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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. [ABSTRACT FROM AUTHOR]

[Display omitted] • LDH of ultrasound method had a surface area 40% greater than conventional method. • The optimal parameters were pH 8, 0.54 g of LDH, 44 min for 95% of phosphate removal. • Mechanism suggesting chemisorption process as rate limiting step. • Data fitted to Redlich-Peterson model exhibiting heterogeneous non-ideal isotherm. • The mechanism for phosphate removal onto LDH was spontaneous and endothermic. The aim of this work was to obtain a Layered Double Hydroxide (LDH) from natural dolomite and to apply the synthetized solid (CaMgAl-LDH) for phosphate removal by adsorption. Both the conventional coprecipitation method and ultrasound-assisted method were used to obtain CaMgAl-LDH. The obtained solids were characterized by N 2 adsorption/desorption, size of pores, X-ray diffraction, and FTIR. Batch scale experiments were carried out to evaluate the phosphate adsorption capacity on CaMgAl-LDH using design of experiments (DOE). The studied parameters were pH, solid dosage, contact time and phosphate removal percentage, which was selected as the response function. Experimental data were fitted to kinetics and isotherms mathematical models. The process thermodynamics was also studied. Results showed that the ultrasound-assisted method was more efficient to obtain LDH even in a short period of sonication. The solids presented good crystallization, structure between layers, and high purity. Besides, LDH obtained by ultrasound exhibited a surface area of ​​about 40% greater than the LDH obtained by the conventional method. The results of LDH application for phosphate removal showed high adsorption capacity (>94%) in several conditions of contact time and pH, even in low solid dosage. The kinetics of the process followed the pseudo-second-order model and Redlich-Peterson was the isotherm model that presented the best adjust. The thermodynamic parameters suggested a spontaneous, endothermic, and randomness process at the solid/solution interface, confirming an adsorption system favorable. The results exhibited that the ultrasound-assisted method is promissory to obtain LDH from mineral sources such as dolomite due to decrease energy expenditure and short synthesis time. It was found the ultrasound-assisted method also improve the solid physicochemical characteristics for its use in the adsorption process, enhancing the phosphate removal. [ABSTRACT FROM AUTHOR]

The present study investigated the adsorption and oxidation of the antibiotic Marbofloxacin (MBX) individually and simultaneously. The concentrations of MBX were monitored over time to assess the efficiency of the simultaneous process besides High-Performance Liquid Chromatography (HPLC) was employed to quantify the MBX degradation. An experimental design of three Box-Behnken Factors was performed to study the influence between the variables. To adsorption as an individual method, the best conditions were achieved at a pH of 7.8, 0.85 g of activated carbon, and a contact time of 42 min. To Fenton, the best conditions were achieved at a ratio of 6.25 (r = [H 2 O 2 ]/[Fe2+]) and a time of 30 min. The final concentration reached by adsorption and Fenton as individual processes were 0.49 and 0.12 mg L−1, respectively, while the concentration of MBX in the simultaneous process reached a final concentration of 0.078 mg L−1. The results indicated that the simultaneous process exhibited greater efficiency in decreasing MBX concentration when compared to individual processes. The formation of degradation products also decreased after treatment, suggesting the potential environmental safety of the combined treatment. Finally, to further comprehend the environmental impact of MBX in water, a toxicity Quantitative Structure-Activity Relationship (QSAR) analysis was conducted to predict its potential toxicity, enabling a more thorough assessment of its ecological risks. It was concluded, that the method offers promising implications for environmental safety. • It was achieved a final concentration after adsorption and Fenton of 0.49 and 0.12 mg L−1, respectively. • The final concentration of MBX in the combined process was 0.078 mg L−1. • The simultaneous implementation reduced the generation of degradation byproducts that may be toxic. • QSAR tool showed the results of the toxicity comparing with MBX concentration was below the values considered toxic in aquatic environments in tests. [ABSTRACT FROM AUTHOR]