November 2014 D-1



# Appendix D: Feedstock Categorization and Definition s

Table of Contents

1. Introduction ......................................

................................................... ................................................... ..................... D-2

2. Summary of Biogenic Feedstock Categories Used .....

................................................... ............................... D-3

3. Biogenic Feedstock Characteristics ................

................................................... ................................................. D -4

3.1. Forest-derived Feedstocks .........................

................................................... ............................................... D-5

3.1.1. Roundwood .........................................

................................................... ................................................... D-5

3.1.2. Logging Residue ...................................

................................................... ................................................ D- 6

3.1.3. Forest-derived Industrial Products and Processing B y-products ...................................... D -7

3.2. Agriculture-derived Feedstocks ....................

................................................... .......................................... D-9

3.2.1. Conventional Agricultural Crops ...................

................................................... ................................ D-9

3.2.2. Agricultural Crop Residues ........................

................................................... ................................... D-10

3.2.3. Agriculture Industrial Products and Processing By-p roducts .......................................... D-11

3.2.4. Dedicated Energy Crops.............................

................................................... .................................... D-13

3.3. Waste-derived Feedstocks ..........................

................................................... ........................................... D-14

3.3.1. Municipal Solid Waste (MSW) .......................

................................................... .............................. D-15

3.3.2. Animal Agriculture Wastes .........................

................................................... .................................. D-16

3.3.3. Wastewater ........................................

................................................... ................................................. D -17

4. Other Possible Feedstock Categories ...............

................................................... ............................................ D-17

4.1. Secondary Use Feedstocks ..........................

................................................... ........................................... D-17

4.2. Feedstock Imports and Exports .....................

................................................... ...................................... D-18

4.3. New, Unconventional, or Otherwise Unanticipated Fee dstocks ........................................... ..... D-18
5. References ........................................

................................................... ................................................... .................... D-19

6. Addendum: Spent Pulping Liquor—Overview of Processe s and Possible Alternate Fates ..... D-21

6.1. Joint Production of Industrial Products and By-prod ucts .............................................. .............. D-21

6.2. Overview of Pulping Processes .....................

................................................... ....................................... D-22

6.3. Generation of Pulp and Black Liquor ...............

................................................... .................................. D-23

6.4. Biogenic CO 2 Emissions from Kraft Black Liquor Chemical Recover y .................................... D-26
6.5. Alternate Pathways for Black Liquor ...............

................................................... .................................. D-27
6.5.1. Alternate Fate Scenario 1: Black Liquor Incineratio n without Energy Recovery ..... D-29

6.5.2. Alternate Fate Scenario 2: Black Liquor Decompositi on in a Wastewater Treatment System.... ..........................................

................................................... ................................................... . D-30November 2014 D-2

6.5.3. Discussion ........................................

................................................... ................................................... . D-31

6.6. References for Addendum ...........................

................................................... ........................................... D-31



## List of Tables
Table D-1. Biogenic Feedstocks. ...................

................................................... ................................................... ........... D-3 Table D-2. Elemental Composition of Black Liquor (W eight % of BLS).................................... ................. D-25 Table D-3. AVOIDEMIT

for Scenario 1 Where Black Liquor Is Incinerated W ithout Energy Recovery. ........................................

................................................... ................................................... ............... D-29 Table D-4. AVOIDEMIT

for Scenario 2 Where Black Liquor Is Disposed Thro ugh Wastewater Treatment. ........................................

................................................... ................................................... ............. D-30 

## List of Figures
Figure D-1. Products of the Kraft Mill Digester (Tr an and Vakkilainnen, 2008)......................... ........... D-24 Figure D-2. Simplified Representation of the Kraft Pulping and Chemical Recovery System (EPA, 2009). ............................................

................................................... ................................................... ................... D-26 Figure D-3. Simplified Diagram Showing How Biogenic CO 2 Emissions Are Emitted from Both Kraft Recovery Furnace and Lime Kiln. ...................

................................................... ........................................ D-27



## 1. Introduction

The purpose of this appendix is to describe the cat egorization of biogenic feedstocks used in the assessment framework. A biogenic feedstock can be d efined as any organic material originating from modern or contemporarily grown plants, animals , or microorganisms, excluding material embedded in geological formations or fossilized, th at is used for combustion or product processes or otherwise decomposes at a stationary source. A m ultitude of feedstocks meet this definition, though some feedstocks are more commonly used for b ioenergy than others. Feedstocks differ in physical properties; origin (including local climat e and biogeochemical attributes); species; growth rates; management (from planting to harvesting); an d whether they are deliberately raised as an energy feedstock or if they can be used for other p urposes (e.g., human or animal consumption), are reclaimed wastes from other processes, or are salva ged following extreme events such as hurricanes or insect outbreaks. Duration of typical growth or decay periods also can differentiate feedstocks. Annual crops, for example, might be acc ounted for differently than perennial crops, and both might be accounted for differently than waste- derived feedstocks. Furthermore, a feedstock in continuous supply may need to be accounted for diff erently than a feedstock available only occasionally (e.g., short growing seasons, feedstoc ks that result from fire or insect infestation).
This appendix first lays out the broad feedstock ca tegorization used in the framework. It then discusses the various feedstock attributes of commo nly used biogenic feedstocks and why certain feedstocks are grouped together. This appendix also generally discusses other feedstock categories, including secondary use feedstocks, imports, and em erging markets. The list of feedstocks included in this categorization is not exhaustive and may ne ed modification per specific policy applications and/or as new feedstocks come into the biogenic fee dstock market. The broad feedstock categorizations in this appendix are not intended t o represent specific regulatory definitions that currently exist or that may need to be developed as part of policy applications of the framework.November 2014 D-3



## 2. Summary of Biogenic Feedstock Categories Used

To account for differing feedstock characteristics, the framework separates biogenic feedstocks that might be used in a stationary source into three bas ic categories:

1. Forest-derived feedstocks: biomass derived from nat ural forests, tree plantations, and wood products production processes; 2. Agriculture-derived feedstocks: biomass derived fro m agricultural operations; and 3. Waste-derived feedstocks: biomass derived from any source of animal, industrial, or municipal waste.
The framework uses these categories because they ar e large enough to capture the important differences among feedstocks in terms of their biop hysical attributes but small enough to be more manageable and understandable for application in a stationary sources context. Table D-1 includes examples of biogenic feedstocks under these common categories that have been used commercially, or could be used commercially in the near future, f or bioenergy purposes.

Table D-1. Biogenic Feedstocks.

Forest-derived Feedstocks Agriculture-derived Feedstocks Waste-derived Feedstocks Roundwood: Pulpwood, saw logs

Logging Residue: Branches and limbs, debris

Industrial Products and Processing By-products :

• No current alternative market uses, such as pulping liquor

• Has current alternative market uses, such as mill residues (bark, peeler shaving, sawdust); ethanol; pellets Conventional Agricultural Crops: Camelina, corn, canola, sorghum, soybeans, sugarcane, wheat

Agricultural Crop Residues: Barley straw, corn stover, oat straw, rice straw, wheat straw

Dedicated Energy Crops: Miscanthus, napier grass, switchgrass, short rotation woody crops (e.g., hybrid poplar, poplar, willow, eucalyptus)

Industrial Products and Processing Byproducts:

• No current alternative market uses, such as: shells, husks, and cobs

• Has current alternative market uses, such as animal fats, oils, and greases; distillers grains; ethanol; biodiesel Municipal Solid Waste: Urban wood waste, yard trimmings, food waste from industrial processes, kitchen
scraps

Animal Wastes: Livestock manure, litter,
manure wastewater

WastewaterNovember 2014 D-4



## 3. Biogenic Feedstock Characteristics

The feedstock categories are based on the key chara cteristics of feedstocks themselves as well as the feedstock source conditions that may lead to di fferent net biogenic carbon-based emission profiles and thus merit different treatment under t he framework. These characteristics generally include similarities and differences between feedst ock growth and decay cycles, typical management and land use patterns associated with fe edstock production, potential alternate market and carbon fate pathways, and other factors. More specifically, these characteristics include the following:

• Time scale over which feedstock carbon sequestratio n and emissions occur. For some feedstocks, carbon sequestration into the feedstock can occur over a short time (i.e., a year or less). For other feedstocks, sequestration occur s over a much longer time (i.e., decades to hundreds of years). Although emissions to the atmos phere occur instantaneously during combustion, some emissions-associated feedstock los ses (e.g., decay) or alternative pathways may take place over days, weeks, months, o r even years during storage and handling.

• Alternate fate pathways (assumptions about “What wo uld have happened otherwise?”). Baseline assumptions can involve consideration of t he end-of-life emissions profile of each feedstock were it not used at the stationary source for energy. The baseline assumptions vary according to the feedstock type and could vary if there are other possible market uses. For example, some feedstocks may be left undisturbe d to decompose if not used for energy, thereby emitting both CO 2 and CH 4 , which is avoided when the feedstocks are combuste d. If not used for energy, some feedstocks would otherwis e have to be disposed of (landfilled or other means). Conversely, some feedstocks may have been used in other markets if they were not being used at a stationary source for bioe nergy production.

• Land use/land-use management changes. The cultivation and use of certain biogenic feedstocks can create market competition that stimu lates a shift in land use or land use management changes. Changes in land use and related management activities can generate emissions that contribute to the net atmospheric co ntribution from using the feedstock at a stationary source.

• Leakage: The use of some feedstocks for bioenergy may have G HG emissions effects outside of the biogenic feedstock production assessment bou ndary caused by the biogenic feedstock production activities (e.g., replacement of diverte d crop, livestock, or forest products due to a change in land use from conventional products to biogenic feedstocks). The directionality and magnitude of these leakage effects may vary sig nificantly according to feedstock type, location, and other factors. Further discussion can be found in Appendix E.

• Storage and handling losses. Various steps involved in converting a biogenic fe edstock into a bioenergy product may involve losses of the biogeni c carbon during transportation, storage, and handling. These feedstock losses vary according to the feedstock type.November 2014 D-5

The following subsections discuss how different fee dstock categories could be considered within the framework according to their different characte ristics.



