Nicholas P. Cheremisinoff. Handbook of Solid Waste Management and Waste Minimization Technologies
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concerns with this option are the integrity of the pipeline, liability issues, and the
economic support of neighboring polluting industries which might use the gas.
Internal combustion engines are the dirtiest technology for burning landfill gas.
They emit the most carbon monoxide and NO
x
and they may be the largest dioxin
source of the available technologies.
Gas turbines are somewhere in the middle in terms of carbon monoxide and NO
x
emissions. There isn't enough data on dioxin emissions from landfill gas turbines
to provide an extensive comparison.
Fuel cells are the most expensive technology, and they are still largely
experimental. EPA describes fuel cells as "potentially one of the cleanest energy
conversion technologies available." In order not to poison the fuel cells,
halogenated contaminants must first be removed and destroyed, for example by
pyrolysis.
One option is to convert the methane recovered from landfills into methyl alcohol
or methanol. Other novel ideas include converting the carbon dioxide in landfill
gas to dry ice for sale to industry.
The concept of cleaning up the landfill gas to pipeline quality, while
environmentally friendly, is not cost-effective. Since natural gas prices are so
low, this is not expected to be economical anytime soon. It also requires a high
degree of cleaning and filtering the gas. To the extent that the gas is not
adequately filtered, the landfill gas will be degrading the quality of the natural
gas by adding more contaminants to the system.
LIFE CYCLE COST CONSIDERATIONS
The advantages of energy recovery from landfill gas include decreased emissions
of methane, NMOCs, and toxics (e.g., benzene, carbon tetrachloride, and
chloroform). Although carbon dioxide (CO
2
) emissions increase with energy
recovery, the net atmospheric balance is a positive one because CO
2
emissions
are significantly less radiative, which means that the greenhouse effect is less
than methane emissions.
The average size of a landfill gas energy recovery project is about 3 megawatts,
with typically over 95% availability. The number of commercial energy recovery
projects has grown from a handful in the 1980s to more than 130 in 1990s. Even
though there has been a large increase in projects, there are more than 700
landfills across the U.S. that could install landfill gas energy recovery systems.
About 30 of the original conversion and direct use projects initiated in the 1970s
and 1980s have had to shut down due to more competitive market conditions.
Therefore, although the advantages of landfill gas energy recovery are significant
from an environmental standpoint, there are few successful commercial projects
relative to the number of MSW landfills because of prevailing market conditions
and the array of other barriers that confront project developers. According to M.
Doom, J. Pacey, and D. Augenstein (see Landfill Gas Energy Utilization
Experience: Discussion of Technical and Non-Technical Issues, Solutions, and
Trends, EPA-600/R-95-035, prepared by E.H. Pechan and Associates, Inc., for
the Air and Energy Engineering Research Laboratory, USEPA, Washington,
D.C, March 1995), the principle barriers to gas recovery and conversion to
energy include:
• Low oil and gas prices (current and projected future)
• Need for expensive new, sometimes untested, technology (e.g., fuel
cells)
• High transportation costs (e.g., dedicated pipelines have to be built for
relatively small supplies of gas)
• High debt-service rates for projects that generate electricity or pipeline-
quality gas
• Limited or unstable marketplace
• Obtaining third-party project financing at reasonable cost (financing is
difficult, time-consuming, and proportionately more costly for small
projects than for large ones)
• Difficulties obtaining air permits, especially for projects located in
ozone, nitrogen oxide, and carbon monoxide nonattainment areas,
because air boards and utilities often have lengthy permit processes and
contract negotiations
• Difficulties in negotiating power contracts with local utilities because
they are primarily interested in purchasing low-cost power without
considering environmental externalities (e.g., offsets from power plants
using fossil fuel)
• Unforeseen costs resulting from compliance with new air quality rules
and regulations, and declining energy revenues that cannot be adjusted
to offset new costs
• Taxation by some states (e.g., California) on LFG extraction and energy
conversion facilities
• Difficulties in complying with overlapping federal and state energy
policies and environmental regulations that may affect these projects
The most significant barrier is low oil and natural gas prices, which make
recovery and conversion, with its high initial capital costs, lack of economies of
scale, and high transportation costs, uncompetitive in many situations. Table 5
Although LLC studies do not appear in the literature, in general the most
economical options for landfill gas utilization are direct uses such as process heat
and boiler fuel, where the end users are in relatively close proximity (no more
than 1 or 2 miles) to the landfill, and whose gas supply needs closely match
production at the landfill. In the United States, end users are infrequently located
near landfills and rarely require continuous fuel in the amounts produced;
however this is not always the case in other countries. This situation can be found
more frequently in Central and Eastern Europe. Boiler fuel is the most typical
direct use and can be attractive when conventional equipment can be retrofitted
with minimal modifications. Boilers are generally less sensitive to landfill gas
trace constituents and therefore require less cleanup than other alternatives. End-
use options include industrial applications such as kilns, lumber drying, oil
refining, hotel heating, and cement manufacturing. These are likely economically
attractive candidates because of the continuous need and availability of the fuel.
