Unlike the other biofuels mentioned so far, biogas is a gas and not a liquid. It is produced from the anaerobic (without oxygen) breakdown of organic matter that can include anything ranging from manure to sewage to plant material and even crops. It is given the generic name biogas because it is composed of several different chemicals.
The Chemicals in Biogas
The main chemical of interest in biogas is methane, which typically constitutes half of the mixture. The rest of the gas includes carbon dioxide, water, oxygen, hydrogen, nitrogen, and often a small amount of hydrogen sulfide. The presence of many of these other chemicals can be eliminated through refinement, processing, and through controlled production procedures.
Biogas is produced through the use of bacteria or other microorganisms that digest and degrade organic matter. These bacteria work only in oxygen-free (anaerobic) environments and participate in fermentation reactions similar to those used in the production of beer or wine.
Most biogas is produced from wastewater treatment facilities or from landfills. In these facilities, the process of fermentation is carefully monitored to ensure that methane constitutes at least 50% of the gas produced. At times, concentrations can reach as high as 75%. The methane is then refined and purified, often on site, before being used. Often, the produced fuel is either used directly on site for energy generation or is pumped into a pipeline for distribution. Biogas can also be compressed and transported by truck.
Other biofuels run into the question of land-use and how growing feedstock on virgin soil can actually lead to a carbon debt that takes centuries to pay off. Biogas is different because it is often made directly from animal waste, which has many environmental benefits.
First of all, manure and sewage have one major problem, which is that they contain high amounts of nitrogen. When left to decompose in the presence of oxygen, this nitrogen is converted to nitrogen dioxide with is 310 times more effective at trapping heat in the atmosphere than carbon dioxide. In fact, methane itself is 21 times more effective at trapping heat than carbon dioxide. So, biogas helps in two ways. To start, by converting waste to methane in anaerobic conditions, the production of nitrogen dioxide is avoided altogether. On top of the reduction in nitrogen dioxide is the fact that methane is never released. Because it is burned as a fuel, it produces only carbon dioxide and water (ideally), which means that the impact on global warming is greatly reduced by refining animal waste into biogas.
In North America, using all available animal waste (including landfills and sewage) would produce electricity to meet about 3% of energy needs. Thought of another way, one cow produces enough methane to power a 100 watt light bulb for a day and there are roughly 100,000,000 cattle in the United States (which is only about 1/3 of the 280,000,000 in India).
The largest investor in biogas technology is Germany with nearly 6,000 plants producing nearly 2.3 GW of electrical power. This investment is part of Germany's push for energy independence and greener technology.
Behind Germany, the United States, the United Kingdom, India, and China are all major producers of biogas. Coincidentally, the U.S., India, and China constitute three of the four largest cattle-owning nations in the world with the fourth (second by ranking) being Brazil.