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J. Querellou et al.
and is predicted to reach the sum of over a billion USD. Microalgae show some
advantages compared to terrestrial plants: unicellular algae can under favourable
conditions achieve photosynthesis rates greatly exceeding that of higher plants.
Marine microalgae offer two other main advantages: their exploitation does not
need to be in conflict with fresh water or food supply. Compared to higher plants,
the culture in controlled ponds or photobioreactors allows a fine regulation of the
metabolism by adjusting on line the level of entering nutrients. In addition, culture
of these photosynthetic organisms requires the supply of CO 2 and nutrients such
as nitrogen and phosphorous which further explains the rising number of programs
dealing with gas abatement and wastewater management. It is important to distinguish the production in controlled photobioreactors with illuminations or natural
light, which allows for very high productivities with high costs from productions
in natural environment in open ponds for which costs are lower. Indeed, extensive cultivation in outdoor ponds offers the best competitiveness with the major
drawback that these cultures are more “natural” and thus more difficult to control.
With the exception of cultures in extreme media such as high salt or high pH, the
pollution with local endemic species is very likely to occur as well as the contamination with various grazers. However, where the usual terrestrial crops yield around
a gram per square meters per day, the average yield for microalgae lies between
10 and 30 g/m 2 /day. Algal cultivations have thus the potential to produce substantial amounts of biofuels, without competing with the food production industry in
terms of use of arable land and fresh water. There are, however, several technological challenges that need to be overcome in order to produce algal biofuels at
competitive prices (Cadoret and Bernard 2008).
The four main suggested alternatives for biofuel production from algae are: production of biodiesel, hydrogen and ethanol as well as biomass for fermentation
(Chisti 2007).
8.4.4 Algae for Biodiesel Production
Some algae and especially microalgae stock lipids as energy reserve. Among 3,000
contenders studied by the National Renewable Energy laboratory, NREL (Sheehan
et al. 1998), candidates were identified with an oil content of up to 75% of dry
weight (Schenk et al. 2008). The normal yields are usually around 40% for most
of the best candidates (Rodolfi et al. 2009). To produce biodiesel algae are grown
under conditions that induce lipid production; the algae are harvested; the lipids are
extracted and converted to a useful fuel. It has been calculated that the production
of more than 100 m 3 biodiesel per hectare per year is theoretical feasible and 10–50
m 3 /ha/year, beyond the 6 m 3 /ha/year of the oil palm (Chisti 2007). To achieve high
biodiesel production, it will be necessary to improve our knowledge of the biochemistry of lipid synthesis in different algae as well as increasing our understanding of
the physiology of lipid metabolism. The diatom Phaeodactylum tricornutum can
contain up to 31% of dry weight as lipids (Sheehan et al. 1998) and its genome has
J. Querellou et al.
and is predicted to reach the sum of over a billion USD. Microalgae show some
advantages compared to terrestrial plants: unicellular algae can under favourable
conditions achieve photosynthesis rates greatly exceeding that of higher plants.
Marine microalgae offer two other main advantages: their exploitation does not
need to be in conflict with fresh water or food supply. Compared to higher plants,
the culture in controlled ponds or photobioreactors allows a fine regulation of the
metabolism by adjusting on line the level of entering nutrients. In addition, culture
of these photosynthetic organisms requires the supply of CO 2 and nutrients such
as nitrogen and phosphorous which further explains the rising number of programs
dealing with gas abatement and wastewater management. It is important to distinguish the production in controlled photobioreactors with illuminations or natural
light, which allows for very high productivities with high costs from productions
in natural environment in open ponds for which costs are lower. Indeed, extensive cultivation in outdoor ponds offers the best competitiveness with the major
drawback that these cultures are more “natural” and thus more difficult to control.
With the exception of cultures in extreme media such as high salt or high pH, the
pollution with local endemic species is very likely to occur as well as the contamination with various grazers. However, where the usual terrestrial crops yield around
a gram per square meters per day, the average yield for microalgae lies between
10 and 30 g/m 2 /day. Algal cultivations have thus the potential to produce substantial amounts of biofuels, without competing with the food production industry in
terms of use of arable land and fresh water. There are, however, several technological challenges that need to be overcome in order to produce algal biofuels at
competitive prices (Cadoret and Bernard 2008).
The four main suggested alternatives for biofuel production from algae are: production of biodiesel, hydrogen and ethanol as well as biomass for fermentation
(Chisti 2007).
8.4.4 Algae for Biodiesel Production
Some algae and especially microalgae stock lipids as energy reserve. Among 3,000
contenders studied by the National Renewable Energy laboratory, NREL (Sheehan
et al. 1998), candidates were identified with an oil content of up to 75% of dry
weight (Schenk et al. 2008). The normal yields are usually around 40% for most
of the best candidates (Rodolfi et al. 2009). To produce biodiesel algae are grown
under conditions that induce lipid production; the algae are harvested; the lipids are
extracted and converted to a useful fuel. It has been calculated that the production
of more than 100 m 3 biodiesel per hectare per year is theoretical feasible and 10–50
m 3 /ha/year, beyond the 6 m 3 /ha/year of the oil palm (Chisti 2007). To achieve high
biodiesel production, it will be necessary to improve our knowledge of the biochemistry of lipid synthesis in different algae as well as increasing our understanding of
the physiology of lipid metabolism. The diatom Phaeodactylum tricornutum can
contain up to 31% of dry weight as lipids (Sheehan et al. 1998) and its genome has