EPA
United
Environmental Protection
Agency Office of Air and Radiation June 2011
AVAILABLE AND EMERGING TECHNOLOGIES
FOR REDUCING GREENHOUSE GAS EMISSIONS
FROM MUNICIPAL SOLID WASTE LANDFILLS
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Available and Emerging Technologies for Reducing
Greenhouse Gas Emissions from Municipal Solid Waste
Landfills
Prepared by the
Sector Policies and Programs Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
June 2011
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of
Abbreviations and Acronyms 4
I. Introduction 6
II. Purpose of this Document 6
III. Description of Municipal Solid Waste Landfills 6
IV. Summary of Control Measures 8
V. Available Control Technologies for GHG Emissions from MSW Landfills 10
A. LFG Collection Efficiency Improvement 10
B. LFG Control Devices 12
C. Increase of CH4 Oxidation 17
D. Economic Analysis 18
VI. Bioreactor Landfill Systems 20
VII. Management Practices 21
EPA Contact 22
References 23
Appendix A 26
Calculations to Estimate Cost Effectiveness for CO2e Reduced 26
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ADEME
ATSDR
BAAQMD
BACT
Btu
CCAR
CCTP
CEC
CH4
CHP
CNG
CO
CO2
CO2e
CPTR
DER
GHG
HAP
H2
H2S
kW
Ib
LFG
LFGcost
LFGE
LMOP
LNG
Mg
MSW
MT
MW
MWh
N2
N2O
NESHAP
NMOC
NOX
NREL
NSPS
O2
ppmv
PSD
psi
RCRA
scfm
SOX
French Agency for Environmental and Energy Management
Agency for Toxic Substances and Disease Registry
Bay Area Air Quality Management District
Best available control technology
British thermal units
California Climate Action Registry
Climate Change Technology Program
California Energy Commission
Methane
Combined heat and power
Compressed natural gas
Carbon monoxide
Carbon dioxide
Carbon dioxide equivalents
Cost Incurred Per Metric Ton of Reduced CO2e
Distributed Energy Resource
Greenhouse gas
Hazard air pollutants
Hydrogen
Hydrogen sulfide
Kilowatts
Pound
Landfill gas
Landfill Gas Energy Cost Model
Landfill gas energy
Landfill Methane Outreach Program
Liquefied natural gas
Megagrams
Municipal solid waste
Metric ton
Megawatts
Megawatt-hour
Nitrogen
Nitrous oxide
National Emission Standards for Hazardous Air Pollutants
Nonmethane organic compounds
Nitrogen oxides
National Renewable Energy Laboratory
New Source Performance Standard
Oxygen
Parts per million by volume
Prevention of significant deterioration
Pounds per square inch
Resource Conservation and Recovery Act
Standard cubic feet per minute
Sulfur oxides
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SWICS Solid Waste Industry for Climate Solutions
WARM Waste Reduction Model
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I,
This document is one of several white papers that summarize readily available information on
control techniques and measures to mitigate greenhouse gas (GHG) emissions from specific
industrial sectors. These white papers are solely intended to provide basic information on GHG
control technologies and reduction measures in order to assist States and local air pollution
control agencies, tribal authorities, and regulated entities in implementing technologies or
measures to reduce GHG under the Clean Air Act, including, where applicable, in permitting
under the prevention of significant deterioration (PSD) program and the assessment of best
available control technology (BACT). These white papers do not set policy, standards or
otherwise establish any binding requirements; such requirements are contained in the applicable
EPA regulations and approved state implementation plans.
II,
This document provides information on control techniques and measures that are
available to mitigate GHG emissions from the municipal solid waste landfill sector at this time.
Because the primary GHG emitted by the municipal solid waste landfill industry are methane
(CH/t) and carbon dioxide (CO2), the control technologies and measures presented in this
document focus on these pollutants. While a large number of available technologies are
discussed here, this paper does not necessarily represent all potentially available technologies or
measures that that may be considered for any given source for the purposes of reducing its GHG
emissions. For example, controls that are applied to other industrial source categories with
exhaust streams similar to the municipal solid waste sector may be available through
"technology transfer" or new technologies may be developed for use in this sector.
The information presented in this document does not represent U.S. EPA endorsement of
any particular control strategy. As such, it should not be construed as EPA approval of a
particular control technology or measure, or of the emissions reductions that could be achieved
by a particular unit or source under review.
Ill,
The term municipal solid waste (MSW) landfill refers to an entire disposal facility in a
contiguous geographic space where municipal waste is placed in or on land. The term does not
cover land application units, surface impoundments, injection wells, or waste piles. Many MSW
landfills receive other types of waste, such as construction and demolition debris, industrial
wastes, and sludge. The information presented in this paper refers to landfills that primarily
receive MSW, as defined in the criteria for MSW landfills under the Resource Conservation and
Recovery Act (RCRA) regulations (40 CFR Part 258).
According to 2009 data, 54% of MSW in the United States was landfilled, 12% was
incinerated, and 34% was recycled or composted (EPA, 2010a). There were approximately
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1,800 operational landfills in the United States in 2006 (EPA, 2010b). These landfills accepted
approximately 132 million tons of MSW in 2009 (EPA, 2010a).
After placement in a landfill, a portion of organic waste (such as paper, food waste, and
yard trimmings) decomposes. Landfill gas is produced by microorganisms under anaerobic
conditions and is comprised of approximately 50% CH4, 50% CC>2, and trace amounts of
nonmethane organic compounds (NMOC). Landfill gas generation occurs under a four phase
process, as shown in Figure 1. First, CC>2 is produced under aerobic conditions. After oxygen
(62) is depleted, CC>2 and hydrogen (H2) are produced under anaerobic conditions. Then CC>2
production depletes in proportion to the CH4 that is produced. Finally, CH4, CC>2 and nitrogen
(TSk) production stabilize. Significant LFG production typically begins one or two years after
waste disposal in a landfill and can continue for 10 to 60 years or longer (ATSDR, 200la).
100
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80
Aerobic
r ' ).
