This study used red mud (RM), steel slag (SS), and desulfurization slag (DS) as raw materials to construct three catalytic oxidation systems, namely RM-DCDA/H₂O₂, SS-DS/H₂O₂, and SS-DS/peroxymonosulfate (PMS), to promote the utilization of industrial solid waste and enhance the treatment of recalcitrant antibiotic wastewater. The ciprofloxacin (CIP) degradation performances, influencing factors, and preliminary reaction mechanisms of these systems were investigated. RM formed an Fe₃N/C composite structure after acidification and dicyandiamide-assisted calcination. The Fe₃N active phase, coexistence of Fe²⁺/Fe³⁺, and N-doped C structure facilitated H₂O₂ activation and electron transfer. The SS-DS catalyst exhibited a rough and porous structure and contained Fe, Ca, and S species, which could provide reactive sites for H₂O₂ and PMS activation, following acid modification and urea-assisted calcination. Under the necessary reaction conditions, the CIP degradation efficiencies of the RM-DCDA/H₂O₂, SS-DS/H₂O₂, and SS-DS/PMS systems reached 94.60%, 92.58%, and 95.17%, respectively. These results indicate that RM- and SS-derived materials can be used for CIP oxidative degradation; however, the values should not be interpreted as a strict comparison of the intrinsic catalytic activity because the operating conditions differed among the systems. Parametric experiments showed that the catalyst dosage, oxidant concentration, and initial pH influenced the degradation efficiency. The H₂O₂-based systems were more suitable under acidic conditions, whereas the SS-DS/PMS system showed wider pH adaptability. Coexisting anion and humic acid experiments indicated that the systems were tolerant to natural organic matter, whereas HCO₃⁻ and HPO₄²⁻ inhibited degradation. CIP was further oxidized in total organic C and recycling experiments; however, it was difficult to completely mineralize it within a short reaction time, and the catalyst retained relatively high activity after repeated use. Radical quenching experiments suggested that ·OH and ·O₂⁻ participated in the degradation reactions in the RM-DCDA/H₂O₂ and SS-DS/H₂O₂ systems. In the SS-DS/PMS system, comparative quenching experiments revealed that non-radical singlet oxygen (¹O₂) was the dominant reactive species, while SO₄⁻· and ·OH contributed only marginally. In conclusion, RM and SS-DS can be used as low-cost raw materials to prepare industrial solid-waste-derived catalysts for the oxidative degradation of CIP, thereby providing a reference for industrial solid waste valorization and antibiotic wastewater treatment.

Municipal sludge anaerobic digestion (AD) is often constrained by limited substrate accessibility due to extracellular polymeric substances (EPSs), microbial cell walls, and compact floc structures. This review integrates pretreatment technologies and EPS characteristics through a five-dimensional conceptual framework: cell disruption, EPS solubilization, particle-size reduction, soluble chemical oxygen demand (SCOD) release, and enhanced biodegradability. The framework connects structural changes with substrate accessibility and digestion performance. Physical, chemical, and biological pretreatment methods are critically compared using study-specific evidence and descriptive numerical ranges rather than pooled estimates. Thermal hydrolysis promotes cell disruption and organic matter solubilization, while other methods offer complementary mechanisms with distinct operational constraints. However, increased SCOD does not necessarily translate into improved biodegradability or methane recovery. Similarly, improvements in laboratory-scale biochemical methane potential (BMP) cannot be directly extrapolated to full-scale digesters. Pretreatment effectiveness should therefore be evaluated by considering biodegradability, net methane gain, energy and chemical inputs, and downstream environmental impacts. This framework supports the interpretation of heterogeneous evidence and the selection of context-specific pretreatment strategies.