Recovery of microalgal biomass and metabolites: process options and economics

https://doi.org/10.1016/S0734-9750(02)00050-2Get rights and content

Abstract

Commercial production of intracellular microalgal metabolites requires the following: (1) large-scale monoseptic production of the appropriate microalgal biomass; (2) recovery of the biomass from a relatively dilute broth; (3) extraction of the metabolite from the biomass; and (4) purification of the crude extract. This review examines the options available for recovery of the biomass and the intracellular metabolites from the biomass. Economics of monoseptic production of microalgae in photobioreactors and the downstream recovery of metabolites are discussed using eicosapentaenoic acid (EPA) recovery as a representative case study.

Introduction

Microalgae can be used to produce numerous high-value bioactives Borowitzka, 1986, Bubrick, 1991, Pulz et al., 2001, Li et al., 2001, Banerjee et al., 2002. Production of microalgae-derived metabolites requires processes for culturing the alga Ben-Amotz and Avron, 1987, Molina Grima, 1999, Molina Grima et al., 1999, Sánchez Mirón et al., 1999, Tredici, 1999, Borowitzka, 1999, Pulz, 2001, Pulz et al., 2001, recovery of the biomass, and further downstream processing to purify the metabolite from the biomass. As with many microbial processes for producing bioactives, the downstream recovery of algal products can be substantially more expensive than the culturing of the alga. This review examines some commercially relevant options for recovering microalgal products. A case study is used to illustrate the economics of recovery of eicosapentaenoic acid (EPA), an essential fatty acid from microalgae. EPA is an established neutraceutical and evidence is emerging for its therapeutic benefits in disease management Peet et al., 2001, Peet et al., 2002.

Section snippets

Production of microalgal biomass

Production of microalgal biomass can be carried out in fully contained photobioreactors or in open ponds and channels. Open-culture systems are almost always located outdoors and rely on natural light for illumination (Terry and Raymond, 1985). Closed photobioreactors may be located indoors or outdoors Sánchez Mirón et al., 1999, Pulz, 2001, but outdoor location is more common because it can make use of free sunlight. Design and operation of the microalgal biomass production systems have been

Recovery of biomass

Harvesting of biomass requires one or more solid–liquid separation steps. Biomass can be harvested by centrifugation, filtration or in some cases, gravity sedimentation. These processes may be preceded by a flocculation step. Recovery of biomass can be a significant problem because of the small size (3–30 μm diameter) of the algal cells. Culture broths are generally relatively dilute (<0.5 kg m−3 dry biomass in some commercial production systems) and hence large volumes need to be handled to

Dehydration of biomass

Harvesting generally results in a 50- to 200-fold concentration of algal biomass. The harvested biomass slurry (5–15% dry solids) must be processed rapidly, or it can spoil within a few hours in a hot climate. The specific postharvest processing necessary depends strongly on the desired product. Dehydration or drying of the biomass is commonly used to extend the shelf-life of the biomass especially if biomass is the final product. Drying methods that have been used for microalgae include spray

Process economics: a case study of EPA production

Here, we discuss the economics of producing EPA from the marine microalga P. tricornutum, as a representative case study for producing high-value intracellular products from microalgae. The case study is useful in identifying potential bottlenecks to commercializing microalgae-derived products.

Conclusion

Several options exist for recovering and processing microalgal biomass to obtain intracellular metabolites produced by microalgae. For commercial recovery of high-value products, centrifugation appears to be the preferred method of recovering the biomass from the broth. Centrifugation may be preceded by a flocculation step to improve recovery. When centrifugal recovery is not feasible, for example when the alga being recovered is fragile, microfiltration can be a suitable alternative. To the

References (82)

  • H.B. Li et al.

    Preparative isolation and purification of lutein from the microalga Chlorella vulgaris by high-speed counter-current chromatography

    J. Chromatogr. A

    (2001)
  • G.B. Lim et al.

    Separation of astaxanthin from red yeast Phaffia rhodozyma by supercritical carbon dioxide extraction

    Biochem. Eng. J.

    (2002)
  • L.M. Lubian

    Concentrating cultured marine microalgae with chitosan

    Aquacult. Eng.

    (1989)
  • M.A. McCausland et al.

