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Appendix D: Feedstock Categorization and Definitions 

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 By-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-products .......................................... 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 Feedstocks ................................................ D-18

5. References .................................................................................................................................................................. D-19

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

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

6.2. Overview of Pulping Processes ............................................................................................................... D-22

6.3. Generation of Pulp and Black Liquor .................................................................................................... D-23

6.4. Biogenic CO2 Emissions from Kraft Black Liquor Chemical Recovery .................................... D-26

6.5. Alternate Pathways for Black Liquor .................................................................................................... D-27

6.5.1. Alternate Fate Scenario 1: Black Liquor Incineration without Energy Recovery ..... D-29

6.5.2. Alternate Fate Scenario 2: Black Liquor Decomposition in a Wastewater Treatment 

System.... ................................................................................................................................................. D-30
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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 (Weight % of BLS)..................................................... D-25

Table D-3. AVOIDEMIT for Scenario 1 Where Black Liquor Is Incinerated Without Energy 

Recovery. ............................................................................................................................................................. D-29

Table D-4. AVOIDEMIT for Scenario 2 Where Black Liquor Is Disposed Through Wastewater 

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

List of Figures 

Figure D-1. Products of the Kraft Mill Digester (Tran 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 CO2 Emissions Are Emitted from Both Kraft 

Recovery Furnace and Lime Kiln. .............................................................................................................. D-27

1. Introduction 

The purpose of this appendix is to describe the categorization of biogenic feedstocks used in the 

assessment framework. A biogenic feedstock can be defined as any organic material originating 

from modern or contemporarily grown plants, animals, or microorganisms, excluding material 

embedded in geological formations or fossilized, that is used for combustion or product processes 

or otherwise decomposes at a stationary source. A multitude of feedstocks meet this definition, 

though some feedstocks are more commonly used for bioenergy than others. Feedstocks differ in 

physical properties; origin (including local climate and biogeochemical attributes); species; growth 

rates; management (from planting to harvesting); and whether they are deliberately raised as an 

energy feedstock or if they can be used for other purposes (e.g., human or animal consumption), are 

reclaimed wastes from other processes, or are salvaged 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 accounted 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 differently than a feedstock available only 

occasionally (e.g., short growing seasons, feedstocks that result from fire or insect infestation). 

This appendix first lays out the broad feedstock categorization used in the framework. It then 

discusses the various feedstock attributes of commonly used biogenic feedstocks and why certain 

feedstocks are grouped together. This appendix also generally discusses other feedstock categories, 

including secondary use feedstocks, imports, and emerging markets. The list of feedstocks included 

in this categorization is not exhaustive and may need modification per specific policy applications 

and/or as new feedstocks come into the biogenic feedstock market. The broad feedstock 

categorizations in this appendix are not intended to represent specific regulatory definitions that 

currently exist or that may need to be developed as part of policy applications of the framework.
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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 basic categories: 

1. Forest-derived feedstocks: biomass derived from natural forests, tree plantations, and wood 

products production processes; 

2. Agriculture-derived feedstocks: biomass derived from 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 are large enough to capture the important 

differences among feedstocks in terms of their biophysical 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, for 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 

Wastewater 
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3. Biogenic Feedstock Characteristics 

The feedstock categories are based on the key characteristics of feedstocks themselves as well as 

the feedstock source conditions that may lead to different net biogenic carbon-based emission 

profiles and thus merit different treatment under the framework. These characteristics generally 

include similarities and differences between feedstock growth and decay cycles, typical 

management and land use patterns associated with feedstock production, potential alternate 

market and carbon fate pathways, and other factors. More specifically, these characteristics include 

the following: 

• Time scale over which feedstock carbon sequestration 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 occurs over a much longer time (i.e., decades to 

hundreds of years). Although emissions to the atmosphere occur instantaneously during 

combustion, some emissions-associated feedstock losses (e.g., decay) or alternative 

pathways may take place over days, weeks, months, or even years during storage and 

handling. 

• Alternate fate pathways (assumptions about “What would have happened otherwise?”). 

Baseline assumptions can involve consideration of the 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 undisturbed to decompose if not used for energy, 

thereby emitting both CO2 and CH4, which is avoided when the feedstocks are combusted. If 

not used for energy, some feedstocks would otherwise 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 bioenergy production.

• Land use/land-use management changes. The cultivation and use of certain biogenic 

feedstocks can create market competition that stimulates 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 contribution from using the feedstock at a 

stationary source. 

• Leakage: The use of some feedstocks for bioenergy may have GHG emissions effects outside 

of the biogenic feedstock production assessment boundary caused by the biogenic feedstock 

production activities (e.g., replacement of diverted 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 significantly 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 feedstock into a 

bioenergy product may involve losses of the biogenic carbon during transportation, storage, 

and handling. These feedstock losses vary according to the feedstock type. 
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The following subsections discuss how different feedstock categories could be considered within 

the framework according to their different characteristics. 

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 production 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 competition 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 sawtimber markets, as few stems are left to grow into 

sawtimber size classes (Abt & Abt, 2013). The interaction 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, show that the assumed rate of logging residue 

recovery has a substantial influence on timber market response, and by extension, possible future 

changes to forest land management. 

In this section, characteristics of roundwood, logging residue, and forest-derived industrial 

products and processing by-product feedstocks are presented. 

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. Roundwood 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 sequestration and emissions occur. Roundwood 

feedstocks typically have a longer harvest cycle than agriculture-derived feedstocks like 

traditional crops or dedicated energy crops. Example harvest cycles for roundwood pulp 

and sawtimber production are about 11 to 15 years for pulpwood and 25 years for 

sawtimber grown on plantations in the southern United States and 45+ years for sawtimber 

in the Pacific Northwest. Note that the overall average 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 than energy, 

could lead to long-term carbon sequestration. For example, 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 pulp and paper products would 

generally have shorter sequestration time frames than more durable products) (Skog, 

2008). Additionally, roundwood use at stationary sources for the sole purposes of 

bioenergy production could detract from roundwood use 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, changes in demand for roundwood 

biomass, whether for bioenergy or other uses, can lead to changes in production, potentially 
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causing direct land use or land use management changes. Such changes, including, for 

example, shortening rotation ages/increasing harvest 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 could 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 pastureland 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 cropland). 

