Biohydrogen production by immobilized purple nonsulfur bacteria

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2018
Sağır, Emrah
Biological hydrogen production by purple non-sulfur bacteria is an attractive route to build a large scale hydrogen production system in outdoor natural conditions from various renewable sources. In this study, biological hydrogen production was carried out by agar immobilized purple non-sulfur bacteria in indoor and outdoor conditions. A novel photobioreactor (1.4 L volume) was built and operated continuously for 20 to 64 days in sequential batch mode for long-term hydrogen production using agar-immobilized Rhodobacter capsulatus YO3. The immobilized panel photobioreactor was also operated under natural outdoor conditions to show the feasibility of hydrogen production on a pre-pilot scale. The experiments were carried out in Middle East Technical University, Ankara, Turkey between May and June, 2016. The effects of initial sucrose concentration on hydrogen production, productivity and yield were examined in a long-term operation. Long-term hydrogen production was realized either on sucrose or sugar beet molasses by agar (4% w/v) immobilized Rhodobacter capsulatus YO3. The highest hydrogen yield and hydrogen productivity obtained were 19 mol H2/mol sucrose and 0.73 mmol H2 L-1h-1 in indoors on 5 mM initial sucrose. The effects of higher initial sucrose concentration on hydrogen production were also investigated. The highest hydrogen yield and productivity were 6.1 ± 0.2 mol H2/mol sucrose and 0.87 ± 0.06 mmol H2 L-1h-1, respectively on 10 mM sucrose. The highest hydrogen yield (9.1mol H2/mol sucrose) and productivity (0.64 mmol H2 L-1h-1) were obtained by using sugar beet molasses in indoor conditions. The highest productivity of 0.79±0.04 mmol H2 L-1 h-1 and yield of 5.2±0.4 mol H2/mol sucrose were obtained in outdoors. The present study demonstrated that the immobilized system is feasible for long-term hydrogen production even under varying temperature and illumination. The immobilized system also prevented sudden pH drops by sucrose utilization during the process. Hydrogen production from glucose was carried out as the last part of the study, which was carried out in University of Montreal, Canada. For this purpose, microaerobic dark fermentation was employed to demonstrate and enhance hydrogen production from glucose. Therefore, immobilized cultures of R. capsulatus JP91 and R. palustris CGA009 have been used in single and sequential dark and photofermentative processes. Response surface methodology with the Box-Behnken design was employed to optimize the key parameters such as glucose, inoculum and oxygen concentrations. The highest hydrogen yield and productivity obtained were 7.8 mol H2/mol glucose and 0.15 mmol H2 L-1h-1, respectively by R. capsulatus JP91. These results indicated that biohydrogen production by immobilized purple non-sulfur bacteria is promising particularly for large-scale outdoor natural conditions.

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Citation Formats
E. Sağır, “Biohydrogen production by immobilized purple nonsulfur bacteria,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.