provides a comparison of current costs for different landfill gas energy recovery
technologies.
Table 5. Comparison of Costs for Energy Recovery Technologies
(1992 Dollars, Unless Otherwise Noted)
Technology/use
Internal combustion
engine/electricity
generation
Gas turbine/electricity
generation
Steam turbine/electricity
generation
Boiler/direct heat
Organic rankine/heat
recovery
Fuel cell/electricity
generation
Capital costs
(dollars per kilowatt)
900 to 1200
1000 to 1500
900
a
1000 to 1500
1000 to 1500
3000+
b
O&M costs
(dollars per
kilowatt-hour)
0.013 to 0.020
0.01 to 0.015
0.001
a
0.005 to 0.018
0.005
NA
a
1993 dollars.
b
1995 dollars, using 1995 technology.
NA = not available.
Sources: T.D. Williams, "Making Landfill Gas an Asset," Solid Waste and
Power (July/August 1992), p. 22; and CE. Anderson, "Selecting Electrical
Generating Equipment for Use with Landfill Gas," Proceedings of the SWANA
16th Annual Landfill Gas Symposium (Louisville, KY, March 1993).
ELECTRICITY GENERATION
As noted earlier, the primary applications for landfill gas electricity generation
are internal combustion engines, gas turbines, and fuel cells. Most of the
operating landfill energy recovery projects sell electricity under contract to a
utility. Internal combustion engines are economical where the supply of gas is
enough to produce 1 to 3 megawatt-hours. Turbines are most economical at sites
with output of over 3 megawatt-hours. The advantages of internal combustion
engines include comparatively low capital costs (between $950 and $1250 per
kilowatt), good efficiency, a high degree of standardization, and portability,
which facilitates transportation from one landfill site to another. A major
disadvantage with internal combustion engines is emissions. There are two types
of internal combustion engines, each having distinct emissions characteristics.
Stoichiometric combustion engines generate high nitrous oxides (NO
x
) emissions.
Lean-burn engines generate lower NO
x
and CO emissions, so they are better
suited for applications where these emissions are a concern.
There are several disadvantages in using gas-fed turbines. They typically have
parasitic energy losses of 17% of gross output. By comparison, internal
combustion engines only have about 7%. Other disadvantages include poor
turndown performance compared to internal combustion engines, and difficulties
may occur when they are operated at less than a full load. Additional problems
are combustion chamber melting, corrosion, and accumulation of deposits on
turbine blades.
Fuel cells may become attractive because of their higher energy efficiency,
negligible emissions impact, and suitability for all landfill sizes. Fuel cells have
low labor and maintenance costs. At present, however, economic and technical
disadvantages make fuel cells clearly uncompetitive with more conventional
applications. This includes the high capital cost of designing an landfill gas
cleanup process that can remove the trace constituents from the gas since fuel
cells require a higher grade of gas purification than other options. There is also a
very high capital investment required, costing about $3,000 per kilowatt using
state-of-the-art technology. Because of continued advances in fuel cell technology
and the possibility of more stringent future emissions requirements that may
make other technologies more costly, fuel cells will could eventually become
competitive.
