An overview of the global waste-to-energy
industry
Article by Nickolas J. Themelis in Waste Management
World (www.iswa.org), 2003-2004
Review Issue, July-August 2003, p. 40-47
Nickolas J. Themelis |
Despite the expansion of the global waste-to-energy (WTE) industry in
the past decade, hundreds of millions of tonnes of municipal solid
wastes still end up in landfills. For every tonne of waste landfilled,
greenhouse gas emissions in the form of carbon dioxide increase by
at least 1.3 tonnes. This article provides an overview of the WTE industry,
and reviews recent advances made in the US in decreasing dioxin and
mercury emissions. The recently established Waste-to-Energy Research
and Technology Council hopes to bring together global academic and
industrial expertise with the aim of improving WTE technologies.
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Worldwide, about 130 million tonnes of municipal
solid waste (MSW) are combusted annually in over
600 waste-to-energy (WTE) facilities that produce
electricity and steam for district heating and recovered
metals for recycling. Since 1995, the global WTE industry
increased by more than 16 million tonnes of MSW.
Currently, there are WTE facilities in 35 nations, including
large countries such as China and small ones such as
Bermuda. Some of the newest plants are located in Asia.
According to a directive from the European Union,1
landfilling of combustible materials must be phased out
within the decade. However, it is not clear that the capital
investments required will be made by all of the member
countries. Some of them have little WTE capacity and some
- for example, Greece - none at all. The current EU installed
capacity and per-capita use of WTE for the disposal of
municipal solid waste is shown in Table 1.2 For
comparison, the use of WTE amounts to 314 kg per capita
in Japan, 252 kg in Singapore, and 105 kg in the US. One of
the newcomers to WTE is China, with seven plants in
operation and an estimated annual capacity of 1.6 million
metric tonnes per year.
Current state of the global WTE industry
A 2002 review of the European WTE industry by the
International Solid Waste Association showed that the total
installed capacity was more than 40 million tonnes per
year and the generation of electrical and thermal energy
was 41 million GJ and 110 GJ, respectively (Table 1). It
should be noted that, in contrast to Europe, the US makes
very little use of the exhaust steam from the power-generating
turbines for either district or industrial heating.
A good example of cogeneration of thermal and electric
energies is the Brescia WTE facility in Italy (see page 45)
that provides an estimated 650 kWh of electricity per
tonne of MSW combusted. In the cold season, it supplies at
least as much energy as for district heating.3
TABLE 1. Reported WTE capacity in Europe2
Country |
Tonnes/year (in 1999) |
Kilograms/capita |
Thermal energy (gigajoules) |
Electric energy (gigajoules) |
Austria |
450,000 |
56 |
3,053,000 |
131,000 |
Denmark |
2,562,000 |
477 |
10,543,000 |
3,472,000 |
France |
10,984,000 |
180 |
32,303,000 |
2,164,000 |
Germany |
12,853,000 |
157 |
27,190,000 |
12,042,000 |
Hungary |
352,000 |
6 |
2,000 |
399,000 |
Italy |
2,169,000 |
137 |
3,354,000 |
2,338,000 |
Netherlands |
4,818,000 |
482 |
|
9,130,000 |
Norway |
220,000 |
49 |
1,409,000 |
27,000 |
Portugal |
322,000 |
32 |
1,000 |
558,000 |
Spain |
1,039,000 |
26 |
|
1,934,000 |
Sweden |
2,005,000 |
225 |
22,996,000 |
4,360,000 |
Switzerland |
1,636,000 |
164 |
8,698,000 |
2,311,000 |
UK |
1,074,000 |
18 |
1,000 |
1,895,000 |
Total reported |
40,484,000 |
154.5
(average) |
109,550,000 |
40,761,000 |
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The US WTE industry represents about 23% of the global
capacity; 66% of that is concentrated in seven states on the
East Coast (Table 2).
