Arthrospira platensis cultivation in seawater culture media for CO2 capture and production of valuable compounds.

This study investigated the effects of different culture media (Zarrouk as Control Experiment [ZCE], Zarrouk using Seawater [ZSW], and Seawater with Nutrients [NSW]) on CO2 fixation, biomass growth, and bioproduct composition of Arthrospira platensis, aiming to save the fresh water. Immediate CO2 reduction of up to 50 % was observed with ZCE, whereas ZSW and NSW initially contributed to CO2 production due to natural microorganisms and salinity stress. However, higher CO2 fixation rates were achieved by the end of the experiment after 25 days (86 %). ZSW outperformed ZCE with 80 % CO2 sequestration compared to 70 % from day 14 until the 20th day of the experiment, due to the rapid biomass growth after acclimatization. Biomass productivity was highest in ZSW, reaching 48 mg/L d by day 20, comparable to ZCE. NSW exhibited unique biofilm formation, increasing biomass to 1.1 ± 0.21 g/L despite reduced protein and carbohydrate content due to stress factors. Metabolic adjustments induced by salinity promoted enhanced lipid biosynthesis in NSW, with lipid yields surpassing those in ZCE and ZSW. Protein production was highest in ZCE (35-52 %), due to its nutrient-rich composition. Salinity increased carbohydrate accumulation and decreased protein and pigment production. C-phycocyanin and C-allophycocyanin levels were significantly lower in ZSW and NSW than in ZCE. The chlorophyll-a content remained constant but suboptimal in all media, probably due to the lack of NaHCO3. The study highlights Spirulina's adaptability to different media, with seawater-based systems providing low-cost biomass and bioproducts alternatives.