will significantly warm the water in a river near the location where the
power plant is to be built. Such a change would be drastic enough to
change the ecosystem of the river. Therefore, the water would have to be
cooled to within a few degrees of the temperature of the river, prior to
discharge. This is typically accomplished with the use of cooling towers,
which are responsible for transferring the excess heat from the discharge
water to the surrounding air, prior to letting the water flow back into the
river. See Figure 26-5.
Choosing Environmentally Friendly Energy,
Power, and Transportation Sources
There are many environmentally friendly alternatives to using conven-
tional energy, power, and transportation sources. These alternatives,
however, are often not as economical or convenient as traditional sources.
For instance, let us say you live in a suburb and work in a city less than
10 miles away. You typically drive to work, but you would like to consider
some environmentally friendly transportation alternatives. Riding a
bicycle is the most economical and environmentally friendly alternative
(in addition to being the healthiest), but it is also the least convenient. A
compromise might be to consider commuting with other people from the
neighborhood who also work in the city, thereby using only one vehicle,
instead of three or four. Another popular and economical alternative is to
use mass transit, such as a subway or bus system. This method of
Thermal pollution:
A form of pollution
most commonly
associated with
power plants, in
which expelled
waste heat
adversely affects
aquatic life.
Energy, Power, Transportation, and the Environment 619
Fuel
Boiler
Steam
Turbine
Generator
Condenser
Electricity
Water source
Intake
(cool)
Discharge
(warmer)
Heat
Figure 26-5. A typical thermal electric generating station, shown in schematic
form. Large power plants require tremendous amounts of cooling water. The
cooling water, shown in color, flows from the intake through the condenser to
remove heat from the steam in the turbine loop. The water is returned to its
source at a higher temperature, which can affect fish and other forms of
aquatic life. A system must be designed to accommodate a specific site in a
way that is not harmful to the environment.
G R E E N T E C H
Carpooling helps
reduce the
environmental impact
of commuters. To
help encourage
carpooling, over 20
states so far have
added high-
occupancy vehicle
lanes to their
highways. It is illegal
for single riders to
use these lanes.