pathways in dark conditions, redirecting photosynthesis to produce hydrogen, acids,
and alcohols (such as ethanol). The third way is via “photofermentation,” which is
impracticable in nature. The last route requires the use of genetic engineering to
redirect the preexisting biochemical pathways of microalgae for a more subjective
and efficient production of bioethanol.
Photosynthesis is a vital process that drives the synthesis of all biofuels, by
converting light energy into biomass, carbon storage products (carbohydrates and
lipids), and a small amount of H 2 . In green algae, the light-harvesting complex
(LHC) (chlorophylls and carotenoids) absorbs photons from sunlight as chemical
energy. This energy is used by the photosystem II (PS II) for the catalytic oxidation
of water to form protons, electrons, and molecular oxygen. Low-potential electrons
are transferred to the electron transport chain for the reduction of ferredoxin and
then the formation of nicotinamide adenine dinucleotide phosphate (NADPH). An
electrochemical gradient is formed, and the release occurs after oxidation of water
in the thylakoid lumen, which is used to produce adenosine triphosphate (ATP) by
ATP synthase. Photosynthetic products (NADPH and ATP) are substrates for the
Calvin–Benson cycle, where CO 2 is fixed as C3 molecules that are assimilated to
form sugars, lipids, and other biomolecules essential for cell growth.
Biofuels from microalgae have been the subject of intense research mainly
focused on the production of biodiesel and biogas, although bioethanol and biohydrogen are also considered. The production pathways and operating conditions
vary for each biofuel. Studies have already demonstrated the potential viability of
Fig. 1 Routes of bioethanol production from microalgae (adapted from de Farias Silva and
Bertucco 2016)
11 Biofuels from Microalgae: Bioethanol
233
and alcohols (such as ethanol). The third way is via “photofermentation,” which is
impracticable in nature. The last route requires the use of genetic engineering to
redirect the preexisting biochemical pathways of microalgae for a more subjective
and efficient production of bioethanol.
Photosynthesis is a vital process that drives the synthesis of all biofuels, by
converting light energy into biomass, carbon storage products (carbohydrates and
lipids), and a small amount of H 2 . In green algae, the light-harvesting complex
(LHC) (chlorophylls and carotenoids) absorbs photons from sunlight as chemical
energy. This energy is used by the photosystem II (PS II) for the catalytic oxidation
of water to form protons, electrons, and molecular oxygen. Low-potential electrons
are transferred to the electron transport chain for the reduction of ferredoxin and
then the formation of nicotinamide adenine dinucleotide phosphate (NADPH). An
electrochemical gradient is formed, and the release occurs after oxidation of water
in the thylakoid lumen, which is used to produce adenosine triphosphate (ATP) by
ATP synthase. Photosynthetic products (NADPH and ATP) are substrates for the
Calvin–Benson cycle, where CO 2 is fixed as C3 molecules that are assimilated to
form sugars, lipids, and other biomolecules essential for cell growth.
Biofuels from microalgae have been the subject of intense research mainly
focused on the production of biodiesel and biogas, although bioethanol and biohydrogen are also considered. The production pathways and operating conditions
vary for each biofuel. Studies have already demonstrated the potential viability of
Fig. 1 Routes of bioethanol production from microalgae (adapted from de Farias Silva and
Bertucco 2016)
11 Biofuels from Microalgae: Bioethanol
233