Microalgal Photobioreactors Scaleup and Optimisation Barbosa Thesis

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microalgae photobioreactors

Text of Microalgal Photobioreactors Scaleup and Optimisation Barbosa Thesis

  • Microalgal photobioreactors:Microalgal photobioreactors:Microalgal photobioreactors:Microalgal photobioreactors:

    ScaleScaleScaleScale----up and optimisationup and optimisationup and optimisationup and optimisation

  • PromotorPromotorPromotorPromotor

    Prof. Dr. Ir. J. Tramper

    Hoogleraar in de Bioprocestechnologie, Wageningen Universiteit

    CoCoCoCo----promotorpromotorpromotorpromotor

    Dr. Ir. R. H. Wijffels

    Universitair hoofddocent sectie Proceskunde, Wageningen Universiteit

    Samenstelling promotiecommissieSamenstelling promotiecommissieSamenstelling promotiecommissieSamenstelling promotiecommissie

    Prof. Dr. A. Richmond (Ben-Gurion University of the Negev, Israel)

    Prof. Dr. M. Tredici (Universit degli Studi di Firenze, Italia)

    Prof. Dr. Ir. W. H. Rulkens (Wageningen Universiteit, Nederland)

    Prof. Dr. L. R. Mur (Universiteit van Amsterdam, Nederland)

  • Maria Joo Gante de Vasconcelos Barbosa

    Microalgal photobioreactors:Microalgal photobioreactors:Microalgal photobioreactors:Microalgal photobioreactors:

    ScaleScaleScaleScale----up and optimisationup and optimisationup and optimisationup and optimisation

    ProefschriftProefschriftProefschriftProefschrift

    ter verkrijging van de graad van doctor

    op gezag van de Rector Magnificus

    van Wageningen Universiteit,

    Prof. Dr. Ir. L. Speelman

    in het openbaar te verdedigen

    op vrijdag 12 september 2003

    des namiddags te half twee in de aula.

  • Barbosa, M.J.G.V. 2003. Microalgal photobioreactors: Scale-up and optimisation.

    Ph.D. Thesis, Wageningen University, Wageningen, The Netherlands With summary in Dutch

    Keywords: microalgae, cultivation, light regime, hydrodynamic stress, optimisation, productivity,

    photobioreactors, A-stat., scale-up.

    ISBN: 90-5808-898-7

  • Aos meus pais

    minha av Regina

  • ContentsContentsContentsContents

    Chapter 1 Introduction and thesis outline 9

    Chapter 2 Microalgae cultivation in air-lift reactors: modeling biomass yield and growth

    rate as a function of mixing frequency 17

    Chapter 3 Hydrodynamic stress and lethal events in sparged microalgae cultures 37

    Chapter 4 Overcoming shear stress of microalgae cultures in sparged photobioreactors 57

    Chapter 5 Optimisation of cultivation parameters in photobioreactors for microalgae

    cultivation using the A-stat technique 73

    Chapter 6 Optimisation of biomass, vitamins and carotenoid yield on light energy in a flat

    panel reactor using the A-stat technique 91

    Chapter 7 High-cell density cultures: design and operational characteristics of

    photobioreactors 115

    References 137

    Summary 149

    Samenvatting 153

    Acknowledgements 159

    Curriculum Vitae 163

  • 9

    1111

    Introduction and thesis outlineIntroduction and thesis outlineIntroduction and thesis outlineIntroduction and thesis outline

    Products from microalgae and cyanobacteriaProducts from microalgae and cyanobacteriaProducts from microalgae and cyanobacteriaProducts from microalgae and cyanobacteria

    For millennia, aquatic environments have been a source of food, minerals and natural products.

    Concomitant to the increase in Human population and its needs, there is an urge for the discovery

    and sustainable development of new resources. In the sea, very different and extreme

    environments can be found, hosting unusual biochemical processes of importance to industry,

    nutrition, medicine, research and the environment. Marine organisms represent therefore a vast

    resource with potential benefits in many different areas (Table 1.1).

