Find out about anaerobic digestion and what to consider when using this technology.
Anaerobic digestion is a treatment process which harnesses natural bacteria to produce biogas and a residue known as digestate, from waste biodegradable materials, such as agricultural manure and slurry, food waste and sewage sludge.
Anaerobic digestion can also be used to produce biogas from non-waste feedstocks, such as miscanthus or maize crops, grown specifically for the purpose.
Biogas is rich in methane and is a source of renewable energy. It is already commonly used in sewage works to power electricity generators and provide heat. Biogas can also be upgraded by removing the carbon dioxide and impurities, to produce biomethane. This can be used as a vehicle fuel, or it can be injected into the natural gas grid network.
Digestate is typically a pumpable material that can be further separated into a fibre and a liquor. It can be beneficially applied to farmland as a fertiliser and soil conditioner.
What you must do
If the biodegradable material fed into an anaerobic digestion plant is a waste, or contains any waste, the digestate produced would normally be classified as waste and be subject to waste regulation controls.
We have produced a quality protocol which sets out circumstances where digestate can be regarded as a non-waste product and free from waste regulation. Manure and slurry fed into anaerobic digester plants is a special case, and although we will apply waste regulatory controls to this activity, the use of the remaining digestate as a fertiliser on agricultural land in England and Wales will normally be free from such controls. This is explained in our position statement:
The storage of waste and its recovery using anaerobic digestion is regulated under the Environmental Permitting Regulations.
Using anaerobic digestion – now and in the future
Anaerobic digestion is very well established in the UK as a treatment technology for sewage sludge (66 per cent of all sewage sludge was treated in this way in 2007).
Although there are currently very few anaerobic digestion plants used for treating other materials, we expect to see a significant growth in the use of this technology for treating food wastes and agricultural manure and slurry over the next few years.
Anaerobic digestion can be carried out in small-scale systems such as those on farms and operated by farmers or used by businesses with large amounts of food waste. Alternatively it can be carried out in large, centralised systems such as those treating municipal food waste diverted from landfill by local authorities, or those using manures and slurries from several farms.
You can find out more about anaerobic digestion on the Biogas website. This is an independent portal developed with Government support to provide a gateway to information about anaerobic digestion technologies for a range of potential stakeholders.
Our view on anaerobic digestion
We support the use of AD as one of the ways of diverting biodegradable wastes from landfill, recovering value from them and reducing emissions of greenhouse gases.
There are a number of emerging technologies for treating biowastes and a few well established ones. They recover the carbon contained in biowastes in one of two ways – either as a source of soil organic matter when the treated biowastes are beneficially applied to land, or as a source of energy.
Soil is a very important resource. Among many other functions it is the biggest carbon store in the world (1,500 gigatonnes). An estimated 45 per cent of European soils have low organic matter content, including areas of the UK (source EU Commission Soil Thematic Strategy, PDF, 246KB).
Biogas as a renewable energy source
Biogas could be a very significant renewable energy source for the UK. The Government is committed to meeting targets to use energy from renewable sources like biogas.
Anaerobic digestion and the environmental impacts of biowastes
In terms of environmental impacts, there is no single best way to treat and recover value from biowastes. The most appropriate option in any case will depend on a number of variables, such as the type and nature of the waste, the location of the treatment site and the availability of markets for the recovered products.
There is also some uncertainty over the relative value of carbon, when used as a source of energy, compared with its long-term value in augmenting soil organic matter. We want what is best for the environment.
We will support any initiative where the variables have been considered and the waste is dealt with in a way which maximises the recovered value while minimising the environmental impact. We believe the combined energy recovery and recycling achievable through anaerobic digestion often make it the best recovery option for certain biowastes, such as agricultural manure and slurry and separately-collected food waste.
To find out more about biowastes, see our biowastes page:
Other technologies are important. These include composting, which is one of the most popular options for garden wastes and thermal technologies, which are often the best treatment for some dry biowastes.
The Government is encouraging the development of anaerobic digestion across the country. We are supporting them in this by ensuring that there is an appropriate regulatory framework for it. See the Government’s report below: