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 fo r Waste-Derived Biogenic Feedstocks

................................................. ................................................... ................................................... ........................... N-7 1.2. Biogenic Municipal Solid Waste Management .........

................................................... ......................... N-9 2. Biogenic MSW Disposal in MSW Landfills and Associat ed 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 Meth odology .................................. 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 (Fla ring) 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 U ncontrolled Landfill ............. N-26 2.5. Sensitivity Analysis for MSW Landfill Biogas ......

................................................... ........................... N-28 3. Disposal of Biogenic MSW through Combustion and Ass ociated 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-37November 2014 N-2

4. Livestock Waste Management through Anaerobic Proces ses 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 Wast e ................................................. ................ N-40 4.1.1. Calculating the Numerator .........................

................................................... .................................. N-41 4.1.2. Methodology When Biogas Flow Rate and Methane Conce ntration Data Are Available .

................................................. ................................................... ................................................... .............. N-42 4.1.3. Calculating the Denominator .......................

................................................... ................................ N-46 4.1.4. Methodology When Biogas Flow Rate and Methane Conce ntration 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 M easurement 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 Liv estock and Food Waste ......................... N-6 3 5. Livestock Waste Management through Direct Combustio n 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 Wa ste . 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 Facilit ies 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 Treatme nt of Wastewater and Wastewater Sludge ..................

................................................... ................................... N-90 6.3. Sensitivity Analysis for Wastewater Treatment .....

................................................... ....................... N-93November 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 th e Waste Feedstocks Discussed in this Appendix. ............

................................................... ...................................... N-9 Table N-3. Percent of MSW Generated and Recovered b y MSW Class in 2012 (EPA, 2014a). ......... N-10 Table N-4. Summary of Parameters Used When Calculat ing 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 Calculat ing 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 Calculat ing a BAF for Livestock Waste Management through Anaerobic Digestion. ......................

................................................... ............................................. N-47 Table N-9. Sensitivity Analysis of Anaerobic Digest ion Using Biogas Measurement Data. 1 .............. N-64 Table N-10. Sensitivity Analysis of Anaerobic Diges tion Using Animal Population Data. 1 ................ N-64 Table N-11. Summary of Parameters Used When Calcula ting an Illustrative BAF for Livestock Waste Management through Combustion. ....................

................................................... .................................... N-73 Table N-12. Sensitivity Analysis of Anaerobic Diges tion 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 Sludg e Treatment Processes (from RTI International, 2010). .........................

................................................... ................................................... N-85 Table N-14. Summary of Parameters Used When Calcula ting an Illustrative BAF for Wastewater Treatment. ........................................

................................................... ................................................... ............. N-88 Table N-15. Sensitivity Analysis for Wastewater Tre atment. ........................................... ............................. N-93 

## List of Figures Figure N-1. Carbon Balance for an Uncontrolled Land fill. ............................................. .................................. N-13 Figure N-2. Carbon Balance for a Controlled Landfil l. ................................................ ....................................... 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 CO 2 and CH 4 emissions from stationary sources that use waste-derived biog enic feedstocks, and illustrates how the framework could be adapted to derive assessment fac tors for these biogenic feedstocks. For the purposes of this appendix, the waste-derived biogen ic 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 combusto r, 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 biogen ic feedstocks include the following:

• Landfill gas 1 generated through the decomposition of municipal s olid waste (MSW) in a landfill;

• The biogenic fraction of MSW;

• Biogas generated from the decomposition of livestoc k waste, 2 biogenic MSW, and/or other food waste in an anaerobic digester;

• Livestock waste; and

• Biogas generated through the treatment of waste wat er, due to the anaerobic decomposition of biological materials. The following emission pathways that result in biog enic CO 2 emissions from stationary sources using waste-derived biogenic feedstocks are evaluat ed:

• 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 use d 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 use d to manage wastewater and associated sludges. This appendix is organized by the aforementioned em issions pathways. These selected pathways are not meant to represent an exhaustive list of al l possible alternate fate pathways. Included in thi s appendix are illustrative methods for how the frame work 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 abo ve. These illustrative methods are complemented with illustrations of biogenic assessm ent factor ( BAF ) values derived through application of the framework to the selected emissi on pathways. In the context of stationary sources, greenhouse ga s (GHG) emissions from waste-management options can be categorized into direct emissions an d indirect emissions. 3 The illustrative framework applications in this appendix address poi nt source biogenic CO 2 and CH 4 emissions from stationary sources using waste-derived feedstocks. Point source emissions of biogenic CO 2 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 (CH 4 ) and 50% CO 2 , with small percentages of other gases, such as volatile organic compounds (VO Cs). 2 In this appendix, “livestock waste” refers to eliminated products (e.g., manure, litter, urine) resul ting from the digestive process by farm animals (e.g., cattle, sh eep, goat, swine, poultry, equine animals, etc.) an d associated biogenic materials managed as waste materials (e.g. , bedding materials and uneaten animal feed). 3 Indirect emissions refer to emissions released dir ectly to the atmosphere, rather than through a stac k or vent. Indirect emissions include uncollected GHGs (e.g., biogas) that are released to the atmosphere and col lected 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 land fill gas and biogas are combusted, combustion results in the destruction of CH 4 and the emission of CO 2 . However, since combustion efficiency is less than 100%, not all CH 4 is destroyed, such that some uncombusted CH 4 is released as a point source emission. CH 4 has a significantly higher global warming potentia l (GWP) than CO 2 . 4 As a result, destruction of CH 4 that would have been released to the atmosphere as an indirect emission in the absence of combustion results in a reduction of CO 2 -equivalent (CO 2 e) contribution to the atmosphere.
Indirect emissions of CH 4 and CO 2 occur at landfills, wastewater treatment facilitie s, and in livestock settings including housing, conveyances, uncovered lagoons storing livestock waste and/or food waste, and land application areas. Indirect emissio ns of CH 4 and CO 2 also have the potential to occur via other waste management techniques, including an aerobic digesters. Note that some waste management strategies may result in both direct and indirect GHG emissions (e.g., landfills, wastewater treatment facilities, and anaerobic dige sters). Table N-1 summarizes different GHG emissions pathways related to the management of was te. Table N-1. Waste Management GHG Emissions Pathways Considered.

Type of Waste Waste

Management Option Biogenic

Feedstock Direct Emissions 1 Indirect Emissions

MSW Landfill Landfill gas CH 4 and CO 2 emissions from combustion of collected landfill gas (flare or EGU) CH 4 and CO 2 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 CO 2 emissions (oxidation from decomposition) 2

MSW MSW combustor MSW CO 2 emissions from combustion, typically in an EGU CH 4 and CO 2 emissions from pretreatment handling practices

4 Methane is a potent GHG, with a 100-year global warming potential (GWP) of 21 (IPCC, 1996). It shouldbe noted that in the IPCC Fourth Assessment Report, the 100- year GWP of CH 4 was revised to 25 (IPCC, 2007). To comply with international reporting standards under the UN FCCC, official emission estimates reported by the U nited States use the IPCC Second Assessment Report GWP values (I PCC 1996). The United States will transition to usi ng the revised GWPs beginning in 2015. In this framework, the GWP of 25 is used for the central examples with in each section. The GWPs of 21 and 28 are used in the sens itivity analyses for each section.November 2014 N-6

Type of Waste Waste

Management Option Biogenic

Feedstock Direct Emissions 1 Indirect Emissions

Livestock waste Housing,

conveyances, storage in an open lagoon, pond, pit, or pile 3 Biogas N/A CH 4 and CO 2 emissions from uncovered lagoon, pond, or pit

Livestock waste and/or food waste Anaerobic

digester Biogas CO 2 emissions from combustion of collected biogas (flare or EGU) Potential for indirect CH 4 emissions from digester if not all CH 4 produced is captured; CH 4 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 CO 2 emissions (oxidation from decomposition)

Livestock waste Livestock waste

combustor Manure and

litter CO 2 emissions from

combustion, often in an EGU; CH 4 emissions from incomplete combustion CH 4 and CO 2 emissions from pretreatment handling practices

Wastewater Aerobic

wastewater treatment process Wastewater N/A CO 2 and CH 4 emissions from uncovered treatment ponds (CH 4 emissions from instances where partial anaerobic conditions are present) Wastewater Anaerobic

wastewater treatment process Biogas CO 2 emissions from combustion of collected biogas (flare or EGU) Potential for indirect CH 4 emissions from digester if not all CH 4 produced is captured; CH 4 emissions from digester effluent
1 Point source emissions consist primarily of combus tion emissions (i.e., CO 2 ) and secondarily of uncombusted CH 4 emissions via incomplete destruction of biogas duri ng combustion (EPA, 2008b).
2 If compost piles become anaerobic, CH 4 and N 2 O may also be generated and emitted. 3 The term conveyances refers to indirect emissions f rom 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-de rived biogenic feedstocks addressed in this appendix and the other forest- and agricultural-der ived 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 outs ide of generating materials for the waste stream (e.g., for manufacture of consumer and indus trial products, such as newspaper, food, andNovember 2014 N-7

construction materials). Materials in the waste str eam represents material that has been discarded, where final disposition of the material must be man aged 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 stra tegy with an alternative emissions pathway. Whatever the waste management strategy, it would re sult in biogenic CO 2 emissions and likely some amount of CO 2 e GHG emissions (e.g., CH 4 emissions as a result of anaerobic decomposition). Evaluating the carbon cycle effects of waste manage ment at a stationary source involves a comparison of the biogenic CO 2 and CH 4 emissions at the stationary source against an alte rnative emissions pathway that would have resulted under an alternate management strategy. Evaluating these alternate waste management GHG emi ssions pathways does not require an analysis of the carbon cycle effects that transpire d during the growth and harvest of the primary biogenic materials on the landscape. As a result, m any of the biogenic attributes related to the carbon cycle effects of the growth, harvest, and us e of other biogenic feedstocks are not relevant for waste-derived biogenic feedstocks. In many cases, a s demonstrated in this appendix, a number of the terms in the assessment factor equation drop ou t when evaluating emission pathways related to waste-derived biogenic feedstocks. 

### 1.1. A Simplified Biogenic Assessment Factor Equation fo r Waste-Derived Biogenic Feedstocks
The BAF equation presented in the framework for the non-wa ste-derived feedstocks (i.e., forestryderived, agriculture-derived) can be simplified forapplication to waste-derived biogenic feedstocks. This section provides the simplified ge neral assessment factor equation which is then modified to calculate illustrative BAF values for waste-derived feedstocks under differen t 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 biog enic emissions that could have occurred on the feedstock landscape with out biogenic feedstock removal (e.g., avoided decomposition or burning), or per an alternative ma nagement strategy. The AVOIDEMIT term can be adjusted by the emission pathways specific to th e type of waste-derived feedstock and waste management strategy. For example, for certain bioga s waste feedstocks, AVOIDEMIT can be adjusted by the biogas collection efficiency, bioga s combustion efficiency, or other factors affecting emission pathways. As a result, some of the terms i n 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 docu ment): = (
 + 
 +  + ) (  ) ()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 a nd Processing ( L ), and the Feedstock Carbon Embodied in Products ( P). As a result, the full assessment framework equation as applied to biogenic CO 2 emissions from waste-derived feedstocks can be simplified to Equat ion N.1.
 = 
 (EQ. N.1)
AVOIDEMIT

represents the avoided biogenic emissions that cou ld have occurred per an alternative management strategy instead of the waste-derived fe edstock’s use in bioenergy production, relative to biogenic feedstock consumption. As discussed in the main document, negative, positive and zero BAF s (which is the same as AVOIDEMIT in this appendix), have different implications. A positive value implies that use of the feedstock for bioener gy production contributes more emissions to the atmosphere than would have occurred under the alter native 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 alternati ve management practice. In practice, as applied here, the AVOIDEMIT

term is a proportion expressed as tCO 2 e avoided (i.e., the emissions reduced, in CO 2 e, resulting from an alternate waste management str ategy to the combustion method) per tCO 2 e emitted using the combustion method (i.e., the em issions, in CO 2 e, resulting from the combustion waste management strategy). The AVOIDEMIT term is applied because the waste management strategy (e.g., collection and combustio n of landfill gas) typically results in avoided CO 2 e emissions that would have occurred in the absence of that management strategy (e.g., had the landfill gas not been collected and combusted, it m ay have been released as an indirect emission). 5 The AVOIDEMIT

term, as applied to the waste-derived biogenic fee dstocks 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 discussi on about illustrative methodologies for the calculatio n 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 thi s 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 wa ste feedstock.

5 This treatment is conceptually comparable to how t he 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 was te treatment option and the associated BAF calculations are explained in the text. The parameterization of vari ables used in the calculations presented here are i llustrative only; parameter values used in these calculations may not apply to all applications of the framework vis-à-v is the use of wastederived biogenic feedstocks used at stationary sour ces. 

### 1.2. Biogenic Municipal Solid Waste Management Biogenic MSW refers to the biogenic (organic) fract ion of MSW. In 2012, approximately 250.9 million tons of MSW were generated in the United St ates (EPA, 2014a). Biogenic materials were theNovember 2014 N-10

largest component of MSW before recycling (see Tabl e N-3). Of the total MSW generated, 135 million tons (53.8%) went to landfills, 86.6 millio n tons (34.5%) were recovered (e.g., recycled or composted), and 29.3 million tons (11.7%) were comb usted with energy recovery (this includes biogenic as well as fossil fuel-based materials, su ch as plastics). The proportions of waste recycled, composted, incinerated, or landfilled differ region ally due to multiple factors, including local economics, regulatory differences at the state and local levels, public perceptions, and infrastructure requirements (Bogner et al., 2007; E PA, 2010c). However, there is a lack of literature describing the degree to which composition of MSW c an vary from region to region. Therefore, for the purposes of the framework, we will use a nation al 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 CO 2 and CH 4 in a given landfill, whereas the goal of the frame work methodology for waste-derived feedstocks is ultimat ely concerned with how the CO 2 and CH 4 from MSW is treated used in one activity versus another. From this perspective, CO 2 and CH 4 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 pl ants. The excess capacity of the digestion system can be supplemented from food waste (e.g., E MBUD 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 Associat ed GHG Emissions Pathways GHG emissions pathways at MSW landfills result in C H 4 and CO 2 emissions. In general, landfillrelated CH 4 and CO 2 emissions are of biogenic origin and primarily resu lt from the decomposition, under anaerobic or aerobic conditions, of organic m atter such as food, yard wastes, and paper. The decomposition of organic matter in a landfill occur s through a series of microbial reactions, primarily under anaerobic conditions (Bogner, 1992) . Methane and CO 2 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 compos ition of landfill gas ranges from 45% to 55% CH 4 and CO 2, but is generally assumed to be half CH 4 and half CO 2 (EPA

, 2010a). Landfill gas also contains small amounts of nitrogen, oxygen, and hyd rogen; less than 1% non-methane organic compounds (NMOCs); and trace amounts of inorganic c ompounds (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 co mpaction of the waste. There are two general pathways for CH 4 and CO 2 emissions from landfills—indirect emissions and direct emissions (i.e., point source combustion emi ssions). These two emissions pathways are affected by the presence of an active gas collectio n and control system (i.e., flare or EGU). The remainder of this section first discusses the emiss ion 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 th at 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 bi ogas is not collected from uncontrolled landfills, the biogas may be managed through the us e of a topsoil cover to passively treat the uncollected biogas via CH 4 oxidation. Indirect emissions are the primary emis sions 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 CH 4 and CO 2 through the landfill soil cover. A fraction of the CH 4 in the biogas (ranging from 10% to 35% (IPCC, 2006; EPA, 2013c; SWICS, 2009) will be oxidized by bacteria in the cover soi l 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 collect ion system consists of network of pipes and collection wells strategically placed throughou t the disposal areas to collect and transport the biogas to a central control system. Acontrol system typically involves a combustion device such as a flare, turbine, or boil er for combustion of the collected landfill gas. Controlled landfills also include a topsoil co ver to passively treat the remaining landfill gas that is not collected via CH 4 oxidation. In the United States, there are approxi mately 594 operational landfill gas-to-energy projects, at whi ch landfill gas is used as fuel for generation of electricity or process heat in indust rial applications (EPA, 2013a).November 2014 N-12

Approximately 25% of the roughly 2,400 currently op erating 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 a dditional, existing domestic MSW landfills have the potential to capture landfill ga s for energy use (EPA, 2013a). The primary GHG emissions pathway at controlled landfills is di rect emissions of CO 2 (see Figure N-2).
o Direct emissions: The primary GHG emissions pathway at controlled lan dfills is point source emissions of CO 2 . The CH 4 in the landfill gas that is collected and combusted will be converted to CO 2 ; the CO 2 in the collected landfill gas will be directly emitted as CO 2 ; and the CH 4 in the collected landfill gas that is not combusted will be directly emitted as CH 4 . o Indirect emissions: Both CH 4 and CO 2 will be emitted through the landfill soil cover. A fraction of the CH 4 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 soil s. When organic materials are landfilled, a portion of the carbon in the materials will not readily degrade due to several factors, including environme ntal conditions (e.g., moisture, pH, temperature), and the creation of anaerobic environ ments through waste disposal and compaction. When the environment in which wastes are placed bec omes 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 i s referred to as carbon storage because this carbon is permanently removed from the global carbon cycle

. Cellulose and hemicellulose are the major biodegrad able 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). Th e 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 stor age factors for several materials of the MSW stream (Barlaz, 1998; ICF, 2008), including yard wa ste, 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 t hat is anaerobically decomposed in the landfill, suggesting that 50% of the biogenic carbon placed i n a landfill becomes stored carbon.November 2014 N-13

Figure N-1. Carbon Balance for an Uncontrolled Landfi ll.

