Environmental Engineering Reference
In-Depth Information
embodied energy of about 20 GJ/kg, 100 times more
than aluminum from bauxite, 200 times more than a
car, and 1,000 times more than crude steel from ore.
Extending this analysis to personal computers, E. D.
Williams (2004) calculated that total energy embodied
in a typical machine produced in 2000 (Pentium III pro-
cessor, 30 GB hard drive, 42.5-cm monitor) amounted
to 6.4 GJ, or roughly 270 MJ/kg. Given the machine's
average three-year useful life, during which it will use
some 420 kWh of electricity (or 1.5 GJ of primary en-
ergy), its lifetime cost is dominated by the embodied
energy. Moreover, the high energy intensity of produc-
tion and the rapid turnover translate into an unusually
high annual life cycle energy burden of 2.6 GJ, about
30% more than for a refrigerator. But it would be mis-
leading to use this comparison between the mass of a
microchip and the mass and energy of inputs needed to
produce it as the basis for judging the relative energetic
and environmental merits of microchips and computers.
Extension of useful life is obviously desirable, but overall
energy and material impacts of microelectronics cannot
be judged without also considering the savings it brings
or the cost of its alternatives.
The production of paper, the carrier of civilization's
memories and messages, follows a well-established route
from logging to pulping to formation of the product in
Fourdrinier machines, where the pulp is laid on a contin-
uous wire mesh at the wet end of the machine, most of
water is expelled in the felt press section, and the process
is finished by passing paper over a series of heated cylin-
ders. Most of the pulp is now produced by chemical
(kraft) process, but semichemical and mechanical pro-
cesses are also used (Ruth and Harrington 1998). A sec-
toral analysis for U.S. paper and paperboard production
resulted in an average embodied cost of 35 GJ/t
(Brown, Hamel and Hedman 1996). The cheapest kinds
(unbleached packaging paper made with mechanical
pulp) need less than 20 GJ/t, but good-quality writing,
typing, copying, and topic paper (made with chemical,
mostly sulfate, pulp) costs well over 30 GJ/t, or about
as much as good-quality finished steel.
But the highest-quality paper (the coated stock most
commonly encountered in art topics) actually needs less
energy (5%-12%, or as little as 32 GJ/t) than the pro-
duction of uncoated papers (offset, standard topic) of
similar weight and brightness (Hein and Lower 1978).
This difference is due primarily to the coated stock's
lower fiber content; to produce and apply the coating
materials is cheaper than to make fiber from wood. Paper
from recycled stock is less energy-intensive, but the dif-
ference is reduced if the product needs de-inking (
>
2
GJ/t) and bleaching (@5 GJ/t). Typical printing costs
are about 2 MJ/m
2
. Contrary to expectations, the elec-
tronic age has boosted the demand for paper, and in the
richest countries its per capita use has surpassed 200 kg
or 300 kg per capita.
10.4 Crops and Animal Foods: Subsidized Diets
Extraction of coal and cheap steel introduced new labor-
saving machines but could not displace animate power in
fieldwork and irrigation or remove the shortages of nitro-
gen, the key limiting nutrient. This began to change only
at the beginning of the twentieth century with the intro-
duction of tractors and the synthesis of ammonia. Later
came the first pesticides, herbicides, and high-yielding
cultivars, and since the l960s this agricultural moderniza-
tion has also reached the poor world. Systematic study of
the energy cost of modern food production started only
in the early 1970s (Heichel 1976; Pimentel et al. 1973;
G. Leach 1975), but the literature increased so rapidly
