How Anaerobic Digestion Works

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Anaerobic digestion is a process through which bacteria break down organic matter, such as manure, wastewater biosolids and food waste, in the absence of oxygen. All anaerobic digestion systems adhere to the same basic principles whether the feedstock is food waste, animal manures or wastewater sludge.

The organic matter is broken down by the bacteria and as the bacteria “work”, they convert organic matter and other intermediate organic components to create a biogas yield, which rises to the top of the digester.

The biogas yield that is generated is made mostly of methane, the primary component of natural gas. Recovered biogas can be an energy source for electricity, heating or transportation fuel. The solid waste then falls down the digestion chamber and can be used to make organic fertiliser.

Every tonne of food waste recycled by anaerobic digestion as an alternative to a landfill can reduce greenhouse gas emissions, one of the many benefits of anaerobic digestion. Some types of organic matter break down more easily than others.

Generally, the more “digestible” the organic matter is, the more biogas can be produced.

The Outputs Of Anaerobic Digestion

Anaerobic digestion produces biogas and digestate.

Biogas Yield

The biogas produced is composed primarily of methane (CH4), varying from 50 to 75 percent. The other components of the biogas produced is carbon dioxide (CO2), hydrogen sulfide (H2S), water vapour and traces of other gases.

This gas can then be purified further to create renewable natural gas (RNG), which has a concentration of methane at 90% or higher. This is done by removing the carbon dioxide, hydrogen sulfide, water, or other components.


Digestate is the solids and liquids left over after the digestion process. They can have their own uses and applications, such as nutrient-rich fertiliser, animal bedding, a base for creating bioplastics and other bio-based products, and much more.

To help with the performance process and for anaerobic plants to operate effectively they require a variety of nutrients for the micro-organisms to grow and function properly. See OMEX range of trace element additives.

Anaerobic digestion

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How does Anaerobic Digestion work?
September 22nd 2020 09:52 am

The literal meaning of Anaerobic Digestion is 'in the absence of Oxygen'. It is a process through which bacteria break down organic matter, such as manure and food waste, to produce biogas and biofertiliser. This happens in a sealed, oxygen free tank called an Anaerobic Digester.   As this organic matter is broken down by the bacteria the organic matter is converted to generate biog... Continue reading how anaerobic digestion works