The removal mechanisms of four natural steroid hormones-estradiol, estrone, testosterone, and progesterone-by nanofiltration (NF) membranes were investigated. Two nanofiltration membranes with quite different permeabilities and salt retention characteristics were utilized. To better understand hormone removal mechanisms, the membrane average pore size was determined from retention data of inert organic solutes of various molecular weights and a pore transport model that incorporates steric (size) exclusion and hindered convection and diffusion. Results indicate that, at the early stages of filtration, adsorption (or partitioning) of hormones to the membrane polymer is the dominant removal mechanism. Because the adsorptive capacity of the membrane is limited, the final retention stabilizes when the adsorption of hormones into the membrane polymer has reached equilibrium. At this later filtration stage, the overall hormone retention is lower than that expected based solely on the size exclusion mechanism. This behavior is attributed to partitioning and subsequent diffusion of hormone molecules in the membrane polymeric phase, which ultimately results in a lower retention. Hormone diffusion in the membrane polymeric matrix most likely depends on the size of the hormone molecule, hydrogen bonding of hormones to membrane functional groups, and hydrophobic interactions of the hormone with the membrane polymeric matrix.

This study investigates the retention mechanisms of three pharmaceuticals-sulfamethoxazole, carbamazepine, and ibuprofen-by nanofiltration (NF) membranes. Laboratory-scale experiments were carried out with two well-characterized NF membranes, with the goal of relating pharmaceutical retention behavior to membrane characteristics, physicochemical properties of the pharmaceutical molecules, and solution chemistry. Results show that retention of pharmaceuticals by a tight NF membrane is dominated by steric (size) exclusion, whereas both electrostatic repulsion and steric exclusion govern the retention of ionizable pharmaceuticals by a loose NF membrane. In the latter case, speciation of pharmaceuticals may lead to a dramatic change in retention as a function of pH, with much greater retention observed for ionized, negatively charged pharmaceuticals. For uncharged pharmaceutical species, intrinsic physicochemical properties of the pharmaceutical molecules can substantially affect their retention. In its neutral form, ibuprofen adsorbs considerably to the membrane because of its relatively high hydrophobicity. Similarly, polarity (represented by the dipole moment) can influence the separation of molecules that are cylindrical in shape because they can be directed to approach the membrane pores head-on due to attractive interaction between the molecule polar centers and fixed charged groups on the membrane surface. This phenomenon is probably inherent for high dipole moment organic compounds, and the governing retention mechanism remains steric in nature.

Environmental Science and Technology (Revised version January 2005): note also CORRECTION published in EST 39(18): 7344* Corresponding author: Phone +61 2 9385 5082, fax: +61 2 9313 8624, email: andrew.feitz@unsw.edu.au AbstractA comparison of estrone (E1), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) removal at a coastal enhanced primary and inland advanced sewage treatment plant (STP) is reported. The average concentration of estrogens in the raw sewage is similar to reports in other studies. The sequential batch reactor at the advanced STP removed on average 85% of the incoming E1 and 96% of the E2. Further removal was observed during later microfiltration with the estrogen concentration below detection (<0.1 ng.L -1 ) after reverse osmosis. Some 6% of the influent E1+E2 was removed in the waste activated sludge. The detection of EE2 in the waste activated sludge (0.42 ng.g -1 solids dry weight), undetectable in the raw sewage, suggests that EE2 is resistant to biological treatment in the sequential batch reactor and is primarily removed due to sorption. Little estrogen removal was observed at the enhanced primary with only 7% of E1 and 0% of E2 removed. Low removal is expected based on the degree of estrogens partitioning in the organic fraction given the relatively low solids concentration, but surprisingly, some 43% of E2, 24% of E1 and 100% of EE2 remains associated with the solids fraction in the treated effluent. Further research is necessary to determine whether the low level of estrogen removal for the coastal treatment plant will adversely affect the receiving marine environment. 2 IntroductionThere are increasing concerns that the release of steroid estrogens post wastewater treatment is leading to abnormal reproductive systems in freshwater and marine dwelling animals (1-3). Human excretion is considered to be the primary source of steroid estrogens from the urban environment and are is released by individuals into sewerage system in both conjugated and unconjugated forms at µg levels per day (4-6). Johnson and Williams (6) recently developed a model to estimate the quantities of estrogens by the human population, taking in consideration conjugation and metabolism of natural and synthetic hormones in the body and the different quantities released by different population groups. The average human excretion of estrogens per head is reported to be 10.5 µg.d -1 for estrone (E1), 6.6 µg.d -1 for 17β-estradiol (E2), with an additional 3.3 µg.d -1 transformation of the E1 to E2 in the sewer (6). The population normalized concentration of the synthetic steroid 17α-ethinylestradiol, an active agent in the contraceptive pill, is 1 µg.d -1 per head (6).