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Human activities generate more than 105 billion tonnes of organic waste annually, which, when it decomposes, emits copious amounts of the greenhouse gas (GHG) methane. Yet only 2% of this waste is recycled.
Managing this waste better through anaerobic digestion (AD) and methane utilisation could reduce GHG emissions by 10%. Achieving this needs strong political will and effective long-term policies.
Last May, one of Europe’s largest AD plants began operating in Tønder, Denmark. The Tønder Biogas plant will process 930,000 tonnes of mostly agricultural waste annually and capture methane (CH4) equivalent to the energy needs of 20,000 homes per year and reduce CO2 emissions by 175kt. Additionally, the processed digestate is rich in organic material and nutrients, and makes an excellent fertiliser.
The UK’s first gas-to-grid AD plant was Rainbarrow Farm in Poundbury, Dorset, which began operating in 2012 and had a major upgrade in 2020. As well as providing enough gas for 7,500 homes in winter, the plant also produces soil conditioner made from digestate, and high-purity CO2 for the food industry.
Both Denmark and the UK have a multiplicity of AD installations, ranging from SME and small-farm units to enormous AD plants at sewage works and waste-treatment plants. The size variation indicates the scalability of AD technologies.
AD plants work well with agricultural waste, and in the UK, for example, a small but growing proportion (around 10%) of farmers are benefiting from them.
“Farmers started to install AD when new environmental laws from the 1970s required them to use tanks to store manure. Covering the tanks to keep out rain meant that there was a way to capture and use the CH4 emitted from the manure,” explains Angela Bywater, who has worked in the AD sector for more than20 years, recently completed a PhD on farm AD, and is currently working as a specialist for the Global Center for Sustainable Bioproducts. “Once farmers take up AD, you also see a shift in perception and they regard the manure as a resource, and look closely at carbon and nitrogen optimisation,” she adds.
According to the UK’s Anaerobic Digestion and Bioresources Association, the UK has around 750 AD plants, with many using the generated methane onsite for heat and electricity, through technologies such as combined heat and power plants. There are now more than 145 biogas plants in the UK that feed the methane into the national grid. About 5% of the UK’s natural gas is biomethane, according to IEA Bioenergy, but this could double with the right policies and economic frameworks.
Successive Danish governments realised this, have fully embraced biogas, and now focus on fostering biomethane production for injection into their national grid. Denmark leads Europe in biogas development, with plants contributing 40% of the country’s natural gas, and projected to reach 100% by 2030. China leads the world in terms of volume of biogas produced.
The history of AD spans millennia. Historians record that ancient civilisations in Asia and the Middle East used biomethane for cooking and heating baths, and, in the 19th century, AD plants from Mumbai to Birmingham provided biogas for cooking, heating water, powering street lamps and purifying water at Victorian waste-water treatment works.
Put simply, AD is an effective technology that has multiple benefits and a crucial role in mitigating climate change. The process is well understood, constantly improving, mature, flexible and scalable. It also has other benefits; as well as digestate serving as a fertiliser, the CO2 in biogas can be separated and used in the food industry and in greenhouses, and as a feedstock for other products, such as methanol. Additionally, the sector has the potential to create millions of renewable resources jobs worldwide.
The World Biogas Association (WBA) has examined the global application and
potential of AD. In its report, the Global Potential of Biogas, the WBA wrote that just 3% of livestock manure is treated using AD. If this proportion rose to just 35% by 2030, this would increase electricity production fifteenfold and reduce CO2 by a factor of 12.The WBA also reports that 98% of organic wastes globally are not treated, yet greater AD deployment could cut total GHG emissions by 10%, by mitigating the impact of CH4 emissions, and displacing fossil-fuel CH4 and chemical fertilisers. However, apart from a few notable exceptions, there are
obstacles to the adoption of AD.
According to the International Energy Agency, the global annual growth rate for the biogas sector ranges from 8% to 32%, as there is growing recognition of the importance and value of biogas as a renewable resource, among many other benefits. The greatest prospects are in developing countries. However, the sector is far from reaching its full potential.
At the World Biogas Summit 2025, hosted by the WBA, many attendees cited regulatory and planning obstacles, different standards and a lack of financial certainty as barriers to installing AD plants. Meanwhile, in a handful of countries, such as Denmark, a political will has fostered AD growth, through harmonised standards, bipartisan political support, a strong national strategy, investment in infrastructure, and financial certainty. Governments elsewhere have noted this. “In France and Italy, there are aspirations from the top,” says Bywater, “while in France, for example, one food company is providing grants to farmers to install AD plants, to reduce its own scope 3 GHG emissions”.
International cooperation in AD has also fostered many successes. Bywater says: “Such cooperation is hugely important for many reasons: for example, researchers see how others work and exchange information, so they are not sitting in a silo. We also see how other policymakers are working together. You also get to look at other technologies within AD and the wider bioproduct space, as well as bio-electrochemical systems through to CO2 production and utilisation, and bioplastic production.”
Securing finance can be a big challenge for AD deployment. “Operators and investors need certainty. In the UK, there are no tax breaks to do the right thing,” says Bywater. “Second, the permitting and planning systems need to be easier to navigate, simpler and a lot faster.”
The UK, for example, has had a series of support schemes such as the Feed-in Tariff and Renewable Heat Incentive, with the current Green Gas Support Scheme (GGSS) focusing solely on large gas-to-grid AD plants, thereby omitting smaller on-farm AD. The GGSS provides payments over 15 years, whereas the equivalent scheme in Denmark has 20-year terms.
“Although we are waiting for a government announcement later this year, there is currently a policy vacuum and therefore no long-term AD investment certainty when the GGSS closes in early 2028,” says Bywater. Moreover, UK policies have so far focused on the energy aspects of AD. “The wider environmental benefits of AD, such as digestate, need to be incentivised as well as energy,” she adds.
That said, the UK’s Clean Flexibility Roadmap and Clean Power 2030 Action Plan show that the government is changing its previously narrow view of AD, recognising that it has numerous benefits. There is a need for much stronger political will. David Newman, former president of the WBA, asserted in the WBA report Biogas: Pathways to 2030: “If we do not address methane emissions from organic wastes, all our efforts to tackle the climate crisis will fail. Anaerobic digestion is one of the ready-to-go, ready-to-scale technologies that can do this. The path we must take is clear.”
Rick Gould MISEP CEnv is an environmental scientist and writer
