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AWWA ACE56310

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AWWA ACE56310 An Alternative Approach to Determining Dose Distribution and Microbial Inactivation in UV Reactors Using Computational Fluid Dynamics (CFD)

Conference Proceeding by American Water Works Association, 06/16/2002

Ducoste, Joel; Linden, Karl

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This paper reports on a study that was done to evaluate the use of an Eulerian based approach for modeling microbial inactivation and dose distribution in UV reactors. In the Eulerian approach, microbial movement was simulated as a reacting continuous tracer with reaction kinetics based on the best-fit inactivation model for the target microorganism. The Eulerian approach was applied to a baffled and an unbaffled open channel UV reactor that were used in a study by Chiu et al (1999a, 1999b) and in a 12-in. diameter two-lamp closed conduit UV reactor. The results from the Eulerian approach simulations were compared to the microbial inactivation and dose distribution results that were produced using a Lagrangian particle tracking technique. Overall, the effluent microbial inactivation results that were produced using the Eulerian approach agreed well with particle tracking results. Deviations between the Eulerian and particle tracking approaches might be due to the turbulence model selection. Further research using other turbulence models needs to be done to determine the impact of these models on the effluent microbial inactivation results. The Eulerian based dose distribution was developed by converting the effluent viable microbial concentration into an equivalent dose using a disinfection log survival equation (i.e., series event model or Chick-Watson model). Two probability density functions were evaluated with the Eulerian based dose distribution: density function based on cell flow rate fraction in the effluent plane; and, density function based on the cell mass rate fraction in the effluent plane. The results showed that the flow-rate fraction density function was in good agreement with the particle tracking density function that is based on the fraction of total particles. As with the particle tracking density function, the flow-rate fraction density function produced a dominant peak in the high dose range for Chiu et al. (1999a) open channel reactor with a minor peak in the low dose range. The dominant peak in the high dose range was due to the large fraction of the flow that moves through lamp central region. For the same open channel reactor, however, the mass-rate fraction density function produced only one dominant peak in the low dose region since a larger fraction of viable microorganisms comes from the near wall regions. As a result, the mass-rate fraction density function may provide engineers with a more sensitive way of quantifying the impact of design changes on the microorganisms receiving low UV doses. Includes 14 references, tables, figures.

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Edition: Vol. - No. Published: 06/16/2002 Number of Pages: 16 File Size: 1 file , 470 KB