Anaerobic
"S"
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70
60
SO
40
30
20
10
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Figure 1: Production phases of landfill gas (ATSDR, 2001a)
Landfills are the second largest anthropogenic source of CH4 in the United States;
approximately 22% of total U.S. anthropogenic CH4 in 2008 (EPA, 2010b). The global warming
potential of CH4 is 21 times that of CC>2, making CH4 a more potent GHG than CC>2. Typically,
GHG emissions are expressed in terms of carbon dioxide equivalents (CC^e) that weigh
emissions using global warming potentials. For example, a landfill emitting 1,000 metric tons of
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CH4 and 1,000 metric tons of CC>2 would have CO2e emissions of 22,000 metric tons [= (1,000 x
21)+ 1,000].
Landfills primarily use the "area fill" method which consists of waste placement on a
liner, spreading the waste mass in layers, and compaction with heavy equipment. Daily cover is
then applied to the waste mass to prevent odors, blowing litter, scavenging, and vectors (carriers
capable of transmitting pathogens from one organism to another). Landfill liners may be
comprised of compacted clay or synthetic materials to prevent off-site gas migration and to
create an impermeable barrier for leachate. A final cover or cap is placed on top of the landfill,
after an area or cell is completed, to prevent erosion, infiltration of precipitation, and for odor
and gas control.
Methane generation in landfills is a function of several factors, including: (1) the total
amount of waste; (2) the age of the waste, which is related to the amount of waste landfilled
annually; (3) the characteristics of the MSW, including the biodegradability of the waste; and (4)
the climate where the landfill is located, especially the amount of rainfall. Methane emissions
from landfills are a function of methane generation, as discussed above, and (1) the amount of
CH4 that is recovered and either flared or used for energy purposes, and (2) the amount of CH4
that leaks out of the landfill cover, some of which is oxidized.
IV. of
Table 1 summarizes the GHG control measures presented in this document. Where
available, the table includes emission reduction potential, capital costs, operating and
maintenance costs, and any important details on the applicability of the control.
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Table 1. Summary of GHG Control Measures for MSW Landfills
Measure
LFG
Collection
Efficiency
Improvement
Flare
Turbine
Engine
Microturbine
Small Engine
CHP Engine
CHP Turbine
CHP
Microturbine
Direct Use
(boilers,
heaters, etc.)
Biocover
Biofiltration
Bed
Applicability
All landfills with
gas collection
systems
All landfills with
gas collection
systems
For larger
landfills with
gas collection
systems
All landfills
Landfills with
passive or no gas
collection
systems
CH4
Reduction"
Varies
99%
99%
96-98%
99%
96-98%
96-98%
99%
99%
Varies by
technology
Up to 32%
Up to 19%
Typical
Capital
Costs"
$24,000/acre
$l,400/kW
(>3 MW)
$l,700/kW
(>800 kW)
$5,500/kW
(<1 MW)
$2,300/kW
(<1 MW)
$2,300/kW
(>800 kW)
NA
NA
$960/scfmc +
$330,000/miled
$48,000/acre
NA
Typical
Annual
O&M
Costs"
$4,100/acre
$130/kW
$180/kW
$380/kW
$210/kW
$180/kW
NA
NA
$90/scfnf'd
NA
NA
Cost
Effectiveness
($/metric ton of
CO2e reduced)6
NA
$6 - $25
$12 -$18
$12 -$16
$2 -$13
$11
$7 - $57
$4 -$51
$9 - $64
NA
$745
NA
Notes/Issues
Cost and performance
varies depending on the
type of cover material.
Emits secondary criteria
pollutant emissions (e.g.
NOx and CO.
No revenue.
Emits secondary criteria
pollutant emissions (e.g.
NOx and CO).
Generates revenue for
landfills.
No extensive retrofit.
Low cost.
a References provided in section V of this document for the different control measures.
b Costs for collection system & flare, turbines, engines, microturbines, small engines, and direct use obtained from Chapter 4
(Project Economics and Financing) of LMOP's Landfill Gas Energy Project Development Handbook (EPA, 2010c), Costs
for CHP engines determined by evaluating the engine case study in the handbook as a CHP engine using LMOP's LFGcost
model (EPA, 20lOd).
0 Costs for gas compression and treatment.
d Costs for pipeline and condensate management system (if applicable).
e Cost effectiveness obtained from analysis done by BAAQMD for conventional landfills with a medium compacted waste
density (BAAQMD, 2008), with adjustments made to determine the costs per metric ton of CO2e reduced from the
combustion of CH4, instead of the costs per metric ton of CO2e avoided from displacement of power generation. See section
V.D and Appendix A for additional information.
NA = not available
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Ľ, for
This section describes the available technologies for controlling GHG emissions from
MSW landfills. The available control technologies are divided into three categories: LFG
collection efficiency improvement, LFG control devices, and increase of CH4 oxidization. An
economic analysis of the control technologies discussed is also included. It should also be noted
that large landfills with emissions exceeding 50 megagrams (Mg) NMOC or more are required
by New Source Performance Standards (NSPS) to control and/or treat LFG to significantly
reduce the amount of toxic air pollutants released. In essentially all cases, controls required by
the NSPS will co-control the GHG emissions.
-
Collection efficiency is contingent upon landfill design and the manner in which landfills
are operated and maintained. Gas collection efficiency can be improved by implementing
rigorous gas well and surface monitoring and leak identification and repair. Factors contributing
to variability in collection efficiency are discussed below.
There are two types of LFG collection systems, active and passive. Passive systems rely
on the natural pressure gradient between the waste mass and the atmosphere to move gas to
collection systems. Most passive systems intercept LFG migration and the collected gas is
vented to the atmosphere. Active systems use mechanical blowers or compressors to create a
vacuum that optimizes LFG collection (ATSDR, 200la).
For active gas collection systems, the collection efficiency depends primarily upon the
design and maintenance of the collection system and the type of materials used to cover the
landfill (BAAQMD, 2008). In the background information document for the draft updated
landfill AP-42 chapter, a typical collection efficiency range of 50% to 95% is given with a
suggested average of 75% (EPA, 2008a).
EPA's Office of Research and Development has completed a field test program using
optical remote sensing technology (EPA's OTM-10) to quantify LFG collection efficiency.
Sampling was conducted at three MSW landfills to evaluate CH4 emissions across the landfill
footprint to compare to the quantity of extracted gas (i.e., rate of fugitive CH4 vs. rate of
collected CH4). The preliminary results suggest gas collection efficiencies from 36% to 85%
reflecting a range based on landfill design and operational differences. The report is under
review and is expected to be released in 2011.