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 (CH 4 and CO 2 ) released directly from the landfill cover to the atmosphere. The amount and rate of total CH 4 generation in landfills, as well as the amount of indirect emissions of CH 4 and CO 2 , depends upon the quantity and composition of the la ndfilled material, as well as the landfill design and surrounding environmental conditions. If not co llected and combusted, a portion of the CH 4 generated in a landfill oxidizes to CO 2 as it travels through the top layer of the landfil l cover; the remaining unoxidized portion of the landfill gas is emitted through the landfill cover. This process results in indirect emissions of both CH 4 and CO 2 through the landfill cover. Methane oxidation efficiency is directly affected b y the thickness, physical properties, moisture content, and temperature of landfill cover soils. T he rate of CH 4 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 CH 4 and the remaining CH 4 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., temp erature and soil moisture) van vary as a function o f climate, such that the efficiency of CH 4 oxidation may vary regionally and seasonally (Spok as and Bogner, 2011). In hot, arid climates, CH 4 oxidation in landfill cover soils can be limited, resulting in higher indirect CH 4 emissions than in cooler, wetter climates. In hot, arid climates soil moisture is limited for much of the year, thus reducing CH 4 oxidation rates, and seasonally high soil temperatures prevent methanotrophic activity (Chant on et al., 2011a, Spokas and Bogner, 2011). The IPCC (2006a) and EPA (2009a) default value for the CH 4 oxidation fraction in cover soils of modern, managed landfills such as those found in th e United States is 10% of generated CH 4 . EPA considers 10% to be a conservative (lower end) defa ult oxidation fraction. Some studies point to an average CH 4 oxidation rate of approximately 40% (ranging from negligible to 100%) of the total CH 4 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 fi eld and laboratory studies have shown large variations in oxidation rates, particularly for lan dfills with active gas collection and control syste ms, EPA expanded the default oxidation fraction value t o include those based on the calculated CH 4 flux 6 rate in grams per square meter per day (g/m 2 /day) to the bottom of a landfill’s cover soil prio r to any oxidation (EPA, 2013c, 40 CFR § 98).

• For high rates of CH 4 flux (greater than 70 g/m 2 /day) the default oxidation fraction is 10%;

• For moderate rates of CH 4 flux (10 to 70 g/m 2 /day) the default oxidation fraction is 25%;

• For low rates of CH 4 flux (less than 10 g/m 2 /day) the default oxidation fraction is 35%

6 The methane flux rate is referred to as the contin uous flow of methane from an area within a landfill where methane is produced to the atmosphere over a specif ied 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 CO 2 and, depending on the destruction efficiency (DE) of the combustion device, CH 4 emissions from landfill gas collection and combustion through flaring or us e as a fuel in an EGU (often referred to as landfil l gas-to-energy projects). 7 Landfill gas collection systems vary in landfill ga s collection efficiency (CE). Recovery ranges from 35% to 90% of the gas generated in a particular lan dfill 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 f rom 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 effi ciencies may vary substantially, and due to the cost of determining the amount of landfill gas gene rated 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 t o 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 colle ction system. Collected landfill gas may be combusted using a fla re, as a fuel for an EGU, or directly in boilers an d other applications. Landfill gas may be purified to create compressed natural gas or liquefied natural gas, or for injection into natural gas pipe lines. Of the total estimated CH 4 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 C H 4 in the landfill gas to CO 2 , resulting in CO 2 emissions. 8 A portion of the collected gas will not be combust ed due to inefficiencies in the combustion device, thus this fraction of CH 4 will be emitted to the atmosphere as CH 4 . Destruction efficiencies for CH 4 in landfill gas range from 90% to 99.9% (IPCC, 2006 ; SWICS, 2009; New Zealand Ministry for the Environment, 2010; EPA, 2013c). Ad ditionally, the CO 2 in the collected gas will not be combusted and will be directly emitted as CO 2 . 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 emissi ons of non-methane organic compounds (NMOC). Landfills that emit 50 Mg or more of NMOC p er year are required by EPA regulations to install a landfill gas capture and control system i n order to control NMOC emissions (EPA, 1996). To

7 Typically, both GHG emissions pathways will be pre sent at a landfill, as landfills with landfill gas collection and destruction systems generally do not capture all CH 4 generated in the landfill. Uncaptured CH 4 will either be oxidized via methanotrophic activity in the cover s oils, or will be released directly to the atmospher e as indirect emissions. 8 Note that as the combustion process is never compl ete, some CH 4 in landfill gas is not destroyed and therefore stack gas emissions contain a small percentage of C H 4 .November 2014 N-16

comply with EPA regulations, landfill operators mus t, at a minimum, collect and combust their biogas. A co-benefit of NMOC emissions control is the destruction of CH 4 present in the landfill gas.
Both uncontrolled and controlled landfills include liners and leachate collection systems to prevent pollutants from migrating beyond the landfill, whic h can result in ground and/or surface water pollution. 9 Both uncontrolled and controlled landfills also st ore 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 no t 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 5 0%. 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 include s leachate collection and treatment, groundwater monitoring, inspection of the final cov er and maintenance as required, and monitoring to ensure that CH 4 is not migrating off-site. Collection and combusti on of landfill gas may continue throughout this period. EPA regulation s (40 CFR § 258.61) specify a 30-year postclosure monitoring period unless this period is ext ended 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 di rect biogenic emissions resulting from the collection and combustion of landfill gas. The biog enic feedstock from an MSW landfill is the biogas generated from MSW decomposition and the biogas col lected 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 b enefits 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 re ductions achieved through capture and combustion of landfill gas, compared to an alternate, Reference case emissions pathway of indirect CH 4 and CO 2 emissions through the landfill cover (had the land fill gas not been collected and combusted). In other words, biogenic emissions from a controlled landfill are being compared to the biogenic emissions from a n uncontrolled landfill. In practice, as applied here, the AVOIDEMIT term is expressed as 1 minus the ratio of metric t ons of CO 2 e (tCO 2 e) avoided (i.e., the point and indirect emissions, in CO 2 e, of the collected biogas had that biogas not been collected and combusted, after acco unting for indirect emissions of CO 2 and CH 4 , and the CH 4 oxidation that would have occurred in the landfill cover soil) per tCO 2 e 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. Leachat e collection and removal systems sit on top of the liners to remove leachate from the landfill for collection an d disposal. 10A closed landfill as referred to in this context means a landfill that no longer accepts waste for d isposal.November 2014 N-17

combustion (i.e., the emissions, in CO 2 e, of the collected and combusted biogas, after acc ounting for the CE of the gas collection system and the DE of t he biogas destruction device). For the biogas feedstock that is generated and collected from land fills, the AVOIDEMIT term can be conceptually expressed by 1 minus a simplified ratio of CO 2 e emissions of the treatment fates:


 =  − +,  -	-./00/120	341.	54-65.-25	675-4265/8-	51	91.:;05/1 2 +,  -	-./00/120	341.	91.:;05/12	54-65.-25 (EQ.N.2) Note that the same amount of biogas and constituent s of the biogas are considered for both the actual and alternate treatment fates.
2.3.1. Boundaries and Assumptions for MSW Landfilling Meth odology The methodology presented in this appendix for trea tment of MSW through landfilling does not consider offsets from electricity generation, carbo n 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 sc ope and major assumptions made are provided as follows:

• Offsets—Landfill gas-to-energy projects reduce foss il 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 ben efits, for the current year of a landfill gas energy project if desired (EPA, 2012b).

• Carbon storage—Carbon storage refers to the fractio n of carbon remaining in the biogenic materials after accounting for the carbon exiting t he system as landfill gas or that is dissolved in the leachate. The amount of carbon sto rage will vary with environmental conditions in the landfill, but can be generally th ought 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 M SW landfilling in this framework because the amount of carbon storage in a given lan dfill 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 exp ected to be insignificant, especially for instances where the biogas destruction device is co -located at a landfill.

• Operation of the gas collection system—One importan t assumption to note is that the methodology for MSW landfilling assumes the landfil l gas collection system is operating continuously. It is possible to perform the calcula tions 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 equ ations used to calculate the CO 2 and CH 4 emissions from landfills with gas collection and co ntrol.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 followingemissions pathways from an MSW landfill with or without gas collection and control the amount of

• Indirect CH 4 emissions from the landfill surface;

• Indirect CO 2 emissions from the landfill surface;

• Direct CH 4 emissions from the CH 4 in the collected landfill gas that is not combuste d (as a result of a combustion efficiency less than 100%);

• Direct CH 4 emissions in the collected landfill gas that is co mbusted and converted to CO 2 ; and

• Direct CO 2 emissions in the collected biogas that is emitted as CO 2 .   	 !	"# 		&%!<"&&!=
=  > ? ( > ? − > ?  + > ? @ ) + A > ?  × ?? C D +   +   @ (EQ. N.3)
Where:
CO 2 e emissions = metric tons CO 2 e emissions from MSW landfilling (MT/year).
GWP HI J = 100-year GWP of CH 4 , 25 (IPCC, 2007).
CH 4 R = the amount of CH 4 recovered and sent to the landfill gas destruction device (Equation N.4).
CH 4 D = amount of CH 4 destroyed via combustion (Equation N.5).
CH 4 U = amount of uncollected CH 4 emitted through landfill cover surface; separate calculations for landfills with gas collec tion and landfills without gas collection (Equation N.6 or Equation N. 7, depending on the presence of a gas collection system).
CO 2 R = the amount of CO 2 recovered, sent to the landfill gas destruction dev ice, and emitted to the atmosphere (Equation N.8).
CO 2 U = amount of uncollected CO 2 emitted through landfill cover surface (Equation N.9 or Equation N.10, depending on the pr esence of a gas collection system). 44/16 = molecular weight ratio of CO 2 to CH 4 . Equation N.3 can be grouped and explained in three major parts:

• The first part, GWP HI J ( CH M R − CH M D + CH M U ) , accounts for the amount of CH 4 that is collected, but not combusted (CH 4 R – CH 4 D) plus the amount of CH 4 in the generated landfill gas that is not collected and emitted as indirect e missions through the landfill cover surfaceNovember 2014 N-19

as CH 4 . Because the terms in Equation N.3 need to be in u nits of tCO 2 e, these quantities must be adjusted by the 100-year GWP for CH 4 . • The second part, (CH 4 D × 44/16), accounts for the quantity of CH 4 that is collected and oxidized to CO 2 during combustion. The amount of CH 4 destroyed needs to be adjusted by the 44/16 conversion factor because the gas is bein g converted to CO 2 . • The third part, CO 2 R + CO 2 D + CO 2 U, accounts for all of the CO 2 emissions (direct and indirect).
o CO 2 R is the amount of CO 2 in the biogas that is collected and sent to the de struction device; this quantity will be directly emitted as C O 2 ; o CO 2 D is the amount of CO 2 that is collected, but not passed through the destr uction device;
o CO 2 U is the amount of CO 2 in the generated landfill gas that is not collecte d and emitted as indirect emissions through the landfill cover surface as CO 2 . This quantity of CO 2 is not adjusted for oxidation as the gas passes th rough the cover.
The annual amount of CH 4 that is collected, or recovered, from the landfill gas and sent to the destruction device can be calculated using Equation N.4. The CH 4 concentration in the landfill gas is typically monitored, or may be assumed as a percent age 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:
CH 4 R = amount of CH 4 recovered from the landfill and sent to the landfil l gas

destruction device (metric tons CH 4 /year). V = annual volumetric flow rate of biogas to the landfill gas destruction device

(cubic feet biogas per year), as determined from da ily monitoring.
C HI J = average annual CH 4 concentration of biogas (percent, fraction, wet bas is). 0.0423 = density of CH 4 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 metr ic tons. Equation N.5 can be used to calculate the quantity of CH 4 destroyed in a landfill gas destruction device. As mentioned previously, achieving 100% des truction efficiency is not feasible, thus the amount of CH 4 recovered must be adjusted by the destruction, or combustion, efficiency of the landfill gas destruction device. This adjustment ac counts for the proportion of collected CH 4 in the biogas that is not destroyed by the destruction dev ice. The collected CH 4 in the landfill gas that is not combusted is a direct source of CH 4 emissions to the atmosphere.November 2014 N-20

+Q ? \ = 	 +Q ? R × \] (EQ. N.5) Where:
CH 4 D = CH 4 destroyed at a landfill gas destruction device (met ric tons CH 4 /year).
CH 4 R = amount of CH 4 recovered and sent to the landfill gas destruction device

(Equation N.4).
DE = CH 4 destruction efficiency from flaring or combustion i n an EGU, decimal

percent. The DE varies with the type of landfill ga s destruction device used; it can be estimated as the lesser of the manufactur er’s specified destruction efficiency and 0.99 (EPA, 2013c). The presence of a landfill gas collection system af fects the amount of indirect CH 4 emissions from the landfill. When calculating the amount of indire ct CH 4 emitted from a landfill with gas collection, only the uncollected portion of CH 4 in the landfill gas is adjusted for oxidation. Alt ernatively, for a landfill without gas collection, all of the CH 4 in the generated landfill gas is adjusted for oxid ation. Equations N.6 and N.7 can be used to determine the amount of uncollected, or indirect, CH 4 emissions from a landfill with gas collection and a landfill without gas collection, respectively. Both equations adjust the amount of CH 4 recovered by the term, 1/CE, which represents the p ortion of generated landfill gas that is not collected by the gas collection system. Equation N.6 subtracts the term CH 4 R to account for the quantity of CH 4 that is collected and sent to the destruction devi ce so that only the uncollected portion is adjusted fo r oxidation. Note that this term is not included in Equation N.7 because all CH 4 generated must be adjusted for oxidation in landfi lls 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 col lection system, decimal percent
CH 4 R = the amount of CH 4 recovered and sent to the landfill gas device

(Equation N.4)
OX = methane oxidation fraction
The amount of CO 2 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

CO 2 R = the amount of CO 2 recovered and sent to the landfill gas destruction

device (metric tons CO 2 /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 − C HI M /100%) = average annual CO 2 concentration of landfill gas, (C = average annual

CH 4 concentration of biogas, percent, fraction wet basi s). 0.1160 = density of CO 2 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 metr ic tons. Calculating indirect CO 2 emissions from the landfill surface is similar to that used to calculate indirect CH 4 emissions from the landfill surface (see Equations N.6 and N.7). Equations N.9 and N.10 present two ways to calculate indirect CO 2 emissions from either a landfill with a gas collection system, or one without. Both equations are adjusted by the CE in order to c onsider only the portion of uncollected CO 2 that is emitted as CO 2 through the landfill cover surface and the portion of uncollected CH 4 that is emitted through the landfill cover surface and oxid ized to CO 2 by the methanotrophic bacteria. The conversion factor of 44/16 is applied to the portio n of CH 4 in the uncollected gas that is oxidized to CO 2 .
+,  ^, _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 co llection system, decimal percent.
CO 2 R = amount of CO 2 recovered and sent to the landfill gas destruction device (Equation N.8).
CH 4 R = the amount of CH 4 recovered and sent to the landfill gas destruction

device (Equation N.4).
OX = methane oxidation fraction. 44/16 = molecular weight ratio of CO 2 to CH 4.November 2014 N-22

Several parameters are presented and used in the eq uations in the remainder of this section. Table N-4 presents the parameters used, typical or defaul t values, ranges presented in the literature, and references. Table N-4. Summary of Parameters Used When Calculati ng 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 CH 4 flux rates EPA, 2013c;

SWICS, 2009

Concentration of CH 4 in the landfill gas or biogas C HI J 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 landfillsand 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 CH 4 for a flare EPA, 2011a;

EPA, 2013c

Destruction efficiency (of an EGU) DE 0.97 0.96 to 0.99 Fraction DE of CH 4 in a direct use system (e.g., boilers, heaters) varies by technology EPA, 2011a;

EPA, 2013c

Density of CH 4 in landfill gas – 0.0423 – lbs/scf At 520 oR or 15.74 oC and 1 atm EPA, 2011a;

EPA, 2013cNovember 2014 N-23

Parameter Description Symbol Value Used in Examples Range Units Comments Reference (for value column) Density of CO 2 in landfill gas – 0.1160 – lbs/scf At 520 oR or 15.74 oC and 1 atm Calculated

value 1
CE = collection efficiency; DE = destruction effici ency; EGU = electricity generating unit; F = fracti on of CH 4 in landfill gas; lbs/scf = pounds per standard cubic foot; OX = oxid ation fraction; R = Rankine
1 This value is calculated using a 60 degree Fahrenh eit conversion: 44.01 * (2.20462/836.6) = 0.1160, w here 44.01 = the molecular weight of CO 2 ; 2.20462 is a unit conversion factor from kilogram s 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 calc ulating a BAF value for landfill gas. In order to derive a BAF

value for landfill gas, the numerator and denomina tor 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 numera tor in the AVOIDEMIT term).
2.4.1. Example Calculations for a Controlled Landfill (Fla ring) 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 r ecovered approximately 150 million cubic feet of landfill gas in the past year. The landfill gas mon itoring system automatically corrects for temperature and pressure, and computed an annual av erage CH 4 concentration in the gas of 55%. Step 1: Calculate the Amount of CH 4 and CO 2 Recovered by the Landfill Gas Collection System The starting point for both treatment fates for tre atment through MSW landfilling is the amount of gas recovered. Equations N.4 and N.8 can be used to calculate the amount of CH 4 and CO 2 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 TT D × T. CT × XT XT ×   × T.?X? ,TTT = WXX?. g		  Step 2: Calculate the CO 2 e Emissions for MSW Landfilling without Biogas Coll ection and Control The numerator calculates the CO 2 e emissions profile of the biogas feedstock had the gas not been collected and combusted. Because there is no gas co llection or control for the alternate fate, the CH 4 R, CH 4 D, CO 2 R, and CO 2 D terms in Equation N.3 can be dropped, leaving onl y the CH 4 U and CO 2 U terms. Equations N.7 and N.10 can be used to calcul ate the amount of indirect CH 4 and CO 2 emittedNovember 2014 N-24

by a landfill without gas collection and control, a ssuming 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 CO 2 e emissions profile of the gas feedstock had the ga s not been collected and combusted is calculated using Equation N.3:
  	 !	"# 		&%!<"&&!=	j$k *$	=%	( &&( $ !
= X ( T − T + iT.  ) + AT × ?? C D + T + XWT. Ci = X, gX. Tg		   Step 3: Calculate the CO 2 e Emissions with Gas Collection and Control (Flarin g) The denominator calculates the CO 2 e emissions profile of the gas feedstock had the ga s been collected and combusted using a flare with a destru ction efficiency of 99%. Equation N.5 can be used to calculate the CH 4 D 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 CH 4 and CO 2 emitted by a landfill with gas collection and contr ol, 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?. g n + 	T. T m `  T. hX × Xg?. WXa − Xg?. WX n

× ?? C = WWT. h		  Equation N.3 can now be used to calculate the CO 2 e 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 × ?? C D + 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 Equati on 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, indi cate that combustion of collected landfill gas feedstock by a stationary source resul ts in a net CO 2 e emissions reduction relative to releasing the collected landfill gas directly to th e 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 calculat ed in Section 2.4.1, thus the value of the numerator is the same as in Section 2.4.1. The deno minator 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 generati on by the EGU are not included in the framework. Step 1—Calculate the CO 2 e Emissions for MSW Landfilling without Gas Collect ion and Control The numerator will be the same as that calculated i n Example 1 when the same CE and OX values are used (Equations N.7 and N.10). Similar to Examp le 1, the net CO 2 e 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 × ?? C D + T + XWT. Ci = X, gX. Tg		   Step 2—Calculate the CO 2 e Emissions with Gas Collection and Control (EGU) The denominator calculates the CO 2 e 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 CH 4 D term in Equation N.3:
+Q ? \ = Xg?. WX	 × T. ih = XWC. g	lY	> ? The quantities of indirect CH 4 and CO 2 (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?. g n + 	T. T m `  T. hX × Xg?. WXa − Xg?. WX n

× ?? C = WWT. h		  Equation N.3 can now be used to calculate the CO 2 e 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 × ?? C a + 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 combu stion 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 t hrough the year. The alternate treatment fate is similar to the numerator calculated in Sect ion 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 collectio n system and control device operated during the year (fRec). Step 1: Calculate the Amount of CH 4 and CO 2 Recovered by the Landfill Gas Collection System The starting point for both treatment fates, the am ount 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 TT D × T. CT × XT XT ×   × T.?X? ,TTT = WXX?. g		  Step 2: Calculate the Fraction of Hours the Recover y System Operated During the Year fRec = actual operating hours of the recovery syste m/number of hours in the year In this example, the gas collection system was inst alled and fully operational on May 1 stin a nonleap year. There are 244 days between May 1 stand December 31 st, or 5856 hours. Therefore, fRec = 5856/8760 = 0.66849.November 2014 N-27

Step 3: Calculate the CO 2 e Emissions for MSW Landfilling without Gas Collect ion and Control Equations N.7 and N.10 are slightly modified by div iding the amount of recovered CH 4 and CO 2 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?i D	× (  − 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?i D × ??

