Introduction

According to the latest IPCC report, we are not able to reach the 1.5°C target by 2050 with reduction and avoidance voluntary carbon market (VCM) methods alone but need to heavily supplement them with carbon dioxide removal (CDR) projects and credits.¹

Biochar is one of the most currently scalable CDR technologies² and is going to be the focus of this blog.

1. Definition and Overview of Biochar

Biochar is charcoal that is produced by heating organic material, such as wood, crop residues, or manure, in a low-oxygen environment. The typical process for developing biochar is known as pyrolysis, which breaks down the organic material into a carbon-rich material that can be used as a soil amendment or a carbon sequestration method³, with residence times of approximately 2000 years⁴ making it an ideal technology for CDR. See figure 1 for a picture of biochar.

When added to soil, biochar can increase water retention, nutrient availability, and microbial activity, which can lead to increased crop yields and reduced fertiliser use.⁵

From my experience working as a project developer in Ghana and Sierra Leone, I can agree with BeZero’s CDR scalability report that biochar has one of the lowest cost and resource barriers to entry compared to other CDR methods and really shines as it has the ability to developed in very low tech environments with high financial and resource constraints.

What are the main uses of biochar?

Biochar has a variety of potential uses across a range of sectors, including agriculture, forestry, water treatment, and energy. There are over 60 different uses, from pillow stuffing to shielding people from radioactive radiation, which can be found here; however, the key potential uses are:⁶

1. Soil amendment: Biochar can be used as a soil amendment to improve soil quality and fertility. It can increase soil porosity, water-holding capacity, and nutrient retention, which can lead to increased crop yields.
2. Carbon sequestration: Biochar has a high carbon content and can sequester carbon in the soil for long periods of time, which can help mitigate climate change.
3. Water treatment: Biochar can be used as a filtration medium for water treatment, as it has a high surface area and can adsorb pollutants such as heavy metals, pesticides, and pharmaceuticals.
4. Livestock feed supplement: Biochar can be used as a feed supplement for livestock, as it can bind to toxins and reduce their absorption in the digestive tract.
5. Energy production: Biochar can be used as a renewable energy source through the process of combustion, gasification, or pyrolysis.
6. Waste management: Biochar can be used as a method of waste management, as it can be produced from organic waste materials such as agricultural residues and forest debris.

Overall, biochar has the potential to provide sustainable solutions across a range of sectors and can contribute to the transition to a circular economy.

2. Biochar Production

Biochar production is the process of converting biomass into a carbon-rich material through the process of pyrolysis, a thermal decomposition process that occurs in the absence of oxygen and results in the breakdown of the organic material into solid, liquid, and gas components, biochar, bio-oil and biogas respectively.⁷ See our infographic in figure 2 for the big picture summary.

1. Feedstock preparation: This step is where biomass materials are collected and prepared for pyrolysis. Depending on the methodology this can either be purposely grown biomass, such as elephant grass or bamboo, or waste agricultural residues such as wood chips, sawdust or straw. Under investigation agricultural residues can be collected from a variety of unusual localities such as seaweed or chicken litter⁸. Here is good paper to illustrate how project developers can market size the most probable biochar feedstocks in a country: biochar feedstocks in Ghana⁹. However Verra¹⁰ and the European Biochar Certificate¹¹ do limit them to a few certain types to reduce GHG accounting complexity.
   The biomass after collection is then typically sun dried, as the thermal heat capacity of water takes a lot of energy from fuel to remove which is expensive, and shred to a uniform size for pyrolysis.
2. Pyrolysis: The prepared biomass is heated to high temperatures in the absence of oxygen, with lower energy requirement than intuitively expected as after 250°C the process becomes an exothermic process.¹² The pyrolysis process can be carried out in different types of equipment, such as a kiln¹³, a retort¹⁴, or a reactor¹⁵. The temperature, heating rate, and residence time of the biomass in the pyrolysis reactor, depending on the technology, can be controlled to produce different types of biochar with varying properties.¹⁶
3. Char collection and cooling: The pyrolysis process produces solid biochar, liquid bio-oil, bio-gas and other combustible gases. The biochar is typically separated from the other products and cooled to prevent further combustion.¹⁷
4. Post-processing: The biochar may be further processed to improve its properties, such as by grinding to a finer particle size or activating it with chemical or physical methods. Post processing, typically for soils, is a mix between impregnation, doping the biochar with varying different chemicals for soil health; and activation which is the increasing of surface area or pore density,¹⁸ for an extra increase in water retention capability.
5. Application: Biochar can be used as a soil amendment, as a carbon sequestration tool, or in industrial applications such as water treatment or energy production. There are over 60 different applications for biochar.
   
   

What are the properties of Biochar?

There are many factors that affect biochar: it is good to have a solid baseline for what the natural characteristics of biochar are.

