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MEMORANDUM TO: Air and Radiation Docket EPA
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- 0401 FROM: EPA Office of Transportation and Air Quality DATE: May 30 , 2014 SUBJECT: Support for Classification of Biofuel Produced from Waste Derived

Biogas as Cellulosic Biofuel and Summary of Lifecycle Analy sis Assumptions and Calculations for Electricit y Produced from Waste Derived Biogas This memorandum provides additional support for EPA’s determination that renewable fuel produced using biogas from landfills, MSW digesters, wastewater treatment facility digesters , and agricultural digesters should be classified as cellulosic biofuel. It also provides information on the key

input assumptions used for the lifecycle anal ys is of electricit y produc ed from waste derived biogas. Assumptions include on
- site emissions of biogas collection as well as efficiencies of electricity generation, use and distribution. Data sources are presented to promote transparency

for our lifecycle anal ys is. This memoran dum also describes the calculations made for the lifecycle anal ys is of electricity produced from waste derived biogas and discuss es , in depth , the choice of baseline used in the lifecycle analy sis.2

**I. Summary**  In the June 14, 2013 Notice of Proposed Rulemaking (NPRM) , EPA proposed to allow compressed natural gas ( CNG ) , liquefied natural gas ( LNG ) and renewable electricity from landfill biogas to qualify

for cellulosic renewable identification numbers (RINs) , and requested comment on whether fuel deriv ed from other sources of biogas should also be allowed to qualify for cellulosic RINs
. The proposal to treat landfill biogas as a cellulosic biofuel feedstock was based on available data and was supported b y a memo to the docket (EPA
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- 0401). This d ocument expands upon the original memo to the docket and provides a summary of additional information provided through the public comment process or developed in response to comments received. Through the comment process, and additional EPA research, EPA has identified additional data that supports a finding that fuel derived from biogas from MSW digesters, municipal wastewater treatment facility digesters , and agricultural digesters is also predominantly

derived from cellulosic components. **II. Determination of the Cellulosic**  **Content of**  **Waste Derived Biogas**  A. Biogas from Landfills For the purposes of th is memorandum, the terms “cellulosic” or “cellulosic content ” are intended to refer to the sum of the cellulose, hemicellulose, and lignin comp onents of a feedstock
. a However, when calculating the “adjusted cellulosic content” of a feedstock, which is a percentage value, the cellulosic co ntent is divided by the volatile organic fraction because o nl y th is portion is reactive and can contribute to the production of biogas. For municipal solid waste (MSW) in landfills, the non
- organic fraction is composed of metal, cement and other inorganic materials that will not yield methane in the landfill. Review and analy sis of available data characterizing MSW landfill material and its associated biogas indicate that the organic fraction of MSW is predominately cellulosic and the biogas generated from MSW is predominantly derived from the cellulosic components
. The Barl az research cited in the June 2013 NPRM most directly attempts to answer the question of what percent of the MSW landfill biogas is derived from the cellulosic components of the MSW. Results from this study are outlined in Table 1 and Figure s 1 and 2 , and s how that methane does not appear until day 41, indicating that the initial decomposition was aerobic, involving loss of sugars to carbon dioxide and water. During this time period, about 20% of the MSW was lost, including fractions of cellulose and hemice llulose (Fig. 1 top). Once the originall y present ox ygen was consumed, the reactors became anaerobic and methane production began (Fig. 1)
. Large amounts of both cellulose and hemicellulose were converted during this period (Fig. 1 top), and lignin accumulated in the residue (Fig. 1 bottom). Overall, 71% of the

a This is based on the definition of “cellulosic biofuel” in Clean Air Act Section 211(o)(1)(E).3

cellulose and 77% of the hemicellulose were converted during the reaction, roughl y half aerobically

and half anaerobically (Table 1). These data s how that a substantial fraction of the cellulosic content of MSW is converted. In fact, b ased on the abundance of different biochemicals in the MSW and theoretical methane potentials for the different components (e.g., cellulose , proteins), the authors d etermined that 91% of the total methane in this sample was derived from cellulosic components. This research indicates that a predominant portion of the biogas from MSW landfills comes from anaerobic digestion of the cellulosic content of MSW, namely cellulose and hemicellulose
. **Table 1**

**– Chemical composition of**  **m unicipal**  **s olid**  **w aste**  **(MSW) from different studies, the**  **percent of each type of compound lost in a degradation experiment and the percent of total methane potential from the different components.**  Barlaz et al. (1989) 1 % Composition (average of 14 studies) % Composition % Lost during decomposition % of total

methane potential Cellulose 38 ± 14 51 71 74 Hemicellulose 8 ± 2 12 77 15 Lignin 16 ± 6 15 8 0 * Protein 3 ± 1 4 n.d. 8 Volatile Solids 69 ± 16 79 n.d. 100 Average % "Cellulosic" ** 90 ± 30 *** 100 **** 91 b
* The authors assumed that lignin had a methane potential of zero because lignin is known to react very slowly under anaerobic conditions. ** Calculated relative to the measured concentration of volatile solids. *** Standard error calculated by propagation of error.   Note that this value is artificially high due to measurement uncertainties

b 91% represents the portion of the biogas derived from cellulose and hemicellulose, and is calculated by dividing the sum of their methane potential fractions by the total methane potential fraction for cellulose, hemicellulose, and protein. As calculated by Barlaz et al., there may be slight differences in numbers due to rounding.4

** Figure 1**

**– Chemical Composition of degrading MSW versus time**  **: 2**  **% of original mass remaining for total mass, cellulose, hemicelluloses and lignin, with cumulative methane**  **yield plotted on the right axis. Methane first appeared (at very low concentration) on day 41.** 5

