Degradation of chloramphenicol by thermally activated persulfate in aqueous solution

The feasibility of using thermally activated persulfate (TAP) to degrade chloramphenicol (CAP) in aqueous solution was evaluated. Results showed that CAP degradation followed a pseudo-first-order model under all conditions tested and the observed rate constants well fitted the Arrhenius equation. CAP degradation rate constants (k_obs) increased with increased temperature and sodium persulfate (SPS) dosage. A lower pH resulted in a greater increase in CAP degradation and the highest degradation efficiency was obtained at pH 2.96. Scavenging tests suggested that sulfate radicals (SO4-) predominated under acidic conditions, whereas hydroxyl radicals (HO) gradually predominated under alkaline conditions. Coexisting Cl^- ions slightly enhanced decomposition at an appropriate concentration ([Cl^-]₀/[SPS]₀=1:1) but inhibited degradation at other levels. The effects of NO3-,H2PO4- and HPO42- on CAP degradation were negligible, whereas NO2-, HCO3-, and HA significantly inhibited CAP decomposition. The highest degradation rate was achieved with a single SPS injection. Considering that CAP oxidation in the multi-phases of wastewater matrices by TAP presented slower kinetics, 62.2-96.3% removal efficiencies were achieved within 160min. The TOC removal ratios after 160min TAP oxidation increased from 10.7% to 90.1% as the [SPS]₀/[CAP]₀ increased from 1:1 to 80:1, respectively. Overall, eleven intermediate products during TAP oxidation were identified, and a primary reaction mechanism was proposed.