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Biochar Production and Storage
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This Protocol provides the requirements and procedures for the calculation of net carbon dioxide equivalent (CO2e) Removal from the atmosphere via the production of biochar and its durable Storage.
Biochar is a durable carbon-rich solid material produced from the pyrolysis of waste biomass. Pyrolysis is a thermochemical conversion process, where biomass is heated in an oxygen free environment to produce a mixture of solid biochar and condensable and non-condensable gasses. There are several storage options for biochar produced by pyrolysis, such as application to surface soil in agricultural settings, burial in the shallow subsurface, and incorporation into building materials. In each of these settings, a substantial fraction of the organic carbon content can be stored durably. The amount of carbon stored within biochar may decrease over time if the biochar is exposed to oxidizing conditions. Several physical and chemical properties of the biochar, as well as environmental factors associated with the application site, affect the rate at which organic carbon in the biochar can be potentially released back into the atmosphere. This Protocol adopts a conservative approach to crediting, with only the highly durable fraction of the organic carbon content in the biochar being eligible for the generation of Credits.
This Protocol accounts for the quantification of the gross amount of CO2 removed via the production and durable storage of biochar and all cradle-to-grave life-cycle Greenhouse Gas (GHG) emissions associated with the process, to determine the net carbon dioxide equivalent (CO2e) removal.
This Protocol is developed to adhere to the requirements of ISO 14064-2: 2019 – Greenhouse Gasses – Part 2: Specification with guidance at the Project level for quantification, monitoring, and reporting of greenhouse gas emission reductions or removal enhancements. This Protocol ensures:
In addition to carbon sequestration potential, the application of biochar to agricultural soils might have several co-benefits, including, but not limited to, the following:
This Protocol mainly utilizes and is intended to be compliant with the following standards and protocols:
Additional reference standards that inform the requirements and overall practices incorporated in this Protocol include:
Additional standards, methodologies and protocols that were reviewed, referenced or for which attempts were made to align with or leverage during development of this Protocol include:
This Protocol was developed based on the current state of the art, publicly available science regarding biochar production and storage. The Protocol will be updated in future versions as the science underlying biochar production and storage evolves and the overall body of knowledge and data across all processes is increased, for examples regarding Feedstock supply, thermochemical conversion, and durable storage.
This Protocol will be reviewed at a minimum every 2 years and/or when there is an update to scientific published literature which would affect net CO₂e removal quantification or the monitoring guidelines outlined in this Protocol. Because biochar production and storage is a novel Carbon Dioxide Removal (CDR) approach, this Protocol incorporates requirements that may be more stringent than some current relevant regulations or other protocols related to biochar for CDR. In particular, requirements for demonstrating Durability of biochar will be updated as the stability of CO2 captured by biochar becomes well demonstrated and documented, and biochar degradation is proven to be limited.
This Protocol applies to projects and associated operations that meet all of the following project conditions:
Following the Isometric Standard, Credits issued under this Protocol are contingent on the implementation, transparent reporting and independent Verification of comprehensive safeguards. These safeguards encompass a wide range of considerations, including environmental protection, social equity, community engagement and respect for cultural values. The process mandates that safeguard plans be incorporated into all major project phases, with detailed reports made accessible to Stakeholders. Adherence to and verification of environmental and social safeguards is a condition for all Crediting Projects.
Project Proponents must comply with all national and local laws, regulations and policies, and receive a permit for any project activities undertaken from the relevant authority. Where relevant, projects must comply with international conventions and standards governing human rights and uses of the environment, when conducted within or foreseeably impacting party jurisdictions.
Project Proponents must document activities conducted under The Project that would require it to obtain environmental permits.
The Project must consider environmental and social impacts at all project locations, including the biomass sourcing, pyrolysis and biochar deployment sites as well as during biomass/biochar transportation. Appropriate measures must be implemented to identify and eliminate potential risks to terrestrial and aquatic ecosystems and biodiversity. Where risks cannot be eliminated, the Project Design Document (PDD) must identify measures to monitor ecosystem health and mitigate adverse effects through a project-specific mitigation plan. Mitigation plans must be carried out by subject matter experts, in consultation with Isometric. Refer to Section 3.7 of the Isometric Standard for further guidelines on environmental and social impacts.
Environmental and social risk assessment in adherence with Section 3.7 of the Isometric Standard must be completed to identify potential risks, followed by the development of tailored mitigation plans. These plans must encompass specific actions to avoid, minimize or rectify identified impacts. Effective implementation of these measures must also be accompanied by a robust monitoring plan to detect negative impacts and stop projects when necessary.
The severity of these risks vary based on site specifics and the intensity and duration of activities. Environmental and social risk identification, assessment, avoidance, and mitigation planning will be unique to each Project’s technical, environmental, and social contexts. The risks identified in this Protocol are a minimum set to which Isometric and the supplier can add risks on a case by case basis, which would be included in the PDD.
The Project Proponent must conduct an environmental risk assessment which adheres to Section 3.7.1 of the Isometric Standard. Potential additional environmental risks associated with biochar production and storage are listed below.
Polycyclic Aromatic Hydrocarbons (PAHs) and heavy metals are pollutants of concern that may be found in biochar8,9:
The Project Proponent must conduct a social risk assessment which adheres to Section 3.7.2 of the Isometric Standard on Social Impacts. In particular, this should include specific risks to human health that may be associated with biochar production, application and/or storage during the Project, for example during transport and application due to dust.
In accordance with Section 3.5 of the Isometric Standard, Project Proponents must demonstrate active stakeholder engagement through a Stakeholder Input Process throughout project planning and operation, ensuring that all risk mitigation strategies contribute to sustainable project outcomes. Local stakeholders situated in the vicinity of the project site may contribute an in-depth understanding of the local system and provide invaluable insights and recommendations on the potential risks, necessary safeguards and specific monitoring needs. The Stakeholder Input Process must adhere to requirements outlined in Section 3.5 of the Isometric Standard, and evidence of these meetings must be submitted in the PDD.
Project Proponents must include in the PDD a plan for information sharing, emergency response and conditions for stopping or pausing a deployment. Plans for pausing or stopping a deployment must be in place in instances where there may be:
The following topics are covered briefly in this Protocol due to their inclusion in the Isometric Standard, which governs all Isometric Protocols. See in-text references to the Isometric Standard for further guidance.
