The role of effluent nitrate in trace organic chemical oxidation during UV disinfection Olya S. Keen a , Nancy G. Love b , Karl G. Linden a, * a Department of Civil, Environmental and Architectural Engineering, University of Colorado, UCB 428, Boulder, CO 80309, USA b Department of Civil and Environmental Engineering, University of Michigan, 1351 Beal Avenue, 183 EWRE, Ann Arbor, MI 48109, USA article info Article history: Received 30 April 2012 Received in revised form 17 June 2012 Accepted 26 June 2012 Available online 10 July 2012 Keywords: Advanced oxidation Hydroxyl radical Nitrate Nitrite Micropollutants Wastewater treatment Ultraviolet disinfection abstract Most conventional biological treatment wastewater treatment plants (WWTPs) contain nitrate in the effluent. Nitrate undergoes photolysis when irradiated with ultraviolet (UV) light in the 200e240 and 300e325 nm wavelength range. In the process of nitrate photol- ysis, nitrite and hydroxyl radicals are produced. Medium pressure mercury lamps emitting a polychromatic UV spectrum including irradiation below 240 nm are becoming more common for wastewater disinfection. Therefore, nitrified effluent irradiated with poly- chromatic UV could effectively become a de facto advanced oxidation (hydroxyl radical) treatment process. UV-based advanced oxidation processes commonly rely on addition of hydrogen peroxide in the presence of UV irradiation for production of hydroxyl radicals. This study compares the steady-state concentration of hydroxyl radicals produced by nitrate contained in a conventional WWTP effluent to that produced by typical concen- trations of hydrogen peroxide used for advanced oxidation treatment of water. The quantum yield of hydroxyl radical production from nitrate by all pathways was calculated to be 0.24  0.03, and the quantum yield of hydroxyl radicals from nitrite was calculated to be 0.65  0.06. A model was developed that would estimate production of hydroxyl radicals directly from nitrate and water quality parameters. In effluents with >5 mg-N/L of nitrate, the concentration of hydroxyl radicals is comparable to that produced by addition of 10 mg/L of H 2 O 2 . Nitrifying wastewater treatment plants utilizing polychromatic UV systems at disinfection dose levels can be expected to achieve up to 30% degradation of some micropollutants by hydroxyl radical oxidation. Increasing UV fluence to levels used during advanced oxidation could achieve over 95% degradation of some compounds. ª 2012 Elsevier Ltd. All rights reserved. 1. Introduction Recent findings by researchers across the world indicate that pharmaceuticals and other micropollutants in wastewater treatment plant effluents have a significant effect on aquatic life (Lye et al., 1997; Routledge et al., 1998; Vajda et al., 2008; Painter et al., 2009; Foster et al., 2010). In light of these reports on ecological implications, and the recognized connection between wastewater effluent and drinking water influent in the urban water cycle, advanced treatment options for wastewater will likely be required or desired in the near future. Advanced oxidation processes (AOPs) have been studied as a potential technology for reducing environmental contamination by pharmaceuticals in effluents (Klavarioti et al., 2009; Rosario-Ortiz et al., 2010) since current conven- tional and advanced wastewater treatment processes are not * Corresponding author. Tel.: þ1 303 492 4798; fax: þ1 303 492 7317. E-mail address: karl.linden@colorado.edu (K.G. Linden). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 46 (2012) 5224 e5234 0043-1354/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2012.06.052