November 2014 N-1 

Appendix N. Assessing Emissions from Waste-Derived 

Biogenic Feedstocks 

Table of Contents 

1. Introduction ................................................................................................................................................................. N-3

1.1. A Simplified Biogenic Assessment Factor Equation for Waste-Derived Biogenic Feedstocks 

 .................................................................................................................................................................................. N-7

1.2. Biogenic Municipal Solid Waste Management ..................................................................................... N-9

2. Biogenic MSW Disposal in MSW Landfills and Associated GHG Emissions Pathways ............... N-11

2.1. Indirect Emissions from MSW Landfills .............................................................................................. N-14

2.2. Direct Emissions from MSW Landfills .................................................................................................. N-15

2.3. Method for Calculating an Illustrative BAF Value for Biogenic Emissions from MSW 

Landfilling ............................................................................................................................................................ N-16

2.3.1. Boundaries and Assumptions for MSW Landfilling Methodology .................................. N-17

2.3.2. Explanation of MSW Landfilling Methodology ........................................................................ N-18

2.4. Example AVOIDEMIT and BAF Calculations for Landfill Biogas ................................................. N-23

2.4.1. Example Calculations for a Controlled Landfill (Flaring) Compared to an Uncontrolled 

Landfill ..................................................................................................................................................... N-23

2.4.2. Example Calculations for a Controlled Landfill (EGU) Compared to an Uncontrolled 

Landfill ..................................................................................................................................................... N-25

2.4.3. Example Calculations for a Controlled Landfill (EGU) with a Gas Collection System 

Installed Mid-Way through the Year Compared to an Uncontrolled Landfill ............. N-26

2.5. Sensitivity Analysis for MSW Landfill Biogas .................................................................................... N-28

3. Disposal of Biogenic MSW through Combustion and Associated GHG Emissions Pathways .. N-29

3.1. Method for Calculating an Illustrative BAF Value for Biogenic Emissions Resulting From 

MSW Combustion ............................................................................................................................................. N-30

3.1.1. Calculating the Numerator .............................................................................................................. N-30

3.1.2. Calculating the Denominator .......................................................................................................... N-32

3.2. Example AVOIDEMIT and BAF Calculations for MSW Combustion .......................................... N-34

3.2.1. Example Calculations for MSW Combustion Compared to a Landfill with Gas 

Collection (EGU) ................................................................................................................................... N-34

3.2.2. Example Calculations for MSW Combustion Compared to a Landfill without Gas 

Collection ................................................................................................................................................ N-36

3.3. Sensitivity Analysis for MSW Combustion .......................................................................................... N-37
November 2014 N-2 

4. Livestock Waste Management through Anaerobic Processes and Associated GHG Emissions 

Pathways ......................................................................................................................................................................... N-38

4.1. Method for Calculating an Illustrative BAF Value Applied to Biogenic Emissions Resulting 

from Anaerobic Digestion of Livestock and Food Waste ................................................................. N-40

4.1.1. Calculating the Numerator .............................................................................................................. N-41

4.1.2. Methodology When Biogas Flow Rate and Methane Concentration Data Are Available . 

 ..................................................................................................................................................................... N-42

4.1.3. Calculating the Denominator .......................................................................................................... N-46

4.1.4. Methodology When Biogas Flow Rate and Methane Concentration Data Are Not 

Available .................................................................................................................................................. N-49

4.2. Illustrative AVOIDEMIT and BAF Calculations for Livestock Waste Management ............. N-56

4.2.1. Illustrative Calculations when Anaerobic Digester Measurement Data Are Available .... 

 ..................................................................................................................................................................... N-56

4.2.2. Example Calculations for Livestock Waste Management Prior to Installation of an 

Anaerobic Digester (When Measurement Data are Not Available) ................................ N-59

4.3. Sensitivity Analysis for Anaerobic Digestion of Livestock and Food Waste ......................... N-63

5. Livestock Waste Management through Direct Combustion or Thermochemical Processing and 

Associated GHG Emissions Pathways .................................................................................................................. N-65

5.1. Method for Calculating an Illustrative BAF Value Applied to Biogenic Emissions Resulting 

from Combustion of Livestock Waste ...................................................................................................... N-66

5.1.1. Calculating the Numerator .............................................................................................................. N-67

5.1.2. Calculating the Denominator .......................................................................................................... N-71

5.2. Example AVOIDEMIT and BAF Calculations for Direct Combustion of Livestock Waste . N-74

5.2.1. Example Calculation for Direct Combustion and Land Application of Livestock Waste .. 

 ..................................................................................................................................................................... N-74

5.2.2. Calculation for Direct Combustion and an Uncovered Anaerobic Lagoon................... N-78

5.3. Sensitivity Analysis for Livestock Waste Management through Direct Combustion ........ N-79

6. Wastewater Disposal in Wastewater Treatment Facilities and Associated GHG Emission 

Pathways ......................................................................................................................................................................... N-80

6.1. Method for Calculating an Illustrative BAF Value Applied to Biogenic Emissions Resulting 

from Combustion of Biogas from Wastewater Treatment .............................................................. N-82

6.1.1. Calculating the Numerator .............................................................................................................. N-83

6.1.2. Calculating the Denominator .......................................................................................................... N-86

6.2. Example AVOIDEMIT and BAF Calculations for the Collected Biogas from Treatment of 

Wastewater and Wastewater Sludge ........................................................................................................ N-90

6.3. Sensitivity Analysis for Wastewater Treatment ............................................................................... N-93
November 2014 N-3 

7. References .................................................................................................................................................................. N-94

List of Tables 

Table N-1. Waste Management GHG Emissions Pathways Considered. ....................................................... N-5

Table N-2. Illustrative Example BAF Values Associated with the Treatment Methods of the Waste 

Feedstocks Discussed in this Appendix. ..................................................................................................... N-9

Table N-3. Percent of MSW Generated and Recovered by MSW Class in 2012 (EPA, 2014a). ......... N-10

Table N-4. Summary of Parameters Used When Calculating an Illustraive BAF for MSW Landfilling.

 .................................................................................................................................................................................. N-22

Table N-5. Sensitivity Analysis for MSW Landfilling. ......................................................................................... N-29

Table N-6. Summary of Parameters Used When Calculating an Illustrative BAF for MSW 

Combustion. ........................................................................................................................................................ N-33

Table N-7. Sensitivity Analysis for MSW Combustion. ...................................................................................... N-38

Table N-8. Summary of Parameters Used When Calculating a BAF for Livestock Waste Management 

through Anaerobic Digestion. ...................................................................................................................... N-47

Table N-9. Sensitivity Analysis of Anaerobic Digestion Using Biogas Measurement Data.1 .............. N-64

Table N-10. Sensitivity Analysis of Anaerobic Digestion Using Animal Population Data.1 ................ N-64

Table N-11. Summary of Parameters Used When Calculating an Illustrative BAF for Livestock Waste 

Management through Combustion. ........................................................................................................... N-73

Table N-12. Sensitivity Analysis of Anaerobic Digestion using Animal Population Data.1 ................ N-80

Table N-13. Illustrative Representative Values for Methane Correction Factor (MCF) and Biomass 

Yield (λ) by Treatment System for both Wastewater and Sludge Treatment Processes (from 

RTI International, 2010). ............................................................................................................................... N-85

Table N-14. Summary of Parameters Used When Calculating an Illustrative BAF for Wastewater 

Treatment. ........................................................................................................................................................... N-88

Table N-15. Sensitivity Analysis for Wastewater Treatment. ........................................................................ N-93

List of Figures 

Figure N-1. Carbon Balance for an Uncontrolled Landfill. ............................................................................... N-13

Figure N-2. Carbon Balance for a Controlled Landfill. ....................................................................................... N-13

Figure N-3. Comparison of Waste and Proximate Fuel Analyses (Adapted from ASTM, 2013). ..... N-51

1. Introduction 

This appendix describes various emissions pathways that result in biogenic CO2 and CH4 emissions 

from stationary sources that use waste-derived biogenic feedstocks, and illustrates how the 

framework could be adapted to derive assessment factors for these biogenic feedstocks. For the 

purposes of this appendix, the waste-derived biogenic feedstock can be defined as the portion of the 

biogenic waste material whose management results in point source emissions (i.e., stack 

emissions). For example, for MSW sent to a combustor, the biogenic feedstock is the entire biogenic 

fraction of the MSW sent to the combustor. For MSW sent to a landfill, the biogenic feedstock is the 

collected landfill gas—an amount representing less than the entire biogenic fraction of the 

landfilled MSW. 
November 2014 N-4 

As discussed in this appendix, waste-derived biogenic feedstocks include the following: 

• Landfill gas1 generated through the decomposition of municipal solid waste (MSW) in a 

landfill; 

• The biogenic fraction of MSW; 

• Biogas generated from the decomposition of livestock waste,2 biogenic MSW, and/or other 

food waste in an anaerobic digester; 

• Livestock waste; and 

• Biogas generated through the treatment of waste water, due to the anaerobic 

decomposition of biological materials. 

The following emission pathways that result in biogenic CO2 emissions from stationary sources 

using waste-derived biogenic feedstocks are evaluated: 

• Combustion of landfill gas, through either a flare or combustion in an electric generating 

unit (EGU); 

• Combustion of MSW; 

• Combustion of biogas from an anaerobic digester used to manage livestock waste and/or 

food waste, through either a flare or combustion in an EGU; 

• Combustion of livestock waste; and 

• Combustion of biogas from an anaerobic digester used to manage wastewater and 

associated sludges. 

This appendix is organized by the aforementioned emissions pathways. These selected pathways 

are not meant to represent an exhaustive list of all possible alternate fate pathways. Included in this 

appendix are illustrative methods for how the framework can be applied to waste-derived biogenic 

feedstocks used at stationary sources to assess net biogenic carbon-based contributions to the 

atmosphere using the example pathways described above. These illustrative methods are 

complemented with illustrations of biogenic assessment factor (BAF) values derived through 

application of the framework to the selected emission pathways. 

In the context of stationary sources, greenhouse gas (GHG) emissions from waste-management 

options can be categorized into direct emissions and indirect emissions.3 The illustrative 

framework applications in this appendix address point source biogenic CO2 and CH4 emissions from 

stationary sources using waste-derived feedstocks. Point source emissions of biogenic CO2 occur as 

a result of combustion of landfill gas, biogas, MSW, or livestock waste. Combustion typically occurs 

 

1

 Landfill gas and biogas consists of approximately 50% methane (CH4) and 50% CO2, with small percentages of 

other gases, such as volatile organic compounds (VOCs). 

2

 In this appendix, “livestock waste” refers to eliminated products (e.g., manure, litter, urine) resulting from the 

digestive process by farm animals (e.g., cattle, sheep, goat, swine, poultry, equine animals, etc.) and associated 

biogenic materials managed as waste materials (e.g., bedding materials and uneaten animal feed). 

3

 Indirect emissions refer to emissions released directly to the atmosphere, rather than through a stack or vent. 

Indirect emissions include uncollected GHGs (e.g., biogas) that are released to the atmosphere and collected GHGs 

(e.g., biogas) that are subsequently leaked to the atmosphere. 
November 2014 N-5 

in a flare or in an EGU. In applications where landfill gas and biogas are combusted, combustion 

results in the destruction of CH4 and the emission of CO2. However, since combustion efficiency is 

less than 100%, not all CH4 is destroyed, such that some uncombusted CH4 is released as a point 

source emission. CH4 has a significantly higher global warming potential (GWP) than CO2.

4 As a 

result, destruction of CH4 that would have been released to the atmosphere as an indirect emission 

in the absence of combustion results in a reduction of CO2-equivalent (CO2e) contribution to the 

atmosphere. 

Indirect emissions of CH4 and CO2 occur at landfills, wastewater treatment facilities, and in livestock 

settings including housing, conveyances, uncovered lagoons storing livestock waste and/or food 

waste, and land application areas. Indirect emissions of CH4 and CO2 also have the potential to occur 

via other waste management techniques, including anaerobic digesters. Note that some waste 

management strategies may result in both direct and indirect GHG emissions (e.g., landfills, 

wastewater treatment facilities, and anaerobic digesters). Table N-1 summarizes different GHG 

emissions pathways related to the management of waste. 

Table N-1. Waste Management GHG Emissions Pathways Considered. 

Type of Waste 

Waste 

Management 

Option 

Biogenic 

Feedstock Direct Emissions1 Indirect Emissions 

MSW Landfill Landfill gas CH4 and CO2 emissions 

from combustion of 

collected landfill gas 

(flare or EGU) 

CH4 and CO2 emissions at 

the landfill cap, leaks in 

landfill gas header piping 

and wells, leachate 

collection sumps, and 

cracks or penetrations in 

the landfill surface or side 

slopes 

Food waste Aerobic 

digestion 

(composting) 

Food waste N/A CO2 emissions (oxidation 

from decomposition)2

MSW MSW combustor MSW CO2 emissions from 

combustion, typically 

in an EGU 

CH4 and CO2 emissions 

from pretreatment 

handling practices 

 

4

 Methane is a potent GHG, with a 100-year global warming potential (GWP) of 21 (IPCC, 1996). It should be noted 

that in the IPCC Fourth Assessment Report, the 100-year GWP of CH4 was revised to 25 (IPCC, 2007). To comply 

with international reporting standards under the UNFCCC, official emission estimates reported by the United States 

use the IPCC Second Assessment Report GWP values (IPCC 1996). The United States will transition to using the 

revised GWPs beginning in 2015. In this framework, the GWP of 25 is used for the central examples within each 

section. The GWPs of 21 and 28 are used in the sensitivity analyses for each section. 
November 2014 N-6 

Type of Waste 

Waste 

Management 

Option 

Biogenic 

Feedstock Direct Emissions1 Indirect Emissions 

Livestock 

waste 

Housing, 

conveyances, 

storage in an 

open lagoon, 

pond, pit, or 

pile3

Biogas N/A CH4 and CO2 emissions 

from uncovered lagoon, 

pond, or pit 

Livestock 

waste and/or 

food waste 

Anaerobic 

digester 

Biogas CO2 emissions from 

combustion of 

collected biogas (flare 

or EGU) 

Potential for indirect CH4

emissions from digester if 

not all CH4 produced is 

captured; CH4 emissions 

from digester effluent 

Livestock 

waste 

Aerobic 

digestion treated 

waste (e.g., 

handled as a 

solid or sprayed 

on a field) 

Manure and 

litter 

N/A CO2 emissions (oxidation 

from decomposition) 

Livestock 

waste 

Livestock waste 

combustor 

Manure and 

litter 

CO2 emissions from 

combustion, often in 

an EGU; CH4 emissions 

from incomplete 

combustion 

CH4 and CO2 emissions 

from pretreatment 

handling practices 

Wastewater Aerobic 

wastewater 

treatment 

process 

Wastewater N/A CO2 and CH4 emissions 

from uncovered treatment 

ponds (CH4 emissions 

from instances where 

partial anaerobic 

conditions are present) 

Wastewater Anaerobic 

wastewater 

treatment 

process 

Biogas CO2 emissions from 

combustion of 

collected biogas (flare 

or EGU) 

Potential for indirect CH4

emissions from digester if 

not all CH4 produced is 

captured; CH4 emissions 

from digester effluent 

1 Point source emissions consist primarily of combustion emissions (i.e., CO2) and secondarily of uncombusted CH4

emissions via incomplete destruction of biogas during combustion (EPA, 2008b). 

2 If compost piles become anaerobic, CH4 and N2O may also be generated and emitted. 

3The term conveyances refers to indirect emissions from the piping when transferring waste to and from units. The term 

pile refers to poultry litter storage piles. 

There are critical differences between the waste-derived biogenic feedstocks addressed in this 

appendix and the other forest- and agricultural-derived biogenic feedstocks addressed by the 

framework. The biologically based material in waste-derived feedstocks was removed from the 

land base for economic and production purposes outside of generating materials for the waste 

stream (e.g., for manufacture of consumer and industrial products, such as newspaper, food, and 
November 2014 N-7 

construction materials). Materials in the waste stream represents material that has been discarded, 

where final disposition of the material must be managed in some fashion (EPA, 2011b). As a result, 

if waste-derived feedstocks had not been processed or used by a stationary source, the material 

would have been managed through an alternative strategy with an alternative emissions pathway. 

Whatever the waste management strategy, it would result in biogenic CO2 emissions and likely 

some amount of CO2e GHG emissions (e.g., CH4 emissions as a result of anaerobic decomposition). 

Evaluating the carbon cycle effects of waste management at a stationary source involves a 

comparison of the biogenic CO2 and CH4 emissions at the stationary source against an alternative 

emissions pathway that would have resulted under an alternate management strategy. 

Evaluating these alternate waste management GHG emissions pathways does not require an 

analysis of the carbon cycle effects that transpired during the growth and harvest of the primary 

biogenic materials on the landscape. As a result, many of the biogenic attributes related to the 

carbon cycle effects of the growth, harvest, and use of other biogenic feedstocks are not relevant for

waste-derived biogenic feedstocks. In many cases, as demonstrated in this appendix, a number of 

the terms in the assessment factor equation drop out when evaluating emission pathways related 

to waste-derived biogenic feedstocks. 

1.1. A Simplified Biogenic Assessment Factor Equation for Waste-Derived 

Biogenic Feedstocks 

The BAF equation presented in the framework for the non-waste-derived feedstocks (i.e., forestryderived, agriculture-derived) can be simplified for application to waste-derived biogenic 

feedstocks. This section provides the simplified general assessment factor equation which is then 

modified to calculate illustrative BAF values for waste-derived feedstocks under different waste 

management strategies, shown in later sections. 

In the assessment factor equation presented in the main body of the framework, the Avoided 

Emissions (AVOIDEMIT) term accounts for the avoidance of estimated biogenic emissions that 

could have occurred on the feedstock landscape without biogenic feedstock removal (e.g., avoided 

decomposition or burning), or per an alternative management strategy. The AVOIDEMIT term can 

be adjusted by the emission pathways specific to the type of waste-derived feedstock and waste 

management strategy. For example, for certain biogas waste feedstocks, AVOIDEMIT can be 

adjusted by the biogas collection efficiency, biogas combustion efficiency, or other factors affecting

emission pathways. As a result, some of the terms in the equation as presented in Equation 2 in the 

main document of the framework are not relevant to the waste-derived feedstocks discussed in this 

appendix as illustrated below: 

 =



 	 =

()(
 + 
 +  + )()()



The BAF is then simplified to (Equation 3 in the main document): 

 = (
 + 
 +  + )()() 
November 2014 N-8 

When only the waste-derived biogenic feedstocks are considered, the following terms can be 

dropped: Net Growth on the Production Landscape (GROW), Total Net Change in Production Site 

Non-feedstock Carbon Pools (SITETNC), Leakage Associated with Feedstock Production (LEAK), the 

Feedstock Carbon Losses during Storage, Transport and Processing (L), and the Feedstock Carbon 

Embodied in Products (P). 

As a result, the full assessment framework equation as applied to biogenic CO2 emissions from 

waste-derived feedstocks can be simplified to Equation N.1. 

 = 
 (EQ. N.1) 

AVOIDEMIT represents the avoided biogenic emissions that could have occurred per an alternative 

management strategy instead of the waste-derived feedstock’s use in bioenergy production, relative 

to biogenic feedstock consumption. As discussed in the main document, negative, positive and zero 

BAFs (which is the same as AVOIDEMIT in this appendix), have different implications. A positive 

value implies that use of the feedstock for bioenergy production contributes more emissions to the 

atmosphere than would have occurred under the alternative management strategy. A zero value 

implies that both practices are equivalent in terms of how much emissions they contribute to the 

atmosphere. A negative value implies that using the feedstock for bioenergy production contributes 

less emissions to the atmosphere than the alternative management practice. In practice, as applied 

here, the AVOIDEMIT term is a proportion expressed as tCO2e avoided (i.e., the emissions reduced, 

in CO2e, resulting from an alternate waste management strategy to the combustion method) per 

tCO2e emitted using the combustion method (i.e., the emissions, in CO2e, resulting from the 

combustion waste management strategy). The AVOIDEMIT term is applied because the waste 

management strategy (e.g., collection and combustion of landfill gas) typically results in avoided 

CO2e emissions that would have occurred in the absence of that management strategy (e.g., had the 

landfill gas not been collected and combusted, it may have been released as an indirect emission).5

The AVOIDEMIT term, as applied to the waste-derived biogenic feedstocks described in this 

appendix, can be conceptually expressed as Equation N.2: 


 =  − 
	 !	"# 	$#%$!$	%&$#!%$'	$ 	( )*$ !


	 !	"# 	( )*$ !	$#%$!$ (EQ.N.2) 

The AVOIDEMIT term is calculated for the specific waste-derived feedstock being managed relative 

to a specific, alternative practice. The following sections of this appendix go into detailed discussion 

about illustrative methodologies for the calculation of a BAF for waste-derived biogenic feedstocks. 

Table N-2 presents a summary of illustrative BAF values calculated from example inputs using the 

methodology presented in subsequent sections of this appendix for the waste-derived biogenic 

feedstocks. These illustrative BAF values are dependent on the assumptions applied to the actual 

waste feedstock and to the alternate fate of the waste feedstock. 

 

5

 This treatment is conceptually comparable to how the AVOIDEMIT term is applied to biogenic feedstocks that are 

harvested from the landscape. 
November 2014 N-9 

Table N-2. Illustrative Example BAF Values Associated with the Treatment Methods of the Waste 

Feedstocks Discussed in this Appendix. 

Waste 

Treatment 

Option 

Biogenic 

Feedstock 

Actual Treatment 

Fate 

Alternate 

Treatment Fate 

Illustrative 

BAF 

Section 

Number 

MSW, landfill Landfill gas Treatment with flares 

(higher DE) 

No gas treatment −1.48 2.2.1 

Landfill gas Treatment with an 

EGU (lower DE) 

No gas treatment −1.38 2.2.2 

Landfill gas Treatment with an 

EGU installed partway 

through the year 

No gas treatment −0.64 2.2.3 

MSW, 

combustion 

Biogenic 

fraction of 

MSW 

Incineration Landfill gas 

treatment with 

flaring or EGU 

–0.02 3.2.1 

Landfill with no gas 

treatment 

–1.52 3.2.2 

Livestock 

waste, 

anaerobic 

digester 

Manure, 

litter, and 

biogas 

Treatment with flares, 

when anaerobic 

digester measurement 

data are available 

Uncovered anaerobic 

lagoon 

-2.56 4.2.1 

Treatment with flares, 

prior to the 

installation of an 

anaerobic digester 

Uncovered anaerobic 

lagoon 

–1.95 4.2.2 

Livestock 

waste, 

combustion 

Manure, 

litter, and 

biogas 

Incineration 1-year litter storage 

prior to field 

spreading 

0.06 5.2.1 

Uncovered anaerobic 

lagoon 

–2.67 5.2.2 

Wastewater 

and 

wastewater 

sludge, 

anaerobic 

digester 

Biogas Treatment with flares Lagoon (with aerobic 

and anaerobic zones) 

–0.88 6.2 

DE = destruction efficiency 

Note: Assumptions and scenario details for each waste treatment option and the associated BAF calculations are 

explained in the text. The parameterization of variables used in the calculations presented here are illustrative only; 

parameter values used in these calculations may not apply to all applications of the framework vis-à-vis the use of wastederived biogenic feedstocks used at stationary sources. 

1.2. Biogenic Municipal Solid Waste Management 

Biogenic MSW refers to the biogenic (organic) fraction of MSW. In 2012, approximately 250.9 

million tons of MSW were generated in the United States (EPA, 2014a). Biogenic materials were the 
November 2014 N-10 

largest component of MSW before recycling (see Table N-3). Of the total MSW generated, 135 

million tons (53.8%) went to landfills, 86.6 million tons (34.5%) were recovered (e.g., recycled or 

composted), and 29.3 million tons (11.7%) were combusted with energy recovery (this includes 

biogenic as well as fossil fuel-based materials, such as plastics). The proportions of waste recycled,

composted, incinerated, or landfilled differ regionally due to multiple factors, including local 

economics, regulatory differences at the state and local levels, public perceptions, and 

infrastructure requirements (Bogner et al., 2007; EPA, 2010c). However, there is a lack of literature 

describing the degree to which composition of MSW can vary from region to region. Therefore, for 

the purposes of the framework, we will use a national average composition based on EPA data 

through 2012 (EPA, 2014a). 

Although composition of MSW may vary from region to region, this mainly contributes to potential 

generation amount of CO2 and CH4 in a given landfill, whereas the goal of the framework 

methodology for waste-derived feedstocks is ultimately concerned with how the CO2 and CH4 from 

MSW is treated used in one activity versus another. From this perspective, CO2 and CH4 from MSW 

can be treated similarly across the U.S. 

Table N-3. Percent of MSW Generated and Recovered by MSW Class in 2012 (EPA, 2014a). 

MSW Class Biogenic? Percent Generated Percent Recovered 

(as percent of generation) 

Paper and paperboard Yes 27.4 64.6 

Yard trimmings Yes 13.5 57.7 

Food scraps Yes 14.5 4.8 

Plastics No 12.7 8.8 

Metals No 8.9 34.0 

Rubber and leather Partial 3.0 17.9 

Textiles Partial 5.7 15.7 

Wood Yes 6.3 15.2 

Glass No 4.6 27.7 

Miscellaneous Uncertain 1.6 negligible 

In the United States, MSW typically has one of four fates (Bogner et al., 2007): 

• Landfilling; 

• Combustion; 

• Processing in an anaerobic digester; or 

• Composting. 

Sections 2 and 3 of this appendix discuss in detail the GHG emissions pathways for MSW landfills 

and MSW combustion, respectively. Food waste can be treated through anaerobic digestion systems 

and is relatively common at wastewater treatment plants. The excess capacity of the digestion 

system can be supplemented from food waste (e.g., EMBUD plant). Waste treatment through 

anaerobic digestion is discussed for both livestock waste management and wastewater treatment. 

Composting is not a stationary source activity, and is therefore not discussed in this appendix. 
November 2014 N-11 

2. Biogenic MSW Disposal in MSW Landfills and Associated GHG 

Emissions Pathways 

GHG emissions pathways at MSW landfills result in CH4 and CO2 emissions. In general, landfillrelated CH4 and CO2 emissions are of biogenic origin and primarily result from the decomposition, 

under anaerobic or aerobic conditions, of organic matter such as food, yard wastes, and paper. The 

decomposition of organic matter in a landfill occurs through a series of microbial reactions, 

primarily under anaerobic conditions (Bogner, 1992). Methane and CO2 are produced through the 

action of methanogenic bacteria as they consume the organic matter and convert it into stabilized 

organic materials and biogas. By volume, the composition of landfill gas ranges from 45% to 55% 

CH4 and CO2, butis generally assumed to be half CH4 and half CO2 (EPA, 2010a). Landfill gas also 

contains small amounts of nitrogen, oxygen, and hydrogen; less than 1% non-methane organic 

compounds (NMOCs); and trace amounts of inorganic compounds (EPA, 2014b). Landfill gas will 

continue to generate for many years, even decades, after an initial mass of waste is placed in a 

landfill due to the slow degradation process and compaction of the waste. 

There are two general pathways for CH4 and CO2 emissions from landfills—indirect emissions and 

direct emissions (i.e., point source combustion emissions). These two emissions pathways are 

affected by the presence of an active gas collection and control system (i.e., flare or EGU). The 

remainder of this section first discusses the emission pathways as they relate to controlled and 

uncontrolled landfills, and then goes into further detail about key parameters affecting the amount 

and type of emissions from these pathways. 

