Unravelling the enhancement of biohydrogen production via adding magnetite nanoparticles and applying electrical energy input

Magnetite nanoparticles (MNP)-caused enhancements for H₂ yield (HY) are usually justified based on oxidation-reduction potential (ORP), iron ions (Fe^+2/+3) concentration, and enzymatic activity, that is pH-dependent. However, the questions “If pH, ORP, and Fe^+2/+3 impacts are excluded, will MNP-caused HY enhancement be still present? and how electrical energy input (EEI) affects HY?” are still unanswered. Herein, control, MNP-supplemented, EEI-applied, FeCl₃-, and Na₂S-supplemented batches, referred as G1, G2, G3, G5, and G6, respectively were conducted, under fixed pH (6.0 ± 0.1). G5 and G6 targeted quantifying sole impact of Fe^+2/+3, and ORP, respectively on HY. G1, G2, G3, G5, and G6 achieved HY values of 1.10 ± 0.05, 1.66 ± 0.07, 1.38 ± 0.06, 1.18 ± 0.04, and 1.16 ± 0.05 mol H₂/mol_hexose, respectively. Neither Fe^+2/+3 release nor ORP reduction significantly affected HY. Further, Clostridium amylolyticum dominance was almost similar among G2, and G3. Metabolites flux analysis and functional genes’ prediction highlighted that G2 achieved highest hydrogenase expression and lowest homoacetogenic H₂ consumption.