Biogas is a mixture of methane and carbon dioxide resulting from the anaerobic decomposition of domestic, industrial and agricultural waste products.
Biogas can be captured and used as an energy source.
There are two common types of biogas:
Sewage waste can be treated to generate solid, liquid and gas products, using anaerobic digestors. The liquid and gas can be siphoned off either to be burnt directly for energy generation or refined into other products. The solid residue can be used as fertiliser.
For more information on the anaerobic digestion, please see the How it works section.
As the waste buried in landfill sites undergoes anaerobic digestion it generates gases. These gases are known collectively as landfill gas (LFG) and can be harvested to be used in the generation of energy.
What is landfill gas?
Biodegradable waste that is buried in landfill sites undergoes a process called anaerobic digestion. This process produces various gases, collectively known as landfill gas (LFG). LFG has a high methane content and this gives it the potential as a fuel, which can then be used to generate electricity or to provide process heat.
Landfill gas can be burned either directly for heat or be used to generate electricity.
Factors including the type of waste, temperature and moisture content of landfill site affect how much gas will be available for extraction.
This process is carried out by creating horizontal or vertical wells in the landfill and drawing the gas out through a system of pipes. The gas is then piped to a generator, which is usually located in the vicinity of the extraction plant.
Is landfill gas a renewable source of energy?
Although landfills are considered environmentally unsustainable, they are the most widespread form of waste disposal. Recycling and other forms of waste management (as well as policy incentives such as landfill taxes) are making some impact on the amount of waste being put in landfills. However, it is likely that landfills will continue to be used for decades to come.
As such, landfill gas is not a strictly renewable source of energy. However, it is making use of otherwise harmful gases.
Is landfill gas an environmentally friendly source of energy?
If landfill gas is not harvested or contained, it escapes into the atmosphere. This is undesirable, as landfill gas contains approximately 50% methane - the gas found in natural gas - which is a greenhouse gas with a much higher global warming potential than carbon dioxide.
The generation of electricity from landfill gas is considered to be an environmentally-friendly solution to the problem of landfill gas, insofar as its use in waste-to-energy processes allows for the effective management of biodegradable waste which would otherwise have detrimental effects on the climate and on air quality.
What is the carbon cycle?
Most biodegradable waste in landfill comes from sources such as food waste, which have a short carbon cycle.
For more information on the carbon cycle, please see the Carbon cycle page.
How common is the use of landfill gas?
According to the Biogas Barometer 2008 produced by the EurObserv'ER project , the UK generated 5,299 GWh of energy from biogas in 2007. According to this report, the UK is currently the second largest biogas-based electricity producer in Europe. Over 90% of this biogas comes from landfill sites.
The Biogas Barometer 2008 produced by the EurObserv'ER project gives details of biogas production in EU Member States.