Microbes and Parameters Influencing Dark Fermentation for Hydrogen Production

Dark fermentation is a promising method for hydrogen (H2) production utilizing the metabolic pathways of diverse microbial communities. This process can be carried out without the need for light, making it easier and more efficient to operate in different environments and at a lower cost. It also utilizes a wide range of substrates, making it highly adaptable to waste-to-energy applications. Clostridium spp. are particularly favored in this method due to their versatile metabolism, ability to utilize a wide range of substrates, and high H2 yields. Anaerobes and facultative anaerobes are mostly used in studies due to their efficient hydrogenase enzyme activity and metabolic pathways. A pH range of 5.5–6.5 and a temperature of 30–37 °C for mesophiles and 55–60 °C for thermophiles are usually preferred in addition to the other parameters such as hydraulic retention time and substrate used. The highest H2 yield of 9.39 mol H2/mol sucrose consumed was obtained by C. beijerinckii using sucrose as a substrate under batch mode conditions at 37 °C and pH 6–7. The review analyzes different bacterial species and examines the influence of optimized parameters required on H2 yield in different bioreactor operating modes.