Effect of Superficial Gas Velocity on Continuous Hydrogen Production by Anabaena sp. in an Internal-loop Airlift Bioreactor

Global warming and rising air pollution which has been caused by using too much fossil fuel has led to look for a new clean source, sustainable and eco-friendly of energy like H 2 , which can be produced by cyanobacteria and microalgae. In this study, Anabaena sp. was used in a continuous operation to achieve biohydrogen production. To this end, an airlift photobioreactor (20 L) was considered. The effects of the gas holdup, liquid circulation velocity, and the amount of dissolved oxygen on hydrogen production were investigated. Gas holdup, liquid circulation velocity, and K L a (mass transfer coefficient) showed an upward trend by increasing the velocity of the inlet gas. Maximum biomass concentration of and maximal H 2 production were observed 1.2 g L -1 d -1 and 371 mL h -1 PBR -1 , respectively under light intensity of 3500 lux/m 2 applying a light-dark cycle in 7 days, at A d /A r of 1.25 and 0.185 and 0.542 cm/s. pH, temperature (30 + 2 °C), light intensity, and inlet gas flow to the bioreactor (containing 98% air and 2% carbon dioxide) were remained steady. Using the airlift photobioreactor with a good mass transfer and light availability to cyanobacteria growth can be a cost-effective and environmentally technology for biological H 2 production.