Page 590 - Environment: The Science Behind the Stories

Carbon Particulate Total hydrocarbons Sulfates Nitrogen
monoxide
matter
oxides
0
Percent reduction versus petrodiesel 40
20

60

80

B20 B100 FIGURE 20.21 At Loyola University Chicago, students and
staff produce biodiesel from waste vegetable oil from the
100
dining halls and use it to fuel this van. They transport this
FIGURE 20.20 Burning biodiesel in a diesel engine emits less mini-diesel reactor to local high schools to teach students about
pollution than burning conventional petroleum-based diesel. alternative fuels.
Shown are percentage reductions in several major pollutants that
one can attain by using B20 (a mix of 20% biodiesel and 80% of lipids that can be converted to biodiesel. Alternatively,
petrodiesel) and B100 (pure biodiesel). Data from U.S. Environmental carbohydrates in algae can be fermented to create ethanol.
Protection Agency.
In fact, a variety of fuels, including jet fuel, can be produced
Which type of pollutant does use of biodiesel help reduce from algae.
most effectively, relative to petrodiesel? Algae can be grown in open ponds, including “raceway”
ponds that circulate algae around a racetrack. More controlled
and intensive production can be achieved in closed tanks or in
biodiesel, or biodiesel can be mixed with conventional pet- closed transparent tubes called photobioreactors (FIGURE 20.22).
rodiesel; a 20% biodiesel mix (called B20) is common today. Algae grow much faster than terrestrial crops, can be harvested
Biodiesel cuts down on emissions compared with petro- every few days, and produce much more oil than other biofuel
diesel (FIGURE 20.20). Its fuel economy is almost as good, it crops. Algae farms can use wastewater, ocean water, or saline
costs just slightly more, and it is nontoxic and biodegradable. water. Because algae need nutrients, wastewater from sewage
Increasing numbers of people are fueling their cars with bio- treatment plants can actually be a good source of water. And
diesel from waste oils (FIGURE 20.21) Some buses and recycling because piping in carbon dioxide speeds their growth, algae
trucks now run on biodiesel, and many state and federal fleets can make use of smokestack emissions. Indeed, placing algae
use biodiesel blends.
Some enthusiasts have taken biofuel use further. Elimi-
nating the processing step that biodiesel requires, they use
straight vegetable oil in their diesel engines (which requires
modifying the engine).
Using waste oil as a biofuel is sustainable, but most
biodiesel today, like most ethanol, comes from crops grown
specifically for the purpose—and these crops have environ-
mental impacts. Growing soybeans in Brazil and oil palms
in Southeast Asia hastens the loss of tropical rainforest CHAPTER 20 • CONVENTI ON AL ENERGY ALTERN ATIVES
(pp. 330–332). Growing soybeans in the United States and
rapeseed in Europe takes up large areas of land as well.
Because the major crops grown for biodiesel and for ethanol
exert heavy impacts on the land, farmers and agricultural
scientists are experimenting with a variety of other crops,
from wheat, sorghum, cassava, and sugar beets to less known
plants such as hemp, jatropha, and the grass miscanthus.

Novel biofuels are being developed FIGURE 20.22 Algae are a leading candidate for next-
generation biofuels. Here algae are seen growing at a demon-
One promising next-generation biofuel crop is algae (better stration facility. Algae grow quickly and productively, can be farmed
known to most of us as green pond scum)! Several species in many places (including locations other crops cannot be grown),
of these photosynthetic organisms produce large amounts and can produce biodiesel, ethanol, or other fuels. 589

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