• Uncontrolled Landfills—An “uncontrolled” landfill refers to a landfill that has no active 

system, such as a gas collection and control system, in place to minimize indirect landfill gas 

emissions to the atmosphere. Though the landfill biogas is not collected from uncontrolled 

landfills, the biogas may be managed through the use of a topsoil cover to passively treat the 

uncollected biogas via CH4 oxidation. Indirect emissions are the primary emissions pathway 

from uncontrolled landfills (see Figure N-1). 

o Direct emissions: None. 

o Indirect emissions: The primary GHG emissions pathway at uncontrolled landfills is 

indirect emissions of CH4 and CO2 through the landfill soil cover. A fraction of the

CH4 in the biogas (ranging from 10% to 35% (IPCC, 2006; EPA, 2013c; SWICS, 

2009) will be oxidized by bacteria in the cover soil as the gas migrates vertically 

through the landfill cover soils. 

• Controlled Landfills—A “controlled” landfill refers to a landfill that has an active landfill gas 

collection and control system in place. The collection system consists of network of pipes 

and collection wells strategically placed throughout the disposal areas to collect and 

transport the biogas to a central control system. A control system typically involves a 

combustion device such as a flare, turbine, or boiler for combustion of the collected landfill 

gas. Controlled landfills also include a topsoil cover to passively treat the remaining landfill 

gas that is not collected via CH4 oxidation. In the United States, there are approximately 594 

operational landfill gas-to-energy projects, at which landfill gas is used as fuel for 

generation of electricity or process heat in industrial applications (EPA, 2013a). 
November 2014 N-12 

Approximately 25% of the roughly 2,400 currently operating or recently closed MSW 

landfills in the United States include landfill gas collection and control systems (flaring or 

energy generation) (EPA, 2013a). An estimated 540 additional, existing domestic MSW 

landfills have the potential to capture landfill gas for energy use (EPA, 2013a). The primary 

GHG emissions pathway at controlled landfills is direct emissions of CO2 (see Figure N-2). 

o Direct emissions: The primary GHG emissions pathway at controlled landfills is 

point source emissions of CO2. The CH4 in the landfill gas that is collected and 

combusted will be converted to CO2; the CO2 in the collected landfill gas will be 

directly emitted as CO2; and the CH4 in the collected landfill gas that is not 

combusted will be directly emitted as CH4. 

o Indirect emissions: Both CH4 and CO2 will be emitted through the landfill soil cover. 

A fraction of the CH4 in the biogas (ranging from 10% to 35% (IPCC, 2006; EPA, 

2013c; SWICS, 2009) will be oxidized by bacteria in the cover soil as the gas 

migrates vertically through the landfill cover soils. 

When organic materials are landfilled, a portion of the carbon in the materials will not readily 

degrade due to several factors, including environmental conditions (e.g., moisture, pH, 

temperature), and the creation of anaerobic environments through waste disposal and compaction. 

When the environment in which wastes are placed becomes anaerobic, the organisms that normally 

break down the waste cannot survive to decompose a portion of the organic materials, thus this 

portion will remain in the landfill. This process is referred to as carbon storage because this carbon

is permanently removed from the global carbon cycle. 

Cellulose and hemicellulose are the major biodegradable components of MSW (Barlaz, 1998; Barlaz, 

2006). Additionally, lignin will not degrade at all when placed in a modern landfill (Barlaz, 1998). 

On a dry weight basis, MSW contains between 30% and 50% cellulose, 7% to 12% hemicellulose, 

and 15% to 28% lignin (Hilger and Barlaz, 2001). The amount of cellulose and hemicellulose in the 

organic materials that will degrade depends on the type of material. Laboratory bench scale 

research has been conducted to quantify carbon storage factors for several materials of the MSW 

stream (Barlaz, 1998; ICF, 2008), including yard waste, food, and various paper products. These 

carbon storage factors represent the mass of carbon stored in a landfill per initial mass of the 

component and range from 0.05 to 0.47 kg of carbon sequestered per dry kg of waste component 

(Barlaz, 1998; ICF, 2008). The 2006 IPCC Guidelines (IPCC, 2006a) recommends a default factor of 

0.5 for the fraction of degradable organic carbon that is anaerobically decomposed in the landfill, 

suggesting that 50% of the biogenic carbon placed in a landfill becomes stored carbon. 
November 2014 N-13 

Figure N-1. Carbon Balance for an Uncontrolled Landfill. 

Figure N-2. Carbon Balance for a Controlled Landfill.
November 2014 N-14 

2.1. Indirect Emissions from MSW Landfills 

The first pathway for GHG emissions from landfills assessed in this framework is indirect emissions 

(CH4 and CO2) released directly from the landfill cover to the atmosphere. The amount and rate of 

total CH4 generation in landfills, as well as the amount of indirect emissions of CH4 and CO2, 

depends upon the quantity and composition of the landfilled material, as well as the landfill design 

and surrounding environmental conditions. If not collected and combusted, a portion of the CH4

generated in a landfill oxidizes to CO2 as it travels through the top layer of the landfill cover; the 

remaining unoxidized portion of the landfill gas is emitted through the landfill cover. This process 

results in indirect emissions of both CH4 and CO2 through the landfill cover. 

Methane oxidation efficiency is directly affected by the thickness, physical properties, moisture 

content, and temperature of landfill cover soils. The rate of CH4 oxidation in landfill cover soils is 

linear to a point, after which the methanotrophs in the cover soils reach an upper limit in their 

ability to oxidize the CH4 and the remaining CH4 passes through the cover soil without being 

oxidized (Chanton et al., 2011b). Methane oxidation efficiency can vary substantially between and 

within landfills. Cover soil properties (i.e., temperature and soil moisture) van vary as a function of 

climate, such that the efficiency of CH4 oxidation may vary regionally and seasonally (Spokas and 

Bogner, 2011). In hot, arid climates, CH4 oxidation in landfill cover soils can be limited, resulting in 

higher indirect CH4 emissions than in cooler, wetter climates. In hot, arid climates soil moisture is 

limited for much of the year, thus reducing CH4 oxidation rates, and seasonally high soil 

temperatures prevent methanotrophic activity (Chanton et al., 2011a, Spokas and Bogner, 2011). 

The IPCC (2006a) and EPA (2009a) default value for the CH4 oxidation fraction in cover soils of 

modern, managed landfills such as those found in the United States is 10% of generated CH4. EPA 

considers 10% to be a conservative (lower end) default oxidation fraction. Some studies point to an 

average CH4 oxidation rate of approximately 40% (ranging from negligible to 100%) of the total 

CH4 arriving at the base of the landfill cover soils (Bogner et al., 2007; Chanton et al., 2009; Chanton 

et al., 2011a; Spokas and Bogner, 2011). Because field and laboratory studies have shown large 

variations in oxidation rates, particularly for landfills with active gas collection and control systems, 

EPA expanded the default oxidation fraction value to include those based on the calculated CH4 flux6

rate in grams per square meter per day (g/m2/day) to the bottom of a landfill’s cover soil prior to 

any oxidation (EPA, 2013c, 40 CFR § 98). 

• For high rates of CH4 flux (greater than 70 g/m2/day) the default oxidation fraction is 10%; 

• For moderate rates of CH4 flux (10 to 70 g/m2/day) the default oxidation fraction is 25%; 

• For low rates of CH4 flux (less than 10 g/m2/day) the default oxidation fraction is 35% 

 

6

 The methane flux rate is referred to as the continuous flow of methane from an area within a landfill where 

methane is produced to the atmosphere over a specified period of time. 
November 2014 N-15 

2.2. Direct Emissions from MSW Landfills 

The second pathway for GHG emissions from landfills is direct, point source emissions of CO2 and, 

depending on the destruction efficiency (DE) of the combustion device, CH4 emissions from landfill 

gas collection and combustion through flaring or use as a fuel in an EGU (often referred to as landfill 

gas-to-energy projects).7 

Landfill gas collection systems vary in landfill gas collection efficiency (CE). Recovery ranges from 

35% to 90% of the gas generated in a particular landfill cell, depending on the placement of the 

piping network and collection wells (Spokas et al., 2006; EPA, 2012a). The default collection 

efficiency recommended by EPA is 75% (the average from a range of 50% to 95%), meaning that 

75% of the landfill gas generated is collected and routed to a control device (EPA, 2008a; EPA, 

2010b; EPA, 2013c). However, actual collection efficiencies may vary substantially, and due to the 

cost of determining the amount of landfill gas generated in a landfill, are not cost-effective and 

therefore difficult to quantify. Very few published studies documenting measured CEs exist, and of 

those, the results are highly variable and appear to be correlated with the type of landfill cover 

system. For example, Spokas et al. (2006) conducted field studies of the methane mass balance at 

three landfills in France and quantified collection efficiencies ranging from 54% to 100%, 

depending on cover type and presence of a gas collection system. 

Collected landfill gas may be combusted using a flare, as a fuel for an EGU, or directly in boilers and 

other applications. Landfill gas may be purified to create compressed natural gas or liquefied 

natural gas, or for injection into natural gas pipelines. Of the total estimated CH4 generated at MSW 

and industrial landfills in 2012, 30.3% was flared, 34.5% was used to generate electricity, and 3.5% 

was oxidized at the landfill cap (EPA, 2014b). 

The combustion process destroys, or oxidizes, the CH4 in the landfill gas to CO2, resulting in CO2

emissions.8 A portion of the collected gas will not be combusted due to inefficiencies in the 

combustion device, thus this fraction of CH4 will be emitted to the atmosphere as CH4. Destruction 

efficiencies for CH4 in landfill gas range from 90% to 99.9% (IPCC, 2006; SWICS, 2009; New Zealand 

Ministry for the Environment, 2010; EPA, 2013c). Additionally, the CO2 in the collected gas will not 

be combusted and will be directly emitted as CO2. 

MSW landfills with a design capacity of 2.5 million megagrams (Mg) and 2.5 million cubic meters of 

waste are required to calculate their annual emissions of non-methane organic compounds 

(NMOC). Landfills that emit 50 Mg or more of NMOC per year are required by EPA regulations to 

install a landfill gas capture and control system in order to control NMOC emissions (EPA, 1996). To 

 

7

 Typically, both GHG emissions pathways will be present at a landfill, as landfills with landfill gas collection and 

destruction systems generally do not capture all CH4 generated in the landfill. Uncaptured CH4 will either be 

oxidized via methanotrophic activity in the cover soils, or will be released directly to the atmosphere as indirect 

emissions. 

8

 Note that as the combustion process is never complete, some CH4 in landfill gas is not destroyed and therefore 

stack gas emissions contain a small percentage of CH4. 
November 2014 N-16 

comply with EPA regulations, landfill operators must, at a minimum, collect and combust their 

biogas. A co-benefit of NMOC emissions control is the destruction of CH4 present in the landfill gas. 

Both uncontrolled and controlled landfills include liners and leachate collection systems to prevent 

pollutants from migrating beyond the landfill, which can result in ground and/or surface water 

pollution.9 Both uncontrolled and controlled landfills also store carbon. A portion of the carbon of 

the landfilled biomass materials will not decompose due to the anaerobic environment created 

through modern landfilling. The carbon that does not decompose is therefore removed from the 

global carbon cycle and stored in the landfill. The fraction of the amount of carbon stored in a 

landfill is typically assumed to be approximately 50%. 

Once a landfill has reached its design capacity, it is closed.10 A final cover is installed and the site 

owner is required to monitor and maintain a closed landfill throughout a post-closure monitoring 

period (EPA, 1996). Post-closure monitoring includes leachate collection and treatment, 

groundwater monitoring, inspection of the final cover and maintenance as required, and 

monitoring to ensure that CH4 is not migrating off-site. Collection and combustion of landfill gas 

may continue throughout this period. EPA regulations (40 CFR § 258.61) specify a 30-year postclosure monitoring period unless this period is extended by a regulatory agency on a site-specific 

basis (EPA, 1996). 

2.3. Method for Calculating an Illustrative BAF Value for Biogenic 

Emissions from MSW Landfilling 

The assessment factor equation can be applied to direct biogenic emissions resulting from the 

collection and combustion of landfill gas. The biogenic feedstock from an MSW landfill is the biogas 

generated from MSW decomposition and the biogas collected from the landfill. This section 

provides a method for calculating an illustrative BAF value to be applied to direct biogenic 

emissions from MSW landfills. The BAF methodology for MSW landfilling neither includes benefits 

from off-setting fossil fuels through landfill gas-to-energy projects, nor any carbon storage. 

In Equation N.2, the AVOIDEMIT term is used to represent the net GHG emissions reductions 

achieved through capture and combustion of landfill gas, compared to an alternate, Reference case 

emissions pathway of indirect CH4 and CO2 emissions through the landfill cover (had the landfill gas 

not been collected and combusted). In other words, biogenic emissions from a controlled landfill 

are being compared to the biogenic emissions from an uncontrolled landfill. 

In practice, as applied here, the AVOIDEMIT term is expressed as 1 minus the ratio of metric tons of 

CO2e (tCO2e) avoided (i.e., the point and indirect emissions, in CO2e, of the collected biogas had that 

biogas not been collected and combusted, after accounting for indirect emissions of CO2 and CH4, 

and the CH4 oxidation that would have occurred in the landfill cover soil) per tCO2e removed via 

 

9

 Synthetic liners and compacted clay soil typically line the sides and bottom of a landfill to protect groundwater and 

the underlying soil from leachate releases. Leachate collection and removal systems sit on top of the liners to 

remove leachate from the landfill for collection and disposal. 

10 A closed landfill as referred to in this context means a landfill that no longer accepts waste for disposal. 
November 2014 N-17 

combustion (i.e., the emissions, in CO2e, of the collected and combusted biogas, after accounting for 

the CE of the gas collection system and the DE of the biogas destruction device). For the biogas 

feedstock that is generated and collected from landfills, the AVOIDEMIT term can be conceptually 

expressed by 1 minus a simplified ratio of CO2e emissions of the treatment fates: 


 =  − +,-	-./00/120	341.	54-65.-25	675-4265/8-	51	91.:;05/12

+,-	-./00/120	341.	91.:;05/12	54-65.-25 (EQ.N.2)

Note that the same amount of biogas and constituents of the biogas are considered for both the 

actual and alternate treatment fates. 

2.3.1. Boundaries and Assumptions for MSW Landfilling Methodology 

The methodology presented in this appendix for treatment of MSW through landfilling does not 

consider offsets from electricity generation, carbon storage, or losses from the gas collection 

system. Assumptions regarding the operation of the gas collection system are also made. The 

rationale for the boundary considered within the scope and major assumptions made are provided 

as follows: 

• Offsets—Landfill gas-to-energy projects reduce fossil fuel usage whereas flaring landfill gas 

does not. However, because this is not a lifecycle analysis, the effects of reduced fossil fuel 

usage is not included in the calculations presented here. The EPA’s Landfill Gas Energy 

Benefits Calculator can be used to estimate direct, avoided, and total greenhouse gas 

reductions, as well as environmental and energy benefits, for the current year of a landfill 

gas energy project if desired (EPA, 2012b). 

• Carbon storage—Carbon storage refers to the fraction of carbon remaining in the biogenic 

materials after accounting for the carbon exiting the system as landfill gas or that is 

dissolved in the leachate. The amount of carbon storage will vary with environmental 

conditions in the landfill, but can be generally thought to be about half of the carbon in each 

biomass material that remains in a landfill. Carbon storage is not considered in the 

treatment of waste-derived biogenic feedstocks by MSW landfilling in this framework 

because the amount of carbon storage in a given landfill will theoretically be equivalent 

despite the treatment fate of the landfill biogas. 

• Losses—Indirect emissions from equipment leaks (e.g., valves, connectors, and open-ended 

lines) on or associated with a wellhead, or in the delivery infrastructure from the biogas 

collection system to the biogas destruction device are possible. However, in the context of 

landfill gas collection and control, losses are expected to be insignificant, especially for 

instances where the biogas destruction device is co-located at a landfill. 

• Operation of the gas collection system—One important assumption to note is that the 

methodology for MSW landfilling assumes the landfill gas collection system is operating 

continuously. It is possible to perform the calculations with a gas collection system that is 

not continuously operated by applying an additional factor to account for the fraction that 

the recovery system was operating (fRec) to the equations used to calculate the CO2 and CH4

emissions from landfills with gas collection and control. 
November 2014 N-18 

2.3.2. Explanation of MSW Landfilling Methodology 

Both the numerator and denominator of the AVOIDEMIT equation can be calculated using 

Equation N.3. This equation considers the following emissions pathways from an MSW landfill with 

or without gas collection and control the amount of

• Indirect CH4 emissions from the landfill surface; 

• Indirect CO2 emissions from the landfill surface; 

• Direct CH4 emissions from the CH4 in the collected landfill gas that is not combusted (as a 

result of a combustion efficiency less than 100%); 

• Direct CH4 emissions in the collected landfill gas that is combusted and converted to CO2; 

and 

• Direct CO2 emissions in the collected biogas that is emitted as CO2. 


	 !	"# 		&%!<"&&!=

= >?

(>? − >? + >?@) + A>? × ??

CD + 
 + 
@ (EQ. N.3) 

Where: 

 CO2e emissions = metric tons CO2e emissions from MSW landfilling (MT/year). 

GWPHIJ = 100-year GWP of CH4, 25 (IPCC, 2007). 

 CH4R = the amount of CH4 recovered and sent to the landfill gas destruction 

device (Equation N.4). 

 CH4D = amount of CH4 destroyed via combustion (Equation N.5). 

 CH4U = amount of uncollected CH4 emitted through landfill cover surface; 

separate calculations for landfills with gas collection and landfills 

without gas collection (Equation N.6 or Equation N.7, depending on the 

presence of a gas collection system). 

 CO2R = the amount of CO2 recovered, sent to the landfill gas destruction device, 

and emitted to the atmosphere (Equation N.8). 

 CO2U = amount of uncollected CO2 emitted through landfill cover surface 

(Equation N.9 or Equation N.10, depending on the presence of a gas 

collection system). 

 44/16 = molecular weight ratio of CO2 to CH4. 

Equation N.3 can be grouped and explained in three major parts: 

• The first part, GWPHIJ

(CHMR − CHMD + CHMU), accounts for the amount of CH4 that is 

collected, but not combusted (CH4R – CH4D) plus the amount of CH4 in the generated landfill 

gas that is not collected and emitted as indirect emissions through the landfill cover surface 
November 2014 N-19 

as CH4. Because the terms in Equation N.3 need to be in units of tCO2e, these quantities must 

be adjusted by the 100-year GWP for CH4. 

• The second part, (CH4D × 44/16), accounts for the quantity of CH4 that is collected and 

oxidized to CO2 during combustion. The amount of CH4 destroyed needs to be adjusted by 

the 44/16 conversion factor because the gas is being converted to CO2. 

• The third part, CO2R + CO2D + CO2U, accounts for all of the CO2 emissions (direct and 

indirect). 

o CO2R is the amount of CO2 in the biogas that is collected and sent to the destruction 

device; this quantity will be directly emitted as CO2; 

o CO2D is the amount of CO2 that is collected, but not passed through the destruction 

device; 

o CO2U is the amount of CO2 in the generated landfill gas that is not collected and 

emitted as indirect emissions through the landfill cover surface as CO2. This quantity 

of CO2 is not adjusted for oxidation as the gas passes through the cover. 

The annual amount of CH4 that is collected, or recovered, from the landfill gas and sent to the 

destruction device can be calculated using Equation N.4. The CH4 concentration in the landfill gas is 

typically monitored, or may be assumed as a percentage between 45% and 55%. 

+Q?R = S ×	

+>?

TT%

× T. T?W × XT°R

Y

×

Z

	65.

×

T.?X?	.-54/9	512

,TTT	7:0 (EQ. N.4) 

Where: 

CH4R = amount of CH4 recovered from the landfill and sent to the landfill gas 

destruction device (metric tons CH4/year). 

V = annual volumetric flow rate of biogas to the landfill gas destruction device 

(cubic feet biogas per year), as determined from daily monitoring. 

CHIJ = average annual CH4 concentration of biogas (percent, fraction, wet basis). 

0.0423 = density of CH4 pounds per standard cubic foot (at 520oR or 15.74oC and 

1 atm). 

T = annual average temperature (oR) at which flow is measured. 

P = annual average pressure (atm) at which flow is measured. 

0.454/1000 = conversion factor from pounds to metric tons. 

Equation N.5 can be used to calculate the quantity of CH4 destroyed in a landfill gas destruction 

device. As mentioned previously, achieving 100% destruction efficiency is not feasible, thus the 

amount of CH4 recovered must be adjusted by the destruction, or combustion, efficiency of the 

landfill gas destruction device. This adjustment accounts for the proportion of collected CH4 in the 

biogas that is not destroyed by the destruction device. The collected CH4 in the landfill gas that is 

not combusted is a direct source of CH4 emissions to the atmosphere. 
November 2014 N-20 

+Q?\ = 	 +Q?R × \] (EQ. N.5)

Where: 

CH4D = CH4 destroyed at a landfill gas destruction device (metric tons CH4/year). 

CH4R = amount of CH4 recovered and sent to the landfill gas destruction device 

(Equation N.4). 

DE = CH4 destruction efficiency from flaring or combustion in an EGU, decimal 

percent. The DE varies with the type of landfill gas destruction device used; 

it can be estimated as the lesser of the manufacturer’s specified destruction 

efficiency and 0.99 (EPA, 2013c). 

The presence of a landfill gas collection system affects the amount of indirect CH4 emissions from 

the landfill. When calculating the amount of indirect CH4 emitted from a landfill with gas collection, 

only the uncollected portion of CH4 in the landfill gas is adjusted for oxidation. Alternatively, for a 

landfill without gas collection, all of the CH4 in the generated landfill gas is adjusted for oxidation. 

Equations N.6 and N.7 can be used to determine the amount of uncollected, or indirect, CH4

emissions from a landfill with gas collection and a landfill without gas collection, respectively. 

Both equations adjust the amount of CH4 recovered by the term, 1/CE, which represents the portion 

of generated landfill gas that is not collected by the gas collection system. Equation N.6 subtracts 

the term CH4R to account for the quantity of CH4 that is collected and sent to the destruction device 

so that only the uncollected portion is adjusted for oxidation. Note that this term is not included in

Equation N.7 because all CH4 generated must be adjusted for oxidation in landfills without gas 

collection. 

+Q?^, _60	9177-95/12 = `A





	×	>?D − 	>?a	× 	 ( − 
b) (EQ. N.6) 

+Q?^, c/5d1;5	_60	9177-95/12 = A





	×	>?D	×	 ( − 
b) (EQ. N.7) 

Where: 

CE = collection efficiency of the landfill gas collection system, decimal percent 

CH4R = the amount of CH4 recovered and sent to the landfill gas device 

(Equation N.4) 

OX = methane oxidation fraction 

The amount of CO2 recovered from the landfill gas that is sent to the destruction device can be 

calculated using Equation N.8. 

+,R = S × ( −

++Q?

TT%

) × T. CC × XT°R

Y

×

Z

	65.

×

T.?X?	.-54/9	512

,TTT	7:0 (EQ. N.8) 

Where: 
November 2014 N-21 

CO2R = the amount of CO2 recovered and sent to the landfill gas destruction 

device (metric tons CO2/year). 

V = annual volumetric flow rate of biogas to the landfill gas destruction 

device (cubic feet biogas per year), as determined from daily 

monitoring. 

(1 − CHIM/100%) = average annual CO2 concentration of landfill gas, (C = average annual 

CH4 concentration of biogas, percent, fraction wet basis). 

0.1160 = density of CO2 pounds per standard cubic foot (at 520oR or 15.74oC

and 1 unit of average annual pressure [atm]). 

T = average annual temperature (oR) at which flow is measured. 

P = atm at which flow is measured. 

0.454/1000 = conversion factor from pounds to metric tons. 

Calculating indirect CO2 emissions from the landfill surface is similar to that used to calculate 

indirect CH4 emissions from the landfill surface (see Equations N.6 and N.7). Equations N.9 

and N.10 present two ways to calculate indirect CO2 emissions from either a landfill with a gas 

collection system, or one without. 

Both equations are adjusted by the CE in order to consider only the portion of uncollected CO2 that 

is emitted as CO2 through the landfill cover surface and the portion of uncollected CH4 that is 

emitted through the landfill cover surface and oxidized to CO2 by the methanotrophic bacteria. The 

conversion factor of 44/16 is applied to the portion of CH4 in the uncollected gas that is oxidized to 

CO2. 

+,^, _60	9177-95/12 = `A





× 
D − 
a + 	
b `A





× >?D − >?a × ??

C

(EQ. N.9)

+,^, c/5d1;5	_60	9177-95/12 = 



× 
 +	A
b × 



× >?D ×

??

C

(EQ. N.10)

Where: 

 CE = collection efficiency of the landfill gas collection system, decimal percent. 

 CO2R = amount of CO2 recovered and sent to the landfill gas destruction device 

(Equation N.8). 

CH4R = the amount of CH4 recovered and sent to the landfill gas destruction 

device (Equation N.4). 

OX = methane oxidation fraction. 

44/16 = molecular weight ratio of CO2 to CH4.
November 2014 N-22 

Several parameters are presented and used in the equations in the remainder of this section. Table 

N-4 presents the parameters used, typical or default values, ranges presented in the literature, and 

references. 

Table N-4. Summary of Parameters Used When Calculating a BAF for MSW Landfilling. 

Parameter 

Description Symbol 

Value 

Used in 

Examples 

Range Units Comments 

Reference 

(for value 

column) 

Oxidation 

fraction 

OX 0.10 0.10 to 0.35 Fraction 0.10 is the 

default used in 

many 

accounting 

methodologies 

IPCC, 2006 

Oxidation 

fraction 

OX 0.25 0.10 to 0.35 Fraction Higher 

oxidation 

fractions are 

observed for 

landfills with 

gas collection 

systems and 

low CH4 flux 

rates 

EPA, 2013c; 

SWICS, 2009 

Concentration 

of CH4 in the 

landfill gas or 

biogas 

CHIJ

0.55 0.45 to 0.60 Percent IPCC, 2006 

Collection 

efficiency 

CE 0.75 0.60 to 0.95 Fraction Higher CEs are 

associated with 

closed landfills 

and welldesigned 

systems with 

low permeable 

covers 

EPA, 2010b; 

EPA, 2013c 

Destruction 

efficiency 

(of a landfill 

gas flare) 

DE 0.99 0.90 to 

0.9977 

Fraction 0.99 is 

considered the 

default DE of 

CH4 for a flare 

EPA, 2011a; 

EPA, 2013c 

Destruction 

efficiency 

(of an EGU) 

DE 0.97 0.96 to 0.99 Fraction DE of CH4 in a 

direct use 

system (e.g., 

boilers, 

heaters) varies 

by technology 

EPA, 2011a; 

EPA, 2013c 

Density of CH4

in landfill gas 

– 0.0423 – lbs/scf At 520 oR or 

15.74 oC and 

1 atm 

EPA, 2011a; 

EPA, 2013c 
November 2014 N-23 

Parameter 

Description Symbol 

Value 

Used in 

Examples 

Range Units Comments 

Reference 

(for value 

column) 

Density of CO2

in landfill gas 

– 0.1160 – lbs/scf At 520 oR or 

15.74 oC and 

1 atm 

Calculated 

value1

CE = collection efficiency; DE = destruction efficiency; EGU = electricity generating unit; F = fraction of CH4 in landfill gas; 

lbs/scf = pounds per standard cubic foot; OX = oxidation fraction; R = Rankine 

1 This value is calculated using a 60 degree Fahrenheit conversion: 44.01 * (2.20462/836.6) = 0.1160, where 44.01 = the 

molecular weight of CO2; 2.20462 is a unit conversion factor from kilograms to pounds; and 836.6 scf/kg-mol is the molar 

volume conversion factor. 

2.4. Example AVOIDEMIT and BAF Calculations for Landfill Biogas 

Three example scenarios are presented here for calculating a BAF value for landfill gas. In order to 

derive a BAF value for landfill gas, the numerator and denominator of the AVOIDEMIT must be 

calculated specific to the treatment and alternate fate of the collected landfill gas feedstock. 

Scenarios differ by the treatment of the collected gas (the denominator in the AVOIDEMIT term) and 

the alternate fate of the collected gas (the numerator in the AVOIDEMIT term). 

