There are several technologies for converting biomass into energy. The primary methods involve releasing the energy through fire, such as with an industrial boiler; converting it through heat, such as producing methane from solid wood; converting it through bacteria or yeast to beak down the biomass, such as making ethanol from corn; and altering the chemical makeup of a biomass feedstock to make it a more efficient energy product, such as turning vegetable oils into 'biodiesel', a clean-burning biofuel that can be used in diesel engines.
Other uses of biomass, such as tapping the energy potential of wastes and residues, likewise offer sustainable options. Agricultural activities, for example, produce both marketable food crops and large quantities of stalks, cobs, straws and stems that could be used for energy. By products from the timber industry, such as the tops and limbs of trees, sawdust, bark and other scraps of wood, can be collected and used for energy. As well, more than 60% of municipal solid waste is composed of organic materials such as paper, cardboard, wood and food wastes that can be burned to recover their energy rather than merely taking up space in a landfill (once buried, however, organic wastes can also be tapped for their methane gas).
In some Pacific island nations, oil from the copra plant is used in its natural form in slightly modified heat engines. In China, electricity is being produced from rice husks where electrical generation from the state network is scarce. Either a gas is made from the rice husks, which is then used in a gas engine generator to produce electricity; or the rice husks are burned in a furnace to heat steam boilers which then drive steam turbines. Although China produced 10 million tonnes of rice husks in 1991, only 1/40th was used to produce electrical power.
A Danish firm developed a system that converts pig slurry into water, gas and manure. The system underwent tests in the year 2000 in central Denmark, processing waste from 20,000 pigs while providing energy to a local electricity works and heating to five farms in addition to providing manure and potable water.