Reduction of COD level in real textile effluent using natural Tunisian clay as a low-cost adsorbent

This study explores the use of untreated local natural clay (NC) sourced from ElHamma-Gabès region in South of Tunisia, as an eco-friendly and low-cost adsorbent for the treatment of textile wastewater from a Tunisian plant. NC was characterized by XRD, SEM, BET and pHzpc analyses to determine its physical and chemical proprieties. Key wastewater parameters including chemical oxygen demand (COD), suspended solids, conductivity, and pH were also monitored to evaluate treatment efficacy. A parametric study optimized the clay dose (0.5 g/L), pH (7.4), and contact time (180 min) for maximum COD removal from 1145 in wastewater to 390 mgO₂/l of COD after treatment, ensuring 66 % of COD removal. Kinetic analysis demonstrated that adsorption followed a pseudo-first-order (PFO) model and it was controlled by both external diffusion and intraparticle diffusion. Equilibrium data were best described by the Sips isotherm model rather than those of Langmuir and Freundlich, revealing a COD maximum adsorption capacity of 776 mgO₂/g clay. The use of untreated natural clay without regeneration or pre-treatment demonstrates a cost-effective and eco-friendly approach for textile wastewater remediation, offering practical potential aligned with environmentally responsible water treatment goals.