Effects of pH on the speciation coefficients in models of bromide influence on the formation of trihalomethanes and haloacetic acids Paolo Roccaro a,* , Gregory V. Korshin b , David Cook c , Christopher W.K. Chow c , Mary Drikas c a Department of Civil and Environmental Engineering, University of Catania, 95125 Catania, Italy b Department of Civil and Environmental Engineering, Box 352700, University of Washington Seattle, WA 98195-2700, United States c Australian Water Quality Centre, Adelaide, South Australia, Australia article info Article history: Received 31 January 2014 Received in revised form 13 May 2014 Accepted 14 May 2014 Available online 2 June 2014 Keywords: Disinfection by-products (DBP) Chlorination Kinetics Modelling Natural organic matter (NOM) SUVA abstract This study investigated effects of pH, bromide and natural organic matter (NOM) level on yields and speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) in chlori- nated water. Experimental data were obtained using two water sources, one with a me- dium (DOC ¼ 1.4 mg/L and SUVA ¼ 2.60 L mg 1 m 1 ) and the other with higher (DOC ¼ 7.7 mg/L and SUVA ¼ 4.26 L mg 1 m 1 ) organic carbon level. The experiments employed the simulated distribution system (SDS) procedure at varying bromide concen- trations and pH values of 7.0, 8.5 and 10. The speciation of THMs and dihalogenated HAAs (DHAAs) was interpreted based on the modelling of mixed halogenation yields via dimensionless ratios of bromination/chlorination reaction rates at each halogen incorpo- ration node. The approach allowed precise modelling of the speciation of THMs and DHAAs at all examined pHs. In the case of DHAA, the dimensionless ratios of the bromination/ chlorination reaction rates were not consistently affected by pH variations. For THMs, increase of pH caused the values of the dimensionless bromination/chlorination reaction rates to decrease in the case of halogenation of the initial reaction sites indicating a decreasing preference toward bromination at this reaction node. A similar trend was observed for the reactivity of dichlorinated reaction intermediate denoted as S Cl2 whose formation precedes the release of CHCl 3 and CHBrCl 2 . A similar but less consistent trend was observed for intermediate S BrCl whose halogenation yields both CHBrCl 2 and CHBr 2 Cl. An opposite trend of increasing preference towards bromination at higher pHs was observed monobrominated intermediate S Br and in some extent dibrominated intermedi- ate S Br2 . These results help develop detailed DBP speciation models which needed to better understand the generation and potential health effects of THMs and HAAs at varying operating conditions and ultimately to adopt measure to minimize their levels in drinking water systems. © 2014 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: þ39 095 7382716; fax: þ39 095 738 2748. E-mail address: proccaro@dica.unict.it (P. Roccaro). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/watres water research 62 (2014) 117 e126 http://dx.doi.org/10.1016/j.watres.2014.05.024 0043-1354/© 2014 Elsevier Ltd. All rights reserved.