sugar cane, fruits and vegetables, and grain milling. Some of this consisted of fruit and vegetable skins and stems, nut shells, pits and seeds, inedible leaves, spoilage, and so forth. Usually, these wastes would be generated in quantities too small to be dried and burned efficiently. However, of the dry sugar and grain milling losses (about 27 MMT) a small amount (about 0.1 MMT) was fed to animals. The same was true for part of the missing mass (11.6 MMT) from meat and fish processing.

Even the bulky and "dry" food processing wastes still contain quite a bit of water, probably about 25 percent. If the 27 MMT of bulky combustible waste biomass of vegetable origin is assumed to have been burned for energy recovery, and if the 20 MMT in dry mass is assumed to be chemically similar to cellulose, the CO2 generated would be around 29.4 MMT, consuming about 21.3 MMT of oxygen and producing about 12 MMT of water vapor in addition to the 7 MMT embodied in the organic material. Of course, the same amount of CO2 would be generated by natural decay processes, as long as they occur in aerobic conditions.

The material losses that we have identified as likely waste are "dry" in the sense that they do not include the weight of washing, cooking, or process water. They also do not assume a priori mass reduction by combustion of biomass for energy recovery. In this connection, a survey by Science Applications International Corporation (SAIC) (1985) commissioned by the U.S. Environmental Protection Agency (EPA) attempted to identify dry wastes from the industrial sectors. The SAIC estimate of dry weight of wastes from the food and feed processing sector was 6.3 MMT (based on 1976 data). This strongly suggests that combustible wastes were, in fact, mostly burned for mass reduction. A significant fraction of the incombustible organic wastes of animal origin (9.3 MMT) and vegetable origin (7.1 MMT) were actually downstream in the retail sector. Thus, our analysis is consistent with SAIC's results.

Forestry and Wood Products10

Wood products are derived from timber tracts, which belong to the forestry sector or are leased from government. As in the case of agriculture, the primary inputs are land, water, and carbon dioxide from the air. Major outputs are timber and oxygen; minor outputs include gums, barks, and maple sap. Several important natural resins and solvents (e.g., turpentine, "naval stores") are derived from gums. Downstream chemical products based on wood distillates include acetone, methyl alcohol, pine oil (pinenes), terpenes, tall oil, and tanning extracts.

Neglecting the minor products, we can construct a rough mass balance for the timber tracts. The data given below imply that the total mass of raw product that was harvested in 1988 was 342 MMT on an air-dried (15 percent moisture) basis, which implies a dry weight of 290 MMT, of which 2 percent consisted of mineral "ash" (see below) and the remainder, 284 MMT, was roughly equivalent to cellulose. The calculated carbon content is thus 114 MMT, which requires an



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