TABLE 2. Major users of WTE in the US4
State |
Number of plants |
Capacity (short US tons/day) |
Connecticut |
6 |
6,500 |
New York |
10 |
11,100 |
New Jersey |
5 |
6,200 |
Pennsylvania |
6 |
8,400 |
Virginia |
6 |
8,300 |
Florida |
13 |
19,300 |
Total |
53 |
69,600 |
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Current state of WTE technology
The dominant WTE technology is mass burning, because of
its simplicity and relatively low capital cost. The most
common grate technology, developed by Martin GmbH
(Munich, Germany), has an annual installed capacity of
about 59 million metric tonnes. The Martin grate at the
Brescia (Italy) plant is one of the newest WTE facilities in
Europe. Figure 1 shows a schematic diagram of its mass-burn
combustion chamber. The Von Roll (Zurich,
Switzerland) mass-burning process follows with 32 million
tonnes worldwide. All other mass-burning and refuse-derived-
fuel (RDF) processes together have a total
estimated capacity of more than 40 million tonnes.
FIGURE 1. Schematic diagram of the Brescia mass-burn combustion chamber 3
The SEMASS facility in Rochester, Massachusetts, USA,
developed by Energy Answers Corp. and now operated by
American Ref-Fuel, has a capacity of 0.9 million
tonnes/year and is one of the most successful RDF-type
processes. The MSW is first pre-shredded, ferrous metals are
separated magnetically, and combustion is carried out
partly by suspension firing and partly on the horizontal
moving grate (Figure 2).
FIGURE 2. Schematic diagram of the SEMASS process at Rochester, Massachusetts, USA
Table 3 shows the enormous expansion in global
WTE capacity, in terms of new Martin and Von Roll
plants, that has taken place since 1995.A total of 154 WTE
facilities have been constructed or are currently under
construction, totalling to a capacity of 16.5 million tonnes.
TABLE 3. Martin and Von Roll new facilities since 1995
Major trends in new WTE construction, 1996-2003 |
Martin plantsa |
Von Roll plantsb |
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Reverse grate |
Horizontal grate |
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Number of new plants, 1996-2001 |
41 |
21 |
55 |
Installed total new capacity, 1996-2001, tonnes/year |
7,800,000 |
3,100,000 |
3,500,000 |
Average plant capacity, 1996-2001, tonnes/year |
182,000 |
148,000 |
64,000 |
Number of new plants, since 2001 (plus those under construction) |
27 |
6 |
14 |
Total new capacity since 2001, tonnes/year |
4,100,000 |
740,000 |
1,150,000 |
Average plant capacity since 2001, tonnes/year |
151,000 |
134,000 |
82,000 |
Largest plant built in 1996-2003, tonnes/year |
1,400,000 |
480,000 |
250,000 |
a Martin capacities were obtained by multiplying reported
daily capacities by 330.5
b Von Roll capacities were calculated by multiplying reported hourly capacities
by 24 x 330.6 |
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WTE emissions
In the late 1980s, WTE plants were listed by the US
Environmental Protection Agency (EPA) as major sources of
mercury and dioxin/furan emissions. However, in response
to the Maximum Available Technology (MACT) regulations
promulgated in 1995 by the US EPA, the US WTE industry
spent more than one billion dollars in retrofitting pollution
control systems and becoming one of the lowest emitters
of high temperature processes. The US EPA recently
affirmed that WTE plants in the US 'produce 2800 MW of
electricity with less environmental impact that almost any
other source of electricity'.7
Dioxins
A memorandum by Walt Stevenson of the US EPA
summarizing EPA data8 showed that the emissions of the
large US WTE plants (about 89% of total US capacity)
decreased from 4260 grams TEQ (toxic equivalent) in 1990
to 12 grams TEQ in 2000. Figure 3 shows the post-MACT
cumulative dioxin emissions of the US WTE facilities, plant
by plant.8,9 The diagonal straight line shows the allowable
limit of toxic dioxins (in grams TEQ) using the present EU
limit of 0.1 ng/m3 and the cumulative processing rate of
MSW (x-axis). It can be seen that the total emissions in the
US are well below the EU limit. The fact that WTEs stopped
being the major emitters of
dioxins in the US is illustrated in
Figure 4 that depicts the
distribution of dioxin sources in
recent years;8,9 it should be
noted that in the same period,
the total dioxin emissions in the
US decreased tenfold, from
14,000 to 1100 grams TEQ.8
FIGURE 3. Post-MACT cumulative dioxin emissions from US WTE plants in 2000; each point represents the emissions of a single plant, in grams TEQ 8,9
The current WTE industry in
the US, and also those in other
developed nations, are an
insignificant source of dioxins.
