Councillors at yesterday's extraordinary council meeting voted almost unanimously to approve "option A" for the upgrade, following a recommendation from the council's infrastructure services committee last week.
The upgrade would see new secondary treatment systems - including ultraviolet (UV) light disinfection, digestion systems and drying techniques - installed at the city's Tahuna wastewater plant.
Only Cr Teresa Stevenson abstained from voting yesterday, saying it was "naive" to think sludge from the plant - which was to be dumped at the Green Island landfill unless alternative uses were confirmed - would not have an environmental impact.
She also believed there had been a lack of community consultation over the upgrade, given option A was to cost $7.1 million more than the $67.2 million budget.
However, Cr Andrew Noone said the additional capital costs needed would be offset by reduced annual operating costs over the life of the plant.
The operating budget was reduced to $3.7 million each year, down from $5.7 million.
Cr Colin Weatherall said yesterday's vote was a "significant milestone" that demonstrated the council's continuing commitment to improving core facilities, while Cr Neil Collins said there had been "plenty of consultation".
Cr Richard Walls was pleased to see the project's progress, as he recalled being unable to swim at Tomahawk Beach as a boy, due to pollution in the area.
He believed the new system would help further reduce bacteria counts, even after the commissioning of the city's new $37 million, 1.1km outfall pipe in January, credited with dramatically improving water quality in the area.
Earlier this month, Tahuna upgrade project manager Brian Turner told the Otago Daily Times the upgrade was needed to ensure the council continued to meet consent requirements for the operation of the Tahuna plant.
Existing Otago Regional Council consents said the practice of using chlorination to disinfect wastewater discharges had to cease by September 1, 2011, as the practice could threaten sea life and the environment, Mr Turner said.
Construction was expected to begin early next year, and once operational, the plant would produce about 4.2 tonnes of dried solid waste each day.
The material could be recycled, if secondary uses such as on golf courses or as a landfill cover could be identified.
Alternatively, it would be burnt at the Tahuna plant, or dumped in landfill pits, as happened now, Mr Turner said.