2.4.1. Example Calculations for a Controlled Landfill (Flaring) Compared to an 

Uncontrolled Landfill 

In this example, a BAF value is calculated for the treatment of collected gas via flares (denominator) 

and the alternate fate is to not collect or control any gas generated in the landfill (numerator). 

Equations N.4 through N.10 can be used to determine the inputs into Equation N.3 as shown below. 

In this example, the landfill with gas collection recovered approximately 150 million cubic feet of 

landfill gas in the past year. The landfill gas monitoring system automatically corrects for 

temperature and pressure, and computed an annual average CH4 concentration in the gas of 55%. 

Step 1: Calculate the Amount of CH4 and CO2 Recovered by the Landfill Gas Collection 

System 

The starting point for both treatment fates for treatment through MSW landfilling is the amount of 

gas recovered. Equations N.4 and N.8 can be used to calculate the amount of CH4 and CO2 recovered 

by the landfill gas collection system: 

+Q?R = XT, TTT, TTT ×	 XX

TT

× T. T?W × XT

XT

×



	

×

T.?X?	

,TTT

= Xg?. WX		>? 

+,R = XT, TTT, TTT × A − XX

TTD × T. CT × XTXT

×



	

×

T.?X?	

,TTT	

	 = WXX?. g		
 

Step 2: Calculate the CO2e Emissions for MSW Landfilling without Biogas Collection and 

Control 

The numerator calculates the CO2e emissions profile of the biogas feedstock had the gas not been 

collected and combusted. Because there is no gas collection or control for the alternate fate, the 

CH4R, CH4D, CO2R, and CO2D terms in Equation N.3 can be dropped, leaving only the CH4U and CO2U 

terms. Equations N.7 and N.10 can be used to calculate the amount of indirect CH4 and CO2 emitted 
November 2014 N-24 

by a landfill without gas collection and control, assuming a representative CE of 75% and 10% 

oxidation fraction: 

+Q?^, c/5d1;5	_60	9177-95/12 = A 

T.hX	× 	Xg?. WXD	× 	 ( − T. T) = 	iT. 		>? 

+,^, c/5d1;5	_60	9177-95/12 = 

T.hX × WXX?. g + 	AT. T × T.hX × Xg?. WXD × ??C

=

															XWT. Ci		


The net CO2e emissions profile of the gas feedstock had the gas not been collected and combusted is 

calculated using Equation N.3: 


	 !	"# 		&%!<"&&!=	j$k *$	=%	( &&($ ! 

= X(T − T + iT. ) + AT × ??

CD + T + XWT. Ci = X, gX. Tg		
 

Step 3: Calculate the CO2e Emissions with Gas Collection and Control (Flaring) 

The denominator calculates the CO2e emissions profile of the gas feedstock had the gas been 

collected and combusted using a flare with a destruction efficiency of 99%. Equation N.5 can be 

used to calculate the CH4D term in Equation N.3: 

+Q?\ = Xg?. WX	 × T. ii = XCg. XT	lY	>? 

Additionally, Equations N.6 and N.9 can be used to calculate the amount of indirect CH4 and CO2

emitted by a landfill with gas collection and control, assuming a representative CE of 75% and 10% 

oxidation fraction: 

+Q?^, _60	9177-95/12 = m`



T. hX	× 	Xg?. WX	a − 	Xg?. WX	n	× 	 ( − T. T) = ?hX. WT		>?

+,^, _60	9177-95/12

= m`



T. hX × WXX?. ga − WXX?. gn + 	T. T m`



T. hX × Xg?. WXa − Xg?. WXn

×

??

C = WWT. h		


Equation N.3 can now be used to calculate the CO2e emissions profile of the feedstock given that the

gas was collected and combusted via flaring: 


	 !	"# 		&%!<"&&!=	j$k	=%	( &&($ ! 

= X(Xg?. WX − XCg. WT + ?hX. WT) + AXCg. XT × ??

CD + WXX?. g + WWT. h =

																			, ?hh. TC		


Step 4: Calculate the BAF Value 

Bringing the numerator and the denominator into the AVOIDEMIT term and calculating the 

assessment factor equation (Equation N.1 and Equation N.2) results in: 

BAF = AVOIDEMIT = 1 – (52,851.08 / 21,477.06) 
November 2014 N-25 

BAF = −1.46

Negative BAF values, such as that calculated in Example 1, indicate that combustion of collected 

landfill gas feedstock by a stationary source results in a net CO2e emissions reduction relative to 

releasing the collected landfill gas directly to the atmosphere without gas collection and 

combustion. 

2.4.2. Example Calculations for a Controlled Landfill (EGU) Compared to an 

Uncontrolled Landfill 

In this example, the same annual volume of landfill gas has been collected as in Section 2.4.1 and a 

BAF value is calculated for the treatment of collected gas via an EGU (denominator). The alternate 

treatment fate is similar to the numerator calculated in Section 2.4.1, thus the value of the 

numerator is the same as in Section 2.4.1. The denominator is also similar to that calculated in 

Section 2.4.1except that the gas DE is 0.97 instead of 0.99 because an EGU typically has a lower DE 

than a flare. The offsets from electricity generation by the EGU are not included in the framework. 

Step 1—Calculate the CO2e Emissions for MSW Landfilling without Gas Collection and 

Control 

The numerator will be the same as that calculated in Example 1 when the same CE and OX values 

are used (Equations N.7 and N.10). Similar to Example 1, the net CO2e emissions profile of the 

biogas feedstock had the gas not been collected and combusted is calculated using Equation N.3: 


	 !	"# 		&%!<"&&!=	j$k *$	=%	( &&($ ! 

= X(T − T + iT. ) + AT × ??

CD + T + XWT. Ci = X, gX. Tg		
 

Step 2—Calculate the CO2e Emissions with Gas Collection and Control (EGU) 

The denominator calculates the CO2e emissions profile of the biogas feedstock had the biogas been 

collected and combusted in an EGU with a DE of 97%. Equation N.5 can be used to calculate the 

CH4D term in Equation N.3: 

+Q?\ = Xg?. WX	 × T. ih = XWC. g	lY	>? 

The quantities of indirect CH4 and CO2 (Equations N.6 and N.9) will be the same as those presented 

in Section 2.4.1: 

+Q?^, _60	9177-95/12 = `A 

T.hX 	× 	Xg?. WX	D − 	Xg?. WX	a	×	 ( − T. T) =

															?hX. W		>?

+,^, _60	9177-95/12	

= m`



T. hX × WXX?. ga − WXX?. gn + 	T. T m`



T. hX × Xg?. WXa − Xg?. WXn

×

??

C = WWT. h		


Equation N.3 can now be used to calculate the CO2e emissions profile of the feedstock given that the

biogas was collected and combusted via an EGU: 
November 2014 N-26 


	 !	"# 		&%!<"&&!=	j$k	=%	( &&($ ! 

															= X(Xg?. WX − XWC. g + ?hX. WT) + `XWC. g × ??

Ca + WXX?. g + WWT. h

= , g. Ti		


Step 4: Calculate the BAF Value 

Bringing the numerator and the denominator into the AVOIDEMIT term and calculating the 

assessment factor equation (Equations N.1 and N.2) results in: 

BAF = AVOIDEMIT = 1 – (52,851.08 / 22,182.09) 

BAF = -1.38

The BAF for this example is slightly greater than the BAF of −1.46 calculated in Section 2.4.1 as a 

result of the lower DE of the EGU relative to combustion using a flare. 

2.4.3. Example Calculations for a Controlled Landfill (EGU) with a Gas Collection 

System Installed Mid-Way through the Year Compared to an Uncontrolled 

Landfill 

In this example, the same annual volume of landfill gas has been collected as in Section 2.4.1 and 

2.4.2. A BAF value is calculated for the treatment of collected gas via a gas collection system and 

EGU (denominator) that was operationalized midway through the year. The alternate treatment 

fate is similar to the numerator calculated in Section 2.4.1 and 2.4.2, thus the value of the 

numerator is the same as in Section 2.4.1 and 2.4.2. The method of calculating the denominator is 

different from that presented in Section 2.4.1 and 2.4.2in that an extra term has been added to 

account for the fraction of hours the gas collection system and control device operated during the 

year (fRec). 

Step 1: Calculate the Amount of CH4 and CO2 Recovered by the Landfill Gas Collection 

System 

The starting point for both treatment fates, the amount of gas recovered, is the same as Section 

2.4.1 and 2.4.2 (Equations N.4 and N.8): 

+Q?R = XT, TTT, TTT × 	 XX

TT

× T. T?W × XT

XT

×



	

×

T.?X?	

,TTT

= Xg?. WX		>? 

+,R = XT, TTT, TTT × A − XX

TTD × T. CT × XTXT

×



	

×

T.?X?	

,TTT	

	 = WXX?. g		
 

Step 2: Calculate the Fraction of Hours the Recovery System Operated During the Year 

fRec = actual operating hours of the recovery system/number of hours in the year 

In this example, the gas collection system was installed and fully operational on May 1st in a nonleap year. There are 244 days between May 1st and December 31st, or 5856 hours. Therefore, fRec = 

5856/8760 = 0.66849. 
November 2014 N-27 

Step 3: Calculate the CO2e Emissions for MSW Landfilling without Gas Collection and 

Control 

Equations N.7 and N.10 are slightly modified by dividing the amount of recovered CH4 and CO2 by 

fRec to give Equations N.11 and N.12: 

+Q?^, c/5d1;5	_60	9177-95/12 = A 

+]

	×	

+Q?R

3R-9 D	× 	 ( − 
b) (EQ. N.21) 

+Q?^, c/5d1;5	_60	9177-95/12 = A 

T.hX	× 	

Xg?.WX

T.CCg?iD	× 	 ( − T. T) = 	, gWh. C?		>? 

+,^, c/5d1;5	_60	9177-95/12 = 



×




"( +	A
b × 

×

>?

"( D × ??C

(EQ. N.12) 

+,^, c/5d1;5	_60	9177-95/12 = 

T.hX

×

WXX?.g

T.CCg?i + 	AT. T × T.hX

×

Xg?.WX

T.CCg?iD × ??C

=

															h, i?. W		


Similar to Section 2.4.1 and 2.4.2, the net CO2e emissions profile of the gas feedstock had the gas not 

been collected and combusted is calculated using Equation N.3: 

CO2e emissions from MSW landfilling without gas collection = 

X(T − T + gWh. C?) + AT × ??

CD + T + hi?. W = hg, gg. 		


Step 4: Calculate the CO2e emissions with gas collection and control (EGU) 

The denominator calculates the CO2e emissions profile of the gas feedstock had the biogas been 

collected and combusted in an EGU with a DE of 97%. Equation N.5 can be used to calculate the 

CH4D term in Equation N.3: 

+Q?\ = Xg?. WX	 × T. ih = XWC. g	lY	>? 

The quantities of indirect CH4 and CO2 (Equations N.6 and N.9) will be the similar to those 

presented in Examples 1 and 2, except that fRec must now be factored into Equations N.6 and N.9 to 

give Equations N.13 and N.14: 

+Q?^, _60	9177-95/12 = mA





	× 	

>?

"( D −	>?n	× 	 ( − 
b) (EQ. N.33) 

+Q?^, _60	9177-95/12 = o` 

T. hX	× 	

Xg?. WX

T. CCg?i	a − 	Xg?. WX	p	×	 ( − T. T)

= ?g. 		>?

+,^, c/5d1;5	_60	9177-95/12 = 



×




"( +	A
b × 

×

>?

"( D × ??C

 (EQ. N.44) 

+,^, _60	9177-95/12	 = o` 

T. hX ×

WXX?. g

T. CCg?ia − WXX?. gp +

T. T o` 

T. hX ×

Xg?. WX

T. CC?i a − Xg?. WXp × ??C = WiXT. g		

November 2014 N-28 

Equation N.3 can now be used to calculate the CO2e emissions profile of the feedstock given that the

biogas was collected and combusted via an EGU: 

CO2e emissions from MSW landfilling with gas collection 

= 25 (1584.35 – 1536.82 + 1411.72) + (1536.82 x 44/16) + 3554.82 + 3950.81 = 

48,213.22 MT CO2e 

Step 5: Calculate the BAF Value 

Bringing the numerator and the denominator into the AVOIDEMIT term and calculating the 

assessment factor equation (Equation N.1 and N.2) results in: 

BAF = AVOIDEMIT = 1 – (78,882.21 / 48,213.22) 

BAF = −0.64

The BAF for this example is approximately two and a half times greater than the BAF of −1.50 

calculated in Section 2.4.2 as a result of the fraction of hours the gas collection and control system

were operational during the year. 

2.5. Sensitivity Analysis for MSW Landfill Biogas 

A simple sensitivity analysis is presented to better understand the relationship between and impact 

of certain key parameters in the framework for MSW landfilling. Key parameters specific to MSW 

landfilling include the oxidation fraction (OX), the collection efficiency (CE) of the landfill gas 

collection system, the destruction efficiency (DE) of the selected combustion device, and the CH4

GWP used (i.e., 21, 25, or 28). Table N-5 presents the range of BAF values after modifying the key 

parameters and using the inputs from Example 2-1 in Section 2.3 of this appendix. Sources for the 

parameter values used here can be found in Table N-4 of Section 2.3.2. The actual fate is MSW 

landfilling with flaring and the alternate fate is MSW landfilling without gas collection and 

combustion. 

Two categories of analyses are presented in Table N-5: the first (1a through 1d) compares the 

impact of modifying the CE and DE values, while the second (2a through 2d) compares the impact 

of modifying all 3 key parameters. In the second set of analyses, a value for OX other than the 

representative value of 0.10 was used in the actual fate (i.e., denominator) calculations. The only 

difference between the a, b, c, and d analyses is the change in OX factors. For example, when 

comparing Analyses 1a and 2a, the only difference is that 1a uses an OX of 0.10 for both the actual 

and alternate fates, while 2a uses different OX values for each fate. Analyses 2a, b, c, and d yield 

lower BAF values than Analyses 1a, b, c, and d. Analysis 2c yields the lowest BAF values and 

Analysis 1b yields the highest BAF value. Despite modifying the key parameters, all BAF values are 

negative. 
November 2014 N-29 

Table N-5. Sensitivity Analysis for MSW Landfilling.

Analysis

Key Parameter and Value BAF 

OX CE Flare DE GWP=21 GWP=25 GWP=28 

1a 0.10 0.75 0.99 −1.319 −1.461 −1.551 

2a Without GCS = 0.10 

With GCS = 0.25 

0.75 0.99 −1.504 −1.681 −1.795 

1b 0.10 0.75 0.98 −1.285 −1.421 −1.508 

2b Without GCS = 0.10 

With GCS = 0.25 

0.75 0.98 −1.465 −1.634 −1.743 

1c 0.10 0.95 0.99 −2.577 −3.031 −3.352 

2c Without GCS = 0.10 

With GCS = 0.25 

0.95 0.99 −2.660 −3.143 −3.485 

1d 0.10 0.75 0.99 −1.319 −1.461 −1.551 

2d Without GCS = 0.10 

With GCS = 0.25 

0.75 0.99 −1.719 −1.940 −2.086 

Note: References for the key parameters and values are presented in Table N-4 of Section 2.3.2. 

Note: Methane is a potent GHG, with a 100-year GWP of 21 (IPCC, 1996). It should be noted that in the IPCC Fourth 

Assessment Report, the 100-year GWP of CH4 was revised to 25 (IPCC, 2007). To comply with international reporting 

standards under the UNFCCC, official emission estimates reported by the United States use the IPCC Second Assessment 

Report GWP values (IPCC, 1996). The United States will transition to using the revised GWPs beginning in 2015. In this 

framework, the GWP of 25 for the central examples within each section. The GWPs of 21 and 28 are used in the sensitivity 

analyses for each section. 

3. Disposal of Biogenic MSW through Combustion and 

Associated GHG Emissions Pathways 

As an alternative to disposing of MSW in a landfill, it can be directly combusted in waste-to-energy 

facilities to generate electricity. In the United States, almost all incineration of MSW occurs at 

waste-to-energy facilities or industrial facilities where energy is recovered (EPA, 2014b). Based on 

data from EPA’s Greenhouse Gas Reporting Program (GHGRP) and EPA’s Emissions and Generation 

Resource Integrated Database (eGRID), there are roughly 142 MSW combustors in the United States 

that emit approximately 30 million metric tons of biogenic CO2e.11 Incineration oxidizes almost all 

of the carbon in the MSW to CO2 (Astrup et al., 2009). Generally less than 0.5% of the carbon 

remains in the ashes (i.e., it is not emitted to the atmosphere, Astrup et al., 2009). 

Although MSW consists mainly of biogenic resources such as food, paper, and wood products, it also 

includes resources derived from fossil fuels, such as tires12 and plastics. After the MSW is delivered 

 

11 Based on GHGRP data for the 2011 reporting year and eGRID data for the 2009 reporting year. 

12 Tires contain a biogenic component in the form of natural rubber. Whole tires (including steel, etc.) from the 

combined grouping of passenger vehicles and trucks are, on average, composed of 28% natural rubber (Rubber 

Manufacturers Association, unpublished data 2013). Tire-derived-fuel is used in cement kilns, utility boilers, pulp 

and paper mills, industrial boilers, and dedicated scrap tire-to-energy facilities (EPA 2009b). 
November 2014 N-30 

to a stationary source facility, it is incinerated in an EGU either “as is” (mass burn without recovery 

of recyclables), as refuse-derived fuel (burn after recyclables have been recovered), or combustion 

with energy recovery of source separated materials in MSW (e.g., wood pallets and tire-derived 

fuel; EPA, 2009b). Point source stack emissions from combustion of biogenic MSW feedstocks are 

primarily CO2. For the purposes of this document, biogenic MSW is the feedstock when disposed of 

in a combustor. 

3.1. Method for Calculating an Illustrative BAF Value for Biogenic 

Emissions Resulting From MSW Combustion 

The assessment factor equation can be applied to direct biogenic CO2 emissions from MSW 

combustion. This section provides an illustrative method for calculating a BAF value that is applied 

to direct biogenic CO2 emissions from MSW combustors. Here, the biogenic feedstock is MSW that is 

collected and incinerated, oxidizing the biogenic waste-feedstock to CO2 emissions. 

Landfilling the biogenic MSW can be considered the alternate fate of the MSW feedstock had it not 

been incinerated. The emissions profile resulting from this alternate fate represents the numerator 

of the emissions ratio term in AVOIDEMIT. Were the MSW to have been disposed of in a landfill, it 

would undergo anaerobic decomposition, resulting in biogas that may or may not be collected and 

destroyed by combustion. However, a portion of the carbon in the biogenic waste-derived feedstock 

does not decompose in the landfill; instead that carbon is stored in the landfill. Such storage 

effectively removes the remaining landfilled carbon from the global carbon cycle by transferring 

that carbon into long-term storage within a landfill (Staley and Barlaz, 2009).13 The factors affecting 

degradation can result in the long-term, potentially permanent, carbon storage of approximately 

50% of total landfilled organic carbon (Bogner et al., 2007; Manfredi et al., 2009). 

In applying the assessment factor equation, net GHG emissions reductions are accounted for in the 

AVOIDEMIT term. In practice, as applied here, the AVOIDEMIT term is a ratio expressed as tCO2e 

avoided (i.e., the emissions, in CO2e, of the MSW had it not been combusted) per tCO2e removed via 

combustion (i.e., the emissions, in CO2e, of the combusted MSW). For the MSW feedstock 

incinerated in an MSW combustor, the AVOIDEMIT term can be conceptually expressed by the 

simplified ratio of: 


 =  − (-./00/120	341.	212-91.:;05/12	54-65.-25	13	lrs)	

(-./00/120	341.	lrs	91.:;05/12) (EQ. N.15)

3.1.1. Calculating the Numerator 

In computing AVOIDEMIT, the numerator (i.e., emissions from MSW treatment alternative to 

incineration) can be calculated under the assumption that had the MSW not been incinerated, it 

 

13 While cellulose, hemicellulose, and lignin (present in paper and wood products) can degrade and be converted to 

CH4 in landfills, the anaerobic conditions in landfills prevent their full degradation (Bogner, 1992; Barlaz, 2006;

Wang et al., 2011). Furthermore, the presence of lignin can inhibit cellulose and hemicellulose degradation (Micales 

and Skog, 1997; Barlaz, 2006). Because lignins effectively prevent degradation, between 84% and 100% of the 

initial carbon in landfilled wood products is sequestered indefinitely (Micales and Skog, 1997; Wang et al., 2011). 

The extent of decomposition varies between types of wood (Wang et al., 2011). 
November 2014 N-31 

would have been landfilled. Given this alternate fate, the value of the numerator must account for 

the fraction of landfilled MSW that decays anaerobically, thereby producing landfill gas that may or 

may not be collected. If the landfill gas is collected and combusted (e.g., flared), the collection 

efficiency and destruction efficiency must be accounted for. In accounting for indirect emissions 

from the landfill cap, the CH4 oxidation via the landfill cover soils must be accounted for. And finally, 

the fraction of landfilled MSW that does not decay such that biogenic carbon is stored within the 

landfill must also be accounted for. The following equation can be used in the numerator of the 

AVOIDEMIT term: 

CO2e emissions avoided by landfilling the MSW (kg CO2e/metric ton MSW wet weight) = 

tsZ+Q?	 ×	 (+Q?01/70 + +Q?91.:;05/12) + +,01/70 + +,91.:;05/12 (EQ. N.16) 

Where: 

GWPHIM = 100-year GWP of CH4, 25 (IPCC, 2007)

 CH4soils = CH4generated × (1 – CE) × (1 – OX) (EQ. N.57) 

 CH4combustion = CH4generated × (CE) × (1 – DE) (EQ. N.68) 

Where: 

 CH4generated = C × Dlfg × (%CH4) × (16/12) (EQ. N.79) 

 C = amount of biogenic C in MSW (kg C/metric ton MSW wet weight). 

 Dlfg = dissimilation coefficient (fraction of biogenic C that leaves the landfill via 

decomposition of biogenic waste). 

 %CH4 = proportion of gas that is CH4. 

 (16/12) = molecular weight ratio of CH4 to C. 

 CE = gas collection efficiency. 

 OX = CH4 oxidation factor associated with the landfill cover soil. 

 DE = gas destruction efficiency (i.e., combustion efficiency of flare or EGU). 

CO2soils = (CO2generated + CH4generated × 44/16 × OX) × (1 – CE) (EQ. N.20) 

CO2combustion = (CO2generated + CH4generated × 44/16 × DE) × CE (EQ. N.21) 

Where:

CO2generated = C × Dlfg × (%CO2) × (44/12) (EQ. N.82) 

Where: 

 C = amount of biogenic C in MSW (kg C/metric ton MSW wet weight). 
November 2014 N-32 

 Dlfg = dissimilation coefficient (fraction of biogenic C that leaves the landfill via 

decomposition of biogenic waste). 

 (%CO2) = proportion of gas that is CO2. 

 (44/12) = molecular weight ratio of CO2 to C. 

 CE = gas collection efficiency. 

 OX = CH4 oxidation factor associated with the landfill cover soil. 

 DE = gas destruction efficiency (i.e., combustion efficiency of flare or EGU). 

3.1.2. Calculating the Denominator 

In the derivation of AVOIDEMIT (Equation N.15), the denominator (i.e., emissions from MSW 

combustion) is based on the carbon content of the point source, stack emissions from the MSW 

combustion device. The value of the denominator is equal to the CO2e of the combusted MSW, 

adjusted by the proportion of combusted biogenic carbon in MSW that is converted from C to CO2. 

MSW combustion results in near-complete oxidation of C to CO2; generally less than 0.5% of the 

initial amount of C remains in solid form (ash) post-combustion. The following equation can be 

used to calculate the total CO2e emissions from MSW combustion (the denominator of the 

AVOIDEMIT term): 

CO2e emissions from MSW combustion (kg CO2e/metric ton MSW wet weight) = 

C × 0.995 × (44/12) (EQ. N.93) 

Where: 

 C = amount of biogenic C in MSW (kg C/metric ton MSW wet weight). 

 0.995 = proportion of C in MSW that is oxidized through combustion (i.e., 

combustion efficiency). 

 (44/12) = molecular weight ratio of CO2 to C. 

After solving for the numerator and the denominator of the AVOIDEMIT term, the BAF value can be 

calculated using Equation N.1. See Section 3.2 for an illustrative example calculation of the 

numerator and denominator in the AVOIDEMIT term and its subsequent application in estimating a 

BAF value. 

Several parameters are presented and used in the equations in the remainder of this section. Table 

N-6 presents the parameters used, typical or default values, ranges presented in the literature, and 

references. 
November 2014 N-33 

Table N-6. Summary of Parameters Used When Calculating an Illustrative BAF for MSW 

Combustion. 

Parameter 

Description Symbol Value Range Units Comments 

Reference 

(for value 

column) 

Oxidation 

fraction 

OX 0.10 0.10 to 0.35 Fraction 0.10 is the 

default used in 

many 

accounting 

methodologies 

IPCC, 2006 

Percent of 

CH4 or CO2

in the 

landfill gas 

%CH4, 

%CO2

0.55 0.45 to 0.60 Percent IPCC, 2006 

Collection 

efficiency 

CE 0.75 0.60 to 0.95 Fraction Higher CEs are 

associated with 

closed landfills 

and welldesigned 

systems with 

low permeable 

covers 

EPA, 2010b; 

EPA, 2013c 

Destruction 

efficiency 

(of a landfill 

gas flare or 

EGU) 

DE 0.99 0.90 to 0.9977 Fraction 0.99 is 

considered the 

default DE of 

CH4 for a flare; 

EGUs may be 

slightly less 

EPA, 2011a; 

EPA, 2013c 

Fraction of 

biogenic 

carbon in 

MSW 

C 90 Dependent on 

the 

composition 

of the MSW 

Kilograms 

Carbon 

per metric 

ton of 

MSW, wet 

weight 

 Staley and 

Barlaz, 2009 

Dissimilation 

coefficient 

Dlfg 0.50 – Percent 50% of the 

biogenic carbon 

in the MSW goes 

into long-term 

storage 

IPCC, 2006 

Combustion 

efficiency of 

an MSW 

combustor 

– 0.995 0.98 to 0.9999 Fraction The proportion 

of carbon in 

MSW that is 

oxidized 

through 

combustion 

IPCC, 2006; 

Astrup et al., 

2009 
November 2014 N-34 

3.2. Example AVOIDEMIT and BAF Calculations for MSW Combustion 

Two example scenarios are presented here for calculating a BAF value for MSW combustion 

compared to an alternate of landfilling with gas collection and an alternate of landfilling without gas 

collection. A hypothetical example is used to calculate AVOIDEMIT and the BAF for MSW 

combustion. Actual AVOIDEMIT and the BAF values will vary depending on the specific 

circumstances of MSW combustion and its alternate fate. 

3.2.1. Example Calculations for MSW Combustion Compared to a Landfill with Gas 

Collection (EGU) 

Equation N.16 can be used to calculate the numerator of the AVOIDEMIT term, but Equations N.17 

through N.22 must be calculated first in order to solve for Equation N.16. To solve for the 

numerator, emissions from non-combustion treatment of MSW, it will be assumed that had the 

MSW not been combusted then it would have been landfilled, thereby producing biogas. Some of 

the biogas would have been collected and combusted, some would have been oxidized via the 

landfill cover soils, and the remainder would have been an indirect emission. All of these emission 

pathways are considered here because the feedstock for combustion of biogenic MSW is the 

biogenic MSW. 

For this hypothetical example, the following conditions apply: 

• The amount of biogenic carbon in MSW is estimated at 90 kg C/metric ton MSW wet weight 

(ww) (i.e., C = 90). 

• The amount of biogenic carbon leaving the landfill is estimated at 50% (Dlfg = 0.5), such that 

50% goes into long-term storage. 

• On a mass basis, 55% of the carbon becomes CH4 and 45% of the carbon becomes CO2. 

• The fraction of CH4 in the landfill gas that is oxidized via cover soils is the default of 0.10 

(OX = 0.1). 

