Physicochemical Behavior of Tetracycline and 17α-Ethinylestradiol with Wastewater Sludge-Derived Humic Substances
2014
Tenenbaum, Idan | Chefetz, Benny | Avisar, Dror
Sorption–desorption behavior of the antibiotic tetracycline (TET) and the synthetic estrogen hormone 17α-ethinylestradiol (EE2) with wastewater sludge and sludge-derived humic substances [humic acid (HA) and humin] was investigated. From acidic functional group capacity and elemental analyses, HA had higher polarity, aromaticity, and acidity than humin; humin contained aliphatic chains with high mineral content. The different physicochemical properties of the pharmaceuticals and sludge components yielded different kinds of sorption–desorption interactions. Partitioning coefficients (Kd) of TET to sludge were higher (1,552 ± 41–4,667 ± 41 L/kg) than EE2 (534 ± 52–609 ± 47 L/kg). TET sorption was highly pH-dependent and maximal at pH 9. Ca²⁺ions enhanced sorption, emphasizing the role of polyvalent metal ions in forming TET–sludge complexes. Humin was the dominant component for TET sorption due to its high inorganic matter content. In contrast, EE2 sorption was independent of solution pH, forming mostly hydrophobic interactions with sludge organic matter. EE2 had a high affinity for HA due to its chemical structure. Desorption of the two pharmaceuticals differed as well. The amount of desorbed TET (18.7 ± 1.3–29.8 ± 2 %) was lower than that of EE2 (60.6 ± 3–62.3 ± 2 %), and the hysteresis index was higher for TET than EE2. While TET desorption tended to be delayed in the solid matrix, EE2 desorbed easily and in accordance with the aqueous equilibrium concentration. The conclusions emphasize the need for further research into frequently used pharmaceuticals with different physicochemical properties and the recognition of sludge application as an important source of distribution for these contaminants in the environment.
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