Fluorescent YG-microspheres (Polysciences Inc.) were evaluated to simulate Cryptosporidium inactivation in a continuous flow system that utilizes multiple disinfectants. Experiments were performed in a disinfection process consisting of an ozone primary stage and a secondary free chlorine stage. Impacts of the chemical disinfectant exposure were calculated by tracking the changes in fluorescence distribution with a flow cytometer. Tests were performed at two flow rates (11- and 15.5-ml/s) and a target concentration-time (Ct) product of 1.4 mg/L-min for ozone and 510 mg/L-min for chlorine. Analysis of the results suggest that the fluorescence decay of YG-fluorescent microspheres does display synergistic effects when free chlorine is used sequentially with ozone in a continuous flow system. The study also included the use of a simple Segregated Flow Reactor (SFR) model to simulate the sequential disinfection process. The model was not effective at predicting fluorescent intensity changes at different intermediate points within the disinfection process stream due to the complexity of the paths taken by the microspheres through the ozone primary disinfectant chamber and its eventual influence on chlorine secondary disinfectant kinetics. An ozone Ct distribution, which utilized the fluorescence microspheres experimental data and was created from the range of paths traveled by the microspheres, displayed a range of Ct values between 0.5 to 3.2 mg/L-min for the low flow condition and 0.8 to 2.2 mg/l-min for the high flow condition. A new model structure was proposed that may improve the simulation of sequential disinfection systems.

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