Higher collection efficiencies may be achieved at landfills with well maintained and
operated collection systems, a liner under the waste, and a cover consisting of a geomembrane
and a thick layer of clay. Studies conducted by the Solid Waste Industry for Climate Solutions
(SWICS) indicate collection systems meeting the requirements of NSPS, Subpart WWW are
often more capable of achieving higher collection efficiencies than collection systems used
solely for energy recovery because it is difficult to optimize gas quality while trying to attain a
high level of gas collection (SWICS, 2009).
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Results of gas collection efficiency studies for various cover materials using flux box
measurements are documented in Spokas et al. (2005). The data were used to develop default
values of percent recovery for the French environment agency (ADEME). These default
collection efficiencies for active gas collection systems are listed in Table 2.
Table 2. LFG Collection Efficiencies for Various Cover Materials
Type of Landfill Cover
Material
Operating cell (no final cover)
Temporary cover
Clay final cover
Geomembrane final cover
Gas Collection Efficiency
35%
65%
85%
90%
Gas collection research studies done by SWICS used flux box data, which may
potentially under estimate gas collection efficiency. The resulting collection efficiencies for
landfills with active gas collection systems are summarized below (SWICS, 2009):
50-70% (mid-range default = 60%) for a landfill or portions of a landfill that are
under daily soil cover;
54-95% (mid-range default = 75%) for a landfill or portions of a landfill that contain
an intermediate soil cover; and
90-99% (mid-range default = 95%) for landfills that contain a final soil and/or
geomembrane cover systems.
As shown in Table 3, the mid-range default values for the three cover types identified
above were adopted as the collection efficiencies listed in the GHG reporting rule for MSW
landfills (40 CFR 98, Subpart HH, Table Fffl-3). The collection efficiency of a passive gas
collection system is assumed to be zero because the pressure gradient is unknown and would
likely vary in time and space.
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Table 3. LFG Collection Efficiencies in the GHG Reporting Rule
Description
Area without active gas collection,
regardless of cover type
Area with daily soil cover and active gas
collection
Area with an intermediate soil cover, or a
final soil cover not meeting the criteria below
to achieve 95% efficiency, and active gas
collection
Area with a final soil cover of 3 feet or
thicker of clay and/or geomembrane cover
system and active gas collection
Gas Collection
Efficiency
0%
60%
75%
95%
As shown is Table 3, landfills with final geomembrane covers have higher collection
efficiencies. Changing the final cover material can improve gas collection efficiency. This
technology is applicable for all landfills. Typically, modern landfills with active gas collection
systems have clay or geomembrane covers in place. An additional geomembrane or clay cover
can be added to older landfills with gas collection systems to reduce LFG emissions (BAAQMD,
2008).
'" '" ''"" "
After collection, LFG may be controlled and/or treated for subsequent sale or use as an
energy source to create electricity, steam, heat, or alternate fuels such as pipeline quality gas or
vehicle fuel. With approximately half the heating value of natural gas (350 to 600 British
thermal units (Btu) per cubic foot), LFG is considered a medium Btu gas. Combustion of LFG is
the most common method used to reduce the volatility, global warming potential, and hazards
associated with LFG. Combustion methods include destruction devices (e.g., flares), electricity
generation units (e.g., reciprocating engines, gas turbines), and energy recovery technologies
(e.g., boilers). During the combustion process, CH4 in LFG is converted to CC>2. Since CH4 has
21 times the global warming potential of CC>2, combustion reduces the global warming effect of
LFG significantly. Although CH4 has 21 times the global warming potential of CC>2, combusting
CH4 reduces the global warming potential only by a factor of 7.6 because the resulting CC>2
weighs more than the CH4 by a factor of 2.75. Combustion of LFG also reduces odors and other
hazards associated with LFG emissions. However, combustion units emit secondary criteria
pollutants, such as carbon monoxide (CO) and nitrogen oxides (NOx), as well as hazardous air
pollutants (HAP). Fuel cells are considered a non-combustion treatment option for LFG that
converts the gas to energy.
The control devices frequently used for LFG and the associated control efficiencies are
described in the following sections. It is important to note that all of the technologies discussed
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below typically require treatment of the LFG prior to entering the control device to remove
moisture, particulates, and other impurities. The level of treatment depends primarily on the type
of control and the types and amounts of contaminants in the LFG. A list of common LFG
constituents is found in Tables 2.4-1 and 2.4-2 of the landfill AP-42 chapter (EPA, 1998a).
Some of the major trace contaminants in LFG that may need to be treated prior to control include
sulfur compounds, such as hydrogen sulfide (H2S), and siloxanes.
Flares
Of the combustion methods, flaring is the most commonly used. However, unlike other
combustion options, flaring does not recover energy. Controlling LFG emissions by flares is
technically feasible for most landfills and many landfills have flares in place. The capital and
maintenance costs associated with flares are relatively low compared to other combustion
technologies. Flares are often used as backup control devices for landfills that have engines or
turbines to generate electricity to limit emissions while these devices are off-line or to respond to
variations in LFG generation.
Two different types of flares are available, open flares and enclosed flares. Open flares
employ simple technology where the collected gas is combusted in an elevated open burner. A
continuous or intermittent pilot light is generally used to maintain the combustion. While open
flares are thought to have combustion efficiencies similar to those of enclosed flares, data are not
available to confirm this because open-air combustion makes them difficult to test. Under NSPS,
Subpart WWW, open flares must meet a minimum Btu content and have a pilot light. For
landfills generating LFG that is unable to meet the Btu content consistently, it may be necessary
to supplement the collected gas with natural gas or another fuel source, which may create an
additional cost for the landfill.
Enclosed flares typically employ multiple burners within fire-resistant walls, which allow
them to maintain a relatively constant and limited peak temperature by regulating the supply of
combustion air (ATSDR, 200Ib). Enclosed flares can be tested for destruction efficiency of
NMOC and HAP. The background information document for the draft updated landfill AP-42
chapter provides an NMOC control efficiency range of 86% to 100% for flares, with an average
of 97.7% (EPA, 2008a). A report published by California's Bay Area Air Quality Management
District (BAAQMD) states that flares typically have CH4 destruction efficiencies of greater than
99.5% (BAAQMD, 2008). Under NSPS, Subpart WWW, enclosed flares are considered to be
incinerators and are required to have a minimum NMOC control efficiency of 98% by weight.
