aimed to focus on enhancing the production and minimizing the production cost of
biofuels.
2.2.3 Third-Generation Biofuel
Third-generation biofuel produced from photosynthetic microalgae can be considered as one of the most sustainable, environment-friendly, economically feasible
fuels. Various types of third-generation biofuels like methane (Gavrilescu and Chisti
2005), biodiesel, and biohydrogen (Kapdan and Kargi 2006) can be produced from
microalgae. Microalgal fuel production does not require arable agricultural land and
is photosynthetic which can fix CO 2 of the atmosphere and CO 2 released from
industrial sources and from soluble carbonates, thus reducing greenhouse gas emissions and promoting a way leading to carbon neutrality that’s why they are being
considered superior than first- and second-generation biofuel (Into et al. 2020).
Microalgae are more diverse than plants. It consists of more than 3 lakh species
which may be found in fresh water and marine habitat (Alam et al. 2015).
Microalgae are single-celled microorganisms that grow well in aqueous suspension
culture that provides easy access to water, carbon dioxide, and other organic or
inorganic nutrients for their growth (Dragone et al. 2010; Anemaet et al. 2010). They
are an ideal candidate for fuel production because they may contain lipid contents in
the cell up to 85% of dry cell mass and they grow very rapidly in the presence of
proper nutrient and double within 24 h (Angermayr et al. 2009). Selection of useful
microalgal strain and their cultivation, biomass harvesting, and biomass oil extraction are quite tedious which require expertise and a huge amount of money. Hence, it
is not yet sustainable for biofuel production (Grima et al. 2003). All microalgal
species can produce triacylglycerols by imposing stressed conditions.
Nannochloropsis and Chlorella microalgae give a high yield of triacylglycerols for
biofuel production (Kleinova et al. 2012). Nitrogen-deprived condition is one of the
most potent stressed conditions for substantial oil accumulation. TAGS are formed
by combining three different fatty acids, and hydroxyl groups of glycerol play an
important role in the arrangement of TAGS. The oils can be converted to biofuels by
simple transesterification process. Microalgal fuel production can only be increased
by combining advanced methods of lipid metabolic process with biotechnological
tools (Chisti 2007).
2.2.4 Fourth-Generation Biofuels
This category of biofuel applies the concept of “cell factory” which harnesses the
solar energy to convert CO 2 into potential biofuel (Patnayat and Sree 2006). Fourthgeneration biofuels can be produced by (1) photosynthetic microorganisms, (2) combining photovoltaics with microbial fuel cells, or (3) synthetic cell components
34
V. Singh et al.
biofuels.
2.2.3 Third-Generation Biofuel
Third-generation biofuel produced from photosynthetic microalgae can be considered as one of the most sustainable, environment-friendly, economically feasible
fuels. Various types of third-generation biofuels like methane (Gavrilescu and Chisti
2005), biodiesel, and biohydrogen (Kapdan and Kargi 2006) can be produced from
microalgae. Microalgal fuel production does not require arable agricultural land and
is photosynthetic which can fix CO 2 of the atmosphere and CO 2 released from
industrial sources and from soluble carbonates, thus reducing greenhouse gas emissions and promoting a way leading to carbon neutrality that’s why they are being
considered superior than first- and second-generation biofuel (Into et al. 2020).
Microalgae are more diverse than plants. It consists of more than 3 lakh species
which may be found in fresh water and marine habitat (Alam et al. 2015).
Microalgae are single-celled microorganisms that grow well in aqueous suspension
culture that provides easy access to water, carbon dioxide, and other organic or
inorganic nutrients for their growth (Dragone et al. 2010; Anemaet et al. 2010). They
are an ideal candidate for fuel production because they may contain lipid contents in
the cell up to 85% of dry cell mass and they grow very rapidly in the presence of
proper nutrient and double within 24 h (Angermayr et al. 2009). Selection of useful
microalgal strain and their cultivation, biomass harvesting, and biomass oil extraction are quite tedious which require expertise and a huge amount of money. Hence, it
is not yet sustainable for biofuel production (Grima et al. 2003). All microalgal
species can produce triacylglycerols by imposing stressed conditions.
Nannochloropsis and Chlorella microalgae give a high yield of triacylglycerols for
biofuel production (Kleinova et al. 2012). Nitrogen-deprived condition is one of the
most potent stressed conditions for substantial oil accumulation. TAGS are formed
by combining three different fatty acids, and hydroxyl groups of glycerol play an
important role in the arrangement of TAGS. The oils can be converted to biofuels by
simple transesterification process. Microalgal fuel production can only be increased
by combining advanced methods of lipid metabolic process with biotechnological
tools (Chisti 2007).
2.2.4 Fourth-Generation Biofuels
This category of biofuel applies the concept of “cell factory” which harnesses the
solar energy to convert CO 2 into potential biofuel (Patnayat and Sree 2006). Fourthgeneration biofuels can be produced by (1) photosynthetic microorganisms, (2) combining photovoltaics with microbial fuel cells, or (3) synthetic cell components
34
V. Singh et al.