Monitoring Plans for this methodology shall include at a minimum, but are not limited to, tracking of the following information:

• amount of biomethane injected into the grid

• mass and waste status of each feedstock input in tonnes of fresh matter (ensuring the dedicated crop and ILUC risk thresholds are not surpassed, see Environmental and Social Do No Harm and Leakage)

• repartition of solid, liquid and raw digestate

• amount and type of electricity use on-site

• description of any major changes in operations

The Project Developer is the party responsible for adhering to the Monitoring Plan.

Projects eligible under this methodology are the anaerobic digestion sites where feedstock inputs are collected, anaerobic digestion occurs, and biogas/energy is generated. The Project Developers are the operators of the anaerobic digestion sites.

The only use of biogas eligible in the current version of the methodology is purifying biogas to biomethane and direct injection into the gas grid. Other uses may be considered on a case by case basis, if Project Developers provide sufficient proof that they 1) still adhere to the eligibility criteria and 2) have a rigorous, conservative GHG reduction quantification method for components that differ from the method described in the present document.

The only use of digestate eligible for carbon credits under this methodology is application to agricultural soils as an organic amendment and fertilizer. Such activities shall be credited with avoided synthetic mineral fertilizer production and use. If digestate is used in a different application, the project is still eligible for credits on the basis of their energy production activities.

Project Scope

One project corresponds to one anaerobic digestion site. It is not possible under this methodology to group multiple sites together as one project.

An anaerobic digestion site is defined as a site with one operations permit and shared infrastructure (e.g. digestion tanks, storage, and treatment facilities).

Only the activities at the biogas site that are deemed additional are part of the project scope.

Use of fossil fuels such as natural gas, oil, and coal are responsible for about 75% of global greenhouse gas (GHG) emissions, and make up 98% of GHG emissions within the energy sector. Alternative energy sources exist with far fewer GHGs emissions, but technological, economic, and administrative barriers prevent and limit their development.

Biogas is a renewable energy source that can be produced via several different pathways. One option is anaerobic digestion, where organic materials such as food waste, animal manure, and agricultural residues are broken down by microorganisms in an oxygen-free environment. Common uses of biogas include:

• Injection: Purification of biogas to biomethane and directly injecting it into the gas network.

• Cogeneration: Generation of electricity and heat by a biogas engine or turbine for a combined heat and power (CHP) system.

• Heat only: Production of heat in a biogas boiler.

• Transport: Compressed natural gas (BioCNG) and liquefied natural gas (BioLNG)

The second output of anaerobic digestion, digestate, is a material rich in organic matter and nutrients that is spread on agricultural fields.

Numerous life cycle assessments (LCAs) have confirmed that using biogas from anaerobic digestion rather than energy from fossil fuels leads to reduced GHG emissions. Yet, biogas makes up a small share of energy consumption: in 2022 in Europe, 20 times more natural gas was used than biogas,.

Project developers shall demonstrate that they meet all eligibility criteria outlined in the Riverse Standard Rules and described below with a specific focus on biogas from anaerobic digestion.

Eligibility criteria that do not require specific methodology instructions are not described here. This includes:

• Measurability

• Real

• Technology readiness level

• Minimum impact

Additionality

To demonstrate additionality, Project Developers shall perform regulatory surplus analysis, plus either investment or barrier analysis, using the Riverse Additionality Template.

No double counting

Project developers shall sign the Riverse MRV & Registry Terms & Conditions, committing to follow the requirements outlined in the Riverse Standard Rules, including not double using or double issuing carbon credits.

Projects shall comply with the requirements set out in the Riverse Double Counting Policy.

No additional measures for double issuance are required under this methodology, because double issuance among actors in the supply chain is unlikely.

Co-benefits

Project Developers shall prove that their project provides at least 2 co-benefits from the UN Sustainable Development Goals (SDGs) framework (and no more than 4).

Common co-benefits of biogas from anaerobic digestion projects, and their sources of proof, are detailed in Table 1. Project Developers may suggest and prove other co-benefits not mentioned here.

SDG 13 on Climate Action by default is not considered a co-benefit here, since it is implicitly accounted for in the issuance of carbon credits. If the project delivers climate benefits that are not accounted for in the GHG reduction quantifications, then they may be considered as co-benefits.

