Fe³⁺-sulfite complexation enhanced persulfate Fenton-like process for antibiotic degradation based on response...

To improve the cycle between Fe³⁺ and Fe²⁺ in persulfate (PS) Fenton-like system, sulfite (Na₂SO₃) was used as the iron complexing agent to enhance the degradation of sulfamethoxazole (SMX) antibiotic in water. Response surface methodology (RSM) was applied to regulate the operation parameters for the Fe³⁺/Na₂SO₃/PS synergistic system. Based on the RSM, the SMX could be completely degraded when the concentration of Fe³⁺, Na₂SO₃, and PS were 0.4, 0.5, and 2.5 mM, respectively. The result showed that the synergistic process represented a high Fe³⁺ utilization rate and SMX degradation efficiency. After 1 h reaction, 100.00% of SMX and 27.80% of total organic carbon were removed under the ambient conditions containing the initial SMX concentration of 10 μM and initial pH of 5.96. Free radical masking and electron spin-resonance tests proved that hydroxyl radical (HO) and oxysulfur radicals (SO_x^-, x = 3, 4, 5) were all played the significant role in the antibiotic removal, and the primary active radical was HO. The SMX decomposition pathways based on the formed intermediates was proposed through the high-performance liquid chromatography and mass spectrum analyses. The toxicity assessment prediction indicated that the toxicities of decomposed SMX byproducts were reduced after the coupling treatment.