Biochar carbon removal (BCR) (also called pyrogenic carbon capture and storage ) is a negative emissions technology. It involves the production of biochar through pyrolysis of residual biomass and the subsequent application of the biochar in soils or durable materials (e.g. cement, tar). The carbon dioxide sequestered by the plants used for the biochar production is therewith stored for several hundreds of years, which creates carbon sinks.
The term refers to the practice of producing biochar from sustainably sourced biomass and ensuring that it is stored for a long period of time. The concept makes use of the photosynthesis process, through which plants remove CO2 from the atmosphere during their growth. This carbon dioxide is stabilised within the biochar during the production process and can subsequently be stored for several hundreds or thousands of years.
Biochar Carbon Removal falls into the category of carbon dioxide removal (CDR) technologies. [1] It is considered to be a rapidly implemented and capital-efficient negative emissions technology ideal for smaller scale installations such as farmers, and also to help rural diversification in developing countries. [2] [3] [4] [5] This is, amongst others, reflected in the guidance documents of the Science Based Targets initiative. [6] [7]
Scientifically, this process is often referred to as Pyrogenic Carbon Capture and Storage (PyCCS). [8] [9] The term Biochar Carbon Removal (BCR) was first introduced by the European Biochar Industry Consortium (EBI) in 2023 [10] and has since been adopted by various institutions and experts.
Beyond carbon sequestration, biochar application has various other potential benefits, such as increased yield and root biomass, water use efficiency and microbial activity. [11]
Biochar is produced through the pyrolysis process. Biomass (e.g. residual plant material from landscaping or agricultural processes) is reduced to smaller pieces is heated to 350–900 °C (662–1,652 °F) under oxygen-deficient conditions. This results in solid biochar and by-products (bio-oil, pyrogas). [12] [9] In order to maximise the carbon storage potential, typically those biochar technologies are used that minimise combustion and avoid the loss of pyrogas into the atmosphere. [8]
In low-oxygen conditions, the thermal-chemical conversion of organic materials (including biomass) produces both volatiles, termed pyrolytic gases (pyrogases), as well as solid carbonaceous co-products, termed biochar. While the pyrogases mostly condense into liquid bio-oil, which may be used as an energy source, biochar has been proposed as a tool for sequestering carbon in soil. [13]
The global biochar market is expected to reach USD 368.85 million by 2028. [14]
Internationally there are several voluntary standards that regulate the biochar production process and product quality. These include the following (non-exhaustive list):
Three main carbonaceous products are generated during pyrolysis, which can be stored subsequently in different ways to produce negative emissions: a solid biochar for various applications, a pyrolytic liquid (bio-oil) pumped into depleted fossil oil repositories, and permanent-pyrogas (dominated by the combustible gases CO, H2 and CH4) that may be transferred as CO2 to geological storage after combustion. [1]
In 2022/2023, biochar carbon removal accounted for 87–92% of all delivered carbon removals. [16]
The potential extent of carbon removal with biochar is the subject of ongoing research. Using current waste from the farming and forestry industry worldwide, an estimated 6% of global emissions, equivalent to 3 billion tonnes of CO2, could be removed annually over a 100 year time frame. [17] More broadly, the potential is quantified to be between 0.3 and 4.9 billion tonnes of CO2 per year (GtCO2 yr−1). [18]
There is evidence that biochar, produced at pyrolysis temperature over 600 °C (1,112 °F), resembles inertinite and thus highly stable. [19] [20]
The level to which carbon dioxide is fixed and stored, depends both on the biochar production process and the subsequent application. If produced under certain conditions, 97% of the total organic carbon in biochar is highly refractory carbon, i.e. carbon that has near infinite stability. This implies that biochar can have a very high permanence in terms of carbon dioxide storage. [21]
There are several applications that are considered to store CO2 for long periods of time:
Biochar Carbon Removal is increasingly seen as a promising negative emissions technology suitable for offsetting and carbon markets.
Trade in BCR credits is still limited to a small number of suppliers and credit off-takers. In 2022, out of 592,969 carbon dioxide removal credits purchased on the voluntary carbon market, 40% were based on biochar carbon removal projects. [24]
For the purpose of generating carbon credits, there are several internationally recognised voluntary biochar standards and methodologies. These include the following (non-exhaustive list): [25]
Several biochar production and carbon credit standards define criteria for permissible biomass feedstocks for biochar carbon removal. For example, the European Biochar Certificate (EBC) features a positive list of permissible biomasses for the production of biochar. This list includes agricultural residues, cultivated biomass, residues from forestry operations and sawmills, residues from landscaping activities, recycled feedstock, kitchen waste, food processing residues, textiles, anaerobic digestion, sludges from wastewater treatment, and animal by-products. [26]
A carbon sink is a natural or artificial process that "removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere". These sinks form an important part of the natural carbon cycle. An overarching term is carbon pool, which is all the places where carbon on Earth can be, i.e. the atmosphere, oceans, soil, plants, and so forth. A carbon sink is a type of carbon pool that has the capability to take up more carbon from the atmosphere than it releases.