Table 1 Summary of common co-benefits provided by electronic device refurbishing projects. Co-benefits are organized under the United Nation Sustainable Development Goals (UN SDGs) framework.

Substitution

The biomethane generated and injected into the gas grid must be a valid substitute for natural gas, as modeled in the baseline scenario.

This is typically already required by energy companies that manage the gas network that the biomethane is injected into. Project Developers shall provide contracts with the relevant energy company, where clauses require the final product to meet specific characteristics making it substitutable for natural gas.

The co-product of anaerobic digestion, digestate, must be a valid substitute for mineral fertilizer, which digestate is assumed to replace in the baseline scenario. Numerous scientific studies have confirmed that digestate has a high fertilization value, sometimes comparable with that of mineral fertilizer. Fertilization value is largely dependent on nutrient concentration, which shall be measured via laboratory tests for a sample of digestate from each project.

The amount of mineral fertilizer avoided in the project scenario shall correspond to the nutrient content of the digestate (see the Project avoided mineral fertilizer section for more details). This ensures that digestate is modeled as a realistic substitute for mineral fertilizer based on project-specific data.

Environmental & social do no harm

Project Developers shall prove that the project does not contribute to substantial environmental and social harms.

Projects must follow all European, national, and local environmental regulations related to, for example, anaerobic digestion management, feedstock storage, feedstock sourcing, digestate storage, and digestate spreading.

To be eligible under this methodology, projects shall use no more than 10% dedicated crops in their feedstock input mixture in the first year of the crediting period. This decreases to 5% in the second year, and 3% in the remaining years. This shall be monitored each year during the crediting period.

It is environmentally preferable to use waste, manure, and slurry as feedstocks rather than intermediate energy crops, but this may not be preferable to farmers/biogas producers for financial or productivity reasons. Although this methodology does not impose a strict threshold on intermediate energy crops in the feedstock mix, the example below highlights how biogas producers are incentivized to use waste, manure, and slurry as feedstocks.

ESDNH risk evaluation

Project Developers shall fill in the Biogas from anaerobic digestion risk evaluation, to evaluate the identified environmental and social risks of projects,. The identified risks include:

• Use of dedicated crops, leading to competition for food and agricultural land;

• Reliance on energy crops rather than waste, manure, and/or slurry;

• Distant transport of feedstock inputs (>100 km) leading to increased greenhouse gas emissions from transport;

• Energy intensive processing;

• Methane leaks from digestion process and storage facilities;

• Leaching of runoff from manure, slurry or digestate storage, increasing eutrophication risks;

• Leaching of excess nutrients from digestate spreading, increasing eutrophication risks;

• Air quality, volatile odors from manure, slurry or digestate storage;

• Landscape conversion from rural to industrial;

• Workers health and safety.

Leakage

Targets alignment

Biogas from anaerobic digestion projects must prove that they lead to at least a 45% reduction in GHG emissions compared to the baseline scenario. This is aligned with the European Union’s 2040 Climate targets, as described in the Riverse Standard Rules.

The scope of the reduction is the system boundary used in GHG quantification, described in the Baseline scenario and Project scenario sections below.

This shall be proven using the GHG reduction quantification method described below.

This methodology covers projects that produce biogas from anaerobic digestion of agricultural products, residues and wastes. It includes both energy production from biogas and the production of digestate, a valuable organic amendment.

Appendix 1: Ecoinvent processes

List of ecoinvent 3.10 processes used in the GHG reduction quantification model

General

General GHG reduction quantification rules can be found in the Riverse Standard Rules.

Calculations of GHG emissions for the baseline and project scenarios shall follow a robust, recognized method and good practice guidance. The overall methodological approach is a comparative life cycle assessment (LCA) at the project-scale, based on ISO 14064-2:2019.

Biogas from anaerobic digestion projects are only eligible for avoidance Riverse Carbon Credits.

Biogas from anaerobic digestion projects have one shared universal main function: energy production.

Projects that use manure and/or slurry as feedstock inputs have an additional function: improved manure/slurry management, which leads to fewer GHG emissions during storage and spreading, and higher nutrient availability reducing the need for mineral fertilizers.

The baseline scenario represents the functionally equivalent set of activities that would occur in the absence of the project. Therefore, the baseline scenario includes:

• conventional energy production (mix of fossil fuels and biogas already present in the energy mix).

