Degradation of sulfachloropyridazine by UV-C/persulfate: kinetics, key factors, degradation pathway

Abstract

Antibiotics are frequently detected in water, which can pose a great threat to human health. In this paper, an ultraviolet/persulfate (UV-C/PS) advanced oxidation process was utilized to remove a common antibiotic sulfachloropyridazine (SCP) efficiently from groundwater. The degradation mechanism and kinetics were investigated by researching several key influencing factors, including two radical scavengers (tert-butanol and methyl alcohol), dosages of PS, initial pH, anions (H₂PO₄⁻, HPO₄²⁻, Cl⁻, HCO₃⁻ and NO₃⁻) and natural organic matter. The degradation of SCP followed a pseudo-first-order kinetic model and better degradation was achieved in acidic conditions than in alkaline conditions. The effect of scavengers indicated that both SO₄⁻˙ and HO˙ contributed to the degradation of SCP and SO₄⁻˙ played a major role. The degradation rate constants of SCP with SO₄⁻˙ and HO˙ at the initial pH of 6.3 were calculated to be k_SCP,HO˙ = 0.867 × 10⁹ M⁻¹ s⁻¹ and k_SCP,SO4⁻˙ = 3.073 × 10⁹ M⁻¹ s⁻¹ in the UV-C/PS system by the relative rate method. Increasing the concentration of PS obviously facilitated the degradation and mineralization rates of SCP, which could reach 100% and 90%, respectively, at a PS dosage of 4.0 mM after 2 h. Also, H₂PO₄⁻ and Cl⁻ promoted the degradation of SCP, whereas the removal of SCP was restrained by the addition of HPO₄²⁻, HCO₃⁻ and large dosages of NO₃⁻. The proposed degradation pathway of SCP was obtained by analyzing the intermediates.