Trihalomethane species model for drinking water supply systems

Abstract

Despite the existence of significant knowedge on complex mechanisms of THM formation, a simple kinetic model to predict THM species concentration is not available, hindering application of knowlwdge for regulatory, monitoring and operational control. The parallel second order reaction (2R) model containing fast and slow reactants has been well established to describe the chlorine decay kinetics under distribution conditions. The proposed THM species model expands the 2R model by systematically incorporating the initial unproductive (not forming THM) chlorine consumption and assuming each THM species is formed at a fixed yield (µg-THM species/mg- productive chlorine consumption). The model concept is tested on 15 water samples that contain a wide range of dissolved organic carbon, specific UV absorbence, and bromide concentrations collected from Australia and US. In all samples, the model describes the THM species concentrations well (error < 3 µg/L in 84% of model estimates) as long as the chlorine profile is described accurately (R2 > 0.984). The model formulated from the minimum data (initial and two other data points of Cl2 and THM species) predicts the rest of concentrations of THM species from only chlorine measurements. To fully optimise the system or adopt in regulatory monitoring, the effect of changes due to bulk water quality, operational conditions and wall (and biofilm) effects on THM formation kinetics should be established. A similar concept could be extended to other DBP, but rigorous testing is needed.