If the project uses manure and/or slurry, the baseline scenario also includes:

• conventional manure and slurry management with higher GHG emissions, and

• avoided mineral fertilizer production from manure and slurry application.

Functional unit

If the only function of the project is energy production, the functional unit is 1 GWh of energy delivered.

If the project uses manure and/or slurry as feedstock inputs, then the functional unit is 1 GWh of energy delivered plus the management and use of the equivalent amount of manure/slurry.

Data sources

The required primary data for GHG reduction calculations from projects are presented in Table 2. These data shall be included in the project’s Project Design Document (PDD) and made publicly available.

Table 2 Summary of primary data needed from projects and their source for initial project certification and validation. Asterisks (*) indicate which data are required to be updated annually during verification (see Monitoring Plan section).

Secondary data taken from the literature are used to define default values, or provide conversion rates, to obtain the following elements:

• Nitrogen, dry matter content, and biochemical methane potential (BMP) of cow and chicken manure and slurry (Table 3);

• Percentage of Nitrogen in manure, slurry and different types of digestate (raw, liquid and solid) lost as N2O during storage (Table 3);

• Rate of N2O emissions per kg of manure, slurry, digestate, and mineral fertilizer spread on agricultural fields (Table 3 and Table 6);

• Amount of N, K2O and P2O5 mineral fertilizer avoided per tonne of manure and slurry

• Average number of days manure and slurry are stored in the baseline scenario;

• Characteristics of methane, biogas and biomethane;

• Leakage rates of methane throughout the biogas production from digestion, purification, boiler for internal use, injection and distribution;

• Percent of biogas produced that is used internally;

• Emission rates of methane and N2O from combustion of biomethane, in kg/MJ;

• Amount and density of digestate produced from feedstock inputs;

• Gas mix in the baseline scenario, considering the market shares for natural gas, biomethane and biogas;

• These values and their sources are provided in the Assumptions section.

The ecoinvent database version 3.10 (hereafter referred to as ecoinvent) shall be the main source of emission factors unless otherwise specified. Ecoinvent is preferred because it is traceable, reliable, and well-recognized. The ecoinvent processes selected are detailed in Appendix 1.

Assumptions

1. Feedstock inputs that are categorized as waste come with no impacts from their production or first life. They enter the project system boundary during the transport to the biogas site. This includes inputs such as manure, slurry, silo grain residue, spent beer grains, recirculated digestate, or damaged produce that can’t be sold.

2. In the baseline scenario, the transport distance for manure and/or slurry collection to the storage and use point is assumed to be 10 km.

3. Emissions of N2O and methane due to manure and slurry storage before the digestion process are linearly related to the amount of days manure and slurry are stored on site. If Project Developers do not have an estimation of this value, an average of 15 days is assumed. In the baseline scenario, this is assumed to be 180 days.

4. Emissions of N2O from slurry storage, in the project scenario, are sufficiently small (0.01-0.05% life cycle GHG emissions) that they can be excluded. This is because N2O emissions from slurry storage are generally small, plus the shortened storage duration in the project scenario minimizes them further.

5. Manure and slurry from pigs, horses, sheep, and other animals are modeled using the same characteristics as cow manure. Only chicken manure is treated differently, due to its high nitrogen content (Table 3).

6. Buildings and main infrastructure at the biogas site have an assumed lifetime of 20 years. Infrastructure amounts are modeled and extrapolated from the main digester exterior volume (m³) to simplify data collection, after numerous certification projects showed small impacts from infrastructure (1-2% of project life cycle GHG emissions). The ecoinvent process for the anaerobic digestion plant present in Appendix 1 is used, considering 1 m³ of digester volume annually.

7. Activated carbon used for biogas purification is modeled using a ratio of 0.2 tonnes of activated carbon/GWh of energy produced. The value was taken from biogas projects previously certified by Riverse, and results are not sensitive to changes in this value.

8. In the project scenario, the amount of biogas self-consumed for onsite heating is assumed to be 4%. Results are not sensitive to changes in this value, which can regularly vary from 2-6% according to previous project data.

