1 

### MEMORANDUM

TO: Air and Radiation Docket EPA-HQ-OAR-2012-0401

FROM: EPA Office of Tran sportation and Air Quality
DATE: May 20, 2013

SUBJECT: Cellulosic Content of Various Feedstocks

This memorandum provides information on EPA’s evaluation of components generally found in
feedstocks that would be used to produce cellu losic biofuels. As discussed in the Preamble a 

### , we find that no feedstock contains exclusively cellu lose, hemicellulose and lignin. This is not
surprising since all organisms require other type s of molecules, including proteins, membrane
lipids, starches, and DNA/RNA, to fulfill essen tial functions of the ce ll such as enzymatic
catalysis of biochemical reactions , energy storage and coding of genetic information. However,
we find that all of the biomass generally cons idered “cellulosic” feedstocks, including corn
stover and switchgrass, contain greater than 70% of their biomass carbon in cellulose,
hemicellulose and lignin, and most of these feed stocks contain 85-90% ce llulosic components.

A. BACKGROUND

The “cellulosic components” of feedst ock consist of the major structural components: cellulose, hemicellulose, and lignin. These materials are also referred to as “lignocellulosic”. They are known as structural components because they are the main components of plant cell walls that provide strength, mechanical s upport and protection to the cell. These components can be
defined as follows 1 

### :

a Regulation of Fuels and Fuel Additives: RFS Pathways II and Technical Amendments to the RFS 2 Standards, Section V.A.1.2 

###  Cellulose — A structural carbohydrate that is the principal constituent of wood and other biomass. It is a polymer of glucose with a repeating unit of C 6 

### H 10 

### O 5 

### strung together by ßglycosidic linkages.

 Hemicellulose — A structural ca rbohydrate that consists of s hort, highly branched chains of sugars. In contrast to cellulose, which is a polymer of only glucose, a hemicellulose is a polymer of multiple different sugars, incl uding five-carbon sugars (usually D-xylose and L-arabinose), six-carbon s ugars (D-galactose, D-glucose, and D-mannose) and uronic acid. The sugars are highly s ubstituted with acetic acid.

 Lignin — The major noncarbohydrate structural cons tituent of plant biomass, lignin is an irregular polymer that gives plan t cells much of their mechanical strength. It has a large, complex, cross-linked, and highly aromatic stru cture derived principa lly from coniferyl alcohol (C 10 

### H 12 

### O 3 

### ). Because of its extensive cr oss-linking and complex chemical structure, lignin is very diffi cult to break down biochemically.

Biomass also includes other organic compounds that perform essential func tions in the cells, including energy storage, enzymatic catalysis of biochemical reactions and selective transport of
molecules into or out of the cell b 

### . These other compounds include but are not restricted to:

 Extractives — Any number of different compou nds in biomass that are not an integral part of the cellular structure. The compounds can be extracted from biomass by means of polar and non-polar solvents in cluding hot or cold water, et her, benzene, methanol and other solvents. The types of extractives found in biomass samples may include free sugars, pigments, membrane lipids, oils, and many other compounds.

 Protein — A protein molecule is a chain of up to several hundred amino acids that is folded into a more or less compact structur e. Because about 20 different amino acids are

b Feedstocks also contain inorganic components often referred to as “ash” which do not contribute to biofuel produced.3 

### used by living matter in making proteins, the variety of prot ein types is enormous. In their biologically active states , proteins function as catalysts in metabolism and to some
extent as structural elem ents of cells and tissues.

 Starch — A molecule composed of long chains of  -glucose molecules linked together. These linkages occur in chains of  -1,4 linkages with branches formed as a result of 

- 1,6 linkages. This polysaccharid e is widely distributed in the vegetable kingdom and is stored in all grains and tube rs. Starch is highly amorphous, making it readily attacked by human and animal enzyme systems and broken down into glucose.

There is significant variation in the data re ported on feedstock component compositions (see for example data on corn stover in Table 1), due in pa rt to the natural hetero geneity of plants, much of which may result from:

 Differences between different varieties or species within a generic feedstock type 2



### ,

 Variability in the environmental conditions where the feedstock was grown 2



### ,

 Sampling of different parts of the plant which may have different composition (e.g. whole plant versus stalks and leaves), 2



###  Harvesting of the feedstock at different stages of maturity, 3



###  Variability in feedstock co mposition in different years, 2



###  Differences in the agronomic practices used to grow the crop, 2 

### and

 Degradation or alteration of the biomass during storage. 4 

### Additional apparent variability may appear if comparing results determined using different analytical methods or even from variability be tween analytical batches in the same laboratory. 5



### Examination of one research study provides an example of both the compositional variability
observed within one feedstock and of how differen t factors may contribute to this variability. This study analyzed the composition of 508 commer cial hybrid corn stover samples collected from 47 sites in 8 states over 3 harvest years. 2 