**Figure 2** 

**– Chemical Composition of degrading MSW v**  **ersus time**  **: percent composition of**  **MSW over time, with the area between curves corresponding to the percent of total mass in**  **that component. The “other” material (white) includes metals, plastics and cement, as well**  **as organic materials such as proteins a nd starches.**  **The circles show the cumulative production of meth**  **ane in the reaction containers.** R ecent studies have also confirmed that the organic fraction of MSW is still predominantly comprised of cellulos e, hemicellulose, and lignin 2 c
. Moreover, there is a strong and direct correlation between the amount of cellulosic materials present in the MSW and the amount of biogas that can be produced

– demonstrating that anaerobic digestion is convert ing cellulosic biomass to biogas
. 3 Based on the average of 14 studies, MSW contains 38% cellulose, 8% hemicellulose and 16% lignin, with smaller amounts of proteins, sugars and other organic materials (Table 1). 4 Since the average organic fraction of the MSW is 69% , the average adjusted c ellulosic content of the landfill MSW is 90%. MSW composition varies considerabl y depending on, for example, the amount of yard waste versus food waste versus metal waste deposited. It is worth noting that the studies examined were published over 2 7 years (1982 to 2009), during a time period in which recycling expanded considerabl y, leading to substantial changes in the types of materials deposited in landfills. Despite these changes, the cellulosic content of the organic fraction of MSW, the portio n capable of contributing to biogas production, has not changed substantially during this time
. 1 However, the data reviewed b y EPA indicates that the vast majority of volatile solids in landfills are composed of cellulosic components 1

. Eleazer et al. (1997) 5 analyz ed the decomposition of a variety of components of MSW, including leaves, paper, food and MSW itself. They found a correlation between the percent of cellulose and hemicellulose in the MSW and the yield of methane from the different samples, with methane yi eld increasing as the cellulose and hemicellulose increased. This study demonstrate d that biogas can be produced from the cellulosic portions of MSW and supports the conclusion that landfill biogas is predominately derived from cellulosic components . While the fraction of the biogas being generated from cellulosic components may vary slightly from location to location depending on the composition of the MSW, the volatile solids in MSW appear to always contain a large proportion of cellulosic materials d , and a large proportion of the biogas generated will be derived from cellulose and hemicellu lose. Therefore, w e conclude that biogas derived fuel is predominantly cellulosic, and that all volumes of fuel made from landfill biogas qualify for cellulosic biofuel RINs.

c This study compared data collected to other available data. d Barlaz et. al. (1989) and Eleazer et. al. (1997)6

B. Biogas from Separated MSW Digesters, Agricultural Digesters, and Municipal Wastewater Treatment Facility

Digesters For the reasons described below, EPA is exten ding its assessment that biogas derived from MSW landfills is predominantly cellulosic to include biogas from MSW digesters, municipal wastewater treatment facility digesters, and agricultural digesters
. O rganic wastes in the United States that may be available for, and susceptible to, anaerobic decomposition to produce biogas can be generall y characterized as falling into one of four categories
. The first includes the organic fraction of municipal solid waste ( OFMSW ) , the second is biosolids from municipal wastewater treatment facilities, the third is agriculture waste (including animal manure) , and the fourth is wastes that do not fall into any of the first three categories
. Almost all of the organic wastes anaerobically digested i n the U.S. fall into one of the first three categories e , and their adjusted cellulosic content is on average above 75%. ( Table 4 ). Given our understanding of anaerobic digestion in MSW landfills, described above, we are confident that anaerobic d igesters processing predominantly cellulosic materials, including materials from an y of these first three general waste categories described above, would produce biogas that is predominantly cellulosic in origin. For our final rule we have identified three digester ty

pes that we believe will process wastes that are predominantl y cellulosic: separated MSW digesters, municipal wastewater treatment facility digesters and agricultura l digesters. Digesters processing the fourth category of organic wastes described above may accept large quantities of non - cellulosic materials, such as waste fats, oils and grea ses or industrial food wastes ( e.g., food and beverage production wastes that are primarily composed of sugar or starch )
. While the materials comprising the fourth category may meet EPA’s definition of renewable biomass , we do not have enough information at this time to determine that the biogas from these materials would be derived from predominantly cellulosic components . Therefore, biogas digesters primarily processing non
- cellulosic materials such as those listed in the fourth category are considered non
- cellulosic, and transportation fuel derived from biogas prod uced at th e se digesters may qualify for advanced biofuel RI

Ns. Finally , determinations regarding the cellulosic content of various ty pes of organic wastes discussed in this memo apply onl y in the context of production of biogas through anaerobic digestion
. Our determination that fuel derived from certain feedstocks that are anaerobicall y digested to produce biogas should be considered of cellulosic origin does not apply to fuels produced from the same organic waste s that are converted t o fuel using a biomass conversion process other than anaerobic digestion
. One of the reasons for this limitation is that the anaerobic digestion process is known to convert cellulosic components of org anic wastes to biogas , and this cannot be extended to all biomass treatments
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. Separated MSW Digesters

e “Municipal Solid Waste Generation, Recycle, and Disposal in the United States: Facts and Figures for 2012”. U.S. Environmental Protection Agency: http://www.epa.gov/osw/nonhaz/municipal/msw99.htm7

