The amount of accumulated hydrogen achieved 1.01 mol of H2 in 746 h of photo-fermentation by R. capsulatus (Fig. 3a). As it may be observed in Fig. 3b, the maximum productivity of 208.40 mmol H2/L d was verified in 52 h. Thereafter, this parameter decreased and after 265 h it decayed gradually and varied with 44 and 60 mmol H2/L d. By concerning on the specific productivity, the highest magnitude 121.82 mmol H2/gvs d, and decreased following the same tendency observed in volumetric productivity, since the biomass growth was gradual during the assay. With respect to the cell growth, there was an increment from 0.53 gvs/L to 2.5 gvs/L of the biomass concentration in 424 h. After that, it was constant until the end of the process. The production of biogas attained 8.27 L in 787 h.