NONCOMBUSTION TECHNOLOGIES
Noncombustion technologies were developed in the 1990s as an alternative to
combustion, which produces compounds that contribute to smog, including
nitrogen oxides, sulfur oxides, carbon monoxide, and particulate matter.
Noncombustion technologies fall into two groups: energy recovery technologies
and gas-to-product conversion technologies. Regardless of which noncombustion
technology is used, the landfill gas must first undergo pretreatment to remove
impurities such as water, NMOCs, and carbon dioxide. Numerous pretreatment
methods are available to address the impurities of concern for a specific landfill.
After pretreatment, the purified landfill gas is treated by noncombustion
technology options.
As noted, energy recovery technologies use landfill gas to produce energy
directly. Currently, the phosphoric acid fuel cell (PAFC) is the only
commercially available noncombustion energy recovery technology. Other types
of fuel cells (molten carbonate, solid oxide, and solid polymer) are still under
development. The PAFC system consists of landfill gas collection and
pretreatment, a fuel cell processing system, fuel cell stacks, and a power
conditioning system. Several chemical reactions occur within this system to
create water, electricity, heat, and waste gases. The waste gases are destroyed in
a flare.
Gas-to-product conversion technologies focus on converting landfill gas into
commercial products, such as compressed natural gas, methanol, purified carbon
dioxide and methane, or liquefied natural gas. The processes used to produce
each of these products varies, but each includes landfill gas collection,
pretreatment, and chemical reactions and/ or purification techniques. Some of the
processes use flares to destroy gaseous wastes.
Noncombustion energy recovery systems are not used as widely as combustion-
based systems. Fuel cells are a promising new technology for producing energy
from landfill gas that does not involve combustion. This technology has been
demonstrated and in the future may become more economically competitive with
other options. One option that does not involve combustion of landfill gas at or
near the landfill is purifying the landfill gas to remove constituents other than
methane, producing a high British thermal unit (Btu) gas that can be sold as
pipeline quality natural gas. Although the high-Btu gas is eventually combusted,
it would not contribute to any emissions near the landfill. Another option is using
compressed landfill gas as a vehicle fuel.
Both combustion and noncombustion energy recovery systems have three basic
components: (1) a gas collection system; (2) a gas processing, treatment, and
conversion system; and (3) a means to transport the gas or final product to the
user. Gas is collected from the landfill by the use of active vents. It is then
transported to a central point for processing. Processing requirements vary,
depending on the gas composition and the intended use, but typically include a
series of chemical reactions or filters to remove impurities. For direct use of
landfill gas in boilers, minimal treatment is required. For landfill gas injection
into a natural gas pipeline, extensive treatment is necessary to remove carbon
dioxide. At a minimum, the gas is filtered to remove any particles and water that
may be suspended in the gas stream.
Below are some examples of how gas collected from landfills is being reused for
power.
• In Raleigh, North Carolina, Ajinomoto Pharmaceutical Company has
used landfill gas as fuel in boilers at its facility since 1989. The steam
produced by the boilers is used to heat the facility and warm
pharmaceutical cultures. This project has prevented pollution equivalent
to removing more than 23,000 cars from the road.
• In Pittsburgh, Pennsylvania, Lucent Technologies saves $100,000 a year
on fuel bills by using landfill gas to generate steam for space heating and
hot water.
• The City of Riverview, Michigan, works with the local utility, Detroit
Energy, to recover landfill gas and create electricity with two gas
turbines. The project generates enough power to meet the energy needs
of more than 3700 homes.
• The Los Angeles County Sanitation District in California has succeeded
in turning landfill gas into a clean alternative vehicle fuel. Landfill gas is
compressed to produce enough fuel per day to run an 11-vehicle fleet,
ranging from passenger vans to large on-road tractors.
