What is Anaerobic Digestion?

Anaerobic Digestion is the simple, natural breakdown of organic waste into biogas (methane and carbon dioxide) and digestate (a natural fertiliser) by two groups of micro-organisms, bacteria and archaea. Since many of these are intolerant to oxygen, this process is known as anaerobic.

Biogas is the gas produced when bacteria break down organic matter in the absence of oxygen.  It is made up of mainly methane (CH4) and carbon dioxide (CO2), with small amounts of water vapour, particulates, and other gases. Biogas can be processed and used for a variety of energy needs, such as the generation of heat, power and fuel.

By 2020, anaerobic digestion has the potential to generate 10 - 20 TWh of heat and power per year. To put this in context, the UK's largest power station Drax sold 27.1 TWh of electricity in 2012.

Anaerobic digestion has numerous benefits:

  1. It turns waste into a resource. Instead of sending waste to landfill, we can use it to produce energy and fertiliser.
  2. It produces fuel. Biogas can be used instead of fossil fuels.
  3. It produces fertiliser. Fertilisers are made from fossil fuels. The digestate from this can replace some synthetic fertilisers as its richer in nutrients, but can also be used as feedstock for ethanol production, and in low-grade building materials, like fibreboard.
  4. It reduces our carbon footprint. The methane produced during AD is burned as fuel, and therefore releases CO2 into the atmosphere.  Because it comes from biomass, this does not contribute to climate change. However, if the same waste was left to degrade in a landfill site, the methane produced could escape into the atmosphere: methane has a global warming potential 23 times larger than that of CO2. Therefore, harvesting and using methane from biomass can help to prevent climate change.
  5. It can benefit many different people. AD benefits the local community, the environment, industry, farmers and energy entrepreneurs and government. 
Alice Bayfield