Degradation of ciprofloxacin in sludge by peroxymonosulfate activated by CoFe2O4: Performance, degradation pathways and mechanism

Ciprofloxacin (CIP) is a bio-refractory contaminant in waste activated sludge. This study successfully fabricated CoFe₂O₄ magnetic nanoparticles (CoFe₂O₄ MNPs) as peroxymonosulfate (PMS) activators for CIP degradation. The effects of experimental parameters (PMS and catalyst dosage, pH, and initial CIP concentration) on degradation were thoroughly examined. Results showed that under optimal conditions, 88.3 % of CIP was degraded by CoFe₂O₄ MNPs activating PMS. Radical quenching experiments identified SO₄·^-, ·OH, and ·O₂^- as the key radicals in CIP degradation. Crucially, CIP degradation in the sludge system was closely associated with sludge floc disruption and cell lysis, leading to CIP release from the solid to the liquid phase—a process distinct from degradation in the liquid phase alone. Thermodynamic analysis confirmed that the enhanced hydrophilicity of sludge promoted this release. The study also deduced CIP degradation pathways and evaluated the toxicity of intermediates. CoFe₂O₄ MNPs demonstrated stability and reusability, efficiently degrading CIP over four cycles with minimal Co and Fe ion leaching. These findings support the potential application of the CoFe₂O₄/PMS system for degrading other antibiotics in excess sludge.