• Pattonville High School in Maryland Heights, Missouri, is located
within 1 mile of a municipal solid waste landfill. The landfill supplies
methane gas to heat the 40000-square-foot high school, saving the
Pattonville School District thousands of dollars in annual heating costs.
Pattonville High School was the first high school to use landfill gas as its
source of heat.
FEEDSTOCK CHEMICALS FOR MANUFACTURING
This approach involves the use of expensive cleanup, purification, and processing
equipment to bring the gas to the quality standards of alternative feedstocks, such
as natural gas. Using landfill gas as a chemical manufacturing feedstock remains
largely uneconomical as long as the price of conventional feedstocks (e.g.,
natural gas) remains low. Other disadvantages are high transportation costs and a
need for proximity to the end user. Landfill sites have found that gas pipelines
cannot exceed 1 or 2 miles to be cost-effective. Potential uses for the feedstock
include production of methanol and diesel fuels.
PIPELINE-QUALITY GAS
This option involves the conversion of landfill gas from a medium heating value
gas into high heating value gas for local gas distribution networks or, in
compressed form, for vehicular fuel. This option remains uneconomical as long
as the prices of natural gas and oil remain relatively low. Disadvantages include
the need for a more thorough and expensive purification process than in some
other options (but the same as in feedstock for chemical manufacturing processes
and fuel cell applications), high transportation costs, and need for proximity to
the end-user.
A SHORT REVIEW
Landfill gas is the single largest source of man-made methane emissions in the
United States, contributing to almost 40% of methane emissions each year.
Consequently, a growing trend at landfills is to use recovered methane gas from
landfills as an energy source. Collecting landfill gas for energy use greatly
reduces the risk of explosions, provides financial benefits for the community,
conserves other energy resources, and potentially reduces the risk of global
climate change. Currently in the U.S., approximately 325 landfill gas energy
recovery projects prevent emissions of over 150 billion cubic feet of methane per
year (or more than 300 billion cubic feet of landfill gas). Approximately 220 of
these projects generate electricity, producing a total of more than 900 megawatts
per year. Another 68 projects are under construction in 2001, and more than 150
additional projects are in the planning stages. Previous studies by EPA and the
Electric Power Research Institute estimate that up to 750 of the landfills in the
United States could profitably recover and use their methane emissions. There
are several technologies that enable the use of landfill gas to be recovered and
applied to the generation of energy, however, many of these have been only
partially successful at the local level. In general, the poor quality of landfill gas
makes it costly to rely upon it as a form of green energy, and the capital
investments are high for large-scale applications. Because landfill gas contains
toxic constituents, end-of-pipe treatment technologies must be heavily relied upon
in order to purify and concentrate the gas to a sufficiently high heating value.
This brings one to realize that P2 must play a more dominant role in reducing the
environmental impacts of landfill gas. Doing nothing is simply not an option
because off-site gas migration can lead to the risk of fire, explosions, and
greenhouse gases. In order for P2 to have a broad impact, such things as phasing
out of halogens in industrial use must be implemented aggressively. This is a way
in which we can stop chlorine, fluorine and bromine pollution and the
organohalogens (dioxins, furans, etc.) that come with them. The technology of
landfilling itself needs to be re-examined. There are communities in the United
States which are recycling 80 to 90% of their waste. It is the act of mixing
materials together that makes waste on a large scale. Source separation and
recycling minimizes and can even prevent this.
RECOMMENDED RESOURCES
General information about landfill emissions and emissions monitoring can be
found in the following resources. In addition, state and federal environmental
officials are an excellent resource for site- specific insights.
1.
Information related to the CAA regulations for municipal solid waste
landfills and landfill emissions estimation can be found at
http:
//www. epa. gov/ttn/atw/landfill/landflpg. html. The actual regulatory
text, which includes emissions estimation, testing, and monitoring
requirements, can be found in 40 CFR Part 60, Subparts Cc and WWW.
2.
