Updated September 2026.
A “circular economy” tries to turn waste back into something useful instead of burying or burning it for nothing. Bioenergy fits neatly into that idea. Food scraps, manure, sewage sludge, crop leftovers and forestry offcuts all contain energy that can be recovered. Done well, it cuts waste, pollution and fossil fuel use all at once. Done badly, it can do more harm than good. Here is how to tell the difference.
How waste becomes energy
- Anaerobic digestion. Bacteria break down wet waste such as manure, food scraps and sewage in sealed tanks, producing biogas, which is mostly methane. The gas can run engines to make electricity, or be cleaned into “renewable natural gas” and piped like ordinary gas. What’s left over is a nutrient-rich fertilizer.
- Landfill gas capture. Buried rubbish rots and gives off methane anyway. Capturing it stops a potent greenhouse gas escaping and turns it into fuel. In the US, the EPA counted 542 landfill gas energy projects operating in 2024.
- Waste-to-energy plants. These burn household rubbish that can’t be recycled to make electricity and district heating. Sweden is the famous example: less than 1% of its household waste goes to landfill, and it imports rubbish from other countries to keep its plants running.
- Liquid fuels from residues. Used cooking oil and animal fats are already refined into renewable diesel and jet fuel. Brazil has run cars on sugarcane ethanol for decades, and it now also turns the leftover cane fiber into power.
When it works, and when it doesn’t
The climate benefit depends almost entirely on what the feedstock would otherwise have done:
- Clear win: capturing methane from manure or landfill that would have escaped anyway. Methane traps far more heat than CO₂ over a few decades, so capturing it has an outsized benefit.
- Usually good: genuine waste and residues with no better use.
- Questionable: burning whole trees, or growing crops specifically for fuel on land that could grow food or store carbon. That can compete with food, drive deforestation, and release more carbon than it saves for decades.
- A trade-off: incinerating waste beats landfill, but it still releases the carbon in plastics. Waste that could be recycled should be.
More: Exploring Bioenergy, Biomass Energy and Algae Biofuel.
