Evaluation of Continuous Flow Ultraviolet Light Emitting Diode

0932116

Ducoste

The proposed research plan seeks to integrate bench-scale and pilot-scale experimental and numerical techniques for comprehensive characterization of an ultraviolet light emitting diode (UV LED) continuous flow reactor. Data from these experiments will provide the necessary information to develop and validate a computational fluid dynamics (CFD) model of a UV LED disinfection system. The validated CFD model will be combined with a heuristic optimization routine to construct an efficient continuous flow UV LED system based on desired optimality criteria (i.e., minimize the total power input while achieving the required effluent log inactivation or maximize the effluent log inactivation given a target total power input). Overall, this research will allow engineers to determine whether UV LED based continuous flow UV reactor systems can achieve high disinfection system efficiencies and offer an alternative technology that replaces mercury vapor UV lamps.

The acceptance of UV as an effective disinfection process for treating drinking water sources and its potential use in water reuse applications have led to considerable growth over the last 10 years. Such growth has ignited researchers to improve the effectiveness of UV reactor designs and perform research to discover novel ways to increase the power output of low pressure lamps, improve the efficiency of low and medium pressure lamps, increase the lamp operating life, and develop new UV emission sources. However, a majority of the UV lamp technologies contain mercury, which is considered hazardous waste and poses environmental and public health threats if not properly disposed or if lamps are broken. Lamp breakage may occur during the transportation or installation of the lamps within the treatment process as well as by a foreign object strike while the UV system is in operation. Other UV light technologies that have emerged (i.e., pulsed and excimer lamps and UV LEDs) do not contain mercury. However, little research has been performed with UV LEDs to assess their capabilities as an effective UV emission light source within continuous flow UV systems.

This research program proposes to examine the UV disinfection efficiency of UV LED continuous flow reactors by 1) performing collimated beam experimental tests that determine the UV response of target non-pathogenic microorganisms and UV sensitive fluorescence microspheres at multiple UV LED wavelengths, 2) developing a numerical model that describes the UV LED light distribution, UV dose distribution, and microbial log inactivation of continuous flow UV LED reactors, 3) performing pilot-scale experiments on a UV LED reactor over a range of flows and UV transmittance to validate numerical models, and 4) developing an optimal UV LED reactor based on the output from a combined optimization routine and CFD model.

The proposed research represents one of the first comprehensive and direct efforts to quantify the disinfection performance of a distributed point light source within a continuous flow UV reactor that may lead to improved disinfection efficiencies without geometric constraints due to incorporation of a cylindrical light source. Previous studies have only investigated UV LEDs with bench scale tests to assess either log inactivation of E-coli or the degradation of phenol under advance oxidation conditions with peroxide. The proposed study is a necessary first step to evaluating this alternative UV light source as a benign replacement to current mercury vapor UV lamps in continuous flow systems.

This project will contribute to the education of one PhD and one MS student in Environmental Engineering. These students will be selected from the pool of applicants to the Civil, Construction, and Environmental Engineering (CCEE) Department, with special consideration for applicants from under-represented groups. The graduate students will be extensively involved in all areas of research: 1) experimental design, setup, and execution, 2) development and execution of numerical simulations, 3) presentation of research results at national and international conferences and peer reviewed publications. The graduate students will be trained in many disciplines (chemical engineering, microbiology, and computational modeling) due to the proposed research approach. It is essential that future engineers receive interdisciplinary training given the complex nature of environmental problems. This project clearly requires knowledge in microbiology, reaction engineering, parameter estimation, and numerical programming. A partnership involving Sensor Electronic Technologies, a UV LED manufacturer, will help ensure the success of the various phases involved in this research.