GHG quantification

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.

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).

Parameter	Unit	Source proof
Amount and type of feedstock used*	tonne of fresh matter	Track records from the biogas site
Average weighted distance for transporting each feedstock type from its source until the biogas site	km	Track records from the biogas site; map with the two points location and distance
Average number of days manure and slurry are kept stored, if applicable (optional)	Days	Estimate
On-site electricity consumption during the reference year*	kWh/year	Electricity bills
The external volume of the site's main digester	m³	Licensing or design official document containing this parameter
Biomethane injected into the grid	m³ and GWh	Gas grid injection receipts
Digestate covered during storage	Percent	Any official document containing this parameter or estimates based on the volume of each storage facility
Repartition of solid, liquid and raw digestate stored and spread*	Percent	Records of digestate sales plus description of if/how digestate is separated
Whether leaks are recovered and recirculated during purification	Yes/No	Any official document containing this parameter
Efficiency of purification process (optional)	Percent of methane released with offgas	Machinery technical specifications
Average number of days that feedstock spends in the digester (residence time)	Days	Any official document containing this parameter or estimates
Nitrogen (total N), potassium (K2O) and phosphorus (P2O5) content in the digestate, per digestate type	kg/tonne of material	Official laboratory tests
Average distance that digestate is transported by road transport, per digestate type	km	Track records from the biogas site; map with the two points location and distance

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 (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 .

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 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 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.

11. Nutrient availability in digestate, manure and slurry is . 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 unless otherwise stated).

Parameter	Value for Chicken	Value for Cow
Fresh matter as nitrogen (%)		-
Dry matter in manure (%)	-	24
-Dry matter as nitrogen (%)	-	2.7
Nitrogen lost as N2O per 180 days of storage (%)	2	2
Rate of N2O released from manure spreading (kgN2O/t of manure spread)	0.177	0.177
	86	51
Methane emissions during storage (as % of BMP)	1.5	1.5

Table 3b Summary of slurry characteristics (from unless otherwise stated).

Parameter	Value
Dry matter in slurry (%)	4.27
Dry matter as nitrogen (%)	7.11
Nitrogen lost as N2O per 180 days of storage (%)	0.08
Rate of N2O released from slurry spreading (kgN2O/t of manure spread)	0.057
	19
Methane emissions during storage (as % of BMP)	36

Project Scenario

Figure 1 The system boundary and scope of the project scenario are shown. They are broken down into four life cycle stages, each described in the corresponding sections below.

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 detailed in Table 3 (see example in the box below).

For example, if manure is stored at the biogas site 18 days on average before being added to the digester, this represents 10% of the average 180 days of conventional manure storage. As shown in Table 3, when manure is stored for 180 days:

• 2% of its nitrogen is emitted as N2O, and

• 1.5% of its BMP is emitted as methane.

When this storage time is shortened to 18 days in the biogas scenario, (10% of the conventional storage duration):

• the nitrogen emission rate is reduced to 0.2% (10% of 2%), and

• the methane emission rate is reduced to 0.15% of BMP (10% of 1.5%).

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 (Equation 6). The calculated expected methane produced value should be 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).

Calculations - Feedstock provisioning, transport, and storage

This step calculates the GHG emissions from the producing/cultivating feedstock inputs and transporting them to the biogas site. If the project uses manure as an input, this stage calculates the N2O emissions from its storage.

$\textbf{(Eq.1)}\ E_{production} = \ \sum(Non\ waste_{feedstock, i}*EF_{feedstock, i})$

where,

• $E_{\ production}$ represents the sum of GHG emissions due to feedstock type i production, in kgCO$_2$eq.

• $Non\ waste_{feedstock, i}$ represents the amount of feedstock type i, in tonnes of fresh matter, for non-waste feedstock only.

• $EF_{\ feedstock, i}$ represents the emission factor of feedstock type i production in kgCO$_2$eq/tonne. Refer to for the ecoinvent process used.

$\textbf{(Eq.2)}\ E_{transport} = \sum(W_i*D_i)*EF_{truck\ transport}$

where,

• $E_{transport}$ represents the sum of GHG emissions due to feedstock transport, in kgCO$_2$eq.

• $W_i$ represents the sum of feedstock type $i$ weight, in tonnes, for all feedstocks regardless of waste status (waste or non-waste).

• $D_i$ represents the distance of the feedstock collection, in kilometers.

• $EF_{truck\ transport}$ represents the emission factor of truck transport in kgCO$_2$eq/t.km. Refer to Appendix 1 for the ecoinvent process used.

Equation 3 shall be used if the project uses manure as a feedstock input.

$\begin{aligned}\textbf{(Eq.3)}\ E_{P\ N2O\ manure\ storage} = \sum &W_{manure, i}*\ \% N*R_{N\ as\ N2O}\\ &*N_{to\ N2O}*\frac{Days\ stored}{180}*\ GWP_{N2O}\end{aligned}$

where,

• $E_{P\ N2O\ manure\ storage}$ represents the sum of GHG emissions from N$_2$O due to the storage of manure type i (chicken or cow) in the project scenario, in kgCO$_2$eq.

• $W_{manure, i}$ represents the mass of manure type i used as feedstock in the project scenario, in kg.

