A variable parabolic reaction coefficient model for chlorine decay in bulk water

Area of Science:

• Environmental Engineering
• Water Chemistry
• Chemical Kinetics

Background:

• First-order models are common for chlorine decay but lack accuracy.
• Variable reaction coefficient models offer higher accuracy but are complex and lack analytical solutions.

Purpose of the Study:

• To develop a variable parabolic reaction coefficient model for simulating and predicting chlorine decay in bulk water.
• To provide an analytical solution for this new model.

Main Methods:

• Incorporated decreasing reactivity into a variable coefficient based on chlorine-reactive species concentration.
• Derived an analytical solution for the model.
• Validated the model using experimental data (varying chlorine concentrations, temperatures, rechlorination, water mixing).
• Established parameter-temperature relationships using the Arrhenius equation.
• Subtracted pipe wall chlorine consumption to apply laboratory-derived parameters to system models.
• Proposed a method to determine model parameters for output water in water distribution networks (WDN).

Main Results:

• The variable parabolic reaction coefficient model demonstrated accuracy under various conditions.
• An analytical solution was successfully derived, simplifying application.
• The Arrhenius equation effectively related model parameters to temperature.
• A method was proposed for determining parameters in WDNs with unknown initial conditions.

Conclusions:

• The developed variable parabolic reaction coefficient model offers a more accurate and analytically solvable approach to chlorine decay prediction.
• The model's ability to incorporate decreasing reactivity and its applicability to real-world WDN scenarios represent significant advancements in water quality management.