C = h, i?. W		  Similar to Section 2.4.1 and 2.4.2, the net CO 2 e emissions profile of the gas feedstock had the ga s not been collected and combusted is calculated using Eq uation N.3:
CO 2 e emissions from MSW landfilling without gas collec tion =
X ( T − T + gWh. C? ) + AT × ?? C D + T + hi?. W = hg, gg. 		   Step 4: Calculate the CO 2 e emissions with gas collection and control (EGU) The denominator calculates the CO 2 e emissions profile of the gas feedstock had the bi ogas been collected and combusted in an EGU with a DE of 97%. Equation N.5 can be used to calculate the CH 4 D term in Equation N.3:
+Q ? \ = Xg?. WX	 × T. ih = XWC. g	lY	> ? The quantities of indirect CH 4 and CO 2 (Equations N.6 and N.9) will be the similar to tho se presented in Examples 1 and 2, except that fRec mus t now be factored into Equations N.6 and N.9 to give Equations N.13 and N.14:

+Q ? ^, _60	9177-95/12 = m A   × > ? "( 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?i a − 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 CO 2 e emissions profile of the feedstock given that the biogas was collected and combusted via an EGU:
CO 2 e emissions from MSW landfilling with gas collectio n = 25 (1584.35 – 1536.82 + 1411.72) + (1536.82 x 44/ 16) + 3554.82 + 3950.81 = 48,213.22 MT CO 2 e 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) r esults in:
BAF = AVOIDEMIT

= 1 – (78,882.21 / 48,213.22) BAF = −0.64 The BAF for this example is approximately two and a half t imes greater than the BAF of −1.50 calculated in Section 2.4.2 as a result of the frac tion 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 bette r 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), th e collection efficiency (CE) of the landfill gas collection system, the destruction efficiency (DE) of the selected combustion device, and the CH 4 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 se t 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 t he change in OX factors. For example, when comparing Analyses 1a and 2a, the only difference i s that 1a uses an OX of 0.10 for both the actual and alternate fates, while 2a uses different OX val ues 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 CH 4 was revised to 25 (IPCC, 2007). To comply with int ernational reporting standards under the UNFCCC, official emission estim ates reported by the United States use the IPCC Sec ond Assessment Report GWP values (IPCC, 1996). The United States w ill transition to using the revised GWPs beginning in 2015. In this framework, the GWP of 25 for the central examples w ithin 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 S tates, 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 (G HGRP) and EPA’s Emissions and Generation Resource Integrated Database (eGRID), there are rou ghly 142 MSW combustors in the United States that emit approximately 30 million metric tons of b iogenic CO 2 e. 11 Incineration oxidizes almost all of the carbon in the MSW to CO 2 (Astrup et al., 2009). Generally less than 0.5% of the carbon remains in the ashes (i.e., it is not emitted to th e 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 tires 12 and plastics. After the MSW is delivered

11 Based on GHGRP data for the 2011 reporting year an d 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 (Ru bber 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 recover y of recyclables), as refuse-derived fuel (burn afterrecyclables 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 fro m combustion of biogenic MSW feedstocks are primarily CO 2 . For the purposes of this document, biogenic MSW i s 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 di rect biogenic CO 2 emissions from MSW combustion. This section provides an illustrative m ethod for calculating a BAF value that is applied to direct biogenic CO 2 emissions from MSW combustors. Here, the biogenic feedstock is MSW that is collected and incinerated, oxidizing the biogenic w aste-feedstock to CO 2 emissions. Landfilling the biogenic MSW can be considered the alternate fate of the MSW feedstock had it not been incinerated. The emissions profile resulting f rom this alternate fate represents the numerator of the emissions ratio term in AVOIDEMIT . Were the MSW to have been disposed of in a landfi ll, 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 ca rbon 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 landfil l (Staley and Barlaz, 2009). 13 The factors affecting degradation can result in the long-term, potentiall y permanent, carbon storage of approximately 50% of total landfilled organic carbon (Bogner et a l., 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 tCO 2 e avoided (i.e., the emissions, in CO 2 e, of the MSW had it not been combusted) per tCO 2 e removed via combustion (i.e., the emissions, in CO 2 e, 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 assumptio n that had the MSW not been incinerated, it

13 While cellulose, hemicellulose, and lignin (presen t in paper and wood products) can degrade and be co nverted to CH 4 in landfills, the anaerobic conditions in landfill s prevent their full degradation (Bogner , 1992; Barlaz, 2006 ; Wang et al., 2011). Furthermore, the presence of li gnin can inhibit cellulose and hemicellulose degrad ation (Micales and Skog, 1997 ; Barlaz, 2006). Because lignins effectively prevent degradation, between 84% and 100% of the initial carbon in landfilled wood products is seque stered 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 fa te, the value of the numerator must account for the fraction of landfilled MSW that decays anaerobi cally, thereby producing landfill gas that may or may not be collected. If the landfill gas is collec ted and combusted (e.g., flared), the collection efficiency and destruction efficiency must be accou nted for. In accounting for indirect emissions from the landfill cap, the CH 4 oxidation via the landfill cover soils must be acc ounted 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:
CO 2 e emissions avoided by landfilling the MSW (kg CO 2 e/metric ton MSW wet weight) =
tsZ+Q ? × ( +Q ?01/70 + +Q ?91.:;05/12 ) + +, 01/70 + +, 91.:;05/12 (EQ. N.16) Where: GWP

HI M = 100-year GWP of CH 4 , 25 (IPCC, 2007)
CH 4soils = CH 4generated × (1 – CE) × (1 – OX) (EQ. N.57)
CH 4combustion = CH 4generated × (CE) × (1 – DE) (EQ. N.68) Where:
CH 4generated = C × D lfg× (%CH 4 ) × (16/12) (EQ. N.79) C = amount of biogenic C in MSW (kg C/metric ton MSW wet weight).
D lfg= dissimilation coefficient (fraction of biogenic C that leaves the landfill via decomposition of biogenic waste).
%CH 4 = proportion of gas that is CH 4 . (16/12) = molecular weight ratio of CH 4 to C. CE = gas collection efficiency.
OX = CH 4 oxidation factor associated with the landfill cover soil. DE = gas destruction efficiency (i.e., combustion efficiency of flare or EGU).
CO 2soils = (CO 2generated + CH 4generated × 44/16 × OX) × (1 – CE) (EQ. N.20) CO 2combustion = (CO 2generated + CH 4generated × 44/16 × DE) × CE (EQ. N.21) Where:
CO 2generated = C × D lfg× (%CO 2 ) × (44/12) (EQ. N.82) Where: C = amount of biogenic C in MSW (kg C/metric ton MSW wet weight).November 2014 N-32

D lfg= dissimilation coefficient (fraction of biogenic C that leaves the landfill via decomposition of biogenic waste). (%CO 2 ) = proportion of gas that is CO 2 . (44/12) = molecular weight ratio of CO 2 to C. CE = gas collection efficiency.
OX = CH 4 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 p oint source, stack emissions from the MSW combustion device. The value of the denominator is equal to the CO 2 e of the combusted MSW, adjusted by the proportion of combusted biogenic ca rbon in MSW that is converted from C to CO 2 . MSW combustion results in near-complete oxidation o f C to CO 2 ; generally less than 0.5% of the initial amount of C remains in solid form (ash) pos t-combustion. The following equation can be used to calculate the total CO 2 e emissions from MSW combustion (the denominator of the AVOIDEMIT

term):
CO 2 e emissions from MSW combustion (kg CO 2 e/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 CO 2 to C. After solving for the numerator and the denominatorof 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 eq uations in the remainder of this section. Table N-6 presents the parameters used, typical or default va lues, ranges presented in the literature, and references.November 2014 N-33

Table N-6. Summary of Parameters Used When Calculati ng 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 CH 4 or CO 2 in the landfill gas %CH 4 ,

%CO 2 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 landfillsand 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 CH 4 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., 2009November 2014 N-34



### 3.2. Example AVOIDEMIT and BAF Calculations for MSW Combustion Two example scenarios are presented here for calcul ating a BAF value for MSW combustion compared to an alternate of landfilling with gas co llection and an alternate of landfilling without ga s collection. A hypothetical example is used to calcu late 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 f ate.
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 s olve 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 land filled, 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 condit ions apply:

• The amount of biogenic carbon in MSW is estimated a t 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% (D lfg= 0.5), such that 50% goes into long-term storage.

• On a mass basis, 55% of the carbon becomes CH 4 and 45% of the carbon becomes CO 2 . • The fraction of CH 4 in the landfill gas that is oxidized via cover soil s is the default of 0.10 (OX = 0.1).

• Landfill gas collection efficiency is 75% (CE = 0.7 5).

• Destruction efficiency of the collected landfill ga s is 99% (DE = 0.99). Step 1: Calculate the CH 4 and CO 2 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:
CH 4generated = 90 kg C per metric ton MSW ww × 0.5 × (55/100) × (16/12) = 33.0 kg CH 4per metric ton MSW ww
CO 2generated = 90 kg C per metric ton MSW ww × 0.5 × (45/100) × (44/12)
= 74.25 CO 2 per metric ton MSW wwNovember 2014 N-35

Using the computed value from Equation N.19, Equati on N.17 can be solved:
CH 4soils = 33.0 × (1 – 0.75) × (1 – 0.1) = 7.425 kg CH 4 per metric ton MSW ww Using the computed value from Equation N.19, Equati on N.18 can be solved:
CH 4combustion = 33.0 × (0.75) × (1 – 0.99) = 0.2475 kg CH 4per metric ton MSW ww Using the computed values from Equations N.19 and N .22, Equation N.20 can be solved:
CO 2soils = (74.25 + (33.0 × 44/16 × 0.1)) × (1 – 0.75) = 20.8312 kg CO 2 per metric ton MSW ww Using the computed values from Equations N.19 and N .22, Equation N.21 can be solved:
CO 2combustion = (74.25 + (33.0 × 44/16 × 0.99)) × 0.75 = 123.0694 kg CO 2 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:
CO 2 e emissions avoided by not having landfilled the MS W (kg CO 2 e/metric ton MSW ww) = 25 × (7.425 + 0.2475) + 20.8312 + 123.0694 = 335.713 kg CO 2 e per metric ton MSW ww Step 2: Calculate the CO 2 Emitted Through MSW Combustion Next, the denominator (total CO 2 e emissions from MSW combustion) of the AVOIDEMIT term can be solved (kg CO 2 e/metric ton MSW wet weight) using Equation N.23:
CO 2 e 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 t ake into account any reduction in fossil fuel usage as a result of any heat, power, or both that may ha ve 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 landfille d without gas collection or combustion, then CH 4soils and CO 2soils would increase in value while CH 4combustion and CO 2combustion would both be 0. Step 1: Calculate the CH 4 and CO 2 Generated and Emitted by a Landfill without Gas Collection To calculate the numerator, Equations N.19 and N.22 must first be solved:
CH 4generated = 90 kg C per metric ton MSW ww × 0.5 × (55/100) × (16/12) = 33.0 kg CH 4per metric ton MSW ww
CO 2generated = 90 kg C per metric ton MSW ww × 0.5 × (45/100) × (44/12)
= 74.25 CO 2 per metric ton MSW ww Using the computed value from Equation N.19, Equati on N.17 can be solved. The collection efficiency is 0 in this equation since there is no gas collection system.
CH 4soils = 33.0 × (1 – 0) × (1 – 0.1) = 29.7 kg CH 4per metric ton MSW ww Using the computed values from Equations N.19 and N .22, Equation N.20can be solved:
CO 2soils = (74.25 + (33.0 × 44/16 × 0.1)) × (1 – 0) = 83.325 kg CO 2 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:
CO 2 e emissions avoided by not having landfilled the MS W (kg CO 2 e/metric ton MSW ww) = 25 × (29.7 + 0) + 83.325 + 0 = 825.825 kg CO 2 e per metric ton MSW wwNovember 2014 N-37

Step 2: Calculate the CO 2 e Emitted Through MSW Combustion Next, the denominator (total CO 2 e emissions from MSW combustion) of the AVOIDEMIT term can be solved (kg CO 2 e/metric ton MSW wet weight) using Equation N.23:
CO 2 e 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 t ake into account any reduction in fossil fuel usage as a result of any heat, power, or both that may ha ve 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 c ombustion and the alternate fate of landfilling with gas collection and flaring. Key parameters imp acting the BAF include the destruction and collection efficiencies (DE and CE, respectively) a nd the GWP for CH 4 (21, 25, and 28). In each of the six analyses, the DE of the landfill gas was adjust ed 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 fa tes and essentially cancels out.
The BAF values are most negative compared to the other ana lyses, when MSW combustion is compared to a landfill with a 75% CE and 97% DE, in dicating that MSW combustion results in a greater reduction of CO 2 e 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 i s 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 Proces ses and Associated GHG Emissions Pathways Livestock waste management can produce CH 4 , CO 2 , and N 2 O emissions. In 2012, livestock waste management emissions in the United States were esti mated at 52.9 Tg CO 2 e for CH 4; 14 and 18.0 Tg CO 2 e for N 2 O (EPA, 2014b). Waste from dairy cattle and swine h ad the highest CH 4 emissions; waste from beef and dairy cattle had the highest N 2 O emissions (EPA, 2014b). Methane is produced under anaerobic conditions in l ivestock waste storage and treatment systems, such as liquids or slurries in lagoons, ponds, tank s, pits, or piles. In the United States, the majori ty of livestock waste is handled as a solid (e.g., in sta cks or drylots) or deposited on pasture, range, or paddock lands, where it tends to decompose aerobica lly and produce little or no CH 4 (EPA, 2014b). Carbon dioxide is also produced under anaerobic con ditions and generated when CH 4 in the biogas is combusted.
Both direct and indirect N 2 O emissions are emitted during livestock waste mana gement. Direct N 2 O emissions from livestock waste are produced as part of the nitrogen cycle through the nitrification and denitrification of the organic nitrogen in live stock dung and urine. The production of direct N 2 O emissions from livestock waste depends on the compo sition of the manure and urine, the type of

14 This accounts for CH 4 reductions due to capture and destruction of CH 4 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 N 2 O emissions to occur, the manure must first be hand led aerobically where ammonia (NH 3 ) or organic N is converted, via nitrification, to nitrates and nitrites, and then handled anaerobically where the nitrates and nitrit es are reduced to dinitrogen gas (N 2 ), with intermediate production of N 2 O and nitric oxide (NO), via denitrification (EPA, 2014b). These emissions are most likely to occur in dry man ure handling systems that have aerobic conditions, but that also contain pockets of anaero bic conditions due to saturation. A very small portion of the total N excreted is expected t o convert to N 2 O in the waste management system.

• Indirect N 2 O emissions are produced when nitrogen is lost from the system through volatilization (as NH 3 or NO x ) or through runoff and leaching of nitrogen duringwaste treatment, storage and transportation (EPA, 2014b). The vast majority of volatilization losses from these operations are NH 3 (EPA, 2014b).
The framework does not consider N 2 O emissions; therefore the methodology presented in the remainder of this section does not consider N 2 O emissions. With the rise of concentrated animal feeding operat ions (CAFOs), the traditional use of livestock waste as a soil amendment (where it decomposes aero bically) is not practical (Santoianni et al., 2008). 15 As a result, the use of liquid-based management sy stems (e.g., uncovered lagoons, pits, anaerobic digesters) that promote anaerobic conditi ons is increasing in popularity (EPA, 2014b). There are two general pathways for GHG emissions fr om 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 bio gas. 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 CH 4 emissions (EPA, 2009b). Volatile solids contained in livestock waste degrade under anaerobic conditions, thus gene rating CH 4 biogas. If the biogas produced in uncovered lagoons, pits, ponds, or open tanks is no t collected, it is released directly to the atmosphere. Livestock waste management using anaerobic digester s allows the generated biogas to be captured and destroyed. Anaerobic digesters used for livesto ck waste management range in technology from contained vessels to covered lagoons. Anaerobic dig esters are designed and operated for waste stabilization resulting from the microbial reductio n of complex organic compounds to CO 2 and CH 4 .

