ABSTRACT

Biohydrogen has immense potential to be a renewable alternative to the existing non-renewable fossil fuels. It can be produced directly from solar energy by the action of photosynthetic microorganisms like cyanobacteria and microalgae. These organisms produce hydrogen to remove the excess reducing equivalents produced during the photosynthetic electron transport. Depending upon the oxygenic or anoxygenic environments, different mechanisms such as biophotolysis and photofermentation, respectively, have been reported for hydrogen generation in phototrophs. By providing suitable growth conditions in a closed photobioreactor or an open pond system, hydrogen can be harnessed for renewable energy production from these organisms. Currently, the hydrogen production rates reported so far are not attractive for large-scale production. Several factors influence the hydrogen production by photosynthetic organisms such as light penetration, mode of agitation, gas exchange, temperature, and reactor geometry (in case of photobioreactors). In this chapter, the fundamental aspects of photobiological hydrogen production are described with clear illustrations of different mechanisms, metabolic pathways, and key enzymes involved in the process. The various parameters influencing hydrogen productivity have been discussed. Moreover, recent advancements with respect to photobioreactor designs, alteration in media components, new isolates, coculturing, and genetic improvements have been emphasized.