Biomass is the collective term for all organic substances of relatively recent non-geological origin that can be used for energy production. This includes industrial, commercial, and agricultural wood and plant residues, such as municipal organic waste, animal manure, and also crops directly produced for energy purposes. Biomass can be solids such as wood and straw, or liquids as biofuels, or gaseous as biogases.
In other words, biomass resources are any form of organic material that can be originally used as not only an energy source but also as foods, fertilizers, forages, medicine, and other chemical products. However, under the hasty rise in energy prices and growing concerns about global warming, biomass energy(or bio-energy for simplicity) is especially becoming a subject of worldwide attention.
Bio-energy originates from the process of photosynthesis, and it is reserved as a form of chemical energy in hydrocarbons, being contained in land-based and water-based vegetation and various kinds of organic wastes. Photosynthesis is the fundamental chemical process in which green plants and certain other organisms utilize the energy of sunlight to convert carbon dioxide and water into organic chemical energy. Photosynthesis shows the important effect of absorbing carbon dioxide out of the atmospheric environment, and it is often described as the most important chemical reaction on earth. Therefore, biomass energy is non-fossil energy, and recognized as carbon neutral energy rather than as a renewable energy source based upon the assumption that exhausted carbon dioxide is compensated by the process of photosynthesis.
Bio-energy was utilized in 1860 to meet over 70% of the world’s total energy needs, mainly by means of the conventional combustion of wood fuel for heating and cooking. In 2000, the percentage contribution of bio-energy to the world’s energy demand had decreased to about 10％. However, in terms of millions of barrels of oil equivalent consumption per day, bio-energy usage had increased from 5 out of a total consumption of 7 in 1860, to about 20 out of a total consumption of 200 in 2000. The scope of bio-energy applications also increased many-fold during this period, and those had included a wider variety of fuels, organic chemicals, and products.
Typical biofuels and bio-conversion technologies are briefly described as follows,