. "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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Where specific citations are not given, basic data for this section are from Hoffman (1991), United States Department of Agriculture (1992), and Bureau of Census (1988).
For the sake of clarity, it should be noted that ''harvested output" of corn—by far the dominant grain—refers to shelled corn, not ears. The husks and ears are left behind on the farm, along with stalks. Similarly, wheat straw and chaff are separated from the wheat grains by the harvester and left behind.
To calculate the totals, it is necessary to sum up individual figures given by the United States Department of Agriculture (USDA) in a variety of different units, some volumetric and some in mass terms. Unfortunately, although the USDA does provide conversion coefficients, it does not calculate aggregated totals, except for grains.
It should be noted that although the totals of commercial high-protein feeds remain comparatively stable from year to year, the composition varies significantly. We are unable to account in detail for the exported "feeds and fodders" (11.4 MMT in 1988), which apparently originate in the processing sector (Bureau of the Census, 1991).
These estimates do not represent either the "fresh" weight of manure—which is relatively wet—or the "dry" weight of its solid content. Being based on inputs, the manure is assumed to have the same water content as the feeds (i.e., about 50 percent). In the case of cattle and pigs, actual fresh weight of animal manure is about four times greater than a similar volume of feed and at least in the case of other animals is at least twice as heavy.
Unless otherwise specified, production, export, and import data in this section are from Bureau of the Census (1988) tables 1148, 1149, 1156, 1163, 1166, 1167, 1168, 1173, 1175, and 1177. Data on per capita consumption of foods are given in tables 207 and 208. Beverages were not taken into account.
See United Nations Statistical Office (1988) tables on "Lard," ISIC 3111-31, and "Oils and fats of animals, unprocessed," ISIC 3115-07.
See United Nations Statistical Office (1988) table on "Hides, cattle and horses, undressed—total production," ISIC 3111-311. This refers to fresh weight, prior to tanning.
See United Nations Statistical Office (1988) tables on "Poultry, dressed, fresh (Total Production)," ISIC 3511-10, and "Poultry, dressed, fresh (Industrial Production)," ISIC 3511-101. For mysterious reasons, the latter figure is slightly larger.
Unless otherwise specified, data in this section are from Bureau of the Census (1991).
These data are essentially consistent with Ulrich (1990); however, Ulrich's table 51 appears inconsistent with Ulrich's table 7 as regards imports and exports of pulp. Table 7 includes pulp imputed to downstream paper and paperboard products. We account for imports and exports of downstream products separately.
Imports of "pulp products" shown in Ulrich (1990, table 4) apparently refer to pulp itself and to the pulp equivalent of paper and paper products, not pulpwood. The United States was a net exporter of pulp and a net importer of paper products.
Of this, 5.4 MMT were exported and 0.6 MMT was used for other purposes (Bureau of the Census, 1991, table 1194).
Actually, this is a lower limit, because it includes only inorganic materials (kaolin, alum, etc.) that we have been able to account for explicitly from published sources.
An attractive future possibility is to ferment or otherwise convert the hemicellulosics (sugars) to ethanol. Until now, all known fermenting agents produce an enzyme, lactate dehydrogenase, that breaks down the hemicellulosics into a mixture of ethanol and lactic acid. A new discovery at Imperial College, London, may change this situation. It is a mutant strain of the fermenting bacterium Bacillus stearothermophilus, which lacks the lactate enzyme and thus converts hemicellulosics directly to ethanol, without the usual mixture of lactic acid. Unfortunately, the mutation appears unstable and the organism reverts back to the original form, which produces