### 3.1. Forest-derived Feedstocks
Forest-derived feedstocks currently constitute one of the largest sources of bioenergy in the United States (EIA, 2011). The majority of that energy pro duction is currently derived from wood products processing. However, increased demand for bioenergy can result in higher prices being paid for bioenergy feedstock, and in doing so, increase comp etition with existing forest products markets, especially pulpwood (Becker et al., 2009; Galik et al., 2009; Lundmark, 2006). Increasing demand for pulpwood can have cascading effects on sawtimbe r markets, as few stems are left to grow into sawtimber size classes (Abt & Abt, 2013). The inter action between bioenergy harvests and broader timber market effects is somewhat dependent on the rate at which and the cost at which residues can be recovered. Abt & Abt (2013), for example, sh ow that the assumed rate of logging residue recovery has a substantial influence on timber mark et response, and by extension, possible future changes to forest land management.
In this section, characteristics of roundwood, logg ing residue, and forest-derived industrial products and processing by-product feedstocks are p resented.

3.1.1. Roundwood

Roundwood biomass includes trees of commercial size , species, and quality from a forest or plantation in an area with commercial markets. Roun dwood is most often sent to sawmills or pulp and paper mills, though it is occasionally used for energy purposes (as clean chips, for example) at dedicated or cofiring electricity generating unit ( EGU) facilities.

• Time scale over which feedstock carbon sequestratio n and emissions occur. Roundwood feedstocks typically have a longer harvest cycle th an agriculture-derived feedstocks like traditional crops or dedicated energy crops. Exampl e harvest cycles for roundwood pulp and sawtimber production are about 11 to 15 years f or pulpwood and 25 years for sawtimber grown on plantations in the southern Unit ed States and 45+ years for sawtimber in the Pacific Northwest. Note that the overall ave rage age of the U.S. forest inventory is older than these values because of the inclusion of less actively managed forest area.

• Alternate fate pathways: Roundwood, if used for industrial purposes other th an energy, could lead to long-term carbon sequestration. For e xample, if the wood were used for furniture, buildings, or pulp and paper, its carbon would be sequestered for longer than if it is burned immediately for energy purposes (though p ulp and paper products would generally have shorter sequestration time frames th an more durable products) (Skog, 2008). Additionally, roundwood use at stationary so urces for the sole purposes of bioenergy production could detract from roundwood u se in other markets.

• Land use/land use management changes: Roundwood biomass can have several markets competing for the same raw material. For instance, pulp and biomass-to-energy markets can compete for the same tree sections. As such, ch anges in demand for roundwood biomass, whether for bioenergy or other uses, can l ead to changes in production, potentiallyNovember 2014 D-6

causing direct land use or land use management chan ges. Such changes, including, for example, shortening rotation ages/increasing harves t frequency, can in turn cause the landscape to have different GHG emissions profiles and equilibrium states.

• Leakage: Increasing use of roundwood for energy production would likely also have ramifications throughout related commodity markets, causing leakage effects such as indirect land use change. For example, leakage coul d take the form of additional land outside of accounting boundaries converting from a previous use to accommodate displaced market demand (e.g., shifting cropland or pasturela nd to forestland, which could result in higher carbon sequestration on those newly forested lands, but potential carbon emissions due to conversion of other lands elsewhere to cropl and).

• Storage and handling losses: Roundwood biomass is often harvested, preprocessed
, transported, and used within a matter of days or we eks, which limits storage losses. However, depending on location, there may be longer storage needs at certain times during the year, and some degradation of woody biomass and associated dry matter loss could occur during storage and handling. The degree to wh ich dry matter loss occurs depends largely on moisture content, where woody materials with high moisture levels are more likely to be colonized by fungi and mold, which can cause dry matter losses. In addition, the longer biomass is stored, the greater the dry matte r loss, other things being equal. Accounting for forest-derived feedstocks like round wood should cover losses in storage and material handling to provide a complete link betwee n feedstock available at the source location and that used in the stationary source.

3.1.2. Logging Residue
Logging residues include biomass derived from harve st operations including treetops and nonmerchantable sections of the stem, branches, and ba rk left on the ground after logging. If not left to decompose or open burned on site at the logging ope ration site, logging residues are often sent to sawmills or pulp and paper mills, though they are a lso used for energy purposes, either at EGUs or to fuel internal processes at sawmills and pulp and paper mills. 1

• Time scale over which feedstock carbon sequestratio n and emissions occur. If left in the forest, logging residues may be either burned or left to de cay over a period that can range from days to years, depending on the size and nature of the woody material and the surrounding environmental conditions (e.g., moisture, soil type , exposure to light) (Turner et al., 1993; Turner et al., 1995). Materials such as leaves of d eciduous trees will decompose within a couple of years, while conifer needles will often t ake several years. In general, the wetter the biomass on the forest floor, the faster these r esidues will break down. If not burned, non-merchantable large woody material would decay s lowly in the forest, and its carbon

1 Traditional harvests (removing tree boles and leav ing tops and limbs on site) in some instances may t ransition to more intensive practices such as whole-tree harvest ing/chipping. In this presentation of the framework , whole-tree use is not attributed exclusively to the roundwood feedstock, because the practice also includes the h arvest of what traditionally would have been left as residue. Thus , a whole-tree harvest can be viewed as removing tw o feedstocks: roundwood and logging residue. Thus, under the fram ework, whole trees could be divided into both round wood and logging residue.November 2014 D-7

content in the forest can be estimated from samplin g surveys. It can take several decades for pine logs with high resin content to fully deco mpose.

• Alternate fate pathways: If left in the forest, logging residues may be eith er burned or left on site to decay over a period that can range from day s to years (as discussed above), which can have different net biogenic contributions to th e atmosphere. Under current biomass market prices in most regions, logging residues are often not collected, and procurement of residue does not trigger the harvest operation (DOE , 2011).

• Land use/land use management changes: The type of harvest operation (e.g., whole tree versus non-whole tree harvest), stand and timber st ructure, and soil conditions play significant roles in the abundance and merchantabil ity of logging residues. For instance, hardwoods in general yield higher percentages in no n-timber biomass than softwoods. If soils are wet, logging residue material may be used to stabilize skid trails resulting in no surplus for feedstock supply. Extracting biomass fo r energy production often requires the simultaneous harvest of more valuable wood (timber, pulpwood) to justify the cost of collecting the residue material. Under current mark et conditions, increased demand for logging residues for bioenergy production is unlike ly to expand the harvest area (i.e., land use change) though it could change the intensity of residue collection operations (i.e., a land use management change). If more logging residues ar e collected as biogenic feedstocks for energy production, this management change could imp act the soil carbon contributions to the harvest landscape and, conversely, remove the v olume of woody matter decaying on the forest floor or being burned on site.

• Leakage: Under current market conditions, there are no comme rcial alternative markets for logging residues and thus few pathways for increase d logging residue removal inspire leakage effects such as indirect land use change. H owever, if the demand for logging residues increases substantially (e.g., as markets for bioenergy feedstocks develop), this could alter current practices to the extent that le akage could potentially occur.

• Storage and handling losses . As noted above, to the extent that forests are ha rvested and used on a fairly continuous year-round basis with o nly days, possibly weeks, between harvest and use, there will tend to be relatively l ittle storage and handling loss. However, the longer storage is required, the greater dry mat ter loss will occur, other things being equal. Within forest-derived feedstock types, loggi ng residues are more likely to experience feedstock losses during transport, storage, and han dling than roundwood because of the smaller size of the feedstock pieces. Nonetheless, processing losses of forest-derived biomass are generally expected to be minimal.

3.1.3. Forest-derived Industrial Products and Processing B y-products
Usual practices within the forest industry generate a wide variety of forest industrial products and processing by-products. These by-products include l iquids such as black liquor from the pulping process and mill residues such as bark, shavings, s awdust, sanderdust, hog fuel, and unusable bole components (due to knots, holes, etc.). 2 Consideration of forest-derived industrial process ing

2 Forest products are characterized by a joint produ ction function, as any products are produced from a single tree. Forest product industrial entities will try to opti mize production to maximize the amount of high-valu e productsNovember 2014 D-8

products and by-products should include assessment of whether these materials have current alternative market uses to bioenergy or not. Most r esidues from wood processing facilities are currently used for onsite energy production or sold for other forest products (e.g., particleboard). Deviating by-products that do have current market u ses to additional energy production instead of their traditional use could have potential impacts on those traditional markets. For example, markets for sawdust, shavings, and chips from sawmi lls are well established. Sawdust and shavings may be used in composite wood products such as part icleboard, medium density fiberboard (MDF), or pellets, shavings may be sold to farmers or pet owners for animal bedding, and bark may be sold for use as mulch or fuel. Very small amounts of mil l residue go unused (USDA, 2007; U.S. Department of Energy, 2011). In addition, chips are often sold to pulp mills (USDA, 2007). Bark, slabs, edges, and other material may be burned on s ite at forest product mills for heat and energy production. Thus, when mill residues that were used in other markets are diverted into energy production, it may be an indication that leakage ef fects are possible (i.e., if sawdust goes to a biomass energy entity rather than a pulp mill, the pulp mill will need to make up the shortfall, possibly by increasing pulpwood harvests).
An example of a forest industrial processing by-pro duct with no current alternative market use is spent pulping liquor. Spent pulping liquor (e.g., b lack liquor from the kraft pulping process) contains nearly half the original energy content of the wood and is not currently sold on the market, because it is typically combusted within the pulp m ill chemical recovery process for purposes of reclaiming pulping chemicals and producing energy. If not combusted for chemical recovery and energy, black liquor-producing entities would need to dispose of the material (e.g., treatment in wastewater treatment systems, decay in lagoons, com bustion without energy). When evaluating black liquor combustion on site for energy versus p ossible alternates fates (disposal and potential CH 4 and CO 2 emissions from decay), black liquor combusted for on-site energy is expected to have less net atmospheric biogenic CO 2 contributions. Also, because black liquor producti on is contingent on paper production and related paper ma rket demand and prices, it is therefore unlikely that changes in demand for or prices of bl ack liquor would lead to changes in paper production and related land use, harvest, or forest management decisions (e.g., no effect on landscape attributes). This may also be the case fo r other industrial processing by-products with no current alternative market uses. More information a nd analysis on black liquor can be found in Addendum A to this appendix.

• Time scale over which feedstock carbon sequestratio n and emissions occur: For this feedstock category, the analysis of the time scale for feedst ock-related carbon fluxes will depend on the feedstock and landscape attributes and/or alter nate paths associated with the feedstock (e.g., the feedstock production site and the altern ate fate pathways [discussed below]).

