Decontamination of textile effluents via the adsorption process on various raw clay minerals enhanced by ozonation: a modeling approach and optimization

This study seeks to characterize three different clays and compare their capability to decontaminate a textile effluent using the adsorption process and to explore the synergistic effects of ozonation on the treatment. Response surface methodology, based on central composite design, was used to investigate the impact of three key parameters, namely, solution pH, clay dosage, and contact time, on the adsorption process. The three clays were sourced from distinct regions across Tunisia: Rommana, Tabarka, and Medenine. The analysis of the clays revealed that the Rommana green clay (RGC) was predominantly composed of smectite, the Tabarka white clay (TWC) was rich in kaolinite, and the Medenine red clay (MRC) contained a combination of illite and kaolinite. Under optimal conditions for color removal, the attained efficiencies for removing color, chemical oxygen demand (COD), and total suspended solids (TSS) were as follows: 86.89%, 57.2% and 80.7% for RGC; 80.56%, 55.02% and 75.28% for TWC; and 81.7%, 56.8% and 75.5% for MRC, respectively. Results show that RGC exhibited the highest adsorption percent of dye removal (≅87%) at the optimal conditions evaluated via the CCD design of the response surface methodology (pH ≈ 3.98, adsorbent dose 7 g L⁻¹, contact time = 89 min). The enhancement of the adsorption process through ozonation achieved color removal efficiencies of 98.2%, COD removal efficiencies of 71.4%, and TSS removal efficiencies of 89.3% for RGC; 98.15%, 70.13%, and 88.74% for TWC; and 98.3%, 70.32%, and 88.56% for MRC, respectively, in compliance with the Tunisian standard for river discharge. The treated effluent can be used in the irrigation of saline plants.