Calculation methods to perform mass balance of endocrine disrupting compounds in a submerged membrane bioreactor: fate and distribution of estrogens during the biological treatment

The purpose of this paper is to report the study of the fate and distribution of three endocrine disrupting compounds (estrogens); Estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2) in a laboratory scale submerged membrane bioreactor (SMBR). For this matter, both aqueous and solids phases were analyzed for the presence of E1, E2 and EE2. The outcome of this study was that three SMBRs showed enhanced elimination of estrogens in different operational conditions; the estrogen removal was close to 100% in SMBR. Additionally, E1, E2 and EE2 were detected in SMBR sludge at concentrations of up to 41.2, 37.3 and 36.9 ng g⁻¹ dry weight, respectively. The estrogen removal in the SMBRs was directly influenced by a combination of simultaneous biodegradation–adsorption processes, indicating that the main removal mechanism of the estrogens in the SMBRs is the biodegradation process. The E1, E2 and EE2 were biologically degraded in the SMBR (87–100%). The sorption of estrogens onto activated sludge was from 2%. Therefore, a high potential for estrogen removal by biodegradation in the SMBR was observed, allowing less estrogen concentration in the dissolved phase available for the adsorption of these compounds onto biological flocs. Two different methods were carried out for mass balance calculations of estrogens in SMBR. For the first method, the measured data was used in both liquid and solid phases, whereas for the second one, it was in aqueous phase and solid–water distribution coefficients (K_d) value of E1, E2 and EE2. The purpose of these methodologies is to make easier the identification of the main mechanisms involved in the removal of E1, E2 and EE2 in a SMBR. Both methods can be applied in order to determine the mechanism, fate and distribution of estrogens in a SMBR.