Manganese ferrite nanoparticles enhanced biohydrogen production from mesophilic and thermophilic dark fermentation

In this work, Manganese ferrite nanoparticles (MnFe 2O4 NPs) were synthesized, and their potential to increase the biohydrogen (bio-H2) yield of glucose in mesophilic and thermophilic fermentations was evaluated. Material characterization showed that the MnFe 2O4 NPs were perfectly synthesized, with a specific surface area of 43.97 m2g−1. Both mesophilic and thermophilic fermentation obtained the highest bio-H2 yields of 272.7 and 183.4 mL H2/g glucose in the 400 mg/L MnFe 2O4 NPs group, which values were increased by 40.1% and 131.9% (37 °C and 55 °C), respectively, compared to their control groups. Soluble microbial products (SMPs) showed that MnFe 2O4 NPs enhanced the butyrate pathway. Three-dimensional fluorescence spectroscopy analysis showed that MnFe 2O4 NPs increased the extracellular polymer content of anaerobic sludge. The results showed that MnFe 2O4 NPs distinctly increased the abundance of Clostridium_sensu_stricto 1 (39.49%) in the microbial community during mesophilic fermentation and improved the abundance of the dominant bacteria Clostridium_sensu_stricto_7 (25.59%) and Longlinea (21.36%) during thermophilic fermentation. Real-time PCR analysis showed that hydrogenase gene (hycl) expression increased exponentially after the addition of MnFe 2O4 NPs, and increasing the fermentation temperature improved the hydrogenase activity. We found that MnFe 2O4 NPs promoted to bio-H2 production in both mesophilic and thermophilic fermentation, and it contributed more significantly to thermophilic fermentation than mesophilic fermentation