Abstract
Arthrospira platensis (Spirulina) is the most cultivated microalga worldwide. Improving its cultivation in terms of biomass productivity, quality, or production cost could significantly impact the Spirulina industry. The objectives of this paper were defined as to contribute to this goal. Spirulina biomass productivity was investigated through medium choice. A modified Zarrouk’s medium was selected as it gave higher final dry weights and longer sustained growth than Hiri’s and Jourdan’s media. Then, in order to reduce Spirulina production cost, modified Zarrouk’s medium was rationalized by testing different dilutions. It was found that modified Zarrouk’s medium could be diluted up to five times without impacting the growth rates in a 28-days batch cultivation. Higher dry weights were even observed after 21 days of batch cultivation (1.21 g/L for 20%-modified Zarrouk’s medium in comparison to 0.84 g/L for modified Zarrouk’s medium). Iron uptake was then investigated as one of the major contributors to Spirulina nutritional quality. An increase in iron content was obtained by replacing iron sulfate by iron EDTA at a concentration of 10 mgFe/L (2.11 ± 0.13 mgFe/gbiomass for EDTA-FeNa, 3 H2O at 10 mgFe/L compared to 0.18 ± 0.13 for FeSO4,6H2O at 2 mgFe/L). Impact of light intensity on Spirulina biomass productivity was also investigated in a 2 L Photobioreactor (PBR). Specific growth rates were calculated for Photosynthetically Photon Flux Densities (PPFD) from 85 to 430 µmol/m2/s. At 430 µmol/m2/s, photoinhibition was not observed and the specific growth rate was maximum (0.12/day). Finally, a 40-day cultivation experiment was conducted in a 1000 L PBR giving a maximum daily areal productivity of 58.4 g/m2/day. A techno-economic analysis gave production cost two to 20 times higher for PBR (from 18.71 to 74.29 €/kg) than for open ponds (from 3.86 to 9.59 €/kg) depending on Spirulina productivity.
Highlights
Arthrospira platensis is an aquatic, filamentous cyanobacterium which is often classified as a blue/green microalga
Media conventionally used in lab-scale experiments and by Spirulina producers were compared in triplicates, i.e., modified Zarrouk’s medium (ZM), modified HM and modified JM
Spirulina biomass productivity can be significantly improved by using the appropriate medium
Summary
Arthrospira platensis is an aquatic, filamentous cyanobacterium which is often classified as a blue/green microalga. The common name of its commercialized biomass is “Spirulina” (the name used in this paper) which production makes this microorganism to be the most cultivated worldwide [1]. The Spirulina production has been estimated to be between 3000 and 20,000 tons/year. In 2014, in France, 105 Spirulina farmers were registered in the association “Fédération des Spiruliniers de France”. Spirulina is considered to be a nutraceutical due to its high nutritional quality (proteins, essential amino acids and fatty acids, polysaccharides, carotenoids, vitamins, and iron) [2]. Spirulina is almost exclusively produced in open ponds which are low-cost, and easy to build and operate. The difficulty of these systems are the low biomass productivity [3,4], less than
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