Separated MSW may

be processed in a s eparated MSW digester to produce biogas and biogas
- derived transportation fuels . As discussed in the March 2010 rule, the organic fraction of MSW generall y consists of yard waste and heterogeneous post
- consumer food waste. f The biochemical conversion process es by which organic material is converted to biogas, known as anaerobic digestion, are thermody namicall y identical in both landfills and anaerobic digest ers . The only differences between the anaerobic conversion processes in these sy stems are kinetic (reaction rate)
. While the environmental conditions in landfill systems favor the anaerobic digestion of organic matter thermodynamically, the conversion process is not optimized kinetically . In fact, landfills can be viewed as anaerobic digesters that have not been optimized for efficient reaction kinetics, and are therefore only capable of passivel y generating biogas over long periods of time. Waste digeste rs, b y contrast, activel y perform the anaerobic biochemical processes that landfills allow passively because they

are designed to optimize sy stem kinetics. Therefore, waste digesters more rapidl y and efficiently convert biomass to biogas. For example, whil e processing the same amount of identical biomass, a waste digester s ystem would generate more useable biogas on a substantially shorter time
- scale than a landfill sy stem. However, despite kinetic differences, the bioconversion processes occurring in land fills and waste digesters are essentially

identical . Therefore, EPA finds that fuels made from biogas derived from digesters processing separated MSW are predominantly cellulosic in origin and, therefore that the entire volume of fuel made from such biogas qualifies for cellulosic biofuel RINs
. EPA notes that the CAA requires that renewable fuel be produced from “renewable biomass” as that term is defined in CAA 211(o)(1)(I). MSW is not identified in the statute as renewable biomass. However, EP A determined that “separated MSW” as defined in 40 CFR 80.1426(f)(5)(i)(C), qualifies as renewable biomass for purposes of renewable fuel production provided that it is collected according to a plan submitted and approved b y EPA pursuant to 40 CFR 80.1426( 5)(ii)
. Material that could have been disposed of in a MSW landfill, but was diverted from it, does not automatically qualify on that basis as separated MSW. Rather, such waste must qualify

as a different t ype of renewable biomass, such as animal waste, separated food waste, or separated yard waste to be an eligible feedstock for renewable fuel production. A
“ s eparated MSW digester” for purposes of today ’s rule is a digester processing separated MSW as defined in EPA regulations pursuant to an anaerobic digestion process , and refers to the renewable biomass fraction of MSW , which is essentially a mixture of yard wastes and post consumer food wastes. 2 . Agricultural Digesters There are approximately 250 agricultural digester projects in the U.S. Of these agricultural digesters about 40 % are co - digesters process ing a mixture of animal manure , on farm crop residues , and small amounts of other biogenic wastes
. There are no consistent data to

f U.S. E PA’s waste characterization trends show that post
- consumer food scraps and yard waste account for more than 86% of the OFMSW.8

portray the exact mixture of material being digested in individual digesters on a continuous basis because both the material composition and relative proportions of digested material varies over time. H owever , in aggregate, over 90% of the material processed in agricultural digesters is animal manure , and the remaining portion consists mainly of plant residues and other on
- farm wastes that are predominately cellulosic in origin such as crop residues and separated yard waste . g T his section provides information on both animal manure and on
- farm crop residues

– th e main components processed in agricultural digesters. Data used to estimate the aggregate composition of animal manure were obtained from a comprehensive review published by the Pacific Northwest National Laboratory covering four ty picall y digested cate gories of animal manure (dairy , cattle, swine, and poultry) 6

. Although these studies reported the cellulose, hemicelluloses, and lignin on a total solids basis, they did not calculate an adjusted cellulosic content based on the fraction of the material that could be converted to biogas
. To obtain an adjusted cellulosic content, we normalized the reported values based on the volatile organic fraction
. When possible (e.g., if the studies analyzed the same categories of manure) and if comparable (e.g., pro vided the breakdown of cellulosic components in the same way) , differing data were averaged. A weighted average based on the ty pe and volume of animal manure digested , based on data from AgSTAR was used to estimate the cellulosic content for animal manure in aggregate. The adjusted cellulosic content was calculated by summing the cellulosic fractions (cellulose, hemicellulose, and lignin) and dividing by the volatile fraction capable of contributing to biogas production. The volatile fra ction capable of contributing to biogas was assumed to be the volatile solids minus the organic nitrogen which would be converted to nitrogen gas or other inorganic nitrogen species rather than methane or carbon dioxide.

g U.S. EPA AgSTAR ’s digester project information, overall digester biogas data and a representative sample co
digester inputs wer e used to estimate the aggregate digester material. Some of these data are available at AgSTAR’s online database: http://www.epa.gov/agstar/projects/index.html#database
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**Table 2**

**– Data used to as**  **sess the cellulosic content of animal manure** Animal Manure Cattle (%) Poultry

(%) Swine

(%) % of treated

animal manure Source h Cellulose 25 22 22 25 (1) Hemicellulose 23 12 14 21 Lignin 1 9 7 7 17 Volatile Solids Organic Nitrogen 84 3 62

3 76

3 82

3 (2) Treated Volume 79 1 20
-- (3) Adjusted Cellulosic % 80
The aggregate cellulosic content of animal manure (highlighted in green in Table 2 ) was found to be 25% cellulose, 21% hemicellulose, and 17% lignin , which means the cellulosic components equal 63% . The volatile solids and organic nitrogen were found to be 8 2 % and 3% respectivel y , which results in a volati le fraction of 79 % capable of contributing to biogas production
. Based on these values , the average adjusted cellulosic content of the biomass treated in animal manure digesters is estimated to be 80 % . While this estimate assumes that the digester material would be exclusively animal manure, it is common practice to co - digest mix tures of animal wastes, farm/ crop residues an d other wastes. As described in a separate memo to the docket i , materials that we have determined meet the RFS regulatory definition of “crop residue” have on average an adjusted cellulosic content of 8 4 %
. T he addition of such crop residues would therefore ty

picall y increase the overall cellulosic content of the biomass being treated in manure digesters
. Similarly , EPA has determined that “separated yard waste”, as that term is defined in 40 CFR 80.1426(5)(i) , should be deemed to be composed enti rely of cellulosic materials. See 40 CFR 80.1426(5)(i) (A). Such materials may also be added to waste digesters in an agricultural setting , perhaps in combination with manure and/or crop residues . We have defined the term “agricultural waste digester” as those digesters processing animal manure, crop residue and separated yard waste, and we have specified in Table 1 to 80.1426 that fuel produced from biogas collected at such digesters qualifies as cellulosic biofuel for which cellulosic RINs may be gen erated for the entire volume. EPA understands that incidental de minimis quantities
h (1) Val ue added Chemicals from Animal Manure . Chen et. al.. Pacific Northwest National Laboratory (2003): http://www.pnl.gov/main/publications/external/technical_reports/PNNL

