Biogas methane is methane created from biologically created organic matter. The important thing to remember is that the term has entered common usage through the need to distinguish biogas derived methane from fossil fuel methane. Fossil fuel derived methane is known as 'natural gas'. Natural gas comes from mineral reserves, where it has been stored in the ground since its formation from living plants and animals hundreds of thousands of years ago. Natural gas/methane also comes sometimes from coal mines and coal measures which emit it.
So, in other words, biogas methane means 'green', 'renewable' methane, as opposed to natural gas which when burnt contributes to the greenhouse effect.
In addition to the biogas methane energy sources usually talked about, there are others which are not mineral gas created and these are either natural and un-natural in their origins, as follows:-
1. Gas being created naturally all the time in peat bogs and organic marine silts;
2. Methane produced in the stomachs of animals by the digestion of their foods (eg ruminants);
3. Biogas being created in farm slurry tanks etc, while farmers hold it waiting for dry weather when they can spread the manure/slurry on to their fields;
4. Landfill gas which is simply biogas created in landfills where the conditions are anaerobic.
If any sources of methane are emitted and rise from ground level into the atmosphere they are thought to be very potent causes of greenhouse warming. In fact, methane is about 20 times more active in absorbing the sun's heat, and causing global warming, than carbon dioxide.
Anaerobic decomposition in all these cases, produces methane biogas. At the same time it produces, carbon dioxide, some hydrogen, and other gases in traces. AD also produces a little heat, and a final product with a higher nitrogen content than is produced by aerobic fermentation.
The biogas production process which is usually inferred when people talk about biomethane is Anaerobic Digestion. This is a process which consists of feeding biomass to a large digester, in which methane-producing bacteria, under airless conditions, convert it into the energy-rich biogas.
The action of mixing and heating with the digester allows the bacteria to come into contact with the feedstock material, which provides food for the bacteria to multiply and convert the complex organic compounds into much simpler mostly soluble compounds. For example, sugars and starches, which then react in further stages giving off methane gas, which comprises about two thirds of biogas. The gas, a mixture of methane and CO2, is used for direct combustion in cooking or lighting applications, or to power combustion engines for motive power or electricity generation.
Methane (CH4) biogas technology is a renewable energy technology that uses various forms of biomass (animal dung, crop waste) and converts it into a useful energy source in the form of a gas (about 70% methane), via anaerobic microbial digestion. Methanogens are organisms that make methane via a unique metabolic pathway with unique enzymes. This produces a mixture of gases, primarily methane and carbon dioxide, and a nutrient-rich slurry. The CH4 rises into the gas holder where it is contained by a water seal. When the mixture of methane and air (oxygen) burn a blue flame is emitted, producing large amount of heat energy.
Methane biogas can be used for all the purposes in which natural gas is used, and can be used as the renewable equivalent of LNG as well.
Methane biogas has in the past been more expensive to produce that simply drilling for natural gas and pumping vast quantities of natural gas to our homes and industries. The biomethane needs "scrubbing" before it is clean enough to use in normal natural gas burning equipment. If it is not scrubbed, or not scrubbed adequately it will cause corrosion.
Methane biogas is about to become much more important as an energy source than it has been in the past, due to the ever rising cost of natural gas.
Thinking more about building a digester? Steve Last is web master for the fact filled Anaerobic Digestion Community web site where much more methane biogas and digester information is available.
Steve Last is also a regular contributor of dog breed related articles at The Dog Breeds Compendium.