Environmental Engineering Reference
In-Depth Information
rather steep decline in efficiency ratios. Are these trade-
offs acceptable, or are they sign of a fatal dependence on
nonrenewable energies?
The answers depend on circumstances. Countries with
relatively abundant farmland as well as those with high
intakes of meat could substantially cut their energy subsi-
dies by growing more cereal and oil crops in rotation
with feed and feed legumes (alfalfa, soybeans) and by
reducing their carnivory, which, in any case, does not of-
fer advantages compared to only moderately meaty diets
(Smil 2002). Populous countries with limited farmland
have to rely on intensive cultivation unless they are will-
ing to return to traditional low-yield cultivars and hence
to overwhelmingly vegetarian diets. But the subsidies can
be managed much more efficiently. Nitrogen losses are at
least 50% and commonly 60%-70% of the applied nutri-
ent (Cassman, Dobermann, and Walters 2002), and
Asian irrigation efficiencies could be doubled.
Drastic reductions of mechanical power would be
much harder to accomplish. Matching the power of
U.S. tractors in the year 2000 with horses would require
building up an equine stock of at least 250 million head,
about ten times the record number of horses in 1918. At
least 300 million ha, twice the total of U.S. arable land,
would be needed to feed the animals. And doing away
with insecticides would lower edible harvests by 10%-
50%. This critical dependence need not be alarming. In
the short run there is no shortage of conservation adjust-
ments, and as already noted, energy inputs into farming
are only a small share of TPES. They are relatively small
even in comparison with energy uses in other sectors of
the modern food system, which extends beyond the farm
gate to include processing, storage, transportation, distri-
bution, wholesale and retail, cooking, household refriger-
ation, and waste management.
None of these diverse activities can be quantified by a
single mean, but the rates of 50-100 MJ/kg of retail
product are common in processing and packaging; 1-3
MJ/kg for storage; up to 10 MJ/kg per week for cool-
ing or freezing; 1-4 MJ/kg for shopping; 5-7 MJ/kg of
food for home cooking; and 2-4 MJ/kg for a dishwash-
ing event (Dutilh and Linnemann 2004). Because of a
high degree of spatial concentration of modern special-
ized production (both nationally and internationally),
energy-intensive food transport now spans increasing dis-
tances between growers and consumers. In North Amer-
ica fruits and vegetables commonly travel 2,500-4,000
km, and the global total of international food shipments
surpassed 800 Mt in 2000, four times the mass in 1960
(Halweil 2004). As a result, energies used in food
processing, distribution, and wholesale and retail can
be twice as large as those consumed by field farming
and animal husbandry, and food preparation takes 30%-
50% of all energies used in an affluent nation's food
chain.
Food processing is a major consumer of fuels and elec-
tricity (Singh 1986; Biesot and Moll 1995; Ram´rez
2005). Wheat flour can be produced with as little as 1.3
MJ/kg; white rice may need no more than 1.5 MJ/kg;
and pasta making takes 4-5 MJ/kg. Fermentations pro-
ducing beverages with low alcoholic content consume a
relatively small amount of energy: beer less than 1 MJ/
L, wine about 2 MJ/L. Dutch meat processing averages
less than 1.5 MJ/kg for beef, about 2 MJ/kg for pork, 3
MJ/kg for chicken, and 5.5 MJ/kg for processed meats.
Sugar refining needs up to 35 MJ/kg, cheese making as
little as 3.5-5 MJ/kg and as much 20 MJ/kg. Soft
drinks need 20-25 MJ/kg, the distillation of liquors at
least 20-25 MJ/L. Breakfast cereals need in excess of
12 MJ/kg, tomato juice about 5 MJ/kg, frozen citrus
