Enhanced Fenton‑like treatment of real leather wastewater using sulfidated zero‑valent iron: Performance, mechanism, and phosphorus recovery.

Leather wastewater with high levels of organophosphorus compounds (OPs) and chemical oxygen demand (COD) poses serious environmental challenges. In this study, sulfidated zero‑valent iron (S‑ZVI) was employed to activate H2O2 for the treatment of real leather wastewater, with the aim of overcoming the passivation and limited reactivity of conventional ZVI in complex wastewater matrices. Compared with bare ZVI, S‑ZVI exhibited enhanced electron transfer and sustained Fe2+ release, enabling efficient generation of hydroxyl radicals (HO•). At a low iron dosage of 0.3 g/L, the S-ZVI/H2O2 system decreased TP from 4.4 to 0.4 mg/L while reducing COD from 133 to below 60 mg/L, meeting typical discharge standards for both parameters. Molecular‑level analysis confirmed that refractory organics were transformed into smaller, more oxygenated, and less aromatic molecules, while OPs underwent oxidative degradation, collectively accounting for the efficient COD removal. Mechanistic investigations further revealed that OPs were oxidatively converted to orthophosphate and subsequently incorporated into iron (hydr)oxide flocs, with inorganic phosphorus accounting for 86% of the total phosphorus. Furthermore, calcination of these phosphorus-rich flocs enabled resource recovery with a phosphorus recovery efficiency of 87.7%. This work provides a practical strategy for simultaneous pollutant elimination and resource recovery from industrial wastewater rich in organophosphorus compounds.