For each specific project to be evaluated under this Protocol, the Project Proponent must document project characteristics in a Project Design Document (PDD) as outlined in Section 3.2 of the Isometric Standard. The PDD will form the basis for Project Validation and evaluation in accordance with this Protocol, and must include consideration of processes unique to biomass such as:
Projects must be validated and net CO2e removals verified by an independent third party, consistent with the requirements described in this Protocol and in Section 4 of the Isometric Standard.
The Validation and Verification Body (VVB) must consider the following requisite components:
The threshold for Materiality, considering the totality of all omissions, errors and mis-statements is 5%, in accordance with Section 4.3 of the Isometric Standard.
Verifiers must also verify the documentation of Uncertainty of the GHG Statement as required by Section 2.5.7 of the Isometric Standard. Qualitative Materiality issues may also be identified and documented, such as:
Project validation and verification must incorporate site visits to project facilities in accordance with the requirements of ISO 14064-3, 6.1.4.2, including site visits during validation and initial verification to the biomass pyrolysis site and the biochar application site. Validators should, whenever possible, observe operation of the biochar processing and application to ensure full documentation of process inputs and outputs through visual observation.
Verifiers and validators must comply with the requirements defined in Section 4 of the Isometric Standard. In addition, teams must maintain and demonstrate expertise associated with the specific technologies of interest, including biomass growth or production, biomass processing and pyrolysis, sampling, analysis, and data processing.
CDR via biochar is often a result of a multi-step process (such as biomass growth, harvesting, transport, pyrolysis, processing, and storage), with activities in each step potentially managed and operated by a different operator, company, or owner. When there are multiple parties involved in the process, and to avoid Double Counting of net CO2e removals, a single project proponent must be specified contractually as the sole owner of the Credits. Contracts must comply with all requirements defined in Section 3.1 of the Isometric Standard.
The Project Proponent must be able to demonstrate Additionality through compliance with Section 2.5.3 of the Isometric Standard. The baseline scenario and counterfactual utilized to assess additionality must be project-specific, and are described in Section 7.2 of this Protocol.
Additionality determinations should be reviewed and completed at the time of initial verification or whenever project operating conditions change significantly, such as the following:
Any review and change in the determination of additionality shall not affect the availability of Carbon Finance and Credits for the current or past Crediting Periods. If the review indicates the Project has become non-additional, this shall make The Project ineligible for future Credits11.
The uncertainty in the overall estimate of the net CO2e removal as a result of the Project must be accounted for. The total net CO2e removed for a specific Reporting Period, [math: RP], CO2eRemoval, RP, must be conservatively determined in accordance with the requirements outlined in Section 2.5.7 of the Isometric Standard.
Projects must report a list of all input variables used in the net CO2e removal calculation and their uncertainties, including:
The uncertainty information should at least include the minimum and maximum values of a variable. More detailed uncertainty information should be provided if available, as outlined in Section 2.5.7 of the Isometric Standard.
In addition, a sensitivity analysis that demonstrates the impact of each input parameter’s uncertainty on the final net CO2e uncertainty must be provided. Details of the sensitivity analysis method must be provided such that a third party can reproduce the results. Input variables may be omitted from an uncertainty analysis if they contribute to a < 1% change in the net CO2e removal. For all other parameters, information about uncertainty must be specified.
In accordance with the Isometric Standard, all evidence and data related to the underlying quantification of the net CO₂e removal and environmental and social safeguards monitoring will be available to the public through Isometric's platform. This includes:
The Project Proponent can request certain information to be restricted (only available to authorized Buyers, the Registry and Validation and Verification Bodies (VVBs)) where it is subject to confidentiality. This includes emissions factors from licensed databases. However, all other numerical data produced or used as part of the quantification of net CO₂e removal will be made available.
The scope of this Protocol includes GHG sources, sinks and reservoirs (SSRs) associated with a biochar CDR project. A cradle-to-grave GHG Statement must be prepared encompassing the GHG emissions relating to the activities outlined within the system boundary.
GHG emissions associated with The Project may be as direct emissions from a process or storage system or as indirect emissions from combustion of fuels, electricity generation, or other sources. Emissions for processes within the system boundary must include all GHG SSRs from the construction or manufacturing of any project-specific physical site and associated equipment; closure and disposal of each site and associated equipment; and operation of each process (including biochar production, processing, characterization, transport and spreading) to include Embodied Emissions of consumables in the process.
Any emissions from sub-processes or process changes that would not have taken place without the CDR project, such as subsequent transportation and refining, must be fully considered in the system boundary. Any activity that ultimately leads to the issuance of Credits should be included in the system boundary. Biomass feedstock emissions must be calculated as outlined in the Biomass Feedstock Accounting Module. This allows for accurate consideration of additional, incremental emissions induced by the CDR process.
The system boundary must include all SSRs controlled by and related to the Project, including but not limited to the SSRs in Figure 1 and Table 1. If any GHG SSRs within Table 1 are deemed not appropriate to include in the system boundary, they may be excluded provided that robust justification and appropriate evidence is provided in the PDD.
