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produced from R. rubrum grown on CO 2 gas was a copolymer composed of
86% b-HB and 14% b-HV (Young et al., 2007).

6.6 MICROALGAE CULTIVATION TOWARDS BIODIESEL
PRODUCTION

Recently, microalgae have drawn considerable attention as an alternative
source of biomass that is capable of generating fuel from the sequestration of
carbon from both organic and inorganic sources by photosynthetic machin-
ery. Algae are rapidly growing species whose carbon-fixing rates are much
higher than those of terrestrial plants. It is estimated that algae yield is about
60,000 L per hectare compared to 300 100 L from soya and canola crops
(Brown et al., 2010). Microalgae commonly double their biomass within
24 h, and this time period during the exponential growth phase (GP) can
be as short as 3.5 h (Chisti, 2007; Harrison et al., 2012). The cultivation
of algae does not require arable land because algae can be grown in artificial
ponds, on land unsuitable for agriculture, surface of lakes, coastal waterways,
or in vats on wasteland (Duan and Savage, 2010). Algae-based biofuels have
become focal point in current research due to, carbon neutrality, renewabil-
ity, abundant availability, higher combustion efficiency, and higher biode-
gradability (Zhang et al., 2003). Algae-based fuels address the major
constraints of first- and second-generation biofuels i.e., food vs fuel and food
security issues. Microalgae can grow very fast and is capable of producing
several fold higher biomass compared to terrestrial crops and trees, requires
low and marginal land and produces higher lipid and carbohydrate yields
(Singh et al., 2011). Production of biofuels from microalgae is gaining accep-
tance because of its higher economic feasibility and environmental sustain-
ability compared to agro-based fuels. According to an estimate, the
productivity of algae-derived biofuels is predicted to be on the order of
5000 gal/acre/year, which is approximately two orders of magnitude greater
than the yield from terrestrial oil seed crops such as soybeans (Demirbas,
2008; Weyer et al., 2009). Algae-derived biodiesel is currently being pro-
moted as a third-generation biofuel feedstock as it does not compete with
food crops, it can be produced on non-arable land (Dragone et al., 2010;
Hu et al., 2008b), and its scalability has potential (Harrison et al., 2012).

6.6.1 Mode of Nutrition
Biosynthesis of triglycerides by utilizing CO 2 (by biofixation) or wastewater
under stress conditions by a photoautotrophic, heterotrophic (photo/dark),
or mixotrophic mechanism enumerates the potential of microalgae for