In this study, we investigated the ability of a magnetic wood biochar (WB)-based composite catalyst (Fe₃O₄–WB) to catalyze sodium persulfate (PS) for the remediation of estuary sediment contaminated with polycyclic aromatic hydrocarbons (PAHs). The effects of various critical parameters, including the catalyst dose and initial pH, were investigated. The degradation of the PAHs was found to be related to the number of rings in their structure. The results showed that Fe₃O₄–WB is an efficient catalyst for the removal of high-ring PAHs (HPAHs), with the highest degradation rates for the 6-, 5-, and 4-ringed PAHs being 90%, 84%, and 87%, respectively, for a PS concentration of 2 × 10⁻⁵ M, catalyst concentration of 3.33 g/L, and pH of 3.0. That the reduction rate of the HPAHs was greater than that of the low-ring PAHs can be attributed to the strong affinity of the HPAHs for biochar derived from wood biomass. Overall, this study revealed that the WB-mediated electron transfer catalysis of the surface functional groups in a wide range of pH in the Fe₃O₄–WB/PS system and potentially application in the remediation of sediments contaminated with PAHs.

Waste reutilization is always highly desired in the environmental engineering and science community. In this study, Fe-SCG biochar was functionalized by modifying spent coffee grounds (SCG) with magnetite (Fe³⁺) at 700 °C and applied for the oxidative removal of tetracycline (TC) with the presence of persulfate (PS). The effects of pH, dosage of biochar and sodium persulfate and initial TC concentration on TC degradation were investigated in a batch system. Our results show that higher TC degradation efficiency was obtained at low pH, low initial TC concentration, and at high dosages of PS and biochar. The highest removal efficiency (96%) was achieved by Fe-SCG/PS under the conditions of pH = 2.0, [Fe-SCG] = 2.5 g/L, [PS] = 60 mM and [TC] = 1 mM. The proposed Fe-SCG catalyst could be a promising effective biochar for the remediation of other emerging organic contaminants.