Figure 1: Process flow diagram showing system boundary for biochar projects[Image: Figure 1]
Table 1. Scope of activities and GHG SSRs to be included in the system boundary
| Activity | GHG Source, sink or reservoir | GHG | Scope | Timescale of emissions and accounting allocation |
|---|---|---|---|---|
Project Establishment | Equipment and materials manufacture | All GHGs | Embodied emissions associated with equipment and materials manufacture for project establishment (lifecycle modules A1-312). To include product manufacture emissions for equipment, buildings, infrastructure and temporary structures. | Before project operations start - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 8.5.1) |
Equipment and materials transport to site | All GHGs | Transport emissions associated with transporting materials and equipment to the project site(s) (lifecycle module A412). | ||
Construction and installation | All GHGs | Emissions related to construction and installation of the project site(s) (lifecycle module A512). To include energy use for construction, installation and groundworks, as well as waste processing activities and emissions associated with land use change. | ||
Initial surveys and feasibility studies | All GHGs | Any embodied, energy and transport emissions associated with surveys or feasibility studies required for establishment of the project site. | ||
Misc. | All GHGs | Any SSRs not captured by categories above, for example staff transport. | ||
Operations | Biomass feedstock sourcing | All GHGs | Any embodied, energy and transport emissions associated with biomass cultivation and harvesting. | Over each Reporting Period - must be accounted for in the relevant Reporting Period (See Section 8.5.2) |
Biomass feedstock transport | All GHGs | Transport of biomass including to biomass processing site and all other transport of biomass ahead of biochar production. | ||
Biomass feedstock processing | All GHGs | Any embodied, energy and transport emissions associated with biomass feedstock processing. | ||
| Pyrolysis | All GHGs | Emissions associated with pyrolysis including:
| ||
Direct emissions | All GHGs | Direct emissions released during pyrolysis. See Section 9.2.1 for calculation details. | ||
Biochar processing | All GHGs | Emissions associated with biochar processing and characterization including:
| ||
Biochar storage | All GHGs | Emissions associated with biochar storage including:
| ||
Biochar transport | All GHGs | All transport of biochar including to biochar processing site and to the biochar storage site. | ||
CO₂ Stored | CO₂ only | The gross amount of CO₂ removed and durably stored from a biochar project over a Reporting Period. | ||
Sampling required for MRV | All GHGs | Any embodied, energy and transport emissions associated with sampling for MRV purposes, including transportation to collect samples, shipping of samples for laboratory analysis and sample processing. | ||
Staff travel | All GHGs | Flight, car, train or other travel required for the project operations, including contractors and suppliers required on site. | ||
Surveys | All GHGs | Equipment, energy use and transport associated with surveys e.g. ecological surveys. | ||
| Misc. | All GHGs | Any SSRs not captured by categories above. | ||
| End-of-Life | End-of-life of project facilities | All GHGs | Anticipated end-of-life emissions (lifecycle modules C1-412). To include deconstruction and disposal of the project site(s), equipment, vehicles, buildings or infrastructure. | After Reporting Period - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 8.5.3) |
| Misc. | All GHGs | Any emissions SSR not captured by categories above. |
The Project Proponent must consider all GHGs associated with SSRs, in alignment with the United States Environmental Protection Agency’s definition of GHGs, which includes: carbon dioxide (CO₂), methane (CH4), nitrous oxide (N20) and fluorinated gasses such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3). For CO2 stored, only CO2 shall be included as part of the quantification. For all other activities all GHGs must be considered. For example, the release of CO2, CH4, and N2O is expected during diesel consumption.
All GHGs must be quantified and converted to CO2e in the GHG Statement using the 100-year Global Warming Potential (GWP) for the GHG of interest, based on the most recent volume of the IPCC Assessment Report (currently the Sixth Assessment Report).
Miscellaneous GHG emissions are those that cannot be categorized by the GHG SSR categories provided in Table 1. The Project Proponent is responsible for identifying all sources of emissions directly or indirectly related to project activities and must report any outside of the SSR categories identified as miscellaneous emissions.
Emissions associated with a project's impact on activities that fall outside of the system boundary of a project must also be considered. This is covered under Leakage in Section 8.5.4.
Ancillary activities (such as supplementary research and development activities and corporate administrative activities) that are associated with a project but are not directly or indirectly related to the issuance of Credits can be excluded from the system boundary.
Biochar may have additional impacts on GHG emissions beyond the scope of this Protocol. For example, there may be potential for increased Soil Organic Carbon (SOC) as a result of biochar application to soil. These potential secondary climate effects are uncertain at this time and are not covered by this Protocol.
Embodied emissions associated with system inputs considered to be waste products can be excluded from the accounting of the GHG Statement system boundary provided the appropriate criteria are met.
For waste energy inputs, for example the use of waste heat, refer to the Energy Use Accounting Module.
Refer to Energy Use Accounting Module for eligibility criteria.
For waste biomass feedstocks, refer to the Biomass Feedstock Accounting Module. All eligibility criteria described in the Biomass Feedstock Accounting Module must be satisfied in order to exclude biomass sourcing emissions from the system boundary. Emissions relating to any processing and transport of biomass feedstock must be included in the system boundary.
See Biomass Feedstock Accounting Module for eligibility criteria.
For all other waste inputs, the following criteria shall be considered. If EC1 in Table 2 is satisfied, embodied emissions associated with the waste product input can be excluded from the system boundary. Market leakage emissions associated with waste inputs may also be excluded from the system boundary, as compliance with EC1 would result in no change to the waste producer behavior (i.e. no market leakage) and indicates there are no alternative users of the waste product (i.e. no replacement emissions).
Table 2. Waste input emissions exclusion criteria, EC1
| Criteria | Description | Documentation required |
|---|---|---|
| EC1 | No payment was made for the material, or only a “tipping fee” is paid. | Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, buyer, seller and date. Additionally, a signed affidavit from the Project Proponent stating that no in-kind compensation was made to the feedstock supplier must be provided. |
If EC2 and EC3 in Table 3 are both satisfied, embodied emissions associated with the waste product input can be excluded from the system boundary. Market leakage emissions associated with waste inputs may also be excluded from the system boundary, as compliance with EC2 and EC3 would result in no significant change to the waste producer behavior (i.e. no market leakage) and there are no alternative use cases for the waste product (i.e. no replacement emissions).
Table 3. Waste input emissions exclusion criteria, EC2 and EC3
Criteria | Description | Documentation required |
|---|---|---|
EC2 | The amount of the waste product used by the CDR project was not already being utilized as a valuable product by another party for non-CDR uses. Therefore, the producer of the waste product has no alternative use case for the waste product. | Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, buyer, seller and date. Additionally, a signed affidavit from the Project Proponent stating that no in-kind compensation was made to the feedstock supplier must be provided. |
EC3 | Payments for the waste product do not constitute a significant share of upstream operations revenue for the waste producer. | Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, buyer, seller and date. Additionally, a purchase agreement of waste material that documents that payments from the project do not constitute a large share of upstream operations revenue must be provided. |
In some instances, the project activities may be integrated into existing activities, such as biochar spreading while tilling. Activities that were already occurring, and would continue to occur in the absence of The Project, may be omitted from the system boundary of the GHG accounting if evidence of this is provided.
The biomass pyrolysis process may result in the production of co-products, such as bio-oil, pyrolysis gas (bio-gas), electricity and heat. To allocate project emissions associated with CDR and co-product(s), the Project Proponent may use one or a combination of, where relevant, the following co-product allocation procedures outlined below.
Procedure 1: Allocate all emissions to CDR
Projects may opt to allocate all project emissions to CDR. The co-product(s) must still comply with all relevant emission accounting regulations and requirements, which may mean emissions are double counted. Removals must not be double counted. This is the most conservative approach to take.
Procedure 2: Divide the process into sub-processes
Where possible, the process may be divided into sub-processes. For example it may be possible to isolate processes relating to processing of the co-product, or the biochar process may be a retrofit to an existing process.
Eligibility criteria, evidence requirements and GHG system boundary considerations are set out in Table 4. One of EC4 or EC5 must be satisfied in order to divide the process into sub-processes.
