recovery of Chlorella sorokiniana finding that phases could be recycled at least five
times.
On the other hand, high-value pigments are commonly extracted using solvents
or supercritical fluids. Enhancement of pigment extraction has also been investigated through combination of solvent extraction with other methods, such as
ultrasound or microwaves (Halim et al. 2010; Pasquet et al. 2011).
Lastly, classical solvent extraction can be used for carbohydrate recovery but
improvements in recovery have been reported using fluidized bed extraction or
ultrasonic-assisted extraction. However, this enhancement was associated with
higher operating costs (Zhao et al. 2013). Wu et al. (2017) proposed a high-speed
counter current chromatography (HSCCC) combined with ATPS extraction to
recover high-purity polysaccharides in a single-step extraction process.
Carbohydrates from microalgae have aroused recent interest in the biorefinery
process (IEA 2017; Templeton et al. 2012).
Emergent technologies for protein recovery include the liquid biphasic flotation
based on the combination of ATPS and solvent sublation. This technique allows the
integration of concentration, separation, and extraction into one step, along with a
higher concentration coefficient (Phong et al. 2017a, b).
3.1.4 Fractionation
Fractionation could be required in purification train after extraction and depending
on the application of microalgae products. It focuses on the primary recovery and
partial purification of products with no loss in products and functionality. The goals
of fractionating microalgae biomass are either to separate lipids, proteins, and
carbohydrates for further valorization of each fraction or to obtain a specific
compound. Hence, the microalgal extracts from either hydrophobic and hydrophilic
phase can be separated using common techniques based on density differences and
further selective techniques (see Table 4), such as ionic exchange chromatography,
charged membranes or protein precipitation (Schwenzfeier et al. 2011, 2014) allow
isolation of proteins from a common hydrophilic phase where carbohydrates are
also present. On the other hand, complex high-cost downstream processing is used
when isolation of a specific compound, such as PUFAs, from lipid fraction
(Dibenedetto et al. 2016) or high-grade protein is required (Halim et al. 2016).
Therefore, developments in fractionation are still limited for high-value products
due to its high cost and feasibility is only attainable in domains, such as food,
health, and cosmetics. Indeed, this is an incipient area that needs development but
thanks to biopharmaceutical field, mild extraction techniques are being adopted for
microalgae specialty products.
Membrane technologies are commonly used for biomass harvesting (Drexler and
Yeh 2014). They provide a thin barrier to restrict the interactions between the
solvent and solute depending on their properties and membrane characteristics;
however, finest filtration methods, such as microfiltration (MF), ultrafiltration (UF),
nanofiltration (NF), and reverse osmosis (RO), allow selective product separation.
5 Microalgae Biorefineries for Energy …
107
times.
On the other hand, high-value pigments are commonly extracted using solvents
or supercritical fluids. Enhancement of pigment extraction has also been investigated through combination of solvent extraction with other methods, such as
ultrasound or microwaves (Halim et al. 2010; Pasquet et al. 2011).
Lastly, classical solvent extraction can be used for carbohydrate recovery but
improvements in recovery have been reported using fluidized bed extraction or
ultrasonic-assisted extraction. However, this enhancement was associated with
higher operating costs (Zhao et al. 2013). Wu et al. (2017) proposed a high-speed
counter current chromatography (HSCCC) combined with ATPS extraction to
recover high-purity polysaccharides in a single-step extraction process.
Carbohydrates from microalgae have aroused recent interest in the biorefinery
process (IEA 2017; Templeton et al. 2012).
Emergent technologies for protein recovery include the liquid biphasic flotation
based on the combination of ATPS and solvent sublation. This technique allows the
integration of concentration, separation, and extraction into one step, along with a
higher concentration coefficient (Phong et al. 2017a, b).
3.1.4 Fractionation
Fractionation could be required in purification train after extraction and depending
on the application of microalgae products. It focuses on the primary recovery and
partial purification of products with no loss in products and functionality. The goals
of fractionating microalgae biomass are either to separate lipids, proteins, and
carbohydrates for further valorization of each fraction or to obtain a specific
compound. Hence, the microalgal extracts from either hydrophobic and hydrophilic
phase can be separated using common techniques based on density differences and
further selective techniques (see Table 4), such as ionic exchange chromatography,
charged membranes or protein precipitation (Schwenzfeier et al. 2011, 2014) allow
isolation of proteins from a common hydrophilic phase where carbohydrates are
also present. On the other hand, complex high-cost downstream processing is used
when isolation of a specific compound, such as PUFAs, from lipid fraction
(Dibenedetto et al. 2016) or high-grade protein is required (Halim et al. 2016).
Therefore, developments in fractionation are still limited for high-value products
due to its high cost and feasibility is only attainable in domains, such as food,
health, and cosmetics. Indeed, this is an incipient area that needs development but
thanks to biopharmaceutical field, mild extraction techniques are being adopted for
microalgae specialty products.
Membrane technologies are commonly used for biomass harvesting (Drexler and
Yeh 2014). They provide a thin barrier to restrict the interactions between the
solvent and solute depending on their properties and membrane characteristics;
however, finest filtration methods, such as microfiltration (MF), ultrafiltration (UF),
nanofiltration (NF), and reverse osmosis (RO), allow selective product separation.
5 Microalgae Biorefineries for Energy …
107