Definition
What is biochar?
Biochar is a plant-based charcoal made by heating biomass to a high temperature with little or no oxygen (pyrolysis or gasification), intended for a use other than burning: soil, animal feed, bedding, compost or filtration.
Its use is what sets it apart from charcoal: charcoal is burned, biochar is kept. Its value comes from its porous structure, which offers a very large internal surface to microorganisms, water and nutrients, and from its very stable carbon, which breaks down over centuries rather than months.
At a glance
| Feedstock | Dry biomass, mostly woody: husks, shells, fruit stones, vine prunings, forestry residues, pruning waste, woody invasive plants. |
|---|---|
| Process | Pyrolysis or gasification, usually between 400 and 900 °C. Temperature changes the porosity, pH and stability of the biochar. |
| Co-products | Syngas and heat, usable for cooking, drying, heating a greenhouse or water. |
| Uses | Soil amendment, additive in fermented feed, animal bedding, compost accelerator, water and air filtration. |
| Climate | Part of the carbon captured by the plant stays stored in the soil for centuries. |
| European framework | EBC certification (European Biochar Certificate); sold as a fertilising product under EU Regulation 2019/1009. |
Biochar in the waste hierarchy
Biochar corresponds to level 4 of the organic waste hierarchy described by Paul Olivier: we only carbonise what can no longer feed an animal (level 1), larvae and worms (level 2) or a compost (level 3). Carbonising edible leftovers would be a loss.
In this approach, biochar is first of all a co-product of heat: woody waste is gasified to cook, dry or heat, and the carbon-rich residue becomes biochar. It then moves through the other levels before reaching the soil.
Biochar → fermented feed → manure → larvae and worms → compost → soil
According to Paul Olivier, putting biochar straight into the soil is not always the best option: after passing through feed, bedding or compost first, it arrives “charged” with nutrients and microorganisms.
Frequently asked questions
- What is the difference between biochar and charcoal?
- They are made in a similar way, but used differently. Charcoal is a fuel. Biochar is kept for soil, livestock or filtration, and its production aims for consistent quality: few tars, high porosity, low contaminant content.
- Is biochar a fertiliser?
- No. Biochar alone provides few nutrients. It is a carrier: it holds water and nutrients and hosts microorganisms. That is why it is used “charged”, through a compost, vermicompost, bedding or urine.
- How long does biochar stay in the soil?
- A large share of its carbon persists for centuries or longer, depending on the production temperature. This is why biochar is recognised as a durable carbon storage method.
- Which biomass should be used?
- Brown and woody waste that composts poorly: nut and almond shells, fruit stones, vine prunings, forestry residues, pruning wood, rice husks, woody invasive plants. Never waste that is still edible.
- Can biochar filter water?
- Yes. Its porous surface captures part of the pollutants, odours and some excess nutrients such as phosphate. Its effectiveness depends on the biomass and the temperature, and must be measured for each source.
- Can I make it myself?
- On a small scale, yes, with a top-lit updraft gasifier (TLUD), which produces both clean heat and biochar. Beyond household use, a pyrolysis unit is subject to environmental regulations, which vary by country.
Sources and references
- Paul Olivier, Waste Transformation and Closed-Loop Farming (presentation).
- European Biochar Certificate (EBC): biochar certification guidelines.
- Regulation (EU) 2019/1009 on fertilising products, component material category 14 (pyrolysis and gasification materials).