(isobutanol, isopentanol, and others) from the protein fraction. However, it becomes
clear that the use of residual biomass alone to produce energy is not as favorable as
it looks at first glance.
4.2 Strategy II: Coproduction of High-Value-Added
Products and Biofuels
Microalgae are important producers of many high-value nutraceutical compounds,
such as polyunsaturated fatty acids or astaxanthin that can justify the high cost of
microalgae cultivation and processing technologies (Liang et al. 2015; Shah et al.
2016). Under this scenario, the fixed CO 2 is valorized and biofuels are produced
after extraction of high-value products. Some examples include astaxanthin produced by Haematococcus pluvialis, this high-value-added molecule is already
commercialized (Lorenz and Cysewski 2000), and its market price is 7000 USD/kg
(Hariskos and Posten 2014; Shah et al. 2016). This microalga is an excellent
candidate for this strategy because astaxanthin accounts for approximately 5% of
the total cell dry weight, representing only a small fraction of it. Astaxanthin is
produced under nitrogen limitation and simultaneously with triglycerides that
constitute up to 60% of dry weight (Solovchenko 2015) and can be utilized for
biodiesel. In this way, after astaxanthin extraction, biodiesel can be produced from
lipids and biogas from residual biomass (Shah et al. 2016). Another organism
suitable for the biorefinery of high-value-added compound is Nannochloropsis
(Chua and Schenk 2017) due to its rapid growth, high oil productivities, and
omega-3 fatty acid content, specifically the EPA whose market price is up to USD
100 per liter. Furthermore, in the biorefinery configuration, the high edible protein
content makes this alga feasible for food or feed. Other high-value molecules in
microalgae biomass are: vitamins, pigments, etc., and other examples of studies
exploring this strategy are shown in Table 5. As can be seen, pigment as high-value
compound coupled to production of biodiesel from lipid fraction or other biofuels
from the leftover biomass is the most commonly studied scenario.
One of the major challenges of this strategy is that despite the fact that the
projected demand for high-value products from microalgae is increasing, these
products are still produced in relatively small amounts; therefore, the biofuel supply
cannot be guaranteed.
4.3 Strategy III: Coproduction of Medium-Value-Added
Compounds and Biofuels
The approach of integration of medium-value products (carbohydrates, lipids,
and proteins) into biofuels production was proposed by Wijffels et al. (2010).
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P.-L. Gorry et al.
clear that the use of residual biomass alone to produce energy is not as favorable as
it looks at first glance.
4.2 Strategy II: Coproduction of High-Value-Added
Products and Biofuels
Microalgae are important producers of many high-value nutraceutical compounds,
such as polyunsaturated fatty acids or astaxanthin that can justify the high cost of
microalgae cultivation and processing technologies (Liang et al. 2015; Shah et al.
2016). Under this scenario, the fixed CO 2 is valorized and biofuels are produced
after extraction of high-value products. Some examples include astaxanthin produced by Haematococcus pluvialis, this high-value-added molecule is already
commercialized (Lorenz and Cysewski 2000), and its market price is 7000 USD/kg
(Hariskos and Posten 2014; Shah et al. 2016). This microalga is an excellent
candidate for this strategy because astaxanthin accounts for approximately 5% of
the total cell dry weight, representing only a small fraction of it. Astaxanthin is
produced under nitrogen limitation and simultaneously with triglycerides that
constitute up to 60% of dry weight (Solovchenko 2015) and can be utilized for
biodiesel. In this way, after astaxanthin extraction, biodiesel can be produced from
lipids and biogas from residual biomass (Shah et al. 2016). Another organism
suitable for the biorefinery of high-value-added compound is Nannochloropsis
(Chua and Schenk 2017) due to its rapid growth, high oil productivities, and
omega-3 fatty acid content, specifically the EPA whose market price is up to USD
100 per liter. Furthermore, in the biorefinery configuration, the high edible protein
content makes this alga feasible for food or feed. Other high-value molecules in
microalgae biomass are: vitamins, pigments, etc., and other examples of studies
exploring this strategy are shown in Table 5. As can be seen, pigment as high-value
compound coupled to production of biodiesel from lipid fraction or other biofuels
from the leftover biomass is the most commonly studied scenario.
One of the major challenges of this strategy is that despite the fact that the
projected demand for high-value products from microalgae is increasing, these
products are still produced in relatively small amounts; therefore, the biofuel supply
cannot be guaranteed.
4.3 Strategy III: Coproduction of Medium-Value-Added
Compounds and Biofuels
The approach of integration of medium-value products (carbohydrates, lipids,
and proteins) into biofuels production was proposed by Wijffels et al. (2010).
122
P.-L. Gorry et al.