Integrative Advanced Oxidation and Biofiltration for Treating Pharmaceuticals in Wastewater Yaal Lester 1 , Diana S. Aga 2 , Nancy G. Love 3 , Randolph R. Singh 2 , Ian Morrissey 1 , Karl G. Linden 1* ABSTRACT: Advanced oxidation of active pharmaceutical ingredients (APIs) in wastewater produces transformation products (TPs) that are often more biodegradable than the parent compounds. Secondary effluent from a wastewater treatment plant was treated using UV-based advanced oxidation (LPUV/H 2 O 2 and MPUV/NO 3 ) followed by biological aerated filtration (BAF), and different APIs and their transformation products were monitored. The advanced oxidation processes degraded the APIs by 55–87% (LPUV/H 2 O 2 ) and 58–95% (MPUV/NO 3 ), while minor loss of APIs was achieved in the downstream BAF system. Eleven TPs were detected following oxidation of carbamazepine (5) and iopromide (6); three key TPs were biodegraded in the BAF system. The other TPs remained relatively constant in the BAF. The decrease in UVabsorbance (UVA 254 ) of the effluent in the BAF system was linearly correlated to the degradation of the APIs (for the MPUV/NO 3 –BAF), and can be applied to monitor the biotransforma- tion of APIs in biological-based systems. Water Environ. Res., 88, 1985 (2016). KEYWORDS: Advanced oxidation, biofiltration, organic contaminants, transformation products, wastewater treatment. doi:10.2175/106143016X14504669767454 Introduction Advanced oxidation processes (AOPs) are efficient at degrading active pharmaceutical ingredients (APIs) in wastewa- ter, through the enhanced generation of hydroxyl radicals (HO*). This highly reactive oxidant can degrade a vast range of contaminants, potentially leading to full mineralization (Ray et al., 2006). However, for technical and economic reasons, full mineralization of contaminants is rarely achieved, and in these instances the process produces a large number of transformation products (TPs) (Fatta-Kassinos et al., 2011). Formation of persistent TPs is a potential drawback of AOPs, especially if the biologically active part of a molecule remains unmodified and the product retains some level of potency. Examples of relevant TPs are widespread in the scientific literature. Vogna et al. (2004) showed that acridine, a carcinogen, was a TP from the UV/H 2 O 2 treatment of carbamazepine. Kondrakov et al. (2014) found that photocatalytic oxidation of bisphenol A resulted in the formation of the hazardous DNA- binding agent, bisphenol A 3,4-quinone. Others have demon- strated an increase in both acute- and geno-toxicity of a solution containing the surfactant NP-10 (using Vibrio fischeri and Salmonella typhimurium respectively), following its exposure to UV/H 2 O 2 and photo-Fenton (although acute toxicity decreased to its initial value at the end of the treatment) (Karci et al., 2014). Clearly, AOPs provide only a partial solution for mitigating APIs contamination, and a more integrative treatment approach is needed. An attractive alternative for the removal of APIs and TPs is the combination of AOP and a subsequent biological process. An analogous solution is widely used for ozone treatment of APIs, relying on the fact that ozone cleavage of olefin groups and aromatic rings produces TPs that are more biodegradable than the parent compound (H¨ ubner et al., 2014); which are readily removed by subsequent biological treatment. Production of biodegradable TPs can be expected during advanced oxidation, since the transformation pathway typically involves addition of hydroxyl groups to the parent molecule (e.g. to aromatic rings). Hydroxylation of aromatic rings enables ring- opening (by bacteria in the biological treatment), which is a critical step in biotransformation of aromatic compounds. The products of ring cleavage (i.e. carboxylic acids) can be further biotransformed and mineralized (Harayama et al., 1992). A recent study conducted in our lab showed that UV/H 2 O 2 TPs of carbamazepine (which is biologically recalcitrant), which contain a hydroxyl or carbonyl group, were mineralized in a bench-scale activated sludge reactor (Keen et al., 2012). Similar results were obtained for iopromide, an x-ray contrast agent (Keen et al., 2015). Other researchers demonstrated an increase in contam- inants biodegradability (presented as the ratio of biological oxygen demand-BOD 5 /chemical oxygen demand-COD), follow- ing different AOPs (Kalinski et al., 2014; Romero et al., 2014; Villegas-Guzman et al., 2015). An integrative treatment approach that includes oxidation and biotransformation has the potential to remove persistent APIs and TPs from wastewater effluent. The objective of this study was to demonstrate the in situ application of UV-based AOP (UV/AOP), followed by biological aerated filtration (BAF), for the removal of APIs and TPs from secondary wastewater effluent. The selected AOPs were UV/H 2 O 2 and UV/NO  3 , which demonstrated efficient degradation of APIs in our previous study (Lester et al., 2014). Biological aerated filter (BAF) was chosen due to its relatively small footprint and low hydraulic retention time (HRT). 1 Department of Civil, Environmental, and Architectural Engineering, University of Colorado, UCB 428, Boulder, Colorado 80309, United States 2 Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, NY 14260, United States 3 Civil and Environmental Engineering Department, University of Michigan, Ann Arbor, Michigan 48109, United States * Department of Civil, Environmental, and Architectural Engineering, University of Colorado, UCB 428, Boulder, Colorado 80309, United States; email: karl.linden@colorado.edu November 2016 1985