502INDUSTRIAL ECOLOGY
INTRODUCTIONIndustrial ecology is an emerging field of study that deals
with sustainability. The essence of industrial ecology was
defined in the first textbook of the field in this way:Industrial ecology is the means by which humanity can
deliberately and rationally approach and maintain sustain-
ability, given continued economic, cultural, and technologi-
cal evolution. The concept requires that an industrial system
be viewed not in isolation from its surrounding systems, but
in concert with them. It is a systems view in which one seeks
to optimize the total materials cycle from virgin material,
to finished material, to component, to product, to obsolete
product, and to ultimate disposal. Factors to be optimized
include resources, energy, and capital. (Graedel and Allenby,
2003, 18)Industrial ecology is industrial and technological in the
sense that it focuses on industrial processes and related
issues, including the supply and use of materials and energy,
adoption of technologies, and study of technological envi-
ronmental impacts. Although social, cultural, political, and
psychological topics arise in an industrial-ecology context,
they are often regarded as ancillary fields, not central to
industrial ecology itself (Allenby, 1999).
Industrial ecology’s emphasis on industries and technolo-
gies can be explained with the “master equation” of industrial
ecology. Originating from the IPAT equation (impact, popu-
lation, affluence, and technology; Ehrlich and Holdren, 1971;
Commoner, 1972), the master equation expresses the relation-
ship between technology, humanity, and the environment in the
following form:Environmental impact PopulationGDP
Person
Environmental impacct
Unit of GDP(1)where GDP is a countrys or region’s gross domestic product,
the measure of industrial and economic activity (Graedel
and Allenby, 2003, pp. 5–7; Chertow, 2000a).
In this equation, the population term, a social and demo-
graphic one, has shown a rapid increase in the past severaldecades, and continues to increase. The second term, per-
capita GDP, is an economic indicator of the present popula-
tion’s wealth and living standards. Its general trend is rising
as well, although there are wide variations among countries
and over time. These trends make it clear that the only hope
of maintaining environmental interactions in the next few
decades at an acceptable level is to reduce the third term, envi-
ronmental impacts per unit of GDP, to a greater degree than is
the product of the increases in the first two terms—a substan-
tial challenge! This third term is mainly technological and is a
central focus of industrial ecology.
The name “industrial ecology,” combining two normally
divergent words, relates to a radical hypothesis—the “biologi-
cal analogy.” This vision holds that an industrial system is a
part of the natural system and may ideally mimic it. Because
biological ecology is defined as the study of the distribu-
tion and abundance of living organisms and the interactions
between those organisms and their environment, industrial
ecology may be regarded as the study of metabolisms of tech-
nological organisms, their use of resources, their potential
environmental impacts, and their interactions with the natural
world.
The typology of ecosystems has been characterized as
three patterns (Figure 1a–c). A Type I system is a linear
and open system that relies totally on external energy and
materials. In biology, this mode of action is represented by
Earth’s earliest life forms. A Type II system is quasi-cyclic,
with much greater efficiency than Type I. However, it is not
sustainable on a planetary scale, because resource flows
retain a partially linear character. Only a Type III system
possesses a real cyclic pattern, with optimum resource
loops and external reliance only on solar energy. This is
how the natural biosphere behaves from a very long-term
perspective.
The evolutionary path from Type I to Type III taken by
nature (from open to cyclic, from unsustainable) provides per-
spective on the evolution of industrial ecosystems. Historically,
the industrial system has mimicked the Type I pattern, with
little concern about resource constraints. The best of today’s
industries come close to Type II (Figure 1d), and a Type III
industrial system is a vision of a possible sustainable future
for industrial ecosystems.
The biological analogy has been explored in other ways
as well. From a metaphysical perspective, industrial ecology’s
philosophy might be labeled as: “nature as model,” “learning
from nature,” and “orientation by nature” (Isenmann, 2002).C009_002_r03.indd 502C009_002_r03.indd 502 11/18/2005 10:30:24 AM11/18/2005 10:30:24 AM