Materials Characterization Paper

In Support of the

Advanced Notice of Proposed Rulemaking –

Identification of Nonhazardous Materials That Are Solid Waste

Biomass - Agricultural Residues and Food Scraps

December 16, 2008

==============================================================

1.	Definitions of Agricultural Residues and Food Scraps

Agricultural residues include crop residues remaining in fields after
harvest (primary residues) and processing residues generated from the
harvested portions of crops during food, feed, and fiber production
(secondary residues).

Food scraps are generated at all stages of the food system including
farming, storage, processing, wholesaling, retail, and consumption
(Scott Kantor et al. 1997). Food scraps, broadly defined, include both
the portion of harvested crops and livestock that does not enter the
retail market and the portion of food discarded by retailers and
consumers. In this paper, food scraps generated by retailers and
consumers are not considered because they enter the waste stream as
municipal solid waste (MSW) (EPA 2006, Simmons et al. 2006). Food scraps
generated in the manufacture and distribution of food are produced
through spoilage, removal of unusable portions, discard of substandard
products, and packaging failure.

2.	Annual Quantities of Agricultural Residues and Food Scraps Generated
and Used

Sectors that Generate Agricultural Residues and Food Scraps: 

NAICS 111: Crop Production

NAICS 11511: Support Activities for Crop Production

NAICS 311: Food Manufacturing

NAICS 312 Beverage and Tobacco Product Manufacturing

Quantities and Prices of Agricultural Residues and Food Scraps
Generated: 

Current annual production of agricultural residues from major crops is
around 500 million dry tons (Milbrandt 2005, Haq and Easterly 2006).
These crops include barley, canola, corn, cotton, dry beans, flax, oats,
peanuts, peas, potatoes, rice, rye, safflower, sorghum, soybeans,
sugarcane, sunflowers, and wheat, among others. The fraction of this
amount that can be removed from fields in a sustainable manner (i.e.,
while maintaining cropland fertility and quality) varies widely from 113
million tons by Perlack et al. (2005) to 173 million tons by Milbrandt
(2005)). Newer analyses soon to be published tend to be even lower.

Sugarcane production from 2005 through 2007 averaged 13.5 million tons
of cane (ERS 2008). This yielded approximately 3.8 million tons of
bagasse assuming 0.28 lbs. of bagasse produced per pound of cane (Macedo
et al. 2004).Domestic production of peanut hulls was approximately 0.27
million tons in 1999 (Özyurt and Realff 2002).

Total quantities of secondary agricultural residues and industrial food
scraps produced on an annual basis are not readily accessible from the
available literature.

Further analysis could be used to derive an estimate of industrial food
scrap production by applying known conversion factors for weight
reductions that occur as crops and livestock are processed into retailed
food products. These conversion factors range from 5 percent for fresh
fruit to 30 percent for meat, poultry, and processed vegetables (Scott
Kantor et al. 1997, Jones Putman and Allshouse 1999).

Around 75 million tons, or two-thirds, of the 113 million tons of
sustainably harvestable primary agricultural residue estimated by
Perlack et al. (2005) is corn stover, which is composed of corn stalks,
husks, and shelled cobs. Processing facilities experience marginal
feedstock costs from $54 to $84 per dry ton depending on the fraction of
stover collected from the field and transportation distance (Petrolia
2008).

Haq and Easterly (2006) provide a detailed list of supply curves for
primary and secondary agricultural residues. These could be updated for
current collection and transportation costs given recent increases in
energy prices.

Trends in Generation of Agricultural Residues and Food Scraps:

Total primary agricultural residue production fluctuates with 1) the
amount of US land in crop production and 2) the relative proportion of
crops, each with its own residue production rate. Current trends suggest
that higher food prices will drive additional land into crop production
(Secchi and Babcock 2007), thereby potentially increasing residue
production.

Domestic sugarcane production has decreased over the past decade (ERS
2008), thus reducing the total amount of secondary agricultural residue
(bagasse) combusted in sugar mills. Conversely, new methods for
utilizing sugarcane “trash,” or field residue, may increase total
biomass use from this crop (Macedo et al. 2008).

Trends in other secondary agricultural residue and food scraps are not
readily available.

