The disinfection characteristics of an open channel ultra-violet (UV) disinfection reactor is investigated numerically. The computational fluid dynamics (CFD) model used in this study is based on the volume of fluid (VOF) method to capture the water–air interface. The Lagrangian particle tracking method is used to calculate the microbial particle trajectory and the discrete ordinate (DO) model is used to calculate the UV intensity field inside the reactor. A commercial CFD software package ANSYS FLUENT is used to solve the governing equations. Custom user defined functions (UDFs) are developed to calculate the UV doses. A post-processor is developed in MATLAB to implement the inactivation kinetics of the microbes. The post-processor provides the probabilistic dose distribution and reduction equivalent dose (RED) values achievable in the reactor. The numerical predictions are compared with available experimental data to validate the CFD model. A parametric study is performed to understand the effects of different parameters on disinfection performance of the reactor. The low/high dosed particle trajectories, which can provide an insight for hydraulic and optical characteristics of the reactor for possible design improvements, are identified.

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