- 14495.pdf ; (2 )[Animal] Manure Production and Nutrient Content . Chastain et. al.. Clemson University, Swine
– http://www.clemson.edu/extension/livestock/camm/camm_files/swine/sch3a_03.pdf, Dairy – https://www.clemson.edu/extension/livestock/camm/camm_file s/dairy/dch3a_04.pdf, Poultry
– http://www.clemson.edu/extension/livestock/camm/camm_files/poultry/pch3b_00.pdf ; (3) AgSTAR Digester Database. U.S. Environment al Protection Agency: http://www.epa.gov/agstar/projects/ i See “Cellulosic Content of Various Feedstocks: 2014 Update” placed in docket EPA
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of non
- cellulosic materials, or materials that are not renewable biomass, may be introduced into agricultural digesters. This practice would not disqualify the resulting fuel from qualifying as renewable fuel under the RFS program providing that such incidental de minimis feedstock contaminants are either impractical to remove or are related to customary feedstock production and transport. See 40 CFR 18.1426(f)(1). 3 . Municipal Wastewater Treatment Facility Digesters Municipal wastewater treatment facility (MWT F ) digesters are anaerobic digester s that process the sludge, undissolved solids, and biosolids derived from municipal wastewater whether or not the facility is owned by a municipality . The composition of wastes processed in MWTF tend to be heterogeneous, but are generall y composed of human wastes and highl y fibrous tissue products. Wastes that are processed in municipal wastewater treatment facilities are often treated aerobically , but more and more are be ing configured to employ anaerobic digestion as part of the facility ’s primary treatment sy stem, allowing biogas to be produced
. T he data used to assess the cellulosic content of wastewater solids is presented in Table 3
. **Table 3**

**– Data used to assess the cellulosic content of wastewater solids** 

j Primary sludge refers to the untreated was tewater solids whereas activated sludge (AS) and biosolids refer to solids separated from wastewater following treatment at the wastewater facility. Characteristics of Wastewater Solids Wastewater Type j % C % H % L % Convertible Solids % AC % AH % AL Source Primary 29.3 72.9 40.2 Champagne, 2009 7 Primary 11.5 26.5 74.1 15.5 35.8 Cheung, 1997 8 Primary 17 9 62.6 27.2 14.4 Wang, 2008 9 AS 13.8 78.7 17.5 Champagne, 2009 4 AS 9 16 13 49.3 18.3 32.5 26.4 Wang, 2008 6 Biosolids 14 19 8 49.0 28.6 38.8 16.3 Wang, 2008 6 Averages % AC % AH % AL % ACC Average of AS and Biosolids Data 22 36 21 7911

C = ; cellulose; H = hemicellulose ; L= Lignin; AC = adjusted cellulose; AH = adjusted hemicellulose; AL = adjusted lignin ; AS =activated sludge; ACC = adjusted cellulosic content While there are substantial data characterizing the solids composition of municipal wastewater, there are somewhat less data characterizi ng the composition of materials entering the digesters specificall y. W e chose to use the subset of peer
- reviewed data highlighted in green in Table 3 ) that analyzes the activated sludge and biosolids for the purposes of calculating the average adjusted cellulosic content of materials that would be expected to enter wastewater treatment facility

digesters. This is because the broader data set did not i nclude data for the fraction of hemicellulose in primary sludge and it does not adequatel y represent the material entering the digester. As will be discussed forthwith, the material entering a digester is better represented b y activated sludge and biosoli ds
. The wastewater treatment process is designed to oxidize dissolved organics, remove nutrients such as aqueous nitrogen and phosphorus species, and separate suspended solids. A ty pical process will involve several steps as part of three broader sy stems : the primary treatment sy stem (pretreatment, primary clarification and anaerobic digestion) , the secondary treatment sy stem (aeration, clarification , internal sludge recycle, and disinfection) and the tertiary treatment sy stem (nutrient removal and solids handling ). Anaerobic digestion at wastewater treatment facilities ty

pically occurs as part of the process’ primary treatment; however data characterizing primary

sludge does not adequatel y represent the material entering the digesters because the primary

sludge is separated from the wastewater and partially treated prior to entering the digester. The material that enters the digester includes the undissolved solids that are recovered from the primary

clarification tank and the solids that are allowed to settle out in a secondary clarification tank
. Therefore, the data for activated sludge and biosolids are more likely to represent the material entering the wastewater facility digesters. In addition, the data related to activated sludge and bi osolids is more consistent and comparable, and therefore provide a more robust estimate of the cellulosic content. The data c onsidered ( in green shaded area in Table 3 ) offered consistent and comparable data, including values for cellulose, hemicellulose, and lignin individually , and the volatile solids representing the organic fraction of the wastewater solids that can be converted via anaerobic digestion was reported in each of these studies . The average adjusted cellulosic content was obtained by

dividing the reported cellulosic fraction by the volatile organic fraction that can be converted to methane
. Based on th e data for activated slu d ge and biosolids , th e material entering the digesters is determined to be on average composed of 13 % cellulose, 22 % hemicellulose, and 13 % lignin , for a total of 48 % cellulosic components
. The volatile solids and organic nitrogen were found to be 64 % and 3% respectively , which results in a convertible organic fraction of 61 %. When the cellulosic component is divided by the organic fraction that can be converted to methane , the average adjusted cellulosic content of the material used to12

generate the biogas through anaerobic digestion from wastewater treatment facilities is, on average, 79 % ( Table 4 )
. Therefore, we have determined that fuels made from biogas collected at MWTF digesters is predominantly cellulosic, such that the entire volume of fuel produced qualifies for cellulosic biofuel RINs. **Table 4**

