Category
Biochar
Biochar is the porous, stable solid carbon left when biomass is heated in the absence of oxygen. It carries by far the best delivery ratio of any durable pathway (22% from 2022 through the second quarter of 2025) and the field’s most contested durability methodology.
One of eight durable carbon removal pathways presented by CDR Türkiye, all intended to store carbon for centuries to millennia.
Overview
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How it is made Biochar is produced by heating agricultural or forest residue above 350°C under controlled and limited oxygen that prevents combustion.
The heat drives off volatile fractions as gas and liquid, leaving porous carbon behind that resists decay. The carbon the plant took from the air stays in that solid form instead of decomposing back to the atmosphere, and that is precisely where the removal claim comes from.
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Strength: delivery The pathway’s present strength is delivery.
Between 2022 and the second quarter of 2025, 658–683 kilotonnes were delivered, and the 22% delivery ratio is by far the best of any pathway; biochar accounted for 48.1% of the first million credits retired on the Puro registry. Prices sit at the low end of the field: $125–145 per credit across 2025, each credit standing for one tonne of CO2 removed.
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Weak link: durability accounting The weak link is durability accounting.
Published claims span 100 years to a 100-million-year half-life, and the spread comes from decay model choice rather than measurement. The Puro methodology counts at least 200 years for biochar that a laboratory test shows to be sufficiently carbonised, and the EU delegated regulation likewise calculates the share counted as permanent as the carbon remaining after 200 years. But its own definition names no number of years, saying only that stable biochar is expected to store carbon for at least several centuries, so 200 years is a calculation horizon rather than a legal threshold. Verification after soil application is close to infeasible: one study needed 140 soil samples per quarter hectare to bring the margin of error down to 5%.
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Türkiye: feedstock and data In Türkiye the feedstock side looks comfortable and the data side does not.
The Ministry of Energy’s collectable, economic biomass potential is 3.9 million tonnes of oil equivalent (Mtoe) per year, while peer-reviewed work puts primary agricultural residues at 39.4 Mt per year and secondary processing residues at 6.8 Mt per year. That second study already nets out competing uses (soil protection, animal feed, heating), and this is where the sustainability question sits: how much of the residue can actually be collected, how much has to stay in the soil, and how much is already spoken for. Academic estimates of Türkiye’s biochar removal potential exist, but no national assessment applies the constraints a CDR methodology would require, and the 3.9 Mtoe figure is an energy-sector estimate rather than a CDR feedstock estimate.
IPCC 2019 Refinement, Biochar Appendix CDR.fyi Nasdaq CORCCHAR index Sanei et al., Int. J. Coal Geology Puro.earth Biochar Edition 2025 EU Delegated Regulation C(2026) 553 Akyürek, Polish Journal of Environmental Studies Lotz et al., Frontiers in Climate Turkish Ministry of Energy, biomass page Bahadıroğlu et al., YYU J. Agricultural Sciences
Technologies and applications
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Technology types
The technical methods that capture, convert or store the carbon.
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Technology type
Slow pyrolysis
A production route in which biomass is heated without oxygen for a long time, so the dominant product is solid char.
- How it works
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- Preparation
Agricultural or forest residue is collected and dried.
- Heating
Heat above 350°C is applied in an oxygen-free reactor for a long time.
- Separation
Volatile fractions leave as gas and liquid; stable carbon remains as a solid.
- Cooling
The char is cooled under control so the ignition risk is removed.
- Lab test
A sample is tested in the laboratory to see how thoroughly carbonised the char is, and the durability class follows from the result.
- Preparation
- Durability
- Contested
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Threshold: 200 years
Applies to biochar that a laboratory test shows to be sufficiently carbonised; it is the floor the methodology treats as durable, not a measured lifetime.
- What it rests on
- The 200-year figure is a methodology threshold, not a measured lifetime. Published claims span 100 years to a 100-million-year half-life and the spread comes from decay model choice. The long heating time raises char yield, which is why most commercial biochar is produced this way.
- Puro.earth Biochar Edition 2025
- Türkiye context
- Primary agricultural residues run at 39.4 Mt per year and secondary processing residues at 6.8 Mt per year; feedstock does not appear to be the constraint.
- Bahadıroğlu et al., YYU J. Agricultural Sciences
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Technology type
Fast pyrolysis
A production route in which biomass is heated very rapidly so the dominant product is liquid bio-oil, with char as a by-product.
- How it works
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- Milling
Biomass is milled fine and its moisture is reduced.
- Flash heating
It is heated to about 450–550°C without oxygen, for a very short time.
- Char separation
The char is separated from the hot vapour before the vapour is cooled.
- Vapour separation
The remaining vapour is cooled rapidly and condenses into liquid bio-oil.
- Product split
Bio-oil goes to a separate storage route; char not burned for process heat follows the biochar route.
- Milling
- Durability
- Contested
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Threshold: 200 years
Applies to the char fraction only; the durability of the liquid fraction is set by where it ends up, not by this route.
- What it rests on
- Char yield is lower than in slow pyrolysis, so removal per tonne of biomass is lower too. The bio-oil raises a separate question: burnt as fuel it delivers no removal, and injected underground it falls under BiCRS, where no peer-reviewed permanence study exists.
- Puro.earth Biochar Edition 2025
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Technology type
Gasification
A thermochemical route in which biomass is converted to a fuel gas under restricted oxygen, leaving solid char as a by-product.