### Glucan composition (a proxy for cellulose content) in these samples varied by more than 10% of the total mass, ranging from 26.5% to 37.6% of total mass (Table 1). Lignin concen trations fell between 11.2% and 17.8% of total mass. Standard deviations (as percentages) for the three major components were 5% for4 

### hemicellulose, 6% for cellulose and 8% for lignin, indicating that most of the measurements fell within more narrow ranges. Standard deviations for the minor components (extractives, protein and inorganics/ash) are relative ly larger, ranging from 16% fo r ash to 22% for protein. The authors found that harvest year was the largest source of vari ability, probably reflecting the important influence of weathe r on composition. Within a given sample year, environmental factors such as soil type and w eather appeared to account for more variability than did the corn hybrid variety, although the hybrid variety also affected the variability in composition.

It is likely that variability when comparing different studies woul d be greater than that observed for this one study because of differences in the an alytical methods used, as well as due to other factors that this study controlled for such as the part of the plan t used and how the material was stored. Accordingly, this study li kely underestimates the amount of variability we could expect to see in our comparison.

The purpose of this document is to present EP A’s understanding of the cellulosic content of
different biofuel feedstocks. Given the variab ility in the data, we report ranges whenever
available. We also take a cons istent approach to looking at th e data (described in the next section). The data itself we grouped into broad categories including cellulosic components (cellulose, hemicellulose and lignin), other orga nics (extractives, prot ein), and inorganics (inorganics, ash). Each of these main com ponents has sub-components as described in the following section. More detailed information about each analysis is available in a spreadsheet posted on the docket. c

c “Cellulosic Content of Various Feed stocks Spreadsheet – for the docket”, which has been placed in docket EPAHQ-OAR-2012-0401.5 

### Table 1. Average biochemical composition of corn stover based on 508 samples from 47 sites in 8 states over 3 harvest years, includi ng the standard deviation and range of the estimates. 2 

### Values labeled “Reported” are as re ported in the paper. Values labeled “Used” are the values used in our analysis, wh ich are calculated as described in the text based on the reported values.

*Standard deviation calculated by propagation of error. 

### Average Std. Dev. Range Cellulose Reported: Glucan 31.9 2. 0 26.5

‐ 37.6 Used: Total Cellulose 31.9 2. 0 Hemicellulose Reported: Xylan 18.9 1.3 14.8

‐ 22.7 Galactan 1.5 0.2 0.8

‐ 1.9 Arabinan 2.8 0.3 1.6

‐ 3.6 Mannan 0.3 0.1 0.0

‐ 0.7 Acetyl 2.2 0.3 0.9

‐ 2.9 Used: Total Hemicellulose 25.7 1.4 Lignin Reported: Lignin 13.3 1.1 11.2

‐ 17.8 Used: Total Lignin 13.3 1.1 Extractives Reported: Ethanol solubles 3.3 0.4 1.7

‐ 4.1 Sucrose 3. 6 2.1

‐ 1.0

‐ 10. 0 Water

‐ extractible (other) 8. 6 2.3 1.4

‐ 15.7 Used: Total extractives (organic) 15.5 3.1 Protein Reported: Protein 3.7 0.8 1.1

‐ 5.4 Used: Protein 3. 7 0.8 Inorganics/Ash Extractible inorganics (soil) 2.5 0.5 0.0

‐ 4.8 Structural inorganics (ash) 3.9 0.9 0.8

‐ 6.6 Used: Total inorganics 6.4 1. 0 Percent Recovery Reported: Component closure 96.4 1. 6 Used: % Recovery 96.4 1.6 Cellulosic Composition Cellulosic Components 70.9 2. 7 Other Organics 19.2 3. 2 Inorganics (Ash) 6.4 1. 0 Adjusted Cellulosic Composition 78.6 3.3 * * * * *

* *6 

### B. EPA’S APPROACH

In order to determine what percentage of feedst ocks typically considered “cellulosic”, such as corn stover and switchgrass, is composed of cellulose, hemicellu lose and lignin, EPA surveyed the scientific literature to assemble a range of estimates of the composition of different feedstocks. To do this, we reviewed 12 scien tific publications, reports or communications and
the DOE Biomass online database. Most of the studies used so me version of the procedure outlined by the National Renewable Energy Laborato ry’s (NREL) Standard Biomass Analytical
Procedure. 6 

### These procedures involve separation of extractives followed by determination of structural components via a two- stage sulfuric acid hydrolysis, followed by analysis of the individual sugars via HPLC. Lignin is measured in the acid soluble and acid insoluble fractions. Proteins are determined based on the nitrogen content of the material, and ash content is determined after heating of the sample. One study used near-infrare d spectroscopy (NIRS) / partial least squares modeling, calibrated with the NREL methods. An accompanying spreadsheet lists the methods used for each study, along with the compounds reported by the
authors and how EPA made its calculations based on this reported data. d



