2.1 Biodiesel
“How do scientists make biodiesel from microalgae?” The answer lies in the ability
of microalgae to synthesize huge amounts of free fatty acids and accumulate them
in storage form of lipids, i.e., triglycerides (TAGs), in their cells. These lipids are
then used as feedstocks for biodiesel production. The lipid bodies are extracted and
the TAGs would be converted to the corresponding methyl/ethyl esters through a
reaction called transesterification. The term “biodiesel” has been considerably more
frequently cited in patent databases than bioalcohol or hydrogen (de la Jara et al.
2016). Further details on converting algal oil to biodiesel, from extraction to catalytic conversion, have been provided in the following patents: US7977076B2,
US4341038, US8475543B2, US20110136189, and US20160053191A1.
2.2 Bioalcohols
Some microalgae contain carbohydrates (generally not cellulose) that can be used as
feedstock for alcoholic fermentation. It should be highlighted that bioalcohols
production process from microalgae is very simplified owing to the fact that
microalgae cells do not require lignin and hemicelluloses for their structural support
and therefore, no chemical and enzymatic pretreatment step would be required to
extract sugars. Nevertheless, a simple and economically justified physical pretreatment process such as extrusion and mechanical shear is still required to break
down the cell wall to release the fermentable sugars for subsequent conversion into
bioalcohols such as bioethanol (John et al. 2011). In spite of all the aforementioned
favorable features, fermentative fuels produced from algae are still faced by some
challenges such as low fermentable carbohydrate content of algae biomass compared with other starchy crops such as maize. Some nutritional limitations such as
nitrogen starvation and genetic manipulation have been considered in the published
patents as promising solutions to overcome this shortcoming. Suitable starting
materials, methods of fermentation, involved strains and enzymes as well as general
processes and systems to produce and isolate alcohols from microalgal feedstock
have been the subject of numerous patents such as US patent applications
5578472A, 7135308B1, 7507554, and 9260730.
2.3 Biohydrogen
Hydrogen is promoted by many because of possessing the potential to be a clean
sustainable energy carrier. Photoautotrophic H 2 producing green algae, including
Chlamydomonas reinhardtii, has been shown to metabolize H 2 under anoxic
conditions. In the photosynthetic system, H 2 can be produced through
294
A. F. Talebi et al.
“How do scientists make biodiesel from microalgae?” The answer lies in the ability
of microalgae to synthesize huge amounts of free fatty acids and accumulate them
in storage form of lipids, i.e., triglycerides (TAGs), in their cells. These lipids are
then used as feedstocks for biodiesel production. The lipid bodies are extracted and
the TAGs would be converted to the corresponding methyl/ethyl esters through a
reaction called transesterification. The term “biodiesel” has been considerably more
frequently cited in patent databases than bioalcohol or hydrogen (de la Jara et al.
2016). Further details on converting algal oil to biodiesel, from extraction to catalytic conversion, have been provided in the following patents: US7977076B2,
US4341038, US8475543B2, US20110136189, and US20160053191A1.
2.2 Bioalcohols
Some microalgae contain carbohydrates (generally not cellulose) that can be used as
feedstock for alcoholic fermentation. It should be highlighted that bioalcohols
production process from microalgae is very simplified owing to the fact that
microalgae cells do not require lignin and hemicelluloses for their structural support
and therefore, no chemical and enzymatic pretreatment step would be required to
extract sugars. Nevertheless, a simple and economically justified physical pretreatment process such as extrusion and mechanical shear is still required to break
down the cell wall to release the fermentable sugars for subsequent conversion into
bioalcohols such as bioethanol (John et al. 2011). In spite of all the aforementioned
favorable features, fermentative fuels produced from algae are still faced by some
challenges such as low fermentable carbohydrate content of algae biomass compared with other starchy crops such as maize. Some nutritional limitations such as
nitrogen starvation and genetic manipulation have been considered in the published
patents as promising solutions to overcome this shortcoming. Suitable starting
materials, methods of fermentation, involved strains and enzymes as well as general
processes and systems to produce and isolate alcohols from microalgal feedstock
have been the subject of numerous patents such as US patent applications
5578472A, 7135308B1, 7507554, and 9260730.
2.3 Biohydrogen
Hydrogen is promoted by many because of possessing the potential to be a clean
sustainable energy carrier. Photoautotrophic H 2 producing green algae, including
Chlamydomonas reinhardtii, has been shown to metabolize H 2 under anoxic
conditions. In the photosynthetic system, H 2 can be produced through
294
A. F. Talebi et al.