Evaluation of Computational Fluid Dynamics (CFD) for Modeling UV-Initiated Advanced Oxidation Processes

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The use of ultraviolet-initiated (UV-initiated) advanced oxidation processes (AOP) is rapidly becoming an attractive alternative for the degradation of emerging organic contaminants that are not easily removed using conventional water treatment processes. Design and optimization of UV/H2O2 systems must incorporate both reactor design (hydrodynamics, lamp orientation) and chemical kinetics (reaction mechanisms, kinetic rate constants). This research lays the groundwork for a protocol for using CFD models to simulate UV-initiated AOPs and, in doing so, provides the start for an improved design process to meet the needs of the water treatment community. In this CFD model, the combination of turbulence sub-models, fluence rate sub-models, and kinetic rate equations results in a comprehensive and flexible design tool for predicting the effluent chemical composition from a UV-initiated AOP reactor. To validate the CFD simulation, the results of the model under various operating conditions were compared to pilot reactor trials for the target contaminants of an organic dye (methylene blue) and an antibiotic (sulfamethoxazole). The CFD model tends to under-predict the percent removal of methylene blue within the reactor. In addition, the percent difference between the pilot and the CFD results increases with increasing flow rates. Similar to the methylene blue trials, the CFD simulations for sulfamethoxazole degradation under-predict the percent removals measured in the pilot reactors. The sensitivity to model parameters was evaluated. The MSSS sub-model predicted higher fluence rate values than that of the RAD-LSI sub-model. This increase in fluence rate translates to higher contaminant removal percentages predicted for both methylene blue and SMX. The turbulence sub-model selection for this reactor configuration was found to not significantly impact the predicted removal for methylene blue. As expected, the overall degradation of methylene blue was a strong function of the value of the second-order kinetic rate constant describing the reaction between methylene blue and the hydroxyl radical. Further, the overall removal of methylene blue was shown to be sensitive to the concentration of the radical scavenger dissolved organic carbon in the water matrix.



modeling, emerging contaminants, methylene blue, ultraviolet light, advanced oxidation, CFD





Civil Engineering