Comparison of mesophilic and thermophilic dark fermentation with nickel ferrite nanoparticles supplementation for biohydrogen production.

In this work, nickel ferrite nanoparticles (NiFeO NPs) was prepared to improve hydrogen (H) production by dark fermentation. Moderate amounts (50-200 mg/L) promoted H generation, while excess NiFeO NPs (over 400 mg/L) lowered H productivity. The highest H yields of 222 and 130 mL/g glucose were obtained in the 100 mg/L (37 °C) and 200 mg/L NiFeO NPs (55 °C) groups, respectively, and the values were 38.6% and 28.3% higher than those in the control groups (37 °C and 55 °C). Soluble metabolites showed that NiFeO NPs enhanced the butyrate pathway, corresponding to the increased abundance of Clostridium butyricum in mesophilic fermentation. The endocytosis of NiFeO NPs indicated that the released iron and nickel favored ferredoxin and hydrogenase synthesis and activity and that NiFeO NPs could act as carriers in intracellular electron transfer. The NPs also optimized microbial community structure and increased the levels of extracellular polymeric substances, leading to increased H production.