Zero waste groups challenge biogas report claims

close up of cows

A group of zero waste and regenerative horticulture advocates are challenging a recent report on the potential of biogas production for New Zealand.

The group is concerned that the report advocates major investment in an organic waste processing technology that risks locking-in current industrial agricultural practices that harm New Zealand’s soils and waterways, contribute to climate change and incur an opportunity cost for adopting regenerative farming practices.

The report, Biogas and Biomethane in NZ – Unlocking New Zealand’s Renewable Natural Gas Potential, was co-produced by Firstgas Group, Beca and Fonterra, and part-funded by the government’s Energy Efficiency and Conservation Authority (EECA). 

The report discusses a technology called anaerobic digestion (AD) that turns organic waste into biogas, to be used for energy and fuel, and digestate, which can be used as a fertiliser.

“The biogas report makes various claims about the ‘green’ credentials of AD and its by-products,” says Liam Prince of The Rubbish Trip. “But these benefits are largely assessed against the unsustainable status quo we have now, rather than other practices that could potentially provide far greater emissions reductions and environmental benefits.”

The report barely considers the downsides of this technology, and makes no substantial comparisons with other approaches to reducing, diverting and processing organic waste. 

“Rather than investing in techno-fixes to make the immediate problem of food waste ‘go away’, we should be focusing on preventing and reducing food waste in the first place – especially as roughly 8% of global emissions* come from food loss and waste,” says Dorte Wray of the Zero Waste Network.

“We need to take a strategic, holistic approach to food waste to provide guidance for all sectors across the food system. It must also be cohesive with te ao Māori and Te Tiriti obligations, as well as action on other issues including climate, freshwater quality, waste reduction, resilience, and the health and wellbeing of soils, food systems and communities,” Dorte Wray continues.

“The NZ biogas report doesn’t analyse unintended consequences of AD that can undermine its benefits. These include things like possible ‘fugitive’ emissions from the various gas treatment processes and the handling and storage of feedstocks and digestate, and operational emissions from things like trucking feedstocks – not to mention that the system involves burning gas, which emits carbon into the atmosphere,” says Liam Prince.

A 2020 study called Bad Energy: Defining the true role of biogas in a net zero future by UK-based group Feedback showed that investment in AD is often less effective than other renewable energy technologies at abating greenhouse gas emissions. The study also showed that AD can disincentivise initiatives aimed at reducing waste at source, which would result in far greater emissions reductions than AD would offset in a business-as-usual scenario.

The NZ biogas report also deals with the potential role of digestate in NZ’s agricultural sector, and indicates that the economic viability of AD relies on a strong market for digestate.

“The proposition that nitrogen-rich digestate be used at scale as a fertiliser demonstrates the presumption underlying this report that current destructive industrial agricultural practices will continue. But these practices are degrading our soils, polluting our waterways, contaminating drinking water, and contributing to climate change,” says Liam Prince. 

The report acknowledges that the capital investment required for AD and related infrastructure is significant – from the digesters themselves, to the various gas and digestate treatment and processing facilities.

“There is a real risk that investing heavily in AD will lock NZ into this technology, shutting out other options and possibly leaving us with stranded assets in future. This risk is only amplified by the fact that the report’s best-case-scenario models are conditional on AD being favoured as the ‘frontrunner’ in policy settings, over and above other organic waste processing options such as composting,” says Kate Walmsley of Kaicycle.

“We recognise that AD may have a role to play in diverting organic waste from landfill, but the approach this report takes lacks nuance and context – we shouldn’t treat AD as a catch-all, silver bullet when, in most cases, better alternatives exist,” says Liam Prince.

“Ultimately, preventing and reducing waste and pollution at source – which includes redesigning, regulating and phasing out harmful industrial food production processes – should be the highest priority. With organic waste we can’t avoid, we should prioritise localised organics and composting systems that reduce emissions by minimising transport requirements and by using techniques that retain and sequester more carbon in compost and soil rather than emitting it. These techniques also produce high-quality ‘living’ compost that’s rich in microbial biodiversity,” says Kate Walmsley. 

A recent report by the International Solid Waste Association comparing the benefits of compost and digestate concluded that ample evidence exists for the positive long-term effects of compost on soil health, in terms of soil organic matter content, structure, microbial activity, and carbon sequestration, but that such benefits have not yet been demonstrated scientifically for digestate. 

“Many farmers are exploring regenerative practices that restore and maintain long-term soil health. These include swapping out nitrogen-heavy fertilisers for microbial-rich compost to help restore the natural capacity of soil systems to provide plant-available nutrients”, says Sarah Smuts-Kennedy of For the Love of Bees

“We are already seeing pressure on access to good quality compost as the commercial sectors transition. AD will compete with the resources required to produce compost, making it either very expensive or unavailable at the scale required to support a national transition to regenerative farming,” says Sarah Smuts-Kennedy.

When assessing climate change solutions, these wider implications need to be fully understood. Investments at this critical point of transition to a circular, low-carbon economy need to serve holistic outcomes.”


Supported by:

Zero Waste Network

The Rubbish Trip

For the Love of Bees

Urban Farmers Alliance


Go Well Consulting

Community Compost, Nelson

Para Kore


Bailey Peryman, PhD Scholar (Food Systems)

The CarbonCycle Company

Mauri Ora Consulting – Waste Minimisation Educator and Consultant


*For this 8% figure, see the UN Food and Agriculture Organization’s fact sheet: Food wastage footprint and climate change available here: