ABSTRACT

This chapter summarizes the state of the art of photofermentation (PF) processes for hydrogen (H2) production by overviewing existing understanding of the microbiology of PF process, different photobioreactor (PBR) designs, conversion efficiencies of different purple nonsulfur bacteria (PNSB) strains, and process operational parameters such as pH, temperature, and nutrient requirements. PNSB are gram-negative photoheterotrophs, which normally carry out photosynthesis under anaerobic conditions. PNSB accumulates poly-β-hydroxybutyrate (PHB), an intracellular storage of carbon and energy formed under physiological stress, particularly at high carbon-to-nitrogen (C/N) ratios, higher ammonia concentrations, or sulfur-deprived conditions. The selection of inoculum culture age can be critical to obtain a higher performance of PF systems. It has been found that the PNSB inoculum from the exponential phase of growth curve is suitable for better performance of PBRs for biohydrogen production. The organic loading rate (OLR) and the hydraulic retention time (HRT) strongly affect the performance of PBRs as they determine the substrate degradation efficiency and the hydrogen production rate.