There are several methods of converting biomass into energy. These methods include burning, alcohol fermentation, pyrolysis, and anaerobic digestion.
Direct burning of biomass is the most straightforward method of energy production. Mankind has burned wood and other forms of biomass for thousands of years, to keep warm, to cook food, and eventually to forge weapons and other tools.
The energy released by direct combustion takes the form of heat, and can be used to directly influence the temperature of a small environment or to power steam-driven turbines to produce electricity. Unfortunately, the burning of biomass is the cause of a great deal of pollution and has contributed to the so-called "greehouse effect" and global warming.
A relatively new field of research is the development of high energy crops specifically designed to be burned for power generation. Because at most only about 5% of a plant's mass is edible, the potential for large-scale biomass production is relatively great.
At the moment, however, growing large amounts of crops is still quite expensive. Thus, other methods of biomass energy production are being pursued with somewhat greater success. These methods include alcohol fermentation, anaerobic fermentation, and pyrolyis.
In alcohol fermentation, the starch in organic matter is converted to sugar by heating. This sugar is then fermented by yeast (as in the production of beer and wine). The resulting ethanol (also known as ethyl alcohol or grain alcohol) is distilled and then blended with another fuel. "Gasohol," the end product, has been used successfully in Brazil and the United States as an alternative to regular gasoline. The drawback to this method of biomass energy conversion is that the process itself requires the use of fossil fuels, and is therefore somewhat inefficient.
Anaerobic digestion converts biomass, especially waste products, into methane (a major component of natural gas) and carbon dioxide. The biomass is mixed with water and stored in an airtight tank. This form of biomass energy conversion is attractive because it converts human, animal, and agricultural waste into a gas that is readily used as an energy source. Although the process is quite costly, it is relatively efficient.
Pyrolyisis involves the heating of biomass in the absence of oxygen. Biomass such as wood or agricultural waste is heated to around 1000 degrees Fahrenheit and allowed to decompose into gas and charcoal (carbon). A major advantage of pyrolysis is that carbon dioxide, one of the main drawbacks to most biomass energy conversion processes, is not produced. A disadvantage, however, is that the biomass must be heated to relatively high temperatures, a process that in and of itself requires significant amounts of energy.