Biogas is produced by anaerobic digestion with anaerobic bacteria or fermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops. It is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes.
The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel. It can be used for any heating purpose. It can also be used in a gas engine to convert the energy in the gas into electricity and heat, in a cogeneration plant.
Composition of biogas
The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55% - 75% methane, which for reactors with free liquids can be increased to 80% - 90% methane using in-situ gas purification techniques. As produced, biogas contains water vapor. The fractional volume of water vapor is a function of biogas temperature.
Benefits of biogas
When biogas is used, many advantages arise. The use of biogas in generators can generate enough electricity to meet a non-negligible percentage of electricity expenditure. In addition, biogas could potentially help reduce global climate change. Normally, manure from livestock farms that is left to decompose releases two main gases that cause global climate change: nitrous oxide and methane. These two gases warm the atmosphere more than carbon dioxide.
By converting cow manure into methane biogas via anaerobic digestion, the millions of cattle would be able to produce billions of kilowatt hours of electricity, enough to power millions of homes. Furthermore, by converting cattle manure into methane biogas instead of letting it decompose, global warming gases could be reduced by 99 million metric tons or 4%.