Calibration of WatPro

In order to maximize model accuracy, WatPro can be calibrated for each water treatment facility. An example for Total Trihalomethane (TTHM) calibration is presented as applied to the Britannia Water Treatment Plant (Ottawa, Ontario). The Britannia facility uses chlorine as the primary disinfectant and, typically, treated flow rates range from 155,000 m3/d to 260,000 m3/d.

Study Objectives

Calibration Procedures

Uncalibrated Model for TTHM Formation

The form of the TTHM model used in WatPro is based on research conducted by Amy et. al. (Amy G., Chadik and Chowdhury, "Developing Models for Predicting Trihalomethane Formation Potenial and Kinetics", Journal AWWA, 79:7:89-97 (July, 1987)). The emperical model developed by Amy et. al. is presented below.

TTHM = 0.00309*[(TOC*UV)^0.44]*[Cl2^0.409]*[t^0.265]
*[T^1.06]*[(pH-2.6]^0.715]*[(Br+1)^0.03]
where:

WatPro Schematic of the Britannia Water Treatment Facility

The schematic used to represent the Britannia facility is presented below.


Modeling Results

The predictive capabilty of the calibrated TTHM model is greatly enhanced relative to the uncalibrated model. This is illustrated in the figure below.

The model predicts that higher levels of TTHMs typically will form if the existing dosage of chlorine is increased to meed the target 4.2 log reduction of Giardia. This is illustrated in the figure below.

As water temperatures decline, the site specific calibrated model is able to maintain predictive accuracy while the uncalibrated model loses its predictive accuracy for TTHMs. This is illustrated in the figure below.

Modeling Summary/Implications