Response Surface Optimization of Chlorhexidine Adsorption onto Glutaraldehyde-Crosslinked Chitin–Hydroxyethyl Cellulose Composite in a Fixed-Bed Column

Abstract

The occurrence and persistence of pharmaceutical contaminants such as chlorhexidine (CHX) in aquatic environments pose significant environmental and public health concerns because of their ecotoxicity and contribution to antimicrobial resistance. In this study, a sustainable hybrid adsorbent, cross-linked hydroxyethyl cellulose–activated snail shell chitin (C-HEC-ASSC), was synthesized and evaluated for the removal of CHX in a continuous fixed-bed column. Physicochemical characterization confirmed successful hybridization, with the surface area increasing from 2.85 to 27.21 m² g⁻¹. FTIR analysis revealed the formation of ether (C–O–C) and imine (C = N) linkages, XRD showed enhanced crystallinity, and SEM micrographs demonstrated a rougher and more porous surface morphology. Response Surface Methodology (RSM) was employed to optimize column operating conditions, and the quadratic model was highly significant (R² = 0.9997, p < 0.0001). The optimum CHX removal efficiency of 67.45% was achieved at a contact time of 60 min, temperature of 40 °C, flow rate of 5 L min⁻¹, and bed height of 50 cm. Adsorption occurred through a combination of external film diffusion, intraparticle diffusion, electrostatic attraction, hydrogen bonding, π–π interactions, and surface complexation. These findings demonstrate the potential of the C-HEC-ASSC composite as an environmentally sustainable adsorbent for the continuous treatment of pharmaceutical wastewater.