Table 4. Procedure 2 Eligibility Criteria, EC4 and EC5
Criteria | Description | Documentation required |
|---|---|---|
EC4 | The biochar production process is a retrofit to an existing facility that was operable prior to the introduction of the CDR process. The purpose of the existing facility must not have been CDR prior to retrofit. | Records of existing facility activities dating back 3 years must be provided for a major infrastructure projects where a planning application was required. For all other projects, records of the existing facility activities dating back 6 months is required. The distinction between major infrastructure projects and other projects is to ensure that the biochar process is a retrofit, as major infrastructure project construction may be staged over many years. |
EC5 | The process has components and operations that are physically separate from one another. | Evidence of separation, for example engineering diagrams showing separate equipment or electricity metering systems for separate components of the process. Sub-processes that can be isolated from the CDR process and do not contribute to CDR may be excluded from the system boundary. |
Procedure 3: Substituting emissions
Project Proponents may use the substitution method to incorporate emissions associated with a substitute co-product into the system boundary as an avoided burden. This is referred to as "expanding the system boundary" in ISO 14044:2006. In practice, the co-product emissions are substitutes with emissions for an equivalent product and subtracted from total project GHG emissions.
The calculation approach to be followed is set out below:
Procedure 4: Carbon mass balance if the co-product leads to crediting
Physical allocation based on carbon mass balance shall be used in instances where the co-product leads to crediting for CDR with Isometric, for example if the process produces both biochar and bio-oil. This is so that emissions are distributed according to the CO₂ balance output of the system. The requirement for crediting to be with an Isometric project ensures that co-product allocation can be traced and verified appropriately and according to the same set of allocation and emissions accounting requirements. The co-product allocation between CDR products can be made after process subdivision and substitution has taken place, however EC1 for subdivision is not viable where there is more than one CDR product.
The baseline scenario for biochar projects assumes that the activities associated with the biochar Project do not take place and that any infrastructure associated with the biochar Project is not built.
The counterfactual is the CO₂ stored in the biomass feedstock that would have remained durably stored in the biomass in the absence of the Project. This is called ineligible biomass in the Biomass Feedstock Accounting Module. The Biomass Feedstock Accounting Module sets out requirements for establishing ineligible biomass as part of the Counterfactual Storage Eligibility criteria. The Biomass Feedstock Accounting Module includes details for quantification of [math: {CO}_{2}^{}e_{Counterfactual, RP}^{}].
See Section 3 of the Biomass Feedstock Accounting Module for requirements.
The Reporting Period, RP, for biochar projects represents an interval of time over which removals are calculated and reported for verification. The equations used to calculate net CO2e removals will pertain to all GHG emissions and CO2 removals occurring over a Reporting Period. In most cases, the Reporting Period will be an interval of time bounded by a batch of biomass feedstock sourcing, pyrolysis, biochar processing and biochar storage activities, for example a spreading event.
For all storage pathways associated with biochar, it is necessary to calculate the carbon content of the biochar, [math: C_{biochar}]. Guidelines for determining biochar carbon content are outlined below, and should be used in conjunction with the relevant storage Module.
In addition to biochar quantification, upfront characterization is required to assess CO2 removed via the production of biochar and biochar durability. The requirements for this are set out in Biochar Storage in Agricultural Soils Module 1.0, Section 3).
GHG emission calculations must include all emissions related to the project activities that occur within the Reporting Period. This includes: (a) any emissions associated with project establishment allocated to the Reporting Period (See Section 8.5.1) (b) any emissions that occur within the Reporting Period (See Section 8.5.2), (c) any anticipated emissions that would occur after the Reporting Period that have been allocated to the Reporting Period (See Section 8.5.3) and (d) leakage emissions that occur outside of the system boundary that are associated with the Reporting Period (See Section 8.5.4).
Total net CO2e removal is calculated for each Reporting Period, and is written hereafter as [math: {CO}_{2}^{}e_{Removal, RP}^{}]. The final net CO2e removal quantification must be conservatively determined, giving high confidence that at a minimum, the estimated amount of CO2e was removed.
In line with the Isometric Standard, this Protocol requires that Removal Credits are issued ex-post. Credits may be issued once CO₂ has been durably stored in the identified storage reservoir.
Net CO2e removal for the production of biochar and its durable storage for each Reporting Period, [math: RP], can be calculated by Equation 1.
[math: CO_2e_{Removal, RP} = CO_2e_{Stored, RP} - CO_2e_{Counterfactual, RP} - CO_2e_{Emissions, RP}]
(Equation 1)
Where:
Reversals which occur after Credits have been issued are separately accounted for by the Buffer Pool, and are therefore not included in Equation 1. See Section 5 of the Biochar Storage in Agricultural Soils Module and Section 5.6 of the Isometric Standard for further information regarding the handling of reversals.
The method of calculation for [math: CO_2e_{Stored, RP}] will depend on the method of storage. Refer to the relevant storage Module for requirements (see Section 10).
[math: C_{biochar}] can be calculated for either a blend of biochars (Storage Batch), or for individual Production Batches.
A ‘Production Batch’, [math: p], typically consists of utilizing a single type of biomass feedstock, often of a single source of origin, converting the biomass to biochar via pyrolysis, and transporting that biochar to the storage site for storage. The unique characteristics of the biomass used, the pyrolysis process, the produced biochar characteristics, transportation distances, and storage site characteristics will be the same for all of the biochar within a Production Batch. The process leading to the formation of a 'Production Batch' is a 'Production Process'.
The total amount of CO2 contained in the stored biochar can be calculated as follows.
Where all biochar Production Batches are blended prior to storage:
[math: CO_2e_{Stored,\ n} = \frac{C_{biochar,\ n}\cdot m_{biochar, n}}{C_{CO_{2}}}]
(Equation 2)
Where biochar Production Batches are not blended prior to storage:
[math: CO_2e_{Stored,\ n} = \sum_{p=1}^{k} \bigg(\frac{C_{biochar,\ p}\cdot m_{biochar,\ p}}{C_{CO_{2}}} \bigg)]
(Equation 3)
Where:
The total carbon content in biochar must be assessed following ASTM D5373: Standard Test Methods for Determination of Carbon, Hydrogen and Nitrogen in Analysis Samples of Coal and Carbon in Analysis Samples of Coal and Coke, or an equivalent procedure that yields the percent weight of carbon (%wt of C) in the biochar. Alternative methods or analytical equipment which determine total carbon content may be utilized if justified and documented to be equivalent to ASTM D5373. For example, EPA 9060A can be used for analysis of liquid samples, in the case where a biochar may be applied as a slurry.
