Biohydrogen Production: A Focus on Dark Fermentation Technology

Hydrogen is considered a promising alternative to fossil fuels due to its clean combustion and high-energy content compared to other resources (i.e., methane or ethanol). However, hydrogen is produced from fossil-energy based processes leading to considerable greenhouse gas (GHG) emissions. One of the main solutions to hasten the energy transition is to develop efficient green processes for hydrogen production. Biological-based technologies have specifically demonstrated to have the least impact on the environment due to the low energy requirements (mild temperatures and pressures) and scarce GHG emissions. Among biological processes, Dark Fermentation (DF) appears to be the most effective and feasible technology for efficient hydrogen production at an industrial scale. DF has the advantage of valorizing a wide range of carbohydrate-rich organic waste without light energy through microbial consortia. Nonetheless, this technology deserves in-depth research since it still presents limited yields and productivity that hamper its industrial development. This book chapter aims to give an overview of DF biohydrogen production, presenting the state of the art. In this sense, DF's underlying mechanisms of biohydrogen production are detailed. The influence of operational parameters was assessed focusing on optimizing biohydrogen production and favoring the growth of biohydrogen-producing bacteria. Finally, the different roles of the microbial communities participating in the DF process are unraveled.