The zero-valent iron mediated anaerobic phosphate reduction system drives the recovery of dual products from phosphorus-enriched sludge

Abstract

This study developed a zero-valent iron (ZVI) mediated anaerobic phosphate reduction system that innovatively recovers resources from phosphorus-rich sludge by coupling phosphine (PH₃) generation with vivianite crystallization. The system overcomes the low recovery efficiency and limited product diversity of traditional methods by enabling multiphase transformation of elemental phosphorus. This was achieved by optimizing the ZVI-driven carbon and phosphorus metabolic network (influent COD 3000 mg/L, TP 50 mg/L). Cumulative PH₃ production reached 46.15 mg/L, vivianite yield was 810 mg, and the iron utilization rate increased to 58 %. Microbiome analysis revealed multi-level regulatory effects of ZVI on microbial community. At the phylum level, Bacteroidetes (+8.1 %) promoted ZVI corrosion; Spirochaetes (+7.44 %) facilitated electron transfer network formation; Caldiserica (+9.3 %) and Actinobacteria (+2.7 %) synergistically catalyze phosphate reduction and enhance PO₄³⁻ availability. At the genus level, Atopobium (+7 %) promoted organophosphorus mineralization; Caldisericum (+8 %) and Prevotellaceae (+8.67 %) activated phosphorus-reducing bacteria via H₂ oxidation and fatty acid metabolism; Megasphaera (+4.33 %) regulated pH to optimize Fe²⁺–PO₄^3- co-precipitation, creating a “phosphorus release-reduction-fixation” microenvironment. Thermodynamic analysis confirmed that the strong reducing capacity of ZVI drives the coupled pathways of vivianite precipitation (Δ_rG_m^θ = −397.78 kJ/mol) and PH₃ biosynthesis (Δ_rG_m^θ = −110.82 kJ/mol). Through chemical–biological synergy, this study proposes a novel strategy for the efficient and sustainable utilization of phosphorus-rich sludge.