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Table Title		Table Formats
Highlights		PDF	EXCEL	HTML
1.	Municipal Solid Waste (MSW) Heat Content and Biogenic/Non-Biogenic Shares, 1989-2005
2.	Municipal Solid Waste (MSW) Consumption: Biogenic (Renewable) and Non-Biogenic Energy (Non-Renewable)
3.	Municipal Solid Waste Disposal (MSW)
4.	Typical Heat Content of Materials in Municipal Solid Waste (MSW)
5.	Municipal Solid Waste (MSW) Material Categories in Biogenic and Non-Biogenic Groups
A1.	Municipal Solid Waste (MSW) Weights by Category, 1989-2005
A2.	Paper and Paperboard Products Weights in Municipal Solid Waste (MSW) by Category, 2005
A3.	Plastic Products Weights in Municipal Solid Waste (MSW) by Category, 2005
A4.	Rubber and Leather Products Weights in Municipal Solid Waste (MSW) by Category, 2005
B1.	Calculations to Obtain Average Million Btu Per Ton for Municipal Solid Waste (MSW)
B2.	Biogenic and Non-Biogenic Contributions to Total Million Btu/Million Ton of Municipal Solid Waste (MSW)
Figures		PDF	EXCEL	HTML
1.	Trends in Municipal Solid Waste (MSW) Composition
2.	Municipal Solid Waste (MSW) Disposal

MSW is primarily composed of residential solid waste but also includes some types of non-hazardous commercial, institutional and industrial wastes. MSW can be problematic to discard because of its large volume: one commonly adopted solution is to combust the MSW, which both decreases the volume of material and creates energy that can be recovered in the form of heat or steam. Because some materials have higher heat content than others, the amount of energy that can be produced by combusting MSW is a function of the composition of the waste stream.^[3] For example, certain types of plastics have more than three times the heat content of yard trimmings or organic textiles. In general, combustible non-biogenic materials are characterized by higher heat contents per unit weight than combustible biogenic materials. Thus, the ratio of biogenic to non-biogenic material volumes can have a considerable effect on the heat content of the waste stream.

Summary of Activities [back to top]

Using data from EIA, the Environmental Protection Agency (EPA), and fuel-specific Btu values, EIA determined two interrelated trends in the composition of the MSW stream. First, the heat content (per unit weight) of the waste stream has been steadily increasing over time. Second, the shares of energy contributed to the waste stream by biogenic and non-biogenic components have been changing over time. In 1989, biogenic materials contributed two-thirds of the heat content of the waste stream. By 2005, that number had dropped to 56 percent (see Table 1 and Figure 1). This change can likely be attributed to the changing composition of the MSW stream, as increasingly more plastics are being discarded at the same time that decreasing amounts of paper and paper products are entering the waste stream.

Based on this historical information, EIA has developed estimates of biogenic and non-biogenic MSW energy consumption (Table 2) to aid EIA in predicting the change in MSW composition over time. In keeping with the above trends, EIA estimates that non-biogenic MSW energy consumption grew slightly faster than total MSW energy consumption over the period from 1989-2005.

EIA is applying these results beginning with data for 2006, reporting only the biogenic portion of MSW as renewable energy for purposes of the National Energy Information System. The non-biogenic portion will be reported as a component of Other Non-Renewable Waste.^[4] That is, MSW consumption data will be divided into renewable and non-renewable energy based on the estimated heat content of the biogenic and non-biogenic portions of MSW (Table 1). MSW data will be revised back to 2001 in the Electric Power Monthly (EPM) (Table 2). EIA is publishing MSW generation and consumption split into its biogenic (renewable) and non-biogenic (non-renewable) portions in the March 2007 publications of the Monthly Energy Review and the EPM, which publish December 2006 preliminary data for the first time, and revises 2001 through November 2006 data.

The remainder of this article describes the history of MSW and the methodology EIA will use to estimate the portions of energy derived from biogenic and non-biogenic MSW.

Figure 1. Trend in MSW Composition

Source: Table 1 and Environmental Protection Agency, Municipal Solid Waste in the United States: 2005 Facts and Figures. http://www.epa.gov/msw/msw99.htm

History [back to top]

Although the first facility that combusted MSW for energy came on line in New York City in 1898, the industry did not experience rapid growth until 1978 with the enactment of the Public Utility Regulatory Policy Act (PURPA).^[5] This legislation made it mandatory for utilities to purchase electricity from qualifying facilities (QFs), which were defined as “cogeneration or small power production facilities that meet certain ownership, operating, and efficiency criteria established by the Federal Energy Regulatory Commission pursuant to (PURPA).” This new law improved the economics of the many MSW waste-to-energy plants that qualified as QFs. PURPA mandated the price paid for electricity be equal to the utility’s avoided cost of energy and capacity, and this resulted in MSW QFs receiving a higher price for their power than they might otherwise have received.^[6] MSW plants also benefited from the increased cost of landfilling due to increases in “tipping fees” (the cost to dump waste at a landfill), making disposing of MSW at a waste-to-energy plant less expensive than at a landfill in many cases.