(e.g., saw lumber) and minimize the amounts of low- value products (e.g., pulp, black liquor). Although there is some responsiveness to relative price movements (e.g., h igher demand and prices for wood pellets may lead t o an increased proportion of scrap going to this use and a decreased proportion going to particleboard), th e elasticity of transformation between outputs may be very inelasti c, and even with a negative price some low-value pr oducts would still necessarily be produced as a by-product of the production of high-value products (e.g., sa wdust, black liquor).November 2014 D-9

• Alternate fate pathways: The alternate fate of forest-derived industrial pro ducts and processing by-products can vary widely per feedstoc k (those with and without alternative market uses) and per stationary source process. In the case of feedstocks with alternative market uses, these feedstocks typically would not b e used for energy if there is a highervalue use (e.g., as raw material for pulping or com posite wood products), and these feedstocks would pass through the stationary source through means other than the stack. For those feedstocks with no other current market u ses, the alternate fate pathways could include use for energy (e.g., as boiler fuel) and d isposal (e.g., through non-energy-related burning, landfilling, on-site storage), which might include decay causing CH 4 and CO 2 emissions.

• Land use/land use management changes: Under current market conditions, there is no evidence of land use or land use management changes related to producing forest-derived industrial products and by-products.

• Leakage: If demand for forest-derived industrial products an d processing by-products increases for energy use, leakage could occur if th ese feedstocks currently have alternative market uses.

• Storage and handling losses: With some feedstocks in this category that require storage, the longer a feedstock is stored, the greater dry matte r loss will occur, other things being equal. Within forest-derived feedstock types, industrial p roducts and process by-products are more likely to experience feedstock losses during s torage and handling than roundwood because of the smaller size of the feedstock pieces (Thornqvist and Jirjis, 1990; Jirjis, 1995; Afzal, 2010).
Furthermore, some products from the forestry sector are purposefully produced for energy production. These products include pellets or other fuels produced from woody biomass (these are covered in the secondary use feedstocks section bel ow).



### 3.2. Agriculture-derived Feedstocks
Although the majority of biogenic feedstocks that h ave been used for energy generation in the United States to date are derived from forest mater ials, there is potential for large-scale use of agricultural feedstocks as well. Traditional agricu ltural crops that have historically been grown for food, feed, and fiber could be used as bioenergy fe edstocks, as could crop residues, dedicated energy crops, or industrial products and processing by-products. This section describes characteristics of these agricultural feedstocks, s eparating them into three categories: (1) crops grown primarily for bioenergy use, whether conventi onal or dedicated energy crops; (2) crop residues; and (3) agricultural-derived industrial p roducts and processing by-products.

3.2.1. Conventional Agricultural Crops
The conventional agricultural crops category includ es feedstocks from crops traditionally grown for food, feed, textile, or other uses, such as cor n and soybeans. These crops can be converted at stationary sources into conventional starch-based f uels, electricity, biodiesel, and cellulosic fuels. Use of these feedstocks in bioenergy production cou ld result in changes in their production, price, and trade and potentially result in direct and/or i ndirect land use change. Crops for which only theNovember 2014 D-10

processing by-products from a multiproduct processi ng activity (e.g., soybean oil, rice hulls) are used for bioenergy are covered under the agricultur e industrial processing by-products subcategory below.

• Time scale over which feedstock carbon sequestratio n and emissions occur: Growth and harvest of, and related sequestration and emissions from, conventional crops generally occur at time scales of a few months to a year. Eve n though the net atmospheric biogenic contribution from the growth and harvest of the fee dstock itself is in balance, other factors such as land use management and land use changes an d related soil carbon effects can affect the overall assessment outcome.

• Alternate fate pathways: If conventional crops are not used for bioenergy, t hey would be used for other purposes, such as food, animal feed, or fiber or the production of liquid biofuels.

• Land use/land use management changes: There can be direct land use change effects if the demand for agricultural crops for bioenergy causes changes in land use and land use management. Changes in demand for agricultural biom ass can lead to changes in cropping patterns, and production practices (e.g., intensifi cation) can lead to changes in GHG emissions (e.g., impacts on soil carbon levels).

• Leakage: Leakage effects related to conventional crops for e nergy purposes can be substantial. The new or diverted production of feed stocks can affect commodity markets and thus lead to changes in production that alter l and uses and land use management outside of the bioenergy feedstock supply chain (Mu rray et al., 2004; Searchinger et al., 2009; EPA, 2010a). For example, if forested land is converted to crop production for energy uses, the carbon storage occurring on the landscape changes in both standing biomass and soil carbon pools. Also, other forested lands outsi de of the bioenergy supply chain could become managed or be managed differently to meet th e market product demand displaced when the original forestland was converted to crops for energy use.

• Storage and handling losses . Agricultural feedstocks generally need to be proc essed before they can be used for energy, which can lead to low levels of decomposition or physical feedstock losses. Additionally, because of their se asonal nature, conventional agricultural biomass needs to be stored to provide a year-round supply of energy. Thus, agricultural biomass may experience more feedstock losses than f orest biomass, on average, simply because it typically needs to be stored longer. Dry matter losses during storage inside buildings are expected to be less than 5% (Collins et al., 1997; Huhnke, 2006; Shinners et al., 2007). Outside storage could lead to substantially greater losses because of the exposure to weather and increased losses to pests.

3.2.2. Agricultural Crop Residues
Agricultural crop residues, such as corn stover, wh eat straw, and rice straw, can be collected for conversion or combustion at stationary sources to g enerate electricity and cellulosic fuels. These residues are traditionally tilled into the soil, pr oviding nutrients for the next planted crop. Howeve r, crop residue management changes, such as the remova l of residues that would otherwise remain on the field or be open burned, result in impacts o n soil conditions (e.g., increased erosion) as wellNovember 2014 D-11

as soil carbon levels (e.g., lower carbon inputs to the soil). In addition, in some instances (e.g., t he removal of corn stover) there may also be a loss of nitrogen in the soil. In such cases, to address th is loss of soil nitrogen following the removal of corn stover, additional fertilizer may be added to ensure continuing yields of the main corn crop. Thu s, additional N 2 O emissions may be incurred as a result of residue removal.

• Time scale over which feedstock carbon sequestratio n and emissions occur: Crop residues are generated on an annual basis when crops are harvest ed, with subsequent decomposition taking place over a period of months or years depen ding on production practices and environmental conditions.

• Alternate fate pathways: Agricultural residues, like forest residues, would decay, emitting CO 2 and CH 4 , and make small contributions to soil carbon if th ey are not removed for bioenergy or other uses. Removing residues may incr ease the return of carbon to the atmosphere from the residues in the short term and reduce the amount of carbon stored in the soils over a longer term.

• Land use/land use management changes: In the case of changes only to land use management, there may potentially be effects from r emoving agricultural residues from the landscape and using agricultural processing by-prod ucts, because land use management changes can affect soil GHG fluxes.

• Leakage: In addition, to the extent that a market develops f or crop residues, this additional coproduct of crop production may increase returns t o production of agricultural crops with marketable residues and induce land movements from other uses to crop production with residues.

• Storage and handling losses . Accounting for agricultural feedstocks such as re sidues and byproducts should cover any losses in storage and mat erial handling. Although these losses may be small compared with feedstock use (less than 10%), these losses in the supply chain are required to link what is being used in the stat ionary source process to what is grown at the feedstock source location.

3.2.3. Agriculture Industrial Products and Processing By-p roducts
Similar to those produced in the forestry sector, a griculture industrial products and processing byproducts are considered in two subcategories: those with current alternative market uses and those without. Again, if these industrial product and pro cessing by-product feedstocks are used to produce bioenergy instead of traditional market use s, this alternative use for energy can potentially disrupt the traditional markets and have related la nd use and/or land use management changes.
Examples of agriculture industrial processing by-pr oducts with a current alternative market use include animal fats, oils, and greases that come fr om livestock production and distillers grains that are produced during the grain ethanol production pr ocess. Animal fats, oils, and greases are used in a variety of markets, including the manufacture of beauty products, pet foods, and many other goods. Distillers grains are used as animal feed, o ften serving as a substitute for corn and soybean meal in feedlots.November 2014 D-12

Examples of agriculture industrial processing by-pr oducts with no current alternative market use (outside of renewable fuel production) include shel ls, husks, and cobs.
However, some agriculture-derived products are prod uced for energy purposes but not necessarily for use at stationary sources. These include ethano l and biodiesel produced from a variety of agriculture sources: grains, oilseeds, cellulosic m aterial, sugar-based crops, and more. These products tend to be produced for use in the mobile source sector, but their use in a stationary source remains a possibility.

• Time scale over which feedstock carbon sequestratio n and emissions occur: For this feedstock category, the time scale over which sequestration o ccurs for the primary crop is typically less than a year because the biogenic feedstock is derived from the production of annual crops. For emissions from the industrial products a nd by-products, the time period over which emissions would take place will depend on the specific feedstock being considered and the alternate fate pathways.

• Alternate fate pathways: The alternate fate of agriculture industrial produc ts and processing by-products varies across feedstocks and by station ary source process. Some feedstocks have active alternative markets, whereas others do not currently have alternative market uses. In the case of feedstocks currently being use d in alternative uses (e.g., distillers grains, oils), they would typically not be used in energy p roduction as long as there are highervalued uses. For feedstocks without current alterna tive market uses, the alternate fate pathways could include use for energy. Materials su ch as corn shells, husks, and cobs may be spread back on the field as the combine harvests the grain, which helps maintain soil quality. Thus, using these materials in alternate w ays may necessitate the addition of more fertilizer or other soil amendments to maintain soi l quality. A given alternate fate pathway for these feedstocks may potentially result in CO 2 and CH 4 emissions from decay.

• Land use/land use management changes: Under current market conditions, using agricultural industrial products and processing by- products that are currently being used in making animal feed, cosmetics, or alternative fuels not used at stationary sources is likely to lead to market impacts. Land use may change as dema nd for agricultural commodities that generate industrial products and by-products that c an be used for energy production increases. Diverting the use of by-products that ar e not currently used in other markets is less likely to have effects on land use, though the re may be effects on land productivity and input use due to nutrient removal, as discussed abo ve. It is also possible that creating a new demand for corn by-products (e.g., shells, husks, a nd cobs), for instance, would lead to more land moving into corn if the additional revenue ava ilable from corn by-products becomes sufficiently high.