    Evaluation of live microalgae and microbial pastes as supplementary food for juvenile Pacific oyster (Crassostrea gigas)

    Aquaculture

    (1999)
  • J. Morales et al.

    Harvesting marine microalgae species by chitosan flocculation

    Aquaculture Eng.

    (1985)
  • M. Peet et al.

    Two double-blind placebo-controlled pilot studies of eicosapentaenoic acid in the treatment of schizophrenia

    Schizophr. Res.

    (2001)
  • M. Peet et al.

    A dose-ranging exploratory study of the effects of ethyl-eicosapentaenoate in patients with persistent schizophrenic symptoms

    J. Psychiatr. Res.

    (2002)
  • B. Petrusevski et al.

    Tangential flow filtration: a method to concentrate freshwater algae

    Water Res.

    (1995)
  • B. Pushparaj et al.

    Microbial biomass recovery using a synthetic cationic polymer

    Bioresour. Technol.

    (1993)
  • N. Rossignol et al.

    Membrane technology for the continuous separation microalgae/culture medium: compared performances of cross-flow microfiltration and ultrafiltration

    Aquacult. Eng.

    (1999)
  • A. Sánchez Mirón et al.

    Comparative evaluation of compact photobioreactors for large-scale monoculture of microalgae

    J. Biotechnol.

    (1999)
  • H.H. Suh et al.

    Characterization of bioflocculant produced by Bacillus sp. DP-152

    J. Ferment. Bioeng.

    (1997)
  • K.L. Terry et al.

    System design for the autotrophic production of microalgae

    Enzyme Microb. Technol.

    (1985)
  • R.C. Tilton et al.

    The flocculation of algae with synthetic polymeric flocculants

    Water Res.

    (1972)
  • F.G. Acién Fernández et al.

    Modelling of biomass productivity in tubular photobioreactors for microalgal cultures: effects of dilution rate, tube diameter and solar irradiance

    Biotechnol. Bioeng.

    (1998)
  • A. Banerjee et al.

    Botryococcus braunii: a renewable source of hydrocarbons and other chemicals

    Crit. Rev. Biotechnol.

    (2002)
  • H. Belarbi et al.

    A process for high and scaleable recovery of high purity eicosapentaenoic acid esters from microalgae and fish oil

    Enzyme Microb. Technol.

    (2000)
  • P.A. Belter et al.

    Bioseparations: Downstream Processing for Biotechnology

    (1988)
  • A. Ben-Amotz et al.

    The biotechnology of mass culturing of Dunaliella for products of commercial interest

  • J.R. Benemann et al.

    Development of microalgae harvesting and high rate pond technologies in California

  • R. Bermejo Román et al.

    Chromatographic purification and characterization of b-phycoerythrin from Porphyridium cruentum. Semipreparative HPLC separation and characterization of its subunits

    J. Chromatogr. A

    (2001)
  • A. Blanchemain et al.

    Increased production of eicosapentaenoic acid by Skeletonema costatum cells after decantation at low temperature

    Biotechnol. Tech.

    (1999)
  • M.A. Borowitzka

    Microalgae as sources of fine chemicals

    Microbiol. Sci.

    (1986)
  • M.A. Borowitzka

    Closed algal photobioreactors: design considerations for large-scale systems

    J. Mar. Biotechnol.

    (1996)
  • M.A. Borowitzka

    Microalgae for aquaculture: opportunities and constraints

    J. Appl. Phycol.

    (1997)
  • R.J.P. Cannell

    Algal biotechnology

    Appl. Biochem. Biotechnol.

    (1990)
  • M. Cartens et al.

    Eicosapentaenoic acid (20:4n-3) from the marine microalga Phaeodactylum tricornutum

    J. Am. Oil Chem. Soc.

    (1996)
  • Y. Chisti

    Strategies in downstream processing

  • Y. Chisti

    Shear sensitivity

  • Y. Chisti et al.

    Fermentation technology, bioprocessing, scale-up and manufacture

  • J.M. Cohen et al.

    Natural and synthetic polyelectrolytes as coagulants and coagulant aids

    Bull. U. S. Dept. Health, Educ. Welf.

    (1957)
  • Cited by (1804)

    View all citing articles on Scopus
    View full text