Modern WTE facilities in Europe
have dioxin emissions that are
much lower than the EU limit.
For example, the level of dioxin
emissions of the state-of-the-art
Brescia (Italy) plant is only 0.01
ng TEQ/m3.3
FIGURE 4. The distribution of dioxin sources in the US in recent years, showing how waste-to-energy ceased to be a major contributor of dioxin emissions 8,9
Mercury
The use of mercury in the US decreased from 3000 tonnes
per year in the 1970s to less than 400 tonnes by the end of
the century.10 Due to the lower input and also the use of
activated carbon injection and fabric bag filters, the US
WTE emissions decreased by a factor of 60 between 1987
and 2000. Figure 5 shows that, by 2000, WTE mercury
emissions were a small fraction of those from coal-fired
power plants.
FIGURE 5. Mercury emissions from WTE (1989-1999) and coal-fired power plants 10
Environmental benefits of WTE
Despite the great reduction in emissions attained by WTE
facilities in the last 15 years, some environmental groups in
the US continue to oppose new WTE facilities on principle,
unaware that the only alternative for MSW disposal -
landfills - have much larger environmental impacts. For
every tonne of waste landfilled, greenhouse gas emissions
in the form of carbon dioxide increase by at least
1.3 tonnes. During the life of a modern landfill and for a
mandated period after closure, aqueous effluents are
collected and treated chemically; however, chemical
reactions and volume decrease of the landfilled MSW can
continue for decades and centuries. Thus, there is potential
for future contamination of adjacent waters. It is for this
reason that communities built on sandy soil, such as those
in Long Island in New York State and the state of Florida
have opted for WTE disposal of their MSW.
Landfill gaseous emissions
Modern landfills try to collect the biogas produced by
anaerobic digestion. However, the number of gas wells
provided is limited (about one well per 4,000 m2 of
landfill),11 so that only part of the biogas is actually
collected. Landfill biogas generally contains about 54%
methane and 46% carbon dioxide. On the assumption that
25% of the landfilled MSW is biodegradable (food, plant,
wastes, paper, leather, wood), the maximum amount of
natural gas generated by biodegradation has been
estimated at 130 Nm3/metric tonne.12 The maximum
capacity of landfilled MSW to produce methane is reported
by Franklin13 to be 62 standard m3 of CH4 per tonne. Also,
the compilation of US landfill gas data by Berenyi11 showed
the annual capture of landfill gas to be 8 billion Nm3
(778 million scfd).
Putting these numbers together and assuming that the
landfill gas is generated only from the current deposition of
MSW in US landfills (109 million tonnes in 1999) leads to
the following calculation:
Amount of non-captured methane |
= Amount generated - Amount captured
= (109 million tonnes MSW x 62 Nm3/tonne)- (8 billion Nm3 x 0.54)
= 2.4 billion Nm3 of methane
= 1.7 million tonnes of methane
= 39.1 million tonnes of carbon equivalent
= 0.369 tonnes of carbon equivalent/tonne MSW
= 1.32 tonnes of CO2 /tonne MSW |
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The carbon equivalent number was obtained by
multiplying methane emissions by its global warming
potential of 23 times that of carbon dioxide.14 This
calculation for US methane emissions can be compared
with the estimate of global carbon emissions from waste
treatment of 60-100 million tonnes per year.15 Also, the
above estimate of 1.32 tonnes of CO2 per tonne MSW is
close to the estimate by Thorneloe et al.16 and lower than
the estimates of about 1.5 tonnes of CO2, by Batchelor et al.,17
for Australia, and by Ayalon et al.18 for Israel.