In California, flares are required to have minimum CH4 destruction efficiencies of 99% (CCR,
Article 4, Subarticle 6, Section 95464(b)(2)(A)(l)).
Electricity Generation
Internal combustion engines are the most widely used technology for the conversion of
LFG to electricity. Advantages of this technology include: low capital cost, high efficiency, and
adaptability to variations in the gas output of landfills. The operation of reciprocating engines at
low pressure (12-30 pounds per square inch (psi)) also yields less condensate than operation at
13
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higher pressure (60-160 psi) (Potas, 1993). Internal combustion engines are primarily used at
sites where gas production can generate 100 kilowatts (kW) to 3 megawatts (MW) of electricity,
or where sustainable LFG flow rates to the engines are approximately 50 to 960 cubic feet per
minute (cfm) at 50% CH4 (EPA, 2010d). For sites able to produce more than 3 MW of
electricity, additional engines may be added.
Turbines are an alternative to internal combustion engines. Turbines using LFG require a
dependable gas supply for effective operation, and are generally suitable for landfills when gas
production can generate at least 3 MW, or where sustainable LFG flow rates to the turbines are
over approximately 1,050 cfm at 50% CH4 (EPA, 2010d). Typically, LFG-fired turbines have
capacities greater than 5 MW. Advantages of this technology when compared to internal
combustion engines include: a greater resistance to corrosion damage, relatively compact size,
and lower operation and maintenance costs. When compared with other generator options,
turbines require additional power to run the plant's compression system.
Microturbines can be used instead of internal combustion engines for LFG energy
conversion. This technology generally works best for small scale recovery projects that supply
electricity to the landfill or to a site that is in close proximity to the landfill. Single microturbine
units have capacities ranging between 30 and 250 kW, and are most suitable for applications
below 1 MW, or where sustainable LFG flow rates to the microturbines are below approximately
350 cfm at 50% CH4 (EPA, 2010d). Sufficient LFG treatment is generally required for
microturbines and involves the removal of moisture and other contaminants (EPA, 2010c).
In general, turbines have a higher CH4 destruction efficiency (greater than 99.5%) than
internal combustion engines (roughly 96%) (BAAQMD, 2008). For landfills subject to NSPS,
Subpart WWW, control technologies are required to have a minimum control efficiency of 98%
by weight NMOC reduction or an outlet concentration of 20 parts per million by volume (ppmv),
dry basis as hexane at 3% O2, of NMOC. In California, LFG control devices other than flares
must achieve a CH4 destruction efficiency of at least 99% by weight; and lean burn internal
combustion engines must reduce the outlet CH4 concentration to less than 3,000 ppmv, dry basis,
corrected to 15% O2 (CCR, Article 4, Subarticle 6, Section 95464(b)(3)(A)). Lean burn internal
combustion engines are not defined within this California regulation; however, the NSPS for
stationary spark ignition internal combustion engines (40 CFR 60, Subpart JJJJ) defines lean
burn engines as any two-stroke or four-stroke spark ignited engine that does not meet the
definition of a rich burn engine. Rich burn engines are defined as any four-stroke spark ignited
engine where the manufacturer's recommended operating air/fuel ratio divided by the
stoichiometric air/fuel ratio at full load conditions is less than or equal to 1.1.
Cogeneration
Cogeneration, also known as combined heat and power (CHP), is the use of LFG to
generate electricity while recovering waste heat from the LFG combustion device. The thermal
energy recovered is usually in the form of steam or hot water that can be used for on-site heating,
cooling, or process needs. Cogeneration systems are typically more efficient and often more cost
effective than separate systems for heat and power (EPA, 2008b). Combustion technologies
14
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generally suitable for CHP include internal combustion engines, gas turbines, and microturbines.
There are also boiler/steam turbine applications where LFG is combusted in large boilers for
steam generation that is then used by turbines to create electricity (EPA, 2010c).
The CH4 control efficiency for cogeneration is directly linked to the electricity generation
unit combusting LFG. Landfills subject to NSPS, Subpart WWW, must meet the same
requirements for cogeneration as those listed above for electricity generation.
Direct Use
Landfill gas may be used to offset traditional fuel sources such as natural gas, coal, and
fuel oil used in industrial, commercial, and institutional applications. Direct use of LFG is
primarily limited to facilities within 5 miles of a landfill. There are, however, facilities that have
used LFG as a fuel at distances greater than 10 miles. Direct use applications for landfills
include: boilers (LFG used solely or co-fired with other fuels), direct thermal technologies (e.g.
dryers, heaters, kilns), and leachate evaporation. Innovative uses of LFG include heating
greenhouses, firing pottery, glassblowing, metalworking, and heating water for an aquaculture
(fish farming) operation (EPA, 2010c).
Control efficiencies of CH4 for LFG direct use applications vary depending on the type of
technology employed. For landfills subject to NSPS, Subpart WWW, control technologies are
required to have a minimum control efficiency of 98% by weight NMOC reduction or an outlet
concentration of 20 parts per million by volume (ppmv), dry basis as hexane at 3% C>2, of
NMOC. In addition, if a boiler or process heater is used as the control device, the collected LFG
must be routed into the flame zone.
Alternate Fuels
Purification techniques can be used to convert LFG to pipeline-quality natural gas,
compressed natural gas (CNG), or liquefied natural gas (LNG). Purification of LFG for the
production of natural gas typically involves the removal of inert constituents by adsorption
(molecular sieve), absorption with a liquid solvent, and membrane separation. The production of
pipeline-quality gas includes processing LFG to increase its energy content and pressurizing the
pipeline that is connected to the gas production facility (CCTP, 2005).
The conversion of LFG to CNG and LNG require similar processes, and the resulting
products can be used as vehicle fuel. First, the corrosive materials are removed through the use
of phase separators, coalescing filters, and activated carbon adsorbents. Next, water and C>2 are
removed. A cryogenic purifier is then used to remove CC>2, which yields high quality gas that is
over 90% CH4 (CCTP, 2005).
