The Dunedin City Council looks set to delay part of the planned $74.3 million stage two upgrade to the Tahuna wastewater treatment plant.
The upgrade is to improve the quality of wastewater treatment at the plant, and the processing of solid materials generated by the wastewater treatment process.
However, council staff have recommended aspects of the plant's upgrade associated with the processing of solid materials be deferred for two years, while wastewater treatment upgrades proceed as planned.
Wastewater aspects of the upgrade needed to be in place by September 1, 2011, to meet Otago Regional Council resource consent requirements.
Council wastewater treatment manager Iain Satterthwaite, in a report to yesterday's DCC infrastructure services committee, said more consideration was needed into the best way of dealing with sludge from the Tahuna plant.
The council also needed to consider how best to handle by-products from other wastewater treatment plants and the gas generated from the Green Island landfill.
The council has been investigating using methane gas from the landfill as a power source, possibly helping power the Green Island wastewater treatment plant.
Mr Satterthwaite said deferring the Tahuna solids work for two years would give council time to consider a more "holistic" approach to treatment, beneficial reuse and disposal issues across the city.
Among the issues, the closure of the Graeme Lowe Otago fellmongery in Green Island in July had seen demand for the Green Island wastewater plant cut by half, he said.
That meant "bigger-picture" issues, such as the possibility of combining the processing of the entire city's solid waste materials at the Green Island plant, needed more consideration.
Councillors at yesterday's meeting voted to approve the decision to defer aspects of the upgrade, subject to final approval at the next full council meeting on December 14.