• Landfill gas collection efficiency is 75% (CE = 0.75). 

• Destruction efficiency of the collected landfill gas is 99% (DE = 0.99). 

Step 1: Calculate the CH4 and CO2 Generated and Emitted by a Landfill with Gas 

Collection and Combustion in an EGU 

To calculate the numerator, Equations N.19 and N.22 must first be solved: 

CH4generated = 90 kg C per metric ton MSW ww × 0.5 × (55/100) × (16/12) 

 = 33.0 kg CH4 per metric ton MSW ww 

CO2generated = 90 kg C per metric ton MSW ww × 0.5 × (45/100) × (44/12) 

 = 74.25 CO2 per metric ton MSW ww 
November 2014 N-35 

Using the computed value from Equation N.19, Equation N.17 can be solved: 

CH4soils = 33.0 × (1 – 0.75) × (1 – 0.1) 

 = 7.425 kg CH4 per metric ton MSW ww 

Using the computed value from Equation N.19, Equation N.18 can be solved: 

CH4combustion = 33.0 × (0.75) × (1 – 0.99) 

 = 0.2475 kg CH4 per metric ton MSW ww 

Using the computed values from Equations N.19 and N.22, Equation N.20 can be solved: 

CO2soils = (74.25 + (33.0 × 44/16 × 0.1)) × (1 – 0.75) 

 = 20.8312 kg CO2 per metric ton MSW ww 

Using the computed values from Equations N.19 and N.22, Equation N.21 can be solved: 

CO2combustion = (74.25 + (33.0 × 44/16 × 0.99)) × 0.75 

 = 123.0694 kg CO2 per metric ton MSW ww 

Using the computed values from Equations N.17, N.18, N.20, and N.21, the numerator (i.e., 

Equation N.16) can be solved: 

CO2e emissions avoided by not having landfilled the MSW (kg CO2e/metric ton MSW ww) 

= 25 × (7.425 + 0.2475) + 20.8312 + 123.0694 

= 335.713 kg CO2e per metric ton MSW ww 

Step 2: Calculate the CO2 Emitted Through MSW Combustion 

Next, the denominator (total CO2e emissions from MSW combustion) of the AVOIDEMIT term can be 

solved (kg CO2e/metric ton MSW wet weight) using Equation N.23: 

CO2e emissions from MSW combustion 

 = 90 × 0.995 × (44/12) 

 = 328.350 

Step 3: Calculate the BAF Value 

Next, the AVOIDEMIT term can be computed and input into the assessment factor equation 

(Equations N.1 and N.2): 
November 2014 N-36 

BAF = AVOIDEMIT

 = 1 – (335.711 / 328.350) 

 = −0.022 

It should be noted that this calculation does not take into account any reduction in fossil fuel usage

as a result of any heat, power, or both that may have been generated in the MSW incineration 

process. 

3.2.2. Example Calculations for MSW Combustion Compared to a Landfill without 

Gas Collection 

If the alternate fate of the MSW had been landfilled without gas collection or combustion, then 

CH4soils and CO2soils would increase in value while CH4combustion and CO2combustion would both be 0. 

Step 1: Calculate the CH4 and CO2 Generated and Emitted by a Landfill without Gas 

Collection 

To calculate the numerator, Equations N.19 and N.22 must first be solved: 

CH4generated = 90 kg C per metric ton MSW ww × 0.5 × (55/100) × (16/12) 

 = 33.0 kg CH4 per metric ton MSW ww 

CO2generated = 90 kg C per metric ton MSW ww × 0.5 × (45/100) × (44/12) 

 = 74.25 CO2 per metric ton MSW ww 

Using the computed value from Equation N.19, Equation N.17 can be solved. The collection 

efficiency is 0 in this equation since there is no gas collection system. 

CH4soils = 33.0 × (1 – 0) × (1 – 0.1) 

 = 29.7 kg CH4 per metric ton MSW ww 

Using the computed values from Equations N.19 and N.22, Equation N.20can be solved: 

CO2soils = (74.25 + (33.0 × 44/16 × 0.1)) × (1 – 0) 

 = 83.325 kg CO2 per metric ton MSW ww 

Using the computed values from Equations N.17 and N.20 the numerator (i.e., Equation N.16) can 

be solved: 

CO2e emissions avoided by not having landfilled the MSW (kg CO2e/metric ton MSW ww) 

= 25 × (29.7 + 0) + 83.325 + 0 

= 825.825 kg CO2e per metric ton MSW ww 
November 2014 N-37 

Step 2: Calculate the CO2e Emitted Through MSW Combustion 

Next, the denominator (total CO2e emissions from MSW combustion) of the AVOIDEMIT term can be 

solved (kg CO2e/metric ton MSW wet weight) using Equation N.23: 

CO2e emissions from MSW combustion 

= 90 × 0.995 × (44/12) 

= 328.350 

Step 3: Calculate the BAF Value 

Next, the AVOIDEMIT term can be computed and input into the assessment factor equation 

(Equations N.1 and N.2): 

BAF = AVOIDEMIT

 = 1 – (825.825 / 328.350) 

 = −1.52 

It should be noted that this calculation does not take into account any reduction in fossil fuel usage

as a result of any heat, power, or both that may have been generated in the MSW incineration 

process. 

3.3. Sensitivity Analysis for MSW Combustion 

A simple sensitivity analysis on the key parameters in the MSW combustion methodology is 

presented in Table N-7 for the actual fate of MSW combustion and the alternate fate of landfilling 

with gas collection and flaring. Key parameters impacting the BAF include the destruction and 

collection efficiencies (DE and CE, respectively) and the GWP for CH4 (21, 25, and 28). In each of the 

six analyses, the DE of the landfill gas was adjusted between 97% and 99%, and the CE was 

adjusted 60% to 95%, representing a range of low to high performing landfill gas collection system 

efficiencies. Sources for the parameter values used here can be found in Table N-6 of Section 3.1.2. 

The inputs used in the analyses are equivalent to those shown in the example calculations in 

Section 3.2 of this appendix. Note that the carbon content of the MSW does not impact the 

calculated BAF values because it is a factor in both treatment fates and essentially cancels out. 

The BAF values are most negative compared to the other analyses, when MSW combustion is 

compared to a landfill with a 75% CE and 97% DE, indicating that MSW combustion results in a 

greater reduction of CO2e emissions (see Analysis 4, regardless of the GWP value). Alternatively, the 

most positive BAF value is generated when MSW combustion is compared to a highly efficient 

landfill gas collection and combustion system (i.e., Analysis 6). 

Analyses 7 through 12 highlight the areas where the BAF value changes from negative to positive as 

a result of the CE for each GWP value when the DE is held constant at 99%. The BAF values were all 

negative when a DE of 97% was held constant despite the changes in CE and GWP. 
November 2014 N-38 

Table N-7. Sensitivity Analysis for MSW Combustion.

Analysis 

Key Parameter and Value BAF 

CE DE GWP=21 GWP=25 GWP=28 

1 0.60 0.99 −0.174 −0.321 −0.431 

2 0.60 0.97 −0.196 −0.348 −0.462 

3 0.75 0.99 −0.141 −0.022 −0.386 

4 0.75 0.97 −0.241 −0.395 −0.510 

5 0.95 0.99 0.398 0.376 0.359 

6 0.95 0.97 −0.302 −0.458 −0.575 

7a 0.70 0.99 −0.011 

8 a 0.71 0.99 0.006 

9b 0.76 0.99 −0.003 

10 b 0.77 0.99 0.017 

11c 0.79 0.99 −0.002 

12 c 0.80 0.99 0.020 

a The point at which the BAF changes from negative to positive with a GWP of 21.

b The point at which the BAF changes from negative to positive with a GWP of 25. 

c The point at which the BAF changes from negative to positive with a GWP of 28. 

Note: References for the key parameters and values are presented in Table N-6 of Section 3.1.2. 

4. Livestock Waste Management through Anaerobic Processes 

and Associated GHG Emissions Pathways 

Livestock waste management can produce CH4, CO2, and N2O emissions. In 2012, livestock waste 

management emissions in the United States were estimated at 52.9 Tg CO2e for CH4;14 and 18.0 Tg 

CO2e for N2O (EPA, 2014b). Waste from dairy cattle and swine had the highest CH4 emissions; waste 

from beef and dairy cattle had the highest N2O emissions (EPA, 2014b). 

Methane is produced under anaerobic conditions in livestock waste storage and treatment systems, 

such as liquids or slurries in lagoons, ponds, tanks, pits, or piles. In the United States, the majority of 

livestock waste is handled as a solid (e.g., in stacks or drylots) or deposited on pasture, range, or 

paddock lands, where it tends to decompose aerobically and produce little or no CH4 (EPA, 2014b). 

Carbon dioxide is also produced under anaerobic conditions and generated when CH4 in the biogas 

is combusted. 

Both direct and indirect N2O emissions are emitted during livestock waste management. Direct N2O 

emissions from livestock waste are produced as part of the nitrogen cycle through the nitrification 

and denitrification of the organic nitrogen in livestock dung and urine. The production of direct N2O 

emissions from livestock waste depends on the composition of the manure and urine, the type of 

 

14 This accounts for CH4 reductions due to capture and destruction of CH4 at facilities using anaerobic digesters. 
November 2014 N-39 

bacteria involved in the process, and the amount of oxygen and liquid in the waste management 

system. 

• For direct N2O emissions to occur, the manure must first be handled aerobically where 

ammonia (NH3) or organic N is converted, via nitrification, to nitrates and nitrites, and then 

handled anaerobically where the nitrates and nitrites are reduced to dinitrogen gas (N2), 

with intermediate production of N2O and nitric oxide (NO), via denitrification (EPA, 2014b). 

These emissions are most likely to occur in dry manure handling systems that have aerobic 

conditions, but that also contain pockets of anaerobic conditions due to saturation. A very 

small portion of the total N excreted is expected to convert to N2O in the waste management 

system. 

• Indirect N2O emissions are produced when nitrogen is lost from the system through 

volatilization (as NH3 or NOx) or through runoff and leaching of nitrogen during waste 

treatment, storage and transportation (EPA, 2014b). The vast majority of volatilization 

losses from these operations are NH3 (EPA, 2014b). 

The framework does not consider N2O emissions; therefore the methodology presented in the 

remainder of this section does not consider N2O emissions. 

With the rise of concentrated animal feeding operations (CAFOs), the traditional use of livestock 

waste as a soil amendment (where it decomposes aerobically) is not practical (Santoianni et al., 

2008).15 As a result, the use of liquid-based management systems (e.g., uncovered lagoons, pits, 

anaerobic digesters) that promote anaerobic conditions is increasing in popularity (EPA, 2014b). 

There are two general pathways for GHG emissions from anaerobic management of livestock 

waste:16

• Uncontrolled anaerobic storage and treatment, typically in an uncovered pit or lagoon; and 

• Anaerobic digestion, with capture and destruction of the generated biogas. 

Under uncontrolled anaerobic storage and treatment systems, livestock wastes are typically 

deposited as a liquid slurry in uncovered lagoons, pits, ponds, or open tanks. This storage practice 

results in significant indirect CH4 emissions (EPA, 2009b). Volatile solids contained in livestock 

waste degrade under anaerobic conditions, thus generating CH4 biogas. If the biogas produced in 

uncovered lagoons, pits, ponds, or open tanks is not collected, it is released directly to the 

atmosphere. 

Livestock waste management using anaerobic digesters allows the generated biogas to be captured 

and destroyed. Anaerobic digesters used for livestock waste management range in technology from 

contained vessels to covered lagoons. Anaerobic digesters are designed and operated for waste 

stabilization resulting from the microbial reduction of complex organic compounds to CO2 and CH4. 

 

15 Aerobic management of manure may include dry lots (including feedlots), high-rise houses for poultry production 

(poultry without litter), poultry production with litter, deep bedding systems for cattle and swine, manure 

composting, aerobic treatment units, and field spreading of manure as a soil amendment. 

16 Food waste from industrial and commercial food processing may also be managed through these approaches. 
November 2014 N-40 

The decomposition process occurs much faster and is more complete in an anaerobic digester than 

in an uncontrolled anaerobic storage lagoon (Manfredi and Christensen, 2009). As a result, 

anaerobic digesters have higher rates of CO2 and CH4 generation. The increase in waste degradation 

and stabilization is mainly accomplished by recirculating the collected leachate within the 

anaerobic digester. This process enhances microbial degradation of complex organic compounds to 

simple organics and gaseous biogas products (primarily CO2 and CH4). 

The vast majority of anaerobic digesters used for livestock waste treatment in the United States 

collect the biogas for energy use, but flaring of the gas is also practiced (EPA, 2012c, 2013b). 

Combustion of the biogas produced in an anaerobic digester destroys (via oxidation) most of the 

CH4 contained in biogas; the primary resulting emission is CO2.

17 The 192 anaerobic digester 

systems used for livestock waste management in the United States avoid an estimated 1.3 million 

metric tons CO2e, annually compared to other livestock waste management options (EPA, 2013b). 

Although the use of anaerobic digesters is increasing in the United States, they are still in limited 

use considering the number of livestock operations, and are found primarily on large-scale 

livestock operations. By the end of 2011, approximately 2% of U.S. livestock operations used 

anaerobic digesters in waste management (EPA, 2012c). 

Because anaerobic digesters are designed to enhance CH4 generation, poor design, operation, or 

maintenance of anaerobic digesters can result in significant indirect CH4 emissions. For example, 

CH4 can leak from a digester cover or can be vented during digester start-ups, shutdowns, and 

malfunctions (Bogner et al., 2007; EPA, 2008b; Climate Action Reserve, 2013). However, under 

normal working conditions, GHG emissions from controlled biological treatment in an anaerobic 

digester are small relative to indirect CH4 emissions from uncontrolled anaerobic storage and 

treatment systems (Bogner et al., 2007, and references therein). As a consequence, using anaerobic 

digester systems with biogas combustion typically results in substantial net GHG emissions 

reductions compared to conventional livestock waste storage and treatment, particularly for liquid 

wastes. 

4.1. Method for Calculating an Illustrative BAF Value Applied to Biogenic 

Emissions Resulting from Anaerobic Digestion of Livestock and Food 

Waste 

The assessment factor equation can be applied to point source biogenic CO2 emissions from an 

anaerobic digester used to store and treat livestock or food waste.18 This section provides an 

illustrative method for calculating a BAF value that is applied to point source biogenic CO2

emissions from anaerobic digesters used to manage livestock waste. 

 

17 Because biogas destruction is not 100% efficient, some CH4 is released without combustion (EPA, 2009b). 

18 In concept, food waste and yard trimmings managed in an anaerobic digester can be treated similarly to livestock 

waste managed in an anaerobic digester. However, the focus of this section is on livestock waste. With additional 

data, biogenic emissions from food waste and yard trimmings could be calculated. Data needs include the total 

volatile content of food waste and yard trimmings (may vary within and across regions), the proportion of carbon in 

the volatile matter, and the maximum CH4 producing capacity of food waste and yard trimmings managed in an 

anaerobic digester. 
November 2014 N-41 

Here, the biogenic feedstock is biogas that is collected from an anaerobic digester. As described 

previously, biogas combustion, whether the biogas is flared or used as a fuel to generate energy, 

oxidizes the CH4 contained in the biogas to CO2. The destruction of CH4 results in a net reduction of 

GHG emissions relative to a scenario in which biogas produced through the anaerobic storage and 

treatment of livestock waste is not captured and combusted, but instead is released to the 

atmosphere as an indirect emission. 

Equation N.1, BAF = AVOIDEMIT, can be used to calculate a BAF value for anaerobic digestion of 

livestock waste. The AVOIDEMIT term is used to represent the net CO2e emissions reductions that 

are achieved through biogas capture and combustion. The AVOIDEMIT term accounts for net CO2e 

emissions reductions relative to the alternative emissions pathway of indirect CH4 and CO2

emissions (i.e., as a result of uncontrolled, anaerobic storage and treatment of livestock waste 

without biogas collection and combustion). 

In practice, as applied here, the AVOIDEMIT term is a ratio expressed as tCO2e avoided (i.e., the 

emissions, in CO2e, that would have occurred had the livestock waste been managed in a waste 

management system other than an anaerobic digester) per tCO2e emitted via combustion (i.e., the 

emissions, in CO2e, of the combusted biogas that was generated in an anaerobic digester, after 

accounting for both the combustion efficiency of the biogas destruction device and any losses of 

biogas from the anaerobic digester19). For the biogas feedstock collected from anaerobic digesters, 

the AVOIDEMIT term can be conceptually expressed as: 


 =

 − (-./00/120	341.	7/8-0519u	c605-	.626_-.-25	0v05-.	675-4265/8-	51	62	626-41:/9	w/_-05-4)

(-./00/120	341.	91.:;05/12	13	:/1_60	_-2-465-w	/2	62	626-41:/9	w/_-05-4) (EQ N.24)

4.1.1. Calculating the Numerator 

In computing AVOIDEMIT, the numerator (i.e., emissions from a livestock waste management 

system alternative to an anaerobic digester) can be calculated by assuming that if an anaerobic 

digester were not used to manage livestock waste, then this waste would have been managed under 

a different waste management option,20 such as an uncovered anaerobic lagoon. The CH4 that would 

have been generated under this alternative fate can be estimated using methods presented in IPCC 

(2006b) and EPA (2009b). Equation N.25 can be used to estimate the annual CO2 and CH4 emissions 

 

19 Biogas losses can occur from indirect CH4 emissions from an anaerobic digester could occur as a result of leaks 

from a digester cover or through venting during digester start-ups, shutdowns, and malfunctions. Biogas leaks may 

occur prior to delivery of the collected biogas to the combustion unit for CH4 destruction, leaks may occur as CH4

emissions from digester effluent, or as a result of remaining undigested volatile solids. 

20 There are multiple livestock waste management scenarios alternative to using an anaerobic digester. Of these 

alternatives, aerobic treatment would produce the least amount of CH4 (zero CH4 production) whereas an uncovered 

anaerobic lagoon would generate the most (see EPA 2009b, Table A-3). Depending on ambient temperature, CH4

production in an uncovered anaerobic lagoon ranges from 66% to 80% of the maximum amount of CH4 that could 

potentially be produced from the livestock waste. The appropriate alternative livestock waste management scenario 

should be used when this calculation is made. 
November 2014 N-42 

resulting from a livestock waste management strategy other than an anaerobic digester (e.g., had 

the waste been managed using an uncovered anaerobic lagoon). 

Total CO2e emissions from a livestock waste management other than anaerobic digestion = 

(avoided CO2 emissions) + (avoided CH4 emissions) (EQ. N.25) 

The avoided CO2 emissions from a livestock waste management alternate to anaerobic digestion is 

equal to the degradable carbon in the volatile solids of the livestock waste after removing the 

amount of carbon which becomes CH4 and then converting the remaining available carbon to CO2 as 

done using Equation N.26: 

Avoided CO2 emissions (metric tons CO2e/year) = 

[(Z+,

 × 12/44) – (x81/w-w+Q?/tsZ+Q? × 12/16)] × (44/12) (EQ. N.26) 

Where: 

PHyz = Potential maximum CO2 emissions if all degradable carbon is converted to

CO2 (metric tons CO2/year), see Equation N.34. 

(12/44) = molecular weight ratio of C to CO2 (converts potential CO2 emissions to 

carbon). 

AvoidedHIJ = avoided CH4 emissions, metric tons CO2e/year (see Equation N.33). 

GWPHIJ = 100-year GWP for CH4, 25 (IPCC, 2007). 

(12/16) = molecular weight ratio of C to CH4 (converts CH4 emissions to carbon). 

(44/12) = molecular weight ratio of CO2 to C (converts C less that associated with the 

CH4 emissions back to CO2 emissions). 

The most accurate data from which to estimate the total amount of carbon that can be degraded is 

measurement data on the biogas flow rate and methane concentration from an anaerobic digester 

that is already in use. If an anaerobic digester is not currently used, or if no biogas measurement 

data are available, then the amount of carbon that can be degraded will need to be estimated from 

animal population data. 

4.1.2. Methodology When Biogas Flow Rate and Methane Concentration Data Are 

Available 

For each anaerobic digester, the annual flow of CH4 sent to the biogas combustion device can be 

calculated using Equation N.27: 

+Q? = S × 	 +

TT%

× T. T?W × XT°R

Y

×

Z

	65.

×

T.?X?	

,TTT	

 (EQ. N.107) 

Where: 
November 2014 N-43 

CH4F = CH4 flow from the anaerobic digester to the biogas combustion device 

(metric tons CH4/year). 

V = Annual volumetric flow rate of biogas to the biogas destruction device 

(actual cubic feet biogas per year), as determined from daily monitoring.21

C = Average annual CH4 concentration of biogas (percent by volume, wet 

basis). 

0.0423 = Density of CH4 pounds per standard cubic foot (at 520oR or 15.56oC and 

1 atm). 

T = Average annual temperature (oR) at which flow is measured.23

P = Average annual pressure (atm) at which flow is measured.23

0.454/1,000 = conversion factor from pounds to metric tons. 

To account for the biogas collection efficiency, leaks from the anaerobic digester must be estimated 

(such leaks are indirect emissions to the atmosphere). Equation N.28 can be used to calculate the 

CH4 lost (metric tons per year) from an anaerobic digester: 

+Q? = 	 +Q? × (+])

+]

(EQ. N.28) 

Where: 

CH4L = amount of CH4 lost via leaks from the anaerobic digester, prior to 

combustion (metric tons CH4/year). 

CH4F = CH4 flow from the anaerobic digester to the biogas combustion device 

(Equation N.27). 

CE = collection efficiency22 of the anaerobic digester. 

For each anaerobic digester, the annual flow of CO2 in biogas that is sent with the CH4 to the biogas 

combustion device can be calculated using Equation N.29: 

+, = S × ( −

>?

TT%

−

l

TT%

) × T. CT × XT°R

Y

×

Z

	65.

×

T.?X?	.-54/9	512

,TTT	7:0 (EQ. N.119) 

 

21 If the pressure or temperature fluctuates significantly during the year, it would be more accurate to calculate the 

annual methane flow as the sum of monthly flow volumes, corrected to standard conditions by the monthly average 

temperature and pressure. 

22 Biogas collection efficiency is dependent upon the type of anaerobic digester and its cover. Biogas collection 

efficiency for a covered anaerobic lagoon depends on the cover type: collection efficiency for a bank to bank, 

impermeable cover is 0.975; collection efficiency for a modular, impermeable cover is 0.70. Biogas collection 

efficiency is 0.99 for a complete mix, fixed film, or plug flow digester that is an enclosed vessel (EPA 2009b, Table 

A-4; 40 CFR 98.363, Table JJ-6). Collection efficiency is the amount of biogas flow from the digester to the 

combustion device divided by the total amount of biogas generated. 
November 2014 N-44 

Where: 

CO2F = CO2 flow from the anaerobic digester to the biogas combustion 

device (metric tons CO2/year). 

V = Annual volumetric flow rate of biogas to the biogas destruction 

device (cubic feet biogas per year), as determined from daily 

monitoring.23

(1 – CHIJ

/100%-M/100%) = Average annual CO2 concentration of biogas (volume fraction, 

wet basis), where C = average annual CH4 concentration of 

biogas (volume percent, wet basis) and M = moisture content 

of biogas (volume percent, wet basis). 

0.1160 = Density of CO2 pounds per standard cubic foot (at 520oR or 

15.74oC and 1 atm). 

T = Annual average temperature (oR) at which flow is measured.25

P = Annual average pressure (atm) at which flow is measured.25

0.454 /1,000 = conversion factor from pounds to metric tons. 

Equation N.30 can be used to calculate the CO2 lost (metric tons per year) from each anaerobic 

digester: 

+, = 	 +, × (+])

+]

(EQ. N.30) 

Where: 

CO2L = amount of CO2 lost via leaks from the anaerobic digester, prior to combustion 

(metric tons CO2/year). 

CO2F = CO2 flow from the anaerobic digester to the biogas combustion device 

(Equation N.29). 

CE = collection efficiency of the anaerobic digester. 

Equation N.31 can be used to calculate the total CH4 generation from the anaerobic digester. 

Y1567	+Q?	t-2-465/12 = 	 +Q? + +Q? (EQ. N.31) 

Where: 

 

23If the pressure or temperature fluctuates significantly during the year, it would be more accurate to calculate the 

annual CO2 flow as the sum of monthly flow volumes, corrected to standard conditions by the monthly average 

temperature and pressure 
November 2014 N-45 

Total CH4 Generation = the quantity of methane generated from the anaerobic digester 

(metric tons CH4/year). 

CH4F = CH4 flow from the anaerobic digester to the biogas combustion 

device in metric tons CH4/year (Equation N.27). 

CH4L = amount of CH4 lost via leaks from the anaerobic digester, prior to 

combustion in metric tons CH4/year (Equation N.28). 

Equation N.32 can be used to calculate the total CO2 generation from the anaerobic digester. 

Y1567	+,	t-2-465/12 = 	 +, + +, (EQ. N.32) 

Where: 

Total CO2 Generation = the quantity of CO2 generated from the anaerobic digester (metric 

tons CO2/year). 

CO2F = CO2 flow from the anaerobic digester to the biogas combustion 

device in metric tons CO2/year (Equation N.29). 

CO2L = amount of CO2 lost via leaks from the anaerobic digester, prior to 

combustion in metric tons CO2/year (Equation N.30). 

The CH4-producing potential of a specific livestock waste management system is represented by a 

methane conversion factor (MCF). An anaerobic digester is expected to produce methane at near 

the maximum methane generation potential (i.e., at a MCF of 1). Most manure management systems 

will not produce the maximum amount of CH4 possible because the conditions in the systems are

not ideal for CH4 production. The value of this parameter ranges from 0% to 100%, reflecting the 

capability of a system to produce the maximum achievable CH4 (the higher the MCF, the greater the 

potential for CH4 production). For liquid systems (e.g., uncovered anaerobic lagoons), MCF values 

are temperature dependent; in order to assign the appropriate MCF for the type of liquid system 

used, the average ambient temperature at the system’s location must be known (see EPA, 2009b, 

Table A-3). 

The avoided CH4 emissions parameter in Equation N.25 can be estimated using Equation N.33 when 

CH4 generation data are available from an anaerobic digester: 

x81/w-w	+Q?	]./00/120 = 	 Y1567	+Q?	t-2-465/12 × l+slr × tsZ>? (EQ. N.123) 

Where: 

Avoided CH4 Emissions = the quantity of methane emitted, in CO2 equivalence, from the 

alternative waste management system (metric tons CO2e/year). 

Total CH4 Generation = the quantity of methane generated from the anaerobic digester 

(metric tons CH4/year). 
November 2014 N-46 

MCFWMS = CH4 conversion factor (proportion represented as a decimal) for 

the alternative-scenario, waste management system (see EPA, 

2009b, Table A-3). 

GWPCH4 = 100-year GWP of CH4, 25 (IPCC, 2007). 

The potential CO2 emissions can be calculated from the total CH4 and CO2 generation from the 

anaerobic digester using Equation N.34 as follows. 

Z15-25/67	+,	]./00/120 = (Y1567	+Q?	t-2-465/12 × ??/C) + Y1567	+,	t-2-465/12

 (EQ. N.134) 

Where: 

Potential CO2 emissions = maximum CO2 emissions if all degradable carbon is converted 

to CO2 (metric tons CO2/year). 

Total CH4 Generation = the quantity of methane generated from the anaerobic digester 

(metric tons CH4/year). 

Total CO2 Generation = the quantity of CO2 generated from the anaerobic digester 

(metric tons CO2/year). 

44/16 = molecular weight ratio of CO2 to CH4 emissions. 

Equation N.26 can then be used to calculate the avoided CO2 emissions and Equation N.25 can be 

used to calculate the total CO2e emissions from a livestock waste management other than anaerobic 

digestion. 

