UV Process Flow Visualization and Quantification using 3-Dimensional Laser Induced Fluorescence

Application of UV is becoming increasingly popular for drinking water disinfection since it effectively inactivates Cryptosporidium parvum oocysts and Giardia lamblia cysts at relatively low doses. Guidance and regulations for UV disinfection require that utilities verify dose delivery by validation testing. UV reactor validation is currently accomplished using the biodosimetry method, which determines a reduction equivalent dose (RED) value from the inactivation of a test microorganism. Biodosimetry has several limitations including: 1) inability to measure the dose distribution delivered by the reactor, 2) difficulty of directly extrapolating the result to the REDs of other microbes that have different inactivation kinetics, and 3) relatively high costs and time required for analysis, which prevents real-time measurement of dose delivery. To address some of these deficiencies, recent research has investigated the use of fluorescent microspheres as non-biological surrogates to measure dose distributions. While dose distributions measured in this way provide RED estimates for microbes with different inactivation kinetics, this technique also does not provide spatial information on dose delivery within the reactor. Computational fluid dynamics (CFD) models can predict spatial information, estimates of the dose distribution, and RED for different microbes. But the accuracy of these models have not been experimentally verified.The objective of this AWWARF-funded study is to develop an innovative laser-induced fluorescence (LIF)-based method to measure real time, three-dimensional mixing behavior and dose delivery distributions within UV reactors. Model pilot-scale UV reactors equipped with low-pressure UV lamps configured to represent current commercial technologies will be tested. We will use a custom-designed LIF system to capture and quantitatively analyze real-time 3D distributions of fluorescent dye within the reactor. From conservative tracer tests with UV lamps off, we will visualize and quantitatively analyze the mixing behavior within a UV reactor. This novel 3DLIF technique is expected to provide: 1) a highly innovative and unique method for UV reactor validation and optimization; 2) a novel diagnostic tool to better understand temporal and spatial phenomena occurring inside the UV reactor, which has not been possible with current experimental techniques; 3) better understanding of the current CFD model limitations (e.g., wall reflection, lamp shadowing effects, non-steady state hydraulics, non-uniform lamp output, etc); and 4) empirical data to visualize transient flow hydrodynamics within UV reactors, against which LES based CFD model simulation, which will be also developed in this study, can be compared.