**– Estimated average composition of anaerobically digested cellulosic biomass in the**  **United States**

Source: This table represents the aggregate data from Table 1, Table 2, and Table 3 k

. **III. Lifecycle Analysis of Biogas**  **- Derived**  **Electricity Pa**  **thways** Under anaerobic conditions, organic wastes naturally decompose to produce biogas , and controlled management of organic waste digestion can reduce GHG emissions that would have occurred alternativel y. T he following sections describe the assumptions, analy t ical methods and conclusions regarding the lifecycle GHG emissions associated with electricity produced from waste derived biogas. A. Assumptions used in the Lifecycle Anal ys is Table 5 outlines key

assumptions used in determining the lifecycle GHG emissions associated with electricit y produce d from waste derived biogas
. EPA used these values in our lifecycle anal ys is as described in the subsequent sections. **Table 5**

**– Key Assumptions for the Life**  **cycle Analysis of Electricity**  **produced from**  **Waste Derived**  **Biogas Category**  **Assumption Source**  **Notes**

k Table 1
– Barlaz et. al. (1989); Table 2
– see footnote j; Table 3
– Champagne et. al. (2009) and Wang (2 008) Aggregate Composition of Digested Biomass % OFMSW % wastewater biosolids % animal manure
Cellulose 38 1 3 25 Hemicellulose 8 22 21 Lignin 16 1 3 17 Volatile Solids Organic Nitrogen 69

-- 64 3 82 3 Adjusted Cellulosic Content 90 79 8013

**On -**  **Site Emissions from Combustion of Biogas (considers CH 4**  **and N 2**  **O only)** Emissions from Flaring 1004 g CO 2 - e q / mmBtu biogas

GREET1_2011 10 Value given is for Renewable Natural Gas Emissions from Stationary Reciprocating Engines 9634 g CO 2 - e q / mmBtu biogas Value given is for Biogas Emissions from Turbines 554 g CO 2 - e q / mmBtu biogas Value given is for Natural Gas; Emissions are assumed to be the same for Biogas Emissions from Combined Cycle Gas Turbines 554 g CO 2 - e q / mmBtu biogas Value given is for Natural Gas; Emissions are assumed to be the same for Biogas % of Gas
- to - Energy Projects using Reciprocating Engines 70.6 % of total capacity (in MW) EPA LMOP

Database of Operational Projects 11 Percentages exclude

microturbines, which are used in 0.3% of projects % of Gas
- to - Energy Projects using Turbines 23.8 % of total capacity (in MW) Includes both gas and steam turbines ; excludes microturbines % of Gas
- to - Energy Projects using Combined Cycle Gas Turbines 5.6 % of total capacity (in MW) Weighted Average Emissions for Gas
- to - Energy Projects 6965 g CO 2 - e q / mmBtu biogas Calculated from

data referenced in this table **Upstream Emissions**  U.S. Average Electricity Production 219,823 g CO 2 - e q / mmBtu electricity RFS Final Rule 12

**Table 5 , continued**  **Renewable Electricity Generation** Efficiency of Electricity Generation from Biogas 11,700 Btu biogas/kWh EPA LMOP LFGE

Benefits Calculator 13 Weighted average of gas
to - energy projects Electricity
- Ethanol Conversion 22.6 kW
- h/gal ethanol RFS Final Rule 614

Parasitic Loss Efficiencies for Reciprocating Engine
Generator Sets 93%

EPA LMOP Data 14 Parasitic Loss Efficiencies for Turbine
- Generator Sets 88% Use this value for Combined Cycle Gas Turbines as well Electricity Demand for Biogas Collection Blowers 0.002 kWh/ft 3 For flaring and gas
- to energy projects U.S. Average Transmission and Distribution Losses 6.6% U.S. EIA State Electricity Profiles 1515

B
. Calculations for the Li fecycle Anal ys is of Renewable Electricity Produced from Waste Derived Biogas l

. The lifecycle anal ys is of renewable electricit y produced from waste derived biogas focused on emissions associated with production of the fuel. We did not consider any emissions associated with transportation of the renewable electricity (although losses are accounted for) , and no tailpipe emissions, so the only significant GHG emissions are derived from fuel production. The first step in determining the lifecycle GHG emissions associated with production of renewable electricity from waste derived biogas was to determine how much electricity (in mmBtu) could be produced from a gi ven amount of biogas (in mmBtu) based on values for the efficiency of ty pical electricity

generation at landfills or waste digesters provided by EPA’s Landfill Methane Outreach Program ( LMOP ; Table 5 ) Table V.B.
- 1 in the Preamble outlines this calculation. We then apportioned the electricity generation proportionatel y according to the generation technology

used (engines, turbines, combined cycle turbines) using the % of total capacity values given above. We used the parasitic loss efficiency values for en gines and turbines (above) to determine the size of the parasitic losses for each category of electricity generation and subtracted these values from the generation values above. We then summed the amounts of electricity remaining after these losses to de termine the net amount of electricit y produced from the biogas after parasitic losses. We subtracted the amount of this energy that would be used to power the biogas collection s ys tem . We also calculated how much of the electricit y leaving the facility w ould be lost during transmission and distribution using data from EIA (see Table 5 ) and subtracted this amount from the total electricity. In the end, we determined that 0.236 mmBtu electricity would be delivered to the consumer for each mmBtu biogas comb usted
. There were two components of electricity production that figured in the lifecycle anal ys is: on
- site emissions and upstream emissions (Table V.B.
- 2 in the Preamble). Based on the relationship between electricit y production and biogas combustion , th e emissions factor for flaring , and the weighted average emissions factor for gas - to - energy projects listed above ( Table 5 ) , we determined the amount by which on
- site emissions at the biogas source would change. We used the value for the U.S. average GHG emissions from electricity production to calculate the amount of emissions in the flaring baseline scenario that are due to the grid electricity used to power the biogas collection sy stem . This am ount was assigned as a credit, since these emissions would be eliminated upon installation of a gas
- to - energy project because renewable electricity would power the biogas collection sy stem . Adding together the values for on
- site and upstream emissions yi e lds li fecycle GHG emissions of 12 kg CO 2 - eq/mmBtu electricity , which is an 87 %

