Biohydrogen production by dark fermentation: scaling-up and technologies integration for a sustainable system

Currently, the use of alternative renewable energies is broadly supported in many countries, some of which are seriously evaluating the possibility of using hydrogen as an alternative fuel in their power systems. Hydrogen production by biological processes, such as dark fermentation, is a very promising alternative. However, this process has only been studied on the laboratory scale, and there is limited experience at the pilot scale. The main reasons of non-scaling hydrogen production by dark fermentation at large scale are unpurified hydrogen production, stability of the bioprocesses, as well as their low conversion yields joined at the formation of byproducts. Improvement of energetic yields of dark fermentation requires a better knowledge of the microorganisms involved in the mixed culture and their possible interactions, as well as the use of appropriate substrates and strategies, such as solid-state fermentation, the purification of hydrogen and the coupling of dark fermentation with other biological processes as anaerobic digestion. The present work offers an overview of the current knowledge dealing with H₂-production by dark fermentation and its integration into a concept of an environmental biorefinery. Several key points are addressed, such as the benefits of using local waste as substrates, the new solid-state fermentation processes, the coupling of hydrogen purification with the production process, the association of the H₂-producing process with other biological processes, such as anaerobic digestion towards biohythane production (H₂/CH₄). Information about pilot plant experiments was added to illustrate the feasibility of producing fermentative hydrogen and methane from organic waste at a pilot scale, as developed at Feng Chia University (Taiwan).