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The data gathered for this study vary significantly in quality and consistency. On some topics, no data at all are available. The effects of the limitations on the results of the analysis varied from trivial to major. The 20 year time period chosen for the life-cycle analysis of energy and emissions severely strained the limits of knowledge about many of the options. In addition, the review of the data often indicated the need for research to help to eliminate barriers to the more widespread adoption of certain options. This subsection provides a broad overview of important data gaps and potential research needs.
Cost data in the literature are limited, and the range of capital and operating cost estimates is broad. The capital cost variations reflect inconsistencies in the sources of the estimates rather than predictable variations based on the type of technology or the size of the facility. Some sources fail to report the assumptions on which published cost data are based, and even if the assumptions are known, the bases may be so different that the results are not actually comparable.
For example, the year when a facility was built strongly affects the interest rate paid for the capital, as well as the regulations that apply at the time of construction. Whether a project is privately or publicly funded also affects the interest rates on the capital costs. Location-specific differences, including those in the costs of associated activities such as road improvement, will also affect the comparability of the data. Most of the technologies are typically financed through public bonds in some form, and prospectuses are available for those projects. Even these disclosures may not define or cover all the costs of the facility, however. Some bond issues include costs unrelated to project costs. Operating costs are also affected by local differences in factors such as labor rates, labor contracts, safety rules, and crew sizes that are rarely reported in the open literature. Accounting systems, especially those used by cities and private owners and operators of landfills, vary widely. Cost data on separadon/recycling and composting are scarce. To facilitate comparisons of the various strategies for managing MSW, costs for all the systems could be built up from system components using a consistent set of assumptions.
The most extensive data are available on the combustion options. Because combustion is a controlled process that is completed within a short period of time, inputs and outputs, especially of energy, can be measured effectively.
Figure ES.4
VOLUME LANDFILLED(a) (PER TON OF MSW)
Figure ES.5
FIELD ERECTED MASS BURN-ELECTRICITY PRODUCTION PLANTS
EFFECT OF PLANT CAPACITY ON CAPITAL INVESTMENT(a)
Figure ES.6
RDF SPREADER STOKER-FIRED ELECTRICITY PRODUCTION PLANTS
EFFECT OF PLANT CAPACITY ON CAPITAL INVESTMENT(a)
Figure ES.7
LANDFILL CAPITAL AND O & M COSTS(a)
and
Figure ES.8
MATERIALS RECYCLING FACILITIES (MRF)
EFFECT OF PLANT CAPACITY ON CAPITAL INVESTMENT(a)
(High Technology)
Figure ES.9
COMPOSTING OF MSW
EFFECT OF PLANT CAPACITY ON CAPITAL INVESTMENT(a)
Landfilling is a less controlled process than combustion, and conditions in a landfill change over time. Unexpected leaks and emissions are difficult to locate, and the results of efforts to monitor emissions are therefore less precise for landfills than they are for combustion facilities. The variation from landfill to landfill is also substantial. Sophisticated models of the reactions in a landfill have been constructed, and the data collected in actual studies are generally consistent with the predictions of the models. However, few studies have attempted to quantify air and water releases from landfills over long periods of time; long-term data on ash monofills are especially scarce.
Data on separation and recycling, with or without curbside collection, are limited, in part because the approach is relatively new. Successful recycling depends more strongly than the other disposal options on nontechnical factors that have not been widely studied. For example, few studies have been found of quantities of recyclables set out for curbside collection over a period of several years. In addition, the success of a recycling operation depends on finding beneficial uses for the products. Extensive data about energy requirements for remanufacturing are available, but only incomplete and out-of-date information on environmental releases during manufacture and remanufacture were found. The lack of systems studies that follow MSW recyclables from curbside to a remanufacturer's product shipping dock is a significant barrier to conducting a life-cycle analysis that compares recycling with alternative MSW management strategies.
