A thermodynamic analysis on adsorption of estrogens in activated sludge process

The adsorption behaviors of estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2), and equol were studied with a deactivated sludge subjected to heat treatment at 80 °C for 30 min. The heat-treatment hardly changed the adsorption features of activated sludge (AS). The adsorption equilibrium of all estrogens was approached within 10 min at 20 °C, and a high removal of estrogens was achieved simultaneously. The equilibrium data were well fitted by a Freundlich isotherm. The adsorption behaviors of E1, E2, E3 and EE2 in the AS system were independent of their Kow values. Thermodynamic analysis revealed that the adsorption behaviors of E1, E2, E3 and EE2 could be considered as an exothermic, physical and reversible process, resulting in their higher adsorption capacities at lower temperature. Regarding equol, its adsorption was an endothermic, chemical and irreversible process.