4.1.3. Calculating the Denominator 

The total amount of CH4 and CO2 emissions from an anaerobic digester, as represented in the 

denominator of the AVOIDEMIT term, is a calculation of the amount of CH4 sent to the biogas 

destruction device, minus the amount of CH4 destroyed during combustion, plus the amount of CH4 

leaked to the atmosphere (the latter accounts for CH4 collection efficiency). To convert that 

calculation to CO2e, it is multiplied by the GWP of CH4. To account for the CO2 emitted as a result of 

CH4 combustion, the amount of CH4 destroyed during combustion is added. To this is added the 

amount of CO2 in the biogas that flows to the biogas combustion device where it is then emitted to 

the atmosphere. The following Equation (N.35) can be used to calculate the total amount of CO2e 

emissions from an anaerobic digester: 

+,-	]./00/120x\ = >?(+Q? − +Q?\ + +Q?) + +Q?\ × ??/C + +, + +,	

(EQ. N.145)

Where: 

CO2e EmissionsAD = CO2e emissions from anaerobic digestion (metric tons/year). 
November 2014 N-47 

GWPHIJ

 = 100-year GWP of CH4, 25 (IPCC, 2007). 

CH4F = CH4 flow to the biogas combustion device (Equation N.27). 

CH4D = amount of CH4 destroyed via combustion (Equation N.36). 

CH4L = amount of CH4 lost via leaks prior to combustion (Equation N.28).

CO2F = CO2 flow to the biogas combustion device (Equation N.29). 

CO2L = amount of CO2 lost via leaks prior to combustion (Equation N.30).

44/16 = molecular weight ratio of CO2 to CH4. 

Equations for most of these terms have already been presented. Equation N.36 can be used to 

calculate the metric tons of CH4 destroyed (per year) in a biogas destruction device: 

+Q?\ = 	 +Q? × \] (EQ. N.156) 

Where: 

CH4D = CH4 destroyed at a biogas combustion device (metric tons CH4/year). 

CH4F = CH4 flow from the anaerobic digester to the biogas combustion device 

(Equation N.27). 

DE = CH4 destruction efficiency from flaring or combustion in an EGU. DE varies with 

the type of biogas destruction device used; it can be estimated as the lesser of 

the manufacturer’s specified destruction efficiency and 0.99 (EPA, 2013c). 

Section 4.2.1 provides an illustrative example calculation of the AVOIDEMIT term and its 

subsequent application in estimating a BAF for the management of livestock waste in an anaerobic 

digester when biogas measurement data are available. 

Several parameters are presented and used in the equations in the remainder of this section. Table 

N-8 presents the parameters used, default values, ranges presented in the literature, and 

references. 

Table N-8. Summary of Parameters Used When Calculating an Illustrative BAF for Livestock Waste 

Management through Anaerobic Digestion. 

Parameter 

Description Symbol Value Range Units Comments 

Reference 

(for value 

column) 

Concentration 

of CH4 in the 

biogas 

CHIJ

0.55 0.40 to 0.60 Fraction EPA, 2013c 

Density of CH4 – 0.662 – kg CH4/m3 At 532°R, or 

22.22°C, and 1 

atm 

EPA, 2009b 
November 2014 N-48 

Parameter 

Description Symbol Value Range Units Comments 

Reference 

(for value 

column) 

Density of CO2 – 0.1160 – Pounds 

per 

standard 

cubic foot 

At 520oR or 

15.74oC and 1 

atm 

Calculated 

value3 

Methane 

conversion 

factor for the 

specific waste 

management 

strategy 

MCFWMS 0.66 Depends on 

the type of 

system and 

temperature 

Percent Value 

presented is 

for an 

uncovered 

anaerobic 

lagoon in a 

cool climate 

below 10°C 

EPA, 2009b, 

Table A-3 

Typical animal 

mass, by animal 

type 

TAMAT 604 Numerous kg/head Determined 

using either 

default values 

or farmspecific data 

EPA, 2009b, 

Table A-2; 

IPCC, 2006, 

Table 10A4-

10A9 

Volatile solids 

excretion rate 

by animal type 

VSAT 9.34 Depends on 

the type of 

animal group 

kg 

VS/day/kg 

animal 

mass 

Value 

presented is 

used in the 

example 

calculations in 

Section 4.0.1 

EPA, 2009b, 

Table A-2; 

EPA, 2013c, 

Tables JJ-2 

and JJ-3 

Maximum CH4-

producing 

capacity for 

each animal 

type 

B0 0.24 0.17 to 0.78 m3 CH4 /kg 

volatile 

solids 

Value 

presented is 

for dairy cows

EPA, 2009b, 

Table A-2 

Destruction 

efficiency 

DE 0.99 0.90 to 0.9977 Fraction 0.99 is 

considered a 

default

EPA, 2011a; 

EPA, 2013c 

Collection 

efficiency 

CE 0.99 0.70 to 0.99 Decimal 

percent 

0.99 is for an 

enclosed 

vessel, plug 

flow digester

EPA, 2009b, 

Table A-4 

Fraction of 

volatile solids 

in livestock 

waste 

VolatileCarbon_AT 0.2979 0.20 to 0.40 kg volatile 

solids in 

total dried 

solids/kg 

of total 

dried 

solids, dry 

basis 

Value is 

determined 

from waste 

volatile solids 

analysis2

Sweeten et al., 

2002 

1 VSAT can be determined using either default values or farm-specific data. 
November 2014 N-49 

2 If only fuels proximate analysis is available, estimate the volatile solids as the sum of the volatile matter and fixed carbon 

from the fuels proximate analysis (see Figure N-3).

3 This value is calculated using a 60 degree Fahrenheit conversion: 44.01 * (2.20462/836.6) = 0.1160, where 44.01 = the 

molecular weight of CO2; 2.20462 is a unit conversion factor from kilograms to pounds; and 836.6 scf/kg-mol is the molar 

volume conversion factor.

4.1.4. Methodology When Biogas Flow Rate and Methane Concentration Data Are Not 

Available 

When biogas measurement data are not available, the CH4 and CO2 emissions must be estimated 

based on animal type and population data. Potential CO2 emissions can be solved using the 

following equation: 

Potential CO2 emissions = 

Σanimal type (TVSAT × VolatileCarbonAT × (44/12) × 365 × 1/1000) (EQ. N.167) 

Where: 

Σ animal type = If the alternate waste management system accepts waste from more 

than one animal type then this calculation must be computed for each 

animal type and then summed across animal types. 

TVSAT = Total volatile solids excreted by animal type (kg/day); see 

Equation N.38 to calculate TVSAT. 

VolatileCarbonAT = Fraction of degradable carbon in the volatile solids of the livestock 

waste (see Equation N.39). 

(44/12) = molecular weight ratio of CO2 to C. 

365 = number of days per year (i.e., 365 days/year). 

1/1,000 = conversion factor from kg to metric tons. 

Total volatile solids excreted by animal type (TVSAT) may be calculated using Equation N.38 and by 

referring to tables external to this appendix (Table A-2, EPA, 2009b and Tables JJ-2 and JJ-3, 40 CFR 

98.363): 

TVSAT = (PopulationAT × TAMAT × VSAT/1000) (EQ. N.178) 

Where: 

TVSAT = Total volatile solids excreted per animal type (kg/day). 

PopulationAT = Average annual animal population (head), by animal type.24

 

24 For static populations (e.g., dairy cows, breeding swine), average annual animal populations are estimated using 
November 2014 N-50 

TAMAT = Typical animal mass, by animal type; determined using either default 

values (see EPA, 2009b, Table A-2) or farm specific data (kg/head). 

VSAT = Volatile solids excretion rate by animal type, using either default values 

(see 40 CFR 98.363, Tables JJ-2 and JJ-3) or farm specific data (kg 

VS/day/kg animal mass). 

The fraction of degradable carbon in the volatile solids of the livestock waste (VolatileCarbonAT) can 

be estimated using results from proximate and ultimate analyses25 of the livestock waste specific to 

the waste of animal type being managed (Equation N.39). Data needed to estimate this parameter 

can be directly measured or, more simply, can be taken from the body of published scientific 

literature.26 However, it is important to understand the differences between the volatile solids 

measurement methods and the proximate fuel analysis methods. Figure N-3 compares the methods 

and nomenclature typically used for these different analytical methods. 

 

annual animal inventory or equivalent. For growing populations (e.g., meat animals such as beef and veal cattle), 

average annual animal populations are estimated using the average number of days each animal is kept at the facility 

and the number of animals produced annually (e.g., growing population = days onsite × (number of animals 

produced annually / 365)). 

25 Characteristics of a biogenic fuel can be described using proximate and ultimate analyses based on a sample’s 

complete combustion to CO2 and liquid water. The proximate analysis gives moisture content, volatile content, 

carbon remaining (fixed carbon), and mineral ash. The ultimate analysis gives the sample’s elemental composition 

as proportions of carbon, hydrogen, oxygen, nitrogen, and sulfur. Standardized test methods have been developed, 

for example, see Table 3 in Demirbas (2004). 

26 For example, ASAE Standard D384.2 (2005) is useful for estimating general characteristics of livestock and 

poultry manure. Li et al. (2008) and Henihan et al. (2003) present specific results of proximate and ultimate analyses 

of chicken litter characteristics; Sweeten et al. (2002 and 2003) present similar specific results but of cattle manure. 

It should be noted that Sweeten et al. (2002 and 2003) pertain to the composition of Texas feedlot beef cattle 

manure, values may not be suitable for calculating BAF values across all cattle types, regions, etc. 
November 2014 N-51 

Figure N-3. Comparison of Waste and Proximate Fuel Analyses (Adapted from ASTM, 2013).

The VolatileCarbonAT term represents the amount of carbon in the livestock waste solids that 

degrades during livestock waste management. Assuming there is negligible carbon remaining in the 

residue and that the fixed carbon is not readily biodegradable, VolatileCarbonAT term can be 

estimated as follows: 

VolatileCarbonAT = 

+64:12–/-w	+64:12	

S1765/7-	r17/w0 =

+64:12–/-w	+64:12	

S1765/7-	l655-4		/-w	+64:12 (EQ. N.189) 

Where: 

VolatileCarbonAT = fraction of the degradable carbon in the volatile solids of the livestock 

waste (kg degradable carbon in volatile solids/kg of volatile solids, dry 

basis).27 

Carbon = fraction of carbon in livestock waste (kg carbon in total dried solids/kg 

of total dried solids), dry basis (from ultimate analysis). 

Fixed Carbon = fraction of dry solids in livestock waste that does not volatilize when 

heated to 900 °C in nitrogen (kg fixed carbon in total dried solids/kg of 

total dried solids) but is lost when heated in air at 600 °C, dry basis 

(from fuels proximate analysis; see Figure N-3). 

 

27 If the mass of fixed carbon is not 100% carbon then the amount of carbon in the volatile matter may be 

underestimated, thus giving a low-biased estimate of the VolatileCarbonAT term (though the bias is likely small). 
November 2014 N-52 

Volatile Solids = fraction of volatile solids in livestock waste (kg volatile solids in total 

dried solids/kg of total dried solids), dry basis (from waste volatile 

solids analysis). If only fuels proximate analysis is available, estimate 

the volatile solids as the sum of the volatile matter and fixed carbon 

from the fuels proximate analysis (see Figure N-3). 

Volatile Matter = fraction of dry solids that does is lost when heated to 900 °C in 

nitrogen (kg volatile matter/kg of total dried solids), dry basis. 

The avoided CH4 emissions parameter in Equation N.25 can be populated using Equation N.40, 

which estimates the annual avoided CH4 emissions generated from a manure management strategy 

alternate to anaerobic digestion: 

Avoided CH4 emissions (metric tons CO2e/year) = 

Σanimal type (TVSAT × VSWMS × Days × B0 × MCFWMS × 0.662 × 1 /1000 × tsZ+Q?) (EQ. N.40)

Where: 

Σ animal type = If the alternate waste management system accepts waste from more than 

one animal type then this calculation must be computed for each animal 

type and then summed across animal types. 

TVSAT = Total volatile solids excreted by animal type (kg/day); the TVSAT equation 

is presented above (Equation N.38). 

VSWMS = Proportion of total manure for each animal type that is managed in each 

waste management system (assumed to be equivalent to the amount of 

volatile solids in each waste management system). 

Days = Number of days per year (i.e., 365 days/year). 

B0 = Maximum CH4-producing capacity for each animal type (m3 CH4/kg volatile 

solids; see EPA, 2009b, Table A-2). 

MCFWMS = CH4 conversion factor (proportion represented as a decimal) for the 

alternative-scenario, waste management system (see EPA, 2009b, Table A3). 

0.662 = density of CH4, kg CH4/m3 (at 532°R, or 22.22°C, and 1 atm). 

1/1000 = conversion factor from kg to metric tons. 

GWPHIJ = 100-year GWP of CH4, 25 (IPCC, 2007). 

The maximum amount of CH4 that could potentially be produced from livestock waste managed 

under ideal conditions is calculated by multiplying the total volatile solids by the maximum CH4-

producing capacity of the livestock waste (B0). The B0 values vary by animal type and diet (see EPA, 
November 2014 N-53 

2009b, Table A-2). Most manure management systems will not produce the maximum amount of 

CH4 possible because the conditions in the systems are not ideal for CH4 production. The CH4-

producing potential of a specific livestock waste management system is represented by a methane 

conversion factor (MCF). The value of this parameter ranges from 0% to 100% and reflects the 

capability of a system to produce the maximum achievable CH4 (the higher the MCF, the greater the 

potential for CH4 production). For liquid systems (e.g., uncovered anaerobic lagoons), MCF values 

are temperature dependent: in order to assign the appropriate MCF for the type of liquid system 

used, the average ambient temperature at the system’s location must be known (see EPA, 2009b, 

Table A-3). 

Summing the avoided CO2 emissions and the avoided CH4 emissions (Equation N.25, metric tons 

CO2e/year) is the final computation in estimating the numerator in the AVOIDEMIT term for a 

livestock waste management strategy alternative to an anaerobic digester. 

As before, the denominator of the AVOIDEMIT emission ratio term (i.e., the emissions from 

combustion of biogas generated in an anaerobic digester) is based on the flow, loss, and destruction 

terms presented previously (see Equation N.35). However, in the lack of direct biogas measurement 

data, these terms must be estimated based on the animal population equations just presented. 

As noted previously, the maximum amount of CH4 that could potentially be produced from livestock 

waste managed under ideal conditions is calculated by multiplying the total volatile solids by the 

maximum CH4-producing capacity of the livestock waste (B0). Thus, total CH4 generation can be 

estimated using Equation N.41, which is similar to Equation N.40 except that MCFWMS is assumed to 

equal 1 and the CH4 emissions are not converted to CO2 equivalence. 

Total CH4 generation (tons CH4/yr) = 

Σanimal type (TVSAT × VSWMS × Days × B0 × 0.662 × 1/1000) (EQ. N.41) 

Where: 

Σ animal type = If the alternate waste management system accepts waste from more than 

one animal type then this calculation must be computed for each animal 

type and then summed across animal types. 

TVSAT = Total volatile solids excreted by animal type (kg/day); the TVSAT equation 

is presented above (Equation N.38). 

VSWMS = Proportion of total manure for each animal type that is managed in each 

waste management system (assumed to be equivalent to the amount of 

volatile solids in each waste management system). 

Days = Number of days per year (i.e., 365 days/year). 

B0 = Maximum CH4-producing capacity for each animal type (m3 CH4/kg volatile 

solids; see EPA, 2009b, Table A-2). 

0.662 = density of CH4, kg CH4/m3 (at 532°R, or 22.22°C, and 1 atm). 
November 2014 N-54 

1/1000 = conversion factor from kg to metric tons. 

CH4 sent to the biogas destruction device can be calculated based on the collection efficiency of the 

anaerobic digester using Equation N.42: 

+Q? = 	Y1567	+Q?	t-2-465/12 × +] (EQ. N.42) 

Where: 

CH4F = CH4 flow from the anaerobic digester to the biogas combustion 

device (tons CH4/yr). 

Total CH4 generation = total quantity of CH4 generated in the anaerobic digester (tons 

CH4/yr; see Equation N.41). 

CE = collection efficiency28 of the anaerobic digester. 

The CH4 that is not collected and sent to the biogas destruction device can be calculated by 

rearranging Equation N.28: 

+Q? = 	Y1567	+Q?	t-2-465/12 − +Q? (EQ. N.193) 

Where: 

CH4L = amount of CH4 lost via leaks from the anaerobic digester, prior to 

combustion (metric tons CH4/year). 

Total CH4 generation = total quantity of CH4 generated in the anaerobic digester (tons 

CH4/yr; see Equation N.31) 

CH4F = CH4 flow from the anaerobic digester to the biogas combustion 

device (Equation N.42). 

Given the potential CO2 emissions from Equation 37 and re-arranging Equation N.34 yields the 

following equation for estimating the total CO2 generation from the anaerobic digester. 

Y1567	+,	t-2-465/12 = 	 Z15-25/67	+,	]./00/120 − (Y1567	+Q?	t-2-465/12 × ??/C) 

 (EQ. N.204) 

Where: 

 

28 Biogas collection efficiency is dependent upon the type of anaerobic digester and its cover. Biogas collection 

efficiency for a covered anaerobic lagoon depends on the cover type: collection efficiency for a bank to bank, 

impermeable cover is 0.975; collection efficiency for a modular, impermeable cover is 0.70. Biogas collection 

efficiency is 0.99 for a complete mix, fixed film, or plug flow digester that is an enclosed vessel (EPA 2009b, Table 

A-4; 40 CFR 98.363, Table JJ-6). Collection efficiency is the amount of biogas flow from the digester to the 

combustion device divided by the total amount of biogas generated. 
November 2014 N-55 

Total CO2 Generation = the quantity of CO2 generated from the anaerobic digester 

(metric tons CO2/year). 

Potential CO2 emissions = maximum CO2 emissions if all degradable carbon is converted to

CO2 (metric tons CO2/year from equation N.34). 

Total CH4 Generation = the quantity of methane generated from the anaerobic digester 

(metric tons CH4/year; Equation N.41). 

44/16 = molecular weight ratio of CO2 to CH4 emissions. 

Similar to the CH4 flow and loss terms, the CO2 flow and loss terms can be calculated based on the

collection efficiency of the anaerobic digester as follows: 

+, = 	Y1567	+,	t-2-465/12 × +] (EQ. N.215) 

+, = 	Y1567	+,	t-2-465/12 − +, (EQ. N.226) 

Where: 

CO2F = CO2 flow from the anaerobic digester to the biogas combustion 

device (tons CO2/yr). 

Total CO2 generation = total quantity of CO2 generated in the anaerobic digester (metric 

tons CO2 /year; see Equation N.44). 

CE = collection efficiency29 of the anaerobic digester. 

CO2L = amount of CO2 lost via leaks from the anaerobic digester, prior to 

combustion (metric tons CO2/year). 

Equation N.36, presented previously, can be used to calculate the metric tons of CH4 destroyed (per 

year) in a biogas destruction device. All of the parameters needed to determine the CO2e emissions 

from the anaerobic digester using Equation N.35 are then available. 

Section 4.2.2 provides an illustrative example calculation of the AVOIDEMIT term and its 

subsequent application in estimating a BAF for the management of livestock waste in an anaerobic 

digester prior to the availability of biogas measurement data 

 

29 Biogas collection efficiency is dependent upon the type of anaerobic digester and its cover. Biogas collection 

efficiency for a covered anaerobic lagoon depends on the cover type: collection efficiency for a bank to bank, 

impermeable cover is 0.975; collection efficiency for a modular, impermeable cover is 0.70. Biogas collection 

efficiency is 0.99 for a complete mix, fixed film, or plug flow digester that is an enclosed vessel (EPA 2009b, Table 

A-4; 40 CFR 98.363, Table JJ-6). Collection efficiency is the amount of biogas flow from the digester to the 

combustion device divided by the total amount of biogas generated. 
November 2014 N-56 

4.2. Illustrative AVOIDEMIT and BAF Calculations for Livestock Waste 

Management 

4.2.1. Illustrative Calculations when Anaerobic Digester Measurement Data Are 

Available 

When anaerobic digester flow and concentration data are available, these data provide a more 

accurate estimate of the degradable carbon quantities in the livestock wasted. Therefore, the 

potential CH4 and CO2 emissions from the alternate treatment pathway should be estimated from 

these measurement data rather than from animal population data. Again, this example is for a dairy 

farm in a cool climate (average ambient temperature below 10°C) and is comparing the alternate 

treatment of the livestock waste in an uncovered anaerobic lagoon to an anaerobic digester. 

In this hypothetical example, the daily average volumetric biogas flow rate from the anaerobic 

digester is 54,500 ft3 per day and the annual volumetric flow volume is 19,892,500 (e.g., 54,500 

ft3/day × 365 days/year). In this hypothetical example, the average annual CH4 concentration of 

biogas was measured to be 52.1% (wet basis). Based on daily monitoring, the annual average 

temperature of the biogas from the anaerobic digester was 77oF (537oR) at 1.005 atm, both of 

which were measured where the flow is measured. 

Step 1: Calculate the CH4 Emissions from the Anaerobic Digester 

The amount (metric tons/year) of CH4 sent from the anaerobic digester to the biogas combustion 

device, CH4F, is calculated as (Equation N.42): 

+Q? = S × 	

+>?

TT × T. T?W ×

XT

Y

×

Z

	65.

×

T. ?X?	

, TTT	

CH4F = 19,892,500 × 0.521 × 0.0423 × (520/537) × (1.005/1) × (0.454/1000) 

 = 193.6950 metric tons CH4/year. 

The next term to solve in calculating the denominator of the AVOIDEMIT term is CH4D, the amount 

of CH4 destroyed at a biogas combustion device (metric tons CH4/year). This can be calculated using 

Equation N.36: 

+Q?\ = 	 +Q? × \] 

The CH4 DE is estimated as the lesser of the manufacturer’s specified DE and 0.99 (EPA, 2013c). A 

DE value of 0.99 will be used for this example. Thus, the CH4 destroyed at biogas combustion device 

can be estimated as: 

CH4D = 193.6950 × 0.99 

 = 191.7581 MT CH4/year. 

The next term in the denominator of the AVOIDEMIT term, CH4L, accounts for the CE. To calculate 

CH4 leakage (metric tons CH4/year) from an anaerobic digester, Equation N.28 can be used: 
November 2014 N-57 

+Q? = 	 +Q? × (+])

+]

The previously computed value for CH4F can be used in this example. The CE is dependent upon the 

type of anaerobic digester and its cover (for default values, see EPA, 2009b, Table A-4; 40 CFR 

98.363, Table JJ-6). This hypothetical example is for an enclosed vessel, mixed plug flow digester 

where the CE is 0.99, such that: 

CH4L = 193.6950 × (1 – 0.99) / 0.99 

 = 1.9565 metric tons CH4/year. 

Step 2: Calculate the CO2 Emissions from the Anaerobic Digester 

The next parameter to solve for in the denominator of the AVOIDEMIT term is CO2F, the annual flow 

of CO2 in biogas sent (mixed with CH4) to the biogas combustion device. This can be calculated using 

Equation N.29: 

+, = S ×  − ` +>?

TT%a − ` lTT%a × T. CT ×

XT

Y

×

Z

	65.

×

T. ?X?	

, TTT

The values for V, C, T, and P are the same when solving for CO2F (Equation N.29) as for when 

solving for CH4F (Equation N.27). The only change is in the density of the gas, from CH4 (0.0423 

lbs/ft3) to that of CO2 (0.1160 lbs/ft3) and that Equation N.29 incorporates the fraction of biogas 

that is not CH4 or water vapor (i.e., 1 – CHIJ

/100%-M/100%). As most anaerobic digesters operate 

at temperature above 30°C (above 86°F), it can be assumed the cooled biogas (at the flow 

measurement point) is saturated with water (relative humidity of 100%). Using a psychometric 

chart, 77°F air holds approximately 20 grams water per kg dry air. Using the molecular weight of 

18 g/mol for water and 29 g/mol for air, the moisture content of the biogas is estimated to be 3.1% 

(i.e., (20/18)/[(1000/29)+(20/18)]). Using Equation N.29, CO2F can be estimated as: 

CO2F = 19,892,500 × (1 – 0.521-0.031) × 0.1160 × 520/537 × 1.005 × 0.454/1,000 

 = 459.1102 MT CO2/year 

The final parameter to solve for in the denominator of the AVOIDEMIT term is CO2L, the annual flow 

of CO2 in biogas lost from the digester. This can be calculated using Equation N.30, using the value of 

CO2F just calculated and the gas collection efficiency (0.99; same as used to determine CH4L), as 

follows: 

+, = 	 +, ×

( − +])

+]

CO2 = 459.1102 × (1 – 0.99) / 0.99 

 = 4.6375 MT CO2/year. 
November 2014 N-58 

Step 3: Calculate the CO2e Emissions from the Anaerobic Digester (Denominator) 

With estimated values for each of the terms in the denominator of the AVOIDEMIT term, the 

denominator can be solved using Equation N.35: 

+,-	]./00/120x\ = 	X(+Q? − +Q?\ + +Q?) + +Q?\ × ??/C + +, + +,

CO2e emissions from the anaerobic digester (metric tons /year) 

= 25 × (193.6950 – 191.7581 + 1.9565) + 191.7581 × 44/16 + 459.1102+4.6375 

= 1,088.4175 metric tons CO2e /year 

Step 4: Calculate the CO2e Emissions from the Alternate Fate (Numerator) 

Now that the terms for the denominator are determined, these values can be used to estimate the 

total CH4 and CO2 generation from the alternate treatment fate (uncovered lagoon) using 

Equations N.31 and N.32. 

Total CH4 generation (MT CH4/year) = CH4F + CH4L 

Total CH4 generation = 193.6950 + 1.9565 

 = 195.6515 

Total CO2 generation = CO2F + CO2L 

Total CO2 generation = 459.1102 + 4.6375 

 = 463.7477 

For an anaerobic digester, the CH4 conversion factor, MCF, is assumed to be 1; for the alternativescenario’s waste management system, the CH4 conversion factor is projected to be 0.66 (see EPA, 

2009b, Table A-3; for uncovered anaerobic lagoon in a cool climate below 10°C,30 MCFWMS = 0.66). 

Applying Equation N.33, the avoided CH4 emissions: 

Avoided CH4 emissions (metric tons/year) = Total CH4 generation × MCFWMS × GWPCH4

= 195.6515 × 0.66 × 25 

= 3,228.2498 MT CO2e per year. 

The potential CO2 emissions are calculated from the total CH4 and CO2 generation from the 

anaerobic digester as: 

Potential CO2 emissions = (Total CH4 generation × 44/16) + Total CO2 generation 

 

30 Table A-3 in EPA 2009b assigns CH4 conversion factors based on ambient temperature, thus accounting for the 

influence of climate on CH4 production. 
November 2014 N-59 

Potential CO2 emissions = (195.6515 × 44/16) +463.7477 

 = 1,001.7893 MT CO2 per year 

With estimates of both the potential CO2 emissions and the avoided CH4 emissions, the avoided CO2 

emissions resulting from a dairy manure management strategy other than an anaerobic digester 

can be calculated using Equation N.26 as follows. 

Avoided CO2 emissions = ((Potential CO2 emissions × 12/44) – (Avoided CH4

emissions/25 × 12/16)) × (44/12) 

= ((1,001.7893 × 12/44) – (3,228.2498/25 × 12/16)) × (44/12) 

= 646.6818 MT CO2 per year 

Summing the estimated, avoided CH4 and CO2 emissions (both in metric tons CO2e per year), that 

result from a dairy manure management strategy other than an anaerobic digester, the total 

avoided CO2e emissions can be estimated in units of metric tons CO2e per year, thus solving the 

numerator of the AVOIDEMIT term (Equation N.24): 

Total avoided CO2e emissions 

= (avoided CO2 emissions) + (avoided CH4 emissions) 

= 646.6818 + 3,228.2498 

= 3,874.9317 MT CO2e per year 

Step 5: Calculate the BAF Value 

With both the numerator and denominator of the AVOIDEMIT term having been computed, a BAF

value can be estimated using Equations N.1 and N.2:

BAF = AVOIDEMIT 

BAF = 1 – W,gh?.iWh		

,Tgg.?hX		

BAF = –2.56 

A negative BAF value calculated for this hypothetical scenario indicates that a biogas feedstock 

produced in an anaerobic digester from the treatment of dairy manure and flared by a stationary 

source results in net CO2e emissions reductions. 

