JR-fernbrook32webHow Anaerobic Digestion works

The process of Anaerobic Digestion is relatively simple, but highly effective. Anaerobic means without oxygen, so this is an oxygen-less process that happens in airtight sealed containers.

STEP 1: All of the feed stock (including food waste, crop residues, slurry and manure) is placed into buffer tanks and mixed into a thick ‘soup’.

STEP 2: The ‘soup’ is then pumped into different temperature controlled vessels known as digesters.

STEP 3: Inside the digesters a number of naturally occurring bacteria digest the ‘soup’, releasing a mixture of gases, collectively known as Biogas.

STEP 4: Biogas is 60% methane and 40% carbon dioxide, with small traces of contaminant gases such as hydrogen sulphide and ammonia. We remove the carbon dioxide and contaminants from the Biogas, leaving pure methane – a renewable natural gas that can be burned to provide heat, electricity or road fuel.

STEP 5: The undigested remains of the ‘soup’ and dead bacteria are called Digestate, and are rich in key plant nutrients such as nitrogen, phosphate and potassium. The Digestate is pasteurised to kill off any harmful bacteria, leaving a wonderfully rich, organic fertiliser and compost.



The UK produces over 120 million tonnes of organic material that is suitable for Anaerobic Digestion each year. This includes:

•    90-100 million tonnes of agricultural by-products like manure and slurry
•    12-20 million tonnes of food waste (from households and industry)
•    1.7 million tonnes of sewage sludge

For more information visit: http://www.biogas-info.co.uk/index.php/faq.html


The amount of energy that an Anaerobic Digester can produce depends on the sort of material that goes into it. Generally though, 1 tonne of food waste will generate 300kWh of energy.

If all of the UKs food waste was processed this way, it could generate enough electricity to power 350,000 homes!

Commercial Incentives for AD operators

There are now a number of UK Government financial incentives aimed at encouraging the production of renewable energy.

Renewables Obligation Certificates (ROCs)

The Renewables Obligation is a Government scheme that supports the use of electricity from renewable sources. It is aimed specifically at biomass electricity plants, including Anaerobic Digesters. The certificates are traded between energy suppliers and have a fixed commercial value, which is guaranteed until 2037. This gives renewable energy investors long-term revenue certainty.

Feed in Tariffs (FiTs)

Aimed at small-scale renewable electricity production, this Government scheme offers a guaranteed payment for each kWh of electricity that is generated. An additional tariff is also paid where this electricity is exported to the National Grid.

Anaerobic Digestion is the only biomass technology that is supported under this scheme. Plants generating up to 5MW are eligible.

Renewable Heat Incentive

This is a similar scheme to FiTs, providing a financial reward to any organisation or property that uses a Biomass system (including Anaerobic Digestion) to provide their heating. Income through this incentive is guaranteed for up to 20 years.

Electricity Market Reform

This is a government policy to incentivise investment in low-carbon electricity. Linked to the Energy Act 2013, this policy includes a number of mechanisms to ensure the long-term affordability of electricity AND provide long-term revenue for new low-carbon initiatives, such as Anaerobic Digestion.

Benefits for the environment

  • Reduce the amount of biodegradable waste that gets sent to landfill each year.
  • Decrease the long-term, harmful effects of methane and carbon dioxide being released from rotting food waste.
  • Turn waste into a renewable, sustainable source of energy
  • Produce an entirely organic fertiliser

Benefits for Food Waste Producers

  • A more cost-effective method of food waste disposal; Anaerobic Digestion is typically 15-20% cheaper than equivalent landfill taxes.
  • An environmentally responsible method of waste disposal that helps boost your Corporate Social Responsibility rating.

Benefits for AD operators

  • Saving time moving and processing manure
  • Generate income from waste processing (e.g tipping fees and fertiliser sales)
  • Reduce water consumption and increase self-sufficiency.
  • Generate long-term revenue through a variety of different UK Government incentives.