Practical Applications of Dark Fermentation for Hydrogen Production

Among the biological processes that produce hydrogen, dark fermentation is the most developed technology with the potential to be used on an industrial scale. However, there are still several challenges in implementing the industrial application of this process. Using residual carbon sources is crucial in ensuring economic viability and reducing carbon dioxide emissions during hydrogen production by dark fermentation. For this reason, in the last two decades, efforts have been intensified to improve the yields and volumetric hydrogen production rates from residual biomass. This chapter begins with a critical analysis of the advantages and disadvantages of using organic wastes (agricultural residues, food processing industries, organic fraction of municipal solid waste, and effluents from livestock farms), indicating the suitability of each one. Section 4.2 presents the types of reactors used for hydrogen production and the advantages and challenges of each design. The reactor configuration substantially impacts the retention of hydrogen-producing microorganisms and the mass transfer. Mass transfer is vital for the transport of the substrate toward the microorganisms and for the transfer of the hydrogen produced toward the headspace of the reactors for its recovery. The control of homoacetogenesis, one of the consuming pathways of the produced hydrogen, also depends on the reactor configuration and operating conditions. Section 4.3 presents the cases that have been scaled up and the challenges involved in going from laboratory to pilot scale. Finally, Sect. 4.4 shows the combination of dark fermentation with another process. It is discussed that dark fermentation can be coupled to anaerobic digestion for methane production from residual volatile fatty acids to increase the energy conversion efficiency. The mixture of hydrogen and methane (biohythane) is suitable for stabilizing combined heat and power units, improving combustion efficiency.