Mechanistic-Based Disinfection and Disinfection Byproduct Models

EPA Grant Number: R826831
Title: Mechanistic-Based Disinfection and Disinfection Byproduct Models
Investigators: Westerhoff, Paul , Amy, Gary , Chowdhury, Zaid , Reckhow, David A.
Institution: Arizona State University - Main Campus , Malcolm Pirnie , University of Colorado at Boulder , University of Massachusetts - Boston
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: December 15, 1998 through December 14, 2001
Project Amount: $339,583
RFA: Drinking Water (1998) RFA Text |  Recipients Lists
Research Category: Drinking Water , Water


We propose developing a mechanistic-based numerical model for chlorine decay and regulated DBP (THM and HAA) formation derived from (free) chlorination; the model framework will allow future modifications for other DBPs and chloramination. Predicted chlorine residual and DBP results will be compared against predictions from several other quasi-mechanistic models. We anticipate a significant improvement in prediction accuracy over existing empirical models. Several modeling hypotheses are proposed as a basis for a mechanistic-based model for disinfectant decay and DBP formation. The central modeling hypothesis is that a two-site reaction mechanism can be used to predict disinfectant decay in the presence of natural organic matter (NOM). It assumes that NOM contains both slow and fast disinfectant-reacting and DBP-forming sites. NOM site densities and concentrations are related to the concentration, size, structure and functionality of NOM. Our model will also include fitted rate constants that are a function of pH and temperature. A series of distribution functions, based upon the predicted ratios of free-bromine to free-chlorine, will be used to estimate each of the four trihalomethane species (THM4) and each of the nine haloacetic acid species (HAA9).


DBP experimental data from completed projects conducted by the Investigators and other researchers will be integrated into a single Unified Database. Existing empirical models and newly developed numerical models will initially be calibrated with our Unified Database. Additional experimental data will be collected since prior databases lack complete documentation of NOM characteristics before and during disinfection addition. Controlled laboratory disinfection and DBP formation studies will be conducted using water collected at several points through different water treatment plants, including raw, coagulated, softened, and pre-oxidized (ozone and/or chlorine dioxide) waters, thus the waters represent a wide range of water qualities and NOM characteristics. Experiments will investigate the affects of pH and temperature, and NOM, bromide, and free-chlorine concentrations; DBP hydrolysis studies will also be conducted.

Expected Results:

A numerical computer model and software will be developed that can predict involving (i) inorganic ions, (ii) disinfectant consumption, (iii) THM4 and HAA9 formation, and (iv) THM4 and HAA9 stability. The model will be robust and flexible, making it easy to incorporate additional reactions for other disinfectants (e.g., chloramines) or DBPs in the future.

Publications and Presentations:

Publications have been submitted on this project: View all 23 publications for this project

Supplemental Keywords:

drinking water treatment, environmental chemistry, oxidation., RFA, Scientific Discipline, Water, Applied Math & Statistics, Mathematics, Environmental Chemistry, Analytical Chemistry, Drinking Water, monitoring, chlorine decay, oxidation, chemical byproducts, disinfection byproducts (DPBs), unified database, chlorine-based disinfection, treatment, chloramines, water quality, DBP risk management, drinking water contaminants, drinking water system, mechanistic-based models

Relevant Websites:

Progress and Final Reports:

  • 1999 Progress Report
  • 2000 Progress Report
  • Final Report