One of the best and cleanest systems to produce electric energy is represented by fuel cells, whose natural fuel is hydrogen. In this paper, the production of hydrogen rich biogas is studied. This process contributes to create a system for biomass recovery, which eliminates organic pollutants and produces energy with high ef®ciency without atmospheric emissions. The study has been based on Escherichia coli and Enterobacter aerogenes strains. The research deals with batch reactors and veri®cation of optimal conditions of hydrogen production. The realization of the optimal working conditions would conduce to the realization of a reactor suitable to feed a stack of the above mentioned fuel cells. In view of industrial applications, some different ways have been considered to greatly enhance the process performance, in terms of rate of hydrogen production, ef®ciency of hydrogen utilization and/ or biosynthesis of valuable subproducts.List of symbols C glucose concentration at the end of the fermentation (g l A1 ) C 0 initial glucose concentration (g l A1 ) n hydrogen evolution (mmol) n max maximum hydrogen evolutiion (mmol) r max maximum rate of hydrogen evolution (mmol l A1 h A1 ) r max maximum speci®c rate of hydrogen evolution (mmol h A1 g A1 cells ) Y max maximum yield (mmol H 2 mmol A1 glucose )
IntroductionFuel cells can be considered to be one of the cleanest and most ef®cient systems to convert the chemical energy stored in several categories of substances, owing to their high conversion ef®ciency and environmental compatibility. Among these substances hydrogen plays a pre-eminent role, thanks to its good reactivity and high oxidation energy [1]. Moreover, hydrogen is an attractive energy source for replacing conventional fossil fuels, both from the economic and environmental standpoints [2]. In general, there are two ways to produce hydrogen with living organisms: one is hydrogen production by photosynthetic organisms and the other is fermentative hydrogen production. Several facultative and strictly anaerobic bacteria were used in the fermentation of different substrates [3±5].The main advantages of the fermentative hydrogen production may be summed up as follows [6]:± production for 24 hours a day without light; ± use of photosynthetic products as substrates; ± use of industrial and/or agricultural wastes as substrates; ± metabolites, except hydrogen, can also be used.Moreover, as the rate of fermentative hydrogen production rate is usually higher than the photohydrogen evolution one, hydrogen bio-production via fermentation appears most likely the technique to be adopted in view of industrial application. Fermentation of high BOD wastes or by-products seems to be a very promising way for producing hydrogen to be used in fuel cells, as it simultaneously allows a good recovery of energy and some valuable by-products, satisfying the need of environmental protection. To this purpose, research on economical feasibility of a continuous bioprocess suitable to feed phosphoric acid fuel cell (PAFC) has been undert...