The widespread discharge of antibiotics into aquatic environments contributes to the emergence and spread of antimicrobial resistance. Conventional tertiary wastewater treatments are often not specifically designed to remove trace antibiotic residues, creating a need for scalable, high-performance and sustainable adsorbent materials. Here, we present a patented solid-state crosslinking method for sodium alginate that addresses key scalability limitations associated with conventional wet ionotropic gelation. A range of metal ions, including Ca²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Fe³⁺ and Al³⁺, was used to fabricate metal–alginate polymeric matrices. FTIR, ICP-MS and SEM-EDS confirmed effective crosslinking, with enhanced surface crosslinking and improved ease of production compared with standard preparation methods. The resulting metal–alginate particles demonstrated strong antibiotic adsorption performance. Fe-ALG and Zn-ALG showed high maximum adsorption capacities for ciprofloxacin, doxycycline and amoxicillin, supporting their potential as broad-spectrum antibiotic-removal materials. To assess real-world applicability, selected metal–alginate systems were tested using treated sewage-water samples collected from sites in the UK and Türkiye. Ciprofloxacin was detected in these samples and quantified by HPLC and LC-MS. While Zn-ALG showed excessive swelling in real sewage-water matrices, Fe-ALG displayed superior structural stability, with limited swelling of approximately 20%. In laboratory-scale vertical filtration columns, Fe-ALG packed beds removed ciprofloxacin to below the analytical detection limit across a broad pH range. ICP-MS analysis further confirmed negligible Fe³⁺ leaching, below 0.02 ppm, and the filtration system retained high removal performance over multiple regeneration cycles. These findings demonstrate the potential of solid-state-crosslinked Fe-ALG as a scalable, regenerable and bio-based filtration medium for antibiotic removal from wastewater effluents. The technology offers a promising polymeric platform for sustainable wastewater remediation and industrial filtration applications.