• $\% N$ represents the percent of manure mass as nitrogen.

  • For chicken manure, this is 1.4% of fresh matter as nitrogen, as shown in Table 3 in the Assumptions section.

  • For cow and all other manure types, this is 0.65% of fresh matter as nitrogen, as shown in Table 3 in the Assumptions section (2.7% of dry matter as nitrogen * 24% dry matter)

• $R_{N\ as\ N2O}$ represents the rate of nitrogen emitted as N$_2$O from conventional manure storage of 180 days. According to Table 3, this equals 2%.

• $Days\ stored/180$ represents the number of days manure is kept stored in the project scenario. A default value of 15 days can be assumed if no project data is available. 180 represents the conventional manure storage duration of 180 days.

• $N_{to\ N2O}$ represents the conversion of nitrogen to N$_2$O equivalents by multiplying by the ratio of their molecular mass (1.57).

• $GWP_{N2O}$ represents the global warming potential of N$_2$O over 100 years, which is .

Equation 4 shall be used if the project uses manure and/or slurry as a feedstock input.

$\begin{aligned}\textbf{(Eq.4)}\ E_{P\ CH4\ storage} = \sum &W_{i}*{BMP}_{i}*E_{BMP\ CH4}*\\ &{\rho CH}_{4}*{\frac{Days\ stored}{180}*GWP}_{bio\ CH4}\end{aligned}$

where,

• $E_{\ P\ CH4\ storage}$ represents the emissions of methane from storage of manure and/or slurry

• $W_{i}$ is explained in equation 2, and only applies to manure and slurry

• $BMP_{i}$ represents the biomethane potential of feedstock type $i$, in nm$^3$ of CH$_4$ per tonne of fresh matter, presented in Table 3.

• $E_{BMP\ CH4}$ represents methane emissions during storage as % of BMP, presented in Table 3.

• ${\rho CH}_{4}$ represents the methane density, which is kg/m³.

• $Days\ stored/180$ was described in Equation 3.

• ${GWP}_{bio\ CH4}$ represents the global warming potential of biogenic CH$_4$ over 100 years, which is kgCO$_2$eq/kg CH$_4$

$\textbf{(Eq.5)}\ Total\ E_{feedstock} = E_{production} + E_{transport} + E_{manure\ storage, i}$

where,

• ${Total\ E}_{feedstock}$ represents the sum of GHG emissions due to feedstock production, transport, and if applicable, manure storage.

$\textbf{(Eq.6)}\ CH_{4\ expected\ m³} = \ \sum({Feedstock}_{i}*BMP_{i})$

where,

• $CH_{4\ expected\ m³}$ represents the expected amount of methane produced during the reference year in m³. This value is cross checked against the actual $CH_{4\ total\ produced\ m³}$from Equation 11 to evaluate the validity and uncertainty in reported feedstock input amounts and types (see description above).

• $BMP_{i}$ is explained in Eq.4.

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 . 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.

Process		Leak rate as percent of methane produced
Digestion	0.5% biogas produced leaked by volume	0.28%	page 36
Boiler leakage	0.25% internally used methane by volume leaked from the boiler	0.0055%	page 35, assuming 4% biogas produced used internally
Purification of gas	Project data, or default value of 0.7%, or 0% of methane produced by volume	0.7%	page 38
Injection	0.1% input biomethane leaked by volume	0.097%	page 76
Distribution	0.13% input biomethane leaked by volume	0.126%	Table 52
Sum		1.20%

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

Parameter	Biogas	Biomethane
Lower heating value (LHV) (MJ/m³)	22.
Methane content (% volume)

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 .

The most impactful direct emissions from the biomethane combustion step were taken from Table 53 in . 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.

Calculations - Digestion and biomethane management

This step calculates the GHG emissions from anaerobic digestion and biomethane management ($Total\ E_{Digestion}$).

$\textbf{(Eq.7)}\ E_{electricity} = Electricity_{kWh}*\ EF_{electricity}$

where,

• $E_{electricity}$ represents the sum of GHG emissions due to on-site electricity consumption, in kgCO$_2$eq.

• $Electricity_{kWh}$ represents the total on-site electricity consumption, in kWh.

• $EF_{electricity}$ represents the emission factor for electricity, in kgCO$_2$eq/kWh. Refer to Appendix 1 for the ecoinvent process used.

$\textbf{(Eq.8)}\ E_{AC} = W_{AC/GWh}*GWh_{produced}*EF_{AC}$

where,

• ${\ E}_{AC}$ _r_epresents the sum of GHG emissions due to on-site activated carbon consumption, in kgCO$_2$eq.

• $W_{AC/GWh}$ represents the weight of activated carbon used per GWh of energy produced, which is assumed to be 0.2 tonnes/GWh.

• ${GWh}_{produced}$ represents the GWh of energy produced by the project annually.

• ${EF}_{AC}$ represents the emission factor for activated carbon, in kgCO$_2$eq/kg. Refer to Appendix 1 for the ecoinvent process used

$\textbf{(Eq.9)}\ E_{infrastructure} = EF_{anaerobic\ plant}*\ \frac{D_{volume\ m^{3}}}{500m^{3}} \div 20\ years$

where,

• $E_{infrastructure}$ represents the sum of GHG emissions due to infrastructure and machinery manufacture, transport and end of life, in kgCO$_2$eq.

