Synthesis of Biodiesel/Bio-Oil from Microalgae - Biotechnological Applications of Microalgae - page 109

compression ignition engines. However, it can also be utilized as fuel to run generator
sets, etc.
8.5 BIOFUEL/BIODIESEL FROM MICROALGAL OIL
AS A POTENTIAL ALTERNATIVE TO OTHER FUELS
As microalgae possess a simple cellular structure, their capability to efficiently
convert solar energy into chemical energy is high. The production of oil per unit
area of land from selected microalgae is around 30 times greater than that of ter-
restrial plants. The scenario thus looks promising for the production of biodiesel
from the microalgal oil. There are various steps involved—from the stage of cul-
tivation of microalgae to the final stage of production of bio-oil or biodiesel. The
intermediate steps include harvesting, dewatering, concentration, and extraction
of microalgal oil. The composition of fatty acids and other constituents present
in plant and animal oils varies considerably from microalgal oil. In addition to
triglycerides and free fatty acids, microalgal oil contains hydrocarbons, sterols,
wax and sterol esters, and free alcohols that cannot be saponified. The major
components in microalgae include carbohydrates, proteins, and lipids. In gen-
eral, the lipid content of microalgal biomass increases when they are deprived
of certain nutrients (nitrogen and silicon). However, the deprivation of nitrogen
and silicon does not necessarily favor all species viz. Euglena , Nannochloropsis
strains where cell division has been found to be blocked. There are certain species
(such as Escherichia coli and Saccharomyces cerevisiae ) that can be converted to
oleaginous species (microbes that can accumulate more than 20% of their cellular
dry weight in lipid) by genetic engineering. Although there are several species of
microalgae, only a few have been explored with respect to their potential for high
biomass yield and lipid content. The FAME content in the biodiesel should have
a minimum value of 96.5%, as per the recommendation of EN 14103 (Sarin et al.,
2009). However, biodiesel synthesized from only a few of the microalgal species
has fulfilled the minimum criteria of ester content in biodiesel as specified by the
EN. The reason for this may be attributed to the presence of unsaponifiable constit-
uents in the microalgae. Microalgal species not fulfilling the minimum specified
criteria of ester content limits their suitability for biodiesel production. However,
microalgal oil can be converted to bio-oil by pyrolysis or thermochemical catalytic
liquefaction. The bio-oil can be further upgraded by chemical or physical means.
While the chemical upgradation includes processes such as catalytic esterifica-
tion, catalytic hydroprocessing, and catalytic cracking, the physical upgradation
can be done by char removal, hot vapor filtration, liquid filtration, or solvent addi-
tion (Xiong et al., 2011). The present status for the production of biodiesel and
bio-oil from microalgae is cost intensive. However, the major advantage that the
microalgae provide is their growth in aquatic environments and their noncompeti-
tiveness with terrestrial plants. India and many other countries have a vast coastal
area where microalgae can be grown, cultured, and harvested. The other important
benefit of microalgae is the suitability of some of the species in wastewater. Thus,
microalgae cultured with wastewater will have the dual benefit: of the production
of oil and the treatment/disposal of wastewater. Numerous strains of microalgae