Valorization of Crab Shell Waste in Ceramic Membrane Fabrication and Chitosan Extraction: Adsorption Optimization and Filtration Performance for Cu(II) Removal

Chitosan with a degree of deacetylation (DDA) exceeding 75% was obtained from blue crab ( Callinectes sapidus ) shells through an energy‐efficient deacetylation process (100°C, 1 h). The resulting chitosan exhibited a medium molecular weight (201.6 kDa), a p K a of 7.13 ± 0.14, a low residual protein content (0.17% ± 0.04%) and an extraction yield of 20.63% ± 0.55%. Response Surface Methodology (RSM) was applied to optimize Cu 2+ adsorption, yielding optimal conditions of 0.65 g/L chitosan, 57 min contact time, and 144 mg/L initial Cu 2+ concentration, achieving a maximum adsorption capacity of 103 mg/g. Kinetic analysis indicated a pseudo‐second‐order model, confirming chemisorption as the dominant mechanism via complexation with chitosan functional groups. Clay and blue crab shell composite membranes were developed as an eco‐friendly water treatment approach, exhibiting a contact angle of 35.91° ± 0.98° and an open porosity of 35.83% ± 0.88%. The membranes were functionalized via HCl‐assisted chitosan dip‐coating. Dead‐end filtration demonstrated that dip‐coated membranes significantly outperformed untreated ones, with Cu 2+ rejection increasing from 83.7% to 99.62% at 10 mg/L, from 63.83% to 85% at 30 mg/L, and from 60.18% to 76.28% at 50 mg/L.