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Ecogas director Andrew Fisher. Photo/Ecogas/Supplied

Energy from waste: Should we burn or 'digest' our waste?

Different approaches to converting waste to energy have differing fortunes, as Glenda Lewis explains.

Plans to build a waste-to-energy plant on the job-hungry West Coast have not gone smoothly. Buller ran the idea out of town; now Hokitika promoters are failing to sell the already politically blighted scheme to the town’s citizens. Renew Energy’s proposed $260 million plant would take train- and truckloads of general waste from a contractor in Christchurch and burn it to generate enough electricity to power the region. The company says the technology is low-emission and is used safely around the world.

“Westland, not Wasteland”, argue objectors, unimpressed by the prospect of a new industry that could involve hundreds of trucks that at present return to the West Coast empty – but would create tonnes of ash to dispose of and mar the region’s scenic image.

In Sweden, burning waste has worked well as part of an advanced integrated waste system, which has high rates of recycling. The country has matched its energy output with commercial and residential demand for heat and electricity to extract much greater efficiency from the scheme.

Read more: How the new circular bio-economy could deal with the problem of plastic

“Burning waste and getting some return from it may be preferable to badly managed, overstuffed landfills leaking chemicals and rubbish into the environment and giving off methane and carbon dioxide,” says Florian Graichen, a scientist from Rotorua-based Scion Research. But only as an interim solution.

“If you are trying to build a circular economy, burning waste is the very last resort. You first do everything you can to reuse, upcycle, recycle and redesign products to avoid waste or find renewable alternatives.

“Once you have built a multimillion-dollar waste-to-energy plant, it will be a beast with a big appetite, and that may be a strong incentive to continue on as we are, instead of investing in a proper redesign of the system.”

The Westland community has already seen the catastrophic result of an old and insecure landfill collapsing in an extreme-weather event. The type of plant proposed would burn dry waste, including plastic packaging.

A newly opened anaerobic digestion plant in England. Photo/Getty Images

At Reporoa in the Waikato, Ecogas plans an anaerobic digestor plant that will take source-separated food waste, such as orange peels, banana skins, tea bags and rotten sandwiches that cannot be diverted to food-rescue programmes or stock feed.

Paul Bennett, science leader of clean technologies at Scion, says the plant is “a fundamentally different process” to waste incineration.

The waste streams are blended to create a “feed”, which is pumped into a controlled oxygen-free tank. Inside the tanks, micro-organisms convert the waste food into biogas, which is 60% methane and 39% carbon dioxide (CO2). It is an alternative to the fossil fuel-derived natural gas comprising 90% methane and 9% CO2 that industry and households receive in the North Island.

Anaerobic digestor plants are tried-and-true technology. There are more than 2000 in Europe, including in Sweden, with many facilities more than 30 years old. Scion has helped Ecogas test and prove the technology.

The Reporoa plant is co-funded by Ecogas (created by community-owned power generator Pioneer Energy and Auckland firm Ecostock) and a $7 million loan from the Provincial Growth Fund. It will be built next to T&G Global glasshouses, which can use heat, electricity and biogas from the plant.

Ecogas director Andrew Fisher says the plant will sequester 3500 tonnes of carbon a year, the equivalent of 546ha of trees or annual planting of 218,400 trees.

Most of New Zealand’s food waste at present goes to the 134 landfills throughout the country. The company is talking to local businesses, iwi and councils about sourcing additional food waste to add to that already committed.

Fisher has spent more than two years operating a pilot anaerobic digestor plant in Wiri, Auckland, with the support of the Bio-Processing Alliance. “It has been a 12-year process to get to this point.”

He says this country needs to be open to all pathways if it is to meet its zero-carbon targets, “and it starts by piloting real-world science here in New Zealand”.

He sympathises with what proponents of the waste-to-energy plant on the West Coast are trying to achieve but thinks they’ve gone about it the wrong way.

“To date, the West Coast communities have not seen the science proven in a safe pilot-scale operation or seen the results in a local context, so community confidence has not been established. It’s not surprising that the reaction has been negative.

“As well as the lost productivity and business growth, the carbon footprint of all those empty trucks returning to the Coast remains.”

This article was first published in the October 12, 2019 issue of the New Zealand Listener.