• Storage and handling losses: Roundwood biomass is often harvested, preprocessed, 

transported, and used within a matter of days or weeks, 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 which 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 matter loss, other things being equal. 

Accounting for forest-derived feedstocks like roundwood should cover losses in storage and 

material handling to provide a complete link between feedstock available at the source 

location and that used in the stationary source. 

3.1.2. Logging Residue 

Logging residues include biomass derived from harvest operations including treetops and nonmerchantable sections of the stem, branches, and bark left on the ground after logging. If not left to

decompose or open burned on site at the logging operation site, logging residues are often sent to 

sawmills or pulp and paper mills, though they are also 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 sequestration and emissions occur. If left in the forest, 

logging residues may be either burned or left to decay 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 deciduous trees will decompose within a 

couple of years, while conifer needles will often take several years. In general, the wetter 

the biomass on the forest floor, the faster these residues will break down. If not burned, 

non-merchantable large woody material would decay slowly in the forest, and its carbon 

 

1

 Traditional harvests (removing tree boles and leaving tops and limbs on site) in some instances may transition to 

more intensive practices such as whole-tree harvesting/chipping. In this presentation of the framework, whole-tree 

use is not attributed exclusively to the roundwood feedstock, because the practice also includes the harvest of what 

traditionally would have been left as residue. Thus, a whole-tree harvest can be viewed as removing two feedstocks: 

roundwood and logging residue. Thus, under the framework, whole trees could be divided into both roundwood and 

logging residue. 
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content in the forest can be estimated from sampling surveys. It can take several decades 

for pine logs with high resin content to fully decompose. 

• Alternate fate pathways: If left in the forest, logging residues may be either burned or left on 

site to decay over a period that can range from days to years (as discussed above), which 

can have different net biogenic contributions to the 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 structure, and soil conditions play 

significant roles in the abundance and merchantability of logging residues. For instance, 

hardwoods in general yield higher percentages in non-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 for energy production often requires the 

simultaneous harvest of more valuable wood (timber, pulpwood) to justify the cost of 

collecting the residue material. Under current market conditions, increased demand for 

logging residues for bioenergy production is unlikely 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 are collected as biogenic feedstocks for 

energy production, this management change could impact the soil carbon contributions to 

the harvest landscape and, conversely, remove the volume of woody matter decaying on the 

forest floor or being burned on site. 

• Leakage: Under current market conditions, there are no commercial alternative markets for 

logging residues and thus few pathways for increased logging residue removal inspire 

leakage effects such as indirect land use change. However, 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 leakage could potentially occur.

• Storage and handling losses. As noted above, to the extent that forests are harvested and 

used on a fairly continuous year-round basis with only days, possibly weeks, between 

harvest and use, there will tend to be relatively little storage and handling loss. However, 

the longer storage is required, the greater dry matter loss will occur, other things being 

equal. Within forest-derived feedstock types, logging residues are more likely to experience 

feedstock losses during transport, storage, and handling 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 By-products 

Usual practices within the forest industry generate a wide variety of forest industrial products and 

processing by-products. These by-products include liquids such as black liquor from the pulping 

process and mill residues such as bark, shavings, sawdust, sanderdust, hog fuel, and unusable bole 

components (due to knots, holes, etc.).2 Consideration of forest-derived industrial processing 

 

2

 Forest products are characterized by a joint production function, as any products are produced from a single tree. 

Forest product industrial entities will try to optimize production to maximize the amount of high-value products 
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products and by-products should include assessment of whether these materials have current 

alternative market uses to bioenergy or not. Most residues 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 uses 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 sawmills are well established. Sawdust and shavings 

may be used in composite wood products such as particleboard, 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 mill 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 site 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 effects 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-product with no current alternative market use is 

spent pulping liquor. Spent pulping liquor (e.g., black 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 mill 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, combustion without energy). When evaluating 

black liquor combustion on site for energy versus possible alternates fates (disposal and potential 

CH4 and CO2 emissions from decay), black liquor combusted for on-site energy is expected to have 

less net atmospheric biogenic CO2 contributions. Also, because black liquor production is 

contingent on paper production and related paper market demand and prices, it is therefore 

unlikely that changes in demand for or prices of black 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 for other industrial processing by-products with no 

current alternative market uses. More information and analysis on black liquor can be found in 

Addendum A to this appendix. 

• Time scale over which feedstock carbon sequestration and emissions occur: For this feedstock 

category, the analysis of the time scale for feedstock-related carbon fluxes will depend on 

the feedstock and landscape attributes and/or alternate paths associated with the feedstock 

(e.g., the feedstock production site and the alternate 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., higher demand and prices for wood pellets may lead to an 

increased proportion of scrap going to this use and a decreased proportion going to particleboard), the elasticity of 

transformation between outputs may be very inelastic, and even with 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). 
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• Alternate fate pathways: The alternate fate of forest-derived industrial products and 

processing by-products can vary widely per feedstock (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 be used for energy if there is a highervalue use (e.g., as raw material for pulping or composite 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 uses, the alternate fate pathways could 

include use for energy (e.g., as boiler fuel) and disposal (e.g., through non-energy-related 

burning, landfilling, on-site storage), which might include decay causing CH4 and CO2

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 and processing by-products 

increases for energy use, leakage could occur if these 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 matter loss will occur, other things being equal. 

Within forest-derived feedstock types, industrial products and process by-products are 

more likely to experience feedstock losses during storage 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 below). 

3.2. Agriculture-derived Feedstocks 

Although the majority of biogenic feedstocks that have been used for energy generation in the 

United States to date are derived from forest materials, there is potential for large-scale use of 

agricultural feedstocks as well. Traditional agricultural crops that have historically been grown for 

food, feed, and fiber could be used as bioenergy feedstocks, as could crop residues, dedicated 

energy crops, or industrial products and processing by-products. This section describes 

characteristics of these agricultural feedstocks, separating them into three categories: (1) crops 

grown primarily for bioenergy use, whether conventional or dedicated energy crops; (2) crop 

residues; and (3) agricultural-derived industrial products and processing by-products. 

3.2.1. Conventional Agricultural Crops 

The conventional agricultural crops category includes feedstocks from crops traditionally grown 

for food, feed, textile, or other uses, such as corn and soybeans. These crops can be converted at 

stationary sources into conventional starch-based fuels, electricity, biodiesel, and cellulosic fuels.

Use of these feedstocks in bioenergy production could result in changes in their production, price, 

and trade and potentially result in direct and/or indirect land use change. Crops for which only the 
November 2014 D-10 

processing by-products from a multiproduct processing activity (e.g., soybean oil, rice hulls) are 

used for bioenergy are covered under the agriculture industrial processing by-products 

subcategory below. 

• Time scale over which feedstock carbon sequestration 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. Even though the net atmospheric biogenic 

contribution from the growth and harvest of the feedstock itself is in balance, other factors 

such as land use management and land use changes and related soil carbon effects can affect 

the overall assessment outcome. 

• Alternate fate pathways: If conventional crops are not used for bioenergy, they 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 biomass can lead to changes in cropping 

patterns, and production practices (e.g., intensification) can lead to changes in GHG 

emissions (e.g., impacts on soil carbon levels). 

• Leakage: Leakage effects related to conventional crops for energy purposes can be 

substantial. The new or diverted production of feedstocks can affect commodity markets 

and thus lead to changes in production that alter land uses and land use management 

outside of the bioenergy feedstock supply chain (Murray 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 outside of the bioenergy supply chain could 

become managed or be managed differently to meet the 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 processed before 

they can be used for energy, which can lead to low levels of decomposition or physical 

feedstock losses. Additionally, because of their seasonal 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 forest 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, wheat straw, and rice straw, can be collected for 

conversion or combustion at stationary sources to generate electricity and cellulosic fuels. These 

residues are traditionally tilled into the soil, providing nutrients for the next planted crop. However, 

crop residue management changes, such as the removal of residues that would otherwise remain 

on the field or be open burned, result in impacts on soil conditions (e.g., increased erosion) as well
November 2014 D-11 

as soil carbon levels (e.g., lower carbon inputs to the soil). In addition, in some instances (e.g., the 

removal of corn stover) there may also be a loss of nitrogen in the soil. In such cases, to address this 

loss of soil nitrogen following the removal of corn stover, additional fertilizer may be added to 

ensure continuing yields of the main corn crop. Thus, additional N2O emissions may be incurred as 

a result of residue removal. 

• Time scale over which feedstock carbon sequestration and emissions occur: Crop residues are 

generated on an annual basis when crops are harvested, with subsequent decomposition 

taking place over a period of months or years depending on production practices and 

environmental conditions. 

• Alternate fate pathways: Agricultural residues, like forest residues, would decay, emitting 

CO2 and CH4, and make small contributions to soil carbon if they are not removed for 

bioenergy or other uses. Removing residues may increase 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 removing agricultural residues from the 

landscape and using agricultural processing by-products, because land use management 

changes can affect soil GHG fluxes. 

• Leakage: In addition, to the extent that a market develops for crop residues, this additional 

coproduct of crop production may increase returns to 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 residues and byproducts should cover any losses in storage and material 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 stationary source process to what is grown at 

the feedstock source location. 

3.2.3. Agriculture Industrial Products and Processing By-products 

Similar to those produced in the forestry sector, agriculture 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 processing by-product feedstocks are used to 

produce bioenergy instead of traditional market uses, this alternative use for energy can potentially 

disrupt the traditional markets and have related land use and/or land use management changes. 

Examples of agriculture industrial processing by-products with a current alternative market use 

include animal fats, oils, and greases that come from livestock production and distillers grains that 

are produced during the grain ethanol production process. 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, often serving as a substitute for corn and soybean 

meal in feedlots. 
November 2014 D-12 

Examples of agriculture industrial processing by-products with no current alternative market use 

(outside of renewable fuel production) include shells, husks, and cobs. 

However, some agriculture-derived products are produced for energy purposes but not necessarily 

for use at stationary sources. These include ethanol and biodiesel produced from a variety of 

agriculture sources: grains, oilseeds, cellulosic material, 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 sequestration and emissions occur: For this feedstock 

category, the time scale over which sequestration occurs 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 and 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 products and processing 

by-products varies across feedstocks and by stationary source process. Some feedstocks 

have active alternative markets, whereas others do not currently have alternative market 

uses. In the case of feedstocks currently being used in alternative uses (e.g., distillers grains, 

oils), they would typically not be used in energy production as long as there are highervalued uses. For feedstocks without current alternative market uses, the alternate fate 

pathways could include use for energy. Materials such 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 ways may necessitate the addition of more 

fertilizer or other soil amendments to maintain soil quality. A given alternate fate pathway 

for these feedstocks may potentially result in CO2 and CH4 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 demand for agricultural commodities that 

generate industrial products and by-products that can be used for energy production 

increases. Diverting the use of by-products that are not currently used in other markets is 

less likely to have effects on land use, though there may be effects on land productivity and 

input use due to nutrient removal, as discussed above. It is also possible that creating a new 

demand for corn by-products (e.g., shells, husks, and cobs), for instance, would lead to more 

land moving into corn if the additional revenue available from corn by-products becomes 

sufficiently high. 

• Leakage: If there is sufficient demand for agricultural industrial products and processing 

by-products for use in energy production, there could 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 losses or 

decomposition of some feedstocks, with losses tending 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, miscanthus, energy sorghum, and short-rotation 

woody crops (e.g., poplar, willow), can be converted at stationary sources into heat and power, 

cellulosic fuels, and biodiesel. Direct and indirect land use change can occur as a result of dedicated 

feedstock production because existing forestlands, croplands, or grasslands would likely need to be 

converted to grow these feedstocks since they are not currently produced commercially at large 

scales in the United States. 

• Time scale over which feedstock carbon sequestration and emissions occur: Growth and 

harvest of dedicated energy crops generally occur at 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 conditions). For some energy crops like sweet 

sorghum, sequestration and emissions related to a single 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 contribution from the growth and harvest 

of the feedstock itself is considered in balance, though other factors such as land use 

management and land use changes and related soil carbon impacts can affect the overall net 

contribution outcome. For energy crops with rotations longer than a year, the rotation ages 

and harvest regimes (and thus resulting sequestration and emissions related to growth and 

harvest) depend largely on specific species and site 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 time. In some circumstances, dedicated 

feedstocks may have substantial direct land use and/or leakage impacts related to 

cultivation if its production has displaced other land 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 dedicated 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 commodities. Changes in demand for energy 

crops could displace traditional crops and forest products, and these changes in cropping 

patterns and production practices can cause substantial GHG emissions changes. For 

example, land may be converted from traditional crops 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 regime all affect 

species growth and influence management decisions (in addition to cost for the latter). Management regimes for 

energy crops can vary widely, from active management 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 production can be substantial. 

The new or diverted production of feedstocks can affect commodity markets and thus lead 

to changes in production that alter land uses and land 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 converted 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 leakage and related emissions effects elsewhere, 

particularly if forested or grassed lands are brought 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 some energy crops have shorter rotations 

and thus a seasonal nature, these feedstocks may need to be stored to provide a year-round 

supply of energy. Therefore, energy crop biomass may 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 biologically 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 manufacture of consumer and industrial products 

such as newspaper, food, and construction), after which it is disposed of. Given that the treatment 

of waste itself does not drive the management of the growth and harvesting of biomass, it is more 

difficult to quantify a connection between the consumption 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 waste management system emits carbon as CO2

(and CH4) that would have otherwise been returned to the atmosphere as predominantly CO2 from 

natural decay of waste, regardless of the management or status of the land providing the biological 

material. The human management of the waste materials affects only the timing or location of these 

GHG emissions. 

In addition to biogenic CO2 emissions, waste management systems can emit large quantities of CH4

if they manage wastes under anaerobic conditions. Methodologies for estimating and accounting for 

CH4 from waste management are available and widely used in many GHG accounting programs. 

Many waste systems already account for CH4 using methodologies from the EPA Greenhouse Gas 

Reporting Program (GHGRP). The decision to consider avoided CH4 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 CO2 emissions from waste management sources to the 

biogenic CO2e emissions implications associated with decomposition of the same waste in other 

types of managed systems. For example, an assessment of waste materials diverted from a landfill 

to an incinerator for energy production could consider the biogenic CO2 emissions that occur at one 

point in time (at the incinerator) against the avoided CO2 and CH4 generated over decades through 

decomposition in the landfill and also avoided carbon storage in the landfill (EPA, 2010b, 2013; 

IPCC, 2006), or it could consider the biogenic CO2 emissions against the CO2 that would be emitted 

through the natural decay of the original biomass. 

Feedstocks listed here are those that would have been 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, commercial, and institutional entities. It contains a 

variety of biogenic materials, the composition of which varies by region, season, and long-term 

trends in waste generation. The average national composition of MSW in 2011 was estimated by 

EPA (2013) in Municipal Solid Waste Generation, Recycling, 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 carbon 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, 2013). Disposal of MSW in landfills causes 

some of the biogenic materials to be converted to methane; well over half of the methane (CH4) 

generated in U.S. MSW landfills is captured for combustion (EPA, 2013). 

• Time scale over which feedstock carbon sequestration 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 components 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 of 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 degradation of MSW in a 

landfill will generally contain about 50% methane and 50% CO2 (by volume, dry basis). For 

landfills with no gas collection system, this landfill gas will be emitted to the atmosphere. 

For landfills with gas collection and combustion systems, a significant portion of the 

methane in the landfill gas can be converted to CO2 prior to release into the atmosphere. 

Composting can be used as an alternative to MSW landfilling, 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 within the compost pile. Direct combustion of 
November 2014 D-16 

MSW is another alternate pathway; essentially all of the carbon in MSW is converted and 

released as CO2, 

• 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 MSW prior to 

receipt at the centralized treatment location is not considered. For example, only that 

portion of MSW as received at the landfill is considered 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 or uncaptured and released to the 

atmosphere. Storage of the waste at an MSW combustor facility is assumed to have 

negligible emissions because of the relatively short 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, digesters, 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 animal agriculture waste to be biogenic (IPCC, 

2006). Decomposition of the manure can occur through anaerobic or aerobic decomposition. Some 

manure management systems combust CH4 from anaerobic treatment. 

• Time scale over which feedstock carbon sequestration and emissions occur: Animal 

agriculture waste degradation typically occurs over several weeks to several months. 

• Alternate fate pathways: Animal agriculture waste degradation typically generates 

predominately CO2 (for aerobic systems) or a mixture of CO2 and CH4 (for anaerobic, 

facultative, or anoxic systems), depending on the type of manure management system used. 

