Anaerobic Digestion

Anaerobic digestion of organic material produces biogas. Using a series of filters and security features, the biogas can be cleaned to a high quality gas that can either be used directly as a fuel in specially prepared engines or used a fuel for vehicles. The technology for producing and collecting biogas has been tried and tested over many years and Organics has a lengthy experience of project development.

Anaerobic Digestion can be carried out at any scale, from a small scale anaerobic digestion tank on a single farm to large scale covered lagoons.

What is Anaerobic Digestion?

Anaerobic digestion involves the breakdown of organic waste by bacteria in an oxygen-free environment. It is commonly used as a waste treatment process but also produces a methane-rich biogas which can be used to generate heat and/or electricity.

What is the equipment requirement?

Anaerobic digstion equipment consists, in simple terms, of a digester tank that has to be heated, a gas holding tank to store the biogas, a flare stack to burn excessive biogas and, if electricity is to be produced, a gas-burning engine/generator set.

What happens inside the tank?

The organic waste is broken down in the tank and up to 60% of this waste is converted into biogas. The rate of breakdown depends on the nature of the waste and the operating temperature. Typically, biogas has a calorific value of between 50% and 70% that of natural gas and can be combusted directly in modifed natural gas boilers or used to generate energy.

How does the process work?

The digestion process takes place in a warmed, sealed airless container (the digester) which creates the ideal conditions for the bacteria to ferment the organic material in oxygen-free conditions.
The digestion tank needs to be warmed and mixed thoroughly to create the ideal conditions for the bacteria to convert organic matter into biogas (a mixture of carbon dioxide, methane and small amounts of other gases).

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Methane Reduction

Methane is a major greenhouse gas. Current disposal practices for slurry and food residues cause methane to be released through natural processes. AD exploits this process so that the gas can be used as a fuel. A well-managed AD scheme will aim to maximise methane generation, but not release any gas to the atmosphere.

Energy Production

AD provides an energy source with no net increase in atmospheric carbon. Using fossil fuels for energy production creates carbon dioxide which causes climate change, resulting in a warming of the planet. By replacing energy from fossil fuels, AD can help reduce overall quantities of carbon dioxide in the atmosphere and reduce dangers of climate change.

Displace fossil fuel

The feedstock for AD is a renewable resource, and does not deplete finite fossil fuels. Energy generated through this process can help reduce the demand for fossil fuels (if used to replace energy from fossil fuels). The use of the fibre and liquor as a contribution to fertiliser regimes can in turn reduce fossil fuel consumption in the production of synthetic fertiliser

Nutrient Recycling

AD products (liquid fertiliser and fibre), when applied correctly to agricultural crops, can reduce the need for synthetic fertilizers within an overall fertilizer programme and reduce runoff to rivers of highly toxic ammonia that can decimate fish populations.

Land Management

Poor disposal of animal slurries can cause land and ground water pollution. AD meets regulatory requirements and site license conditions, creating an integrated management system which reduces the likelihood of this happening and reduces the possibility of fines and sanctions being imposed for such pollution.

Odour Control

Anaerobic Digestion can reduce odour from farm slurries and food residues by up to 80% thus obviating the requirement for expensive odour control perfume systems or for upsetting Mrs. Murphey’s afternoon lunch party. AD is carried out under controlled conditions that ensure that all generated gas are contained within a closed tank and are only released either to be used as a fuel for energy generation or burned under controlled conditions.


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