Trihalomethane species model for drinking water supply systems.

Area of Science:

• Environmental Chemistry
• Water Quality Management
• Chemical Kinetics

Background:

• Complex mechanisms of trihalomethane (THM) formation are known, but a simple kinetic model for predicting THM species concentration is lacking.
• This gap hinders the application of knowledge for regulatory, monitoring, and operational control of THM in drinking water.
• Existing models for chlorine decay kinetics, like the parallel second-order reaction (2R) model, provide a basis for developing predictive THM models.

Purpose of the Study:

• To develop and validate a simple kinetic model for predicting THM species concentration in drinking water.
• To expand the established 2R chlorine decay model by incorporating unproductive chlorine consumption and fixed THM yield.
• To assess the model's accuracy across diverse water quality conditions and geographical locations.

Main Methods:

• The proposed THM species model expands the 2R model by including initial unproductive chlorine consumption.
• Each THM species is assumed to form at a fixed yield relative to productive chlorine consumption.
• The model's concept was tested on 15 water samples from Australia and the US with varying dissolved organic carbon, UV absorbance, and bromide concentrations.

Main Results:

• The model accurately described THM species concentrations in all tested samples, with errors less than 3 µg/L in 84% of estimates.
• Model performance was highly dependent on accurate chlorine profile description (R² > 0.984).
• A model formulated with minimal data (initial and two other chlorine and THM data points) successfully predicted remaining THM concentrations using only chlorine measurements.

Conclusions:

• The developed kinetic model effectively predicts THM species concentrations using chlorine measurements, offering a practical tool for water management.
• Further research is needed to establish the effects of bulk water quality, operational conditions, and wall/biofilm interactions on THM formation kinetics for full optimization and regulatory adoption.
• The model's concept shows potential for extension to other disinfection byproducts (DBPs), requiring rigorous validation.