Mercury emissions from landfills
Mercury concentration in US MSW has been estimated at
about one part per million.10 On this basis, the amount of
mercury disposed annually in US landfills is about 120
tonnes per year (i.e. about 25% of the present mercury
consumption in the US). Most of the mercury in MSW is in
metallic form (fluorescent lamps, thermometers, etc.), and
the vapour pressure of mercury at landfill temperatures
(40°C) is 0.007 mm Hg, as compared with the vapour
pressure of water of 5.67 mm Hg at 40°C.Therefore, if an
exposed water droplet evaporates in one hour, then a
mercury droplet of the same size will evaporate in four
weeks.10 Also, the conditions in an MSW landfill (such as
temperature, moisture, and reducing capacity) are
favourable for aqueous mobilization of mercury (e.g. in
the form of methyl mercury). However, since both
gaseous emissions and aqueous
mobilization are dispersed
sources, they are not easy to
measure.
TABLE 4. Gaseous emissions of US landfills
Volatile compound |
Molecular weight |
Mean concentration
in landfill gas,19 ppbv |
Landfill emissions,
kg/million tonnes of MSW |
Acetone |
58.08 |
6,838 |
826 |
Benzene |
78.01 |
2,057 |
339 |
Chlorobenzene |
112.56 |
82 |
17 |
Chloroform |
119.39 |
245 |
61 |
1,1-Dichloroethane |
98.97 |
2,801 |
574 |
Dichloromethane |
84.80 |
25,694 |
4,539 |
Diethylene chloride |
58.00 |
2,835 |
339 |
Ethyl benzene |
106.16 |
7,334 |
1,626 |
Methyl ethyl ketone |
72.10 |
3,092 |
461 |
1,1,1-Trichloroethane |
133.42 |
615 |
174 |
Trichloroethylene |
131.40 |
2,079 |
565 |
Toluene |
92.13 |
34,907 |
6,704 |
Tetrachloroethylene |
165.85 |
5,244 |
1,809 |
Vinyl chloride |
62.50 |
3,508 |
461 |
Styrenes |
104.15 |
1,517 |
330 |
Vinyl acetate |
62.50 |
5,663 |
1,017 |
Xylenes |
106.16 |
2,651 |
583 |
Total VOC emissions |
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20,435 |
Ammonia |
17.03 |
550,000 |
- |
Sulphides/mercaptans |
60.00 |
500,000 |
- |
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Volatile organic compounds
The annual gaseous emissions of
landfills in the US can be
estimated by multiplying the
above estimate of non-captured
landfill gas flow (about 46 Nm3 of
methane plus CO2 escaping per
tonne of MSW) by the reported
concentrations of volatile organic
compounds (VOC) in landfill
gas.19 Table 4 shows the estimated
emissions from US landfills,
expressed on the basis of
kilograms per million tonnes of
MSW landfilled.
The next generation of
WTE processes
The existing WTE combustion
chambers have been developed
largely empirically. Their size, percentage of excess air used,
and the volume of process gas are much larger than for
coal-fired power plants of the same combustion capacity.
Therefore, the capital and maintenance costs of a WTE
facility are nearly three times as high as that for a coal-fired
power plant generating the same amount of electricity.