• Leakage: If there is sufficient demand for agricultural ind ustrial products and processing by-products for use in energy production, there cou ld be leakage because these products are diverted from their current market uses.

• Storage and handling losses: It is possible that there would be some physical lo sses or decomposition of some feedstocks, with losses tendi ng to increase with length of storage, other things being equal.November 2014 D-13

3.2.4. Dedicated Energy Crops
Dedicated energy crops, including switchgrass, misc anthus, energy sorghum, and short-rotation woody crops (e.g., poplar, willow), can be converte d at stationary sources into heat and power, cellulosic fuels, and biodiesel. Direct and indirec t land use change can occur as a result of dedicate d feedstock production because existing forestlands, croplands, or grasslands would likely need to be converted to grow these feedstocks since they are n ot currently produced commercially at large scales in the United States.

• Time scale over which feedstock carbon sequestratio n and emissions occur: Growth and harvest of dedicated energy crops generally occur a t time scales of a year or a few years, with short-rotation woody crops having the longest growth cycle in this subcategory (3 to 20 years, depending on site and management conditio ns). For some energy crops like sweet sorghum, sequestration and emissions related to a s ingle rotation typically occur over the course of a few months to a year. For these energy crops on rotations similar to traditional agricultural crops, the net atmospheric biogenic co ntribution from the growth and harvest of the feedstock itself is considered in balance, t hough other factors such as land use management and land use changes and related soil ca rbon impacts can affect the overall net contribution outcome. For energy crops with rotatio ns longer than a year, the rotation ages and harvest regimes (and thus resulting sequestrati on and emissions related to growth and harvest) depend largely on specific species and sit e and management conditions. 3 Many energy crops also have extensive root systems that are left during bole/limb harvests to regenerate for multiple cycles. These root systems and minimal/no tillage practices can lead to high levels of soil carbon sequestration over ti me. In some circumstances, dedicated feedstocks may have substantial direct land use and /or leakage impacts related to cultivation if its production has displaced other l and use types (especially in the case of displaced forest), which may have implications for landscape carbon equilibrium over time.

• Alternate fate pathways: If not used for bioenergy, there would be no dedica ted planting of energy crops aside from those cultivated currently for biofuel production, which is not yet conducted on large scales commercially.

• Land use/land use management changes: There can be direct land use change effects if the demand for dedicated energy crops causes changes in land use and land use management. Numerous alternative energy crops could be grown on land currently being used for production of other forestry or agricultural commod ities. Changes in demand for energy crops could displace traditional crops and forest p roducts, and these changes in cropping patterns and production practices can cause substan tial GHG emissions changes. For example, land may be converted from traditional cro ps such as corn or soybeans to energy crops, which would lead to increases in soil carbon sequestration as well as other carbon

3 Site requirements, regeneration potential, growth and yield estimates, pests, and fertilization regim e all affect species growth and influence management decisions ( in addition to cost for the latter). Management reg imes for energy crops can vary widely, from active managemen t to low-intensive/unmanaged regimes, which causes widely different growth and harvest-related emissions.November 2014 D-14

pools. Land converted from forests to energy crops can increase GHG emissions from the landscape initially.

• Leakage: Leakage effects related to dedicated energy crop pr oduction can be substantial. The new or diverted production of feedstocks can af fect commodity markets and thus lead to changes in production that alter land uses and l and use management outside of the energy feedstock supply chain (Murray et al., 2004; Searchinger et al., 2009; EPA, 2010a). For example, if corn-producing cropland is converte d to a short-rotation woody crop for energy production, this change displaces corn from the marketplace and the corn could be replaced by production elsewhere. Even though there may be more carbon sequestration occurring on the production landscape (due to more carbon stored in root systems and soil carbon pools), there is potential significant leaka ge and related emissions effects elsewhere, particularly if forested or grassed lands are broug ht into crops.

• Storage and handling losses . Dedicated energy feedstocks generally need to be processed before they can be used for energy, which can lead to low levels of decomposition or physical feedstock losses. Additionally, because so me energy crops have shorter rotations and thus a seasonal nature, these feedstocks may ne ed to be stored to provide a year-round supply of energy. Therefore, energy crop biomass ma y experience more feedstock losses than forest biomass, on average. Dry matter losses during storage inside buildings are expected to be less than 5% (Collins et al., 1997; Huhnke, 2006; Shinners et al., 2007). Outside storage could lead to substantially greater losses because of the exposure to weather and increased losses to pests.



### 3.3. Waste-derived Feedstocks

A critical difference between waste and other biolo gically based material is related to the connection to the land providing the material. The biologically based material in waste is removed from land for other certain end uses (e.g., for man ufacture of consumer and industrial products such as newspaper, food, and construction), after w hich it is disposed of. Given that the treatment of waste itself does not drive the management of th e growth and harvesting of biomass, it is more difficult to quantify a connection between the cons umption of waste-derived feedstocks at stationary sources and the landscape from which the biogenic component of the feedstock was originally produced.

The treatment of waste-derived feedstocks at a wast e management system emits carbon as CO 2 (and CH 4 ) that would have otherwise been returned to the at mosphere as predominantly CO 2 from natural decay of waste, regardless of the managemen t or status of the land providing the biological material. The human management of the waste materia ls affects only the timing or location of these GHG emissions.
In addition to biogenic CO 2 emissions, waste management systems can emit large quantities of CH 4 if they manage wastes under anaerobic conditions. M ethodologies for estimating and accounting for CH 4 from waste management are available and widely use d in many GHG accounting programs. Many waste systems already account for CH 4 using methodologies from the EPA Greenhouse Gas Reporting Program (GHGRP). The decision to consider avoided CH 4 emissions in an analysis should be made in the context of the type of baseline that is most appropriate given the policy context.November 2014 D-15

This framework considers the comparison of CO 2 emissions from waste management sources to the biogenic CO 2 e emissions implications associated with decomposit ion of the same waste in other types of managed systems. For example, an assessmen t of waste materials diverted from a landfill to an incinerator for energy production could consi der the biogenic CO 2 emissions that occur at one point in time (at the incinerator) against the avoi ded CO 2 and CH 4 generated over decades through decomposition in the landfill and also avoided carb on storage in the landfill (EPA, 2010b, 2013; IPCC, 2006), or it could consider the biogenic CO 2 emissions against the CO 2 that would be emitted through the natural decay of the original biomass.

Feedstocks listed here are those that would have be en produced in the waste sector regardless of any potential use for bioenergy production. In this way, they are not comparable to various residue feedstocks listed elsewhere in this document.

3.3.1. Municipal Solid Waste (MSW)
MSW includes waste generated by residential, commer cial, and institutional entities. It contains a variety of biogenic materials, the composition of w hich varies by region, season, and long-term trends in waste generation. The average national co mposition of MSW in 2011 was estimated by EPA (2013) in Municipal Solid Waste Generation, Rec ycling, and Disposal in the United States Detailed Tables and Figures for 2011. The biogenic fractions of MSW include paper, food waste, yard waste, wood, diapers, natural fiber textiles, and natural rubber. MSW is defined slightly differently by different states. Both the overall c arbon content and the ratio of fossil carbon to biogenic carbon of MSW vary widely. About one-third of MSW generated is recycled (including composting). Of the MSW that is not recycled, about 80% of MSW is disposed of through landfilling, and 20% of MSW is treated using combustion (EPA, 20 13). Disposal of MSW in landfills causes some of the biogenic materials to be converted to m ethane; well over half of the methane (CH 4 ) generated in U.S. MSW landfills is captured for com bustion (EPA, 2013).

• Time scale over which feedstock carbon sequestratio n and emissions occur: MSW waste disposed of in a landfill will degrade slowly over one to several decades. Food waste typically degrades more quickly than other MSW comp onents like wood and paper wastes. The time scale of MSW degradation is also affected by the climate, with faster degradation occurring in moist, warm climates. It is generally estimated that half of the biogenic carbon disposed of in an MSW landfill will not degrade and will remain sequestered in the landfill. The time scale for composting MSW is on the order o f 1 month. The time scale for MSW combustion is very short, on the order of minutes.

• Alternate fate pathways: Landfill gas generated as a result of the degradati on of MSW in a landfill will generally contain about 50% methane a nd 50% CO 2 (by volume, dry basis). For landfills with no gas collection system, this landf ill gas will be emitted to the atmosphere. For landfills with gas collection and combustion sy stems, a significant portion of the methane in the landfill gas can be converted to CO 2 prior to release into the atmosphere. Composting can be used as an alternative to MSW lan dfilling, particularly for food and yard wastes. Degradation of MSW in composts is primarily aerobic, but methane emissions occur as a result of anaerobic pockets that develop withi n the compost pile. Direct combustion ofNovember 2014 D-16

MSW is another alternate pathway; essentially all o f the carbon in MSW is converted and released as CO 2 ,

• Land use/land use management changes : Not applicable.

• Leakage: Not applicable.

• Storage and handling losses . Loss of MSW due to storage or transport of the MS W prior to receipt at the centralized treatment location is no t considered. For example, only that portion of MSW as received at the landfill is consi dered in the methodology. All emissions from “storage” of the waste at an MSW landfill are considered part of the emissions source, whether the emissions are captured for combustion o r uncaptured and released to the atmosphere. Storage of the waste at an MSW combusto r facility is assumed to have negligible emissions because of the relatively shor t on-site storage times and is not specifically considered in the methodology.

3.3.2. Animal Agriculture Wastes
Livestock manure, litter, and manure wastewater are typically treated in a manure management system that stabilizes and/or stores wastes in one or more of the following system components: uncovered anaerobic lagoons, liquid/slurry systems with and without covers (including but not limited to ponds and tanks), storage pits, digester s, solid manure storage, dry lots (including feedlots), high-rise houses for poultry production (poultry without litter), poultry production with litter, deep bedding systems for cattle and swine, manure composting, and aerobic treatment units. International convention considers all carbon in an imal agriculture waste to be biogenic (IPCC, 2006). Decomposition of the manure can occur throug h anaerobic or aerobic decomposition. Some manure management systems combust CH 4 from anaerobic treatment.

