Response surface optimization of the efficiency of ZnCl2-impregnated activated carbon from residual coffee grounds in the removal of Eriochrome Black T dye-contaminated wastewater

This study explores the use of activated carbon derived from residual coffee grounds impregnated with ZnCl2 as an effective adsorbent for removing EBT, a contaminant in synthetic aqueous solutions. Batch and column adsorption methods were employed, with parameters such as adsorbent dose, initial concentration, and contact time investigated in batch adsorption. In contrast, only adsorption height and initial concentration were studied in column adsorption. Surface structure analysis was conducted through scanning electron microscopy (SEM) at an acceleration of 15 kV, and 200 x and 500 x magnification, and the functional groups were identified via Fourier transform infrared (FTIR) spectroscopy. The response surface methodology-central composite design (CCD) was utilized to determine the optimum independent variable conditions. Isotherm and kinetic analysis were employed to investigate the adsorption process and mechanism. Results indicate that the adsorbent exhibits a porous honeycomb structure and possesses an effective aromatic functional group with C = C - C stretch for EBT removal. Optimum batch adsorption values were found to be 0.3 g adsorbent dose, 50 mg/L initial concentration, and 90 min contact time, achieving 93.26% EBT removal. In column adsorption, the best conditions were 7 cm adsorbent height and 40 mg/L concentration, with 92.66% EBT removal. Langmuir and Freundlich models were used for isotherm analysis, with the best-fitted model being Langmuir for batch adsorption and Freundlich for column adsorption. Pseudo-first-order and pseudo-second-order models were considered for kinetic analysis, with the best-fitted model being pseudo-second order for both batch and column adsorption.