UVC-LED the Wave of the Future

INTRODUCTION
In the wastewater industry, energy and operation costs are major factors in selection of a disinfection technology. Ultraviolet Light Emitting Diode (UV-C LED) systems based on a solid-state technology, generally tends to operate with low electrical consumption and less relative space to conventional technology. A comparison of LED UV to UV systems applied to wastewater indicating that there was large (over 50 percent) cost savings for this technology when applied to wastewater systems. UVC LED Technology currently is on a rapid development scale. UVC LED units were produced 2 years ago have changed dramatically the output and decreasing the production costs. Testing of three different UV-C LED water disinfection pilot-scale units at the U.S. Environmental Protection Agency (EPA) Test and Evaluation Facility in Cincinnati, OH. The pilot-scale testing included collimated beam testing and flow-through testing for both drinking water and municipal wastewater. During the first two studies the test runs targeted MS-2 bacteriophage and other organisms. The focus of the third test was on Legionella inactivation.
BACKGROUND
In much the same way that visible light emitting diodes (LEDs) have revolutionized the general lighting industry, UV-C LEDs are now viewed as the 'next generation' in UV-C disinfection and are expected to rapidly replace conventional mercury arc lamps in water disinfection applications. LEDs are made from crystalline compound semiconductors that emit light when energized. UV-C LED system integrators purchase many single-packaged UV-C LEDs and combine them into a larger UV-C LED reactor which is then equipped with electronics, thermal management system, optics, and housing to create a finished UV-C LED system or module. Point-of-use (POU) UV-C LED systems for the treatment of potable water are already commercially available and market competitive, but larger-capacity UV-C LED systems for municipal water and wastewater disinfection are still under development.
RESULTS<b/>
The primary objectives of this project were to evaluate the disinfection performance, reliability, and energy use requirements of three small-scale UV-C LED water disinfection units (e.g., one at 10 gallons per minute (gpm) and two at 20 gpm rated sizes) for a variety of test conditions. Test conditions included treating water to achieve public supply drinking water, municipal treated secondary wastewater, combined sewer, and reuse water requirements. Both Collimated beam and flow through testing was conducted to validate the removal of MS-2 and Legionella. MS-2 Testing Results of MS-2 Testing can be divided into two group. Collimated beam testing was Collimated Beam Results MS-2 bacteriophage was added to the dechlorinated water to conduct this test. The Ultraviolet Transmittance (UVT) was 98.7% at 280 nm. Collimated beam tests were performed at 280 nm with results shown in Fig. 1. Reuslts of testing indicate a 0.5 log removal of MS-2 per 5 mJ/cm2 increase in dose. These results match with data presented and used for development of NWRI response curves. Extrapolating the data, a 5 long inactivation would indicate that a 5 log removal of MS-2 could be achieved at a dose of 50 mJ/cm2 if the removal remained linear. Typically the inactivation curve is more geometric, therefore the predicted dose would probably be more closely to 100 mJ/cm2. Flow-Through Results Due to the piping configuration at the EPA T&E Facility, the flow rate to the unit was limited to 22.7 liters per minute (6 gpm). Flow-through testing was only conducted with MS-2 bacteriophage.. The test water was inoculated with MS-2. The MS-2 was fed at a rate of 93 mL/min. The water flowed through the unit for 3 minutes and then inlet and outlet samples were collected at 8-minute intervals. The results for both pilot unit 1 and 2 are shown in Figure 2. At 22.7 liters per minute (6 gpm), the pilot unit 1 could provide a 3-log removal at a dose of 85 mJ/cm2. Pilot unit 2 achieved a 4-log removal at 85 mJ/cm2 and with a flow rate of 15.14 liters per minute (4 gpm). Based on these flow rates, the power input would be in the range of 200-250 kilowatt-hours per million gallons (kWh/MG).
LEGIONELLA TESTING
Legionella Testing was conducted by USEPA to validate the dose response that could be achieved four different SerioGroups at three wave lengths. UVC-LED disinfection efficacy were evaluated for four Lp strains representing three clinically significant serogroups (sg1, 4, and 6) in drinking water utilizing both a collimated beam (at 255, 265, and 280 nm) and a point-of-entry (POE) treatment set-up (280nm). Understanding the inactivation differences between Lp serogroups in drinking water, especially for UVC-LED POE applications, will help determine the most effective remediation strategies needed to target specific isolates during contamination events. The focus of the testing was to examine the inactivation of legionella at 280 nm a that was the wavelength of the unit shown in Figure 3. However, for the POE tests, only sg6 displayed the highest reduction (mean ± standard deviation) of 5.0 ± 0.5 log10 CFU/mL compared to 3.5 ± 0.5, 3.3 ± 0.2, and 3.6 ± 0.1 log10 CFU/mL for sg1, sg1 DW, and sg4, respectively.
DISCUSSION<b/>
Using the flow-through pilot test results, the project team developed scale-up factors to project energy use values for UV-C LED water disinfection. Because of the flowrate limitations, the energy use projections for the UV-C LED system are preliminary, and we provide the energy use values in relatively wide ranges. We project the energy use for UV-C LED disinfection of drinking water is in the 65-250 kWh/MG range. The projection is for a UV-C LED system treating drinking water with 90% transmittance at a UV dose of 40 mJ/cm2. The energy use projections for UV-C LED disinfection systems are comparable to conventional UV mercury vapor lamp systems. The energy use requirements for disinfecting drinking water are approximately 60-120 kWh/MG for medium-pressure mercury vapor lamp systems and 50-200 kWh/MG for low-pressure mercury-vapor lamp systems.
CONCLUSION
A summary will be provided of the advances of LED UV, focusing on its ability to reduce microbial transfer across several applications. There are often limits in place that prevent fully utilizing newer technology. When capital and operating costs come down, availability of products, new possibilities open up to apply technology. UV LED technology can be seen to following the same path. Test results collected by USEPA on the use of UVC-LED on MS-2 as well as Legionella have been shown to be able to achieve similar results to that in low pressure UV applications. System can be applied to point of use applications cost effectively and improvements in design will allow for deployment in larger flow systems.