l The analysis was performed for biogas generated at a landfill offering a conservative estimate, as digester performance and biogas recovery is greater than landfill systems. Landfills lose approximately 20% of the total biomass to aerobic oxidation and as much as 30% to fugitive emissions.16

reduction in emissions from the petroleum gasoline baseline (Table V.B.
- 2 in the Preamble). Because the drivetrains of electric vehicles are roughl y 3 times as efficient as those of traditional internal combustion cars, we also calculated GHG emissions taking this improved efficiency into account. For these calculations, we determined the GHG emissions for each lifecycle stage per mmBtu of a “fuel equivalent”, assuming that it would take three times the energy of a liquid fuel to drive a car as far as a given amount of electricity. The lifecycle GHG emissio ns from electricit y produced from waste derived biogas considering this factor are 4 kg CO 2 - e q/mmBtu fuel equivalent, or a 96 % reduction in GHG emissions from the petroleum baseline m
. According to both of these calculations , renewable electricity produced from waste derived biogas c ould qualify as either cellulosic or advanced biofuel. C
. Choice of Baseline for Waste Derived Biogas Treatment When conducting a lifecycle anal ys is of greenhouse gas emissions for biofuels produced from waste derived biogas, it is important to choose an appropriate baseline for comparison. The baseline assumption is important becaus e, as per the approach outlined in the March 2010 RFS rule, 6 the lifecycle calculations are based on a scenario approach. The results are determined based on a comparison of the biogas
- based biofuel scenario to a baseline scenario that would have happened if the biogas was not used to produce transportation fuels. There are two main components of the baseline to consider, how use of waste - derived biogas for transportation fuels would impact waste disposal, and how it would impact the current or alternativ e treatment of the biogas. If waste management methods were impacted b y use of biogas for transportation fuel, there could be indirect GHG emissions impacts. However, waste management policies are ty picall y controlled b y state and local governments, an d there are man y unique factors that influence these decisions. We have not seen any evidence or data to suggest that the RFS in general has had or will have a substantial impact on existing waste disposal practices across the U.S., and therefore we belie ve that there will not be significant GHG impacts associated with the biogas
- based pathway s adopted in this rule. T herefore no GHG impacts from waste disposal changes are included in the GHG anal ys is
. This is consistent with the March 2010 RFS final rule which concluded that municipal solid waste has no agricultural or land use change GHG emissions associated with its production. B iogas can be handled and/or processed in one of three primary way s: venting to the atmosphere, collection and flaring, and collection with use in a gas
- to - energy or gas - to - fuel project. Theoreticall y, any of the above scenarios could serve as a baseline scenario for our lifecycle anal ys is since all three occur at biogas source sites in the U.S. W e first examine how the preva lence of flaring and gas
- to - energy projects at landfills has changed over time and what

m The analysis was performed for biogas generated in a landfill system offering a conservative estimate, as digester performance and biogas recovery from digesters is greater than landfill systems.17

impacts this has had on total methane emissions from landfills. W e then outline the implications of using other possible baselines and discuss wh y we propose to use fl aring as the baseline. Historical uses for landfill biogas Figure 3 , below, shows how the uses of landfill biogas in the U.S. changed over a 20
- ye ar period from 1990 to 2010 based on data from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990
- 2010. 16 During this time period, the amount of methane produced in landfills increased b y 50%, however, the amount of methane released from these same landfills decreased by roughl y 25% between 1990 and 2000 and has remained mostly constant since then . This large reduction in methane emissions is due primarily to the institution of EPA regulations, finalized in 1996, requiring large landfills to capture and treat their biogas. 17 In parallel, the Landfill Methane Outreach Program ( LMOP ) has facilitated the development of an array of projects to collect and beneficiall y use landfill biogas, particularl y from smaller, unregulated landfills. 18 These emissions reductions were achieve d via a 12
- fold increase in the amount of methane that wa s flared from 1990 to 2010 and a 6
- fold increase in the amount of methane used in gas
- to - energy

projects over the same time period ( Figure 3 ). From 1990 to 2000, flaring and gas - to - energy

projects increase d more or less in tandem, but from about 2000 to 2005 , gas - to energy projects stabilized whereas flaring projects continued to increase. Leading up to 2010 , the importance of flaring projects declined slightly whereas gas
- to - energy projects increased substantially , such that in 2010, the amounts of methane destro yed b y each ty pe of project were almost equivalent. Today , most of the methane that is still emitted derives from small landfills that are not required to capture and treat their biogas. Smaller proportions derive from leakage at landfills that do capture their biogas; EPA’s Compilation of Air Pollution Emission Factors ( AP

42 ) estimates collection efficiencies at such landfills ty picall y range from 60% to 85%, with an average of 75% capture efficiency most commonly assumed
. 1918

**Figure 3** 

**– Am**  **ounts of methane generated at, emitted from, flared at, and used in gas**  **- to**  **** **energy projects at landfills in the U.S . from 1990**  **- 2010.**  **8** Possible alternative baseline scenarios The results of our landfill biogas lifecycle anal ys is would have been very different if

