Modeling a continuous flow ultraviolet Light Emitting Diode reactor using computational fluid dynamics

Abstract

The use of ultraviolet (UV) light for water treatment disinfection has become increasingly popular due to its ability to inactivate chlorine-resistant microorganisms without the production of known disinfection by-products. Currently, mercury-based lamps are the most commonly used UV disinfection source; however, these lamps are toxic if broken during installation or by foreign object strike during normal operation. In addition, disposal of degraded, hazardous mercury lamps can be challenging in rural and developing countries for point-of-use (POU) drinking water disinfection applications. UV Light Emitting Diodes (LEDs) offer an alternative, non-toxic UV source that will provide design flexibility due to their small size, longer operating life, and fewer auxiliary electronics than traditional mercury-based lamps. Modeling of UV reactor performance has been a significant approach to the engineering of UV reactors in drinking water treatment. Yet, no research has been performed on the experimental and modeling of a continuous flow UV-LED reactor. A research study was performed to validate a numerical computational fluid dynamics (CFD) model of a continuous flow UV-LED water disinfection process. Reactor validation consisted of the following: (1) hydraulic analysis using tracer tests, (2) characterization of the average light distribution using chemical actinometry, and (3) microbial dose–response and inactivation using biodosimetry. Results showed good agreement between numerical simulations and experimental testing. Accuracy of fluid velocity profile increased as flow rate increased from 109mL/min to 190mL/min, whereas chemical actinometry saw better agreement at the low flow rate. Biodosimetry testing was compared only at the low flow rate and saw good agreement for log inactivation of bacteriophage Qβ and MS-2 at 92% and 80% UV transmittance (UVT). The results from this research can potentially be used for the design of alternative point-of-use drinking water disinfection reactors in developing countries using UV LEDs.