POST PRINT of the paper which is printed in Water Research 2012 46(4) Pages 167–1175. The publishers’ version is available at: http://dx.doi.org/10.1016/j.watres.2011.12.003 Suspended biofilm carrier and activated sludge removal of acidic pharmaceuticals P. Falås*, A. Baillon-Dhumez*, H. R. Andersen**, A. Ledin*, J. la Cour Jansen* * Water and Environmental Engineering, Department of Chemical Engineering, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden **Department of Environmental Engineering, Technical University of Denmark, B113, DK-2800 Kgs Lyngby, Denmark Keywords: Pharmaceuticals; Activated sludge; Biofilm carriers Abstract - Removal of seven active pharmaceutical substances (ibuprofen, ketoprofen, naproxen, diclofenac, clofibric acid, mefenamic acid, and gemfibrozil) was assessed by batch experiments, with suspended biofilm carriers and activated sludge from several full-scale wastewater treatment plants. A distinct difference between nitrifying activated sludge and suspended biofilm carrier removal of several pharmaceuticals was demonstrated. Biofilm carriers from full-scale nitrifying wastewater treatment plants, demonstrated considerably higher removal rates per unit biomass (i.e. suspended solids for the sludges and attached solids for the carriers) of diclofenac, ketoprofen, gemfibrozil, clofibric acid and mefenamic acid compared to the sludges. Among the target pharmaceuticals, only ibuprofen and naproxen showed similar removal rates per unit biomass for the sludges and biofilm carriers. In contrast to pharmaceutical removal, the nitrification capacity per unit biomass was lower for the carriers than the sludges, which suggests that neither the nitrite nor the ammonia oxidizing bacteria are primarily responsible for the observed differences in pharmaceutical removal. The low ability of ammonia oxidizing bacteria to degrade or transform the target pharmaceuticals was further demonstrated by the limited pharmaceutical removal in an experiment with continuous nitritation and biofilm carriers from a partial nitritation/anammox sludge liquor treatment process. 1. Introduction Detection of pharmaceuticals in wastewater effluents and receiving waters has increased the awareness of the potential threat that pharmaceuticals pose on the aquatic environment. Removal efficiency of pharmaceuticals at wastewater treatment plants (WWTPs) is often highly dependent on the biological treatment step (Carballa et al., 2004; Zorita et al., 2009) and it has been indicated that the biological treatment design can influence the overall removal of estrogenic activity (Kirk et al., 2002; Svenson et al., 2003) and pharmaceuticals (Kasprzyk-Hordern et al., 2009). Several comparative studies on pharmaceutical removal in biological systems have been presented, often focusing on activated sludge systems and membrane bioreactors (Bernhard et al., 2006; Clara et al., 2005 a; De Wever et al., 2007; Lesjean et al., 2005; Radjenović et al., 2009). The importance of solid retention time (SRT) on pharmaceutical removal in systems with suspended bacteria cultures is widely discussed and it has been indicated that a prolonged SRT can promote removal of some pharmaceuticals (Clara et al., 2005 b; Falås et al., in press;