Improved biohydrogen evolution through calcium ferrite nanoparticles assisted dark fermentation.

Dark fermentation (DF) is a green hydrogen (H2) production process, but it is far below the theoretical H2 yield. In this study, calcium ferrite nanoparticles (CaFe2O4 NPs) were produced to augment H2 yield via DF. The highest H2 yield of 250.1 ± 6.5 mL/g glucose was achieved at 100 mg/L CaFe2O4 NPs. Furtherincreasein CaFe2O4 NPs above 100 mg/L, such as 600 mg/L, would slightly lower H2 yield to 208.6 ± 2.6 mL/g glucose. The CaFe2O4 NPs in DF system released calcium and iron ions, promoting granular sludge formation andDF microbial activity. Soluble metabolites revealed that butyric acid was raised by CaFe2O4 NPs, which indicated the improved metabolic pathway for more H2. Microbial structure composition further illustrated that CaFe2O4 NPs could increase the abundance of dominant microbial populations, with the supremacy of Firmicutes up to 71.22 % in the bioH2 evolution group augmented with 100 mg/L CaFe2O4 NPs.