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Why anaerobic digestion? A summary

When we at ADBA are in day-to-day discussions with government department's we are so often trapped into explaining how AD can meet the objectives of that particular department. This is frustrating for us but of course government can be highly specialised and it is difficult for individual civil servants to understand the full picture. Food waste collections of course hugely contribute to the energy and climate goals of the Department for Business, Energy and Industrial Strategy, but are rarely discussed in that department.

But as an industry I think we need to be clear on the value we bring across the economy. So find below a summary of what we at ADBA believe:


How AD contributes to a clean-growth economy


Anaerobic digestion (AD) is unique among technologies in delivering not only carbon emission reductions in four ways, but also secure, flexible UK energy, cleaner air, farming diversification, food security, clean growth and jobs, exports, and a sustainable resource-management solution.


1. Clean growth

The UK has committed to halving its emissions by 2025 on 2009 levels. There is, however, a policy gap between the target agreed by the Government as part of the Paris Climate Agreement and what is currently in place. If the UK were to use all of its suitable feedstocks for AD, it would reduce the UK’s greenhouse gas emissions by 21 million tonnes, or 4% of its total, within 15 years. AD is unique in being able to reduce emissions in four ways across the waste and farming sectors by:

  • Displacing fossil-fuel combustion. If all suitable UK feedstock was used for AD, it could supply 30% of UK household gas or electricity, 80% of fuel for lorries, or more fuel than is used by the entire bus fleet. This avoids the emissions from the natural gas, coal, diesel or petrol that would otherwise be burnt for energy.
  • Avoiding methane emissions from landfill. By diverting to AD the two million tonnes of UK food waste currently being sent to landfill, the AD process avoids the methane leakage that occurs as food waste rots in landfills. Methane has a global-warming potential 21 times that of carbon dioxide, and landfills today still emit some methane.
  • Avoiding the emissions associated with the production of artificial fertiliser. More than five tonnes of carbon dioxide are emitted for each tonne of nitrogen fertiliser produced, so when digestate is used in place of factory-produced fertiliser, the factory emissions are avoided.
  • Avoiding methane emissions from manure and slurry management and sewage sludge. Methane produced by rotting manure and slurry is one of the hardest sources of UK and global emissions to avoid. AD can ensure this major source of agricultural emissions is avoided.

AD is already reducing UK emissions by 1% across these areas. By providing these multiple carbon reductions, AD delivers cost-effective carbon savings. In hard-to-decarbonise sectors such as agriculture, heat, waste and transport, the anaerobic digestion of wastes offers the most cost-effective decarbonisation technology. For example, the anaerobic digestion of manures can reduce emissions at a cost of £48/tonne CO2e, under half the abatement cost of the planned Hinkley Point C nuclear plant.

As well as climate-change benefits, biogas offers human-health benefits through reduced air pollution. Biomethane-fuelled vehicles result in improved air quality from dramatically reduced nitrogen-oxide emissions, particulate-matter-free combustion, and fewer (as of yet unregulated) ozone promoters, aldehydes and non-methane hydrocarbons. These air-quality and emissions benefits have been achieved through constant progress in engine technology and gas-vehicle development.


2. Secure, flexible energy

Delivering renewable energy not only reduces carbon emissions but contributes to the UK’s energy security. UK imports of natural gas have doubled in the last ten years as UK production has declined. Imports of liquefied natural gas (LNG) from unstable regions of the world such as Qatar and Algeria now make up 30% of UK gas imports, up from 3% ten years ago. If all suitable UK feedstock was used to produce biogas through AD, displacing natural gas, the UK’s gas imports would fall by 16%, saving the UK £2bn per year at time when the UK is recording the largest trade deficit of any G7 economy. AD is currently reducing UK gas imports by 2%.

Biogas can deliver electricity, heat and/or transport fuel. It can be stored as biomethane in the UK’s existing gas grid, meaning it is delivered to households and businesses on demand. As biogas is produced from UK waste, residues and crops, there is no form of energy that is more secure. This gas can be produced quickly relative to other energy technologies by a mature industry already powering the equivalent of a million homes.