The pyrolysis process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere.
Climate engineering is an umbrella term for both carbon dioxide removal and solar radiation modification, when applied at a planetary scale. However, these two processes have very different characteristics. For this reason, the Intergovernmental Panel on Climate Change no longer uses this overarching term. Carbon dioxide removal approaches are part of climate change mitigation. Solar radiation modification is reflecting some sunlight back to space. All forms of climate engineering cannot be standalone solutions to climate change, but need to be coupled with other forms of climate change mitigation. Some publications place passive radiative cooling into the climate engineering category. This technology increases the Earth's thermal emittance. The media tends to use climate engineering also for other technologies such as glacier stabilization, ocean liming, and iron fertilization of oceans. The latter would modify carbon sequestration processes that take place in oceans.
Bioenergy is a type of renewable energy that is derived from plants and animal waste. The biomass that is used as input materials consists of recently living organisms, mainly plants. Thus, fossil fuels are not regarded as biomass under this definition. Types of biomass commonly used for bioenergy include wood, food crops such as corn, energy crops and waste from forests, yards, or farms.
Carbon capture and storage (CCS) is a process in which a relatively pure stream of carbon dioxide (CO2) from industrial sources is separated, treated and transported to a long-term storage location. For example, the burning of fossil fuels or biomass results in a stream of CO2 that could be captured and stored by CCS. Usually the CO2 is captured from large point sources, such as a chemical plant or a bioenergy plant, and then stored in a suitable geological formation. The aim is to reduce greenhouse gas emissions and thus mitigate climate change. For example, CCS retrofits for existing power plants can be one of the ways to limit emissions from the electricity sector and meet the Paris Agreement goals.
Carbon sequestration is the process of storing carbon in a carbon pool. It plays a crucial role in limiting climate change by reducing the amount of carbon dioxide in the atmosphere. There are two main types of carbon sequestration: biologic and geologic.
Pyrolysis oil, sometimes also known as biocrude or bio-oil, is a synthetic fuel with few industrial application and under investigation as substitute for petroleum. It is obtained by heating dried biomass without oxygen in a reactor at a temperature of about 500 °C (900 °F) with subsequent cooling, separation from the aqueous phase and other processes. Pyrolysis oil is a kind of tar and normally contains levels of oxygen too high to be considered a pure hydrocarbon. This high oxygen content results in non-volatility, corrosiveness, partial miscibility with fossil fuels, thermal instability, and a tendency to polymerize when exposed to air. As such, it is distinctly different from petroleum products. Removing oxygen from bio-oil or nitrogen from algal bio-oil is known as upgrading.
Biochar is the lightweight black residue, consisting of carbon and ashes, remaining after the pyrolysis of biomass, and is a form of charcoal. Biochar is defined by the International Biochar Initiative as the "solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment".
In the context of energy production, biomass is matter from recently living organisms which is used for bioenergy production. Examples include wood, wood residues, energy crops, agricultural residues including straw, and organic waste from industry and households. Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into pellet fuel or other forms of fuels. Other plants can also be used as fuel, for instance maize, switchgrass, miscanthus and bamboo. The main waste feedstocks are wood waste, agricultural waste, municipal solid waste, and manufacturing waste. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.
The Virgin Earth Challenge was a competition offering a $25 million prize for whoever could demonstrate a commercially viable design which results in the permanent removal of greenhouse gases out of the Earth's atmosphere to contribute materially in global warming avoidance. The prize was conceived by Richard Branson, and was announced in London on 9 February 2007 by Branson and former US Vice President Al Gore.
Slash-and-char is an alternative to slash-and-burn that has a lesser effect on the environment. It is the practice of charring the biomass resulting from the slashing, instead of burning it. Due to incomplete combustion (pyrolysis) the resulting residue matter charcoal can be utilized as biochar to improve the soil fertility.
