What is anaerobic digestion?

It’s a long-established and important technology that helps us manage our waste – things like food waste, sewage and animal manure – while also producing renewable energy and fertiliser.

AD uses microorganisms to break down waste organic matter without oxygen being present. Anaerobic digesters come in a number of different sizes from food waste treatment plants processing industrial quantities of waste to on-site plants on farms to micro-digesters that could fit in a container or even in your back garden!

When the feedstock is added to the digester the organic matter goes through four biochemical reactions which occur simultaneously:

• Hydrolysis – Enzymes released by bacteria split long chain organic compounds (fats and proteins) into simple organic compounds (sugars and amino acids)

• Acidogenesis – Products produced by hydrolysis are converted by bacteria into organic acids as well as forming acetate, hydrogen and carbon dioxide.

• Acetogenesis – Bacteria convert the organic acids and alcohols into acetic acid, hydrogen and carbon dioxide.

• Methanogenesis – Bacteria convert the products produced by the other processes into methane and carbon dioxide.

The process also produces a nutrient-rich biofertiliser called digestate.

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