Sustainable treatment of bio-treated municipal solid waste leachate by catalytic ozonation-MBR using a catalyst derived from Fenton iron sludge

For bio-treated leachate treatment, conventional nanofiltration–reverse osmosis (NF–RO) systems are plagued by high costs, membrane fouling, and the generation of large volumes of hazardous concentrate, which poses a severe secondary pollution risk. Meanwhile, the disposal of Fenton iron sludge (FIS), a toxic byproduct of advanced oxidation, presents a critical environmental liability. To mitigate these issues, we valorized FIS into a high-performance FIS/γ-Al₂O₃ catalyst and integrated it with catalytic ozonation and membrane bioreactor (MBR) for bio-treated leachate treatment. The FIS/γ-Al₂O₃ catalyst enhanced ozone decomposition kinetics by 7.8-fold (0.264 vs. 0.034 min−1) compared to non-catalytic ozonation, significantly improving UV₂₅₄ (39.4%), TOC (42.1%), and COD (32.2%) removal. Multi-characterization techniques (BET, XRD, FTIR) revealed that thermal decomposition of FIS organics formed a mesoporous structure (240.7 m2·g−1) with abundant surface hydroxyl groups, facilitating •OH generation which is key to refractory pollutant degradation. Notably, the catalyst retained > 90% activity under high salinity (5 g Cl−·L−1), and the BOD₅/COD ratio increased by a factor of ∼4, from 0.063 to 0.250, enhancing downstream biodegradability. This integrated process eliminates concentrate generation while meeting stringent discharge standards. In a 24-day pilot-scale study (0.6 m3·h−1, 4 h HRT, 250 mg·L−1 ozone), the process achieved 90.58% COD removal (effluent: 43 mg·L−1), meeting China’s Grade 1 A discharge standard. Herein, an innovative method that utilizes FIS-derived catalysts for leachate treatment was established. This method not only avoids the production of NF–RO concentrate but also transforms FIS from a hazardous waste into a functional resource, thereby providing a sustainable solution for its safe disposal.