Modeling of THM and HAA Formation in Surface Waters upon Chlorination

The more stringent drinking water Disinfection By-Product (DBP) regulations have led utilities to examine and optimize their disinfection processes. Practical models for THM and HAA formation will assist utilities in minimizing DBP formation. Production of TTHM and HAA9 is proportional to chlorine consumption in the Missouri surface waters. A new mechanistic model was developed to predict the TTHM and HAA9 formation in raw and alum treated waters based on the decay rate constants obtained in the chlorine decay modeling. DBP yield coefficient can be used to predict TTHM and HAAs formation in specific waters and can also be used to compare the TTHMFP and HAAFP between different waters. DBP formation rates were initially rapid corresponding with the rapid consumptionof chlorine followed by a slower declining rate of production. DCAA and TCAA were the main species among the nine HAAs. Brominated species were preferentially formed in the early part of the reaction period and maintained the same concentrations after 24 hours. There was no big difference in the specificTHMFP and formation kinetics among the various molecular weight fractions (CH3 to CH6).