AD or not AD: what’s the role of biogas in a net zero future?
This post is by Martin Bowman, senior policy and campaigns manager at Feedback.
Anaerobic digestion, or AD, the process of producing ‘biogas’ from organic matter like crops and food wastes, has been presented as the silver bullet to many of the UK’s environmental woes. It promises to do everything from producing green gas for heating and biofuels to providing greener fertiliser for our crops. A recent AD industry conference was boldly titled ‘There’s no net zero without biogas’. The industry is hungry for growth, aiming to build over 100 AD plants per year and, because AD is economically unviable without subsidies, the industry wants the government to pay out millions more to support its ambitions.
AD looks appealing when compared with undesirable alternatives, like food left to rot in landfill, uncovered manures belching methane and oil burnt for fuel. Almost all previous studies have focused on these comparisons. However, to avoid the climate crisis, we need to imagine the most ambitious path we can to a better future and throw everything we have at making it a reality, using the best available evidence as our guide.
Going for AD risks crowding out better options
So Feedback set out to investigate the role AD has to play in an optimal net zero future, collaborating with researchers at Bangor University on a comprehensive Life Cycle Assessment. Our new report, based on this research, found that, at best, AD is often sub-optimal and, whilst it does have some role to play, it needs to be kept to its ‘sustainable niche’ to avoid crowding out better alternatives. The results suggest we may want to consider how quickly we can electrify heat and transport as a priority, to wean ourselves off a reliance on gas as much as possible.
Bioenergy crops, like maize and grass, are currently the most controversial feedstock processed by AD plants. The Soil Association has previously highlighted that 75 per cent of sites with late harvested maize used for AD showed high or severe levels of soil erosion. Our report shows that there are far better uses of land than bioenergy crops from almost every perspective. We found that solar PV generates 12–18 times more energy per hectare than maize or grass grown for AD. Alternatively, the land the industry aspires to use for maize could instead be used to grow enough peas to feed 1 million people per year, grown in rotation this is much better for soils. And planting trees saves 11.5 times more emissions per hectare than growing grass as a bioenergy crop. Subsidies to AD would, therefore, be far better spent on alternatives.
AD may divert food waste from human or animal consumption
Previously, waste-based AD feedstocks have been considered fairly uncontroversial. However, here too, Feedback’s report indicates there are causes for concern. We found that preventing food waste results in direct emissions savings over nine times higher than sending it to AD. The savings are about 40 times higher when trees are planted on the spared grassland from food waste prevention. Three times more emissions are saved by using food waste for animal feed rather than for AD. This accords with the government’s current Food and Drink Waste Hierarchy but, worryingly, we found evidence that imbalanced support for AD may be diverting perfectly edible food away from human and animal consumption.
Public money is currently poured into subsidising AD plants, while preventing food waste is mostly neglected and left to voluntary action by businesses. Halving UK food waste through ambitious regulation, with afforestation on the three million hectares of grassland spared, would save and offset an astonishing 11.3 per cent of the UK’s current total greenhouse gas emissions. This would also release enough cropland to feed 28 per cent of the UK population. The grassland spared mainly comes from avoided beef, lamb and dairy waste, and the cropland spared mainly comes from other types of avoided waste food (including avoided animal feed). It is important to note that some of this grassland and cropland would be spared overseas, as a result of avoiding waste of imported food, so some of the tree planting and food production possible on this spared land would occur overseas. This is a huge opportunity but voluntary measures are currently on track to achieve less than half of the potential emissions savings.
Regulation should be raising ambition and levelling the playing field. For instance, it should be mandatory for large UK food businesses to report their food waste and participate in commitments to reduce it, alongside binding targets to halve UK food waste, and increasing taxes on landfill and incineration.
AD risks perpetuating or even expanding intensive livestock farming
Finally, AD has been seen by the livestock industry as a panacea for its colossal manure and slurry problem, promising to capturing methane and produce bio-fertilizer. However, Feedback’s analysis shows that highly subsidised AD has been explicitly used in Northern Ireland to facilitate the explosive growth in the intensive livestock industry, through lowering waste disposal costs and helping factory farms to gain planning permission and bypass nitrate regulations.
The AD industry in the UK wants subsidies to be raised to a similarly high level to those deployed by Northern Ireland during this boom, raising the risk of an incentive for growth in the very industry AD is meant to be mitigating the effects of. Meanwhile, the NFU have used AD as a sticking plaster solution to help argue against the need for dietary change. Yet we found that halving UK beef, lamb and dairy consumption, and planting trees on the spared grassland, could reduce the UK’s domestic agricultural emissions by 156 per cent. In comparison, if almost all of the UK’s manure was sent to AD (which is highly unlikely), it would only bring down UK agriculture emissions by a maximum of 27 per cent. It would be far more effective to prioritise reducing meat production in the first place.
A recent WWF report revealed the urgent need to integrate a transition to sustainable food systems into all nations’ Nationally Determined Contributions, the commitments they will take to COP26, the next UN climate summit in Glasgow in 2021. Food waste prevention, dietary shifts to sustainable plant-based proteins and tree planting should be top priorities in this vision as they are high impact actions to bring down carbon emissions. AD may have a role as a last resort for waste disposal, but we must ensure that imbalanced support for it does not detract from preventing waste in the first place. We do not have the luxury to settle for second best, only the highest ambition will do.