New insights into the degradation of chloramphenicol and fluoroquinolone antibiotics by peroxymonosulfate activated with FeS: Performance and mechanism

SO4?- and ?OH are recognized as valid reactive species in the FeS-activated persulfate system. However, whether other reactive species are generated in this process remains unclear. In this study, a FeS-based peroxymonosulfate (PMS) (FeS/PMS) system was developed for the degradation of chloramphenicol (i.e., chloramphenicol (CAP) and thiamphenicol (TAP)) and fluoroquinolone (i.e., ciprofloxacin (CIP) and norfloxacin (NOR)) antibiotics. In addition to SO4?- and ?OH, Fe(IV) was identified as another reactive species by using methyl phenyl sulfoxide (PMSO) and methyl phenyl sulfone (PMSO2) as probe compounds. Although Fe(IV) participated in antibiotic degradation, the contribution of Fe(IV) was smaller than that of SO4?- due to its low redox potential and weak competition ability. Efficient degradation of antibiotics was achieved in the FeS/PMS system within 120 min using 6 mM PMS and 0.6 g/L FeS at initial pH of 7.0, with removal percentages of 93.5%, 98.5%, 100% and 100% for CAP, TAP, CIP and NOR, respectively. The S2- acted as an electron donor to facilitate continuous Fe(III) reduction and Fe(II) regeneration. Based on the degradation intermediates of antibiotic, the reaction pathways were proposed to involve side chain cleavage, hydroxylation, denitration, deoxygenation, decarboxylation and dehalogenation. In addition to its performance in simulated waters, the FeS/PMS system also presented effective antibiotic degradation in real surface water. This study provides new insights into the mechanism of multiple reactive species generation in the FeS-activated PMS process and extends the potential engineering applications in antibiotic degradation and in situ water quality remediation.