Abstract
Photo‐evolution of hydrogen from synthesis gas using Rhodospirillum rubrum was studied in batch fermentation. Culture of R. rubrum was initially grown on malate, also with various initial concentrations of acetate and synthesis gas. The synthesis gas was a mixture of H~2~, CO and CO~2~. It was found that the doubling time of bacterium on 2.5 g/l of malate, and 2.5 g/l and 6 g/l of acetate were 8.4, 31.8, and 68.6 h, respectively. The growth of R. rubrum was not significant at high concentration of acetate. The cell density of microbe was 0.3 g/l on 2.5 g/l malate for incubation period of 5 days. The cell concentrations of 1.4 and 0.41 g/l were obtained in 2.5 and 6 g/l of acetate, respectively for duration of 5 days. Inhibition of substrate was clearly observed on cell yield and hydrogen production with high concentration of acetate. Maximum hydrogen production (1.8 mmol/l) was obtained when R. rubrum was grown on 2.5 g/l of acetate. Effect of agitation rate was carried out and it was found that more hydrogen production (1.8 mmol) was achieved at 250 rpm. Mass transfer and kinetic studies were performed on 2.5 g/l of acetate. Maximum specific growth rate (m̈m) and Monod constant (KH) were obtained at 9.8 h^−1^ and 0.14 atm, respectively. No substrate inhibition occurred at CO concentration of 0.56 atm.