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Advanced oxidation processes based on persulfate activation can produce strong reactive oxygen species, which can effectively degrade a variety of organic pollutants. However, finding cost-effective activation methods and materials have become the key in the research process of this oxidation technology. With the discovery of the catalytic activity of biochar, the application of carbonaceous materials in persulfate activation has recently emerged. In this study, recyclable magnetic biochar was prepared from dewatered piggery sludge, and was used to activate peroxymonosulfate to degrade antibiotic tetracycline. Results showed that the catalytic activity of magnetic biochar was stronger than that of unmagnetized sludge biochar, and magnetic biochar showed better separation and sustainability in recovery and reuse. Neutral pH condition was also favorable for biochar and magnetic biochar to activate peroxymonosulfate. Peroxymonosulfate activation using magnetic biochar is an economical, efficient and environmentally friendly method for organic pollutants degradation. [Display omitted] • The catalyst with high efficiency and low cost was prepared by Fe 3 O 4 modification. • Magnetic biochar showed a high activity for the activation of peroxymonosulfate. • Reveal the mechanism of tetracycline degradation catalyzed by magnetic biochar. • Valuable utilization of agricultural waste piggery sludge was proposed. [ABSTRACT FROM AUTHOR]

• The recycled Fenton sludge showed a high activity for the activation of persulfate. • The existence of Cu(II) can increase the oxygen vacancies of the recycled sludge. • Tetracycline can be decomposed through six possible pathway processes. • The catalytic mechanism by the recycled catalyst is deciphered. • It is a cost-effective and environmentally friendly way to gain active catalysts. Fenton reaction has been widely applied as a unique oxidative method in the treatment of industrial wastewater. However, it generates a massive amount of Fe sludge, which mostly contains other hazardous heavy metal waste that can harm the environment and humans. In this study, we proposed a sustainable method to eliminate the side effect of the Fenton reaction and turn the Fenton sludge containing Cu into an efficient catalyst in the activation of peroxymonosulfate (PMS) to degrade tetracycline (TC). The existence of Cu, which can increase the oxygen vacancies of the sludge, is attributed to the activation efficiency compared with Fe sludge devoid of Cu. X-ray diffraction and X-ray photoelectron spectroscopy results show that Fe is present in the form of α- Fe 2 O 3 and γ- Fe 2 O 3 , whereas Cu mostly exists in the valence state of Cu(II). The influence of catalyst and PMS dosage, pH, and recycling times on the PMS reaction is illustrated. OH , SO 4 − O 2 – and 1O 2 are the critical reactive oxygen species. TC can be decomposed into CO 2 and H 2 O through six possible pathway processes with these free radicals. Given its sustainable treatment and high catalytic efficiency, dealing with Fe sludge that contains heavy metals serves as a modal practice for harmful waste treatment and can be popularized for a broader application. [ABSTRACT FROM AUTHOR]