### As discussed, Table 1 shows how EPA combined th e data reported in one paper into the values used for our analysis. Some of the studies reported a concentration for “cellulose” or “hemicellulose”, but most reported concentrations for the individual sugars that comprise these biomolecules. For example, most studies report a concentration for glucan or glucose, almost all
of which is contained in cellulose. We assumed that the concentration of cellulose was equivalent to the reported concen tration of glucan or glucose, as shown in Table 1. This may be a slight overestimation since hemicellulose also c ontains some glucose; however, concentrations of glucose in cellulose are likely to dwarf that in hemicellulose, so this approximation should be reasonably accurate. For hemicellulose, studies re ported some combination of concentrations for xylan/xylose, galactan/galactose, arabinan/ara binose, mannan/mannose, rhamnose and fucose, as

d “Cellulosic Content of Various Feed stocks Spreadsheet – for the docket”, which has been placed in docket EPAHQ-OAR-2012-0401.7 

### well as acetyl/acetate and uronic acids. To estimate total hemicellulose concentration, we
summed the concentrations of thes e individual components. Note that this value may slightly
underestimate the true concentratio n of hemicellulose since it excl udes any glucose contained in this biomolecule. Lignin was reported as either “lignin”, “Klason lignin” or both “acid soluble lignin” and “acid insoluble lignin” . For our estimates, we combin ed the concentrations of all types of lignin reported. One source 4 

### reported only acid detergent li gnin (ADL) for a number of different feedstocks. This study also stated that acid insoluble lignin (which is generally much
more concentrated than acid sol uble lignin) tends to be 2-4 time s more concentrated than ADL for grasses, whereas acid insoluble lignin is only about 30% higher th an ADL for legumes. Accordingly, for these samples, we multiplied the reported ADL value by 3 for grasses and by 1.3 for legumes. However, this estimate introdu ces considerable uncerta inty into the total cellulosic content values, so th ese numbers should be considered less certain than the other values. Studies reported a number of differe nt types of “extractives”, including compounds extracted with ethanol, ethanol/toluene, water, an d hot water, as well as sucrose, organic acids, individual sugars (Glc, Fru, Raf, Sta) and fats/lipids. We added all of these components together
to estimate the concentration of total extractives . Studies generally dete rmined the concentration of protein (if calculated) by multiplying the nitr ogen content of the sample (as mass %) by 6.25 to scale up to total protein content. 7 

### When reporting the total inor ganic, or “ash”, content of a sample, studies mostly reported one value. However, some studies reported a value for extractible inorganics and one fo r structural inorganics (ash; Ta ble 1). Two studies reported a value for “volatile solids”, which is essentially ever ything but the ash. 8,9 

### For these studies, we
calculated the ash conten t by subtracting the vola tile solids con centration from 100%. We also added together the cellulose, hemicellulose and lignin concentrations to determine the total
cellulosic concentrati on, and added protein and extractiv es together to determine the concentration of “other organics”.

Once we had calculated the concentrations (a s mass %) for cellulose, hemicellulose, lignin, extractives, protein, and ash, we added these components togeth er to determine the percent recovery for each analysis (Table 1). Pe rcent recoveries ranged from 88% to 106%. e 

### Recoveries

e For studies in which they analyzed all components. Some studies did not report concentrations of protein, extractives or ash, in which case percent recoveries were lower. For these cases, we did not adjust the composition to adjust for percent recovery.8 

### may be lower than 100% because of losses during sample processing or because portions of the material were not analyzed. Recoveries greater than 100% indicate that one or more analytical method used over-reports the amount of material recovered. We adjusted the percent cellulosic value to account for the percent r ecovery: in cases of recoveries greater than 100%, the values were adjusted lower; in cases of recoveries less than 100%, valu es were adjusted higher. We also adjusted the cellulosic cont ent to account for the ash conten t of the feedstock. Inorganic (ash) materials are not likely to end up in the fi nal fuel product made from the feedstock, and if they did, they would not contri bute to the fuel heating cont ent (which is how RINs are determined). Our calculations therefore adjusted the final cellulosic composition to reflect the percent of the organic (non-ash) component of the feedstock that is cellulose, hemicellulose or lignin. The “Adjusted Cellulosic Composition” shown in Table 1 de monstrates the results of the adjustments for percent recovery and inorgani c content for corn stover from one study, as
described above.

