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How does Anaerobic Digestion work?

Anaerobic digestion is a complex biological process involving the breakdown of organic matter in the absence of oxygen in large, sealed, and insulated vessels with controlled heating and mixing.

How does Anaerobic Digestion work?

Anaerobic digestion is a complex biological process involving the breakdown of organic matter in the absence of oxygen in large, sealed, and insulated vessels with controlled heating and mixing.

The process is an environmentally friendly way of recycling food waste and transforming it into green energy. Another output is biofertiliser, a nutrient-rich organic material used to fertilise farmland.

Every year in the UK, around 9.5 million tonnes of food waste is produced, according to WRAP around 70% of this was intended for human consumption. Where possible, businesses should be looking at recycling this food waste through their local food waste recycling facilities.

These food waste recycling facilities will recycle food waste in a sustainable and environmentally friendly way, through the anaerobic digestion process.

Anaerobic digestion process steps
  1. Food waste is collected and taken to an AD plant.
  2. Separate food waste – liquid and food waste are mixed together the process of anaerobic digestion starts.
  3. Hydrolysis process starts – liquid is pumped into tanks and the anaerobic digestion process starts.
  4. Pasteurisation – waste heat created is used here to heat the mixture to 70 degrees to kill any harmful pathogens.
  5. Digestion – the pasteurised feedstock enters the tank and this is where the majority of biogas is captured. The gas naturally rises as part of this process and is captured and regulated here.
  6. Electricity – regulated gas is captured and used to generate electricity.
  7. Renewable energy – the energy captured as part of the AD process is 100% renewable and capture in three forms: heat, gas and digestate for nutrient rich fertiliser.

What are the advantages of anaerobic digestion?


As well as being a cost-effective process, one of the advantages of the natural process of anaerobic digestion is that it has a positive impact on the environment and replaces the need for fossil fuel derived fuels.

Renewable energy:

The energy that is generated during the process of anaerobic digestion is an enhanced natural process, which uses organic materials to produce biogas.

This green energy is much like other forms of green energy, natural and a sustainable way of reducing the impact on the environment. Usually, when food waste is not disposed of correctly, it can be left in landfill to rot and it creates methane (CH4) which is harmful to the environment.

Anaerobic digestion plant

We have a number of anaerobic digestion plants across the UK, all with the capability of dealing with large amounts of food waste from across a variety of industries.

Commercially, businesses benefit from using local AD plants to recycle their food waste, sustainably because it reduces landfill taxes they’d face and also large transport costs from moving food waste material unnecessary long distances. Making use of their local AD plants, or the facilities within a group of AD plants has its advantages.

What does Anaerobic digestion produce?

Setting aside the green energy element of the AD process, the residual output, digestate or biofertiliser, is put to good use as a fertiliser across local fields and reduces the use of harmful and environmentally damaging crop sprays and pesticides.

Anaerobic digestion and wastewater treatment

As part of the anaerobic digestion process, industrial wastewater is used to create a ‘sludge’ which forms part of the materials that move through the tanks. This water is derived from several sources, for example as a by-product of the food manufacturing process.

The liquids are all tested before entering the AD sites as all liquid has to be a certain specification, to avoid damage to the plant machinery.

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