Feedback’s response to the ADBA’s article ‘Why you MUST invest in anaerobic digestion and biogas to build back greener’

6th Nov 20 by Martin Bowman, Senior Policy and Campaign Manager

Feedback provides some clarity and accuracy on our research findings on AD.

Feedback welcome the ADBA’s response to our Executive Director’s recent article in Responsible Investor – however, since the ADBA misrepresent our view and the issues, we hope that this response provides some clarity. For more info, read our report on AD.

A summary of Feedback’s advice to investors

Don’t invest in:

  • AD plants which run on bioenergy crops like maize or grass – even if these are co-digested
  • AD plants built on newly built or newly expanded intensive livestock farms
  • AD plants which lower the costs of animal waste disposal for intensive livestock farms
  • AD plants which process food waste edible to humans or animals
  • AD plants which charge little or nothing for waste disposal or actively pay for wastes, and thus disincentivise waste prevention

Do invest in:

  • AD plants which digest sewage feedstocks
  • AD plants which process only manures and slurries on smaller-scale more sustainable livestock farms
  • AD plants which take on unavoidable food waste which is not edible to humans or animals
  • AD plants which charge higher gate fees to take on food wastes or animal slurries


First, the points on which we agree: AD does have some role in a sustainable future, as a last-resort waste management option – as we argue in our report, there is a ‘sustainable niche’ for AD. AD is certainly better than landfill and incineration of food waste, and is preferable to open storage of manure and slurries – practices which should be heavily taxed and banned as soon as possible. To be clear, this will require some growth in the AD industry, and investment to this end – so it is sometimes sustainable to invest in AD, within limits and in some specific situations. We also agree that sewage treatment by AD is part of this sustainable niche. ADBA’s false claim that Feedback assume AD can only be used to treat food waste is misplaced – our report and the Life Cycle Assessment (LCA) study on which it is based, examine bioenergy crops, manure and slurries too.

However, crucially we model two scenarios: the “industry driven AD” scenario in line with ADBA’s ambitions for AD industry growth, and the “climate optimised AD” scenario where environmentally preferable alternative uses for AD feedstocks are maximized (like food waste prevention) with remaining feedstocks used for AD. In the climate-optimised scenario, we model no bioenergy crops and about a third less food waste going to AD, and additionally we model a context where meat production (and thus availability of manure and slurries) is roughly halved – but all available slurries go to AD in both scenarios. The LCA found that the climate optimised scenario resulted in over double the emissions savings, as well as generating more energy (generated by solar PV on land previously used for bioenergy crops) and significantly higher food production on spared cropland.

ADBA’s presentation of AD as a “win-win-win-win” solution is a simplistic fantasy, although not a surprising stance to take for a body set up to promote the AD industry. Our ground-breaking LCA study, completed in collaboration with academic experts at Bangor University, shows a far more complex and nuanced picture, with some serious limitations to AD. Below, we highlight four key problems:

The first problem is that, as the ADBA acknowledge, AD is far less effective than waste prevention. In fact, preventing food waste results in 9 times more emissions savings than sending it to AD, and if trees are planted on the spared grassland, about 40 times more. The ADBA also often ignore animal feed – our LCA found that sending food waste to animal feed saves 3 times more emissions than sending it to AD. This makes food waste prevention, and using food waste as animal feed, far more effective green investments – and means that only unavoidable food waste inedible to both humans and animals should be sent to AD. Within the current legal framework, there is plenty of scope to increase the processing of food waste like bread for animal feeds – and EU-funded research found that it is possible to feed food waste containing meat to pigs and chickens safely, if EU law is reformed to allow this in a safely regulated fashion. When it comes to manures and slurries, these wastes can be prevented too – through shifts from meat to plant-based diets. For instance, switching from pig meat to a plant-based protein alternative such as tofu results in a 74% reduction in emissions and 80% in land use – land which can then be used for tree planting to offset emissions even further. The emissions savings from sending slurries to AD are far smaller in comparison – so investing in plant-based alternatives to meat would be a far greener investment, from pulses and beans to plant-based burgers and milks. Investors looking to green their portfolios should aim to support dietary shifts as a priority, with AD only used to mitigate the emissions of a smaller, more sustainable livestock sector.

The second problem is that high subsidies to AD create perverse incentives, sometimes actively impeding the better waste prevention alternatives mentioned above. It is completely disingenuous of the ADBA to claim that they are not advocating for high subsidies locked in for decades – their own report clearly advises that AD subsidies are returned to the very high levels of 2011-15, that large-scale AD is subsidised at the same high levels as small-scale plants, and that these be guaranteed for decades into the future. In Northern Ireland, AD subsidies at a similar high level to those advocated by the ADBA were explicitly designed as a means to support an explosion in the size of the country’s intensive livestock industry. Through reducing the industry’s waste disposal costs (even paying for their waste), enabling sites to gain planning permission and bypass environmental regulations, highly subsidised AD plants actually helped expand the polluting industry it was meant to be reducing the environmental effects of. In the case of food waste too, testimonies to a House of Lords enquiry complained that high AD subsidies created perverse incentives to send edible food to AD rather than ensure it is eaten, and Feedback has found many other instances of such complaints. In one case, Feedback’s investigations found an AD plant in a port that in a single day was processing an estimated 60,000 cucumbers, 10,000 figs, 4,000 cabbages and many other foods – which all appeared edible. In this context of distorting high subsidies, investments in some AD plants may thus actively prevent far more sustainable alternatives. The better way to make AD plants financially sustainable without creating these perverse incentives is to tax or ban worse alternatives to AD, such as incineration, landfill, and open manure storage, thus pushing up the supply of wastes to AD and gate fees they can charge for collection.

The third problem is that AD’s emissions mitigation potential significantly declines over time. This is a big problem, since AD plants often take decades of highly subsidised operation to break even on their high up-front costs. The reason for the decline is that as society decarbonises, the emissions that AD currently mitigates are often avoided by other means – for instance, as the electricity grid shifts to renewables, heat and transport are electrified, landfill and open manure storage are banned, AD begins to compare less and less favourably with alternatives. Our study found that some AD feedstocks like grass even begin to have a negative rather than positive environmental impact in a net zero context. This means that the green credentials of investments in AD will decline significantly over time. In comparison, food waste prevention, tree planting, dietary change and solar PV consistently far outperform AD in future decarbonisation contexts (see our report for more detail on this).

The final problem with AD is that, although the AD industry claim that they only want “unavoidable” wastes to go to AD, they have a strong incentive to downplay how much waste is “avoidable” to maximize their growth. The ADBA nowhere in its report mentions dietary shifts away from meat as an option and only currently support the UK’s unambitious voluntary targets on food waste, which pledge only a 24% reduction in post-farmgate food waste between 2015 and 2030. A 50% reduction in UK meat consumption, a genuine 50% reduction in UK food waste from farm to fork through ambitious regulation, and tree planting on the millions of hectares of land that would be spared by these measures, could together mean that UK agriculture could be net carbon negative by 2040 without recourse to BECCS. The AD industry is eager portray agriculture as “difficult to decarbonise” because it actively sidelines these more ambitious alternatives.


*Using 2007 as a baseline year, excluding inedible food waste, using per capita figures which also use a 2007 baseline year.

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