9. The mass of digestate produced is estimated to be 85-95% of the mass of feedstock inputs. A benchmark of 90% is often considered, according to the literature, expert partner consultation, and a sample of projects’ applications for environmental licenses, where they must do a detailed estimate of digestate production (“Facilities classified for environmental protection”, in French Installations classées pour la protection de l'environnement, ICPE). A conservative value of 85% was chosen. Indeed, the annual amount of digestate produced is not measured at project sites. Rather, sites measure the amount sold. Due to temporal, seasonal restrictions on when digestate can be spread, the amount sold over one calendar year does not correspond to the amount produced in that year. Records of digestate sold are still collected from project developers to validate that this is a reasonable approximation.

10. Methane emissions during digestate storage are reduced when the digestate is covered (e.g. airtight covers on tanks, not piles of solid digestate under a roof or rain covers). It is assumed that covers reduce methane emissions by 80%.

11. Nutrient availability in digestate, manure and slurry is equivalent to that of mineral fertilizer. For example, 1 kg of nitrogen applied to soils in digestate is assumed to substitute 1 kg of mineral nitrogen fertilizer.

Table 3a Summary of cow and chicken manure characteristics (from Esnouf et al., 2021 unless otherwise stated).

Table 3b Summary of slurry characteristics (from Esnouf et al., 2021 unless otherwise stated).

Project Scenario

The project scenario consists of anaerobic digestion, which serves three functions: 1) biomethane production, 2) digestate production, and if the project uses manure or slurry as a feedstock, 3) improved manure/slurry management. This process is broken down into 4 life cycle stages, displayed in Figure 1:

• Feedstock provisioning, transport, and storage;

• Digestion and biomethane management;

• Digestate storage and spreading;

• Avoided fertilizer production.

Feedstock provisioning, transport, and storage

Project Developers shall provide the amount of each type of feedstock input used annually in tonnes of fresh matter.

Feedstock input types considered in the model include several types of energy cover crops, straw, whole-grain corn crops, manure, slurry, recirculated digestate, and various agro-industrial waste/by-products.

The production and cultivation impacts from non-waste feedstock inputs are modeled using the ecoinvent processes outlined in Appendix 1. These include dedicated crops, energy cover crops, and straw.

Project Developers shall provide the distance that feedstock inputs are transported from their origin to the site. Transport is assumed to be done by truck (see ecoinvent process in Appendix 1). When there are multiple sources of a feedstock, the average weighted distance for each feedstock type shall be used.

Manure and slurry may be stored onsite for several days or weeks if they cannot be added to the digester immediately upon their delivery to the biogas site. During this storage period, methane and N2O are emitted linearly over time. When they are stored for 180 days (a conventional non-biogas scenario), 2% of its nitrogen is emitted as N2O, plus some methane expressed as a fraction of BMP (Table 3). Manure is stored at biogas sites for fewer days than in a conventional scenario, which results in fewer N2O and methane emissions. The ratio of average days manure and slurry are stored at the biogas site, to the average storage duration of 180 days, is used to adjust the N2O and methane emission benchmarks detailed in Table 3 (see example in the box below).

Project Developers rarely have detailed receipts and tracking proof of feedstock inputs, even if they informally manage this very precisely for operations. In the absence of proof, calculations are used here to cross check expected biogas production from the given feedstock inputs vs the actual amount of biogas produced. Project Developers shall calculate the expected annual biogas production using the biochemical methane potential (BMP) of the sum of each feedstock input, available in public databases (Equation 6). The calculated expected methane produced value should be within 10% of the actual methane produced value based on injection receipts, calculated in the following section in Equation 11. Discrepancy here suggests high uncertainty which may result in a higher discount factor (see Uncertainty Assessment section).

Digestion and biomethane management

Project Developers shall provide the amount of electricity used onsite annually, in kWh/year, and the electricity source (e.g. grid or onsite solar). A black-box approach is used for electricity consumption, and only the total amount of electricity used on-site is required (i.e. not broken down into different uses).

Leakages of methane throughout the project steps are calculated using leakage rates from the literature, and are summarized in Table 4. Even though modern anaerobic digestion plants only leak small amounts of methane, they can represent important sources of GHG emissions through the life cycle. Project sites have sensors to measure large, exceptional methane leaks, but the amounts considered in the GHG reduction quantification are below the threshold of most sensors.

Table 4 Rates of methane and biogas leakage from different steps in the project scenario, based on volume of gas.

Project Developers should provide methane leakage rates from offgas during the purification step. This is typically provided in technical documents or contracts for purification machinery. If this value is not available, a default leakage rate of 0.7% of methane by volume will be used. If offgas is captured and used, this value may be zero.

