The degradation of chloramphenicol by O3/PMS and the impact of O3-based AOPs pre-oxidation on dichloroacetamide generation in post-chlorination

Abstract

The frequent detection of chloramphenicol (CAP) in wastewater and surface water gives rise to concerns on its fatal myelosuppression and aplastic anemia. Recently, the combination of ozone and peroxymonosulfate (O3/PMS) has received wide attention in removing pollutants due to the multiple oxidants (i.e., O3, hydroxyl radicals (OH) and sulfate radicals (SO4−)) existed therein. This study showed that O3/PMS could effectively degrade CAP under various conditions. The second-order rate constant of CAP with O3, OH and SO4− was 0.291±0.005, 2.27(±0.03)×109 and 1.02±0.02×108M-1s-1, respectively. The degradation efficiency of CAP was significantly enhanced as PMS concentration or pH increased. Bicarbonate (HCO3−) at concentration of 5 mM slightly inhibited CAP degradation at pH 7. Chloride (Cl−) at concentration of 0.5 mM enhanced CAP removal at pH 7, while this enhancement gradually weakened as Cl− concentration further increased. The degradation efficiency of CAP first increased with increasing natural organic matter (NOM) concentrations (0.1–0.3 mg/L), while it was completely suppressed at higher NOM concentrations (0.5 mg/L). Four degradation products in total of CAP were identified in O3-based processes (i.e., O3, O3/TBA, O3/H2O2, O3/PMS and O3/PMS/tert-butyl alcohol (TBA) systems. Besides, these transformation products by OH, SO4− and/or O3 were also distinguished. Finally, the impact of O3/PMS pre-oxidation on the formation of dichloroacetamide (DCAcAm) from CAP during post-chlorination process was investigated. Compared with the traditional O3 and O3/H2O2 processes, O3/PMS pre-oxidation generally led to the least generation of DCAcAm under similar conditions, where SO4− rather than OH was conducive to relieve the formation of DCAcAm. Moreover, the presence of NOM obviously alleviated the formation of DCAcAm by O3/PMS pre-oxidation.