Photofermentative hydrogen production by immobilized photosynthetic bacteria: Current perspectives and challenges

The energy consumption in the world is substantially increasing due to the increase in human activities and the energy-requiring industrialization. For decades, fossils fuels have been used as a primary resource in the world. However, considerable fossil fuel consumption has negative impacts and outcomes on the environment. In this sense, hydrogen is regarded as a clean, versatile, and alternative fuel of the future against fossil fuel-dependent energy production. Among different hydrogen production methods, biological hydrogen production offers a more environmentally friendly pathway. Photofermentative biological hydrogen not only profits from utilizing a variety of organic substrates but also, purple non-sulfur bacteria (PNSB), mainly preferred bacteria in this method, operate under a broad range of wavelengths of the light spectrum. In order to improve this process, cell immobilization has been introduced. A number of immobilization techniques, support materials, immobilized photobioreactors were overviewed. The critical factors affecting hydrogen production in immobilized systems were also highlighted. The present work covers a review of recent advances and applications, especially in the last decade in biohydrogen production by immobilized photosynthetic bacteria through natural and synthetic routes. Furthermore, techno-economic aspects (costs, challenges, barriers, etc.) of biohydrogen were evaluated and Analytical Hierarchy Process (AHP) approach was assessed in the case of photobioreactor design. Extensive hydrodynamic, heat and mass transfer issues in addition to large and pilot-scale future studies are recommended to demonstrate the feasibility of the immobilized system.