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Encyclopedia of Physical Science and Technology EN002C-60 May 17, 2001 20:23

Biomass Utilization, Limits of 161

TABLE I Annual Biomass Production in the United States Each year, worldwide, an estimated 5300 million dry
tons of biomass are burned directly as a fuel, providing
Land area Biomass production
6
6
(10 /ha) (10 /t) about 88 quads of energy. Rural poor in developing coun-
tries obtain up to 90% of their energy needs by burning
Cropland and crops 192 1,083 biomass. In developing countries, about 2 billion tons of
Pasture and forage 300 900 fuelwood, 1.3 billion tons of crop residues, plus nearly
Forests 290 580 1 billion tons of dung are burned each year.
Other 135 68 Although some deforestation results from the use of fu-
Total area 917 — elwood, the most significant environmental impacts result
Total biomass — 2,631 from burning crop residues and dung. When crop residues
15
Total energy (10 /kcal) 11.8 and dung are removed from the land and used as a fuel
Biomass production (t/ha) 2.9 this leaves the cropland without vegetative protection and
exposed to wind and water erosion. Erosion destroys the
[FromPimentel,D.,andKounang,N.(1998), Ecosystems1,416–426.]
productivity of cropland, by robbing the soil of nutrients,
essential water, soil organic matter, and adequate rooting
of fossil energy each year, this means that it is consuming
depth.
85% more fossil energy than the total energy captured by
Cooking requires relatively large amounts of fuel and is
all its plant biomass each year.
essential for preventing disease, improving nutrition, and
increasing the palatability of many foods. The transfer
C. United States Agricultural and Forest of heat from the woodfire in a stove to the food product
Products and Biofuels is about 33% efficient, while over an open fire, the heat
Including crops and forages from pastures, the United transfer to the food is only about 10% efficient. Under
usual cooking conditions, from 2 to 3 kcal are required to
States harvests approximately 1307 million tons of
cook 1 kcal of food.
biomass per year in agricultural products and approxi-
mately 100 million tons of biomass per year as forest
products (Table II). Together the energy value of harvested TABLE II Total Annual Amount of Solar Energy Harvested in
agricultural and forest products total 6352 10 12 kcal/yr the Form of Agricultural and Forest Biomass in the U.S.
(Table II). These data suggest that the United States is
6
Tons (10 ) Energy (10 12 kcal)
harvesting in the form of agricultural and forest products,
54% of the total energy captured each year by the United Corn 194 873
States biomass annually (Tables I and II). This total does Wheat 71 320
not include the biomass harvested now and used as biofuel. Rice 6 27
Soybeans 51 230
Sorghum 22 99
II. CONVERSION OF BIOMASS
Potatoes 16 72
RESOURCES
Vegetables 6 27
Fruits 5 23
In addition to using biomass directly as food, fiber, lumber,
Nuts 0.8 4
and pulp, biomass is utilized as a fuel. The total biofuel
Oil seeds 9 41
utilized in the United States is slightly more than 3 quads Sugarcane 2.5 20
(800 × 10 12 kcal) per year. If the biofuel energy is added
Sugar beets 2 27
to that harvested as agricultural and forest products, then
Pulses 1 5
the total biomass energy harvested from the United States Oats 7 32
12
terrestrial ecosystem is 7332 × 10 kcal/yr. This is equiv-
Rye 1 5
alent to 62% of the total biomass energy produced in the
Barley 13 59
United States each year. Harvesting this 62% is having a
Total 407.3 1,853
negative impact on biodiversity in the nation.
Pasture forage 900 4,050
Forest products 100 450
A. Direct Heating Totals 1,407 6,352
Heat production is the most common conversion system Total per capita (tons) 5.2
6
for using biomass resources. Heat from wood and other Total per capita (10 /kcal) 23.3
biomass resources is utilized for cooking food, heating [From Pimentel, D., and Kounang, N. (1998), Ecosystems 1, 416–
homes, and producing steam for industry. 426.]