UCLA

This study reports a factor 5.5 increase in hydrogen production of Anabaena variabilis ATCC 29413 using Allen-Arnon medium compared with BG-11 and BG-11o media. The results were obtained with a flat panel photobioreactor made of acrylic and operated in two stages at 30oC. Stage 1 aims at converting carbon dioxide into biomass by photosynthesis while Stage 2 aims at producing hydrogen. During Stage 1, the photobioreactor is irradiated with 65 umol/m2/s of light and sparged with a mixture of air and carbon dioxide. During Stage 2, irradiance is increased to 150 umol/m2/s and the photobioreactor is sparged with pure argon. The parameters continuously monitored are (1) the cyanobacteria concentration, (2) the pH, (3) the dissolved oxygen concentration, (4) the nitrate and (5) the ammonia concentrations in the medium, and (6) the hydrogen concentration in the effluent gas. The three media BG-11, BG-11o, and Allen-Arnon are tested under otherwise similar conditions. The light to biomass energy conversion efficiency varied between 5.5 and 10.5% and was similar for all media. The cyanobacteria concentrations during Stage 2 were 1.10 and 1.17 kg dry cell/m3 with BG-11 and Allen-Arnon media, respectively, while it could not exceed 0.76 kg dry cell/m3 with medium BG-11o. The average specific hydrogen production rates were about 1 and 0.9 L/kg dry cell/h in media BG-11 and BG-11o, respectively. In contrast, it was about 5.6 L/kg dry cell/h in Allen-Arnon medium. The maximum light to hydrogen energy conversion efficiencies achieved were 0.26%, 0.16%, and 1.32% for BG-11, BG-11o, and Allen-Arnon media, respectively. The larger specific hydrogen production rates, efficiencies, and cyanobacteria concentrations achieved using Allen-Arnon medium are attributed to the presence of vanadium, and higher concentrations of molybdenum, magnesium, calcium, sodium, and potassium in the medium.