This Protocol provides two alternative methods for the frequency with which carbon content must be measured and quantified. The first method (A) involves measuring every batch, the second method (B) involves only sampling a proportion of all batches, and conservatively estimating the carbon content of unsampled batches.
Method A: Measure every Batch
Using this method, the carbon content of the Production Batch must be quantified through direct measurement, either by:
For details regarding the acceptable minimum number of samples to be taken for each sampled Batch, see minimum number of samples per Batch below. If multiple samples are taken per Batch, the average [math: C_{biochar}] content of these samples must be used.
Method B: Sampling a Production Process
For a given Production Process of a feedstock, samples must be taken directly for an agreed upon number of Production Batches, to ensure there is enough data to estimate carbon content for future Production Batches with appropriate statistical significance. Until the time at which this threshold is reached, Method A must be used.
Subsequently, samples must be taken at least every 10 Production Batches. The frequency of sampling Production Batches can alternatively be agreed upon with Isometric prior to verification, provided the production process conditions can be proven to be stable over the course of the Project.
For the acceptable minimum number of samples to take per Batch, see minimum number of samples per Batch below.
For batches which are not sampled, carbon content must be conservatively estimated, as follows:
[math: C_{Biochar} = \mu_{CC} - \sigma_{\overline{CC}}]
(Equation 4)
[math: \sigma_{\overline{CC}} = \frac{\sigma_{CC}}{\sqrt{n_{samples}}}]
(Equation 5)
Where:
Eligible samples are those taken in the previous 6 months before a specific Production Batch was produced. Older samples may not be used.
Additionally, batches must be subject to random sampling, to alleviate the risk of any given batch containing a substance with a substantially different carbon content.
A random sampling approach must be agreed upon with Isometric and documented in the Project Design Document, whereby Isometric will contact the Project Proponent on randomly selected days, at an agreed cadence, which must be no less frequent than once per month, on average. Once contacted, the Project Proponent must sample the carbon content of the subsequent batches processed.
If the Project Proponent is unable to carry this random sampling out on 3 occasions within a 6 month period, or if within a 6 month period more than 3 measurements are below 3 standard deviations from the mean, this will trigger a project review by Isometric.
If there is a significant change to a Production Process for a feedstock, which is likely to alter the average carbon content of the feedstock, or if significant deviations in carbon content are detected, the feedstock should be considered as a new Production Process. This means that sampling must be restarted, with all prior samples no longer able to be used for estimating carbon content.
Minimum number of samples per Batch
For all measurements taken, samples must be from a well mixed and representative aliquot of the biochar. To account for the possibility of variation within a single Production Batch either of the following approaches must be adopted:
Process for handling carbon content measurement outliers
This process applies only if method B is used to calculate carbon content and should be used whether a batch was sampled or not. For a given Production Process, an Outlier is defined as any individual sample which lies more than 3 standard deviations, [math: \sigma_{CC}], above or below the mean. To minimize the potential overall impact of outlier measurements, all carbon content measurement outliers must be handled via the applying the technique of "winsorization”, as follows.
For a given measurement, [math: m], the winsorized measurement [math: m_w] is defined as follows:
Where [math: \mu] and [math: \sigma_{CC}] are calculated from all carbon content samples from the same Production Process taken within 6 months of the removal for which the carbon content is being calculated. For estimating the carbon content from sampled batches, only historical samples should be used to calculate [math: \mu] and [math: \sigma_{CC}] and not samples from the batch being calculated. The standard deviation, [math: \sigma_{CC}], should be calculated with the formula for sample standard deviation.
The winsorized measurement, [math: m_w], must be used for the determination of carbon content.
This winsorization process must only be applied once a minimum number of 90 measurements have been taken, to ensure statistical significance.
The Project Proponent must monitor occurrences of outliers, and investigate if significantly more than the statistically expected number occurs, as it may be indicative of a systematic issue. This may be checked at verification, at the discretion of the verifying VVB.
The mass of biochar applied is measured via determination of weight of delivered biochar to the application site using a calibrated scale. This serves as proof of delivery to site for storage, as well as providing a weight measurement. The total mass of applied biochar may be determined by the difference in biochar delivery truck weight measured upon arrival at the application site and at departure, after offloading of biomass, either into storage or directly applied.
Any truck scale used must have a current certification in accordance with applicable local, state, or federal regulations for legal-for-trade weights and measures. Testing and calibration of scales must utilize certified weights in accordance with local, state, or other regulations. Calibration weights must meet NIST Handbook 4413 specifications, and scale testing and calibration must be performed by a state certified entity.
In the event that truck scales are not available at the delivery site, for this purpose, prior to verification, it can be agreed with Isometric to instead provide a signed document for record of receipt, and/or photograph of delivery, for each completed delivery. This serves as alternative proof of delivery to the delivery site for storage. In this case, all details of weight measurements carried out at the production site, including all precautions taken to prevent mass loss during transportation, must be outlined in the PDD.
The Project Proponent must maintain the following records as evidence of gross CO2e stored in applied biochar:
Records of all C analyses and application masses (e.g. weigh scale tickets) must be maintained by the Project Proponent for verification purposes for a period of at least five years.
Other Considerations - CO2eStored, n
Biochar application processes should be monitored to ensure that any process upsets or equipment failures and resulting spills of biochar are monitored, documented, quantified, and accounted for in the GHG Statement of the project batch. For each batch, where a process upset results in loss of biochar, that amount must be deducted from the delivered amount of biochar based on delivery weigh tickets. Such amounts must be allocated directly to the specific biochar application.
Type: Counterfactual
[math: CO_2e_{Counterfactual,\ RP}] describes the CO2 that would have been removed from the atmosphere and stored beyond 15 years in the baseline scenario.
The calculation of [math: CO_2e_{Counterfactual,\ RP}] is determined by the requirements outlined in Section 2 of the Biomass Feedstock Accounting Module.
See Biomass Feedstock Accounting Module for calculation of [math: CO_2e_{Counterfactual,RP}].
Type: Emissions
[math: CO_2e_{Emissions,\ RP}] is the total quantity of GHG emissions from operations and allocated embodied emissions for each Reporting Period [math: RP]. This can be calculated as:
[math: CO_{2}e_{ Emissions,\ RP} = CO_{2}e_{Establishment,\ RP} + CO_{2}e_{Operations,\ RP} \\ + CO_{2}e_{End-of-life,\ RP} + CO_{2}e_{Leakage, RP}]
(Equation 6)
Where:
The following sections set out specific quantification requirements for each variable.
