Tapping into organic waste potential

Who knew that dumpsters full of food scraps or date-expired edibles are a potential energy and fertiliser gold mine? Right now, most food waste goes straight into the country’s landfills but Bioenergy Association chief executive Brian Cox says the future lies with smart solutions that harness this waste for electricity generation from biogas and the production of high grade fertilisers.
As he observes, landfills are fast filling up and the cost of dumping waste is also poised to rise.
“The government has signalled that the levy for disposable waste is likely to rise and that could have a significant flow-on effect for businesses sending their food waste to landfills.”
Alternatives do exist and are already working at scale in other parts of the world. Brian cites Sydney as an example of a city that is collecting a large volume of commercial food waste and converting it into biogas using an anaerobic digester. This biogas is then being used to make electricity.
Some food waste can simply be recycled. For example, South Auckland’s EcoStock is routinely collecting date expired bread, de-packing it and then recycling the bread into animal foods.
“Of course, you can’t recycle all waste food that way – for example, you cannot feed old pies or date expired sugary chocolate to animals. EcoStock is trialing an anaerobic digester to manage all this other food waste. It goes into a big steel container and they then collect the biogas off it and use it to make electricity.
The solids that are left are pathogen free and can be used as high grade fertiliser.” Currently, EcoStock collects waste from organisations such as Foodstuffs, Progressive Enterprises and Goodman Fielder.
The company is growing rapidly and employs nearly 40 staff. If more food waste was used to generate electricity, the added bonus would be a reduction in greenhouse gas emissions. I
n fact, Brian suggests the Government should be targeting waste in the
food processing sector as a first step towards making New Zealand carbon-neutral by 2050.
“Big commercial companies producing a lot of organic food waste could explore having their own anaerobic digester to make biogas to generate electricity for on-site use or for heating water.
The alternative would be to have someone else collecting food waste from a number of companies and putting it all through a centralised facility.
“There is growing interest in this whole area and I think we will see that grow even more once the disposable waste levy goes up…Rather than paying someone to take waste away to the landfill, it could well wind up being cheaper in the long run to have it collected and made into biogas for electricity generation. Of course, this is what has happened in Sydney.”
Other countries are further down the food wasteinto-energy route than New Zealand and Brian suggests that’s partially because the cost of energy here is comparatively cheap.
“Locating your digester next to a sewage works that is already making gas makes a lot of sense because you then get economies of scale.” Melbourne’s new food waste to energy plant – ReWaste – provides a great example of what can be achieved.
Developed by Yarra Valley Water, the plant has the capacity to process around 33,000 tonnes a year of waste food and other organic waste and is sited next to a sewage treatment plant.
Effectively, the combined plants can produce enough biogas to run both sites, along with surplus energy. Similar facilities are being used successfully throughout the world, including in Europe and the United States.
It represents a real shift in focus away from treating organics as waste, instead recognising their value as a source of energy. Landfills don’t fill so fast and businesses save on dumping fees.
“Here in New Zealand, we are starting to look more in this direction – for example, Palmerston North’s wastewater treatment plant has been reconfigured to collect biogas from the waste that is then turned into electricity to power the facility.”
In fact, the city council has also laid a pipeline to extract methane gas from a closed landfill as a supplementary source of biogas.
The Bioenergy Association provides support and bioenergy information to its members and is an advocate on bioenergy related policy. More info is available online at www.bioenergy.org.nz
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