The amount of biogas self-consumed in a boiler for onsite heating is assumed to be 4% (see Assumptions section).

The biogas and biomethane characteristics presented in Table 5 are used.

Table 5 Characteristics of biogas and biomethane

The amount of activated carbon used in purification is estimated to be 0.2 tonnes/GWh of energy produced (see Assumptions section). Other processes related to purification were excluded, given that they are consistently minor sources of impacts in biogas LCAs.

The most impactful direct emissions from the biomethane combustion step were taken from Table 53 in Esnouf et al., 2021. This includes 4.93e-7 kg N2O/MJ biomethane, and 1.96E-06 kg biogenic CH4/MJ biomethane.

All infrastructure and machinery are included in this step, even if some are actually used for digestate or feedstock storage described in other sections.

Infrastructure and machinery are modeled in ecoinvent with a process that includes production, transport and disposal of the main materials for an agricultural biogas plant (see Appendix 1). The ecoinvent process represents a site with a main digester of 500 m3.

Project Developers shall provide the external volume of their site’s main digester, in m3. This is used to adjust the amount of the ecoinvent infrastructure and machinery process used. For example, if the project’s main digester has a volume of 250 m3, it will only be assigned half of the impacts modeled in the ecoinvent process.

It is assumed that infrastructure has a lifetime of 20 years. This means that for calculating impacts of 1 year of operations of the project, infrastructure and machinery will be allocated 1/20th of their total impacts.

Digestate storage and spreading

The amount of digestate produced annually is estimated to be 85% of the mass of feedstock inputs (see the Assumptions section).

Project Developers shall provide the repartition of digestate types (raw, liquid, and/or solid phase) that are stored and spread. If the repartition is different for the storage and spreading stages (e.g. stored raw, spread as liquid and solid), then the repartition that leads to higher project emissions shall be applied to all digestate management, in order to maintain a conservative approach. Data shall come from the repartition of digestate types sold annually.

Project Developers shall provide an estimate of the residence time, (the number of days feedstock spends in the digester).

Methane emissions during digestate storage are calculated as a function of residence time in the digester and percent of methane produced that is emitted, as illustrated in Figure 10.1 of Hartig 2010. The linear regression equation obtained from that dataset is presented in Eq. 21, and shall be used to predict methane leakage rates from digestate storage for a given project’s residence time.

It is assumed that storing digestate under airtight covers reduces methane emissions from storage by 80%. Project Developers shall report what fraction of their digestate storage is covered vs. uncovered.

Nitrous oxide emissions from digestate storage are calculated using 1) the amount of digestate stored, 2) the nitrogen content of digestate, provided by Project Developers in the form of laboratory analyses and 3) emission rates from the literature, summarized in Table 6.

Table 6 Percent of nitrogen present in digestate that is emitted as N2O from digestate storage and spreading.

Digestate transport from the biogas site to the farm for spreading is included when this transport is done by truck. No impacts are included for transport via irrigation pipeline, assuming that they would be below the impact threshold.

Nitrous oxide emissions from digestate spreading on soil is calculated using 1) the amount of digestate spread (which may differ from the amount stored if some digestate is recirculated as feedstock), 2) the nitrogen content of digestate, provided by Project Developers in the form of laboratory analyses and 3) an emission rate of 1% of nitrogen added to soils in digestate is lost in N2O, according to the IPCC Tier 1 emission factor for organic amendments.

Project avoided fertilizer

The project is credited with avoiding synthetic mineral fertilizer production thanks to digestate spreading. This is because the project is multifunctional and makes a co-product digestate, which is treated using the common LCA practice of system expansion and substitution[48].

Project Developers shall provide the nutrient contents of all digestate types, measuring total N, P2O5, and K2O.

Amount of digestate spread is described and calculated in the previous section.

As described in the Assumptions section, nutrient availability in digestate is equivalent to that of mineral fertilizer, so for example spreading 1 kg of P2O5 from digestate is modeled as substituting the production of 1 kg of P2O5 mineral fertilizer production.

Along with avoiding nitrogen fertilizer production, digestate spreading also avoids N2O emissions from fertilizer spreading. These are calculated using the amount of nitrogen avoided by digestate, and nitrogen emission rates from mineral fertilizers, which equals 1% of applied N emitted as N2O.

