Carbon black-polytetrafluoroethylene electrode electrically activated persulfate for the treatment of metronidazole wastewater

In this paper, a carbon black-polytetrafluoroethylene (C-PTEE) cathode, made of carbon black and PTFE, was used to electroactive persulfate (PS) for the degradation of the metronidazole (MNZ) in wastewater. The cathode performance and operating conditions were optimized by single-factor experiments. When the C/PTFE ratio was 1:1, the pressure was 15 MPa, and the calcining temperature was 300℃, 100 mg L⁻¹ MNZ was completely degraded in 120 min. The effect of electrolytes on the degradation of MNZ was investigated. It was found that the reactive oxygen species (ROS) generated by the reaction of electrolytes in the NaCl and Na₂SO₄ systems could achieve the complete removal of MNZ, and the removal efficiency was much higher than that of the NaNO₃ system. The operating factors on the removal of MNZ were invested, and 99.8% of MNZ was removed in 120 min at conditions of pH = 4, j = 100 mA cm⁻², [PS] = 58 mmol L⁻¹, and [MNZ] = 100 mg L⁻¹. Hydroxyl radicals (·OH) and sulfate radicals(·SO₄⁻) were detected in the persulfate system by electron spin resonance (ESR). Meanwhile, it is found that electron transfer, ·SO₄⁻, and ·OH are attributed to the removal of MNZ detected by the free radical quenching experiment, and their contribution to the removal of MNZ was 27.8%, 22.3%, and 49.9%, respectively. Three possible degradation paths of MNZ were proposed, and ECOSAR was used to predict the toxicity of intermediates degraded by MNZ. The results showed that some intermediates of MNZ were more toxic than MNZ but eventually became non-toxic inorganic substances with the process of degradation.

In this study, a carbon black-polytetrafluoroethylene (C-PTFE) cathode was prepared to electroactive persulfate to treat metronidazole (MNZ) pharmaceutical wastewater. The conditions of electrode preparation, operation factors and the degradation mechanism of MNZ were investigated, and the energy consumption of this system was comprehensively evaluated, aiming to guide the industrial-scale application.