Some biomass is formed when animals eat plants and, through the digestion and excretion process, turn it into biomass, and the rest is formed when microorganisms eat plant material, or the plants are consumed by fire. Either way, all biomass has a carbon base and is made of a blend of organic molecules that have hydrogen and also usually have oxygen, nitrogen and other atoms.
Fossil fuels like gas, oil and coal also come from biological material, but biomass is different in terms of the time frame involved. While fossil fuels take carbon out of the atmosphere over centuries, biomass takes it out while the plant is growing. When managed properly, biomass comes to harvest but also is constantly replenished. This ensures a closed cycle of carbon so that the atmospheric levels of carbon dioxide do not change.
Biomass comes in one of five different categories. Virgin wood comes from wood processing or cultivation in the woods. Energy crops have a high yield and are intentionally grown for use in energy applications. Agricultural residues result from harvesting crops or processing produce. Food waste results from the manufacturing, preparation and processing of food and beverages, as well as waste from the consumer. Industrial waste comes from a variety of industrial and manufacturing processes. Chemical and thermal conversion technologies exist to make all of these usable as clean energy sources.