Abstract: This review systematically introduced three different pathways of hydrogen production by hydrogenase in green algae under anaerobic condition, including direct hydrogen production via photosystem II, indirect hydrogen production independent of photosystem II and hydrogen production by dark fermentation. The advantages and disadvantages of each pathway were analyzed. However, limited by technology and high costs, hydrogen production by green algae was still in the laboratory-scale, and will take a long time to achieve industrial production. Aiming at the efficient hydrogen production, this review described the latest outcome in this field and summarized the methods for optimizing the hydrogen production, including hydrogenase modification, reducing the oxygen content, lowering the cyclic electron transfer rate, reducing the Calvin-cycle, remodeling the light harvesting complex, pretreatment of the biomass and photo-bioreactor design. The future development of hydrogen production by green algae was also discussed.

Key words: green algae, photosynthesis, hydrogenase, biohydrogen production mechanism, biohydrogen production efficiency