Industrial ecosystems can be broadly defined to include all types of production, processing, and consumption. It is useful to define five major components of an industrial ecosystem, as shows in Fig. 39.3.
These are:
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(1) A primary materials producer,
(2) A source or sources of energy,
(3) A materials processing and manufacturing sector,
(4) A waste processing sector, and
(5) A consumer sector.
In such an idealized system, the flow of materials among the four major hubs is very high. Each constituent of the system evolves in a manner that maximizes the efficiency with which the system utilizes materials and energy.
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It is convenient to consider the primary materials producers and the energy generators together because both materials and energy are required in order for the industrial ecosystem to operate. The primary materials producer or producers may consist of one or several enterprises devoted to providing the basic materials that sustain the industrial ecosystem.
Most generally, in any realistic industrial ecosystem a significant fraction of the material processed by the system consists of virgin materials. In a number of cases, and increasingly so as pressures build to recycle materials, significant amounts of the materials come from recycling sources.
Finished materials from primary materials producers are fabricated to make products in the materials processing and manufacturing sector, which is often a very complex system.
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For example, the manufacture of an automobile requires steel for the frame, plastic for various components, rubber in tires, lead in the battery, and copper in the wiring, along with a large number of other materials. Typically, the first step in materials manufacturing and processing is a forming operation.
For example, sheet steel suitable for making automobile frames may be cut, pressed, and welded into the configuration needed to make a frame. At this step some wastes may be produced that require disposal.
An example of such wastes consists of carbon fiber-epoxy composites left over form forming parts such as jet aircraft engine housings. Finished components from the forming step are fabricated into finished products that are ready for the consumer market.
In the consumer sector, products are sold or leased to the consumers who use them. The duration and intensity of use vary widely with the product; paper towels are used only once, whereas an automobile may be used thousands of times over many years.
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In all cases, however, the end of the useful lifetime of the product is reached and it is either (1) discarded, or (2) recycled. The success of a total industrial ecology system may be measured largely by the degree to which recycling predominates over disposal.
Recycling has become so widely practiced that an entirely separate waste processing sector of an economic system may now be defined. This sector consists of enterprises that deal specifically with the collection, separation, and processing of recyclable materials and their distribution to end users.
Such operations may be entirely private or they may involve cooperative efforts with governmental sectors. They are often driven by laws and regulations that provide penalties against simply discarding used items and materials, as well as positive economic and regulator incentives for their recycle.
The strong analogy between natural ecosystems and efficient industrial systems was first clearly stated in 1989 by Frosch and Gallopoulos.
A natural ecosystem, which is usually driven by solar energy and photosynthesis, consists of an assembly of mutually interacting organisms and their environment, in which materials are interchanged in a largely cyclical manner. It is possible to visualize an analogous industrial ecosystem in which materials are cycled, driven by an energy source (Table 39.1).
An idealized industrial ecosystem with no materials input and no wastes is illustrated in Fig. 39.4. The energy requirements of such a system are rather high and the materials flows within the system itself are quite high. Such a system is an idealized one that can never be realized in practice, but it serves as a useful goal around which more practical and achievable systems can be based.
