transporting, reprocessing) can be kept low and the grade of end use of the recycled material kept high to maintain the high intrinsic energy content of these materials, then in terms of energy consumption, recycling is an attractive option. Otherwise, recycling is a less attractive option, and an energy recovery strategy is preferable.

Commentary on the Example

The range of correct values for some of the energy inputs considered in this analysis was particularly broad for the manufacture of ceramic and glass cups. But the analysis revealed that the break-even points are not as sensitive to changes in this parameter (the fabrication energy of the reusable cup types) as they are to the energy required for washing and sanitizing the reusable cups or fabricating the disposable cups. This analysis also demonstrated that the high fabrication energy required for the reusable cups became unimportant over enough uses, say 500 or more, compared with the energy required to wash and sanitize them for reuse. It also revealed that the wash energy alone is as much or more than that required to make a polystyrene foam cup in the United States and more than half that required to make a paper cup. Therefore, from an energy standpoint, use of disposable cups is appropriate, especially in situations where the return and reuse rate of the reusable cups is likely to be low.

Many people may prefer to use a ceramic, glass, or reusable polystyrene cup rather than a disposable cup. It is difficult to determine how much weight should be given to this "personal-preference" factor. However, this comparison of energy consumption demonstrates that it is environmentally reasonable to use the disposable cup types when the return rate of reusable cups is likely to be low, or for situations of one-time use such as for large parties, because the energy required for manufacture of the disposable cup types is less than, or very close to, the energy needed to clean a reusable cup.

Finally, this analysis confirms that there is environmental merit in having a diversity of cup types available depending on type of use. In certain circumstances, disposable cups may actually use fewer resources and cause less environmental impact than ceramic, china, or glass cups.

Concluding Notes

In an energy-based analysis of relative ecological merit, it is crucial to define clearly the boundaries to be used. The analyst must also be prepared to adjust these boundaries as the data are gathered if the initial limits to the system appear inappropriate.

Energy costs of raw materials will vary with location, so the area where the technology is being studied has to be specified. Correction factors may have to be used to adjust the energy components used in the analysis, but they should be



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