Recycled plastics may fuel capital

06:49, Apr 10 2009

Wellington's plastics could be turned into methane gas under an ambitious plan to reduce offshore recycling and help power the city.

Human waste could provide extra fuel, with sewage sludge a possible additive to create more gas which could power 250,000 homes.

Using a process called pyrolysis, the hi-tech project could be a local answer to the problem of Wellington's plastic waste.

Wellington company SpectioNZ has been asked to do a feasibility study by Grow Wellington, Wellington City Council and Kapiti Coast District Council.

SpectioNZ co-director Mike Henare said about 20,000 tonnes of plastic went into Wellington regional landfills each year. "If you captured the energy from that plastic, you could power something like quarter of a million homes."

The process of turning plastic into gas was fully enclosed and would not generate any emissions, or leave any residue if the plastic used was clean. "If the plastic was dirty there could be a small amount of what is called pitch [left over]. It is basically harmless."

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Co-director Murray Friar said residents were "throwing energy away". "As far as plastics are concerned, and even something as unexpected as sewage sludge, the potential energy is enormous."

Pyrolysis works by heating organic material in the absence of air. As the material heats up, its carbon breaks down and it is converted into gas.

Pyrolysis plants overseas were "huge and expensive", Mr Henare said. Smaller versions were planned for New Zealand, allowing them to be located at smaller landfills and handle different types of waste.

Wellington and Kapiti councils were asked which waste they most wanted to get rid of, choosing plastic and sewage sludge respectively.

WCC sends its recycled plastic to China, but is keen to look for a local way to deal with it.

SpectioNZ was asked to do a feasibility study through Grow Wellington's centres of excellence programme. "We are very keen to support local solutions for smarter ways of doing things," project manager Steven Finlay said.

He stressed it was early days for the project. SpectioNZ will report back in three months.

The first plant would be a small demonstration model, Mr Friar said.

A one-megawatt methane gas plant opened at Wellington landfill last April, producing enough power for more than 1000 homes.

The Dominion Post