Geometry Defeaturing Effects in CFD Model-Based Assessment of an Open-Channel-Type UV Wastewater Disinfection System

Computational fluid dynamics (CFD) is a popular tool in the water industry for assessing ultraviolet (UV) reactor performance. However, due to the size of open-channel-type UV reactor systems, the CFD model requires significant computational time. Thus, most evaluations have been conducted using very simplified models. In order to ensure the reliability of this simplified CFD model, precise numerical modeling and validation by measurements are necessary considering the geometry defeaturing level. Therefore, simplified geometries in four defeatured levels were prepared for the CFD model, and simulations were performed to determine the level of geometric simplicity required to derive reliable results. A bioassay test was also conducted for a pilot-scale open-channel-type UV reactor that has the same geometrical configuration as the CFD model. Good agreement was observed between the bioassay test and CFD model results. It was found that the reduction equivalent dose (RED) is not significantly affected by geometry defeaturing under the assumption that the inlet flow conditions are relatively uniform. In multiple bank operation, the addition of banks yields a linear increment of the RED in the CFD model, however, a lower RED than the measured value was presented, especially for serial bank addition. The related aspects of the detailed flow physics and disinfection characteristics were also presented. These results are expected to provide useful information for CFD modeling, reactor design, and the assessment of the open-channel-type UV reactors.