Burning best in meantime

The Tahuna waste treatment plant. Photo by Gerard O'Brien.
The Tahuna waste treatment plant. Photo by Gerard O'Brien.
The incinerator at the Tahuna waste treatment plant in Dunedin will burn 24 hours a day, seven days a week from September this year, and will do so for the next two years.

The city council agreed to that option, while water and waste staff wait for new technology with better environmental outcomes to be tested in other areas.

The need to get rid of extra sludge will start when the first stage of the Tahuna liquid stream process upgrade is completed in September, part of work on secondary treatment.

Cr Jinty MacTavish raised concerns about the issue at annual plan deliberations, asking what the effect would be on the amount of carbon being put into the atmosphere.

Water and waste services manager John Mackie said it was not the best option in that respect, but it did make the most of existing infrastructure.

It allowed time for an alternative that would deal properly with the issue.

"It's a global issue," he said.

"We're struggling with the best use for human bio-solids.

"There are risks with putting it on land, there are all sorts of things to address."

Mr Mackie said the world was on the cusp of developing new technologies, something that had been pushed along by carbon credit money.

"Two years is ample to get a robust option without being the first to take on that technology."

Asked if it might take longer than two years, he said consent for burning the sludge at Tahuna would run out in July 2013, and that was a deadline.

However, a report on the issue from solid waste manager Ian Featherston noted an option of extending the consent and deferring adoption of alternative technology.

Not all the sludge could be burned at Tahuna, so some would go to sludge digesters at the council's Green Island waste facility, where electricity could be generated from the process.

The remainder would go to landfill.

Asked about a "build, own and operate" possibility, under which a company would build a plant and deal with the waste, Mr Mackie said that was a possibility.

He wanted $16.4 million left in the budget in the meantime for a plant, in case that did not go ahead.

- david.loughrey@odt.co.nz

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