Students Tackle Disinfection Issues Using Drinking Water Treatment Simulator

Excerpted from Environmental Science and Engineering Magazine (Canada), November, 1999, pp 16-17.

In a recent innovative assignment, Civil Engineering students at the University of Toronto pooled their talents to address a growing drinking water issue. Teams of students in the graduate course taught by Dr. Robert Andrews used computer simulation to determine how best to optimize a water treatment plant to meet tough new standards for disinfectant residual and disinfectant by-product (DBP) concentrations, while maintaining the mandatory reduction of indicator microbes.

The students used Enviromega’s WatPro water treatment simulator for their assignment. Research on DBP formation completed by Dr. Andrews and his graduate students has been incorporated into the model, so that WatPro is state-of-the-art. For example, models for by-product formation when using chlorine dioxide as the primary disinfectant have recently been added to the model.

The assignment marked a new approach by Dr. Andrews and his research associate, Ron Hofmann, to address real-world problems in the classroom. For the assignment, student teams assumed the role of consulting firms. The aspiring engineers were required to prepare a report addressing the concerns of a municipality faced with stringent new limits on total trihalomethanes (TTHMs) and haloacetic acids (HAAs). The criteria would be similar to those proposed in the U.S. for the Stage II Disinfectant/Disinfection By-Product Rule. The students were called upon to evaluate potential scenarios, then recommend an optimal water treatment process train, taking into account both operational and regulatory constraints.

The problem was presented so that there was no easy solution. In fact, there was no single "correct" answer. The students would be forced to accept some trade-offs, having to justify them as they would in real life. Good judgement, guided by the predictions of the software, was required.
Simulation allowed the students to test a variety of process options in a short interval of time, allowing them to quickly determine strategies which could, or could not, be considered as viable alternatives. As well, the students determined that many different factors needed to be evaluated, from raw water quality, to the removal or organic DBP pre-cursor material, to the choice of disinfectant, to the required contact time in order to ensure adequate disinfection.

The student response to the assignment was very enthusiastic. It presented an opportunity to creatively apply the theories that they were learning in the classroom, with the ability to immediately see the outcome. A computer model gives the students an immediate cause-and-effect response across the entire treatment train. Prof. Andrews stated that "The overall quality of the reports was excellent, and the students were able to grasp and solve difficult real-life engineering problems by using the model in the classroom".

The WatPro schematic at right depicted the increase in THM concentrations through a water treatment plant .

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