MSW waste-to-energy plants have high capital costs, and in order to make these plants financially viable, project financers required the plant to obtain a reliable stream of low-cost fuel. Usually, a plant would enter into a “flow contract” in which a municipality delivered its waste stream to a specific plant. Thus, certain facilities held a de facto monopoly over a certain locality’s MSW. In some cases, these contracts were seen as restricting interstate commerce in municipal wastes, and in 1994 the U.S. Supreme Court upheld a challenge to flow control, finding that it violated the interstate commerce clause of the Constitution. This ruling partially or fully voided many flow supply contracts and created an added constraint on the waste-to-energy industry. Subsequent to this ruling, few plants have been able to come on line.

EIA tracks all electricity-generating plants with a capacity greater than 1 megawatt on survey forms EIA-906 “Power Plant Report” and EIA-920 “Combined Heat and Power Plant Report”, including information on all MSW combustion facilities that meet this minimum capacity requirement. Historically, MSW and landfill gas (LFG) have been reported as the same fuel code on these surveys, but starting in 2001, MSW and LFG were reported as separate fuels. Therefore EIA has data that depict total MSW consumption from the year 2001 onward.

EPA maintains historical data on MSW (Table 3 below).

Figure 2. Municipal Solid Waste Disposal

Source: Table 3 and Environmental Protection Agency, Municipal Solid Waste in the United States: 2005 Facts and Figures. http://www.epa.gov/msw/msw99.htm

Data Sources [back to top]

Splitting MSW energy inputs into biogenic and non-biogenic components required three categories of data. First, the total amount of energy input to MSW combustion plants was obtained from EIA Forms EIA-906 and EIA-920 (Table 2). Second, data concerning the composition of the MSW stream were obtained from EPA’s publication Municipal Solid Waste in the United States, which has been published yearly or bi-annually since 1995 (see Appendix, Table A1 for data from 1989-2005). Third, the energy content applicable to each of the combustible materials in the MSW plant input stream was obtained from the best sources EIA could identify. For most biomass fuels, EIA used Btu values published in Table B6 of the Renewable Energy Annual (Average Heat Content of Selected Biomass Fuels), http://www.eia.doe.gov/cneaf/solar.renewables/page/rea_data/tableb6.html. The heat content values for the remaining biomass fuels and all non-renewable fuels were obtained from various non-EIA sources. Table 4 lists the Btu content used for each component of the waste stream and the sources for that data. In some cases, the Btu value calculated was an average of several sources.

Methodology Used to Estimate Biogenic and Non-Biogenic-Sourced MSW [back to top]

Beginning in 1989 and for each year that EPA data exist, the potential quantities of combustible MSW discards (which include all MSW material available for combustion with energy recovery, discards to landfill, and other disposal) shown in Table A1 were multiplied by their respective Btu contents (Table 4). These EPA-based categories of MSW were then classified into biogenic and non-biogenic groupings (Table 5). From this, EIA was able to calculate how much of the energy potentially consumed from MSW should be attributed to renewables (biogenic) and how much should be put in the category of “other, non-renewable (non-biogenic) fuels.”

Specifically, the procedure to calculate the division is as follows: (For calculations with 2005 as an example, see Appendix B)
   1. Obtain the total weight of MSW discarded in a data year (Table A1).
   2. For materials that are not combusted, set Btu values to zero, (e.g., glass and metals).^[7]    3. Separate the remaining MSW weights into biogenic and non-biogenic fuel groups (Table 5). These two groups represent the weight of biogenic and non-biogenic materials that are theoretically available to MSW plants for combustion.
   4. Multiply the Btu per ton factors from Table 4 by the total number of tons of each materials group estimated to be available for combustion. This provides both a weighted average estimate of the total Btu available to MSW plants for each EPA fuel group and a total weighted Btu per ton value for an average ton of MSW.
   5. Calculate the biogenic and non-biogenic percentages of the estimated waste stream input to MSW combustion facilities.
   6. Multiply these percentages by the MSW consumption data (in Btu) to estimate the total Btus available from biogenic versus non-biogenic sources (Table 2).
   7. Repeat for all data years, and interpolate linearly between years to obtain the final estimates of shares of biogenic and non-biogenic MSW energy consumption (Table 1).

