One-step treatment of refractory organic pollutants from landfill leachate: alternating magnetic field synergies persulfate activation and in-situ coagulation

Sequential oxidation-coagulation processes for landfill leachate (LL) treatment are hindered by high chemical consumption and operational complexity. To address this issue, we present an alternating magnetic field (AMF)-driven zero-valent iron–peroxydisulfate (PDS) system, which achieved ~90% removal of chemical oxygen demand (COD, initial concentration: 1470 mg L⁻¹) from aged LL within 120 min. Mechanistic insights into temporal coupling of oxidation and coagulation revealed that AMF could address the dilemmas of sequential processes in terms of pH and interface limitations. This could be realized by synergistically enhanced Fe²⁺/Fe³⁺ cycle based on optimized iron passivation/leaching process, and enhanced local kinetics of mass transfer and reaction. The unique iron (oxy)hydroxide flocs formed under AMF exhibited a lower Fe-O coordination number and abundant unsaturated sites, enabling over 90% removal of PO₄³⁻, CO₃²⁻ and HCO₃⁻ (300–2000 mg L⁻¹) in aged LL. Removal of inorganic anions could alleviate radical quenching during oxidation of recalcitrant dissolved organic matter (DOM). The system fragmented recalcitrant DOM into biodegradable intermediates and thus significantly improved effluent biodegradability. With an electrical energy per log order removal (EE/O) of 8.8 kWh m⁻³ for real LL treatment, this study provides a novel synergistic strategy for removal of DOM, making aged LL treatment more effective, economically efficient and sustainable.