4.2.2. Example Calculations for Livestock Waste Management Prior to Installation of 

an Anaerobic Digester (When Measurement Data are Not Available) 

Prior to the installation of an anaerobic digester, the only information available to determine the 

carbon content of the livestock waste and to project the methane generation potential of the 

anaerobic digester are the equations presented correlating the potential CO2 emissions and the 
November 2014 N-60 

avoided methane emissions to animal type and population. This example illustrates how to 

determine the assessment factor based only on the animal population data. 

Step 1: Calculate the CO2e Emissions from the Alternate Fate (Numerator) 

To calculate the numerator of the AVOIDEMIT term, the total volatile solids in the managed 

livestock waste must be estimated in order to calculate the avoided CO2 and CH4 emissions. 

Parameters in equation N.25 can be estimated using a hypothetical example of a dairy farm in a cool 

climate (average ambient temperature below 10°C) consisting of 500 dairy cows with a typical 

animal mass of 604 kg, and a volatile solids excretion rate of 9.34 kgVS/day/1,000 kg animal mass 

(see 40 CFR 98.363, Tables JJ-2 and JJ-3). Equation N.38 may be used to calculate total volatile 

solids excreted per animal type: 

TVSAT = (PopulationAT × TAMAT × VSAT/1,000) 

= 500 × 604 × 9.34 / 1,000 

= 2,820.68 kg/day 

With TVSAT estimated, the avoided CH4 emissions resulting from a dairy manure management

strategy other than an anaerobic digester can be calculated. In this hypothetical example, the 

alternative fate evaluated is management of the manure using an uncovered anaerobic lagoon. 

When calculating the avoided CH4 emissions associated with the alternative fate of this scenario’s 

dairy manure, several parameters are needed, including the maximum CH4-producing capacity for 

dairy cattle (see EPA, 2009b, Table A-2, for the appropriate default value; for dairy cows, B0 = 0.24 

m3 CH4/kg); and a CH4 conversion factor for the alternative-scenario’s waste management system 

(see EPA, 2009b, Table A-3; for uncovered anaerobic lagoon in a cool climate below 10°C,31 MCFWMS

= 0.66). Equation N.40 can be used to calculate the avoided CH4 emissions: 

Avoided CH4 emissions (metric tons/year) 

= (TVSAT × VSWMS × Days × B0 × MCFWMS × 0.662 × 1 /1,000 × 25) 

= (2,820.68 kg/day × 1 × 365 days/year × 0.24 m3 CH4/kg × 0.66 × 0.662 kg CH4/m3 × 

1 metric ton/1,000 kg × 25) 

= 2,698.9812 metric tons CO2e per year 

In order to estimate avoided CO2 emissions from a dairy manure management strategy other than 

an anaerobic digester, the proportion of the carbon in the volatile matter of the dairy manure 

(VolatileCarbonAT) must be calculated. In the VolatileCarbonAT term, the fixed carbon is removed 

from the total carbon in the dairy manure because the fixed carbon is assumed not to degrade. Data 

 

31 Table A-3 in EPA 2009b assigns CH4 conversion factors based on ambient temperature, thus accounting for the 

influence of climate on CH4 production. 
November 2014 N-61 

results from proximate and ultimate analyses of cattle manure (Sweeten et al., 2002)32 were used to 

populate parameter values in Equation N.39: 

VolatileCarbonAT = 

+64:12–/-w	+64:12	

S1765/7-	r17/w0

=

+64:12–/-w	+64:12	

S1765/7-	l655-4		/-w	+64:12

=

T.iXi	T.h	

T.XTT.h

 = 0.2979 

With TVSAT and VolatileCarbonAT estimated, the potential maximum CO2 emissions (Equation N.25) 

resulting from a dairy manure management strategy other than an anaerobic digester can then be 

estimated. In this scenario, the alternate fate is manure management using an open anaerobic 

lagoon. Because there is only one animal type (dairy cows), Equation N.37 only needs to be 

calculated once, as follows: 

Potential CO2 emissions = (TVSAT × VolatileCarbonAT × (44/12) × 365 × 1 /1000) 

 = 2,820.68 × 0.2979 × (44/12) × 365 × 1 /1,000 

= 1,124.5755 MT CO2 per year 

With estimates of both the potential CO2 emissions and the avoided CH4 emissions, the avoided CO2 

emissions resulting from a dairy manure management strategy other than an anaerobic digester 

can be calculated. For this calculation the total potential CO2 emissions from the decomposition of 

TVSAT must first be converted to carbon. From this the CH4 emissions, converted to carbon must be 

subtracted. The result is then converted back to CO2 (see Equation N.26). 

Avoided CO2 emissions = ((Potential CO2 emissions × 12/44) – (Avoided CH4 emissions/25 × 

12/16)) × (44/12) 

 = ((1,124.575 × 12/44) – (2,698.9812/25 × 12/16)) × (44/12) 

 = 827.6877 MT CO2 per year 

Summing the estimated, avoided CH4 and CO2 emissions (both in metric tons CO2e per year), that 

result from a dairy manure management strategy other than an anaerobic digester, the total 

avoided CO2e emissions can be estimated in units of metric tons CO2e per year, thus solving the 

numerator of the AVOIDEMIT term (Equation N.25): 

Total avoided CO2e emissions 

= (avoided CO2 emissions) + (avoided CH4 emissions) 

 

32 Data specific to Wisconsin dairy cattle would be preferred but in the absence of these data, data from Sweeten et 

al. (2002) were applied. 
November 2014 N-62 

= 827.6877 + 2,698.9812 

= 3,526.6689 MT CO2e per year 

Step 2: Calculate the CO2e Emissions from the Actual Fate (Denominator) 

In order to calculate the emissions from the anaerobic digester (i.e., denominator of the AVOIDEMIT

term), these same equations can be used to calculate the projected emissions from the total CH4 and 

CO2 generation. 

The total CH4 generation for the anaerobic digester is calculated using Equation N.41. 

Total CH4 generation (metric tons CH4/year) 

= (TVSAT × VSWMS × Days × B0 × 0.662 kg CH4/m3 × 1 metric ton/1,000 kg) 

= (2,820.68 kg/day × 1 × 365 days/year × 0.24 m3 CH4/kg × 0.662 kg CH4/m3 × 1 

metric ton/1,000 kg) 

= 163.5746 MT CH4/year. 

The potential CO2 emissions have already been calculated (1,124.5755 metric tons CO2/year). 

However, the methane produced will lower the CO2 emissions from the anaerobic digester. The 

total CO2 generation is calculated by subtracting the carbon associated the CH4 generation from the 

potential CO2 emissions using Equation N.44 as follows: 

Total CO2 generation (metric tons CO2/year) 

= ((Potential CO2 emissions) – (Total CH4 generation × 44/16)) 

 = ((1,124.5755 × 12/44) – (163.5746 × 12/16)) × (44/12) 

 = 674.7453 MT CO2 per year 

The actual flow and loss terms can be computed from the capture efficiency of the anaerobic 

digester using Equations N.42, N.43, N.45, and N.46. The collection efficiency is dependent upon the 

type of anaerobic digester and its cover (for default values, see EPA, 2009b, Table A-4; 40 CFR 

98.363, Table JJ-6). This hypothetical example is for an enclosed vessel, mixed plug flow digester 

where the collection efficiency is 0.99, such that:

CH4_F = Total CH4 generation × CE = 163.5746×0.99 = 161.9389 

CH4_L = Total CH4 generation − CH4_F = 163.5746 − 161.9389 = 1.6357 

CO2F = Total CO2 generation × CE = 674.7453×0.99 = 667.9978 

CO2L = Total CO2 generation − CO2F = 674.7453 − 667.9978 = 6.7475 
November 2014 N-63 

The next term to solve in calculating the denominator of the AVOIDEMIT term is CH4D, the amount 

of CH4 destroyed at a biogas combustion device (MT CH4/year). This can be calculated using 

Equation N.36: 

+Q?\ = 	 +Q? × \] 

CH4F was previously solved. The CH4 DE is estimated as the lesser of the manufacturer’s specified 

destruction efficiency and 0.99 (EPA, 2013c). A DE value of 0.99 will be used for this example. Thus, 

the CH4 destroyed at biogas combustion device can be estimated as: 

CH4D = 161.9389 × 0.99 

 = 160.3195 MT CH4/year. 

With estimated values for each of the terms in the denominator of the AVOIDEMIT term, the 

denominator can be solved using Equation N.35: 

+,-	]./00/120x\ = 	X(+Q? − +Q?\ + +Q?) + +Q?\ × ??/C + +, + +,

CO2e emissions from the anaerobic digester (MT /year) 

= 25 × (161.9389 – 160.3195 + 1.6357) + 160.3195 × 44/16 + 667.9978+6.7475 

= 1,197.0014 MT CO2e /year 

Step 3: Calculate the BAF Value 

With both the numerator and denominator of the AVOIDEMIT term having been computed, a BAF

value can be estimated using Equations N.1 and N.2:

BAF = AVOIDEMIT 

BAF = 1 – W,XC.CCgi	

,ih.TT?	

BAF = –1.95 

A negative BAF value calculated for this hypothetical scenario indicates that a biogas feedstock 

produced in an anaerobic digester from the treatment of dairy manure and flared by a stationary 

source results in net CO2e emissions reductions. 

4.3. Sensitivity Analysis for Anaerobic Digestion of Livestock and Food 

Waste 

For the livestock and food waste assessments, the parameter that has the greatest variability is the 

methane correction factor (MCF) for the waste management system employed as an alternative to 

anaerobic digestion. The biogas collection efficiency and the biogas destruction efficiency impact 

the BAF value, as does the global warming potential of CH4. The total biogas flow rate or the total 

volatile solids produced (if animal population correlations are used) does not impact the BAF value 

as they impact both the numerator and denominator by a constant factor. However, the relative 
November 2014 N-64 

ratio of CH4 produced versus CO2 produced does impact the BAF value. Table N-9 presents the 

results of the sensitivity analysis performed when using biogas measurement data to calculate BA. 

Table N-10 presents the results of the sensitivity analysis performed when using animal population 

data to calculate BAF. Sources for the parameter values used here can be found in Table N-8 of 

Section 4.1.3. 

Table N-9. Sensitivity Analysis of Anaerobic Digestion Using Biogas Measurement Data.1

Analysis Key Parameter 

Varied 

Key Parameter 

Value 

BAF Value Calculated at the Specified MCF Value 

MCF=0.05 MCF=0.3 MCF=0.5 MCF=0.8 

1 GWPHIJ21 −0.10 −0.90 −1.54 −2.50 

2 GWPHIJ25 −0.12 −1.08 −1.85 −3.00 

3 GWPHIJ28 −0.13 −1.21 −2.07 −3.37 

4 CHIJ40% −0.09 −0.88 −1.50 −2.44 

5 CHIJ50% −0.12 −1.08 −1.85 −3.00 

6 CHIJ60% −0.14 −1.27 −2.18 −3.55 

7 DE 0.99 −0.12 −1.08 −1.85 −3.00 

8 DE 0.95 0.03 −0.80 −1.47 −2.47 

9 CE 0.99 −0.12 −1.08 −1.85 −3.00 

10 CE 0.70 0.47 0.01 −0.35 −0.90 

1 The following central tendency values were used unless specified as the parameter varied. The moisture content was not 

varied as it has a limited range (1% to 5%) and did not significantly impact the calculated BAF. 

• GWPHIJ

= 25 

• CHIJ= 50% 

• M (moisture content) = 3% 

• DE = 0.99 

• CE = 0.99 

Note: References for the key parameters and values are presented in Table N-8 of Section 4.1.3. 

Table N-10. Sensitivity Analysis of Anaerobic Digestion Using Animal Population Data.1

Analysis Key Parameter 

Varied 

Key 

Parameter 

Value 

BAF Value Calculated at the Specified MCF Value 

MCF=0.05 MCF=0.3 MCF=0.5 MCF=0.8 

1 GWPHIJ21 −0.09 −0.87 −1.48 −2.41 

2 GWPHIJ25 −0.11 −1.04 −1.79 −2.90 

3 GWPHIJ28 −0.13 −1.17 −2.01 −3.26 

4 Bo 0.15 −0.06 −0.54 −0.93 −1.51 

5 Bo 0.30 −0.11 −1.04 −1.79 −2.90 

6 Bo 0.50 −0.18 −1.65 −2.84 −4.61 

7 VolatileCarbon_AT 0.20 −0.16 −1.51 −2.58 −4.20 

8 VolatileCarbon_AT 0.30 −0.11 −1.04 −1.79 −2.90 

9 VolatileCarbon_AT 0.40 −0.09 −0.80 −1.36 −2.22 

10 DE 0.99 −0.11 −1.04 −1.79 −2.90 

11 DE 0.95 0.03 −0.78 −1.43 −2.40 

12 CE 0.99 −0.11 −1.04 −1.79 −2.90 
November 2014 N-65 

Analysis Key Parameter 

Varied 

Key 

Parameter 

Value 

BAF Value Calculated at the Specified MCF Value 

MCF=0.05 MCF=0.3 MCF=0.5 MCF=0.8 

13 CE 0.70 0.46 0.01 −0.35 −0.89 

1 The following central tendency values were used unless specified as the parameter varied. 

• GWPHIJ= 25 

• Bo = 0.30 

• VolatileCarbon_AT = 0.30 

• DE = 0.99 

• CE = 0.99 

Note: References for the key parameters and values are presented in Table N-8 of Section 4.1.3. 

The following observations are noted. At the selected central tendency values, the two 

methodologies yield very similar results. If the ratio for CH4 generation to CO2 generation had been 

exactly the same for both methodologies, identical BAF values would be produced. When MCF 

increases, it directly increases the “Avoided CH4 emissions” and the BAF values go down (or become 

more negative). Increasing the global warming potential of methane (GWPCH4

), will increase the 

absolute value of the calculated BAF (i.e., if the BAF is negative, increasing GWPCH4 will make it 

more negative; if the BAF is positive, increasing GWPCH4will make BAF increase). When CH4

generation increases at a constant overall “potential CO2 emissions” rate (increasing CCH4

 or 

increasing Bo), the impact will be similar to increasing the global warming potential of methane 

(i.e., it will increase the absolute value of the calculated BAF). In the biogas measurement method, 

the CO2 generation is inversely related to the biogas methane concentration (CCH4) and is not really 

an independent variable. In the animal population method, the “potential CO2 emissions” is a 

function of the carbon content of the volatile solids (VolatileCarbon_AT) and can vary 

independently of the maximum methane generation (Bo). Increasing the VolatileCarbon_AT 

increases the CO2 emissions relative to CH4 emissions, so increasing VolatileCarbon_AT acts similar 

to decreasing CCH4

or Bo. If the fraction of methane emitted from anaerobic digestion, estimated as 

1 − DE×CE, exceeds the fraction of methane emitted from the alternative waste management 

system, estimated as MCF, then the BAF value will be positive. 

5. Livestock Waste Management through Direct Combustion or 

Thermochemical Processing and Associated GHG Emissions 

Pathways 

Direct combustion of livestock waste presents an alternative to management through anaerobic 

storage and treatment, or aerobic treatment, such as composting or field spreading as a soil 

amendment. Direct combustion of livestock waste is currently not a common management practice 

in the United States. Management applications typically involve combustion of poultry litter for 

electricity generation, space heating (e.g., of poultry houses), or combined heat and power (Kelleher 

et al., 2002; Santoianni et al., 2008).33 There are also emerging thermochemical conversion 

 

33 Poultry litter is a mixture of animal bedding materials (e.g., straw, wood chips, or corn husks), manure, and 

feathers (Santoianni et al., 2008). 
November 2014 N-66 

processes that can be used to convert and capture the energy in livestock waste via pyrolysis, 

gasification, co-firing, or direct liquefaction (Cantrell et al., 2008; Santoianni et al., 2008). 

Direct combustion or thermochemical conversion of livestock waste is not expected to result in a 

net increase in CO2e emissions relative to alternative GHG emissions pathways that could be used to 

manage the livestock waste.34 Combustion or thermochemical processing is expected to result in 

net GHG emissions reductions compared to GHG emissions pathways that involve anaerobic storage 

and treatment of livestock waste. In short, if the livestock waste were not combusted or processed 

at high temperatures at a stationary source, resulting in biogenic CO2 emissions, its alternate fate 

would have resulted in CH4 and/or CO2 emissions through anaerobic decay, aerobic decay, or both. 

Combustion can, however, introduce toxic metals into the environment. 

The biomass contained in livestock waste is the digestive byproducts of consumed plant and animal 

matter. This represents carbon originally contained in plant matter, often in the form of agricultural

crops, produced on a short-rotation basis.35 As a result, the biomass contained in livestock manure 

that is combusted (with resulting biogenic CO2 emissions) is typically derived from plant matter 

CO2 uptake during annual or short, multi-year growth and harvest cycles. 

Stationary source combustion or processing of livestock waste can result in the removal of 

atmospheric CO2. For example, ash produced from the combustion of livestock waste can be used as 

an agricultural fertilizer, and pyrolysis can be used to produce biochar—a process that stabilizes 

carbon and can result in long-term carbon storage (Cantrell et al., 2008; Santoianni et al., 2008). 

5.1. Method for Calculating an Illustrative BAF Value Applied to Biogenic 

Emissions Resulting from Combustion of Livestock Waste 

The assessment factor equation can be applied to point source biogenic CO2 emissions from a 

stationary source combusting livestock waste. This section provides an illustrative method for 

calculating a BAF value that is applied to point source biogenic CO2 emissions from a stationary 

source combusting livestock waste. 

Here the biogenic feedstock is livestock waste, in a form suitable for combustion.36 In applying the 

assessment factor equation to this feedstock, the avoided GHG emissions reductions that would 

have occurred in the absence of combustion of livestock waste at a stationary source are accounted 

for in the AVOIDEMIT term of Equation N.1 (BAF = AVOIDEMIT). The AVOIDEMIT term represents 

the net GHG emissions reductions that are achieved through combustion of livestock waste, as 

compared to the emissions pathway from an alternate fate (e.g., treatment via field spreading or in 

an uncovered anaerobic lagoon). Similar to the other waste-derived biogenic feedstocks, the 

alternative GHG emissions pathway is accounted for in the numerator of the AVOIDEMIT term, 

 

34 In the case of thermochemical processing, this does not include fossil fuel energy inputs used to generate process 

heat. 

35 This would apply to both plant- and animal-based livestock feeds. 

36 Combustion of biomass with high moisture content can be problematic; pre-drying of livestock waste may be 

required. Some operations have addressed this problem by mixing livestock waste with woody materials (e.g., saw 

dust) (Santoianni et al., 2008). 
November 2014 N-67 

whereas the denominator accounts for the GHG emissions resulting from the actual waste 

management strategy used. 

In practice, as applied here, the AVOIDEMIT term contains a ratio of the emissions, in CO2e, of the 

alternative livestock waste management process (had that feedstock not been combusted) to the 

emissions, in tCO2e, from the combustion of the livestock waste, after accounting for the 

combustion efficiency of the manure combustor. For the feedstock of livestock waste suitable for 

combustion, the AVOIDEMIT term can be conceptually expressed by the simplified ratio of: 

AVOIDEMIT = 1- (-./00/120	341.	54-65.-25	675-4265/8-	51	91.:;05/12)

(-./00/120	341.	54-65.-25	:v	91.:;05/12) (EQ N.47)

5.1.1. Calculating the Numerator 

In computing AVOIDEMIT, the numerator (i.e., emissions from treatment alternative to combustion) 

can be calculated by assuming that if livestock waste were not managed using combustion, then this 

waste would have been managed under one or more different waste management systems. For 

example, the alternative pathway may be associated with waste storage followed by an aerobic land 

application or it could be anaerobic stored and treated in an uncovered lagoon.37 The GHGs that 

would have been generated under these alternative fates can be estimated using methods 

presented in IPCC (2006b) and EPA (2009b). To estimate the annual CO2 and CH4 emissions 

resulting from a livestock waste management strategy other than combustion, the numerator of the 

AVOIDEMIT term can be estimated using Equation N.48. 

Total CO2e emissions from a livestock waste management alternate to combustion = 

(avoided CO2 emissions) + (avoided CH4 emissions) (EQ. N.48) 

The avoided CO2 emissions from a livestock waste management alternate to combustion is equal to 

the available carbon in the volatile solids of the livestock waste after removing the amount of 

carbon which becomes CH4 and then converting the remaining available carbon to CO2. This 

calculation (Equation N.48) is the same as Equation N.25 which was previously used in the 

calculation of emissions from anaerobic digesters for livestock waste management: 

Avoided CO2 emissions (metric tons CO2e/year) = 

[(PCO2 × 12/44) – (Avoided CH4 emissions/tsZ+Q? × 12/16)] × (44/12) (EQ. N.239)

Where: 

PCO2 = Potential maximum CO2 emissions, see Equation N.50. 

 

37 There are multiple livestock waste management scenarios alternative to combustion of livestock waste. An 

uncovered anaerobic lagoon would generate the most (see EPA, 2009b, Table A-3). Depending on ambient 

temperature, CH4 production in an uncovered anaerobic lagoon ranges from 66% to 80% of the maximum amount of 

CH4 that could potentially be produced from the livestock waste. The appropriate alternative livestock waste 

management scenario should be used when this calculation is made. 
November 2014 N-68 

(12/44) = molecular weight ratio of C to CO2 (converts potential CO2

emissions to carbon). 

Avoided CH4 emissions = avoided CH4 emissions, metric tons CO2e/year (see 

Equation N.53, below). 

GWPCH4 = 100-year GWP for CH4. 

(12/16) = molecular weight ratio of C to CH4 (converts CH4 emissions to 

carbon). 

(44/12) = molecular weight ratio of CO2 to C (converts C less that 

associated with the CH4 emissions back to CO2 emissions). 

Potential CO2 emissions can be solved using Equation N.50, which was also used in estimating the 

emissions associated with livestock waste management via an anaerobic digester: 

Potential CO2 emissions = 

Σanimal type (TVSAT × VolatileCarbonAT × (44/12) × 365 × 1/1,000) (EQ. N.50) 

Where: 

Σ animal type = If the alternate waste management system accepts waste from more 

than one animal type then this calculation must be computed for each 

animal type and then summed across animal types. 

TVSAT = Total volatile solids excreted by animal type (kg/day); the TVSAT

equation is presented below (Equation N.51). 

VolatileCarbonAT = Fraction of degradable carbon in the volatile solids of the livestock 

waste (see Equation N.52). 

44/12 = molecular weight ratio of CO2 to C. 

365 = number of days per year (i.e., 365 days/year). 

1/1,000 = conversion factor from kg to metric tons.

Total volatile solids excreted by animal type (TVSAT) may be calculated using the following equation 

(previously presented under livestock waste management using anaerobic digester) and referring 

to tables external to this appendix (Table A-2, EPA, 2009b and Tables JJ-2 and JJ-3, 40 CFR 98.363): 

TVSAT = (PopulationAT × TAMAT × VSAT/1,000) (EQ. N.51) 

Where: 

TVSAT = Total volatile solids excreted per animal type (kg/day). 
November 2014 N-69 

PopulationAT = Average annual animal population (head), by animal type.38

TAMAT = Typical animal mass, by animal type; determined using either default 

values (see EPA, 2009b, Table A-2) or farm specific data (kg/head). 

VSAT = Volatile solids excretion rate by animal type, using either default values 

(see 40 CFR 98.363, Tables JJ-2 and JJ-3) or farm specific data (kg 

VS/day/kg animal mass). 

The fraction of degradable carbon in the volatile solids of the livestock waste (VolatileCarbonAT) can 

be estimated using results from proximate and ultimate analyses39 of the livestock waste specific to 

the waste of animal type being managed (see Equation N.52). Data needed to estimate this 

parameter can be directly measured or, more simply, can be taken from the body of published 

scientific literature.40

VolatileCarbonAT = 

+64:12–/-w	+64:12	

S1765/7-	r17/w0

=

+64:12–/-w	+64:12	

S1765/7-	l655-4		/-w	+64:12

(EQ. N.52) 

Where: 

VolatileCarbonAT = Fraction of the degradable carbon in the volatile solids of the livestock 

waste (kg degradable carbon in volatile solids/kg of volatile solids, dry 

basis).41

Carbon = Fraction of carbon in livestock waste (kg carbon in total dried 

solids/kg of total dried solids), dry basis (from ultimate analysis).

Fixed Carbon = Fraction of dry solids in livestock waste that does not volatilize when 

heated to 900 °C in nitrogen (kg fixed carbon in total dried solids/kg of 

total dried solids) but is lost when heated in air at 600 °C, dry basis 

(from fuels proximate analysis; see Figure N-3). 

 

38 For static populations (e.g., dairy cows, breeding swine), average annual animal populations are estimated using 

annual animal inventory or equivalent. For growing populations (e.g., meat animals such as beef and veal cattle), 

average annual animal populations are estimated using the average number of days each animal is kept at the facility 

and the number of animals produced annually (e.g., growing population = days onsite × (number of animals 

produced annually / 365)). 

39 Characteristics of a biogenic feedstock can be described using proximate and ultimate analyses based on a 

sample’s complete combustion to CO2 and liquid water. The proximate analysis gives moisture content, volatile 

content, carbon remaining (fixed carbon), and mineral ash. The ultimate analysis gives the sample’s elemental 

composition as proportions of carbon, hydrogen, oxygen, nitrogen, and sulfur. Standardized test methods have been 

developed, for example, see Table 3 in Demirbas (2004). 

40 For example, ASAE Standard D384.2 (2005) is useful for estimating general characteristics of livestock and 

poultry manure. Li et al. (2008) and Henihan et al. (2003) present specific results of proximate and ultimate analyses 

of chicken litter characteristics; Sweeten et al. (2002 and 2003) present similar specific results but of cattle manure. 

41 If the mass of fixed carbon is not 100% carbon then the amount of carbon in the volatile solids may be 

underestimated, thus giving a low-biased estimate of the VolatileCarbonAT term (though the bias is likely small). 
November 2014 N-70 

Volatile Solids = Fraction of volatile solids in livestock waste (kg volatile solids in total 

dried solids/kg of total dried solids), dry basis (from waste volatile 

solids analysis). If only fuels proximate analysis is available, estimate 

the volatile solids as the sum of the volatile matter and fixed carbon 

from the fuels proximate analysis (see Figure N-3). 

Volatile Matter = fraction of dry solids that does is lost when heated to 900 °C in 

nitrogen (kg volatile matter/kg of total dried solids), dry basis. 

Equation N.53 can be used to estimate the annual avoided CH4 emissions generated from a manure 

management strategy alternate to combustion: 

Avoided CH4 emissions (metric tons CO2e/year) = 

Σanimal type (TVSAT × VSWMS × Days × B0 × MCFWMS × 0.662 × 1/1,000 × tsZ+Q?) (EQ. N.53) 

Where: 

Σanimal type = If the alternate waste management system accepts waste from more than 

one animal type then this calculation must be computed for each animal 

type and then summed across animal types. 

TVSAT = Total volatile solids excreted by animal type (kg/day); (Equation N.51). 

VSWMS = Proportion of total manure for each animal type that is managed in each 

waste management system (assumed to be equivalent to the amount of 

volatile solids in each waste management system). 

Days = Number of days per year (i.e., 365 days/year). 

B0 = Maximum CH4-producing capacity for each animal type (m3 CH4/kg volatile 

solids; see EPA, 2009b, Table A-2). 

MCFWMS = CH4 conversion factor (proportion represented as a decimal value) for the 

alternative-scenario, waste management system (see EPA, 2009b, Table 

A-3). 

