The sludge-derived biochar is considered an effective emerging contaminants adsorbent for wastewater treatment. In this paper, red mud and steel slag (RMSS) was used for improving sludge dewaterability and enhancing the sludge-derived biochar adsorption capacity. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and a scanning electron microscope (SEM) were employed to comprehensively characterize the mineral composition, functional group, and morphology of the adsorbent. RMSS was able to improve the sludge dewatering performance by providing a skeleton structure to promote drainage and Fe(III) to decrease the Zeta potential. The dosage of 20 mg/g RMSS was able to reduce the specific resistance to filtration (SRF) and the Zeta potential of sludge from 1.57 × 10¹³ m/kg and −19.56 mV to 0.79 × 10¹³ m/kg and −9.10 mV, respectively. The co-pyrolysis of RMSS and sludge (2:8) induced the formation of biochar containing FeAl₂O₄ (PS80). The PS80 exhibited a large surface area (46.40 m²/g) and high tetracycline (TC) removal capacity (98.87 mg/g) when combined with H₂O₂ (PS80-H₂O₂). The adsorption process of TC onto PS80 and PS80-H₂O₂ was well described by the pseudo-first-order and pseudo-second-order kinetic model, indicating physisorption and chemisorption behavior. The results indicated that co-pyrolysis of RMSS sludge PS80-H₂O₂ could enhance the biochar adsorption capacity of TC, attributable to the degradation by ·OH generated by the heterogeneous Fenton reaction of FeAl₂O₄ and H₂O₂, the release of adsorbed sites, and the improvement of the biochar pore structure. This study proposed a novel method for the use of RMSS to dewater sludge as well as to induce the formation of FeAl₂O₄ in biochar with effective TC removal by providing a Fe and Al source, achieving a waste-to-resource strategy for the integrated management of industrial solid waste and sewage sludge.

In order to improve the utilization of nanoscale zero-valent iron (nZVI) in activating persulfate (PS), a composite material of nZVI/CSW with nZVI supported on calcium sulfate whiskers (CSWs) was synthesized in this study. The activity of the nZVI/CSW-PS system was evaluated by the removal of methyl orange (MO) in the aqueous phase. With the optimization of response surface methodology (RSM), the degradation efficiency of 20.0 mg L⁻¹ MO could increase to 98.13% in 5 min at the dosage of 1.03 g L⁻¹ nZVI/CSW-2, 3.51 mM PS at a temperature of 40.8 °C. The results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests showed that the nZVI particles were well dispersed on the CSW surface in a Fe²⁺/CSW molar ratio of 0.25 : 1, which is approximate to the theoretical value of 3.698 mg g⁻¹ thin-layer-Fe supported on CSW. Furthermore, the results demonstrated that the thin-layer nZVI particles were the most efficient in activating PS, and nZVI was rapidly dispersed during the dissolution process of CSW, which greatly increased the reaction rate. γ-FeOOH is the main reaction product of nZVI/CSW-2. This study provides a novel advanced oxidation system with nZVI/CSW in wastewater pollution control.