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The North Shore could get a hydro-power station - courtesy of a new $116 million sea outfall for the city's wastewater-treatment plant.
The contents of the outfall will drop about 15 storeys from the plant at Rosedale through a tunnel under city streets, parks and homes before discharging out at sea.
"That 45m drop is quite a lot of water pressure which you could harness to generate power," said the city council's general manager of infrastructure services, Geoff Mason.
"There's a potential generation of about 250kW from investing in a little turbine plant."
It might generate up to 80 per cent of the city's power needs.
He said a report on whether the economics stacked up was being prepared and would guide any decision.
Work had started on the outfall, due for completion in 2010, but it was not too late to incorporate a turbine.
The idea raises the prospect of using the same waste for two separate power-generation processes.
Electricity is needed to pump sewage up to the plant in city sewers.
But during the treatment process, methane gas is given off - enough to supply 65 per cent of the plant's power needs, cutting bills by $45,000 a month.