- How it works
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- Feeding
Dried biomass is fed into the gasifier.
- Partial combustion
Restricted oxygen at high temperature produces a combustible synthesis gas.
- Gas cleaning
Tars and particulates are removed from the synthesis gas.
- Char collection
Solid char remaining at the reactor base is collected separately.
- Lab test
The char is tested in the laboratory for how thoroughly carbonised it is and classified for durability.
- Feeding
- Durability
- Contested
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Threshold: 200 years
Applies to the char fraction only; the carbon in the synthesis gas returns to the atmosphere when it is burnt.
- What it rests on
- Char yield is lower than in pyrolysis and gasification char typically carries more ash; both pull removal per tonne down. The primary product here is energy and the removal is a by-product, which makes the allocation of the removal claim decisive.
- Puro.earth Biochar Edition 2025
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Technology type
Hydrothermal carbonisation Hydrothermal carbonisation (HTC)
A route in which wet biomass is processed in hot water under pressure and converted into a solid product known as hydrochar.
- How it works
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- Wet feed
High-moisture biomass is fed to the reactor without drying.
- Pressurised heating
The vessel is heated at a pressure that keeps water in the liquid phase, where the reaction proceeds.
- Solid separation
The hydrochar formed is filtered out of the liquid phase.
- Dewatering
The separated solid is pressed to remove water.
- Lab test
The degree of carbonisation is tested in the laboratory and compared against the durability threshold.
- Wet feed
- Durability
- Contested
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Unlikely to meet the threshold
Hydrochar is less stable than pyrolysis biochar and does not readily meet the durable-removal threshold.
- What it rests on
- The advantage is that no drying is needed, so wet streams such as food waste and sewage sludge can be processed directly. In exchange the product is less thoroughly carbonised and often fails the laboratory test, landing outside the band the methodology treats as durable.
- Puro.earth Biochar Edition 2025
Application areas
The sectors, facilities and end uses where the method is applied.
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Application area
Soil application
The use route in which finished biochar is worked into agricultural soil, where it is both stored and alters soil properties.
- How it works
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- Milling
The char is brought to a particle size that mixes into soil.
- Spreading
Milled char is spread across the field with dust controlled.
- Incorporation
Tillage works the char into the root zone.
- Record
Applied quantity and parcel are entered into the registry.
- Milling
- Durability
- Contested
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Depends on prior measurement
The record comes from the carbon measured before application; monitoring afterwards is limited in practice.
- What it rests on
- The durability record is kept on the production side because verification in soil is close to infeasible: one study needed 140 soil samples per quarter hectare to bring the margin of error down to 5%. The laboratory carbonisation test is not a reliable guide to permanence on its own either.
- Lotz et al., Frontiers in Climate
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Application area
Biochar as a concrete additive
The use route in which biochar is mixed into cementitious material and the carbon stays locked inside the hardened material.
- How it works
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- Fine milling
The char is milled fine enough to disperse in the mix.
- Mixing
Milled char is blended with cement, aggregate and water at a set dose.
- Setting
The mix hardens and the char stays locked inside it.
- Strength check
Samples confirm the dose has not compromised structural strength.
- Fine milling
- Durability
- Early stage
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Depends on the structure’s life
The carbon stays in the concrete for the life of the structure; what happens afterwards depends on demolition and recycling practice.
- What it rests on
- Its advantage over soil application is verification: the char sits inside a closed material and the sampling problem found in soil does not arise. Against that, the dose is capped by strength requirements, so carbon stored per unit of construction stays small.
Frequently asked questions
What is biochar?
Biochar is the porous, stable solid carbon obtained by heating biomass above 350°C under limited oxygen that prevents combustion; the IPCC separates three classes by temperature: low at 350–450°C, medium temperature pyrolysis at 450–600°C, and high temperature pyrolysis and gasification above 600°C. Volatile fractions leave as gas and liquid while carbon that resists decay remains. Turkish-language material on this site writes the term as biyoçar.
Is biochar durability really 200 years?
200 years is a methodology threshold rather than a measured lifetime: the Puro methodology treats biochar that a laboratory test shows to be sufficiently carbonised as durable for at least 200 years. The EU delegated regulation uses the same 200 years, but as the horizon over which it calculates the share counted as permanent; its own definition names no number of years and instead expects stable biochar to store carbon for at least several centuries. Published claims span 100 years to a 100-million-year half-life, and the spread comes from decay model choice rather than measurement.
Can biochar be verified after it goes into soil?
Barely. One study needed 140 soil samples per quarter hectare to bring the margin of error down to 5%. The laboratory carbonisation test is not a reliable guide to permanence on its own either, so verification leans on measurement at the production stage, before application.
What do biochar credits cost?
Nasdaq’s biochar credit price index ran at $125–145 per credit across 2025. Market prices were $150–250/t in 2024–25 and producer break-evens $100–180/t. This is the lowest price band in the field.
When does biochar stop counting as a removal?
Where the feedstock is diverted from another use and a fossil input takes its place, the net calculation collapses. Where the syngas and oil released during pyrolysis are burnt for energy, that carbon returns to the atmosphere and the removal is only the stable carbon left in the solid. Where process heat is fossil, or the biomass is harvested from forest and carries a carbon debt, the claim shrinks again.