Influence of Volumetric Air Flow on Cyanobacteria Biomass Production in a Bubble Column Photobioreactor Using an Innovative Culture Medium and Phycocyanin Extraction

Health problems have made it necessary to look for new sources of biocompounds for the food industry. Cyanobacteria offer a solution due to the compounds inside their biomass, such as pigments and protein. Rice husk aqueous extract was evaluated as an innovative culture medium using four concentrations (16, 32, 48 and 64 g/L, respectively) for the biomass production of Limnothrix sp. Rice husk aqueous extract at a concentration of 48 g/L showed the best results for Limnothrix sp. biomass production as well as phycocyanin and protein contents. Furthermore, cultivation of Limnothrix sp. was carried out in bubble column photobioreactors, evaluating three volumetric air flows (157, 180 and 570 mL/min, respectively). With an air flow of 180 mL/min and specific photobioreactor geometry (height-to-diameter ratio of 10.67), the bubble size, measured with Sauter diameter, was 10.81 ± 0.36 mm, ensuring mixing inside and resulting in the highest biomass production (2.95 ± 0.07 g/L dry weight (DW)), with protein and phycocyanin contents of 0.29 ± 0.01 g/g and 100.83 ± 0.10 mg/g, respectively, over 24 days of cultivation. Consequently, the hydrodynamics resulting from the volumetric air flow inside bubble column photobioreactor systems influence the growth of cyanobacteria and the accumulation of protein and phycocyanin for application in the food industry and third-generation biorefineries.