15 Aerobic management of manure may include dry lots (including feedlots), high-rise houses for poultry production (poultry without litter), poultry production with l itter, deep bedding systems for cattle and swine, m anure composting, aerobic treatment units, and field spre ading of manure as a soil amendment. 16 Food waste from industrial and commercial food pro cessing may also be managed through these approache s.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 (Manfre di and Christensen, 2009). As a result, anaerobic digesters have higher rates of CO 2 and CH 4 generation. The increase in waste degradation and stabilization is mainly accomplished by recircu lating the collected leachate within the anaerobic digester. This process enhances microbial degradation of complex organic compounds to simple organics and gaseous biogas products (primar ily CO 2 and CH 4 ). The vast majority of anaerobic digesters used for l ivestock waste treatment in the United States collect the biogas for energy use, but flaring of t he gas is also practiced (EPA, 2012c, 2013b). Combustion of the biogas produced in an anaerobic d igester destroys (via oxidation) most of the CH 4 contained in biogas; the primary resulting emission is CO 2 . 17 The 192 anaerobic digester systems used for livestock waste management in the United States avoid an estimated 1.3 million metric tons CO 2 e, annually compared to other livestock waste manag ement options (EPA, 2013b). Although the use of anaerobic digesters is increasi ng 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, approxima tely 2% of U.S. livestock operations used anaerobic digesters in waste management (EPA, 2012c ). Because anaerobic digesters are designed to enhance CH 4 generation, poor design, operation, or maintenance of anaerobic digesters can result in si gnificant indirect CH 4 emissions. For example, CH 4 can leak from a digester cover or can be vented du ring digester start-ups, shutdowns, and malfunctions (Bogner et al., 2007; EPA, 2008b; Clim ate Action Reserve, 2013). However, under normal working conditions, GHG emissions from contr olled biological treatment in an anaerobic digester are small relative to indirect CH 4 emissions from uncontrolled anaerobic storage and treatment systems (Bogner et al., 2007, and referen ces therein). As a consequence, using anaerobic digester systems with biogas combustion typically r esults 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 Liv estock and Food Waste The assessment factor equation can be applied to po int source biogenic CO 2 emissions from an anaerobic digester used to store and treat livestoc k or food waste. 18 This section provides an illustrative method for calculating a BAF value that is applied to point source biogenic CO 2 emissions from anaerobic digesters used to manage l ivestock waste.

17 Because biogas destruction is not 100% efficient, some CH 4 is released without combustion (EPA, 2009b). 18 In concept, food waste and yard trimmings managed in an anaerobic digester can be treated similarly t o livestock waste managed in an anaerobic digester. However, th e focus of this section is on livestock waste. Withadditional data, biogenic emissions from food waste and yard trimmings could be calculated. Data needs include th e total volatile content of food waste and yard trimmings ( may vary within and across regions), the proportionof carbon in the volatile matter, and the maximum CH 4 producing capacity of food waste and yard trimming s managed in an anaerobic digester.November 2014 N-41

Here, the biogenic feedstock is biogas that is coll ected from an anaerobic digester. As described previously, biogas combustion, whether the biogas i s flared or used as a fuel to generate energy, oxidizes the CH 4 contained in the biogas to CO 2 . The destruction of CH 4 results in a net reduction of GHG emissions relative to a scenario in which bioga s produced through the anaerobic storage and treatment of livestock waste is not captured and co mbusted, 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 CO 2 e emissions reductions that are achieved through biogas capture and combustion. The AVOIDEMIT term accounts for net CO 2 e emissions reductions relative to the alternative em issions pathway of indirect CH 4 and CO 2 emissions (i.e., as a result of uncontrolled, anaer obic storage and treatment of livestock waste without biogas collection and combustion). In practice, as applied here, the AVOIDEMIT term is a ratio expressed as tCO 2 e avoided (i.e., the emissions, in CO 2 e, that would have occurred had the livestock waste been managed in a waste management system other than an anaerobic digester) per tCO 2 e emitted via combustion (i.e., the emissions, in CO 2 e, of the combusted biogas that was generated in an anaerobic digester, after accounting for both the combustion efficiency of th e biogas destruction device and any losses of biogas from the anaerobic digester 19 ). For the biogas feedstock collected from anaerobi c digesters, the AVOIDEMIT

term can be conceptually expressed as:

 =

 − (-./00/120	341.	7/8-0519u	c605-	.626_-.-25	0v05-.	6 75-4265/8-	51	62	626-41:/9	w/_-05-4)

(-./00/120	341.	91.:;05/12	13	:/1_60	_-2-465-w	/2	6 2	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 w aste 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 CH 4 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 CO 2 and CH 4 emissions

19 Biogas losses can occur from indirect CH 4 emissions from an anaerobic digester could occur a s a result of leaks from a digester cover or through venting during dig ester start-ups, shutdowns, and malfunctions. Bioga s leaks may occur prior to delivery of the collected biogas to the combustion unit for CH 4 destruction, leaks may occur as CH 4 emissions from digester effluent, or as a result of remaining undigested volatile solids. 20There are multiple livestock waste management scen arios alternative to using an anaerobic digester. O f these alternatives, aerobic treatment would produce the l east amount of CH 4 (zero CH 4 production) whereas an uncovered anaerobic lagoon would generate the most (see EPA 2 009b, Table A-3). Depending on ambient temperature, CH 4 production in an uncovered anaerobic lagoon ranges from 66% to 80% of the maximum amount of CH 4 that could potentially be produced from the livestock waste. T he appropriate alternative livestock waste manageme nt scenario should be used when this calculation is made.November 2014 N-42

resulting from a livestock waste management strateg y other than an anaerobic digester (e.g., had the waste been managed using an uncovered anaerobic lagoon).
Total CO 2 e emissions from a livestock waste management other than anaerobic digestion = (avoided CO 2 emissions) + (avoided CH 4emissions) (EQ. N.25) The avoided CO 2 emissions from a livestock waste management altern ate to anaerobic digestion is equal to the degradable carbon in the volatile soli ds of the livestock waste after removing the amount of carbon which becomes CH 4 and then converting the remaining available carbon to CO 2 as done using Equation N.26:
Avoided CO 2 emissions (metric tons CO 2 e/year) = [( Z +,  × 12/44) – ( x81/w-w +Q ? / tsZ +Q ? × 12/16)] × (44/12) (EQ. N.26) Where:
P

Hy z = Potential maximum CO 2 emissions if all degradable carbon is converted to

CO 2 (metric tons CO 2 /year), see Equation N.34. (12/44) = molecular weight ratio of C to CO 2 (converts potential CO 2 emissions to

carbon).
Avoided HI J = avoided CH 4 emissions, metric tons CO 2 e/year (see Equation N.33).
GWP HI J = 100-year GWP for CH 4 , 25 (IPCC, 2007). (12/16) = molecular weight ratio of C to CH 4 (converts CH 4 emissions to carbon). (44/12) = molecular weight ratio of CO 2 to C (converts C less that associated with the

CH 4 emissions back to CO 2 emissions).
The most accurate data from which to estimate the t otal amount of carbon that can be degraded is measurement data on the biogas flow rate and methan e 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 Conce ntration Data Are Available For each anaerobic digester, the annual flow of CH 4 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

CH 4 F = CH 4 flow from the anaerobic digester to the biogas com bustion device

(metric tons CH 4 /year). V = Annual volumetric flow rate of biogas to the b iogas destruction device

(actual cubic feet biogas per year), as determined from daily monitoring. 21 C = Average annual CH 4 concentration of biogas (percent by volume, wet

basis). 0.0423 = Density of CH 4 pounds per standard cubic foot (at 520oR or 15.56o C 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 metr ic tons. To account for the biogas collection efficiency, le aks from the anaerobic digester must be estimated (such leaks are indirect emissions to the atmospher e). Equation N.28 can be used to calculate the CH 4 lost (metric tons per year) from an anaerobic diges ter:
+Q ?  = 	 +Q ?  × (+]) +] (EQ. N.28)
Where:
CH 4 L = amount of CH 4 lost via leaks from the anaerobic digester, prior t o combustion (metric tons CH 4 /year).
CH 4 F = CH 4 flow from the anaerobic digester to the biogas comb ustion device

(Equation N.27). CE = collection efficiency 22 of the anaerobic digester. For each anaerobic digester, the annual flow of CO 2 in biogas that is sent with the CH 4 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 signific antly during the year, it would be more accurate to calculate the annual methane flow as the sum of monthly flow volu mes, corrected to standard conditions by the monthl y average temperature and pressure. 22 Biogas collection efficiency is dependent upon the type of anaerobic digester and its cover. Biogas c ollection efficiency for a covered anaerobic lagoon depends o n the cover type: collection efficiency for a bank to bank, impermeable cover is 0.975; collection efficiency f or a modular, imp ermeable 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 (E PA 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 bi ogas generated.November 2014 N-44

Where:
CO 2 F = CO 2 flow from the anaerobic digester to the biogas comb ustion device (metric tons CO 2 /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 – C HI J /100%-M/100%) = Average annual CO 2 concentration of biogas (volume fraction, wet basis), where C = average annual CH 4 concentration of biogas (volume percent, wet basis) and M = moisture content of biogas (volume percent, wet basis). 0.1160 = Density of CO 2 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 met ric tons. Equation N.30 can be used to calculate the CO 2 lost (metric tons per year) from each anaerobic digester:

+,   = 	 +,   × (+]) +] (EQ. N.30)
Where:
CO 2 L = amount of CO 2 lost via leaks from the anaerobic digester, prior t o combustion

(metric tons CO 2 /year).
CO 2 F = CO 2 flow from the anaerobic digester to the biogas comb ustion device

(Equation N.29). CE = collection efficiency of the anaerobic digest er. Equation N.31 can be used to calculate the total CH 4 generation from the anaerobic digester.
Y1567	+Q ? t-2-465/12 = 	 +Q ?  + +Q ?  (EQ. N.31) Where:

23 If the pressure or temperature fluctuates significa ntly during the year, it would be more accurate to calculate the annual CO 2 flow as the sum of monthly flow volumes, correctedto standard conditions by the monthly average temperature and pressureNovember 2014 N-45

Total CH 4 Generation = the quantity of methane generated fr om the anaerobic digester (metric tons CH 4 /year).
CH 4 F = CH 4 flow from the anaerobic digester to the biogas comb ustion device in metric tons CH 4 /year (Equation N.27).
CH 4 L = amount of CH 4 lost via leaks from the anaerobic digester, prior t o combustion in metric tons CH 4 /year (Equation N.28). Equation N.32 can be used to calculate the total CO 2 generation from the anaerobic digester.
Y1567	+,  t-2-465/12 = 	 +,   + +,   (EQ. N.32) Where:
Total CO 2 Generation = the quantity of CO 2 generated from the anaerobic digester (metric tons CO 2 /year).
CO 2 F = CO 2 flow from the anaerobic digester to the biogas comb ustion device in metric tons CO 2 /year (Equation N.29).
CO 2 L = amount of CO 2 lost via leaks from the anaerobic digester, prior t o combustion in metric tons CO 2 /year (Equation N.30).
The CH 4 -producing potential of a specific livestock waste management system is represented by a methane conversion factor (MCF). An anaerobic diges ter 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 CH 4 possible because the conditions in the systems are not ideal for CH 4 production. The value of this parameter ranges fro m 0% to 100%, reflecting the capability of a system to produce the maximum achie vable CH 4 (the higher the MCF, the greater the potential for CH 4 production). For liquid systems (e.g., uncovered a naerobic lagoons), MCF values are temperature dependent; in order to assign the a ppropriate 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 CH 4 emissions parameter in Equation N.25 can be estima ted using Equation N.33 when CH 4 generation data are available from an anaerobic di gester: x81/w-w	+Q ? ]./00/120 = 	 Y1567	+Q ? t-2-465/12 × l+ slr × tsZ>? (EQ. N.123) Where:
Avoided CH 4 Emissions = the quantity of methane emitted, in CO 2 equivalence, from the alternative waste management system (metric tons CO 2 e/year).
Total CH 4 Generation = the quantity of methane generated fro m the anaerobic digester (metric tons CH 4 /year).November 2014 N-46

MCF WMS = CH 4 conversion factor (proportion represented as a dec imal) for the alternative-scenario, waste management system ( see EPA, 2009b, Table A-3).
GWP CH4 = 100-year GWP of CH 4 , 25 (IPCC, 2007). The potential CO 2 emissions can be calculated from the total CH 4 and CO 2 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 CO 2 emissions = maximum CO 2 emissions if all degradable carbon is converted to CO 2 (metric tons CO 2 /year).
Total CH 4 Generation = the quantity of methane generated fro m the anaerobic digester (metric tons CH 4 /year).
Total CO 2 Generation = the quantity of CO 2 generated from the anaerobic digester (metric tons CO 2 /year). 44/16 = molecular weight ratio of CO 2 to CH 4 emissions. Equation N.26 can then be used to calculate the avo ided CO 2 emissions and Equation N.25 can be used to calculate the total CO 2 e emissions from a livestock waste management other than anaerobic digestion.
4.1.3. Calculating the Denominator The total amount of CH 4 and CO 2 emissions from an anaerobic digester, as represent ed in the denominator of the AVOIDEMIT term, is a calculation of the amount of CH 4 sent to the biogas destruction device, minus the amount of CH 4 destroyed during combustion, plus the amount of CH 4 leaked to the atmosphere (the latter accounts for C H 4 collection efficiency). To convert that calculation to CO 2 e, it is multiplied by the GWP of CH 4 . To account for the CO 2 emitted as a result of CH 4 combustion, the amount of CH 4 destroyed during combustion is added. To this is ad ded the amount of CO 2 in the biogas that flows to the biogas combustion d evice where it is then emitted to the atmosphere. The following Equation (N.35) can b e used to calculate the total amount of CO 2 e emissions from an anaerobic digester:
+,  -	]./00/120 x\ =  > ? (+Q ?  − +Q ? \ + +Q ? ) + +Q ? \ × ??/C + +,   + +,   (EQ. N.145) Where:
CO 2 e Emissions AD = CO 2 e emissions from anaerobic digestion (metric tons/y ear).November 2014 N-47

GWP HI J = 100-year GWP of CH 4 , 25 (IPCC, 2007).
CH 4 F = CH 4 flow to the biogas combustion device (Equation N.27 ).
CH 4 D = amount of CH 4 destroyed via combustion (Equation N.36).
CH 4 L = amount of CH 4 lost via leaks prior to combustion (Equation N.28).
CO 2 F = CO 2 flow to the biogas combustion device (Equation N.29 ).
CO 2 L = amount of CO 2 lost via leaks prior to combustion (Equation N.30). 44/16 = molecular weight ratio of CO 2 to CH 4 . Equations for most of these terms have already been presented. Equation N.36 can be used to calculate the metric tons of CH 4 destroyed (per year) in a biogas destruction device : +Q ? \ = 	 +Q ?  × \] (EQ. N.156) Where:
CH 4 D = CH 4 destroyed at a biogas combustion device (metric ton s CH 4 /year).
CH 4 F = CH 4 flow from the anaerobic digester to the biogas comb ustion device

(Equation N.27).
DE = CH 4 destruction efficiency from flaring or combustion i n 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 calc ulation of the AVOIDEMIT term and its subsequent application in estimating a BAF for the management of livestock waste in an anaero bic digester when biogas measurement data are available

. Several parameters are presented and used in the eq uations in the remainder of this section. Table N-8 presents the parameters used, default values, r anges presented in the literature, and references. Table N-8. Summary of Parameters Used When Calculati ng an Illustrative BAF for Livestock Waste Management through Anaerobic Digestion.

