Utilization of CO2 nanobubbles for Spirulina cultivation

One of the strategies for CO₂ mitigation through microalgae biomass and high-value compound production has gained significant attention. However, adding CO₂ directly into the water can result in CO₂ loss from the system to the atmosphere. The use of nanobubble technology is a promising approach to improve CO₂ solubility in algal culture media. The effects of various dilution rates (0.1, 0.2, and 0.3 d^-1) on biomass production and high-value chemical accumulation in Spirulina (Arthrospira platensis strain BP) were examined in this work. Cells were grown in a modified Zarrouk medium supplemented with CO₂ nanobubbles (pH 8) and NaHCO₃ of either 4 g L^-1 (M1) or 8 g L^-1 (M2). Using CO₂ nanobubbles increased bicarbonate concentrations by approximately 360 mg L^-1 in M1 medium and 1340 mg L^-1 in M2 medium. The highest biomass productivity was achieved under semi-continuous cultivation, at a dilution rate of 0.3 d^-1 with 129 ± 4 mg L^-1 d^-1 in M1 medium and 164 ± 7 mg L^-1 d^-1 in M2 medium. In addition, phycocyanin, a high-value chemical, increased when cultivated in M2 medium. The phycocyanin reached 27.3 ± 0.6 mg L^-1 d^-1 at a dilution rate of 0.3 d^-1. Thus, these findings indicate the potential application of CO₂ nanobubbles for microalgae production. Further studies are needed, nevertheless, to improve efficiency and feasibility for use on an industrial scale.

Keywords: bicarbonate, CO₂ nanobubbles, phycocyanin, Spirulina