Key Points

  • Anaerobic digestion (AD) turns organic waste into three useful resources:
  • Methane rich biogas, a concentrated fibre soil conditioner and a valuable liquid fertiliser
  • Digestion neutralises the wastes reducing odours by up to 80%
  • Food processing waste and domestic kitchen/garden wastes can be diverted from landfill into digesters.
  • Reduces emissions of Methane (CH4) a powerful greenhouse gas

Why is it important?

Anaerobic Digestion (AD) uses locally available waste products to produce a biogas to provide heat and power.

This reduces use of non-renewable energy sources by using the biogas produced, offsetting CO2 emissions and allowing local communities become more self sufficient in energy.

AD also greatly reduces the emissions of Methane a powerful greenhouse gas, from slurry and other organic wastes and can divert food/garden waste away from limited landfill resources.

Holsworthy Biogas Plant in North Devon

How does it work?

  • An anaerobic digester is a large, airless, mixed and warmed vessel that creates the ideal environment for breaking down organic matter into an odour free, methane rich biogas.
  • This biogas can be collected, contained and then burned to create electricity and/or heat or in some cases processed further into a vehicle fuel.
  • The other by-product of the process is fertiliser; this can be separated out into a fibre and liquor; this can be re-applied to the farm land recycling nutrients.
  • Higher gas yields are obtained from co-digesting a mix of fatty and liquid wastes.
  • Typical wastes include animal slurries, food processing waste, kitchen waste and green waste.

 

How much energy can it generate?

Energy generation depends on the size of the digester, differing sizes of system are available from single on farm digesters to large Centralised Anaerobic Digesters (CAD), which collect waste from the surrounding area.

Large CAD systems like the Holsworthy digester in North Devon (pictured above, the first CAD in the UK) collects farm slurries from 30 nearby farms and produces 14.4 million kWh of electricity per year (enough for around 3,600 homes) and will provide heat for a health centre, hospital, swimming pool, school and council offices.

A single small on farm AD unit using on farm waste, rated 10kWe (electrical capacity) would produce around 52 thousand kWh (enough for around 13 homes) of electrical energy and provide heat that can be used on farm for heating and any other local heat demand.