When anaerobic treatment systems are used, the CH4 in the biogas can be collected and 

combusted to CO2. For dry animal agriculture wastes, direct combustion of the manure is an 

alternative treatment option, which will convert and release the biogenic carbon as CO2

emissions. 

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

• Leakage: Not applicable. 

• Storage and handling losses: Most manure treatment occurs on site, and the methodology 

considers all emissions from the storage or treatment of the manure, whether the emissions 

are captured for combustion or uncaptured and released 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 centralized treatment location is not specifically 

considered; the methodology primarily considers only the quantity of waste as received at 

the centralized treatment location. Storage of the manure prior to direct manure 
November 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 that treat or remove pollutants and 

contaminants, such as soluble organic matter, suspended solids, pathogenic organisms, and 

chemical contaminants, from wastewater prior to its reuse or discharge from the facility. Sources 

include municipal and industrial wastewater treatment facilities. International convention 

considers all CO2 generated as a result of aerobic wastewater treatment to be biogenic (IPCC, 2006). 

Some wastewater treatment facilities use anaerobic processes, which results in CH4 emissions; 

some facilities capture and combust CH4 derived from anaerobic digestion. 

• Time scale over which feedstock carbon sequestration and emissions occur: Wastewater 

treatment processes degrade organic matter over a time scale of a few hours to a few days, 

although some large surface impoundments can have residence times as long as several 

months. 

• Alternate fate pathways: Aerobic wastewater treatment processes convert the degradable 

organic matter almost entirely to CO2; anaerobic, wastewater treatment processes convert

approximately 50% or more of the organic carbon to CH4; and facultative or anoxic 

wastewater treatment processes produce CO2 predominately, but also produce appreciable 

amounts of CH4. Gas generated in anaerobic wastewater treatment systems can be collected 

and combusted to convert the CH4 in the biogas to CO2 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 storage or treatment of the wastewater, 

whether the emissions are captured for combustion or uncaptured and released to the 

atmosphere. When centralized treatment is used, loss 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 methodology primarily considers only the 

quantity of wastewater as received at the centralized 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 product or by-product (i.e., primary stationary 

source) that is used for energy production at a different stationary source (i.e., secondary stationary 

source). For example, if a secondary stationary source chooses to use for energy an agriculture- or 

forest-derived industrial processing product such as distillers grains or woody residuals from a 

primary stationary source, the net biogenic emissions value (landscape and process attributes from 

the original feedstock at the primary source) for the biogenic feedstock carbon of that material 
November 2014 D-18 

could be used at the secondary entity. Hypothetically, 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 certain 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 transferred for use at a secondary stationary 

source. For example, counting total biogenic feedstock 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 different possible policy treatments for secondary 

feedstocks is outside the scope of this report. 

4.2. Feedstock Imports and Exports 

International feedstock production and the importation 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 related commodities have the potential to 

significantly affect domestic supply chains, and, conversely, U.S. biogenic feedstock production can 

affect international commodity markets and land use activities. The framework could either include 

or exclude international biogenic feedstocks, depending on policy requirements and international 

agreements related to GHG emissions accounting. However, decisions as to the inclusion/exclusion 

of international feedstocks and the treatment of such 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 Feedstocks 

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 or under consideration for bioenergy production. 

However, new and unconventional or otherwise unanticipated 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 with this in mind, though some emerging 

feedstocks (e.g., algae) will require additional parameters that could be added on an as-needed 

basis. 

For purposes of this report, biogenic feedstocks have been classified broadly into the feedstock 

categories identified above based on the physical attributes 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 existing regulations, certain feedstocks are already 

regulated using specific definitions. Thus, although tire-derived fuel might fall under the wastederived feedstock categorization in the framework presented here because of its attributes relative 
November 2014 D-19 

to biogenic CO2 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 Sustainability 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. Turner, 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 Industry. 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 Administration. 

http://www.eia.gov/totalenergy/data/annual/pdf/aer.pdf. 

EPA. 2010a. Renewable Fuel Standard Program (RFS2) Regulatory Impact 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/renewablefuels/420r10006.pdf. 

EPA. 2010b. Methane and Nitrous Oxide Emissions from Natural Sources. EPA 430-R-10-001. 

Washington, DC: U.S. Environmental Protection Agency. 

http://www.epa.gov/nitrousoxide/pdfs/Methane-and-Nitrous-Oxide-Emissions-From-NaturalSources.pdf 

EPA. 2013. Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and 

Figures for 2011. Washington, DC: U.S. Environmental Protection Agency. 

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 States -- 

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 Inventories, edited by L.B.H.S. 

Eggleston, K. Miwa, T. Ngara, and K. Tanabe. Kanagawa, Japan: National Greenhouse Gas 

Inventory Programme, Intergovernmental Panel on Climate 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. Estimating leakage from forest carbon sequestration 

programs. Land Economics, 80 (1):109-124. 
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Searchinger, T.D., S.P. Hamburg, J. Melillo, W. Chameides, 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 harvested 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 Agricultural Sciences, Department of Forest 

Products. 

