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The AD sector at a glance

Anaerobic digestion (AD) is the ready-to-use technology that decarbonises the hardest to decarbonise sectors of heat, transport, waste management and agriculture, by reducing emissions from rotting organic wastes, providing low-carbon biofertilisers, and displacing fossil fuels with green gas.

The AD sector recycles organic wastes into renewable energy and a low carbon biofertiliser, digestate, that recovers nutrients and organic matter to help restore depleted soils. In so doing, the sector contributes to the creation of a truly circular economy.

Our latest estimates show that the UK’s AD industry has the potential of delivering a 6% cut in the UK’s emission, a third of the savings needed to meet the 2030 carbon budget, while creating 60,000 direct and indirect jobs.

AD’s Environmental Benefits

Recycling organic wastes

All organic wastes must be processed. When left to rot in the open air, they release the potent greenhouse gas (GHG) methane directly into the atmosphere. AD enables these emissions to be captured and harnesses them as a valuable renewable fuel. Consequently, AD is recognised as the most efficient technology to treat organic waste (WRAP, 2017), yet with over 140 million tonnes of organic wastes left undigested in the UK every year, the AD sector is currently achieving just one fifth of its full potential. Coherent policy is therefore urgently required throughout the waste management system to simultaneously increase the collection and diversion of this undigested waste to the preferred technology: AD.

Deep decarbonisation

AD prevents GHG emissions in three key ways:

  • prevention of emissions from decomposing wastes
  • displacement of fossil fuels through its generation of biogas
  • displacement of artificial fertilisers through its production of digestate

DEFRA’s conversion factors (2019) recognise for every tonne of food waste digested 616 kg CO2e emissions are prevented, compared to landfill. There are over 10 million tonnes of food wasted post-farm-gate. Digesting this would alone reduce GHG emissions by 6.2 million tonnes CO2e per year. Recycling food waste however does not make up for the absurd quantity of food that is wasted every year. We believe that only unavoidable food waste should be sent to anaerobic digestion. This has been made evident in ADBA’s own modelling, which accounts for a very high reduction in the amount of food waste generated. In line with the Committee on Climate Change’s net zero modelling, ADBA’s model assumes a 50% reduction to food waste. In the UK, all avoidable food waste is estimated to be 7 million tonnes, still leaving 3 million tonnes of unavoidable food waste to be treated through AD.

Of course, AD is not restricted to food waste; all organic material is suitable to varying degrees for digestion, from sewage, manures and slurries to industrial waste and green waste. The CCC says that AD needs to be used more widely on farms if the UK is to meet its fifth carbon budget. For the UK to achieve its Net Zero by 2050 target, it must optimise its management of all bioresources through AD. The following provides indicative estimates the cost per tonne of CO2 saved, based on average load factors and average cost per MWe capacity:

AD                         ≈ £1,100 per tonne of CO2 saved

Offshore wind   ≈ £825 per tonne of CO2 saved

Solar PV              ≈ £2,300 per tonne of CO2 saved

Biomethane: green gas today

Government support for AD has always focused on its ability to generate renewable energy – specifically biomethane, a sustainable gas which acts as a direct substitute for fossil natural gas. While electrification and hydrogen are often earmarked as a future solution, their implementation will be highly disruptive and costly, and in the case of the latter, remain hampered by technological barriers (e.g. CCUS). AD is the only technology able to decarbonise these sectors immediately.

Key stat: “Biogas has the potential to decarbonise the UK’s entire HGV fleet or heat a quarter of UK homes.”

Balancing of the energy network

AD creates flexibility within the energy system – it can easily be stored and transported through the existing energy infrastructure, providing low carbon energy when and where demanded. Importantly, it can also be used to generate base load electricity, used to produce green hydrogen and to store excess renewable electricity via electrolysis and biomethanation. As the wind and solar capacity has increased over the last decade, we are now experiencing periodic negative energy pricing, whereby electricity generation exceeds demand. These conditions cost the National Grid Electricity System Operator significant sums of money. It was reported that system operators paid more than £6.6 million to balance the network on 26th May 2019 alone,  this has resulted in legislation to enable distribution network operators (DNOs) to cut off renewable energy generators to prevent negative pricing. Renewable electricity should not be wasted. By using excess electricity to create green hydrogen, low carbon energy can be stored as a gas. Hydrogen can be subsequently fed directly into an AD plant, binding with CO2 to form biomethane, increasing its yields by 40% and utilising the CO2 captured in the AD process. This process transforms AD from a carbon neutral to a carbon negative technology.

