Preparation of catalysts by backwashing waste sludge with various Fe/Mn mass ratio to activate peroxymonosulfate for the degradation of tetracycline: Performance and mechanism

Tetracycline (TC) is a widely used antibiotic, which poses a significant threat to aquatic environments. In this study, the backwashing sludge with different Fe/Mn mass ratio was obtained by adjusting the concentration of Fe 2 + and Mn 2+ in the influent water of filters. After dehydrating, drying and thermal treatment, the sludge was prepared as Fe-Mn binary catalysts to activate peroxymonosulfate (PMS) for removing TC from water. The removal performance, influence factors, and the degradation mechanism were investigated. The results indicated the prepared Fe-Mn sludge catalysts could effectively activate PMS to degrade TC and the activity was significantly influenced by the Fe/Mn ratio in the influent water. With Fe/Mn of 1:1 and 6:1, the sludge could be directly used as high activity catalysts; with Fe/Mn of 3:1, thermal treatment at 400 °C was required to enhance the activity. The fluidized-bed experiments showed that the Fe-Mn sludge catalysts had excellent activity stability and the ion leaching experiment indicated that the safe operational pH for the sludge catalysts should be above 5. The identification and quantification of reactive oxygen species proved that Mn was more beneficial to the generation of 1 O 2 , while Fe was more beneficial to the generation of SO 4 •─ and •OH, and TC was primarily degraded by 1 O 2 . Finally, based on the results of LC-MS characterization, the degradation pathway of TC was proposed, and the toxicity of the intermediates was assessed. The results provide new insights into the utilization of the Fe-Mn waste sludge as PMS catalysts for antibiotic removal.