Physical Characteristics:

• Particle size: Biochar can range in particle size from fine dust to large chunks, depending on the pyrolysis conditions and post-processing techniques used.
• Porosity: Biochar typically has a high level of porosity, which can range from micro- to macropores. Porosity can affect the biochar’s ability to retain water, nutrients, and other compounds.
• Surface area: Biochar has a high surface area, which can range from a few hundred to several thousand square meters per gram. Surface area can affect the biochar’s ability to adsorb nutrients, pollutants, and other compounds.
• Color: Biochar can range in colour from light brown to black, depending on the degree of carbonization.

Chemical Characteristics:

• Carbon content: Biochar typically has a high carbon content, ranging from 50% to over 90% depending on the pyrolysis conditions.
• pH: Biochar can have a range of pH values depending on the feedstock and pyrolysis conditions. Biochar with a high pH can help neutralize acidic soils.
• Nutrient content: Biochar can contain nutrients such as nitrogen, phosphorus, and potassium, depending on the feedstock and pyrolysis conditions.
• Cation exchange capacity (CEC): Biochar has a high CEC, which can help it retain nutrients and other compounds.

Overall, the physical and chemical characteristics of biochar can vary widely depending on the production process and application. Understanding these characteristics is important in selecting the appropriate biochar for a specific application.

3. Alternative methods of creating biochar & reasons for the heterogeneity of biochar production

When it comes to biochar production besides feedstock, there are two key elements that should be taken into consideration:

1. Physical parameters (temperature, pressure, time taken to process)
2. Technology level of the facility (what is the ability of the facility to scale, capture GHG’s and other useful bioproducts such as bio-oil and bio-gas)

The interplay of these two variables explains much of the heterogeneity when creating biochar. Biochar has multiple different methods of production under different physical parameters, with the most dominant method being slow pyrolysis, however there are a few other options such as fast pyrolysis, gasification, hydrothermal carbonisation and torrefaction. Each of these different processes is optimal for different regions, feedstocks and biochar application. Currently Verra¹⁹ and Puro.earth²⁰ are the only two registries that have active approved methodologies for the creation and application of biochar for soil amendment. Within these methodologies there is no current de-facto standard on the equipment and physical process for production of biochar. This gives rise to a large heterogeneity in biochar production.

Verra, the registry which has issued two thirds of all carbon credits follows the European Biochar Certificate — EBC Guidelines for Sustainable production of Biochar²¹ and splits the production methods technologies into two broad categories, high technology, and low technology facilities. This is useful to mentally partition them into, as biochar is an extremely accessible CDR technology with low financial barriers; the technology level just depends on the level of scale of a project, the inputs needed, and the level of capex investment available to the project developer. Sometimes biochar is the byproduct of facilities primarily creating bio-oil or a project developer might use fast pyrolysis as it is more accessible for local communities rather than gasification.

High technology facilities are defined by:

a) Pyrolytic greenhouse gases produced during pyrolysis must be recovered or combusted — greenhouse gases are not allowed to escape into the atmosphere

b) At least 70% of the heat energy produced by pyrolysis must be used (taking in to consideration heat transfer efficiencies)

c) Pollution controls such as thermal oxidiser or other emission controls are present that meet local, national or international emission thresholds

d) Production temperature is measured and reported.

If any of these conditions are not met, the facility is categorised as a low technology facility, which are dominant in places where investment for high technology facilities is not possible yet availability of cheap low cost biomass is high, such as emerging markets and agricultural economies.

Combining these two concepts of (1) physical parameters and (2) facility technology level, here are some of the most common methods of biochar production labelled with their potential to be a low or high technology facility, with some of their tradeoffs to illustrate the reasons for the heterogeneity of biochar production:

1. (Low-High) Slow pyrolysis²²: This method involves heating biomass at low temperatures (300–500°C) in the absence of oxygen for several hours to produce biochar, bio-oil, and gases. This method produces biochar with a higher yield and lower ash content but may require more energy and time than fast pyrolysis.
2. (Low-High) Fast pyrolysis²³: This method involves heating biomass at high temperatures (500–600°C) in the absence of oxygen for a short duration of time (a few seconds to a few minutes) to produce biochar, bio-oil, and gases. It is accessible for local communities due to its smaller scale.
3. (High) Gasification²⁴: This method involves heating biomass at high temperatures (800–1000°C) in the presence of a limited amount of oxygen to produce a combustible gas (syngas), a mixture of methane and hydrogen and biochar. The resulting biochar is typically less carbonised and has a lower yield than biochar produced by pyrolysis.
4. (High) Hydrothermal carbonization²⁵: This method involves treating wet biomass with heat and pressure in the presence of water to produce a hydrochar, a carbon-rich material that can be used as biochar. The resulting biochar has a high degree of carbonization and can be produced from wet biomass, such as sewage sludge or food waste.
5. (High) Microwave pyrolysis²⁶: This method involves heating biomass using microwaves to produce biochar, and is a novel technique under research but with potentially very high scalability when at a higher technology readiness level.

To supplement these definitions and tradeoffs between methods of production, figure 3 illustrates more precisely how the physical parameters temperature and time contribute to slow pyrolysis, fast pyrolysis and gasification.