Parameter Description Symbol Value Range Units Comments Reference (for value column) Concentration of CH 4 in the biogas C HI J 0.55 0.40 to 0.60 Fraction EPA, 2013c

Density of CH 4 – 0.662 – kg CH 4 /m 3 At 532°R, or 22.22°C, and 1 atm EPA, 2009bNovember 2014 N-48

Parameter Description Symbol Value Range Units Comments Reference (for value column) Density of CO 2 – 0.1160 – Pounds per standard cubic foot At 520oR or

15.74oC and 1 atm Calculated

value 3

Methane conversion factor for the specific waste management strategy MCF WMS 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 TAM AT 604 Numerous kg/head Determined using either default valuesor farmspecific data EPA, 2009b,

Table A-2; IPCC, 2006, Table 10A4- 10A9 Volatile solids excretion rate by animal type VS AT 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 CH 4 - producing capacity for each animal type B 0 0.24 0.17 to 0.78 m 3 CH 4 /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 analysis 2 Sweeten et al.,

2002

1 VS AT can be determined using either default values or f arm-specific data.November 2014 N-49 2 If only fuels proximate analysis is available, est imate the volatile solids as the sum of the volatil e matter and fixed carbon from the fuels proximate analysis (see Figure N-3). 3 This value is calculated using a 60 degree Fahrenh eit conversion: 44.01 * (2.20462/836.6) = 0.1160, w here 44.01 = the molecular weight of CO 2 ; 2.20462 is a unit conversion factor from kilogram s to pounds; and 836.6 scf/kg-mol is the molar volume conversion factor.
4.1.4. Methodology When Biogas Flow Rate and Methane Conce ntration Data Are Not Available When biogas measurement data are not available, the CH 4 and CO 2 emissions must be estimated based on animal type and population data. Potential CO 2 emissions can be solved using the following equation:
Potential CO 2 emissions =
Σ animal type (TVS AT × VolatileCarbon AT × (44/12) × 365 × 1/1000) (EQ. N.167) Where:
Σ animal type = If the alternate waste management system accept s waste from more than one animal type then this calculation must be computed for each animal type and then summed across animal types.
TVS AT= Total volatile solids excreted by animal type ( kg/day); see

Equation N.38 to calculate TVS AT . VolatileCarbon AT= Fraction of degradable carbon in the volatile s olids of the livestock

waste (see Equation N.39). (44/12) = molecular weight ratio of CO 2 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 (TVS AT ) may be calculated using Equation N.38 and by referring to tables external to this appendix (Tabl e A-2, EPA, 2009b and Tables JJ-2 and JJ-3, 40 CFR 98.363):
TVS AT = (Population AT × TAM AT × VS AT /1000) (EQ. N.178) Where:
TVS AT= Total volatile solids excreted per animal type (kg/day). Population AT= Average annual animal population (head), by anim al type. 24

24 For static populations (e.g., dairy cows, breeding swine), average annual animal populations are esti mated usingNovember 2014 N-50

TAM AT= Typical animal mass, by animal type; determined using either default

values (see EPA, 2009b, Table A-2) or farm specific data (kg/head).
VS AT= Volatile solids excretion rate by animal type, using either default values

(see 40 CFR 98.363, Tables JJ-2 and JJ-3) or farm s pecific data (kg VS/day/kg animal mass). The fraction of degradable carbon in the volatile s olids of the livestock waste (VolatileCarbon AT ) can be estimated using results from proximate and ultim ate analyses 25 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 ta ken from the body of published scientific literature. 26 However, it is important to understand the differe nces 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 ve al cattle), average annual animal populations are estimated usi ng the average number of days each animal is kept a t the facility and the number of animals produced annually (e.g., growing population = days onsite × (number of anima ls produced annually / 365)). 25 Characteristics of a biogenic fuel can be describe d using proximate and ultimate analyses based on a sample’s complete combustion to CO 2 and liquid water. The proximate analysis gives moi sture content, volatile content, carbon remaining (fixed carbon), and mineral ash. T he ultimate analysis gives the sample’s elemental c omposition as proportions of carbon, hydrogen, oxygen, nitroge n, 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 livestoc k and poultry manure. Li et al. (2008) and Henihan et al. (2003) present specific results of proximate and u ltimate analyses of chicken litter characteristics; Sweeten et al. (2002 and 2003) present similar specific res ults but of cattle manure. It should be noted that Sweeten et al. (2002 and 20 03) pertain to the composition of Texas feedlot bee f 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 A nalyses (Adapted from ASTM, 2013). The VolatileCarbon AT term represents the amount of carbon in the livesto ck waste solids that degrades during livestock waste management. Assumin g there is negligible carbon remaining in the residue and that the fixed carbon is not readily bi odegradable, VolatileCarbon AT term can be estimated as follows:
VolatileCarbon AT = +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:
VolatileCarbon AT= fraction of the degradable carbon in the volatil e solids of the livestock waste (kg degradable carbon in volatile solids/kg o f volatile solids, dry basis). 27 Carbon = fraction of carbon in livestock waste (kgcarbon in total dried solids/kg

of total dried solids), dry basis (from ultimate an alysis). Fixed Carbon = fraction of dry solids in livestock waste that does not volatilize when heated to 900 °C in nitrogen (kg fixed carbon in to tal 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 the n the amount of carbon in the volatile matter may b e underestimated, thus giving a low-biased estimate o f the VolatileCarbon ATterm (though the bias is likely small).November 2014 N-52

Volatile Solids = fraction of volatile solids in l ivestock 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 matt er 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 soli ds), dry basis.
The avoided CH 4 emissions parameter in Equation N.25 can be popula ted using Equation N.40, which estimates the annual avoided CH 4 emissions generated from a manure management strat egy alternate to anaerobic digestion:
Avoided CH 4 emissions (metric tons CO 2 e/year) =
Σ animal type (TVS AT × VS WMS × Days × B 0 × MCF WMS × 0.662 × 1 /1000 × tsZ +Q ? ) (EQ. N.40) Where:
Σ animal type = If the alternate waste management system accept s waste from more than one animal type then this calculation must be compu ted for each animal type and then summed across animal types.
TVS AT= Total volatile solids excreted by animal type ( kg/day); the TVS ATequation

is presented above (Equation N.38).
VS WMS = Proportion of total manure for each animal type that is managed in each

waste management system (assumed to be equivalent t o the amount of volatile solids in each waste management system). Days = Number of days per year (i.e., 365 days/yea r).
B 0 = Maximum CH 4 -producing capacity for each animal type (m 3 CH 4 /kg volatile

solids; see EPA, 2009b, Table A-2).
MCF WMS = CH 4 conversion factor (proportion represented as a dec imal) for the

alternative-scenario, waste management system (see EPA, 2009b, Table A3).
0.662 = density of CH 4, kg CH 4 /m 3 (at 532°R, or 22.22°C, and 1 atm). 1/1000 = conversion factor from kg to metric tons.
GWP HI J = 100-year GWP of CH 4 , 25 (IPCC, 2007).
The maximum amount of CH 4 that could potentially be produced from livestock waste managed under ideal conditions is calculated by multiplyingthe total volatile solids by the maximum CH 4 - producing capacity of the livestock waste (B 0 ). The B 0 values vary by animal type and diet (see EPA,November 2014 N-53

2009b, Table A-2). Most manure management systems w ill not produce the maximum amount of CH 4 possible because the conditions in the systems are not ideal for CH 4 production. The CH 4 - producing potential of a specific livestock waste m anagement system is represented by a methane conversion factor (MCF). The value of this paramete r ranges from 0% to 100% and reflects the capability of a system to produce the maximum achie vable CH 4 (the higher the MCF, the greater the potential for CH 4 production). For liquid systems (e.g., uncovered a naerobic lagoons), MCF values are temperature dependent: in order to assign the a ppropriate 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 CO 2 emissions and the avoided CH 4 emissions (Equation N.25, metric tons CO 2 e/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 dige ster) is based on the flow, loss, and destruction terms presented previously (see Equation N.35). How ever, in the lack of direct biogas measurement data, these terms must be estimated based on the an imal population equations just presented. As noted previously, the maximum amount of CH 4 that could potentially be produced from livestock waste managed under ideal conditions is calculated by multiplying the total volatile solids by the maximum CH 4 -producing capacity of the livestock waste (B 0 ). Thus, total CH 4 generation can be estimated using Equation N.41, which is similar to Equation N.40 except that MCF WMS is assumed to equal 1 and the CH 4 emissions are not converted to CO 2 equivalence.
Total CH 4 generation (tons CH 4 /yr) =
Σ animal type (TVS AT × VS WMS × Days × B 0 × 0.662 × 1/1000) (EQ. N.41) Where:
Σ animal type = If the alternate waste management system accept s waste from more than one animal type then this calculation must be compu ted for each animal type and then summed across animal types.
TVS AT= Total volatile solids excreted by animal type ( kg/day); the TVS ATequation

is presented above (Equation N.38).
VS WMS = Proportion of total manure for each animal type that is managed in each

waste management system (assumed to be equivalent t o the amount of volatile solids in each waste management system). Days = Number of days per year (i.e., 365 days/yea r).
B 0 = Maximum CH 4 -producing capacity for each animal type (m 3 CH 4 /kg volatile

solids; see EPA, 2009b, Table A-2).
0.662 = density of CH 4, kg CH 4 /m 3 (at 532°R, or 22.22°C, and 1 atm).November 2014 N-54

1/1000 = conversion factor from kg to metric tons.
CH 4 sent to the biogas destruction device can be calcul ated based on the collection efficiency of the anaerobic digester using Equation N.42:
+Q ?  = 	Y1567	+Q ? t-2-465/12 × +] (EQ. N.42) Where:
CH 4 F = CH 4 flow from the anaerobic digester to the biogas comb ustion device (tons CH 4 /yr).
Total CH 4 generation = total quantity of CH 4 generated in the anaerobic digester (tons CH 4 /yr; see Equation N.41). CE = collection efficiency 28 of the anaerobic digester.
The CH 4 that is not collected and sent to the biogas destr uction device can be calculated by rearranging Equation N.28:
+Q ?  = 	Y1567	+Q ? t-2-465/12 − +Q ?  (EQ. N.193) Where:
CH 4 L = amount of CH 4 lost via leaks from the anaerobic digester, prior t o combustion (metric tons CH 4 /year).
Total CH 4 generation = total quantity of CH 4 generated in the anaerobic digester (tons CH 4 /yr; see Equation N.31)
CH 4 F = CH 4 flow from the anaerobic digester to the biogas comb ustion device (Equation N.42). Given the potential CO 2 emissions from Equation 37 and re-arranging Equati on N.34 yields the following equation for estimating the total CO 2 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 c ollection efficiency for a covered anaerobic lagoon depends o n 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 (E PA 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 bi ogas generated.November 2014 N-55

Total CO 2 Generation = the quantity of CO 2 generated from the anaerobic digester (metric tons CO 2 /year).
Potential CO 2 emissions = maximum CO 2 emissions if all degradable carbon is converted to CO 2 (metric tons CO 2 /year from equation N.34).
Total CH 4 Generation = the quantity of methane generated fro m the anaerobic digester (metric tons CH 4 /year; Equation N.41). 44/16 = molecular weight ratio of CO 2 to CH 4 emissions.
Similar to the CH 4 flow and loss terms, the CO 2 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:
CO 2 F = CO 2 flow from the anaerobic digester to the biogas comb ustion device (tons CO 2 /yr).
Total CO 2 generation = total quantity of CO 2 generated in the anaerobic digester (metric tons CO 2 /year; see Equation N.44). CE = collection efficiency 29 of the anaerobic digester.
CO 2 L = amount of CO 2 lost via leaks from the anaerobic digester, prior to combustion (metric tons CO 2 /year). Equation N.36, presented previously, can be used to calculate the metric tons of CH 4 destroyed (per year) in a biogas destruction device. All of the pa rameters needed to determine the CO 2 e emissions from the anaerobic digester using Equation N.35 are then available. Section 4.2.2 provides an illustrative example calc ulation of the AVOIDEMIT term and its subsequent application in estimating a BAF for the management of livestock waste in an anaero bic digester prior to the availability of biogas measur ement data

29 Biogas collection efficiency is dependent upon the type of anaerobic digester and its cover. Biogas c ollection efficiency for a covered anaerobic lagoon depends o n the cover type: collection efficiency for a bank to bank, impermeable cover is 0.975; collection efficiency f or a modular, impermeable cover is 0.70. Biogas col lection efficiency is 0.99 for a complete mix, fixed film, or plug flow digester that is an enclosed vessel (E PA 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 bi ogas generated.November 2014 N-56



### 4.2. Illustrative AVOIDEMIT and BAF Calculations for Livestock Waste Management
4.2.1. Illustrative Calculations when Anaerobic Digester M easurement Data Are Available When anaerobic digester flow and concentration data are available, these data provide a more accurate estimate of the degradable carbon quantiti es in the livestock wasted. Therefore, the potential CH 4 and CO 2 emissions from the alternate treatment pathway sho uld be estimated from these measurement data rather than from animal popu lation 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 an aerobic lagoon to an anaerobic digester. In this hypothetical example, the daily average vol umetric biogas flow rate from the anaerobic digester is 54,500 ft 3 per day and the annual volumetric flow volume is 1 9,892,500 (e.g., 54,500 ft 3 /day × 365 days/year). In this hypothetical example , the average annual CH 4 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 digest er was 77oF (537oR) at 1.005 atm, both of which were measured where the flow is measured. Step 1: Calculate the CH 4 Emissions from the Anaerobic Digester The amount (metric tons/year) of CH 4 sent from the anaerobic digester to the biogas comb ustion device, CH 4 F, is calculated as (Equation N.42):

+Q ?  = S × + >?

TT × T. T?W × XT

Y × Z 	65. × T. ?X? , TTT CH 4 F = 19,892,500 × 0.521 × 0.0423 × (520/537) × (1.00 5/1) × (0.454/1000)
= 193.6950 metric tons CH 4 /year. The next term to solve in calculating the denominat or of the AVOIDEMIT term is CH 4 D, the amount of CH 4 destroyed at a biogas combustion device (metric ton s CH 4 /year). This can be calculated using Equation N.36:
+Q ? \ = 	 +Q ?  × \] The CH 4 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. Thu s, the CH 4 destroyed at biogas combustion device can be estimated as:
CH 4 D = 193.6950 × 0.99
= 191.7581 MT CH 4 /year.
The next term in the denominator of the AVOIDEMIT term, CH 4 L, accounts for the CE. To calculate CH 4 leakage (metric tons CH 4 /year) from an anaerobic digester, Equation N.28 ca n be used:November 2014 N-57

+Q ?  = 	 +Q ?  × (+]) +] The previously computed value for CH 4 F can be used in this example. The CE is dependent upon the type of anaerobic digester and its cover (for defau lt values, see EPA, 2009b, Table A-4; 40 CFR 98.363, Table JJ-6). This hypothetical example is f or an enclosed vessel, mixed plug flow digester where the CE is 0.99, such that:
CH 4 L = 193.6950 × (1 – 0.99) / 0.99
= 1.9565 metric tons CH 4 /year. Step 2: Calculate the CO 2 Emissions from the Anaerobic Digester The next parameter to solve for in the denominator of the AVOIDEMIT term is CO 2 F, the annual flow of CO 2 in biogas sent (mixed with CH 4 ) to the biogas combustion device. This can be calc ulated using Equation N.29:

+,   = S ×   − ` + > ?

TT% a − ` l

TT% a  × T. CT × XT

Y × Z 	65. × T. ?X? , TTT The values for V, C, T, and P are the same when sol ving for CO 2 F (Equation N.29) as for when solving for CH 4 F (Equation N.27). The only change is in the density of the gas, from CH 4 (0.0423 lbs/ft 3 ) to that of CO 2 (0.1160 lbs/ft 3 ) and that Equation N.29 incorporates the fraction of biogas that is not CH 4 or water vapor (i.e., 1 – C HI J /100%-M/100%). As most anaerobic digesters operate at temperature above 30°C (above 86°F), it can be a ssumed the cooled biogas (at the flow measurement point) is saturated with water (relativ e 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 moistu re content of the biogas is estimated to be 3.1% (i.e., (20/18)/[(1000/29)+(20/18)]). Using Equation N.29, CO 2 F can be estimated as:
CO 2 F = 19,892,500 × (1 – 0.521-0.031) × 0.1160 × 520/ 537 × 1.005 × 0.454/1,000
= 459.1102 MT CO 2 /year The final parameter to solve for in the denominator of the AVOIDEMIT term is CO 2 L, the annual flow of CO 2 in biogas lost from the digester. This can be calcu lated using Equation N.30, using the value of CO 2 F just calculated and the gas collection efficiency (0.99; same as used to determine CH 4 L), as follows:

+,   = 	 +,   × ( − +])

+] CO 2 = 459.1102 × (1 – 0.99) / 0.99
= 4.6375 MT CO 2 /year.November 2014 N-58

Step 3: Calculate the CO 2 e Emissions from the Anaerobic Digester (Denominato r) With estimated values for each of the terms in the denominator of the AVOIDEMIT term, the denominator can be solved using Equation N.35:
+,  -	]./00/120 x\ = 	X(+Q ?  − +Q ? \ + +Q ? ) + +Q ? \ × ??/C + +,   + +,  
CO 2 e emissions from the anaerobic digester (metric ton s /year) = 25 × (193.6950 – 191.7581 + 1.9565) + 191.7581 × 44/16 + 459.1102+4.6375 = 1,088.4175 metric tons CO 2 e /year Step 4: Calculate the CO 2 e Emissions from the Alternate Fate (Numerator) Now that the terms for the denominator are determin ed, these values can be used to estimate the total CH 4 and CO 2 generation from the alternate treatment fate (unco vered lagoon) using Equations N.31 and N.32.
Total CH 4generation (MT CH 4 /year) = CH 4 F + CH 4 L
Total CH 4generation = 193.6950 + 1.9565
= 195.6515
Total CO 2 generation = CO 2 F + CO 2 L
Total CO 2 generation = 459.1102 + 4.6375
= 463.7477 For an anaerobic digester, the CH 4 conversion factor, MCF, is assumed to be 1; for th e alternativescenario’s waste management system, the CH 4 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 MCF WMS = 0.66). Applying Equation N.33, the avoided CH 4 emissions:
Avoided CH 4 emissions (metric tons/year) = Total CH 4 generation × MCF WMS × GWP CH4 = 195.6515 × 0.66 × 25 = 3,228.2498 MT CO 2 e per year. The potential CO 2 emissions are calculated from the total CH 4 and CO 2 generation from the anaerobic digester as:
Potential CO 2 emissions = (Total CH 4generation × 44/16) + Total CO 2 generation

30Table A-3 in EPA 2009b assigns CH 4 conversion factors based on ambient temperature, th us accounting for the influence of climate on CH 4 production.November 2014 N-59