• $EF_{anaerobic\ plant}$ represents the emission factor of an anaerobic digestion site's infrastructure and machinery. It is modeled for a site with a main digester exterior volume of 500 m$^3$. Refer to Appendix 1for the ecoinvent process used.

• $D_{volume\ m^{3}}$ represents the volume of the project site's main digester, in m³. It is divided by 500 m$^3$ to obtain the fraction of the ecoinvent process impacts to assign to the project

• $20\ years$ represents the assumed site lifetime, and is used to normalize infrastructure and machinery impacts to 1 year.

Methane leakages during the digestion, purifying, injection, and distribution phases are detailed below.

$\begin{aligned}\textbf{(Eq.10)}\ L_{CH4\ tota{l\%}} = &L_{digestion\%}*Biogas_{\% CH4}\\&+ (L_{boiler\%}*Biogas_{internal\%}*Biogas_{\% CH4}) \\&+ ((\ L_{injection\%}+ L_{distribution\%})*Biomethane_{\% CH4})\\&+ L_{purification\%}\end{aligned}$

where,

• $L_{CH4_\ total\%}$ represents the total amount of methane losses in the system, as a percentage of total volume of methane produced.

• $L_{digestion\%}$represents the percentage of biogas produced that is leaked during the digestion process. This value is assumed 0.5%, as presented in Table 4.

• $L_{boiler\%}$ represents the percentage of internally used methane that is leaked, which is 0.25% according to Table 4.

• $Biogas_{internal\%}$represents the percentage of biogas produced that is used internally, assumed 4%, as presented in the Assumptions section.

• $Biogas_{\% CH4}$represents the percentage of methane in biogas. This value is assumed to be 55%, as presented in the Assumptions section.

• $\ L_{injection\%}$ represents the percentage of biomethane leaked during the gas injection into the grid, which is 0.1% according to Table 4.

• $L_{distribution\%}$represents the percentage of biomethane leaked during the biomethane distribution to the final user, which is 0.13% according to Table 4.

• $Biomethane_{\% CH4}$ represents the percentage of methane in biomethane. This value is considered 97%, as presented in Assumptions section.

• $L_{purification\%}$represents the percentage methane produced that is leaked in the purification process. This value is estimated at 0.7% if data is not available for the project.

Losses from Eq. 10 add up to 1.2% losses of total methane produced, if the default value for purification leakage of 0.7% is used (Table 4). The amount of methane produced before losses is presented in Eq. 11.

$\textbf{(Eq.11)}\ CH_{4\ total\ produced\ m^3} = \frac{{Biomethane}_{injected\ m³\ }*{Biomethane}_{\% CH4}}{(1 - L_{CH4\ total})}$

where,

• $CH_{4\ total\ produced\ m^3}$ represents the volume of methane produced, in m³, before losses. This value shall be cross checked against the expected CH$_4$ produced, calculated in Equation 6.

• ${Biomethane}_{injected\ m³\ }$ represents the m$^3$ of biomethane injected into the gas grid annually.

$\textbf{(Eq.12)}\ E_{loss\ bio\ CH4}\ = \ CH_{4\ total\ produced\ m³}*L_{CH4\ total\%}*{\rho CH}_{4}*{GWP}_{bio\ CH4}$

where,

• $E_{loss\ bio\ CH4}$ represents the sum of GHG emissions from biogenic CH$_4$ leakages, in kgCO$_2$eq.

• ${\rho CH}_{4}$ and ${GWP}_{bio\ CH4}$ were explained in Equation 1.

The amount of methane and N2O emissions from biomethane combustion shall also be considered, to match the scope of the baseline scenario, which includes natural gas combustion.

$\begin{aligned}\textbf{(Eq.13)}\ E_{loss\ CH4\ combustion} = &Biomethane_{injected\ m^3}*Biomethane_{LHV}\\*\ &CH_{4\ ER}*GWP_{biog\ CH4}\end{aligned}$

where,

• $E_{loss\ CH4\ combustion}$ represents GHG emissions from biogenic CH$_4$ leakages, in kgCO$_2$eq, due to biomethane combustion.

• $Biomethane_{injected\ m³}$ is described in Equation 11.

• $Biomethane_{LHV}$ represents the lower heating value of biomethane, presented in Table 5 in the Assumptions section_._

• $CH_{4\ ER}$ represents biomethane's combustion emission rate, in kg CH$_4$/MJ biomethane.

• ${GWP}_{bio\ CH4}$ was described in Equation 4.

$\textbf{(Eq.14)}\ E_{N2O} = Biomethane_{injected\ m³}*{Biomethane}_{LHV}*N2O_{ER}*{GWP}_{N2O}$

where,

• $E_{N2O}$ represents the sum of N$_2$O direct emissions due to methane combustion, in kgCO$_2$eq.

• $Biomethane_{injected\ m^3}$ is described in Equation 11.

• $Biomethane_{LHV}$ is described in Equation 13.

• $N2O_{ER}$ represents biomethane's combustion emission rate, in kg N$_2$O/MJ biomethane.

