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into energy, thereby conserving valuable fossil fuels. The waste stream also contains valuable materials--steel, aluminum, paper, glass--that can be recycled. Generally, although not in all cases, it takes less energy to manufacture a product from recycled materials than from virgin materials when all stages of materials acquisition, processing, manufacturing, and transportation are considered. To get a better appreciation for the opportunities for recovering energy and recycling materials, a closer look at the waste stream would be desirable.

The Waste Stream

EPA estimates that about 125 million tons of municipal wastes were generated from residential and commercial sources in the U.S. in 1971 (3.32 lbs/person/day). Table 1 shows a breakdown of the waste stream, cross-referenced by material and by product. Product source categories are presented in millions (106) of tons on an "As Generated" basis. The materials in the waste stream are presented in millions of tons on both an "As Generated" and an "As Disposed"

This waste generation rate is lower than the widely quoted 190 million tons/year (5.3 lbs/capital/day) estimated in the 1968 National Survey of Community Solid Waste Practices. The National Survey was based on a sample of collected tonnage estimates (rather than systematic measurements) that were extrapolated to a national scale. These more recent estimates are primarily based on national material production and product marketing data. It is the judgement of EPA that these new figures are accurate to within approximately 25 percent and the 1968 survey over-estimated the national municipal solid waste stream.

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basis. "As Generated" measures the weight of the material before

it is mixed with other wastes. "As Disposed" measures the weight

of the material after being mixed in trash cans and collection trucks. The difference between the two is the result of the migration of moisture from the wetter materials (food and yard wastes) to materials that absorb moisture (note the increase in the weight of paper) and to products to whose surface the moisture adheres (such as glass and metals).

The figures in Table 1 include wastes generated in household, commercial and business establishments and institutions (schools, hospitals, etc.) and excludes industrial process wastes, agricultural and animal wastes, abandoned automobiles, ashes, street sweepings, construction and demolition debris, and sewage sludges. The 125 million ton figure includes only those materials discarded into the waste stream and, therefore, excludes certain amounts of newsprint, corrugated and other materials that are already being recycled.

Large quantities of agricultural, forestry and industrial wastes and sewage sludge are generated each year. The amount of energy recoverable from these wastes may be significant; however, these wastes are not included in this analysis because the economic feasibility of recovering energy from them has not been determined.

The amount of products consumed and wastes generated has been growing at a rate estimated at 3 percent per year over the last decade. The population increased about 13 percent during the 1960's.

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Although the population is growing slower now than in earlier years, the generation of wastes continues to increase.

These trends indicate a projected 3 to 4 percent annual increase in the amount of wastes generated in the years ahead. This means that more wastes will be available for energy recovery and materials recovery. More importantly, however, it means that the demand on supplies of natural resources will be greater and that more energy will be required to convert those resources into usable products. Thus, the need to conserve energy and to consume fewer products should become more apparent.

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ENERGY CONSERVATION THROUGH SOURCE REDUCTION

Source reduction is defined as the reduction in the generation

of solid waste through a reduction in the consumption of materials and products. There are four general approaches to achieve source

reduction:

1. Product reuse (e.g., returnable bottles)

2.

Reduce resource intensiveness (e.g., smaller autos)

3. Increased product lifetime (e.g., longer lasting household appliances)

4.

Decreased product consumption (e.g., reduced packaging
consumption)

Table 1 indicates some of the broad product categories in the waste stream that could be impacted by source reduction measures.

Almost invariably, any source reduction action will result in the conservation of energy. Although the energy conservation impacts of most of the many possible source reduction actions have not been quantified, an estimate was made of the potential energy savings resulting from a reduction in one product category, packaging, to put the energy conservation potential of source reduction in perspective. If per capita packaging consumption in 1972 were reduced to the levels that existed in 1958, over 560 trillion Btu's could have been saved in 1972, the equivalent of 267,000 B/DOE (Appendix I).

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