Table ES.1 presents air emissions generated by the major integrated waste management strategies (per ton of MSW, over a 25 year period). This table shows releases for each strategy as a whole; Sections 5 through 9 in the report text, Volume I of "Data Summary of Municipal Solid Waste Management Alternatives," break down emissions for key steps.
The releases occur at different rates during the individual steps-collection/transportation, processing, and final disposal-in each strategy. Transportation releases occur while MSW or recyclable materials are in transit; combustion, MRF processing, and recycling also release emissions over a short period of time. Composting and landfilling release air emissions over periods ranging from months to the entire 20 years covered in this life-cycle analysis (landfills actually release emissions for periods much longer than 20 years).
The single values that have been derived for this study are not an adequate basis for making fine distinctions between individual options. Every option has a range of performance values that vary with the design, operation, and maintenance of the equipment used and the nature of the MSW being processed when the environmental releases were measured. For example, extensive data on emissions from mass burning and RDF were used for this analysis, but they cannot be used to determine whether one option will be consistently better than the other in actual operadon. Large-scale differences between strategies like landfilling, combustion, or composting, however, can be used to compare the probable results of using one strategy or another.
In general, releases of organic gases to the air are largest for strategies that landfill a large percentage of the MSW. Landfill emissions consist of about 55% methane; about 2% by volume is other organic gases, and the remainder is CO2.
In contrast, releases of metals and CO2 to the atmosphere are largest for the strategies that include combustion of a large percentage of the MSW. Combustion emissions include almost no organics, but extremely small quantities of dioxins and furans are emitted (as shown in Table ES.1 in millionths of pounds per ton of MSW). Landfilling and other organic processes (composting, anaerobic digestion) release extremely small quantities of metals, if any, to the air.
Curbside collection of recyclables increases the emissions from the pick up and transportation step of the MSW management strategy, but reduces the emissions from the disposal step (landfill or combustion) because the smaller amount of material that remains for disposal produces lower releases. As indicated in Table ES.l, comparisons of Strategies 1 and 6, 2 and 7, and 4 and 8 show that some emissions increase and others decrease, but all the changes are relatively small. This study does not cover releases during the remanufacturing step because inadequate data were found.
Water Emissions
The water emitted from a landfill is called leachate. Environmental concerns about landfills include the amount of toxic material (metals, organics, dioxins, and other components of MSW) that is released from the landfill by leaching, and the final destination of the leachate. Most new landfills are capped when they are filled, and regulations require them to have a liner and a leachate collection system, and to treat the collected leachate. In spite of these practices, application of a hydrologic model developed by the EPA has shown that about 25% of the rainwater that falls on a landfill can leak in, and 13% of the amount that enters the landfill can escape the collection system and leak out through the liner.
Table ES.1
AIR EMISSIONS FOR COMMON STRATEGIES
(Pounds per Ton of MSW at the Curb-Total for 20 Years)
Strategy (See Key)
1 2 3 4 5 6 7 8 9 10 11
Air Emissions
Particulates 0.02 0.086 0.07 0.05 0.46 0.02 0.08 0.05 0.02 0.47 0.47
Carbon monoxide 0.79 1.47 1.33 2.06 23.24 0.94 1.55 2.09 0.94 23.29 23.94
Hydrocarbons 0.08 0.08 0.08 0.08 2.32 0.09 0.09 0.09 0.09 2.34 2.34
Nitrogen oxides 0.32 5.1 4.1 2.64 9.30 0.38 4.7 2.47 0.38 9.36 9.36
Methane 14.34 0.00 0.00 2.29 13.82 13.05 0.00 2.06 5.16 12.47 0.00
Carbon dioxide 437 1650 1320 1460 421 397 1485 1313 157 379 1440
Water 188 1140 912 970 180 171 1026 872 68 164 992
NMOC 0.75 0.00 0.00 0.12 0.72 0.68 0.00 0.11 0.37 0.65 0.00
Dioxin/furan{10(-6)lb} NA 0.014 0.011 0.0038 NA NA 0.012 0.0034 NA NA 0.011
Sulfur dioxide NA 2.45 1.96 1.10 NA NA 2.21 0.99 NA NA 2.13
Hydrogen chloride NA 1.40 1.12 0.26 NA NA 1.26 0.24 NA NA 1.22
Metals{10(-6)lb}
Antimony NA NA NA ND NA NA NA ND NA NA NA
Arsenic NA 4.1 3.3 ND NA NA 3.69 ND NA NA 3.6
Cadmium NA 8.0 6.4 ND NA NA 7.2 ND NA NA 6.9
Chromium NA 19 15 87 NA NA 17 78 NA NA 16.5
Lead NA 10 8.0 320 NA NA 9 288 NA NA 8.7
Mercury NA 230 184 55 NA NA 207 50 NA NA 200
Nickel NA 17 14 64 NA NA 15 57 NA NA 14.8
Zinc NA NA NA 170 NA NA NA 153 NA NA NA
Total Metals{10(-6)lb} NA 288 230 696 NA NA 259 626 NA NA 251
Source: SRI International
Notes: ND = Not detected; NA = Not analyzed; NMOC = Non-Methane Organic Compounds.
Key: 1 = Landfill with Gas Recovery 7 = Curbside MRF + Mass Burn
2 = Mass Burn 8 = Curbside MRF + RDF for Direct Firing
3 = On-Site MRF + Mass Burn 9 = Curbside MRF + RDF for Composting
4 = RDF for Direct Firing 10 = Curbside MRF + Landfill + Yard Waste Composting
5 = Yard Waste Composting + Landfill 11 = Curbside MRF + Mass Burn + Yard Waste Composting
6 = Curbside MRF + Landfill
Click here for table in WK1 format.
