[Study on the sorption behavior of tetracycline onto activated sludge]

The batch sorption methods were employed to investigate the sorption behavior of tetracycline (TC) on the activated sludge. It was shown that the mixed liquor suspended solids (MLSS) and the initial concentration of TC had great impacts on equilibrium time, adsorption capacity and adsorption rate. Compared with pseudo first-order model, pseudo second-order model showed the better agreement. At 10, 25 degrees C, the Langmuir model was the best isotherm to describe the experimental data for adsorption of TC on activated sludge, and the maximum adsorption capacities were 31.14, 70.95 mg x g(-1) respectively; at 40 degrees C, the linear isotherm confirmed the agreement. The data were also modeled by D-R isotherm to determine the type of adsorption. At 10 degrees C (E was 9.13 kJ x mol(-1)), the dominant type was physical, and at 40 degrees C (E was 7.07 kJ x mol(-1)), the dominant type was chemical. With the temperature increasing, the adsorption capacity increased. Ion exchange is one mechanism for adsorption of TC on activated sludge. When the initial concentrations of TC were 5, 10, 20 mg x L(-1), with the Na+ concentration increasing from 0 mol x L(-1) to 0.1 mol x L(-1), the adsorption capacities decreased by 15.32%, 15.00%, 20.12% respectively. The maximum adsorption capacity was got at pH 6 when pH varied from 5 to 10.