3.	Uses of Agricultural Residues and Food Scraps

Combustion Uses of Agricultural Residues and Food Scraps:

In 2007, approximately 6.0 million tons of agricultural residues were
burned as fuel, 92 percent of which (Btu basis) provided useful thermal
output (EIA 2008). The remaining 8 percent was used to produce
electricity. Around 71 percent of total agricultural residues combusted
(Btu basis) were secondary residues used in the food processing
industry, mostly sugarcane bagasse at sugar mills (EIA 2007). The
remaining 29 percent was used in the Agriculture, Forestry, and Mining,
and the Paper and Allied Products industries (EIA 2008).

An emerging market for corn stover and other primary and secondary
agricultural residues is for use as a heat and power source for the
production of corn and cellulosic ethanol (Morey et al. 2006, Farrell
and Gopal 2008).

Non-Combustion Uses of Agricultural Residues and Food Scraps:

Primary agricultural residues play an important role in maintaining
cropland production.  Removing them can increase erosion, reduce crop
productivity, and deplete soil carbon and nutrients (Graham et al.
2007). Recent work has shown that cropland is particularly susceptible
to loss of soil carbon with increased residue removal (Wilhelm et al.
2007).

Primary agricultural residues are often harvested to provide animal
bedding.

Certain secondary agricultural residues can be spread upon cropland as
soil treatments. Such is the case with peanut hulls, where a majority in
Georgia (40 percent of US production) are used in granular carriers for
lawn and garden insecticide and fertilizer products, with the remainder
sold for livestock feed and bedding (Özyurt and Realff 2002).

Non-combustion uses for food scraps can include composting. 

Quantities of Agricultural Residues and Food Scraps Landfilled: 

Primary agricultural residues are not landfilled to an appreciable
extent.

Data on the quantity of food scraps landfilled are not readily
accessible in the available literature. Further inquiry may reveal these
amounts. For example, Annex 3 to the “Inventory of U.S. Greenhouse Gas
Emissions and Sinks: 1990-2006” report describes a methodology (Pages
A-179 and A-180) that was followed to estimate methane generation at
industrial landfills (EPA 2008). This included gathering information on
food processing wastes diverted to landfills. 

Quantities of Agricultural Residues and Food Scraps Stockpiled/Stored:

Primary agricultural residues tend to degrade rapidly after harvest and
are largely decomposed by the following planting season.

Quantities of secondary agricultural residues and food scraps stockpiled
or stored are unknown.  

Exhibit 1:  Overview of Generation and Use of Agricultural Residues and
Food Scraps

Commodity	Annual Quantity Generated 	Annual Quantity Used as Fuel	Annual
Quantity Landfilled	Annual Quantity in Other Uses	Total Quantity
Stockpiled



Cement Kilns	Other





---------- Million Tons -----------

Primary Ag. Residues	500a	N/I	6.0 Combined	0	327–387b	0

Secondary Ag. Residues	N/I	N/I

N/I	N/I	N/I

Food Scraps	N/I	N/I	N/I	N/I	N/I	N/I



Notes: aTotal primary agricultural residue from major crops. bMinimum
amount needed to remain on land to maintain soil fertility and moisture,
and prevent erosion and carbon loss.

N/I = not identified



4.	Management and Combustion Processes for Agricultural Residues and
Food Scraps

Types of Units Using Agricultural Residues and Food Scraps:

The discussion for this section centers on the use of bagasse in sugar
mills. Bagasse is burned in fuel cells, horseshoe boilers, and spreader
stoker boilers (EPA 1996). Other emerging technologies of combusting
agricultural residues and food scraps are described in Farrell and Gopal
(2008).

Sourcing of Agricultural Residues and Food Scraps:

Agricultural residues and food scraps are generated from harvesting
crops and processing crops and livestock into food products for retail
sale.

Bagasse is produced when chopped and crushed cane is milled through a
series of grooved rolls, thereby releasing cane juices.

Processing of Agricultural Residues and Food Scraps: 

Bagasse does not require special processing before being combusted.

State Status of Agricultural Residues and Food Scraps:

As of September 2006, approximately 50 percent of states had renewable
fuels portfolio standards requiring that varying percentages of power
generated within the individual states come from alternative fuels
(including biomass) by a designated future date; several more states
have enacted such regulations since then (DOE 2006).