C. CELLULOSIC CONCENTRAT IONS IN BIOMASS

EPA considered the component con centrations of several different types of feedstocks, including several types of crop residue, gr asses including miscanthus and switchgrass, a variety of woods and branches, based on the categories of “cellulo sic” feedstocks included in Table 1 to CFR §
80.1426. Data derived from twelve different scie ntific publications, repo rts or communications and from the Department of Energy’s Bioma ss Feedstock Composition and Property Database, which contains compositional data for over 150 feedstock samples. 10 

### Because of the high degree of natural variability in biomass (discussed a bove), the average compositions are likely more meaningful than any single value reported. This is because no single value can reflect the compositional range and variability present in that type of biomass, particularly if this value derives from a small number of samples. Howeve r, examination of the range of values observed and the average values calculated should provide in sight into the degree of variability present, as well as the most common composition, and thus be more informative. The data are summarized9 

### in Tables 2-4, and a more detailed presentation of the data reported in each paper and EPA’s use of this data can be found in an accompanying spreadsheet f



### .

a. Crop Residue

EPA found information about the biochemical com position of a number of types of crop residue, including corn stover, sugarcane bagasse, and st raw from wheat, rice, soybeans, rye and barley (Table 2). Of these, corn stover is widely considered to be the predominant choice of crop residue for biomass production. As shown in Table 2, EPA examined data on the composition of
corn stover from four different sources. Based on the report ed data, cellulosic components comprised between 71 and 83% of the total mass of corn stover (Table 2). Other organic compounds made up 10 to 19% of th e total and inorganics were 5- 12% of the total mass. When the data has been adjusted for percent recove ry and inorganic conten t, cellulosic components constitute 78-89% of the total organic biomass of corn stover, with an average concentration of
84%. Data for wheat straw came from three sour ces, and data for this type of crop residue agreed very well with that for corn stover, with adjusted cellu losic compositions ranging between 81% and 92%, with an average of 87%. EPA also considered the composition of sugarcane bagasse and straw from rice, soybeans, rye and barley, with data derived from one source for each biomass type except for sugarcane bagasse, which derived from two sources. Bagasse had an extremely high adjusted cellulosic compos ition of 94-98%. The composition of rice straw was very similar to that of both corn stover and wheat straw (Table 2). Both soybean straw and rye straw had cellulosic contents that were almo st 10% lower than any other type of other crop residues (69% for both). However, for these samp les, total lignin was not reported so we had to adjust the reported acid detergent lignin content using commonly observed relationships. 4 

### These numbers are accordingly only estimates and may in fact be much higher. Similarly, the calculated % cellulosic of the barley straw wa s 102%, which is physical ly impossible. We performed a similar adjustment of the acid detergent lignin content of this sample, so it is likely that we overestimated the lignin content of this sample. The average cellulosic content of all types of crop residues (excluding those with estimated lignin conten t) is 90%, with a range of 78-

f “Cellulosic Content of Various Feed stocks Spreadsheet – for the docket”, which has been placed in docket EPAHQ-OAR-2012-040110 

### 98% (Table 2). These data suggest that on av erage around 85-90% of the organic mass of crop residues is composed of cellu lose, hemicellulose and lignin, with crop residues generally containing more than 75% cellulosic materials.

Table 2. Percent composition of crop residues, including percentages as reported (raw and unadjusted) for total cellulosic material, oth er organic materials and inorganics (ash) and cellulosic composition adjust ed for percent recovery and presence of inorganics.

Reported Composition

Cellulosic Components Other Organics Inorgan

‐ ics (Ash) Adjusted Cellulosic Composition Source Crop Residue Corn Stover 80% 10% 12% 89% DOE Database 10 71% 19% 6% 79% Templeton et al. (2009) 2 72% 20% 5% 78% Templeton et al. (2010) 5 83% 11% 6% 88% Lee et al. (2007) 4

Corn Stover Average 77% 15% 7% 84%

Wheat Straw 74% 17% 10% 81% DOE Database 83% 7% 9% 92% NREL data 11 82% 12% 6% 87% Lee et al. (2007) Wheat Straw Average 80% 12% 9% 87% Other crop residues Rice Straw 74% n.d. 15% 86% Guo et al. (2009) 12 Sugarcane Bagasse 90% n.d. 8% 98% Guo et al. (2009) Sugarcane Bagasse 92% 6% 4% 94% Templeton et al. (2010) Soybean Straw 65%* 29%* 6% 69%* Lee et al. (2007) Rye Straw 65%* 29%* 6% 69%* Lee et al. (2007) Barley Straw 91%* ‐ 2%* 11% 102%* Lee et al. (2007) Crop Residue Average 77% 14% 9% 90% 

### *For these samples, lignin was reported as acid detergent lignin (ADL), which can be considerably lower than total lignin, which was re ported for the other samples. Total lignin was estimated for these samples by multiplying ADL by 1.3 for soybeans (a legume) or by 3 for rye and barley (types of grass) as discussed in the text. These estimated values were not used in calculating the average.

