Application of non-biological surrogates for analysis of sequential disinfection continuous flow systems

Abstract

ABSTRACT Brannon RichardsJoel Ducoste (corresponding author)Department of Civil, Construction, andEnvironmental Engineering,North Carolina State University,208 Mann Hall CB 7908,Raleigh, NC 27695-7908,USAE-mail: jducoste@eos.ncsu.edu Fluorescent YG-microspheres (Polysciences Inc.) were evaluated to simulate Cryptosporidiuminactivation in a continuous flow system that utilizes multiple disinfectants. Experiments wereperformed in a disinfection process consisting of an ozone primary stage and a secondary freechlorine stage. Impacts of the chemical disinfectant exposure were calculated by tracking thechanges in fluorescence distribution with a flow cytometer. Tests were performed at two flowrates (11- and 15.5-ml/s) and a target concentration-time (Ct) product of 1.4mg/L-min for ozoneand 510mg/L-min for chlorine. Analysis of the results suggest that the fluorescence decay ofYG-fluorescent microspheres does display synergistic effects when free chlorine is usedsequentially with ozone in a continuous flow system. The study also included the use of a simpleSegregated Flow Reactor (SFR) model to simulate the sequential disinfection process. The modelwas not effective at predicting fluorescent intensity changes at different intermediate pointswithin the disinfection process stream due to the complexity of the paths taken by themicrospheres through the ozone primary disinfectant chamber and its eventual influence onchlorine secondary disinfectant kinetics. An ozone Ct distribution, which utilized the fluorescencemicrospheres experimental data and was created from the range of paths traveled by themicrospheres, displayed a range of Ct values between 0.5 to 3.2mg/L-min for the low flowcondition and 0.8 to 2.2mg/l-min for the high flow condition. A new model structure wasproposed that may improve the simulation of sequential disinfection systems.