Turner, D.P., J.J. Lee, G.J. Koerper, and J.R. Barker, editors. 1993. The Forest Sector Carbon Budget of 

the United States: Carbon Pools and Flux under Alternative 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. Lee. 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 Update: 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 Processes 

and Possible Alternate Fates 

6.1. Joint Production of Industrial Products and By-products 

Some industries may produce by-products useful for bioenergy generation in the process of making 

their primary market products. For example, manufacturers 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, which generate black liquor that is burned on site 

to recover chemicals for reuse in the pulping process 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 other industries, black liquor is not only limited in 

commercially viable alternative uses, but it also has 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, paper) and minimize the amounts of low-value 

products (e.g., black liquor). Although there is some responsiveness to relative price movements 

(e.g., higher demand and prices for wood pellets may lead to an increased proportion of scrap going 

to this use and a decreased proportion going to particleboard), the elasticity of transformation 

between outputs may be very inelastic, and even with 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 outcome from biomass production and usage, 

the SAB Panel advocated the use of a future anticipated baseline approach that would capture 

additionality—“i.e., the extent to which forest carbon 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 along 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 forest 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 different options for simulating an increase in 

demand for a biogenic feedstock relative to a “business as usual” case. One option is to introduce 

into, or shock, a model with X additional tons of production of a specific biogenic feedstock, which 

will likely result in increased production of all the other products that are jointly produced with 

that bioenergy feedstock. The landscape effects associated with increased production of the specific 

biogenic feedstock would be conflated with the effects of the increased production of other jointly 

produced products. Another option is to shock a model 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 interest 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 increase 
November 2014 D-22 

production of or increase procurement of raw materials to generate that by-products-based 

biogenic feedstock. For black liquor, it would be expected that a model run that increased the 

demand for and price of black liquor explicitly would result in very little change in forest harvest 

and land use decisions, because even a large increase in the price for black liquor would have a 

small impact on the value of the overall product mix. 

For residues and materials diverted from the waste stream, the SAB Panel endorsed considering 

their alternate fates (e.g., some forest residues may be burned if not used for bioenergy, wastederived materials might be otherwise landfilled) and information about decay (e.g., using decay 

functions to evaluate ecosystem carbon storage in forest residues not burned for energy or 

disposal). Furthermore, in the case of waste-derived materials, the SAB stated that “after calculating

decay rates and considering alternate fates, including avoided methane emissions, the agency may 

wish to declare certain categories of feedstocks with 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 avoided” (Swackhamer and Khanna, 2011). In 

terms of net atmospheric contributions of biogenic CO2e4 emissions, as shown in the following 

sections of this addendum, it is more beneficial that black liquor is burned for on-site energy use 

and chemical recovery because black liquor has no other commercially viable alternative uses and 

no practical disposal options. It is also unlikely that changes in demand for or prices of black liquor 

would lead to changes in land use, harvest, or forest management decisions because black liquor is 

not produced for its value alone but is only produced as a by-products of manufacturing high-value 

pulp for use in papermaking. 

The purpose of this addendum is to provide background information on the chemical pulping 

process leading to generation of black liquor and to explore hypothetical alternate fates of black 

liquor in the context of biogenic CO2e accounting and avoided emissions. The information in this 

appendix, including example calculations of alternate 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 fates 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 manufactured at mills that also produce virgin 

pulp or at mills that do not produce pulp but instead purchase pulp or use recycled fiber to 

manufacture paper. Some mills produce only market pulp to sell to other mills and do not 

manufacture paper. 

 

4 This addendum generally uses CO2e in the context of biogenic emissions because both CO2 and CH4 are 

specifically discussed. 
November 2014 D-23 

Different processes are used for pulp production. Kraft 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 secondary (recycled) fiber pulping. Non-chemical 

processes do not produce spent pulping liquor. Approximate 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 this addendum focuses on the kraft pulping 

process. 

Chemical (i.e., kraft, soda, and sulfite) pulping involves “cooking” of raw materials (e.g., wood chips) 

using aqueous chemical solutions and elevated temperature 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 (Na2S) to digest wood, while the similar soda process uses 

only NaOH to digest the wood. The cooking liquor in the sulfite pulping process is an acidic mixture 

of sulfurous acid (HSO3) and bisulfite ion (HSO3

-). The bases used in cooking liquor preparation are

typically calcium, magnesium, and sodium. Semi-chemical pulping uses a combination of chemical 

and mechanical (i.e., grinding) energy to extract pulp 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 and semi-chemical pulp mills employ chemical 

recovery processes to reclaim spent cooking chemicals. Typically, a combustion unit (e.g., recovery 

furnace) is used to recover the cooking chemicals from 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 solution. 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, digestion 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 process (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 that becomes wood fiber in the digester is 

referred to as pulp yield. The remainder of the wood can generally be assumed to partition to the 

black liquor. 

The yield of pulp (expressed as a percentage by weight 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 yields for the kraft process are 40 to 50% (Smook, 

2002). The lowest yield is obtained from drastic chemical digestion that gives pulp consisting of 

nearly pure cellulose fibers. The yield of pulp obtained by digesting wood also depends on the 

chemical composition of the wood. Because the principal chemical components of the normal 

roundwood of most species do not vary much in amount, the percentage yield of pulp obtained by a 

given process does not vary greatly from one species 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 cooking chemicals (inorganics) and dissolved 

organics. The BLS exiting the washer in the weak black liquor are sent for further processing in the 

kraft recovery system, which regenerates the inorganic pulping chemicals, burns the dissolved 

organics for energy production, and sometimes results in the recovery of other organic byproducts. Weak black liquor exiting the washing process typically contains 13 to 17% BLS (Smook, 

2002). Weak black liquor is evaporated and concentrated to 65 to 80% solids prior to burning in 

the recovery furnace. 

A nominal value of 1.6 tons of BLS per air-dried short ton of pulp (ADTP) is often used to represent 

BLS production, though this value ranges from approximately 1.3 to 1.9 ton BLS/ton pulp (1,300 to 

 

5

 Note that commercial pulp production rates are usually referred to in “air dried” units, which are generally 

considered to have a moisture content of 10%. “Moisture-free” or “bone-dried” mass refers to pulp or wood 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 based on its solids content. The solids alone 

comprise a complex mixture of both inorganic and organic constituents. The inorganic constituents 

in black liquor are derived from the cooking liquor and comprise various sodium and sulfur 

compounds, including NaOH, sodium sulfate (Na2SO4, also known as “salt cake”), Na2S, sodium 

thiosulfate (Na2S2O3), sodium carbonate (Na2CO3), and sodium chloride (NaCl). Collectively, 

inorganic salts constitute between 18 and 25% of the solids in black liquor. 