, instead of landfills that flare their biogas, we had chosen as a baseline either landfills that do not capture and treat (e.g., that vent) their biogas or those with existing gas
- to - electricit y projects. Here, we examine in detail the possible use of thes e three baselines for the renewable electricity pathway
. Renewable Electricity Pathway
. Table 5 below shows the results of lifecycle anal ys es for the renewable electricity pathway calculated using each of these three baseline scenarios. For the scenario involving conversion of a landfill that is venting its methane to a gas
- to - ene rgy project, the primary

change is in the on
- site emissions at the landfill. Under the venting scenario, the landfill would be releasing large amounts of methane, a potent greenhouse gas, to the atmosphere, so that collecting the methane to use in a gas
- to - energy project would be accompanied b y reductions in GHG emissions at the landfill of 1959 kgCO 2 - eq/mmBtu electricit y ( Table 6 ). Another, smaller change relative to the flaring baseline is that because venting landfills do not collect their biogas, they would not have been using an y electricity to power blowers for gas collection, so this is not a factor in this scenario. The l arge reduction in methane emissions from the landfill results in a 2099% reduction in GHG emissions relative to

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

1990 1995 2000 2005 2010**M e** **t h** **a n** **e (** **G g** **/ y** **r )** 

**Ye ar** 



### Usage of methane

Generated Emitted Flared Energy19

the gasoline baseline upon conversion from a venting landfill to a landfill with a gas
- to electricit y project. Consideration of the improved ef ficiency of electric vehicles results in a 765% reduction in GHG emissions relative to the baseline ( Table 6 ). This demonstrates that renewable electricity would easily qualify as a cellulosic biofuel if we used landfills that vented (did not treat) their biogas as the baseline for comparison. **Table 6**

**– Comparison of total lifecycle greenhouse gas emissions (kg CO**  **2 -**  **eq/mmBtu electricity**  **or gasoline ) for renewable electricity produced from landfill biogas using three**  **different baselines. Numbers in parenthe**  **ses show values calculated per mmBtu fuel equivalent, which considers the greater efficiency of electric vehicles compared to gasoline**  **vehicles.**

Li fecycle Stage From Landfills that Vented Biogas From Landfills

that Flared Biogas From Landfills

that Converted Biogas to Electricity 2005

Gasoline Baseline On
- site emissions
- 1959 (
- 653) 25 (8) Upstream (electricity production for blowers)
- 13 (
- 4) New electricit y generation 220 (73) **Total Emissions: -**  **1959 (**  **- 653)**  **12 (4)**  **220 (73)**  **98 % Change from**  **Gasoline Baseline -**  **2 099**  **% (**  **- 765%)**  **- 87**  **% (**  **- 96%)**  **124% (**  **- 25%)**  The use of landfills that flare their biogas was discussed in the Preamble. Under this scenario, installation of electricity generators would result in increased on
- site emissions due to less efficient combustion of generators versus flares. The other factor in this lifecycle analy sis is reduced upstream emissions from grid ele ctricity that was used to collect the biogas under a flaring scenario but would be replaced b y renewable electricity upon installation of gas
- to electricit y capability. Overall emissions using a flaring baseline were 12 kg CO 2 /mmBtu electricit y, correspon ding to an 87% reduction in GHG emissions versus the gasoline baseline. These reductions increase to 96% upon consideration of the increased efficiency of electric vehicles. In contrast, if our baseline is landfills that already capture their biogas and use it to generate electricity , there are no phy sical changes at the landfill , and the only change is that this renewable electricity is tracked to transportation uses. In this case, the lifecycle GHG emissions increase relative to gasoli ne, as shown in T able 6
. Because there is no phy sical change at the landfill, neither on
- site emissions nor upstream electrical production to power gas collection20

blowers changes. However, this scenario could require additional electricity to be produced to replace that diverted for use in the transportation sector, and this new electricity , which we assume is derived from the grid, is accompanied by additional GHG emissions of 220 kg CO 2 - eq/mmBtu electricity. The possible need for this additional electricity can be best understood b y stepping through Figure 4 below. The left side of the figure shows the baseline situation in which combustion of biogas at a landfill generates electricit y that is added to the shared electrical grid. Electricity from the grid is then with drawn for a variety of uses. The transportation sector is completely

separate from these sectors. However, if the electricit y is directed to the transportation sector, as shown on the right side of the figure, all of these sectors are connected. EPA is required b y the Energy Independence and Security Act of 2007 (EISA) to compare the GHG emissions of renewable fuels to those of the petroleum (gasoline or diesel) fuel baseline, which means that in order to link the transportation sector to the electrical sector, we compare electricity used in electrical vehicles (EVs) to gasoline vehicles. As shown in Figure 4 , the net result is that additional electricity is withdrawn from the shared grid to po wer EVs (that replace gasoline vehicles). However, the demand for electricity for other uses would not change in this scenario (i.e., the balance of inputs and outputs from the grid box in Figure 4 must remain constant), which requires that the electricit y diverted to transportation uses must be replaced with electricity from other sources. This electricity comes with additional GHG emissions of 220 kg CO 2 - eq/mmBtu electricity ( Table 6 ) and results in a 124% increase in GHG emissions compared with the gas oline baseline , such that renewable electricity using a gas
- to - energy baseline would not qualify

as a renewable fuel under the RFS program . Consideration of the increased efficiency of electric vehicles reduces these emissions to a 25% decrease versus the baseline, which would allow the electricity to qualify as a renewable fuel but not as a n advanced or cellulosic biofuel.

