Evaluating Sequential Disinfection in a Water Treatment System Using a Non-biological Surrogate.
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Date
2005-01-11
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Abstract
Fluorescent YG-microspheres (Polysciences Inc.) were evaluated to simulate Cryptosporidium inactivation in a flow-through system that utilizes multiple disinfectants. Experiments were performed in a disinfection process consisting of an ozone primary stage and a secondary free chlorine treatment stage. Impacts of the chemical disinfectant exposure were calculated by tracking the changes in fluorescence distribution with a flow cytometer. Microspheres were initially pretreated to reduce their fluorescence intensity to a level that would allow them to closely mimic Cryptosporidium. Microsphere survival ratios (N/No) were calculated by replicating the inactivation of Cryptosporidium observed by Driedger et al. [6] and selecting an appropriate fluorescence intensity threshold in a histogram analysis. The results from these flow-through experiments suggest that the fluorescence decay of YG-fluorescent microspheres does display synergistic effects when free chlorine is used sequentially with ozone. This study also included the use of numerical models to simulate sequential disinfection processes. Femlab 3.0a and the Segregated Flow Reactor method were used to evaluate sequential disinfection processes. These numerical models were set up to mimic the experimental conditions observed in this research. The sequential disinfection inactivation predicted in these models was similar to the experimental fluorescence decay of the microspheres. However, the models were not effective at predicting fluorescent intensity changes at different intermediate points within the disinfection process stream.
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Keywords
modeling, microsphere, Cryptosporidium, disinfection, sequential, chlorine, ozone
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Degree
MS
Discipline
Civil Engineering
