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 sludge 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 reduced 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 mg/g to 0.44-0.49 mg/g with sludge concentration increasing from 500 to 4000 mg/L, keep almost unchanged at pH 3-10 and sharply decrease when pH >10. The adsorption capacity was also found being fluctuated in the range of 2.0-3.0 mg/g when Ca²⁺ concentration< 0.5 mol/L and increased rapidly above 0.5 mol/L. Addition of methanol and acetonitrile could improve 17-Ethinylestradiol desorption effect, which increased with the organic solvents content, and desorption degree of acetonitrile was higher than methanol.

Keywords
Adsorption behavior; Desorption hysteresis; Organic carbon; Synthetic estrogen; Various sludges