Exploring 17a-ethinylestradiol removal, mineralization, and bioincorporation in engineered bioreactors Taewoo Yi a , Susan Mackintosh b , Diana S. Aga b , Willie F. Harper, Jr. c, * a Department of Environmental Science and Engineering, Ewha Womans University, Seoul 120-750, South Korea b Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA c Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA article info Article history: Received 3 June 2010 Received in revised form 12 October 2010 Accepted 17 October 2010 Available online 23 October 2010 Keywords: Pharmaceuticals Sorption Wastewater Bioreactors microautoradioaugraphy abstract This research investigated removal, mineralization, and bioincorporation of 17a-ethiny- lestradiol (EE 2 ) in membrane bioreactors and conventional bioreactors. When the influent EE 2 concentration was >50 mg/L, the membrane bioreactor (MBR) biomass removed more EE 2 than conventional bioreactor (CBR) biomass in continuous tests, likely because the sorption partitioning coefficients are higher for MBR biomass. Microautoradiography was carried out to investigate the distribution of EE 2 within the aggregates retrieved from the bioreactors, and the results revealed concentration gradients present within the floc. Experiments using radiolabeled 14 C-EE 2 experiments (done with 24.5 mg/L EE 2 ) showed that EE 2 removal rates and the amount of EE 2 mineralized were similar in MBRs and CBRs. Direct measurements and bioenergetic estimates suggest that EE 2 -related carbon is probably incorporated into active biomass, despite the fact that EE 2 was added at a concentration that was much lower than that of the primary growth substrates. Published by Elsevier Ltd. 1. Introduction There is continuing interest in removal of 17a-ethinylestradiol (EE 2 ), a key emerging contaminant that has been detected in surface waters and groundwater (Kolpin et al., 2002). EE 2 has been linked to developmental anomalies in wildlife (such as feminized male fish) (Parkkonen et al., 2000). These negative effects appear to occur at very low concentrations (i.e. <10 ng/L) (e.g. Rodgers-Gray et al., 2000), making it important to avoid discharging EE 2 into water bodies. Because EE 2 is primarily introduced into domestic wastewater via urine and medical waste, wastewater treatment processes are important barriers for preventing the proliferation of EE 2 into the aquatic environ- ment. In order to improve removal of EE 2 in wastewater treat- ment plants, we must improve our understanding of how EE 2 is removed and mineralized in wastewater treatment systems. The activated sludge process is the most commonly used method for treatment of domestic wastewater, hence removal of EE 2 by activated sludge biomass has received considerable attention. Sorption of EE 2 to activated sludge biomass is thermodynamically favorable (Xu et al., 2008), the equilibrium partitioning coefficients (expressed as log(K d )) are generally between 2.3 and 2.7 (Clara et al., 2004; Ternes et al., 2004; Yi et al., 2006). The available data on K d allow practitioners to model sorption in activated sludge processes. Biodegradation, on the other hand, is an area where consensus is still devel- oping. A significant number of reports now suggest that nitrifying sludges (i.e. those that include autotrophic nitrifiers and heterotrophs) can co-metabolically remove EE 2 (Yi and Harper, 2007; Shi et al., 2004). However, the involvement of nitrifiers has been directly contested by Gaulke et al. (2008), who found that the slow-growing autotrophs were not * Corresponding author. Tel.: þ1 412 624 9548; fax: þ1 412 624 0135. E-mail address: wharper@pitt.edu (W.F. Harper Jr.). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 45 (2011) 1369 e1377 0043-1354/$ e see front matter Published by Elsevier Ltd. doi:10.1016/j.watres.2010.10.022