AWWA WQTC65845

The objective of this project was to identify the disinfection calculation method (i.e., model) that best describes the actual inactivation achieved in a continuous-flow ozone contactor. This objective was accomplished by conducting disinfection tests at a pilot-scale ozone contactor owned by the Southern Nevada Water Authority (SNWA). The testing was conducted using B. subtilis bacterial spores as the model microorganism spiked into the feed water to the ozone contactor. The measured inactivation of the spores was compared to that predicted by three different disinfection models: Conventional CefflluentT10 (CeffT10) Method; Integrated Residual Method; and, Segregated Flow (SFA) Method. To apply the models, three steps were implemented: Step 1 - identify the disinfection rate kinetics of the test microorganism; Step 2 - identify the values of the operational parameters under which the tests were conducted (e.g., flow rate, ozone residual values); and, Step 3 - utilize the model to calculate the inactivation of the test microorganism under the specific operational parameters. Step 1 was accomplished using bench-scale testing with the specific goal of identifying the inactivation coefficient, k10, of the test organism with ozone. Step 2 was accomplished by conducting tracer tests on the ozone contactor to characterize its hydraulics, as well as by operating the ozone contactor under different ozone dose conditions and collecting ozone residual samples from various locations in the contactor. Step 3 was accomplished by utilizing the data gathered in Steps 1 and 2 and calculating the inactivation of the test organism at each of the sets of contactor operating conditions. The study reported herein was partially funded by the Awwa Research Foundation under its Tailored Collaboration Funding program (project number 3168). This manuscript includes some of the results obtained. The full project results will be presented in the project final report which can be obtained from the Research Foundation. Includes tables, figures.