• $GWP_{N2O}$ is explained in Equation 3.

$\textbf{(Eq.15)}\ E_{direct\ emissions} = \ E_{loss\ CH4,\ biog} + {\ E}_{loss\ CH4\ combustion} + E_{N2O}$

where,

• $E_{direct\ emissions}$ represents the sum of direct GHG emissions (CH$_4$ and N$_2$O) due to leakages and losses in the digestion, purifying, injection, distribution and combustion steps, in kgCO$_2$eq.

$\textbf{(Eq.16)}\ Total\ E_{digestion} = E_{electricity} + E_{AC} + E_{infrastructure} + E_{direct\ emissions}$

where,

• ${Total\ E}_{digestion}$ represents the sum of GHG emissions due to the digestion, purifying, injection, and distribution step, in kgCO$_2$eq.

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.

For example, if 6000 tonnes of feedstock inputs are used annually, the assumed total amount of digestate produced is 6000*85% = 5100 tonnes of digestate.

If the digestate is not separated into liquid and solid phases, then raw digestate storage and spreading is considered, with the relevant raw digestate emission rates.

If the digestate is separated, then sales data will be used to determine the repartition of solid and liquid digestate (sales data do not represent production data, as described in the Assumptions section).

If the project sells 4500 tonnes of liquid digestate and 500 tonnes of solid digestate annually, then the ratio is 90% liquid and 10% solid. Then, according to the production value of 6000 tonnes, we would assume that 90% liquid (5400 tonnes) and 10% solid (600 tonnes) digestate was produced.

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 . 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 and .

Step	Digestate form	Value (%)
Spreading	Raw, liquid, and solid	1
Storage	Raw	0.08
Storage	Liquid	0.08
Storage	Solid	2

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 .

Calculations - Digestate storage and spreading

This step calculates the GHG emissions from the digestate produced (stored and spread) life cycle stage ($Total E_{digestate}$).

$\textbf{(Eq.17)}\ D_{raw} = (\sum({feedstock}_{i})*Digestate_{\%}) - D_{recirculated}$

where,

• $D_{raw}$ represents the total amount of raw digestate produced, stored and spread by the project annually, in tonnes of fresh matter.

• $\sum({feedstock}_{i})$ represents the sum of all feedstock inputs, in tonnes of fresh matter.

• $Digestate_{\%}$ represents the ratio of the total feedstock input mass that becomes digestate at the end of the digestion. This is assumed to be 85% as presented in the Assumptions section.

• $D_{recirculated}$ represents the amount of digestate produced that is recirculated in the digester, in tonnes of fresh matter.

$\textbf{(Eq.18)}\ D_{i.t} = D_{raw}*D_{type\ i\%}$

where,

• $D_{i.t}$ represents the amount of digestate type i (raw, liquid, or solid form) produced (stored and spread), in tonnes of fresh matter. If no digestate separation process occurs, the amount of digestate produced is equal to the amount of raw digestate produced ($D_{raw.t}$).

• $D_{raw}$ was calculated in Equation 17.

• $D_{type\ i\%}$ represents the percent of all digestate produced that is digestate type i (whether raw, liquid, or solid).

$\textbf{(Eq.19)}\ D_{\ CH4\ loss\%} = (8.34 - 1.48*ln(residence\ time))/100$

where,

• $D_{CH4\%}$ represents methane leakage from digestate storage, as a function of total methane produced.

• $residence\ time$ represents the average number of days that feedstock spends in the digester.

$\textbf{(Eq.20)}\ D_{\% weighted\ avg\ covered} = \frac{\sum(D_{i.t}*D_{i\ stored\ covered\ \%})}{\sum(D_{i.t})}$

where,

• $D_{\% weighted\ avg\ covered}$ represents the weighted average percent of all digestate types that are stored under covered conditions.

• $D_{i.t}$ is calculated in Equation 18.

• $D_{i\ stored\ covered\ \%}$ represents the percentage of digestate type i stored under covered conditions.

$\begin{aligned}\textbf{(Eq.21)}\ E_{reduction\ CH4\ covered} = &(D_{\% weighted\ avg\ covered}*{LR}_{covered})\\ &+ \ (1 - D_{\% weighted\ avg\ covered})\end{aligned}$

where,

• $E_{reduction\ CH4\ covered}$ represents the total weighted average of methane emission reductions thanks to covering digestate during storage.

• $D_{\% weighted\ avg\ covered}$ was calculated in Equation 20.

• ${LR}_{covered}$ represents the leakage reduction of methane obtained by covering digestate during storage. This value is 0.2.

$\textbf{(Eq.22)}\ E_{D.\ CH4} = {CH_{4\ {total\ produced\ m³}_{}}}_{\ }*{\rho CH}_{4}*D_{CH4\ loss\%}*E_{reduction\ CH4\ covered}*{GWP}_{bio\ CH4}$

where,

• $E_{D.\ CH4}$ represents the sum of GHG emissions from methane due to digestate storage, in kgCO$_2$eq.

• $CH_{4\ {total\ produced\ m³}_{}}$represents the amount of methane produced during the reference year in m³, from Equation 1.