The type of LFG alternative fuel production and end use will affect the CFL; control
efficiency. For landfills subject to NSPS, Subpart WWW, control technologies are required to
have a minimum control efficiency of 98% by weight NMOC reduction or an outlet
concentration of 20 parts per million by volume (ppmv), dry basis as hexane at 3% O2, of
15
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NMOC. If the collected gas is routed to a treatment system, including purification and
conversion devices, then vented gases from the treatment system must meet these requirements.
Fuel Cells
A fuel cell is an electrochemical cell that converts energy from a fuel into electrical
energy. Electricity is generated from the reaction between a fuel supply and an oxidizing agent.
The products of basic fuel cell reactions are CO2, water vapor, heat, and electricity (Vargas,
2008). The difference between a battery and a fuel cell is that in a battery, all reactants are
present within the battery and are slowly being depleted during the use of the battery. In a fuel
cell, reactants (fuel) are continuously supplied to the cell (CEC, 2003). Fuel cells are used in a
variety of applications to generate clean electricity without the use of combustion such as in
generating transportation fuels for car, boats, and buses. Also fuel cells can serve as a power
source in remote locations such as spacecraft, remote weather stations, parks, and in military
applications. Fuel cells running on hydrogen are compact and lightweight and have no major
moving parts.
For LFG applications, fuel cells use hydrogen from CH4 to generate electricity (EPA,
1998b). Fuel cells have an advantage over combustion technologies in that the energy efficiency
is typically higher without generating combustion by-products such as NOX, CO, and sulfur
oxides (SOx) (EPA, 1998c). If fuel cells are used to generate electricity from landfill CFLt, then
a gas cleanup system is required to ensure that the catalyst within the fuel cell is not
contaminated by trace constituents that are present in LFG. Trace constituents include sulfur and
chlorine compounds which can inhibit performance and poison the catalyst (NREL, 1998).
EPA's Office of Research and Development conducted a review of fuel cells for LFG
applications. The phosphoric acid fuel cell was identified as most appropriate because it is
commercially available and has been successfully demonstrated at two landfills. Other types of
fuel cells (molten carbonate, solid oxide, polymer electrolyte membrane) may also be applicable
for LFG applications as further fuel cell development is conducted. The first demonstration of a
fuel cell was at the Penrose Landfill in California. The second was at a Connecticut landfill.
Both demonstrations used a 200 kW phosphoric acid fuel cell manufactured by ONSI
Corporation (EPA, 1998b). The energy efficiency for the demonstration at the Connecticut
landfill was 37% at 120 kW and could have been higher if the waste heat had been utilized. The
trace constituents removed in the gas clean up system were flared. An environmental and
economic evaluation of a commercial fuel cell energy system concluded that there is a large
potential market for fuel cells in this application. The major disadvantage is that the cost is
higher compared to combustion technologies such as internal combustion engines and turbines.
For landfills subject to NSPS, Subpart WWW, control technologies are required to have a
minimum control efficiency of 98% by weight NMOC reduction or an outlet concentration of 20
parts per million by volume (ppmv), dry basis as hexane at 3% O2, of NMOC. If the collected
gas is routed to a treatment system, including conversion devices, then vented gases from the
treatment system must meet these requirements.
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'-
The technologies to increase the CH4 oxidation rate include biocovers and biofiltration
beds. The principle of these technologies is the use of methanotrophic bacteria, which oxidize
LFG, specifically CH4, to water, CC>2, and biomass. Methanotrophic bacteria possess the CH4
mono-oxygenase enzyme that enables them to use CH4 as a source of energy and as a carbon
source. These bacteria are usually found in agricultural soils, forest soils, and compost. These
technologies are primarily in the research and development phase, rather than widespread
application. The details of these two technologies are discussed below.
Biocovers
A biocover is an additional final cover that functions as a CH4 oxidation enhancer to
convert CH4 into CO2 prior to venting to the atmosphere. A biocover is composed of two
substrate layers: a gas dispersion layer and a CH4 oxidation layer. The gas dispersion layer is an
additional permeable layer of gravel, broken glass, or sand beneath the porous media of the CH4
metabolizing layer. This layer is added to evenly distribute the uncaptured LFG to the CH4
oxidation media and to remove excess moisture from the gas. The CH4 oxidation media can be
made of soil, compost, or other porous media. This media is usually seeded with methanotrophic
bacteria from the waste decomposition.
This control technology does not require extensive retrofit and is applicable to all
landfills, including uncontrolled and older landfills with passive or active collection systems.
The biocover itself is not known to affect the functionality of an existing or new gas collection
and control system. In addition, it has low secondary criteria pollutant emissions. Biocovers can
be used as additional final cover to improve the CH4 oxidation rate. According to Abichou et al.
(2006), biocover applications increased the average CH4 oxidation rate up to 32%.
Biofiltration Beds
Similar to biocovers, biofiltration beds aim to further oxidize CH4 from passively
collected LFG. The collected LFG is passed through a vessel containing CH4-oxidizing media
prior to venting to the atmosphere or to a control system. This control technology is only
feasible for small landfills or landfills with passive gas collection systems due to the size of the
biofiltration bed required to treat an air/LFG mixture. In addition, due to the nature of passive
gas collection systems, this technology lacks the ability to control and monitor the LFG
collection. According to Morales (2006), a pilot project shows that the radial biofiltration bed
design has a CH4 oxidation rate of 19%.
A benefit of using a biofiltration bed compared to LFG combustion is that biofiltration
beds produce only CC>2 and water vapor. Unlike other combustion-based mitigation measures, a
biofiltration bed does not emit secondary pollutants such as NOX, SOX, and particulate matter.
This technology requires few safety controls for operation, and no start up or shut down
procedures.
17
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...-''''
The economic analysis for GHG control technologies is based on a cost effectiveness
value, which is defined in this paper as the cost to remove one metric ton of CC^e. The cost of
LFG control technologies can be estimated using the Landfill Gas Energy Cost Model
(LFGcost), which was developed by EPA's Landfill Methane Outreach Program (LMOP) (EPA,
2010d). This model includes direct and indirect costs associated with LFG energy (LFGE)
projects. The direct costs are the costs for equipment, including basic treatment of LFG, and
installation. The indirect costs include costs for engineering, design, and administration; site
surveys and preparation; permits, right-of-ways, and fees; and mobilization/demobilization of
construction equipment. Costs estimated by LFGcost are based on costs for average project
sites. Individual landfills should adjust costs based on site-specific parameters and conditions.