b. Grasses – Including Switc hgrass and Miscanthus

For our analysis of the chemical composition of grasses, EPA gathered information about switchgrass, miscanthus and twelve other types of grasses (Table 3). This included four studies11 

### of switchgrass, three studies of miscanthus and one or two studies each of the remaining grasses. Of these grasses, switchgrass a nd miscanthus have been intensiv ely studied for use as biofuels feedstocks. The composition of th ese two types of grasses were si milar to each other, with the studies reporting switchgrass to contain 71-85% cellulo sic components and miscanthus to have 77-86% reported cellulosic materials. The av erage adjusted cellulosic compositions of both switchgrass and miscanthus are 85%. EPA has adde d energy cane as an allowable feedstock for cellulosic fuels under RFS in a recent rulemaking g 

### , and giant reed and napi ergrass have also been proposed as feedstocks for biofuels. These thr ee grasses all had adjusted cellulosic compositions of 79-87% cellulosic. The adjusted cellulosic composition of the remaining grasses ranged from 72% to 98%, although many of the studies only re ported acid detergent li gnin, requiring us to estimate total lignin content based on this num ber as discussed above, leading to greater uncertainty in the cellulosic content. However, cellulosic materials comprised greater than 70% of the adjusted mass of all of the grasses studied (Table 3).

Table 3. Percent composition of grasses, including percentages as reported (raw and unadjusted) for total cellulosic composition, other organic materials and inorganics (ash) and cellulosic composition adjusted for percent recovery and presence of inorganics
Reported Composition

Cellulosic Components Other Organics Inorgan

‐ ics (Ash) Adjusted Cellulosic Composition Source Grasses Switchgrass 79% 17% 5% 82% DOE Database 10 75% 15% 6% 83% NREL data 11 71% 13% 7% 85% Dien et al. (2006) 3 85% 9% 6% 90% Lee et al. (2007) 4 Switchgrass Average 77% 14% 6% 85%

Miscanthus 85% n.d. 4% 89% Guo et al. (2009) 12 86% 12% 2% 88% Lee et al. (2007)

77% n.d. 1% 78% Villaverde et al. (2010) 13
Miscanthus Average 83% 12% 2% 85%

Other grasses Giant reed 83.5 n.d. 3.7 87% Scordia et al. (2011) 14

g Regulation of Fuels and Fuel Additives: Identification of Additional Qualifying Renewable Fuel Pathways Under the Renewable Fuel Standard Program, 78 FR 14190, 14217 (March 5, 2013)..12 Energy cane 75.2 19.6 5.2 79% BP data 15 Napiergrass 83.4 13.1 3.5 86% BP data Reed Canarygrass 58% 21% 11% 73% Dien et al. (2006) Reed Canarygrass 66%* 26%* 8% 72%* Lee et al. (2007) Big Bluestem 83% 11% 6% 88% Lee et al. (2007)

Tall Fescue 64% 25% 11% 72% Lee et al. (2007) Indiangrass 86%* 6%* 8% 93%* Lee et al. (2007) Little Bluestem (66%)† (27%)† 7% (71%)† Lee et al. (2007) Prarie Cordgrass 92%* 2%* 6% 98%* Lee et al. (2007) Intermediate Wheatgrass 82%* 12%* 6% 87%* Lee et al. (2007) Smooth Bromegrass 86%* 6%* 8% 93%* Lee et al. (2007) Timothy 73%* 21%* 6% 78%* Lee et al. (2007) Other Grasses Average 78% 15% 7% 81% 

### *For these samples, lignin was reported as acid detergent lignin (ADL), which can be considerably lower than total lignin, which was re ported for the other samples. Total lignin was estimated for these samples by multiplying ADL by 3 as discussed in the text. These estimated values were not used in calculating the average. †Lignin was not measured for this sample, so thes e values are much lower than the true value. This sample was not used in calculating the average for grasses.

c. Wood, Tree Branches and Leaves

EPA gathered compositional data for wood from 10 di fferent species of tree (Table 4), including seven hardwoods and three softwoods, as well as on two different samples of tree branches. The studies reported between 83 a nd 94% cellulosic components by mass for all woods and adjusted cellulosic compositions of 83 to 97%. The adjusted compositi on of the branch samples was very similar to that of the wood samples, with 86% and 89% cellulosic components, although one of the branch samples contained large amounts (18 %) of inorganic materials, probably due to incorporation of non-branch materials such as so il. Two studies also determined the composition of samples of leaves and determined adjusted cellulosic compositions of 74% and 89%. The very high (37% by mass) proportion of inorganic materials in one of the leaf samples is almost certainly due to the inclusion of soil in the samp le, as mentioned for the branch sample from this same study. The average adjusted cellulosic composition from woods and branches was 92%,
whereas the value for leaves was 82%.

