Differential contributions of iron-based nanoparticles to dark fermentative biohydrogen production: Towards a rational selection of application

Iron-based nanoparticles can effectively enhance biohydrogen production (BHP) from dark fermentation (DF) process. In this study, the differential physicochemical-biochemical coupling enhancement effects of iron-based nanoparticles was investigated. nZVI effectively boosted the BHP yield to 1.79 mol H₂/mol substrate (0.82–1.25 mol H₂/mol substrate without nanoparticles) with in-situ construction of an electron-transfer network via Fe2+ release and transformation into Fe₃O₄/γ-FeOOH. γ-Fe₂O₃ primarily enhanced the maximum BHP rate (R_m) by 86% to 132% through partial reduction and moderate electron donation, whereas stable Fe₃O₄ mainly shortened the lag phase (λ) by 41.68% via conductivity. nZVI enriched Clostridium from 27.64% to 58.65% while suppressing Limosilactobacillus from 52.14% to 3.08%. However, γ-Fe₂O₃ and Fe₃O₄ selectively stimulating non-dominant hydrogen-producing bacteria, with a less pronounced inhibitory effect on Limosilactobacillus (37.82% and 49.95%, respectively). These findings provide a mechanistic basis for the targeted selection of nanoparticles based on the differential contributions to BHP kinetics and microbial structure during DF.