Coupling Fe(0) electrocoagulation with peroxymonosulfate for efficient phosphorus recovery from NTMP: Synergistic adsorption and catalysis on magnetite

The efficient decontamination and resource recovery of organophosphonate-laden wastewater remain a critical environmental challenge. In this study, a sequential “electrocoagulation-oxidation” coupled process integrating iron electrocoagulation (EC) with peroxymonosulfate (PMS) activation was developed for the degradation of nitrilotris(methylene phosphonic acid) (NTMP). The initial EC stage achieved near-complete (∼100% within 20 min) NTMP removal via adsorption, and subsequent PMS oxidation of the iron precipitates under optimal conditions (50 mA, Fe:PMS molar ratio of 3:1 transformed 53.20% of the adsorbed NTMP into orthophosphate. Notably, the sequential post-addition of PMS yielded significantly superior mineralization efficiency compared to the pre-addition strategy. Advanced solid-phase characterizations revealed that the activation mechanism is driven by in-situ generated structural Fe(II), predominantly hosted within magnetite formed under neutral initial pH. Mechanistic investigations using radical quenching and electron paramagnetic resonance (EPR) spectroscopy identified sulfate radicals (SO 4 • - ) as the dominant reactive species, with a minor contribution from Fe(IV). The oxidation proceeded primarily via surface-mediated C-P bond cleavage, resulting in the in-situ immobilization of the released orthophosphate on the iron mineral matrix. Crucially, phytotoxicity assays using perennial ryegrass confirmed that this oxidative treatment significantly reduced the ecotoxicity of the precipitates and converted the pollutants into a bioavailable phosphorus source. This work establishes the sequential EC-PMS process as a promising, sustainable strategy for the simultaneous decontamination of phosphonates and the recovery of phosphorus resources.