Microalgal Downstream Processing
Harvesting, Drying, Extraction,
Separation, and Purification
Xavier C. Fretté
Introduction
Microalgae are now well established as crops for mankind with farms and production units spread around
the world. These microalgae are produced with the aim to be sold as entire organisms (dry powder),
or for specific compounds of interest to be extracted for further commercialization. Most microalgal
compounds of interest fall into the following categories: lipids, carotenoids, polymers, and proteins
(among others phycobilliproteins). However, there is an increasing demand for other types of compounds,
for example, phenolic substances for their antioxidative properties (Goiris et al. 2012) as well as other
compounds for their anti-inflammatory, antimicrobial, antiviral, and antitumoral activities (Guedes et al.
2011). Several family-owned SMEs are producing and commercializing dried microalgae worldwide, for
example, Arthrospira platensis sold as granules and powder by more than 20 companies located around
the town of Hyeres in South Eastern France. However, currently the industrial production of microalgae
is mainly related to high-value compounds as the production costs are still very high. Such alga-biotech
companies are producing and commercializing astaxanthin (Cyanotech, Hawai; Mera Pharmaceuticals,
Hawai; Fuji Health Science, Japan), β-carotene (Betatene, Western Biotechnology and AquaCarotene, all
in Australia), and the ω-3 fatty acids EPA and DHA (Cellana Inc., Hawai). Within the last decade, there
has been a renewed interest in microalgal biodiesel and biofuel production. However, the production cost
of these products make them noncompetitive compared to fossil fuels and therefore it has been estimated
that the production costs of such microalgal low-value compounds should be reduced by at least an order
of magnitude, for them to be economically viable (Greenwell et al. 2010).
The major obstacle in processing microalgae is their size and the fact that they are grown in water,
which implies removal of the culture broth and, in the case of marine microalgae, desalting the harvested
culture. Most common methods used today are centrifugation, flocculation, flotation, filtration, and/or
a combination of these methods. Centrifugation is the most efficient method allowing recovery of over
6
Department of Chemical Engineering Biotechnology and Environmental Technology, Faculty of Engineering, University of
Southern Denmark, Campusvej 55, 5230 Odense M - Denmark.
Email: xafr@kbm.sdu.dk
Harvesting, Drying, Extraction,
Separation, and Purification
Xavier C. Fretté
Introduction
Microalgae are now well established as crops for mankind with farms and production units spread around
the world. These microalgae are produced with the aim to be sold as entire organisms (dry powder),
or for specific compounds of interest to be extracted for further commercialization. Most microalgal
compounds of interest fall into the following categories: lipids, carotenoids, polymers, and proteins
(among others phycobilliproteins). However, there is an increasing demand for other types of compounds,
for example, phenolic substances for their antioxidative properties (Goiris et al. 2012) as well as other
compounds for their anti-inflammatory, antimicrobial, antiviral, and antitumoral activities (Guedes et al.
2011). Several family-owned SMEs are producing and commercializing dried microalgae worldwide, for
example, Arthrospira platensis sold as granules and powder by more than 20 companies located around
the town of Hyeres in South Eastern France. However, currently the industrial production of microalgae
is mainly related to high-value compounds as the production costs are still very high. Such alga-biotech
companies are producing and commercializing astaxanthin (Cyanotech, Hawai; Mera Pharmaceuticals,
Hawai; Fuji Health Science, Japan), β-carotene (Betatene, Western Biotechnology and AquaCarotene, all
in Australia), and the ω-3 fatty acids EPA and DHA (Cellana Inc., Hawai). Within the last decade, there
has been a renewed interest in microalgal biodiesel and biofuel production. However, the production cost
of these products make them noncompetitive compared to fossil fuels and therefore it has been estimated
that the production costs of such microalgal low-value compounds should be reduced by at least an order
of magnitude, for them to be economically viable (Greenwell et al. 2010).
The major obstacle in processing microalgae is their size and the fact that they are grown in water,
which implies removal of the culture broth and, in the case of marine microalgae, desalting the harvested
culture. Most common methods used today are centrifugation, flocculation, flotation, filtration, and/or
a combination of these methods. Centrifugation is the most efficient method allowing recovery of over
6
Department of Chemical Engineering Biotechnology and Environmental Technology, Faculty of Engineering, University of
Southern Denmark, Campusvej 55, 5230 Odense M - Denmark.
Email: xafr@kbm.sdu.dk