EPA maintains a Web site (http://www.epa.gov/ttn/emc), with general
information about emissions sampling methodologies; some of this
information is specific to emissions monitoring at landfills.
3.
EPA. Guidance on Collection of Emissions Data to Support Site-specific
Risk Assessments at Hazardous Waste Combustion Facilities, EPA/ 530-D-
98-002,
1998.
4.
Scotto, R. L, Minnich, T. R, and Leo, M. R. 1991, A Method for
estimating VOC emission rates from area sources using remote optical
sensing. In the Proceedings of the AWMA/EPA International Symposium on
the Measurement of Toxic and Related Air Pollutants, Durham, NC, May
1991.
5.
Augenstein, D., R. Morck, J. Pacey, D. Reinhart, and R. Yazdani, "The
Bioreactor Landfill—An Innovation in Solid Waste Management,"
Proceedings of the Texas Natural Resource Conservation Commission
Environmental Trade Fair, Austin, TX, May 1999.
6. Baldwin, T., R. Ham, P. O'Leary, J. Spear, and P. Stecker, A Design
Guide for Innovative Methane Production at Landfills, Council of Great
Lakes Governors Regional Biomass Program, 1997.
7.
Fagan, D.A. and R. Johncox. "A 750-TPD In-place Biostabilization of
MSW Demonstration Project at the Ontario County (NY) Landfill,"
Proceedings of the Federation of New York Solid Waste Association's 1999
Spring Solid Waste Conference, Saratoga Springs, NY, April 1999.
8. New York State Department of Environmental Conservation, Division of
Solid & Hazardous Materials, 6 NYCRR Part 360 Solid Waste Management
Facilities, January 1997.
9. Othman, M.A., R. Bonaparte, and B.A. Gross. "Preliminary Results of
Survey of Composite Liner Field Performance," Proceedings of the W
h
Geosynthetic Research Institute Conference, Philadelphia, PA, December
1996.
10.
Pacey, John, "Bioreactor Landfill Performance Expectations." MSW
Management, December 1998.
11.
Phaneuf,
RJ. "Landfill Bioreactor Design and Operation: A New York State
Regulatory Perspective," Proceedings of Landfill Bioreactor Seminar. US
Environmental Protection Agency, EPA/600/R-95/146, September 1995.
12.
US Environmental Protection Agency. 40 CRF Parts 257 and 258 Solid
Waste Disposal Facility Criteria; Final Rule. October 9, 1991.
Chapter 5
VOLUME REDUCTION
TECHNOLOGIES
INTRODUCTION
There are a wide range of technology options to select from for volume reduction
purposes. These include incineration, size reduction, composting, concentrating
techniques, and drying. Municipal solid waste disposal generally relies upon the
first three, but industry often has unique applications and utilizes incineration,
size reduction, concentrating methods, and drying more frequently. Among these
technology groups, incineration (unless coupled with energy production), drying,
size reduction, and concentrating techniques for the most part represent treatment
practices. In other words, they are within the end-of-pipe category of options for
waste management. They can be applied to incrementally improve environmental
performance and achieve savings in operational costs for handling and disposing
of large volumes of wastes, but they are not applied as source reduction methods.
They can be effectively applied in pollution prevention and waste minimization
projects as ancillary techniques, and hence the operational experiences in
standard treatment practices provide useful guidelines. Composting also is not
source reduction, but it is a form of recycling.
SIZE REDUCTION
As received, most solid waste has a low bulk density and is composed of a wide
variety of objects in all sizes and shapes. This is especially the case for MSW.
Solid waste shredding machines are not capable of destroying waste matter, but
only of converting it into a form more easily and economically handled for
processing. Hammer mills in one adaptation or another are the most commonly
used size reduction machine.
The machines are variously called shredders, crushers, pulverizers, mills, and
hoggers. Shredder is the most frequently used term. At one time, both capacity
and durability posed important limitations to the application of waste shredders
on a large scale. This is no longer true. Today, shredders are in service which