Microalgal Reactors: A Review of Enclosed System Designs and Performances

Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr. António Bernardino de Almeida, P-4200-072 Porto, Portugal.
Biotechnology Progress (Impact Factor: 2.15). 12/2006; 22(6):1490-506. DOI: 10.1021/bp060065r
Source: PubMed


One major challenge to industrial microalgal culturing is to devise and develop technical apparata, cultivation procedures and algal strains susceptible of undergoing substantial increases in efficiency of use of solar energy and carbon dioxide. Despite several research efforts developed to date, there is no such thing as "the best reactor system"- defined, in an absolute fashion, as the one able to achieve maximum productivity with minimum operation costs, irrespective of the biological and chemical system at stake. In fact, choice of the most suitable system is situation-dependent, as both the species of alga available and the final purpose intended will play a role. The need of accurate control impairs use of open-system configurations, so current investigation has focused mostly on closed systems. In this review, several types of closed bioreactors described in the technical literature as able to support production of microalgae are comprehensively presented and duly discussed, using transport phenomenon and process engineering methodological approaches. The text is subdivided into subsections on: reactor design, which includes tubular reactors, flat plate reactors and fermenter-type reactors; and processing parameters, which include gaseous transfer, medium mixing and light requirements.

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    • "However, issues associated with PBR include oxygen removal and reactor overheating. As a byproduct of photosynthesis from algae, oxygen can inhibit the photosynthesis process at concentrations beyond air saturation (Carvalho et al., 2006). To overcome the overheating issue, cooling water spray may be necessary and the water consumption associated can be significant (Pate, 2008). "
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    • "Photobioreactors (PBRs) are closed systems for microalgae cultivation and there are currently three main design groups available (Carvalho et al., 2011). These designs are tubular (Molina et al., 2001), flat panel (Issarapayup et al., 2009) or fermenter-type (Carvalho et al., 2006). Tubular and flat-panel PBRs are designed for the efficient harvest of sunlight and are therefore based on the principle of high area to volume ratios. "
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    ABSTRACT: Chlamydomonas reinhardtii (CCAP 11/32C) cells were grown in liquid culture under photoautotrophic conditions using a photobioreactor (PBR) based on oscillatory baffled reactor (OBR) technology. A flotation effect was observed when using a porous gas sparger which resulted in accumulation of microalgae at the top of the column. Linear growth was achieved with a different sparger, designed to produce larger, faster rising gas bubbles. Changes in the mixing intensity had no effect on the maximum growth rate of 0.130OD750/day (±0.010) achieved which was 95% higher than that achieved in T-flasks of 0.067OD750/day (±0.011) under comparable conditions. The increase in growth rate achieved in the OBR was probably a result of increased gas transfer, and exponential growth was not achieved probably due to the relatively low light intensity used of 78μmol/m2s (±20). The results demonstrate the feasibility of OBR technology for use as PBRs with the potential for the duel culture and harvest of microalgal biomass through manipulation of the bubble diameter. This could greatly improve bioprocess economics for microalgae culture.
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    • "PBRs are thus known to display significantly higher biomass productivities, also enabling the culture of sensitive strains (Ugwu et al., 2008). High investment and operational costs (e.g., capital, maintenance, and energy; Carvalho et al., 2006) are important economic constraints as far as their widespread use is concerned. However, further developments in PBR design, and implementation of large-scale facilities, mainly driven by the research in the field of biofuels, are expected to decrease these costs, enabling the culture of microalgal biomass for the exploitation of high-value products, such as PUFA. "
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    ABSTRACT: The role of polyunsaturated fatty acids (PUFAs), and n-3 PUFA in particular, has been long known. It is recognized that n-3 PUFA prevents cardiovascular diseases, inhibits and treats inflammatory conditions, and aids brain development and function. For these reasons, the World Health Organization and Food and Agriculture Organization of the United Nations have advised dietary intakes of 300–400 mg of n-3 PUFA (e.g., eicosapentaenoic or EPA and docosahexaenoic or DHA) for the general adult population, provided mainly by oily fish. However, considering the close-to-depletion state of fish stocks and the safety concerns raised by fish contamination with metals and persistent organic pollutants, new sources of n-3 PUFA are needed. Microalgae are primary producers of n-3 PUFA, and some Chlorophyta species such as Nannochloropsis and Tetraselmis can be excellent sources of EPA, while the Haptophyta species Isochrysis galbana and Pavlova lutheri are outstanding sources of DHA. Besides being excellent n-3 PUFA producers, microalgae can be easily cultured and their EPA and DHA content can be modulated.
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