Any organic source of energy or chemicals that is renewable. Its major components are (1) trees (wood) and all other vegetation; (2) agricultural products and wastes (corn, fruit, garbage ensilage, etc.); (3) algae and other marine plants; (4) metabolic wastes (manure, sewage); and (5) cellulosic urban waste. Conversion of these is performed in several ways: (1) by combustion(heat); (2) by fermentation (alcohol); (3) by gasification (synthesis gas); and (4) by anaerobic digestion (methane). In terms of energy, wood is by far the most important component of biomass. It has become a significant source of industrial heat, e.g., in paper mills and power plants, and intensive cultivation of trees for this purpose is under way. Wood is also a potential source of alcohols; ethyl alcohol is produced from wood on large scale in Brazil as a gasoline substitute. Agricultural wastes are fermented or gasified to synthesis gas; manures and municipal waste yield methane (biogas) on digestion. In 1981, biomass supplied 3.5% of U.S. energy requirements, and this is expected to increase substantially.
