Anaerobic digestion (AD) is the breakdown of organic material by bacteria in a sealed tank with no oxygen. Feedstocks include food waste, animal slurry and manure, crop residues and purpose-grown crops such as maize. The process yields two products: biogas and digestate.
What it produces
| Product | What it is | Typical use |
|---|---|---|
| Biogas | Mostly methane and carbon dioxide | Burned in an engine to make electricity and heat |
| Biomethane | Biogas upgraded by removing CO2 and impurities | Injected into the gas grid or used as vehicle fuel |
| Digestate | The nutrient-rich material left over | Spread on farmland as a fertiliser |
Sewage works and landfill sites produce biogas in a similar way. UK energy statistics count them separately from AD plants.
UK numbers
Figures from the Digest of UK Energy Statistics 2026, covering 2025:
- Capacity: about 640 MW of AD electricity generating capacity.
- Electricity: about 3.6 TWh generated from AD.
- Sites: 764 AD electricity generating stations at the end of 2025.
- Grid injection: AD biogas injected into the gas grid equalled 419 thousand tonnes of oil equivalent, roughly 4.9 TWh.
DESNZ notes that falling output from ageing landfill sites has been offset by growth in AD, so total electricity from biogases has stayed broadly stable since 2015.
Benefits and limits
AD captures methane from wastes such as slurry that would otherwise release it, and it turns food waste into energy and fertiliser. Its climate benefit depends on the feedstock: plants run on purpose-grown crops use farmland, and methane leaking from tanks or digestate stores can erode the gains. Biomethane can replace some fossil gas without new pipes, but UK supply is small compared with total gas demand.
Read more: Biomass energy: how it works, where it is used and the debate.