Seaweeds: A Promising Source for Sustainable Development - Environmental Sustainability: Role of Green Technologies - page 79

Algae are among the fastest growing plants in
the world, and about 50 % of their weight is oil.
This lipid oil can be used to make biodiesel for
cars, trucks, and airplanes. Microalgae have
much faster growth rates than terrestrial crops.
The per-unit area yield of oil from algae is esti-
mated to be between 20,000 and 80,000 L/acre/
year; this is 7-31 times greater than the next best
crop, palm oil (Chisti 2007 ). It is possible that US
demand for liquid fuel could be achieved by
cultivating algae in one tenth the area currently
devoted to soybean cultivation (Scott and Bryner
2006 ). The lipid and fatty acid contents of micro-
algae vary in accordance with culture conditions.
Most current research on oil extraction is focused
on microalgae to produce biodiesel from algal
oil. Algal oil can be processed into biodiesel as
easily as oil derived from land-based crops.
The production of microalgal biodiesel requires
large quantities of algal biomass. The algae that
are used in biodiesel production are usually
aquatic unicellular green algae. This type of algae
is a photosynthetic eukaryote characterized by
high growth rates and high population densities.
Under good conditions, green algae can double
their biomass in less than 24 h (Schneider 2006 ;
Chisti 2007 ). Additionally, green algae can have
huge lipid contents, frequently over 50 % (Schneider
2006 ; Chisti 2007 ). This high-yield, high-density
biomass is ideal for intensive agriculture and may
be an excellent source for biodiesel production.
A one ha algae farm on wasteland can produce
over 10-100 times as much oil compared to any
other known source of oil crops. While a crop
cycle may take from 3 months to 3 years for
production, algae can start producing oil within
3-5 days, and thereafter oil can be harvested on a
daily basis. Algae can be grown using sea water
and non-potable water on wastelands where noth-
ing else grows. Algae farming for biofuels is
expected to provide a conclusive solution to the
food vs. fuel debate. The production of biodiesel
has recently received much attention worldwide.
In order to resolve the worldwide energy crisis,
seeking for lipid-rich biological materials to
produce biodiesel effectively has attracted much
renewed interest. Algae have emerged as one
of the most promising sources for biodiesel

production. It can be inferred that algae grown
in CO 2 -enriched air can be converted into oily
substances. Such an approach can contribute to
solving the major problems of air pollution,
resulting from CO 2 emissions and future crises
due to a shortage of energy sources (Sharif
Hossain et al. 2008 ).
The process for producing microalgal oils
consists of a microalgal biomass production step
that requires light, CO 2 , water, and inorganic
nutrients. The latter are mainly nitrates, phosphates,
iron, and some trace elements. Approximately
half of the dry weight of microalgal biomass is
carbon, which is typically derived from CO 2 .
Therefore, producing 100 tons of algal biomass
fi xed roughly 183 tons of CO 2 . This CO 2 must be
fed continually during daylight hours. It is often
available at little or no cost (Chisti 2008 ). The
optimal temperature for growing many microal-
gae is between 293 and 303 K. A temperature
outside this range could kill or otherwise damage
the cells. There are three well-known methods to
extract oil from algae: (1) expeller/press, (2) solvent
extraction with hexane, and (3) supercritical
fl uid extraction. A simple process is to use a press
to extract a large percentage (70-75 %) of the oils
from algae. Algal oil can be extracted using
chemicals. The most popular chemical for solvent
extraction is hexane, which is relatively inexpen-
sive. Supercritical fl uid extraction is far more
effi cient than traditional solvent separation methods.
Supercritical fl uids are selective, thus providing
the high purity and product concentrations (Paul
and Wise 1971 ). This method alone can allow one
to extract almost 100 % of the oils. In supercritical
fl uid CO 2 extraction, CO 2 is liquefi ed under
pressure and heated to the point where it has the
properties of both a liquid and a gas. This lique-
fi ed fl uid then acts as the solvent in extracting the
oil. The lipid and fatty acid contents of microal-
gae vary in accordance with culture conditions.
Algal oil contains saturated and monounsaturated
fatty acids. The fatty acids exist in algal oil in the
following proportions: 36 % oleic (18:1), 15 %
palmitic (16:0), 11 % stearic (18:0), 8.4 % isolin-
oleic (17:0), and 7.4 % linoleic (18:2). The high
proportion of saturated and monounsaturated
fatty acids in this alga is considered optimal from