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Application of a three-compartment model as a tool to understand the partition of 17α-ethinylestradiol in mixed liquor systems

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A new methodology previously used to study partitioning of polycyclic aromatic hydrocarbons (4.2 > log Kow > 6.6) in complex heterogeneous systems such as mixed liquor in bioreactors was applied to the synthetic hormone 17α-ethinylestradiol (EE2), that is an organic micropollutant commonly present in sewage. This model considers the mixed liquor as a three-compartment matrix, in which the pollutant coexists in three states: freely dissolved, sorbed to particles, and sorbed to dissolved and colloidal matter (DCM). In this way, it is possible to gain a better knowledge about the affinity of the pollutant for all these phases, through the determination of equilibrium constants Kpart and KDCM. According to the results, the measured partition coefficients related to EE2 are in the range of 315–439 L/kg (log Kd 2.5–2.64). The values of Kpart and KDCM determined by this model were 384 L/kg and 45 L/kg, respectively, which indicate that EE2 tends to sorb mainly on particles, while the affinity for DCM is poor. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 257-262, 2013