A pilot-scale floating closed culture system for the multicellular cyanobacterium Arthrospira platensis NIES-39

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.

Bicarbonate Concentration Induces Production of Exopolysaccharides by Arthrospira platensis That Mediate Bioflocculation and Enhance Flotation Harvesting Efficiency

“…For A. platensis, the only studies reporting cases of bio-flocculation describe that nutrient deprived conditions or high salinity can trigger an accumulation of carbohydrates in cells, which changes the density of the cells and allows their flocculation and settling. It is clear in these studies that no EPS are responsible for the flocculation observed 25,27,29,28 . In our study, the cells are not nutrient-deprived or grown at high salinities.…”

“…For A. platensis, three cases of bio-flocculation have been reported. In these three cases, the same mechanism is described where bio-flocculation is directly induced by the accumulation of carbohydrates by the cells under nutrient stress conditions (phosphorous and nitrogen) or at high salinities, leading to an increase in their specific density [27][28][29] . However in these conditions, the nutrient deprivation results in reduced cell growth and biomass production.…”

Characterization of the polysaccharides chemical diversity of the cyanobacteria Arthrospira platensis

“…The category "High Salinity" included results obtained for the biomass grown in media containing from 0.25 to 1 M NaCl added in the Zarrouk medium [35,36] and for medium consisting of a mix of seawater and deionized water with addition of 2.5 g L −1 NaNO 3 , 0.01 g L −1 FeSO 4 •7H 2 O, and 0.08 g L −1 Na 2 EDTA [37].…”

Conversion of NaHCO3 to Na2CO3 with a growth of Arthrospira platensis cells in 660 m2 raceway ponds with a CO2 bicarbonation absorber

“…With a further WRB increase to 4.5, the helix pitch and trichome length decreased from 57 to 42 μm and from 613 to 503 μm, respectively. It is evident that with the growth of A. platensis , the helix pitch and trichome length increased (Toyoshima et al ., ). The A. platensis cells, which are helical shaped, proliferates along the longitudinal axis.…”

“…However, few studies have reported on the activities in this area. An NaHCO 3 plant in this area produces large amounts of by-products consisting of 40-70% NaHCO 3 and 5-10% Na 2 CO 3 , which are suitable raw materials for the microalgal cultivation industry (Lu et al, 2011;Toyoshima et al, 2015;Chen et al, 2016;Yuan et al, 2018). However, after several years of development, numerous problems have become apparent when using NaHCO 3 by-products as a carbon source.…”