Degradation of phenanthrene in aqueous solution by a persulfate/percarbonate system activated with CA chelated-Fe(II)

A persulfate/percarbonate (PS/SPC) system activated with citric acid (CA) chelated-Fe(II), which combined the benefits of sole PS and SPC systems, was conducted for phenanthrene (PHE) degradation in aqueous solution. The effects of oxidant concentration, Fe(II)-CA dosage, PS/SPC molar ratio and initial solution pH were investigated in the laboratory. The results indicated that the addition of CA could remarkably enhance PHE removal, and PHE could be degraded completely at 0.5 mM PS, 0.5 mM SPC and 0.5 mM Fe(II) with 0.1 mM CA in 60 min. PHE oxidation process was more efficient in acidic condition, which presented a two-stage degradation pattern and PHE removal followed a pseudo-first-order kinetic model in the second stage. The results of free radical probe tests, scavenging tests and EPR analysis demonstrated that center dot OH was the predominant radical for PHE oxidation. The major degradation intermediates of PHE were identified by LC-MS, and the possible reaction mechanism and PHE degradation pathways were proposed.