No easy solution to fixing stench

By John Maslin

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Wanganui's mayor has acknowledged that long-term options for the city's beleaguered wastewater treatment plant loom as a major issue for the Wanganui District Council.

Mayor Annette Main's comment comes on the eve of a meeting of the council's infrastructure and property committee this afternoon which will get a preliminary report into its fouled treatment system by wastewater specialists Cardno BTO.

The Wellington consulting company was commissioned last month to advise council on short-term and long-term measures to address the issues with the plant next to the city's airport.

Ms Main said said the various strategies tried so far will not deal with the root cause of the smell but were about reducing it to an acceptable level to comply with the abatement notice from Horizons Regional Council for objectionable odour.

The consultants' report on the long-term viability of the plant was still about 10 weeks away.

"The report will be independently peer reviewed by other specialists and will look at whether we should continue with the current plant and how we can make it work effectively, or whether the plant isn't viable and we need to look at alternative options," she said.

"Either way, we know that we have some major decisions and expense ahead of us but we need to ensure that we have a viable, sustainable solution for dealing with our wastewater now and into the future."

Ms Main said the community had shown huge tolerance of the problems experienced since the plant was commissioned in 2007 and recently when smells from the ponds have spread across most of the city and beyond.

She said there was an expectation that decisions will be made to ensure the ponds comply with the consent requirements and that "never again will people have to live with the level of odour that has affected the city since the plant began operating".

Committee chairman Councillor Ray Stevens said Cardno BTO's report to be tabled today said that in the medium-term, the key strategy was to improve aeration in at least the top 3metres of the main pond to reduce the stench.

"Aeration equipment is being progressively installed and other medium-term odour mitigation strategies are being investigated but are dependent on the success of the aeration strategy," Mr Stevens said.

Before the consultants were called in, council officers had tried a number of stop-gap measures. These included the bio-augmentation programme as well as building an atomiser fence to neutralise the odour.

They had also added products to the ponds to increase oxygen levels, adding doses of sodium nitrate at Beach Rd pumping station as well as turning off the floating aerators in the main pond as the machines were drawing sludge from the bottom of the pond and increasing the odour. The sludge produces the smelly hydrogen sulphide gases.

Mr Stevens said a number of other short-term measures suggested by Cardno BTO have been introduced.

These included adding hydrogen peroxide at Beach Rd to increase aeration and reduce odour when the wastewater reaches the treatment plant and applying hydrated lime to the ponds to suppress the odour and aid settlement of the sludge.

Other suggestions were for short-term odour controls.

Meanwhile, council engineers were continuing to snuff out the stench and that included dropping another 20 tonne of lime slurry into the ponds on Friday.

- Wanganui Chronicle

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