Diggers at the burnt-out Bromley wastewater plant. Photo:
New wastewater treatment plant aerators should reduce the risk of a putrid stench hanging over Christchurch's eastern suburbs for a second winter, the city council says.
Contractors hope to have installed the 16 aerators in the first of Bromley's six oxidation ponds by May, to churn more oxygen into the water and improve its biological health.
A catastrophic fire badly damaged the plant's two trickling filters in November 2021, affecting the quality of effluent flowing into the system.
Christchurch City Council Three Waters operations manager Adam Twose said tests showed the water quality was deteriorating with fewer daylight hours, but it would improve once the five disc and 11 vertical shaft aerators were in action.
"We're noticing that the amount of dissolved oxygen in there is reducing, which ties in with the sun going down...so that biological activity is starting to drop off," he said.
"Hopefully we should have these aerators in the pond before any odour does return."
The months-long stench from the burnt-out filters and ponds badly affected the health of people living nearby, who last year complained of nausea, headaches, worsening asthma and sleepless nights.
Many people in Bromley were afraid concentrations of hydrogen sulphide could again hit levels that make them feel ill.
But Twose said it was a different situation this winter.
"All the trickling filter media, which was the source of one of the odours, that's all gone. We've put the temporary activated sludge plant in, which is doing the majority of the work the trickling filters used to do," he said.
"These aerators that we're putting onto oxidation pond one are simply the belts and braces, just to make sure we've reduced the chance of generating odours as much as possible."
A fire broke out in November 2021. Photo: Screenshot / Christchurch City Council
A Fire and Emergency New Zealand investigation found the fire most likely started when contractors accidentally ignited maintenance tape or the fibreglass roof of one of the trickling tanks with a heating tool.
The report noted investigators were unable to determine exactly how the blaze broke out because the Goleman Group contractors declined to be interviewed.
The council said options for a permanent solution for the fire-damaged plant would be put to the council once insurance processes were settled, but warned that could still take months.
The council's head of Three Waters Helen Beaumont, who has been responsible for overseeing its response to the fire, and infrastructure, planning and regulatory services general manager Jane Davis were currently off work.
Chief executive Dawn Baxendale said both women were still on the council's phone and email lists, following a technical glitch that resulted in their removal from the system for a brief period.
Mary Richardson was temporarily managing Jane Davis's portfolio, while Brent Smith was stepping in for Helen Beaumont.
The mayor and councillors had been advised, Baxendale said.
Staff would not reveal the reason for their absence.