Bioprocesses Coupling for Biohydrogen Production: Applications and Challenges

The decarbonisation of industry based on the sustainable use of resources is one of the main objectives of our current society. To achieve this, rich-carbohydrate residual streams constitute a cost-effective feedstock from which hydrogen can be produced via dark fermentation (DF). In recent years, bench-scale testing has delivered encouraging results. Nonetheless, the low hydrogen productivity obtained still prevents the upscaling of this technology. A possible solution to overcome this technical barrier might be to couple DF with other available bioprocesses. The resulting coupling would enhance substrate exploitation and increase hydrogen productivity. The biohydrogen produced could be used either as an energetic vector or as a platform molecule for added-value compound production. This chapter aims to comprehensively review the existing bioprocesses under investigation coupled with DF as a pivotal technology for biohydrogen production. More specifically, technologies such as microbial electrolysis cells, microalgae cultivation, biomethanation, photofermentation, and lactate production are evaluated. Aspects such as the optimal operational conditions that favour the coupling in each case and the hydrogen yields obtained, are reported. Furthermore, the advantages and disadvantages of the process couplings are also discussed. Finally, current challenges and future perspectives that each hydrogen production platform entails are pointed out to set the way forward in the coming years.