They emphasized that a process for biodiesel from microalgae lipid production only
is unlikely to be economically viable and that all biomass bulk components should
be valorized in order to develop a feasible and sustainable process. This idea
promotes diversification of market sectors, introducing microalgae products not
only in the energy sector. According to Hariskos and Posten (2014), bulk chemicals
constitute a market volume of >10,000 tons/year with prices from only a few USD/
kg up to 100 USD/kg and represent 11% of crude oil destined to petrochemical
synthesis. As was seen before, the main components of microalgal biomass depend
on the strain and common contents are: lipids (30–50%), proteins (50–70%), carbohydrates (50%), and pigments (Chew et al. 2017). These biochemicals involve
the use of protein for feed or food; carbohydrates for bioactive materials, cosmetics,
nutritional, and pharmaceutical applications; and lipids, which depending on the
length chain, have application as surfactants, cosmetics, solvents, lubricants, or
biopolymers (Hariskos and Posten 2014; IEA 2017). Most of the studies focused
mainly on lipids for biodiesel and proteins for food or feed. But others include
bioethanol production (Table 5).
Under the coproduction strategies (II and III), the selection of mild and selective
separation techniques is important to keep the properties of the most biomass
components. Therefore, an adequate progression of harvesting followed by cell
disruption (Lee et al. 2012) and a further suitable mild and selective extraction and
purification sequence of metabolites of interest must be chosen.
Regarding the definition of the best order of extraction of metabolites, it depends
on the strain and properties of the products to be recovered. Ansari et al. (2017)
showed for Scenedesmus obliquus that the sequence of extraction: proteins–lipids–
carbohydrates was the most convenient. However a different strategy was proposed
by Dong et al. (2016), who suggested that a combined algal processing (CAP) is
much better than parallel algal processing (PAP). Instead of extracting lipids from
algal biomass prior to alcoholic fermentation as in PAP, lipids are extracted from
the anaerobic digestion cake. CAP turns out to be highly efficient for sugar conversion, and lipid loss is negligible. CAP reduces the biofuel cost of microalgae by
9%. However, it is important to mention that this study did not evaluate the cost of
bioproducts in a complete biorefinery scheme, using the whole biomass. Table 5
shows different studies using this strategy.
Under this strategy, the high efficiency of fractionation in a sequential process is
one of the principal bottlenecks and represents a challenge to overcome. The main
goal of this approach is to maximize biomass production and valorization in order
to prioritize the use of biomass to obtain products of value by giving more
importance to the production of materials, rather than its use for energy (Keegan
et al. 2013).
5 Microalgae Biorefineries for Energy …
123
is unlikely to be economically viable and that all biomass bulk components should
be valorized in order to develop a feasible and sustainable process. This idea
promotes diversification of market sectors, introducing microalgae products not
only in the energy sector. According to Hariskos and Posten (2014), bulk chemicals
constitute a market volume of >10,000 tons/year with prices from only a few USD/
kg up to 100 USD/kg and represent 11% of crude oil destined to petrochemical
synthesis. As was seen before, the main components of microalgal biomass depend
on the strain and common contents are: lipids (30–50%), proteins (50–70%), carbohydrates (50%), and pigments (Chew et al. 2017). These biochemicals involve
the use of protein for feed or food; carbohydrates for bioactive materials, cosmetics,
nutritional, and pharmaceutical applications; and lipids, which depending on the
length chain, have application as surfactants, cosmetics, solvents, lubricants, or
biopolymers (Hariskos and Posten 2014; IEA 2017). Most of the studies focused
mainly on lipids for biodiesel and proteins for food or feed. But others include
bioethanol production (Table 5).
Under the coproduction strategies (II and III), the selection of mild and selective
separation techniques is important to keep the properties of the most biomass
components. Therefore, an adequate progression of harvesting followed by cell
disruption (Lee et al. 2012) and a further suitable mild and selective extraction and
purification sequence of metabolites of interest must be chosen.
Regarding the definition of the best order of extraction of metabolites, it depends
on the strain and properties of the products to be recovered. Ansari et al. (2017)
showed for Scenedesmus obliquus that the sequence of extraction: proteins–lipids–
carbohydrates was the most convenient. However a different strategy was proposed
by Dong et al. (2016), who suggested that a combined algal processing (CAP) is
much better than parallel algal processing (PAP). Instead of extracting lipids from
algal biomass prior to alcoholic fermentation as in PAP, lipids are extracted from
the anaerobic digestion cake. CAP turns out to be highly efficient for sugar conversion, and lipid loss is negligible. CAP reduces the biofuel cost of microalgae by
9%. However, it is important to mention that this study did not evaluate the cost of
bioproducts in a complete biorefinery scheme, using the whole biomass. Table 5
shows different studies using this strategy.
Under this strategy, the high efficiency of fractionation in a sequential process is
one of the principal bottlenecks and represents a challenge to overcome. The main
goal of this approach is to maximize biomass production and valorization in order
to prioritize the use of biomass to obtain products of value by giving more
importance to the production of materials, rather than its use for energy (Keegan
et al. 2013).
5 Microalgae Biorefineries for Energy …
123