One of the objectives of the Waste-to-Energy Research and
Technology Council is to apply engineering science in
understanding the phenomena occurring in the best of the
existing WTE processes and then to implement this
knowledge during the design of the next generation of
WTE facilities. Two obvious means for increasing the
turbulence and transport rates in the WTE chamber are
oxygen enrichment, as practised in the metallurgical
industry, and flue gas recirculation. The latter has already
been implemented very successfully in the Brescia WTE
facility. Also, Martin GmbH has already piloted oxygen
enrichment on a large scale and is in the process of
building two 'next generation' plants, in Arnoldstein,
Austria, and in Sendai, Japan, in collaboration with
Mitsubishi Heavy Industries. Figure 6 is a schematic
diagram of the Martin Syncom-Plus® process that will be
used in these plants. In addition to oxygen enrichment
of the air injected through the grate, Syncom-Plus makes
use of an infrared camera for monitoring the temperature
of the bed on the grate and a sophisticated control
system to ensure complete combustion and produce
a bottom ash that is nearly fused and ready to be
used beneficially.
FIGURE 6. The Syncom-Plus process of Martin GmbH 5
The WTE Research and Technology Council
During the course of several graduate studies of various
facets of integrated waste management, the Earth
Engineering Center (EEC) of Columbia University came to
the realization that, despite the importance of
WTE technology to the US, there were no
industrial or government research centres
dedicated to advancing the WTE technology. The
only organization addressing the concerns of the US WTE
facilities and of the major WTE companies (American Ref-
Fuel, Covanta Energy, Montenay-Onyx, and Wheelabrator) is
the Integrated Wastes Services Association (IWSA) formed
in 1991. Its role does not include R&D, however.
Therefore, in the spring of 2002, EEC and IWSA, with
the help of Columbia's Earth Institute, founded the Waste-to-
Energy Research and Technology Council (WTERT).One
of the objectives is to link academic research groups
working on various aspects of WTE technology, as well as
engineers in the WTE industry and government agencies
concerned with waste-to-energy and integrated waste
management. The mission of the Council is to advance both
the economic and environmental performance of waste-to-energy
technologies, and this includes both conservation
of resources and environmental quality.
Two views of Brescia WTE facility in Italy. Photo: ASM Brescia
At the present time, WTERT is sponsored by its
founders, the US EPA, the Solid Wastes Processing Division
of ASME International, the Municipal Waste Management
Association of the US Conference of Mayors, and other
organizations. One of the services provided by WTERT is
the interactive database 'SOFOS' that provides information
on technical papers and reports related to the integrated
management of solid wastes.
The following academic groups are currently
participating in the WTERT University Consortium:
- Earth Engineering Center, Department of Earth and
Environmental Engineering, and Department of Civil
Engineering, Columbia University, USA
- Marine Sciences Research Center, State University of
New York at Stony Brook, USA
- Department of Civil and Environmental Engineering,
Temple University, USA
- Department of Applied Earth Sciences, Delft University
of Technology, the Netherlands
- Sheffield University Waste Incineration Center
(SUWIC), UK.
WTERT welcomes other universities interested in the goals
of the Council to join this consortium.
Conclusion
Worldwide, about 130 million tonnes of municipal solid
wastes are combusted annually in WTE facilities that
produce electricity and steam for district heating and also
recover metals for recycling. Since 2001, there have been
47 new WTE facilities that either have started or are under
construction, adding 6 million tonnes to the total capacity.
WTE expansion in the US has been stymied by
environmental opposition that does not consider the
enormous reduction in gas emissions made by the US WTE
industry following implementation of the US EPA
regulations for Maximum Available Control Technology and
by the fact that existing legislation does not recognize the
significant environmental benefits of WTE, in terms of
energy generation, environmental quality, and reduction of
greenhouse gases.
In the last few years, there have been significant
advances in WTE technology that include the use of
implementation of flue gas recirculation and the design of
new plants that will use oxygen enrichment of the primary
air. The importance of WTE in the universal effort for
sustainable development and its need for R&D resources
has led to the formation of the Waste-to-Energy Research
and Technology Council. This organization brings together
several universities concerned with waste management.
The Council started operations by making an inventory of
the global WTE industry and the research resources
available. The overall goal of the Council is to improve the
economic and environmental performance of technologies
that can be used to recover materials and energy from
solid wastes.
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