GHG emissions associated with [math: CO_{2}e_{Establishment,\ RP}] should include all historic emissions incurred as a result of project establishment, including but not limited to the SSRs set out in Table 1.
Project establishment emissions occur from the point of project inception through to before the first removal activity takes place. GHG emissions associated with project establishment may be allocated in one of the following ways, with the allocation method selected and justified by the Project Proponent in the PDD:
The anticipated lifetime of The Project should be based on reasonable justification and should be included in the PDD to be assessed as part of project validation.
Allocation of [math: CO_{2}e_{ Emissions,\ RP}] emissions to removals must be reviewed at each Crediting Period renewal and any necessary adjustments made. If the Project Proponent is not able to comply with the allocation schedule described in the PDD (e.g., due to changes in delivered volume or anticipated project lifetime), the Project Proponent should notify Isometric as early as possible in order to adjust the allocation schedule for future removals. If that is not possible, the Reversal process will be triggered in accordance with the Isometric Standard, to account for any remaining emissions.
GHG emissions associated with [math: CO_{2}e_{Operations,\ RP}] should include all emissions associated with operational activities including but not limited to the SSRs set out in Table 1. This includes direct emissions from pyrolysis, [math: CO_2e_{Direct, RP}], for which calculation and measurement details are set out in Section 9.2.
For biochar projects, the Reporting Period begins when the activity associated with a batch of Removals begins, and ends upon application of biochar from that batch at the storage site. As an example, for Projects storing biochar in agricultural soils, the Reporting Period begins with biomass feedstock sourcing and ends with biochar application to agricultural soils. The Reporting Period may cover a set period of time, for example a one month period of activity, inclusive of biomass sourcing through to application on agricultural soils for batches of Removals that fall into that month.
[math: CO_{2}e_{Operations,\ RP}] emissions must be attributed to the Reporting Period in which they occur. Allocation may be permitted in certain instances, on a case by case basis, in agreement with Isometric.
[math: CO_{2}e_{End-of-life,\ RP}] includes all emissions associated with activities that are anticipated to occur after the Reporting Period, but are directly or indirectly related to the Reporting Period. For example this could include end-of-life emissions for project facilities (indirectly related to all deployments).
GHG emissions associated with [math: CO_{2}e_{End-of-life,\ RP}] may occur from the end of the Reporting Period onward, and typically through to completion of project site deconstruction and any other end-of-life activities.
GHG emissions associated with activities that are directly related to each deployment must be quantified as part of that Reporting Period. GHG emissions associated with activities that are indirectly related to all deployments may be allocated in the same ways as set out in [math: CO_{2}e_{End-of-life,\ RP}].
Given the uncertain nature of [math: CO_{2}e_{End-of-life,\ RP}] emissions, assumptions must be revisited at each Crediting Period and any necessary adjustments made. Furthermore, if there are unexpected [math: CO_{2}e_{End-of-life,\ RP}] emissions associated with a Reporting Period, or The Project as a whole, that occur after The Project has ended, then the Reversal process will be triggered to compensate for any emissions not accounted for.
[math: CO_{2}e_{Leakage,\ RP}] includes emissions associated with a Project's impact on activities that fall outside of the system boundary of a Project.
It includes increases in GHG emissions as a result of The Project displacing emissions or causing a knock on effect that increases emissions elsewhere. This includes emissions associated with activity-shifting, market leakage and ecological leakage.
It is the Project Proponent's responsibility to identify potential sources of leakage emissions. At a minimum, biochar Projects must account for market leakage emissions associated with biomass feedstocks in accordance with the Biomass Feedstock Accounting Module.
[math: CO_{2}e_{Leakage,\ RP}] emissions must be attributed to the Reporting Period in which they occur. Allocation may be permitted in certain instances, on a case by case basis in agreement with Isometric.
This section of the Protocol outlines requirements for emissions accounting relating to energy use, transportation, and embodied emissions associated with a Project.
This section sets out specific requirements relating to quantification of energy use as part of the GHG Statement. Emissions associated with energy usage result from the consumption of electricity or fuel.
Examples of electricity usage may include, but are not limited to:
Examples of fuel consumption may include, but are not limited to:
The Energy Use Accounting Module provides guidance on how energy-related emissions must be calculated in a CDR Project. It sets out the calculation approach to be followed and acceptable emissions factors.
Refer to Energy Use Accounting Module for the calculation guidelines.
This section sets out specific requirements relating to quantification of emissions related to transportation.
Emissions associated with transportation include transportation of products and equipment as part of a Reporting Period process. Examples may include, but are not limited to:
The Transportation Emissions Accounting Module provides guidance on how transportation-related emissions must be calculated in a CDR Project so that they can be subtracted in the net CO2e removal calculation. It sets out the calculation approach to be followed and acceptable emissions factors.
Refer to Transportation Emissions Accounting Module for the calculation guidelines.
This section sets out specific requirements relating to quantification of embodied emissions as part of the GHG Statement. Embodied emissions are those related to the life cycle impact of equipment and consumables.
Examples of project-specific materials and equipment that must be considered as part of the embodied emission calculation include but are not limited to:
The Embodied Emissions Accounting Module sets out the calculation approach to be followed including allocation of embodied emissions, life cycle stages to be considered, data sources and emission factors.
Refer to Embodied Emissions Accounting Module for the calculation guidelines.
Pyrolysis is the process of thermochemical conversion of a solid biomass feedstock. The biomass is heated to a temperature greater than 300°C without addition of an oxidizing atmosphere. Pyrolysis of biomass results in a product mixture containing solid biochar, liquid bio-oil, and gasses. The gasses contain both condensable volatiles (bio-oil), and non-condensable pyrolysis gasses (predominantly CH4, with H2, CO, CO₂ and light hydrocarbons).
There are a wide range of technologies for achieving pyrolysis of solid biomass, which can generally be categorized into "slow pyrolysis" and "fast pyrolysis" based on the heating rate and residence time of biomass in the pyrolysis chamber. Slow pyrolysis processes are ideal to maximize the yield of pyrolysis towards the solid biochar product, and minimize the production of bio-oil and pyrolysis gasses. Several reactor configurations can be used to achieve slow pyrolysis of biomass to produce biochar, including both batch reactors and semi-batch reactors (e.g. fixed-beds, fluidized-beds, etc.). Any type of reactor configuration is eligible under this Protocol, provided that the reactor design requirements set out in Section 9.1 below are satisfied. A brief overview of common reactor configurations covered under this Protocol are provided in the Table 2 below. However, novel reactor configurations not belonging to any of the categories listed here will be acceptable provided that the appropriate reactor design documentation according to Section 9.1 is supplied in the PDD. All reactor designs, including the reactor type, engineering design diagrams and materials selection must be described in the PDD.
