. "Use of Materials Balances to Estimate Aggregate Waste Generation in the United States." Measures of Environmental Performance and Ecosystem Condition. Washington, DC: The National Academies Press, 1999.
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phosphates and alumina) dry weight. In addition, about 3,600 MMT of water was used for flotation, most of which was evaporated in ponds, leaving semisolid sludges. Waste water discharged into rivers and streams by the mining industry amounted to 2,840 million gallons per day, or 3,900 MMT for the year.
By contrast, the weight of solid wastes from metallurgical conversion and fossil fuel combustion processes, including metallurgical reduction (smelting), amounted to only about 146.4 MMT. We have included in this category 76 MMT of fly ash and bottom ash from thermal power generators and 14.4 MMT of flue gas desulfurization waste but excluded 14.4 MMT of iron/steel slag that have commercial uses.
Organic pretreatment wastes are more difficult to account for. Crop residues, mostly recycled to land, amounted to about 360 MMT. Timber residues from logging operations amounted to 155 MMT, mostly burned or recycled to forest soils. (In some countries, both agricultural and timber residues are collected and burned as fuel, but this is relatively rare in the United States.) About 180 MMT (50 percent dry) of animal wastes—manure, urine, and dead animals—were produced, of which an estimated 155 MMT were probably recycled to cultivated land and the remainder lost in other unspecified ways. An additional 110 MMT of organic wastes (50 percent dry) were generated in the food processing sector and disposed of in various unspecified ways, including waterways. About 5 MMT were lost in the wood products and pulp and paper sectors.
Gaseous combustion products constituted another very large waste stream. We estimate gross emissions of 5,046 MMT CO2, of which 4,726 MMT were from fossil fuel combustion. However, thanks to a take-up of 1,002 MMT by the agricultural sector and 368 MMT by the forestry sector, net emissions of CO2 were 3,759 MMT. (By the same token, industrial activities, mainly fuel combustion, consumed 5,393 MMT of oxygen, whereas agriculture and forestry produced 891 MMT of oxygen, for a net consumption of 4,732 MMT.) Other gaseous emissions included 32 MMT SO2 from coal and EPA's estimate of 20 MMT NOx from fossil fuel combustion. Our methodology is not well suited to estimating fugitive or particulate emissions. However, we note that petroleum refineries may have emitted as much as 4.3 MMT of hydrocarbons that are not accounted for anywhere else.
Process water contaminated by acids or other wastes was also emitted in significant quantities by the petroleum refining and metallurgical sectors. The quantitative values discussed above are summarized in Table 7.