Optimization of Hydrogen Production by Co-culture of Clostridium beijerinckii and Rhodobacter sphaeroides Bacteria

Abstract

The biological methods of hydrogen generation have attracted a significant interest recently. In this work the hybrid system applying both dark fermentation bacteria in co-culture was tested. Objective of this work was to investigate the optimization of different parameters on coculture of Clostridium beijerinckii DSM-791 and Rhodobacter sphaeroides O.U.001. The effect of glucose concentration (1–5 g/L), temperature and initial pH (6,5–7,5) was analyzed. Moreover the influence of organic nitrogen sources were tested for their capacity to support hydrogen production (yeast extract, peptone, glutamic acid). Fermentations were conducted in batch tests with glucose as sole substrate. Hydrogen production in mixed culture was compared with pure cultures. The process was greatly affected by pH and light/dark bacteria ratio. Liquid metabolites, namely acetic and butyric acids, from the dark fermentation step were the source of organic carbon for photosynthetic bacteria. This increased the hydrogen yield in comparison to single-step dark fermentation to over 4 mol H₂/mol glucose. Obtained results showed that combination of photo and dark fermentation may increase hydrogen production and conversion efficiency of complex substrates or wastewaters.