Combined Process for Caffeine Treatment in Aqueous Solution by Adsorption/Regeneration and Fenton Oxidation

Abstract

This study aims to assess the efficiency of caffeine mitigation in an aqueous solution through a combination of adsorption and the Fenton reaction, using granular activated carbon (GAC). The present study also investigates the reduction in the concentration of oxidation byproducts in the solution and the regeneration of the solid. The combined process was conducted in four consecutive cycles using optimal values determined in individual technique studies. For the individual adsorption study, a Box–Behnken design was employed, with varying pH (3 to 11), GAC concentration (1.0 to 10.0 g L−1), and contact time (10 to 120 min). In the individual Fenton study, based on a factorial design, concentrations of FeSO4·7H2O (4 to 20 mg L−1) and H2O2 (25 to 150 mg L−1) were used at reaction times of 5 and 60 min. GAC was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), specific area (BET), and pore size (BJH) throughout all stages of experimentation. The outcomes show that the adsorption achieved a 93.4% removal rate under the optimal experimental conditions (natural pH, 65 min, and 10 mg L−1) and the Fenton reaction achieved a 98.92% degradation rate at a 37.5 ratio of H2O2/FeSO4·7H2O. The combined process also achieved an efficiency of over 95.7% of caffeine removal in four cycles, reducing the Total Organic Carbon (TOC) by more than 47.65% and 20.6% at 5 and 60 min of the Fenton reaction, respectively. Regeneration efficiencies of 99.6%, 91.8%, and 93.8% for the other three evaluated cycles were obtained. These findings suggest that the combined process is a promising solution for the treatment of effluents contaminated with caffeine.