Effect of iron-based materials on sulfide control in sewer systems

H₂S causes severe corrosion damage to infrastructure and concrete structures in sewers. In this study, FeOOH, Fe₃O₄, Fe₂O₃ and Fe+C were proposed to control H₂S, and the effects of iron species on sulfur metabolizing bacteria, related genes and enzymes were investigated in sewers. The results showed microbes in sewers enhanced S^2- removal capacity of iron-based materials up to 17.92-fold. Iron-based materials inhibited SO₄^2- reduction, promoted COD decomposition, and supplied alkalinity downstream. The S^2- control performances were 405.14, 283.97, 107.22 and 68.59 mg S/g Fe for FeOOH, Fe₂O₃, Fe+C and Fe₃O_4, respectively. FeOOH maintained zero H₂S(g) emission for 10 days and exhibited the highest FeS formation (383.27 mg S/g Fe), attributed to its readily disrupted crystal structure and abundant iron-reducing bacteria (Magnetospirillum and Aeromonas). Fe₂O₃ enhanced direct interspecies electron transfer (DIET) activity, which redirected electrons away from SO₄^2- reduction. Fe+C exhibited limited S^2- control efficiency due to restricted DIET and low chemical oxidation rate in sewers. Simulation results predicted that bio-reduced Fe²⁺ ions from iron-based materials might reduce SO₄^2- binding affinity to extracellular sulfate-binding protein, and interact with intracellular SO₄^2- reductase through forming metal coordination bonds. These findings provided multi-level (materials-microbe-enzyme) mechanistic understanding of sulfur transformation driven by different iron species.