6 Apr 2023

To minimise odours over the cooler months, 16 new aerators on the Christchurch wastewater treatment plant’s oxidation ponds will begin surging to life from next week.

Operations Manager, Adam Twose, says once they’re connected, the 11 vertical shaft and five disc aerators will churn more than 300kg of oxygen into the first pond’s wastewater every hour.

“The higher levels of oxygen should improve the biological health of the pond and see better-quality wastewater then flow through the pond network,” Mr Twose says.

“Contractors will begin commissioning and testing the first aerators next week, and this process will take a couple of weeks to complete.”

Mr Twose says wastewater treatment plant staff who monitor the ponds’ biological health are recording indicators that the water quality is changing.

“While the biological oxygen demand – the loading on the ponds – hasn’t increased dramatically, the colder temperatures, rain, and reduced sunlight hours are beginning to lower the ponds’ dissolved oxygen levels.”

Mr Twose says that although the plant’s temporary treatment process continues to work well, cooler, dry weather is forecast for the next week. This could lead to less ideal natural environmental conditions for the biological health of the ponds.

“We are updating the pond health tracker on the wastewater fire recovery webpage and turning Pond 1 back to ‘red’. A ‘red’ pond means its water quality is poor and there’s a high probability that it will emit odours.

“Treatment plant staff have reported a slight increase in odour in the immediate vicinity of Pond 1, and some haze on the water surface where we know there are greater accumulations of sludge on the bottom of the pond.

“When we turn on the aerators, it’s possible there will also be some initial localised odour as this sludge is disturbed. We’ll mitigate any potential effects this has on the local community by taking weather and wind direction into account as we begin commissioning the aerators.”

For more information on the wastewater fire recovery project, visit ccc.govt.nz/wastewaterfire.