Environmental Engineering Reference
In-Depth Information
period of time. This chapter provides an overview of the production of
biodiesel from microalgae and includes algae cultivation, biomass
production, harvesting, and downstream processing, along with a list of
companies aiming to develop biodiesel from microalgae.
Keywords
Microalgae • Biomass • Biofuel • Transesterifi cation • Triacylglycerol
1
Introduction
barrels/day in 2006, it is estimated to reach 107
million barrels/day by 2030.
Dependency on fossil fuel, primarily in the
transportation sector, has encouraged research on
biofuels. One-fi fth of global CO
2
emissions is
from the transport sector. The global number of
vehicles has been roughly estimated to rise to two
billion by the year 2050 (Balat and Balat
2010
).
The transportation sector would be responsible
for 80 % of this increase (US Energy Information
Administration 2009) and would consume 76 %
of the world oil production by 2030 (International
Energy Agency
2008
). A recent study has shown
that microalgae biofuels have the potential to
replace 17 % of oil imports used for transporta-
tion fuel in the USA by 2022 (Wigmosta et al.
2011
). Moreover, following the BP oil spill in the
Atlantic Ocean, the US administration is consid-
ering reducing its oil imports by one-third by
2021, using, among others, biofuels to do so
(Banerjee
2011
). The only possible alternative to
overcome all these problems is to produce 'algal
biodiesel'.
Fossil fuels are the largest contributor of
greenhouse gases. They are about to reach peak
production and are predicted to be exhausted in
the future due to their limited and non-renewable
nature. Therefore, the current use of fossil
fuels is widely recognized as unsustainable
(Hemaiswarya et al.
2012
). In the year 2007, the
US Department of Energy reported that the burn-
ing of fossil fuels produces around 21.3 billion
tonnes (
gigatonnes [Gt]) of carbon dioxide
(CO
2
) per year; however, it is estimated that nat-
ural processes can only absorb about half of that
amount, resulting in a net increase of 10.65 bil-
lion tonnes of atmospheric CO
2
per year. Carbon
dioxide is one of the greenhouse gases that
enhances radioactivity and contributes to global
warming (a rise in the average surface tempera-
ture of the earth), which a majority of climate
scientists agree is going to cause major adverse
effects. Data show that, between 1989 and 2008,
the proven oil reserves seem to have increased
from 1,006 to 1,333 billion barrels. The annual
world primary energy consumption was mea-
sured at 12,274.6 million tonnes of oil equivalent
(MTOE). Fossil fuels accounted for 87.08 % of
primary energy consumption, with the main
fuels being oil (33.07 % share), coal (30.34 %),
and natural gas (23.67 %); the minor fuels
account for 17.08 % of primary energy con-
sumption, and include nuclear energy (4.15 %),
hydroelectricity (6.45 ,%), and renewables
(6.48 %) (BP
2011
). On the other hand, while the
world oil consumption was about 86 million
≡
2
Biodiesel
Biodiesel is a monoalkyl ester; the basic chemi-
cal reaction required to produce biodiesel is the
transesterifi cation of lipids, either triglycerides or
oil, with alcohol (Fukuda et al.
2001
). The result
is a fatty acid alkyl-ester, which is the biodiesel
material used in engines (e.g. fatty-acid methyl-
ester [FAME]); this reaction is performed at high
pH. The alcohols used include methanol and, to a
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