Photofermentative hydrogen production using purple non-sulfur bacteria Rhodobacter sphaeroides O.U.001 in an annular photobioreactor: A case study

For meeting the increasing demand of energy, biohydrogen production is to be considered in higher yield. Biohydrogen can be produced both by dark and photofermentative process. In this study, the photofermentative pathway is followed by using dl malic acid (IUPAC name: 2-hydroxybutanedioic acid, molecular weight: 134.08744 g mol−1, molecular formula: C4H6O5) as carbon source. Pure strain of purple non-sulfur (PNS) bacteria: Rhodobacter sphaeroides strain O.U.001 was studied to produce biohydrogen using the photobioreactor. The photobioreactor was constructed aiming the uniform light distribution. The objective of this study was to investigate the performance of 1 L annular photobioreactor operating in indoor conditions. The highest rate of hydrogen production was obtained at 92 h. In the designed photobioreactor, using Rhodobacter sphaeroides strain O.U.001 (initial dl malic acid concentration of 2.01 g L−1) at an initial pH of 6.8 ± 0.2, temperature 32 ± 2 °C, inoculum volume 10% (v/v), inoculum age of 48 h, 250 rpm (rotation per minute) stirring and light intensity of 15 ± 1.1 W m−2, the average H2 production rate was about 6.5 ± 0.1 mL H2 h−1 L−1 media and yield 4.5 ± 0.05 mol of H2 mol−1 of dl malic acid. Luedeking–Piret model was applied for the data fitting to determine the relationship between the cell growth and photofermentative hydrogen production. The photofermentative hydrogen production by this PNS bacterium was found to be microbial mixed growth associated function.