Potential CO 2 emissions = (195.6515 × 44/16) +463.7477 = 1,001.7893 MT CO 2 per year With estimates of both the potential CO 2 emissions and the avoided CH 4 emissions, the avoided CO 2 emissions resulting from a dairy manure management strategy other than an anaerobic digester can be calculated using Equation N.26 as follows.
Avoided CO 2 emissions = ((Potential CO 2 emissions × 12/44) – (Avoided CH 4 emissions/25 × 12/16)) × (44/12) = ((1,001.7893 × 12/44) – (3,228.2498/25 × 12/16)) × (44/12)
= 646.6818 MT CO 2 per year Summing the estimated, avoided CH 4 and CO 2 emissions (both in metric tons CO 2 e per year), that result from a dairy manure management strategy othe r than an anaerobic digester, the total avoided CO 2 e emissions can be estimated in units of metric ton s CO 2 e per year, thus solving the numerator of the AVOIDEMIT term (Equation N.24):
Total avoided CO 2 e emissions = (avoided CO 2 emissions) + (avoided CH 4emissions) = 646.6818 + 3,228.2498 = 3,874.9317 MT CO 2 e 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 in dicates that a biogas feedstock produced in an anaerobic digester from the treatmen t of dairy manure and flared by a stationary source results in net CO 2 e emissions reductions.
4.2.2. Example Calculations for Livestock Waste Management Prior to Installation of an Anaerobic Digester (When Measurement Data are No t Available) Prior to the installation of an anaerobic digester, the only information available to determine the carbon content of the livestock waste and to projec t the methane generation potential of the anaerobic digester are the equations presented corr elating the potential CO 2 emissions and theNovember 2014 N-60

avoided methane emissions to animal type and popula tion. This example illustrates how to determine the assessment factor based only on the a nimal population data. Step 1: Calculate the CO 2 e 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 calcu late the avoided CO 2 and CH 4 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) co nsisting of 500 dairy cows with a typical animal mass of 604 kg, and a volatile solids excret ion 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:
TVS AT = (Population AT × TAM AT × VS AT /1,000) = 500 × 604 × 9.34 / 1,000 = 2,820.68 kg/day
With TVS ATestimated, the avoided CH 4 emissions resulting from a dairy manure management strategy other than an anaerobic digester can be ca lculated. In this hypothetical example, the alternative fate evaluated is management of the man ure using an uncovered anaerobic lagoon. When calculating the avoided CH 4 emissions associated with the alternative fate of this scenario’s dairy manure, several parameters are needed, includ ing the maximum CH 4 -producing capacity for dairy cattle (see EPA, 2009b, Table A-2, for the ap propriate default value; for dairy cows, B 0 = 0.24
m 3 CH 4 /kg); and a CH 4 conversion factor for the alternative-scenario’s w aste management system (see EPA, 2009b, Table A-3; for uncovered anaerobic lagoon in a cool climate below 10°C, 31 MCF WMS = 0.66). Equation N.40 can be used to calculate the avoided CH 4 emissions:
Avoided CH 4 emissions (metric tons/year) = (TVS AT × VS WMS × Days × B 0 × MCF WMS × 0.662 × 1 /1,000 × 25) = (2,820.68 kg/day × 1 × 365 days/year × 0.24 m 3 CH 4 /kg × 0.66 × 0.662 kg CH 4 /m 3 × 1 metric ton/1,000 kg × 25) = 2,698.9812 metric tons CO 2 e per year In order to estimate avoided CO 2 emissions from a dairy manure management strategy o ther than an anaerobic digester, the proportion of the carbon in the volatile matter of the dairy manure (VolatileCarbon AT ) must be calculated. In the VolatileCarbon ATterm, the fixed carbon is removed from the total carbon in the dairy manure because t he fixed carbon is assumed not to degrade. Data

31 Table A-3 in EPA 2009b assigns CH 4 conversion factors based on ambient temperature, th us accounting for the influence of climate on CH 4 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:
VolatileCarbon AT = +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 TVS ATand VolatileCarbon ATestimated, the potential maximum CO 2 emissions (Equation N.25) resulting from a dairy manure management strategy o ther 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 (dair y cows), Equation N.37 only needs to be calculated once, as follows:
Potential CO 2 emissions = (TVS AT× VolatileCarbon AT × (44/12) × 365 × 1 /1000) = 2,820.68 × 0.2979 × (44/12) × 365 × 1 /1,000 = 1,124.5755 MT CO 2 per year With estimates of both the potential CO 2 emissions and the avoided CH 4 emissions, the avoided CO 2 emissions resulting from a dairy manure management strategy other than an anaerobic digester can be calculated. For this calculation the total p otential CO 2 emissions from the decomposition of TVS ATmust first be converted to carbon. From this the C H 4 emissions, converted to carbon must be subtracted. The result is then converted back to CO 2 (see Equation N.26).
Avoided CO 2 emissions = ((Potential CO 2 emissions × 12/44) – (Avoided CH 4 emissions/25 × 12/16)) × (44/12) = ((1,124.575 × 12/44) – (2,698.9812/25 × 12/16)) × (44/12)
= 827.6877 MT CO 2 per year Summing the estimated, avoided CH 4 and CO 2 emissions (both in metric tons CO 2 e per year), that result from a dairy manure management strategy othe r than an anaerobic digester, the total avoided CO 2 e emissions can be estimated in units of metric ton s CO 2 e per year, thus solving the numerator of the AVOIDEMIT term (Equation N.25):
Total avoided CO 2 e emissions = (avoided CO 2 emissions) + (avoided CH 4emissions)

32 Data specific to Wisconsin dairy cattle would be p referred but in the absence of these data, data fro m Sweeten et al. (2002) were applied.November 2014 N-62

= 827.6877 + 2,698.9812 = 3,526.6689 MT CO 2 e per year Step 2: Calculate the CO 2 e Emissions from the Actual Fate (Denominator) In order to calculate the emissions from the anaero bic digester (i.e., denominator of the AVOIDEMIT term), these same equations can be used to calculat e the projected emissions from the total CH 4 and CO 2 generation.
The total CH 4 generation for the anaerobic digester is calculate d using Equation N.41.
Total CH 4 generation (metric tons CH 4 /year) = (TVS AT × VS WMS × Days × B 0 × 0.662 kg CH 4 /m 3 × 1 metric ton/1,000 kg) = (2,820.68 kg/day × 1 × 365 days/year × 0.24 m 3 CH 4 /kg × 0.662 kg CH 4 /m 3 × 1 metric ton/1,000 kg)
= 163.5746 MT CH 4 /year. The potential CO 2 emissions have already been calculated (1,124.5755 metric tons CO 2 /year). However, the methane produced will lower the CO 2 emissions from the anaerobic digester. The total CO 2 generation is calculated by subtracting the carbon associated the CH 4 generation from the potential CO 2 emissions using Equation N.44 as follows:
Total CO 2 generation (metric tons CO 2 /year) = ((Potential CO 2 emissions) – (Total CH 4generation × 44/16)) = ((1,124.5755 × 12/44) – (163.5746 × 12/16)) × (4 4/12)
= 674.7453 MT CO 2 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 defau lt values, see EPA, 2009b, Table A-4; 40 CFR 98.363, Table JJ-6). This hypothetical example is f or an enclosed vessel, mixed plug flow digester where the collection efficiency is 0.99, such that:
CH 4_F = Total CH 4generation × CE = 163.5746×0.99 = 161.9389
CH 4_L = Total CH 4generation − CH 4_F = 163.5746 − 161.9389 = 1.6357
CO 2 F = Total CO 2 generation × CE = 674.7453×0.99 = 667.9978
CO 2 L = Total CO 2 generation − CO 2 F = 674.7453 − 667.9978 = 6.7475November 2014 N-63

The next term to solve in calculating the denominat or of the AVOIDEMIT term is CH 4 D, the amount of CH 4 destroyed at a biogas combustion device (MT CH 4 /year). This can be calculated using Equation N.36:
+Q ? \ = 	 +Q ?  × \] CH 4 F was previously solved. The CH 4 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 CH 4 destroyed at biogas combustion device can be estima ted as:
CH 4 D = 161.9389 × 0.99
= 160.3195 MT CH 4 /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:
+,  -	]./00/120 x\ = 	X(+Q ?  − +Q ? \ + +Q ? ) + +Q ? \ × ??/C + +,   + +,  
CO 2 e 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 CO 2 e /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 in dicates that a biogas feedstock produced in an anaerobic digester from the treatmen t of dairy manure and flared by a stationary source results in net CO 2 e emissions reductions. 

### 4.3. Sensitivity Analysis for Anaerobic Digestion of Liv estock and Food Waste For the livestock and food waste assessments, the p arameter that has the greatest variability is the methane correction factor (MCF) for the waste manag ement system employed as an alternative to anaerobic digestion. The biogas collection efficien cy and the biogas destruction efficiency impact the BAF value, as does the global warming potential of CH 4 . The total biogas flow rate or the total volatile solids produced (if animal population corr elations are used) does not impact the BAF value as they impact both the numerator and denominator b y a constant factor. However, the relativeNovember 2014 N-64

ratio of CH 4 produced versus CO 2 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 Digesti on 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 GWP HI J 21 −0.10 −0.90 −1.54 −2.50 2 GWP HI J 25 −0.12 −1.08 −1.85 −3.00 3 GWP HI J 28 −0.13 −1.21 −2.07 −3.37 4 C HI J 40% −0.09 −0.88 −1.50 −2.44 5 C HI J 50% −0.12 −1.08 −1.85 −3.00 6 C HI J 60% −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 unl ess 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

. • GWP

HI J = 25

• C HI J = 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 Digest ion 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 GWP HI J 21 −0.09 −0.87 −1.48 −2.41 2 GWP HI J 25 −0.11 −1.04 −1.79 −2.90 3 GWP HI J 28 −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 −2.90November 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 unl ess specified as the parameter varied.

• GWP

HI J = 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 select ed central tendency values, the two methodologies yield very similar results. If the ra tio for CH 4 generation to CO 2 generation had been exactly the same for both methodologies, identical BAF values would be produced. When MCF increases, it directly increases the “Avoided CH 4 emissions” and the BAF values go down (or become more negative). Increasing the global warming poten tial of methane ( GWP CH 4 ), will increase the absolute value of the calculated BAF (i.e., if the BAF

is negative, increasing GWP CH 4 will make it more negative; if the BAF is positive, increasing GWP CH 4 will make BAF increase). When CH 4 generation increases at a constant overall “potenti al CO 2 emissions” rate (increasing C CH 4 or increasing Bo), the impact will be similar to incre asing the global warming potential of methane (i.e., it will increase the absolute value of the c alculated BAF ). In the biogas measurement method, the CO 2 generation is inversely related to the biogas meth ane concentration ( C CH 4 ) and is not really an independent variable. In the animal population m ethod, the “potential CO 2 emissions” is a function of the carbon content of the volatile soli ds (VolatileCarbon_AT) and can vary independently of the maximum methane generation (Bo ). Increasing the VolatileCarbon_AT increases the CO 2 emissions relative to CH 4 emissions, so increasing VolatileCarbon_AT acts si milar to decreasing C CH 4 or Bo. If the fraction of methane emitted from anae robic 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 Combustio n or Thermochemical Processing and Associated GHG Emissi ons Pathways Direct combustion of livestock waste presents an al ternative to management through anaerobic storage and treatment, or aerobic treatment, such a s 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 typic ally involve combustion of poultry litter for electricity generation, space heating (e.g., of pou ltry 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 mate rials (e.g., straw, wood chips, or corn husks), man ure, 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 (Ca ntrell et al., 2008; Santoianni et al., 2008).
Direct combustion or thermochemical conversion of l ivestock waste is not expected to result in a net increase in CO 2 e emissions relative to alternative GHG emissions p athways that could be used to manage the livestock waste. 34 Combustion or thermochemical processing is expecte d to result in net GHG emissions reductions compared to GHG emissi ons 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, result ing in biogenic CO 2 emissions, its alternate fate would have resulted in CH 4 and/or CO 2 emissions through anaerobic decay, aerobic decay, or both. Combustion can, however, introduce toxic metals int o the environment. The biomass contained in livestock waste is the dig estive 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 ma nure that is combusted (with resulting biogenic CO 2 emissions) is typically derived from plant matter CO 2 uptake during annual or short, multi-year growth a nd harvest cycles. Stationary source combustion or processing of lives tock waste can result in the removal of atmospheric CO 2 . For example, ash produced from the combustion of livestock waste can be used as an agricultural fertilizer, and pyrolysis can be us ed 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 Wa ste The assessment factor equation can be applied to po int source biogenic CO 2 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 CO 2 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 a voided GHG emissions reductions that would have occurred in the absence of combustion of lives tock 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 othe r 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 doe s not include fossil fuel energy inputs used to gen erate process heat. 35 This would apply to both plant- and animal-based l ivestock 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 probl em 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 emissi ons resulting from the actual waste management strategy used. In practice, as applied here, the AVOIDEMIT term contains a ratio of the emissions, in CO 2 e, of the alternative livestock waste management process (had that feedstock not been combusted) to the emissions, in tCO 2 e, from the combustion of the livestock waste, afte r 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 simplifi ed 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 alt ernative to combustion) can be calculated by assuming that if livestock was te were not managed using combustion, then this waste would have been managed under one or more dif ferent 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 tre ated in an uncovered lagoon. 37 The GHGs that would have been generated under these alternative f ates can be estimated using methods presented in IPCC (2006b) and EPA (2009b). To estim ate the annual CO 2 and CH 4 emissions resulting from a livestock waste management strateg y other than combustion, the numerator of the AVOIDEMIT

term can be estimated using Equation N.48.
Total CO 2 e emissions from a livestock waste management alter nate to combustion = (avoided CO 2 emissions) + (avoided CH 4 emissions) (EQ. N.48) The avoided CO 2 emissions from a livestock waste management altern ate to combustion is equal to the available carbon in the volatile solids of the livestock waste after removing the amount of carbon which becomes CH 4 and then converting the remaining available carbon to CO 2 . This calculation (Equation N.48) is the same as Equation N.25 which was previously used in the calculation of emissions from anaerobic digesters f or livestock waste management:
Avoided CO 2 emissions (metric tons CO 2 e/year) = [(PCO 2 × 12/44) – (Avoided CH 4emissions/ tsZ +Q ? × 12/16)] × (44/12) (EQ. N.239) Where:
PCO 2 = Potential maximum CO 2 emissions, see Equation N.50.

37 There are multiple livestock waste management scen arios alternative to combustion of livestock waste. An uncovered anaerobic lagoon would generate the most (see EPA, 2009b, Table A-3). Depending on ambient temperature, CH 4 production in an uncovered anaerobic lagoon ranges from 66% to 80% of the maximum amount of CH 4 that could potentially be produced from the livesto ck waste. The appropriate alternative livestock was te management scenario should be used when this calcul ation is made.November 2014 N-68

(12/44) = molecular weight ratio of C to CO 2 (converts potential CO 2 emissions to carbon).
Avoided CH 4 emissions = avoided CH 4 emissions, metric tons CO 2 e/year (see Equation N.53, below).
GWP CH 4 = 100-year GWP for CH 4 . (12/16) = molecular weight ratio of C to CH 4 (converts CH 4 emissions to carbon). (44/12) = molecular weight ratio of CO 2 to C (converts C less that associated with the CH 4 emissions back to CO 2 emissions).
Potential CO 2 emissions can be solved using Equation N.50, which was also used in estimating the emissions associated with livestock waste managemen t via an anaerobic digester:
Potential CO 2 emissions =
Σ animal type (TVS AT × VolatileCarbon AT × (44/12) × 365 × 1/1,000) (EQ. N.50) Where:
Σ animal type = If the alternate waste management system accept s waste from more than one animal type then this calculation must be computed for each animal type and then summed across animal types.
TVS AT= Total volatile solids excreted by animal type ( kg/day); the TVS AT

equation is presented below (Equation N.51).
VolatileCarbon AT= Fraction of degradable carbon in the volatile so lids of the livestock

waste (see Equation N.52). 44/12 = molecular weight ratio of CO 2 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 (TVS AT ) may be calculated using the following equation (previously presented under livestock waste managem ent 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):
TVS AT = (Population AT × TAM AT × VS AT /1,000) (EQ. N.51) Where:
TVS AT= Total volatile solids excreted per animal type (kg/day).November 2014 N-69

Population AT= Average annual animal population (head), by ani mal type. 38
TAM AT= Typical animal mass, by animal type; determined using either default

values (see EPA, 2009b, Table A-2) or farm specific data (kg/head).
VS AT= Volatile solids excretion rate by animal type, using either default values

(see 40 CFR 98.363, Tables JJ-2 and JJ-3) or farm s pecific data (kg VS/day/kg animal mass). The fraction of degradable carbon in the volatile s olids of the livestock waste (VolatileCarbon AT ) can be estimated using results from proximate and ultim ate analyses 39 of the livestock waste specific to the waste of animal type being managed (see Equatio n 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
VolatileCarbon AT = +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:
VolatileCarbon AT= Fraction of the degradable carbon in the volatil e solids of the livestock waste (kg degradable carbon in volatile solids/kg o f volatile solids, dry basis). 41 Carbon = Fraction of carbon in livestock waste (kgcarbon in total dried

solids/kg of total dried solids), dry basis (from u ltimate 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 to tal 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 esti mated using annual animal inventory or equivalent. For growing populations (e.g., meat animals such as beef and ve al cattle), average annual animal populations are estimated usi ng the average number of days each animal is kept a t the facility and the number of animals produced annually (e.g., growing population = days onsite × (number of anima ls produced annually / 365)). 39 Characteristics of a biogenic feedstock can be des cribed using proximate and ultimate analyses based on a sample’s complete combustion to CO 2 and liquid water. The proximate analysis gives moi sture content, volatile content, carbon remaining (fixed carbon), and miner al ash. The ultimate analysis gives the sample’s el emental composition as proportions of carbon, hydrogen, oxy gen, nitrogen, and sulfur. Standardized test method s have been developed, for example, see Table 3 in Demirbas (20 04). 40For example, ASAE Standard D384.2 (2005) is useful for estimating general characteristics of livestoc k and poultry manure. Li et al. (2008) and Henihan et al. (2003) present specific results of proximate and u ltimate 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 the n the amount of carbon in the volatile solids may b e underestimated, thus giving a low-biased estimate o f the VolatileCarbon ATterm (though the bias is likely small).November 2014 N-70

Volatile Solids = Fraction of volatile solids in l ivestock 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 matt er 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 soli ds), dry basis. Equation N.53 can be used to estimate the annual av oided CH 4 emissions generated from a manure management strategy alternate to combustion:
Avoided CH 4 emissions (metric tons CO 2 e/year) =
Σ animal type (TVS AT × VS WMS × Days × B 0 × MCF WMS × 0.662 × 1/1,000 × tsZ +Q ? ) (EQ. N.53) Where:
Σ animal type = If the alternate waste management system accepts waste from more than one animal type then this calculation must be compu ted for each animal type and then summed across animal types.
TVS AT= Total volatile solids excreted by animal type ( kg/day); (Equation N.51).
VS WMS = Proportion of total manure for each animal type that is managed in each

waste management system (assumed to be equivalent t o the amount of volatile solids in each waste management system). Days = Number of days per year (i.e., 365 days/yea r).
B 0 = Maximum CH 4 -producing capacity for each animal type (m 3 CH 4 /kg volatile

solids; see EPA, 2009b, Table A-2).
MCF WMS = CH 4 conversion factor (proportion represented as a dec imal value) for the

alternative-scenario, waste management system (see EPA, 2009b, Table A-3).
0.662 = density of CH 4, kg CH 4 / m 3 (at 531.67°R, or 22.22°C, and 1 atm). 1/1000 = conversion factor from kg to metric tons.
GWP CH 4 = 100-year GWP of CH 4 , 25 (IPCC, 1996).
The maximum amount of CH 4 that could potentially be produced from livestock waste managed under ideal conditions is calculated by multiplyingthe total volatile solids by the maximum CH 4 - producing capacity of the livestock waste (B 0 ). The B 0 values vary by animal type and diet (see EPA, 2009b, Table A-2). Most manure management systems w ill not produce the maximum amount of CH 4 possible because the conditions in the systems are not ideal for CH 4 production. The CH 4 -November 2014 N-71

producing potential of a specific livestock waste m anagement system is represented by a methane conversion factor (MCF). The value of this paramete r ranges from 0% to 100% and reflects the capability of a system to produce the maximum achie vable CH 4 (the higher the MCF, the greater the potential for CH 4 production). For liquid systems (e.g., uncovered a naerobic lagoons), MCF values are temperature dependent: in order to assign the a ppropriate 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 CO 2 emissions and the avoided CH 4 emissions (Equation N.48, metric tons CO 2 e/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 t reatment by combustion) is based on the carbon content of the p oint source, stack emissions from the waste combustion unit. The value of the denominator is eq ual to the CO 2 e 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 combust ed nor emitted to the atmosphere as a pointsource emission. Combustion of livestock waste does not create or emit CH 4 ; the only GHG associated with this process is CO 2 . The principal products of livestock waste combust ion include CO 2 , carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO x ), sulfur oxides (SO x ), inorganic bottom ash, and fly ash (Antares Group In c. et al., 1999). Carbon monoxide and HC are important indicators of incomplete combustion; with complete combustion, CO 2 is the primary carbon-based emission (Antares Group Inc. et al., 1 999).
Total CO 2 e emissions from combustion of livestock waste can be computed using the following equation:
CO 2 emissions from incineration of livestock waste (MT CO 2 e/year) =
Σ animal type (TVS AT × TotalCarbon AT × DE × (44/12) × 365 ×1/1,000) (EQ. N.244) Where:
TVS AT= total volatile solids excreted per animal type (kg/day), see Equation N.51.

