Photobioreactor design and illumination systems for H2 production with anoxygenic photosynthetic bacteria: A review

H2 constitutes a clean, renewable and energy-efficient fuel. However, in order to make it a renewable fuel effectively utilizable at industrial level, key issues about its economically and environmentally sustainable production have still to be solved. Microbial hydrogen production is a process having a low environmental impact and, among microbial processes, photofermentation is considered a promising and sustainable solution. However, the energy input for the biological processes is still larger than the energy output in the form of H2 gas. A possibility for improving this ratio lies in the increase of the efficiency of the process and at the same time in the reduction of the electricity consumption, both issues related with an optimal photobioreactor design. This review is focused on the recent advances made on photobioreactor design towards higher light conversion efficiency, hydrogen production rate and substrate conversion in hydrogen production processes carried out with purple non sulfur bacteria, with a particular attention on the light source an on the illumination protocols. The recent achievements in outdoor hydrogen production in large scale photobioreactors are also reviewed.