Table 4. Percent composition of woods, tree branches and leaves, including percentages as reported (raw and unadjusted) for total cellulos ic composition, other organic materials and13 

### inorganics (ash) and cellulosic composition adju sted for percent recovery and presence of inorganics
Reported Composition

Cellulosic Components Other Organics Inorgan

‐ ics (Ash) Adjusted Cellulosic Composition Source Wood, Tree Branches & Leaves Black Locust 88% 8% 3% 92% DOE Database 10 Eucalyptus 94% 3% 1% 97% DOE Database Eucalyptus 83% n.d. 0% 83% Wang et al. (2007) 16 Hybrid Poplar 89% 4% 1% 96% DOE Database American Sycamore 87% 4% 1% 96% DOE Database Eastern Cottonwood 88% 3% 1% 97% DOE Database Yellow Poplar 89% 3% 2% 97% DOE Database Red Oak 84% n.d. 0% 84% Wang et al. (2007) Monterey Pine 91% 3% 0% 97% DOE Database Radiata Pine 88% n.d. 1% 89% Wang et al. (2007) Spruce 90% n.d. 2% 91% Wang et al. (2007) Branches 86% n.d. 3% 89% Eleazer et al. (1997) 8 Branches 70% n.d. 18% 86% Komilis and Ham (2003) 9 Wood & Branches Average 88% 4% 1% 92% Leaves 86% n.d. 3% 89% Eleazer et al. (1997) Leaves 47% n.d. 37% 74% Komilis and Ham (2003) Leaves Average 67% n.d. 20% 82%



### D. IMPLICATIONS FOR CELLULOSIC BIOFUELS

In the March 2010 final RFS rule, EPA approve d a number of feedstocks for production of
cellulosic biofuels. In a subsequent rulemaking h 

### , we added energy cane to the list of approved feedstocks. These approved feedstocks are:

Cellulosic biomass from crop residue, sl ash, pre-commercial thinning and tree residue, annual covercrops, switchgrass, miscanthus and energy cane; cellulosic components of separated yard waste; cellulosic components of separated food waste; and cellulosic com ponents of separated MSW

h Regulation of Fuels and Fuel Additives: Identification of Additional Qualifying Renewable Fuel Pathways Under the Renewable Fuel Standard Program, 78 FR 14190, 14217 (March 5, 2013).14 

### In this rulemaking, we are also proposing to a llow fuels produced from biogas from landfills to qualify as cellulosic biofuels. In th is section, we discuss the cellulosic fraction of feedstocks that are already approved under RFS as part of a pa thway eligible to generate cellulosic RINs. To help this discussion, the data from Ta bles 2-4 above are su mmarized in Table 5.

Table 5. Summary of Adjusted Cellulosic Comp osition for different types of feedstocks.
Data are derived from Tables 2-4 above.

Feedstock Type Average Adjusted Cellulosic Composition Crop Residue 90% Switchgrass 85% Miscanthus 85% Other Grasses 81% Wood and Branches 92% Leaves 82%



### a. Crop Residues

As discussed above, crop residues have an av erage adjusted cellulosic composition of 83% (Tables 2 & 5). With the exception of two samp les for which we estimated lignin content, the adjusted cellulosic content was never lower than 78% of the total organic mass. Based on this analysis, it is clear that a large majority of th e biomass of different t ypes of crop residues is derived from cellulose, hemicellulose and lignin.

The types of residues analyzed here are considered to be re presentative of the crop residue category as listed in Table 1 to § 80.1426. In the current Notice of Proposed Rulemaking (NPRM), “Modifications to Renewable Fuel St andard Program, E15 Misfueling Mitigation Regulations, and Ultra Low Sulfur Diesel Re quirements,” we are seeking comment on the clarifications that crop residues be defined as:

Crop residue is the biomass left over from the harv esting or processing of planted crops from existing agricultural la nd and any biomass removed from existing agricultural land that facilitates crop management (including bi omass removed from such lands in relation to invasive species control or fire management), whether or not the biomass includes any portion of a crop or crop plant. Biomass is c onsidered crop residue only if the use of that15 

### biomass for the production of renewable fuel has no significant impact on demand for the feedstock crop, products produced from that f eedstock crop, and all substitutes for the crop and its products, nor any other impact that would result in a si gnificant increase in
direct or indire ct GHG emissions.