42 Combustion efficiency of livestock waste varies wi th the type of boiler used, moisture content, and p article size of the feedstock. In an efficient combustor, very litt le carbon in poultry litter is left unburned (Antar es Group Inc. et al. 1999). One published value of combustion efficiencyfor combustion of broiler litter, based on the carbon content in the ash is 96% (Costello, 2007).November 2014 N-72 TotalCarbon AT= fraction of the carbon in the volatile solids o f the livestock waste, see

Equation N.55. DE = livestock waste destruction efficiency (i.e., combustion efficiency of

incinerator). 44/12 = molecular weight ratio of CO 2 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 (TotalCarbon AT ) can be estimated using results from proximate and ultimate analyses 43 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 oxidiz e during the manure combustion process. Thus, it is assumed that all of the combustible carbon exist s in the volatile solids fraction of the dried soli ds. Data needed to estimate this parameter can be direc tly measured or, more simply, can be taken from the body of published scientific literature. 44
TotalCarbon AT = +64:12 S1765/7-	r17/w0 = +64:12

S1765/7-	l655-4		/-w	+64:12 (EQ. N.255)
Where:
TotalCarbon AT= fraction of carbon in the volatile solids of th e livestock waste, (kg carbon in volatile solids/kg of volatile solids, dry basis ). Carbon = fraction of carbon in livestock waste (kgcarbon in total dried solids/kg

of total dried solids), dry basis (from ultimate an alysis).
Volatile Solids = fraction of volatile solids in li vestock 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 a nd fixed carbon from the fuels proximate analysis (see Figure N-3).

43 Characteristics of a biogenic feedstock can be des cribed using proximate and ultimate analyses based on a sample’s complete combustion to CO 2 and liquid water. The proximate analysis gives moi sture content, volatile content, carbon remaining (fixed carbon), and miner al ash. The ultimate analysis gives the sample’s el emental composition as proportions of carbon, hydrogen, oxy gen, nitrogen, and sulfur. Standardized test method s have been developed, for example, see Table 3 in Demirbas (20 04). 44 For example, ASAE Standard D384.2 (2005) is useful for estimating general characteristics of livestoc k and poultry manure. Li et al. (2008) and Henihan et al. (2003) present specific results of proximate and u ltimate 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 to tal 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 denominatorof the AVOIDEMIT term, the BAF

can be calculated using Equation N.1. See Section 5.2.2 fo r 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 co mbustion. Several parameters are presented and used in the eq uations in the remainder of this section. Table N-11 presents the parameters used, typical or defau lt values, ranges presented in the literature, and references. Table N-11. Summary of Parameters Used When Calculat ing 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 TAM AT 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 VS AT 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 CH 4 - producing capacity for each animal type B 0 0.24 0.17 to 0.78 m 3 CH 4 /kg

volatile solids Value

presented is for dairy cows EPA, 2009b,

Table A-2

Density of CH 4 -- 0.662 -- kg CH 4 /m 3 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-4November 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 analysis 2 Sweeten et al.,

2002

1 VS AT can be determined using either default values or f arm-specific data.
2 If only fuels proximate analysis is available, est imate the volatile solids as the sum of the volatil e 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 mana ge 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., TVS AT , VolatileCarbon AT , and the potential maximum CO 2 emissions).
5.2.1. Example Calculation for Direct Combustion and Land Application of Livestock Waste Step 1: Calculating the Avoided CH 4 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 CH 4 emissions. Parameters in Equation N.48 can be esti mated using a hypothetical example of an operation set in norther n Georgia, consisting of 400,000 broilers per year, with a typical animal mass of 0.9 kg, and a v olatile solids excretion rate of 15 kg VS/day/1000 kg animal mass (see 40 CFR 98.363, Table JJ-2). Equ ation 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 CH 4 conversion factor (MCF WMS ) used to calculate avoided CH 4 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 e ffect on the value of the BAF

. 46 Large quantities of poultry litter are removed fro m the poultry house during annual clean-out. If pos sible, 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 manag ed in anaerobic lagoons, it is more common to use this management strategy for pullets.November 2014 N-75

TVS AT = (Population AT × TAM AT× VS AT /1,000) = 400,000 × 0.9 kg × 15 kgVS/day/kg animal mass/1,0 00 = 5,400 kg/day
With TVS ATestimated, the avoided CH 4 emissions resulting from a poultry litter manageme nt strategy other than an anaerobic digester can be ca lculated. In this hypothetical example set in a temperate region (e.g., northern Georgia) with an a verage temperature of 16oC, the alternative fate could have been to store the chicken litter as a so lid prior to its application as a soil amendment; the chicken litter would be stored for approximatel y 1 year prior to its land application (EPA, 2001). In this first hypothetical scenario, the only litte r-producing animal type is broilers, and the only alternate waste management system of the poultry pr oduction with litter is solid storage prior to land application. When calculating the avoided CH 4 emissions associated with the alternative fate of chicken litter under this scenario, several paramet ers are needed, including the maximum CH 4 - producing capacity for broilers (see EPA, 2009b, Ta ble A-2, for the appropriate default value; for broilers, B 0 = 0.36 m 3 CH 4 /kg); and a CH 4 conversion factor for the alternative-scenario’s w aste management system (see EPA, 2009b, Table A-3; for s olid storage in a temperate climate, MCF WMS = 0.04). Equation N.53 can be used to calculate the a voided CH 4 emissions:
Avoided CH 4 emissions (metric tons CO 2 e per year) = 25 × (TVS AT × VS WMS × 365 days/year × B 0 × MCF WMS × 0.662 kg CH 4 /m 3 × 1 metric ton/1,000 kg) = 25 × (5,400 × 1 × 365 × 0.36 m 3 CH 4 /kg × 0.04 × 0.662 × 1/1,000)
= 469.7287 MT CO 2 e per year. Step 2: Calculating the Avoided CO 2 from the Alternate Treatment To estimate the avoided CO 2 emissions from a poultry litter management strategy other than combustion, the fraction of degradable carbon in th e volatile solids of the chicken litter must be calculated. For the scenarios presented here (Secti on 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 r esults of the proximate analysis on a wet basis, those parameters must be converted to a dry basis b y 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 VolatileCarbon ATterm, the fixed carbon is removed from the total c arbon in the poultry litter because the fixed carbon is a ssumed not to degrade. Using these data, Equation N.52 can be parameterized as follows:

VolatileCarbon AT = +64:12–/-w	+64:12 S1765/7-	r17/w0 

## = +64:12–/-w	+64:12 S1765/7-	l655-4		/-w	+64:12November 2014 N-76 = T.g	T.TCgg T.CXCT.TCgg = 0.2959
With TVS ATand VolatileCarbon ATestimated, the potential maximum CO 2 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 CO 2 emissions = (TVS AT × VolatileCarbon AT × (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 CO 2 per year With estimates of both the potential CO 2 emissions and the avoided CH 4 emissions, the avoided CO 2 emissions resulting from an aerobic poultry litter management strategy can be calculated. For this calculation the total potential CO 2 emissions from the decomposition of TVS ATmust first be converted to carbon. From this is subtracted the CH 4 emissions after converting them to carbon. The result is then converted back to CO 2 (see Equation N.49):
Avoided CO 2 emissions = ((Potential CO 2 emissions × 12/44) – (Avoided CH 4emissions/25 × 12/16)) × (44/12) = ((2,138.4693 × 12/44) – (469.7287 / 25 × 12/16)) × (44/12) = 2,086.7990 MT CO 2 per year Step 3: Calculating the CO 2 e 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 CH 4 and the avoided CO 2 emissions (Equation N.48). This summation represents the tota l avoided CO 2 e emissions (in metric tons CO 2 e per year) that result from storage of the solid litter: Total avoided CO 2 e emissions = (avoided CO 2 emissions) + (avoided CH 4 emissions) = 2,086.7990 + 469.7287 = 2,556.5277 metric tons CO 2 e per year.November 2014 N-77

Step 4: Calculating the CO 2 e from the Anaerobic Digester (Denominator) Equation N.54 can be used to calculate the denomina tor 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 t otal volatile solids excreted per broiler (TVS AT ) is still applicable. For combustion, however, the frac tion 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 (TotalCarbon AT ) is calculated as:

TotalCarbon AT = +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 CO 2 e emissions from combusting the litter from the 400 ,000 broilers assuming a 96% destruction efficiency of the waste 48 is calculated as:
CO 2 emissions from incineration of poultry litter (met ric tons CO 2 e/year)
= TVS AT × TotalCarbon AT × (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 CO 2 e per year Step 5: Calculating the BAF Value After solving for the numerator and the denominatorof the AVOIDEMIT term associated with this litter management strategy (i.e., litter storage pr ior 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 wi th the type of boiler used, moisture content, and p article size of the feedstock. In an efficient combustor, very litt le carbon in poultry litter is left unburned (Antar es Group Inc. et al., 1999). One published value of combustion efficiencyfor 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 altern ate disposal scenario of storing the chicken litter as a solid prior to its application as a soi l 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 manag ement strategy of this chicken litter via storage and treatment in an open anaerobic lagoon. 49 An uncovered anaerobic lagoon is capable of generating more CH 4 than is management via solid storage prior to land application. As a result the calculated avoided CH 4 emissions and the avoided CO 2 emissions will differ. However, between these two scenarios, the calculated values for TVS AT(5,400 kg/day), VolatileCarbon AT(0.2959), and the potential maximum CO 2 emissions (2,138.4693 metric tons CO 2 per year) would not be different; those values calculated above, can be im ported into the equations needed to calculate the avoided CH 4 emissions and the avoided CO 2 emissions (Equations N.53, and N.49, respectively). Step 1: Calculating the Avoided CH 4 Emissions from the Alternate Fate When calculating the avoided CH 4 emissions associated with the alternate fate of th e chicken litter under this scenario, several parameters are needed, including the maximum CH 4 -producing capacity for broilers (see EPA, 2009b, Table A-2, f or the appropriate default value; for broilers, B 0 = 0.36 m 3 CH 4 /kg; this is the same as under the previous example ); and a CH 4 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, MC F WMS = 0.75). The following equation (Equation N.53) can be used to calculate the avoide d CH 4 emissions for treatment of this chicken litter via an uncovered anaerobic lagoon:
Avoided CH 4 emissions (metric tons CO 2 e /year) = 25 × (TVS AT × VS WMS × 365 days/year × B 0 × MCF WMS × 0.662 kg CH 4 /m 3 × 1 metric ton/1,000 kg) = 25 × (5,400 kg/day × 1 × 365 × 0.36 m 3 CH 4 /kg × 0.75 × 0.662 kg CH 4 /m 3 × 1/1,000) = 8,807.4135 MT CO 2 e per year Step 2: Calculating the CO 2 Emissions from the Alternate Fate With estimates of both the potential CO 2 emissions and the avoided CH 4 emissions, the avoided CO 2 emissions resulting from an uncovered anaerobic lag oon poultry litter management strategy can be calculated. For this calculation, the total potenti al CO 2 emissions from the decomposition of TVS AT must first be converted to carbon. From this is sub tracted the CH 4 emissions after converting them to carbon. The result is then converted back to CO 2 (see Equation N.49):

49 As previously mentioned, chicken litter from broil ers can be managed in anaerobic lagoons, though it is more common to use this management strategy for pullets.November 2014 N-79

Avoided CO 2 emissions = ((Potential CO 2 emissions × 12/44) – (Avoided CH 4emissions/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 CO 2 e Emissions from the Alternate Fate Summing the estimated, avoided CH 4 and CO 2 emissions (both in metric tons CO 2 e per year) that result from an uncovered, anaerobic lagoon manageme nt strategy for poultry litter (Equation N.25), the numerator of the AVOIDEMIT term for this scenario can be computed as:
Total avoided CO 2 e emissions = (avoided CO 2 emissions) + (avoided CH 4 emissions) = 1,169.6538 + 8,807.4135 = 9,977.0673 MT CO 2 e per year Step 4: Calculating the BAF Value The denominator of the AVOIDEMIT term represents the CO 2 e 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 Equ ation 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 strateg y (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 u sed here can be found in Table N-11 of Section 5.1.2. The parameter that has the greatest variabil ity 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 CH 4 (GWP_CH 4 ) also decreases the BAF value. The methane generation potential (Bo) and the volatile carbon content (Vol atileCarbon_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 increasingNovember 2014 N-80

TotalCarbon_AT increases BAF (including making negative BAF less negative). In the same manner, the waste combustor destruction efficiency (DE) onl y impacts the denominator. Since the destruction efficiency here reflects the fraction o f the total carbon that is oxidized in the combusto r, lowering DE reduces the emissions in the denominato r causes BAF to decrease (or become more negative). Table N-12. Sensitivity Analysis of Anaerobic Digest ion 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 GWP HI J 21 0.21 −0.35 −0.80 −1.47 2 GWP HI J 25 0.18 −0.50 −1.05 −1.87 3 GWP HI J 28 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 unl ess specified as the parameter varied.

• GWP

HI J = 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 Facilit ies and Associated GHG Emission Pathways
Wastewater from domestic and industrial sources is treated to remove soluble organic matter, suspended solids, pathogenic organisms, and chemica l contaminants from the wastewater prior to its discharge into natural water systems. In the Un ited States, approximately 20% of domestic wastewater is treated in septic systems or other on site systems, while the rest is collected and treated centrally (EPA, 2014b). Centralized wastewa ter 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 removingnutrients. In the United States, there are approximately 14,780 wastewater treatment plants (L ono-Batura et al., 2012).November 2014 N-81

Soluble organic matter in wastewater is generally r emoved via biological processes in which microorganisms biodegrade the organic matter under aerobic or anaerobic conditions. Sludges (also referred to as wastewater biosolids after the y have been treated) are the product of most wastewater treatment systems (Bogner et al., 2007; RTI International, 2010). Carbon dioxide, CH 4 and N 2 O can be produced and released to the atmosphere at various stages between the initial point of wastewater collection and its final disposal, in cluding wastewater transport, sewage treatment processes, and anaerobic digestion of wastewater orsludges (Bogner et al., 2007). In the United States, domestic and industrial wastewater treatmen t accounted for approximately 2.3% of CH 4 emissions in 2012 (totaling 12.8 Tg CO 2 e) and 1.2% of N 2 O emissions (totaling 5.0 Tg CO 2 e) (EPA, 2014b). Methane is microbially produced under anaerobic con ditions. Domestic wastewater CH 4 emissions originate from both septic systems and from central ized treatment systems. Within centralized systems, CH 4 emissions can arise from aerobic systems that are n ot 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 lagoo ns), 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 le aks, 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 a naerobic 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).
N 2 O is an intermediate product of microbial nitrogen cycling; it is generated via the treatment of domestic wastewater during both nitrification and d enitrification of the nitrogen present, usually in the form of urea, ammonia, and proteins. These comp ounds are converted to nitrate (NO 3 ) through the aerobic process of nitrification. Denitrificati on occurs under anoxic conditions, and involves the biological conversion of nitrate into N 2 (EPA, 2014b). The amount of nitrogen present in th e influent wastewater determines the N 2 O generation potential. Collection of biogas generated in the wastewater tr eatment process is primarily, if not entirely, restricted to treatment systems using anaerobic dig esters. Anaerobic digesters are used to enhance the degradation process of wastewater and wastewate r sludge, thereby producing biogas. If the CH 4 generated by an anaerobic wastewater treatment proc ess or anaerobic sludge digestion process is captured and combusted (in a flare or other combust ion device), then CH 4 is destroyed and converted to CO 2 , resulting in a net decrease in GHG emissions. N 2 O is not a product of wastewater treatment via an anaerobic digester. It is unknown how many U.S. wastewater treatment fa cilities 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 tha n 40% of the large wastewater treatment facilities in the U.S; this sector has potential to expand (Lono-Batura et al., 2012). Collected bioga sNovember 2014 N-82

from waste water treatment facilities is most commo nly flared, though some wastewater treatment facilities use it for energy generation or sell it for use off-site; several facilities reported relea sing the collected biogas directly to the atmosphere (Lo no-Batura et al., 2012). Because anaerobic digesters enhance the waste degradation process, th ereby increasing the rate of CH 4 generation, biogas produced in an anaerobic digester and releas ed directly to the atmosphere without combustion would result in greater CH 4 emissions than had the treatment not utilized an a naerobic 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 po int source biogenic emissions that result from the combustion of biogas from an anaerobic digesterused 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 tre atment 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 colle cted 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 CH 4 contained in biogas to CO 2 . This results in a net reduction of GHG emissions relative to an alternate GHG emissions pathway in w hich biogas produced through the anaerobic treatment of wastewater is not captured and combust ed, but instead is released to the atmosphere as an indirect emission. In instances where the alternate GHG emissions path way involves uncontrolled anaerobic treatment of wastewater, use of anaerobic digester systems typically results in substantial net GHG emissions reductions. However, because anaerobic di gesters are designed to enhance CH 4 generation, poor design, operation, or maintenance of anaerobic digesters can result in significant indirect CH 4 emissions. For example, CH 4 can leak from a digester cover or can be vented du ring digester start-ups, shutdowns, and malfunctions (Bo gner et al., 2007; EPA, 2008b; Climate Action Reserve, 2013). However, under normal working condi tions, GHG emissions from controlled biological treatment in an anaerobic digester are s mall relative to indirect CH 4 emissions from uncontrolled anaerobic storage and treatment system s (Bogner et al., 2007, and references therein). In instances where the alternative GHG emissions pa thway involves aerobic treatment of wastewater, use of an anaerobic digestion system wi th 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 ae robically, producing CO 2 as the primary decay product (e.g., in a shallow lagoon or in an a eration tank associated with activated sludge wastewater treatment processes), or they would have decayed anaerobically, producing both CH 4 and CO 2 (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 (w here 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 CO 2 e avoided (i.e., the emissions, in CO 2 e, resulting from an alternative wastewater treatment scenario of aerobi c, anaerobic, or a combination of aerobic and anaerobic treatment) per units of CO 2 e removed via combustion (i.e., the emissions, in C O 2 e, of the biogas generated in an anaerobic digester—accountin g for biogas collection and combustion efficiencies). For the biogas feedstock collected f rom the treatment of wastewater in an anaerobic digester, the AVOIDEMIT term can be conceptually expressed using the simpl ified 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 a lternative to an anaerobic digester) can be calculated by building u pon the methods developed for EPA by RTI International (2010). To compute the emissions prof ile of the treatment method that is alternate to an anaerobic digester, the CO 2 e emissions resulting from the alternate treatments of wastewater and wastewater sludge must be summed:
AVOIDEMIT

numerator = CO 2 WW + CO 2 S + ( tsZ +Q ? × (CH 4 WW + CH 4 S)) (EQ. N.267) Where:
CO 2 WW = CO 2 emission rate from wastewater treatment (MT CO 2 /year), see Equation N.58.
CO 2 S = CO 2 emission rate from wastewater sludge treatment (MT CO 2 /year), see

