Bioprocess strategies for enhancing the outdoor production of Nannochloropsis gaditana : an evaluation of the effects of
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RESEARCH PAPER
Bioprocess strategies for enhancing the outdoor production of Nannochloropsis gaditana: an evaluation of the effects of pH on culture performance in tubular photobioreactors L. Moraes1 · G. M. Rosa1 · I. M. Cara4 · L. O. Santos2 · M. G. Morais3 · E. Molina Grima4 · J. A. V. Costa1 · F. G. Acién Fernández4 Received: 1 August 2019 / Accepted: 7 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A priority of the industrial applications of microalgae is the reduction of production costs while maximizing algae biomass productivity. The purpose of this study was to carry out a comprehensive evaluation of the effects of pH control on the production of Nannochloropsis gaditana in tubular photobioreactors under external conditions while considering the environmental, biological, and operational parameters of the process. Experiments were carried out in 3.0 m3 tubular photobioreactors under outdoor conditions. The pH values evaluated were 6.0, 7.0, 8.0, 9.0, and 10.0, which were controlled by injecting pure CO2 on-demand. The results have shown that the ideal pH for microalgal growth was 8.0, with higher values of biomass productivity (Pb) (0.16 g L−1 d−1), and C O2 use efficiency ( ECO2 ) (74.6% w w−1); RCO2/biomass value obtained at −1 this pH (2.42 gCO2 gbiomass ) was close to the theoretical value, indicating an adequate CO2 supply. At this pH, the system was more stable and required a lower number of CO2 injections than the other treatments. At pH 6.0, there was a decrease in the Pb and ECO2 ; cultures at pH 10.0 exhibited a lower Pb and photosynthetic efficiency as well. These results imply that controlling the pH at an optimum value allows higher CO2 conversions in biomass to be achieved and contributes to the reduction in costs of the microalgae production process. Keywords Biomass · Carbon dioxide · CO2 efficiency · Microalga · pH control
Introduction Biotechnological applications using microalgae have expanded, owing to the skill of these microorganisms to produce biomass enriched in compounds such as proteins, lipids, pigments, carbohydrates, and fatty acids [1]. * J. A. V. Costa [email protected] 1
Laboratory of Biochemical Engineering, College of Chemistry and Food Engineering, Federal University of Rio Grande, Rio Grande‑RS 96203‑900, Brazil
2
Laboratory of Biotechnology, College of Chemistry and Food Engineering, Federal University of Rio Grande, Rio Grande‑RS 96203‑900, Brazil
3
Laboratory of Microbiology and Biochemistry, College of Chemistry and Food Engineering, Federal University of Rio Grande, Rio Grande‑RS 96203‑900, Brazil
4
Department of Chemical Engineering, University of Almería, 04120 Almería, Spain
Microalgae are used in wastewater treatment [2], carbon dioxide fixation [3], biofertilizers, biofuels, food items, feeds, cosmetic products [4], high-value compounds (including pigments such as astaxanthin and β-carotene), and polyunsaturated fatty acid production [5–7]. Nannochloropsis gaditana is a unicellular microalga
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