Sustainable Dye Removal Using Fish Scale-Derived Biosorbent: Performance and Mechanisms

Abstract

In the context of sustainable methodologies for wastewater remediation, the present work describes the design and testing of an efficient biosorbent prepared from Sardina pilchardus fish scales (SPFS). The biosorbent exhibits excellent adsorption capacity toward two dyes, Methylene Blue (MB) and Congo Red (CR). Physicochemical and morphological analyses confirmed the porous nature and functional surface chemistry of the material, which are essential for dye adsorption. The adsorption process exhibited fast kinetics, with equilibrium achieved within 30 minutes for both dyes. The pseudo-second-order (PSO) model was followed, indicating that chemisorption regulated the adsorption. Isotherm modeling revealed that the Langmuir–Freundlich model gave the best fit, suggesting a heterogeneous surface supporting both monolayer and multilayer adsorption. The biosorbent displayed outstanding performance, achieving maximum adsorption capacities of 187.634 mg/g for CR and 129.694 mg/g for MB, ranking it among the most efficient bio-derived adsorbents reported. Thermodynamic analysis indicated the processes are exothermic, spontaneous, and favorable. Despite a slight efficiency decrease at higher temperatures, the material maintained high regenerability, supporting its repeated use. These results highlight the promise of fish-scale-derived biosorbents as low-cost, sustainable, and effective candidates for dye removal in wastewater treatment.