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 S2- removal capacity of iron-based materials up to 17.92-fold. Iron-based materials inhibited SO42- reduction, promoted COD decomposition, and supplied alkalinity downstream. The S2- control performances were 405.14, 283.97, 107.22 and 68.59 mg S/g Fe for FeOOH, Fe2O3, Fe+C and Fe3O4, 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 SO42- reduction. Fe+C exhibited limited S2- 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 SO42- binding affinity to extracellular sulfate-binding protein, and interact with intracellular SO42- reductase through forming metal coordination bonds. These findings provided multi-level (materials-microbe-enzyme) mechanistic understanding of sulfur transformation driven by different iron species.