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There is an urgent need to develop technologies for removing CO2 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 NaHCO3 since AP utilizes HCO3−as a carbon source. These culture conditions result in signifcant amounts of CO2 escaping into the atmosphere, instead of being sequestered during cultivation. Here, we investigated whether ambient air (0.042% CO2) 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 NaHCO3 and aeration with 0.236 vvm air with 2% CO2 (“NaHCO3/CO2-based”) to compensate carbon loss due to CO2 outgassing, and (2) Zarrouk medium without NaHCO3 and a gas fow with ambient air (0.926 vvm) as the only carbon source (“air-based”). The air-based production resulted in the biofxation of 3.78 gCO2/L during the linear growth phase. With NaHCO3/CO2-based production, a comparable amount of 3.42 gCO2/L was obtained while 659.12 g of CO2 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 NaHCO3 but using ambient air with atmospheric CO2 as the only carbon source is possible without reducing productivity. These results improve our understanding of how atmospheric CO2 can be reduced by culturing AP. [ABSTRACT FROM AUTHOR]

A vertical flat-type bioreactor consisting of transparent polyethylene (food safe) was constructed, which is characterized by a flexible design and allows the adjustment of a light path of 1 cm – 8.5 cm and a working volume of 1.5 l – 4 l. To characterize the performance of the bioreactor, cultivation experiments were performed with the cyanobacterium Arthrospira platensis (AP). The growth was assessed continuously by monitoring optical density and intermittently by measuring the dry weight of the AP biomass. An on-line measurement technique for estimating biomass production rate in a photosynthetic microalgae culture was developed. The oxygen produced by AP in the culture medium was flushed out sparging using a mixture of air and CO2 (1%). Factors which might influence the AP growth were monitored: pH, temperature, oxygen concentration and the filling level were corrected automatically to compensate evaporation losses. As an example, the huge influence of the light intensity on the AP growth was tested. The increase of the photon flux density of 15 to 1200μmol/(l · d) led to a 22-fold increase of the productivity and a 3.1-fold shorter doubling time. Using an online measurement technique - together with the control of the growth process via a wireless local area network (WLAN) router and virtual private network - allows monitoring the growth of Arthrospira platensis remotely. [ABSTRACT FROM AUTHOR]