Furthermore, Table IV.D.-1 to that NPRM also lists the feedstocks that would be considered under the crop residue category including:

 Bagasse

 Corn Kernel Fiber (excluding the corn starch component)

 Corn Stover

 Citrus Residue

 Rice Straw

 Wheat Straw

We presented data specifically for corn stove r, wheat straw, rice straw and bagasse in the previous section and anticipate that citrus resi due would have a similar composition to the types of crop residue analyzed. For corn kernel fiber, as discussed in the NPRM, the percentage will vary, but as much as 20% of the final fuel could be derived from corn starch. By definition, corn starch ethanol can only qualify as a rene wable fuel, not as an advanced fuel.

b. Slash, Pre-Commercial Thinnings, and Tree Residue

The March 2010 final RFS rule established the following definitions for slash, pre-commercial thinnings and tree residue:

Slash is the residue, including treetops, bran ches, and bark, left on the ground after logging or accumulating as a result of a storm, fire, delimbing, or other similar
disturbance.16 

### Pre-commercial thinnings are trees, including unhealthy or diseased trees, removed to reduce stocking to concentrate growth on mo re desirable, healthy trees, or other vegetative material that is re moved to promote tree growth.

Tree residue is slash and any woody residue genera ted during the processing of planted trees from tree plantations for use in lumber , paper, furniture or other applications, provided that such woody residue is not mixed with similar re sidue from trees that do not originate in tree plantations.

Based on these definitions, it is cl ear that woody material, ranging in size from tree trunks to branches to twigs, would comprise the majority of these feedstocks, along with some bark and likely some residual leaves. Based on the data in Tables 4 and 5, an average of 92% of wood and branches was cellulosic materials, and around 82% of leaves were composed of these compounds. Accordingly, EPA concludes that almost all of the material present in slash, precommercial thinnings and tree residue is composed of from cellulose, he micellulose and lignin.

c. Annual cover crops

A January 2012 supplemental rulemaking i 

### defined annual cover crops as follows:

Annual cover crop means an annual crop, planted as a rotation between primary planted crops, or between trees and vines in orchards and vineyards, t ypically to protect soil from erosion and to improve the soil between peri ods of regular crops. An annual cover crop has no existing market to which it can be so ld except for its use as feedstock for the production of renewable fuel.

Common cover crops include a wide variety of types of plants, including different types of grasses and grains (e.g., buckwheat, oats, annual ry egrass, etc), legumes (e.g. clover, hairy vetch and field peas), and plants from the mustard fa mily (e.g., arugula, forage radish and mustard). 17

i Regulation of Fuels and Fuel Additives: 2012 Renewable Fuel Standards; Final Rule, 77 FR 1320, 1358 (January 9, 2012).17 

### Because cover crops are so diverse, it is likely th at their cellulosic content also varies widely. Accordingly, EPA has not attempted to constr ain the cellulosic content of “cover crops”. Instead, we will consider the cellulosic content of cover crops on a case-by-case basis as we determine whether to approve that crop as a feedstock.

d. Switchgrass

As shown in Table 3, four different studies of switchgrass found adjusted cellulosic compositions of 82-90%, with an average of 85% , indicating that the vast majority of switchgrass biomass is composed of cellulose, hemicellulose and lignin.

e. Miscanthus

Similar to switchgrass, an average of 85% of mi scanthus biomass is cellulose, hemicellulose and lignin (Table 3).

f. Energy cane

As discussed above, one analysis of energy cane found that it cont ained 79% cellulosic materials.

g. Cellulosic components of separated yard wa ste; Cellulosic components of separated food waste; and Cellulosic co mponents of separated MSW

For these feedstocks we specifically outlined how th ey would be considered as part of the final rule published on March 26, 2010 (75 FR 14670). We reiterate this in the current NPRM. We
determined that:

Waste streams kept separate since generati on from MSW that consis t of yard waste are expected to be composed almost entirely of woody material or leaves, and therefore will be deemed to be composed of cellulosic materials.18 

### Waste streams consisting of food wastes, how ever, may contain both cellulosic and noncellulosic materials. We will deem wast e streams consisting of food waste to be composed entirely of non- cellulosic materials,

For separated MSW, EPA is not aware of a test method that is able to distinguish
between cellulosic- and starch -derived renewable fuel. Under these circumstances, EPA believes that it is appropriate for producers to base RIN assignment on the predominant component and, therefore, to assume that the bi ogenic portion of their fuel is entirely of cellulosic origin.