Table 2: Overview of common reactor types
| Reactor type | Description |
|---|---|
| Fixed-bed reactor | Solid biomass is loaded into a vessel. Heat is applied to the vessel to increase the temperature of the biomass. Once the target pyrolysis temperature is reached, and potentially sustained for some period of time, the solid biochar product is collected in a batch-mode. Gaseous and solid products self-separate within the reactor. |
| Auger reactor | Solid biomass is continuously fed to and transported through a cylindrical vessel using a screw-type fitting. Heat is applied to the exterior of the vessel. As biomass is transported along the length of the reactor, its temperature is increased. The target pyrolysis temperature is reached at the product exit point from the reactor. Gaseous and solid products are collected and separated at the reactor outlet. The biochar product is collected continuously. |
| Rotary kiln reactor | Solid biomass is continuously loaded at the top of an inclined rotating drum. As more biomass is added to the vessel, biomass inside the vessel is transported downwards. Heat is applied to the exterior of the vessel. As biomass is transported along the length of the reactor, its temperature is increased. The target pyrolysis temperature is reached at the product exit point from the reactor. Gaseous and solid products self-separate at the reactor outlet. The biochar product is collected continuously. |
Maximum pyrolysis temperature may be manipulated in order to increase the yield of solid biochar products and their relative carbon stability. For example, pyrolysis at higher temperatures may lower the yield of the solid biochar. However, thermal breakdown of biochar is positively correlated with increasing temperatures - yielding biochar with lower volatile content that is more stable. The optimum range for pyrolysis temperature is 500–800°C to miaximise the production of highly stable biochar14.
An engineering design diagram of the chemical reactor used to achieve pyrolysis must be included in the PDD. The design diagram must include details of the dimensions of the reactor, the locations of material inflows/outflows, the positioning of sensors for the monitoring of temperature/pressure, details of any internal equipment such as agitators or heating/cooling coils and details of any external heat transfer equipment (including heat exchange fluid entry/exit points and corresponding sensors for flow rate and temperature). A sufficient number of viewpoints must be included in the engineering design diagram to show the positioning of all of the key components listed above. Any other process equipment essential to the safe and effective operation of the pyrolyzer not listed above should be included and highlighted in the engineering design diagram.
In instances where Project Proponents wish to expand an existing Project, or to submit a new Project for validation, where the reactor vessels used to achieve pyrolysis of biomass are manufactured according to the same design diagrams as those submitted for initial project validation, it is not necessary to resubmit a new design diagram at each subsequent validation event. In cases where the design of the reactor vessel differs to that from the original project validation, submission of updated design diagram documentation is required.
The reactor design must include sensors necessary to quantify any loss of pyrolysis gasses during operation of the reactor to leakage. This should include, at minimum, sensors to determine the outflow of pyrolysis gasses from the flue gas outlet, which can be used in conjunction with a suitable reactor model to determine the amount of pyrolysis gasses produced and to estimate any loss of these gasses by unmonitored and unintentional leakage to the environment. The chemical reactor model used to characterize reactor performance and estimate pyrolysis gas losses should consider all physical and chemical mechanisms relevant to the operation of the chosen reactor type. The chemical reactor model should incorporate a chemical kinetics model which is based on the latest scientific understanding for the chosen reactor configuration. The model should be demonstrated to be validated using empirical data and should include a process mass balance accounting for the product yields. Details of the validation of the chemical reactor model should be provided in the PDD.
Alternatively, in situations where it is not possible to develop a high-quality mathematical reactor model to represent pyrolyzer operations, it is permissible to deploy one of the following alternative approaches to verify that there is no substantial unintended leakage of gaseous products from the system:
It is anticipated that the operation of the pyrolyzer will occur at high temperature, and may occur at elevated pressure. Appropriate considerations need to be made in the design of the reactor to mitigate potential adverse operational conditions. Details must be provided in the PDD to describe the selection of materials for each component of the reactor, including suitable justification of these choices from the perspectives of thermal and mechanical resilience. For reactors operating at high pressures, considerations should be made relating to the operating pressure, vessel shape/size, positioning of material inlets/outlets, and positioning of sensors to ensure mechanical integrity of the reaction vessel. Such considerations should be made in compliance with a suitable local standard which provides regulations for the design and fabrication of pressure vessels, such as 2014/68/EU (the "Pressure Equipment Directive") or an appropriate regional equivalent standard in the region of project operation. If no such regional standard exists in the region of operation, Project Proponents are required to use the 2014/68/EU standard.
An appropriate reactor maintenance plan should be in place, and must be detailed in the PDD. The maintenance plan should outline how the Project Proponent will ensure the structural integrity of the reactor vessel to mitigate against potential material loss events. This includes suitable monitoring and mitigation for mechanical and thermal degradation events which may lead to the failure of the vessel and subsequent release of materials into the environment. All maintenance plans should be in compliance with a suitable local standard which provides regulations for the maintenance of pressure vessels, such as 2014/68/EU or an appropriate regional equivalent standard in the region of project operation.
The thermochemical conversion of solid biomass to produce biochar in a pyrolysis process also produces a gas as a significant co-product. The gas contains both volatile condensable components (bio-oil) and non-condensable components (pyrolysis gasses; predominantly CH4, with H2, CO, CO₂ and light hydrocarbons). Depending on the specific technologies deployed by The Project, there are various options for handling the gaseous co-product eluted from the pyrolyzer. Each of the permissible options for handling the gaseous product, and the associated requirements for emissions accounting for each, are detailed in this Section.
The gasses eluted from the pyrolyzer are fed to a condenser, or any other suitable gas-liquid separation unit, to separate the condensable and non-condensable fractions of the gaseous product. The resulting (condensable) liquid-phase is bio-oil, and the (non-condensable) gas-phase is pyrolysis gasses. There are three permissible end-use emissions accounting approaches for the produced bio-oil:
There are four permissible end-use emissions accounting approaches for the produced pyrolysis gasses:
All non-CO2 emissions to the atmosphere, via any of the approaches described above, must be converted to tonnes of CO2e using the 100-year Global Warming Potential (GWP) for the relevant GHGs, based on the most recent volume of the IPCC Assessment Report (presently the Sixth Assessment Report).
