“The weather conditions were optimal before we turned on the aerators above the sludge blanket, and the odours were thankfully far from the worst-case scenario we had planned for,” he said.

Twose said the retention cycle for the water is three days, and they expect to start seeing an improvement in the pond’s dissolved oxygen and biological oxygen demand levels from next week. Better quality wastewater will then flow through the pond network.

“As the health of the pond improves, the minor localised smell that’s currently coming off the pond will also reduce, putting us in the best possible position to deal with odours from the pond network over the winter months,” Twose said. “The project is part of the wastewater fire recovery project, and it is expected that the aerators will ensure the ponds continue to stay healthy and function well in the longer term.”

Council had been working to address the odour issues since a fire at the wastewater treatment plant in July 2020, which damaged critical infrastructure, causing an increase in odours.