Effect of Brij 35 and saponin surfactants on adsorption of diethylstilbestrol as an emerging estrogenic contaminant by clinoptilolite in batch and fixed-bed column experiments

Abstract

In this study, natural clinoptilolite was modified by saponin and Brij 35 surfactants to remove diethylstilbestrol(DES) from wastewater in batch and continuous systems. The optimum pH, amount of adsorbent, contact time, andtemperature were 11, 10 g/L, 12 h, and 35 °C, respectively, for the process. The equilibrium data agreed well withthe Langmuir isotherm for natural clinoptilolite (NC), natural clinoptilolite modified by Brij 35 (NC-Brij), and naturalclinoptilolite modified by saponin surfactants (NC-saponin) compared to other isotherms. The maximum adsorptioncapacities resulting from the Langmuir isotherm for NC, NC-Brij, and NC-saponin were 8.012, 23.64, and 39.525mg/g, respectively. Fixed-bed column experiments were performed under various operational conditions to evaluatethe performance of the adsorbent bed breakthrough curve. The lumped method solves bed equations to determinethe axial dispersion coefficient (Dz) and overall mass transfer coefficient (Koverall) parameters. Comparison of thekinetic models indicated that the DES adsorption process was well described by the intraparticle diffusion model for NC,pseudo-second-order and fractional power kinetic models for NC-Brij, and pseudo-second-order model for NC-saponin.The negative Gibbs free energy and positive enthalpy changes for NC, NC-Brij, and NC-saponin confirmed that theremoval reaction of DES was spontaneous and the adsorption was endothermic, respectively.