Modeling virus transport and inactivation in a fluoropolymer tube UV photoreactor using Computational Fluid Dynamics

Fluoropolymer tube photoreactors employing external UV lamps to irradiate the fluid conveyed by semitransparent tubes are currently used for water and wastewater applications based on their intrinsic simplicity in system assembly and claims that the hydrophobic characteristics of the tube material reduce fouling. Nonetheless, there is limited published information to date on the short and long term disinfection efficiency and the potential implications of these factors for operational costs. In this paper, empirical and numerical bioassay experiments on virus inactivation were conducted on a pilot-scale fluoropolymer tube photoreactor using MS2 and T1 bacteriophages to gain further insight into delivered dose. Simulated and observed MS2 and T1 reduction equivalent doses displayed good agreement with an error (relative to the observed RED) ranging from -13.7% to +4.4% for MS2 (average =-3.9%) and from -5.6% to +27.0% for T1 (average = +4.6%).The impact of the fluoropolymer UV absorption on disinfection was also assessed. Integrating sphere measurements revealed that absorption events occurring in the fluoropolymer tubes play a pivotal role in determining disinfection efficiency. At 253.7 nm, the diffuse transmission of UV light was the dominant radiative transfer mechanism and a considerable proportion of incident photon flux (13.5%) was absorbed by the fluoropolymer tube. As highlighted by the model sensitivity analysis, the fluoropolymer absorption coefficient was found to be the most important factor affecting bacteriophage inactivation. Although further research will be conducted to investigate potential efficiency enhancements attainable through shape optimization and internal UV reflectors, CFD predictions indicated that the current electrical efficiency of the investigated photoreactor (0.0190-0.0289kWhm-3 MS2log-1) was considerably higher than conventional UV photoreactors (0.0044-0.0049kWhm-3 MS2log-1) suggesting that fluoropolymer tube UV technologies may not be ideal for high-flow installations or energy sensitive applications