Fate of effluent organic matter and DBP precursors in an effluent-dominated river: A case study of wastewater impact on downstream water quality Baiyang Chen a, *, Seong-Nam Nam b , Paul K. Westerhoff c , Stuart W. Krasner d , Gary Amy e,f a Chinese Environmental Scholars and Professionals Network, 3004 S 101st Drive, Phoenix, AZ 85353, United States b University of Colorado, Dept. of Civil, Environmental & Architectural Engineering, ECOT 441, 1111 Engineering Dr., Boulder, CO 80309, United States c Arizona State University, Department of Civil & Environmental Engineering, Engineering Center, Box 5306, Tempe, AZ 85287-5306, United States d Metropolitan Water District of Southern California, Water Quality Laboratory, 700 Moreno Avenue, La Verne, CA 91750, United States e UNESCO-IHE, Institute for Water Education, P.O. Box 3015, 2601 DA Delft, The Netherlands f Technical University of Delft, 2600 AA Delft, The Netherlands article info Article history: Received 2 October 2008 Received in revised form 25 December 2008 Accepted 14 January 2009 Published online 3 February 2009 Keywords: Disinfection by-product Effluent organic matter Dissolved organic nitrogen Wastewater Fate and transport abstract The impact of treated wastewater discharges on downstream water quality was evaluated in an effluent-dominated stream in the Southwest USA. The fate and transport of effluent organic matter (EfOM) and disinfection by-product (DBP) precursors was studied. Nitrifi- cation and biodegradation were important mechanisms. Changes in DBP formation potential along the river appeared to correlate with dissolved organic carbon (DOC) and organic nitrogen concentrations and specific ultraviolet absorbance. The mean oxidation state of carbon (MOC) decreased in value along the river. MOC decreases paralleled decreases in the biodegradability of residual DOC (i.e., lower biodegradable DOC/DOC ratio). The EfOM was biodegradable by up to 40 percent, both in the stream and in a laboratory reactor, and many DBP precursors (e.g., haloacetonitriles, certain nitrosamines) decreased in concentration. Alternatively, the DBP yields for trihalomethanes or haloacetic acids either remained the same or increased slightly, suggesting that these precursors were part of the recalcitrant organic matter (OM). ª 2009 Elesevier Ltd. All rights reserved. 1. Introduction In addition to planned water recycling and reclamation programs, unintentional indirect potable reuse of wastewater has been recognized over the past few decades (Bunch et al., 1961), which will likely increase in the future as upstream wastewater treatment plants (WWTPs) discharge water into rivers or lakes that serve as downstream drinking-water supplies. Drought and competing in-stream demands may result in substantial (e.g., 37–77% in one effluent-impacted river) contribution of treated wastewater towards the stream flow (Krasner et al., 2008). Attention has recently focused on * Corresponding author. Tel.: þ1 480 840 4647; fax: þ1 602 944 8605. E-mail addresses: poplar_chen@hotmail.com (B. Chen), nams@colorado.edu (S.-N. Nam), p.westerhoff@asu.edu (P.K. Westerhoff), skrasner@mwdh2o.com (S.W. Krasner), g.amy@unesco-ihe.org (G. Amy). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres 0043-1354/$ – see front matter ª 2009 Elesevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.01.020 water research 43 (2009) 1755–1765