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

Biomass and pigments production in photosynthetic bacteria wastewater treatment: Effects of photoperiod

“…Similar results were also reported in microalgae culturing; the microalgae biomass under intermittent illumination was higher than under continuous illumination (Janssen et al, 2000;Liao et al, 2014;Xue et al, 2011). Nevertheless, Li et al (2011) reported an opposite point view that exposure of R. sphaeroides ZX-5 to light/dark cycles decreased the bacterial biomass production compared to continuous illumination. Obviously, a proper light/dark cycle was important for both PSB and microalgae.…”

Photofermentative Hydrogen Production in Outdoor Conditions

“…Under continuous illumination, maximum hydrogen production rate and substrate conversion efficiency of 92.41 ml H2/L/h and 90.54% were obtained respectively. These values decreased to 89.96 ml H2/L/h and 85.35% under 12-h light/12-h dark cycle and 86.91 ml H2/L/h and 80.97% under 12-h dark/12-h light cycle, respectively [40]. Similar results were reported by Uyar et al [62], who found that the average hydrogen production rate and the total hydrogen produced by R. sphaeroides cells exposed to light/dark cycles were lower compared to the continuously illuminated cultures.…”

“…Recirculation of the evolved gas has been proposed [34], however, the PNSB have hydrogenase enzyme that can breakdown the produced hydrogen to protons and electrons, thus reducing the amount of gas produced. Moreover, reduction of hydrogen partial pressure by decreasing total gas pressure in the PBR headspace was shown to improve hydrogen production [40].…”

“…Sunlight intensity of over 1.0 kW/m 2 was found to be deterrent to hydrogen production [69]. Studies on light/dark cycle have demonstrated that little or no hydrogen was produced during the dark periods but bacteria survived and hydrogen production recovered once illumination resumed [4,40].…”

“…The experiment was carried out in a 400 ml water jacketed-glass column PBR using a combined system of H. salinarum packed cells with R. sphaeroides O.U.001 cells [42]. Shaking during the stationary phase of cell growth was shown to enhance hydrogen production more rather than mixing during growth (exponential) phase [40].However, vigorous mixing at high circulation rates may lead to cell damage and incur higher running costs. The use of mechanical agitators was depicted to be not suitable for mixing cultures in flat plate PBRs as their light path is short (narrow width).…”