Competitive adsorption studies of caffeine and diclofenac aqueous solutions by activated carbon

• We investigated the simultaneous adsorption in batch and fixed bed systems.
• SRS and the extended Freundlich multi-component isotherm models were studied.
• PSDM model has been used to predict the fixed-bed breakthrough curves.
• The external and internal mass-transfer coefficients were calculated.

Equilibrium and dynamic studies on the adsorption removal of caffeine and diclofenac onto granular activated carbon (GAC) were developed. In the competitive adsorption, lower adsorption capacities for caffeine and diclofenac, 190.9 and 233.9 mg g−1, respectively, were reported compared with the single adsorption system. Sheindorf–Rebhun–Sheintuch and the extended Freundlich multi-component isotherm models were also used to describe the simultaneous adsorption of caffeine and diclofenac from binary system. The caffeine and diclofenac equilibrium adsorption data were best adjusted to the extended Freundlich model, providing lower percentage error values (ε) of 0.29 and 0.28 for caffeine and diclofenac, respectively.Breakthrough curves of caffeine and diclofenac aqueous solutions were obtained at different operational conditions (initial concentration, volumetric flow rate and column length). Therefore, adsorption parameters, such as adsorption capacities at breakthrough and saturation points, length of mass transfer zone, fractional bed utilization and micropollutant removal percentage were obtained. In general, the caffeine removal percentages at breakthrough time are higher than the diclofenac recovery. Pore and Surface Diffusion (PSDM) model has been used to predict the fixed-bed breakthrough curves for caffeine–diclofenac aqueous solutions. Bi number values, ranged from 1 to 100, were obtained, indicating that the surface diffusion inside the micropores represents the rate-controlling step in the process for the experimental conditions used in the study.