The types of LFG control projects included in LFGcost, Version 2.2 (EPA, 2010d) are as
follows:
LFG collection and flaring systems;
Direct LFG utilization projects;
Electricity generation with standard turbines (greater than 3 MW);
Electricity generation with standard reciprocating engines (800 kW and greater);
Processing LFG into a high Btu gas (1,000 standard cubic feet per minute (scfm) to
10,000 scfm);
Electricity generation with microturbines (30 kW to 750 kW);
Electricity generation with small reciprocating engines (100 kW to 1 MW);
Leachate evaporators (500 gallons/day and greater);
Electricity generation and hot water production with CUP reciprocating engines (800
kW and greater);
Electricity generation and steam production with CHP turbines (greater than 3 MW);
and
Electricity generation and steam production with CUP microturbines (30 kW to 300
kW).
In 2008, California's BAAQMD published an economic analysis study on LFG control
options using EPA's LFGcost software. This study was performed for MSW landfills of varying
sizes (1.5, 3.0, and 5.9 million Mgs), types (conventional and bioreactor), and waste densities
(low, medium, and high). The cost effectiveness values contained in the BAAQMD study for
electricity generation technologies are based on CC^e reduced due to avoided electricity
production at the power plant. These values were adjusted to determine cost effectiveness values
in terms of CO2e reduced from the combustion of CH4 and CO2e reduced from both the
combustion of CH4 and avoided electricity generation. Appendix A contains the calculation
procedures used to adjust the original cost effectiveness values in the BAAQMD report. The
cost effectiveness for adding LFG combustion options to conventional landfills with a medium
compacted waste density (100,000 tons of waste in place per acre) are provided in Table 4.
18
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Table 4. Cost Effectiveness for Various LFG Combustion Technologies
a,b
LFG Combustion Technology
Flare
Engine
Turbine
Microturbine
Small Engine
CHP Engine0
CHP Turbine0
CHP Microturbine0
Cost Effectiveness
($/metrictonofCO2e
reduced)
$6 - $25
$12 -$16
$12 -$18
$2 -$13
$11
$7 - $57
$4 -$51
$9 - $64
Cost Effectiveness
($/metrictonofCO2e
reduced and through
avoided electricity )
NA
$11 -$14
$12 -$16
$1 -$12
$11
$6 - $52
$4 - $47
$8 - $59
a Source: BAAQMD, 2008. Except for flares, values presented in BAAQMD, 2008 were based on CO2e
avoided through reduction in electricity generated. These values were adjusted to take into account the
CO2e reduced through combustion of CH/L. See Appendix A for detailed calculations.
b Except for flares, all cost effectiveness values shown do not include costs for the gas collection system.
A gas collection system would increase the cost effectiveness by between $5 and $10 per metric ton of
CO2e reduced.
0 CHP values do not include CO2e reductions due to reduction of fuel use where the heat or steam is being
used.
In general, it is more economical for larger landfills with high waste densities to install
LFG control technologies since their LFG generation rates are higher. The cost of installing
combustion technologies is lower for landfills with pre-existing gas collection systems. Flaring
is the cheapest combustion technology for most landfills, but flares do not have the potential to
generate revenue from LFGE projects.
The cost effectiveness for biocovers was estimated to be $745 per metric ton
reduced, according to the report prepared by BAAQMD (2008). Since the cost estimates for
biocovers were based on a few test sites, the actual cost effectiveness may vary widely.
19
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VI.
A bioreactor is typically defined as an MSW landfill where enhanced microbial processes
are used to expedite waste decomposition and biological stabilization. To properly manage the
stabilization process, certain system design and operational modifications are required
(Townsend, 2008). A bioreactor landfill employs the addition of liquid and air into the landfill
cell to enhance microbial processes. The most common liquid recirculated in bioreactor landfills
is leachate (waste liquid that drains from the landfill), but other liquids may be added to account
for lack of moisture in the waste mass (BAAQMD, 2008).
A hybrid (both aerobic and anaerobic enhancements) bioreactor landfill uses two primary
processes:
Air is injected in the top portion of the cell to increase aerobic activity; and
Liquid is injected into the lower (older) portions of the cell to regulate moisture and
promote anaerobic activity (BAAQMD, 2008).
While the term bioreactor is not specifically defined under Subtitle D of the Resource
Conservation and Recovery Act (RCRA), there are provisions that allow for short term research,
development, and demonstration (ROD) permits specific to bioreactor operations (Townsend,
2008). RCRA Subtitle D prohibits the disposal of bulk liquids unless an RDD permit is granted
and allows leachate and LFG condensate recirculation for landfills meeting composite liner
requirements. There are also provisions for the prevention of gas migration.
Enhanced degradation in bioreactor landfills also accelerates LFG generation. Compared
to conventional landfills, decomposition reaches a higher peak at the year of closure and then
declines more rapidly. For anaerobic bioreactors, CH4 generation rates typically increase 200-
250% (Pichtel, 2005). Since LFG is generated more rapidly and the CH4 concentration in LFG is
greater for bioreactor landfills, the gas can be collected and sold for energy recovery earlier than
non-bioreactor landfills. To account for accelerated LFG generation and ultimately mitigate
GHG emissions from bioreactors, the National Emission Standards for Hazardous Air Pollutants
(NESHAP) for landfills requires installation of the collection system and controls prior to liquids
addition (40 CFR 63, Subpart AAAA). It should also be noted that under the NESHAP
bioreactors are defined as having a minimum average moisture content of 40% by weight. The
NESHAP definition of bioreactors also excludes leachate and LFG condensate.
The feasibility of a bioreactor landfill depends on the landfill characteristics and climate.
The potential disadvantages of bioreactor landfills include increased odors, physical instability of
the waste mass, liner instability, surface seeps, and landfill fires from air addition. Benefits
include increased disposal capacity (i.e., more waste can be placed within a fixed volume of
landfill air space), shorter post-closure maintenance periods for LFG and leachate management,
and better profiles for energy recovery from LFG.
