Agricultural waste an un-tapped source of energy

Denmark, with a similar population to New Zealand, has replaced nearly 40 percent of their natural gas supply with biogas generated from organic waste, and have plans to get this to 100 percent by 2034.

The Swedes are also investing heavily in producing biogas from agricultural and other organic waste, with new biogas plants being built to use farm manure as the main feedstock – the daily manure produced by just 15 cows is enough to power the average house for a day.

Waste from agricultural processing such as abattoirs is another source of biogas. The Australians are also tapping into the opportunity with around 240 biogas plants already operating, with at least one plant using waste from an abattoir.

Food scraps are already being processed at New Zealand’s only utility scale biogas plant, readying our country for the first pipeline-ready biomethane to be injected into our gas network thanks to a collaboration between Ecogas and Firstgas Group.

Beyond food waste, New Zealand could also look to cow manure as a feedstock to produce biogas.

The Wood Beca report, released with the Government’s gas transition papers, estimates that New Zealand has enough accessible and economic organic feedstock to replace around 7 PJ of gas up to 2035, which is equivalent to nearly all commercial (excluding industrial) or all residential natural gas use in New Zealand today.

Developing these sources of biogas will lead to material reductions in NZ’s carbon emissions by diverting these waste streams from farms, landfills and other emitting facilities.

As well as producing energy that would otherwise go to waste, the process would also go a fair way to mitigate the environmental issues around effluent run-off on dairy farms and divert food scrap waste from going into landfills or worse.

The outputs from collecting and fermenting organic waste in anaerobic digesters are not limited just to biogas either – the CO2 produced during the process as part of the natural carbon cycle can be harnessed for use in other manufacturing industries, further reducing fossil-fuel use.

Nitrogen-rich fertiliser is also produced as part of the process, and this can be returned to the land – completing the waste management cycle. A real example of the circular economy in action.

There are problems in collecting manure in New Zealand. For example, unlike in Europe and many other countries, much of our livestock is free range rather than housed in barns. However chief executive of GasNZ, Janet Carson, says this should not be insurmountable.

“With the development of a renewable market and infrastructure around biogas, gas is more than a transition fuel, it is a fuel in transition. We just need to harness its potential and that includes looking for the energy in waste, wherever that waste might be.”

She says that the food waste feedstock is currently more accessible than manure and Māori would have a view on how gas made from “that sort of waste” was best utilised.

Nonetheless, she says the main point is that organic waste is abundant and it can collected and utilised. “With a focus on the biogas opportunity it is very possible that we can find a way to realise its potential.”