• Time scale over which feedstock carbon sequestratio n and emissions occur: Animal agriculture waste degradation typically occurs over several weeks to several months.

• Alternate fate pathways: Animal agriculture waste degradation typically gene rates predominately CO 2 (for aerobic systems) or a mixture of CO 2 and CH 4 (for anaerobic, facultative, or anoxic systems), depending on the t ype of manure management system used. When anaerobic treatment systems are used, the CH 4 in the biogas can be collected and combusted to CO 2 . For dry animal agriculture wastes, direct combust ion of the manure is an alternative treatment option, which will convert an d release the biogenic carbon as CO 2 emissions.

• Land use/land use management changes : Not applicable.

• Leakage: Not applicable.

• Storage and handling losses: Most manure treatment occurs on site, and the meth odology considers all emissions from the storage or treatme nt of the manure, whether the emissions are captured for combustion or uncaptured and relea sed to the atmosphere. When centralized treatment is used, loss or degradation of animal agriculture wastes due to storage or transport prior to receipt at the centra lized treatment location is not specifically considered; the methodology primarily considers onl y the quantity of waste as received at the centralized treatment location. Storage of the manure prior to direct manureNovember 2014 D-17

combustion is assumed to have negligible emissions due to the relatively short on-site storage times and is not specifically considered in the methodology.

3.3.3. Wastewater
Wastewater is typically treated through processes t hat treat or remove pollutants and contaminants, such as soluble organic matter, suspe nded solids, pathogenic organisms, and chemical contaminants, from wastewater prior to its reuse or discharge from the facility. Sources include municipal and industrial wastewater treatme nt facilities. International convention considers all CO 2 generated as a result of aerobic wastewater treatm ent to be biogenic (IPCC, 2006). Some wastewater treatment facilities use anaerobic processes, which results in CH 4 emissions; some facilities capture and combust CH 4 derived from anaerobic digestion.

• Time scale over which feedstock carbon sequestratio n and emissions occur: Wastewater treatment processes degrade organic matter over a t ime scale of a few hours to a few days, although some large surface impoundments can have r esidence times as long as several months.

• Alternate fate pathways: Aerobic wastewater treatment processes convert the degradable organic matter almost entirely to CO 2 ; anaerobic, wastewater treatment processes convert approximately 50% or more of the organic carbon to CH 4 ; and facultative or anoxic wastewater treatment processes produce CO 2 predominately, but also produce appreciable amounts of CH 4 . Gas generated in anaerobic wastewater treatment s ystems can be collected and combusted to convert the CH 4 in the biogas to CO 2 prior to release into the atmosphere.

• Land use/land use management changes : Not applicable.

• Leakage: Not applicable.

• Storage and handling losses: Most wastewater treatment operations occur on site , and the methodology considers all emissions from the storag e or treatment of the wastewater, whether the emissions are captured for combustion o r uncaptured and released to the atmosphere. When centralized treatment is used, los s or degradation of degradable carbon in the wastewater due to storage or transport prior to receipt at the centralized treatment location is not specifically considered; the method ology primarily considers only the quantity of wastewater as received at the centraliz ed treatment location.


## 4. Other Possible Feedstock Categories

4.1. Secondary Use Feedstocks
Secondary use feedstocks are feedstocks that leave the stationary source where the original biogenic feedstock material is transformed into a p roduct or by-product (i.e., primary stationary source) that is used for energy production at a dif ferent stationary source (i.e., secondary stationar y source). For example, if a secondary stationary sou rce chooses to use for energy an agriculture- or forest-derived industrial processing product such a s distillers grains or woody residuals from a primary stationary source, the net biogenic emissio ns value (landscape and process attributes from the original feedstock at the primary source) for t he biogenic feedstock carbon of that materialNovember 2014 D-18

could be used at the secondary entity. Hypothetical ly, the same treatment could be used in the case of energy products such as pellets or ethanol used for energy at a secondary stationary source.
Secondary use feedstocks could be addressed in many different ways, and different policy applications of the framework may necessitate certa in treatments. One consideration when applying the framework in specific policy contexts is how to avoid possible instances of doublecounting landscape and process attribute values as they relate to biogenic materials used or processed at the primary stationary source and tran sferred for use at a secondary stationary source. For example, counting total biogenic feedst ock attributes values at both the primary and secondary stationary sources could result in double -counting these values. For a more detailed example, see Appendix F. Evaluation of all the diff erent possible policy treatments for secondary feedstocks is outside the scope of this report.



### 4.2. Feedstock Imports and Exports
International feedstock production and the importat ion of those feedstocks can significantly affect overall biogenic feedstock resource availability in the United States and demand pressures on those resources. The pricing and flow of feedstocks and r elated commodities have the potential to significantly affect domestic supply chains, and, c onversely, U.S. biogenic feedstock production can affect international commodity markets and land use activities. The framework could either include or exclude international biogenic feedstocks, depen ding on policy requirements and international agreements related to GHG emissions accounting. How ever, decisions as to the inclusion/exclusion of international feedstocks and the treatment of su ch feedstocks if included would depend on the specific application of the framework. The general framework description and illustrative examples given in this report do not address the export of U .S. feedstocks or the import of feedstocks produced abroad.



### 4.3. New, Unconventional, or Otherwise Unanticipated Feeds tocks
The framework is designed to be flexible so it can be modified as needed to be applicable to nearly all domestic biogenic feedstocks currently in use o r under consideration for bioenergy production. However, new and unconventional or otherwise unanti cipated feedstocks may emerge over time. Feedstock categorization in the framework should be broad enough that any feedstocks not already included can fit into the predefined categories if possible and if not, new categories could be made. The current feedstock categories are structured wit h this in mind, though some emerging feedstocks (e.g., algae) will require additional pa rameters that could be added on an as-needed basis.
For purposes of this report, biogenic feedstocks ha ve been classified broadly into the feedstock categories identified above based on the physical a ttributes those feedstocks possess. This categorization does not represent a formal or legal definition, nor does it intend to replace any existing legal definitions. For example, under exis ting regulations, certain feedstocks are already regulated using specific definitions. Thus, althoug h tire-derived fuel might fall under the wastederived feedstock categorization in the framework p resented here because of its attributes relativeNovember 2014 D-19

to biogenic CO 2 accounting, it is classified as a fuel under other policy applications. The same might be true for other feedstocks.


## 5. References

Abt, R. C., & Abt, K. L. 2013. Potential Impact of Bioenergy Demand on the Sustain ability of the Southern Forest Resource. Journal of Sustainable Forestry, 32, 175-194. Afzal, M., A. Bedane, S. Sokhansanj, and W. Mahmood . 2010. Storage of comminuted and uncomminuted forest biomass and its effect on fuel quality. BioResources, 5(1):55-69. Becker, D. R., Skog, K., Hellman, A., Halvorsend, K . E., & Mace, T. 2009. An outlook for sustainable forest bioenergy production in the Lake States. Energy Policy, 37, 5687-5693. Collins, M., D. Dirtsch, J. C. Henning, L. W. Turne r, S. Isaacs, and G. D. Lacefield. 1997. Round Bale Hay Storage in Kentucky . AGR-171, Kentucky Cooperative Extension Service.
DOE. 2011. U.S. Billion-Ton Update : Biomass Supply for a Bioenergy and Bioproducts Indu stry . U.S. Department of Energy. R.D. Perlack and B.J. Stokes (Leads), ORNL/TM-2011/224. Oak Ridge National Laboratory, Oak Ridge, TN.
EIA. 2011. Annual Energy Review 2011 . Figure 10.1 Renewable Energy Consumption by Major Source. Washington, DC: U.S. Energy Information Adm inistration. http://www.eia.gov/totalenergy/data/annual/pdf/aer. pdf.
EPA. 2010a. Renewable Fuel Standard Program (RFS2) Regulatory I mpact Analysis . Washington, DC: U.S. Environmental Protection Agency. EPA 420-R-10- 006. Washington, DC: U.S. Environmental Protection Agency. http://www.epa.gov/otaq/renewabl efuels/420r10006.pdf.
EPA. 2010b. Methane and Nitrous Oxide Emissions from Natural So urces . EPA 430-R-10-001. Washington, DC: U.S. Environmental Protection Agenc y. http://www.epa.gov/nitrousoxide/pdfs/Methane-and-Ni trous-Oxide-Emissions-From-NaturalSources.pdf
EPA. 2013. Municipal Solid Waste Generation, Recycling, and Di sposal in the United States: Facts and Figures for 2011 . Washington, DC: U.S. Environmental Protection Ag ency. http://www.epa.gov/epawaste/nonhaz/municipal/msw99. htm

. Galik, C. S., Abt, R. C., & Wu, Y. 2009. Forest biomass supply in the Southeastern United St ates -- implications for industrial roundwood and bioenergy production . Journal of Forestry, 107, 69-77. Jirjis, R. 1995. Storage and drying of wood fuel. Biomass and Bioenergy, 9:181-190. Huhnke, R.L. 2006. Round Bale Hay Storage. BAE-1716. Oklahoma Extension Service.
IPCC. 2006. 2006 IPCC Guidelines for National Greenhouse Gas In ventories , edited by L.B.H.S. Eggleston, K. Miwa, T. Ngara, and K. Tanabe. Kanaga wa, Japan: National Greenhouse Gas Inventory Programme, Intergovernmental Panel on Cli mate Change, IGES. Lundmark, R. 2006. Cost structure of and competition for forest-based biomass . Scandinavian Journal of Forest Research,, 21, 272-280. Murray, B.C., B.A. McCarl, and H.-C. Lee. 2004. Est imating leakage from forest carbon sequestration
programs. Land Economics, 80 (1):109-124.November 2014 D-20

