What is Biomass?
Biomass is any organic matter—wood, crops, seaweed, animal wastes—
that can be used as an energy source. Biomass is probably our oldest
source of energy after the sun. For thousands of years, people have
burned wood to heat their homes and cook their food.
Biomass gets its energy from the sun. All organic matter contains
stored energy from the sun. During a process called photosynthesis,
sunlight gives plants the energy they need to convert water and carbon
dioxide into oxygen and sugars. These sugars, called carbohydrates,
supply plants and the animals that eat plants with energy. Foods rich in
carbohydrates are a good source of energy for the human body!
Biomass is a renewable energy source because its supplies are not
limited. We can always grow trees and crops, and waste will always exist.
Types of Biomass
We use four types of biomass today—wood and agricultural products,
solid waste, landfill gas and biogas, and alcohol fuels.
1. Wood and Agricultural Products
Most biomass used today is home grown energy. Wood—logs, chips,
bark, and sawdust—accounts for about 49 percent of biomass energy.
But any organic matter can produce biomass energy. Other biomass
sources include agricultural waste products like fruit pits and corncobs.
Wood and wood waste, along with agricultural waste, are used to
generate electricity. Much of the electricity is used by the industries
making the waste; it is not distributed by utilities, it is cogenerated. Paper
mills and saw mills use much of their waste products to generate steam
and electricity for their use. However, since they use so much energy,
they need to buy additional electricity from utilities.
Increasingly, timber companies and companies involved with wood
products are seeing the benefits of using their lumber scrap and sawdust
for power generation. This saves disposal costs and, in some areas, may
reduce the companies’ utility bills. In fact, the pulp and paper industries
rely on biomass to meet half of their energy needs. Other industries
that use biomass include lumber producers, furniture manufacturers,
agricultural businesses like nut and rice growers, and liquor producers.
2. Solid Waste
Burning trash turns waste into a usable form of energy. One ton (2,000
pounds) of garbage contains about as much heat energy as 500 pounds
of coal. Garbage is not all biomass; perhaps half of its energy content
comes from plastics, which are made from petroleum and natural gas.
Power plants that burn garbage for energy are called waste-to-energy
plants. These plants generate electricity much as coal-fired plants do,
except that combustible garbage—not coal—is the fuel used to fire
their boilers. Making electricity from garbage costs more than making
it from coal and other energy sources. The main advantage of burning
solid waste is that it reduces the amount of garbage dumped in landfills
by 60 to 90 percent, which in turn reduces the cost of landfill disposal. It
also makes use of the energy in the garbage, rather than burying it in a
landfill, where it remains unused.
3. Landfill Gas
Bacteria and fungi are not picky eaters. They eat dead plants and
animals, causing them to rot or decay. A fungus on a rotting log is
converting cellulose to sugars to feed itself. Although this process is
slowed in a landfill, a substance called methane gas is still produced as
the waste decays.
New regulations require landfills to collect methane gas for safety and
environmental reasons. Methane gas is colorless and odorless, but it
is not harmless. The gas can cause fires or explosions if it seeps into
nearby homes and is ignited. Landfills can collect the methane gas,
purify it, and use it as fuel.
Methane, the main ingredient in natural gas, is a good energy
source. Most gas furnaces and stoves use methane supplied by
utility companies. In 2003, East Kentucky Power Cooperative began
recovering methane from three landfills. The utility now uses the gas
at five landfills to generate 16 megawatts of electricity—enough to
power 7,500 to 8,000 homes.
Today, a small portion of landfill gas is used to provide energy. Most
is burned off at the landfill. With today’s low natural gas prices, this
higher-priced biogas is rarely economical to collect. Methane,
however, is a more powerful greenhouse gas than carbon dioxide. It is
better to burn landfill methane and change it into carbon dioxide than
release it into the atmosphere.
Methane can also be produced using energy from agricultural and
human wastes. Biogas digesters are airtight containers or pits lined
with steel or bricks. Waste put into the containers is fermented without
oxygen to produce a methane-rich gas. This gas can be used to
produce electricity, or for cooking and lighting. It is a safe and clean-
burning gas, producing little carbon monoxide and no smoke.
Biogas digesters are inexpensive to build and maintain. They can be
built as family-sized or community-sized units. They need moderate
temperatures and moisture for the fermentation process to occur.
For developing countries, biogas digesters may be one of the best
answers to many of their energy needs. They can help reverse the
rampant deforestation caused by wood-burning, and can reduce air
pollution, fertilize over-used fields, and produce clean, safe energy for
Use of Biomass
Until the mid-1800s, wood gave Americans 90 percent of the energy
used in the country. Today, biomass provides about 4.1 percent of the
total energy we consume. Biomass has largely been replaced by coal,
natural gas, and petroleum.
Almost half of the biomass used today comes from burning wood and
wood scraps such as saw dust. More than one-third is from biofuels,
principally ethanol, that are used as a gasoline additive. The rest comes
from crops, garbage, and landfill gas.
Industry is the biggest user of biomass. Over 51 percent of biomass is
used by industry. Electric utilities use 11 percent of biomass for power
generation. Biomass produces 0.7 percent of the electricity we use.
Transportation is the next biggest user of biomass; almost 24 percent
of biomass is used by the transportation sector to produce ethanol and
The residential sector uses 11 percent of the biomass supply. About
one-tenth of American homes burn wood for heating, but few use
wood as the only source of heat. Most of these homes burn wood in
fireplaces and wood stoves for additional heat.
Using Biomass Energy
Usually we burn wood and use its energy for heating. Burning,
however, is not the only way to convert biomass energy into a
usable energy source. There are four ways:
Fermentation: There are several types of processes that can
produce an alcohol (ethanol) from various plants, especially
corn. The two most commonly used processes involve using
yeast to ferment the starch in the plant to produce ethanol. One
of the newest processes involves using enzymes to break down
the cellulose in the plant fibers, allowing more ethanol to be
made from each plant, because all of the plant tissue is utilized,
not just the starch.
Burning: We can burn biomass in waste-to-energy plants to
produce steam for making electricity, or we can burn it to
provide heat for industries and homes.
Bacterial Decay: Bacteria feed on dead plants and animals,
producing methane. Methane is produced whenever organic
material decays. Methane is the main ingredient in natural gas,
the gas sold by natural gas utilities. Many landfills are recovering
and using the methane gas produced by the garbage.
Conversion: Biomass can be converted into gas or liquid fuels
by using chemicals or heat. In India, cow manure is converted
to methane gas to produce electricity. Methane gas can also be
converted to methanol, a liquid form of methane.
Biomass and the Environment
Environmentally, biomass has some advantages over fossil fuels such
as coal and petroleum. Biomass contains little sulfur and nitrogen, so
it does not produce the pollutants that can cause acid rain. Growing
plants for use as biomass fuels may also help keep carbon dioxide levels
balanced. Plants remove carbon dioxide—one of the greenhouse
gases—from the atmosphere when they grow.