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

The adsorption and desorption behaviors of 17α-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 ≈ anoxic sludge ≈ 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 17α-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 17α-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 Ca ²⁺ concentration was <0. 5 mol/L and increased rapidly above 0. 5 mol/L. Addition of methanol and acetonitrile could improve 17α-ethinylestradiol desorption effect, which increased with the content of organic solvents, and the desorption degree of acetonitrile was higher than methanol.