The term biomass covers a broad range of materials that offer themselves as fuels or raw materials and that have in common that they are all derived from recently living organisms. This definition clearly excludes traditional fossil fuels, since although they also derive from plant (coal) or animal (oil and gas) life, it has taken millions of years to convert them to their current form. For the purpose of this book, we have chosen to include all agricultural and forestry wastes as well as purpose-grown material as biomass, thus clearly including animal refuse such as poultry litter. There is still a potential overlap between what is classified as waste and what as biomass. We have considered human sewage sludge as well as wastes from industrial processes as waste. Black liquor, an intermediate material in the paper industry with important fuel use, is treated here as biomass.
Although biomass is not a major industrial fuel, it supplies 15-20% of the total fuel use in the world. It is used mostly in nonindustrialized economies for domestic heating and cooking. In industrialized countries the use of biomass as a fuel is largely restricted to the use of by-products from forestry and the paper and sugar industries. Nonetheless, its use is being encouraged as part of a strategy for C02 abatement.