0.662 = density of CH4, kg CH4 / m3 (at 531.67°R, or 22.22°C, and 1 atm). 

1/1000 = conversion factor from kg to metric tons. 

GWPCH4= 100-year GWP of CH4, 25 (IPCC, 1996). 

The maximum amount of CH4 that could potentially be produced from livestock waste managed 

under ideal conditions is calculated by multiplying the total volatile solids by the maximum CH4-

producing capacity of the livestock waste (B0). The B0 values vary by animal type and diet (see EPA, 

2009b, Table A-2). Most manure management systems will not produce the maximum amount of 

CH4 possible because the conditions in the systems are not ideal for CH4 production. The CH4-
November 2014 N-71 

producing potential of a specific livestock waste management system is represented by a methane 

conversion factor (MCF). The value of this parameter ranges from 0% to 100% and reflects the 

capability of a system to produce the maximum achievable CH4 (the higher the MCF, the greater the 

potential for CH4 production). For liquid systems (e.g., uncovered anaerobic lagoons), MCF values 

are temperature dependent: in order to assign the appropriate MCF for the type of liquid system 

used, the average ambient temperature at the system’s location must be known (see EPA, 2009b, 

Table A-3). 

Summing the avoided CO2 emissions and the avoided CH4 emissions (Equation N.48, metric tons 

CO2e/year) is the final computation in estimating the numerator in the AVOIDEMIT term for a 

livestock waste management strategy alternative to combustion. See Section 5.2.2 for two 

illustrative example calculations of the numerator in the AVOIDEMIT term and its subsequent 

application in estimating a BAF. 

5.1.2. Calculating the Denominator 

In the derivation of AVOIDEMIT, the denominator (emissions from livestock waste treatment by 

combustion) is based on the carbon content of the point source, stack emissions from the waste 

combustion unit. The value of the denominator is equal to the CO2e of the combusted livestock 

waste, adjusted by the combustion efficiency of the incinerator.42 This adjustment is to account for 

the proportion of feedstock that is neither combusted nor emitted to the atmosphere as a pointsource emission. Combustion of livestock waste does not create or emit CH4; the only GHG 

associated with this process is CO2. The principal products of livestock waste combustion include 

CO2, carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), sulfur oxides (SOx), 

inorganic bottom ash, and fly ash (Antares Group Inc. et al., 1999). Carbon monoxide and HC are 

important indicators of incomplete combustion; with complete combustion, CO2 is the primary 

carbon-based emission (Antares Group Inc. et al., 1999). 

Total CO2e emissions from combustion of livestock waste can be computed using the following 

equation: 

CO2 emissions from incineration of livestock waste (MT CO2e/year) = 

Σanimal type (TVSAT × TotalCarbonAT × DE × (44/12) × 365 ×1/1,000) (EQ. N.244) 

Where: 

TVSAT = total volatile solids excreted per animal type (kg/day), see 

Equation N.51. 

 

42 Combustion efficiency of livestock waste varies with the type of boiler used, moisture content, and particle size of 

the feedstock. In an efficient combustor, very little carbon in poultry litter is left unburned (Antares Group Inc. et al. 

1999). One published value of combustion efficiency for combustion of broiler litter, based on the carbon content in 

the ash is 96% (Costello, 2007). 
November 2014 N-72 

TotalCarbonAT = fraction of the carbon in the volatile solids of the livestock waste, see 

Equation N.55. 

DE = livestock waste destruction efficiency (i.e., combustion efficiency of 

incinerator). 

44/12 = molecular weight ratio of CO2 to C. 

365 = number of days per year (i.e., 365 days/year). 

1/1,000 = conversion factor from kg to metric tons. 

The fraction of total carbon in the volatile solids of the livestock waste (TotalCarbonAT) can be 

estimated using results from proximate and ultimate analyses43 of the livestock waste specific to 

the waste of animal type being managed. It is again assumed that there is negligible carbon in the 

residue, but the fixed carbon is expected to oxidize during the manure combustion process. Thus, it 

is assumed that all of the combustible carbon exists in the volatile solids fraction of the dried solids. 

Data needed to estimate this parameter can be directly measured or, more simply, can be taken 

from the body of published scientific literature.44

TotalCarbonAT = 

+64:12	

S1765/7-	r17/w0 =

+64:12	

S1765/7-	l655-4		/-w	+64:12 (EQ. N.255) 

Where: 

TotalCarbonAT = fraction of carbon in the volatile solids of the livestock waste, (kg carbon 

in volatile solids/kg of volatile solids, dry basis). 

Carbon = fraction of carbon in livestock waste (kg carbon in total dried solids/kg 

of total dried solids), dry basis (from ultimate analysis).

Volatile Solids = fraction of volatile solids in livestock waste (kg volatile solids in total 

dried solids/kg of total dried solids), dry basis (from waste volatile 

solids analysis). If only fuels proximate analysis is available, estimate the 

volatile solids as the sum of the volatile matter and fixed carbon from the 

fuels proximate analysis (see Figure N-3). 

 

43 Characteristics of a biogenic feedstock can be described using proximate and ultimate analyses based on a 

sample’s complete combustion to CO2 and liquid water. The proximate analysis gives moisture content, volatile 

content, carbon remaining (fixed carbon), and mineral ash. The ultimate analysis gives the sample’s elemental 

composition as proportions of carbon, hydrogen, oxygen, nitrogen, and sulfur. Standardized test methods have been 

developed, for example, see Table 3 in Demirbas (2004). 

44 For example, ASAE Standard D384.2 (2005) is useful for estimating general characteristics of livestock and 

poultry manure. Li et al. (2008) and Henihan et al. (2003) present specific results of proximate and ultimate analyses 

of chicken litter characteristics; Sweeten et al. (2002 and 2003) present similar specific results but of cattle manure.
November 2014 N-73 

Volatile Matter = fraction of dry solids that does is lost when heated to 900 °C in nitrogen 

(kg volatile matter/kg of total dried solids), dry basis (from fuels 

proximate analysis; see Figure N-3) 

Fixed Carbon = fraction of dry solids in livestock waste that does not volatilize when 

heated to 900 °C in nitrogen (kg fixed carbon in total dried solids/kg of 

total dried solids) but is lost when heated in air at 600 °C, dry basis 

(from fuels proximate analysis; see Figure N-3). 

After solving for the numerator and the denominator of the AVOIDEMIT term, the BAF can be 

calculated using Equation N.1. See Section 5.2.2 for two illustrative example calculations of the 

numerator and denominator in the AVOIDEMIT term and its subsequent application in estimating a 

BAF for livestock waste management by way of direct combustion. 

Several parameters are presented and used in the equations in the remainder of this section. Table 

N-11 presents the parameters used, typical or default values, ranges presented in the literature, and 

references. 

Table N-11. Summary of Parameters Used When Calculating an Illustrative BAF for Livestock 

Waste Management through Combustion. 

Parameter 

Description Symbol Value Range Units Comments 

Reference 

(for value 

column) 

Typical 

animal mass, 

by animal 

type 

TAMAT 604 Numerous kg/head Determined 

using either 

default values 

or farm-specific 

data 

EPA, 2009b, 

Table A-2; 

IPCC, 2006, 

Table 10A4-

10A9 

Volatile solids 

excretion rate 

by animal 

type 

VSAT 9.34 Depends 

on the 

type of 

animal 

group 

kg VS/day/kg 

animal mass 

Value 

presented is 

used in the 

example 

calculations in 

Section 4.0.1 

EPA, 2009b, 

Table A-2; EPA, 

2013c, Tables 

JJ-2 and JJ-3 

Maximum 

CH4-

producing 

capacity for 

each animal 

type 

B0 0.24 0.17 to 

0.78 

m3 CH4 /kg 

volatile solids 

Value 

presented is for 

dairy cows 

EPA, 2009b, 

Table A-2 

Density of CH4 -- 0.662 -- kg CH4/m3 At 532°R, or 

22.22°C, and 1 

atm 

EPA, 2009b 

Destruction 

efficiency 

DE 0.96 0.90 to 

0.9977 

decimal 

percent 

 EPA, 2009b, 

Table A-4 
November 2014 N-74 

Parameter 

Description Symbol Value Range Units Comments 

Reference 

(for value 

column) 

Fraction of 

volatile solids 

in livestock 

waste 

Volatile 

Carbon_AT 

 0.20 to 

0.40 

kg volatile 

solids in total 

dried 

solids/kg of 

total dried 

solids, dry 

basis 

Value is 

determined 

from waste 

volatile solids 

analysis2

Sweeten et al., 

2002 

1 VSAT can be determined using either default values or farm-specific data. 

2 If only fuels proximate analysis is available, estimate the volatile solids as the sum of the volatile matter and fixed carbon 

from the fuels proximate analysis (see Figure N-3).

5.2. Example AVOIDEMIT and BAF Calculations for Direct Combustion of 

Livestock Waste 

Two example scenarios of alternative management for poultry litter are presented here. Both 

examples are set in northern Georgia and consist of 400,000 broilers (chickens).45 In the first 

example, the alternative management strategy is to store the chicken litter as a solid prior to its 

application as a soil amendment; the chicken litter would be stored for approximately 1 year prior 

to its land application (EPA, 2001).46 In the second example, the alternative management strategy, 

although not as commonly used, is to store and manage the chicken litter from broilers in an 

uncovered anaerobic lagoon.47 Several of the calculated parameter values can be used in both 

scenarios (i.e., TVSAT, VolatileCarbonAT, and the potential maximum CO2 emissions). 

5.2.1. Example Calculation for Direct Combustion and Land Application of Livestock 

Waste 

Step 1: Calculating the Avoided CH4 from the Alternate Treatment 

To calculate the numerator of the AVOIDEMIT term, the total volatile solids must be estimated in 

order to calculate the avoided CH4 emissions. Parameters in Equation N.48 can be estimated using a 

hypothetical example of an operation set in northern Georgia, consisting of 400,000 broilers per 

year, with a typical animal mass of 0.9 kg, and a volatile solids excretion rate of 15 kg VS/day/1000 

kg animal mass (see 40 CFR 98.363, Table JJ-2). Equation N.51 may be used to calculate total 

volatile solids excreted per animal type: 

 

45 Regional differences in ambient temperature affect the value of the CH4 conversion factor (MCFWMS) used to 

calculate avoided CH4 emissions. Therefore, the geographic location of the manure management system has an 

effect on the amount of generated emissions and the value of the BAF. However, the number of animals (e.g., 

broilers) whose waste is managed does not have an effect on the value of the BAF. 

46 Large quantities of poultry litter are removed from the poultry house during annual clean-out. If possible, the 

annual clean-out typically is timed to coincide with the time land is available for land application (EPA, 2001). 

47 Although chicken litter from broilers can be managed in anaerobic lagoons, it is more common to use this 

management strategy for pullets. 
November 2014 N-75 

TVSAT = (PopulationAT × TAMAT × VSAT/1,000) 

= 400,000 × 0.9 kg × 15 kgVS/day/kg animal mass/1,000 

= 5,400 kg/day 

With TVSAT estimated, the avoided CH4 emissions resulting from a poultry litter management 

strategy other than an anaerobic digester can be calculated. In this hypothetical example set in a 

temperate region (e.g., northern Georgia) with an average temperature of 16oC, the alternative fate 

could have been to store the chicken litter as a solid prior to its application as a soil amendment; 

the chicken litter would be stored for approximately 1 year prior to its land application (EPA, 

2001). 

In this first hypothetical scenario, the only litter-producing animal type is broilers, and the only 

alternate waste management system of the poultry production with litter is solid storage prior to 

land application. When calculating the avoided CH4 emissions associated with the alternative fate of 

chicken litter under this scenario, several parameters are needed, including the maximum CH4-

producing capacity for broilers (see EPA, 2009b, Table A-2, for the appropriate default value; for 

broilers, B0 = 0.36 m3 CH4/kg); and a CH4 conversion factor for the alternative-scenario’s waste 

management system (see EPA, 2009b, Table A-3; for solid storage in a temperate climate, MCFWMS = 

0.04). Equation N.53 can be used to calculate the avoided CH4 emissions: 

Avoided CH4 emissions (metric tons CO2e per year) 

= 25 × (TVSAT × VSWMS × 365 days/year × B0 × MCFWMS × 0.662 kg CH4/m3 × 1 metric 

ton/1,000 kg) 

= 25 × (5,400 × 1 × 365 × 0.36 m3 CH4/kg × 0.04 × 0.662 × 1/1,000) 

= 469.7287 MT CO2e per year. 

Step 2: Calculating the Avoided CO2 from the Alternate Treatment 

To estimate the avoided CO2 emissions from a poultry litter management strategy other than 

combustion, the fraction of degradable carbon in the volatile solids of the chicken litter must be 

calculated. For the scenarios presented here (Section 5.2), data (results from proximate and 

ultimate analyses of poultry litter) from Li et al. (2008) can be used to populate parameters in 

Equation N.48. Because Li et al. (2008) presented results of the proximate analysis on a wet basis, 

those parameters must be converted to a dry basis by dividing each of them by the proportion of 

the dry content of the chicken litter (i.e., divide the fixed carbon and the volatile solids each by (1–

moisture content)). In the VolatileCarbonAT term, the fixed carbon is removed from the total carbon 

in the poultry litter because the fixed carbon is assumed not to degrade. Using these data, 

Equation N.52 can be parameterized as follows: 

VolatileCarbonAT = 

+64:12–/-w	+64:12		

S1765/7-	r17/w0

=

+64:12–/-w	+64:12	

S1765/7-	l655-4		/-w	+64:12
November 2014 N-76 

=

T.g	T.TCgg	

T.CXCT.TCgg

= 0.2959 

With TVSAT and VolatileCarbonAT estimated, the potential maximum CO2 emissions (Equation N.50) 

resulting from a chicken litter management strategy alternative to combustion can then be 

estimated. In this scenario, the alternate fate is solid manure storage for approximately 1 year 

before it is ultimately used as a land application. Because waste management is limited to litter 

from only one animal type (broilers), Equation N.50 only needs to be calculated once, as follows: 

Potential CO2 emissions 

= (TVSAT × VolatileCarbonAT × (44/12) × 365 days/year × 1 metric ton/1,000 kg)

 = 5,400 × 0.2959 × (44/12) × 365 × 1/1,000 

= 2,138.4693 MT CO2 per year 

With estimates of both the potential CO2 emissions and the avoided CH4 emissions, the avoided CO2 

emissions resulting from an aerobic poultry litter management strategy can be calculated. For this 

calculation the total potential CO2 emissions from the decomposition of TVSAT must first be 

converted to carbon. From this is subtracted the CH4 emissions after converting them to carbon. 

The result is then converted back to CO2 (see Equation N.49): 

Avoided CO2 emissions 

 = ((Potential CO2 emissions × 12/44) – (Avoided CH4 emissions/25 × 12/16)) × (44/12) 

 = ((2,138.4693 × 12/44) – (469.7287 / 25 × 12/16)) × (44/12) 

 = 2,086.7990 MT CO2 per year 

Step 3: Calculating the CO2e from the Alternate Fate (Numerator) 

The final calculation in solving for the numerator of the AVOIDEMIT term for this scenario of 

chicken litter management is to sum the estimated, avoided CH4 and the avoided CO2 emissions 

(Equation N.48). This summation represents the total avoided CO2e emissions (in metric tons CO2e 

per year) that result from storage of the solid litter: 

Total avoided CO2e emissions 

= (avoided CO2 emissions) + (avoided CH4 emissions) 

= 2,086.7990 + 469.7287 

= 2,556.5277 metric tons CO2e per year. 
November 2014 N-77 

Step 4: Calculating the CO2e from the Anaerobic Digester (Denominator) 

Equation N.54 can be used to calculate the denominator of the AVOIDEMIT term. In both of the 

scenarios presented here, poultry litter management is limited to that from only one animal type 

(i.e., broilers). The above calculated values for total volatile solids excreted per broiler (TVSAT) is 

still applicable. For combustion, however, the fraction of total carbon, rather than degradable 

carbon, in the volatile solids must be calculated. Using Equation N.55, fraction of carbon in the 

volatile solids of the poultry litter (TotalCarbonAT) is calculated as: 

TotalCarbonAT = 

+64:12		

S1765/7-	r17/w0

=

+64:12	

S1765/7-	l655-4		/-w	+64:12

= 

T.g	

T.CXCT.TCgg

= 0.3914 

Given these values, the total CO2e emissions from combusting the litter from the 400,000 broilers 

assuming a 96% destruction efficiency of the waste48 is calculated as: 

CO2 emissions from incineration of poultry litter (metric tons CO2e/year) 

= TVSAT × TotalCarbonAT × (44/12) × DE × days/year × 1 metric ton/1,000kg 

 = 5,400 × 0.3914 × (44/12) × 0.96 × 365 × 1/1,000 

 = 2,715.5019 metric tons CO2e per year 

Step 5: Calculating the BAF Value 

After solving for the numerator and the denominator of the AVOIDEMIT term associated with this 

litter management strategy (i.e., litter storage prior to a land application), the BAF can be calculated 

using Equation N.1 and Equation N.2: 

BAF = AVOIDEMIT 

= 1 – 

,XXC.Xhh	.-54/9	5120	+,-/v-64

,hX.XTi	.-54/9	5120	+,-/v-64

= 0.06 

 

48 Combustion efficiency of livestock waste varies with the type of boiler used, moisture content, and particle size of 

the feedstock. In an efficient combustor, very little carbon in poultry litter is left unburned (Antares Group Inc. et al., 

1999). One published value of combustion efficiency for combustion of broiler litter, based on the carbon content in 

the ash is 96% (Costello, 2007). 
November 2014 N-78 

The BAF is small, but positive, indicating that the alternate disposal scenario of storing the chicken 

litter as a solid prior to its application as a soil amendment has emissions similar to, but slightly 

lower than manure combustion. 

5.2.2. Calculation for Direct Combustion and an Uncovered Anaerobic Lagoon 

The second scenario presented is an alternate management strategy of this chicken litter via 

storage and treatment in an open anaerobic lagoon.49 An uncovered anaerobic lagoon is capable of 

generating more CH4 than is management via solid storage prior to land application. As a result the 

calculated avoided CH4 emissions and the avoided CO2 emissions will differ. However, between 

these two scenarios, the calculated values for TVSAT (5,400 kg/day), VolatileCarbonAT (0.2959), and 

the potential maximum CO2 emissions (2,138.4693 metric tons CO2 per year) would not be 

different; those values calculated above, can be imported into the equations needed to calculate the 

avoided CH4 emissions and the avoided CO2 emissions (Equations N.53, and N.49, respectively). 

Step 1: Calculating the Avoided CH4 Emissions from the Alternate Fate 

When calculating the avoided CH4 emissions associated with the alternate fate of the chicken litter 

under this scenario, several parameters are needed, including the maximum CH4-producing 

capacity for broilers (see EPA, 2009b, Table A-2, for the appropriate default value; for broilers, B0 = 

0.36 m3 CH4/kg; this is the same as under the previous example); and a CH4 conversion factor for 

the alternative-scenario’s waste management system (see EPA, 2009b, Table A-3; for an uncovered 

anaerobic lagoon in a temperate climate of 16°C, MCFWMS = 0.75). The following equation 

(Equation N.53) can be used to calculate the avoided CH4 emissions for treatment of this chicken 

litter via an uncovered anaerobic lagoon: 

Avoided CH4 emissions (metric tons CO2e /year) 

= 25 × (TVSAT × VSWMS × 365 days/year × B0 × MCFWMS × 0.662 kg CH4/m3 × 1 metric 

ton/1,000 kg) 

= 25 × (5,400 kg/day × 1 × 365 × 0.36 m3 CH4/kg × 0.75 × 0.662 kg CH4/m3 × 1/1,000) 

= 8,807.4135 MT CO2e per year 

Step 2: Calculating the CO2 Emissions from the Alternate Fate 

With estimates of both the potential CO2 emissions and the avoided CH4 emissions, the avoided CO2 

emissions resulting from an uncovered anaerobic lagoon poultry litter management strategy can be 

calculated. For this calculation, the total potential CO2 emissions from the decomposition of TVSAT

must first be converted to carbon. From this is subtracted the CH4 emissions after converting them 

to carbon. The result is then converted back to CO2 (see Equation N.49): 

 

49 As previously mentioned, chicken litter from broilers can be managed in anaerobic lagoons, though it is more 

common to use this management strategy for pullets.
November 2014 N-79 

Avoided CO2 emissions 

 = ((Potential CO2 emissions × 12/44) – (Avoided CH4 emissions/21 × 12/16)) × (44/12) 

 = ((2,138.4693 × 12/44) – (7,398.2273/21 × 12/16)) × (44/12) 

 = 1,169.6538 MT CO2 per year 

Step 3: Calculating the CO2e Emissions from the Alternate Fate 

Summing the estimated, avoided CH4 and CO2 emissions (both in metric tons CO2e per year) that 

result from an uncovered, anaerobic lagoon management strategy for poultry litter (Equation N.25), 

the numerator of the AVOIDEMIT term for this scenario can be computed as: 

Total avoided CO2e emissions 

= (avoided CO2 emissions) + (avoided CH4 emissions) 

 = 1,169.6538 + 8,807.4135 

= 9,977.0673 MT CO2e per year 

Step 4: Calculating the BAF Value 

The denominator of the AVOIDEMIT term represents the CO2e emissions associated with 

combustion of the poultry litter (in this case, litter from 400,000 broilers). The computed value of 

the denominator was previously calculated using Equation N.54 and is unchanged by the alternate 

fate of the managed poultry litter. Therefore, both the numerator and the denominator of the 

AVOIDEMIT term associated with this waste management strategy (i.e., an uncovered anaerobic 

lagoon) have been calculated. The BAF can be computed using Equations N.1 and N.2: 

BAF = AVOIDEMIT 

 = 1 – 

i,ihh.TChW	

,hX.XTi		

 = –2.67 

5.3. Sensitivity Analysis for Livestock Waste Management through Direct 

Combustion 

Table N-12 presents the results of the sensitivity analysis performed for the direct combustion of 

livestock waste. Sources for the parameter values used here can be found in Table N-11 of Section 

5.1.2. The parameter that has the greatest variability is the methane correction factor (MCF) for the 

waste management system employed as an alternative to direct livestock waste combustion. 

Increasing the MCF decreases the BAF (including making negative BAF values more negative). 

Increasing the GWP of CH4 (GWP_CH4) also decreases the BAF value. The methane generation 

potential (Bo) and the volatile carbon content (VolatileCarbon_AT) of the waste has a similar affect; 

increasing Bo or VolatileCarbon_AT decreases BAF. The total carbon content (TotalCarbon_AT) is 

only used in the denominator of the emission ratio term of AVOIDEMIT, so increasing 
November 2014 N-80 

TotalCarbon_AT increases BAF (including making negative BAF less negative). In the same manner, 

the waste combustor destruction efficiency (DE) only impacts the denominator. Since the 

destruction efficiency here reflects the fraction of the total carbon that is oxidized in the combustor, 

lowering DE reduces the emissions in the denominator causes BAF to decrease (or become more 

negative). 

Table N-12. Sensitivity Analysis of Anaerobic Digestion using Animal Population Data.1

Analysis Key Parameter 

Varied 

Key 

Parameter 

Value 

BAF Value Calculated at the Specified MCF Value 

MCF=0.05 MCF=0.3 MCF=0.5 MCF=0.8 

1 GWPHIJ21 0.21 −0.35 −0.80 −1.47 

2 GWPHIJ25 0.18 −0.50 −1.05 −1.87 

3 GWPHIJ28 0.16 −0.61 −1.23 −2.16 

4 Bo 0.15 0.25 −0.09 −0.36 −0.77 

5 Bo 0.30 0.18 −0.50 −1.05 −1.87 

6 Bo 0.50 0.09 −1.05 −1.96 −3.32 

7 VolatileCarbon_AT 0.20 0.41 −0.27 −0.82 −1.64 

8 VolatileCarbon_AT 0.30 0.18 −0.50 −1.05 −1.87 

9 VolatileCarbon_AT 0.40 −0.04 −0.73 −1.27 −2.09 

10 TotalCarbon_AT 0.30 −0.23 −1.25 −2.07 −3.30 

11 TotalCarbon_AT 0.45 0.18 −0.50 −1.05 −1.87 

12 TotalCarbon_AT 0.60 0.39 −0.13 −0.53 −1.15 

13 DE 0.99 0.19 −0.48 −1.03 −1.84 

14 DE 0.98 0.18 −0.50 −1.05 −1.87 

15 DE 0.95 0.16 −0.55 −1.11 −1.96 

1 The following central tendency values were used unless specified as the parameter varied. 

• GWPHIJ= 25 

• Bo = 0.30 

• VolatileCarbon_AT = 0.30 

• TotalCarbon_AT = 0.45 

• DE = 0.99. 

Note: References for the key parameters and values are presented in Table N-11 of Section 5.1.2. 

6. Wastewater Disposal in Wastewater Treatment Facilities and 

Associated GHG Emission Pathways 

Wastewater from domestic and industrial sources is treated to remove soluble organic matter, 

suspended solids, pathogenic organisms, and chemical contaminants from the wastewater prior to 

its discharge into natural water systems. In the United States, approximately 20% of domestic 

wastewater is treated in septic systems or other onsite systems, while the rest is collected and 

treated centrally (EPA, 2014b). Centralized wastewater treatment systems, such as publicly owned 

treatment works, may include a variety of processes, ranging from treatment in lagoons to 

advanced tertiary treatment technology for removing nutrients. In the United States, there are 

approximately 14,780 wastewater treatment plants (Lono-Batura et al., 2012). 
November 2014 N-81 

Soluble organic matter in wastewater is generally removed via biological processes in which 

microorganisms biodegrade the organic matter under aerobic or anaerobic conditions. Sludges 

(also referred to as wastewater biosolids after they have been treated) are the product of most 

wastewater treatment systems (Bogner et al., 2007; RTI International, 2010). Carbon dioxide, CH4 

and N2O can be produced and released to the atmosphere at various stages between the initial point 

of wastewater collection and its final disposal, including wastewater transport, sewage treatment 

processes, and anaerobic digestion of wastewater or sludges (Bogner et al., 2007). In the United 

States, domestic and industrial wastewater treatment accounted for approximately 2.3% of CH4 

emissions in 2012 (totaling 12.8 Tg CO2e) and 1.2% of N2O emissions (totaling 5.0 Tg CO2e) (EPA, 

2014b). 

Methane is microbially produced under anaerobic conditions. Domestic wastewater CH4 emissions 

originate from both septic systems and from centralized treatment systems. Within centralized 

systems, CH4 emissions can arise from aerobic systems that are not well managed (resulting in 

anaerobic conditions) or that are designed to have periods of anaerobic activity (e.g., constructed 

wetlands), anaerobic systems (e.g., anaerobic lagoons), a mixed aerobic and anaerobic systems (e.g., 

facultative lagoons with surface aerobic zones and deeper anaerobic zones), and from anaerobic 

digesters if captured biogas is released through leaks, venting, or incomplete combustion (Bogner 

et al., 2007; RTI International, 2010; EPA, 2014b). During collection and treatment, wastewater 

may be accidentally or deliberately managed under anaerobic conditions. Wastewater and 

wastewater sludge may be further biodegraded under aerobic conditions or anaerobic conditions, 

including anaerobic digestion, agricultural reuse, or incineration (Bogner et al., 2007; EPA, 2014b). 

N2O is an intermediate product of microbial nitrogen cycling; it is generated via the treatment of 

domestic wastewater during both nitrification and denitrification of the nitrogen present, usually in 

the form of urea, ammonia, and proteins. These compounds are converted to nitrate (NO3) through 

the aerobic process of nitrification. Denitrification occurs under anoxic conditions, and involves the

biological conversion of nitrate into N2 (EPA, 2014b). The amount of nitrogen present in the 

influent wastewater determines the N2O generation potential. 

