Microalgae as an Attractive Source for Biofuel Production - Environmental Sustainability: Role of Green Technologies - page 125

lesser extent, ethanol; the main by-product is
glycerol. This chemical reaction is sensitive to
water. The quality and productivity of biodiesel is
affected by the presence of water, because sapon-
ifi cation reactions occur (soap formation) when
water combines with the lipid. Excess unsatu-
rated fatty acid levels are a major problem in
biodiesel production because they may induce
cross-linking of fatty acid chains, causing the
formation of tar.
Poly-unsaturated fatty acids (PUFAs) are a
potential co-product of biodiesel from microal-
gae. PUFAs from microalgae are a vegetable

origin alternative to fi sh oils and other oils rich in
omega-3 fatty acids. In the biodiesel process,
PUFAs would be extracted prior to esterifi cation,
as these fatty acids are not the most suitable raw
material for esterifi cation. As far as biodiesel
esterifi cation is concerned, the main by-product
is glycerol. Glycerol is a versatile chemical, with
over 1,500 known commercial applications,
though this market has become somewhat satu-
rated due to strong growth in worldwide biodiesel
production. Glycerol could be used for mixed
fermentation together with sugar and protein res-
idues from the lipid extraction step.

CH 2 -OCOR 1 CH 2 -OH R 1 -COOCH 3

CH-OCOR 2 + 3HOCH 3 Catalyst CH-OH + R 2 -COOCH 3

CH 2 -OCOR 3 CH 2 -OH R 3 -COOCH 3

Triglyceride Methanol Glycerol Methyl esters

(Parent oil) (Alcohol) (Biodiesel)

2.1 Advantages of Biodiesel

does not contain aromatic compounds and other
chemical substances that are harmful to the envi-
ronment. Recent research (Sharp 1996 ) has indi-
cated that 90 % of atmospheric pollution and
95 % of cancers can be decreased with the use of
biodiesel.
Biodiesel appears to have signifi cant eco-
nomic potential; the price of fossil fuels will
undoubtedly increase in the future because of
their non-renewable nature (Cadenas and
Cabezudo 1998 ). Finally, the fl ash point and bio-
degradability of biodiesel is better than diesel
fuel (Ma and Hanna 1999 ).

For several reasons, biodiesel fuel seems to be an
alternative energy resource. The advantages of
using biodiesel fuels are as follows.
Biodiesel has higher lubricity than petroleum
diesel and is a renewable energy resource that
could be sustainably supplied. It is understood
that the petroleum reserves are to be depleted in
less than 50 years at the present rate of consump-
tion (Sheehan et al. 1998 ).
Biodiesel appears to have several favorable
environmental properties: a low release of CO 2
and very low sulfur content (Antolin et al. 2002 ;
Vicente et al. 2004 ). The release of sulfur and
carbon monoxide would be reduced by 30 and
10 %, respectively, with the use of biodiesel.
Additionally, the use of biodiesel as an energy
source can reduce the level of gas that is gener-
ated during combustion, and the relatively high
oxygen content of biodiesel can decrease the
level of carbon monoxide. Moreover, biodiesel

2.2 Sources of Biodiesel

Production

The current sources of commercial biodiesel
include soybean oil, palm oil, animal fat, and
waste cooking oil. These sources can be classi-
fi ed into three generations.