Effects of light/dark cycle, mixing pattern and partial pressure of H2 on biohydrogen production by Rhodobacter sphaeroides ZX-5

Abstract The effects of light/dark cycle, mixing pattern and partial pressure of H 2 on the growth and hydrogen production of Rhodobacter sphaeroides ZX-5 were investigated. The results from light/dark cycle culture showed that little or no hydrogen production was observed during the dark periods, and the hydrogen production immediately recovered once illumination was resumed. Also, it was found that the optimum condition of shaking velocity was 120 rpm for hydrogen photo-fermentation. Meanwhile, shaking during H 2 production phase (i.e., cell growth stationary phase) of photo-fermentation played a crucial role on effectively enhancing the phototrophic hydrogen production, rather than that during cell exponential growth phase. The other factor evaluated was hydrogen partial pressure in the culture system. The substrate conversion efficiency increased from 86.07% to 95.56% along with the decrease of the total pressure in the photobioreactor from 1.082 × 10 5 to 0.944 × 10 5  Pa, which indicated that reduction of H 2 partial pressure by lowering the operating pressure substantially improved H 2 production in an anaerobic, photo-fermentation process.