A CFD Modeling Protocol for Simulating the UV/H2O2 Advanced Oxidation Process
- Scott M. Alpert, PhD, PE, Hazen and Sawyer
- Joel J. Ducoste, PhD, North Carolina State University
Computational fluid dynamics (CFD) is becoming an effective tool for the design of ultraviolet-initiated (UV-initiated) advanced oxidation processes (AOP) for the degradation of emerging organic contaminants that are not easily removed using conventional water treatment processes. While some numerical techniques have been developed for understanding UV/AOP performance, these techniques are limited in their applicability for analyzing full-scale UV/AOP systems while incorporating both reactor design and chemical kinetics.
Design factors such as upstream hydraulic configurations, internal reactor layout, and lamp arrangement, may influence process performance. Water quality effects, including the impact of light- and radical-scavengers, will determine not only the size of the treatment system but also the appropriate placement in the treatment scheme. Thus, the availability of dynamic and rigorous models like the ones described by this protocol will streamline design and result in more cost-effective and efficient UV/AOP systems. As more emerging contaminants, such as pharmaceuticals and personal care products, are identified in drinking water supplies, these numerical models will become increasingly important. The main objective of this paper is to introduce a protocol for creating a CFD model that simulates the UV-initiated advanced oxidation process (as included as part of the upcoming AwwaRF (WRF) Report 3176). In doing so, the paper identifies critical and non-critical model criteria that need to be addressed during the development and use of such a model.
As a result of their complexity, CFD/AOP models may be divided into at least three separate CFD codes to decrease computational expense and improve convergence. The three major components are the hydrodynamics/turbulence model, the fluence rate distribution model, and the advanced oxidation kinetics model. The hydrodynamics/turbulence model predicts the spatial variations in fluid velocity, pressure, and macroscale turbulent mixing that occurs in the reactor. The fluence rate model simulates the spatial distribution of UV light intensity throughout the reactor. The kinetics model describes the chemical reactions occurring in the fluid, including both direct photolysis and advanced oxidation. A fourth model that may be implemented is a dedicated mixing model that may better characterize the microscale mixing and/or mixing-limited conditions that affect the advanced oxidation reactions in the reactor. It is important to note that if the fluence rate and kinetics models are separated, any change in UV transmittance as a result of species reactions in the fluid flow is decoupled from the calculation of light distribution.
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