ENVIRONMENTAL ENGINEERING:GREEN ENGINEERING

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GREEN ENGINEERING

While many of the earlier legislative efforts were oriented toward ‘‘end-of-pipe’’ technologies, where pollution was captured and disposed of after being generated, the focus is now shifting to legislation that favors recycling, reuse, and reduction of waste generation. The problem with end-of-pipe tech- nologies is that frequently the waste product, while no longer in the air, water, or earth, must still be disposed of in some manner. If a product is designed from its inception with the goal of reducing or eliminating waste not only during the production phase but also for its total life cycle, from product delivery to salvage, resources can be greatly conserved. This philosophy results in the design concept of ‘‘cradle to reincarnation’’ rather than ‘‘cradle to grave’’ because no well-designed product is ever disposed of—it is recycled (Graedel et al. 1995). Many phrases have been adopted into the expanding lexicon of green engineering. Total cost assessment (TCA), design for the environment (DFE), design for recycling (DFR), and life-cycle assessment are some of the many phrases that summarize efforts to look beyond the traditional design scope when designing and manufacturing a product.

Product Design

There is a threshold for the economic feasibility of recycling. If only a small portion of a product is recyclable or if great effort is required to extract the recyclable materials, then it may not be eco- nomically feasible to recycle a product. If, however, the product is designed to be largely recyclable and is designed in a manner that facilitates easy removal, then reuse and recycling will be econom- ically reasonable. Consider the personal computer. The rapid rate at which computing power has expanded has resulted in a proportionate turnover in computers in the workplace. However, no such improvement in computer externals has accompanied that in computer internals, so last year’s com- puter case could in theory hold this year’s computer processor, motherboard, memory, and so on.

SNAG-0336

The computer is an excellent example where design for recycling could be applied. While the ele- ments in Table 4 are based on computer and electronic production, similar principles can be adopted for other processes.

Process Design

In many cases, recycling of process material streams is both environmentally and economically sound. While efforts to minimize the use of hazardous air pollutants (HAPs) such as toluene and xylene continue, some applications, such as cleanup solvents for spraypainting, still require the properties of HAP-containing solvents. However, HAP emissions can be minimized through the use of solvent- recovery systems. These systems reduce emissions to the atmosphere, thus reducing permitting costs, and they also reduce purchasing costs by reducing the total volume of virgin cleanup solvent nec- essary.

In other cases, waste minimization technologies can result in enhanced product quality. A con- tinuous process data analysis system is one example. Rather than operator experience and intuition guiding when to cycle a process bath, computer analysis can be instituted to monitor key indicators of the process solution and automatically adjust the bath conditions. The result can be longer bath life, a more consistent product, and greater product engineer confidence (Dickinson 1995).

Total Cost Analysis

In some cases, an immediate benefit from a process change or recycling effort will not be evident. Any number of organizational, legal, or economic obstacles could distort the analysis of process options. Alternative budgeting and accounting methods are necessary to provide a more holistic perception of the process alternatives. Total cost analysis assesses the potential profitability of a green engineering proposal with several key differences from traditional methods. These differences are (White and Savage 1999):

1. Included in the inventory of costs, savings, and revenues are compliance training, testing, liability, and product and corporate image.

2. Rather than being lumped into overhead accounts, specific costs and savings are placed into process and product lines.

3. Longer time horizons are used to capture longer-term benefits.

4. Profitability indicators capable of incorporating the time value of money, long-term costs, and savings are used.

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