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Abstract: H2 is a clean, renewable and energy-efficient fuel. However, in order for it to be a fuel effectively utilizable at an industrial level, key issues about its economically and environmentally sustainable production have still to be solved. Microbial hydrogen production is a process with 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 higher than the energy output in the form of H2 gas. One possibility for improving this ratio is to increase the efficiency of the process while at the same time reducing electricity consumption, both of which relate to the issue of an optimal photobioreactor design. This review focuses on recent advances made in photobioreactor design towards higher light conversion efficiency, a greater hydrogen production rate and substrate conversion in hydrogen production processes carried out with purple non sulfur bacteria, giving particular attention to the light source and to illumination protocols. Recent achievements in outdoor hydrogen production in large scale photobioreactors are also reviewed. [Copyright &y& Elsevier]

Abstract: Research on photobiological H2 production processes is pointing towards the use of low cost substrates as sources of reduced carbon for H2 generation. Those substrates (either wastewaters or effluents derived from other fermentation processes) are often rich not only in carbon, but also in fixed nitrogen. is an inhibitor of nitrogenase-mediated H2 production in purple non sulfur bacteria. A Rhodopseudomonas palustris mutant strain (NifA*), which constitutively expresses nitrogenase genes, was utilized in order to test the use of containing fermentation products for photobiological production of H2. The strain was grown on both synthetic and waste-derived containing media. The nifA* mutant produced H2 in the presence of high concentrations of , both in a synthetic medium and in a real vegetable waste-derived medium resulting in higher H2 levels than the wild-type strain. Thus, this study demonstrates that the NifA* strain is well suited to overcome the effects of inhibitory naturally occurring as it converts agricultural waste into biofuel. [Copyright &y& Elsevier]

Abstract: Sunlight represents an important choice for low cost photosynthetic cultures irradiation, especially in up-scaled processes. The aim of this study was the assessment of the hydrogen production performances of Rhodopseudomonas palustris strain 42OL cultivated outdoors, under sunlight, in a 50L tubular photobioreactor. Moreover, bacteriochlorophyll a fluorescence was used for the first time as a tool for monitoring the physiological status of Rp. palustris mass cultures. The maximum H2 production rate of 27.2mlL−1 h−1, and the mean rate per illuminated surface of 3.54±1.53Lm−2 d−1 obtained resulted the highest so far reported for outdoor experiments carried out with purple bacteria in tubular photobioreactors of comparable dimensions. The in-situ measurement of bacteriochlorophyll a fluorescence (F v/F m) showed that the photosystem was unaffected by changing light irradiance during the day and remained fully active over the whole period of hydrogen production. [Copyright &y& Elsevier]