Data on composting of MSW are also limited. Data on emissions during processing are incomplete, and available studies have been less rigorous than analyses of emissions from either landfills or combustors. Data on emissions from the use of the compost are also scarce, and data on energy requirements are incomplete. Technical and marketing difficulties also constitute barriers to successful application. Composting operations may seem attractive as low-cost alternatives to combustion or landfilling, but inexpensively constructed facilities often suffer serious operating problems. At the other end of the process, at least one large technically successful MSW composting plant has had great difficulty finding markets for the compost product.
Anaerobic digestion is in its infancy in the United States, and no commercial facilities are operating. Adequate data on actual energy use and production, emissions, and composition and use of the compost product cannot be gathered until a commercial plant is constructed and successfully operated.
RDF cofiring is comparatively well characterized. The primary barrier to more widespread use is the difficulty in finding suitable incentives for communities, utilities, and industry to establish mutually beneficial cofiring projects on furnaces with grates.
No commercial gasification or pyrolysis plants are operating in the United States, and the data available on plants operated in the 1970s are out of date. Gasification and pyrolysis of MSW are unproven. At current fossil fuel prices, demand for the gas they produce could be small, and little incentive may exist for additional development of MSW gasification/pyrolysis facilities. If chemical feedstocks can be made by pyrolysis/gasification, the economic considerations may change.
In summary, for combustion processes, extensive data are available on costs, and well-verified data are available on energy and emissions. Less consistent data are available on landfilling, and few data have been found on collection, separation, and remanufacturing and on composting.
OTHER PROJECT DOCUMENTATION
The findings of this study are published in a two-volume report and 10 appendixes. The appendixes provide detailed summaries of the literature on the various options, as well as bibliographies of the references cited in the appendixes. In addition to this executive summary, those documents include:
"Data Summary of Municipal Solid Waste Management Alternatives. Volume I: Report Text" Final Report, June 1992, SRI International. This report describes major findings in detail.
"Data Summary of Municipal Solid Waste Management Alternatives. Volume II: Exhibits" Final Report, June 1992, SRI International. This volume contains detailed cost summaries, the data base, and other background information.
"Collection and Evaluation of Comparative Data for Waste Management Alternatives. Appendixes":
Appendix A. Mass Burn Technologies, April 1992, wTe Corporation
Appendix B. RDF Technologies, February 1992, wTe Corporation
Appendix C. Fluidized-Bed Combustion, April 1992, wTe Corporation
Appendix D. Pyrolysis and Gasification of MSW, April 1992, wTe Corporation
Appendix E. Material Recovery/Material Recycling Facilities, April 1992, wTe Corporation
Appendix F. Landfills, April 1992, wTe Corporation
Appendix G. Composting, April 1992, wTe Corporation
Appendix H. Anaerobic Digestion of MSW, April 1992, wTe Corporation
Appendix I: Alphabetically Indexed Bibliography, April 1992, wTe Corporation
Appendix J: Numerically Indexed Bibliography, April 1992, wTe Corporation.
NOTES:
(1) As described, for example, by the Society of Environmental Toxicology and Chemistry (SETAC).
(2) Energy consumed in transportation is reported as the fuel consumed. About 15% of the Btu content of crude oil is used in converting it to gasoline or diesel fuel and transporting it to the point of use. That factor is not included in the estimates.
(3) This estimate includes residential, commercial and institutional solid waste, plus some similar types of wastes from industrial sources, in accordance with the U.S. Environmental Protection Agency's (EPA's) "Characterization of MSW in the U.S.: 1990 Update."
(4) Most or all of tbe energy used to make about 80% of virgin paper comes from the wood waste and black liquor. Recycling mills that process only used paper rely on fossil fuels. Published estimates of energy savings from using old paper as a feedstock vary from 10 million Btu per ton of paper product to zero. Some of these estimates vary according to the grade of paper produced. In this report a value of 5 million Btu per ton, which was reported in at least two studies, was assumed as the energy saving for using cardboard and old newspaper as feedstocks to make new products.
(5) Measured as chemical oxygen demand (COD).
(6) Measured as total organic carbon (TOC).
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