A new facility could transform 350,000 tonnes of unrecyclable rubbish into lower-carbon electricity and roading material. But the company needs to convince the public that burning waste is better than sending it to landfill.

The $350 million plant – proposed for the South Canterbury town of Waimate – would be the first of its kind in New Zealand, though the facilities are common overseas. It would produce the electricity of a small wind farm, which could reduce the amount of fossil fuels burned to generate power.

The process also creates toxic and hazardous substances that must be treated. Critics say rubbish combustion plants can undermine waste minimisation measures.

The facility – proposed by South Island Resource Recovery, a group of one national and two international organisations – would receive waste from across the South Island, board director Paul Taylor​ said.

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The intention is for recyclable materials, including plastics, metal, glass, card and paper, to be sorted out of the rubbish before it arrives at the factory. “We don’t want to compete with recyclables.”

The rest – a mix of organic matter, textiles, treated timber, industrial sludge, construction materials, commercial waste and even nappies – would be sent into the incinerator.

The heat from the fire would be used to create steam and hot water. Nearby factories could access this for cleaning and heating, potentially replacing a coal or gas boiler, Taylor said.

But most steam would push a turbine and create electricity, he added. This could reduce the load on fossil-fuelled power plants, and feed a growing appetite for electricity in cars and industry.

However, the generation would be small – providing about a quarter of the power of Genesis’ new wind farm in Taranaki. To make it economic, the plant will charge collectors to take rubbish off their hands, as landfills do.

Ash is one byproduct of the process. Carbon dioxide, from biological sources and fossil plastic, is another. This could be directed to local greenhouses to reduce their reliance on fossil fuels, Taylor said.

The most troubling substances are hazardous gases, such as carbon monoxide, and tiny particles of pollution.

Again, combusting plastic is especially problematic, releasing hazardous substances such as dioxins and mercury.

Taylor said the air from the incinerator would undergo seven steps of treatment, to remove toxic compounds. The only gas that would leave the plant was water vapour.

The water in the system would also pick up contaminants, so would be treated on site. The liquid would be returned to the system for reuse, Taylor said.

“This technology has been developed in the northern hemisphere for the past 25 to 30 years. What we are talking about here is the best available technology,” he added.

Metals would be removed from the leftover ash using magnets, and recovered. Meanwhile, the toxic substances (known as fly ash) would be treated using a special furnace, running on the power of the factory. This is heated to more than 3000 degrees Celsius, so everything becomes molten. After cooling, it would be transformed into a glass-like substance, Taylor said.

“All of those harmful or hazardous elements are tied up in that inert material.”

The solid waste could be mixed to become a base material for new roads or concrete surfaces.

The facility’s proposed location is on the state highway and near the train line between Christchurch and Dunedin. Road, and one day rail, could be used for deliveries, Taylor said.

As an alternative, landfills are not ideal. The rubbish also releases toxic substances in the liquid that flows through the waste and can leak out – though newer landfills are lined to prevent this.

Buried deep within a landfill, organic matter breaks down without air, producing the potent greenhouse gas methane. (Agriculture is the country’s biggest source of this gas.)

Some landfills capture gas and combust it, with this heat also being used to create electricity.

But independent waste expert Fraser Scott, of True North Consulting​, said some methane escapes – about 32 per cent, according to government figures, though he considers this an underestimate.

Scott said, if designed right, waste combustion systems could complement recycling and composting initiatives. Many materials could not be reused or recycled, he added. “[It] is always going to be a better solution than landfill.”

On the flip side, plastic sits in a landfill, releasing no greenhouse gas. If burnt, the material is a source of fossil carbon dioxide.

Auckland University of Technology (AUT) researcher Jeff Seadon​ said the most effective way to reduce material going to landfill would be to require manufacturers to thoughtfully design their wares – which is the aim of the Government’s product stewardship regulations.

Not all waste is equal: leftover wood from forestry could be used to replace coal in boilers.

Seadon was concerned rubbish incineration could erode waste minimisation initiatives. The country has made good progress reducing the amount of organic waste sent to landfill. Yet overseas, Seadon spotted easy-to-recycle plastics and paper being fed into these plants.

“It encourages this keep-on-wasting approach,” he added. “It is detrimental to our progress.”

Taylor said countries with the most avid recyclers – such as Germany, Austria and Belgium – had incineration facilities.

South Island Resource Recovery will pit its proposed plant against alternatives in a lifecycle analysis, to quantify the lifetime greenhouse emissions.

The waste-combustion facility has not sought resource consent. The group wants to present the idea to Waimate, including iwi and local residents, first.

“We want to make sure we are working alongside the community and making them understand this,” he added. “It is not new internationally but it is new to New Zealand.”

Convincing people of the merits – in an era of high concern about rubbish – would be vitally important, Scott said.

“Looking at many of the plants that have been built, it is the public’s opinion that causes the biggest challenge.”

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