Abstract
Microalgae are considered to be efficient bio-resources for biofuels and bio-based chemicals because they generally have high productivity. The filamentous cyanobacterium Arthrospira (Spirulina) platensis has been widely used for food, feed, and nutrient supplements and is usually cultivated in open ponds. In order to extend the surface area for growing this alga, we designed a pilot-scale floating closed culture system for cultivating A. platensis on open water and compared the growth and quality of the alga harvested at both subtropical and temperate regions. The biomass productivity of A. platensis NIES-39 was ca. 9 g dry biomass m−2 day−1 in summer at Awaji Island (warm temperature region) and ca. 10 and 6 g dry biomass m−2 day−1 in autumn and winter, respectively, at Ishigaki Island, (subtropical region) in Japan. If seawater can be used for culture media, culture cost can be reduced; therefore, we examined the influence of seawater salt concentrations on the growth of A. platensis NIES-39. Growth rates of A. platensis NIES-39 in diluted seawater with enrichment of 2.5 g L−1 NaNO3, 0.01 g L−1 FeSO4·7H2O, and 0.08 g L−1 Na2EDTA were considerably lower than SOT medium, but the biomass productivity (dry weight) was comparable to SOT medium. This is explained by the heavier cell weight of the alga grown in modified seawater media compared to the alga grown in SOT medium. Furthermore, A. platensis grown in modified seawater-based medium exhibited self-flocculation and had more loosely coiled trichomes.
Highlights
Development of clean and sustainable biofuels has gained significant support owing to global climate change, the shortage of energy, and petroleum supplies
In the cultures from 26 August to 30 September, 2013 (35 days), A. platensis NIES-39 was grown in SOT and 1/4 SW media
In the cultures from 9 October to 18 November, 2013 (40 days), A. platensis NIES-39 was grown in SOT and 1/4 SW media in the water bath simultaneously
Summary
Development of clean and sustainable biofuels has gained significant support owing to global climate change, the shortage of energy, and petroleum supplies. In order to achieve large-scale commercial uses of photosynthetic microorganisms, it is important to reduce the production cost by developing low-cost culture facilities and culture media and efficient harvesting methods. A. platensis has been widely used for foods, feeds, and nutrient supplements (Anupama and Ravindra 2000; Spolaore et al 2006) owing to its high nutritional value (Converti et al 2006). It has great potential as a source of bioenergy, because its photosynthetic storage
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