Effect of hydrodynamic parameters on hydrogen production by Anabaena sp. in an internal-loop airlift photobioreactor

Global warming and air pollution caused by fossil fuel emissions have triggered the search for a clean, sustainable, and eco-friendly energy source such as H₂, which can be produced by cyanobacteria and microalgae. In this study, Anabaena sp. was used in a photobioreactor to achieve biohydrogen production. To this end, hydrodynamic parameters such as gas holdup, liquid circulation velocity, oxygen mass transfer coefficient, and gas velocity were investigated. Results showed that the gas holdup, liquid circulation velocity, and oxygen mass transfer increased by increasing the inlet gas velocity without causing detrimental shear stress to cyanobacteria. A biomass concentration of 1.2 g L^-1 and a total H₂ production of 371 mL were recorded after 7 days using an inlet gas velocity of 0.524 cm s^-1 and a light intensity of 140 μmol photons m^-2 s^-1. Using a superficial gas velocity of 0.524 cm s^-1 resulted in the optimum gas holdup, mass transfer, and light availability to Anabaena sp. The growth of cyanobacteria in an internal-loop airlift photobioreactor was found to be a cost-effective and environmentally friendly technology for hydrogen production. (author)