Comparing the adsorption and desorption characteristics of 17α-ethinylestradiol on sludge derived from different treatment units

The adsorption and desorption behaviors of 17 alpha-ethinylestradiol on various sludges derived from different treatment units of a sewage treatment plant were investigated using batch equilibration experiments. The results showed that adsorption process could be well described by pseudo-second-order kinetic model and fast adsorption played a main role. Adsorption ability varied as the order of aerobic sludge approximate to anoxic sludge approximate to primary sludge > sludge cake > anaerobic sludge. Adsorption/desorption isotherms were well fitted by the modified Freundlich model, and K'(f) values increased with the organic matter content. Thermodynamic analysis indicated that 17 alpha-ethinylestradiol adsorption/desorption was exothermic and conducted spontaneously. After heat treatment for removing the organic carbon, K'(f) values decreased by more than 78%, but organic carbon normalized adsorption constant was 7.76-29.51 mg/g. The 17 alpha-ethinylestradiol adsorption capacity was found to decrease from 0.95-1.39 to 0.44-0.49 mg/g with sludge concentration increasing from 500 to 4,000 mg/L, being almost unchanged at pH 3-10 and sharply decreasing with pH > 10. The adsorption capacity was also found to fluctuate in the range of 2.0-3.0 mg/g when Ca2+ concentration was <0.5 mol/L and increased rapidly above 0.5 mol/L. Addition of methanol and acetonitrile could improve 17 alpha-ethinylestradiol desorption effect, which increased with the content of organic solvents, and the desorption degree of acetonitrile was higher than methanol.