Enhanced hydrogen photoproduction by marine green microalga platymonas subcordiformis grown under CO₂-supplemented air bubble bioreactor

The kinetics of cell growth and photohydrogen evolution of P. subcordiformis grown under CO₂-supplemented air bubble bioreactor is investigated. The highest cell growth was achieved as φ(CO₂) got to 3%, and was supplemented to the air, with a specific growth rate of 0.134 d^-1. The hydrogen photoproduction was enhanced by 70% for cells grown under 3% of φ(CO₂), with a specific hydrogen production rate of 3.24 mmol/(g·h)^-1. The metabolic analysis of algal cells indicated a significant increase in starch accumulation with the increasing CO₂ concentrations. The highest starch content was achieved under 3% of φ(CO₂) supplemented alga cells, 2.1 times the control culture in air. The improved hydrogen production may correlate with the increased starch accumulation where CO₂ serves as the sole carbon source. These results suggest that hydrogen photoproduction by marine green alga can be beneficial from CO₂-supplemented cultivation, which exerts a positive impact on the greenhouse gas mitigation.