Biochar, the new climate-friendly black gold

Biochar is closely intertwined with our use of biomass. Biomass (forests, plants, etc.) absorbs CO2 from the atmosphere through photosynthesis. If the biomass is left to degrade, it naturally re-emits its CO2 into the air in a gaseous state until another plant absorbs it. To prevent CO2 from returning to the atmosphere, innovative technologies are being experimented with to stabilise this carbon gas and prevent its escape into the atmosphere. Out of all these promising advances, biochar is emerging as a solution capable of playing a key role.

What is biochar?

The term 'biochar' is short for 'bio-charcoal'. It is sometimes referred to as "agrichar" and refers to charcoal of plant origin achieved through biomass pyrolysis. Biochar is formed from wood residues (natural or industrial residues from forest maintenance, agriculture or the wood industry, such as bark, harvested wood or straw) or dry crop residues (coffee bean hulls, for instance). These residues are heated to around 500 degrees, in an oxygen-free environment, to prevent combustion, which would reduce them to ash. The result is a product similar to charcoal, but with characteristics that make it unique and precious.

The magic of stable carbon 

What makes biochar so extraordinary is its ability to store carbon stably over very extended periods of time. In other words, it acts as a carbon trap, preventing carbon dioxide (CO2) from entering the atmosphere and contributing to global warming. This is why it is often referred to as climate-friendly “black gold”.

Biochar’s benefits for the environment

• Carbon sequestration: Biochar resembles a charcoal made of persistent (i.e. very stable) organic carbon, which when applied to the soil helps sequester more carbon, while improving the soil's fertility properties. Its permanence depends on the type of soil and the temperature at which the biochar is produced, and varies from a few decades to several centuries. One tonne of biochar can sequester from 1.3 to 3 tonnes of CO2-equivalent over a period of several centuries, depending on the nature of the resource and the process used. Because of its capacities and stability, biochar has been considered a powerful carbon sink since 2018, classified by the IPCC as a "Negative Emission Technology", i.e. capable of extracting CO2 from the atmosphere sustainably and irreversibly. This chain furthermore offers the advantage of putting local resources to work and finding a use for them locally.
• Improved soil fertility: When incorporated into the soil, biochar has the capacity to improve its structure, adjust its pH, increase its water retention capacity and increase its ability to retain essential nutrients. These improvements play a significant part in fostering plant growth, thus bringing about higher crop yields. What's more, the benefits of biochar extend beyond a mere increase in harvests: it also contributes to reducing emissions of gases other than CO2 from the soil, makes plants more resistant to drought, and acts as a solution, the benefits of which have been recognised since ancient times, particularly in the Amazon region.
• Reduced greenhouse gas emissions : Complementing its capacity to store carbon, the use of biochar in agriculture helps reduce greenhouse gas emissions stemming from agricultural practices. One example is the reduction in methane (CH4) emissions from soils, a greenhouse gas that can be more potent than carbon dioxide (CO2).
• Reduced deforestation: The use of biochar can reduce the pressure on forests as a source of fuel, as it can be produced from non-forest biomass.

Applications of biochar

Biochars offer a wide range of applications that contribute to environmental sustainability, reducing greenhouse gas emissions and improving soil, water and air quality. Their potential in the fight against climate change and the promotion of sustainable agriculture makes them a valuable material in our arsenal of environmental solutions.  Here are some of the ways in which biochar can be applied: 

• Soil amendment: It can be blended into the soil to improve its quality and increase crop yields.
• Treatment of organic waste: Biochars can be used in the composting of organic waste to reduce emissions of methane, a potent greenhouse gas.
• Water filtration: Biochars are effective in eliminating water contaminants, such as heavy metals and organic chemicals, by acting as a natural absorbent.
• Soil decontamination: Biochars can be used to detoxify soil contaminated by heavy metals, hydrocarbons and other pollutants.
• Power generation: Biochars can be used as fuel to produce energy, which in turn helps reduce the use of fossil fuels and CO2 emissions. At CarbonLoop, for example, 3,000 tonnes of biomass can be used to produce 4 gigawatt hours of electricity and 500 tonnes of biochar a year. As a result, the production system is self-sustaining and the gases generated by pyrolysis are not released into the atmosphere.
• Air quality improvement: Biochars can be used to trap and eliminate atmospheric pollutants, thereby improving air quality.

Challenges

• Estimated potential, taking into account the limited availability of biomass and uncertainties due to the lack of large-scale trials of biochar application to agricultural soils under field conditions.
• Risk of conflicts over the resource’s use.
• Not all soils are suited to biochar. It is very beneficial, for example, to tropical soils, highly weathered and generally acidic, and which have lost their nutrients and the ability to retain them. However, it is much less so in temperate zones and chalky soils.
• Its high production cost, although with the carbon credit market developing, the situation is changing and offers the prospect of exponential growth.

ENGIE’s initiatives in the field of biochars:

Lab Crigen, one of ENGIE Group’s research centres, recently initiated promising trials to study the use of biochars from anaerobic digestates. These biochars are attracting a great deal of interest as an innovative approach to improving soil fertility.  

Concurrently, Crigen is exploring the use of biochars as adsorbents to capture atmospheric pollutants such as hydrogen sulphide (H2S), a pollutant commonly emitted when biomass is burned. Crigen is also testing these same biochars as booster material, to optimise the anaerobic digestion of various substrates in bioreactors. Although these promising initiatives are underway, the complete results are not yet available. However, they do attest to ENGIE's commitment to exploring innovative solutions for environmental sustainability and the reduction of greenhouse gas emissions.

Research on the industrial applications of biochar has grown exponentially in recent years, boosted by the carbon credit market. It remains nonetheless essential to consider biochar as one of several solutions available, not regarding it as "the" magic solution.