Current challenges in nano-engineered biomass valorization: A comprehensive review from the whole procedure of biomass fermentation perspective

Dark fermentation has been widely regarded and appraised as an efficient and green route for biohydrogen production. Lignocellulosic biomass is a readily available and abundant feedstock that could be used as a sustainable feedstock for biohydrogen generation. However, low yield of biohydrogen is an inherent issue of the bioprocess restricting its further development towards commercial margins. Recently, the supplement of nano-additives has aroused more attention as a process improvement strategy because of their ability to accelerate process performance and their strengths of low energy consumption and easy operation. Nevertheless, the utilization of nanomaterials for biomass fermentation is still in its infancy. Here we review and evaluate the feasibility of nanotechnology in each procedure of biomass to biohydrogen to improve the economic feasibility of the process. Numerous aspects such as the possibility of utilizing nanomaterials as an alternative to chemical pretreatment techniques have been highlighted in this review. Additionally, the effect of these nanostructured materials (e.g., metal-based nanoparticles, nanocomposites, and graphene-based nanomaterials) on biohydrogen fermentation and the potential functional mechanisms were also analyzed in detail. Moreover, the assessment on how the immobilized nanoparticles affect enzymatic efficiency and how well they can block inhibitory chemicals were elaborated. Further, the sustainability of biomass fermentation was assessed in terms of science economics as well as carbon neutrality to improve the overall benefits of the process. Finally, the review suggests ways in which the nano-engineered bioprocesses might be improved, as well as suggested avenues for further research.