Photosynthesis, photobioreactor design and light conversion efficiency in hydrogen production with anoxygenic photosynthetic bacteria

Hydrogen can be considered the energy vector of the future as it constitutes a clean, renewable and energy-efficient fuel. However, in order to make H2 a renewable fuel effectively utilizable at industrial level, key issues about its economically and environmentally sustainable production have still to be solved. In the case of the photofermentative production of hydrogen with PNSB, an efficient utilization of light is still the most critical problem to be addressed for turning this promising biological process into an actual industrial technology. In the last years, there was an impressive increase in the number of studies aimed at improving the design of photobioreactors for optimizing hydrogen production, especially towards large scale, cost effective production systems. At the same time, it emerged an advance in the knowledge on what is still needed for industrially exploit PNSB for photoproduction of hydrogen, for example efficient and economic light distribution and mixing systems. In this presentation, the steps that bring to the formation of a molecule of hydrogen from the absorption of light energy will be outlined, stressing the metabolic hurdles during this process that finally affect photosynthetic efficiency. An overview on some recent data corresponding to different strategies to optimize photosynthetic efficiency will be given, in order to put in light on how tightly closed are the inner mechanisms of the cell metabolism and the final results of large-scale hydrogen production processes.