Hydrogen production using purple non-sulfur bacteria (PNSB) cultivated under natural or artificial light conditions with synthetic or fermentation derived substrates

Aim: The aim of this thesis is to verify the feasibility of the hydrogen production process both in sunlight irradiation in an up-scaled system and with the use of low cost substrates in laboratory conditions, aspects investigated separately. Methods and Results: The experimentation carried out under natural irradiation in a semi-pilot scale photobioreactor of 50 L of volume has demonstrated the full feasibility of the process. The production rates and the total amount of hydrogen produced were higher than the values so far reported in literature for experimentations in dimensionally-comparable devices conducted outdoors, under solar light conditions. Yet, the process needs to be further optimized in order to achieve a constant and durable production of hydrogen. Products of fermentations conducted by mesophilic or thermophilic chemoheterotrophic bacteria or by microbial communities residing on vegetable residues. The substrate that made possible the highest hydrogen production with the PNSB tested was the one deriving from the spontaneous fermentation of vegetable wastes. Furthermore, a genetically modified strain of Rhodopseudomonas palustris, insensitive to ammonium, was used. The results obtained were very promising, as the strain showed to be able to produce hydrogen completely independently from the ammonium concentration, thus leading to large quantities of gas produced. Conclusions: The results obtained during the research activity of this doctorate proved the feasibility of hydrogen production processes using PNSB under natural light conditions and growing on low cost substrates, even if further investigations are needed to improve the efficiency of light utilization by PNSB when using solar light and the efficiency of conversion of substrate to hydrogen when using low cost substrates. Impact of the study: With the present theses a first step was towards a semi pilot scale H2 production process was made, with cultures irradiated by natural sunlight. A further step towards the scale-up was the use of low cost substrates, possibly using PNS bacterial strains (such as ammonium insensitive strains) that allow to obtain larger H2 amounts.