The organic compounds found in black liquor are derived 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 pulping 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 ranges in kraft liquor are: 

• Lignin derived (39 to 54%); primarily consisting of polyaromatic macromolecules with 

lesser amounts of molecular weight alcohols, aldehydes, and simple phenolic compounds 

such as phenol, p-methyl phenol, catechol, and guaiacol; 

• 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 constituents (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 parameters. 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 (Weight % 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, CO3 8 Included in C and O above 

Sulfate, SO4 3 Included in S and O above 
November 2014 D-26 

6.4. Biogenic CO2 Emissions from Kraft Black Liquor Chemical Recovery

To assess biogenic CO2 emissions associated with the kraft pulping process, it is helpful to 

understand how biogenic CO2 emissions are currently estimated for kraft pulp mills. Carbon 

originating in the wood input into the pulping process 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 kraft pulping and chemical recovery process, 

biomass carbon from the wood is dissolved and either emitted as biomass CO2 from the recovery 

furnace or captured in sodium carbonate (Na2CO3) in the smelt discharged from the bottom of the 

recovery furnace. In the process of converting the Na2CO3 into new pulping chemicals, this biogenic 

carbon (i.e., the carbonate ion) is transferred to calcium carbonate (CaCO3). In the lime kiln, the 

CaCO3 is converted to calcium oxide (i.e., CaO or lime, a material used in the chemical recovery 

process) and biogenic CO2, which is released to the atmosphere (EPA, 2009). 

Figure D-2. Simplified Representation of the Kraft Pulping and Chemical Recovery System (EPA, 

2009). 

The majority of the wood-derived carbon within the black liquor either: 

• Exits the pulping process as biogenic CO2 emissions from the recovery furnace stack; or 

• Reacts with sodium compounds to form Na2CO3 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 recovery loop to the lime kiln 

(becoming CaCO3 along the way). In the lime kiln, the CaCO3 is converted to CaO, emitting the 

biogenic CO2 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 CO2 emissions from the recovery 

furnace and lime kiln are not shown). 

Figure D-3. Simplified Diagram Showing How Biogenic CO2 Emissions Are Emitted from Both Kraft 

Recovery Furnace and Lime Kiln. 

The emission factors used to estimate biogenic CO2 emissions from the black liquor chemical 

recovery process are based on the carbon content of black liquor and therefore account for biogenic 

CO2 emissions from both the recovery furnace and lime kiln. Thus, rather than depicting the 

biogenic CO2 accounting boundary around the recovery furnace as the sole biogenic CO2 emissions 

unit, it would be more consistent with the current biogenic CO2 emissions estimation practice 

(including that required under the U.S. EPA’s Greenhouse Gas Reporting Program) to consider the 

biogenic CO2 emissions unit as the entire pulping process. 

Fossil-fuel-related CO2 emissions are estimated separately for the recovery furnace and lime kiln. 

The only other non-biogenic carbon introduced into the process is from carbonated makeup 

chemicals, for which CO2 emissions are estimated using a mass balance approach. Fossil-fuel and 

makeup chemical CO2 emissions estimates are independent of the biogenic CO2 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 because U.S. mills have taken steps to maximize 

recovery of black liquor. If black liquor is not reused within the pulping process and instead is 

Biogenic CO2

Emissions from 

wood burning 

Black liquor (mix of 

wood C and 

inorganics) 

Recovery 

furnace 

Smelt containing Na2CO3

created by reaction with 

the wood-burning CO2) 

Chemical recovery 

(Na2CO3 CaCO3)

Lime kiln 

(CaCO3CaO)

Biogenic CO2

from conversion 

of CaCO3CaO 
November 2014 D-28 

disposed of, disposal methods might involve incineration 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 equivalent saltcake; 

• Reduction in biological oxygen demand load on the effluent 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 chemical recovery furnaces as opposed to disposing 

of black liquor. Depending on its volume and concentration, if released into the environment, black 

liquor can be odorous, toxic to aquatic life, and cause 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 senses in very low concentrations. Although the 

cellulosic constituents in black liquor may be biodegradable, lignin is very difficult to biodegrade, 

leaving a portion of the COD and much of the dark brown color to be discharged to receiving waters 

following wastewater treatment. EPA has established Best Management Practice regulations to 

protect the environment from the negative consequences of spent pulping liquor spills (40 CFR 

430.03, 430.28, and 430.58). These rules were promulgated in 1998 as part of the effluent 

guidelines and standards for the pulp, paper, and paperboard 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 treatment of black liquor sent for incineration 

without energy recovery or wastewater treatment. The black liquor is the biogenic feedstock in this 

example (as opposed to the wood input to the pulping 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 generated 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-feedstock carbon pools (SITETNC); 

leakage associated with feedstock production (LEAK); the feedstock carbon losses during storage, 

transport and processing (L); and the feedstock carbon embodied in products (P). As a result, the 

assessment framework equation as applied to estimating biogenic CO2 emissions from the alternate 

fate of black liquor feedstocks can be simplified to: 

BAF = AVOIDEMIT 

AVOIDEMIT represents the avoided biogenic emissions that could 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 value implies that both practices are equivalent in 

terms of how much emissions they contribute to the atmosphere. A negative value implies that 

using the feedstock for bioenergy production contributes less emissions to the atmosphere than the 

alternative management practice. 

The CO2e emissions in the AVOIDEMIT equation above include both CO2 and methane (CH4) 

resulting from each feedstock management alternative. The following subsections present 

calculations of CO2e emissions for the two hypothetical alternative management approaches. 

6.5.1. Alternate Fate Scenario 1: Black Liquor Incineration 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 produced from burning the black liquor would 

remain and could be recovered in either case. No emissions would be avoided by treating the black 

liquor through incineration, and the stack emissions would be about the same as combustion 

without energy recovery. Therefore, the resulting hypothetical example BAF is 0. 

