Optimization of Adsorption Parameters for Polycyclic Aromatic Hydrocarbon (PAH) Removal Using Acid-Activated Carbon Derived from Crustacean Shell Waste

The aim of this study was to demonstrate the potential of acid-activated carbons derived from shell waste as sustainable and efficient adsorbents for PAH removal from contaminated water. Activated carbon was synthesized from periwinkle shells, clam shells, whelk shells, and a 1:1 composite of clam and whelk shells. The precursor materials were carbonized at 450 °C under limited-oxygen conditions and chemically activated using H₂SO₄ at 750 °C. The resulting adsorbents—Periwinkle Shell Acid-Activated Carbon (PSAAC), Clam Shell Acid-Activated Carbon (CSAAC), Whelk Shell Acid-Activated Carbon (WSAAC), and Clam-Whelk Shell Acid-Activated Carbon (CWSAAC)—were characterized using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX)and physicochemical analysis. Among the synthesized materials, CSAAC exhibited the highest surface area (1277 m²/g), indicative of enhanced adsorption potential. Batch adsorption experiments were conducted to evaluate the influence of adsorbent dosage and contact time on PAH removal efficiency. CWSAAC demonstrated the highest removal efficiency, achieving 98.93% at a 1 g dosage. The removal efficiency of the adsorbents followed the trend: CWSAAC (98.93%) > CSAAC (98.92%) > PSAAC (98.77%) > WSAAC (96.62%). Adsorption isotherms were modeled using Langmuir, Freundlich, Henry, Elovich, and Janovich models. The Freundlich and Langmuir models best described PAH adsorption for PSAAC, CSAAC, and CWSAAC, with CSAAC exhibiting the highest Langmuir monolayer adsorption capacity (23.995 mg/g). In contrast, WSAAC adsorption was best described by the Henry isotherm, indicating a preference for low-concentration adsorption. Kinetic studies revealed that PAH adsorption followed a pseudo-second-order model, suggesting that chemisorption was the dominant mechanism.These findings highlight the potential of acid-activated carbons derived from crustacean shell waste as cost-effective and sustainable adsorbents for PAH remediation in contaminated water systems.