• $D_{CH4\ loss\%}$ was calculated in Equation 19.

• $E_{reduction\ CH4\ covered}$ was calculated in Equation 21.

• ${\rho CH}_{4}$ and ${GWP}_{bio\ CH4}$ is explained in Equation 1.

$\textbf{(Eq.23)}\ E_{D.\ N2O\ storage\ } = \sum(D_{i.t}*D_{i.N}*D_{i.N\ los{s\ storage}_{\%}})*N_{to\ N2O}*{GWP}_{N2O}$

where,

• $E_{D.\ N2O\ storage\ }$ represents the sum of GHG emissions due to N$_2$O leakages during digestate storage, in kgCO$_2$eq.

• $D_{i.t}$ is calculated in Equation 18.

• $D_{i.N}$ represents the Nitrogen content in the digestate type i (raw, liquid, or solid), in kg/tonne.

• $D_{i.N\ los{s\ storage}_{\%}}$ represents the percentage of Nitrogen leaked during digestate type i storage, as presented in Table 6.

• $N_{to\ N2O}$ and ${GWP}_{N2O}$ are explained in Equation 3.

$\textbf{(Eq.24)}\ E_{D.\ N2O\ spreading} = \sum(D_{i.t}*D_{i.N})*D_{i.N\ los{s\ spreading}_{\%}}*N_{to\ N2O}*{GWP}_{N2O}$

where,

• $E_{D.\ N2O\ spreading\ }$ represents the sum of GHG emissions from N$_2$O during digestate spreading, in kgCO$_2$eq.

• $D_{i.t}$ is calculated in Equation 18.

• $D_{i.N}$ is explained in Equation 23.

• $D_{i.N\ los{s\ spreading}_{\%}}$ represents the percentage of nitrogen emitted as N$_2$O during digestate type i spreading, as presented in Table 6.

• $N_{to\ N2O}$ and ${GWP}_{N2O}$ are explained in Equation 3.

$\textbf{(Eq.25)}\ E_{\ transport} = \sum(D_{i\ t}*D_{i.spreading.km})*EF_{truck\ transport}$

where,

• $E_{\ transport}$ represents the sum of GHG emissions due to the transport of digestate from the biomethane site until the spreading point, in kgCO$_2$eq.

• $D_{i.t}$ is calculated in Equation 18.

• $D_{i.\ spreading.km}$ represents the distance from the biogas site to the location where the digestate type i will be spread, measured in kilometers.

• $\ EF_{truck\ transport}$ represents the emission factor of truck transport in kgCO$_2$eq/t.km. Refer to Appendix 1 for the ecoinvent process used.

$\textbf{(Eq.26)}\ Total\ E_{digestate} = E_{D.\ CH4\ } + E_{D.\ N2O\ loss\ storage\ } + E_{D.\ N2O\ loss\ spreading\ } + E_{\ transport}$

where,

• ${Total\ E}_{digestate}$ represents the sum of GHG emissions due to the digestate storage and spreading life cycle stage, in kgCO$_2$eq.

• $E_{D.\ CH4}$ was calculated in Equation 22.

• $E_{D.\ N2O\ loss\ storage\ }$ was calculated in Equation 23.

• $E_{D.\ N2O\ loss\ spreading\ }$was calculated in Equation 24.

• $E_{\ transport}$ was calculated in Equation 25.

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.

Calculations - Project avoided fertilizer

This step calculates the GHG emissions from the project’s avoided fertilizer production and use ($Total E_{P.avoided fertilizer}$).

$\textbf{(Eq.27)}\ E_{P.\ NPK\ avoided} = - \sum_{i}^{}\sum_{j}^{}(D_{i\ spread.t}*C_{i.\ j})\ *EF_{j\ fertilizer}$

where,

• ${\ E}_{P.\ NPK\ avoided}$ represents the sum of GHG emissions avoided due to the substitution of mineral fertilizer production by digestate spreading, in kgCO$_2$eq. P denotes the project scenario, to differentiate between the same variable calculated in the baseline scenario.

• $D_{i.t}$ is calculated in Equation 18

• $C_{i,\ j}$ represents the content of nutrient 𝑗 (N, P205,and K2O) in digestate type 𝑖, in kg nutrient/tonne of digestate.

• $EF_{j\ fertilizer}$ represents the emission factor of production of synthetic N, P2O5, or K2O fertilizer in kgCO$_2$eq/kg. Refer to Appendix 1 for the ecoinvent process used.

$\textbf{(Eq.28)}\ E_{P.N2O\ avoided} = - \sum (D_{i\ spread.t}*D_{i.N})*ER_{N\ as\ N2O}\ *N_{to\ N2O}*{GWP}_{N2O}$

where,

• $E_{P.N2O\ avoided}$ represents the sum of GHG emissions avoided due to the substitution of mineral fertilizer use, and subsequent N$_2$O emissions, by digestate spreading, in kgCO$_2$eq. P denotes the project scenario, to differentiate between the same variable calculated in the baseline scenario.

• $D_{i.t}$ is calculated in Equation 18.

• $D_{i.N}$ is explained in Equation 23.

• $ER_{N\ as\ N2O}$ represents the rate of applied nitrogen emitted as N$_2$O, which equals 1%.