    Table 1.1. Products from microalgae

    ProductProductProductProduct ApplicationsApplicationsApplicationsApplications

    Biomass Biomass Health food Functional food Feed additive Aquaculture Soil conditioner

    Coloring substances & Antioxidants

    Xantophylls (astaxanthin and canthaxanthin) Lutein -carotene Vitamins C and E

    Food and feed additives Cosmetics

    Fatty acids-FA Arachidonic acid-AA Eicosapentaenoic acid-EPA Docosahexaenoic acid-DHA -linolenic acidGCA Linoleic acid-LA

    Food additive

    Enzymes Superoxide dismutase-SOD Phosphoglycerate kinase-PGK Luciferase and Luciferin Restriction enzymes

    Health food Research Medicine

    Polymers Polysaccharides Starch Poly--hydroxybutyric acid-PHB

    Food additive Cosmetics Medicine

    Special products Peptides Toxins Isotopes Aminoacids (proline, arginine, aspartic acid) Sterols

    Research Medicine

  • Chapter 1

    10

    Among aquatic microorganisms microalgae and cyanobacteria are a very interesting source of a

    wide range of compounds (Table 1.1) (Benemann et al., 1987; Cohen, 1999; Skulberg, 2000; Pulz et

    al., 2001). They do not only have the capacity to produce high-value compounds, but also the

    ability to do it using only sunlight, carbon dioxide and seawater. For this reason microalgae and

    cyanobacteria are called photoautotrophic microorganisms, i.e. they need light as their main

    energy source (phototrophic) and they can grow on a very simple culture medium (autotrophic).

    This is possible due to the only biological process of importance that can harvest energy from the

    sun photosynthesis.

    Photobioreactors Photobioreactors Photobioreactors Photobioreactors

    After identification of a strain and product of interest, the step to follow is the development of

    bioprocesses to establish the link between discovery and commercialisation. Reactor design and

    optimisation is an essential step to bring the new product to the store shelf.

    The cultivation system can vary depending on the product and strain. Open systems can be used

    for very fast growing strains or for strains that grow at extreme conditions, such as high pH or

    high salinities. However, for the majority of the strains and products with applications in the

    pharmaceutical industry, monoalgal or even axenic cultures are required. In order to meet these

    standards and aiming at attaining a cost-effective process, several closed systems have been

    developed in the last years (Pulz and Scheibenbogen, 1998; Tredici, 1999). As in conventional

    heterotrophic cultivations, also in microalgal biotechnology high volumetric productivities are

    required to reduce the size of cultivation systems and consequently reduce production and

    downstream processing costs. This entails a high efficiency of light utilization besides high

    biomass concentrations because light energy is the growth limiting substrate. The basic idea of

    using sunlight to produce high-value compounds brings along several limitations, which are

    related to the light regime inside the cultivation system and have to be considered in the design

    and scale-up of photobioreactors.

    High-cell density cultures can be achieved in microalgae biotechnology with a proper reactor

    design and process optimisation (Richmond, 2000). For this reason it is important to build up

    general knowledge in this field, with emphasis on the most critical scale-up and operational

    parameters: light and mass transfer, shear and mixing rates. These parameters are closely

    interrelated and they determine the productivity and efficiency of the system (Figure 1.1).

    Moreover, maximisation of productivity also implies the optimisation of cultivation parameters and

    knowledge on growth and production kinetics (Figure 1.1).

  • Introduction and thesis outline

    11

    Figure 1.1. Scale-up parameters of photobioreactors.

    In this thesis we have only considered vertical gas-sparged photobioreactors such as air-lift

    reactors, bubble columns and flat panels, due to its simple construction and operation. Moreover,

    these configurations show clear advantages for microalgae biotechnology: (1) the mass transfer is

    high in these systems and (2) short liquid circulation times can be obtained.

    The aims of the present thesis are:

    Characterize the most critical scale-up aspects of gas-sparged photobioreactors, with

    emphasis on light regime and hydrodynamic stress.

    Develop optimisation tools for photobioreactors

    Light regime, productivity and light efficiencyLight regime, productivity and light efficiencyLight regime, productivity and light efficiencyLight regime, productivity and light efficiency

    In a high cell-density culture, a light gradient inside the photobioreactor will always occur due to

    light absorption and mutual shading by the cells. Depending on the mixing characteristics of the

    system, the cells will circulate between light and dark zones of the reactor. The main limiting

    factor for the development of microalgal biotechnology is that light energy cannot be stored and

    homogenized inside the reactor.

    In photobioreactors, the light regime is determined by the light gradient and the liquid circulation

    time. Strong light can be efficiently used by working at the optimal cell density in combination

    with a proper liquid circulation time (Richmond, 2000).

    Light/dark cycles have been proven to determine the light efficiency and productivity of

    photobioreactors. Very fast alternations between high light intensities and darkness (from less

    Liquid circulation time

    Hydrodynamic stress

    Mass transfer

    Light Regime Optimisation

    Liquid circu