Trivalent Metal Coordination Drives Ultrafast Antibiotic Shuttling to Soft Interfaces of Sewage Sludge

The inefficacy of the conventional activated sludge process (ASP) against high-concentration antibiotic streams, compelling energy-intensive pretreatments, represents a major hurdle for low-carbon wastewater treatment. We resolved this by repurposing waste-activated sludge (WAS), the main ASP byproduct, shifting its function from microbial effect to leveraging its inherent soft-matter interfaces. Owing to its high affinity for trivalent metal ions, WAS is transformed into a high-performance adsorbent via minimal Al³⁺ functionalization. This enhanced the tetracycline binding capacity by 2.6-fold through coordination-driven immobilization at the Al³⁺–extracellular polymeric substance interface. A coordination-mediated interfacial shuttling mechanism, involving the rapid “hitchhiking” of antibiotics via precomplexed Al³⁺ to the interface, enabled 95.6% removal of oxytetracycline from real pharmaceutical wastewater in a prototype reactor. This strategy reduces life-cycle costs to <17% of that of conventional pretreatments and could be extended to other ligand-bearing antibiotics (e.g., fluoroquinolones). Ultimately, this interfacial shuttling effect upgrades the WAS soft interface into a selective separation platform.