Biogas firing power plants seen as viable

17:00, Jul 11 2012

Southland's poo and waste could produce enough natural gas to fire power plants, a study has shown.

Venture Southland has been investigating waste-to-energy technology and has identified natural gas production from waste and poo as the most viable for near-term energy production.

Biodigestors installed at the Clifton wastewater treatment works capture, store and then use biogas produced through anaerobic digestion – as bacteria break down the poo, methane and hydrogen are produced.

Gas from the three digestors at the plant heats the plant's office, keeps the digestors at the right temperature and flares off excess gas.

Venture's Energy from Waste Report suggested further investment could boost production at the plant.

"The total cost of upgrading the facility could cost in the order of $3 million, but this investment could pay back within eight years," the report says.


The upgrade would enable the digestors to process waste from other sources, such as meatworks. The resulting gas could be used to generate electricity and heat, with some gas potentially bottled for domestic use.

Invercargill City Council drainage manager Malcolm Loan said the idea was being looked at but there were complications – stinky complications – not considered by the report.

"(In 2007) we had a wool scourer right next to us and we were taking their sludge. It was more than doubling the sludge load ... the holding system we had was creating odour."

However, it was worth considering the proposal in more detail, he said.

Enterprise and strategic projects manager Steve Canny said it might seem as if waste-to-energy was not important now, but as fossil fuel prices rose it would be important to have other options.

Food waste in landfill sites can also be used to produce biogas. Venture believed this was viable because it did not require the councils to change their waste transport systems.

It called for a cost-benefit analysis to look at where and how separating food and green waste from other landfill rubbish could be done.

"The most obvious opportunity to gather feedstock appears to be a small food waste-only collection in urban areas such as Invercargill city, but exploration into the economic via-bility of extending this into rural areas should also be considered," the report says.

It suggests specialist anaerobic digestors are more efficient than capturing gas from landfill sites, but utilising the existing landfills could be cheaper. Anaerobic digestion of farm waste was a possibility – and this could reduce pollution of water, use of fertilisers and carbon emissions.

Mr Loan said the landfill generation was another area to be looked at.

"The report is preliminary and it is raising some issues that might require further [investigation]," he said.

The Southland Times