Searchinger, T.D., S.P. Hamburg, J. Melillo, W. Cha meides, et al. 2009. Fixing a critical climate accounting error. Science, 326 (5952):527-528. Shinners, K.J., B.N. Binversie, R.E. Muck, and P.J. Weimer. 2007. Composition of wet and dry corn stover harvest and storage. Biomass & Bioenergy, 31:211-221. Skog, K.E. 2008. Sequestration of carbon in harvest ed wood products for the United States. Forest Products Journal, 58:56-72. Thornqvist, T., and R. Jirjis. 1990. Changes in Fuel Chips during Storage in Large Piles , Report No. 219. Uppsala, Sweden: Swedish University of Agricul tural Sciences, Department of Forest Products. Turner, D.P., J.J. Lee, G.J. Koerper, and J.R. Bark er, editors. 1993. The Forest Sector Carbon Budget of the United States: Carbon Pools and Flux under Alte rnative Policy Options . EPA/600/3-93/093. U.S. Environmental Protection Agency, Environmental Research Laboratory, Corvallis, OR. Turner, D.P., G.J. Koerper, M.E. Harmon, and J.J. L ee. 1995. A carbon budget for forests of the conterminous United States. Ecological Applications , 5:421-436.
USDA Forest Service. 2007. Forest Resources in the United States

. http://www.fs.fed.us/nrs/pubs/gtr/gtr_wo78.pdf

. U.S. Department of Energy. 2011. U.S. Billion-Ton U pdate: Biomass Supply for a Bioenergy and Bioproducts Industry. R.D. Perlack and B.J. Stokes (Leads), ORNL/TM-2011/224. Oak Ridge National Laboratory, Oak Ridge, TN.November 2014 D-21



## 6. Addendum: Spent Pulping Liquor—Overview of Processe s and Possible Alternate Fates

6.1. Joint Production of Industrial Products and By-pro ducts
Some industries may produce by-products useful for bioenergy generation in the process of making their primary market products. For example, manufac turers may generate agricultural by-products such as shells, husks, and cobs that have little or no market value and may be disposed of if not used for energy. A second example is kraft pulp mills, w hich generate black liquor that is burned on site to recover chemicals for reuse in the pulping proce ss as well as to produce energy. Other than for on-site use within the pulp mill (i.e., captive use within the mill), black liquor has no commercially feasible alternative use. Unlike by-products in oth er industries, black liquor is not only limited in commercially viable alternative uses, but it also h as limited disposal options (Gaudreault et al., 2012).
Forest products, in general, are characterized by a joint production function, because many products can be produced from a single tree. Firms strive to optimize production to maximize the amount of high-value products (e.g., saw lumber, pa per) and minimize the amounts of low-value products (e.g., black liquor). Although there is so me responsiveness to relative price movements (e.g., higher demand and prices for wood pellets ma y lead to an increased proportion of scrap going to this use and a decreased proportion going to par ticleboard), the elasticity of transformation between outputs may be very inelastic, and even wit h a negative price, some low-value products would still necessarily be produced as a by-product of the production of high-value products (e.g., sawdust, black liquor).
When estimating the landscape biogenic emissions ou tcome from biomass production and usage, the SAB Panel advocated the use of a future anticip ated baseline approach that would capture additionality—“i.e., the extent to which forest car bon stocks would have been growing or declining over time in the absence of harvest for bioenergy.” Capturing additionality requires that the framework model “a ‘business as usual’ scenario alo ng some time scale and compare that carbon trajectory with a scenario of increased demand for biomass” (Swackhamer and Khanna, 2011). Because of the joint-production nature of the fores t products industry, care needs to be taken in how a “scenario of increased demand for biomass” is created.
In a partial equilibrium framework, there are diffe rent options for simulating an increase in demand for a biogenic feedstock relative to a “busi ness as usual” case. One option is to introduce into, or shock, a model with X additional tons of production of a specific biogen ic feedstock, which will likely result in increased production of all t he other products that are jointly produced with that bioenergy feedstock. The landscape effects ass ociated with increased production of the specific biogenic feedstock would be conflated with the effe cts of the increased production of other jointly produced products. Another option is to shock a mod el with an increased price for the specific biogenic feedstock of interest (mechanically, this could be achieved in the model with a subsidy for the specific feedstock). If the feedstock of intere st is jointly produced as a by-product from the production of other products, the increase in price for the specific feedstock is not likely to increa seNovember 2014 D-22

production of or increase procurement of raw materi als to generate that by-products-based biogenic feedstock. For black liquor, it would be e xpected that a model run that increased the demand for and price of black liquor explicitly wou ld result in very little change in forest harvest and land use decisions, because even a large increa se in the price for black liquor would have a small impact on the value of the overall product mi x.

For residues and materials diverted from the waste stream, the SAB Panel endorsed considering their alternate fates (e.g., some forest residues m ay be burned if not used for bioenergy, wastederived materials might be otherwise landfilled) an d information about decay (e.g., using decay functions to evaluate ecosystem carbon storage in f orest residues not burned for energy or disposal). Furthermore, in the case of waste-derive d materials, the SAB stated that “after calculating decay rates and considering alternate fates, includ ing avoided methane emissions, the agency may wish to declare certain categories of feedstocks wi th relatively low impacts as having a very low [biogenic accounting factor], or setting [biogenic accounting factors] equal to 0 or possibly negative values in the case where methane emissions are avoi ded” (Swackhamer and Khanna, 2011). In terms of net atmospheric contributions of biogenic CO 2 e 4 emissions, as shown in the following sections of this addendum, it is more beneficial th at black liquor is burned for on-site energy use and chemical recovery because black liquor has no o ther commercially viable alternative uses and no practical disposal options. It is also unlikely that changes in demand for or prices of black liquo r would lead to changes in land use, harvest, or fore st management decisions because black liquor is not produced for its value alone but is only produc ed as a by-products of manufacturing high-value pulp for use in papermaking.
The purpose of this addendum is to provide backgrou nd information on the chemical pulping process leading to generation of black liquor and t o explore hypothetical alternate fates of black liquor in the context of biogenic CO 2 e accounting and avoided emissions. The information in this appendix, including example calculations of alterna te fate-related biogenic emissions, supports that a 0 or negative assessment factor for black liquor may be reasonable. This finding is based on the joint function production rationale presented above ; the related expectation that there would not be any perverse outcomes with respect to land use, harvest, or forest management decisions; and an analysis of hypothetical potential alternate fat es and related avoided emissions.



### 6.2. Overview of Pulping Processes
The pulp and paper industry consists of facilities that manufacture pulp and/or paper. Pulp is the fibrous raw material for papermaking (Smook, 2002). Pulp is manufactured using either chemical or non-chemical pulping processes. Paper can be man ufactured at mills that also produce virgin pulp or at mills that do not produce pulp but inste ad purchase pulp or use recycled fiber to manufacture paper. Some mills produce only market p ulp to sell to other mills and do not manufacture paper.

4 This addendum generally uses CO 2 e in the context of biogenic emissions because both CO 2 and CH 4 are specifically discussed.November 2014 D-23

Different processes are used for pulp production. K raft pulping is by far the most common pulping process used by plants in the U.S. for virgin fiber . The kraft pulping process produced approximately 86% of all U.S. pulp tonnage in 2010. Non-chemical pulping processes are also used in the U.S., including mechanical pulping and secon dary (recycled) fiber pulping. Non-chemical processes do not produce spent pulping liquor. Appr oximate percentages of U.S. pulp production for other processes in 2010 were sulfite pulping (1 %), semi-chemical pulping (6%), and mechanical pulping (8%) (RISI, 2011). Thus, the remainder of t his addendum focuses on the kraft pulping
process.
Chemical (i.e., kraft, soda, and sulfite) pulping i nvolves “cooking” of raw materials (e.g., wood chip s) using aqueous chemical solutions and elevated tempe rature and pressure to extract pulp fibers. The kraft pulping process uses an alkaline cooking liquor (known as “white liquor”) of sodium hydroxide (NaOH) and sodium sulfide (Na 2 S) to digest wood, while the similar soda process u ses only NaOH to digest the wood. The cooking liquor in the sulfite pulping process is an acidic mixture of sulfurous acid (HSO 3 ) and bisulfite ion (HSO 3 - ). The bases used in cooking liquor preparation are typically calcium, magnesium, and sodium. Semi-chem ical pulping uses a combination of chemical and mechanical (i.e., grinding) energy to extract p ulp fibers. The chemical portion (e.g., cooking liquors, process equipment) of the pulping process and pulp washing steps are very similar to kraft and sulfite processes.

For economic and environmental reasons, chemical an d semi-chemical pulp mills employ chemical recovery processes to reclaim spent cooking chemica ls. Typically, a combustion unit (e.g., recovery furnace) is used to recover the cooking chemicals f rom spent cooking solutions (or liquors). Kraft and soda mills have an additional chemical recovery process in which a lime kiln is used to regenerate a portion of the chemical cooking soluti on. In addition to spent pulping liquor, other byproducts such as turpentine, soap, and tall oil may be produced during the kraft pulping process and are typically sold commercially.



### 6.3. Generation of Pulp and Black Liquor
Wood is the predominant raw material used for pulp and papermaking in the U.S. Following wood input procurement and handling operations, digestio n of wood chips is the first step in kraft pulping. As shown in Figure D-1, the kraft digester has two primary products: pulp and black liquor. About half of the wood input to the kraft pulping p rocess (digester) is dissolved into the solution of spent pulping chemicals to form weak black liquor. The weak black liquor is separated from the pulp by washing and is concentrated in evaporators and sent to the kraft recovery furnace where inorganic pulping chemicals are recovered for reuse and dissolved organics (e.g., lignin) are burned for fuel to make steam and electricity.November 2014 D-24

Figure D-1. Products of the Kraft Mill Digester (Tran and Vakkilainnen , 2008).
The amount of wood input to the pulping process tha t becomes wood fiber in the digester is referred to as pulp yield. The remainder of the woo d can generally be assumed to partition to the black liquor.
The yield of pulp (expressed as a percentage by wei ght on a moisture-free basis) obtained from a given species of wood is influenced by the severity of the pulping process used. A yield figure of 50% means that 1 ton of dry wood yields 0.5 tons of dry pulp. 5 Mechanical pulping processes have yields of 90 to 95%, while chemical processes have yields of 40 to 55%, and semi-chemical processes have yields of 50 to 80%. Typical pulp yi elds for the kraft process are 40 to 50% (Smook, 2002). The lowest yield is obtained from drastic ch emical digestion that gives pulp consisting of nearly pure cellulose fibers. The yield of pulp obt ained by digesting wood also depends on the chemical composition of the wood. Because the princ ipal chemical components of the normal roundwood of most species do not vary much in amoun t, the percentage yield of pulp obtained by a given process does not vary greatly from one specie s to another. The chemical composition of wood, and consequently the yield of chemical pulp, generally varies more between softwoods (coniferous woods) and hardwoods (broadleaf woods) as classes than between the individual woods within these classes (USDA, 1980).
Black liquor solids (BLS) refers to the dry weight of the solids in the black liquor that enters the chemical recovery furnace. BLS contain the spent co oking chemicals (inorganics) and dissolved organics. The BLS exiting the washer in the weak bl ack liquor are sent for further processing in the kraft recovery system, which regenerates the inorga nic pulping chemicals, burns the dissolved organics for energy production, and sometimes resul ts in the recovery of other organic byproducts. Weak black liquor exiting the washing pro cess typically contains 13 to 17% BLS (Smook, 2002). Weak black liquor is evaporated and concentr ated to 65 to 80% solids prior to burning in the recovery furnace.
A nominal value of 1.6 tons of BLS per air-dried sh ort ton of pulp (ADTP) is often used to represent BLS production, though this value ranges from appro ximately 1.3 to 1.9 ton BLS/ton pulp (1,300 to

