Efficient photocatalytic degradation of tetracycline using magnetic biochar derived by iron-rich sludge

Industrial wastewater treatment processes produce a large quantity of iron-rich sludge due to the extensive utilization of iron salt reagent. Reuse of iron-rich sludge is an attractive route for excess sludge disposal and management. In this study, sludge-derived magnetic photocatalyst was prepared using industrial iron-rich sludge as raw materials for the first time. The photocatalytic degradation system constructed by the sludge-derived photocatalysts were evaluated using tetracycline (TC) as the target contaminant, achieving a high degradation rate of 98.3% within 5 h under optimal conditions. Major reactive oxygen species in the photocatalytic systems were investigated using radical quenching experiments and electron paramagnetic resonance spectroscopy. The results suggested that •OH and O₂^•- were activated by photogenerated electrons and holes, respectively. Moreover, bound persistent free radicals induced by quinone-like structure in sludge-derived biochar were the predominant factors affecting radical ¹O₂ formation under the light irradiation. The reactive oxygen species of •OH, O₂^•-, and ¹O₂ played main roles in the degradation of TC. The used magnetic biochar can be effectively separated and recovered in aqueous solutions by the magnetism. This method provides a new cost-effective strategy for antibiotics removal from aqueous solution.