Numerical Modeling of Flow and Disinfection in UV Disinfection Channels

Abstract

The steady two-dimensional turbulent flow in the central region of an open channel in which vertical ultraviolet lamps are arranged in a staggered configuration is predicted using a computational fluid dynamics code incorporating a turbulence model and a boundary-fitted grid. A two-dimensional continuum model of the fate and transport of microorganisms, based on the results of flow simulations and incorporating the series-event model of disinfection kinetics also is presented. From an analysis of the governing transport equation, a dimensionless disinfection parameter that may be useful in discussions of comparative disinfection performance is identified. Model predictions are compared with measurements of flow in the laboratory and measurements of disinfection efficacy in a prototype channel. Good agreement is found between flow predictions and measurements in the flow region upstream of a model lamp/tube, but in the wake region, the measured flow exhibited greater uniformity than the numerical model. Predictions of disinfection process performance are satisfactory at high throughput rates but deteriorate at low throughput rates. Differences in predictions caused by differences in the order of the series-event model were studied and were small when the degree of disinfection was low, but became more important at greater disinfection extents.