5 Note that commercial pulp production rates are usu ally referred to in “air dried” units, which are ge nerally considered to have a moisture content of 10%. “Mois ture-free” or “bone-dried” mass refers to pulp or w ood at 0% moisture.November 2014 D-25

1,900 kg solids/metric ton of pulp) (NCASI, 2011). The heating value of black liquor ranges from 5,400 to 6,600 btu/lb BLS (NCASI, 2011).
The chemical composition of black liquor varies bas ed on its solids content. The solids alone comprise a complex mixture of both inorganic and or ganic constituents. The inorganic constituents in black liquor are derived from the cooking liquor and comprise various sodium and sulfur compounds, including NaOH, sodium sulfate (Na 2 SO 4 , also known as “salt cake”), Na 2 S, sodium thiosulfate (Na 2 S 2 O 3 ), sodium carbonate (Na 2 CO 3 ), and sodium chloride (NaCl). Collectively, inorganic salts constitute between 18 and 25% of th e solids in black liquor.
The organic compounds found in black liquor are der ived from wood. They are either (1) natural wood extractives (or their reaction products) that are released as a result of the pulping process or (2) materials formed through the reactions of the p ulping chemicals with the lignin or cellulose components of wood. Therefore, the compounds can be classified as lignin derived, cellulose derived, or extractives derived. Typical content ra nges in kraft liquor are:

• Lignin derived (39 to 54%); primarily consisting of polyaromatic macromolecules with lesser amounts of molecular weight alcohols, aldehy des, and simple phenolic compounds such as phenol, p-methyl phenol, catechol, and guai acol;

• Cellulose derived (25 to 35%); primarily a mixture of carboxylic acids such as formic, acetic, glycolic, lactic, and glucoisosaccharinic; and

• Extractive derived (3 to 5%); primarily resin acids and fatty acids that are converted to salts at the high pH of the mixture.
In sum, spent pulping liquor can have hundreds of c onstituents (AF&PA, 2001). The exact composition depends on wood type, the concentration of the components in the white liquor used to digest the wood chips, and the actual process pa rameters. Information on different estimates of the elemental composition of black liquor is shown in Table D-2.

Table D-2. Elemental Composition of Black Liquor (W eight % of BLS).

Element TAPPI (Clay, 2008) GA Tech (IPST, Undated) EPA (EPA, 1997 ) Carbon, C 35 34–39 35.2 Hydrogen, H 3.3 3–5 3.6 Oxygen, O 35.7 33–38 35.2 Sodium, Na 19.7 17–25 19.2 Sulfur, S 4 3–7 4.8 Potassium, K 1.6 0.1–2 1.0 Chloride, Cl Unspecified 0.2–2 0.1 Nitrogen, N Unspecified 0.04–2 Unspecified Others, including non-process elements (Ca, Al, Si, Fe) <1 0.1–0.3 0.2

Carbonate, CO 3 8 Included in C and O above Sulfate, SO 4 3 Included in S and O aboveNovember 2014 D-26



### 6.4. Biogenic CO 2 

### Emissions from Kraft Black Liquor Chemical Recover y
To assess biogenic CO 2 emissions associated with the kraft pulping proces s, it is helpful to understand how biogenic CO 2 emissions are currently estimated for kraft pulp m ills. Carbon originating in the wood input into the pulping proc ess primarily apportions to the pulp product and black liquor, as shown in Figure D-1 above.
The kraft chemical recovery process can be depicted by two interconnected loops, the sodium loop and calcium loop, as shown in Figure D-2. In the kr aft pulping and chemical recovery process, biomass carbon from the wood is dissolved and eithe r emitted as biomass CO 2 from the recovery furnace or captured in sodium carbonate (Na 2 CO 3 ) in the smelt discharged from the bottom of the recovery furnace. In the process of converting the Na 2 CO 3 into new pulping chemicals, this biogenic carbon (i.e., the carbonate ion) is transferred to calcium carbonate (CaCO 3 ). In the lime kiln, the CaCO 3 is converted to calcium oxide (i.e., CaO or lime, a material used in the chemical recovery process) and biogenic CO 2 , which is released to the atmosphere (EPA, 2009).

Figure D-2. Simplified Representation of the Kraft Pul ping and Chemical Recovery System (EPA, 2009).
The majority of the wood-derived carbon within the black liquor either:

• Exits the pulping process as biogenic CO 2 emissions from the recovery furnace stack; or

• Reacts with sodium compounds to form Na 2 CO 3 in the smelt that exits the bottom of the recovery furnace as smelt.November 2014 D-27

The carbonate in the smelt makes its way through the chemical rec overy loop to the lime kiln (becoming CaCO 3 along the way). In the lime kiln, the CaCO 3 is converted to CaO, emitting the biogenic CO 2 originating from the wood in the black liquor. The red text in the simplified diagram below shows what happens to the wood-derived carbon (fossil CO 2 emissions from the recovery furnace and lime kiln are not shown).

Figure D-3. Simplified Diagram Showing How Biogenic CO 2 Emissions Are Emitted from Both Kraft Recovery Furnace and Lime Kiln.
The emission factors used to estimate biogenic CO 2 emissions from the black liquor chemical recovery process are based on the carbon content of black liquor and therefore account for biogenic CO 2 emissions from both the recovery furnace and lime kiln. Thus, rather than depicting the biogenic CO 2 accounting boundary around the recovery furnace as the sole biogenic CO 2 emissions unit, it would be more consistent with the current biogenic CO 2 emissions estimation practice (including that required under the U.S. EPA’s Green house Gas Reporting Program) to consider the biogenic CO 2 emissions unit as the entire pulping process.

Fossil-fuel-related CO 2 emissions are estimated separately for the recover y furnace and lime kiln. The only other non-biogenic carbon introduced into the process is from carbonated makeup chemicals, for which CO 2 emissions are estimated using a mass balance appro ach. Fossil-fuel and makeup chemical CO 2 emissions estimates are independent of the biogeni c CO 2 accounting method presented in this report and need not be discussed further in this document.



### 6.5. Alternate Pathways for Black Liquor
Consideration of alternate fate pathways for black liquor (as opposed to reuse within the kraft process) is purely hypothetical for U.S. mills beca use U.S. mills have taken steps to maximize recovery of black liquor. If black liquor is not re used within the pulping process and instead is Biogenic CO 2 Emissions from wood burning

Black liquor (mix of wood C and inorganics) Recovery furnace

Smelt containing Na 2 CO 3

created by reaction with the wood-burning CO 2 )

Chemical recovery ( Na 2 CO 3  Ca CO 3 ) Lime kiln ( Ca CO 3  CaO) Biogenic CO 2 from conversion of CaCO 3  CaONovember 2014 D-28

disposed of, disposal methods might involve inciner ation without the benefit of energy recovery or discharge of the black liquor in liquid form (e.g., weak black liquor) into a wastewater treatment system or lagoon. The benefits of recovering black liquor include:

• Energy value;

• Avoided cost of replacement chemicals, primarily eq uivalent saltcake;

• Reduction in biological oxygen demand load on the e ffluent treatment system; and

• Reduction in color and chemical oxygen demand (COD) discharge in the treated effluent (EPA, 1997).
For many reasons U.S. mills have opted to use chemi cal recovery furnaces as opposed to disposing of black liquor. Depending on its volume and concen tration, if released into the environment, black liquor can be odorous, toxic to aquatic life, and c ause a dark caramel color in water (EPA, 1997). Black liquor contains sulfur from the kraft pulping process, which results in malodorous total reduced sulfur emissions detectable via olfactory s enses in very low concentrations. Although the cellulosic constituents in black liquor may be biod egradable, lignin is very difficult to biodegrade, leaving a portion of the COD and much of the dark b rown color to be discharged to receiving waters following wastewater treatment. EPA has established Best Management Practice regulations to protect the environment from the negative consequen ces of spent pulping liquor spills (40 CFR 430.03, 430.28, and 430.58). These rules were promu lgated in 1998 as part of the effluent guidelines and standards for the pulp, paper, and p aperboard source category (40 CFR Part 430) developed under the Clean Water Act.
In the hypothetical alternate fate pathway examples below, equations from Appendix N of this document were used to estimate emissions from treat ment of black liquor sent for incineration without energy recovery or wastewater treatment. Th e black liquor is the biogenic feedstock in this example (as opposed to the wood input to the pulpin g process) because the black liquor (which is a complex mixture of organic and inorganic chemicals) differs from the wood input to the pulping process both chemically and physically and is gener ated within the pulping process. As explained in Appendix N, the following terms can be dropped from the biogenic assessment factor ( BAF ) equation when conducting an alternate fate analysis : Net feedstock growth on the production landscape ( GROW

); total net change in production site non-feedstoc k carbon pools ( SITETNC ); leakage associated with feedstock production ( LEAK ); the feedstock carbon losses during storage, transport and processing ( L ); and the feedstock carbon embodied in products ( P ). As a result, the assessment framework equation as applied to estimat ing biogenic CO 2 emissions from the alternate fate of black liquor feedstocks can be simplified t o:

BAF = AVOIDEMIT

AVOIDEMIT

represents the avoided biogenic emissions that cou ld have occurred per an alternative management strategy instead of the feedstock’s use in bioenergy production, relative to the feedstock’s use for bioenergy production. The AVOIDEMIT term, as applied to the black liquor biogenic feedstock, is expressed as:

 = 
 −  						 

 				November 2014 D-29

The AVOIDEMIT

term must be calculated for the specific feedstock being managed relative to a specific, alternative practice. A positive AVOIDEMIT value implies that use of the feedstock for bioenergy production contributes more emissions to the atmosphere than would have occurred under the alternative management strategy. A 0 valu e implies that both practices are equivalent in terms of how much emissions they contribute to the atmosphere. A negative value implies that using the feedstock for bioenergy production contri butes less emissions to the atmosphere than the alternative management practice.