As you can see, the quality and characteristics of biochar can be affected by an array of different factors. Each of these methods has its own advantages and disadvantages, and the choice of method depends on the specific requirements of the application. In the future as biochar becomes more dominant in the VCM, more methodologies will come online to address the heterogeneity and adhere to the positive additionality that using different feedstocks or community impact different methods, contextually biochar can create. This nuance will be important to scaling biochar in the VCM on a strategic level.

4. Biochar in the Voluntary Carbon Market

A carbon credit is a unit of measurement that represents one tonne of carbon dioxide equivalent (CO2e) that has been removed or avoided from the atmosphere through a specific carbon reduction project or activity.

Biochar is currently the only CDR technology that is registered in the VCM. Figure 4 below illustrates the overlap between the unregistered CDR projects, 17 registries, and biochar projects. The total approximate number of carbon projects that are available globally, and their proportional sizes according to biochar and different CDR projects is also shown.

The CDR space comprises approximately 2000+ removal projects with approximately 1000 agroforestry projects which are traditionally market defined removals. Biochar is estimated to comprise a large amount of the CDR space, as it has been proposed to be the most scalable CDR technology. Currently Puro.earth is the only registry that has active biochar projects listed with 30 different projects²⁷ and a sum of 86,000 credits issued in total.

Registry vs Unregistered

1. Registries

The exact spread of the Puro registry biochar projects and credits produced can be seen in both figure 5 and 6. In figure 5, the number of credits being produced by biochar project has been increasing by over 2x each year, though this is dominated by a few key projects within the registry, where the first 3 peaks in figure 6 projects production of 23,800, 18,600 and 12,800 issued biochar credits each compared to the median of 600 credits. This trend of year on year increase in biochar credits being created can be expected to keep on increasing further in 2023, with Verra’s release of its methodology in July 2022²⁸. No active biochar project has been fully registered on Verra to date though the process typically takes a year to complete. Once that threshold is reached, we can expect a drastic increase in biochar projects.

2. Unregistered projects

On our global CDR database, there are approximately 37 known biochar projects. Two of the leading companies have committed to deliver, or have plans to scale up to, tens of thousands of tons of carbon dioxide per year (Pacific Biochar²⁹ and Biochar Now³⁰ ).

Future of the biochar in the VCM

According to a BeZero report, biochar is considered the most scalable CDR technology in the suite of current most promising CDR technologies.³² Biochar currently has the lowest barriers to scalability with low financial and MRV readiness. This is particularly interesting when understanding Verra’s and the European Union’s biochar inclusion of low tech and high tech facilities as biochar can be created for low cost means, using any waste biomass and cheap kiln. The problem comes with the high capex costs to ensure that waste CO2 isn’t emitted, and capturing the valuable synsgas and bio-oil. This allows a development pathway to be available for those in higher financial constrained areas, such as emerging markets and economies to produce biochar.

The European Biochar Consortium expects biochar to be capable of delivering carbon removal at climate relevant volumes within 15 years. Biochar production is expected to increase year on year by 70% reaching 6 megatonnes annually by 2030, and 100 megatonnes by 2040.³³

5. Challenges and Limitations

While biochar may sound like the panacea to climate change with its high scalability, it has some challenges and limitations. In the short term, biochar’s major challenge is to maintain the high growth rates for installation, which requires large amounts of financing and political and regulatory support. In the long run, biochar’s major challenge is the availability and aggregation of available biomass.³⁴

The cost of a biochar system depends on the costs of feedstock sources acquisition, transport and processing, and is most adequately adopted in locations with marginal land and high-value crop, and near low-cost feedstock sources.³⁵ The strategic placement of biochar plants therefore becomes paramount, and hubs could be produced to scale the industry to megatonne production.

6. Conclusion

Summary of the main points:

Biochar is one of the most scalable CDR technologies that has low financial and measurement, reporting and verification barriers.

Biochar is mainly used for carbon sequestration and soil amendment, however has over 60 different applications such as water management and in construction materials.

The most common way to create biochar is through this 5 step process:

1. Acquisition of biomass feedstock.
2. Pyrolysis (heating of biomass without oxygen).
3. Char collection and cooling.
4. Post processing — augmenting the properties for their use case, such as doping with appropriate chemicals for soil amendment.
5. Application of biochar product to the use case.

The most common production methods of creating biochar are: slow pyrolysis, fast pyrolysis, gasification and hydrothermal carbonisation.

Biochar facilities and properties are incredibly heterogeneous, when evaluating a biochar project they can be broken down into 3 key principles:

1. Feedstock input (type, cost and aggregation logistics)
2. Physical Parameters (time, temperature and mechanism)
3. High technology facility or Low Technology? (High tech 70% of all GHGs are captured, and temperature has to be controlled)

Currently Puro.earth is the main registry to find biochar projects with 30 projects registered and a cumulative production of 86,000 biochar credits

The European Biochar Consortium expects biochar to be capable of delivering carbon removal at climate relevant volumes within 15 years. Biochar production is expected increase year on year by 70% reaching 6 megatons annually by 2030, and 100 megatons annually by 2040.