• $N_{to\ N2O}$ and ${GWP}_{N2O}$ are explained in Equation 3.

$\textbf{(Eq.29)}\ Total\ E_{P.avoided\ fertilizer} = E_{P.\ NPK\ avoided} + E_{P.N2O\ avoided}$

where,

• ${Total\ E}_{P.avoided\ fertilizer}$ represents the sum of fertilizer GHG emissions avoided due to the use of digestate as an organic amendment, in kgCO$_2$eq.

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.

Figure 2 The system boundary and scope of the baseline scenario are shown. They are broken down into three life cycle stages, each described in the corresponding sections below.

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)

The baseline scenario structure remains valid for the entire crediting period but may be significantly revised earlier if:

• The Project Developer notifies Riverse of a substantial change in project operations or baseline conditions, and/or

• The methodology is revised, affecting the baseline scenario.

The specific values within the baseline scenario will be updated annually, using project data to accurately reflect the equivalent of the project’s annual operations.

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 and consumption. An example is provided below.

For example, for France, gas consumption for 2022 (the most recent year where complete data are available in Eurostat) shows that 1,570,871 m3 of natural gas and 68,736 m3 of biogasses were consumed. This corresponds to 96% natural gas and 4% biogasses. As a result, 1 MJ of biomethane injected by the project is assumed to replace 0.96 MJ of natural gas and 0.04 MJ of biogas.

If data are available on the national repartition of biogasses, the latter amount may be further specified. For example, in France in 2021, were produced. This repartition can be applied to the 0.04 MJ of biogasses mentioned above, to obtain 0.015 MJ of biogas and 0.025 MJ of biomethane.

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.

Calculations - Energy Production

This step calculates the GHG emissions from the baseline energy production life cycle stage, where biomethane is injected into the gas grid ($Total E_{Energy Production}$).

$\textbf{(Eq.30)}\ Gas_{delivered\ MJ} = Biomethane_{injected\ m³}*(1\ - \ L_{distribution\%})*{Biomethane}_{LHV}$

where,

• $Gas_{delivered\ MJ}$ represents the total amount of energy from gas delivered after distribution, in MJ.

• $Biomethane_{injected\ m³}$ represents the amount of biomethane injected into the grid, in m³, from the gas grid injection receipts, described in Equation 11.

• L\_{distribution\%}\represents the percentage of biomethane leaked during the biomethane distribution to the final user, which is 0.13% according to Table 4, described in Equation 10.

• ${Biomethane}_{LHV}$ represents the lower heating value of biomethane, presented in Table 5 in the Assumptions section_._

$\textbf{(Eq.31)}\ E_{NG} = Gas_{delivered\ MJ}*NG_{grid\ \%}*EF_{NG}$

where,

• $E_{\ NG}$ represents the sum of GHG emissions due to natural gas production and use according to the market shares, in kgCO$_2$eq.

• $Gas_{delivered\ MJ}$ is calculated in Equation 30.

• $NG_{\%\ grid}$ represents the fraction of natural gas in the grid, described in paragraph 3.6.1.4.

• $EF_{NG}$ represents the emission factor of natural gas, in kgCO$_2$eq/MJ. Refer to Appendix 2 for the ecoinvent process used.

$\textbf{(Eq.32)}\ E_{bio} = \sum Gas_{delivered\ MJ}*{Gas}_{i.\%\ grid}/{LHV}_{i}*E{F\ bio}_{i}$

where,

• $E_{bio}$ represents the sum of GHG emissions due to biogas and biomethane production according to the market shares, in kgCO$_2$eq.

• $Gas_{delivered\ MJ}$ is calculated in Equation 30

• ${Gas}_{i.\ \%\ grid}$ represents the fraction of biogas type i (biogas and biomethane) in the grid.

• ${LHV}_{i}$ represents the lower heating value used to convert MJ to m³ of biogas type $i$ (biogas and biomethane), presented in Table 5 in the Assumptions section_._

• $EF_{bio\ i}$ represents the emission factor of biogas type i, in kgCO$_2$eq/m³.

$\textbf{(Eq.33)}\ Total\ E_{Energy\ Production} = E_{NG} + E_{bio}$

where,

• ${Total\ E}_{Energy\ Production}$ represents the sum of GHG emissions due to gas production and use in the baseline scenario, in kgCO$_2$eq.

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.

Calculations - Manure and slurry storage and spreading

This step calculates the GHG emissions from the baseline Manure and Slurry Storage life cycle stage ($Total E_{M S}$).

$\textbf{(Eq.34)}\ E_{B.\ transport}\ = \ \sum(M_{i} + S*D_{i})*\ EF_{truck\ transport}$

where,

• $E_{\ B.\ transport}$ represents the sum of GHG emissions from transporting manure and slurry from the location they are stored to where they are spread, in kgCO$_2$eq.

• $M_{i}$ represents the amount of manure of type i (chicken or cow) used as feedstock in the project scenario, in tonnes of fresh matter.

• $\ S$ represents the amount of slurry used as feedstock in the project scenario, in tonnes of fresh matter.

• $D_{i}$ represents the distance of manure/slurry transport for spreading, in kilometers. This is assumed to be 10 km, see the Assumtions section.