Carbon dioxide removal (CDR) is a process in which carbon dioxide is removed from the atmosphere by deliberate human activities and durably stored in geological, terrestrial, or ocean reservoirs, or in products. This process is also known as carbon removal, greenhouse gas removal or negative emissions. CDR is more and more often integrated into climate policy, as an element of climate change mitigation strategies. Achieving net zero emissions will require first and foremost deep and sustained cuts in emissions, and then—in addition—the use of CDR. In the future, CDR may be able to counterbalance emissions that are technically difficult to eliminate, such as some agricultural and industrial emissions.
Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere. BECCS can theoretically be a "negative emissions technology" (NET), although its deployment at the scale considered by many governments and industries can "also pose major economic, technological, and social feasibility challenges; threaten food security and human rights; and risk overstepping multiple planetary boundaries, with potentially irreversible consequences". The carbon in the biomass comes from the greenhouse gas carbon dioxide (CO2) which is extracted from the atmosphere by the biomass when it grows. Energy ("bioenergy") is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods.
Hydrothermal carbonization (HTC) is a chemical process for the conversion of organic compounds to structured carbons. It can be used to make a wide variety of nanostructured carbons, simple production of brown coal substitute, synthesis gas, liquid petroleum precursors and humus from biomass with release of energy. Technically the process imitates, within a few hours, the brown coal formation process which takes place in nature over enormously longer geological time periods of 50,000 to 50 million years. It was investigated by Friedrich Bergius and first described in 1913.
Soil management is the application of operations, practices, and treatments to protect soil and enhance its performance. It includes soil conservation, soil amendment, and optimal soil health. In agriculture, some amount of soil management is needed both in nonorganic and organic types to prevent agricultural land from becoming poorly productive over decades. Organic farming in particular emphasizes optimal soil management, because it uses soil health as the exclusive or nearly exclusive source of its fertilization and pest control.
Blue carbon is a concept within climate change mitigation that refers to "biologically driven carbon fluxes and storage in marine systems that are amenable to management". Most commonly, it refers to the role that tidal marshes, mangroves and seagrasses can play in carbon sequestration. These ecosystems can play an important role for climate change mitigation and ecosystem-based adaptation. However, when blue carbon ecosystems are degraded or lost, they release carbon back to the atmosphere, thereby adding to greenhouse gas emissions.
David Alan Laird is a professor at Iowa State University, Department of Agronomy, Ames, Iowa. Throughout his career as a soil scientist, he made many contributions to clay mineralogy, including developing a model describing the relationship between cation selectivity and the extent of crystalline swelling in expanding 2:1 phyllosilicates. Other work demonstrated the effects of ionic strength and cation charge on the breakup and formation of smectitic quasicrystals and the principle of cation demixing which lent great insight into understanding clay flocculation. Investigations in organic matter interactions with clay minerals led to the development of the idea of dual mode bonding in which amphipathic molecules interact with substrates by both hydrophobic-hydrophobic and hydrophilic-hydrophilic interactions. Laird et al. (2008) showed that smectites, a class of clay minerals found in soil, can adsorb tremendous amounts of organic materials and, hence, strongly influence the transport and bioavailability of organic materials including pesticides applied to the soil. In a study published in 2003, Gonzalez and Laird showed that new carbon derived from decomposing plant material tends to preferentially sorb to the fine clay subfraction of soil. Further work demonstrated that the coarse clay fraction had the greatest carbon to nitrogen ratio, greatest minimum residence time in the soil based on 14C radioisotope dating, and contained carbon most recalcitrant to microbial digestion. Collectively many of Dr. Laird's contributions to soil science have provided insight into understanding soil organic matter and clay interactions and, thus, the genesis of soil peds from the molecular viewpoint.
Carbon farming is a set of agricultural methods that aim to store carbon in the soil, crop roots, wood and leaves. The technical term for this is carbon sequestration. The overall goal of carbon farming is to create a net loss of carbon from the atmosphere. This is done by increasing the rate at which carbon is sequestered into soil and plant material. One option is to increase the soil's organic matter content. This can also aid plant growth, improve soil water retention capacity and reduce fertilizer use. Sustainable forest management is another tool that is used in carbon farming. Carbon farming is one component of climate-smart agriculture. It is also one way to remove carbon dioxide from the atmisphere.
Carbon capture and utilization (CCU) is the process of capturing carbon dioxide (CO2) from industrial processes and transporting it via pipelines to where one intends to use it in industrial processes.
Kenneth Karl Mikael Möllersten is a Swedish researcher. He holds a PhD in chemical engineering and an MSc in mechanical engineering, both from the Royal Institute of Technology (KTH), Stockholm, Sweden. Möllersten is a consultant and researcher at IVL Swedish Environmental Research Institute, was previously affiliated as a researcher with Mälardalen University and is currently affiliated with KTH.