5.	 Agricultural Residues and Food Scraps Composition and Impacts

Composition of Agricultural Residues and Food Scraps:

Most agricultural residues have a high heating value of between 12.9 and
14.6 million btu/ton (6,450 to 7,300 btu/lb) (Wright et al. 2006).
Air-dried biomass is typically around 15 to 20 percent moisture.

Bagasse has an approximate high heating value of 12.1 million btu/ton
(6,065 btu/lb), (Wright et al. 2006). As burned in sugar mills (45 to 55
percent moisture by weight), its heating value is between 6.0 and 8.0
million btu/ton (3,000 and 4,000 btu/lb) (EPA 1996).

The high heat value of peanut hulls is 16.0 million btu/ton (8,031
btu/lb) (Bain et al. 2003).

The heating value of food scraps is likely to be close to the biogenic
portion of MSW, which has an average heat content (moisture content
unknown) of 9,696 btu/ton (4,848 btu/lb). 

Impacts of Agricultural Residues and Food Scraps:

Use of biomass as a substitute for coal in an existing power plant
reduces SO2, NOx, and other emissions (Hong 2007 p.13).

Combustion of corn stover can yield NOx emissions of 0.22 pounds per
MMBtu and SOx emissions of 0.10 pounds per MMBtu (De Kam 2007 p.12). 

Data on emissions from combustion of food scraps are not readily
available.

EPA’s AP-42 includes estimated emission factors for bagasse combustion
in boilers at sugar mills using a variety of control technologies.  For
example, for particulate matter (PM) of unspecified size, bagasse
combustion emits between 0.2 and 2.2 pounds per MMBtu, depending on the
type of control technology utilized.  Estimated emissions of PM-10 are
0.19 lbs./MMBtu when using wet scrubber controls.  Uncontrolled NOx
emissions are 0.17 lbs./MMBtu.  Note that EPA rates the data quality of
emission factors for controlled PM as high (i.e., based on repeated
tests at multiple sites), while the remaining factors are less reliable
estimates (EPA 1996, p. 1.8-4).

Lifecycle Emissions Impacts: 

Use of agricultural residues or food scraps as a replacement for
traditional primary fuels eliminates the environmental impacts
associated with extraction and processing of traditional fuels.  In
addition to the emissions impacts of combustion described above, Exhibit
2 lists the quantities of the total cradle-to-gate emissions for these
fuels based on typical processes in the United States in the late 1990s.
 



Exhibit 2:  Emissions from Extraction and Processing of Traditional
Fuels (Lb./MMBtu)

Pollutant	Coal	Distillate Fuel Oil	Residual Fuel Oil	Wood	Natural Gas

Criteria Pollutants

PM2.5	-	-	-	-	-

PM10	-	-	-	-	-

PM, unspecified	0.246	0.012	0.012	6.67x10-4	0.004

NOx	0.022	0.061	0.062	0.08	0.117

VOCs	0.008	0.361	0.365	-	0.515

SOx	0.022	0.186	0.187	0.003	1.913

CO	0.017	0.046	0.046	0.022	0.223

Pb	2.60x10-7	1.01x10-6	1.00x10-6	-	2.72x10-7

Hg	8.17x10-8	1.87x10-7	1.87x10-7	-	7.18x10-8



Source:

Franklin Associates 1998.

Note:

“-” signifies data not available; may equal zero.

The emission information presented in this table is derived from Life
Cycle Inventory (LCI) data, as compiled by Franklin Associates.   LCI
data identifies and quantifies resource inputs, energy requirements, and
releases to the air, water, and land for each step in the manufacture of
a product or process, from the extraction of the raw materials to
ultimate disposal. The LCI can be used to identify those system
components or life cycle steps that are the main contributors to
environmental burdens such as energy use, solid waste, and atmospheric
and waterborne emissions.  Uncertainty in an LCI is due to the
cumulative effects of input uncertainties and data variability.  

There are several life cycle inventory databases available in the U.S.
and Europe.  For this paper, we applied the most readily available LCI
database that was most consistent with the materials and uses examined.
These LCI data rely on system boundaries as defined by Franklin
Associates, as described in the documentation for this database,
available at:   HYPERLINK
"http://www.pre.nl/download/manuals/DatabaseManualFranklinUS98.pdf" 
http://www.pre.nl/download/manuals/DatabaseManualFranklinUS98.pdf .  





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 The summary table in the reference does not always specify which types
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residues are included.  For example, Nevada includes “agricultural
wastes.”

		

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