Collection of biogas generated in the wastewater treatment process is primarily, if not entirely, 

restricted to treatment systems using anaerobic digesters. Anaerobic digesters are used to enhance 

the degradation process of wastewater and wastewater sludge, thereby producing biogas. If the CH4 

generated by an anaerobic wastewater treatment process or anaerobic sludge digestion process is 

captured and combusted (in a flare or other combustion device), then CH4 is destroyed and 

converted to CO2, resulting in a net decrease in GHG emissions. N2O is not a product of wastewater 

treatment via an anaerobic digester. 

It is unknown how many U.S. wastewater treatment facilities use anaerobic digesters to treat 

wastewater and wastewater sludge. However, a survey of 5,128 U.S. wastewater treatment facilities 

(of the 14,780 facilities) concluded that at least 1,238 (24% of this subsample) treat sludge using 

anaerobic digesters and collect the biogas produced (Lono-Batura et al., 2012). The majority of 

wastewater treatment facilities that use anaerobic digesters are large (treating over one million 

gallons per day). However, this represents less than 40% of the large wastewater treatment 

facilities in the U.S; this sector has potential to expand (Lono-Batura et al., 2012). Collected biogas 
November 2014 N-82 

from waste water treatment facilities is most commonly flared, though some wastewater treatment 

facilities use it for energy generation or sell it for use off-site; several facilities reported releasing 

the collected biogas directly to the atmosphere (Lono-Batura et al., 2012). Because anaerobic 

digesters enhance the waste degradation process, thereby increasing the rate of CH4 generation, 

biogas produced in an anaerobic digester and released directly to the atmosphere without 

combustion would result in greater CH4 emissions than had the treatment not utilized an anaerobic 

digester. 

6.1. Method for Calculating an Illustrative BAF Value Applied to Biogenic 

Emissions Resulting from Combustion of Biogas from Wastewater 

Treatment 

The assessment factor equation can be applied to point source biogenic emissions that result from 

the combustion of biogas from an anaerobic digester used for wastewater treatment. An illustrative 

method is provided for calculating a BAF value that can be applied to point source biogenic

emissions from anaerobic digesters used for the treatment of wastewater. Wastewater treatment 

via an anaerobic digester is the only treatment method that results in point source emissions. 

Here the biogenic feedstock is biogas that is collected from an anaerobic digester used for waste 

water treatment. Biogas combustion, whether biogas is flared or used as a fuel to generate energy, 

oxidizes the CH4 contained in biogas to CO2. This results in a net reduction of GHG emissions 

relative to an alternate GHG emissions pathway in which biogas produced through the anaerobic 

treatment of wastewater is not captured and combusted, but instead is released to the atmosphere 

as an indirect emission. 

In instances where the alternate GHG emissions pathway involves uncontrolled anaerobic 

treatment of wastewater, use of anaerobic digester systems typically results in substantial net GHG 

emissions reductions. However, because anaerobic digesters are designed to enhance CH4

generation, poor design, operation, or maintenance of anaerobic digesters can result in significant 

indirect CH4 emissions. For example, CH4 can leak from a digester cover or can be vented during 

digester start-ups, shutdowns, and malfunctions (Bogner et al., 2007; EPA, 2008b; Climate Action 

Reserve, 2013). However, under normal working conditions, GHG emissions from controlled 

biological treatment in an anaerobic digester are small relative to indirect CH4 emissions from 

uncontrolled anaerobic storage and treatment systems (Bogner et al., 2007, and references 

therein). 

In instances where the alternative GHG emissions pathway involves aerobic treatment of 

wastewater, use of an anaerobic digestion system with biogas capture and combustion in most 

instances would not be expected to result in a net increase of GHG emissions. In these instances, 

wastewater and sludges either would have decayed aerobically, producing CO2 as the primary 

decay product (e.g., in a shallow lagoon or in an aeration tank associated with activated sludge 

wastewater treatment processes), or they would have decayed anaerobically, producing both CH4 

and CO2 (e.g., in a deep, open lagoon). 
November 2014 N-83 

In applying the assessment factor equation (BAF = AVOIDEMIT; Equation N.1), net GHG emissions 

reductions from the use of an anaerobic digester (where the generated biogas is collected and 

destroyed) are accounted for in the AVOIDEMIT term. In practice, as applied here, the AVOIDEMIT

term is a ratio expressed in units of CO2e avoided (i.e., the emissions, in CO2e, resulting from an 

alternative wastewater treatment scenario of aerobic, anaerobic, or a combination of aerobic and 

anaerobic treatment) per units of CO2e removed via combustion (i.e., the emissions, in CO2e, of the 

biogas generated in an anaerobic digester—accounting for biogas collection and combustion 

efficiencies). For the biogas feedstock collected from the treatment of wastewater in an anaerobic 

digester, the AVOIDEMIT term can be conceptually expressed using the simplified ratio of: 


 =  − 	 (-./00/120	341.	54-65.-25	675-4265/8-	51	62	626-41:/9	w/_-05-4)	

(-./00/120	341.	54-65.-25	/2	62	626-41:/9	w/_-05-4) (EQ N.56) 

6.1.1. Calculating the Numerator 

In computing AVOIDEMIT, the numerator (i.e., emissions from a treatment alternative to an 

anaerobic digester) can be calculated by building upon the methods developed for EPA by RTI 

International (2010). To compute the emissions profile of the treatment method that is alternate to 

an anaerobic digester, the CO2e emissions resulting from the alternate treatments of wastewater 

and wastewater sludge must be summed: 

AVOIDEMIT numerator = CO2WW + CO2S + (tsZ+Q?

 × (CH4WW + CH4S)) (EQ. N.267) 

Where: 

CO2WW = CO2 emission rate from wastewater treatment (MT CO2/year), see 

Equation N.58. 

CO2S = CO2 emission rate from wastewater sludge treatment (MT CO2/year), see 

Equation N.61. 

GWPCH4

 = Global warming potential for methane, 25 (IPCC, 2007) 

CH4WW = CH4 emission rate from wastewater treatment (MT CH4/year), see 

Equation N.59. 

CH4S = CH4 emission rate from wastewater sludge treatment (MT CO2/year), see 

Equation N.62. 

CO2 and CH4 emissions from the aerobic treatment of wastewater can be calculated using the 

following two equations: 

+,ss = TC × ,Q40 × cc × ,\ × ]33,\ ×

??

W

×  − l+ss × t+Q?

( − ) 

 (EQ. N.278) 

+Q?ss = TC × ,Q40 × cc × ,\ × ]33,\ ×

C

W

× l+ss × t+Q?

( − )
November 2014 N-84 

 (EQ. N.59) 

Where: 

CO2WW = CO2 emission rate (MT CO2/year). 

CH4WW = CH4 emission rate (MT CH4/year). 

10-6 = Units conversion factor (MT/g). 

OpHrs = Hours wastewater treatment system is operated per year. 

Qww = Wastewater influent flow rate (m3/hr). 

OD = Oxygen demand50 of influent wastewater to the biological treatment unit 

(mg/L = g/m3). 

EffOD = Oxygen demand removal efficiency of the biological treatment unit. 

44/32 = Molar mass ratio of CO2 to O2; representing the conversion factor for 

maximum CO2 generation per unit of oxygen demand. 

16/32 = Molar mass ratio of CH4 to O2; representing the conversion factor for 

maximum CH4 generation per unit of oxygen demand. 

MCFww = CH4 correction factor for wastewater treatment unit, indicating the fraction of 

the influent oxygen demand that is converted anaerobically in the wastewater 

treatment unit.51

BGCH4

 = Fraction of C as CH4 in generated biogas (default is 0.65). 

λ = Sludge biomass yield, expressed as g C converted to sludge per g C consumed 

in the wastewater treatment process (see Equation N.60). 

The variable representing sludge biomass yield (λ) in Equations N.58 and N.59 is an estimate of the 

net sludge generated from the wastewater treatment process, as calculated with Equation N.60. 

 = 0×lSrr0×T.XW

cc×,\×]331w×



W

(EQ. N.60) 

Where: 

 

50 Determined as either the 5-day biochemical oxygen demand (BOD5) or the chemical oxygen demand (COD). The 

BOD5 and COD are two measures of the amount of degradable organic content in wastewater. 

51 MCFww value ranges from 0 to 0.8 (see Table N-4). A MCFww value of zero (no CH4 emissions) is assigned to 

well-managed aerobic decomposition systems. 
November 2014 N-85 

λ = Sludge biomass yield, expressed as g C converted to sludge per g C consumed 

in the wastewater treatment process. 

Qs = Wastewater sludge flow rate (m3/hr). 

Qww = Wastewater influent flow rate (m3/hr). 

MVVSSs = Mixed liquor volatile suspended solids concentration of the waste sludge 

stream (mg/L). 

OD = Oxygen demand of influent wastewater to the biological treatment unit 

(mg/L). 

EffOD = Oxygen demand removal efficiency of the biological treatment unit. 

0.53 = Correction factor for carbon content of the sludge biomass.52

12/32 = Molar mass ratio of C to O2; representing the conversion factor for maximum C 

consumption per unit of oxygen demand. 

If the flow rate of the sludge waste stream is not directly measured then estimated representative 

values for sludge biomass yield can be used as an alternative to Equation N.60. Illustrative 

representative values for sludge biomass yield are specific to the treatment system used (Table N13). 

Table N-13. Illustrative Representative Values for Methane Correction Factor (MCF) and Biomass 

Yield (λ) by Treatment System for both Wastewater and Sludge Treatment Processes (from RTI 

International, 2010). 

Wastewater Treatment Process MCF λ 

Aerated treatment process (e.g., activated sludge system), well managed 0 0.65 

Aerated treatment process, overloaded (i.e., anoxic areas) 0.3 0.45 

Anaerobic treatment process (e.g., anaerobic digester) 0.8 0.1 

Facultative lagoon, shallow (< 2 m deep) 0.2 0 

Facultative lagoon, deep (≥ 2 m deep) 0.8 0 

Sludge Treatment Process 

Aerobic sludge digestion 0 Use λ from 

wastewater 

treatment process 

Anaerobic sludge digestion (e.g., anaerobic digester) 0.8 

Emissions from the treatment of solids (i.e., sludge generated in the wastewater treatment system), 

whether sludge is treated aerobically or anaerobically, can be calculated using the following 

equations: 

 

52 Carbon accounts for 53% of the sludge biomass weight (dry basis). 
November 2014 N-86 

+,r = TC × ,Q40 × cc × ,\ × ]33,\ ×

??

W

×  − l+r × t+Q?

 (EQ. N.61) 

+Q?r = TC × ,Q40 × cc × ,\ × ]33,\ ×

C

W

× l+r × t+Q?

 (EQ. N.62) 

Where: 

CO2S = CO2 emission rate (MT CO2/year). 

CH4S = CH4 emission rate (MT CH4/year). 

10-6 = Units conversion factor (MT/g). 

OpHrs = Hours wastewater treatment system is operated per year.53

Qww = Wastewater influent flow rate (m3/hr). 

OD = Oxygen demand54 of influent wastewater to the biological treatment unit (mg/L 

= g/m3). 

EffOD = Oxygen demand removal efficiency of the biological treatment unit. 

44/32 = Molar mass ratio of CO2 to O2; representing the conversion factor for maximum 

CO2 generation per unit of oxygen demand. 

16/32 = Molar mass ratio of CH4 to O2; representing the conversion factor for maximum 

CH4 generation per unit of oxygen demand. 

λ = Sludge biomass yield, expressed as g C converted to sludge per g C consumed in 

the wastewater treatment process (see Equation N.60). 

MCFS = CH4 correction factor for sludge digestion, indicating the fraction of the treated 

sludge that is converted anaerobically in the wastewater treatment unit.55

BGCH4 = Fraction of C as CH4 in generated biogas (default is 0.65). 

6.1.2. Calculating the Denominator 

In computing AVOIDEMIT, the denominator (i.e., emissions from the treatment of wastewater and 

sludge in an anaerobic digester such that the generated biogas is captured and combusted) can be 

calculated by building upon the methods developed for EPA by RTI International (2010). To 

compute the emissions profile associated with the anaerobic treatment of wastewater and 

wastewater sludge in an anaerobic digester, the CO2e emissions resulting from these treatments 

 

53 A wastewater system may operate continuously except for when it is down for maintenance, 10% of the year (e.g., 

365 × 24 × 0.9 = 8760 hours). 

54 Determined as either the 5-day biochemical oxygen demand (BOD5) or the chemical oxygen demand (COD). The 

BOD5 and COD are two measures of the amount of degradable organic content in wastewater. 

55 MCFww value ranges from 0 to 0.8 (see table 3-1, RTI International, 2010). A MCFww value of zero (no CH4

emissions) is assigned to well-managed aerobic decomposition systems. 
November 2014 N-87 

must be summed while simultaneously accounting for biogas destruction efficiency (via 

combustion) and biogas collection efficiency: 

AVOIDEMIT denominator = CO2WW + CO2S + 25× ((CH4WW – CH4WWD + 

CH4WWL) + (CH4S – CH4SD + CH4SL)) + (CH4WWD × 44/16) + 

(CH4SD × 44/16) (EQ. N.63) 

Where: 

CO2WW = CO2 emission rate from wastewater treatment (MT CO2/year), see 

Equation N.58. 

CO2S = CO2 emission rate from wastewater sludge treatment (MT CO2/year), see 

Equation N.61. 

CH4WW = CH4 emission rate from wastewater treatment (MT CH4/year), see 

Equation N.59. 

CH4WWD = CH4 emission rate from wastewater treatment, adjusted for biogas destruction 

efficiency (MT CH4/year).56 

CH4WWL = CH4 emission rate from wastewater treatment, adjusted for biogas collection 

efficiency (MT CH4/year).57 

CH4S = CH4 emission rate from wastewater sludge treatment (metric ton CO2/year), 

see Equation N.62. 

CH4SD = CH4 emission rate from wastewater sludge treatment, adjusted for biogas 

destruction efficiency (MT CH4/year).58

CH4SL = CH4 emission rate from wastewater sludge treatment, adjusted for biogas 

collection efficiency (MT CH4/year).59

44/16 = molecular weight ratio of CO2 to CH4. 

After solving for the numerator and the denominator of the AVOIDEMIT term, the BAF can be 

calculated using Equation N.1. See Section 6.2 for an illustrative example calculation of the 

numerator and denominator in the AVOIDEMIT term and its subsequent application in estimating a 

BAF for the management of wastewater and wastewater sludge. 

Several parameters are presented and used in the equations in the remainder of this section. 

 

56 Assuming biogas destruction efficiency is 0.99 then CH4WWD = 0.99 × CH4WW. 

57 Assuming biogas collection efficiency is 0.99 then CH4WWL = (1-0.99) × CH4WW. 

58 Assuming biogas destruction efficiency is 0.99 then CH4SD = 0.99 × CH4S. 

59 Assuming biogas collection efficiency is 0.99 then CH4SL = (1-0.99) × CH4S. 
November 2014 N-88 

Table N-14presents the parameters used, typical or default values, ranges presented in the 

literature, and references. 

Table N-14. Summary of Parameters Used When Calculating an Illustrative BAF for Wastewater 

Treatment. 

Parameter 

Description Symbol Value Range Units Comments 

Reference 

(for value 

column) 

Oxygen demand 

of the influent 

wastewater to 

the biological 

treatment unit 

OD – – mg/L or 

g/m3

Determined 

through either 

the BOD5 or the 

COD tests. 

NA 

Oxygen demand 

removal 

efficiency of the 

biological 

treatment unit 

EffOD – – Decimal 

percent 

Determined by 

the wastewater 

treatment 

facility. 

NA 

Fraction of C as 

CH4 in generated 

biogas 

BGHIJ

0.65 0.40 to 

0.70 

Decimal 

percent 

 EPA, 2013c 

Sludge biomass 

yield 

λ – 0 to 

0.65 

Expressed 

as g C 

converted to 

sludge per g 

C consumed 

in the 

wastewater 

treatment 

process 

See 

Equation N.60 

RTI International, 

2010 

Aerated 

treatment 

process (e.g., 

activated sludge 

system), well 

managed 

λ 0.65 Muller et al., 2003; 

Munz, 2008; 

Choubert et al., 

2009; RTI 

International, 2010 

Aerated 

treatment 

process, 

overloaded (i.e., 

anoxic areas) 

λ 0.45 Muller et al., 2003; 

Ammary, 2004; 

Munz, 2008; 

Choubert et al., 

2009; RTI 

International, 2010 

Anaerobic 

treatment 

process (e.g., 

anaerobic 

digester) 

λ 0.1 Ammary, 2004; 

Low and Chase, 

1999; RTI 

International, 2010 

Facultative 

lagoon, shallow 

(< 2 m deep) 

λ 0 RTI International, 

2010 

Facultative 

lagoon, deep 

(≥ 2 m deep) 

λ 0 RTI International, 

2010 
November 2014 N-89 

Parameter 

Description Symbol Value Range Units Comments 

Reference 

(for value 

column) 

WW: Aerated 

treatment 

process (e.g., 

activated sludge 

system), well 

managed 

MCFww 0 0 to 

0.8 

Fraction Indicating the 

fraction of the 

influent oxygen 

demand that is 

converted 

anaerobically in 

the wastewater 

treatment unit 

IPCC, 2006; RTI 

International, 2010 

WW: Aerated 

treatment 

process, 

overloaded (i.e., 

anoxic areas) 

MCFww 0.3 

WW: Anaerobic 

treatment 

process (e.g., 

anaerobic 

digester) 

MCFww 0.8 

WW: Facultative 

lagoon, shallow 

(< 2 m deep) 

MCFww 0.2 

WW: Facultative 

lagoon, deep (≥ 2 

m deep) 

MCFww 0.8 

Sludge: Aerobic 

sludge digestion 

MCFS 0 

Sludge: 

Anaerobic 

sludge digestion 

(e.g., anaerobic 

digestion) 

MCFS 0.8 

Biogas 

destruction 

efficiency 

DE; 

included 

in 

CH4WWD 

and 

CH4SD 

0.99 0.90 to 

0.9977 

Decimal 

percent 

 EPA, 2010d; EPA, 

2011a; EPA, 2013c 

Biogas collection 

efficiency 

CE; 

included 

in 

CH4WWL 

and 

CH4SD 

0.99 0.70 to 

0.99 

Decimal 

percent 

0.99 is used for 

an enclosed 

vessel, 

anaerobic 

sludge digester 

EPA, 2010d, Table 

6-1 
November 2014 N-90 

6.2. Example AVOIDEMIT and BAF Calculations for the Collected Biogas 

from Treatment of Wastewater and Wastewater Sludge 

This example calculation of the BAF is for a hypothetical wastewater treatment system that uses an 

anaerobic digester to treat wastewater and another anaerobic digester to treat sludge. In this 

scenario the wastewater treatment system has an average flow rate of 1 million gallons per day (or 

157.71 m3/hr), an inlet 5-day biochemical oxygen demand (BOD5) of 500 g/m3, and the treatment 

system has a 95% BOD5 removal efficiency. 

Step 1: Calculating the Numerator 

To calculate the numerator of AVOIDEMIT, the emissions from a treatment alternative to an 

anaerobic digester, must be computed. In this hypothetical example, the treatment alternative to an 

anaerobic digester would be a shallow (< 2 m deep), facultative lagoon. For this example, it is 

assumed that the wastewater system would operate continuously throughout the year (365 × 24 = 

8760 hours). Treatment of wastewater sludge is assumed to be outside of the lagoon such that 

there is no sludge biomass yield (λ = 0). Emissions from this alternate treatment pathway can be 

computed using Equation N.57. However, values to populate Equation N.57 must first be calculated 

using Equations N.58 and N.59 (because λ = 0, Equations N.61 and N.62 are equal to zero, thus 

dropping out of Equation N.57). 

CO2 emissions from the wastewater treatment system (a shallow, facultative lagoon) are calculated 

using Equation N.58, (MCFww = 0.2 and λ = 0): 


 = 	 TC ×

>


#

×  × 
 × ""
 ×

??

W

×  −  × >?

( − )

= 10-6 × 8760 × 157.71 × 500 × 0.95 × (44/32) ×[(1 – 0.2 × 0.65) (1 – 0)] 

= 785.0167 MT CO2 per year 

CH4 emissions from the wastewater treatment system (a shallow, facultative lagoon) are calculated 

using Equation N.59, (MCFww = 0.2 and λ = 0): 

>? = 	 TC ×

>


#

×  × 
 × ""
 ×

C

W

×  × >?

( − )

= 10-6 × 8760 × 157.71 × 500 × 0.95 × (16/32) ×[(0.2 × 0.65)(1 – 0)] 

= 42.6550 MT CH4 per year. 

The numerator of AVOIDEMIT can now be solved using Equation N.57: 

AVOIDEMIT numerator = CO2WW + CO2S + (25 × (CH4WW + CH4S)) 

= 785.0108 + 0 + 25 × (42.6547 + 0) 

= 1,851.38 MT CO2e per year 
November 2014 N-91 

Step 2: Calculating the Denominator 

To calculate the denominator of AVOIDEMIT, the emissions from wastewater and wastewater 

sludge treatment using an anaerobic digester, must be computed. Emissions from this treatment 

pathway can be computed using Equation N.63. However, values to populate Equation N.63 must 

first be calculated using Equations N.58, N.59, N.61, and N.62. 

CO2 emissions from the wastewater treatment system (an anaerobic digester) are calculated using 

Equation N.58, (MCFww = 0.8 and λ = 0.1): 


 = 	 TC ×

>


#

×  × 
 × ""
 ×

??

W

×  −  × >?

( − )

= 10-6 × 8760 × 157.71 × 500 × 0.95 × (44/32) ×[(1 – 0.8 × 0.65)(1 – 0.1)] 

= 389.8014 MT CO2 per year 

CH4 emissions from the wastewater treatment system (an anaerobic digester) are calculated using 

Equation N.59, (MCFww = 0.8 and λ = 0.1): 

>? = 	 TC ×

>


#

×  × 
 × ""
 ×

C

W

×  × >?

( − )

= 10-6 × 8760 × 157.71 × 500 × 0.95 × (16/32) ×[(0.8 × 0.65)(1 – 0.1)] 

= 153.558 MT CH4 per year. 

CO2 emissions from the wastewater sludge treatment system (an anaerobic digester) are calculated 

using Equation N.61, (MCFS = 0.8 and λ = 0.1): 


 = 	 TC ×

>


#

×  × 
 × ""
 ×

??

W

×  −  × >?



= 10-6 × 8760 × 157.71 × 500 × 0.95 × (44/32) ×[0.1(1 – 0.8 × 0.65)] 

= 43.3113 MT CO2 per year 

CH4 emissions from the wastewater sludge treatment system (an anaerobic digester) are calculated 

using Equation N.62, (MCFS = 0.8 and λ = 0.1): 

>? = 	 TC ×

>


#

×  × 
 × ""
 ×

C

W

×  × >?



= 10-6 × 8760 × 157.71 × 500 × 0.95 × (16/32) ×[0.1(0.8 × 0.65)] 

= 17.0620 MT CH4 per year. 

Next, the calculated emissions associated with treatment of wastewater and wastewater sludge in 

an anaerobic digester can be used to populate Equation N.63: 
November 2014 N-92 

AVOIDEMIT denominator = 

CO2WW + CO2S 

+ 25× ((CH4WW – CH4WWD + CH4WWL) + (CH4S – CH4SD + CH4SL)) 

+ CH4WWD × 44/16 + CH4SD × 44/16 

Assuming biogas destruction efficiency is 0.99, then: 

• CH4WWD = 0.99 × CH4WW, and 

• CH4SD = 0.99 × CH4S. 

Assuming biogas collection efficiency is 0.99, then: 

• CH4WWL = (1–0.99) × CH4WW, and 

• CH4SL = (1–0.99) × CH4S. 

Applying these assumptions, the denominator of AVOIDEMIT can be expressed as: 

AVOIDEMIT denominator = CO2WW + CO2S 

+ 25× (CH4WW – (0.99 × CH4WW) + ((1–0.99) × CH4WW)) 

+ 25× (CH4S – (0.99 × CH4S) + ((1–0.99) × CH4S)) 

+ (0.99 × CH4WW × 44/16) + (0.99 × CH4S × 44/16) 

AVOIDEMIT denominator = 389.8014 + 43.3113 

+ 25× (153.558 – (0.99 × 153.558) + ((1 – 0.99) × 153.558)) 

+ 25× (17.0620 – (0.99 × 17.0620) + ((1 – 0.99) × 17.0620)) 

+ (0.99 × 153.558 × 44/16) + (0.99 × 17.0620 × 44/16) 

= 982.9357 MT CO2e per year. 

Step 3: Calculating the BAF Value 

After solving for the numerator and the denominator of the AVOIDEMIT term associated with 

wastewater management, the BAF can be calculated using Equations N.1 and N.2: 

BAF = AVOIDEMIT

 = 1 – 

,gX.Wg	

ig.iWXh

 = –0.88 

A negative calculated BAF value, such as that above, indicates that a biogas feedstock produced in 

an anaerobic digester from the treatment of wastewater and wastewater sludge, and used by a 

stationary source results in net CO2e emissions reductions. 
November 2014 N-93 

6.3. Sensitivity Analysis for Wastewater Treatment 

A simple sensitivity analysis on the key parameters in the wastewater treatment methodology is 

presented in Table N-15 for the actual fate of wastewater treatment in an anaerobic digester and 

the alternate fate of placing the waste in a shallow, facultative lagoon. Key parameters impacting 

the BAF include the DE and CE for the anaerobic digester, and the GWP for CH4 (21, 25, and 28). In 

each of the six analyses, the DE of the biogas was adjusted between 95% and 99%, and the CE was 

adjusted to 75%, 90%, and 99%, representing a range of low to high performing biogas collection 

system efficiencies. Sources for the parameter values used here can be found in Table N-14of 

Section 6.1.2. The inputs used in the analyses are equivalent to those shown in the example 

calculations in Section 6.2 of this appendix. 

The BAF values are positive when performing the calculations with a CE lower than 78% despite 

the DE value (95% or 99%) used. Higher CEs yield negative BAF values regardless of the GWP, 

indicating that wastewater management through anaerobic digestion may be a better treatment 

option with respect to CO2 and CH4 emissions pathways. The turning point for the BAF values with 

respect to either a 95% of 99% DE is presented in Analyses 7 through 18. Note that, in order for a 

net CO2e emissions reduction to occur, the anaerobic digester may require a CE of at least 80% to 

85%. 

Table N-15. Sensitivity Analysis for Wastewater Treatment. 

Analysis 

Key Parameter and Value BAF

CE DE GWP=21 GWP=25 GWP=28 

1 0.75 0.99 0.081 0.077 0.075 

2 0.75 0.95 0.140 0.142 0.144 

3 0.85 0.99 −0.143 −0.172 −0.191 

4 0.85 0.95 −0.053 −0.069 −0.079 

5 0.99 0.99 −0.734 −0.884 −0.993 

6 0.99 0.95 −0.537 −0.631 −0.698 

7a 0.79 0.99 0.003 

8a 0.80 0.99 −0.019 

9b 0.78 0.99 0.015 

10 b 0.79 0.99 −0.008 

11c 0.78 0.99 0.009 

12c 0.79 0.99 −0.016 

13d 0.82 0.95 0.013 

14d 0.83 0.95 −0.008 

15e 0.82 0.95 0.005 

16 e 0.83 0.95 −0.019 

17f 0.81 0.95 0.023 

18f 0.82 0.95 −0.001 

a The point at which the BAF changes from negative to positive with a GWP of 21 and DE = 0.99.

b The point at which the BAF changes from negative to positive with a GWP of 25 and DE = 0.99. 
November 2014 N-94 

c The point at which the BAF changes from negative to positive with a GWP of 28 and DE = 0.99. 

d The point at which the BAF changes from negative to positive with a GWP of 21 and DE = 0.95.

e The point at which the BAF changes from negative to positive with a GWP of 25 and DE = 0.95. 

f The point at which the BAF changes from negative to positive with a GWP of 28 and DE = 0.95. 

Note: References for the key parameters and values are presented in Section 6.1. 

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