• $\ EF_{truck\ transport}$ represents the emission factor of truck transport in kgCO$_2$eq/t.km. Refer to Appendix 1 for the ecoinvent process used.

GHG emissions due to direct N$_2$O emissions from manure storage follow the same calculation presented in Equation 3, using a $Days\ stored$ parameter value of $180$. This shall be calculated as a parameter called $E_{B\ N_2O\ M.\ storage}$. GHG emissions due to direct CH$_4$ emissions from manure and slurry storage follow the same calculation presented in Equation 4, using a days stored parameter value of $180$. This shall be calculated as a parameter called $E_{B\ CH_4\ storage}$.

$\textbf{(Eq.35)}\ E_{\ N2O\ M.\ spreading} = \sum M_{i}*\ R_{N2O\ spreading}\ *{GWP}_{N2O}$

where,

• $E_{\ N2O\ M.\ spreading}$ represents the sum of GHG emissions resulting from N$_2$O being directly emitted into the air due to the spreading of manure, in kgCO$_2$eq.

• $M_{i}$ is described in Equation 34.

• $R_{N2O\ spreading}$ represents the rate of N$_2$O released from manure spreading, and equals 0.177 kg N$_2$O/tonne of manure spread, regardless of manure type (Table 3).

• ${GWP}_{N2O}$ is described in Equation 3.

\textbf{(Eq.36)}\ E_{N2O\ S.\ \ storage}\ = S*\ S_{\%\DM}*S_{\% DM\ as\ \ N}\ *S_{\% N\ as\ \ N2O}*N_{to\ N2O}*{GWP}_{N2O}

where,

• $E_{N2O\ S.\ \ storage}$ represents the sum of GHG emissions resulting from N$_2$O being directly emitted into the air due to the storage of slurry, in kgCO$_2$eq.

• $S$ is described in Equation 34.

• $S_{\%\ DM}$ represents the dry matter content of slurry, which is 4.27% (Table 3).

• $S_{\%\ DM\ as\ N}$ represents the percentage of dry matter as nitrogen in slurry, which is 7.11% (Table 3).

• $S_{\% N\ as\ \ N2O}$ represents the percentage of nitrogen lost as N$_2$O during storage of slurry, which is 0.0008% (Table 3).

• $N_{to\ N2O}$ and ${GWP}_{N2O}$ are explained in Equation 3.

$\textbf{(Eq.37)}\ E_{\ N2O\ S.\ \ spreading}\ = S*\ S_{\%\ N2O\ spreading}*{GWP}_{N2O}$

where,

• $E_{\ N2O\ S.\ \ spreading}$ represents the sum of GHG emissions resulting from N$_2$O being directly emitted into the air due to the spreading of slurry, in kgCO$_2$eq.

• $S$ is described in Equation 34.

• $S_{\%\ N2O\ spreading}$ represents the rate of N$_2$O released from slurry spreading, and equals 0.057 kg N$_2$O/tonne of manure spread (Table 3).

• ${GWP}_{N2O}$ is described in Equation 3.

$\begin{aligned}\textbf{(Eq.38)}\ {Total\ E}_{MS} =\ &E_{B.\ transport} + E_{B\ N2O\ M.\ storage}\\+\ &E_{B\ CH4\ storage} + E_{N2O\ M.\ spreading}\\+\ &E_{N2O\ S.\ storage} + E_{N2O\ S.\ spreading}\end{aligned}$

where,

• ${Total\ E}_{MS}$ represents the sum of GHG emissions due to manure and slurry transport, storage, and spreading in the baseline scenario.

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 , 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 ().

Avoided fertilizer type	Manure (kg/tonne manure)	Slurry (kg/tonne slurry)
Nitrogen (N)	2.19	1.67
Potassium (K2O)	12.7	2.05
Phosphorus (P2O5)	2.75	1.59

Calculations - Baseline avoided Fertilizer

This step calculates the GHG emissions from the baseline scenario’s avoided fertilizer production and use ($Total E_{B.avoided\ fertilizer}$).

$\textbf{(Eq.39)}\ E_{B.\ NPK\ avoided} = - \sum_{i}^{}\sum_{j}^{}\ (F_{i}*{RR}_{i.\ j}\ *EF_{j\ fertilizer})$

where,

• $E_{B.\ avoided\ NPK}$ represents the sum of emissions avoided due to the use of manure or slurry as a fertilizer, in kgCO$_2$eq. $B$ denotes the baseline scenario, to differentiate between the same variable calculated in the project scenario.

• $F_{i}$ represents the amount of feedstock (manure or slurry) in tonnes of fresh matter.

• ${RR}_{i.\ j}$ represents the replacement rate of nutrient 𝑗 (N, K2O, and P2O5) from each feedstock type i, in kg nutrient/tonne of feedstock.

• $EF_{j\ fertilizer}$ is described in Equation 27.