Baseline scenario

The baseline scenario represents the GHG emissions that would occur without the project. It includes functionally equivalent processes that provide the same products/services as the Project Scenario.

As described in the Project Scenario section, the project delivers the following products/services, with their corresponding baseline scenario processes:

• Biomethane production and injection into the gas grid: this is assumed to replace the average market mix of gas from the grid, primarily natural gas, with a fraction of biomethane and biogas already present in the mix.

• Digestate production: this is assumed to replace synthetic mineral fertilizer production and application, which is already considered within the project scenario using system expansion and substitution (see Project avoided fertilizer section). It is not considered in the baseline scenario.

• Manure and slurry management (if the project uses manure and/or slurry): this is assumed to replace conventional manure and slurry storage and spreading, which includes emissions from storage, and avoided mineral fertilizer production.

The baseline scenario includes 1 to 3 life cycle stages, depending on the project operations, displayed in Figure 2:

• Energy production

• Manure and slurry storage and spreading (if the project uses manure and/or slurry)

• Avoided fertilizer production and use (if the project uses manure and/or slurry)

Energy production

If the project injects biomethane into the gas grid, the baseline scenario is the market mix of gasses in the national gas supply. This shall include the share of biogas and biomethane already used at the national level.

Natural gas, biogas and biomethane production are modeled using ecoinvent processes detailed in Appendix 1. For natural gas, the process includes all upstream impacts of gas extraction, production, distribution, and combustion in a gas turbine. Biogas and biomethane processes include their production, and combustion was excluded assuming its impact would be very small because they are not fossil fuels.

The total amount of gas considered in the baseline scenario shall equal the amount of energy from biomethane injected by the project biogas site (provided by Project Developers), minus the calculated amount of biomethane lost during the distribution stage, in MJ.

The total amount of gas in the baseline scenario shall be broken down into the amount of natural gas, biogas and biomethane using data from Eurostat datasets covering biogas and natural gas consumption. An example is provided below.

If heat and/or electricity are exported by the project instead of gas injection, the baseline scenario shall include the national mixes of heat and/or electricity, based on Eurostat data for the most recent year (or data of a similar high-quality source). The amount of heat and/or electricity in the baseline scenario shall equal the equivalent amount of energy from heat and/or electricity exported from the project scenario to the grid/external industrial processes (i.e. excluding the amount that is self consumed).

If manure or slurry are not used as feedstock inputs at the biogas site, then this section is the only component of the baseline scenario.

Manure and slurry storage and spreading

This stage shall only be included in the baseline scenario if the biogas project uses manure or slurry as a feedstock input.

This stage includes N2O and methane emissions from manure/slurry storage and spreading, and GHG emissions from transport.

Project Developers shall provide the amount of manure and/or slurry used as feedstock inputs annually, in tonnes of fresh matter.

Project Developers shall specify if manure is from poultry vs any other type of animal. Manure from pigs, horses, sheep, and other animals are modeled using the same characteristics as cow manure, as described in the Assumptions section. Because poultry slurry is uncommon, all slurry is modeled as cow slurry.

Nitrogen content, N2O emission factors, and methane emission rates from storage and spreading for manure and slurry are summarized in Table 3.

Baseline avoided fertilizer

This stage shall only be included in the baseline scenario if the biogas project uses manure or slurry as a feedstock input.

This stage is included to ensure that both the impacts and benefits of manure and slurry management are accounted for in the baseline scenario. It conservatively accounts for the tradeoff between diverting manure and slurry from use as organic soil amendments to biogas production. This diversion is modeled as avoided synthetic mineral fertilizer production and use, due to manure and slurry being used as organic soil amendments.

Similar to the Project avoided fertilizer section, it is assumed that nutrient availability is the same between manure/slurry and mineral fertilizer. For example, 1 kg of P2O5 from manure is modeled as substituting the production of 1 kg of P2O5 mineral fertilizer production.

Avoided N2O emissions are the same as in the Project avoided fertilizer section.

Project Developers shall provide the amounts of manure and slurry used as feedstock inputs, and values from the literature shall be used for converting to amounts of synthetic fertilizer avoided (Table 7).

Table 7 Rates of avoided synthetic fertilizer production and use, from manure and slurry use as organic soil amendments in the baseline scenario (Esnouf et al., 2021, Tables 35 and 38).

