Unveiling the role of sludge flocs interfacial behaviors in enhancing water leakage and simultaneous attenuation of multi-pollutants (PFOA & ARGs) by electro- Fe2+-activated persulfate oxidation.

Abstract

The efficient dewatering and the deep removal of obstinate emerging contaminants (e.g., perfluorooctanoic acid (PFOA) and antibiotic resistance genes (ARGs) remain critical bottlenecks in current sludge management. Persulfate advanced oxidation processes (PS-AOPs) offer great potential in sludge conditioning and pollutant mineralization, however their efficacy strongly hinges on water-organics binding capacity, solid-liquid interface reactivity, radical generation routes, and iron cycling rate. In this study, a pair of high specific-surface helix-leaf electrodes (a total of 5481.8 mm² ) was designed and integrated into Fe²⁺-activated persulfate oxidation processes to drive Fe²⁺ re-generation and highly active radicals formation. Under the optimal operational conditions of 30 V and 2/1.6 mmol Fe²⁺-S₂O₈^2-/g-VS, the sludge achieved an 87 % decrease in capillary suction time (CST) and low moisture content of 52.2 % after pressure filtration. More importantly, such hybrid option produced a 91.03 % degradation of PFOA from total EPS and an exponential elimination (above 90 %) of ARGs. Mechanistically, the electro-Fe²⁺-activated persulfate oxidation encouraged the continuous production of highly active radicals (·OH, SO₄·⁻, ¹O₂, and ·O₂⁻) via ensuring efficient Fe³⁺/Fe²⁺ cycling driven by a robust electro-reduced circumstance. These radicals catalyzed the degradation of extracellular polymeric substances (EPS) and microbial cell rupture, notably reconfiguring protein secondary structures-characterized by the reduction of stable α-helix and β-sheet proportions to 17.79 % and 14.44 %, respectively. This profound structural transformation disrupted the hydrophilic gel matrix, thereby significantly enhancing sludge dewaterability. Concurrently, PFOA was destructed via direct free radical attacks on its molecular structure, while ARGs were eliminated primarily through the unwinding and subsequent cleavage of DNA strands. The research results will provide theoretical support and technical paradigms for the "reduction and emerging pollutant control" of sludge, and promote the green and low-carbon transformation in the field of waste treatment.