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

162 Biomass Utilization, Limits of

In a developing country an average, 600–700 kg/yr of combustion releases more than 200 different chemical pol-
dry biomass per person is used for cooking. For example, lutants into the atmosphere. The pollutants include, up to
the use of fuelwood for cooking and heating in Nepal is 14 carcinogens, 4 cocarcinogens, and 6 toxins that dam-
about 846 kg/yr of biomass per person. Other investigators age cilia, plus additional mucus-coagulating agents. Wood
report that from 912 to 1200 kg/yr of biomass per person smoke contains pollutants known to cause bronchitis, em-
is used for both cooking and heating. In some developing physema, cancer, and other serious illnesses.
countries, fuelwood for cooking and heating may cost al- Globally, but especially in developing nations where
most as much as the food, making it necessary to use crop people cook with fuelwood over open fires, approximately
residues and dung. 4 billion humans suffer continuous exposure to smoke.
A significant amount of wood is converted into char- This smoke which contains large quantities of particulate
coal for cooking and heating. Similar to wood fires for matterandmorethan200chemicals,includingseveralcar-
cooking, open charcoal fires are only about 10% efficient cinogens, results in pollution levels that are considerably
in transferring heat energy to food. However, charcoal has above those acceptable by the World Health Organization
some advantages over wood. First, it is lightweight and (WHO). Worldwide fuelwood smoke is estimated to cause
easy to transport. One kilogram of charcoal contains about the death of 4 million children each year worldwide. In
7100 kcal of potential energy in contrast to a kilogram of India, where people cook with fuelwood and dung, partic-
wood that has about 4000 kcal. Charcoal burns more uni- ulate concentrations in houses are reported to range from
3
formly and with less smoke than wood. 8300 to 15,000 µg/m , greatly exceeding the 75 µg/m 3
However, charcoal production is an energy-intensive maximum standard for indoor particulate matter in the
process. Although charcoal has a high energy content, United States.
from 20,300 to 28,400 kcal of hardwood must be pro- Because of the release of pollutants, some communi-
cessed to obtain the 7100 kcal of charcoal. Considering ties in developed areas, such as Aspen, CO, have banned
this low conversion efficiency ranging from 25 to 35%, wood burning for heating homes. When biomass is burned
charcoal heating for cooking has an overall energy trans- continuously in a confined space for heating, its pollutants
fer efficiency to food of only 2.5–3.5%. Further, the use of accumulate and can become a serious health threat.
charcoal uses more forest biomass than directly burning
the wood.
C. Ethanol Production
Using fuelwood for the production of steam in a boiler
under relatively optimal conditions is 55–60% efficient, Numerous studies have concluded that ethanol production
that is, burning 4000 kcal of air-dried wood provides from does not enhance energy security, is not a renewable en-
2200 to 2400 kcal of steam in the boiler. More often the ergy source, is not an economical fuel, and does not insure
efficiency is less than 55–60%. Steam production is used clean air. Further, its production uses land suitable for crop
to produce electricity and producing a salable product, production and causes environmental degradation.
such as steam, for industrial use. The conversion of corn and other food/feed crops into
Collecting biomass for fuel requires a substantial ethanol by fermentation is a well-known and established
amount of time and human effort. For example, in technology. The ethanol yield from a large plant is about
Indonesia, India, Ghana, Mozambique, and Peru families 9.5 l (2.5 gal) from a bushel of corn of 24.5 kg (2.6 kg/l
spend from 1.5 to 5 hrs each day collecting biomass to use of ethanol). Thus, a hectare of corn yielding 7965 kg/ha
as a fuel. could be converted into about 3063 l of ethanol.
Estimates are that more than half of the people who de- The production of corn in the United States requires a
pendonfuelwoodhaveinadequatesupplies.Insomecoun- significant energy and dollar investment (Table III). For
tries, such as Brazil, where forest areas are at present fairly example, to produce 7965 kg/ha of corn using conven-
abundant, the rural poor burn mostly wood and charcoal. tional production technology requires the expenditure of
However, in many developing countries crop residues ac- about 10.4 million kcal (about 10,000 l of oil equivalents)
count for most of the biomass fuel, e.g., 55% in China, (Table III), costing about $857.17 for the 7965 kg or ap-
77% in Egypt, and 90% in Bangladesh. Estimates are that proximately 10.8c / /kg of corn produced. Thus, for a liter
the poor in these countries spend 15–25% of their income of ethanol, the corn feedstock alone costs 28c / .
for biomass fuel. The fossil energy input to produce the 7965 kg/ha corn
feedstock is 10.4 million kilocalories or 3408 kcal/l of
ethanol (Table III). Although only 16% of United States
B. Health Effects
corn production is currently irrigated, it is included in
Environmentally, burning biomass is more polluting than the analysis, because irrigated corn production is energy
using natural gas, but less polluting than coal. Biomass costly. For the 150 mm of irrigation water applied and