Diclofenac sodium removal by powdered activated carbon of coconut endocarp: process optimization, kinetics, and isotherms

Emerging contaminants (ECs) have been detected in various environmental compartments, especially in aquatic bodies. Among EC, diclofenac sodium (DS) is one of the most ecotoxic and causes hemodynamic changes, thyroid tumors, and adverse effects under chronic exposure. Therefore, some countries have adopted restrictive legislation, encouraging the development of technology to mitigate this situation. Among the available water treatment processes, adsorption is an effective alternative in technical and economic aspects. In this context, this study aimed to evaluate, on a bench scale, the efficiency of DS removal in powdered activated carbon (PAC) of coconut endocarp. The adsorption of DS was analyzed through central composite design (CCD), using four factors: diclofenac sodium concentration (CDS from 50 to 450 mg · L−1), adsorbent concentration (CPAC from 0.2 to 5 g · L−1), contact time (Ct from 5 to 45 min), and pH (from 5 to 9). The results supported response modeling for adsorption capacity, pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetics, intraparticle diffusion (IPD), and Langmuir and Freundlich isotherms. DS demonstrated an affinity for adsorption on PAC. The maximum adsorption capacity was 169.39 mg · g−1 for PAC (CDS of 331.64 mg · L−1, CPAC of 0.2 g · L−1, Ct of 40.6 min, and pH 5) obtained through duplicate confirmation batches.