Equation N.61.
GWP CH 4 = Global warming potential for methane, 25 (IPCC, 2007)
CH 4 WW = CH 4 emission rate from wastewater treatment (MT CH 4 /year), see

Equation N.59.
CH 4 S = CH 4 emission rate from wastewater sludge treatment (MT CO 2 /year), see

Equation N.62.
CO 2 and CH 4 emissions from the aerobic treatment of wastewater can be calculated using the following two equations:

+,  ss = T C × ,Q40 ×  cc × ,\ × ]33 ,\ × ?? W ×   − l+

ss × t +Q ?  (  − ) 

(EQ. N.278)
+Q ? ss = T C × ,Q40 ×  cc × ,\ × ]33 ,\ × C W ×  l+

ss × t +Q ?  (  − ) November 2014 N-84 (EQ. N.59) Where:
CO 2 WW = CO 2 emission rate (MT CO 2 /year).
CH 4 WW = CH 4 emission rate (MT CH 4 /year).
10 -6 = Units conversion factor (MT/g). OpHrs = Hours wastewater treatment system is operat ed per year. Q ww= Wastewater influent flow rate (m 3 /hr). OD = Oxygen demand 50 of influent wastewater to the biological treatment unit (mg/L = g/m 3 ).
Eff OD = Oxygen demand removal efficiency of the biologi cal treatment unit. 44/32 = Molar mass ratio of CO 2 to O 2 ; representing the conversion factor for

maximum CO 2 generation per unit of oxygen demand. 16/32 = Molar mass ratio of CH 4 to O 2 ; representing the conversion factor for

maximum CH 4 generation per unit of oxygen demand.
MCF ww= CH 4 correction factor for wastewater treatment unit, in dicating the fraction of

the influent oxygen demand that is converted anaero bically in the wastewater treatment unit. 51
BG CH 4 = Fraction of C as CH 4 in generated biogas (default is 0.65). λ = Sludge biomass yield, expressed as g C convert ed 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 ×lSrr 0 ×T.XW  cc ×,\×]33 1w × 

W (EQ. N.60)

Where:

50Determined 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 degr adable organic content in wastewater. 51 MCF ww value ranges from 0 to 0.8 (see Table N-4). A MCF ww value of zero (no CH 4 emissions) is assigned to well-managed aerobic decomposition systems.November 2014 N-85

λ = Sludge biomass yield, expressed as g C convert ed to sludge per g C consumed

in the wastewater treatment process. Q s = Wastewater sludge flow rate (m 3 /hr). Q ww= Wastewater influent flow rate (m 3 /hr).
MVVSS s = Mixed liquor volatile suspended solids concentr ation of the waste sludge

stream (mg/L). OD = Oxygen demand of influent wastewater to the b iological treatment unit

(mg/L).
Eff OD = Oxygen demand removal efficiency of the biologi cal treatment unit.
0.53 = Correction factor for carbon content of the sludge biomass. 52 12/32 = Molar mass ratio of C to O 2 ; 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 a lternative 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 s ystem), well managed 0 0.65 Aerated treatment process, overloaded (i.e., anoxic areas) 0.3 0.45 Anaerobic treatment process (e.g., anaerobic digest er) 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 digeste r) 0.8
Emissions from the treatment of solids (i.e., sludg e generated in the wastewater treatment system), whether sludge is treated aerobically or anaerobica lly, can be calculated using the following equations:

52 Carbon accounts for 53% of the sludge biomass weig ht (dry basis).November 2014 N-86

+,  r = T C × ,Q40 ×  cc × ,\ × ]33 ,\ × ?? W ×     − l+

r × t +Q ?  (EQ. N.61)
+Q ? r = T C × ,Q40 ×  cc × ,\ × ]33 ,\ × C W ×    l+

r × t +Q ?  (EQ. N.62)
Where:
CO 2 S = CO 2 emission rate (MT CO 2 /year).
CH 4 S = CH 4 emission rate (MT CH 4 /year).
10 -6 = Units conversion factor (MT/g). OpHrs = Hours wastewater treatment system is operat ed per year. 53 Q ww= Wastewater influent flow rate (m 3 /hr). OD = Oxygen demand 54 of influent wastewater to the biological treatment unit (mg/L = g/m 3 ).
Eff OD = Oxygen demand removal efficiency of the biologi cal treatment unit. 44/32 = Molar mass ratio of CO 2 to O 2 ; representing the conversion factor for maximum

CO 2 generation per unit of oxygen demand. 16/32 = Molar mass ratio of CH 4 to O 2 ; representing the conversion factor for maximum

CH 4 generation per unit of oxygen demand. λ = Sludge biomass yield, expressed as g C convert ed to sludge per g C consumed in

the wastewater treatment process (see Equation N.60 ).
MCF S = CH 4 correction factor for sludge digestion, indicating the fraction of the treated

sludge that is converted anaerobically in the waste water treatment unit. 55
BG CH 4 = Fraction of C as CH 4 in generated biogas (default is 0.65).
6.1.2. Calculating the Denominator In computing AVOIDEMIT , the denominator (i.e., emissions from the treatme nt of wastewater and sludge in an anaerobic digester such that the gener ated biogas is captured and combusted) can be calculated by building upon the methods developed f or EPA by RTI International (2010). To compute the emissions profile associated with the a naerobic treatment of wastewater and wastewater sludge in an anaerobic digester, the CO 2 e emissions resulting from these treatments

53 A wastewater system may operate continuously excep t for when it is down for maintenance, 10% of the y ear (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 degr adable organic content in wastewater. 55 MCF ww value ranges from 0 to 0.8 (see table 3-1, RTI Int ernational, 2010). A MCF ww value of zero (no CH 4 emissions) is assigned to well-managed aerobic deco mposition systems.November 2014 N-87

must be summed while simultaneously accounting for biogas destruction efficiency (via combustion) and biogas collection efficiency:
AVOIDEMIT

denominator = CO 2 WW + CO 2 S + 25× ((CH 4 WW – CH 4 WWD + CH 4 WWL) + (CH 4 S – CH 4 SD + CH 4 SL)) + (CH 4 WWD × 44/16) + (CH 4 SD × 44/16) (EQ. N.63) Where:
CO 2 WW = CO 2 emission rate from wastewater treatment (MT CO 2 /year), see

Equation N.58.
CO 2 S = CO 2 emission rate from wastewater sludge treatment (MT CO 2 /year), see

Equation N.61.
CH 4 WW = CH 4 emission rate from wastewater treatment (MT CH 4 /year), see

Equation N.59.
CH 4 WWD = CH 4 emission rate from wastewater treatment, adjusted f or biogas destruction efficiency (MT CH 4 /year). 56
CH 4 WWL = CH 4 emission rate from wastewater treatment, adjusted f or biogas collection efficiency (MT CH 4 /year). 57
CH 4 S = CH 4 emission rate from wastewater sludge treatment (me tric ton CO 2 /year),

see Equation N.62.
CH 4 SD = CH 4 emission rate from wastewater sludge treatment, ad justed for biogas

destruction efficiency (MT CH 4 /year). 58
CH 4 SL = CH 4 emission rate from wastewater sludge treatment, ad justed for biogas

collection efficiency (MT CH 4 /year). 59 44/16 = molecular weight ratio of CO 2 to CH 4 . After solving for the numerator and the denominatorof 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 sl udge. Several parameters are presented and used in the eq uations in the remainder of this section.

56 Assuming biogas destruction efficiency is 0.99 the n CH 4 WWD = 0.99 × CH 4 WW. 57 Assuming biogas collection efficiency is 0.99 thenCH 4 WWL = (1-0.99) × CH 4 WW. 58 Assuming biogas destruction efficiency is 0.99 the n CH 4 SD = 0.99 × CH 4 S. 59 Assuming biogas collection efficiency is 0.99 thenCH 4 SL = (1-0.99) × CH 4 S.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 Calculat ing 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/m 3 Determined

through either the BOD5 or the COD tests. NA

Oxygen demand removal efficiency of the biological treatment unit Eff OD – – Decimal percent Determined by

the wastewater treatment facility. NA

Fraction of C as CH 4 in generated biogas BG HI J 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, 2010November 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 MCF ww 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) MCF ww 0.3

WW: Anaerobic treatment process (e.g., anaerobic digester) MCF ww 0.8

WW: Facultative lagoon, shallow (< 2 m deep) MCF ww 0.2

WW: Facultative lagoon, deep (≥ 2 m deep) MCF ww 0.8

Sludge: Aerobic sludge digestion MCF S 0 Sludge: Anaerobic sludge digestion (e.g., anaerobic digestion) MCF S 0.8

Biogas destruction efficiency DE;

included in CH 4 WWD and CH 4 SD 0.99 0.90 to

0.9977 Decimal

percent EPA, 2010d; EPA, 2011a; EPA, 2013c

Biogas collection efficiency CE;

included in CH 4 WWL and CH 4 SD 0.99 0.70 to

0.99 Decimal

percent 0.99 is used for

an enclosed vessel, anaerobic sludge digester EPA, 2010d, Table

6-1November 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 ave rage flow rate of 1 million gallons per day (or 157.71 m 3 /hr), an inlet 5-day biochemical oxygen demand (BOD 5) of 500 g/m 3 , 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 hypot hetical 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 co ntinuously throughout the year (365 × 24 = 8760 hours). Treatment of wastewater sludge is assu med 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 po pulate Equation N.57 must first be calculated using Equations N.58 and N.59 (because λ = 0, Equat ions N.61 and N.62 are equal to zero, thus dropping out of Equation N.57).
CO 2 emissions from the wastewater treatment system (a s hallow, facultative lagoon) are calculated using Equation N.58, (MCF ww= 0.2 and λ = 0):

   = 	 T C × >

# ×   × 
 × ""  × ?? W ×   −   ×  > ?  (  −  ) 

= 10 -6 × 8760 × 157.71 × 500 × 0.95 × (44/32) ×[(1 – 0.2 × 0.65) (1 – 0)]
= 785.0167 MT CO 2 per year CH 4 emissions from the wastewater treatment system (a s hallow, facultative lagoon) are calculated using Equation N.59, (MCF ww= 0.2 and λ = 0):

> ?  = 	 T C × >

# ×   × 
 × ""  × C W ×    ×  > ?  (  −  ) 
= 10-6 × 8760 × 157.71 × 500 × 0.95 × (16/32) ×[ (0.2 × 0.65)(1 – 0)]
= 42.6550 MT CH 4per year. The numerator of AVOIDEMIT can now be solved using Equation N.57:
AVOIDEMIT

numerator = CO 2 WW + CO 2 S + (25 × (CH 4 WW + CH 4 S))

= 785.0108 + 0 + 25 × (42.6547 + 0) = 1,851.38 MT CO 2 e per yearNovember 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. Howeve r, values to populate Equation N.63 must first be calculated using Equations N.58, N.59, N.6 1, and N.62.
CO 2 emissions from the wastewater treatment system (an anaerobic digester) are calculated using Equation N.58, (MCF ww= 0.8 and λ = 0.1):

   = 	 T C × >

# ×   × 
 × ""  × ?? W ×   −   ×  > ?  (  −  ) 

= 10 -6 × 8760 × 157.71 × 500 × 0.95 × (44/32) ×[(1 – 0.8 × 0.65)(1 – 0.1)]
= 389.8014 MT CO 2 per year CH 4 emissions from the wastewater treatment system (an anaerobic digester) are calculated using Equation N.59, (MCF ww= 0.8 and λ = 0.1):

> ?  = 	 T C × >

# ×   × 
 × ""  × C W ×    ×  > ?  (  −  ) 

= 10 -6 × 8760 × 157.71 × 500 × 0.95 × (16/32) ×[(0.8 × 0.6 5)(1 – 0.1)]
= 153.558 MT CH 4 per year. CO 2 emissions from the wastewater sludge treatment syst em (an anaerobic digester) are calculated using Equation N.61, (MCF S = 0.8 and λ = 0.1):

   = 	 T C × >

# ×   × 
 × ""  × ?? W ×     −   ×  > ? 

= 10 -6 × 8760 × 157.71 × 500 × 0.95 × (44/32) ×[0.1(1 – 0. 8 × 0.65)]
= 43.3113 MT CO 2 per year CH 4 emissions from the wastewater sludge treatment syst em (an anaerobic digester) are calculated using Equation N.62, (MCF S = 0.8 and λ = 0.1):

> ?  = 	 T C × >

# ×   × 
 × ""  × C W ×      ×  > ? 

= 10 -6 × 8760 × 157.71 × 500 × 0.95 × (16/32) ×[0.1(0.8 × 0.65)]
= 17.0620 MT CH 4 per year. Next, the calculated emissions associated with trea tment of wastewater and wastewater sludge in an anaerobic digester can be used to populate Equat ion N.63:November 2014 N-92

AVOIDEMIT

denominator =
CO 2 WW + CO 2 S + 25× ((CH 4 WW – CH 4 WWD + CH 4 WWL) + (CH 4 S – CH 4 SD + CH 4 SL))
+ CH 4 WWD × 44/16 + CH 4 SD × 44/16 Assuming biogas destruction efficiency is 0.99, the n:

• CH 4 WWD = 0.99 × CH 4 WW, and

• CH 4 SD = 0.99 × CH 4 S. Assuming biogas collection efficiency is 0.99, then :

• CH 4 WWL = (1–0.99) × CH 4 WW, and

• CH 4 SL = (1–0.99) × CH 4 S. Applying these assumptions, the denominator of AVOIDEMIT can be expressed as:
AVOIDEMIT

denominator = CO 2 WW + CO 2 S

+ 25× (CH 4 WW – (0.99 × CH 4 WW) + ((1–0.99) × CH 4 WW)) + 25× (CH 4 S – (0.99 × CH 4 S) + ((1–0.99) × CH 4 S)) + (0.99 × CH 4 WW × 44/16) + (0.99 × CH 4 S × 44/16)
AVOIDEMIT

denominator = 389.8014 + 43.3113

+ 25× (153.558 – (0.99 × 153.558) + ((1 – 0.99) × 1 53.558)) + 25× (17.0620 – (0.99 × 17.0620) + ((1 – 0.99) × 1 7.0620)) + (0.99 × 153.558 × 44/16) + (0.99 × 17.0620 × 44/1 6) = 982.9357 MT CO 2 e per year. Step 3: Calculating the BAF Value After solving for the numerator and the denominatorof 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 wastewa ter and wastewater sludge, and used by a stationary source results in net CO 2 e 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 wast ewater treatment in an anaerobic digester and the alternate fate of placing the waste in a shallo w, facultative lagoon. Key parameters impacting the BAF include the DE and CE for the anaerobic digester, and the GWP for CH 4 (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 valu es 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 calculatio ns with a CE lower than 78% despite the DE value (95% or 99%) used. Higher CEs yield ne gative BAF values regardless of the GWP, indicating that wastewater management through anaer obic digestion may be a better treatment option with respect to CO 2 and CH 4 emissions pathways. The turning point for the BAF values with respect to either a 95% of 99% DE is presented in A nalyses 7 through 18. Note that, in order for a net CO 2 e emissions reduction to occur, the anaerobic diges ter may require a CE of at least 80% to 85%. Table N-15. Sensitivity Analysis for Wastewater Tre atment.
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 7 a 0.79 0.99 0.003 8 a 0.80 0.99 −0.019 9 b 0.78 0.99 0.015 10 b 0.79 0.99 −0.008 11 c 0.78 0.99 0.009 12 c 0.79 0.99 −0.016 13 d 0.82 0.95 0.013 14 d 0.83 0.95 −0.008 15 e 0.82 0.95 0.005 16 e 0.83 0.95 −0.019 17 f 0.81 0.95 0.023 18 f 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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