Avoided GHG emissions

Avoided GHG emissions are calculated by subtracting the sum of the project scenario GHG emissions from the sum of the baseline GHG scenario emissions.

Uncertainty assessment

See general instructions for uncertainty assessment in the Riverse Standard Rules. The outcome of the assessment shall be used to determine the percent of avoided emissions to eliminate with the discount factor.

The assumptions that are estimated to have high uncertainty (i.e. high variability and high impact) are:

• The amount of digestate produced is estimated from 85-95% of feedstock input weight. A conservative assumption of 85% was taken.

• Digestate stored in a covered area with gas recovery has 20% of gasses leaked

The assumptions that are estimated to have medium uncertainty are:

• Nutrient availability in digestate is equivalent to that of mineral fertilizer

The assumptions that are estimated to have low uncertainty are:

• Waste feedstock inputs come with no production impacts.

• The distance for waste feedstock collection of manure and/or slurry in the baseline scenario is assumed to be 10 km).

• In case Project Developers do not have an estimation of days manure is stored onsite, an average of 15 days is considered. In the baseline scenario, this is assumed to be 180 days.

• N2O emissions from slurry storage are generally small and, therefore, excluded from the project scenario’s GHG assessment.

• Manure and slurry from pigs, horses, sheep, and other animals are modeled considering the same characteristics as cow manure.

• In the project scenario, buildings and main infrastructure have a lifetime of 20 years and overall infrastructure impact based on the external volume of the main digester, leading to grouping infrastructure equipment and network into the same category rather than assessing specific equipment's impacts.

• Activated carbon used by the project is accounted for in a ratio of 0.2 t/GWh of energy produced .

• The amount of biogas self-consumed is assumed to be 4%

The baseline scenario selection has low uncertainty and is mostly standardized. It accounts for project-specific information regarding the amount of biomethane injected into the gas grid, type of feedstock, quality of digestate, and national gas market share statistics.

Numerous equations and models are used in this methodology and have low uncertainty:

• Most are basic conversions that have been taken from the scientific literature, especially Esnouf et al., 2021, which is a rigorous, detailed LCA of biomethane production that underwent critical review and was published by INRAE Transfert, a subsidiary of the French National Institute for Research in Agronomics.

• The linear regression model from Hartig 2010 has medium uncertainty

  1. Estimates and secondary data used in this methodology have varying levels of uncertainty and are assessed in Table 8.

  2. The uncertainty at the methodology level is estimated to be low. This translates to an expected discount factor of at least 3% for projects under this methodology.

Table 8 Presentation of all secondary data and estimates used, and an assessment of their uncertainty.

Projects that reduce GHG emissions and are issued Riverse Carbon Credits typically also contribute to a circular economy. The assessment of a project's circularity is considered under the co-benefits criteria and represents the Sustainable Development Goal (SDG) number 12.2.

The Material Circularity Indicator (MCI) is the selected measure of circularity, due to its comprehensive assessment of material flows and alignment with global standards, notably established by The Ellen MacArthur Foundation.

The MCI examines the mass of material flows throughout a product's lifecycle. It evaluates how efficiently materials circulate within a closed-loop system, assigning “more circular” scores to systems that minimize waste and optimize resource reuse. The formula uses input parameters such as material feedstock amount and type (e.g. from recycled, reused, or biological sources), recycling rates, and lifespan extension potential to quantify a product's circularity.

A detailed description and formulas for calculating the MCI are documented in the dedicated methodology document, on pages 22 to 31 (following the Product-level Methodology under the Whole product approach). Figure 3 summarizes the MCI material flows for biogas and natural gas production.

The MCI is a unitless indicator that varies from 0 to 1, where 0 represents a fully linear product and 1 is fully circular. The project scenario MCI is compared to the baseline scenario MCI, measuring how much more circular the project scenario is than the baseline.

The MCI methodology has been applied to biogas production using the input data presented in Table 9.

Figure 3 Summarized representation of the MCI material flows. *Energy recovery as part of a circular strategy only applies to biological materials following the MCI's conditions.

Table 9 All variables needed to calculate the Material Circularity Indicator (MCI) for the Riverse Biogas from anaerobic digestion methodology are detailed below. The full methodology and equations can be found in the dedicated methodology document.

Download the template here