Enhancing phototropic hydrogen production by solid-carrier assisted fermentation and internal optical-fiber illumination

Three strategies were applied to promote the phototrphic H2 production of an indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 using acetate as the sole carbon substrate. First, a small amount of solid carriers (e.g., activated carbon, silica gel, and clay) was supplemented to fermentation broth to stimulate cell growth and H2 production. Second, the acetate concentration leading to optimal production of H2 was identified. Finally, an innovative optical-fiber illuminating system was designed to facilitate the efficiency of the photobioreactor. The results show that addition of clay and silica gel was effective in promoting H2 production, resulting in 67.2–50.9% and 37.2–32.5% increases in H2 production rate (vH2vH2) and H2 yield (YH2YH2), respectively. For clay-supplemented batch cultures, the optimal acetate concentration was 1000 mg COD/l, leading to a vH2vH2 and YH2YH2 value of 28.5 ml/h/l and 2.97 mol H2/mol acetate, respectively. Moreover, combination of internal optical-fiber illumination system, clay addition, and optimal acetate concentration further elevated the vH2vH2 and YH2YH2 to a maximum level of 43.8 ml/h/l and 3.63 mol H2/mol acetate, respectively. These values are considerably higher than most reported results from relevant studies. Meanwhile, the results of continuous cultures operated at 36 h HRT (hydraulic retention time) show that the high phototrophic H2 production efficiency was stably maintained for over 17 days with a steady-state vH2vH2 and YH2YH2 of 44.0 ml/h/l and 3.57 mol H2/mol acetate, respectively.