20
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Due to its high capital cost, the implementation of a bioreactor landfill design is suitable
primarily for newer active landfill cells that are equipped with the appropriate lining. For
existing landfills, converting conventional landfills to bioreactor landfills would require
significant changes in landfill design.
Organic materials account for about 55% of waste currently reaching landfills, primarily
consisting of food scraps, yard trimmings, wood, and paper/paperboard (EPA, 2010e). Due to
their role as the source of CFLt in landfills, the diversion of these materials prior to landfilling
may be used as a GHG reduction strategy. Diversion methods include composting, recycling,
and anaerobic digestion.
Organic waste diversion from landfills prevents CFLt generation. Methane generation at
landfills is reduced proportionally to the amount of organic waste diverted. For example, CFLt
generation at landfills is halved with a 50% organic waste diversion rate. Combining organic
waste diversion with a gas collection and control system can further reduce GHG emissions.
Recycling reduces the use of and emissions associated with virgin materials, thus
reducing GHG emissions associated with producing the material. Additionally, paper recycling
reduces harvesting of trees, thus stabilizing carbon sequestration from forests. According to
EPA's Waste Reduction Model (WARM), paper recycling reduces GHG emissions using a
lifecycle perspective (EPA, 201 Of). There are, however, processing and manufacturing
emissions associated with recycling (EPA, 2010e).
Well-managed composting operations facilitate aerobic decomposition. While CFLt and
nitrous oxide (N2O) emissions result from anaerobic conditions in the compost pile, a large
degree of uncertainty exists in quantifying these emissions. Production of CH4 and N2O from
composting varies greatly and results from several factors including: moisture content, carbon-
to-nitrogen ratio, stage of the composting process, and the technology used (e.g. windrows,
aerated static piles, and in-vessel). While composting operations may reduce GHG emissions,
there are emissions associated with pre-processing and on-site equipment (e.g. windrow turners,
screens, and blowers); these emissions vary greatly based on the technology used (EPA, 2010e).
Anaerobic digestion is a process where microorganisms break down organic materials in
the absence of oxygen. Organic materials are digested in closed containers, minimizing fugitive
GHG emissions. Anaerobic digestion yields two products: biogas and a solid residue that can be
used as a soil amendment, which can offset conventional fertilizer production and use. Biogas
can be used for electricity generation, fuel, or cogeneration.
21
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Hillary Ward
U.S. EPA
OAQPS/SPPD/CCG
Mail Code El43-01
Research Triangle Park, NC 27711
Phone: 919-541-3154
Ward.Hillary@epa.gov
22
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References
Abichou, 2006. Field Performance ofBiocells, Biocovers, and Biofilters to Mitigate
Greenhouse Gas Emissions from Landfills. Abichou, T., et al. Florida Center for Solid and
Hazardous Waste Management. March 2006.
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BAAQMD, 2008. Greenhouse Gas Mitigation: Landfill Gas and Industrial, Institutional and
Commercial Boilers, Steam Generators and Process Heaters. Bay Area Air Quality
Management District (BAAQMD), prepared by URS Corporation. April 2008.
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http://www.energy.ca.gov/distgen/equipment/fuel cells/fuel cells.html
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http://www.epa.gov/ttn/catc/dir 1 /etech pd.pdf
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EPA, 1998c. Demonstration of Fuel Cells to Recover Energy from Landfill Gas: Phase III.
Demonstration Tests, and Phase IV. Guidelines and Recommendations. National Risk
Management Research Laboratory, U.S. EPA. March 1998.
http://www.epa.gov/nrmrl/pubs/600sr98002/600sr98002.pdf
EPA, 2008a. Background Information Document for Updating AP 42 Section 2.4 for Estimating
Emissions from Municipal Solid Waste Landfills. National Risk Management Research
Laboratory, Air Pollution Prevention and Control Division, U.S. EPA. September 2008.
http://www.epa.gov/ttn/chief/ap42/ch02/draft/db02s04.pdf
EPA, 2008b. Clean Energy Strategies for Local Governments, Section 7.4: Landfill Methane
Utilization, Draft. Landfill Methane Outreach Program (LMOP), Climate Change Division, U.S.
EPA. December 10, 2008.
http://www.epa.gOv/statelocalclimate/documents/pdf/7.4 landfill methane utilization.pdf
EPA, 2010a. Municipal Solid Waste Generation, Recycling, and Disposal in the United States:
Facts and Figures for 2009. Solid Waste and Emergency Response, U.S. EPA. December 2010.
http://www.epa.gov/epawaste/nonhaz/municipal/pubs/msw2009-fs.pdf
EPA, 201 Ob. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008. U.S. EPA.
April 2010. http://epa.gov/climatechange/emissions/usinventoryreport.html
EPA, 2010c. Landfill Gas Energy Project Development Handbook. Landfill Methane Outreach
Program (LMOP), Climate Change Division, U.S. EPA. January 2010.
http://epa.gov/lmop/publications-tools/handbook.html
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9 Air and Waste Divisions, U.S. EPA. September 2010.
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http://www.epa.gov/climatechange/wycd/waste/calculators/Warm home.html
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Oxidizing Biofilters. Morales, J.J., Florida State University, FAMU/FSU College of Engineering.
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114600/unrestricted/JoseMoralesThesis.pdf
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and R. Sanderson, Energy Research Corporation. National Renewable Energy Laboratory
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John. CRC Press. 2005.
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Potas, 1993. Gas Recovery and Utilization from Municipal Solid Waste Landfills. Potas, T.A.,
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Capture by Gas Collection Systems? Spokas, K., et al. Waste Management. July 29, 2005.
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Climate Solutions (SWICS), prepared by SCS Engineers. Version 2.2, January 2009.
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Monitoring: Version 1.0. Townsend, T., et al. Department of Environmental Engineering
Sciences, University of Florida. July 1, 2008.