Direct emissions from a pyrolysis process occur when pyrolysis gasses are emitted to the atmosphere, are combusted in an emissions control unit, or are combusted within the process for the provision of thermal energy for the process. Direct emissions should be calculated as follows:
[math: CO_2e_{Direct, RP} = \sum_{n=1}^{n_c} \sum_{i=1}^{N} m_{i} \cdot C_{n,i} \cdot GWP_n \cdot \Delta t_i]
(Equation 7)
Where:
Direct CO2e emissions, [math: CO_2e_{Direct, RP}], consider non-CO2 emissions only to avoid double counting, given that release of CO2 emissions during pyrolysis will be realized in the reduction of carbon stored in the biochar after pyrolysis of biomass. Carbon stored is calculated as [math: CO_2e_{Stored, RP}], which directly informs net CO2e removal and Crediting. Consideration of non-CO2 emissions during pyrolysis is important given the amount and composition of gasses emitted during pyrolysis may be substantially different to that emitted in the baseline scenario, for example as a result of biomass decay or combustion.
Quantification of [math: CO_2e_{Direct, RP}] requires two primary measurements, the measurement of gas flow and the analysis of gas composition for CH4, H2, CO, and CO2 in the emitted gas stream.
Gas flow rate, [math: m_i], must be:
The concentration of CH4, H2, CO, and CO2 must be:
The Project Proponent must maintain the following records as evidence supporting calculation of direct emissions from the biomass conversion process for a period of at least five years:
For some projects, particularly those deploying pyrolyzers in a highly distributed manner or in remote locations, the measurement of direct emissions to the atmosphere using calibrated gas flow and concentration sensors may not be a practically feasible approach. As an alternative to the measurement requirements established in Section 9.2.2, emissions testing data may be used to estimate [math: m_i] and [math: C_{n,i}] for project operations. For both quantities, suitable measurements must be made during process operations to substantiate that the conducted emissions tests are representative of actual project operations.
The gas flow rate, [math: m_i], should be determined by using calibration curves from emissions testing in conjunction with measurements of the pressure drop in the direct emission stream. The concentration of CH4, H2, CO, and CO2 should be determined using concentration data from emissions testing. Emissions testing data should be produced by a qualified emissions testing company, accredited to the Stack Testing Accreditation Council for ASTM D7036, ISO 17025, or approved by state regulatory authority to perform compliance emissions testing.
For emissions testing to be considered representative of actual project operations, the following criteria must be satisfied:
Measurement of the temperature within the flue stack should be conducted using a calibrated sensor which satisfies the below requirements:
The Project Proponent must maintain the following records as evidence supporting calculation of direct emissions from the biomass conversion process for a period of at least five years:
For all information on what chemical and physical characterization of biochar must be carried out, and for calculation of [math: {CO}_{2}^{}e_{Stored}^{}], please refer to the relevant storage Module.
Durability and monitoring requirements for Biochar Storage in Agricultural Soils.
Isometric would like to thank following contributors to this Protocol and relevant Modules:
Fang, Z., Gao, Y., Bolan, N., Shaheen, S. M., Xu, S., Wu, X., ... & Wang, H. (2020). Conversion of biological solid waste to graphene-containing biochar for water remediation: A critical review. Chemical Engineering Journal, 390, 124611. ↩
Anae, J., Ahmad, N., Kumar, V., Thakur, V. K., Gutierrez, T., Yang, X. J., ... & Coulon, F. (2021). Recent advances in biochar engineering for soil contaminated with complex chemical mixtures: Remediation strategies and future perspectives. Science of The Total Environment, 767, 144351. ↩
Pranagal, J., & Kraska, P. (2020). 10-years studies of the soil physical condition after one-time biochar application. Agronomy, 10(10), 1589. ↩↩2
Seleiman, M. F., Alotaibi, M. A., Alhammad, B. A., Alharbi, B. M., Refay, Y., & Badawy, S. A. (2020). Effects of ZnO nanoparticles and biochar of rice straw and cow manure on characteristics of contaminated soil and sunflower productivity, oil quality, and heavy metals uptake. Agronomy, 10(6), 790. ↩↩2
Hardy B., Sleutel S., Dufey J.E. and Cornelis J-T. (2019) The Long-Term Effect of Biochar on Soil Microbial Abundance, Activity and Community Structure Is Overwritten by Land Management. Front. Environ. Sci. 7:110. doi: 10.3389/fenvs.2019.00110 ↩
Osman, A.I., Fawzy, S., Farghali, M. et al. (2022) Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review. Environ Chem Lett 20, 2385–2485. https://doi.org/10.1007/s10311-022-01424-x↩
Lehmann, J., & Joseph, S. (Eds.). (2015). Biochar for Environmental Management: Science, Technology and Implementation (2nd ed.). Routledge. https://doi.org/10.4324/9780203762264↩
Yao, C., Wang, B., Zhang, J., Faheem, M., Feng, Q., Hassan, M., ... & Wang, S. (2024). Formation mechanisms and degradation methods of polycyclic aromatic hydrocarbons in biochar: A review. Journal of Environmental Management, 357, 120610. ↩↩2↩3
Wang, J., Xia, K., Waigi, M. G., Gao, Y., Odinga, E. S., Ling, W., & Liu, J. (2018). Application of biochar to soils may result in plant contamination and human cancer risk due to exposure of polycyclic aromatic hydrocarbons. Environment International, 121, 169-177. ↩
Human health effects of polycyclic aromatic hydrocarbons as ambient air pollutants: report of the Working Group on Polycyclic Aromatic Hydrocarbons of the Joint Task Force on the Health Aspects of Air Pollution. Copenhagen: WHO Regional Office for Europe; 2021. Licence: CC BY-NC-SA 3.0 IGO. ↩
Schneider, L., Schallert, B., & Kizzier, K. (2022). Methodology for assessing the quality of carbon credits. https://carboncreditquality.org/download/Methodology/CCQI Methodology - Version 3.0.pdf ↩︎ ↩︎ ↩
Life cycle modules as described in BS EN 15978:2011 Sustainability of construction works — Assessment of environmental performance of buildings — Calculation method ↩↩2↩3↩4↩5↩6↩7
NIST. (2023). Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices - 2023 Edition. NIST. https://www.nist.gov/pml/owm/publications/nist-handbooks/handbook-44-current-edition↩
Chatterjee, R., Sajjadi, B., Chen, W. Y., Mattern, D. L., Hammer, N., Raman, V., & Dorris, A. (2020). Effect of pyrolysis temperature on physicochemical properties and acoustic-based amination of biochar for efficient CO2 adsorption. Frontiers in Energy Research, 8, 85. ↩