Simplified chemical chloramine decay model for water distribution systems

Area of Science:

• Environmental Chemistry
• Water Treatment Engineering
• Chemical Kinetics

Background:

• Complex mechanistic models for predicting chloramine loss in ultrapure water are computationally intensive and rarely used outside academic research.
• Existing models often require specialized software and extensive ordinary differential equation (ODE) simulations, limiting practical application in water treatment.

Purpose of the Study:

• To develop a simplified, practical model for predicting chloramine decay in ultrapure water.
• To create a single-line equation with fixed coefficients that accurately estimates the first-order decay coefficient.
• To provide a user-friendly tool for water utilities to assess chloramine stability under various conditions.

Main Methods:

• Developed a simplified predictive model represented by a single-line equation with eight fixed coefficients.
• Validated the model's accuracy in predicting the first-order chloramine decay coefficient across specified ranges of pH, chlorine-to-ammonia ratio, initial dose, and alkalinity at 25°C.
• Incorporated the Arrhenius equation for calculating decay coefficients at different temperatures (4-35°C).

Main Results:

• The simplified model accurately predicts the first-order chloramine decay coefficient as a function of pH, chlorine-to-ammonia mass ratio, initial chloramine dose, and alkalinity.
• A relative model allows for evaluating the individual or collective impact of these water quality parameters.
• A minor adjustment to the initial chloramine concentration is recommended for accurate chloramine profile prediction based on pH.

Conclusions:

• The developed simplified model offers a practical and accurate alternative to complex mechanistic models for chloramine loss prediction in ultrapure water.
• This model can be readily adapted by water utilities for operational use and future integration of other decay factors like NOM, bromide, and microbiological activity.
• The findings facilitate better management of chloramine residuals in water treatment processes.