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LUMES/Bioreactor Landfill OperationV10.pdf
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A
to for COie
Cost effectiveness values in Tables 1 and 4 of this paper were derived from cost
effectiveness values in a report published by California's Bay Area Air Quality Management
District (BAAQMD, 2008). However, the values contained in the BAAQMD report for energy
recovery technologies are in units of dollars per metric ton of CO2e emissions reduced due to
avoided electricity generation at the power plant. The cost effectiveness values from the 2008
BAAQMD report were adjusted to produce cost effectiveness values in units of dollars per
metric ton of CO2e emissions reduced based on the conversion of CH4 to CO2, a less potent
global warming pollutant. Cost effectiveness values were also generated based on the GHG
emission reductions from both the conversion of CH4 to CO2 (referred to as direct CO2e
reductions) and the CO2 emissions avoided from less electricity generated at the power plant
(referred to as avoided CO2e reductions). This appendix details the calculations for both cost
effectiveness values. The cost effectiveness values for flares in the BAAQMD report are based
on CH4 destruction because no energy is recovered (i.e., no electricity avoided); therefore, flare
cost effectiveness values were used directly from the report.
The BAAQMD report presents a range of cost effectiveness values for each technology
to account for different sized landfills (10 acres, 20 acres & 40 acres). The BAAQMD cost
effectiveness values for electricity generation technologies do not include costs for the gas
collection system.
A.I Cost Effectiveness Values Based on Direct COie Reductions
The BAAQMD report referenced the California Climate Action Registry's General
Reporting Protocol for estimating emission reductions from avoided electricity generation.
Tables E.I and E.3 of the General Reporting Protocol contain the 2007 California electricity
emission factors listed below. It was assumed that these factors, in units of pounds (Ib) per
megawatt-hour (MWh), were used to estimate avoided emissions from the power plant (CCAR,
2009).
CO2 electricity emission rate = 878.71 Ib/MWh
CH4 electricity emission rate = 0.0067 Ib/MWh
N2O electricity emission rate = 0.0037 Ib/MWh
To determine the total amount of CO2e reduced from avoided electricity generation,
global warming potentials were applied to the CH4 and N2O emission rates. The consolidated
CO2e emission rate was calculated as follows:
26
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Overall CO2e electricity emission rate = (878.71) + (0.0067 x 21) + (0.0037 x 310)
= 880 Ib CO2e/MWh
The BAAQMD report utilized LMOP's LFGcost software (EPA, 2010c). To properly
adjust the cost effectiveness values, fuel use rates and efficiencies for each electricity generation
technology from LFGcost were used. These default values are provided in Table A-2.
Table A-2. LFGcost Fuel Use Rates and Efficiencies for LFG Electricity Generation
Technologies
LFG Technology
Engine
Turbine
Microturbine
Small Engine
CHP Engine
CHP Turbine
CHP Microturbine
Fuel Use Rate
(Btu/kWh generated)
11,250
13,000
14,000
18,000
11,250
13,000
14,000
Efficiency
(%)
93
88
83
92
93
88
83
Source: EPA, 201 Oc
The example calculation outlined below is for the low value of the cost effectiveness
range for engines ($122 per metric ton (MT) of CO2e avoided). The first step is to use the
overall CO2e electricity emission rate to convert the cost effectiveness value from dollars per
metric ton of CO2e avoided to dollars per amount of electricity produced (in units of MWh), as
follows:
($122/metric ton CO2e) x (metric ton/2205 Ib) x (880 Ib CO2e/MWh) = $48.7 per MWh
The second step is to use the appropriate fuel use rate and efficiency from Table 2 and the
heat content and density of CH4 to calculate the cost in terms of dollars per metric ton of CH4
produced by the landfill, as follows:
($48.7/MWh) x (MWh/1000 kWh) x (kWh/11,250 Btu) x 0.93 x (1012 Btu/ft3 CH4) x
(ft3 CH4/0.0423 Ib CH4) x (2205 Ib/metric ton) = $212 per metric ton CH4
The next step is to calculate the amount of CO2e reduced from the conversion of CH4 to
CO2. The global warming potential of CH4 is 21, which is used to express the amount of CH4
destroyed in terms of CO2e. The amount of CO2 generated from the combustion of CH4 must be
subtracted from the amount of CH4 destroyed using a mass balance method to result in an
accurate measure of CO2e reduced. The overall CO2e reduced is calculated as:
27
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CO2C reduced = (CH4 destroyed as CC^e) - (CO2 generated by CH4 combustion)
CO26 reduced = (21 metric tons CC^e/metric ton CH4) - (44 metric tons CO2/16 metric tons CH4)
CO2e reduced = 18.25 metric tons CO2e per metric ton CH4
Lastly, the dollars per metric ton of CH4 produced by the landfill are divided by the
overall CO26 reduced to estimate the cost effectiveness values in terms of dollars per metric ton
of direct CO2e reduced, as follows:
Adjusted cost effectiveness = ($212/metric ton CH4) x (metric ton CH4/18.25 metric tons CC^e)
Adjusted cost effectiveness = $12 per metric ton direct CO26 reduced
Tables 1 and 4 in the main section of this paper contain the adjusted cost effectiveness
values for direct CC^e reduced for all seven electricity generation technologies.
A.2 Cost Effectiveness Values Based on Direct and Avoided COie Reductions
The original cost effectiveness values in the 2008 B AAQMD report represent avoided
CO26 reductions and the adjusted cost effectiveness values, as discussed in section A.I, represent
direct CO2e reductions. Therefore, the calculation of cost effectiveness values that represent
both direct and avoided CC^e reductions can be accomplished using the original and adjusted
cost effectiveness values. The derivation of the equation used to determine cost effectiveness
values in units of dollars per metric ton of direct and avoided CO26 reductions is as follows:
$/D = $ per metric ton of direct CC^e reduced
$/A = $ per metric ton of avoided CC^e reduced
$/(D+A) = $ per metric ton of direct and avoided CO26 reduced
$/(D+A) = ($/A) / ((D+A)/A) = ($/A) / ((D/A) + (A/A)) = ($/A) / ((D/A) + 1)
$/(D+A) = ($/A)
Using the example calculation for the low cost effectiveness value for engines from
section A. 1, the cost effectiveness value for direct and avoided CC^e reduced is calculated as:
$/D = $12/metric ton of direct CC^e reduced
$/A = $122/metric ton of avoided CC^e reduced
$/(D+A) = ($122/metric ton) / (($122/metric ton)/($12/metric ton) + 1) = $1 I/metric ton
Cost effectiveness for direct & avoided CC^e reduced = $11 per metric ton of CC^e reduced
Table 4 in the main section of this paper contains the cost effectiveness values for direct
and avoided CC^e reduced for all seven electricity generation technologies.
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