Prior research has shown that pH is a major factor affecting yields and speciation of the main classes of DBP. Effects of pH on the speciation coefficients in the formal models of bromide effects on the formation of trihalomethanes (THM) and haloacetic acids (HAA) have not been explored. This study investigated effects of pH, bromide and natural organic matter (NOM) level on yields and speciation of THM and HAA species generated in chlorinated water. Experimental data were obtained using two water sources, one with a medium (DOC = 1.4 mg/L and SUVA = 2.60 L mg-1 m-1) and the other with high (DOC = 7.7 mg/L and SUVA = 4.26 L mg-1 m-1) organic carbon level. The experiments employed the simulated distribution system (SDS) procedure at varying bromide concentrations and pH values of 7.0, 8.5 and 10.Obtained results demonstrate that the changes in the speciation of THM and HAA at varying bromide concentration and pHs ranging from 7 to 10 can be modeled using mathematical expressions derived based on the first-principles kinetic theory of halogen incorporation into reactive sites in NOM. The interpretation of the THM and HAA data for the two investigated waters indicates the presence of considerable site-specificity of sequential halogen incorporation reactions as well as the existence of common effects of pH on the critically important model parameters. For instance, in the case of X2AA, the dimensionless ratios of the bromination/chlorination reaction rates were not consistently affected by pH variations. For THMs, the change of pH impacted the dimensionless bromination/chlorination reaction rates, demonstrating a preference toward bromination which is different for the diverse node of halogen incorporation into NOM.These results help to better understand the generation and potential health effects of THM and HAA at varying operating conditions in water treatment and distribution systems.

Modeling THM and HAA in chlorinated waters: Effect of pH on the speciation coefficients at varying bromide level and SUVA

248th National Meeting (2014)

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