In situ carbon supplementation in large-scale cultivations of Spirulina platensis in open raceway pond

The objective of this study was to estimate the CO2 absorptivity provided by an in situ carbon supply system using a photosynthetic culture of the cyanobacterium Spirulina platensis in an open raceway pond. The effects of initial total carbon concentrations (ranging from 0 to 0.1 mol/L), suspension depths (ranging from 5 to 20 cm) and pH values (ranging from 8.9 to 11.0) on the CO2 absorptivity were studied. The results indicated that CO2 absorptivity was positively correlated with pH value, negatively correlated with total carbon concentration, and only negligibly affected by the suspension depth. The optimum total carbon concentration range and pH range were 0.03 similar to 0.09 mol/L and 9.7 similar to 10.0, respectively. An average CO2 absorptivity of 86.16% and average CO2 utilization efficiency of 79.18% were achieved using this in situ carbon-supply system in large-scale cultivation of Spirulina platensis, with an initial total carbon concentration of 0.06 mol/L and pH value of 9.8. Our results demonstrated that this system could obtain a favorable CO2 utilization efficiency in outdoor, large-scale cultivation of Spirulina platensis in open raceway ponds