**Figure 4**

**– Comparison of scenarios used for evaluating the renewable electricity pathway**  **when using an existing gas -**  **to -**  **energy project as a baseline. Black arrows represent fluxes**  **of greenhouse gases or electricity that are relevant under both scenarios, red arrows represent fluxes that are important only when electricity is directed to transportation use**  **, and blue arrows are flu**  **xes that decrease when electricity is directed to transportation uses .**  However, in reality, the availability of additional renewab le electricity would not have a direct impact on the numbers of EVs on the road and thus would not directly replace gasoline as a fuel. Instead, the renewable electricit y would replace other sources of electricit y (e.g. from21

coal
- or natural gas
- fired power plants) as power for EVs. This scenario would represent a diversion of renewable electricity from general uses to EVs, an d a diversion of grid electricity from general and EV uses to more general uses . This is effectivel y an exchange in the uses for the two ty pes of electricity and would not result in any net change in GHG emissions from the baseline scenario. Thus, if we compare the GHG emissions of a gas
- to - energy project used for transportation to one directed into the shared grid, there would be no change in GHG emissions. The electricity

would not replace gasoline, there would be a 0% change from the petroleum baselin e, and renewable electricity would still not qualify as a renewable fuel under the RFS program. As stated above, EPA is required b y statute to compare to a petroleum fuel baseline, resulting in a very

different lifecycle anal ys is for the resulting renewab le electricity. However, renewable electricity does not qualify as a renewable fuel under either scenario using a gas
- to energy baseline, so these different way s of considering this question lead to the same end result
. Justification for the choice of a f laring baseline scenario Of these three possible baseline scenarios, we believe a flaring baseline is the most logical for the renewable electricity pathway . First, flaring is a possible scenario at all waste digesters . Second, a ssuming that the biogas is flared generally provides a worst case baseline as compared to a venting baseline . If sources that are using flaring will achieve a 60% GHG reduction when converting to electricity production, sources that are venting their methane or portions o f their methane will certainly do so as well. As discussed in the Preamble, we do not consider landfills that vent their biogas to be a realistic baseline for an y of these pathways , and the flaring baseline is the more conservative baseline compared to v enting
. Moreover, venting landfills must be small in size and generate a relatively small amount of biogas, otherwise they would be required to capture and treat their biogas. Accordingl y, we expect that these landfills would not ty

picall y generate enough electricit y from their biogas to justify the capital costs to install generators, so we expect that few of these landfills would convert to gas
- to - energy projects Therefore, these facilities are extremely unlikely to draw biogas from the small, unregulat ed landfills that currentl y vent their biogas. LMOP is currentl y working with some of the larger of these landfills to facilitate the installation of gas
- to - energy projects, so such conversions are economically feasible for at least a subset of these land fills. However, use of venting landfills as a baseline would result in the same classification as would use of flaring landfills as a baseline. In both cases, the fuel produced from landfill biogas qualifies for the RFS program. In contrast with the use of a venting baseline, if we used landfills with existing gas
- to electricit y projects as a baseline, these landfill biogas
- based biofuels would all fail to qualify for the RFS program. It is therefore especiall y important to consider which of these baselines is most appropriate. If we use a flaring baseline and qualify renewable electricity under the RFS program, i t is possible that landfills with existing gas
- to - energy projects may divert their renewable electricity for use as a transportation fuel . In these cases, the renewable electricit y22

would already be produced and added to the grid so there would be no actual change at the landfill . Additionally , Figure 3 shows that gas
- to - energy projects have been expanding since 2003, which suggests that o ther incentives are already promoting installation of gas
- to - energy projects at landfills. In contrast, i f we used facilities with existing gas
- to - energy projects as the baseline for comparison, no renewable electricity from landfill biogas would qualify fo r the RFS program. The use of this baseline would, therefore , exclude renewable electricity from facilities that converted from flaring (or even venting) from qualifying under RFS, even though these projects would be accompanied by real, large reduction s in GHG emissions. Because of this result, we have determined that use of existing gas
- to - energy projects as a baseline would not be appropriate . EPA believes that the Act should be interpreted and implemented to promote the growth in use of renewable fuels for transportation purposes, and to achieve GHG emissions reductions as a consequence. EPA believes that use of a flaring baseline best accomplishes these objectives. One option to deal with the discrepancy in lifecycle results between facilities that used to flare their biogas and those with existing gas
- to - energy projects would be to qualify electricit y produced from these different types of facilities differently. In this case, renewable electricity produced from landfills that installed new ga s - to - electricit y projects would qualify as a cellulosic biofuel whereas renewable electricity produced from landfills with existing gas
- to - electricit y projects would not qualify as renewable fuel under the RFS program. One problem with such a tiered appro ach is that landfills with existing gas
- to - energy projects previously

made the decision to install the gas
- to - energy equipment either to replace flaring or instead of installing flares and thus are already best
- performers. Likewise, under such a s ys tem, e lectricity from all new gas
- to energy facilities would qualify

as cellulosic biofuels, but electricit y from existing facilities would not. However, man y of the new facilities may have installed gas
- to - energy projects regardless of the RFS program, driven by the same incentives that motivated the existing facilities. Given the existence of other incentives to install gas
- to - energy capabilities, discriminating between existing and new gas
- to - energy

projects seems arbitrary

in thi s light. A dditionally , the RFS program does not discriminate against facilities that are already producing renewable fuels, and in fact, the program grandfathers many existing facilities into the program. It would therefo re appear inconsistent with the RFS program to discriminate between facilities that are already creating renewable electricity and those that convert from flaring to gas
- to - energy projects. We considered all of these factors in deciding on a baseline and believe that a flaring baseline is most appro priate. The choice of a single baseline for all renewable fuels produced from waste - derived biogas does not discriminate based on prior use of the biogas and is thus consistent with the qualified pathway s that have been approved to date under the RFS program. As discussed above, most venting landfills are unlikely to install gas
- to - energy

projects because of their small size, thus venting is an inappropriate baseline. Likewise, using existing gas
- to energy projects as a baseline is also inappropriate bec ause this would exclude projects with legitimate GHG emissions reductions (e.g., those that are currently venting or flaring) from23

qualifying. Use of landfills that flare their biogas as a baseline is appropriate because flaring is the main alternative to electricit y generation or liquid fuel production at large landfills , and all existing and future gas
- to - energy projects chose or will choose to generate electricity instead of simply flaring. Using this baseline, all renewable electricity generated from landfill biogas would qualify

as cellulosic biofuel. Allowing renewable fuels produced from landfill biogas to generate RINs will provide an additional financial incentive for landfills to convert from flaring or venting to gas
- to - energy projects and may thus help accelerate the adoption of this technology and lead to additional GHG emissions reductions.

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