Photobiological biohydrogen production

Abstract Photobiologically produced hydrogen (H2) is expected to be one of the strong candidates for renewable energy. The energy source is sunlight, and the e− donors for H2 production are simply H2O for O2-evolving photosynthetic organisms such as cyanobacteria and green algae, and various organic wastes for photosynthetic bacteria. We describe the present status of the researches into photobiological H2 production focusing on cyanobacteria and purple bacteria. In spite of extensive basic studies, no commercially viable production systems are currently operative in a large scale. We describe some analyses on the economy of photobiological H2 production, some efforts for inexpensive large-scale photobiological production of H2, and discuss some technical issues for economical production of H2.