3. Farm diversification and food security

With the UK due to leave the European Union in 2019, farming will be a key policy area for the UK to manage, albeit within World Trade Organisation (WTO) rules. AD supports farming and farm businesses by providing rural jobs and investment to diversify income streams. The UK Government is likely to seek to implement a farm policy that supports the rural economy, provides food security and protects the environment, while seeking to reduce the £3.5bn it currently pays farmers per year. AD can deliver all of these benefits and help reduce the cost of farming support.

AD supports the rural economy by diversifying farm incomes. AD can transform farm material, including slurries, crops, chicken litter, vegetable off-cuts, out-grade crops or animal by-products into a new income stream for the farm. For a farm integrating AD into its business, around a third of the farm income may come from exporting energy. This reduces the volatility of the farm’s income, helping farmers stay profitable in challenging market conditions whilst also supporting food security and stabilising food prices. Some AD companies are also now selling their crop-derived digestate in the retail market, diversifying their income streams even further.

As well as additional income streams, AD can reduce operational costs and improve the productivity of farms.

Reduced costs:

  • By using nutrient-rich digestate produced from farm material, farm fertiliser costs can be reduced and yields increased
  • The on-site generation of renewable energy can displace the need to purchase expensive retail-price energy
  • A rotation of AD and food crops can provide a natural method of managing weeds and crop diseases – for example, environmental consultant ADAS has reported that 58% of the UK wheat crop currently suffers from black-grass. Crop rotations can help tackle this, therefore reducing the cost of expensive chemical treatments

Increased productivity:

  • The application of digestate helps maintain pH and soil fertility and helps build organic matter, therefore improving food and AD crop yields
  • Marginal land can be brought back into productivity, leading to higher income per unit of land
  • New opportunities arise to better protect soil and increase financial returns through the off-season harvest of energy crops, overwintered stubbles and cover crops
  • Wildlife is attracted by the increased variety of crops and reduced chemical inputs

AD protects the environment not only through the digestate, manure-management, crop-rotation and wildlife benefits listed above but also through the emissions reductions outlined above.


4. Industrial Strategy and jobs

Through its Industrial Strategy, the UK is seeking to increase productivity and drive growth across the whole country, thereby creating and sustaining highly skilled jobs.

AD could employ 35,000 people across the construction, manufacturing, plant-operation and export industries if it reached its full potential in the UK. AD already supports approximately 4,000 jobs. Most employment in AD is in the form of rural jobs, which are widely distributed across the country.

Over £3bn has already been invested in AD in the UK, with the potential for a further £9bn in the coming 15 years if the industry grows to its full potential.

The UK already exports over £100m of AD equipment and expertise each year, with the potential for exports of £2.2bn per year if the global AD market develops in line with the global need to reduce emissions.

AD contributes to growth not only through direct employment but also by holding costs down for businesses. As a cost-effective source of carbon abatement, AD can support the UK in remaining a low-cost, competitive economy as it decarbonises, allowing emissions to fall while economic growth accelerates.


5. Sustainable resource management

The UK’s current resource culture is unsustainable. WRAP estimates that the UK throws away ten million tonnes of food waste each year, or 13 million tonnes when food residues from factories are included.

Sending this to AD instead of current treatment would provide enough energy to heat 740,000 homes each year as well as returning nearly 80,000 tonnes of natural fertiliser to soils and reducing methane emissions from landfill. By returning nutrients and organic matter to soils, AD plays a part in creating a circular food system in which nutrients are managed in a sustainable fashion, reducing the dependence on imports from countries such as Morocco, which holds 75% of the world’s phosphate deposits.

Sending food waste to AD requires separating food waste at the household and business level from other waste and recycling. Separating food waste has been linked to food waste reduction as when they have separate food waste collections, consumers become more aware of their waste and consumption, and with the UK currently wasting £13bn of food, even a 2% reduction in this would save the UK £260m. Separating food waste has also been linked to a reduction in the contamination of recycling collections (againthanks to a better understanding of waste), which saves councils money as standard black bags become less odorous and do not need to be collected as frequently.

Scotland, Northern Ireland and Wales have led the way in introducing separate food waste collections, while in England under half of households still do not have a separate collection.

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