The CO 2 e emissions in the AVOIDEMIT equation above include both CO 2 and methane (CH 4 ) resulting from each feedstock management alternativ e. The following subsections present calculations of CO 2 e emissions for the two hypothetical alternative ma nagement approaches.

6.5.1. Alternate Fate Scenario 1: Black Liquor Incineratio n without Energy Recovery
Table D-3 presents emission factors and calculated emissions for incineration of black liquor normalized per ADMT of pulp produced. The emissions from incinerating black liquor without energy recovery would be the same as the emissions from burning the material in a recovery furnace. The inorganic chemicals in the smelt produ ced from burning the black liquor would remain and could be recovered in either case. No em issions would be avoided by treating the black liquor through incineration, and the stack emission s would be about the same as combustion without energy recovery. Therefore, the resulting h ypothetical example BAF is 0.

Table D-3. AVOIDEMIT for Scenario 1 Where Black Liquor Is Incinerated Wi thout Energy Recovery.

Emissions Factors: CO 2 94.4 kg/MMBtu HHV (40 CFR 98, subpart AA) CH 4 0.0019 kg/MMBtu HHV (40 CFR 98, subpart AA) Process Parameters: 1.6 Ton BLS/ADTP (NCASI, 2011) 0.9072 ADMT pulp/ADTP (conversion factor for metric tons: short tons) 1.8 Ton BLS/ADMT pulp (calculated) 6600 Btu/lb BLS based on NCASI, 2011 range of 5,400 to 6,600 Btu/lb for BLS 13.2 MMBtu/ton BLS (calculated) CO 2 2.20 Metric tons CO 2 /ADMT pulp (calculated) CH 4 4.42E-05 Metric tons CH 4 /ADMT pulp (calculated) CH 4 GWP 25 (40 CFR 98, subpart AA) CO 2 e 2.199 Metric tons CO 2 e/ADMT pulp if the black liquor is burned AVOIDEMIT
numerator 2.199 Emissions from treatment alternative (inciner ation without energy recovery) AVOIDEMIT denominator 2.199 Emissions from burning black liquor for chemi cal and energy recovery, metric tons/ADMT pulp BAF = AVOIDEMIT 0 = 1− (emissions from treatment alternative) / (em issions from burning black liquor for chemical and energy recovery)November 2014 D-30

6.5.2. Alternate Fate Scenario 2: Black Liquor Decompositi on in a Wastewater Treatment System
The equations related to CO 2 and CH 4 emissions from wastewater treatment in Section 6.1 of Appendix N were used to evaluate two hypothetical w astewater treatment scenarios for the disposal of black liquor: (1) treatment in a deep a naerobic lagoon; and (2) treatment under aerobic conditions. Under both alternate pathway conditions (anaerobic and aerobic), emissions from treatment of black liquor as wastewater exceeded th ose from the current practice of burning black liquor for chemical and energy recovery. The result ing hypothetical example BAF varied from slightly negative (−0.09) to −1.2 depending on the wastewater management method, indicating that using the black liquor feedstock for bioenergy prod uction contributes less biogenic emissions to the atmosphere than the alternative wastewater manageme nt practice. Table D-4 presents the equation terms and calculated values for avoided emissions f rom wastewater treatment.

Table D-4. AVOIDEMIT for Scenario 2 Where Black Liquor Is Disposed Throug h Wastewater Treatment.

Equation Term Description Anaerobic Deep Lagoon Treatment Aerated Treatment Process with Anoxic Areas Input Values Q ww Wastewater influent flow rate 9.7 m 3 /ADMT pulp 1 9.7 m 3 /ADMT pulp 1 OD Oxygen demand of influent 92,700 mg/l 2 92,700 mg/l 2 EffOD Oxygen demand removal efficiency

of the biological treatment unit 0.75 3 0.75 3

MCF ww CH 4 correction factor (from

Appendix N, Table N-13) 0.8 0.3

BG CH4 Fraction of C as CH4 in generated

biogas (default is 0.65) 0.65 0.65

λ Sludge biomass yield (from

Appendix N, Table N-13) 0 0.45

GWP CH4 Methane global warming potential 25 25 Calculated Values CO 2WW CO 2 emission rate (metric tons

CO 2 /ADMT pulp) 0.45 0.41

CH 4WW CH 4 emission rate (metric tons

CH 4 /ADMT pulp 0.18 0.036

CO 2S CO 2 emission rate (metric tons

CO 2 /ADMT pulp) Not applicable (λ = 0) 0.34

CH 4S CH 4 emission rate (metric tons

CH 4 /ADMT pulp Not applicable (λ = 0) 0.03

AVOIDEMIT
numerator = CO 2WW +CO 2S +

(CH 4WW +CH 4S )*GWP CH4 4.8 2.4

AVOIDEMIT denominator Emissions from burning black liquor

for chemical and energy recovery, metric tons/ADMT pulp 2.2 2.2November 2014 D-31

Equation Term Description Anaerobic Deep Lagoon Treatment Aerated Treatment Process with Anoxic Areas BAF = AVOIDEMIT = 1− (emissions from treatment

alternative) / (emissions from burning black liquor for chemical and energy recovery) −1.2 −0.09

1 Based on typical industry parameters of 1.6 tons BL S/ADTP and assuming that weak black liquor is 15% s olids (i.e. 0.15 ton BLS/ton liquor) with a density of 1.1 g/cm 3 . Thus: 9.7 m 3 /ADMT pulp = (1.6 tons BLS/ADTP) x (ADTP/0.9072 ADM T) x (ton liquor/0.15 ton BLS) x (907185 g/ton liquor) x (cm 3 /1.1 g) x (m 3 /100 3 cm 3 )

2 Chemical oxygen demand for weak black liquor deriv ed from pine (Yang, 2003).

3 A relatively low oxygen demand removal efficiency of 75% was used considering the low biodegradabilit y of the lignin component in the wastewater stream.

6.5.3. Discussion
The two scenarios presented above illustrate that c urrent black liquor management practices (burning for energy and chemical recovery in a reco very furnace) result in the same or less emissions than the hypothetical alternate fate for black liquor (disposal via incineration or wastewater treatment). Black liquor is produced as a by-product from the pulping process and, under current market conditions, has no commerciall y viable alternatives other than use for chemical and energy recovery within the pulping pro cess. Because black liquor is jointly produced with other forest industry products (pulp productio n), black liquor management practices and increased demand and/or price for black liquor are likely to result in no to little change in land use
, harvest, and forest management decisions. The avoid ed emissions associated with disposal of black liquor as compared to the current management practi ce (burning for energy and chemical recovery in a recovery furnace) resulted in hypothetical exa mple BAFs ranging from different negative values to 0, depending on the treatment method. Bec ause of the joint production function rationale as well as the hypothetical alternate fate example calculations conducted above, an estimated BAF of 0 can be considered for black liquor and is cons istent with the approach suggested by the SAB Panel for materials diverted from the waste stream (Swackhamer and Khanna, 2011).



### 6.6. References for Addendum

AF&PA. 2001. High Production Volume (HPV) Chemical Challenge Pro gram Test Plan for Spent Pulping Liquor. American Forest & Paper Assocation. http://www.epa.gov/hpv/pubs/summaries/afpa/c12936.p df

. Clay, D. 2008. Evaporation Principles and Black Liquor Properties. Lake Oswego, OR: Jacobs Engineering. http://www.tappi.org/content/events/08 kros/handouts/3-1.pdf

. EPA. 1997. Technical Support Document for Best Management Prac tices for Spent Pulping Liquor Management, Spill Prevention, and Control. EPA-821-R-97-011. Washington, DC: U.S. Environmental Protection Agency. http://water.epa.gov/scitech/wastetech/guide/pulppa per/upload/1997_11_21_guide_pulppap er_jd_bmp_v2a.pdf

.November 2014 D-32

EPA. 2009. Technical Support Document for the Pulp and Paper S ector: Proposed Rule for Mandatory Reporting of Greenhouse Gases. Washington, DC: U.S. Environmental Protection Agen cy. http://www.epa.gov/ghgreporting/documents/pdf/archi ved/tsd/TSD%20Pulp%20and%20Pa per%202_11_09.pdf

. Gaudreault, C., B. Malmberg, B. Upton, and R. Miner . 2012. Life cycle greenhouse gases and nonrenewable energy benefits of kraft black liquor rec overy . Biomass and Bioenergy 46(0): 683-692.

IPST. Undated. Literature Values of Chemical Species, Elemental Co mposition and Heating Values of North American Black Liquors

. http://www.ipst.gatech.edu/faculty/ragauskas_art/te chnical_reviews/Black%20Liqour.pdf

. NCASI. 2011. Greenhouse Gas and Non-renewable Energy Benefits of Black Liquor Recovery. Technical Bulletin No. 984. Research Triangle Park, NC: Natio nal Council for Air and Stream Improvement, Inc. RISI. 2011. World Pulp Annual Historical Data. Smook, G. 2002. Handbook for Pulp & Paper Technologists. 3rd Ed. Bellingham WA: Angus Wilde Publications Inc. Swackhamer, D., and M. Khanna. September 28, 2011. SAB Review of EPA’s Accounting Framework for Biogenic CO 2 Emissions from Stationary Sources . EPA-SAB-12-011.
Tran, H., and E. Vakkilainnen. 2008. The Kraft Chemical Recovery Process

. http://www.tappi.org/content/events/08kros/manuscri pts/1-1.pdf

. USDA. 1980. Pulp Yields for Various Processes and Wood Species . Madison, WI: USDA Forest Products Laboratory. http://www.fpl.fs.fed.us/documnts/fplrn/fplrn031.pd f. Yang, W., H. Mu, and Y. Huang. 2003. Treatment of b lack liquor from the papermaking industry by acidification and reuse. Journal of Environmental Sciences, 15(5):697-700.