Updated September 2026.
Biomass (wood, crop leftovers, manure, food waste, oils and fats) holds chemical energy captured from sunlight. There are half a dozen main ways to get it back out, each suited to different materials and different end uses. (For the big picture of biomass and its pros and cons, see Biomass Energy.)
The conversion routes
| Process | How it works | Typical inputs | Output |
|---|---|---|---|
| Combustion | Burning, usually in a boiler | Wood chips, pellets, straw, bagasse | Heat, steam, electricity |
| Anaerobic digestion | Bacteria break down wet waste without oxygen | Manure, sewage sludge, food waste | Biogas (mostly methane) plus fertilizer |
| Fermentation | Yeasts turn sugars into alcohol | Corn, sugarcane | Ethanol |
| Transesterification or hydrotreating | Chemically converting oils and fats | Vegetable oil, used cooking oil, tallow | Biodiesel, renewable diesel, sustainable aviation fuel |
| Gasification | Heating with limited oxygen | Wood, dry residues, some wastes | Syngas (CO + H₂) for power, fuels or chemicals |
| Pyrolysis | Heating with no oxygen | Wood, residues | Bio-oil, gas and biochar |
Where each shines
- Anaerobic digestion is often the best climate deal. It captures methane from manure and waste that would otherwise escape, and returns nutrients to fields.
- Renewable diesel and sustainable aviation fuel from waste oils are among the few near-term low-carbon options for trucks and planes, but the supply of waste oil is limited.
- Combined heat and power at sawmills and paper mills uses their own residues very efficiently.
- Biochar from pyrolysis can lock carbon into soil for centuries, and it is one of the more credible forms of carbon removal.
- Bioenergy with carbon capture (BECCS) can, in principle, remove CO₂ from the air, if the biomass is truly sustainable and the carbon is stored permanently.
The sustainability test
Bioenergy is only as green as its feedstock. Waste and residues that would otherwise rot or be burned in the open are usually beneficial. Crops grown on cleared land, or whole trees cut for fuel, can have a carbon debt that takes decades to repay. Good policy rewards the first and screens out the second.
Related: Bioenergy and the Circular Economy and Algae Biofuel.