$(Eq.\ 40)\ E_{B.N2O\ avoided} =- \sum F_{i}*{RR}_{i,\ N}*ER_{N\ as\ N2O}*N_{to\ N2O}*{GWP}_{N2O}$

where,

• ${\ E}_{B.N2O\ avoided}$ represents the sum of GHG emissions avoided due to the substitution of mineral fertilizer use, and subsequent N$_2$O emissions, by manure and/or slurry spreading, in kgCO$_2$eq. $B$ denotes the baseline scenario, to differentiate between the same variable calculated in the project scenario.

• $F_{i.}$ is described in Equation 39.

• ${RR}_{i,\ N}$ represents the replacement rate of N fertilizer in kg per tonne of feedstock type i (Table 7).

• $ER_{N\ as\ N2O}$ represents the rate of applied nitrogen emitted as N$_2$O, which equals 1%.

• $N_{to\ N2O}$ and ${GWP}_{N2O}$ are explained in Equation 3.

$textbf{(Eq.41)}\ Total\ E_{B.avoided\ fertilizer} = \ \ {\ E}_{B.\ NPK\ avoided} + E_{B.N2O\ avoided}$

where,

• ${Total\ E}_{B.avoided\ fertilizer}$ represents the sum of fertilizer GHG emissions avoided due to the use of manure and/or slurry as an organic amendment, in kgCO$_2$eq.

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.

Comparative GHG assessment calculation

The total baseline GHG emissions, total project GHG emissions, and the project's avoided emissions are calculated as follows.

$\begin{aligned}\textbf{(Eq.42)}\ E_{Project} =\ &{Total\ E}_{feedstock} + {Total\ E}_{digestion}\\ + &{Total\ E}_{digestate} + {Total\ E}_{P.avoided\ fertilizer}\end{aligned}$

$\textbf{(Eq.43)}\ E_{baseline} = {Total\ E}_{energy\ production} + {Total\ E}_{MS} + {Total\ E}_{B.avoided\ fertilizer}$

$\textbf{(Eq.44)}\ E_{avoided}\ = \ E_{baseline}\ - \ E_{project}$

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 .

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 , 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 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.

Parameter	Reference in document	Uncertainty assessment
Chicken manure fresh matter as nitrogen (%)	Table 3	The rate of fresh matter as nitrogen contained in chicken manure was taken from a study conducted in 2015. There is low uncertainty in this data sample since chicken feed patterns are assumed to not have significantly changed.
Cow manure and slurry dry matter and nitrogen content	Table 3	These values come from Table 18. Their source was internal expertise and databases from the French National Institute for Research in Agronomics (INRAE), which is expected to have high quality data for these values that are relatively simple to measure. That study underwent critical review. Uncertainty is low.
Nitrogen lost as N2O during manure and slurry storage (%)	Table 3, Table 6	These values come from , Table 34 and 37. Their source was . These are estimated to be reputable scientific sources, but due to the sensitivity of this value, it is estimated to have medium uncertainty.
Rate of N2O released from manure and slurry spreading (kgN2O/t of manure)	Table 3	These values come from, Tables 35 and 38 and were calculated in the study. This is estimated to be a reputable scientific source, but due to the sensitivity of this value, it is estimated to have medium uncertainty.
Nitrogen lost as N2O during digestate, storage (%)	Table 6	These values come from, Table 18. Their source was . These are estimated to be reputable scientific sources, but due to the sensitivity of this value, it is estimated to have medium uncertainty.
Nitrogen lost as N2O during digestate, spreading (%)	Table 6	This value comes from the . Although it is a reputable source, the value taken is a highly generalized global average and actually depends on soil and climatic factors. It is estimated to have medium uncertainty.
Lower heating value of biogas and biomethane (MJ/m³)	Table 5	These characteristics come from the ecoinvent database and International Energy Agency, both of which are reliable sources. Biomethane LHV has low uncertainty since it is a consistent value, but biogas LHV has high uncertainty since the gas content, and therefore energy content, of biogas is variable.
Density (kg/m³)	Equation 4, 12 and 22	Methane density was obtained from a textbook on anaerobic digestion, and has low uncertainty.
Methane content (% volume)	Table 5	Methane percentages in biogas and biomethane were taken from the European Biogas Association. Biomethane has low uncertainty since it is a consistent value, but biogas has high uncertainty since its composition is variable.
Biomethane combustion N2O and CH4 emission rates	Paragraph 3.5.2.7	These values come from , Table 53, and results are not sensitive to them. They are estimated to have low uncertainties.
Leakage rates in the digestion, purification, boiler, injection and distribution process (%)	Table 4	These values come from There is high uncertainty in this data sample. Even though the study is recent and uses reliable data, leakages depend on project-specific factors such as the site design and age. Projects certified under Riverse's biogas methodology are considerably new (built after 2018), which justifies adopting the values for recently built sites from the data sample.
Manure and slurry avoided fertilizer (kg/tonne)	Table 7	The amount of N, K2O, and P2O5 avoided fertilizer per tonne of manure and slurry used in the baseline scenario was taken from the , Tables 35 and 38. There is low uncertainty in these data samples.
Baseline grid gas mix	Paragraph 3.6.1.4	In the baseline scenario, the mix of gasses for energy production is taken from national gas grid market shares from the Eurostat database. These data are estimated to have medium uncertainty, because the most recent data available are from 2022, and because of inherent uncertainty and compatibility issues inherent in such macro, national data.