Elsevier

Process Biochemistry

Volume 46, Issue 4, April 2011, Pages 936-944
Process Biochemistry

Photobioreactor scale-up for a shear-sensitive dinoflagellate microalga

https://doi.org/10.1016/j.procbio.2011.01.005Get rights and content

Abstract

Large scale culture of marine dinoflagellate microalgae has proved difficult owing to their extreme sensitivity to hydrodynamic forces in photobioreactors. This work discusses the scale up of Protoceratium reticulatum dinoflagellate culture from a successful 2 L stirred-tank photobioreactor operation to a 15 L stirred photobioreactor. Both bioreactors were equipped with internal spinfilters for cell retention. A semicontinuous perfusion culture in the 15 L photobioreactor proved to be more productive than fed-batch perfusion culture. Under the best operational conditions, the average cell productivity in the 15 L photobioreactor was 5228 cell mL−1 day−1, or nearly 3.7-fold greater than the best attainable value in static flask cultures, but similar to the results obtained in the 2 L stirred tank. At 9.16 μg L−1 day−1 the average volumetric productivity of yessotoxin in the scaled up operation in the semicontinuous perfusion mode was comparable to the results obtained in the small bioreactor. P. reticulatum has a cell damage threshold shear rate of as low as 0.1 s−1. Notwithstanding this extreme shear sensitivity, the results suggest a good potential for mass scale culture of this dinoflagellate in suitably designed photobioreactors.

Introduction

Dinoflagellates are one of the several divisions of microalgae. Dinoflagellates occur both in freshwater and in the seas. Although microalgae have an established history of commercial use and new uses are emerging [1], this is not the case for dinoflagellates. Dinoflagellates produce many structurally complex bioactive compounds of potential commercial interest [2], but development of marketable products from them has proved difficult. Small quantities of bioactives derived from dinoflagellates can be purchased, but generally at a prohibitively high price and in low purity. Unlike the other microalgae that are commonly grown in large-scale photobioreactors [3], [4], [5], [6], many dinoflagellates appear to be overly sensitive to the myriad of hydrodynamic forces that are encountered in the turbulent environment of a typical photobioreactor.

Photosynthetic marine dinoflagellates respond to hydrodynamic shear forces in diverse ways [7]. Turbulence sensitivity has been studied for several dinoflagellate species, but invariably from an ecological perspective that may be relevant in the natural habitat, but not in photobioreactor culture. Small scale studies that are potentially relevant to photobioreactor culture have been reported using the highly sensitive dinoflagellate Protoceratium reticulatum. This microorganism is damaged by shear rate values as low as 0.1 s−1 [8]. It is therefore a good model system for studies of photobioreactors that are intended for culturing highly shear sensitive microalgae. At operational scales of 2 L or less, the use of modified turbulence regimens and protective additives in the culture medium have been shown to reduce turbulence-associated damage to P. reticulatum [8], [9], [10]. How this successful operational capability at small scale might translate to a larger photobioreactor has not been previously addressed for dinoflagellates.

Scale-up of photobioreactors is complicated by a nonhomogenous distribution of light within the culture as a consequence of the self-shading by cells. For microalgae that are physically robust, increased intensity of agitation can be used to limit the time that a cell spends uninterrupted in the relatively dark interior of the bioreactor. This strategy is not workable with highly fragile dinoflagellates. Therefore, photobioreactor design and scale up methods that have proved successful for many relatively robust microalgae [3] cannot be directly translated to culturing the fragile dinoflagellates. This work reports on scale up of P. reticulatum culture from a previously reported 2 L stirred-tank photobioreactor [7], [9] to a 15 L photobioreactor.

Section snippets

Species and culture medium

Nonaxenic monocultures of the red-tide dinoflagellate Protoceratium reticulatum (GG1AM) were used. This yessotoxins (YTXs)-producer was obtained from the Culture Collection of Harmful Microalgae of IEO, Vigo, Spain. Inocula were grown in filter sterilized (0.22 μm Millipore filter) L1 medium prepared in Mediterranean Sea water [11]. The alga was grown at 18 ± 1 °C under a 12:12 h light–dark cycle. During the photoperiod, the average irradiance at the surface of the cultures was 100 μE m−2 s−1. Four

Results and discussion

Scale-up of mechanically mixed photobioreactors for culturing dinoflagellates was the focus of this work. The scale up study was informed by prior experience of a successful culture in a 2 L photobioreactor, the 2L-STB [7], [9], and the experimentally established limits on shear stress tolerance of P. reticulatum in shake flasks [8], [15]. First, the fluid-dynamics in the 2L-STB were characterized under different operational regimens that had previously proved successful for P. reticulatum

Concluding remarks

Principles for the successful scale-up of a stirred tank photobioreactor for growing the highly fragile dinoflagellate P. reticulatum were assessed. Successful scale-up from a 2 L operation to a 15 L photobioreactor was achieved by increasing the aspect ratio of the reactor to 4.5-fold of the value at the small scale. A relatively large axial flow impeller rotating at a slow speed was used for mixing. Scale up methods for photobioreactors remain largely undeveloped [32]. Although maintaining of

Acknowledgements

This research was supported by the Spanish Ministry of Science and Innovation (CTQ2008-06754-C04-02/PPQ) and the General Secretariat of Universities, Research and Technology of Andalusian Government (TEP-5375).

References (32)

  • E. Molina Grima et al.

    Scale-up of tubular photobioreactors

    J Appl Phycol

    (2000)
  • G. Vunjak-Novakovic et al.

    Air-lift bioreactors for algal growth on flue gas: mathematical modeling and pilot-plant studies

    Ind Eng Chem Res

    (2005)
  • J.J. Gallardo Rodríguez et al.

    New culture approaches for yessotoxin production from the dinoflagellate Protoceratium reticulatum

    Biotechnol Prog

    (2007)
  • J.J. Gallardo Rodríguez et al.

    Carboxymethyl cellulose and Pluronic F68 protect the dinoflagellate Protoceratium reticulatum against shear-associated damage

    Bioproc Biosyst Eng

    (2011)
  • R.R.L. Guillard et al.

    Stichochrysis immobilis is a Diatom not a Chyrsophyte

    Phycologia

    (1993)
  • M.Y. Chisti

    Airlift bioreactors

    (1989)
  • Cited by (64)

    • Combined in-situ immobilization system of Chlorella sp. in photobioreactor

      2023, Case Studies in Chemical and Environmental Engineering
    View all citing articles on Scopus
    View full text