Powering low-carbon transport

According to the UN, air pollution is now the largest environmental health threat in the world, accounting for approximately 7 million deaths globally each year. And transport is one of the greatest contributors to the problem. Biomethane is a ready to use transport fuel that cuts emissions in this clearly hard-to-reach sector. It has the potential to reduce emissions by 60-80% when compared to gasoline, diesel or liquefied petroleum gas. Today, biomethane, upgraded from biogas, is already the same quality as fossil natural gas so can be used in Liquified Natural Gas (LNG) or Compressed Natural Gas (CNG) fuelled vehicles. Biomethane is often compared to biodiesel and bioethanol as alternative biofuels that are already available for commercial use. However, while bioethanol and biodiesel are obtained from food crops such as corn, sugar cane, soybeans and other vegetable oil crops, biomethane is mainly derived from feedstock that is not appropriate for human or animal consumption such as food waste, manures, and sewage sludge. This makes biomethane a more attractive biofuel as it is generated according to circular economy principles, converting wastes into valuable resources. Using biomethane to fuel HGVs can reduce well-to-wheel emissions by 81%, compared to diesel, without considering the potential for CCUS on biomethane plants to make it a carbon negative technology.

Benefits of biomethane and gaseous fuels are not limited to GHG savings: drivers reported increased comfort while driving, quieter engines, and increased engine braking, without compromising overall vehicle reliability. While these systems may be more expensive to install, significant savings from gas prices mean costs can be recovered after just 2 years of operation. However, drivers also expressed concern over the low number of refuelling stations currently installed. For biomethane to be a viable fuel for HGVs, drivers need confidence that they can always reach a refuelling station. Consequently, new infrastructure is urgently required to facilitate the switch to gaseous fuel systems.

Production of biofertiliser ‘digestate’

After the extraction of the energy during the anaerobic digestion process, the remaining solid/liquid residue retains the nutrients from the organic material fed into the digester. The nutrients and remaining organic matter can then be returned to the land to fertilise crops and restore soil health, and therefore are central to developing the UK’s circular economy for organic material. In some countries (e.g. Denmark), AD’s nutrient recovery service is the primary objective of supporting the sector, more so than the renewable energy generation. The use of digestate also helps displace the need for artificial fertilisers, which are highly energy intensive to manufacture and generally involve the mining of finite mineral resources.

AD’s socio-economic benefits

Green jobs

For every MWe-e (megawatt electrical-equivalence) of capacity deployed within the AD sector, an estimated 14 temporary jobs are directly created to design, develop, and construct a plant, and 3 permanent jobs to operate and maintain them. These figures may be doubled when expanded to include the indirect jobs created within the wider bioeconomy, such as those responsible for feedstock procurement and management. Crucially, as plant locations correspond with sources of organic waste/material, these green jobs are evenly distributed across the UK, providing often neglected rural communities with new opportunities for employment and training. When the AD industry is at full capacity, assuming investment in R&D, it is estimated that the industry will be employing over 30,000 people directly and 30,000 indirectly.

Diversification of agricultural economies

With Brexit and the phasing-out of CAP’s Basic Payment Scheme (BPS), it is vital that farms find new sources of revenue to remain operational – BPS typically forms 50-80% of UK farms annual income. AD offers agricultural systems an opportunity to diversify their income, while increasing the sustainability of operations. With over 90 million tonnes of manure already collected and stored by UK farms each year, integrating AD into these systems could support the generation of 17-24 TWh of renewable energy. Based solely on wholesale gas prices (Jan 2020), this gas could bring an additional £160-230 million each year to the agricultural sector. Income and economic resilience may be further supplemented by the sustainable integration of bioenergy crops into farming and the feedstock mix. The Committee on Climate Change (CCC) recognise the need to embrace bioenergy crops to meet the low carbon energy demand necessary for Net Zero, and when sustainably farmed can promote biodiversity and restore soil structure.

Key policy recommendations to unlock AD’s potential

  • Support AD in agriculture, through the introduction of a tariff premium, either as part of the Green Gas Support Scheme (GGSS) or as part of the Environmental Land Management Scheme (ELMS), for the treatment of manures and slurries through AD and a renewable biofertiliser obligation
  • Support for biomethane in transport, through its recognition as a leading low-carbon fuel to decarbonise HGV operations, and better incentives to promote investment in the development of new biomethane plants for transport
  • Establish material hierarchies for all organic wastes with AD as the optimal recycling technology
  • Support for research and innovation
  • Support for small businesses and community projects on circular economy, using AD to transform local waste into local heat and power and local nutrients recovery
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