This NPRM does not propose to change those de terminations, therefore, biofuel produced from separated yard waste is consider ed to be 100% cellulosic, biof uel produced from the biogenetic portion of separated MSW is assumed to be 100% cellulosic, and biofuel produced from separated food waste is assumed to be non-cellulosic un less the producer demonstrates that some portion of the food wast e is cellulosic.

h. Biogas from landfills

One research paper that examined the cellulosi c origin of landfill bi ogas found that 91% of it
derived from cellulose and hemicellulose. 18 

### We discuss this conclusi on in depth in a memo to
the docket. j 

### Accordingly, as with the other feedstocks examined in this memo, it appears that almost all of the landfill biogas is produced from cellu losic components.

j “Support for Cellulosic Determination for Landfill Bioga s and Summary of Lifecycle Analysis Assumptions and Calculations for Biofuels Produced from Landfill Bioga s”, which has been placed in docket EPA-HQ-OAR-2012- 0401.19 

### REFERENCES

1 

### Modified from U.S. Department of Ener gy - Energy Efficiency and Renewable Energy, Biomass Program, Feedstock Composition Glossary, Accessed December 3, 2012, http://www1.eere.energy.gov/biomass/prin table_versions/fee dstock_glossary.html

. 2 

### Templeton, David W., Amie D. Sluiter, Tammy K. Hayward, Bonnie R. Hames, and Steven R. Thomas (2009) Assessing corn stover composition and sources of variability via NIRS. Cellulose, 16, 621-639.

3 

### Dien, Bruce S., Hans-Joachim G. Jung, Kenneth P. Vogel, Michael D. Casler, JoAnn F.S. Lamb, Loren Iten, Robert B. Mitchell, and Ga utum Sarath (2006) Chemical composition and response to dilute-acid pretreatment and enzymatic saccharification of alfalfa, reed canarygrass, and switchgrass. Biomass and Bioenergy, 30, 880-891.

4 

### Lee, DoKyong, Vance N. Owens, Arvid Boe, and Peter Jeranyama (2007) Composition of herbaceous biomass feedstocks. Report prepar ed by North Central Sun Grant Center, South Dakota State University, SGINC1-07, 16 pp.

5 

### Templeton, David W., Christopher J. Scarlata, Justin B. Sluiter, and Edward J. Wolfrum (2010) Compositional analysis of lignocellulosic feed stocks: 2. Method uncertainties. Journal of Agricultural and Food Chemistry, 58, 9054-9062.

6 

### NREL (2011) Standard Biomass Analyti cal Procedure, Accessed January 8, 2012, http://www.nrel.gov/biomass/an alytical_procedures.html

7 

### U.S. Department of Energy - Energy Effi ciency and Renewable Energy, Biomass Program, Feedstock Composition Glossar y, Accessed December 3, 2012, http://www1.eere.energy.gov/biomass/prin table_versions/fee dstock_glossary.html

. 8 

### Eleazer, William E., William S. Ogle, III, Yu-Sheng Wang, and Morton A. Barlaz (1997) Biodegradability of municipal solid wast e components in laboratory-scale landfills. Environmental Science & Technology, 31, 911-917.

9 

### Komilis, Dimitris P and Robert K. Ham (2003) Th e effect of lignin and sugars to the aerobic decomposition of solid wastes. Waste Management, 23, 419-423.

10 

### Department of Energy, Energy Efficiencey & Renewable Energy, Biomass Program, Biomass Feedstock Composition and Property Database, Accessed December 6, 2011, http://www.afdc.energy.gov/ biomass/progs/search1.cgi

11 

### NREL data, email from Mary Biddy, Nati onal Renewable Energy Laboratory, National Bioenergy Center, on January 4, 2013.

12 

### Guo, Gia-Luen, Deng-Chieh Hsu, Wen-Hua Chen, Wei-His Chen and Wen-Song Hwang (2009) Characterization of enzymatic saccharif ication for acid-pretr eated lignocellulosic materials with different lignin compositi on. Enzyme and Microbial Technology, 45, 80-87.

13 

### Villaverde, Juan José, Pablo Ligero and Albert o de Vega (2010) Miscanthus x giganteus as a source of biobased products th rough Organosolv fractionation: A mini review. The Open Agricultural Journal, 4, 102-110.20 14 

### Scordia, Danilo, Salvatore L. Cosentino, Jae-W on Lee, and Thomas W. Jeffries (2011) Dilute oxalic acid pretreatment for biorefining giant reed (Arundo donax L.). Biomass and Bioenergy 35, 3018-3024.

15 

### BP Crop Research Trial data, email from Ruth Scotti, BP Biofuels, February 13, 2013.

16 

### Wang, Xiaoming, Jennifer M. Padgett, Florentino B. De la Cruz, and Morton A. Barlaz (2011) Wood biodegradation in laborat ory-scale landfills. Environm ental Science & Technology, 45, 6864-6871.

17 

### Cornell University College of Agriculture and Life Sciences. Cover Crop Guide, Accessed December 18, 2012, http://www.hor t.cornell.edu/bjorkman /lab/covercrops/index.php

18 

### Barlaz, Morton A., Robert K. Ham, and Daniel M. Schaefer (1989) Ma ss-balance analysis of anaerobically decomposed refuse. Journal of Environmental Engineering, 115(6), 1088-1102.