Decarbonization of Arthrospira platensis production by using atmospheric CO2 as an exclusive carbon source: proof of principle

There is an urgent need to develop technologies for removing CO 2 from the atmosphere to combat climate change. Microalgae and cyanobacteria, such as Arthrospira platensis (AP), have shown promise due to their high photoautotrophic biomass production. Conventional AP culture media are supplemented with high concentrations of NaHCO 3 since AP utilizes HCO 3 - as a carbon source. These culture conditions result in significant amounts of CO 2 escaping into the atmosphere, instead of being sequestered during cultivation. Here, we investigated whether ambient air (0.042% CO 2 ) can be used for growing AP in a culture medium lacking a fossil-based carbon source. AP was cultured in 2 L glass bioreactors containing: (1) Zarrouk medium with 16.8 g/L NaHCO 3 and aeration with 0.236 vvm air with 2% CO 2 (“NaHCO 3 /CO 2 -based”) to compensate carbon loss due to CO 2 outgassing, and (2) Zarrouk medium without NaHCO 3 and a gas flow with ambient air (0.926 vvm) as the only carbon source (“air-based”). The air-based production resulted in the biofixation of 3.78 g CO2 /L during the linear growth phase. With NaHCO 3 /CO 2 -based production, a comparable amount of 3.42 g CO2 /L was obtained while 659.12 g of CO 2 was released into the atmosphere. Total protein, phycocyanin, chlorophyll-a, and carotenoids were present in similar or increased amounts in AP produced by the air-based method. We concluded that cultivation of AP with Zarrouk medium lacking NaHCO 3 but using ambient air with atmospheric CO 2 as the only carbon source is possible without reducing productivity. These results improve our understanding of how atmospheric CO 2 can be reduced by culturing AP.