Biogenic sulfidation regenerates Fe-S interfaces on waste iron sludge for sequential reductive-oxidative degradation...

Iron-based peroxymonosulfate (PMS) activation is often constrained by sluggish Fe(III)/Fe(II) cycling, inefficient interfacial electron transfer, and the limited environmental relevance of chemically sulfidated catalysts. Here, iron sludge (Fh) was regenerated through biogenic sulfidation (BS-Fh) to enhance degradation of chloramphenicol (CAP). The BS-Fh-PMS system exhibited a sequential reduction-oxidation process, in which CAP was first reductively transformed by biogenically generated Fe-S reactive interfaces and then further degraded after PMS addition. The secondary biogenically sulfidated Fh showed the highest overall performance, achieving 91.4% CAP removal, compared with 84.0% for the primary biogenically sulfidated Fh due to the increased abundance of surface Fe(II)-S species, improved interfacial electron transfer, and facilitated Fe(III)/Fe(II) cycling. Quenching and electron spin resonance spectroscopy suggested a dominant contribution of •OH-associated radical oxidation to CAP degradation. Intermediate identification and toxicity prediction suggested that CAP underwent stepwise reductive and oxidative transformation, with most products showing relatively low predicted ecological risks. A comparative life cycle assessment further indicated that the BS-Fh-PMS system required lower chemical inputs and imposed lower environmental burdens than the chemically sulfidated system. These findings suggest that biogenic sulfidation can regulate Fe-S interfacial reactivity and provide an environmentally relevant strategy for improving iron-based PMS activation for antibiotic degradation.