This section reproduces the subsections of Sections 5 through 8 entitled "Missing Data and Research Needs." It is intended to facilitate comparisons of the state of knowledge in the various fields. In addition, aspects of MSW management technologies that might benefit from additional research and development efforts are also described in this section, from a broad perspective(1). The order in which the observations appear should not be interpreted to imply any judgment about the relative importance of the missing data to the life-cycle analysis in this report or to possible efforts to increase the utility of any technology.
The cost data for all the technologies shared certain limitations, although the severity of the problems varied somewhat. Therefore, repetitive statements about missing cost data have been deleted from this section, and general observations about all the cost data are provided in the next subsection.
It was difficult to find data on the quantities of recyclable materials recovered from MSW during RDF operations. A few plants have been well characterized, but no broad data base exists.
Plants that precede mass burning with mixed waste processing are beginning to be operated. However, few data were found on operating results for those plants, on quantity and quality of materials removed, and on the markets for the products.
Few data were found on the amount of bulky waste removed before mass burning. Nor were data available on the amount of bulky material that is sold as scrap or on the fate of bulky materials that have no scrap value.
Although regulations on existing operating MSW combustors have become more restrictive (FR, 1987c; FR 1989a; FR l991a; and the timetable set by the Clean Air Act Amendments of 1990), periodic evaluations of older plants might show that emissions have been reduced as new guidelines governing older plants have been implemented.
Far less information is available on stack emissions from smaller modular mass burn plants. After 1993, when the new guidelines on plants with capacities of less than 250 tons per day go into effect, assessments of emissions from smaller plants will become more available.
Few data on air emissions from the RDF preparation areas or tipping areas of a mass burn plants have been reported. Some of the air is used for combustion, but some is vented.
Long-term studies may also reflect the changing composition of the waste stream. Technological changes over time influence the nature of the waste that is discarded. Examples of such changes include the recent substantial reductions in the mercury in alkaline cells (from 1% to less than 0.1%), the growing popularity of zinc-air cells as replacements for mercury batteries in hearing aids, and the elimination of some metals from inks. In addition, new laws in Europe and California are requiring elimination of lead from the 2 billion wine bottle closures produced each year (Andre and Karpel, 1991).
Some sources have referred to the possibility that free carbon in the flyash portion of the ash might absorb some metals, such as mercury, as well as organics. The role of free carbon as an absorbent might be worth investigating.
No data were found to indicate whether significant reductions in emissions can be achieved by removing retrievable, and possibly recyclable, materials from the MSW prior to combustion.
Methods for reducing emissions from smaller modular mass burn units are needed. Better combustion control is needed for smaller modular combustors to allow them to maintain optimized combustion conditions during charging of new MSW.
The available data were insufficient to support an evaluation of the water emissions from RDF preparation, if any is discharged. Data on the various blowdown streams from combustion operations were also unavailable, perhaps because those streams are entirely consumed in the ash quench tank.
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