Caveats and Assumptions
   1. The data provided by EPA are available only at the national level. Therefore, the assumed rates of recycling or MSW generation may not hold true for all States and regions.
   2. The composite MSW HHV by year (Table 1) is not representative of the MSW HHV reported by EIA respondents. This is because respondent data did not include MSW composition information, which was necessary to divide MSW into biogenic and non-biogenic shares. For the purposes of determining a split, the small difference (between EIA respondent MSW HHV and calculated MSW HHV) most likely does not affect the results.
   3. Discards available for combustion represent the average mixture of MSW available on a national level, which may or may not be representative of the mixture of MSW obtained by any particular MSW combustion facility.
   4. Btu values were obtained from best available sources and may have been developed using different procedures.
   5. All fuels have a range of Btu values from lower heating value (LHV) to higher heating value (HHV).^[8] If the source did not specify which of these the value represented, it was assumed to represent HHV.
   6. The EPA data divide categories of materials into sub-groups (for example, plastics are divided into seven sub-groups), each of which has a specific Btu content. However, in some cases, it is not clear what is included in the “other” category within a fuel group. Because of this, “other plastics” was assigned a heat content equal to the value of the average of all plastics groups not in the “other” category.
   7. Unassigned “Other” is divided evenly between the renewable and non-renewable groups.
   8. MSW input materials were classified as biogenic or non-biogenic according to their predominant composition.
      a. All rubber is assumed to be tires with the metals, fiber, and other material removed. Therefore, the rubber is assumed to be synthetic, and is treated as a non- biogenic material.^[9]
      b. Textiles are all assumed to be composed of biogenic materials and are thus treated as biogenic.
   9. Depending on plant design, some MSW plants may need to remove glass and metals prior to combustion. Because of their poor combustion characteristics, these materials do not produce significant heat when combusted, and may in fact reduce the net heat output of a plant. In order to allow for uniform analysis of waste stream heat contents, the Btu values of glass and metal were set at zero.
   10. For the years EPA did not collect data, values for Btu content and the biogenic/non-biogenic split were interpolated linearly between the nearest prior and subsequent survey years.

Results [back to top]

As a result of this analysis, EIA has decided to split MSW into biogenic and non-biogenic components for its future data releases. This biogenic component of MSW will also be reflected in restatements of prior data back to 2001 when EIA began to collect MSW as a separate fuel.

In standard energy data reports, EIA will now include MSW in renewable energy only to the extent that the energy content of the MSW source stream is biogenic. This approach is more consistent with the definition of renewable energy used by EIA than alternatives that would either include or exclude all MSW from renewable energy. EIA’s treatment of MSW’s contribution to an aggregate measure of renewable energy is not intended to infringe on the prerogative of policymakers at the federal and/or State level to adopt one or more definitions of renewable energy that use a different approach to classifying MSW for their distinct policy purposes. Rather, our aim is to present energy data in a clear and consistent way, with enough detail that others can develop data consistent with whatever definition suits their objective.

As discussed above, the calculations performed revealed two trends.
   1. The Btu content per ton of MSW is steadily increasing over time (Table 1).
   2. The percentage of MSW’s total energy content that comes from biogenic resources is decreasing, while the percentage of energy content from non-biogenic resources is increasing (Figure 1).

These trends are clearly interrelated and are most likely attributable to two factors. First, the percentage of paper and paperboard recycled has increased from 40 percent by weight in 1996 (the first year for which complete data are available) to 50 percent in 2005, while the amount combusted rose by only 3 percent (from 81.5 million tons to 84 million tons). Second, the amount of plastic combusted has increased dramatically, from 19 million tons in 1996 to 28.9 million tons in 2005, while the recycling rate grew only half of 1 percent (from 5.2 percent to 5.7 percent). These two factors have combined to decrease the amount of biogenic material in the waste stream while increasing the amount of non-biogenic material, mainly plastics, which have one of the highest Btu contents of any fuel group in MSW.

The historical trends observed in biogenic/non-biogenic MSW composition and energy content may change as a result of EPA’s national policy designed to increase the recycling rates of all materials in MSW. However, it is difficult to predict if this policy will have differing effects on the biogenic and non-biogenic components of MSW and therefore EIA cannot forecast what effect this policy will have on the heat content of the waste stream. Until the effect of EPA’s policy becomes clear, EIA expects that the energy content of MSW will continue to grow over time. EIA will continue to update its estimates of the biogenic and non-biogenic portions of MSW as revised EPA data become available. For purposes of standard EIA data reports, only the biogenic portion of MSW will be included in aggregate measures of renewable energy.

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