Ash from municipal waste combustors (MWCs)is usually landfilled in separate areas called "ash monofills." Ash monofills can generate 810 times less leachate than MSW landfills.
Table ES.2 shows the total quantity and some of the constituents of leachate from landfills and ash monofills for the major integrated waste management strategies (per ton of MSW, over a 25 year period). The amounts in the table reflect both the percentage that is captured for treatment and the percentage that leaks through the liner. Because leachate is released slowly and continuously over the 20-year period covered in this report, the concentrations of both organics and metals are quite low.
Organics in leachate from an MSW landfill total about 0.16 pound per ton of MSW over a 20-year period(5). Little organic material is left in ash after combustion, and the leachate from an ash monofill includes only about one ten-thousandth of a pound of organics per ton of MSW(6).
Quantities of metals in the leachate are also lower for ash monofills than for MSW landfills. Most metals dissolve more slowly in ash monofills than they do under the more acid conditions in MSW landfills because the ash and excess scrubber lime are not acidic. For example, the concentration of lead in the MSW leachate is 90 ug per liter; lead in leachate from an ash landfill declines to less than 1 ug per liter within 2 years. In comparison, a typical drinking water standard for lead permits about 50 ug per liter.
This analysis does not cover leaching that might result from the waste from processes that remanufacture paper, metals, and plastics separated from MSW for recycling. Few data on those potential emissions were found.
Landfill Space
Figure ES.4 compares landfill volumes required by the common MSW management strategies. The maximum capacity of a landfill is normally determined by volume, not weight. The land area consumed for MSW management is largest if all waste is landfilled; landfill requirements may be up to 90% lower if recyclables are removed, the remaining MSW is burned, and the ash from combustion is land filled. Collection and separation of recyclables saves about 14% of the landfill space in communities that have successful curbside collection programs and market the separated products. A strategy with composting MSW reduces the volume of landfilled material by 50-60% if the compost can be used (recycled). Even if the compost is landfilled, composting saves about 15-25% of the landfill space. The amount of landfill space that can be saved by compost ing separately collected yard waste has not been documented. In the one community used as an example in this study, the savings from composting yard waste totaled less than 5%. The maximum potential savings would result from curbside collection of all the yard waste in MSW; that could save about 17-20% by volume of the total landfill space required.
Table ES.2
EFFLUENT FOR COMMON STRATEGIES
(Pounds her Ton of MSW at the Curb-Total for 20 Years)
Strategy (See Key)
1 2 3 4 5 6 7 8 9 10 11
Effluent
Leachate (gallons) 80 10.08 8.0 18.29 77.12 72.8 9.07 16.46 28.8 69.60 8.77
Leachate 667 84 67 152 643 607 75.6 137 240 580 73
Chloride 1.13 1.17 0.94 0.82 1.09 1.03 1.05 0.74 0.41 0.98 1.02
Sodium 0.73 0.26 0.21 0.26 0.7 0.66 0.23 0.23 0.26 0.63 0.23
Potassium 0.60 0.14 0.11 0.17 0.58 0.56 0.12 0.15 0.21 0.52 0.12
Chemical oxygen dema 0.16 NA NA 0.02 0.15 0.15 NA 0.02 0.056 0.13 NA
Total organic carbon NA 0.0003 0.0002 <0.0002 NA <0.0002 0.0002 <0.0002 NA NA 0.0002
Metals (10(3)lb)
Arsenic 86 ND ND 13.8 82.9 78 ND 12.4 31 74.8 ND
Cadmium 3.0 ND ND 0.48 2.89 2.73 ND 0.43 1.08 2.61 ND
Chromium 163 ND ND 26.10 157 148 ND 23.5 59 142 ND
Copper 43 ND ND 6.88 41.5 39.1 ND 6.19 15 37 ND
Nickel 108 ND ND 17.30 104 98 ND 15.6 38 94 ND
Lead 48 ND ND 7.68 46.3 43 ND 6.91 17 42 ND
Mercury 6.0 ND ND 0.96 5.78 5.46 ND 0.86 2.16 5.22 ND
Zinc NA ND ND NA NA NA ND NA NA NA ND
Total Metals(10(3)lb 457 ND ND 73.10 440 416 ND 65.8 163 270 ND
Source: SRI International
Notes: ND = Not detected; NA = Not analyzed.
Key: 1 = Landfill with Gas Recovery 7 = Curbside MRF + Mass Burn
2 = Mass Burn 8 = Curbside MRF + RDF for Direct Firing
3 = On-Site MRF + Mass Burn 9 = Curbside MRF + RDF for Composting
4 = RDF for Direct Firing 10 = Curbside MRF + Landfill + Yard Waste Composting
5 = Yard Waste Composting + Landfill 11 = Curbside MRF + Mass Burn + Yard Waste Composting
6 = Curbside MRF + Landfill
Click here for table in WK1 format.
Cost Data for the Major Waste Management Options
Figures ES.5 through ES.9 show published estimates of the capital costs for the five most common MSW management options. (Costs of operating trucks for curbside collection are not included.) The costs reported in the literature are often incomplete, and published sources often do not fully report on which costs are included and which are excluded. Furthermore, the estimates from different sources are based on a wide variety of assumptions; thus, even estimates for the same technology may not be fully comparable. The inadequacies and inconsistencies in the cost data found in the literature make it imprudent to rely on the estimates in Figures ES.5 through ES.9 for detailed comparisons of the costs of the various options, for the reasons outlined under "Missing Data." Until cost estimates for waste management options are built from system components using consistent assumptions, the safest way to compare costs is to rely on site-specific quotations from contractors.
Missing Data and Research Needs
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