The designer of Wanganui's upgraded wastewater treatment plant is going to revisit its original concept in a bid to minimise the build-up of sludge in the settlement pond.
Sludge build-up was the problem in the plant when it was commissioned in 2007 and caused major odour problems less than five years later. It forced the Wanganui District Council to an upgrade of the plant, estimated to cost about $24 million.
But it is the on-going operational costs which have created the latest headache for council and it prompted a face-to-face meeting with designers Cardno BTO, in Wellington last Friday to find some resolution.
A peer review of wastewater treatment plant (WWTP) upgrade is at odds with the new design, with reviewers telling council they could not rely on earlier estimates of the amount of sludge that will be "digested" in the primary pond. On their estimates, the peer reviewers said the volume of sludge could make the plant unaffordable.
Yesterday Mayor Annette Main said the project team and council wastewater engineers met Cardno and both have started evaluating sludge management options for the new plant.
Ms Main said the project manager Russell Bell and engineer Arno Benadie said the meeting had been "highly productive".
She said the project team and Cardno would work to determine the viability of a number of sludge management options.
"Some of the options show real promise. However, we're all agreed that we must get this right for the community including ratepayers and commercial and industrial users of the eventual system."
She said the evaluation of each option would include looking at a number of variables in the treatment process and a report would be back before council early in the new year.
"Sludge is a by-product of all waste treatment systems and, because of our unique loads and flows, we require a solution which is unique to us but one that is also cost effective.
"Our team and Cardno understand this and I'm confident that the collective expertise and experience being applied will ensure the council has the right level of information it needs to make the right decisions," Ms Main said.
Concerns about sludge volumes at the Airport Rd plant were signalled when AECOM and CH2Beca carried out the peer review of the design. Both told the council they could not rely on those initial estimates and predicted sludge quantities would increase.
The affordability of the plant depended on its on-going operational costs and Ms Main said that was information the ratepayers and industries that discharge into the system needed to know "so they know what costs they will be faced with".
She termed this approach "completely sensible"
"I'm comfortable with that design but it's those ongoing costs. And if those costs are unaffordable, then how do we reduce them?" she told the Chronicle.