Table D-3. AVOIDEMIT for Scenario 1 Where Black Liquor Is Incinerated Without Energy Recovery. 

Emissions Factors: 

CO2 94.4 kg/MMBtu HHV (40 CFR 98, subpart AA) 

CH4 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) 

CO2 2.20 Metric tons CO2/ADMT pulp (calculated) 

CH4 4.42E-05 Metric tons CH4/ADMT pulp (calculated) 

CH4 GWP 25 (40 CFR 98, subpart AA) 

CO2e 2.199 Metric tons CO2e/ADMT pulp if the black liquor is burned 

AVOIDEMIT 

numerator 

2.199 Emissions from treatment alternative (incineration without energy 

recovery) 

AVOIDEMIT

denominator 

2.199 Emissions from burning black liquor for chemical and energy recovery, 

metric tons/ADMT pulp 

BAF = 

AVOIDEMIT

0 = 1− (emissions from treatment alternative) / (emissions from burning 

black liquor for chemical and energy recovery) 
November 2014 D-30 

6.5.2. Alternate Fate Scenario 2: Black Liquor Decomposition in a Wastewater 

Treatment System 

The equations related to CO2 and CH4 emissions from wastewater treatment in Section 6.1 of 

Appendix N were used to evaluate two hypothetical wastewater treatment scenarios for the 

disposal of black liquor: (1) treatment in a deep anaerobic lagoon; and (2) treatment under aerobic 

conditions. Under both alternate pathway conditions (anaerobic and aerobic), emissions from 

treatment of black liquor as wastewater exceeded those from the current practice of burning black 

liquor for chemical and energy recovery. The resulting 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 production contributes less biogenic emissions to the 

atmosphere than the alternative wastewater management practice. Table D-4 presents the equation 

terms and calculated values for avoided emissions from wastewater treatment. 

Table D-4. AVOIDEMIT for Scenario 2 Where Black Liquor Is Disposed Through Wastewater 

Treatment. 

Equation Term Description 

Anaerobic Deep 

Lagoon Treatment 

Aerated Treatment 

Process with Anoxic 

Areas 

Input Values 

Qww Wastewater influent flow rate 9.7 m3/ADMT pulp1 9.7 m3/ADMT pulp1

OD Oxygen demand of influent 92,700 mg/l2 92,700 mg/l2

EffOD Oxygen demand removal efficiency 

of the biological treatment unit 

0.753 0.753

MCFww CH4 correction factor (from 

Appendix N, Table N-13) 

0.8 0.3 

BGCH4 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 

GWPCH4 Methane global warming potential 25 25 

Calculated Values 

CO2WW CO2 emission rate (metric tons 

CO2/ADMT pulp) 

0.45 0.41 

CH4WW CH4 emission rate (metric tons 

CH4/ADMT pulp 

0.18 0.036 

CO2S CO2 emission rate (metric tons 

CO2/ADMT pulp) 

Not applicable 

(λ = 0) 

0.34 

CH4S CH4 emission rate (metric tons 

CH4/ADMT pulp 

Not applicable 

(λ = 0) 

0.03 

AVOIDEMIT 

numerator 

= CO2WW+CO2S + 

(CH4WW+CH4S)*GWPCH4

4.8 2.4 

AVOIDEMIT

denominator 

Emissions from burning black liquor 

for chemical and energy recovery, 

metric tons/ADMT pulp 

2.2 2.2 
November 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 BLS/ADTP and assuming that weak black liquor is 15% solids (i.e. 0.15 

ton BLS/ton liquor) with a density of 1.1 g/cm3. Thus: 9.7 m3/ADMT pulp = (1.6 tons BLS/ADTP) x (ADTP/0.9072 ADMT) 

x (ton liquor/0.15 ton BLS) x (907185 g/ton liquor) x (cm3/1.1 g) x (m3/1003cm3) 

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

3 A relatively low oxygen demand removal efficiency of 75% was used considering the low biodegradability of the lignin 

component in the wastewater stream. 

6.5.3. Discussion 

The two scenarios presented above illustrate that current black liquor management practices 

(burning for energy and chemical recovery in a recovery 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 commercially viable alternatives other than use for 

chemical and energy recovery within the pulping process. Because black liquor is jointly produced 

with other forest industry products (pulp production), 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 avoided emissions associated with disposal of black 

liquor as compared to the current management practice (burning for energy and chemical recovery 

in a recovery furnace) resulted in hypothetical example BAFs ranging from different negative 

values to 0, depending on the treatment method. Because 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 consistent 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 Program Test Plan for Spent 

Pulping Liquor. American Forest & Paper Assocation. 

http://www.epa.gov/hpv/pubs/summaries/afpa/c12936.pdf.

Clay, D. 2008. Evaporation Principles and Black Liquor Properties. Lake Oswego, OR: Jacobs 

Engineering. http://www.tappi.org/content/events/08kros/handouts/3-1.pdf. 

EPA. 1997. Technical Support Document for Best Management Practices 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/pulppaper/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 Sector: Proposed Rule for Mandatory 

Reporting of Greenhouse Gases. Washington, DC: U.S. Environmental Protection Agency. 

http://www.epa.gov/ghgreporting/documents/pdf/archived/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 recovery. Biomass and Bioenergy 46(0): 683-692. 

IPST. Undated. Literature Values of Chemical Species, Elemental Composition and Heating Values of 

North American Black Liquors. 

http://www.ipst.gatech.edu/faculty/ragauskas_art/technical_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: National 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 CO2 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/manuscripts/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.pdf. 

Yang, W., H. Mu, and Y. Huang. 2003. Treatment of black liquor from the papermaking industry by 

acidification and reuse. Journal of Environmental Sciences, 15(5):697-700.